JPH0878313A - Projection exposure device - Google Patents

Abstract

PURPOSE: To detect projection magnification with high accuracy in a short time in a projection exposure device exposing a pattern on a mask on a photosensitive substrate through a projection optical system. CONSTITUTION: A first reference plate 9 and a second reference plate are mounted at specified places on a reticle stage 5 and a wafer stage respectively. A pair of left and right fundamental marks 60a, 60b of a first reference pattern MM1 formed on the first reference plate 9 and a pair of left and right fundamental marks of a projected image obtained by projecting a second reference pattern formed on the second reference plate onto the reticle stage 5 through a projection optical system are superposed, and observed by a pair of left and right observation optical systems, each displacement in the direction X is measured, and the fluctuation of projection magnification is computed from the measured values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus used, for example, in manufacturing a semiconductor integrated circuit, a liquid crystal display device or the like in a photolithography process, and particularly to efficiently detecting and correcting the magnification of a projection optical system. The present invention relates to a projection exposure apparatus having a mechanism for

[0002]

2. Description of the Related Art Conventionally, in a projection exposure apparatus used for manufacturing a semiconductor integrated circuit, a liquid crystal display device or the like in a photolithography process, a fine pattern of a reticle (or a photomask or the like) can be photographed with high resolution. Projection by a projection optical system for projecting on a resist-coated wafer (or glass plate, etc.) and for projecting a reticle pattern on a pattern already formed on the wafer with high overlay accuracy. It is required to always maintain the image forming characteristics of an image with high accuracy.

However, environmental changes such as atmospheric pressure and temperature around the projection optical system, shape changes due to absorption of illumination light of the reticle or projection optical system, or patterns on the reticle such as when a so-called phase shift mask is used. The imaging characteristics may not be maintained due to factors such as the change in Further, recently, various lighting methods have been devised to deal with a fine pattern of a semiconductor or the like. For example, a ring-shaped illumination method that illuminates the reticle pattern with the illumination light flux by defining the light amount distribution of the illumination light flux on the pupil plane of the illumination optical system or in the vicinity thereof in a ring-shaped manner (Japanese Patent Laid-Open No. 61-91662), Alternatively, the light quantity distribution of the illumination light flux on the pupil plane of the illumination optical system or in the vicinity thereof is maximized at at least one position decentered by a predetermined amount from the optical axis of the illumination optical system, and the illumination light flux is predetermined for the reticle pattern. A modified light source method of inclining and irradiating at an angle, or an inclined illumination method (Japanese Patent Laid-Open No. 4-1011).
Japanese Patent Laid-Open No. 48, Japanese Patent Laid-Open No. 4-408096) and the like have been proposed. In this way, when the normal illumination method is switched to, for example, the annular illumination method or the modified light source method, the imaging characteristics may also change due to changes in the illumination conditions.

For this reason, various correction methods for image forming characteristics have been proposed and put into practical use. Among them, especially regarding a method of correcting the variation of the image forming characteristic due to the absorption of the exposure light of the projection optical system, for example, in JP-A-60-78454, the exposure light to the projection optical system (i-line, KrF excimer laser, etc.) is disclosed. The amount of energy (heat amount) accumulated in the projection optical system due to the incidence of is sequentially calculated, the amount of change in the image formation characteristic due to this accumulated energy amount is obtained, and the image formation characteristic is finely adjusted by a predetermined correction mechanism. Proposed.

In particular, the projection magnification of the projection optical system is a basic performance of the projection optical system, but it often varies depending on factors such as the irradiation heat of the exposure light and the fluctuation of the atmospheric pressure as described above. . For this reason, various techniques have been used to reduce the variation of the projection magnification as small as possible. For example, attempts have been made to seal the interior lenses of the projection optical system to change the internal pressure, or to move some lenses of the projection optical system in the optical axis direction.

Further, in recent years, as the patterns of semiconductor integrated circuits have become finer and finer, changes in distortion (so-called pincushion type and barrel type distortion) cannot be ignored. Then, as the distortion correcting means, a mechanism for moving the reticle in the optical axis direction of the projection optical system, a mechanism for moving a part of the lenses of the projection optical system in the optical axis direction, and light emission of an exposure light source (laser light source etc.) A mechanism for changing the wavelength has been proposed.

Further, recently, there has been an increasing demand for exposing a wider field region while maintaining the image forming characteristics.
In order to respond to this, a scan type exposure apparatus (step and scan type exposure apparatus) has been proposed which scans and exposes a reticle and a wafer relative to a projection optical system. With this method, the maximum diameter of the effective exposure field of the projection optical system can be used by illuminating the reticle in a slit shape, and by scanning, the exposure field can be expanded without being restricted by the optical system in the scanning direction. There are advantages. Further, since only a part of the projection optical system is used, there is an advantage that accuracy such as illuminance uniformity and distortion can be easily obtained.

However, whichever method is used, a method for effectively predicting or detecting variations in projection magnification or distortion is required. Conventionally, as such a method, for example, the energy irradiated to the projection optical system is monitored by using a dose sensor, or the fluctuation of atmospheric pressure is monitored by an atmospheric pressure sensor or the like, and the correction amount is calculated from those measured values. Two methods are used: a so-called indirect method such as prediction and a direct method of measuring a variation amount such as a direct projection magnification or distortion. The latter method of measuring the variation amount of the direct projection magnification is, for example, by measuring the relative displacement amount between the alignment mark formed on the reticle and the alignment mark formed on the wafer or a member equivalent to the wafer. Then, there is a method of obtaining the projection magnification from the result.

[0009]

However, in the conventional projection exposure apparatus, when the indirect method is dealt with, there is an individual difference in the characteristics of the projection optical system for calculating the correction value. , Which caused an error. In order to avoid this, it is necessary to measure the characteristics of the projection optical system for all projection exposure apparatuses, which is a disadvantage that a huge amount of time is required.

Further, as described above, as patterns of semiconductor integrated circuits and the like have become finer in recent years, various illumination methods such as an annular illumination method or a modified light source method can be switched according to the pattern to be transferred. Has become. However, when the illumination method is switched in this way, the characteristics of the projection optical system are changed, and the error in the imaging characteristics increases, and the time required to measure the imaging characteristics increases.

On the other hand, in the case where the above-mentioned direct method is dealt with, the reference mask for measurement must be loaded into the apparatus each time the measurement is performed, which is very troublesome in managing the work itself and the reference mask. In addition, the attitude of the mask changes each time the reference mask is loaded into the apparatus, which causes an image forming error. The present invention has been made in view of the above problems, and an object thereof is to provide a projection exposure apparatus that can measure variations in projection magnification, distortion, and the like of a projection optical system in a short time and with high accuracy.

[0012]

A projection exposure apparatus of the present invention projects an image of a predetermined portion of a transfer pattern formed on a mask (1) under exposure illumination light (EL). In a projection exposure apparatus for projecting onto a photosensitive substrate (3) through an optical system (2), the mask (1) is held and the mask (1) is held by the optical axis (AX of the projection optical system (2). ), A mask stage (5) that is moved in a first direction (Y direction or −Y direction) on a plane perpendicular to the plane), and a first fiducial mark (MM1) arranged on the mask stage (5) are formed. The first reference member (9) and its substrate (3) are held, and the substrate (3) is placed on a plane (XY plane) perpendicular to the optical axis (AX) of the projection optical system (2). A substrate stage (17) that is moved in a second direction (-Y direction or Y direction) corresponding to the direction 1; A second fiducial member (25) disposed on the stage (17) and having a second fiducial mark (WM1) formed thereon, and one fiducial mark ((1) of the first and second fiducial marks (MM1 and WM1). MM1) and mark detecting means (10, 11) for detecting a relative positional deviation amount between the one reference mark (WM1) different from the one reference mark and the image through the projection optical system. It is a thing.

In this case, an example of the first reference mark is a plurality of reference marks (MP) two-dimensionally arranged on the first reference member (9), and the second reference marks (MP) are used at the same time. An example of the reference mark of the second reference member (2
5) A plurality of reference marks (W
P). Another example of the second reference mark is
A projection optical system (2) of the first fiducial mark which is a one-dimensional lattice-like pattern (WM3) formed at a predetermined pitch in a direction intersecting the second direction and which is used at the same time.
Image (MM3) on the substrate stage (17) side via
Is a one-dimensional lattice-like pattern formed substantially in the pitch direction of the second reference mark (WM3) at a pitch different from the predetermined pitch, and the mark detecting means includes the second reference member. The image pickup device (26) is preferably arranged at the bottom of (25C).

Still another example of the second reference mark is a two-dimensional lattice-like pattern (WM4) formed at a predetermined pitch in two different directions, and the first reference mark thereof is The image (MM4) on the substrate stage (17) side through the projection optical system (2) is substantially different from the predetermined pitch in the two pitch directions of the second reference mark (WM4). It is preferable that the mark is a formed two-dimensional lattice pattern, and the mark detecting means is a two-dimensional image pickup device (26) arranged at the bottom of the second reference member (25D). Further, based on the relative positional deviation information, at least one of the magnification and distortion of the projection optical system (2) is set.
It is preferable to have a calculation means (100) for calculating one.

[0015]

According to such a projection exposure apparatus of the present invention, the first fiducial mark (MM1) is provided during waiting time between exposures, for example, between shot exposures or shot exposures, or during wafer exchange. By measuring the relative deviation between the two reference marks of the second reference mark (WM1) and the second reference mark (WM1), it is possible to instantaneously detect the variation in the projection magnification of the projection optical system (2). At this time, since the first reference member (9) is always provided on the mask stage, it is not necessary to separately prepare a reference mask or the like for measurement.

The first and second fiducial marks are two-dimensionally arranged fiducial marks (MP and WP).
In such a case, by averaging a plurality of relative positional deviation amounts, it is possible to detect the variation in the projection magnification with higher accuracy. Further, since the first and second reference marks are arranged two-dimensionally, a change in projection magnification in two directions (X direction, Y direction) perpendicular to the optical axis (AX) and orthogonal to each other is detected. can do.

Furthermore, the first fiducial mark is a one-dimensional grid pattern, and the projected image of the second fiducial mark on the substrate stage (17) has a pitch slightly different from that of the grid pattern. In the case of a three-dimensional grid pattern, since the image sensor (26) detects moire fringes formed by two grids having slightly different pitches, the change in magnification and distortion of the projection optical system (2) is very large. It can be detected with high accuracy.

The first fiducial mark is a two-dimensional grid pattern, and the projected image of the second fiducial mark on the substrate stage (17) has a pitch slightly different from that of the grid pattern. In the case of a two-dimensional grid pattern, since a two-dimensional image sensor detects moire fringes formed by two grids having slightly different pitches, two-direction (X) perpendicular to the optical axis (AX) and orthogonal to each other (X Direction and Y direction), it is possible to detect changes in projection magnification, distortion, and the like with extremely high accuracy.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the projection exposure apparatus according to the present invention will be described below with reference to FIGS. In this example,
The present invention is applied to a step-and-repeat type projection exposure apparatus that reduces a pattern on a reticle by a projection optical system to expose each shot area on a wafer.

FIG. 1 shows a schematic structure of the projection exposure apparatus of this embodiment. In FIG. 1, the exposure illumination light IL emitted from the illumination optical system EL has an angle of about 45 ° with respect to the reticle 1. Dichroic mirror 12 arranged at a tilt angle
Is reflected on the illumination area IA on the reticle 1, and the circuit pattern drawn in the illumination area IA is
Reduction ratio β via the projection optical system 2 (β = 1 / in this example)
It is reduced in 4) and transferred onto the surface of the wafer 3. Here, in FIG. 1, Z is parallel to the optical axis AX of the projection optical system 2.
The axis is taken, and the X axis is parallel to the paper surface of FIG. 1 and the Y axis is perpendicular to the paper surface of FIG. 1 in the plane perpendicular to the optical axis.

FIG. 2 is a plan view showing the structure around the reticle, and the peripheral structure of the reticle 1 will be described in detail with reference to FIGS. In FIG. 1, a reticle 1 on which a circuit pattern is drawn is vacuum-sucked on a reticle stage 5 placed on a reticle base 4, and this reticle stage 5 is perpendicular to the optical axis AX of the projection optical system 2. Within the dimensional plane (XY plane), the reticle 1 is positioned in the X direction, the Y direction, and the rotation direction (θ direction). As shown in FIGS. 1 and 2, the position coordinates of the reticle stage 5 in the two-dimensional plane are determined by the moving mirrors 6, 7, 8 on the reticle stage 5 and the laser interferometers I _RX , I _RY1 , Measured by I _RY2 . The laser interferometer I _RX is arranged near the side surface of the reticle stage 5 in the −X direction, and the movable mirror 6 long in the Y direction is provided at the end of the reticle stage 5 in the −X direction. 5, the X-coordinate values of the laser interferometers 5 are measured, and the laser interferometers I _RY1 and I _RY2 are arranged side by side in the Y direction of the reticle stage 5, and the corresponding corners are provided at the end of the reticle stage 5 in the Y direction. The Y coordinate value of the reticle stage 5 is measured by the cube type moving mirrors 7 and 8. The position of the reticle stage 2 is constantly detected by the laser interferometers I _RX , I _RY1 , and I _{RY2 with} a resolution of about 0.01 μm, for example. Further, the rotation angle of the reticle stage 2 is detected from the difference between the measured values of the laser interferometers I _RY1 and I _RY2 .

Further, as shown in FIG. 2, a first reference plate 9 made of a rectangular transparent glass substrate, which will be described later, is provided near the end in the Y direction near the reticle 1 on the reticle stage 5. There is. In addition, the reticle stage 5-
In the X direction and the upper part near the end in the X direction,
Observing optical systems 10 and 11 for observing the reference plate 9 and the second reference plate 25 made of a transparent glass substrate on the wafer leveling table 17 described later are arranged. The mark position deviation information from the observation optical systems 10 and 11 is sent to the main control system 100, and the main control system 100 calculates the magnification and distortion of the projection optical system 2 based on the position deviation information. The main control system 100 controls the projection exposure apparatus as a whole.

FIG. 3 is a plan view showing the structure around the wafer stage of the projection exposure apparatus of this embodiment. FIG.
The structure around the wafer stage will be described in detail with reference to FIG. The wafer stage includes a wafer holder 18, a wafer leveling table 17, a wafer X stage 16,
And the wafer Y stage 15 are collectively referred to.

As shown in FIG. 1, the wafer 3 is held on the wafer holder 18 by vacuum suction.
Are mounted on the wafer leveling table 17. Further, the wafer leveling table 17 is placed on the wafer X stage 16 which is movable in the X direction by the length corresponding to the diameter of the largest wafer exposed by this projection exposure apparatus, and the wafer X stage 16 is the largest. The wafer is mounted on a wafer Y stage 15 which is movable in the Y direction by a length corresponding to the diameter of the wafer.

The wafer Y stage 15 is driven by a motor 19 via a feed screw 20 and moves in the Y direction relative to an apparatus base (not shown), and the wafer X stage 1 is moved.
6 is driven by the motor 20 via the feed screw 22, and moves in the X direction relative to the wafer Y stage 15. Further, the wafer leveling table 17 can be tilted in an arbitrary direction with respect to the image forming plane of the projection optical system 2 and can be finely moved in the optical axis AX direction (Z direction) by a driving unit (not shown). Further, the wafer leveling table 17 can be rotated around the optical axis.

Further, as shown in FIG. 3, a laser interferometer I _WX is arranged near the center of the side surface of the wafer leveling table 17 in the −X direction, and correspondingly, at the end of the wafer leveling table 17 in the −X direction. the movable mirror 23 is provided for reflecting light from the laser interferometer I _WX, X-coordinate value of the wafer leveling table 17 is measured by a laser interferometer I _WX. On the other hand, Y on the wafer leveling table 17
The coordinate values are the laser interferometers I _WY1 and I _WY2 arranged in pairs in the Y direction of the wafer leveling table 17, and the corresponding moving mirror 24 provided at the end of the wafer leveling table 17 in the Y direction. Measured by Also,
A rectangular second reference plate 25 described later is provided near the periphery of the wafer 3 on the wafer leveling table 17.

Further, in FIG. 1, irradiation for projecting an image of a pinhole, a slit pattern or the like obliquely with respect to the optical axis AX toward the exposure surface of the wafer 3 near the image plane of the projection optical system 2. An oblique incidence type focus position detection system including an optical system 13 and a light receiving optical system 14 that re-images the image from the reflected light beam from the projected image is provided. Wafer 3
The position in the Z direction of the surface of the
4 and auto-focusing is performed based on the detection information so that the surface of the wafer 3 matches the image plane of the projection optical system 2.

Next, the alignment optical system AL of this embodiment shown in FIG. 1 will be described. The alignment optical system AL of the present example measures the amount of positional deviation between the reticle mark and the wafer mark by an FIA (Field Image Alig).
nment) type alignment optical system. FIG. 5 is a block diagram showing the alignment optical system AL. In FIG. 5, the alignment optical system AL is composed of two alignment observation systems AL1 and AL2, both of which can detect the amount of positional deviation in the X and Y directions. As shown in FIG. 1, respective alignment lights AB1 and AB2 emitted from two alignment observation systems AL1 and AL2 of the alignment optical system AL.
Irradiates different areas of the reticle 1 through different areas of the dichroic mirror 12, and further irradiates different areas of the surface of the wafer 3 through the projection optical system 2 after passing through the reticle 1. To do. Each alignment light A irradiated on the surface of the wafer 3
B <b> 1 and AB <b> 2 are reflected on the surface of the wafer 3, and the respective reflected light beams reflected by the wafer 3 pass through different regions of the dichroic mirror 12 together with the respective reflected light beams reflected by the reticle 1 after passing through the projection optical system 2 again. Then, the process returns to the alignment observation systems AL1 and AL2 of the alignment optical system AL.

In one alignment observation system AL1, the alignment light AB1 emitted from the light source 27 of FIG.
Condensing lens 28, beam splitter 29, objective lens 3
After passing 0, it passes through the dichroic mirror 12 of FIG. 1 and is irradiated on the reticle mark 42 formed on the reticle 1 and the wafer mark 40 formed on the wafer 3. Then, the reticle mark 42 and the wafer mark 40
The alignment light reflected by the beam passes through the objective lens 30 of FIG. 5 again and returns to the beam splitter 29. The alignment light reflected by the beam splitter 29 is reflected by the imaging lens 3
The light passes through 1 and is received by the two-dimensional CCD image pickup device 32.

On the other hand, in the alignment observation system AL2,
The alignment light AB2 emitted from the light source 33 passes through the condensing lens 34, the beam splitter 35, and the objective lens 36, and then passes through the dichroic mirror 12 of FIG. 1, and the reticle mark 43 and the wafer 3 formed on the reticle 1. The wafer mark 41 formed above is irradiated. Then, the alignment light reflected by the reticle mark 43 and the wafer mark 41 passes through the objective lens 36 of FIG. 5 again, is reflected by the beam splitter 35, passes through the imaging lens 37, and then is transmitted by the two-dimensional CCD image pickup device 38. Received light.

FIG. 6 shows a two-dimensional CCD image pickup device 32 and 3.
8 shows a state in which the image picked up in 8 is displayed on the CRT display 39. In FIG. 6, a two-dimensional CCD image pickup device 32
A set of images 42A and 40A of the reticle mark 42 and the wafer mark 40, respectively, and a respective image 43 of the reticle mark 43 and the wafer mark 41 captured by the two-dimensional CCD image sensor 38.
A set of images consisting of A and 41A is electrically combined,
It is displayed on one screen of the CRT display 39. By processing this image, the amount of positional deviation between the reticle marks 42 and 43 and the corresponding wafer marks 40 and 41 is detected. The two systems of alignment observation systems AL1 and AL2 have variable intervals in the X direction so that they can handle exposure shots of various sizes.

Next, the positioning and exposure operation of the wafer stage will be described. In FIG. 1, the wafer 3 carried onto the wafer holder 18 by a wafer loader (not shown) is vacuum-sucked on the wafer holder 18, and its alignment is performed by a rough alignment system (not shown) with an accuracy of ± several μm or less. Next, the wafer mark 4 attached to the shot area to be exposed first on the wafer 3
0 and 41 are the two alignment observation systems AL of FIG.
1, AL2 is positioned within the field of view. At this time, the wafer 3 is positioned by a laser interferometer I _WX, I _WY1, wafer X stage 16 based on the measurement values of I _WY2, wafer Y stage 15, at the same time, the reticle mark 4
Alignment observation systems AL1 and AL2 of 2 systems for 2 and 43
Be positioned within the field of view of.

Next, the alignment observation system AL1 measures the relative positional deviation amount (Δxa ₁ , Δya ₁ ) between the position of the reticle mark 42 and the position of the wafer mark 40, and the alignment observation system AL2 measures the reticle mark 43. Relative position deviation amount (Δx and wafer mark 41 position (Δx
a ₂ , Δya ₂ ) is measured. Where Δxa ₁ and Δ
xa ₂ represents the amount of positional deviation in the X direction, and Δya ₁
And Δya ₂ respectively represent the amount of positional deviation in the Y direction. Then, these positional deviation amounts Δxa ₁ , Δya ₁ , Δxa ₂
, Δya ₂ are all 0 (or a predetermined reference value), the reticle stage 5 is finely moved. With the above operation, the alignment is completed. After the alignment is completed, the exposure light is emitted to start the exposure. The alignment is continuously performed during the exposure.

Next, an example of a method for detecting the magnification of the projection optical system in this example will be described with reference to FIGS. 2 and 3, a first reference pattern MM1 including two cross marks 60a and 60b drawn near both left and right ends of the first reference plate 9 which is light-transmissive on the reticle stage 5 is provided. Is formed, and also
Second reference plate 2 of wafer leveling table 17
The second reference pattern WM1 composed of two cross marks 61a and 61b drawn near both left and right ends of
Are formed. This second reference pattern WM1 is
The pattern in which the first reference pattern MM1 is vertically and horizontally inverted is reduced by the reduction magnification β of the projection optical system 2. In FIG. 3, for convenience of description, the second reference pattern WM1 is transferred to the reticle stage 5 via the projection optical system 2.
Shown in the form of the projected image projected above. Hereinafter, in all of the embodiments, not limited to this example, it is assumed that the second reference pattern is designed to have a size obtained by reducing the first reference pattern by the reduction ratio β of the projection optical system 2. Further, any one of the first reference pattern and the second reference pattern is a projected image projected on the wafer leveling table 17 or the reticle stage 5 via the projection optical system 2 in the figure. Shown.

First, the first reference plate 9 on the reticle stage 5 is positioned below the illumination area IA of exposure light. At the same time, the second reference plate 25 on the wafer leveling table 17 is also positioned below the area conjugate with the illumination area IA. This positioning is performed by moving the reticle stage 5 so that the first reference plate 9 enters the illumination area IA in FIG. Then, the reference pattern MM1 of the first reference plate 9 and the second reference pattern WM1 are observed by the observation optical systems 10 and 11. The second reference pattern WM1 shows the second reference pattern projected onto the reticle stage 5 via the projection optical system 2, but for simplicity of explanation, it is as described above. It is omitted. Less than,
The same method is used for the description regarding the projected image.

FIG. 4 is a plan view showing a state of being observed by the observation optical systems 10 and 11. In FIG. 4, the first reference pattern MM1 and the second reference plate on the first reference plate 9 are shown. The second reference pattern WM1 on 25 is overlapped and observed. By the observation optical system 10 shown by the broken line, the mark 60a of the first reference pattern MM1 and the second mark 60a
Of the reference pattern WM1 and the mark 61a of the first reference pattern WM1 and the mark 61b of the second reference pattern WM1 overlap and are observed by the observation optical system 11 also indicated by a broken line. It In the observation optical systems 10 and 11, the relative positional deviation (Δ _x1 , Δ _x2 ) between the first reference pattern MM1 and the second reference pattern WM1 in the X direction is based on the above observed results.
Is detected. In addition, Δ _x1 in the parentheses is the mark 60a of the first reference pattern MM1 and the second reference pattern WM1.
Of shows the X-direction displacement between the mark 61a, delta _x2 denotes the X-direction displacement between the mark 60b and the mark 61b of the second reference pattern WM1 the first reference pattern MM1.

Therefore, at the time of initial adjustment of the projection exposure apparatus,
That is, when the projection magnification of the projection optical system 2 is adjusted,
The first reference pattern MM1 and the second reference pattern MM1
The respective relative marks of the pattern WM1 and the marks
Displacement (Δ_x 0₁ , Δ_x 0 ₂ ) Is measured and the main control system
The difference calculated by the following formula (1) by 100 is
It is recorded in the lens control unit (not shown) as the reference magnification error A0.
Be done.

[0038] _{A0 = Δ x 0 2 -Δ x} 0 1 (1) Next, when exposing a wafer by the exposure method described earlier, the first reference pattern MM by regularly above method
The relative positional deviation (Δ _x1 , Δ _x2 ) between the first and second reference patterns WM1 is measured. The projection magnification error A at this time is obtained by the following equation (2).

A = Δ _x2 −Δ _x1 (2) The value A obtained by the equation (2) and the reference magnification error A0
And the difference ΔA obtained by the following equation (3) is the variation of the projection magnification of the projection optical system 2. ΔA = A−A0 (3) The information on the variation of the projection magnification obtained by the above method is sent to the lens control unit and immediately sent via the drive system (not shown) of the movable lens group of the projection optical system 2. Will be corrected.

As described above, in the projection exposure apparatus according to the present embodiment, the observation optical system 10 observes the first reference pattern provided on the reticle stage 5 and the second reference pattern provided on the wafer leveling table 17. , 11 for superimposing and observing, and thereby the variation of the projection magnification can be easily calculated from the difference between the shifts occurring at two opposite positions in the X direction. Therefore, the variation of the projection magnification can be detected within a short time, and at the same time, the projection magnification can be corrected quickly.

Next, another embodiment of the projection exposure apparatus according to the present invention will be described with reference to FIGS. In this example,
The first and second reference plates shown in the previous embodiment have different configurations. It should be noted that the first and second reference plates have a configuration different from that of the previous embodiment, so that the reticle, the reticle stage, and the size of the reticle base are slightly changed, but the basic configuration and operation are Since this does not change, in FIGS. 7 and 8, parts corresponding to those in FIGS. 2 and 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 7 is a plan view showing the configuration around the reticle stage of this example. In FIG. 7, the first reference plate made of a rectangular glass substrate is provided at the end in the Y direction on the reticle stage 5. 9A is provided. On the first reference plate 9A, a first reference pattern MP is formed by arranging three basic patterns consisting of two cross marks formed in pairs on the left and right sides thereof in three lines at substantially equal intervals in the Y direction. . The most basic pattern in the Y direction is composed of a pair of left and right cross marks 62a and 62b. Similarly, the intermediate basic pattern is composed of cross marks 63a and 63b, and the most basic pattern in the -Y direction is a cross mark. 6
It is composed of 4a and 64b.

FIG. 8 is a plan view showing the structure around the wafer leveling table 17, and in FIG. 8, a second rectangular glass substrate is formed near the left end of the wafer leveling table 17 in the Y direction. Reference plate 25
A is provided. On the second reference plate 25A, a second reference pattern WP is formed by arranging three basic patterns composed of two cross marks formed in pairs at the left and right ends of the second reference plate 25 at substantially equal intervals in the Y direction. . The most basic pattern in the Y direction is a pair of left and right cross marks 65a, 65.
b, and similarly the intermediate basic pattern is
It is composed of cross marks 66a and 66b, and the most basic pattern in the -Y direction is composed of cross marks 67a and 67b. As described above, the array of the second reference pattern WP is shown by the projection image projected on the reticle stage 5 via the projection optical system 2.

Further, similar to the previous embodiment, the first reference plate 9A and the second reference plate on the wafer leveling table 17 are provided on the upper part of the reticle stage 5 near the ends in the -X direction and the X direction, respectively. Observation optical systems 10 and 11 for observing 25A are arranged. With the projection exposure apparatus configured as described above, alignment and exposure operations are performed based on the same procedure as the procedure shown in the previous embodiment.

Next, an example of a method of detecting the magnification of the projection optical system in this example will be described. First, the first reference plate 9A on the reticle stage 5 is positioned below the illumination area IA. Wafer leveling table 1 at the same time
The second reference plate 25A on 7 is also positioned below the illumination area IA. And these two reference plates 9
The respective reference patterns MP and WP on A and 25A are observed by the observation optical systems 10 and 11.

FIG. 9 is a plan view showing a state of being observed by the observation optical systems 10 and 11. In FIG. 9, the first reference pattern MP and the second reference plate MP on the first reference plate 9A are shown. The second reference pattern WP on 25A is observed overlapping. 9A to 9C show observation images for each series that are sequentially observed by the observation optical systems 10 and 11 indicated by broken lines. That is, FIG. 9A shows an observation of the first series of marks, and the observation optical systems 10 and 11
Thus, the image in which the mark 62a of the first reference pattern MP and the 65a of the second reference pattern WP overlap, and the mark 62b of the first reference pattern MP and the second reference pattern W
Images in which P and 65b overlap each other are observed. Then, from the state of FIG. 9A, move the reticle stage 5 to -Y.
The wafer Y stage 15 by moving the wafer Y stage 15 in the direction of the marks 65b and 66b.
When moved in the + Y direction by the distance between and, the state shown in FIG. FIG. 9B shows an image in which the mark 63a of the first reference pattern MP and the mark 66a of the second reference pattern WP overlap and the mark 63b of the first reference pattern MP.
And 66b of the second reference pattern WP are overlapped with each other. Similarly, the reticle stage 5 and the wafer Y
When the stage 15 is moved by a predetermined amount in the −Y direction and the + Y direction, the state shown in FIG. 9C is obtained. FIG. 9 (C)
Is an image in which the mark 64a of the first reference pattern MP and the mark 67a of the second reference pattern WP overlap, and the mark 64b of the first reference pattern MP and the mark 67b of the second reference pattern WP overlap. Shows the image.

As described above, in this example, the observation optical system 10,
11 or the method of moving the reticle stage 5 and the wafer stage in the −Y direction and the + Y direction respectively and sequentially observing each mark of each series, but if necessary, for example, arranging the observation optical system at 6 places, You may observe. In the observation optical systems 10 and 11, on the basis of the above observation results, relative positional deviations (Δ _xm1 , Δ) between the same series marks of the first reference pattern MP and the second reference pattern WP in the X direction, respectively. _xm2 ) is detected.

The relative positional deviation between the first series mark and the third series mark of MP and WP measured by the observation optical systems 10 and 11 as described above is calculated as ( _Δx11 , Δ).
_{x12), (Δ x21, Δ} x22), and (Δ _x31, Δ _x32). Then, the average value of the relative displacements of the three series is calculated by the following equations (4) and (5), and the average value of the relative displacements of the first reference pattern MP and the second reference pattern WP ( As Δ _x1 , Δ _x2 ), the variation value of the projection magnification is calculated by the same calculation as in the previous embodiment.

Δ _x1 = (Δ _x11 + Δ _x21 + Δ _x31 ) / 3 (4) Δ _x2 = (Δ _x12 + Δ _x22 + Δ _x32 ) / 3 (5) Information on the variation value of the projection magnification obtained by the above method is , And is immediately corrected via a drive system (not shown) for the lens group of the projection optical system 2.

Although the above description focuses only on the variation of the projection magnification in the X direction, the variation of the projection magnification in the Y direction can also be measured by the method of this example. For example, Y directions of the first reference pattern 62a and a second reference in the Y direction relative positional deviation delta _Y11 and the first reference pattern with the patterns 65a 64a and a second reference pattern 67a in FIG. 9 The relative positional deviation Δ _Y12 of the observation optical system 1
0, and the relative positional deviation in the Y direction (Δ
_Y11 , _ΔY12 ) may be processed in the same manner as the relative displacement in the X direction described above. Further, the first reference pattern 62
b a second Y direction to the reference pattern 65b of the relative positional deviation delta _Y31, and 64b and the second first reference pattern
Relative displacement Δ in the Y direction with respect to the reference pattern 67b of
_Y32 is measured by, for example, the observation optical system 11, and the relative displacement in the Y direction (Δ _Y31 , Δ _{Y3 2} ) and the relative displacement in the Y direction (Δ _Y11 , Δ _Y12 ) are averaged. It can also be processed.

As described above, in the projection exposure apparatus according to the present embodiment, three series marks are formed on the first reference plate and the second reference plate at equal intervals in the Y direction, and each series mark is formed. Since the relative displacement of the above is averaged to calculate the variation in the projection magnification, the variation in the projection magnification can be accurately detected and corrected. Further, according to the method of this example, it is possible to measure and correct not only the change in the X direction but also the change in the projection magnification in the Y direction. Further, the tendency of distortion of the projected image of the projection optical system 2 can be known from the relative positional deviation of the marks at the six points.

Next, another embodiment of the first reference pattern formed on the first reference plate and the second reference pattern formed on the second reference plate will be described with reference to FIGS.
This will be described with reference to FIG. 10 to 13, parts corresponding to those in FIGS. 2 and 3 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 10 is a plan view showing another embodiment of the first reference pattern and the second reference pattern. In FIG. 10A, left and right pairs are formed on the first reference plate 9B on the reticle stage. A first slit-shaped mark 71a, 71b that is long in the Y direction.
3 shows a reference pattern MM2. The slit-shaped mark is formed by forming a pair of marks each having a relatively thick line pattern having a narrow interval and having a predetermined interval. FIG. 10B shows a second reference formed of two sets of three linear patterns 72a and 72b long in the Y direction formed on the second reference plate 25B on the wafer stage in a left-right pair. A pattern WM2 is shown. FIG. 10 (C)
Indicates that both reference patterns overlap each other within the field of view of the observation optical systems 10 and 11 (indicated by a dashed circle in the figure). In the visual field of the observation optical system 10, the second reference pattern WM2 is formed in the mark 71a of the first reference pattern MM2.
It can be observed that the mark 72a of the mark 72a just entered. In the field of view of the observation optical system 11, the mark 71b of the first reference pattern MM2 and the second reference pattern WM are also included.
It is observed that the second mark 72b and the second mark 72b overlap each other as described above. The relative displacement of these is measured by the observation optical systems 10 and 11, and the error of the projection magnification is measured and corrected based on the measured displacement.

FIG. 11 is a plan view showing still another embodiment of the first reference pattern and the second reference pattern, in which a one-dimensional lattice pattern is used as both reference patterns. FIG. 11A shows a first reference pattern. In FIG. 11A, a one-dimensional grating having a pitch of 4P1 is formed on the first reference plate 9C on the reticle stage. FIG. 11B shows the second reference pattern. In FIG. 11B, the pitch P1 obtained by reducing the first reference pattern to 1/4 is provided on the second reference plate 25C on the wafer stage. A one-dimensional grating having a pitch P2 slightly different from is formed. An image pickup device 2 such as a two-dimensional CCD arranged on the bottom of the reference plate 25C by superimposing projected images of two gratings having different pitches.
When observed with No. 6, the pitch is (P1
Moire fringes of (P2) / (P1-P2) appear. In the moire fringes, the first reference pattern MM3 and the second reference pattern WM3 are overlapped with each other to form a new pitch lattice pattern LM3.
Is formed.

FIG. 11C shows moire fringes imaged by the image pickup device 26, and shows the first reference pattern MM3.
And Δt _X1 and Δt _X2 are the displacements of the one-dimensional lattice of the second reference pattern WM3 in the X direction, the moire fringes are the one-dimensional lattices of the first reference pattern MM3 and the second reference pattern WM3, respectively. For the displacement of
It is known to make the displacement determined by the following equations (6) and (7).

ΔM _X1 = Δt _X1 {P1 / (P1-P2)} (6) ΔM _X2 = Δt _X2 {P2 / (P1-P2)} (7) where ΔM _X1 and ΔM _X2 are respectively the first The X-direction displacement of the moire fringes with respect to the X-direction displacement of the reference pattern MM3 and the X-direction displacement of the moire fringes with respect to the X-direction displacement of the second reference pattern WM3 are shown.

FIG. 12 shows an image pickup device 26 for observing moire fringes generated by the first reference pattern MM3 and the second reference pattern WM3. The image pickup device 26 is provided on the wafer stage on the second reference plate 25C. It is arranged immediately below and detects the displacement of the moire fringes. In this case, the moire fringes are measured at the time of initial adjustment and the initial pattern information is recorded in the lens controller. Then, the moire fringes are measured as needed, and the displacement amount is calculated by the main control system 100 by comparison with the recorded initial pattern. This amount of displacement is the amount of variation in projection magnification and distortion.

FIG. 13 is a plan view showing still another embodiment of the first reference pattern and the second reference pattern, in which a two-dimensional lattice is used as both reference patterns. FIG. 13 (A) shows a first reference pattern MM4. In FIG. 13 (A), the first reference pattern MM4 formed of a two-dimensional lattice having a pitch of 4P3 is arranged on the first reference plate 9D. Has been formed. FIG.
(B) shows the second reference pattern WM4, which is shown in FIG.
3 (B), a second reference composed of a two-dimensional lattice having a vertical and horizontal pitch P4 slightly different from the pitch P3 when the first reference pattern MM4 is reduced to 1/4 on the second reference plate 25D. A pattern WM4 is formed.

When the projected images of these two two-dimensional gratings having different pitches are overlapped and observed by the image pickup device, 1 in FIG.
Similar to the three-dimensional lattice, two-dimensional moire fringes having a pitch of (P3 · P4) / (P3-P4) appear in both the X and Y directions due to the moire effect. The moire fringes are the first reference pattern M.
The M4 and the second reference pattern WM4 overlap to form a two-dimensional lattice pattern LM4 with a new pitch.

FIG. 13C shows a two-dimensional moire fringe observed by the image pickup device. The first reference pattern MM4.
And Δt _X3 and Δt _X4 are the displacements of the two-dimensional lattice of the second reference pattern WM4 in the X direction, the moire fringes are the two-dimensional lattices of the first reference pattern MM4 and the second reference pattern WM4, respectively. For the displacement in the X direction of, the following (8) and (9) are similarly applied in the case of the one-dimensional lattice.
Perform the displacement calculated by the formula.

ΔM _X3 = Δt _X3 {P3 / (P3-P4)} (8) ΔM _X4 = Δt _X4 {P4 / (P3-P4)} (9) However, ΔM _X3 and ΔM _X4 are respectively the first The X-direction displacement of the moire fringes LM4 with respect to the X-direction displacement of the reference pattern MM4 and the X-direction displacement of the moire fringes with respect to the X-direction displacement of the second reference pattern WM4 are shown.

Further, according to the two-dimensional lattice of this example, not only the X direction but also the Y direction displacement can be detected. First
Assuming that the displacements of the two-dimensional lattices of the reference pattern MM4 and the second reference pattern WM4 in the Y direction are Δt _Y3 and Δt _Y4 , respectively, the moire fringes are the same as those of the first reference pattern MM4 and the second reference pattern WM4. For each displacement of the dimensional lattice in the Y direction, the following (10) and (1
Perform the displacement calculated by the equation (1).

ΔM _Y3 = Δt _Y3 {P3 / (P3-P4)} (10) ΔM _Y4 = Δt _Y3 {P4 / (P3-P4)} (11) where ΔM _Y3 and ΔM _Y4 are respectively the first The Y-direction displacement of the moire fringes with respect to the Y-direction displacement of the reference pattern MM4 and the Y-direction displacement of the moire fringes with respect to the Y-direction displacement of the second reference pattern WM4 are shown.

Also in this case, the displacement of the moire fringes in the X and Y directions can be detected by arranging the image pickup device having a substantially square image pickup surface immediately below the second reference plate 25D. In this case, the moire fringes are measured at the time of initial adjustment and the initial pattern information is recorded in the lens controller. Then, if necessary, the moire fringes are measured, and the displacement amount is calculated by comparison with the recorded initial pattern. As a result, a variation in projection magnification and a two-dimensional variation in distortion are detected.

Although the present invention is applied to the step-and-repeat type projection exposure apparatus, the present invention is not limited to the step-and-repeat type projection exposure apparatus, but it is not limited to the reticle and the wafer. The present invention can be similarly applied to a slit scan type or step-and-scan type projection exposure apparatus that performs exposure by scanning relative to a projection optical system.

As described above, the present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention.

[0066]

According to the projection exposure apparatus of the present invention, reference members (reference plates) are arranged on the mask side (on the mask stage) and on the photosensitive substrate (wafer) side (on the substrate stage), respectively. Since the magnification and distortion fluctuation of the projection optical system are detected based on the relative fluctuation amount obtained by measuring the deviation between the reference marks (reference patterns) formed on these reference members, the standard It is not necessary to bother to load the mask and the reference substrate, and it is possible to measure the magnification and distortion variation of the projection optical system within a short time.

Further, since the reference member is still mounted on the apparatus, there is no displacement of the reference member, and there is no error as in the case of using the conventional reference mask. Further, since the reference member is held in a stable state without being taken out and put in unlike the reference mask, there is an advantage that the projection magnification and the like can be measured with high accuracy, with little change over time. When the first and second reference marks are two-dimensionally arranged reference marks, it is possible to detect variations in projection magnification with higher accuracy by averaging, for example. It is possible to detect variations in projection magnification in two orthogonal directions. Also, the tendency of distortion can be detected.

Further, the first fiducial mark is a one-dimensional grid pattern, and the projected image of the second fiducial mark on the substrate stage has a one-dimensional grid having a pitch slightly different from that of the grid pattern. In the case of a circular pattern, since moire fringes formed by two gratings having slightly different pitches are detected, not only the magnification of the projection optical system but also the
Changes in distortion can also be detected with extremely high accuracy.

Further, the first reference mark is a two-dimensional grid pattern, and the projected image of the second reference pattern on the substrate stage has a two-dimensional grid having a pitch slightly different from that of the grid pattern. In the case of a circular pattern, since the moire fringes formed by the two gratings having slightly different pitches are detected by the two-dimensional image pickup element, the projection magnification in two directions orthogonal to each other as well as in one direction perpendicular to the optical axis. Also, it is possible to detect a two-dimensional distortion change and the like with extremely high accuracy. Further, in the case of having a calculation means for calculating at least one of the magnification and the distortion of the projection optical system based on the relative positional deviation information,
The magnification or distortion of the projection optical system is quickly calculated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a projection exposure apparatus according to the present invention.

FIG. 2 is a plan view showing the reticle stage of FIG.

FIG. 3 is a plan view showing the wafer stage of FIG.

4 is a plan view showing a state in which the reference patterns MM1 and WM1 of FIGS. 2 and 3 are observed by the observation optical systems 10 and 11 of FIG.

5 is a configuration diagram showing an alignment optical system AL of FIG. 1. FIG.

6 is a diagram showing an image on a CRT display of a reticle mark and a wafer mark observed by the alignment optical system of FIG.

FIG. 7 is a plan view showing a reticle stage used in another embodiment of the projection exposure apparatus according to the present invention.

8 is a plan view showing a wafer stage used corresponding to the reticle stage of FIG. 7. FIG.

9 is a first reference pattern MP and a second reference pattern MP of FIG. 7 and FIG.
FIG. 6 is a plan view showing how the reference pattern WP of FIG.

FIG. 10 is a plan view showing another embodiment of the first reference pattern and the second reference pattern used in the projection exposure apparatus of the present invention.

FIG. 11 is a plan view showing another embodiment of the first reference pattern and the second reference pattern used in the projection exposure apparatus of the present invention.

FIG. 12 is a front view showing an arrangement of image pickup elements for observing moire fringes generated by the first reference pattern and the second reference pattern of the present invention.

FIG. 13 is a plan view showing still another embodiment of the first reference pattern and the second reference pattern used in the projection exposure apparatus of the present invention.

[Explanation of symbols]

 1 Reticle 2 Projection Optical System 3 Wafer 4 Reticle Base Plate 5 Reticle Stage 6, 7, 8 Reticle Moving Mirror 9, 9A-9D First Reference Plate 10, 11 Observation Optical System 12 Dichroic Mirror 13 Irradiation Optics of Focus Position Detection System System 14 Receiving optical system of focus position detection system 15 Wafer Y stage 16 Wafer X stage 17 Wafer leveling table 18 Wafer holder 23, 24 Wafer moving mirror 25, 25A to 25D Second reference plate 26 Image sensor 27, 33 Light source for alignment 32, 38 Two-dimensional CCD image pickup device 40, 41 Wafer mark 42, 43 Reticle mark AL Alignment optical system AL1, AL2 Alignment observation system MM1 to MM4, MP First reference pattern WM1 to WM4, WP Second reference pattern

Claims (5)

[Claims] 1. A projection exposure apparatus for projecting an image of a predetermined portion of a transfer pattern formed on a mask onto a photosensitive substrate through a projection optical system under exposure illumination light, A mask stage which holds the mask and moves the mask in a first direction on a plane perpendicular to the optical axis of the projection optical system; and a first stage which is arranged on the mask stage and on which a first reference mark is formed. A reference member, a substrate stage for holding the substrate and moving the substrate in a second direction corresponding to the first direction on a plane perpendicular to the optical axis of the projection optical system; A second fiducial member disposed above and having a second fiducial mark formed thereon; one fiducial mark of the first and second fiducial marks;
A projection exposure apparatus comprising: a mark detection unit that detects a relative positional deviation amount between the one reference mark and the other reference mark that is different from the image through the projection optical system. 2. The first fiducial mark comprises a plurality of fiducial marks arranged two-dimensionally on the first fiducial member, and the second fiducial mark on the second fiducial member. Two
2. The projection exposure apparatus according to claim 1, comprising a plurality of reference marks arranged in a dimension. 3. The second fiducial mark is a one-dimensional lattice-like pattern formed at a predetermined pitch in a direction intersecting the second direction, and the projection optical system of the first fiducial mark is formed by the projection optical system. The image on the side of the substrate stage through is a one-dimensional lattice-like pattern formed at a pitch different from the predetermined pitch substantially in the pitch direction of the second reference mark, and the mark detecting means is The projection exposure apparatus according to claim 1, wherein the projection exposure apparatus is an image pickup element arranged at the bottom of the second reference member. 4. The substrate according to claim 1, wherein the second reference mark is a two-dimensional lattice pattern formed at a predetermined pitch in two different directions, and the first reference mark is provided through the projection optical system. The image on the stage side is a two-dimensional lattice-like pattern formed at a pitch different from the predetermined pitch substantially in the two pitch directions of the second reference mark, and the mark detecting unit is configured to 2. The projection exposure apparatus according to claim 1, wherein the projection exposure apparatus is a two-dimensional image pickup element arranged on the bottom of the second reference member. 5. The projection exposure apparatus according to claim 1, further comprising a calculation unit that calculates at least one of a magnification and a distortion of the projection optical system based on the relative position shift amount.