JPH1174172A - Exposure optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure optical system which is superior in parallelism despite being low cost and having short optical path. SOLUTION: An exposure optical system is composed of a light source 10, a light-collecting means 20, a secondary light source forming means 30, and a collimator 40, wherein the collimator 40 is elastically deformed so as to make an angle α at which a light ray A is emitted from the tangential plane 41 of the collimator 40 nearly equal to an angle β at which a light ray B is projected from the tangential plane 41 of the collimator 40. The light ray A is a primary light ray incident on the collimator 40 on the optical axis, and the light ray B is a primary light ray incident on the collimator 40 traveling out of the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for exposing a pattern drawn on a mask to a semiconductor substrate, a glass substrate, or the like (hereinafter, referred to as a substrate), and more particularly, to exposing a pattern with a small space between the mask and the substrate. The present invention relates to an optical system of a so-called proximity exposure apparatus.

[0002]

2. Description of the Related Art An optical system of a conventional proximity exposure apparatus has a configuration as shown in FIG. That is, the light source 10
The light emitted from the light source is collected by the condensing means 20 to the secondary light source creating means 30, where a secondary light source is created. Light emitted from the secondary light source is converted into parallel light by the collimator 40, and irradiates the mask and the substrate provided on the exposure surface 60.

[0003]

However, if the performance of the collimator 40 is insufficient and there is an error in the parallelism of the light beam, the irradiation angle of the light beam will differ depending on the location on the mask. For example, in FIG. 2, when the proximity gap 65 is 100 microns and there is an error of 0.5 degree in the parallelism of light rays, the transfer position shift 66 of the pattern 62 drawn on the mask 61 becomes 0.9 microns. ,
It hinders the production of semiconductors and liquid crystals. For this reason, conventionally, the following two approaches have been taken to improve the performance of the collimator 40.

[0004] The first approach is to use a parabolic mirror for the collimator. It is widely known that the use of an off-axis parabolic mirror as shown in FIG. 3 allows the light emitted from one point to be converted into perfect parallel light. However, in order to manufacture an off-axis paraboloid, it is necessary to generate a paraboloid having a diameter D including the axis as shown in FIG. 3, and it is not easy to polish because the curvature varies depending on the position of the mirror. . For this reason, the use of an off-axis parabolic mirror for the collimator has the disadvantage of extremely high costs.

[0005] A second approach is to use a spherical mirror for the collimator and make the focal length as long as possible. 1
If you try to convert light emitted from a point into parallel light with a spherical mirror,
Parallel errors occur due to spherical aberration. Here, the parallel error is the F number of the spherical mirror (the value obtained by dividing the focal length by the aperture).
Since it is inversely proportional to the square of, the parallel error can be reduced to a level that does not hinder practical use by increasing the focal length. Generally, if the F-number is set to 5 or more, the level becomes practically acceptable. However, increasing the focal length has the disadvantage of increasing the optical path length. In particular, in recent years, the area of the liquid crystal substrate has been increased, and the exposure size has to be about 1 m diagonally. In this case, the focal length is required to be 5 m, and the optical path length from the secondary light source to the exposure surface is as long as 10 m. Such an increase in the size of the apparatus not only increases the cost of the apparatus, but also increases the area occupied by an expensive clean room. Therefore, an object of the present invention is to provide an exposure optical system in which the parallelism of exposure light is improved without increasing the cost of the apparatus and without increasing the size of the apparatus.

[0006]

A light source 10 and a condensing means 2 are provided.
0, the secondary light source creating means 30, and the collimator 40, in the exposure optical system, the angle α at which the light ray A is emitted from the tangent plane 41 of the collimator 40 and the light ray B
The collimator 40 is elastically deformed so that the angle β emitted from the zero tangent plane 41 becomes equal. Here, the ray A is a principal ray on the optical axis that enters the collimator 40, and the ray B is a principal ray that passes off the optical axis and enters the collimator 40.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present embodiment is 740 mm × 620.
FIG. 1 shows an optical system for exposing a region of mm with ultraviolet light (main wavelength: 365 nm) having a uniform intensity. Reference numeral 10 denotes a light source. In this embodiment, an ultra-high pressure mercury lamp is used. However, a xenon mercury lamp or the like may be used depending on a photosensitive material applied on a substrate. Reference numeral 20 denotes a condensing unit, and an elliptical mirror is used in the present embodiment. In addition, the condensing means includes a spherical mirror, a condenser lens, and the like. Reference numeral 30 denotes a secondary light source creating means. In the present embodiment, it comprises a rod 31 and a lens 33.
The light condensed by the light condensing means 20 is input to the rod 31, and total reflection is repeated inside the rod 31, so that a uniform light intensity distribution is obtained on the emission end face 32. The lens 33 enlarges and projects the emission end surface 32 of the rod onto the exposure surface 60, thereby realizing exposure with a uniform illuminance distribution. The secondary light source creating means also includes a fly-eye lens as shown in FIG. This realizes a uniform illuminance distribution on the exposure surface 60 by dividing and superimposing a light beam.

As the collimator 40, a spherical mirror obtained by depositing aluminum on a glass material having a thickness of 8 mm is used. It is located 2.46 m from the secondary light source, has a focal length of 2.5 m and an aperture of 1000 mm × 820 mm. The off-axis angle is set at 28 degrees. In the present invention, since the parallelism of light rays is corrected by the elastic deformation of the collimator 40 as described later, the collimator does not need to use an expensive off-axis parabolic mirror. You don't have to. However, of course, the collimator is not limited to the spherical mirror, and the aspheric mirror may be elastically deformed. The mirror 50 is a plane mirror.

FIG. 5 shows the parallelism of light rays on the exposure surface 60 when the collimator 40 is a perfect spherical surface. The starting point of the arrow indicates the position on the exposure surface 60, and the direction of the arrow indicates the falling direction of the light beam. The length of the arrow indicates the parallelism with the optical axis. Due to the spherical aberration of the collimator 40 and the oblique incidence, the parallelism reaches 0.53 degrees at the worst, and the exposure position error cannot be ignored.

FIG. 6 shows the parallelism of light rays when the collimator 40 is elastically deformed into a shape as shown in FIG. FIG. 7 shows the deformation amount of the collimator 40, and it can be seen that the collimator 40 is deformed by about ± 1 mm from the original spherical surface. As shown in FIG. 6, the parallelism has been improved to a level that is not practically hindered, with the worst value being less than 0.2 degrees.

If the collimator 40 is put in a holder and pressure is applied to some places, elastic deformation as shown in FIG. 7 can be obtained relatively easily.

[0012]

According to the present invention, it is not necessary to off-axis the collimator and polish the paraboloid to improve the parallelism of the exposure light beam. Therefore, the cost of the exposure optical system can be reduced. Further, according to the present invention, it is not necessary to increase the focal length of the collimator to improve the parallelism of the exposure light beam. Therefore, the total optical path length of the exposure optical system can be shortened, and the floor area where the exposure apparatus is installed can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an exposure optical system according to the present invention.

FIG. 2 is a diagram illustrating that an error in the degree of parallelism of exposure light causes transfer deviation of a pattern.

FIG. 3 is a diagram illustrating an off-axis parabolic mirror.

FIG. 4 is a diagram illustrating a fly-eye lens.

FIG. 5 is a diagram illustrating a degree of parallelism of an exposure light with an optical axis when no correction is performed.

FIG. 6 is a diagram illustrating the parallelism with the optical axis of exposure light when the collimator 40 is elastically deformed.

FIG. 7 is a contour diagram showing a deformation amount of the collimator 40.

FIG. 8 is a diagram illustrating a conventional exposure optical system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light source 20 Condensing means 30 Secondary light source creation means 40 Spherical mirror 41 Tangential plane of a spherical mirror

Claims (1)

[Claims] 1. An exposure optical system comprising a light source 10, a condensing means 20, a secondary light source creating means 30, and a collimator 40, wherein an angle α at which a light ray A is emitted from a tangent plane 41 of the collimator 40 and a light ray B is emitted from the tangent plane 41 of the collimator 40 so that the angle β is substantially equal.
An exposure optical system wherein 0 is elastically deformed. Here, the ray A is a principal ray on the optical axis that enters the collimator 40, and the ray B is a principal ray that passes off the optical axis and enters the collimator 40.