JPS6376429A - Optical equipment for illumination - Google Patents

Abstract

PURPOSE:To enable efficient converging and obtaining a simple structure equipment wherein the height of the total equipment is not made too high has little limitation for the design of an illuminating optical system by providing a very high voltage mercury lamp to make a greater area end electrode upward and a converging mirror to make an aperture upward. CONSTITUTION:A pair of electrodes 1A and 1B which have a different area end is provided face to face and a very high voltage mercury lamp 1 which can emit light by the discharge between the electrodes 1A and 1B and a converging mirror 2 for converging the light from the very high voltage mercury lamp 1 are provided. In such an illuminating system, the greater area end electrode 1A of the above-mentioned pair of the electrodes 1A and 1B is provided above the smaller area end electrode 1B and the above mentioned converging mirror 2 is provided to make the aperture-facing upward. This enables efficient converging and realizing optical equipment for illumination which can supply high intensity and uniform illuminating light and has a simple and small size structure wherein the height of the total equipment is not made too high and the limitation for the design of the illuminating optical system is little.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an illumination optical device, and particularly to an illumination optical device for an exposure device used in a photolithography process for manufacturing semiconductor devices.

[Conventional technology]

Exposure equipment generally used in semiconductor manufacturing has the ability to uniformly illuminate an original plate called a reticle or mask on which a predetermined pattern is formed, and to transfer the pattern of this original plate onto a wafer coated with resist. Therefore, it is important for an illumination optical device for this purpose to supply light with high brightness and wavelength characteristics that match the photosensitive characteristics of the resist. For this reason, ultra-high-pressure mercury lamps are used as the illumination light source in illumination optical devices for such exposure equipment.Currently, no alternative light source has been put into practical use. The electric discharge that occurs during the process generates relatively short wavelength light with high brightness, and in response to the recent demand for finer patterns in response to higher integration, shorter wavelength and higher brightness light is generated. Development is progressing to make it possible to emit light, and improvements have been made to the shape of the electrodes as seen, for example, in Japanese Patent Application Laid-Open No. 60-57930.

On the other hand, as an illumination device using an illumination optical system using such an ultra-high pressure mercury lamp as a light source, a configuration as shown in FIG. 4 has been proposed.

[Problem that the invention seeks to solve]

However, when a light-emitting discharge tube is constructed with an electrode shape such as that shown in the above-mentioned Japanese Patent Application Laid-Open No. 60-57930, the distribution state of the light emitted from the light source is uniformly distributed, as is generally thought. For this reason, it has been found that depending on the arrangement of the elliptical mirror for condensing light, efficient condensation may not always be possible, and there is a risk that even efforts to improve brightness will be meaningless.

Although it is possible to make the illumination device as shown in Fig. 4 compact to some extent, the illumination optical system has many bends in the optical path due to mirrors, resulting in a complicated configuration. There was a problem in that the design of the entire device in which the system was mounted was subject to significant restrictions.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an illumination optical device using an ultra-high-pressure mercury lamp as a light source, which can efficiently collect light by appropriately arranging condensing mirrors in accordance with the light distribution characteristics caused by the electrode shape of the discharge tube. An object of the present invention is to provide an illumination optical device which has a compact configuration that does not make the overall height of the device excessively high, and which has a simple configuration with few restrictions on the design of the illumination optical system. .

[Means for solving problems]

The illumination optical device for an exposure apparatus according to the present invention, as shown in the schematic diagram of FIG.
A pair of electrodes LA and IB with different tip areas are used as the electrodes where discharge occurs, which are arranged facing each other, and the electrode (anode) with the larger tip area is placed on the upper side. This is based on the premise that

A condensing mirror 2 such as an elliptical mirror is arranged so that its opening 2a is on the upper side.

[Effect]

In this way, by using a pair of electrodes arranged opposite each other with different tip areas, it is possible to form the cathode tip into a cone shape and the anode tip into a flat tapered shape. By forming this, the light-emitting area can be brought closer to one point than in conventional ultra-high pressure mercury lamps, so high brightness can be obtained. In addition, in such an electrode shape, the light distribution characteristics of the emitted light are different from those in the case of a conventional monolithic electrode shape. Specifically, when the pair of electrodes 1a and lb are both cone-shaped and have a pointed tip as in the conventional case shown in FIG. 3A, the intensity distribution l has a light distribution characteristic centered in a plane almost perpendicular to the axis connecting both electrodes. However, in the case of having an electrode IA (anode) formed in a tapered shape with a flat surface S at the tip and an electrode IB (cathode) whose tip is formed in a cone shape, the As a result, the light distribution characteristics are biased toward the electrode IB, which has a smaller tip area. 1! II, the intensity distribution I is from the perpendicular plane V to the axis connecting both electrodes to the electrode I whose tip area is small.
The light distribution characteristic has a center intensity as the center of gravity of the light amount in a direction tilted by θ toward B.

Therefore, in the present invention, first, the structure of the illumination optical system is increased by arranging a condensing mirror such as an elliptical mirror for condensing the light flux from the ultra-high pressure mercury lamp so that its aperture faces upward. It has a lower structure, and has a simpler structure with fewer bends due to mirrors. Under such an overall configuration of the illumination optical system, an ultra-high pressure water lamp is connected to the condenser mirror 2 whose aperture faces upward (vertically upward), and the area of the tip of the pair of electrodes is Larger electrode IA
By arranging the anode (anode) on the upper side (vertically upward), it is possible to sufficiently concentrate light even against the deviation of the light distribution characteristics as described above, and it is possible to sufficiently concentrate light even with the deviation of the light distribution characteristics as described above. This makes it possible to efficiently condense luminous flux. In the configuration shown in FIG. 1, the ultra-high-pressure mercury lamp serving as the arc tube 1 is arranged so that approximately the middle of both electrodes LA and IB is located on the first focal point of the elliptical mirror 2, and the emitted light is directed to the elliptical mirror 2. After reflection, the light is focused on or near the second focal point F2 of the elliptical mirror 2, and is converted into a parallel beam by the collimator lens 4, which is disposed with its front focal point substantially aligned with the second focal point.

For comparison, Figure 5 shows the electrode L for an upward oriented elliptical mirror.
This is an example of the convergence state of the light beam when the positions of A and 1B are reversed. From the comparison between Figure 1 and Figure 5,
It is clear that in the state shown in the figure, the emitted light cannot be sufficiently focused by the elliptical mirror 2.

In order to obtain the same level of light collection efficiency as shown in Fig. 1, it is necessary to make the elliptical mirror 2 deeper, which is disadvantageous for making a compact device. The distance H1 from the optical axis when the light beam P with the maximum intensity is made parallel to the optical axis Ax by the collimator lens 4 is the fifth
In the configuration shown in the figure, the maximum intensity light vAP is also smaller than the distance H2 from the optical axis when it is parallel to the optical axis Ax by the collimator lens 4. This means that
The central intensity of the light beam is located close to the optical axis, which is not only advantageous for configuring a compact optical system, but also
This is also advantageous in terms of aberration correction.

〔Example〕

An embodiment in which the illumination optical device according to the present invention as described above is mounted on an actual exposure apparatus will be described below. The embodiment according to the present invention shown in FIG. 2 is an example in which the illumination optical device according to the present invention is used as an illumination device for a reduction projection type exposure apparatus.

The ultra-high pressure mercury lamp 1 has a pair of electrodes arranged facing each other, an electrode IA (anode) with a large area at the tip and an electrode ta (thesis) with a small area at the tip. The light flux emitted from the lamp 1, which is placed on the upper side and requires a very high number of man-hours, is focused by the elliptical mirror 2, which is placed with the aperture 2a facing upward. That is, the light emitted by the ultra-high pressure mercury lamp 1 is transmitted to the electrode I whose tip area is larger.
The light is collected by an elliptical mirror 2 arranged with its aperture 2a facing the A side.

Light in a desired short wavelength range matching the photosensitive characteristics of the resist is reflected by the dichroic mirror 3, converted into a parallel beam by the collimator lens 4, and enters the fly-eye integrator 5. The first relay lens 7 configures the entrance surface of the fly-eye integrator 5 to be conjugate to the reticle blind 8 as a field stop, and the second relay lens 9, mirror 11, and main condenser lens 1
2, the reticle surface 13 is configured to be conjugate with the reticle blind 8, and also configured to be conjugate with the wafer surface 16 via the reduction projection lens 14. Further, a diaphragm member 6 for setting illumination conditions is arranged on the exit surface of the fly's eye integrator 5, and the fly's eye integrator 5 is located at this position.
The integrator 5 forms a substantial surface light source.

A light source image is formed at a position 10 between the second relay lens 9 and the mirror 11 by the first relay lens 7 and the second relay lens 9, and the entrance pupil of the reduction projection lens 14 is formed by the main condenser lens 12. A light source image is formed on 15. Further, in order to adjust the focus so that the pattern image on the reticle surface 13 by the projection lens 14 is clearly projected onto the wafer surface 16, the wafer is mounted movably in the optical axis direction and in a plane perpendicular to the optical axis. The stage 17 and the vibration isolating table 18 constitute a reduction projection type exposure apparatus.

In such a reduction projection type exposure apparatus, since the illumination optical device according to the present invention is used, the height of the illumination optical system does not become excessively high, and it can be configured easily and compactly.
As explained in FIG. 2, the high-intensity light obtained by the ultra-high pressure mercury lamp 1, in which a pair of electrodes with different tip areas are disposed facing each other, can be efficiently focused without loss. Moreover, since the center intensity is close to the optical axis, the entire illumination optical system can be made smaller, and the configuration is advantageous in terms of aberration correction of the illumination optical system.

In this embodiment, since the ultra-high pressure mercury lamp 1 is arranged in the opposite direction from the conventional one, it is necessary to take measures to sufficiently satisfy the vaporization conditions for mercury in the mercury lamp. It is possible to obtain high-intensity light emission by the polar groove structure.

〔Effect of the invention〕

As described above, according to the present invention, in an illumination optical device using an ultra-high pressure mercury lamp as a light source, efficient light collection is possible by arranging a collection mirror appropriate for the light distribution characteristics caused by the electrode shape. As a result, it is possible to achieve an excellent illumination optical device that can supply high-intensity and uniform illumination light, and the overall height of the device is not excessively high, the structure is compact, and the illumination optical system is It is possible to realize an illumination optical device with a simple and compact configuration with few restrictions on the design, and the condenser mirror is not limited to an elliptical mirror, but for example a parabolic mirror can be used to directly collimate the light from the light emitting discharge tube. It is also possible to adopt a configuration in which the light is converted into a luminous flux.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration and optical path of the main parts of the illumination optical device according to the present invention, FIG. 2 is a schematic configuration diagram of an embodiment in which the illumination optical device according to the present invention is mounted on a reduction projection type exposure apparatus, and FIG.
3B and 3B are schematic diagrams showing that the light distribution characteristics differ depending on the shape of the pair of electrodes. In FIG. 3A, the pair of electrodes both have a sharp shape, and in FIG. Fig. 4 is a schematic diagram of a conventional reduction projection type exposure apparatus, and Fig. 5 shows a case in which an elliptical mirror is formed with an electrode of an ultra-high pressure mercury lamp for comparison with the present invention. FIG. 3 is a diagram showing a configuration and an optical path when the positional relationship is reversed. [Explanation of symbols of main parts] 1: Ultra-high-pressure mercury lamp 1^; Electrode LB with a larger tip area: Illumination light with a smaller tip area 2: Condensing mirror 2a such as an elliptical mirror: 2a such as an elliptical mirror Aperture of condenser mirror Fig. 1 Fig. 2 Fig. 4

Claims (1)

[Claims] An illumination optical system comprising an ultra-high pressure mercury lamp in which a pair of electrodes having different tip areas are arranged facing each other and emit light by discharge between the electrodes, and a condenser mirror for collecting light from the ultra-high pressure mercury lamp. , the electrode of the pair of electrodes having a larger tip area is placed above the electrode having a smaller tip area, and the condenser mirror is placed with its aperture facing upward. illumination optical device.