Optical: systems and elements – Compound lens system – With curved reflective imaging element
Reexamination Certificate
1999-01-27
2001-02-27
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Compound lens system
With curved reflective imaging element
C359S859000, C359S861000, C359S851000, C359S853000, C355S067000, C378S035000
Reexamination Certificate
active
06195201
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a condenser and illumination systems for projecting the image of a reticle onto a photosensitive substrate as used in photolithography in semiconductor manufacturing, and more particularly to a condenser suitable for use in the extreme ultraviolet or soft X-ray wavelengths having reflective fly's eyes, faceted mirror, or mirror arrays for forming a desired irradiance and desired angular distribution, pupil fill, or radiant intensity.
BACKGROUND OF THE INVENTION
Photolithography is often used in the manufacture of many devices and in particular, electronic or semiconductor devices. In a photolithographic process, the image of a reticle or mask is projected onto a photosensitive substrate. As the element or feature size desired to be imaged on the photosensitive substrate becomes ever smaller, technical problems often arise. One of these problems is illuminating the reticle or mask so that its image can be projected onto the photosensitive substrate. As the element or feature size of semiconductor devices become ever smaller, there is a need for photolithographic systems providing a resolution of less than 0.13 micrometers. In order to achieve the imaging of these relatively small element or feature sizes, shorter wavelengths of electromagnetic radiation must be used to project the image of a reticle or mask onto the photosensitive substrate. Accordingly, it is often necessary for photolithographic systems to operate at the extreme ultraviolet wavelengths, below 157 nanometers, and into the soft X-ray wavelengths, around 1 nanometers. Additionally, projection optics having the required resolution and imaging capabilities often result in utilization of a portion of a ring field. One such projection optic system used in photolithography is disclosed in U.S. Pat. No. 5,815,310 entitled “High Numerical Aperture Ring Field Optical Reduction System” issuing to Williamson on Sep. 29, 1998, which is herein incorporated by reference in its entirety. While the projection optic system disclosed therein can achieve a working resolution of 0.03 microns, there are few illumination sources or illumination systems that can provide the required illumination properties for projecting the image of the reticle or mask onto the photosensitive substrate. An illuminating system is disclosed in U.S. Pat. No. 5,339,346 entitled “Device Fabrication Entailing Plasma-Derived X-Ray Delineation” issuing to White on Aug. 16, 1994. Therein disclosed is a condenser for use with a laser-pumped plasma source having a faceted collector lens including paired facets, symmetrically placed about an axis. Another illumination system is disclosed in U.S. Pat. No. 5,677,939 entitled “Illuminating Apparatus” issuing to Oshino on Oct. 14, 1997. Therein disclosed is an illumination system for illuminating an object in an arcuate pattern having a reflecting mirror with a parabolic-toric body of rotation and a reflection type optical integrator having a reflecting surface for effecting the critical illumination in the meridoinal direction and a reflecting surface for effecting the Kohler illumination in the sagittal direction. Another illuminating system is disclosed in U.S. Pat. No. 5,512,759 entitled “Condenser For Illuminating A Ring Field Camera With Synchrotron Emission Light” issuing to Sweatt on Apr. 30, 1996, which is herein incorporated by reference in its entirety. Therein disclosed is a condenser comprising concave and convex spherical mirrors that collect the light beams, flat mirrors that converge and direct the light beams into a real entrance pupil of a camera, and a spherical mirror for imaging the real entrance pupil through the resistive mask and into the virtual entrance pupil of the camera. Another illumination system is disclosed in U.S. Pat. No. 5,361,292 entitled “Condenser For Illuminating A Ring Field” issuing to Sweatt on Nov. 1, 1994. Therein disclosed is a condenser using a segmented aspheric mirror to collect radiation and produce a set of arcuate foci that are then translated and rotated by other mirrors so that all the arcuate regions are superposed at the mask. Another illumination system is disclosed in U.S. Pat. No. 5,631,721 entitled “Hybrid Illumination System For Use in Photolithography” issuing to Stanton et al on May 20, 1997, which is herein incorporated by reference in its entirety. Therein disclosed is a multi-image optical element, a condenser, and an array or diffractive optical element.
However, these prior illumination systems may not provide the desired illumination and are relatively complicated. Additionally, many of these systems are relatively large, having many surfaces resulting in loss of energy. Some are also difficult to align and may require adjustment.
Accordingly, there is a need for an improved illumination system and condenser for use in the extreme ultraviolet that provides a desired irradiance over a predetermined field or area with a desired irradiance and angular distribution, pupil fill, or radiant intensity for use in photolithography.
SUMMARY OF THE INVENTION
The present invention is directed to an illumination system and particularly a condenser for use in the extreme ultraviolet spectrum that provides a desired illumination. A reflector collects electromagnetic radiation from a source and directs it to a first reflective fly's eye, faceted mirror, or mirror array. The first reflective fly's eye or mirror array has elements or facets preferably having an arcuate shape. The first reflective fly's eye or mirror array has a plurality of individual elements or facets having surface deviations on top of a base surface resulting in a desired irradiance and desired angular distribution, pupil fill, or radiant intensity at a second reflective fly's eye, faceted mirror, or mirror array. The second reflective fly's eye or mirror array is positioned to receive the electromagnetic radiation from the first reflective fly's eye or mirror array. The desired radiant intensity having a desired shape is relayed to a reticle for projection onto a photosensitive substrate.
Accordingly, it is an object of the present invention to provide a desired illumination to a reticle for projection onto a photosensitive substrate.
It is an advantage of the present invention that an arcuate shaped illumination field is formed.
It is a further advantage of the present invention that a desired irradiance and desired radiant intensity or pupil fill is obtained.
It is yet a further advantage of the present invention that uniformity may be adjusted by varying the number of facets and adjusting the size of illumination received.
It is yet a further advantage that radiant intensity at the illumination field may be modified by varying the correlation between facets or the size, shape, and position of facets.
It is a feature of the present invention that a generally concave first reflective fly's eye or mirror array having arcuate facets is imaged by a second reflective fly's eye or mirror array.
It is a further feature of the present invention that a generally convex second reflective fly's eye or mirror array having facets with each facet having a surface deviation forms a desired irradiance and desired radiant intensity at an illumination field.
It is yet a further feature of the present invention that the power of the facets may be modified to obtain the desired illumination field.
These and other objects, advantages, and features will become readily apparent in view of the following detailed description.
REFERENCES:
patent: 5339346 (1994-08-01), White
patent: 5361292 (1994-11-01), Sweatt
patent: 5512759 (1996-04-01), Sweatt
patent: 5581605 (1996-12-01), Murakami et al.
patent: 5631721 (1997-05-01), Stanton et al.
patent: 5677939 (1997-10-01), Oshino
patent: 5815310 (1998-09-01), Williamson
patent: 0 939 341 A2 (1999-09-01), None
patent: 0 955 641 A1 (1999-11-01), None
Jenkins and Winston, Tailored Reflectors for Illuminators, Apr. 1, 1996, Applied Optics vol. 35, No. 10, pp. 16
Koch Donald G.
Kunick Joseph M.
McGuire James P.
Assaf Fayez
Fattibene Arthur T.
Fattibene Paul A.
Fattibene & Fattibene
Schuberg Darren
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