Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-03-17
2001-05-22
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C362S268000, C362S551000, C362S553000
Reexamination Certificate
active
06236449
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an illumination optical apparatus and an exposure apparatus provided with the illumination optical apparatus, and more particularly relates to illumination optical apparatus employing light pipe optical integrators.
BACKGROUND OF THE INVENTION
Japanese Patent Application Kokai No. Hei 8-6175 discloses an illumination optical apparatus suited to exposure apparatus for manufacturing semiconductor devices. This illumination optical apparatus uses an internal reflection, elongate (i.e., rod-type) optical integrator to form a plurality of light source images from a primary light beam from a light source. Such integrators are referred to in the art as “light pipes” and so this term is used hereinafter.
The above-mentioned prior art illumination optical apparatus includes a condenser lens which condenses the primary light beam onto the incident surface of the integrator. This beam is then split by internal reflection within the light pipe into a plurality of secondary light beams. These secondary light beams proceed in predetermined angular directions based on the geometry of the integrator. A plurality of light source images (i.e., virtual light sources) associated with the plurality of secondary light beams are formed along the plane of the incident surface of the integrator. The plurality of secondary light beams, each appearing to emanate from a corresponding light source image, pass through a condenser lens and illuminate a surface to be irradiated, such as a mask.
The increasing degree of integration of semiconductor devices has lead to the commercialization and development of excimer lasers and other intense light sources for use in exposure apparatus for manufacturing semiconductor devices. Excimer lasers, for example, operate at an oscillation wavelength of 248 nm or 193 nm and have a high power output. Accordingly, conventional illumination optical apparatus, such as discussed immediately above, are not generally amenable for use in an exposure apparatus employing such a high-output light source. This is because a light pipe formed of glass material is prone to breaking due to the concentration of light energy at a convergence point formed on the incident surface of the integrator.
SUMMARY OF THE INVENTION
The present invention relates to an illumination optical apparatus and an exposure apparatus provided with the illumination optical apparatus, and more particularly relates to illumination optical apparatus employing light pipe optical integrators.
The present invention takes the abovementioned problems into consideration, and has the goal of providing an illumination optical apparatus wherein the integrator is not prone to breaking when used with a high-output light source like an excimer laser. A further goal is to provide an exposure apparatus provided with the aforesaid illumination optical apparatus.
Accordingly, a first aspect of the present invention is an illumination optical apparatus for illuminating an illumination surface. The apparatus comprises, in order along an optical axis, a light source capable of providing a primary light beam having a cross-section, and a condenser optical system to condense the primary light beam so as to form a convergence point adjacent the condenser optical system. Adjacent the condenser optical system is a light-pipe optical integrator having a rectangular cross-sectional shape with a first side of length dx, a second side of length dy, and a most light-source-wise incident surface axially spaced from the convergence point by a spacing L. The integrator is capable of forming a plurality of secondary light sources and corresponding secondary light beams from the primary light beam. Adjacent the light pipe optical integrator is an imaging optical system to converge the primary and secondary light beams to illuminate the illumination surface. The following conditions are also preferably satisfied:
0.1≦L≦dx/(2×tan &agr;x)
0.1≦L≦dy/(2×tan &agr;y),
wherein &agr;x is an angle of the primary light beam incident the incident surface, as measured in a first plane that includes the optical axis, and &agr;y is an angle of the primary light beam incident the incident surface, as measured in a second plane orthogonal to the first plane.
A second aspect of the present invention is the optical apparatus as described above, further including first and second variable optical members capable of shaping the primary light beam cross-section so as to make this cross-section and the integrator cross-section have a substantially similar size and shape.
A third aspect of the present invention is an exposure apparatus for exposing a pattern present on a mask onto a photosensitive substrate. The exposure apparatus comprises, in order along an optical axis, the illumination optical system as described above, and a projection optical system arranged adjacent the illumination surface so as to project an image of the mask arranged at the illumination surface to expose the mask pattern onto the photosensitive substrate.
A fourth aspect of the invention is a method of uniformly illuminating a surface with an illumination optical apparatus having a light pipe optical integrator with a cross-section, an incident surface and an exit surface. The method comprises the steps of first providing a primary light beam having a primary light beam cross-section, then condensing the primary light beam and forming a convergence point at a position spaced apart from the incident surface, then collecting light emanating from the convergence point at an angle &agr; using the light pipe optical integrator, then forming a plurality of secondary light sources and associated secondary light beams by multiply internally reflecting the light within the light pipe optical integrator, and then finally converging the primary and secondary light beams emanating from the exit surface so as to uniformly illuminate the illumination surface.
REFERENCES:
patent: 4744615 (1988-05-01), Fan et al.
patent: 4918583 (1990-04-01), Kudo et al.
patent: 5059013 (1991-10-01), Jain
patent: 5357312 (1994-10-01), Tounai
patent: 5675401 (1997-10-01), Wangler et al.
patent: 5757470 (1998-05-01), Dewa et al.
patent: 6067146 (2000-05-01), Mulkens et al.
Mathews Alan A.
Nikon Corporation
Oliff & Berridg,e PLC
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