JPH08222495A - Scanning projection exposure method and system - Google Patents

Abstract

PURPOSE: To prevent an image finally projected onto a photosensitive substrate for exposure from deteriorating in resolution when a reticule pattern is projected onto the photosensitive substrate for exposure through a scanning exposure method even if the projected image of a projection optical system is anisotropically distorted. CONSTITUTION: When a slit-like projected image of a projection optical system is distorted into a parallelogram like a projected image 42A tilted at an angle of γ, the scanning direction of a reticule is tilted so as to differ from that of a photosensitive substrate at an angle of γ. When a slit-like projected image of a projection optical system is distorted into a rectangle like a projected image 42B which is erroneously magnified as much as (1+β) in a scanning direction, the scanning speed ratio of the reticule to the photosensitive substrate is changed to 1:(1+β), wherein β denotes a magnifying power error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method and an exposure apparatus used for manufacturing, for example, a semiconductor device or a liquid crystal display device in a photolithography process, and in particular, a mask and a photosensitive substrate are synchronously scanned. By doing so, the present invention relates to a scanning projection exposure method and apparatus such as a so-called slit scan method or step-and-scan method for sequentially projecting and exposing the mask pattern onto the substrate.

[0002]

2. Description of the Related Art When a semiconductor device, a liquid crystal display device, or the like is manufactured by a photolithography process, a pattern image of a reticle (or a photomask, etc.) is applied to a wafer (or a resist, etc.) coated through a projection optical system. A projection exposure apparatus for projecting exposure onto a glass plate or the like is used.
In such a projection exposure apparatus, it is required to transfer a fine pattern without impairing the high resolution of the projection optical system.

In this regard, as a conventional projection exposure apparatus, a projection exposure of a batch exposure system (or also called a “full field system”) in which a pattern of a reticle is collectively reduced and projected onto an entire exposure field on a photosensitive substrate. Equipment (steppers, etc.) was common. However, in recent years
A so-called slit scan method, which is a method of sequentially projecting and exposing a reticle pattern onto a photosensitive substrate, or a step scan method.
A projection exposure apparatus of a scanning exposure method such as an AND scan method has been developed. In this scanning exposure method, 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. On the other hand, exposure is performed by scanning the photosensitive substrate at the same speed ratio as the projection magnification of the projection optical system. Further, instead of illuminating the pattern area of the reticle in a slit shape, there is also a method of limiting the exposure area on the photosensitive substrate to a slit shape by a field stop provided in the projection optical system, for example.

In this scanning exposure method, since the illumination area on the reticle is smaller than that in the batch exposure method, the amount of distortion of the projected image, the field curvature, and the astigmatism, etc. of the focus position in the exposure field are not correct. There is an advantage that the uniformity and the non-uniformity of the illuminance can be suppressed small. Further, the scanning exposure method has an advantage that a large area can be exposed without being restricted by the field size of the projection optical system in the scanning direction.

[0005]

However, in the scanning exposure method, when the projection image is distorted due to the aberration of the projection optical system itself, the image quality is deteriorated by the scanning exposure due to the distortion of the projection image. There was an inconvenience that it would end up. A specific example in which the image quality is deteriorated will be described with reference to FIG. 7. 7A to 7C, the scanning direction of the photosensitive substrate is + x direction (or -x direction).
The non-scanning direction orthogonal to the x direction is defined as the y direction.
A slit-shaped exposure area (that is, a distortion-free projected image) formed by the projection optical system when the projection optical system has no aberration is defined as a rectangular exposure area 41 having a width D in the x direction.

First, as shown in FIG. 7A, the rectangular exposure area 41 is a parallelogram exposure area 4 inclined by an angle γ [rad] with respect to the x-axis due to the aberration of the projection optical system.
When it is transformed into 2A, when the photosensitive substrate is scanned in the x direction,
While one point on the photosensitive substrate crosses the exposure area 42A having the width D, the projected image moves in the non-scanning direction on the photosensitive substrate by approximately D · γ, causing image quality deterioration. Next, when the projection magnification of the projection optical system in the scanning direction is deviated by β,
As shown in (b), the exposure region 41 having the width D has the width (1+
β) Deform into a rectangular exposure area 42B of D. At this time, one point on the photosensitive substrate is exposed to the exposure area 42B in the x direction.
While traversing the area of the upper width D, the projection image is moved in the scanning direction on the photosensitive substrate by β.D in width in synchronization with the scanning of the reticle, so that the image quality is deteriorated. Invite.

Furthermore, as shown in FIG. 7C, the projection magnification in the projection optical system changes in the scanning direction, and the sides of the rectangular exposure region 41 in the non-scanning direction are symmetrically inclined by an angle δ [rad]. When it is transformed into a trapezoidal exposure region 42C, a projected image is a maximum of D · δ in the non-scanning direction on the photosensitive substrate while one point on the photosensitive substrate crosses the exposure region 42C of width D in the x direction. Since it moves, the image quality is deteriorated.

Here, it is assumed that the pattern on the reticle is a line-and-space pattern periodically arranged in the scanning direction, and the pitch of the projected image on the photosensitive substrate in the x direction is p, and the pitch is the same. Let p be about twice the exposure wavelength. In this case, the light intensity distribution I (x) of the projected image is
It can be expressed by Icos {(2π / p) · x}. Now, as an extreme example, if only optical images in which the phases of the projected images are different by ± Δ / 2 are combined, the light intensity distribution IT (x) of the optical image is as follows.

[0009]

[Equation 1] IT (x) = (1/2) [Icos {(2π / p) · x−Δ / 2} + Icos {(2π / p) · x + Δ / 2}] = Icos (Δ / 2) cos {(2π / p) · x} As can be seen from this (Equation 1), the contrast of the composite image is reduced to cos Δ / 2 times that of the original projected image, which reduces the resolution of the composite image. Then, the image quality is deteriorated.

Further, the distortion of the projected image shown in FIGS. 7A to 7C is an anisotropic distortion having a different distortion depending on the direction. On the contrary, when the distortion of the projected image is isotropic, that is, when only the projection magnification changes, it can be easily dealt with by a method such as adjusting the scanning speed ratio between the reticle and the photosensitive substrate. . In view of the above problems, the present invention finally exposes the photosensitive substrate even if the projected image of the projection optical system has an anisotropic distortion when the reticle pattern is exposed on the photosensitive substrate by the scanning exposure method. An object of the present invention is to provide a scanning projection exposure method and a scanning projection exposure apparatus in which the image quality (resolution) of an image exposed on the top does not deteriorate.

[0011]

In the scanning projection exposure method according to the present invention, a projection optical system (PL) for projecting an image of a transfer pattern on a mask (R) onto a photosensitive substrate (W) is used. On the other hand, the mask (R) is scanned in a direction corresponding to the predetermined direction in synchronism with the scanning of the mask (R) in a predetermined direction across the optical axis of the projection optical system. In the scanning projection exposure method of sequentially transferring the image of the pattern on the substrate, an anisotropic component value (parallelogram degree, rectangularity, trapezoidal degree, etc.) in the distortion of the projected image by the projection optical system (PL) ), The image of the pattern of the mask (R) transferred onto the substrate (W) during scanning exposure is distorted.

In this case, it is desirable to distort the pattern of the mask (R) in advance so as to cancel out the anisotropic component value of the distortion of the projected image. Next, the scanning projection exposure apparatus according to the present invention is a projection optical system (P) that projects the image of the transfer pattern on the mask (R) onto the photosensitive substrate (W).
L), a mask stage (RST) that scans the mask (R) in a predetermined direction that crosses the optical axis of the projection optical system, and a direction that crosses the optical axis of the projection optical system (PL) and that predetermined direction. A substrate stage (WST) for scanning the substrate (W) in a corresponding direction, and the mask (R) and the substrate (W) are synchronously scanned with respect to the projection optical system (PL), In a scanning projection exposure apparatus that sequentially transfers the image of the pattern of (R) onto the substrate (W), a storage unit (39) that stores the anisotropic component value of the distortion of the projected image by the projection optical system (PL). ) And the anisotropic component value of the distortion of the projected image stored in the storage means, the image of the pattern of the mask (R) transferred onto the substrate (W) during scanning exposure is distorted. And a distortion control means.

In this case, an example of the distortion control means is a relative angle for changing the relative angle 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). Control means (19), relative speed control means (19) for adjusting the relative speed between the scanning speed of the mask (R) by the mask stage (RST) and the scanning speed of the substrate (W) by the substrate stage (WST), or projection A projection magnification control means (12) for adjusting the projection magnification of the optical system (PL). Furthermore, these relative angle control means (19), relative speed control means (19), and projection magnification control means (12) may be combined in any two or in three.

Further, the exposure amount distribution control means (4, 2) for controlling the distribution of the exposure amount on the substrate (W) according to the adjustment amount of the image of the pattern of the mask (R) by the distortion control means.
It is desirable to provide 2).

[0015]

According to the scanning projection exposure method of the present invention,
The relative scanning angle between the mask and the substrate during scanning exposure so that the projection image of the mask pattern on the substrate during scanning exposure matches the anisotropic component value in the distortion of the projection image of the projection optical system. Since the relative scanning speed, the projection magnification, and the like are controlled and adjusted, it is possible to perform exposure with a minimum deterioration of image quality.
Therefore, the resolution of the image finally formed on the substrate is not impaired.

In this case, if there is no distortion in the mask pattern, an anisotropic distortion corresponding to the distortion of the projection image of the projection optical system remains in the image formed on the substrate. Therefore, in order to eliminate this residual distortion, it is sufficient to distort the mask pattern in advance so as to cancel the distortion of the projected image of the projection optical system. Next, according to the scanning projection exposure apparatus of the present invention,
The exposure method described above can be implemented.

By controlling the exposure dose distribution (or the size of the exposure dose) on the substrate through the exposure dose distribution control means in accordance with the relative scanning speed adjustment, the magnification adjustment during scanning exposure, and the like, There is no uneven exposure or offset of the exposure on the substrate.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a step-and-scan projection exposure apparatus of the present embodiment. In FIG. 1, the illumination light IL generated by a light source 1 passes through a shutter (not shown) and then a collimator lens. And an illuminance homogenizing optical system 2 including a fly-eye lens and the like 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 passes through a relay lens 3 and a movable reticle blind 5
A and fixed reticle blind 5B are reached. The movable reticle blind 5A 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 desired so as to be in close contact with the relay lens 3 side of the reticle blind 5A. The variable ND filter 4 that can be set to the state is installed. The reticle blind 5A is composed of a plurality of movable light-shielding portions (for example, two L-shaped movable light-shielding plates) as disclosed by the present applicant in Japanese Patent Application Laid-Open No. 5-234608. The width of the light-shielding band on the reticle can be reduced by scanning the movable light-shielding portions by, for example, a motor in synchronization with the movement of the reticle and the wafer immediately before and after the scanning exposure. Further, the fixed reticle blind 5B immediately after the movable reticle blind 5A determines an accurate width (slit width) in the scanning direction of the slit-shaped illumination area on the reticle R.

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 (see FIG. 2) 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 illumination area I on the reticle R is
The illuminance distribution in AR is uniform. Variable ND filter 4
Does not necessarily have to be at the position in FIG. 1, and may be on the side closer to the light source or on the reticle side. Details of how to use the variable ND filter 4 will be described later. In addition, variable ND
The operations of the filter control unit 22 and the movable reticle blind 5A are controlled by the main control system 20 that controls the entire apparatus.

The light flux that has passed through the variable ND filter 4 and the reticle blinds 5A and 5B illuminates a reticle R on which a circuit pattern and the like are drawn via a relay lens 6 and a dichroic mirror 7. The reticle R is vacuum-adsorbed on the reticle stage RST, and the reticle stage R
ST two-dimensionally finely moves in a plane perpendicular to the optical axis IX of the illumination optical system to position the reticle R.

Further, the reticle stage RST is provided with a reticle drive unit (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). Further, reticle stage RST is mounted on a reticle base (not shown) so that the entire surface of reticle R can move in the scanning direction with a movement stroke that allows at least the entire surface of reticle R to cross optical axis IX of the illumination optical system. Interferometer 16 is provided at the end of reticle stage RST.
The movable mirror 15 that reflects the laser beam from the optical disk is fixed, and the position of the reticle stage RST in the scanning direction is constantly detected by the interferometer 16 with a resolution of, for example, about 0.5 nm. Reticle stage RST from interferometer 16
Is sent to the stage control system 19, and the stage control system 19 drives the reticle stage RST via a reticle drive unit (not shown) based on the position information of the reticle stage RST. Further, since the initial position of reticle stage RST is determined so that reticle R is accurately positioned at a predetermined reference position by a reticle alignment system (not shown), only the position of movable mirror 15 is measured by interferometer 16. Thus, the position of the reticle R is 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, in the rectangular (slit-shaped) illumination area IAR having the longitudinal direction in the direction (y direction) perpendicular to the scanning direction (x direction) of the reticle R. The reticle R is illuminated, and the reticle R is scanned at the speed V _R in the −x direction (or + x direction) during exposure. The illumination area IAR (the center of which is substantially coincident with the optical axis IX) is projected onto the wafer W via the projection optical system PL to form a slit-shaped exposure area IA. Wafer W
Is in an inverted image formation relationship with the reticle R, the wafer W is scanned at the speed V _W in synchronization with the reticle R in the + x direction (or −x direction) opposite to the direction of the speed V _R , and the wafer W is scanned. The entire shot area SA can be exposed. The scanning speed ratio V _W / V _R 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 the shot area S on the wafer W.
Accurate reduction transfer on A. The width of the illumination area IAR in the longitudinal direction is set to be wider than the pattern area PA on the reticle R and smaller than the maximum width of the light shielding area ST, and the entire area of the pattern area PA is illuminated by scanning. Has become. Although the projection optical system PL is a non-telecentric system in FIG. 2, it is actually a two-sided telecentric system as described above.

Returning to the explanation 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 perpendicular to the scan direction (y 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. in this case,
Wafer stage WST is driven in the xy directions by a wafer stage drive unit (not shown) such as a motor. A movable mirror 17 that reflects the laser beam from the interferometer 18 is fixed to the end of the wafer stage WST.
The position in the xy plane is always detected by the interferometer 18 with a resolution of, for example, about 0.5 nm. 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, 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 surface 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. Wafer stage WST so that optical system PL maintains a predetermined distance.
Used to drive in the z direction. Wafer position information from the wafer position detection system is sent to the stage control system 19 via the main control system 20. Stage control system 19 drives wafer stage WST in the z direction based on this wafer position information.

In the present embodiment, the angle of the parallel flat glass (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 is calibrated. Further, for example, a horizontal position detecting system as disclosed in Japanese Patent Laid-Open No. 58-113706 can be used, or the focal position can be detected at arbitrary plural positions in the image field of the projection optical system PL. By configuring a wafer position detection system (for example, 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 is for correcting changes in the image forming characteristics of the projection optical system PL itself due to changes in atmospheric pressure, absorption of illumination light, and the like. 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 lens element 27 in the projection optical system PL to correct the imaging characteristic.
In the projection optical system PL, the lens element 27 closest to the reticle R is fixed to the support member 28, and the lens elements 29, 30, 3 following the lens element 27 are fixed.
1, ... 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. The support member 28 is connected to the main body of the projection optical system PL via a plurality of expandable / contractible (at least two or more, two in FIG. 1) driving elements 11 such as piezo elements.

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. 3, and the square projection image 32 of FIG. 3 is an image of a square pattern projected by the projection optical system PL without distortion. In this case, the lens element 2
If 7, for example, is moved upward, 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 projected as an isotropically enlarged projected image 32A. It Similarly, when exposure is performed by the scanning exposure method, the slit-shaped exposure area IA ₀ without distortion is also isotropically enlarged to become the exposure area IA ₁ .

When 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 causes the wafer position detection system (13, 1
The exposure surface of the wafer W is controlled so as to always be at the focus position by adding an offset to the zero point reference of 4) by the amount obtained by the calculation. 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 lens element 27, the focus position or the image plane position is adjusted by following 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. Further, the main control system 20 includes an input unit 21 including a magnetic disk, a magnetic tape, a keyboard, or the like for inputting a command or data from an operator, and a distortion of a projected image of the projection optical system PL. A memory 39 for storing the isotropic component value is connected.

Before explaining the method of controlling and adjusting the distortion of the projected image during scanning exposure of this example, the method of controlling the amount of distortion of the projected image and the method of determining the adjustment amount will be described. In FIG.
The main control system 20 uses the self-measurement function of the distortion amount of the projection image of the projection optical system PL, or inputs the result of measuring the actual exposure pattern by an external measuring device via the input means 21, thereby You can know the distortion.
Here, if the (x, y) coordinates of the position of the projection image without distortion are (X, Y) and the coordinates of the position of the projection image with the actual distortion are (X ′, Y ′), then Can be expressed as

[0033]

## EQU2 ## X '= (1 + α + β + K ₁ X + K ₂ Y) X-
(Γ + θ) Y + T _X , Y ′ = θX + (1 + α + K ₁ X + K ₂ Y) Y + T _Y where α is the error of the isotropic projection magnification, β is the rectangular distortion (the error of the projection magnification in the x direction), and γ is Parallelism distortion,
K ₁ and K ₂ are trapezoids, θ is rotation, T _X and T _Y
Represents the overall shift, respectively. The values of these parameters are obtained by substituting the actual measurement data (X ′, Y ′) into (Equation 2) and minimizing the residual error component with respect to the coordinates (X, Y) when there is no design distortion. It can be obtained by such a least squares method.

Of these, the projection magnification ratio α, rotation θ, and shifts T _X and T _Y do not cause image quality deterioration, but if they are corrected prior to exposure, the pattern array exposed on the wafer will become more visible. It is close to the design value. On the other hand, since anisotropic components such as rectangular distortion β, parallelism distortion γ, and trapezoids K ₁ and K ₂ cause image quality deterioration during scanning exposure, it is desirable to correct them as much as possible during scanning exposure.

Next, a method of correcting the distortion of the projected image in the scanning exposure type projection exposure apparatus of this example will be described. First, if there is simply an isotropic projection magnification error α, 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 on the wafer. Match the magnification of the pattern on W (see Figure 3). Next, when scanning exposure is actually performed, the relative speed between the scanning speed of the reticle R and the scanning speed of the wafer W is changed by the ratio α of the magnification error so that the magnifications in the scanning direction match. That is, the reticle R and the wafer W are the projection optical system PL.
The relative scanning is performed at a speed ratio (1: M) according to the projection magnification M of the reticle R.
The moving speed may be faster than M times the scanning speed of.

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. As such a method of correcting the exposure amount, a fixed reticle blind that determines the width of the slit-shaped illumination area by changing the scanning speed itself (not the relative speed but the relative scanning speed) of the reticle R and the wafer W is used. 5B width (length in the scanning direction) is changed, the ratio of the opening time and closing time of a shutter (not shown) that is turned on / off at high speed is changed, or the density of the variable ND filter 4 is changed. For example, there is a method of changing the number of pulses irradiated while one point on the wafer crosses the projection image 32 (exposure area IA), or changing the applied voltage (or charging voltage) applied to the pulse light source.

Next, due to the rectangular distortion β of the projected image, when there is no distortion on the wafer, the slit-shaped exposure area having a width D in the scanning direction has a width in the scanning direction as shown in FIG. 4B. Consider a case where the rectangular exposure area 42B of (1 + β) D is formed. At this time, in addition to the above-described correction of the isotropic magnification error α, the ratio between the scanning speed of the reticle R and the scanning speed of the wafer W may be finely adjusted by the rectangular distortion β. At this time, if the width in the scanning direction of the projection image exposed on the entire shot area on the wafer when there is no distortion is L, the width in the scanning direction of the projection image FB exposed after the correction is (1 + β).
It becomes L.

In the scanning exposure, the wafer W is actually scanned with respect to the slit-shaped exposure area.
In (b), the wafer W is fixed, and the exposure area 42 is formed on the wafer W.
B is shown to move in the + x direction. Therefore,
In FIG. 4B, the wafer W is actually scanned in the −x direction. Also in the following description, for convenience, the exposure region is illustrated as moving on the wafer W in the drawings.

Further, due to the parallelism distortion γ of the projected image, the exposure area of the width D when there is no distortion on the wafer is shown in FIG.
Consider the case where the parallelogram exposure region 42A is inclined by an angle γ [rad] with respect to the x direction as shown in FIG. At this time, the relative angle between the reticle R and the wafer W in the scanning direction is set to the angle γ. Therefore, for example, when the reticle R side is scanned in the + x direction, the wafer W is scanned in the direction inclined by the angle γ with respect to the −x direction, and the exposure area 42A is scanned in the direction indicated by the arrow 43. As a result, deterioration of resolution due to parallelism distortion is eliminated. At this time, the projection image FA exposed after the correction is tilted by the angle γ with respect to the x-axis.

Next, trapezoidal distortion (trapezoids K ₁ and K ₂ )
The correction will be described. The trapezoidal distortion has a component in which the magnification changes in the scanning direction as shown in FIG.
As shown in FIG. 6, it is divided into components in which the magnification changes in the direction orthogonal to the scanning direction. First, a method for correcting trapezoidal distortion in which the magnification changes in the scanning direction will be described with reference to FIG.

In the case of FIG. 5, since the magnification of the projected image increases at a constant rate depending on the exposure position x, the slit-shaped exposure region is exposed from the exposure region IA _i at the exposure start position to the exposure at the end of exposure. It gradually changes to the area IA _f . In this case, the projection magnification of the projection optical system PL may be continuously changed by applying the case where the overall magnification isotropically changed as described above. That is, by changing the projection magnification according to the exposure position x changed by scanning and performing the exposure up to the exposure region at the final position, the projection image on the entire shot region on the wafer W after the scanning exposure is trapezoidal. Is a projected image FC of.

As for the magnification in the scanning direction, as in the case where the overall magnification isotropically changed, the wafer stage W
In order to increase ST at a place where the magnification is large, that is, in the example of FIG. 5, the scanning speed V _W of wafer stage WST is set to position x1.
It suffices to scan along the straight line 36A so that the scanning speed increases continuously up to x2. Also, the exposure amount on the wafer W is controlled so that the exposure amount (illuminance) EL per unit area in the slit-shaped exposure region gradually increases along the straight line 36B, so that the wafer after scanning exposure is controlled. The integrated exposure amount at each point on W becomes constant.

The above operation is summarized as follows.
The control system 20 responds to the measurement value of the interferometer 16 on the reticle side.
Drive the lens element 27 up and down,
Speed of WST, density of variable ND filter 4
As for control (other methods are possible as described above)
It ) Need to do. In this regard, for example
Although there is a correction mechanism for the distortion of only the minute,
An exposure device that cannot correct distortion (for example, lens element
The tilt 27 can only move up and down in parallel with the optical axis IX.
In), the slit-shaped exposure area IA _i~ IA_fTo
Using the method of changing only the magnification component while keeping it rectangular
By doing so, some correction is possible
It At this time, the width of the slit-shaped exposure area in the scanning direction
The smaller the (slit width), the smaller the error.
It is desirable that the exposure be performed with a small width.

Next, referring to FIG. 6, the scanning direction is orthogonal to the scanning direction.
For the method of correcting the trapezoidal distortion in which the magnification changes in the
Explain. At this time, the projection magnification differs in the non-scanning direction.
The reticle R and the wafer W to be scanned.
It is necessary to change the scanning speed ratio in each direction. That is, the wafer W
Scanning exposure is carried out while rotating. Specifically,
As shown in FIG. 6, a slit-shaped exposure area is formed by scanning exposure.
Is the exposure area IA _i, IA_m, IA_fWill change
The relative angle between the reticle R and the wafer W gradually
You can change it. However, strictly speaking, this embodiment
With the method, the projected image will be distorted in a fan shape, and the image quality will be slightly degraded.
Incarnation remains.

In this method, by changing the relative angle between the reticle R and the wafer W, a portion with a larger magnification (position y1 in FIG. 6) than a portion with a smaller magnification (position y2 in FIG. 6).
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. 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. 6 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 fixed reticle blind 5B 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.

Finally, as can be seen from FIGS. 4 to 6, according to the present embodiment, there is no deterioration in the image quality of the pattern after scanning exposure, but the projected images FA, FB, FC, and
The FD is distorted according to the distortion of the projection image (slit-shaped exposure area IA) originally projected by the projection optical system. This is not a problem when all the layers on the wafer are exposed by one projection exposure apparatus or when only one layer is patterned when manufacturing a semiconductor device or the like. When exposure is performed on each layer using a projection exposure apparatus (during mix-and-match), the overlay accuracy between adjacent layers on the wafer deteriorates.

Therefore, when performing mix-and-match, it is desirable to draw the patterns of the respective reticles in advance so as to cancel out the anisotropic distortion of the projection optical system of each projection exposure apparatus. That is, if the pattern on each reticle is drawn in a direction opposite to the distortion of the projection image of the corresponding projection optical system, the projection image formed on the entire shot area on the wafer by scanning exposure will be distorted. Is eliminated and the overlay accuracy is improved.

Although a refraction system is used as the projection optical system in the above embodiments, the present invention is also applicable to the case where a projection optical system including a reflection system or a catadioptric system is used. Further, although the exposure area on the wafer has a rectangular shape, the present invention can be applied to, for example, an arc-shaped exposure area.
As described above, the present invention is not limited to the above-described embodiments, and various configurations can be taken without departing from the gist of the present invention.

[0049]

According to the scanning projection exposure method of the present invention,
In accordance with the anisotropic component value of the distortion of the projected image by the projection optical system, the relative angle of scanning exposure, the relative speed, or the projection magnification, etc. Scanning exposure method mask (reticle, etc.)
Even if the projected image of the projection optical system itself has an anisotropic distortion when exposing the pattern on the photosensitive substrate, the image quality (resolution) of the image finally exposed on the photosensitive substrate deteriorates. There is an advantage not to.

In this case, of the distortion components of the projection image of the projection optical system, the anisotropic component that can be adjusted or controlled during scanning exposure as described above is a rough adjustment during the optical adjustment of the projection optical system. Since it is good, there is also an advantage that the manufacturing period can be shortened. Further, by correcting the mask pattern inversely to the distortion of the projected image, a distortion-free pattern can be obtained after scanning exposure, and the overlay accuracy between adjacent layers is improved.

Next, according to the scanning projection exposure apparatus of the present invention, the above-mentioned projection exposure method can be carried out. When the distortion control means is a relative angle control means for changing the relative angle between the scanning direction of the mask by the mask stage and the scanning direction of the substrate by the substrate stage, for example, parallelogram distortion can be corrected. Further, when the distortion control means is a relative speed control means for adjusting the relative speed between the scanning speed of the mask by the mask stage and the scanning speed of the substrate by the substrate stage, for example, rectangular distortion can be corrected.

Further, when the distortion control means is a projection magnification control means for adjusting the projection magnification of the projection optical system, it is possible to correct trapezoidal distortion which is symmetrical with respect to the axis parallel to the scanning direction. Also,
By combining the relative angle control means and the projection magnification control means and adjusting the relative angle and the projection magnification during scanning, it is possible to correct even the trapezoidal distortion symmetrical in the non-scanning direction.

Further, when the exposure amount distribution control unit for controlling the distribution of the exposure amount on the substrate according to the adjustment amount of the image of the mask pattern by the distortion control unit is provided, the distortion of the projected image by the projection optical system is provided. When the correction is performed, there is an advantage that the exposure amount on the photosensitive substrate can be maintained at an appropriate exposure amount.

[Brief description of drawings]

FIG. 1 is a configuration diagram including a partial cross-sectional view showing an outline of a step-and-scan projection exposure apparatus according to an embodiment of the present invention.

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

FIG. 3 is a diagram showing changes in a projected image when a lens element 27 is driven in the optical axis direction in FIG.

FIG. 4A is a diagram showing a relationship between a slit-shaped exposure area and a projected image on the entire shot area after scanning exposure when parallelogram distortion is generated in the example;
FIG. 6 is a diagram showing a relationship between a slit-shaped exposure area and a projected image on the entire shot area after scanning exposure when rectangular distortion is generated.

FIG. 5 is an explanatory diagram of an exposure method when the magnification changes in the scanning direction and the projected image is distorted into a trapezoidal shape.

FIG. 6 is an explanatory diagram of an exposure method when the magnification changes in the non-scanning direction and the projected image is distorted into a trapezoidal shape.

7A is a diagram showing a parallelogram-shaped distortion of a projected image, FIG. 7B is a diagram showing a rectangular-shaped distortion of a projected image, and FIG.
FIG. 6 is a diagram showing a trapezoidal distortion of a projected image.

[Explanation of symbols]

 1 light source 2 illuminance distribution uniforming optical system 3, 6 relay lens 4 variable ND filter 5A movable reticle blind 5B fixed reticle blind R reticle PL projection optical system W wafer RST reticle stage WST wafer stage 11 drive element 12 imaging property control 16 Interferometer on reticle side 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 section 27 Lens element 39 Memory

Claims (7)

[Claims] 1. A projection optical system for projecting an image of a transfer pattern on a mask onto a photosensitive substrate, and scanning the mask in a predetermined direction across the optical axis of the projection optical system. In a scanning projection exposure method of synchronously scanning the substrate in a direction corresponding to the predetermined direction to sequentially transfer the image of the pattern of the mask onto the substrate, the projection image of the projection optical system A scanning projection exposure method, wherein distortion is applied to an image of the pattern of the mask transferred onto the substrate during scanning exposure in accordance with an anisotropic component value of the distortion. 2. The scanning projection exposure method according to claim 1, wherein the pattern of the mask is pre-distorted so as to cancel out the anisotropic component value of the distortion of the projected image. 3. A projection optical system for projecting an image of a transfer pattern on a mask onto a photosensitive substrate, and a mask stage for scanning the mask in a predetermined direction across the optical axis of the projection optical system. A substrate stage that scans the substrate in a direction that intersects the optical axis of the projection optical system and that corresponds to the predetermined direction, and synchronizes the mask and the substrate with respect to the projection optical system. In a scanning projection exposure apparatus that sequentially transfers an image of the pattern of the mask onto the substrate by scanning, a storage unit that stores an anisotropic component value in the distortion of the projected image by the projection optical system, Distortion control means for applying distortion to the image of the pattern of the mask transferred onto the substrate during scanning exposure in accordance with the anisotropic component of the distortion of the projected image stored in the storage means;
A scanning projection exposure apparatus characterized by being provided with. 4. The distortion control means is relative angle control means for changing a relative angle between a scanning direction of the mask by the mask stage and a scanning direction of the substrate by the substrate stage. 3. The scanning projection exposure apparatus according to item 3. 5. The distortion control means is a relative speed control means for adjusting a relative speed between a scanning speed of the mask by the mask stage and a scanning speed of the substrate by the substrate stage. 3. The scanning projection exposure apparatus according to item 3. 6. The scanning projection exposure apparatus according to claim 3, wherein the distortion control unit is a projection magnification control unit that adjusts the projection magnification of the projection optical system. 7. The exposure amount distribution control means for controlling the distribution of the exposure amount on the substrate according to the adjustment amount of the image of the mask pattern by the distortion control means is provided. 4. The scanning projection exposure apparatus according to 4, 5, or 6.