Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-03-15
2001-08-28
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S071000, C355S077000, C430S396000, C250S492200, C250S492220
Reexamination Certificate
active
06281967
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an illumination apparatus and exposure apparatus and method employing this to form a desired illumination distribution by condensing light from a light source, and in particular relates to an illumination apparatus etc. that is ideal for illumination of a mask for exposing minute semiconductor circuitry on a photosensitive substrate.
BACKGROUND OF THE INVENTION
Conventionally, in illumination apparatus of this type, a plurality of secondary light sources are formed by for example a rod-type optical integrator, and uniform illumination of a mask on which is described a circuit pattern is performed by utilizing the illumination from these secondary light sources. The illuminated circuit pattern is projected onto and exposes a wafer coated with photosensitive material, through a projection lens.
Recently also, attention has been attracted by a technique for improving the resolving power and depth of focus of the optical projection system of the exposure apparatus by altering the pupil shape of the illumination light by changing the shape of aperture stops which are arranged in conjugate positions of the two-dimensional light source, in accordance with the shape of the pattern that is projected onto the wafer.
In an illumination device as above, it is generally considered that the illumination distribution on the mask i.e. the illumination distribution on the wafer when no pattern is formed on the mask should be in a uniform condition; however, due to various causes such as contamination or eccentricity of the optical system or unevenness of the anti-reflective coating, if non-uniformity of the illumination distribution on the wafer is found, more precise exposure can be achieved by adjusting the illumination distribution so as to compensate for this. Furthermore, in some cases, better results are obtained by deliberately providing a distribution of the illumination on the wafer, depending on the shape of the pattern on the mask, and/or aberration of the projection lens, or the pupil shape of the illuminating light etc.
Likewise, although it is generally considered that the pupil shape of the illuminating light should be the same shape for all image heights on the wafer, sometimes better results are obtained by deliberately arranging for different pupil shapes for different image heights.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an illumination apparatus and exposure apparatus and method using this whereby the illumination distribution on the mask or wafer can be compensated to a desired distribution, and wherein the pupil shape (coherence factor) of the illuminating light can be independently altered for various image heights on the wafer.
In order to solve the above problem, an illumination apparatus as claimed in the invention comprises: a rod-type optical integrator forming a large number of light source images from the light from a light source; a relay optical system that illuminates a surface to be illuminated, by respectively condensing light from said large number of light source images formed by the rod-type optical integrator; and illumination control means that respectively independently control the intensity distribution of the light in the large number of light source images, being arranged on the light source side of the rod-type optical integrator.
Since, with the illumination apparatus described above, the optical intensity distributions at a large number of light source images are respectively independently controlled by illumination control means arranged on the light source side of a rod-type optical integrator, the condition of the light that is supplied to the illuminated surface from the light source images can be easily and precisely controlled. Consequently, illumination conditions such as the illumination distribution and/or the pupil shape over the illuminated surface can be regulated to the desired condition. In this context, the meaning of the term “optical intensity distribution” includes both changing the absolute quantity of the intensity and changing the distribution condition.
Also, in a preferred mode, a condensing optical system that directs light through the illumination control means to the rod-type optical integrator is arranged between the illumination control means and the rod-type optical integrator; the illumination control means include an optical filter that controls the transmittance distribution of the light from the large number of light source images respectively independently; and the optical filter is provided in a position that is substantially optically conjugate with the surface to be illuminated, in relation to the condensing optical system, the rod-type optical integrator and relay optical system.
With the illumination apparatus described above, light corresponding to a large number of light source images has its transmittance distribution respectively individually adjusted by passing through the optical filter of the illumination control means, and is easily individually input to the rod-type optical integrator by the condensing optical system, so adjustment of the illumination condition at the surface to be illuminated is easy.
An exposure apparatus as claimed in the invention comprises: a rod-type optical integrator forming a large number of light source images from the light from a light source; a relay optical system that illuminates a mask, by respectively condensing light from the large number of light source images formed by the rod-type optical integrator; a projection system that projects the pattern of the mask onto a photosensitive substrate; and illumination control means that respectively independently control the intensity distribution of the light in the large number of light source images, being arranged on the light source side of the rod-type optical integrator.
With an exposure apparatus as described above, since the illumination control means respectively independently controls the intensity distribution of the light in a large number of light source images, being arranged on the light source side of the rod-type optical integrator, illumination conditions over the surface to be illuminated, such as the illumination distribution and/or the pupil shape, can be adjusted to the desired conditions, making it possible to achieve exposure which is more precise and matches the circumstances.
A method of exposure as claimed in the invention comprises: an optical control step wherein the intensity distribution of the light in a large number of light source images on the light source side of a rod-type optical integrator is independently controlled using this rod-type optical integrator, which forms a large number of light source images from the light from a light source; a step of illuminating a mask by respectively condensing light from the large number of light sources whose optical intensity distribution is respectively independently controlled by this optical control step; and an exposure step of exposing the pattern of the mask onto a photosensitive substrate.
With this exposure method, in the optical exposure step, the optical intensity distribution of the large number of light source images is respectively independently controlled at the light source side of the rod-type optical integrator, so illumination conditions over the surface to be illuminated such as the illumination distribution and/or pupil shape can be adjusted to the desired condition, enabling exposure to be achieved which is more precise and in accordance with the circumstances.
REFERENCES:
patent: 4918583 (1990-04-01), Kudo et al.
patent: 5646715 (1997-07-01), Wangler
patent: 5675401 (1997-10-01), Wangler et al.
patent: 5815248 (1998-09-01), Nishi et al.
patent: 6127095 (2000-10-01), Kudo
Adams Russell
Brown Khaled
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Nikon Corporation
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