JP2000133562A - Reduction stepper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high accuracy of alignment by surely operating pattern detection in a semiconductor wafer to which a photoresist film is applied. SOLUTION: An alignment mark is irradiated through a reduction projecting lens 3 with continuous spectrum lights in two or more wavelength for preventing a photoresist film on a wafer 5 from being sensitized from an illuminating light source 8, and reflected lights from the alignment mark are extracted to the outside part of the reduction projecting lens system by a reflecting mirror 18, and chromatic aberration is corrected by a chromatic aberration correcting lens 16. The image of the alignment mark included in the color aberration- corrected continuous spectrum lights is detected by a TV camera 20, and the positioning of the wafer 5 with the mask is aligned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction projection exposure apparatus, and more particularly, to a semiconductor wafer (hereinafter simply referred to as "mask") in a reduction projection exposure step in the manufacture of semiconductor devices.
The present invention relates to a technique that is effective when applied to alignment of a “wafer”.

[0002]

2. Description of the Related Art As a technique for transferring a circuit pattern formed of a light-shielding film on a mask such as a reticle onto a wafer, there are known techniques.
A technique using a reduction projection exposure apparatus is generally used. In this case, the alignment between the wafer and the mask is performed, for example, as follows.

That is, an alignment mark formed on the surface of a wafer by an uneven step is irradiated with illumination light through a reduction projection lens, and reflected light from the alignment mark is transmitted through a beam splitter or the like to a T mark.
The position of the alignment mark is grasped by detecting the electric signal based on the amount of the reflected light, and the target exposure area of the wafer is positioned with respect to the mask. Such a positioning technique is generally called a through-the-lens (TTL) method.

[0004] By the way, as a document pointing out the future problems of the TTL system, there is Nikkei McGraw-Hill, published on December 1, 1987, "Nikkei Micro Devices" P.
80 to P81.

Here, a general TTL alignment technique will be described with reference to a system diagram shown in FIG.

That is, in FIG. 7, reference numeral 71 denotes a wafer which is a non-exposure target object, reference numeral 72 denotes a reduction projection lens for exposure, and reference numeral 73 denotes a reticle as an original plate.
Denotes a TV camera as a recognition unit, and 75 denotes a mercury lamp that serves both as an exposure light source and an illumination light source. The reduction projection lens 7
A reflecting mirror 76, a relay lens 77, and a beam splitter 78 are arranged on the optical path between the TV camera 2 and the TV camera 74, and the light transmitted by the beam splitter 78 is incident on the TV camera 74. I have.
On the other hand, between the mercury lamp 75 and the beam splitter 78, a band-pass filter 80 and a condenser lens 81 that pass only the E-line (546 nm) out of the wavelength from the mercury lamp 75 are arranged.

As described above, monochromatic E-rays are used as illumination light for pattern detection, and G-rays (436 nm) as exposure light are used at the time of exposure.

The illumination light is irradiated from a beam splitter 78 onto a wafer 71 through a relay lens 77, a reflecting mirror 76, and a reduction projection lens 72, and the reflected light travels back through the above-mentioned path and enters a TV camera 74. The waveform is detected based on the image recognized by the TV camera 74, and the center position of the alignment mark 6 on the wafer 71 is calculated as shown in FIG.

[0009]

However, it has been found by the present inventors that the reduction projection exposure apparatus having the above structure has the following problems.

That is, the wafer to be exposed is provided to the reduction projection exposure apparatus in a state where the photoresist film 82 is applied, but the photoresist film 82 is applied by rotating the wafer 71 and applying a resist solution. Dropping is performed by utilizing the spreading of the resist solution by centrifugal force.

For this reason, the applied thickness of the photoresist film 82 becomes unbalanced around the step of the alignment mark due to the centrifugal force at the time of the rotation, and the deposited shape of the photoresist film 82 becomes asymmetric with respect to the center of the step pattern. . Here, as the illumination light for the alignment, it is general to use a G-line (436 nm) used for exposure at a single wavelength (monochromatic light). The interference fringes caused by the reflected light from the resist film 82 become asymmetric, and the signal voltage waveform obtained from the interference fringes, which is the image recognized by the TV camera, becomes asymmetric and complicated. As a result, the detection of the step pattern of the alignment mark becomes difficult. It was sometimes difficult.

Regarding this point, the above-mentioned literature introduces some solutions, but none of them can provide a sufficient solution.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a reduced projection exposure apparatus capable of reliably detecting a pattern on a wafer having a photoresist film applied thereon and realizing highly accurate alignment. To provide.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0015]

The following is a brief description of an outline of typical inventions disclosed in the present application.

That is, the reduction projection exposure apparatus of the present invention
A wafer having at least one alignment mark on the first main surface is subjected to a reduction projection lens system in which aberration is corrected so as to obtain good optical characteristics with respect to monochromatic exposure light from an exposure light source. The real image is
A reduction projection exposure apparatus that transfers the circuit pattern onto the first main surface of the wafer at a predetermined reduction rate by projecting the photosensitive resist film on a photosensitive resist film formed on the main surface of (a). An XY table for mounting the wafer; (b) substantially exposing the resist film from a reference light source that is a continuous spectrum light source having a uniform spectral distribution within a predetermined bandwidth compared to a line spectrum light source. An optical filter mechanism for selecting a continuous spectrum reference light having a wavelength longer than the exposure light as described above; (c) The optical filter mechanism is selected with the alignment mark at a predetermined position off the optical axis of the reduction projection lens system. The continuous spectrum reference light is incident on the alignment mark along the predetermined incident optical path of the reduction projection lens system by the continuous spectrum reference light. The alignment mark is illuminated, and the continuous speckle reference light is reflected from the alignment mark and the periphery thereof at least in the reduced projection lens system so as to reverse the same or a light path near the incident light path, In order to extract the continuous spectrum reference light to the outside of the reduction projection lens system, the reduction projection lens system projects the real image onto the resist film at a position away from the optical axis center of the reduction projection lens system. (D) the predetermined band of the continuous spectrum reference light taken out of the reduction projection lens system by the reflection means. A chromatic aberration correcting optical system for correcting a predetermined chromatic aberration due to a wavelength difference within the width; (e) chromatic aberration is corrected by the chromatic aberration correcting optical system. An image of the alignment mark included in the continuous spectrum reference light of the corrected portion is detected, and the positional relationship between the wafer and the mask is not directly optically detected. A position detection mechanism for obtaining a positional relationship in the XY plane; (f) a desired portion of the wafer is projected onto the light of the reduction projection lens system based on the detected positional relationship of the alignment mark in the XY plane. The XY with the wafer mounted so as to be positioned at or near the axis
A wafer position determining mechanism for positioning the mask and the wafer by moving a table in the XY plane; (g) moving the desired portion of the wafer to the optical axis of the reduction projection lens system or The circuit pattern on the mask is illuminated by the exposure light in a state where it is positioned in the vicinity thereof, and a reduced real image of the circuit pattern on the mask is reduced on the wafer through the reduction projection lens system. An exposure optical system for transferring the circuit pattern on the mask onto the resist film by projecting the resist pattern on the resist film is included.

According to the above means, the chromatic aberration correcting optical system is provided in the optical path of the illumination light, and the focal length is adjusted corresponding to each wavelength, so that the pattern illumination light has a continuous spectrum of two or more wavelengths or more. Light can be used. For this reason, even when the photoresist film thickness is non-uniform and asymmetric with respect to the alignment pattern of the detection portion, for example, it is possible to prevent undetectability due to the asymmetry of interference fringes such as single-wavelength light, and to perform positioning during alignment. Accuracy can be increased.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of a main part showing a reduction projection exposure apparatus according to an embodiment of the present invention, FIG. 2 is a system diagram showing an optical system of the present embodiment, and FIG. 4A and 4B are explanatory diagrams each showing a chromatic aberration correcting lens, FIG. 4 is a perspective view showing an astigmatism correcting lens used in the present embodiment, and FIGS. 5A to 5C are diagrams in the embodiment. FIGS. 6A and 6B are explanatory diagrams conceptually showing the principle of correction by a chromatic aberration correcting lens, and FIGS. 6A and 6B are explanatory diagrams showing the relationship between an alignment mark formed on a wafer and a detected waveform.

The reduction projection exposure apparatus according to the present embodiment includes an exposure light source 1 composed of a mercury lamp, a condenser lens 2 for focusing exposure light (not shown) emitted from the exposure light source 1,
An exposure optical system including the reduction projection lens 3 is provided.

Between the condenser lens 2 and the reduction projection lens 3, a reticle (original) in which an integrated circuit pattern is formed on a transparent quartz glass substrate or the like with a light-shielding film of chromium (Cr) or the like.
4 are removably arranged.

On the other hand, below the reduction projection lens 3,
On an XY stage (not shown), a wafer (exposure target) 5 which is movable in a horizontal plane is placed. The wafer 5 has predetermined alignment marks 6 and the like formed in steps as shown in FIG.
Further, a photoresist film 7 is applied to the upper surface by a spin coating technique. That is, in FIG. 1, the exposure light emitted from the exposure light source 1 and transmitted through the reticle 4 is reduced to a predetermined magnification (for example, ５) by the reduction projection lens 3 and projected onto the wafer 5, whereby the wafer 5 The photoresist film 7 applied to the surface is exposed in a predetermined pattern.

An illumination light source 8 is provided in the vicinity of the exposure optical system, and illumination light from the illumination light source 8 is supplied to a half mirror via a band-pass filter 10 and a condenser lens 11 provided on the optical path. The light is incident on the beam splitter 12 having a structure.

In this embodiment, the illumination light source 8
Is constituted by a cylindrical mirror 14 which is guided from the exposure light source 1 by a light guiding means such as an optical fiber 13 and which is attached to the tip thereof.

The band-pass filter 10 transmits only the E-line (546 nm) and the D-line (589 nm) of the emission wavelength of the mercury lamp as the exposure light source 1, for example. The passed illumination light is incident on the beam splitter 12 as continuous spectrum light in the visible light range. Beam splitter 12
The relay lens 15 and the chromatic aberration correcting lens 16
And a reflection mirror 1 provided on the side of the reduction projection lens 3.
The structure reaches 8.

On the other hand, on the optical axis of the beam splitter 12, a TV camera 20 as a recognition unit is disposed at a position symmetrical to the relay lens 15 via the relay lens 15.

Next, the chromatic aberration correcting lens 16 which is a characteristic component of the present embodiment will be described in detail.

Prior to the description, FIG.
To explain based on (a) and (b), a and b indicate the distance from the lens 21 to the imaging position, respectively. Here, assuming that the focal length of the lens 21 is f, the relational expression of a, b, and f is

[0028]

(Equation 1)

## EQU1 ## Here, the change Δb of the imaging position when the focal length changes by Δf is given by the above equation (1).

[0030]

(Equation 2)

## EQU1 ## On the other hand, as shown in FIG.
The relational expression between the focal length f of the lens 21 and the refractive index n is as follows.

[0032]

(Equation 3)

In the above equation (3), R indicates the radius of the lens 21 on the spherical surface.

From equation (3), the change Δf in focal length due to the change Δn in refractive index is:

[0035]

(Equation 4)

Substituting this into equation (2) gives

[0037]

(Equation 5)

## EQU4 ## Here, since the imaging magnification m is m = b / a,

[0039]

(Equation 6)

## EQU4 ##

From the equation (6), it can be understood that the imaging position also changes by Δb due to the change Δn in the refractive index. Here, since the wavelength of light and the refractive index n are inversely proportional, if the wavelength becomes longer, the imaging position shifts toward the lens 21 by Δb. This is chromatic aberration. In general, the reduction projection lens 3 used in the reduction projection exposure apparatus is designed to have optimal optical characteristics with respect to G-line as exposure light.
No consideration has been given to the deviation of the focal length when E-line or D-line is used as the illumination light.

Therefore, when continuous spectrum light using E-line and D-line is used to prevent undetectability due to interference fringes, E-line having a short wavelength forms an image relatively near the lens,
Longer wavelength D lines result in imaging at a distance from the lens,
According to the calculation by the inventor, the difference between the image forming positions in the TV camera 20 of both wavelengths passing through the alignment optical system is several tens mm.
It has become to the extent.

In the present embodiment, this point is solved by the chromatic aberration correcting lens 16.

That is, the chromatic aberration correcting lens 16 has a function of maintaining a constant image forming position regardless of the magnitude of the incident wavelength, and forms an image with respect to light having a large incident wavelength, that is, a light having a small refractive index. The distance is adjusted to be small, while the incident wavelength is adjusted to be small for light having a small incident wavelength, that is, light having a large refractive index.

The chromatic aberration correcting lens 16 includes a concave lens 16a made of flint glass and a convex lens 1 made of crown glass, as shown in FIGS. 3 (a) and 3 (b).
6b, and in the present embodiment, the pair of chromatic aberration correcting lenses 16,
16 are used. It should be noted that the combination shown in FIG. In this embodiment, the chromatic aberration correction lens 16 has a wavelength λ = 500 n as a chromatic aberration correction range.
What is necessary is just to be able to correct chromatic aberration in a wavelength band including E-line and D-line of about m to 590 nm, and the chromatic aberration correctable range can be adjusted by changing the interval between the pair of chromatic aberration correcting lenses 16. It is.

FIGS. 5 (a) to 5 (c) conceptually show the principle of the chromatic aberration correcting lens 16 described above. FIG. 5 (a) shows a case where monochromatic light of E-line before chromatic aberration correction is incident. The imaging distance fe, (b) in the case is also the imaging distance fd on the D line,
(c) shows the image formation distance fs between the E-line and the D-line when the chromatic aberration correction lens 16 is disposed on the optical path and the chromatic aberration is corrected. In the figure, the imaging distance fs is (a) and (b)
, The intermediate point of the imaging distance, ie, approximately fs = (fe + f
d) / 2. Therefore, when continuous spectrum light of the E-line and the D-line is used as the illumination light, chromatic aberration can be suppressed and the imaging position can be kept constant. For this reason, it is possible to prevent the position from being undetectable due to the asymmetry of the interference fringes that occurs when monochromatic light of only the E-line or the D-line is used, and the TV camera 20 can detect the alignment pattern with high accuracy.

In this embodiment, on the optical path,
An astigmatism correction lens 17 as shown in FIG. 4 is provided between the pair of chromatic aberration correction lenses 16. The astigmatism correction lens 17 is for correcting the displacement of the detection image on the wafer 5 in the X and Y directions due to the astigmatism light beam, that is, astigmatism, and includes a convex lens 17a made of a cylindrical lens and a concave lens. 17b. Therefore, according to the present embodiment, the illumination light in which both the chromatic aberration and the astigmatism are corrected is incident on the TV camera 20, so that the position can be detected by highly accurate image recognition.

Next, an alignment method according to the present embodiment will be described.

First, when an XY stage (not shown) is moved to emit illumination light from a cylindrical mirror 14 at the tip of an optical fiber 13 as an illumination light source 8, the illumination light passes through a bandpass filter 10 and a condenser lens 11, The illumination light refracted by the beam splitter 12 passes through the relay lens 15, the chromatic aberration correcting lens 16 and the astigmatism correcting lens 17, the reflecting mirror 18, and the reduction projection lens 3, and the wafer 5
A predetermined area is irradiated. The reflected light from the wafer 5 travels backward in the above-described path, and reaches the beam splitter 12 via the reduction projection lens 3, the reflecting mirror 18, the chromatic aberration correcting lens 16 and the astigmatism correcting lens 17. Here, the reflected light passes through the beam splitter 12, passes through the relay lens 15, and enters the TV.
The camera 20 is reached. A signal processing unit (not shown) is connected to the TV camera 20, and a signal waveform is detected from an image recognized by the TV camera 20.

FIG. 6B shows the signal detection waveform.
It is. According to the present embodiment, since the chromatic aberration correcting lens 16 is provided on the optical path of the illumination light, the chromatic aberration, that is, the imaging position of the imaging position is also obtained when the continuous spectrum light of the E-line and the D-line is used as the illumination light. The deviation is corrected. As a result,
When monochromatic light is used as the illumination light source 8, it is possible to avoid the difficulty of detecting the alignment mark 6 due to the interference waveform caused by the nonuniformity of the photoresist film thickness, and as shown in FIG. The detection signal corresponding to the step can be reliably grasped, and the position of the alignment mark 6 is accurately detected. The target portion of the wafer 5 is accurately positioned on the exposure optical system based on the position of the alignment mark 6 obtained in this manner, and thereafter, is radiated from the exposure light source 1, and is condensed by the condenser lens 2, the reticle 4, The integrated circuit pattern on the reticle 4 is transferred onto the photoresist film 7 on the wafer 5 by exposure light (not shown) passing through the reduction projection lens 3.

In the above description, the case where a mercury lamp as an exposure light source is used as an illumination light source has been described, but an independent xenon lamp may be used as a detection light source.

In this case, by using a xenon lamp having relatively uniform light energy at each wavelength, continuous spectrum light can be selectively adopted, and the correction rate of the chromatic aberration correction lens 16 can be adjusted. By setting the optimum correction value, it is possible to prevent the pattern from being undetectable due to the interference of the reflected light, and to perform highly accurate position detection.

The invention made by the inventor has been specifically described based on the embodiments. However, the invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist of the invention. Needless to say, there is.

For example, as an illumination light source, a cylindrical mirror attached to the tip of an optical fiber is shown as an example. However, the illumination light source is not limited to this, and may have any shape such as a polygonal cylindrical body or a polygonal cylindrical body. Good.

In the above description, the case where the invention made by the present inventor is mainly applied to an alignment technique in a so-called field of reduction projection exposure of a wafer is described, but the invention is not limited to this.
It can be widely applied to alignment technology in general reduction projection exposure.

[0056]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, according to the present invention, the chromatic aberration correcting optical system is provided in the optical path of the illumination light, and the focal length is adjusted corresponding to each wavelength, so that a continuous spectrum of two or more wavelengths or more is obtained as the pattern illumination light. Light can be used. Therefore, for example, even when the photoresist film thickness is non-uniform and asymmetric with respect to the alignment pattern of the detection portion, detection failure due to interference such as single-wavelength light can be prevented, and pattern detection can be performed reliably. This makes it possible to increase the positioning accuracy at the time of alignment and perform high-precision alignment.

[Brief description of the drawings]

FIG. 1 is a perspective view of an essential part showing a reduction projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a system diagram showing an optical system in pattern detection according to the present embodiment.

FIGS. 3A and 3B are explanatory diagrams showing a chromatic aberration correcting lens used in the present embodiment. FIG.

FIG. 4 is a perspective view showing an astigmatism correction lens used in the present embodiment.

FIGS. 5A, 5B and 5C are explanatory views conceptually showing the principle of correction by the chromatic aberration correcting lens in the embodiment.

FIGS. 6A and 6B are explanatory diagrams showing a relationship between an alignment mark formed on a wafer and a detected waveform in the embodiment.

FIG. 7 is a system diagram showing an optical system in a conventional pattern detection.

FIGS. 8A and 8B are diagrams for explaining chromatic aberration.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Exposure light source, 2 ... Condensing lens, 3 ... Reduction projection lens, 4 ... Reticle (original), 5 ... Wafer (exposure symmetry), 6 ... Alignment mark, 7.
..Photoresist film, 8 ... illumination light source, 10 ...
Bandpass filter, 11 ... condenser lens, 1
2 ... Beam splitter, 13 ... Optical fiber, 1
4 ... cylindrical mirror, 15 ... relay lens, 16 ... chromatic aberration correction lens, 16a ... concave lens, 16b ...
Convex lens, 17 ... astigmatism correction lens, 17a ...
-Convex lens, 17b-concave lens, 18-reflecting mirror, 20-TV camera, 21-lens, 22-
..Illumination light source (xen lamp), 71 ... wafer, 7
2 ... reduction projection lens, 73 ... reticle (original), 74 ... TV camera (recognition unit), 75 ... mercury lamp (exposure light source, illumination light source), 76 ... reflector, 77 ... relay lens, 78 ... beam splitter, 80 ... bandpass filter, 81 ... condenser lens, 82 ... photoresist film.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinya Nakagawa 1450, Josuihoncho, Kodaira-shi, Tokyo Inside the Musashi Factory, Hitachi, Ltd. (72) Inventor Takayoshi Osakaya 1450, Josuihoncho, Kodaira-shi, Tokyo Hitachi, Ltd. Inside the Musashi Factory

Claims (8)

[Claims] 1. A wafer having at least one alignment mark on a first main surface is masked by a reduction projection lens system in which aberration is corrected so as to obtain good optical characteristics with respect to monochromatic exposure light from an exposure light source. The circuit pattern is transferred onto the first main surface of the wafer at a predetermined reduction ratio by projecting a real image of the upper circuit pattern onto a photosensitive resist film formed on the first main surface. (A) an XY table for mounting the wafer; (b) a reference light source that is a continuous spectrum light source having a uniform spectral distribution within a predetermined bandwidth compared to a line spectrum light source An optical filter mechanism for selecting a continuous spectrum reference light having a longer wavelength than the exposure light so as not to substantially expose the resist film; (c) the reduced projection lens In a state where the alignment mark is located at a predetermined position outside the optical axis of the zoom system, the continuous spectrum reference light is aligned along a predetermined incident optical path of the reduction projection lens system by the selected continuous spectrum reference light. The alignment mark is illuminated so as to be incident on the mark, and the continuous mark reference light and the periphery of the alignment mark are arranged so that the continuous speckle reference light at least in the reduced projection lens system reverses an optical path which is the same as or near the incident optical path. After being reflected from the reduced projection lens system, the continuous spectrum reference light is located at a position away from the optical axis center of the reduced projection lens system so as to be taken out of the reduced projection lens system. Reflection arranged at a position that does not substantially disturb the projection of the real image when projected on the resist film (D) a chromatic aberration correcting optical system for correcting a predetermined chromatic aberration due to a wavelength difference within the predetermined bandwidth of the continuous spectrum reference light taken out of the reduction projection lens system by the reflection means; (e) detecting the image of the alignment mark included in the continuous spectrum reference light of the portion where the chromatic aberration has been corrected by the chromatic aberration correction optical system, without directly optically detecting the positional relationship between the wafer and the mask. A position detecting mechanism for determining a positional relationship between the reduction projection lens system and the alignment mark in the XY plane; (f) a desired position of the wafer based on the detected positional relationship of the alignment mark in the XY plane. The XY mounting the wafer so that the portion of the XY is positioned at or near the optical axis of the reduction projection lens system.
A wafer position determining mechanism for positioning the mask and the wafer by moving a table in the XY plane; (g) moving the desired portion of the wafer to the optical axis of the reduction projection lens system or The circuit pattern on the mask is illuminated by the exposure light in a state where it is positioned in the vicinity thereof, and a reduced real image of the circuit pattern on the mask is formed on the wafer through the reduction projection lens system. A reduction projection exposure apparatus including an exposure optical system for transferring the circuit pattern on the mask onto the resist film by projecting the circuit pattern on the resist film. 2. The reduction projection exposure apparatus according to claim 1, wherein the predetermined bandwidth of the continuous spectrum reference light is such that undesired interference due to unevenness in the thickness of the resist film can be prevented. A reduced projection exposure apparatus which is wide and narrow enough to correct the chromatic aberration of the continuous spectrum reference light so that the alignment mark can be detected with a predetermined accuracy. 3. The reduction projection exposure apparatus according to claim 2, wherein the continuous spectrum reference light is included in a visible light region. 4. The reduction projection exposure apparatus according to claim 3, wherein the continuous spectrum reference light has a relatively uniform intensity distribution within the predetermined bandwidth. 5. The reduction projection exposure apparatus according to claim 4, wherein said exposure light source is a line spectrum light source. 6. The reduction projection exposure apparatus according to claim 5, wherein the continuous spectrum reference light does not enter the mask between the wafer and the light detecting means and is not reflected by the mask. Projection exposure equipment. 7. The reduction projection exposure apparatus according to claim 6, wherein an interval between the chromatic aberration correction lenses in the chromatic aberration correction optical system is adjustable. 8. The reduction projection exposure apparatus according to claim 7, further comprising an astigmatism correction lens.