JPH0594936A - Ring band lighting system - Google Patents

Abstract

PURPOSE:To sharpen the contrast of an image forming lens by the ring band lighting system. CONSTITUTION:The title lighting system is composed of a beam compressor 4 converting the beam diameter of a light source 1 and a light flux 2 emitted from the light source 1, a homogenizer 5 forming a ring band type secondary light source 6 and a focussing lens 7 lighting a mask with the ring band type secondary light source 6. The homogenizer 5 composed of fibers, etc., outputs ring band type light to circular input while the output end is turned into the secondary light source 6. Finally, the contrast of an image forming lens 9 can be sharpened by forming an image of the ring band type secondary light source 6 on an entrance pupil 10 of the image forming lens 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical apparatus of a mask pattern projection exposure apparatus used for manufacturing a semiconductor device such as an LSI.

[0002]

2. Description of the Related Art Conventionally, a light source of an illumination optical apparatus for projection exposure is a g-line having a wavelength of 436 nm emitted from a mercury lamp,
Using a 365 nm i-line or an excimer laser as a light source, the luminance distribution of the illumination light is made uniform, and a two-time light source is formed to form an image of the secondary light source on the entrance pupil of the imaging lens to improve the illumination efficiency. That is, as shown in FIG. 3, a light beam 2 supplied from a light source unit 1 including a light source and a condensing mirror is converted into a parallel light beam by a lens 31, and a plurality of condensing points are obtained by a homogenizer 32 including a plurality of lens elements. Is formed as a secondary light source, and the mask 8 installed on the irradiation surface is illuminated by the condenser lens 7. As such examples, Japanese Patent Laid-Open No. 2-170152 and Japanese Patent Laid-Open No. 64-7672
0, JP-A-63-80243, JP-A-61-26772
2, JP-A-63-73221 and the like.

In Japanese Patent Laid-Open No. 61-267722, the light flux from the mercury lamp is made uniform by an optical integrator (homogenizer) composed of microlenses. In Japanese Patent Laid-Open No. 63-80243, light from a light source is incident on a homogenizer by changing the shape of a light beam by a beam shaping optical system including an anamorphic lens. JP-A-6
In 4-76720, an image rotator is arranged between the light source and the integrator, and the image rotator is rotated during exposure to obtain a uniform exposure amount. JP-A-2
In -170152, an illuminance on the illuminated surface is made uniform by arranging an optical member having an angular transmittance characteristic on the illuminated side of the optical integrator and changing the tilt angle of the optical member with respect to the optical axis. JP-A-63-732
21 proposes a method in which an optical fiber having a different optical path length is used as a homogenizer for the purpose of eliminating the adverse effect of light interference, particularly speckle, when a laser is used as a light source. In both cases, the illuminance distribution of the illumination light source is made uniform and the illuminated object is illuminated efficiently.

On the other hand, the resolution of the optical system depends on the wavelength used and the numerical aperture (NA) of the imaging lens. In practice, partial coherent illumination is generally used to further increase the resolution. That is, the image of the secondary light source formed on the entrance pupil is smaller than the entrance pupil diameter of the imaging lens. By providing such illumination, the resolution is improved.

[0005]

SUMMARY OF THE INVENTION The present invention is a means for obtaining a uniform illuminance distribution and a resolution exceeding the resolution limit of an optical system. Partial coherent illumination is known as a method for obtaining the resolution limit of an optical system. Partial coherent illumination is a method of illuminating an image of a secondary light source formed on the entrance pupil of the imaging lens with a size smaller than the entrance pupil diameter, and can increase the contrast at low spatial frequencies. However, the contrast of high spatial frequencies becomes low on the contrary.
The principle of image formation by partially coherent illumination is described in, for example, Optics of Optical Equipment 2 (Japan Optomechatronics Association, P.
655, 1989).

There is an annular illumination as an illumination system for further improving the resolution. It is known that high frequency contrast is further improved by illuminating the entrance pupil of the imaging lens so as to form an annular shape. To achieve this, a ring-shaped mask may be installed at the position of the secondary light source, but the loss of light amount is large and it is not a good idea.

Therefore, the present invention has been made in view of the above problems, and an optical element for forming a two-dimensional ring-like shape, which is composed of an optical fiber or the like, is installed in a homogenizer, so that an even and uniform ring-like shape can be obtained. It is an object of the present invention to provide an illumination optical device for producing a three-dimensional light source.

[0008]

In order to achieve the above object, the present invention provides a light source for supplying a light flux, an optical element for equalizing the luminance distribution of an illumination light flux, and an optical element for illuminating an illuminated object. The optical element for uniformizing the intensity distribution of the luminous flux is composed of, for example, an optical fiber, and the output end face thereof is in the shape of an annular zone to form an annular secondary light source.

[0009]

According to the present invention, an optical element for making the luminance distribution of an illumination light beam uniform, that is, a light beam having a non-uniform light intensity distribution incident on the input end face of an optical fiber bundle which is a homogenizer, is output in an irregularly arranged annular shape. This is to improve the resolution of the optical system by efficiently illuminating the irradiated object as a ring-shaped secondary source having a more uniform light intensity distribution than the end face.

[0010]

1 is a diagram of an embodiment of the present invention. Light source 1
The emitted light beam 2 is reflected by a reflecting mirror 3, and the beam diameter can be changed by a beam compressor 4 which converts the light beam diameter into an appropriate size. A light beam having an appropriate beam diameter is made uniform by a homogenizer 5 which forms a ring-shaped secondary light source, and a ring-shaped secondary light source 6 is formed by its output end face 22. The ring-shaped secondary light source 6 illuminates the mask 8 with the condenser lens 7. The annular secondary light source 6 illuminates the mask 8 via the condenser lens 7, and then the entrance pupil plane 1 of the imaging lens 9.
At 0, the image is formed like a ring. The secondary light source 6 is an aggregate of point light sources, and the respective illumination light from the secondary light source 6 uniformly illuminates the image forming range of the mask 8 which is the surface to be illuminated through the condenser lens 7, and then, The light enters the image lens 9 and forms an image on the entrance pupil plane 10 of the imaging lens. Such an illumination system is called Koehler illumination. On the other hand, the image of the mask 8 is formed by the imaging lens 9
Is projected onto the wafer 11. As described above, the resolution is improved by performing the annular illumination based on the Koehler illumination. Katie Microelectronics Seminar Interface (KTI Micro
oelectronics seminar int
erface '89, p217), the effect is proved.

FIG. 2 is a schematic view of a homogenizer for producing a secondary light source having an annular shape. The input end face 21 is a circular optical fiber side, and the output end face 22 has a ring shape. Since the respective optical fibers on the input end face 21 are irregularly arranged on the output end face 22, the light flux having a non-uniform intensity distribution incident on the input end face 21 becomes a uniform annular secondary light source on the output end face 22. ..

[0012]

As described above, according to the present invention, the object surface is proved by the secondary light source in the shape of a ring having a uniform light intensity distribution, so that there is no loss of light quantity and the resolution limit of the optical system is exceeded. It is possible to configure an illumination optical system that can obtain a high resolution.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention with annular illumination.

FIG. 2 is a diagram of a homogenizer forming a ring-shaped secondary light source.

FIG. 3 is a diagram of a conventional illumination optical system.

[Explanation of symbols]

 1 Light Source 2 Luminous Flux 3 Reflector 4 Beam Compressor 5 Homogenizer 6 Secondary Light Source 7 Condenser Lens 8 Mask 9 Imaging Lens 10 Entrance Pupil 11 Wafer 21 Input End Face 22 Output End Face 31 Condenser Lens 32 Homogenizer

Claims (2)

[Claims] 1. An illumination optical apparatus having a light source for supplying a light flux, an optical element for making the intensity distribution of the light flux uniform, and an optical element for illuminating an illuminated object, wherein the intensity distribution of the light flux is uniform. An annular illuminating device, characterized in that the optical element for realizing the above is composed of an optical fiber, and the vicinity of the output end face is an annular secondary light source. 2. The annular lighting device according to claim 1, wherein
The optical fiber is an annular illuminating device characterized in that the optical fibers on the input end face are arranged irregularly with respect to the optical fibers on the output end face.