Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-01-11
2001-10-09
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S044000, C359S291000, C359S572000
Reexamination Certificate
active
06301000
ABSTRACT:
BACKGROUND OF THE INVENTION
Micromechanically-actuated reflectors are used as optical phase-shifting elements in several types of spatial light modulators, which function as image generators for applications such as image displays, printing, and maskless lithography. For example, the “Deformable Mirror Light Modulator” described in U.S. Pat. No. 4,441,791, and the “Enhanced Surface Deformation Light Modulator”, U.S. Pat. No. 5,493,439, employ deformable membrane mirrors as light-modulating elements. Another prior-art device in this category, the “Flat Diffraction Grating Light Valve”, U.S. Pat. No. 5,841,579, uses interdigitated groups of alternately fixed and movable ribbon reflectors to form a dynamically variable diffraction grating. Advantages of the grating light valve are that it can operate under high illumination levels and at very high (e.g., megahertz-level) switching rates, and it can be used with broadband illumination. This type of modulator is especially well adapted for display applications, but membrane-type modulators could have advantages for applications that require small pixels and very accurate control of the mirror deflection. For example, DUV lithography (at a 193 nm wavelength) would require maximum deflection amplitudes of approximately 50 to 75 nm, and at EUV wavelengths (e.g., 13 nm) the deflection amplitude would be only 3 to 5 nm. Modem film deposition technology can form membranes such as nitride film membranes with atomic-scale thickness control, making it possible to achieve very precisely-controlled membrane deflection characteristics for DUV or possibly EUV operation. Also, a membrane modulator pixel can be formed as a single, continuous reflector surface, in contrast to the grating light valve, which typically comprises six ribbon reflectors per pixel.
SUMMARY OF THE INVENTION
This invention is an improved light-modulating pixel device, termed a “dual-flexure light valve” (DFLV), which comprises a flexible reflective surface that is electrostatically actuated to alter its shape and thereby phase-modulate reflected light. (In this context the term “light” connotes electromagnetic radiation, which could include DUV or EUV radiation.) An array of such pixels forms a spatial light modulator which functions in conjunction with an imaging system that images the array onto a conjugate image plane. (A printing surface might, for example, be disposed in the image plane.) When the pixel surface is flat, reflected light is efficiently transmitted to a conjugate image point on the image plane. When it is flexed, the pixel acts as a diffracting element, causing the reflected light to be angularly dispersed. A projection aperture in the imaging system filters out the diffracted light; thus a pixel's conjugate image point will appear dark when the pixel is in its flexed state. The pixels could operate as binary-state (ON/OFF) modulators, or they could alternatively operate over a range of deflection levels to provide grayscale intensity control at each conjugate image point.
Each pixel comprises two adjacent flexure regions which operate conjunctively to phase-modulate reflected radiation. An advantage of this dual-flexure design is that the design geometry can be configured so that the diffraction-limited electromagnetic field amplitude over the projection aperture has substantially zero-amplitude nodes at or near the aperture edges, and the edge amplitude remains substantially zero over the full flexure modulation range. (If only a single flexure was used the field amplitude at the aperture edges would tend to increase as the amplitude at the center of the aperture decreases, and the achievable image contrast would be very poor.)
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Choksi et al., “Maskless extreme ultraviolet lithography,”J. Vac. Sci. Technol.B 17(6), Nov./Dec. 1999, pp. 3047-3051.
Folta, J.A. et al., “High density arrays of micromirrors,” Feb. 1999, pp. 1-9 (UCRL-ID-133164/National Technical Information Service,US Dept. of Commerce, Springfield, VA 22161).
Adams Russell
Nguyen Hung Henry
Townsend and Townsend / and Crew LLP
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