Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-04-09
2001-01-23
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S001000, C355S044000, C359S009000, C359S291000, C359S572000, C346S066000
Reexamination Certificate
active
06177980
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to what can be broadly categorized as “image writing.” The invention's primary intended application for image writing would be as a microlithography printer for semiconductor manufacture; however this field may also include applications such as document printing, photographic reproduction, etc.
The following references are hereby incorporated by reference in their entirety for all purposes:
Ref. 1: “Microlens Scanner for Microlithography and Wide-Field Confocal Microscopy” (U.S. patent application Ser. No. 08/803,096; PCT Serial No. PCT/US97/02949; filed Feb. 20, 1997)
Ref. 2: “Method of Making and an Apparatus for a Flat Diffraction Grating Light Valve” (U.S. Pat. No. 5,661,592, issued Aug. 26, 1997)
Ref. 3: “Flat Diffraction Grating Light Valve” (U.S. Pat. No. 5,841,579, issued Nov. 24, 1998)
Ref. 1 proposed the use of a Digital Micromirror Device (DMD, manufactured by Texas Instruments) as a spatial light modulator for a maskless lithography system. The DMD is manufactured in a megapixel (10
6
pixel) configuration and has a mechanical switching time of 20 microseconds; hence the maximum achievable data rate would be 50·10
9
bits per sec per DMD unit (i.e. 50 KHz per pixel times 10
6
pixels). Compared to commercial laser writing systems this is a very high rate, but for wafer production applications much higher throughput would be required. Assuming a minimum feature resolution of 0.1 &mgr;m, a typical 200-mm wafer can have on the order of 3·10
12
resolvable feature elements. The wafer design would require a grid snap significantly smaller than the minimum resolvable spot size; hence the number of image data bits per 200-mm wafer would typically exceed 3·10
13
. Commercial lithography steppers achieve throughput levels on the order of 100 wafers per hour, so a competitive maskless lithography system would need to write at least 100·3·10
13
image bits per hour, which translates to a data rate of about 1 THz (i.e. 10
12
bits per sec).
One method proposed in Ref. 1 to boost throughput would be to operate several DMD units in parallel, but to achieve a 1 THz pixel rate this would require about 20 megapixel DMD units, each with its own associated optics, servo control, and image generation electronics. A more practical and economical approach to improving throughput would be to use a faster spatial light modulator.
SUMMARY OF THE INVENTION
The invention provides imaging systems and techniques that circumvent the tradeoff between image resolution and field size which is the source of much of the complexity and expense of conventional wide-field, high-NA microlithography systems.
In short, this is achieved by using a comparatively low-resolution image projection system in conjunction with a microlens array comprising miniature lens elements. The projection system contains a small aperture stop which is imaged by the microlenses onto an array of diffraction-limited microspots on the printing surface at the microlens focal point positions, and the surface is scanned to build up a complete raster image from the focal point array. An image source includes an array of light-modulating image source elements.
In specific embodiments, the image projection system has a very small numerical aperture but large image field, while each microlens has a large numerical aperture but very small field.
High throughput can be achieved by using a spatial light modulator similar to the Grating Light Valve (GLV, manufactured by Silicon Light Machines in Sunnyvale, Calif.; Ref's. 2, 3). Like the DMD, the GLV is a microelectromechanical system that modulates image pixels by means of mechanically actuated microscopic mirror elements. But rather than tilting the mirrors, the GLV imparts a slight translational motion to the mirrors in order to induce a phase shift in portions of the reflected beam. It functions essentially as a dynamically variable diffraction grating, rapidly modulating the amount of light that is directed into the zero diffracted order. The GLV's switching time is just 20 nanoseconds; hence a megapixel GLV unit could achieve a data rate well in excess of 1 THz.
REFERENCES:
patent: H1525 (1996-04-01), Geil et al.
patent: 2830866 (1958-04-01), Warner
patent: 5170269 (1992-12-01), Lin et al.
patent: 5450157 (1995-09-01), Rees
patent: 5661540 (1997-08-01), Kaihotsu et al.
patent: 5661592 (1997-08-01), Bornstein et al.
patent: 5841579 (1998-11-01), Bloom et al.
Adams Russell
Bindingnavele R
Townsend and Townsend / and Crew LLP
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