CA1181623A - Step-and-repeat projection alignment and exposure system - Google Patents

Abstract

ABSTRACT
An alignment and exposure system is provided with a main stage for positioning a reference mark or a semicon-ductive wafer directly beneath a projection lens. The reference mark is mounted on the main stage by a substage permitting the reference mark to be positioned in alignment with the axes of motion of the main stage and in a plane parallel to and coincident with the image plane of the projection lens. Selected portions of a reticle disposed above the projection lens on another stage may be illuminated with either exposure or nonexposure light by a controllable light source unit. While employing the projection lens and a first objective lens unit to view images of portions of the reference mark or wafer illuminated by projected images of the illuminated portions of the reticle, the main or other stage may be employed to directly align the wafer with respect to the reticle or the reticle with respect to the reference mark. While employing a second objective lens unit to view images of portions of the wafer illuminated by projected images of a pair of prealignment reticles, the main stage may be employed to align the wafer with respect to those reticles.

Description

D ~ ~

IMP~OVED STEP-AND-KEPEAT PROJECTION
ALIÇNMENT_AND EXPOSU~E SYST~l Back~round_and Summary of the Invention This invention relates generally to step and-repeat alignment and exposuresystems utilizing ~ projection lens of the reduction type for the photometric printing of an image o a first object, such as a reticle, upon a second object~ such as a photomask or a semiconductive wafer, and, more sp~cifically, to apparatus for use in such systems to acheive precise relative alignments of a reticle and a semiconductive wafer with respect to . , coordinate axes of motion of a movable stage for holding ~he semiconductive wafer This invention further relates to alignment systems for achieving precise relative alignments of a first object, such as a photomask or a reticle, and a second object, such as a semiconductive wafer or a photomask, and, more par~icularly,. to apparatus for use in such ~-. systems to facilitate precise positioning of the irst . ,~ .
object with respect to an axis of motion of a movable stage for holding the second object.
In the semiconductor industry projection lenses of the reduction type are employed both in the fabrication of photomasks~ and in the processing of semiconductive wafers to form integrated circuits and the like. A high (submicron) resolution pho~omask is typically fabricated by utilizing a precisely controlled stage to successively position adjacent regions of the photomask with respect to an image (formed by such a projection lPns) of a reticle containing a level of ~icrocircui~ry that is printed on the photomask at each of those regions.
This step-and-repeat printing operation l-orms an array of adjacent regions of microcircuitry of one level on the photomask in rows and columns paralle.'.
to ~he coordina~e axes of motion of ~he stage. ';
set of such photomasks, each bearing an array of micro-circuitry of a different level, is typically employed in the abrication of integrated circuits or the like from a semiconductive wafer. In the course of this fabrication, the semiconductive wafer is sequen-tially aligned with each photomask of the set and the level of microcircuitry printed on the photomask is in turn printed on the semiconductive wafer. However, it is also possible to eliminate the operation of fabricating a set of such photomasks by employing a precisely controlled stage to successively position adjacent regions of the s~miconductive wafPr with respect to each of the reticles employed in fabricating the ~- set of pho~omasks so that the level of microcircuitry contained on each of those reticles may be printed directly on the semiconductive wafer at each of thos~
regions during separate step-and-repeat printing opera-tions.
In order to facilitate the precise positioning or alignment of one level of microcircui.try being printed on a semicond~ctive wafer at each of an array of adjacent regions thereof relative to another level of microcircuitry previously prin~ed or yet to be prin~ed ~ 3 on the semlconductive wafer at each of those same regions, it would be hi~hly de.sirable t~ employ a step-and-repeat alignment and exposure system utilizing a projection lens of ~he reduction type in the optical portion thereof while allowing direct viewing and alignment of a reticle, or an image of the reticle, with respect to the coordinate axes of motion of the stage, and further allowing direct view-ing and alignment of microcircuitry previously printed on the semiconductive wafer at each of those regions with respect to the reticle, or image of the reticle.
Unfortunately, however, conventlonal step-and-repeat ~-- alignment and exposure systems utilizing projection lenses of the reduction type do not allow such direct viewing and alignment of either the reticle, or an image of the reticle, or the semiconductive wafer.
In order, for example, to facilitate the precise positioning or alignment of one level of microcircuitry being printed on a semiconductive wafer at each of an array of adjacent regions thereof relative ~o another , level of microcircuitry previously printed or yet to be printed on the semiconductive wafer at each of those same regions, it would be highly desirable to employ a precisely controlled stage having a visible indicium of at least one of the coordinate axes of motion of the stage so as to facilitate the precise and repeatable positioning of a photbmask or a rPticle with respect to that axis of motion of the stage. Unfortunately, however, the stages employed in conventional step-and-repeat alignment and exposure systems do not have such an indicium.

~ 3~

Objects of aspects of this invention as defined herein or in parent application Serial No. 349, 215 are as ~ollows:
An obj~ct of an aspect of this invention is to provide an improved alignment system with a precisely controlled movable stage having a visible reference mark that is indicative of at least one of the coordinate axes of motion of the stage.
An object of an aspect of this invention is to provide an improved step-and-repeat alignment and exposure system incorporating a projection lens of the reduction type in the optical portion thereof while allowing direct viewing and alignment of an image of a first object, such as a reticle, and of a scond object, such as a semiconductive wafer.
An object of an aspect of this invention is to provide the optical portion of the step-and-repeat alignment and exposure system with a viewing port for observing the image plane of the projection lens.
An object of an aspect of this invention is to provide the optical portion of the step-and-repeat alignment and exposure system with masking apparatus or selectively illuminating different portions of the reticle.
An object of an aspect of this inv~ntion is to provide the step-and-repeat alignment and exposure system with a controlled movable stage having a visible reference mark that is indicative of at least one of the coordinate axes of motion of the stage.
An object of an aspec~ of this invention is to provide the step-and-repeat alignment and exposure r~3 system with a reticle alignment subsystem for precisely and repeatably aligning an image of each reticle of a set of different reticles with respect to the axes of motion of the controlled movable stage.
An object of an aspect of this invention is to provide the step-and-repeat alignment and exposure system with a wafer alignment subsystem for precisely aligning a previously-printed array of adjacent regions of microcircuitry on the semiconductive wafer with respect to the axes of motion of the controlled movable stage.
An object of an aspect of this invention is to provide the step-and-repeat alignment and exposure system with a wafer alignment subsystem for directly aligning the previously-printed regions of microcircuitry on the semiconductive wafer with respect to an image of each reticle of a set of different reticles.
An aspect of this invention is as follows:
Alignment apparatus comprising:
an adjustable holder for holding a first object in a first plane;
imaging means for producing an image of the first object in a second plane;
a stage for holding a second object in the second plane;
control means for moving the stage along coordinate axes to position the second object with respect to the image of th~ first object;
an indicium disposed on the stage for being positioned in the second plane to facilitate alignment of the image of the first object with respect to at least one of the axes of motion of the stage;

-4a-said holder being mo~able rotatably and along coordinate axes to facili~ate alignment of images of first and second alignment marks of the first object with respe~
to the indicium;
control means for ~oving the holder rotatably and along coordinate axes to align the images oE the first and second alignmerlt marks of ~he first object with respec~..
to the indicium;
prealignment means for aligning an image of one or more alignment marks of the prealignment means with respect to said one of the axes of motion oE the stage and for projecting that image onto the second object in the second plane when the second object is in a prealignment position; and positioning means, including the stage and the first~mentioned control means, for moving the second object rotatably and along the coordinate axes of motion of the stage to align alignment marks of ,he second object wlth respect to the image of said one or more alignment marks of the prealignment means when the second object is in the prealignment position.
The foregoing and othe.r objects, which will become apparent from an inspection oE the accompanying drawings and a reading of the associated description, are accomplished according to the illustrated preferred embodiment of this invention by providing a step-and-repeat alignment -4b-~ 3~
and exposure system includin~ a main stage controlled for movement ~o different positions along othogonal X and Y a~es; a chuck mo~mted on the main stage for supporting a semiconductive wafer thereon; a substage mounted on the main stage for aligning a reference mark ~n the substage with one of the X and Y axes of mot-~n of the main stage; another stage controlled for allgnlng an lmage of a reticle supported thereon with the reference mark; a projection lens of the reduction type mounted between the main stage and the other stage for imaging illuminated portions of the reticle onto portions of the reference mark or the semïconductive wafer, depending on the position to which the main stage is moved; a light source for directing illumi-nation and exposure light along an optical path extend-ing through the reticle; a pair of filters and a compensating lens mounted for selectively controlling the type of light (i.e., whether illumination light or exposure light) passing along that optical path to the reticle and for accommodating the projection lens for the type of light selected; a pair of shutters mounted for selectively controlling the passage of light along that optical path to the reticle; a plurality of different mask plates mounted for selectively controlling the portions of the reticle illuminated by the light passing along that optical path when one of the shutters-is opened; and a beam splitter mounted between the projection lens and the reticle for providing a viewing port at which an aerial image of the portions of the reference mark or semiconductive wafer illuminated -4c-. ~

. by the projected image o:E ~he i.lluminated portions of the reticle mag be viewed.
~he step-and-r~peat alignment and exposure system also includes a first objective lens unit that may be moved into an operative position for use wi~h an ocular lens uri.t ~o permit viewing of the aerial image provided at the viewing port while the main stage is contrclled to directly align either the reticle with the reference mark or the semiconductive wafer with the reticle; a pair of prealignment reticles mounted above the main stage and aligned with respect to the reference mark ~o permit prealignment of the semi-~- conductive wafer with respect to the reference mark (and, hence, the reticle); and a second objective lens unit for imaging this pair of prealignment reticles onto a corresponding pair of alignment marks on the semi~
conductive waer when the main stage is moved to position the semiconductive wafer directly beneath the second objective lens ~nit and for providing aerial images of the pair of alignment marks on the semi-conductive wafer illuminated by the projec~ed images of the pair of prealignment reticles. This second objective lens unit may be moved into the operative position (in lieu of the first objective lens unit) for use with the ocular lens unit to pel~it viewing of these aerial images while the main stage is controlled to align the pair of alignment marks on the semiconductive wafer with the corresponding pair of prealignment reticles, Once the semiconductive wafer has been so aligned, the main stage may be controlled to step an ql array of adjacent regiorls of the semiconducti.ve wafer directly beneath the projection lens to pe~it direct alignment of selected ones of.those regions with the reticle while employing the first objective lens unit with the ocular lens uni~ for viewing an aerial image of an auxiliary alignment mark previously printed alongside each selected region and illuminated by a corresponding alignment mark on the reticle and to further permit printing of a level of microcircuitry contained on ~he reticle at each of the array of adjacent regions.
Descri ~ion of the Drawings ( , Figures lA-C are perspective views of different portions of a step-and-repeat alignment and exposure sys~em in accordance with the preferred embodiment of the present invention.
Figure 2 is a half-sectional, partially cut-away elevational view of a portion of the step-and-repcat alignment and exposure system of Figures lA-C.
Figure 3A is a plan view o:F a refPrence mark plate employed in the step-and-repeat alignment and exposure system of Figures lA-C.
Figures 3B and 3C are top plan and side eleva~ional views, respectively, of a substage employed in the step-and-repeat alignment and exposure system of Figures lA-C to support the reference mark plate of Figure 3A.
Figure 4 is a plan view of a slide holding two different masks employed in the step-and-repeat alignment and e~posure system of Figures lA-C.

Figure 5 is cl plan v:iew of one of a pair of reti.cle alignment marks con~ained on each reticle employed with the step-and-repeat alignment and exposure system of Figures lA-C.
Figure 6 is a plan view of a portion of a refer-ence mark formed on the refere~ mark plate of Figure 3 as illu~inated by a projected image of a recticle alignment mark.
Figure 7 is a plan view of the end portions of the reference mark formed on ~he reference mark plate of Figure 3 as illuminated by projec~ed images of a pair of reticle alignment marks.
Figure 8 is a plan view of one of a pair of wafer alignment marks contained on a first reticle of a set of reticles employed with the step-and-repeat alignment and exposure system of Figures lA-C.
Figur~ 9A-B are plan views illustrating how a pair of wafer alignment marks is printed on a semi-conduc~ive wafer by the step-and-repeat alignment and e~posure system of Figures lA-C.
Figures lOA-C are plan views illustrating how the ,' - pair of wafer alignment marks printed on the semi-... . .
conductive wafer may be employed in aligning images of a pair of prealignment reticles of the step-and-repeat align-ment and exposure system wlth respect to the reference mark.
Figure 11 is a half-sectional elevational view of a portion of the step-and-repeat alignment and exposure system of Figures lA-C.
Figure 12 (eighth sheet of drawings) is a plan view of the pair of wafer alignment marks printed on the semi-conductive wafer when they are precision prealigned with images o:E the pair of preallcJnment reticles.
Figuxe 13 is a plan view o:E the semiconductive wafer illustrating the manner in.which a step-and-repeat prin~ing operation is performed by the step-and-repeat alignment and exposure system of Figures lA-C.
Figures 14 and 15 are plan views of ?ortions of first and second reticles of a set of reticles employed with the step-and-repeat alignment and exposure system of Figures lA-C.
_ scription of the Preferred Embodiment Referring now to Figures lA-C and 2, there is shown a precision step-and-repeat alignment and exposure system 10 for repeatedly printing one level of microcircuitry, contained on a first object, such as a reticle 12~ at an array of adjacent regions of a - second object, such as a semiconductive wafer 14, in alignment with other levels of microcircuitry previously printed or yet to be printed at those same regions. Alignment and exposure system 10 includes a stage 16 for holdin~ ~he reticle 12, a lO:l projection lens 18 for projecting an image of illuminated portions of the reticle onto a reference mark 26 or the semi-conducti~e wafer 14, a main stage 20 for positioning the reference mark or the semiconductive wafer with respect to the projected image of the illuminated portions of the reticle, a beam splitter 21 and a compound microscope 22 for vie~ing aerial images of portions of the reference mark or semiconductive wafer illuminated by the projec~ed image of the reticle, and ~ 3 a light source unit 24 for selectively illuminating different portions ~f the re~icle (with either illumi-nation or exposure light) for viewing those aerial im~ges during alignment operations and for selectively exposing a photosensitive film on the semiconductive wafer during step-and-repeat printing operations.
With reference now particularly to Figure lA, main stage 20 may comprise an interferometrically-controlled stage of the type shown and described in detail in copending Canadian Patent Application Serial No. 349,305 entitled INTERFERO~TRICALLY CONTROLLED STAÇE T~
PRECISELY ORTHOGONAL ~YES OF ~OTION and filed on April 8, 1980, by Optimetrix Corporation. As fully described in .....
that application, main stage 20 may be moved along orthogonal X and Y axes to any position in a horizontal plane by X and Y axes s~rvo drive units 25 and 27.
Either axis of motion of main stage 20 may therefore be employed as an absolute frame of reference, and the X
axis is so employed, for ali~nment and exposure system 10, as hereinafter explained.
Reference mark 26 may be formed of brigh~ chrome on a reference mark plate 23 fixedly mounted on a substage 30, which is in turn adjustably mounted on main stage 20.
As best shown in Figure 3A, reference mark 26 may comprise a straight line 26a of about 12.7 millimeters in length and about 4 microns in wid~h, and a pair of iden~ical tic marks 26b of about 0.4 millimeters in length and about 4 microns in width. These tic marks 26b symmetrically and orthogonally intersect line 26a near the opposite ends thereof and are spaced 10.3 millimeters apar~ (cen~er-to-center).
As best shown in Figures 3B and 3C, substage 30 may comprise a lower base member 200 fixedly secured to main _9_ stage 20 by screws ~r rivets 202, and an adjustable upper support member 204 secured to the lower base member, for example, by a solid hinge 205 permitting pivotal adjustment of the upper support m~mber with respect to the plane of main stage 20 under control of an adjustmen~ screw 206. This adjustment screw is screwed through a threaded screw hole in a first side potion 208 of upper support member 204 and into abutment with the upper surface of lower base member 200 so as to permit positioning of the upper surface of the upper support member and, hence, of reference mark plate 28 in a plane parallel to a first image plane 77 (see Figure 2) C of projection lens 18 as desired for proper focusing of reference mark 26. A second smaller side portion 21C of upper support ~ember 204 is secured to the first side portion 208, for example, by another solîd hinge 212 permi~ting angular adjustment of the upper surface of the second side portion of the upper support member ~and, hence, of reference mark plate 28, which is fixedly secured to that surface by an adhesive) in a plane parallel to the upper surface of main stage 20 under control of an adjustment screw 214. This adjustment screw is screwed through a threaded screw hole in the flrst side portion 208 of the u~per support member 204 and in~o abutment with the smaller second side portion 210 of the upper support member so as to permit precise alignment of line 26a of refe.rence m~rk 26 with ~he X axis of mo~ion of the main stage as desired to provide a visual indication of the X axis of motion and thereby facilitate use of thP
X axis of motion as an absolute frame of reference for ali~m~nt and exposure system 10. In initially setting up ali~nt and exposure system lO, substage 30 is nanually adjusted ~y adjustment screws 206 and 214 to acheive ~he desiredr~arallel-plane positi ~ ng of reference -9a-m~rk plate 28 and the desired alignment of line ~6a of reference mark 26. ~lthough ~his substage ad~ustment opera-tion should only have to be performed once during the life of alignment a~d exposure ~ys~em 10, it may be advisable to check the parallel-plane p~sitioning of reference mark plate 28 and the alignment of line 26a vf reference mark 26 from time to time. The manner in which the substage adjustment operation is perormed will now be descrihed with reference to the parts of alig~ment and exposure system 10 employed in that operation.
With reference now p~rticularly to Figure lB, light source unit 24 includes a mercury arc lamp 32 for ~mi~ting a spectrum of light energy including both green illuminating light having a wavelength of about 547 nanometers for illumi-nating but not exposing the photosensitive film on semicon-ductive wafer 12, and blue illumina~ing and exposure light having a wavelength of about 436 nanometPrs for both illuminating and exposing ~he photosensitive film on the semiconductive wafer (herein simply referred to as exposure light). Mercury arc lamp 32 is fixedly mounted along a vertically extending portion 34a of an optical path 34a-e of alignment and exposure sy~tem 10. An elliptical reflector 36 surrounds mercury arc lamp 32 and is fixedly coaxially mounted therewith for projecting a beam of light ~mitted by the mercury ~rc lamp downward to a band reflecting plane mirror 38. This band reflecting plane mirror 3~ has a multi-layer dielectric coatin~ for reflecting blue and gr~en light, but transmitting all other light, in the beam of lig`ht to prevent unnecessary energy rom being transmitted along the 3 r~maining portions of optical path 34a-e. Band rerlecting '3~

plane mirror 38 is ~ixedly mounted in optical path 34a-e at ~n ngle of forty-fi~e degrees with respect to the vertically extending portion 34a ~hereof ~o as to deflect thP blue and green light in the beam of light along a horizontally extending p~rtion 34b of that optic~l pa~h to a plane mirror 40.
Plane mirror 40 i5 fixedly mounted in optical path 34a-e at an angle of forty-five degre~s with respect to the hori-zontally extending pDrt.ion 34b thereof so as ~o deflect the beam of blue and green ligh incident thereon upward al~ng an~ther ~er~ically extending portion 34c of tha~ optical path. The beam of light so deflected thereupon passes ~hrough a light integrat~r 42 and, when a normally closed shutter 50 is opened as during the substage adjustment operation, 81SQ through a blue or a green filter 44 or 45 and a pair of positive lenses 45 and 47 to a beam splitter 48. Light intPgrator 42 is fixedly m~unted in the vertically extending portion 34c o~ optical path 34a-e and is employed ~or pro- -~iding the beam of light passing therethrough with a cross section corresponding to ~he entran~e pupil of projection lens 18 and with a uniform intensity distribution in the plane of reticle 12.
Shutter 50 is pivotally mounted adjacent to the verti-cally extending portion 34c of optical path 34a-e and is ~ontrolled ~y a a ~ervo drive unit 51 ~or pivotal movement ~nto that optical path (as shown in solid lines) when closed ~o as to block passage of the beam of light ~herealong and ~or pi~otal movement out of ~hat optical path (as shown in dashed lines) when ~pened ~o as to permit pas~age of the b~am o~ light therealong. Blue filter 44 and green filter 45 are ixedly mcunted in horizontally ~paced relation~hip on ~ lide 52 which is in turn reciprocally mount d in ~ hori-zontal plane orthogonally intersec~ing the ~ertically extending~portion 34c of opti~al path 34a-e. ~lide 52 is moved along the Y axis under control of an air cylinder 54 to position either the blue fil~er 44 or the green filter 45 in the path of the beam of hlue and green light passing upward along the vertically extending poxtion 34c of opti~al path 34a~e when shutter SO is opened. Blue filter 44 is normally sv positioned and therefore pas~es the blue light in ~he beam of light to the pair of pogi~ive lenses 46 and 47 while filtering out the green light a~d any other non-blue light that may still be present in the beam of light.
Positive len~es 46 and 47 are fixedly moun~ed in the vertically extending portion 34c of ~ptical pa~hs 34a-e ~o image the output of light integrator 42 at the entrance pupil of an imaging lens 56. A slide 58 is mounted or movement along ~he Y axis under control of a Y axis s~rvo drive unit 66 co selectively position either ~f two separate ~ask plates 6Q and 62 at ~n ~perati~e position dire~tly between positive lenses 46 and 47 in a horizontal plane orthogonally intersecting the vertically ex~ending portion 34~ of optical path 34a-e at a point midway between those positive lenses. Light appearing in this plane between positive lenses 46 ~nd 47 is im~ged onto reticle 12. During the ~ubstage adjustment operation,slide 58 is mov~d by Y
~xis seruo drive unit 66 to locate mask plate 6? in an ~perative position between positive lens~s 46 and 47.so that a pair of ~mall.circular openings 68a and 6~b of mask plate S2 (best ~hown in Figure 4),. perm~t the blue light pas~ed by blue filter 44 ~o illuminate.a corresponding pair of circular ~re~s ab~u~ 2 millimeters in diame~er aisp~s~d on ~he surface of reticle 12 and containing a pair of re~ic~e alignment marks 78z and 78b~ respectivelyw Beam splitter 48 is fixedly moun~ed in the ~er~ically extending portion 34c of optical path 34a-e so as to reflect eighty percent of the inGiden~ light along a h~rizontally extending porti~n 34d sf that optical path through imaging lens 56 to a plane mirror 70. Imaging lens 5~ i5 fixPdly mounted along the horizon ally extending portion 34d of optical path 34a-e and is employed to image the light passing thr~ugh mask plate 62 at the surface of re~icle 12. Plane mirror 70 is fixedly mounted in optical path 34a e at an angle of forty-five degrees with respect to ~he horizontally extending portion 34d thereof so as to deflect the light incident thereon downward along a vertically extending por-tio~ 34e of that opti~al path. This downwardly deflected light passes ~hrough a positive lens 72, reticle 12, and beam splitter 21 to projection lens 18. Posi~i~e lens 72 is fixedly ~ounted al~ng the vertically extending portion 34e of optical path 34a-e so as to image light appearing at the output p~pil of imaging lens 56 at ~h~ input pupil of pr~jection lens 18.
~ ith reference now particularly to Figures 1~ and 2, each reticle 12 to be employed with alignment and exposure syst~m 10 has a pair Df oppusitely-facing reticle alignment mar~s 78a and 78b spaced 103 millLmeters apart (Ce~ter-to-center) along the X axi~ when the reticle i5 properly aligned on ~tage 16. As best shown in Figure 5, each reticle align-ment ~ark 78a or 78b m~y comprise a pair of light or tran~parent windowe gOa and 80b ~ach ~bout O.75 millimeters ~quare) on a dark or opaque field. These wi~dows ~Oa and 89b are s~mmetrically disp~sed about ~he center 82 of the align-ment mark on opp~site sides of a pair of orthogonal center-lines of the alignment mark (one of those centerlines being coincident with a common centerline o~ both alignment marks).
Stage 16 is provided with a vacuum holder 17, as shown in Figure 2, for releasably holding reticle 12.in place, and is mov~d by X and differentially-controlled Y axes s~rvo drive units 84, 86a, and 86b to adjust the X, Y, and ~
orientation of the reticle as required to precisely align the reticle alignmen~ marks 78a and 78b of the reticle with referenoe m~rk 26 as hereinaftex explained.
Beam splitter 21 is mounted in the vertically extending portion 34e of optical path 34a-~ so a~ to pass eighty per-cent of the light passing through reticle 12 to projection lens 18, which is also mounted in that portion of optical path 34a-e. A compensating lens 76 is pivotally mounted adjacent to projection lens 18 and controlled by a crank 74 and an air ~ylinder 75 for movement out of the ~ertically extending portion 34e of optical path 34a-e (as shown in solid lines) when blUP light is passing therealong to the projection lens, as is normally the case, and for movement into the vertically extending portion 34e of that optical path ~as shown in dashed lines) when green light iS passing therealong to the projection lens. The ~ompensa~ing lens 76 is employed $v compensate or the difference in wavelength of the green light and the blue light since projection lens lB is corrected for the hlue light only.
Projection lens lB focuses the light passing through reticle 12 at the first im~ge plane 77 adj~cent to main stage 20 and directly beneath the projection lens, there~y pro-jecting Lmages of illuminated portions of reticle 12 ~and, hence, of the reticle a~ig~ment marks 78a and 78b containPd on the re~icle and illuminated by mask plate 62 when shutter 50 is opened) onto whatever object is positioned in that image plane directly beneath the projection lens~ ~he por-tions of that object onto which those images are projec~ed are therefore illuminated by the blue light passing through the transparent reticle alignment marXs 78a and 78b on reticle 12~ Twenty percent of the light reflec~ed vertically upward from those portions of that object through projection lens 18 is reflected by beam splitter 21 along horizontally extending portions 87a of a dual optical path 87a-f to a second image plane 79 positioned the same optical distance from the beam splitter as is the reticle 12 and positioned between the beam splitter and objective lenses 88a and 88b o~ compound micro-scope 22. Projection lens 18 focuses this reflected light at the second Lmage plane 79 thereby p~j~ting an aerial image of 0 those portions of the object positioned in the first image plane 77 directly beneath the projection lens (i.e., those portions illuminated by the projected images of the retiale alignment marks 78a and 78b contained on the reticle 12) to the second image plane.
With reference now particularly to Figures lC and 2, ~ompound mi~roscope 22 includes a first objective lens unit 90 employed in the substage adjustment operation being explained and in other precision alignment operations herein-after explained, a second objective lens unit 92 employed in 0 a precision prealignment operation hereinafter explained~

and a binocular lens unit 93 employed with bo~h the first and ~he ~econd objective lens units as h~reinater explained.
The first objective lens uni g0 is moun~ed on a stage 96 horizontally movable along the X axis under control of an X axis servo drive unit 98 and ver~ically movable along a Z axis orthogonal to the X and Y axes under control of a Z
axis sexvo drive unit 100. Each of the objective lenses 88a and 88b ~omprises a 5:1 objective lens mounted on an associated , arm 89, which is in turn pivotally mounted on stage ~6 and 0 coupled by a gear mechanism 102 to a ~ servo drive unit 104 (both of which are also mount~d on stage 96) for moviny the objective lenses closer together or further apar~. Objective lenses 88a and B8b are disposed along corresponding ones of the horizontally extending portions 87a of dual optical path 87a-f adjacent to the seoond image plane 79 for receiving light therefrom. Thus, the objective lenses 88a and 88b can be moved with respect to the second image plane 79 ~s desired for viewing any por~ions of the aerial image projected to ~hat plane.
) A separate beam bender 10S is mounted on each arm 89 along each horizontally extending portion 87a of dual optical path 87a-f for deflecting light passing ~hrough the corres~
ponding objective lens 88a or 88b generally downward along ~ corresponding downwardly extending portion 87b of dual optical path 87a-f to another co~responding beam bender 108.
Each beam bender 108 is mounted on ~he same arm 89 as the corresponding beam bende.r 106 for pivotal movPment there-with as ~he objective lenses 88a and 88b are moved closer together or further apart. Beam benders 108 are mounted ~long the corresponding downwardly extending portions 87b of dual optical path 87a-f fox deflecting light from the ~orres--ponding be~m benders 106 along oorresponding horizontally ex~ending portions 87c of dual optical path 87a-f t~ corres-ponding beam benders 110 *r~m which that light is d~flected ~long other correspQnding horizontally extending portions 87c of dual optical path 87a-f to corresponding faces of a split field prism 112. Split field prism 112 in turn deflects light from each beam bender 110 in side-by-side relationship along a common horizontally ex~ending por~ion 87c of dual optical path 87a-f through a field len~ 114 to another beam bender 116. Beam benders 110, split field prism 112, and field lens 114 are fixedly mounted ~n stage 96 along the respective horizontally ex~ending portions 87~ of dual op~ical path 87a-f.
Beam bender 116 is mounted along the common horizon~ally extending p~rtion 87c of dual optical path 87a-f for swivPl movement thereabout and is disposed for deflecting lighk passing through field lens 114 downward along a d~wnwardly extending portion 87d of that dual optical path through posi-tive lenses 118 and 120 to a beam bender 1~2. Positive lenses 118 and 120 and be~m bender 122 are mounted along the downwardly extending ~ortion 87d of dual optical path 87a-~ for swivel move~ment with beam bender 116 about the common horizontally extending portion B7c of that dual optical path, and to allow relative axial m~vemen~ between posi~ive lens 118 (which is fixedly mounted in a first tube 11~ in fixed relation to beam bender 116~ and positive lens 120 [which is fixedly mounted on a seoond tube 121 in fixed relation to beam ~ender 122, ~he fir~t and second tubes 119 and 121 be.ing &lidably and co~xially ~isposed o~e within the other) as the length of the downwardly extending poxtion 87d of the dual optical path is changed by relative movemen~ of beam benders 116 and 122~ Thus, the downwardly extending portion 87d of dual optical path 87a-f may be moved by a manually controlled X
axis slide 123, on which beam bender 122 is mounted, to locate beam bender 122 in an operative position along a horizontally extending portion B7e o~ dual optical path 87a~f whenever the first objective lens unit 90 is to be employed with binocular lens unit 93, such as in the substage ad,ust-ment operation. In this operative position beam bender 122 deflects light passing through positive lenses 118 and 120 forward along the horizontally extending portion 87e of dual optical path 87a-f to a beam bender 124. This beam bender 124 is fixedly mounted along the horizontally extending por-tion 87e of dual optical path 87a-f for deflecting light from beam bender 122 upward along a v~rtically extending portion 87f of dual optical path 87a~f to ocular lenses 126 of binocular head 94, which is fixedly mounted along that portion of the dual optical path.
The varlous elements of the first objective lens unit 90 an~ binocular lens unit 93 are arranged along dual optical path B7a~f as described above so that the aerial image vi~wed in the second image plane 79 by objective lenses 88a and 88b axe reimage~ at a third im~ge plane 113 directly in front of split field prism 112~ Positive lens 118 is provided with a ocal length equal tv the distance back along dual optical path 87a-f to the third Lmage plane 113, and positive lens 120 is provided with a focal length equal to the distance forward along that dual optical path to a fourth image plane 127 directly in front of ocular lenses 126~ Positive lenses 118 and 120 therefore serve as a relay lens unit for reimaging the reimaged image appearing in the third image plane 113 at the fourth image plane 127 and for accommodating changes in the length of the downwardly extending portion 87d of dual optical path 87a-f while transmittiny light passing between those positive lenses in parallel rays as required to maintain proper focus.
As shown in Figure 2 and described in copending Canadian Patent Application Serial No. 348,698 entitled OPTICAL
FOCUSING SYSTEM and filed on March 28, 1980, by Optimetrix Corporation, stage 16, beam splitter 21, and projection lens - 18 (and, hence, also compensating lens 76) are securely mounted on a tower 2. This tower 2 comprises an upper platform 3 on which stage 16 and beam splitter 21 are mounted, six llpright rods 4 on which the upper platform is securely mounted, and a base 5 on which the rods 4 and the projection lens 18 (and, hence, compensating lens 76) are securely mounted. Stage 16, ~he reticle holder 17 mounted thereon, and the upper platform 3 of tower 2 are provided with clearance openings 6 permitting light passing ~- through the reticle 12 to pass along the vertically extending portion 34e of dual optical path 34a-f through projection lens 18 to whatever object is positioned directly beneath the projection lens. The base 5 of tower

2 is mounted by air bearings on a casting 7, which is in turn fixedly mounted on a granite block 8 on which main stage 20 is mounted as described in Canadian Patent Application Serial No. 349,305. Base 5 of tower 2 is vertically movable wi~h respect to the casting 7 (and, hence, granite block 8) so as to permit vertical movement of the tower and, hence, projec~ion lens 18 rela~ive ~o main stage 20 under contrs:~l of an au~oma~ic optical focusing system described in Canadian Patent Application Serial No. 348,698.
All of the elements ~:f the firs~ objective lens unit 90 and c~:Ç the binc)cular lens unit 93 are securely mounted on an upright por~ioh g of casting 7, while all of the elemen~s of the second objective lens unit 92 are securely mounted on an upright portion 10 of the base 5 of ~ower 2 for ~ertical movement with the tower 2. In addition, all of the elements of light source unit 24 shown in Figure lB are mounted on an upright post (not shown) which is in turn rotatably mounted on castin~ 7 so as to permit those elements to be pivoted away from the other portions of alignment and exposure system 10 for ease of service.
Referring now to Figures lA-C, 2 and 3, the substage adjust-ment operation is performed by employing the X and Y servo drive units 25 and 27 for moving main stage 20 so as to posi-tion refexence mark plate 28 directly heneath projection lens 1~ with the end portions (includi~g tic marks 26b~ of reference 2Q mark 26 (which is nominally oriented along the X axis) illuminated by the projected images of reticle alignment marks 78a and 78b (i.e., by the blue light passing through those reticle alignment marks) contained on reticle 1~. Con-comitantly, ~he X and Z axes servo drive units 9B and 100 and the 4 servo drive unit 104 a~e employed for moving stage 96 and spacing objective lenses 88a and 88b of the first objective lens unit 90 so as to position those obj~ctive lenses for viewing the aerial images of the illuminated end portions of reference mark 26. Since prior to adjustment of substage 30, reference mark plate 28 is likely disposed adjacent to and intersecting, rather than in, the Eirst image plane 77, both of these aerial images of the llluminatPd end portions of reference mark plate 28 will be out of focus (one end portion likely being disposed above and the other end portion below the first image plane). While viewing these out~of-focus aerial images, the operator manually adjusts substage 30 with respect to the plane of main stage 20, and the automatic focusing system described in Canadian Patent Application Serial No. 348,698 automatically moves tower 2 so as to track the average pivotal movement of the substage until both of these aerial images are brought into focus.
At this point reference mark plate 28 is precisely positioned in and parallel to the irst image plane 77, and the aerial images of the end portions of reference mark 26 illuminated by the projected images o reticle alignment marks 78a and 78b contained on reticle 12 are in focus.
While employing one of the objective lenses of the first objective lens unit (for example, the right hand objec-tive lens 88b) to view one of the focused aerial images (for example, the aerial image of the end portion of reference mark 26 illuminated by the projected image of the right hand reticle alignment mark 78b), the operator employs the X axis servo drive unit 25 for moving main stage 20 back and forth along the X axis in a shuttle mode so as to alternate~ly posi-tion each end portion of the reference mark in the projectedimage of the right hand reticle alignment mark 78b and thereby pass line 26a of the reference mark back and forth through that projected image as shown in Figure 6. If line 26a of reference mark 26 is not precisely aligned wlth the X axis o motion of main stage 20, this back-and-forth movement of the main stage ~auses ~he illuminated portion of line 26a t9 rise and fall within the projected imaye of the right hand reticle alignmen~ mark 78b. The operator $hereupon adjusts ~he angular position of substage 30 until the il luminated portion of line 26a of reference mark 26 does not rise and fall within the projected image of the right hand reticle ~lignment mark (i.e., remains in the position shown in Figure 6) as main s~age 20 is m~ved back and forth. This precisely ~- aligns line 26a of referen~e mark 26 with the X axis of motion of main stage 20 and establishes the reference mar~ as an absolute frame of reference for precision alignment operations ko be performed with alignment and exp~sure system 10 as here-inafter explained.
A ~et of n difference reticles 12, each containing a different level of microcircuitry to be successively printed at each of an array of adjacent regions of semicon~uctive ~afer 14 in alig~ment with other levels of microcircuitry previously printed or ye~ ~o be printed at those same regions, is employed in the fabrication of integrated circuits or the 2~ like from the semiconductive wafer. Following th~ substage adjustment opera~ion (and one other set~up operation herein-after described)~ alignment and exposure system 10 may be ~uccessively employed with each xeticle 12 o~ ~he set to suc-cessively per~orm each of these step-and-repeat printing operations on every semiconductive wa~er 14 of a batch of semiconductive wafers being processed by ~he alignment and exposure systemt as describ~d below. Either the first reticle 12 of the first set ~f reticles to be employed wi~h align-ment and exposure sys~em 10 or a special set-up reticle may be employed to perfcrm the previously-described subs~age adjustment operation.
During each step-and-xepeat pxinting opPration, the reticle 12 being employed must first be precisely aligned with res~t to refer~ce mark 26 on substage 30 and, hence, with the X axis of motion of main stage 20. This is accomplished by placing the reticle 12 on ~cuum holder 17 of stage 16 in nominal alignment with the ~ axis of motion of main stage 2Q; ~y employing X and Y axes servo drive uIlits 25 and 27 for moving the main stage ko a position at which reference mark 26 is centered directly beneath projection lens 18 with the end portions of the re~erence mark nominally aligned with the images of the reticle alignment marks 78a and 78b of the reticl~ to be projec~ed snto ref~ence mark pla~e 28 when shutter 50 is opened; by employing Y axis servo drive unit 66 ~or moving slide 58 to a position at which mask plate 62 i5 located in the same operative position between positive lenses 46 and 47 as previously described; by employing ~
servo drive unit 51 to open shutter 50 so as to illuminate the retiele alignment marks 78a and 78b on the reticle and, hence9 the end portions of reference mark 26 falling within the projected images of ~hose reticle alignment marks; by employing slide 123 for ~oving beam bender 122 to the opera-tive position in the horiz~ntally extending portion 87e of optical path 87a-f as described above; by employing the X
axis t Z axis, and ~ servo drive units 98, 10O, and 104 to position the objective le~ses 88~ and 88b for viewing the aexial images of the end p~rtions of referenc~ mark 26 illu-minated by the images of ~he reticle alignmen~ marks 78a and 78b projected onto ~hose end portions; and,while viewing ~hose aerial images,by employing the X axis and differential -2~

Y axis servo drive units 84, ~6a~ and 86b for moving reticie 12 to precisely align t~e images of the reticle ~lig~men~
marks 78a and 78b contained on the reticle with the illuminated end portions of refexence mark 26 as shown in Figure 7~ When 50 aligned the images of transparent windows 80a and 80b of each reticle alignment mark 78a and 78b are symmetrically dispos~d with respect to the line 26a and intersecti~g tic mark 26b of the respective end portion of reference mark 26.
It should be noted that many of the foregoing steps of the xeticle alignment operation will already have been performed in the case of the first reticle o~ ~he first set of reticles being employed wi~h alignment and exposure system 10 if ~hat reticle is initially employed, rather ~han a special set-up reticle,in performing the previously described substage adjust-ment op ra~ion.
Once the first reticle 12 of the set has been aligned ~ith xeference mark 26 as des ribed above, a pair of spaced wafer alignment marks 130a and 130b contained on the first reticle is printed on each semiconductive waer 14 of the batch of semiconductive wafers being processed by alignment and exposure system 10. The wafer alignment marks 130a and 130b printed on s~miconductive wafer 1~ are employed to pre-cision prealign the semiconductive wafer, as hereinafter xplained in preparation for each step-and-repeat printing operation. The same pair of wafer alignment marks 130a and 130b can be employed in preparation for every step-and-r~peat printing operation to be formed on semiconductive wafer 14 so long as that pair of wafer alignment marks does not become obliterated or o~scured during those step-and-repeat printing operations or other processing operations O -2~-following each step-and-repeat printing operation. Additio~al pairs of wafer alignment marks 130a and 130b may also be con-tained on ~he irst reticle 12 and printed on semiconductive wafer 14 during the same wa~er alignment mark printing operation in the event they should later be required.
The wafer alignment marks 130a and 130b contained on ~he fixst reticle 12 are spaced 103 millimeters apart and are disposed directly adjacent to and behind reticle align-ment marks 78a and 7Bb. As best shown in Figure 8~ each of these wafer alignment marks 130a and 130 comprises a light or transparent cross (with orthogonal bars 132a and 132b~
disposed on a dark or opaque field. In preparation f~r printing these wafer alignment marks 130a and 130b on each s~miconductive wafer 14 of the ~atch being processed by align-ment and exposure system lOt a photosensitive film is depo-sited over each semiconductive wafer of the batch. ~he wafer alignment mark printing operation is then successively pex-formed on each semiconductive wafer 14 of the batch i~ the same manner as will now be described for the first semicon-ductive w~er of ~he batch.
The first semiconductive wafer 14 is placed on a vacuum chuck 131 mounted on main stage ~0 for differential movement with respect to the plane of the main stage to permit parallel-plane alignment and focusing of the upper surface of the s~miconductive wafer in the first image plane 77 as described in detail in Canadian Pa~ent Application Serial No. 348,698.
The left hand wafer alignment mark 130a contained on the first xeticle 12 is printed on the left hand side of the first semi-conductive wafer 14 b~ employing Y axis servo drive unit 66 for moving slide 58 to locate mask plate 62 in an operative

3~

position between positi~e lenses ~6 and 47 so as to illuminate ~mall circular portions ~f the reticle containing the left and right hand wafer alig~men~ marks 130a and 130b with blue light when shutter 50 is subsequently opened; by employing X and Y axes servo drive units 25 and 27 or moving main stage 20 to a position at which the left hand side of the semicon-ductive wafer is disposed directly beneath projeGtion lens 18 so that when shutter 50 is subsequently opened the lef~
( hand wafer alignment mark 130a on ~he retiele will be imaged onto the 1 ft hand side of the semiconductive wafer at a l~cation along a center line 134 thereof parallel to the X
axis and at a distance from the center 136 of the semicon~
ductive wafer equal to half the objective spacing of the second objective lens unit 92, while ~he right hand wafer alignment mark 130b on the reticIe will be imaged off and to the left of the semiconduc ive wafer, as shown in Figure 9A;
and by thereu~on momentarily opening shutter 50 so that blue light passing through the aforementioned small circular por-tion of the reticle containing the left hand wafer alignment m~rk 130a selectively exposes a correspondinq portion of the photosensitive film deposited ~n the semiconductive wafer and thereby prints that left-hand wafer alig~ment mark 130a on the semiconductiYe wafer at the aforementioned loca~ion.
Similarly, the right hand wafer alignment mark 130b contained on the first reticle 12 is then printed on the right hand side o~ the first semiconductive waer 14 by employing X and Y axes servo drive units 25 and ~7 for moving main stage 20 to a positi~n at w~ich the right hand side of the semiconduc-tive wafer is disposed directly beneath projection lens 18 so that when shutter 50 is subsequently opened the righ~ hand -2~-p~

wafer alignment mark l30b on ~he re~i~le will be ~naged onto the right ~and side of the s~miconduc~ive waer at a location along centerline 134 thereo~ parallel ~o the X axis and at a diskance from the center 136 of the semiconductiYe wafer equal to half the objective spacing of the second objective lens unit 92, while ~he let hand wafer alignment mark 130a on the reticle will be imaged of and to the right of the semiconductive wafer, as shown in Figure 9B; and by thereupon ~omentarily opening shutter 50 so that bl~e light passing through the aforementioned small circular portion of the reticle ~ontaining the right hand wafer al.ignment maxk 130b ~electively exposes a corresponding portion of the photo-~ensitive film deposited on the semiconduc~i~e wafer and thereby prints that right hand wafer alig~ment mark 130b on the semiconductive wafer at the aforementioned location.
Followin~ the oregoing wafer alignment mark printing opera-tion, the first semiconductive wafer 14 is removed from alignment and exposure system 10 and is subsequently processed in accordance with well known techniques to develop the selec~ively axposed photo~ensitive film thereon, nd,for ex~nple, ~o etch the wafer alignment marks 130a and 130b printed on the semiconductive wafer into the semic~nductive waer.
In initially setting up alignmen~ and exposure system 10 left and right hand prealignment reticles 138a and 13~b are manually adjusted (by adjus~ment screws not shown) to precisely align ~ages of l~t and right hand wafer ali~nt marks 140a and 140b ~espectively contained thereon with the X axis of motion of main stage 20 as hereinafter explained. These wafer alignment marks 140a and 140b are identical to reticle ali.gnment mar~s 78a and 78b contained on reticle 12 but are ~paced apart along the X axis in coIrespondence with the objective spacing of the second obj2ctive lens unit 92 and, hence, with the spacing of the wafer alignment marks 130a and 130b previously printed and then e-tched or otherwise formed on each ~emiconductive wafer 14. Thus, once a semi-conductive wafer 14 has be~n put back in alignment and exposure system 10 and placed on vacuum chuck 131, it may quickly be precisely ~ligned with respect to the X axis of moti~n of main st~ge 20 and~ hence, with respect to reticle 12 by simply employing the X and Y axes servo drive units 25 and 27 for moving the main stage to align the wafer align-ment marks 130a and 130b cn the semiconductive~afer with the ~ges of the co~respondmg ~afer alig~t marks 140a and 140b c~ta~ed on prealignment reticles 138a and 138b, respectively.
The first semiconductive wafer 14 o~ the first batch of semiconductive wafers being processed by alignment and expo-sure system 10 can be used in performing the prealig~ment xeticle adjustment operation. In order to do this the irst semic~ductive wafer 14 has to be precisely aligned with the ~age of first reticle 12 of the first set of reticles being empl~yed with alig~ment and exposure s~stem 10 and, hence, with the X axis of motion of main stage 20 so as to become a secondar~
frame of reference ~or use in aligning prealignment reticles 138a and 138b with the X axis motion of the main stage. This is accomplished by placing the first semiconducti~e wafer 14 on vacuum chuck 131 in nominal alignment with the first reticle 12; by employing the ~ servo drive unit Sl to open shutter 50; by employing the Y axis servo drive unit 66 for moving slide 58 to position mask plate 6~ at an operative -~8-p~sition be~ween positive lenses 46 ancl 47 so as to illuminate small circular regions of r~ticle 1~ containing the left and right hand reticle alig~men~ marks 78a ana 78b as previously described in connection with ~he substage adjuskment and reticle alignment operations; by returning slide 123 and ob~ective lenses 88a and 88b of the first objective ~ens unit 90 to ~he positions des~ribed above in connection with the retlcle alignment operation, if slide 123 and objectiv2 lenses 88a and 88b are not already in those positions (ho~Jever, they should in fact already be in those positions sinoe they do not need to be moved therefrom during alignment of the first reticle of the first set with res~t to the reference mark 26 or ~uring subsequent printing of the wafer alignment marks 130a and 130b on the first semiconductive wafer 14); and by ~mploying main stage 20 to perform successive X axis, ~
rotatio~al~ and Y axis alignments o~ the wafer alig~ment marks 130a and 130b on the first semiconductive wafer with respect to the projected images of the illuminated reticle alig~ment marks 78a and 78b contained on the first reticle.
~0 The X axis alignment of wafer alignment maxks 130a and 130b with respect to the projected images of reticle align-ment marks 78a and 78b may be perormed by employing the X
and Y xes ser~o drive units 25 and 27 for moving main s~age 20 to position the left hand wafer alignment mark 130a ~irectly beneath the projected image of the left~hand reticle alignment mark 78a; by employing the le~t hand objective lens 88a of the first objective lens unit 90 to view the aerial mage of portions of the left hand wafer alignmen-~ mark 130a illuminated by the projected image of the let hand reticle alignment mark 78a; and, while viewing that aerial image, by fur~er ~ l~ ~g ~le X and Y axes servo drive units 25and 27 for moving the main stage to align ~he let hand wafer alignment mark 130a symmetrically with respec~ to the projecte~ image of the left hand reticle alignment mark 78a as shown in Figure lOA. This should normally ~P effective to complete the X axis alignment of both wafer alignment marks 130a and 130b formed on the first semiconductive wafer with respect to the projected images of thP. corresponding xeticle align-ment marks 78a and 78b contained on the ~irst re icle 12~
The ~ rot tion alignmQnt of wafer alignment marks 130a and 130b with respect to the projected images of the reticle alignment marks 78a and 78b may next be performed by employing the X axis servo drive unit 25 for moving main stage 20 to position the right hand waf~r alignment maxk 130b beneath the projected image of the right hand reticle a~ignment mark 78b; by employing the right hand objective lens 88b of ~he first objective lens unit 90 to view the aerial image of portions ~f the right hand wafer alignment mark 130b illuminated by the projected image of the right hand reticle alignment mark 78b; and~ while viewing that a~rial imagel by employing a a servo drive unit 29 for rotating vacuum ch~k 131 on ~e main stage to move the right hand wafer alignment mark 130b as sho~n in Figure lOB from its original position ~indicated in dashed lines) to an intermediate position (indicated in solid lines) approximately half the xo~ational distance (~enter-to center~ between its original position and the posi-tion of the projected image of the right hand r~ticle align-ment mark 78b. This has the effect of moving both wafer alignment marks 130a and 130b formed on the first semiconduc-tive wafer l~ into nominal ~ rotational alignment with the ~ 3 projec~ed imayes o~ khe correspondin~ reticle alig~men~
marks 78a and 78b contained on the ~irst re~icle 12. Each of these wafer alignment marks 130a and 130b is therefore ofset approximately ~he same distance ~center to-center~
along the Y axis from the projected imaye of the corresponding reticle alignment mark 78a ox 7~b as may be seen by comparing the intermediate position o~ the right hand wafer alignment mark l30b ~indicated in solid lines in Figure lOB) relative to the projected image of the right hand reticle alignment mark 78b and the intermediate position of the left hand wafer alig~ment mark 130a (indica~ed in solid lines in Figure lOC) relative to the projPcted image of the left hand reticle alignment maxk 78a.
The Y axis alignment of wafer alig~ment marks 130a and 130b with respect to the projected images of reticle align-ment marks 78a and 78b may be performed by employing thP X
axis servo drive unit 25 for moving main stage 20 to posi-tion the left hand w~fer alignment mark 130a beneath the projected image of the left hand reticle alignment mark 78a;
by employing the left hand objec~ive lens 8~a of the first objective lens unit 90 to Yiew the aerial image of the left hand wafer alignment mark 130a illuminated by the pr~jected image of the left hand reticle alignment mark 78a as shvwn in Figure lOC; and, while viewing that aerial lmage, by employing the Y axis servo dri~e unit 27 ~nd, if nPcessary, the X axis servo drive unit 25 ror moving the main stage to align the left hand wafer alignment mark 130a symmetrically with respect to the projected image of the left hand reticle alignment mark 78a as shown in Fisure 10~ This has the effect of moving both wafer alignment marks 130a and 130b formed on the first semiconducti~e wafer 14 în~o nominal Y axis alignment with the projected image of the corresponding xeticle alignmen~ marks 78a and 78~ con~ained sn the first reticle 12.
A5 mentioned above, the X axis alignmen~ of both wafer alig~ment marks 130a and 130b fonmed on ~he first semicon-ductive wafer 14 with respect to the projected images of the corresponding reticle alignment maxks 78a and 78b contained on the first reticle 12 should be completed a~ the end of the initial X axis alignment s~ep. ~owe~er, if any X axis misalignment should remain, it will be observed and can be eliminated while ~erforming the Y axis alignment step. Due to the difficulty of precisely estimating half the rotational distance ~center-to-c2nter) be~een the right-hand wafer alignment mark 130b and the projected image of the corres-ponding reticle alignment mark 78b during the ~ rotational alignment step and due also to the resulting differences in the distances the le~t and righ hand wafer aligNment marks 130a and 130b are offset along the Y axis from the prvjected ~mages of the corresponding reticle alignment marks 78a and 78b (center-to-center), several iterations of the ~ rota-tional and Y axis alignment steps are normally required ~o compl~te those alignments. Each such iteration of the ~
rotational and Y axis alignment steps should reduce any 4 rotatio~al and Y axis misalignments by at least half. -On~e the X axis, ~ xotational,-and Y axis alig~ments of both wafer alignment marks 130a and 130b on the firs~ semi-conductive wafer l4 with respect to the projected images o the corresponding reticle alignment marks 78a and 78b on the first reticle 12 have been sompleted (i.e~, any X axis, ~ 3~

rota~ional, and Y axis misalig~ments ~ave become unobse.rVable with the first objective lens uni~ sO), ~he wafer alignment marks 130a and 130b o~ the firs~ semiconductive waex are precisely aligned wi~h respect ~o ~he X axis of motion of m~in stage 20. The first semiconductive wafer 14 has there-fore become a secondary frame of reference ~hat may now be employed for aligning the wafer alignment marks 140a and 140b contained on prealignment reticles 138a and 138b, respectively, with the X axis of mo~ion of main stage 20 during the prealign-ment reticle adjustment operation. Aceoxdingly, ~he X and Y
axes servo drive units ~5 and 27 are employed for moving main stage 20 to locate the first semiconductive wafer 14 in the ~realig~ment position shown in Figure 1. In ~his position th left and right hand wafer alignment marks 130a ana 130b on the first semiconductive wafer 14 are disposed beneath the corresponding left and right hand wa~er alignment marks 140a and 140b on the le~t and right hand prealignment reticles 138a and 138b, respectively, and e~uidistantly along the X
axis with respect to the optical axis of projection lens 18.
The manner in which the prealignment reticle adjus~mQnt operation is performed will now be described with reference to the parts of alignment and exposure sys~em 10 employed in that operation.
With reference now particularly to Figures lAr lC, 2 and ll,eac~ of the prealignment reticles 138a and 138b is mounted along a corxesponding vertically extending por~ion 142a of a dual optical path 142a-c (on the upright portion 10 of the ~ase 5 of tower 2~ for both pivotal movement about and translational movement relative to that portion of dual optical path 142a-c (as manually controlled by adjus~ment screws not shown) so as to perm~t alignment of an i~ ye of the wafer alignment m~rk 140a or 140b contained ~hereon wi~h the corres~
pondins wafer alignment mark 130a ox 130b fo~med on the first semiconductive wafer 14. A separate fiber optical light pipe 144 is fixedly mounted at ~ne end along each of the vertically exkending portions 142a of dual optical path 142a-c directly above the corresponding prealignment reticle 138a or 138b.
The other end of each of these fiber optic light pipes 144 i5 optically coupled to a secondary ligh~ source 146 of the projection lamp type for emitting illuminating light having a wavelength of 525 nanometers or greater. Illuminating light from this secondary light source 146 passes through iber optic light pipes 144 and downwardly along the vertically extending portions 142a of dual optical path 142a-c through the corresponding prealignment reticles 138a and 138b.
The ~econd objective lens unit 92 includes a s~parate beam splitter 148 fixedly mounted along each of the vertically extending portions 142a of dual optical path 142a-c f~r transmitting fifty p rcent of the light passing through the corresponding prealignment reticle 138a or 138b downwardly 210ng that poxtion of dual op~ical path 1~ 2a-c . It also includes left and right hand objective lenses 150a and 150b each comprising a 10:1 objective lens fixedly mounted along a corresponding different one of the vextically extending portions 142a of dual optical path 14~a-c directly below the corresponding beam splitter 148. When ~the first semiconduc-tive wafer 14, or any subsequent semiconductiv4 wa~er, is located in the prealign~ent position shown in Figure 1, these left and right hand objective lenses 150a and 150b are disposed directly above left and righ~t hand portions of the semiconducti -34~

wafer that contain the left and xigh~ hand wafer alignment marks 130a and l~Ob, respectively9 since ~hose wafer align-ment m~rks were ~paced apart along the X axis by a distance equal ~o the ob~e~tive spacins ~f the second ohjective lens ~nit 92 as described aboYe~ The lef~ and righ~ hand objective lenses 150a and 150b focus the ligh~ passing thr~ugh the ~orresponding left and right hand prealignment reticles 138a and 138b and the corresponding beam splitt~rs 148 at the first image plane 77 adjacent to main stage 20 and directly beneath those objective lenses, thereby pro jecting images of the left and right hand wafer alignmen~ marks 140a and 140b contained on those prealignment reticles onto the corresponding left and right hand wafer alignment mark containing re~ions of the semiconductive wafer 14 located in the prealignment position. Fifty percent of the light reflected vertically upward from each of these left and riyht hand wafer aligl~ent mark containing reyions of semiconductive wafer 14 through the corresponding objective lens 150a or 150b is reflected by the corresponding beam splitter 148 along a horizontally ex~ending portion 142b of dual optical path 142a-cO
The second objective lens unit 92 also includes a sepaxate beam bender 152 fixedl~I mounted along each horizon-~ally extending poxtion 142b of dual optical path 142a-c adjacent to the eorresponding beam splitter 148 so as to deflect the reflected light therefrom to a corresponding face of a split field prism 154. Split field prism 154 is fixedly mounted along both horizontally extending portions 142b of dual optical path 14~a-c as to deflect the reflected light from each beam bender 152 in sidP-~y-side relationship along a co~mon horizontally extending portion 142c of dual ~ .3 optieal pa~h 142a~c to a fifth ima~e plane 155 positioned directly in fxont o~ split field prism 154 and the same optical distan~e fxom beam spli~ers 148 as are prealignment reticles 138a and ~38b. A 5:1 objec~ive lens 156 is fixedly mounted along the common horizontally extending portion of dual optical path 142a-c for viewing ~he fif~h image plane 155.
The horiæontally extending portion 142c of dual optical path 142a-c is axially align~d wi~h the hori.zontally extending portion 87e of dual optical pa~h 87a-f to permit use of the first and seeond objectivP lens units ~0 and 92 with the same binocular lens unit 93 as dPtermined by the position of slide 123. Accordingly, a positive lens 158 is fixedly m~unted on slide 123 for movemen~ into an operative position in those axially aligned horizontally extending portions 87e and 142c of dual optical paths 87a-f and 14~a-c between beam be~der 124 and objective lens 156, as ~hown in Figures lC and 11, when the second objective lens unit 92 is to be employed~
With positive lens 158 so positioned, light from objective lens 156 passes through positive lens 158 and along horizon-tally extending-portion 87e o dual optical path 87a-f to beam bender 124 from which it is deflected upward along ~ertically extending portion 87f of dua~ optical path 87a-f to ~he fourth image plan~ 127 di~ectly in front of ocular lenses 1~6 of binocular head 94.
~he ~arious ele~ments of the second objective lens unit g2 are arranged along dual optical path 14~a-c as described above so that objective lenses 150a and 150b focus the light reflected from the left and right hand wafer alignment mark containing regions of the semiconductive wafer 14 disposed in the prealignment position at the fifth image plane 155 ~ t.~

directly in fron~ of spli~ field prism 154. This provides aerial Images of the let and right hand wafer aliy~ment marks 130a and 130b disposed on the semiconductive wafer in ~he first Lmage plane 77 direc~ly beneath objective lenses 150a and 150b, ~nd o~ ~he images of ~he corresponding left and right hand waf~r alignment marks 140a and 140h contained on the prealig~ment re~icles 138a and 138b and projec~ed onto the semiconductive wafer directly beneath those ob~ective lenses, in the fifih image plane 155. Objective lens 156 has a focal length equal to the distance from its input pupil ba k along the horizontally extending portion 142c of dual optical path 142a c to the fifth image plane. Positive lens 158, whPn positioned in the axially aligned horîzontally extending partions 87e and 142c of dual optical paths 87a-and 142a-c~ has a focal length equal to the distance orward along portions 87e and 87f of dual optical path 87a-f to the fourth image plane 127 directly in front of ocular lenses 126 of binocular head 94~ Objective lens 156 and positive lens 158 therefore reimage the aerial ~mages provided in the fifth image plane 155 at the fourth image plane 127.
The prealignment reticle adjustment operation may ~here-foxe be performed by employing slide 123 to move positive lens 158 into th~ operatiYe position in the axially aligned horizontally extending portions 87e and 142c of dual optical paths 87a-f and 142a-c; by thereupon employing binocular lens unit 93 with the second objective lens uni~ 92 to view the aerial ~mages of those por~ions of the let and right hand wafer alignment marks 130a and 130b disposed un the ~irst semicondu~tive wafer 14 that are illuminated by the projected images of the ~orresponding wafer alignment marks 140a and 140b disp~sed on pr~alig~menk reticles 138a and 138b; and, while ~iewing ~hose aerial .umages, by manually adjusting the pre-alignment reticles ~o p~si~ion the projected images of the left and right hand wafer alig~ent marks 140a and 140b dis-posed thereon in precise ~ rotati~nalV X axis, and Y axis alignment with the corresponding left and right hand wafer alignment marks 130a and 130b disposed on the first semicon-ductive wafer as shown in Figure 12. This precisely aligns the prealignment reticles 138a and 138b with ~he X axis of motion of main stage 20 and positi~ns them e~uidistantly a~ong the X axis with respect to the ~ptical axis of projec-tion lens 18 5~ that they may subsequently ~e employed in the precision prealignment of other semiconductive wafers 14 without further adjustment. Although the prealig~ment reticle adjustment operation should not normally have to ~e repeated during the lifetime o~ alignment and exposure syst~m 10, i~
may be checked at any time by employin~ another semiconduc-tive wafer in the same manner as described above for the first semiconductive wafer.
29 Each semi~onductive wafer 14 processed by alignment and exposure system 10 subsequent to the pr~is~nt r~ticle adjust-m2nt 4peration, may ~e precisi~n pn~i~ned with-re~x~t bD th~ X axis ~f motion of main stage 20 and with respect to the optical axis of projection lens 18 by simply employing the X and Y
axes servo drive units 2~ and 27 for moving maîn stage 20 to position the ~emiconductive wafer in the prealignment posi-~ tion sho~n in Figure l; by moving slide 123 to move positive lens 158 to the operative position, by employing binocular lens unit 93 to vlew the aerial images provided by ~he second objective lens unit 92 as descrihed above; andl while viewing ~hose aerial images, by ~mploying ~he X axis, Y axis, and ~ servo drive units 25~ 27 9 and 2~ ~or moving the ~ain stage and rotating vacuum chuck 1~ ~o precisely align the left and right hand wafer alignment marks 130a and 130b formed on the semlc~d~tive wafer Wi~l the ~ges of the corresFcnd~g leftand right hand wafer align~en~ marks 140a and 140b contrained on the prealigNment reticles 138a and 138b. Following the precision prealignment of a semiconductive wafer 14 it may be subjected to a step and-repeat printing ope~ation in the same manner as described below for the firs~ semiconductive wafer 14.
Assuming that the first reticle 12 of the irst set of reticles being employed with and the first semiconductive wafer 14 of the first batch of semi~onductive wafers being processed by alignment and exposure system 10 were employed to perorm the previously-described prealignment reticle adjustment operation (rather than a special set-up reticle and a special set-up wafer), the firs~ semiconductive wafer i~ then removed from alignment and exposure system 10 so that a photosensitive film may be deposited over the first semi-conductive wafer along with the other semiconducti~e wafexs of ~he same batch. The first semiconductive wafer i4 is thereafter placed bac~ in alignment and exposure system 10 on ~a~uum ehuck 17 and precision prealigned with prealignment reticles 138a and 138b as described abo~e~ Referring again to Figures lA-C and 2, the first level of microcircuitry con-tained on a central portion 160 of the first reticle may now be printed at each of a desired array of adjacent regions 162 of the first semiconductive wafer as shown in Figuxe 13.
This is accomplished by employing the Y axis servo drive YC'~

unit ~6 for moving slide 58 ~o positi~n mac;k plate 60 in an operative position bet~een~osltive lenses 46 and 47 with a ~quare central opening 69 of mask pla~e 60 permitting illu-mination of the entire micr~circuitry-con~aining ~entral por-tion 160 of the firs~ reticle 12 held ~y vacuum holder 17 when shutter 50 is moved to the open posi~ion shown in dashed lines in Figure l; by employing ~he X and Y axes serVQ drive units 2S and 27 to step main stage 20 so as to successively position each of the desired array of adjacent regions 15~ of the first semiconductive wafer 14 held by vacuum chuck 131 dire~tly beneath projection lens 1~ in the order indicated by the dashed arrows in Figure 13; and by employing the ~ servo drive unit 51 to momentarily move shutter 50 to the open posi-tion when each of those regions 162 of the firs~ semiconductive wafer is so positioned, ~hereby repetitively selectively exposing the photosensitive film deposited on the first semiconductive wafex so as to prink the first level of microcircuitry contained on the first reticle at each of those regions o~ the first ~emiconductive wafer. The s~uare entral opening 69 of mask plate 60 is of a size for penmitking illumination of the entire microcircuitry-containing central portion 160 o each reticle 12 ~an area of abvut lOO millimeters or less square~ as des-cribed above, while preventing illumina~ion and, hence, printing o~ the re~icle alignment marks 78a and 78b and any wafer align-ment marks 130a and 130b ~ontained on the rekicle, during the step-and repeat printing operation~
Following this step-and-repeat printing operation, the ~irst semiconductive wafer 14 is removed from a~ignment and exposure system 10 an~ processed to develop the selectively exposed photosensitive ~ilm thereon and to selectively etch, diffuse~ plate, implant or o~herwise proce.,s ~he first semi-conductive waf r in accordance wi~h well known techni~ues for f~rming the first level of microcircuitry on ~he first ~emiconductive wafer at each of ~he desired array of adjacent regions 162. Each additional semiconducti~e wafer 14 of the firs batch and e~ry semicondu~t.ive wafer of every other ~atch to be processed by alignment and exposure system 10 may also ~e processed with ~he ~irst xeticle 12 ~and possi-( bly a second reticle as hereinaf~er explained~ of the afore-mentioned ~et or any other set of reticles in Qxactly the s~me mannPr as described above in connection with the first semioonductive wafer of the first batch texcep for the prealignment reticle adjustment operation) to initi~lly print and form the lef~ and right hand wafer alignment marks ~30a and 130b ~and possibly othe~ alig~ment marks as herein-after explained) on the semiconductive wafer and then to step-and-repeatedly print ~he first level of microcircuitry contained on khe first reticle (or a second rPticle as here-inaf~er explained~ of the set of reticles at each of the ~esired array of adjacent regions of the semiconductive wafer.
In this case each semieonductiv~ wafer 14 is removed from alignment and exposure system 10 following the initial alig~ment mark printing operation to form the aliynment ~rks on the semiconductive wafer, for examplel by a deep etchin~ ~peration, is then placed back in the alignment and exposure system ana precision prealigned in preparation for the s~ ~nt first-~tep,~r~peatmicrocircuitry printing operation, and is removed again from the aligNment and exposure system follcwing the first step-and-repeat microcircuitry printing operati~n to form the first level of micr~circuitry ~1-on ~he ~emiconduc~ive wafer.
Alterna~ively, however, in cases where ~he steps of fonming the wafer alignmen~ marks and the first level of microcircuitry on a ~emiconduc~ive wafer 14 (okher than the first semi~onductive wa~er employed to perform the prealignment reticle a~justment opera~ion~ d~ not require inc~nsistent processing, such as different depths ~f e~ching, it is not necessary to remDve the semiconductive wafer from alignment ana exposure sys~em 10 be~ween khe initial wafer alignment mark printing operation and the first step-and-repeat microcircuitry printing operation (the waf~r alignment marks 130a and 130b then prin~ed on the semicon-du~tive wafer not ~eing required f~r the prealignment reticle adju~tment operation or for alignment of the first level of micr~circuitry with a previou~ly formed level of micro-circuit~y). ~n such cases the first s~ep-and-repeat printing operation can be performed to print the first level of ~icrocircuitry contained on ~he first reticle of ~he set at e~ch of the de~ir~d axray of adjac nt regions 162 of the se~icu~ducti~e wafer wi~hout first per~orming th2 precision prealignment operation. Upon completion of the irst step-and-repeat printing operat~on, ~he semiconductiva wafer 14 is removed for ~he ~irst tlme ~rom alignment and exposure ~ystem 10 and processed as previously indicated to fcrm the wa~eY
~lignment marks 130a and 130b ~and any sther wafer align-~nt m~rks that may ha~e also ~een printed as hereinaf*er described) on ~he seml~onductive wafer and alss to form the ~irs~ level o~ microclrcuitry at each of the desired array of adjacent regions 162 of ~he semiconductive wafer.
Once the ~irst level of microcircuitry contained on -~2-the ir~t xet:icle 12 (or ~Lhe second ret;cle as hereina~tex descri3:~ed) of ~he se~ o:~ xe~icles ~>eing employed with alignmerlt and exposure system 10 has been printed and formed on ea~ of the desired array of adjacent regions 162 of ea~h ~emieond~ctive wafer 14 of the batch or batches being processed with the alignment and exposure system, that reticle is removed from the vacuum holder 17 of stage 16.
The next reticle 12 of ~he set is then placed on the vacu~m holder 17 of stage 16 in nominal alignment with the X axis of motion ~f main stage 20 and is ~hereupon precisely aligned with respect to the X axis of moticn in exactly the same manner as pre~riously described for ~e first reticle of the set (i.e. 9 by employing the X and Y axes ser~o drive uni~s 25 and 27 for moving the main stage to pc>sition reference mark 26 directly beneath projection lens 18; by employing Y
axis servv drive unit 66 fox moving slide 58 l:o position mask pla~e 6Z in an opPrati~re position between positive lenses 46 and 47 so as ~o illuminate ~he re~icle alignmen~
marks 78a aJld 78b OIl the xeticle when shutter 50 is opened; by 2û employing ~ ;ervo dI:i~e ~n~t 51 to open shutter 50; by employing slide 123 to move ~e~m bender 122 into the operati~e position in ~he horizontally extending portion 87e of dual optical path 87a-f and ther2by permit use of ~he first objective lens unit 90 with ~inocular lens-unit 93 for viewing the aerial im~ges of ~he end portions of reference mark 26, which are ~lluminated by t~e projected images of the reticle alignment marks 78a and 78b; by employing the x axis, Z axis and 9 servo drive units 98, 100 and 104 to position objective lenses 88a and 88b for ~iewing those aerial images;
and, while viewing those aerial images, by employing the axis and differential Y axis servo drive units 8~, 86a and 86b for moving stage 16 so as to precisely align the projected images o~ ~he re~icle alignment marks 78a and 78b with the ill ~ nated end por~ions of ~eference ~ark 26 as previously shown in Figure ~.
The second le~el ~f microcircui~ry con~ained on thi5 ~ext reticle 12 of th~ set is thereupon printed and formed at each of ~he desired array of adjacent retions 162 on each semiconductive wafer 14 of $he ~atch being processed by alignment and expo~ure system lO in alignment with the first level of microcircui~ry previously printed and ~ormed at each of those regions on each of those semiconductive wafers. This is accomplishe~ for each of those semiconductive wafers 14 by deposit.ing a photosensi~ive film over ~he semi-conductive wafer; by placing the semiconductive wafer back in alignment and exposure system lO on ~acuum chuck 131 in nominal aligmnent ~i~h ~he X axis of motion of main stage 20;
by pxecision pr aligning the semicondu~tive wafer in exactly the same manner as pre~iously descri~ed for ~he first semi-conducti~e ~afer ~ei~ processed by the aligNment and exposuxe system ti.e. t ~y employing ~he X and Y ~xes servo drive units 25 and ~7 fox mo~ing the main stage to locate the semiconductive wafer in the prealignment position;
by employîng ~lide 123 to move positive lens 158 into the operati~e positio~ in the axially aligned h~rizont lly ~xtending portions 87e and 142c of dual optical paths 87a-~ and 142a-c and t~ereby permit use of the second object~e l~ns unit g2 ~ith binocular lens unit 93 fvr viewing ~he aerial ~mages of the left and right h~nd wafer alignment mar~s 130a and 13Qb dîsposed on the semiconductive wafer and illuminated ~y the projec~ed ~mages of the c~rresponding left and ri~ht ~and wafer alignment marks 140a and l~Ob disposed on the prealigmment xeticles 138a and 133b and, while -~4-~iew;ng ~hose aerial images~ ~y ~mploying ~he X axis, axis~, and ~ servo drive un~s 2s~ 27S and 29 for moving the m~ln stage and rQta~ing the vacuum chuck ~o as to precisely align ~he left and ri~ht hand wa~er alignmen~ marks 130a and 130b on the semi-conductive wafer with the projec~ed images of the corresponding left and right hand wafer alignment marks 140a and 140b on the prealignment reticles);
by then step-and-repeat printing the second level o-E micro-circuitry contained on ~he central portion 160 of the reticle at each of the ~ame desired array of adjacent regions 162 of the semî~nductive wafer in exactly thP same manner as also previously described for ~he first semiconductive ~afer being processed by the alignment and exposure system (i.e., by employing ~he Y axis servo drive unit 66 for moving slide 58 so as to position mask plate 60 in an operative position ~etween positi~P lenses 46 and 47 and thereby illuminate the entire microcircuitry-containing central portion 160 of the reticle when shutter 50 is opened; by employing the X and Y axes se~vo dri~e units 25 and 27 for stepping the main ~tage to successi~ely position each of the same desired array of adjacent regions 162 of the semiconductive wafer direc~ly ~eneath projection lens 18 in the same order as be~ore; and by employing ~he ~ servo drive uni~ 51 to ~mentarily open shutter 50 when each of those region~ 162 of the semiconductive wafer is so posi~ioned and thereby repetiti~ely selectively expose the photosensitive film deposited on t~ semiconductive wafer so as to print the second level o~ microcircuitry contained on the reticle at each of those regions 162 of the semiconductive wafer);

~y ~hereupon ~emoving the semiconductive wafPr from the ~ 3 alignment and exposure system, and ~y su~sequentlY prQCess-ing the semicona~ctîve wafer to develop ~he ~electi~ely exposed photosensitive film thereon and form the ~econd level of microcircuitry a~ eac~ of the ~ame desired array of adjacen~
regions 162 of the semiconductive wafer.
The foregoing reticle alignment, wafer alignment, printing, and processing operations are repeated for each remainîng reticle 12 of the set of re~icles being employed with alignment and exposure system 10 in processing each ~emiconductive wafer 14 of the ~atch of semiconductive wafers being processea hy the alignment and exposure sys~em so ~s to print and form each successi~e level of microcircuitry contained on those reticles at each of the same desired array of adjacent regions 1~2 on each of those semiconductive wafers in alignment with the levels of microcircuitry prevîously formed at each of those same regions on each of those ~emiconducti~e ~afersO ~ollowing completion of this processing each semiconductive wafer 14 i5 typically scribed alongside each row and column of the desired array of adjacent regions 162 of ~e semiconductive wafer so as ~o form a plurality o~ individual die each containing one of the regions 162.
These dice are ~hen typically subjected t~ die honding, wixe ~onaing, and other well known processing operations to form integrated circuits or the like.
Alignmen~ and ~posure system 10 may al50 he used to perform a precision ~lignment step-and-repeat printîng operation permittin~ each level o~ ~icrocircuitr~ to be ~uccessi~ely printea ~t each of the same desired array of adjacent regions 162 of each semiconductive ~afer 1~ in even more precise alignment ~ith any level or levels of microcircuitry previously prin~ed and formed at ~.ach of ~ho~e ~ame regions ~an could o~herwlse be achie~ed with the ai~ o~ t~e a~o~e identi~ied prealignment operation alon~. In order ~o per~oxm ~his precision alignmen~ s~ep-and~repeat printi~g opera~ion 9 ~he irs~ re~icle 12 of the ~et of reticles ~eing employed wi~h alignment and exposure system lO is also pro~ided, as shown in Figure 14, with a set of ~mall wafer alignmen~ marks 170 vertically arranged in a ~ol D , for example, in the marginal portion of the first reticle along ~he Y axis (as~uming the first reticle is held by vacuum holder 17 of s~age 16 in alignment with the X axis of motion of main ~tage 20 as previously described) and between one side of the microcircuitry-containing portion 160 of the first reticle ~nd the reticle and wafer alignment marks 78b and 130~ also con~ained on the first reticle. These small wafer alignment marks 170 lie within the square area of the flrst reticle illuminated when mask plate 60 is disposed in ;ts operative position between positive len~es 46 and 47 and s~utter 50 is opened (as during the above-dPscri~ed ~tep~and-repeat printlng operation~. The small 20 wafer alignment marks 170 may ~omprise ~rosses of ~he same type as the wafer aligNment marks 130a and 130b (i.e~, light or transparent lines orientea parallel to those of wafer alignment marks 130a and 130b and disposed on a dark or opaque field), but are substantially smaller and are e~ in nu*x~ to ~he ~rl r~ng reticles of the set. In the case where ~he set of small wafer alignment marks 17~ is contained on the first reticle 12 of the ~et along wit~ the first level of microcircuitry, the set of small wafer alignment marks 170 îs automatically print;ed wit~ and alongside each of the desired array o~
adjacent regions 162 ~f the s~miconducti~e wafer 14 during f~

~he irst ~tep-a~d-~epeat printing op2ra'~:ion performPd on th~ ~emiconductive wafer~ The sets of small wa~er alignment m~r~s 170 ~o pri~te~ may be for~ed alongsiae each of the desired array ~f adjacent regions 16~ of the semico~ducti~e marker 14, for example, ~y an e~ching operation ~erformed during subsequent processing o the semiconductive wafer to orm the fis~t level of microcircuitry at each of those regions.
~ Alternatively, howeverr in a ca~e where it is desired to form ~he left and xight hand wafer alignmen~ mark~ 130a and 130b and the set of smaller wafer alignment mark~ 170, ~or exæmple~ ~y a deeper etching operation than may be desixed in fonmlng the firs~ level of microcircuitr~, the left ana riaht hand wafer alignmen~ marks 130a and 130b ~nd the set of smaller wafer alignment marks 170 may be pro~ide~ on the first re~icle 12 of ~he set in ,f- ~he same pos;tions shown in Figure 14 and the first level of microcircuitry may be pxovided on the central portion 160 of the second reticle of the set in ~he same position shown i~ Figures 1~ and 14. ~n such a case, ~he ~et of small wafer ali~nmen~ mar~s 170 may ~hen be printed alongside as many ~ the desired array of adjacent regions 162 of th.e sem~conauctive ~afer 14 (ranging fr~m a minimum of, ~or example, ~ne of t~ose xegions per quadrant of the ~miconductive ~afer to a maximum of, fDr example~ ali of those regions~ as deemed appropriate by the operator.
~his may be done immediately following the previously-described operation of printing ~he lef~ and ri~ht hand waer alignment marks 13~a and 130~ contained on th2 first xeticle 12 of the set onto the s~miconductive wafer 14.

3~

The ~mall ~afer alignment m~rk printiny operation is perormed ~y employing ~he ~ axis servo drive unit 6 6 for ving ~lide 58 to pos;~ion mask pla~e ~0 in its operative position between positive lenses 46 and 47 and there~y illuminate the entire central portion 160 of the reticle 12 and the set o small wafer aliynment m~Lrks 170 ~but not the reticle alignment marks 78a and 78b or the wafer alignment marks 130a and 130~) ~hen shutter 50 is opened; ~y employing ~he X and Y ~xes servo dri~e units 25 and 27 for stepping 1~ main stage 20 to successively position selected ones of the regions 162 alongside which the operator desires t~
print the set of small wafer alignment marks 170 (~uch as, for example, a selected one o~ those regions per quadrant of the semiconductive wafer), directly beneath projection lens 18; and by employing the ~ servo drive unit ~1 to m~mentarily open shutter 50 when each of those selected regions 162 ~f the ~emiconductive wafer is so positioned and thereby ( repetitively selectively e~pose the pho~osensitive ~ilm dep~sited on ~he semiconducti~e wafer so as to print ~he 23 entire se~ o~ ~maller wafer alignment marks 170 contai~ed on the first reticle alongside each of those selected regions 162 on the semiconductive wafer. ~he right and le~t hand wafer alignment marks 130a and 130b and the sets o~ ~maller wafer alignment marks 170 so pxinted may ~here upon be ~ormed on ~he semiconductive wafer 1~ by remo~ing the ~emiconductive wafer from alignment and exposure system 10 - for the ~irst time; and ~y subsequently processing the semi-conductive wafer to develop the selectively exposed photo-sensitive film thereon and, for example, to simultaneously 3Q deeply etch all of ~hose wa~Pr alignmen~ marks into the ~e~uconductive wafer a~ the locations wher~ they were prin~ed.
Following ~he wafer alignment mark printing and for~ing vperations in either of t~e foregoing cases, the first reticle 12 is remo~ed ~rom alig~ment and exposure system 10. The second reticle 12 of the ~et is then plaoed on vacuum holder 17 of stage 16 in nominal alignment with the X axis of motion of main stage 20 and is thereupon precisely aligned with the X axis of motion in exac~ly the same manner as previously described. This second reticle 12 is provided as shown in ~igure 15, with a small wafer aliynment mark 172 in the marginal portion thereof along the Y axis (once the second reticle is aligned with the X axis of motion of main stage 20~ between reticle alignment mark 78b and one sid~ of the microcircuitry-containing central portion 160 [which contains the secona level of microcircuitry in the first-mentioned case and the first level of microcircuitry in the second-mentioned case). The small wafer alignment mark 172 is disposed at the same position on the second reticle 12 as a corresponding first one of the set of nrl 9~l wafer alignment marks 170 contained on ~e first reticle and is therefore il-lumin~ted w~th ~fi~ mucxocircui~ry-containing portion 160 of the second reticle w~en ~as~ plate 60 is disposed in its operati~e position ~etw~en positive lenses 45 ~nd 47 and shutter 50 is opened. ~he small wafer alignment mar~ 172 m~y comprise a pair of square windows of the same type as the reticle alignment mark 78a or 78b (i.e., a pair of light or transparent windows ~mmetrically oriented about the center of ~he waer alignment mark on oppositP sides o~ a pair of orthogonal centerlines thereof and disposea on a dark or opaque fieldl, but is su~stantially smaller ~eing o~ a~o~t the same -50~

~ize as one of the small wafer alignmen~ marks 170 contai~ed o~ ~he first retlcle~. ~n ;dentical small wafer alignment maxk 172 is also provided in ~he s~me m~n~er on each of the succeeding reticles 12 of the set, but at the same position as the ~orresponding succe~ding one of the set of n-l small waXer alignment marks 170 contained on khe first reticle~
Thus, the first through the las~ small wafer alignment marks 172 provided on th~ second through ~he nth rPticles 12 of ' the set of n reticles corresponds to the first through th last small wafer alignment marks 1701 170n 1~ respectivel~, o~ the set of n~l small wafer alignment marks 170 printed ~nd formed alongside each of the selected regions 162 of the semi-conductive wafer 14 (the subscripts 1 through n-l hereinafter being used when referring specifically to the first through k~e last wafer alignment marks, respectively, of a set of n~l small wafer alignmen~ marks 170 formed on the semi-conduc~ive wafex~.
The ma~ner in which the precision alignment step-and-repeat printing speration is performed will now be described with reference to the parts of alignment and ~xposure system 10 employed in ~hat operation. As shown in Fi~uxe lB, a f~ end of a f~bes op~ic light pipe 174 is ~ixedly moun~Pd a~o~g a ~orizontally extending optical path 17S a~ially aligned with the horizontally extending portion 34d of optical path 34a-e~ A second end of this fiber optic light pipe 174 is fixedly mounted adjacent to a blue ilter at a corresponding opening in elliptical reflector 36. A beam of blue ill~minating and exposure light from mercury arc lamp 32 therefor2 passes through iber op tic light pipe 174 3~ and along the horizontally extending optical path 175.

~ 3 A normally clo~ed s~utter 176 pi~otally ~ounted aa~acent to the horîzontally extending opti~al path 175 is pivoted into that optical pat~ ~as shown in solid lines~ when closed ~ ~s to ~loc~ passage ~f ~he ~e~m ~f light ~here-along and is pivoted ~ut of that optical pa~ ~as shown în dashed linesl when opened so as to permit passage o~
~he beam o~ light ~hereal~ng. These pivo~al movements of shutter 176 are controllea ~y a ~ servo drive unit 177 coupled thereto.
The first end of fi~er optic light pipe 1~4, the shutter 176, the ~ se~v~ drive unit 177, and a mask plate 182 are all mounted on a stage 178 for movement therewith along ~he X and Z axes. Stage 178 is moved along the X and Z axes by X and Z axes servo drive uni~s 179 and 181 ~o selectiYely position mas~ plate 182 in a vertical plane or~hoyonally intersecting the horizontally extending optical path 175 at a point midway ~etween fiber optic light pipe 174 and a pos;`.~ive lens 184. Mask plate 182 has a small circular opening lB6 for permitting the beam of light passing along the horizontally extendi~ optical path 175, when shutter 17~ is opened, t~ illuminate a corxesponding circular axea locatea on the ~econd or a~y succeeding reticle 12 (held by vacuum holder 17 of ~taye 16) and containing one land only one~ of ~he small wafer aligNment marks 172 disposed on that reticle.
Positi~e lens 184 is fixedly mounted in the horizontally extending optical path 175 so as to project light passing through ~he small circular opening 186 in mask plate 182 to the entrance pupil of imaging lens 56. Beam splitter 48 txansm~ts t~enty percent of the liyht pa~sin~ through positive lens lB4 ~rward along t~e hDrizontally extending portion 34d of optical path 34a e~ This light ~hereupon passes along the remainder of optica~ pa-~h 34a-e and along dual optical pa~h ~7a-~ in the same manner as previously describ~d in connection with the su~stage adjustmen~ operation so that the f~rst objective lens unit 90 may be used with binocular lens unit 93, as hereinafter described, to view an aerial image of one of ~he small wa~er ali~nmen~ marks 170 on the semicon~uctlve wafer 14/ when that small wafer alignment mark is positioned directly ~eneath projection lens 18 and îlluminated ~y a projected image of the corresponding small wafer alig~ment mark 172 disposed on the second or one of the succeeding reticles of the set.
Once the set of small wa~er alignment marks 170 has been formed on the semiconductive wafer 14 alongside each of the selected regions 162 thereof/ a photosensitive film is deposited over the semicunductive wafer (this is typically done at one ti~e with the other semiconductive wafers o~ the batch). The semiconductiYe wafer 14 is then put baok in ali~nment and e~posure system 10 on vacuum chuck131 i~ nominal alignment with the X axis of motion of main stage 20. It is thereupon pr~ision prealigned with respect to prealignment reticles 138a and 138~ in exactly the same manner as pre~iously described. In preparation for the precision alignment step-and-repeat printing operation, the X and Z axes servo drive units 179 and 181 are employed for moving stage 178 so as to p~sition mask plate 182 fox illuminating only the small wafer alignment mark 172 on ~he second retiole 12, when ~hutter 176 is su~sequently opened. Additionally, slide 123 is employed to ~ove ~eam ~ender 122 into the operative position in ~e horizontally ~xtending portio~ 87e o~ dual optical pa~h 87a f so that binocular lens ~nit ~3 may be used wi~h ~he fir~t v~jective lens uni~ 90 to view an aerial im~ge ~f the ~irst small wafer alignment mar~ 17~1 alongs~d~ a sel~ted regi~ 162 of ~e s~c~d~tive wafer 14 and of the ~ge of the corresponding small ~afer alignmen~ ~ark 172 on the second reticle 12 when s~utter 176 is ~pened.
The precision alignment s~ep-and-repeat printi~g operat;on may n~w ~e performed ~y employing the X and Y axes ser~o dri~e units 25 and 27 for stepping main s~age 20 to posi-ti~n the selected region 162 in t~e f;rst quadrant of the semiconducti~e wafer 14 directly ~eneath projection lens 18, thereby posit~oning the first small wafer alignment mark 1701 disposed alongside that selected region in nominal alignment with the image of ~he corresponding small wafer aligNmen~ mark 172(on the second reticle)to be pr~je~ted on~o the ~emiconductive wafer when the shutter 176 is ~uhse~uently opened; by thereupon employing the ~ servo drive ~nit 177 for m~ving s~utter 176 to t~e op~n position ~s~own in dashed lines) whereupon ~ask plate 182 illuminates the small wafer alignment ~ark 172 contained on the second rPticle without illuminat~ng either of t~e larger reticle alignmerlt marks 78a and 78b or the microcircuitry-containing central portion 160 of the second reticle; ~y employing ~he first objective lens unit ~0 with ~ino~ular lens unit 93 to view ~he aerial image o~ the first ~mall wafer alignment mark 1701 disposed alongside ~e selected region 162 in the first quadrant of the semicon~ucti~e wafer and illuminatea by the projec~ed ima~e of the corresponding ~a-fer alignment mark 172 contained on the second reticle; ~ile viewing that aerial image, by -5~

~mploying the X and Y fixes ~er~o driv~a ~nits 25 and 27 fox m~ing ~he m~in s~age 50 as ~o pxecisely align ~ha~ ~irs~
8mall wafex alig~me~t mark 1701 in the fi.rst quadrant of the ~emiconductive wafer with the projected image of thP ~orres~
ponding small wafer alignment mark 172 on the second reticle;
by measuring and storing the offset distances the main stage is moved along the X and Y axes to move the ~irst small wafer alignment mark 1701 in the first ~uadrant of the semlconductive wafer from its initial nominally aligned position to its final precisely aligned posi~ion relative to the projec~ed image of the corresponding small wafer alignment mark 172 on the second reticle (this may ~e done, for example, by simply employing the counters and the comput~r of the X and Y axes position cc¢ltrol circuits disclosed in Canadian Patent ~pplicaticn Serial No. 349,305 and used for ccntroll m g an m terfercmetrically-cvntrolled stage such as main stage 20); by employing the servo drive unit 177 to move shutter 176 to the closed position ~shown in solid lines~, there~y blocking the passage of l;ght through mask plate 182 to the second reticle; by repeating each of the preceding steps of this paragraph in ex ctly the same manner for the ~irst small wafer alignment mark 1701 formed alongside the selected region 162 in e~ch of th~ re~aining quadrants of the semiconductive wafer (i.e. 7 for each of the small wafer alignment marks 170 formed on the ~emiconducti~e wafer ~nd associated with the second reticle~;
by employing the four resultant pairs of offset distances (or ~alues2 along the X and Y axes to determine the manner in which the main s~age ~hould be moved along ~he X and Y axes during ~he following step-and-repeat printing operation to ~est fi~
those determined pairs of offset values while succesively pri~ting ~he level of ~cxocircui~ry ~on~ained on the secorld reticle at each o~ ~he desl~ed ~rray o~ a~jacen~ re~ions lS2 on ~he semiconductiv wafer (this may be done, for example, by employing the a~ove-menkioned computer ~o compute corrected coordinates or pairs of X and Y axes end points~ in accordance with well known best fit equations for X and Y ~xes ~oordinat~
systems, for each of ~he positions to which ~he main stage is to be stepped during the following step and-repeat printing , opexation); and ~y t~en step-and-repeat printing the level of microcircuitry contained on the central portion 160 of ~he second reticle at each of the desired array of adjacent regions 162 of the semiconductive wafex in exactly the same manner as previously descri~ed, but u~ilizing the corrected coordinates ~or pairs of X and Y axes end points) to determine each of the positions to w~ich the main stage is mo~ed during that step-and-repeat printing operation (this may be done by employing the computer controlled ~ and Y axes position control circuits disclosed in Canadian Patent Application Serial No. 349,305 to drive the X and Y axes servo drive units 25 and 27 for the main stage).
During the foregoing precision alignment step-and-repeat printing operation, the level of microcircuitry contained on the central region 160 o* the second reticle 12 is suc-ces~iv~ly printed at each o* the desired array of adjacent regions 162 on the semiconductive wafer 14 in Yery precise alignment with any level of microcircuitry previously printed and fo~med at those same regions of the semicon~uctive wafer (alignments to within one tenth of a micron bein~ possible).
Upon completion of that precision alig~ment step-and-repeat pxintin~ operation,-t~e semiconductive ~afer 14 is removed ~5~-from alignment and exposure system 10 and processed as previously de~cribed to form che level of microcircuitry so printed at each of the desired array of adjacent regions 162 of the semiconductive wafer. These process-ing operations may also impair or obliterate the first small wafer alignment mark 170l disposed alon~side each of the selected regions 162 of the semiconductive wafer since the beam of light employed for viewing the aerial images of those first small wafer alignment marks includes exposure light as described above. However, this does not affect performance of the remaining precision alignment step-and-repeat printing operations since the remaining small wafer alignment marks 172 - 170n 1 formed on the semiconductive wafer and associated with the remaining reticles of the set are not illuminated until they are actually employed in performing those remaining precision alignment step-and-repeat printing operations with the associated reticles. The semiconductive wafer 14 is successively processed for each succeeding re~icle 12 of the set of reticles in exactly the same manner as de-scribed above for the second reticle to successively print and form each level of microcircuitry contained on those reticles at each of the desired array of adjacent regions 162 of the semiconductive wafer. Following all of these processing operations,the semiconductive wafer 14 may be scribed and otherwise processed as indicated above to form a plurality of integrated circuits or the like.
At some point during the previously-described processing of a semiconductive wafer 14 with alignment and exposure ~0 system 10, the operator may desire to scan the semiconductive wafer to check for possible defec~s (such as might occur ~uring an ~tching or depositing operation) or for same o~her reason.

This may be ~on~ without exposing a photosensitive film deposit2d over t~e ~emicsnduc~ive ~y employi~g air cylinder 54 t~ move green filter 45 into îts operative position in the ~ertically extending portion 34c of optical path 34a-f, thereby passing only green illum.inating light forward along ~hat optic21 pat~ when shutter 50 is opened; ~y employing crank 74 and air cylinder 75 ~o mo~e compensaking lens 76 into its operative position (shown in dashed lines in ~igure lA7, ;- thereby correcting projection lens 18 for green light; by employing ~ servo dri~e unit 51 to open shutter 50, by employing the Y axis ser~o dr;ve unit 66 for moving slide 58 to position mask plate 60 in îts operative p~sition, therehy permitting illumunation of at least a portion o~ whate~er object is positioned on main stage 20 directly ~eneath the proje~tio~
lens ~a reticle 12 may or may not-then ~e held by vacuum holder 17 of stage 16); ~y employ~ng slide 123 ~o mo~e beam bender 122 into its ~perati~e position in the horizontally extending poxt~on 87e of dual op~ical path 87a-f, thereby permittiRg use ~f the first obj~ctive lens unit 90 with the binocular lens unit 93 to view an aerial image of what-~er region of the ~emiconducti~e w~fer may ~e disposed directly beneath ~he projection lens and illuminated by the green li~ht passing through the mask plate 60; and by employing the X and Y axes ~ervo dri~e units 25 a~d 27 for moving the main ~tage to soan the s~iconductive wa~er ben~ath the proj~ction lens.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Alignment apparatus comprising:
an adjustable holder for holding a first object in a first plane;
imaging means for producing an image of the first object in a second plane;
a stage for holding a second object in the second plane;
control means for moving the stage along coordinate axes to position the second object with respect to the image of the first object;
an indicium disposed on the stage for being positioned in the second plane to facilitate alignment of the image of the first object with respect to at least one of the axes of motion of the stage;
said holder being movable rotatably and along coordinate axes to facilitate alignment of images of first and second alignment marks of the first object with respect to the indicium;
control means for moving the holder rotatably and along coordinate axes to align the images of the first and second alignment marks of the first object with respect to the indicium;
prealignment means for aligning an image of one or more alignment marks of the prealignment means with respect to said one of the axes of motion of the stage and for projecting that image onto the second object in the second plane when the second object is in a prealignment position; and positioning means, including the stage and the first-mentioned control means, for moving the second object rotatably and along the coordinate axes of motion of the stage to align alignment marks of the second object with respect to the image of said one or more alignment marks of the prealignment means when the second object is in the prealignment position.

2. Apparatus as in claim 1 wherein:
said first-mentioned control means is operable for moving the stage to a first coordinate position at which the images of the first and second alignment marks of the first object are aligned with respect to reference marks disposed on the stage and to a second coordinate position at which the image of said one or more alignment marks of the prealignment means is aligned with respect to the same reference marks;
whereby said first and second coordinate positions of the stage define a coordinate offset by which the stage can be moved from the second coordinate position to locate a selected region of the second object in alignment with respect to an image of a portion of the first object, thereby facilitating printing of that image at the selected region.

3. Apparatus as in claim 2 wherein:
said first-mentioned control means may subsequently be employed for moving the stage to another first coordinate position to eliminate any subsequent misalignment of the images of the first and second alignment marks of the first object with respect to said reference marks and for moving the stage to another second coordinate position to eliminate any subsequent misalignment of the image of said one or more alignment marks of the prealignment means with respect to said reference marks;
whereby said other first and second coordinate positions of the stage define another coordinate offset by which the stage may be moved from said other second coordinate position to locate a selected region of the second object in alignment with respect to an image of a portion of the first object, thereby facilitating printing of that image at the selected region.

4. Apparatus as in claim 1, 2 or 3 wherein said pre-alignment means includes:
a pair of prealignment reticles, each having an alignment mark;
light source means optically disposed for illum-inating the alignment marks of the prealignment reticles;
and an objective lens unit, optically disposed between the prealignment reticles and the stage, for projecting images of the illuminated alignment marks of the prealign-ment reticles onto the second object when the second object is in the prealignment position and for viewing an aerial image of those images and of the alignment marks disposed on the second object and illuminated by those images.

5. Apparatus as in claim 1, 2 or 3 wherein said posi-tioning means includes:
a vacuum chuck, rotatably supported on the stage, for holding the second object; and drive means, coupled to the vacuum chuck, for rotating the vacuum chuck about a coordinate axis orthogonal to the coordinate axes of motion of the stage.

6. Apparatus as in claim 1, 2 or 3 wherein:
said prealignment means includes a pair of pre-alignment reticles, each having an alignment mark;
said prealignment means includes light source means optically disposed for illuminating the alignment marks of the prealignment reticles;
said prealignment means includes an objective lens unit, optically disposed between the prealignment reticles and the stage, for projecting images of the illum-inated alignment marks of the prealignment reticles onto the second object when the second object is in the prealignment position and for viewing an aerial image of those images and of the alignment marks disposed on the second object and illuminated by those images;
said positioning means includes a vacuum chuck, rotatably supported on the stage, for holding the second object; and said positioning means includes drive means coupled to the vacuum chuck, for rotating the vacuum chuck about a coordinate axis orthogonal to the coordinate axes of motion of the stage.

7. Apparatus as in claim 1, 2 or 3 wherein:
said first object comprises a reticle; and said second object comprises a semiconductive wafer.