JPS61251858A - illumination optical system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to an illumination optical system in a reduction projection exposure apparatus for semiconductor manufacturing, and in particular to an illumination system suitable for obtaining a uniform intensity distribution at the entrance pupil position of a reduction projection lens. It is related to optical systems.

[Background of the invention]

Conventionally, in the case of semiconductor exposure with a line width of Q, about 8 to 2 .mu.m, a reduction projection exposure apparatus has been considered optimal in terms of alignment accuracy, resolution, and throughput. The illumination optical system conventionally used in the reduction projection exposure apparatus described above is
For example, as shown in Figure 5, an ultra-high pressure mercury lamp 1 is connected to an elliptical mirror 2.
The integrator is placed at one focal point P, and the integrator is placed at the other focal point P. This integrator or input lens4. Rod lens group 5. It is formed from an output lens 6, which uses the light emitted from the ultra-high pressure mercury lamp 1 to create a plurality of secondary light sources, and is a condenser lens-e7.
When the reticle 8 is irradiated through the reticle 8, the diffraction image caused by the reticle 8 is removed to reduce illuminance unevenness. Further, in the integrator, the image of the exit surface S1 is reduced by the condenser lens 7 and projected by the reduction projection lens 9.
The image is formed to be formed at the S2 position of the entrance pupil 10 plane, but as described above, the image is formed at the S3 position of the entrance pupil 10 plane, which means that the brightness diaphragm is When the sample is placed near the surface of the condenser on the front focal plane of , Koehler illumination, which is said to provide uniform illumination, can be realized. In the drawing, 11 is a wafer, 12 and 13 are cold mirrors, 14 is a shutter, and 15 is a wavelength filter. Regarding the above-mentioned illumination optical system, for example, Japanese Patent Laid-Open No. 50-103916 and Japanese Patent Laid-Open No. 56-8
It is described in Publication No. 1813. Furthermore, the above wafer 1
The resolution performance of the pattern formed on the reticle 8 is as follows.
It is greatly influenced by the lighting method. In particular, the size of the integrator image and the light intensity distribution focused at the S1 position on the entrance pupil 10 surface of the reduction projection lens 9 are becoming important control items as the mother turn becomes finer. .

For example, FIG. 6 shows the image of the integrator L focused on the S1 position on the entrance pupil 10 of the reduction projection lens 9. In this case, d in the figure is the diameter of the image of the integrator, and D is the diameter of the integrator image. Entrance pupil 1o O diameter (!: f 7:r
= −Shall coherency σ is σ”” o =O−
A value of 5 to 0.7 is considered necessary to obtain good resolution performance or image quality. On the other hand, in conventional illumination optical systems, the intensity distribution of the light of the integrator and image on the entrance pupil 10 surface depends on the imaging state of the ultra-high pressure mercury lamp 1 by the elliptical mirror 2, as shown in FIG. , the horizontal axis is the distance r1 from the optical axis
If the vertical axis is the light intensity I, due to the influence of the rod lens group 5 of each integrator, the light intensity distribution of the actual image of the integrator and its envelope will be as shown in 16.17, and this Since the effective size is smaller than the preset integrator image size d, the resolution performance is lowered. Therefore, in order to obtain an ideal light intensity distribution curve 18 as shown in FIG. 8, a method described in, for example, Japanese Unexamined Patent Publication No. 7359/1983 has been invented. In this method, the light emitted from the integrator illuminates the second integrator through an intermediate lens.The intermediate lens is separated from the second integrator by its focal length, and the first integrator
The light emitted from the point is irradiated onto the entire surface of the second integrator. Therefore, the above method can maintain a uniform light intensity distribution on the exit surface of the second integrator, and even more so on the entrance pupil plane. However, on the other hand, since the second integrator and intermediate lens are added, there is a risk that the overall configuration of the illumination optical system will become complicated and large.

[Purpose of the invention]

The present invention solves the above-mentioned conventional problems and has a simple configuration that makes it possible to make the light intensity distribution uniform on the entrance pupil plane of the reduction projection lens, which is essential for improving the resolution performance of the reduction projection exposure apparatus. The object of the present invention is to provide a compact illumination optical system.

[Summary of the invention]

When the optical fibers are arranged randomly, the light distribution characteristics of the emitted light can be maintained substantially uniformly regardless of the angle of incidence of the incident light. Therefore, in order to achieve the above object, the present invention uses a thin optical fiber bundle in an integrator to make it possible to smooth the strength and weakness of the light intensity, and combines the plurality of thin optical fiber bundles with a cylindrical inner mirror. enables uniform light intensity, and has a simple configuration.
It is characterized by its compact size.

[Embodiments of the invention]

1 to 4 showing embodiments of the present invention will be described below. FIG. 1 is an explanatory diagram of the configuration of an illumination optical system showing an embodiment of the present invention, and FIG. 2 is an enlarged perspective view of the integrator.
FIG. 3 is a sectional view of the integrator, and FIG. 4 is a light intensity distribution diagram on the entrance pupil plane of the reduction projection lens. It should be noted that parts that are the same as those in the prior art are designated by the same reference numerals as in FIG.

In the figure, a Phi/J type integrator is shown, and a mirror 20 having a cylindrical shape and a reflecting surface is fitted into both ends of the mirror 20 with a distance t between them. It is composed of two optical fiber bundles 21 and 22 into which fiber bundles 21m and 22m are inserted, an output lens 23, and a wavelength filter 15, and the light source of the ultra-high pressure mercury lamp 1 and one focal point of the ellipse f#, 2 as in the conventional case. The other focal point P is placed on the entrance surface of the first optical fiber bundle 21, and the image of the exit surface S1 of the second optical fiber bundle 22 is transmitted through the condenser lens 7 to the reduction projection lens 9. It is connected to the S1 position on the entrance pupil plane 10 of . Further, the optical fiber bundles 21 and 22 have N,
Since A (numerical aperture) is constant depending on the type, the direction of light emitted from one point of the first optical fiber bundle 21 falls within the range of angle θ as shown in FIG. Therefore, as shown in FIG. 3, the inner diameter of the inner mirror 20 is set to A, and the second optical fiber bundle 2
When the incident diameter of light on the incident surface of 2 is B, the interval t between the two optical fiber bundles 21 and 22 is expressed by the following equation.

B = 2A θ B = 2tim(T)”; or θ If the relationship is as shown in the above equation, the first optical fiber bundle 21
The light emitted from any one point of the second optical fiber bundle 22 is uniformly irradiated onto the entire surface of the incident surface of the second optical fiber bundle 22, thereby reducing the non-uniformity of the light intensity distribution at the other focal point P. Also second
This will be eliminated at the output surface S of the optical fiber bundle 22. Note that it is also possible to configure the first optical fiber 21 with a rod lens group. Furthermore, when the distance t between the first optical fiber bundle 21 and the second optical fiber bundle 22 is made variable, the envelope of the intensity distribution of the light from the fiber type integrator connected to the S1 position on the entrance pupil 10 surface of the reduction projection lens 9 The lines are 17 in Figure 7, 18 in Figure 8, and 2 in Figure 4.
As shown in 4, the uniformity of the light intensity distribution on the entrance pupil 10 plane of the reduction projection lens 9 can be changed arbitrarily.
It is possible to obtain uniformity that maximizes resolution performance.

〔Effect of the invention〕

As described above, the present invention can easily equalize the light intensity distribution on the entrance pupil plane of the reduction projection lens using an integrator with a simple configuration, so that it is possible to downsize the illumination optical system and reduce the projection exposure. It is possible to improve the resolution performance of the device, and it is effective in manufacturing semiconductors with fine patterns and turns.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the configuration of an illumination optical system used in a reduction projection exposure apparatus showing an embodiment of the present invention, Fig. 2 is an enlarged perspective view of the fiber integrator, and Fig. 3 is a sectional view of the fiber integrator. , FIG. 4 is a light intensity distribution diagram of the fiber integrator on the entrance pupil plane of the reduction projection lens, FIG. 5 is an explanatory diagram of the configuration of the illumination optical system used in the conventional reduction projection exposure apparatus, and FIG.・An explanatory diagram of the physical coherency, FIG. 7 is a light intensity distribution diagram of the integrator on the entrance pupil plane of the reduction projection lens, and FIG. 8 is a light intensity distribution diagram of an ideal integrator.・Ultra high pressure mercury lamp, 2...Oval steel, and...Integrator, 4...Input lens, 5...Rod lens group, 6...Output lens, 7...Condenser lens, 8... - Reticle, 9... Reduction projection lens, 10... Entrance pupil, 11... Wafer, 12.
13...Cold mirror, 14...Shutter, 1
5...' Wavelength filter, 16. 18.24...Light intensity distribution, 17...Envelope,...Fiber type integrator, 20...Inner surface mirror, 21.22...
Optical fiber bundle, 23...output lens. Agent Patent attorney Tadashi Akimoto Jitsu No.

Claims (1)

[Claims] 1. A condensing optical system, an integrator that creates a plurality of light beams from the light from the condensing optical system, and an optical means that illuminates an object to be irradiated with the plurality of light beams from the integrator. In the illumination optical system, the integrator is equipped with a plurality of media that keep the output angle of the output light almost uniform regardless of the angle of incidence of the incident light, and these multiple media are inserted at a predetermined interval. and a cylindrical inner mirror whose intervals are joined by an inner mirror, and the output surface of the integrator is configured to form an image on the entrance pupil of the reduction projection lens held in the illumination optical means. illumination optical system. 2. The illumination optical system according to claim 1, wherein the plurality of media are comprised of optical fiber bundles. 3. The illumination optical system according to claim 1, wherein the plurality of media are constituted by rod lenses. 4. When the interval between the plurality of media is l, the effective emission angle of light from the integrator is θ, and the inner diameter of the inner mirror is A, then the relationship 2A=l・θ is established. An illumination optical system according to claim 1, characterized in that the illumination optical system comprises: