JPH0757991A - Scanning projection aligner - Google Patents

Abstract

PURPOSE:To provide a slit scan exposure system projection aligner in which high superposition accuracy can be sustained. CONSTITUTION:When a pattern 34B previously formed in the shot region on a wafer is distorted in trapezoidal shape, the profile is distorted as shown by the exposure regions IAi, IAm, IAf depending on the exposing position (x) in a slit-like exposing region. The relative angle between a reticle and the wafer is varied gradually depending on the exposing position (x) such that the relative angle is zero in the center and the direction thereof is reversed at the opposite ends in the scanning direction. Furthermore, the distribution of illuminance EL in the exposing region is inclined along y-direction as shown by a line 37.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reticle and a photosensitive substrate which are sequentially scanned while the reticle and the photosensitive substrate are scanned synchronously when a semiconductor device or a liquid crystal display device is manufactured by a photolithography process. The present invention relates to a projection exposure apparatus of a so-called slit scan exposure system, which projects and exposes light on the top.

[0002]

2. Description of the Related Art When a semiconductor element, a liquid crystal display element, or the like is manufactured by a photolithography process, a pattern image of a photomask or reticle (hereinafter, collectively referred to as "reticle") is transferred to a photoresist or the like via a projection optical system. There is used a projection exposure apparatus that performs projection exposure on a substrate (wafer, glass plate, or the like) coated with. In such a projection exposure apparatus, the reticle pattern to be exposed this time is accurately overlapped over the entire exposure field with respect to the chip pattern on the substrate such as a wafer formed by the previous exposure and process processing. It is required to perform the exposure, that is, to perform the exposure while maintaining the overlay accuracy with high accuracy.

Distortion of the projected image of the projection optical system of the projection exposure apparatus is one of the factors that deteriorate the overlay accuracy. In particular, when forming the circuit pattern of each layer on one substrate using different projection exposure apparatuses, if the distortion of the projected image between the projection exposure apparatuses is different, an overlay error occurs. In addition, the substrate may be distorted due to heating due to process treatment, etc., and the previously exposed pattern may be distorted accordingly.
The distortion of the pattern in this case is also the same as the distortion of the projected image by the projection exposure apparatus used last time.

In this regard, as a conventional projection exposure apparatus, an apparatus of a batch exposure system (or also called a “full field system”) for collectively reducing and projecting a pattern of a reticle on the entire exposure field on a photosensitive substrate ( Steppers, etc.) were common. In such a projection exposure apparatus of the batch exposure system, a lens element or a reticle of a projection optical system is driven in the optical axis direction or is tilted with respect to the optical axis to positively form a projection pattern. A method has been proposed in which the pattern is exposed in a trapezoidal shape, and the state of the previously exposed pattern is matched with the state of the distortion (for example, Japanese Patent Laid-Open Nos. 62-7129 and 62-246).
24, JP-A-2-609, and JP-A-2-65.
No. 2).

[0005]

The conventional method of improving the overlay accuracy as described above has been proposed on the premise of the collective exposure method (full field method). However, in recent years, the pattern area of the reticle is illuminated in a slit shape, the reticle is scanned with respect to the slit-shaped illumination area, and the exposure area conjugate with the slit-shaped illumination area is synchronized with the scanning of the reticle. A projection exposure apparatus of a so-called slit scan exposure system, which is a system in which a reticle pattern is sequentially projected and exposed on a photosensitive substrate by scanning the photosensitive substrate, has been developed.

In this slit scan exposure method, the illumination area on the reticle is smaller than that in the batch exposure method.
There is not only the advantage that the amount of distortion of the projected image and the nonuniformity of the illuminance can be suppressed to a small value, but also the advantage that a large area can be exposed without being restricted by the field size of the projection optical system in the scanning direction. is there. However, in the slit scan exposure method, only a part of the field of the projection optical system is used, and the same pattern passes through a plurality of positions in the field of the projection optical system during scanning exposure, so that the lens element of the projection optical system is used. It is not possible to distort the projected image as a whole into a trapezoidal shape or the like by simply inclining. Therefore, the conventional method of improving the overlay accuracy for the batch exposure method has a disadvantage that the overlay accuracy in the projection exposure apparatus of the slit scan exposure method cannot be improved.

In view of the above problems, an object of the present invention is to provide a slit scan exposure type projection exposure apparatus capable of maintaining the overlay accuracy with high accuracy.

[0008]

A first scanning projection exposure apparatus according to the present invention is, for example, as shown in FIGS.
An illumination optical system that illuminates a predetermined illumination area with illumination light (1 to 1
3, 5 to 7), a mask stage (RST) for scanning a mask (R) on which a transfer pattern is formed in a predetermined illumination area in a predetermined direction, and a mask in the predetermined illumination area The image of the pattern of (R) is formed on the photosensitive substrate (W).
It has a projection optical system (PL) for image-forming and projection on it, and a substrate stage (WST) for scanning the substrate (W) in a predetermined direction with respect to an exposure region conjugate with the predetermined illumination region. Of the pattern of the mask (R) is sequentially projected and exposed on the substrate (W) by synchronously scanning the mask (R) and the substrate (W) with respect to the illumination area and the exposure area thereof. In the projection exposure apparatus, the substrate (W)
A relative angle θ that changes the relative angle θ between the scanning direction of the mask (R) by the mask stage (RST) and the scanning direction of the substrate (W) by the substrate stage (WST) according to the distortion of the pattern already formed on the upper side. The angle control means (19) is provided.

The second scanning projection exposure apparatus according to the present invention has the same precondition as that of the first scanning projection exposure apparatus, for example, as shown in FIG.
Relative speed adjusting means (19) for adjusting the relative scanning speed of the scanning speed of the mask (R) by ST) and the scanning speed of the substrate (W) by the substrate stage (WST), and the projection image by the projection optical system (PL). Image forming characteristic correcting means (12) for correcting the distortion of the relative speed adjusting means (19) according to the distortion of the pattern already formed on the substrate (W).
In parallel with adjusting the relative scanning speed between the mask (R) and the substrate (W) via the projection optical system (PL) onto the substrate (W) via the imaging characteristic correction means (12). The distortion state of the projected image is corrected.

In this case, the above-mentioned illumination optical system (1-3, 5
7 to 7), it is desirable to provide an illuminance distribution control means (4) for adjusting the illuminance distribution in the predetermined illumination area according to the state of distortion of the projected image by the projection optical system (PL).

[0011]

According to the first scanning type projection exposure apparatus of the present invention, as shown in FIG. 8, for example, the pattern (34C) formed on the substrate (W) by the steps up to that is formed into a diamond shape. If the substrate (W) is distorted, the substrate (W) is scanned in a direction intersecting the direction (x direction) conjugate with the scanning direction of the mask (R) at an angle θ. As a result, the slit-shaped exposure area (IA _i ) moves along the diamond-shaped pattern (34C), and the overlay error is reduced.

Further, according to the second scanning type projection exposure apparatus, the state of distortion of the pattern formed on the substrate (W) up to that time is obtained in advance. Then, in parallel with scanning the mask (R) and the substrate (W), for example, a projection optical system via the imaging characteristic correction means (12) according to the state of the distortion of the pattern on the substrate (W). The state of distortion of the projected image of the mask pattern is continuously changed by driving the lens element of (PL) or continuously driving the mask (R). As a result, even if the pattern on the substrate (W) is distorted, for example, trapezoidal or barrel-shaped, the projected image of the mask pattern can be distorted accordingly, and the overlay accuracy is improved. Further, in the present invention, in order to correct the magnification error in the scanning direction, the method of controlling the relative scanning speed between the mask (R) and the substrate (W) is also used.

The above-mentioned illumination optical system (1 to 3, 5 to 5)
In the case where the illuminance distribution control means (4) for adjusting the illuminance distribution in the predetermined illumination area according to the state of distortion of the projected image by the projection optical system (PL) is provided in 7), for example, the substrate (W ), The illuminance in the illuminated area is increased in the fast scanning area, and conversely, the illuminance in the illuminated area is decreased in the slow scan area of the substrate (W). Further, for example, when the pattern image of the mask (R) is enlarged through the image formation characteristic correction means (12), the illuminance in the illumination area is increased. Thereby, in order to improve the overlay accuracy, the illuminance distribution of the projected image of the mask pattern projected on the substrate (W) is maintained uniform even when the scanning speed or the state of distortion of the projected image is changed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the scanning projection exposure apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a slit scan exposure type projection exposure apparatus of the present embodiment. In FIG. 1, illumination light IL generated by a light source 1 passes through a shutter (not shown), and then a collimator lens, and The illuminance homogenizing optical system 2 including a fly-eye lens converts the illuminance distribution into a substantially uniform luminous flux.
Examples of the illumination light IL include excimer laser light such as KrF excimer laser light and ArF excimer laser light, harmonics of copper vapor laser and YAG laser, or ultraviolet emission lines (g line, i line, etc.) from an ultrahigh pressure mercury lamp. ) Etc. are used.

The luminous flux emitted from the illuminance homogenizing optical system 2 reaches the reticle blind 5 via the relay lens 3. The reticle blind 5 is arranged on a surface optically conjugate with the pattern formation surface of the reticle R and the exposure surface of the wafer W, and the transmittance distribution is in a desired state so as to be in close contact with the relay lens 3 side of the reticle blind 5. Variable N that can be set
The D filter 4 is installed. In the reticle blind 5, the size (slit width, etc.) of the opening is adjusted by opening and closing a plurality of movable light shielding portions (for example, two L-shaped movable light shielding plates) by, for example, a motor. By adjusting the size of the opening, the illumination area IAR for illuminating the reticle R is set to an arbitrary shape and size.

The variable ND filter 4 is composed of, for example, a double blind structure, a liquid crystal display panel, an electrochromic device, or an ND filter having a desired shape, and the variable ND filter control unit 22 puts the variable ND filter 4 in and out. As a result, the illuminance distribution in the illumination area IAR on the reticle R is intentionally made nonuniform, and as a result, the exposure amount on the wafer W during scanning can be kept constant.
Normally, the entire variable ND filter 4 is 100% transparent, and the illuminance distribution in the illumination area IAR on the reticle R is uniform. Details of the variable ND filter 4 will be described later.

The light flux that has passed through the variable ND filter 4 and the reticle blind 5 illuminates a reticle R on which a circuit pattern and the like are drawn via a relay lens 6 and a dichroic mirror 7. Reticle R is reticle stage RS
This reticle stage RST is vacuum-adsorbed on T,
The reticle R is positioned by finely moving two-dimensionally in a plane perpendicular to the optical axis IX of the illumination optical system.

Further, the reticle stage RST is provided with a reticle drive section (not shown) composed of a linear motor or the like.
It is possible to move at a specified scanning speed in a predetermined direction (scanning direction). Reticle stage RST has a movement stroke that allows the entire surface of reticle R to cross at least the optical axis IX of the illumination optical system. A movable mirror 15 that reflects the laser beam from the interferometer 16 is fixed to the end of the reticle stage RST, and the position of the reticle stage RST in the scanning direction is constantly fixed by the interferometer 16 at a resolution of, for example, about 0.01 μm. To be detected. The position information of the reticle stage RST from the interferometer 16 is sent to the stage control system 19 and
On the basis of position information of the reticle stage RST via a reticle drive unit (not shown),
To drive. Since the initial position of the reticle stage RST is determined so that the reticle R is accurately positioned at a predetermined reference position by a reticle alignment system (not shown), it is only necessary to measure the position of the moving mirror 15 with the interferometer 16. This means that the position of R was measured with sufficiently high accuracy.

Now, the illumination light IL which has passed through the reticle R
Is incident on a projection optical system PL which is telecentric on both sides, and the projection optical system PL applies a photoresist (photosensitive material) to the surface of a projected image obtained by reducing the circuit pattern of the reticle R by, for example, 1/5 or 1/4. Formed on the formed wafer W. In the projection exposure apparatus of the present embodiment, as shown in FIG. 2, the reticle R is illuminated by a rectangular (slit-shaped) illumination area IAR having a longitudinal direction perpendicular to the scanning direction (x direction) of the reticle R. Then, the reticle R is scanned at the speed V _R in the −x direction during exposure. Illumination area I
AR (center is substantially coincident with the optical axis IX) is projected onto the wafer W via the projection optical system PL, and a slit-shaped projection area I
A is formed. Since the wafer W has an inverted imaging relationship with the reticle R, the wafer W is scanned at the speed V _W in synchronization with the reticle R in the direction opposite to the direction of the speed V _R (+ x direction), and the shot on the wafer W is shot. The entire area SA can be exposed. The ratio V _W / V _R of the scanning speed accurately corresponds to the reduction magnification of the projection optical system PL, and the pattern of the pattern area PA of the reticle R is accurately reduced and transferred onto the shot area SA on the wafer W. To be done. Illumination area I
The width in the longitudinal direction of AR is the pattern area P on the reticle R.
It is set to be wider than A and narrower than the maximum width of the light shielding area ST, and the pattern area P is set by scanning.
A The entire surface is illuminated.

Returning to the description of FIG. 1, the wafer W is vacuum-sucked on the wafer holder 9, and the wafer holder 9 is held on the wafer stage WST. The wafer holder 9 can be tilted in an arbitrary direction with respect to the best imaging plane of the projection optical system PL by a driving unit (not shown) and can be finely moved in the optical axis IX direction (z direction). Further, it is also possible to perform a rotating operation around the optical axis IX. On the other hand, wafer stage WST is configured not only to move in the scan direction (x direction) described above, but also to move in a direction (y direction) perpendicular to the scan direction so that it can be arbitrarily moved to a plurality of shot areas. , An operation of scanning and exposing each shot area on the wafer W,
A step-and-scan operation that repeats the operation of moving to the next shot exposure start position is performed. The wafer stage drive unit (not shown) such as a motor is mounted on the wafer stage WS.
Drive T in the xy directions. A movable mirror 1 that reflects the laser beam from the interferometer 18 is provided at the end of the wafer stage WST.
7 is fixed, and the position of wafer stage WST in the xy plane is constantly detected by interferometer 18 with a resolution of, for example, about 0.01 μm. The position information (or speed information) of wafer stage WST is sent to stage control system 19, and stage control system 19 controls wafer stage WST based on this position information (or speed information).

Further, in FIG. 1, a wafer alignment system (described later) for detecting the position of the alignment mark (wafer mark) for alignment on the wafer W is provided, and the measurement result of the alignment system is used for the entire apparatus. Is supplied to the main control system 20 for controlling the operation of the above, and the main control system 20 calculates the array of shot areas on the wafer W and the distortion of this array from the measured position of the wafer mark. At this time, the relative angle between the arrangement direction of the shot areas on the wafer W and the direction conjugate with the scanning direction of the reticle R is also calculated,
This relative angle information is supplied to the stage control system 19.
Based on the relative angle information, the stage control system 19 controls the relative angle of the scanning direction of the reticle R in the scanning direction of the wafer W.

A TTL (through the lens) type wafer alignment system is provided on the side of the projection optical system PL, and the light source 23 of the wafer alignment system is usually H.
A light source that emits light having a wavelength that does not expose the photoresist, such as e-Ne laser light, is used. The light flux generated by the light source 23 enters the beam splitter 26.
The light beam reflected by the beam splitter 26 is reflected by the mirror 2
After being reflected by 5, the wafer mark for alignment on the wafer W is illuminated via the projection optical system PL. The reflected light or diffracted light from the wafer mark is again projected into the projection optical system P.
The light is received by the photoelectric sensor 24 via the L, the mirror 25, and the beam splitter 26. This detection signal is used by the main control system 20.
And the main control system 20 obtains the distortion state of the chip pattern already formed in each shot area on the wafer W from the measured coordinates of the wafer mark. As a result, the wafer W is aligned so that the projection image of the reticle R is accurately superimposed and exposed on the chip pattern of each shot area of the wafer W that was exposed and processed the previous time. Although various methods for aligning the wafer W have been proposed, other methods can be used as well.

Further, the apparatus shown in FIG. 1 supplies an image forming light beam for forming a pinhole or a slit image toward the best image forming plane of the projection optical system PL from an oblique direction with respect to the optical axis IX direction. The oblique incidence type wafer position detection system (focus detection system) including the irradiation optical system 13 and the light receiving optical system 14 that receives the reflected light flux of the imaged light flux on the surface of the wafer W through the slit is projected. It is fixed to a support portion (not shown) that supports the optical system PL. The configuration of the wafer position detection system is disclosed in, for example, Japanese Patent Laid-Open No. 60-168112, and a positional deviation in the vertical direction (z direction) with respect to the image plane of the wafer surface is detected and projected onto the wafer W. It is used to drive the wafer holder 9 in the z direction so that a predetermined space is maintained between the wafer holder 9 and the optical system PL. Wafer position information from the wafer position detection system is sent to the stage control system 19 via the main control system 20. The stage control system 19 drives the wafer holder 9 in the z direction based on this wafer position information.

In the present embodiment, the angle of a parallel flat glass plate (plane parallel) (not shown) provided inside the light receiving optical system 14 is adjusted in advance so that the image plane becomes the zero point reference, and the wafer position is detected. The system shall be calibrated. Further, for example, Japanese Patent Laid-Open No. 58-113706
The horizontal position detecting system as disclosed in Japanese Patent Publication No. JP-A-2003-242242 is used, or the wafer position detecting system is configured so that the focal position at any of plural positions in the image field of the projection optical system PL can be detected. By forming a plurality of slit images in the image field), the inclination of a predetermined region on the wafer W with respect to the image plane may be detected.

By the way, the apparatus shown in FIG. 1 has a projection optical system PL.
A correction mechanism is provided to correct the image forming characteristics of the. This correction mechanism corrects a change in the image forming characteristic of the projection optical system PL itself due to a change in atmospheric pressure, absorption of illumination light, and the like, and also a projected image of the pattern of the reticle R according to the distortion of the previous exposure shot on the wafer W. Has the function of distorting.
The correction mechanism will be described below. The imaging characteristics of the projection optical system PL include focal position, field curvature, distortion, astigmatism, etc., and mechanisms for correcting them are conceivable, but here, only the correction mechanism for distortion of the projected image will be described. To do.

As shown in FIG. 1, in this embodiment, the imaging characteristic control unit 12 drives the reticle R or the lens element 27 in the projection optical system PL to correct the imaging characteristic. In the projection optical system PL, the reticle R
The lens element 27 closest to the lens element 27 is fixed to the support member 28, and the lens element 2 following the lens element 27
.. are fixed to the main body of the projection optical system PL. In the present embodiment, the optical axis IX of the projection optical system PL indicates the optical axis of the main body of the projection optical system PL below the lens element 29. A plurality of support members 28 are expandable and contractible (at least two or more, two are shown in FIG. 1)
Is connected to the main body of the projection optical system PL via the drive element 11.

Here, the lens element 27 is the optical axis IX.
When the image is translated in the direction of, the projection magnification (enlargement / reduction rate of the size of the projected image) changes at a rate of change according to the amount of movement.
This state is shown in FIG. 3A, and the square projected image 32 in FIG. 3A is an image of a square pattern projected by the projection optical system PL without distortion. In this case, if the lens element 27 is moved upward, for example, the projection magnification becomes large and each vertex of the projected image 32 moves in the direction of the arrow, and the square pattern image is isotropically enlarged projected image 32A. Is projected as. Similarly, the slit-shaped exposure area IA ₀ without distortion is also isotropically enlarged and projected as the exposure area IA ₁ .

Next, FIG. 3B shows the case where the lens element 27 is inclined with respect to the plane perpendicular to the optical axis IX.
When the rotation axis at the time of tilt is RX, the apex of the square projected image 32 expands and contracts in the direction of the arrow as shown in FIG. 3B, and is projected as a trapezoidal projected image 32B as a whole. Similarly, the exposure area IA ₀ during scanning exposure also has a trapezoidal shape like the exposure area IA ₂ . Although FIG. 3B shows an example in which the rotation axis RX is taken in the direction (y direction) perpendicular to the scanning direction (x direction), no matter which direction the rotation axis RX is taken, FIG.
Similar to the example of (b), it is possible to make a modification such that one of the magnifications is small with respect to the rotation axis and the other magnification is large.

Next, the case of driving the reticle R will be described. The reticle R is the reticle stage R as described above.
It is placed on ST. Reticle stage RST is connected to a main body (frame) of a projection exposure apparatus (not shown) by a plurality of expandable and contractible drive elements (at least two, two shown in FIG. 1). Although not shown, the projection optical system PL is also fixed to the body of the projection optical system PL, so that the drive element 10 can change the distance between the projection optical system PL and the reticle R. Here, the reticle R is the optical axis IX.
FIG. 3 (c) shows the case of parallel translation. Figure 3
Similar to (a) and (b), in FIG. 3C, the original square projected image 32 changes to a projected image 32C.
The distortion of the projected image 32C is what is called so-called pincushion distortion, and when the reticle R moves in the opposite direction, each apex of the projected image 32 largely moves inward, which causes distortion called so-called barrel distortion. . The exposure area IA ₀ also changes to the exposure area IA ₃ .

When the reticle R or the lens element 27 is driven as described above, the focal position or the image plane changes accordingly, but the amount can be calculated by the main control system 20 from each driving amount. Then, the main control system 20 adds an offset to the zero reference of the wafer position detection system (13, 14) by the amount calculated, and controls so that the exposure surface of the wafer W is always at the focus position. . As a result, even if the focus position or the image plane position of the projection optical system PL changes due to the driving of the reticle R or the lens element 27, the focus position or the image plane position is adjusted according to the change.

The method of correcting the distortion of the projected image is not limited to the above method, and for example, a method of sealing a part of the lens interval inside the projection optical system PL and changing the air pressure inside the projection optical system PL is also used. it can. In the case of the collective exposure method, the square projected image 32 can be changed to an arbitrary shape to some extent by a combination of the above methods, so that the exposure can be performed according to the distortion of the shot area previously exposed on the wafer W. . However, when performing the exposure by the slit scan exposure method, the pattern in each shot area on the wafer W is exposed while passing through the exposure area IA according to the scanning. Therefore, as shown in FIG. 3B, for example, even if the exposure area IA ₀ is a trapezoidal exposure area IA ₂ , the pattern to be exposed is not trapezoidal as a whole, but rather the same pattern is different during the exposure. The image is only blurred as it is exposed to the position. In this embodiment, this problem is solved as follows.

Before describing the correction method, first, a method of obtaining the correction amount will be briefly described. As explained in the prior art, as a cause of the distortion of the previously exposed pattern,
First, the exposure apparatus that has exposed the previous pattern is different from the exposure apparatus that is currently exposed, and the distortion of the projected image of the projection optical system may be different. In this case, the pattern of each shot area on the wafer is distorted when viewed from the exposure apparatus this time. This is because, for example, for a layer (layer) where the pattern on the wafer may be rough, distortion of the projected image is not removed very well, but when using an old exposure apparatus that satisfies the specifications for resolution, Or the distortion of the projected image of each exposure device is within the required accuracy,
When the distortion is irregular, it cannot be ignored.

In this case, the characteristic of the distortion of the projected image of the exposure apparatus that has performed the previous exposure is input to the main control system 20 via the input means 21 of FIG. The input means 21 may be, for example, a magnetic disk device, a magnetic tape device, a keyboard, or the like. The characteristics of the distortion of the projected image are stored in the main control system 20 in the form of a table or the like showing the formula, the coefficient of the formula, or how much each point at a predetermined coordinate position in the shot is exposed during exposure. Is entered. In the main control system 20, a distortion amount of the projection optical system PL of its own and a mathematical formula for obtaining the distortion amount after the correction by the image-forming characteristic correcting means are prepared in advance, and the main control system 20 makes a previous exposure. A correction amount for minimizing the amount of error from the shot is calculated, and the imaging characteristic is corrected via the imaging characteristic control unit 12.

Next, a case will be described in which the above correction alone is insufficient, that is, the wafer W is distorted due to a temperature rise in the process. As described above, each shot area of the wafer W is provided with a wafer mark for alignment, and the coordinates of each shot area can be measured by these wafer marks. The normal alignment is not a die-by-die method in which the coordinate of the wafer mark is measured for each shot, but the coordinate position of, for example, about 10 preselected shot areas (sample shots) per wafer is measured. Then, the shot array of the entire wafer is obtained by statistical processing (for example, the least squares method).
An alignment method (hereinafter referred to as "EGA method") is used (see, for example, JP-A-61-44429).

The shot array calculation (that is, the calculation of the parameters representing the scaling and orthogonality) by the EGA method makes it possible to know what kind of distortion has occurred in the entire wafer. You can estimate how it is deformed. Figure 4
The state of deformation of each shot area on the wafer W is schematically shown. In FIG. 4, the x-coordinate and the y-coordinate of the center of the shot area SA _i are shown on the street line close to each shot area SA _i. Wafer marks Mx _i and My _i for indicating each are formed. The wafer marks Mx _i and My _i are exposed at the same time when the chip pattern is exposed in the shot area SA _i .

The coordinate positions of these wafer marks Mx _i , My _i can be obtained from the detection signal of the photoelectric sensor 24 of the wafer alignment system of FIG. 1 and the measurement value of the interferometer 18 for the wafer stage. After that, as described above, the main control system 20 determines how the centers of the shot areas are arranged in the entire wafer. In the example of FIG. 4, a lattice-shaped array pattern 35 indicated by a chain line is obtained. From this array pattern 35, it can be seen how each shot area is distorted. As a result, each shot area SA _i
The optimum value of the distortion of the projected image exposed this time can be obtained for each time.

As shown in FIG. 5, the cross-shaped wafer mark 3 is provided at, for example, four corners of each shot area SA.
3A to 33D are formed in advance, and these wafer marks 33 are formed.
A method of directly measuring the distortion of the chip pattern formed in each shot area SA by measuring the coordinate positions of A to 33D is also conceivable. By the above method, the correction amount of the distortion of the projected image exposed on each shot area on the wafer W can be obtained.

Next, a method of correcting the distortion of the projected image in the slit scan exposure type projection exposure apparatus of this example will be described. First, when only the magnification component is changed, the projection magnification is matched by moving the lens element 27 of the projection optical system PL in FIG. 1, and the projection magnification in the direction perpendicular to the scanning direction is set to the magnification of the pattern on the wafer W. Match (Fig. 3
(See (a)). Next, when actually performing scanning exposure, the relative speed between the scanning speed of the reticle R and the scanning speed of the wafer W is changed by the ratio of the magnification error to match the magnification in the scanning direction. That is, when it is desired to increase the magnification, the wafer side may be moved quickly.

Further, due to the change in magnification and the difference in relative scanning speed, the actual exposure amount for the wafer W slightly changes with respect to the target exposure amount. This amount of change is usually a level that can be ignored, but it can be corrected if necessary. Such correction of the exposure amount changes the width (length in the scanning direction) of the slit in the illumination area by the reticle blind 5, which changes the scanning speed itself (not the relative speed) of the reticle R and the wafer W. This can be realized by a method of changing, changing the ratio of the opening time and closing time of a shutter (not shown) that is turned on / off at high speed, or changing the density of the variable ND filter 4.

Next, correction for trapezoidal distortion will be described. The trapezoidal distortion is divided into a component whose magnification changes in the scanning direction as shown in FIG. 6 and a component whose magnification changes in the direction orthogonal to the scanning direction as shown in FIG. First, a method of correcting trapezoidal distortion in which the magnification changes in the scanning direction will be described with reference to FIG. FIG. 6 shows a pattern 34A on a shot area on the wafer W for convenience of explanation.
Is fixed so that the slit-shaped exposure region moves (actually, the wafer W side moves with respect to the slit-shaped exposure region).

In the case of FIG. 6, since the magnification of the pattern 34A is increased at a constant rate according to the exposure position x, the case where the overall magnification isotropically changed as described above is applied to apply projection optics. It suffices to continuously change the projection magnification of the system PL. However, since the slit-shaped exposure area itself has a width, the shape of the slit-shaped exposure area IA _i at the initial position is changed to a trapezoid (see FIG. 3B). And
In FIG. 6, scanning exposure is performed by changing the projection magnification according to the exposure position x changed by scanning while exposing the slit-shaped exposure region in a trapezoidal shape, and performing exposure up to the exposure region IA _f at the final position. The projected image afterwards becomes trapezoidal.

The projection magnification may be changed stepwise, that is, every time the wafer is moved by a predetermined distance, without continuously changing the projection magnification. As for the magnification in the scanning direction, the wafer stage WST should be moved faster at a large magnification, that is, in the example of FIG.
The scanning speed V _W of the ST may do it by scanning so as successively faster along the line 36A to the position x1 to x2. Also, the exposure amount on the wafer W is controlled so that the light amount (illuminance) EL per unit area in the slit-shaped exposure region gradually increases along the straight line 36B, so that the wafer W after scanning exposure is controlled. The exposure dose at each point above is constant.

To summarize the above operation, the main control system 20 drives the lens element 27 up and down, speed control of the wafer stage WST, variable ND filter according to the measurement value of the reticle interferometer 16 during scanning exposure. It is necessary to perform the density control of No. 4 (other methods can be considered as described above). In this regard, for example, in an exposure apparatus (for example, the lens element 27 can only move up and down in parallel to the optical axis IX but cannot tilt) in which there is a correction mechanism only for the magnification component, but the distortion for the platform formation cannot be corrected,
By using the method of changing only the magnification component while leaving the slit-shaped exposure areas IA _{i to} IA _f rectangular,
Although it is not perfect, some correction is possible. At this time, the smaller the width of the slit-shaped exposure area in the scanning direction (slit width), the smaller the error. Therefore, it is desirable to perform the exposure with a smaller slit width. This is to prevent the blurring of the image of one pattern due to the change in magnification during exposure.

Next, with reference to FIG. 7, a method of correcting the trapezoidal distortion in which the magnification changes in the direction orthogonal to the scanning direction will be described. Similarly to FIG. 6, FIG. 7 is also illustrated such that the pattern 34B on the wafer W is fixed and the slit-shaped exposure region moves. In this case, as shown in FIG. 7, the exposure area IA _i at the initial position is distorted into a trapezoidal shape such that the magnification on the front side (the lower side on the paper surface of FIG. 7) becomes large. Next, at the start of scanning, the trapezoidal side L1 of the pattern 34B previously exposed,
The relative angle between the reticle R and the wafer W is changed so that the side L2 of the exposure area IA _i becomes parallel. Specifically, it is realized by rotating the wafer W.

Then, as shown in FIG. 7, the positions of the slit-shaped exposure areas are changed to the exposure areas IA _i , I by scanning exposure.
The relative angle is gradually changed according to the change in A _m and IA _f . That is, the previously formed pattern 34B
When the center of the exposure area IA _m coincides with the center of the exposure area IA _m , the relative angle between them becomes 0, and the side L3 of the trapezoidal pattern 34B and the side L4 of the exposure area IA _f become parallel at the end of scanning. Change the relative angle. In this case, the projection image cannot be perfectly superimposed on the pattern 34B as in the case where the scanning direction and the trapezoidal magnification changing direction match (the case of FIG. 6), but the direction approximately orthogonal to the scanning direction It is possible to realize trapezoidal distortion with a variable magnification. However, strictly speaking, in the method of this embodiment, the projected image is distorted into a fan shape.

In this method, by changing the relative angle between the reticle R and the wafer W, a portion having a larger magnification (position y1 in FIG. 7) than a portion having a smaller magnification (position y2 in FIG. 7).
The scanning speed V _W of the wafer W (and thus the relative speed of the wafer W) is increased, so that the magnification in the scanning direction is also corrected. Further, regarding the exposure amount on the wafer W, since the exposure area changes in the direction orthogonal to the scanning direction, the illuminance EL on the lower side of FIG. 7 is changed by the variable ND filter 4 of FIG. 1 as shown by the straight line 37 of FIG. It may be controlled so that it becomes large. Alternatively, the reticle R may be illuminated by changing the shape of the opening of the reticle blind 5 in FIG. 1 so that the width of the slit-shaped exposure area in the scanning direction becomes larger on the lower side in FIG. 7.

In the case of FIG. 7, as in the case of FIG. 6, when the exposure apparatus is not waiting for the trapezoidal distortion correction mechanism, an incomplete method is used in which only the relative angle between the reticle R and the wafer W is changed. May be. As described above, the trapezoidal distortion component can be corrected separately for the component whose magnification changes in the scanning direction and the component whose magnification changes in the direction perpendicular to the scanning direction. As an application example of these, when the image is distorted into a rectangle, only the corresponding isotropic magnification correction corresponding to the scanning direction or the direction corresponding to the scanning direction is performed. Alternatively, it may be carried out by changing the ratio of both.

Further, as shown in FIG. 8, when the pattern 34C formed in the shot area on the wafer W is distorted into a diamond shape, the slit-shaped exposure area IA _{i has} a shape from the start of scanning to the end of scanning. Need not be changed. Then, in a state where the relative angle between the reticle R and the wafer W is changed, the wafer W is scanned at a scanning speed V _W in a direction intersecting at a relative angle θ with respect to the x direction which is a direction conjugate with the scanning direction of the reticle R. By scanning, the projected image can be approximately distorted into a diamond shape in accordance with the pattern 34C.

Further, as shown in FIG. 9, even when the pattern 34D on the wafer W has a pincushion type (or barrel type) distortion, it is completely corrected in the case of the slit scan exposure type projection exposure apparatus. However, the following method can be considered approximately. That is, FIG.
As shown in, the projection magnification is reduced when the center of the pattern 34D in the previously exposed shot area and the center of the exposure area IA _m coincide, and the exposure area IA _i is set at both ends.
And IA _f are made trapezoidal to increase the projection magnification and to perform continuous exposure. Regarding the scanning direction, as indicated by the curve 38A, the scanning speed V _W of the wafer _W (and thus the relative scanning speed) may be small at the center and large at both ends. Similarly, regarding the exposure amount, the curve 38
As indicated by B, the illuminance distribution EL may be large at both ends and small at the center.

By the above-mentioned method, the projected images substantially coincide with each other on the outer peripheral portion of the pincushion-shaped pattern 34D. However, since such distortion is not uniform and isotropic inside, the reticle R is combined with the vertical movement. It is also possible to adopt a method in which a pincushion-shaped distortion is generated in the scanned image itself to increase the correction accuracy compared to the case of FIG. By combining the above methods, it is possible to deal with more complicated shape distortion. Although not described in the above embodiment, the reticle R may be tilted.

In the above embodiment, the distortion state of the projected image of the reticle R to be exposed this time is set in accordance with the distortion of the pattern in the previously exposed shot area. As another embodiment, for example, during exposure of the first layer on the wafer (that is, exposure when it is not necessary to consider overlay), distortion of a projection image of an exposure apparatus that performs exposure of the next layer. A method of distorting the projection image in advance according to the above, or a method of predicting the distortion of the wafer itself due to the process in advance and giving a reverse distortion at the time of exposure to cancel the distortion can be considered. Further, it is possible to correct even when the wafer W absorbs the exposure light and expands during the exposure operation, or the reticle R absorbs the exposure light and the projected image is distorted.

Further, the transmittance distribution (pattern existence ratio distribution) of the pattern formed on the reticle R is remarkably biased. For example, in FIG. 7, the upper half transmits almost no light and the lower half transmits almost all light. In such a case, the projection optical system PL
It is conceivable that the internal heat distribution becomes asymmetric, and as a result, the exposed image is deformed into a trapezoidal shape like the pattern 34B in FIG. Even in such a case, by applying the present invention, the distortion of the exposed image can be corrected. Regarding the calculation of the amount of distortion of the projected image due to these factors, in a batch exposure type exposure apparatus, for example, JP-A-1-83
It is disclosed in the publication. In these methods, the distortion of the projected image is obtained by heat conduction calculation, or the distortion of the projected image is measured by aerial image measurement. A method for optimizing the distortion of the projected image at the time of screen composition (screen joining) is also known.
Although disclosed in Japanese Patent No. 78, the present invention can be applied to this case as well.

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.

[0054]

According to the first scanning type projection exposure apparatus of the present invention, even when the pattern already formed on the substrate is distorted into, for example, a rhombus, the scanning direction of the mask and the scanning direction of the substrate are By changing the relative angle, the overlay error after exposure by the slit scan exposure method can be reduced.

Further, according to the second scanning type exposure apparatus, the state of distortion of the projected image of the mask can be changed every moment according to the scanning position of the mask, so that the pattern already formed on the substrate. Even when is distorted into a trapezoidal shape, it is possible to reduce the overlay error after exposure by the slit scan exposure method. Further, when the illuminance distribution control means is further provided, the illuminance distribution can be changed in accordance with the enlargement / reduction of the projected image. Therefore, even when the projected image is greatly distorted, the The uniformity of the exposure amount on the substrate can be favorably maintained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a slit scan exposure type projection exposure apparatus according to an embodiment of the present invention.

2 is a perspective view showing a scanning state of a reticle R and a wafer W in the projection exposure apparatus of FIG.

3A is a diagram showing a change in a projected image when the lens element 27 is driven in the optical axis direction in FIG. 1, and FIG. 3B is a diagram showing the lens element 27 in a plane perpendicular to the optical axis in FIG. FIG. 1 is a diagram showing a change in the projected image when tilted by
FIG. 9 is a diagram showing changes in a projected image when the reticle R is driven in the optical axis direction.

FIG. 4 is a diagram for explaining an example of a method for measuring distortion of a shot array by a wafer process.

FIG. 5 is a diagram for explaining an example of a method of measuring the distortion of a pattern in a shot region by a wafer process.

FIG. 6 is an explanatory diagram of a method for matching the distortion of a projected image with the trapezoidal distortion whose magnification changes in the scanning direction.

FIG. 7 is an explanatory diagram of a method of adjusting a distortion of a projected image to a trapezoidal distortion whose magnification changes in a direction perpendicular to a scanning direction.

FIG. 8 is an explanatory diagram of a method of matching a distortion of a projection image with a distortion of a rhombus shape.

FIG. 9 is an explanatory diagram of a method of matching the distortion of the projected image with the distortion of the pincushion shape.

[Explanation of symbols]

 1 light source 2 illuminance distribution uniforming optical system 3, 6 relay lens 4 variable ND filter 5 reticle blind R reticle PL projection optical system W wafer RST reticle stage WST wafer stage 10, 11 drive element 12 imaging characteristic control unit 16 reticle side Interferometer 18 Interferometer on wafer side 19 Stage control system 20 Main control system 21 Input means for distortion of projected image 22 Variable ND filter control unit 27 Lens element

Claims (3)

[Claims] 1. An illumination optical system for illuminating a predetermined illumination area with illumination light, a mask stage for scanning a mask on which a transfer pattern is formed in the predetermined illumination area in a predetermined direction, and the predetermined optical system. A projection optical system for image-projecting an image of the pattern of the mask in the illumination region of the image on a photosensitive substrate,
A substrate stage that scans the substrate in a predetermined direction with respect to an exposure region conjugate with the predetermined illumination region, and synchronizes the mask and the substrate with the predetermined illumination region and the exposure region, respectively. In the scanning projection exposure apparatus, which sequentially projects and exposes the image of the pattern of the mask on the substrate by scanning with the mask, the mask by the mask stage according to the distortion of the pattern already formed on the substrate. And a relative angle control means for changing the relative angle between the scanning direction of the substrate and the scanning direction of the substrate by the substrate stage. 2. An illumination optical system that illuminates a predetermined illumination area with illumination light, a mask stage that scans a mask on which a transfer pattern is formed in the predetermined illumination area in a predetermined direction, and the predetermined optical system. A projection optical system for image-projecting an image of the pattern of the mask in the illumination region of the image on a photosensitive substrate,
A substrate stage that scans the substrate in a predetermined direction with respect to an exposure region conjugate with the predetermined illumination region, and synchronizes the mask and the substrate with the predetermined illumination region and the exposure region, respectively. In the scanning projection exposure apparatus, which sequentially projects and exposes the image of the pattern of the mask on the substrate by scanning with the scanning, the scanning speed of the mask by the mask stage and the scanning speed of the substrate by the substrate stage are relative to each other. Relative speed adjusting means for adjusting the scanning speed, and an imaging characteristic correction means for correcting the distortion of the projected image by the projection optical system, according to the distortion of the pattern already formed on the substrate, In parallel with adjusting the relative scanning speed between the mask and the substrate via the relative speed adjusting means, the projection optical system via the image forming characteristic correcting means. Scanning projection exposure apparatus characterized by correcting the distortion state of the projection image onto the substrate by. 3. The illumination optical system is provided with an illuminance distribution control means for adjusting an illuminance distribution in the predetermined illumination area in accordance with a state of distortion of a projected image by the projection optical system. Item 2. A scanning projection exposure apparatus according to Item 2.