JPS6261018A - Optical image forming device - Google Patents

Abstract

PURPOSE:To detect a mark corresponding to a small pattern area by providing an objective optical system so as to tilt with respect to the surface of a sample. CONSTITUTION:The titled device has the objective optical system (objective lenses 12 and 13) observing the surface of the sample (mask or wafer) on which the prescribed pattern (mark, etc.) is formed, and a reflecting mirrors (mirrors 10, 11 and 18) bending the optical axis of the objective optical system so as to be approximately at right angle with respect to the surface of the sample. After the light from the sample surface is reflected by the reflection mirror to make incident on the objective optical system, said system being a device forming the image of a patterns is tilted and arranged with respect to the sample surface so that the bend angle beta of the optical axis, which is made by the reflection mirror, can be within a range of 90 deg.-180 deg., and exclude 90 deg. and 180 deg.. With respect to a small exposure area, the pattern (mark) for positioning can be observable.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an image forming optical device for observing a pattern formed on a sample, and particularly to an image forming optical device for observing a pattern formed on a sample.
The present invention relates to an improvement of a microscope optical system for detecting patterns provided on a mask or a wafer in an exposure apparatus.

(Background of the Invention) In recent years, semiconductor devices, 4Is, and VLSIs have become increasingly finer and more highly integrated.
X-ray exposure equipment with extremely high resolution has been developed and is entering the practical stage. This type of X-ray exposure equipment transfers a pattern by irradiating soft X-rays emitted from a radiation source onto a semiconductor wafer coated with resist through a mask, and the mask and wafer are connected. It uses a gloximity exposure method in which the images are spaced apart by a certain minute distance (gloximity gear).

Furthermore, there are two methods of exposing wafers: batch method and step method.
Many of the devices currently under development employ the latter step-and-repeat exposure method. In the step-per type, the number of wrinkles and holes to be exposed per exposure is smaller than the entire wafer surface.

Wafer step, pinging and exposure are repeated, and although the sloop and temperature are lower than in the batch exposure method, the positioning of the mask and wafer or gloximity adjustment is required for each exposure step. Since the gears and gears can be set, there is an advantage that the overlay accuracy and resolution of each chip on the entire wafer surface can be uniformly improved. The positioning and gear detection are usually performed using an alignment microscope provided above the mask. The specific structure, arrangement, and method of use of this microscope are disclosed in detail in, for example, Japanese Patent Laid-Open No. 132126/1983. Therefore, problems with the alignment microscope in the conventional apparatus will be explained with reference to FIG. FIG. 5 shows the arrangement relationship between the objective lens of the microscope, the mask, and the wafer. A wafer W having an alignment mark Wm is placed on a stage 1 that moves in the x and y directions, and a pattern area PA to be exposed is and alignment mark MY,
A mask M having M# is suctioned to the mask holder 2 in a suspended state. The images of marks MY and Wm are captured by objective lens 3.
．． Mirror 4. and the imaging plane FPI via the relay lens 5.
The images of marks M# and Wm are formed on the objective lens 6,
It is formed on the imaging plane FP2 via the mirror 7 and the relay lens 8.

The objective lenses 3 and 6 are arranged so that their optical axes are perpendicular to the surfaces of the mask M and the wafer W, and the mirror 4.7 bends the optical axes by 90 degrees and transfers the image light beam from the objective lens 3 to the relay lens 5. , leading to 8. The optical axes of the relay lenses 5 and 8 are set parallel to the surfaces of the mask M and the wafer W. In such a configuration, the objective lens 3 and the relay lens 50
and between the objective lens 6 and the relay lens 8, and the objective lens 3 and the mirror 4 are integrated as shown by the arrow A.
The objective lens 6 and mirror 7 are integrally movable in the direction of arrow B (moveable).
, 6 are movable because after detecting the marks MY, M#, and Wm and performing alignment, the pattern area PA is moved.
When transferring onto the wafer W, the objective lenses 3, 6 . This is to prevent the mirrors 4 and 7 from blocking the soft X-rays irradiating the pattern area PA. Since there is an annular mask holder 2 around the periphery of the mask M, when the objective lenses 3 and 6 are retracted to the outside of the mask M, the lower end of the objective lens 3.6 does not mechanically interfere with the mask holder 2. The distance from the surface of the mask M to the lower end of the objective lens 3°6,
A so-called working distance (working distance 111) d is determined. Now, FIG. 6 is a plan view showing the arrangement relationship between the objective lens 3.6 and the pattern area PA. A third objective lens 9 is also shown in FIG. 6, and these three objective lenses 3, 6.9 are marked MY, M#IMX, respectively.
By observing this, misalignment between the mask M and the wafer W in the X direction, y direction, and rotational direction is detected. Marks MY and M# for normal alignment.

MX is provided at a position close to pattern area PA. Therefore, as shown in FIG. 6, when aligning a mask M having a large pattern area PA, the distance SPI between the marks MY and Mθ is sufficiently larger than the diameter 2r of the lens barrel of the objective lenses 3 and 6. Therefore, the objective lens 3.6 is positioned at a distance P as shown in FIG. However,
When aligning a mask M having a small pattern area PA2, when the distance SP2 between the marks MY and M# becomes equal to the diameter 2r of the lens barrel of the objective lenses 3 and 6, the objective lenses 3 and 6 should approach each other until they collide with each other. When it becomes 5P2 (2r), there arises a drawback that marks MY and M- cannot be observed simultaneously with each of the objective lenses 3 and 6.

The outer diameter of the microscope objective lens is the numerical aperture (N,
A,) is determined by the working distance d, so the objective lenses can only approach each other up to a certain fixed position. This means that the pattern area (exposure area) PA cannot be made smaller than a certain value. - As an example, the objective lens N, A, is 0.3, and the working path fid is 5.
If it is a cod, the lens diameter of the single glass lens will be 4 cod or more, and the diameter of the objective lens will be about 6 fi if the hardware of the lens barrel is included. Therefore, in an apparatus with three objective lenses arranged as shown in Fig. 6, the pattern area in which marks MY, M#, and MX can be aligned simultaneously is up to a size of about 6 x 61 Jl, and smaller pattern areas are This has the disadvantage that direct alignment becomes difficult.

(Objective of the Invention) An object of the present invention is to solve these drawbacks and provide an image forming optical device that enables observation of patterns (marks) for alignment even in a smaller exposure area.

(@Akira's Overview) The present invention is an objective optical system (
objective lens 12.13) and the optical axis (A
Reflection d that bends X) so that it is approximately perpendicular to the sample surface
(mirrors 10, 11゜i8), and forms an image of a pattern by reflecting light from the sample surface with a reflecting mirror and then inputting it into an objective optical system. Shaft bending angle (J3) from 90° to 180°
The technical point is to arrange the objective optical system at an angle with respect to the sample surface so that the range is between 90' and 1800 and does not include 90' and 1800. In a further specific embodiment, when the angle formed by the optical axis (AX) and the outermost rays (20a, 20b) determined by N and A of the objective lens on the sample side of the objective lens is -, the bending angle is (β
) is set to β × 180°−2−, and the reflecting mirror (
The inclination angle of the optical axis (AX) bent by the mirror 10.11) with respect to the sample surface (or imaging plane S) is α (α = β - 90
°), the technical point is to set α>θ.

(Embodiment) FIG. 1 is an optical layout diagram showing an objective optical system portion of an image forming apparatus according to an embodiment of the present invention. Unlike a conventional optical system, the light from the marks MY and M# on the mask M is reflected by diagonally arranged mirrors 10 and 11, and is reflected by the objective lens 12, respectively.
．． 13, it is reflected upward by mirrors 14 and 15, and enters mirrors 4 and 7 and relay lens 5.degree. 8 as shown in FIG. 4, forming images of marks MY and M#.

In FIG. 1, the center line tl is a perpendicular line drawn from the soft
is positioned so that it passes through.

Now, in Figure 1, two objective optical systems are shown.

Since they both have the same configuration, only the objective optical system unit OLU of -1000 will be described in detail. A reflection surface 110b is formed on the mirror 10, and the angle formed between this reflection surface 10b and the surface of the mask M is larger than 45 degrees. The optical axis AX of the objective lens 12 bent by the mirror 10 is.

The distance between the mask M and the mirror 10 is perpendicular to the mask surface, and the distance between the mirror 10 and the objective lens 12 is determined to be tilted upward with respect to the mask surface. That is, the bending angle of the optical axis AX by the mirror 101C is set to be 9C or more. The optical path from the objective lens 12 to the mirror 14 is defined as a parallel system (afocal system), and when focusing the objective lens 12, the entire objective optical system unit OLU can be moved up and down, and during alignment and exposure. The microscope can be moved by moving the objective optical system unit OLU and the mirror 7 (see FIG. 4) provided above the mirror 14 together in the direction of arrow B. Note that the tip end surface 10a of the mirror 10 is shaped to be parallel to the center line Ll. This is a point-symmetrically arranged mirror 10.11
This is to make sure that they are as close to each other as possible.

Now, FIG. 2 is an enlarged view for explaining in detail the geometric arrangement relationship between the objective lens 12 and the mirror 10. S is the focal plane (t! image plane) of the objective lens 12, CC is the point where the optical axis AX intersects the image plane S, d is the working distance from the lower end of the mirror 10 to the image plane S, and N.A.
The outermost rays of the luminous flux determined by are 20a and 20b
shall be. The light rays 20a and 20b intersect at an angle 2# at a point CC, and are each tilted at an angle - with respect to the optical axis AX. For example, if N, A, are 0.3, angle 0 is 17.46°. Assuming that the light ray 20a is reflected at the lowermost end of the mirror 10, it is reflected from one point CC to the lowermost end of the mirror 10 (tip surface 1).
The distance ΔR to 0a) on the imaging plane S is expressed as in equation (1).

ΔR=dlItana ・・・・・・・・・・・・
...(1) This relationship holds regardless of the bending angle when a mirror is inserted between the objective lens and the sample to bend the optical path. ．．
3 (#=17.46°), ΔR is approximately 1.6 Mm
becomes. Therefore, in the case of this embodiment, 1.
It is possible to observe a mark located at a position of 6 M, which means that a pattern area of at least 3.2 x 3.2 m 11 squares can be aligned and exposed. As is clear from FIG. 2, it is also a necessary condition to minimize ΔR that the light ray 20 & determined by N and A is set so as to be reflected at the lowest end of the mirror 10.

Incidentally, the bending angle β of the optical axis AX by the mirror 10 is not arbitrarily determined, but is determined within a certain limit. Here, a line passing through the bending point of the optical axis AX at the reflecting surface 10τj b and parallel to the imaging plane S is defined as t2,
Further, if the line intersecting the optical axis AX between the mirror lO and the objective lens 12 and perpendicular to the imaging plane S is 63, then the mirror 10
The angle formed between the optical axis AX and the line t2, that is, the inclination angle α of the objective lens 12, is expressed by the equation (2).

α；β−90°・・・・・・・・・・・・・・・
...(2) As is clear from this Figure 2, α=08
If the objective lens 12 is arranged horizontally so that (β=90°), the working distance d cannot be obtained due to the antinode (outer periphery of the lens) of the objective lens 12.

From this, first of all, in order to ensure the working distance d7, the light ray 20a reflected at the lower end of the mirror 10 must be directed upward with respect to the imaging plane SK, and the relationship of equation (3) is a necessary condition. becomes.

α＞a<or β−90°〉θ)・・・・・・(3) Second
Then, a ray 20b symmetrical to the ray 20a about the optical axis AX must intersect the reflective surface 10b of the mirror 10, and (
4) The relationship in the equation is a necessary condition.

180°−β 90°−1〉□+α ・・・・・・・・・(4
) By rearranging this equation (4), the relationship of equation (5) is finally derived.

α<90°-2# (or β<180°-2#)...(
5) The angle α (or β) may be determined so as to satisfy both the above equations (3) and (5). The range that satisfies both of these conditions is the shaded area shown in FIG.

In the fa3 diagram, the vertical axis represents the angle α.

The horizontal axis represents the angle -. The outer boundary line of the shaded area is outside the range of the conditions of equations (3) and (5) above. The range shown in FIG. 3 is determined based on the conditions determined only by the glass body of the objective lens 12; the actual objective lens 12 has a lens barrel, and its external dimensions and arrangement relationship with the mirror 10. This further limits the practical angle α. In particular, if you try to secure the working distance fid by considering the outer diameter of the lens barrel of the objective lens 12, then α=-
The straight line has a slightly steeper slope, like straight line t4.

It is limited to the shaded area surrounded by the straight line t4 and the straight line of α=90°−2−. The inventors of this application are N, A
, = 0.3 (, 17.5° in #) was designed using the objective lens 12, and the conditions were satisfied at α = 28° (β = 118°), and the mirror 10 was also compact. I understand.

Now, it is fine if only two VC microscopes are arranged facing each other as shown in Fig. 1, but if three VC microscopes are arranged as shown in Fig. 4, the mirrors 10 and 11 are
It is necessary to cut the tip corner of the third microscope at an angle of 45 degrees and the tip corner of the mirror 18 of the third microscope. FIG. 4 is a plan view showing the arrangement of mirrors 10, 11° 18 on the mask, in which each mirror 10, 11, 18 is moved in the direction of arrows A, B, and C in order to detect marks MY, Ml, and MX. When the mirrors are moved out, by cutting off the corners, marks attached to small pattern areas can be detected without mechanical interference between the mirrors.

In the above embodiments of the present invention, a microscope for alignment or gap detection suitable for an X-ray exposure apparatus has been described, but exposure apparatuses of other types are also applicable.

For example, it can be fully used for a Gloximity Aligner-1 that uses ultraviolet light, a reflective Glojection Aligner-1, or a stepper that uses a projection lens.
In addition, it can also be used as an alignment microscope for wafer and mask inspection equipment.

(Effects of the Invention) According to the present invention, it is possible to construct a microscope that has a relatively large numerical aperture and is capable of detecting marks in small pattern areas while ensuring the necessary working distance. It will be done.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the optical arrangement of an image forming apparatus according to an embodiment of the present invention, Fig. 2 is an enlarged view illustrating the geometrical arrangement of the mirror and objective lens, and Fig. 3 is a tilt angle of the objective lens. 4 is a plan view showing the planar shape and arrangement of the mirrors. FIG. 5 is a configuration diagram showing the configuration of an image forming device (alignment microscope) in a conventional X-ray exposure device. FIG. 6 is a diagram showing a planar arrangement of an alignment microscope in a conventional device. [Explanation of symbols of main parts] 10.11. ．． 18...mirror, 12,
13... Objective lens, S... Imaging surface, M... Mask, d... Working distance, A
X: optical axis, β: bending angle.

Claims (2)

[Claims] (1) An objective optical system for observing the surface of a sample on which a predetermined pattern has been formed, and a reflecting mirror for bending the optical axis of the objective optical system so as to be substantially perpendicular to the sample surface; An optical device that forms an image of the pattern by reflecting light from a surface by the reflecting mirror and making it incident on the objective optical system, wherein the bending angle of the optical axis by the reflecting mirror is from 90° to 180°. between 90° and 180
An image forming optical device characterized in that the objective optical system is tilted with respect to the sample surface so that the objective optical system is in a range that does not include . (2) When the angle between the light beam corresponding to the numerical aperture of the objective optical system and the optical axis is θ, the bending angle is 180
In addition to setting the angle smaller than the angle determined by °−2θ, the angle of inclination of the optical axis bent by the reflecting mirror with respect to the sample surface is α.
2. The apparatus according to claim 1, wherein α>θ is determined so that α>θ is satisfied.