JPH06215998A - Projection aligner - Google Patents

Abstract

PURPOSE:To improve the focusing performance by positively utilizing the coherence of a light similarly to the case of using a plurality of photomasks and to eliminate an alignment between optical members corresponding to the photomasks. CONSTITUTION:A photomask 2 is illuminated with exposure light from an illumination optical system 1, the image of the photomask 2 is focused on a bleaching material 14 coating a light transmission board 13 via a first focusing optical system 3, and the image focused on the material 14 is refocused on a photosensitive board 6 via a second focusing optical system 5. Since the material 14 increases its light permeability when an exposure amount is increased, the material 14 substantially performs the function as a second photomask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for projecting and exposing a pattern on a photomask onto a photosensitive substrate when a semiconductor device, a liquid crystal display device, a thin film magnetic head or the like is manufactured by a lithography process. The present invention relates to a projection exposure apparatus.

[0002]

2. Description of the Related Art For example, when a semiconductor element such as an LSI, a liquid crystal display element, a thin film magnetic head, or the like is manufactured by a lithography process, a pattern of a photomask or reticle (hereinafter, referred to as "photomask") is formed with a photoresist. 2. Description of the Related Art A projection exposure apparatus is used which performs projection exposure on a photosensitive substrate such as a coated wafer.

FIG. 3 shows a main part of a conventional projection exposure apparatus.
In FIG. 3, the photomask 101 is held substantially vertically and horizontally with respect to the optical axis of an illumination optical system (not shown), and is transilluminated with exposure light having a predetermined wavelength emitted from the illumination optical system. . The photomask 101 which has been widely used conventionally has a structure in which a light-shielding pattern made of a metal such as chromium is formed on a transparent substrate, and when it is transmitted and illuminated, diffracted light corresponding to the pattern shape is generated.
These diffracted lights are collected again on the image plane by the imaging optical system 103, whereby the pattern image of the photomask 101 is transferred onto the exposure surface of the wafer 105 held so as to match the image plane.

[0004]

In the prior art as described above, there is a device requirement that the photomask 101 be illuminated by the exposure light with a uniform illuminance, so the light source of the illumination optical system. Could not have spatial coherency. That is, the photomask 101
If the exposure lights that illuminate the photomask have different coherence with each other, which have different illumination angles with respect to the optical axis of the projection optical system, interference fringes are formed on the photomask 101, and the photomask It becomes incompatible with the request to uniformly illuminate 101. Therefore, the spatial coherency of the light source cannot be taken as a parameter for improving the performance of the projection optical system.

In this regard, Japanese Patent Application No. 4-27703 has recently been applied.
As disclosed by the present applicant in Japanese Patent Application No. 2 and Japanese Patent Application No. 4-277033, the present inventor has invented a method of performing exposure using a plurality of photomasks. FIG. 4 shows a projection exposure apparatus according to the applicant's prior application. In FIG. 4, the illumination optical system 1 emits exposure light of a predetermined wavelength. A first photomask 2, a first imaging optical system 3, a second photomask 4, a second imaging optical system 5, and a photosensitive substrate 6 are arranged in order from the illumination optical system 1. Then, a projection optical system is constituted by the first image-forming optical system 3 and the second image-forming optical system 5 which are arranged in series, and with respect to the second image-forming optical system 5,
The photosensitive substrate 6 and the second photomask 4 are conjugate with each other, and
Regarding the imaging optical system 3, the second photomask 4 and the first photomask 2 are almost conjugate.

In the configuration of FIG. 4, the first photomask 2 is
Illuminated by the exposure light 7 from the illumination optical system 1 arranged above, the pattern formed on the first photomask 2 produces diffracted light 8 and 9 of the exposure light 7.
Illuminates the pattern on the second photomask 4 via the first imaging optical system 3. At this time, the diffracted lights 8 and 9 have coherence with each other. Further, as a result of being illuminated by the diffracted lights 8 and 9, diffracted lights 10 and 11 are generated from the pattern formed on the second photomask 4, and these diffracted lights 10 and 11 of the photosensitive substrate 6 pass through the second imaging optical system 5. Form an image on top.

In the configuration of FIG. 4, consider as an example the case where an isolated opening pattern is formed on both the first photomask 2 and the second photomask 4. Then, when the projection magnification of the first imaging optical system 3 is β, the second photomask 4
The isolated opening pattern above is approximately β times the isolated opening pattern on the first photomask 2. However, the actual size and shape of these isolated aperture patterns are independently adjusted on the first photomask 2 and the second photomask 4 so that good imaging characteristics can be obtained. In this case,
Since the diffracted lights 8 and 9 emitted from the first photomask 2 have coherence with each other, the edge-enhanced phase shift mask is included in the projected image of the second photomask 4 on the photosensitive substrate 6. Imaging properties similar to those used are obtained.

As another example of the configuration of FIG.
Both on the first photomask 2 and the second photomask 4,
Consider a case where a line-and-space pattern, which is a one-dimensional periodic pattern, is formed. And those two
Direction of one one-dimensional periodic pattern (period direction)
Are parallel to each other. In this case, oblique illumination such as so-called modified illumination is suitable, but considering the case of the oblique illumination, the diffracted lights 8 and 9 emitted from the first photomask 2 have coherence with each other. Since it has, the projected image on the photosensitive substrate 6 of the second photomask 4 is
Imaging characteristics with higher contrast can be obtained than when using the so-called modified illumination method.

Further, for example, even when only the phase pattern is formed on the first photomask 2 and only the light shielding pattern is formed on the second photomask 4, the same image forming characteristic as when the phase shift mask is used is obtained. be able to. That is, in the projection exposure apparatus according to the prior application of the applicant, the lights that are diffracted at one point on the first photomask 2 and illuminate the second photomask 4 at different angles have mutual coherence. By positively utilizing this, the image forming performance on the photosensitive substrate 6 is improved.

However, in the projection exposure apparatus according to the prior application of the present applicant, it is difficult to align the first photomask 2 and the second photomask 4 with each other, and the two photomasks and the photomask are exposed. There is a disadvantage in that relative alignment (alignment) with the substrate 6 is also difficult. In view of the above point, the present invention provides coherence between lights that illuminate the photomasks at different angles as in the case of using a plurality of photomasks, thereby improving the imaging performance. An object of the present invention is to provide a projection exposure apparatus that facilitates relative alignment between optical members corresponding to the plurality of photomasks.

[0011]

A projection exposure apparatus according to the present invention comprises an illumination optical system (1) for illuminating a photomask (12) on which a transfer pattern is formed with exposure light, as shown in FIG. 1, for example. A projection exposure apparatus which projects an image of the pattern of the photomask (12) onto the photosensitive substrate (6), forms an intermediate image of the pattern of the photomask (12) under the exposure light. The imaging optical system (3), the optical filter plates (13, 14) arranged near the surface on which the intermediate image is formed and having the bleaching effect, and the optical filter plates (13, 14) are transmitted. The second imaging optical system (5) for re-imaging the intermediate image on the photosensitive substrate (6) under the exposure light.

Here, the bleaching effect means an effect of increasing the light transmittance of the portion when the light is irradiated.

[0013]

In the present invention, the photomask (1
2) is the first photomask, the optical filter plate (13,
14) is referred to as a second photomask, the light diffracted by the pattern on the first photomask (12) is reflected on the second photomask (13, 14) by the first photomask (12). Form a pattern image. By the way, the second photomasks (13, 14) are, for example, those obtained by coating a material having a bleaching effect on a light transmissive substrate,
Depending on the image formed on the second photomask (13, 14), the light transmittance of the bright part becomes high. That is, the in-plane transmittance distribution of the second photomask (13, 14) corresponds to the in-plane transmittance distribution of the first reticle (12), that is, the pattern arrangement. Therefore, the first photomask (12) and the second photomask (13, 14) are aligned and installed, and it is not necessary to perform alignment. Moreover, it is possible to give coherence to the lights that illuminate the second photomask (13, 14) at different angles,
Imaging performance can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the projection exposure apparatus according to the present invention will be described below with reference to FIGS. In FIG. 1, parts corresponding to those in FIG. 4 are designated by the same reference numerals.
FIG. 1 shows a simplified main part of a projection exposure apparatus of this embodiment. In FIG. 1, an illumination optical system 1 emits exposure light of a predetermined wavelength. A photomask 12, a first imaging optical system 3, and a light-transmissive substrate 1 in order from the illumination optical system 1.
3, the second imaging optical system 5 and the photosensitive substrate 6 are arranged. Then, a substance having a bleaching effect (hereinafter referred to as “bleaching material”) 14 is applied onto the light-transmissive substrate 13.

The bleaching material is a substance whose transmittance increases with exposure amount, and FIG. 2 shows a typical characteristic of the transmittance with respect to the exposure amount. In the characteristic of FIG. 2, the transmittance rapidly and continuously changes from almost 0% to near 100% in a region where the exposure amount exceeds a predetermined threshold value. Examples of such a bleaching material include, for example, aryl nitrone, α- (4-diethylaminophenyl) -N-phenyl nitrone, α- (4-diethylaminophenyl) -N.
-(4-Chlorophenyl) nitrone or the like can be used. Such a bleaching material has conventionally been applied to the surface of a photosensitive substrate and used for the purpose of enhancing the contrast of a projected image.

Returning to FIG. 1, a projection optical system is composed of the first image-forming optical system 3 and the second image-forming optical system 5 arranged in series, and the second image-forming optical system 5 and the photosensitive substrate 6 are provided. The arranging surface of the bleaching material 14 on the light-transmissive substrate 13 is substantially conjugated, and the photomask 1 is used for the first imaging optical system 3.
2 and the arrangement surface of the bleaching material 14 are almost conjugate.
In this example, the photomask 12 is illuminated with the exposure light 7 from the illumination optical system 1, and the pattern formed on the photomask 12 produces diffracted light 8 and 9 of the exposure light 7. 9 forms an image of the pattern on the photomask 12 on the bleaching material 14 on the substrate 13 via the first imaging optical system 3. At this time, the diffracted lights 8 and 9 have coherence with each other, and the interference fringes of the diffracted lights 8 and 9 interfere with each other.
2 is a pattern image.

Now, when an image of the pattern of the photomask 12 is formed on the bleaching material 14, the bleaching material 14 is exposed in accordance with the distribution of lightness and darkness of the image, and the image intensity distribution is The light transmittance of the bright part becomes high. The transmittance distribution of the bleaching material 14 in this state is substantially similar to the transmittance distribution in the pattern formation surface of the photomask 12, that is, the pattern arrangement. Therefore, an image of the pattern of the photomask 12 is formed on the photosensitive substrate 6 via the second imaging optical system 5 according to the transmittance distribution of the bleaching material 14. At this time, since the diffracted lights 8 and 9 that illuminate the bleaching material 14 have coherence with each other, this improves the optical imaging performance.

Moreover, since the transmittance distribution in the bleaching material 14 is determined according to the pattern image of the photomask 12, the position of the photomask 12 and the light-transmissive substrate 13 coated with the bleaching material 14 is positioned. It is not necessary to perform alignment, and exposure can be performed quickly. In this embodiment, when the bleaching material 14 is properly exposed, a fixing process for fixing the transmittance of the bleaching material 14 is performed without moving the light transmissive substrate 13. Is desirable. By using the bleaching material 14 and the light-transmissive substrate 13 after the fixing process, it is possible to perform exposure on a large number of photosensitive substrates 6 under the same conditions.

Further, in the above embodiment, the target pattern is projected and exposed by using one photomask, one substrate coated with the bleaching material, and two image forming optical systems. However, with the same principle, one photomask,
Projection exposure may be performed using two or more substrates each coated with a bleaching material and three or more imaging optical systems. Further, in the above-mentioned embodiment, the image forming optical system is a refraction system, and the transmission type photomask is used.
The scope of application of the present invention is not limited to this example,
The same applies when the imaging optical system is a reflective system or when a reflective photomask is used.

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.

[0021]

According to the present invention, since the optical filter plate having the bleaching effect is used as the second photomask, the photomask is used similarly to the case where a plurality of actual photomasks are used. By providing coherence between the lights that illuminate at different angles, it is possible to improve the imaging performance. Moreover, there is an advantage that relative alignment work (alignment) between the photomask corresponding to the plurality of photomasks and the optical filter plate is unnecessary.

Therefore, a mechanism for alignment of the apparatus is not required in constructing the apparatus, the structure of the projection exposure apparatus can be simplified, and alignment time is not required during exposure, and throughput can be improved. Further, according to the present invention, the distortion (distortion aberration) of the aberrations of the imaging optical system does not necessarily have to be individually corrected in the first and second imaging optical systems, and the first and second Two
It is sufficient if it is corrected as the entire image forming optical system including the image forming optical system. This is a design margin when designing the optical system, and can be passed on to the improvement of other aberration performances.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of a relationship between an exposure amount of a bleaching material and a transmittance.

FIG. 3 is a schematic configuration diagram showing a main part of a conventional projection exposure apparatus.

FIG. 4 is a schematic configuration diagram showing a projection exposure apparatus according to the applicant's prior application.

[Explanation of symbols]

 1 Illumination Optical System 3 First Imaging Optical System 5 Second Imaging Optical System 6 Photosensitive Substrate 12 Photomask 13 Light Transmissive Substrate 14 Bleaching Material

Claims (1)

[Claims] 1. A projection exposure apparatus that has an illumination optical system that illuminates a photomask on which a transfer pattern is formed with exposure light, and projects the image of the pattern of the photomask onto a photosensitive substrate. A first image-forming optical system for forming an intermediate image of the pattern of the photomask under the conditions of: An optical filter plate having a bleaching effect that increases the transmittance for light, and a second imaging optics that re-images the intermediate image on the photosensitive substrate under the exposure light transmitted through the optical filter plate. And a projection exposure apparatus.