Photocopying – Projection printing and copying cameras – With focusing or projection screen
Reexamination Certificate
2000-09-01
2002-07-23
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
With focusing or projection screen
C355S040000, C355S043000
Reexamination Certificate
active
06424404
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the use of microlens arrays for printing (including microlithography) and microscopy applications. The above-noted co-pending patent application (Ser. No. 08/803,096, hereafter '096) discloses an imaging system comprising a microlens array that is used to either project an image onto a printing surface, or to acquire an image of an imaging sample surface, by scanning the surface across the microlens array's focal plane. There are advantages to using very small (e.g., micron-scale) microlenses for such applications. For example, the microlenses' focusing resolution may be limited by chromatic dispersion and by the size of the illumination source (if an extended source such as an arc lamp is used), but the effect of these factors can be mitigated by using small microlenses. (If the microlenses are sufficiently small these factors become insignificant and focusing resolution is dominated by diffraction.) If the microlens material has significant optical absorption over the operating wavelength range, it would also be advantageous to use small microlenses in order to minimize the absorption loss. However, very small microlenses cannot easily be formed without incurring significant fill factor losses. The microfabrication processes may not be able to produce accurately profiled lens surfaces if the microlens apertures are closely juxtaposed. The structure supporting the microlenses can also take up a lot of space between microlenses (particularly if the structural material is not optically transparent and has open light transmission channels). Furthermore, if the microlens array is integrated with electronic or micromechanical components (e.g., surface proximity sensors or microlens focus actuators), the space required to accommodate these elements can also significantly limit the lens fill factor.
SUMMARY OF THE INVENTION
The invention comprises a plurality of compound lenses, wherein each compound lens preferably comprises two microlens elements, which are designated as a “first-stage” microlens L
1
and a “second-stage” microlens L
2
. L
1
is a comparatively large, low-power element which focuses incident illumination onto L
2
, and L
2
is a much smaller, higher-power element which focuses the illumination onto a highly-resolved focal point on or close to an imaging sample or a printing surface. (In a microscopy application, the compound lens also functions to collect reflected or back-scattered radiation from the focal point.) The L
1
elements are closely juxtaposed to achieve a high fill factor, whereas the L
2
elements, being much smaller, cover a much smaller area fraction on the L
2
aperture plane. Thus, this design configuration provides sufficient clearance space between the second-stage elements to accommodate sensors, actuators, data paths, or structural elements without incurring significant fill-factor-related efficiency losses.
More generally, each compound lens could comprise N microlens elements L
1
, L
2
, . . . L
N
(N being an integer greater than 1), wherein each element L
m
(1≦m<N) focuses the illuminating radiation onto the next element L
m+1
in the sequence and the last element L
N
focuses the radiation onto a focal point on or close to the imaging sample or printing surface. (This focal point is referred to as the compound lens's “terminal focal point” and element L
N
is referred to as the “terminal lens element”.) Typically, L
1
is a comparatively large element with low optical power, and the succeeding elements are progressively smaller and have progressively higher optical power. (The “focusing” action of the microlenses is more analogous to that of a condenser lens than of an imaging lens, in that each microlens functions to condense incident illuminating radiation onto a target illumination spot. Unlike conventional imaging systems, the microlenses do not necessarily have well-defined focal planes, or if they do they need not operate at exactly their design focal lengths.)
The invention could be especially useful when used in conjunction with focus-actuated microlenses. In this embodiment, each terminal microlens element is formed on a flexible layer that is supported over a substrate, and the microlens's focus position is controlled by means of electrostatic interaction between conductors on the layer and on the substrate. A single-stage array of microlenses of this type would incur significant fill factor losses associated with the focus actuator mechanism and control circuitry, but the multi-stage configuration circumvents this limitation. Focus-actuated microlenses could be used in lithography applications to perform conformal lithographic printing on complex surface topographies, thus reducing the need for planarization in semiconductor wafer processing. For microscopy applications, focus-actuated microlenses could make it possible to perform high-resolution, conformal imaging on three-dimensional surface topographies.
Any of the single-stage microlens printing and microscopy systems disclosed in the '096 application (or other cross-referenced applications) could be adapted for use with the present invention by replacing the single-stage microlens array with a multi-stage microlens array, such as (for example) the focus-actuated array described above.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specificationa and the drawings.
REFERENCES:
patent: 5517279 (1996-05-01), Hugle et al.
patent: 5631721 (1997-05-01), Stanton et al.
patent: 5982552 (1999-11-01), Nakama et al.
patent: 6016185 (2000-01-01), Cullman et al.
patent: 6133986 (2000-10-01), Johnson
patent: WO 97/34171 (1997-09-01), None
patent: WO 98/12603 (1998-03-01), None
Davidson, Mark, “A Microlens Direct-Write Concept for Lithography,” SPIE vol. 3048, pp. 346-355 (1977).
Völkel, R. et al., “Microlens lithography,” Conference: 1996 Display Manufacturing Technology Conference, Digest of Technical Papers, First Edition, pp. 95-96 (Publisher: Soc. Inf. Display, Santa Ana, Ca).
Völkel, R. et al., “Microlens array imaging system for photolithography,”Opt. Eng.35(11) (Nov. 1996); pp. 3323-3330.
Völkel, R. et al., “Microlens lithography: A new approach for large display fabrication,”Microelectronic Engineering30 (1996); pp. 107-110.
Völkel, R. et al., “Microlens lithography and smart masks,”Microelectronic Engineering35 (1997); pp. 513-516.
Adams Russell
Nguyen Hung Henry
Townsend and Townsend / and Crew LLP
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