Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1999-02-16
2001-07-03
Wu, Shean C. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S311000, C430S312000, C430S314000, C430S323000, C430S394000, C430S313000, C430S396000
Reexamination Certificate
active
06255038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing a plurality of discrete arrays of sub-micron structures in a photoresist etch mask by interferometric or holographic lithography techniques; each of the arrays is bounded by regions not subjected to the interferometric lithography.
2. Discussion of the Prior Art
Holographic or interferometric lithography is now a proven technology for creating structures having sizes smaller than a micron in a continuous, two-dimensional, periodic array. For example, U.S. Pat. Nos. 4,402,571, and 4,496,216, to Cowan, et al. and U.S. Pat. No. 5,142,385, to Anderson et al., the entire disclosures of which are incorporated herein by reference, disclose methods and apparatus for producing a periodic and continuous surface relief pattern in a surface by exposing a photosensitive material to a laser interference fringe pattern and then developing the photosensitive material. Interferometric lithography exploits the mutual coherence of multiple optical beams derived from a single laser; the beams are overlapped in a selected region of space and interfere to produce patterns of light and dark areas, or fringe patterns, repeating on a scale proportional to the laser wavelength. The fringe patterns are recorded in photosensitive media such as photoresist. Conventional contact or projection photomasks are not required and so interferometric lithography has become known as “maskless” lithography.
Interferometric lithography has been used in a laboratory environment in attempting to produce a flat panel display having a distributed cathode; the display is known as a Field Emission Display (FED). A FED is a distributed cathode, flat panel analog to the well known Cathode Ray Tube (CRT) and can include billions of microscopic cathode electron ‘guns’ in an array distributed over the surface of a display substrate. Electrons emitted from the microscopic, cone shaped cathodes, under the influence of a large accelerating potential, strike a phosphor screen disposed opposite a common anode, and are thereby converted to photons (i.e., light). In making the cathode matrix in a FED, it has been discovered that the most critical fabrication step is patterning of an array of high resolution features such as holes or cathode emitter tips. In the prior art, a photosensitive medium such as photoresist was employed to record an image of a hole array formed by a conventional photolithographic technique such as contact printing with shadow masking techniques, optical projection, or electron beam writing. The array of holes in photoresist was then used as an etch mask in forming the emitter wells.
It would be desirable to use interferometric lithography in making an etch mask for fabricating FEDs, but the continuous nature of interferometric lithography fringe patterns is not suitable for use in an etch mask which must have cathode cone holes (or tips) only in preselected pixel or sub-pixel regions. In other technologies, a similar problem exists, for example, in making a Dynamic Random Access Memory (DRAM), Central Processing Unit (CPU) or a logic chip, high density patterns in an etch mask must be confined within or combined with other patterns for leadouts, contact vias or individual device area patterns. There is a need, therefore, for a method to selectively negate exposure to interferometric fringe patterns in areas outside selected regions such as the pixel region, but without a requirement for removing the photoresist. There is also a need for a method or process for making an etch mask for producing FEDs which requires the fewest number of process steps and which can be completed in the least amount of time, to satisfy economic requirements as dictated by the marketplace.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to overcome the above mentioned difficulties by providing a method for making an etch mask having a plurality of discontinuous and discrete arrays containing a high density of high resolution features created by interferometric lithography.
Another object of the present invention is providing an efficient and effective method for making an etch mask segmented in a selected number of discontinuous subareas in which high resolution interferometric lithography can be used to provide sub-micron sized structures.
The aforesaid objects are achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.
In accordance with the method of the present invention, patterns of sub-micron structures in a photoresist etch mask are produced by interferometric or holographic lithography techniques after image-wise exposure using photolithographically generated pattern overlays. In the first step, negative pattern overlays are used to create a plurality of sub-pixel regions of blocked or shaded photoresist bounded by a larger, rectangular region of exposed or illuminated photoresist. In the second step, the photoresist etch mask layer is chemically affected, either thermally or by flooding or immersion in a gaseous or liquid environment, such as saturation with ammonia vapor, thereby rendering the formerly exposed rectangular region of photoresist insensitive to further light exposure and insoluble in subsequent etching steps. In the third step, a sub-micron, high resolution light interference pattern is modulated or apertured in the photoresist layer etch mask, in situ, by the now insensitive, low resolution photoresist negative pattern, whereupon the light interference pattern causes periodic arrays of sub-micron exposed spots only in sub-pixel regions of the light sensitive photoresist. In the fourth step, the photoresist layer is chemically developed and the exposed spots are etched away, leaving a plurality of discrete (i.e., separate) periodic arrays of sub-micron holes in the etch mask.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, particularly when taken in conjunction with the accompanying drawings, wherein like reference numerals in the various figures are utilized to designate like components.
REFERENCES:
patent: 3591252 (1971-07-01), Lu
patent: 4037969 (1977-07-01), Feldman et al.
patent: 4104070 (1978-08-01), Moritz et al.
patent: 4402571 (1983-09-01), Cowan et al.
patent: 4440850 (1984-04-01), Paul et al.
patent: 4496216 (1985-01-01), Cowan
patent: 4789214 (1988-12-01), Vilhelmsson et al.
patent: 4839250 (1989-06-01), Cowan
patent: 4874213 (1989-10-01), Cowan
patent: 4888260 (1989-12-01), Cowan
patent: 5003567 (1991-03-01), Hawryluk et al.
patent: 5055383 (1991-10-01), Koblinger et al.
patent: 5142385 (1992-08-01), Anderson et al.
patent: 5176970 (1993-01-01), Hawryluk et al.
patent: 5178974 (1993-01-01), Hawryluk et al.
patent: 5216257 (1993-06-01), Brueck et al.
patent: 5334342 (1994-08-01), Harker et al.
patent: 5343292 (1994-08-01), Brueck et al.
patent: 5384464 (1995-01-01), DeFornel et al.
patent: 5415835 (1995-05-01), Brueck et al.
patent: 5430816 (1995-07-01), Furuya et al.
patent: 5705321 (1998-01-01), Brueck et al.
patent: 6027388 (2001-02-01), Jones et al.
patent: 6042998 (2000-03-01), Brueck et al.
C.O. Bozler, C.T. Harris, S. Rabe, D.D. Rathman, M.A. Hollis, and H.I. Smith, “Arrays of gated field-emitter cones having 0.32 um tip-to-tip spacing”, J. Vac. Sci. Technol. B 12(2), Mar./Apr. 1994, pp. 629-632.
C.A. Spindt, “Field Emitter Arrays for Vacuum Microelectronics”, IEEE Transactions On Electron Devices, vol. 38, No. 10, Oct. 1991, pp. 2355-2363.
Z. Huang, N.E. McGruer, and K. Warner, “200 nm Gated Field Emitters”, IEEE Electron Device Letters, vol. 14, No. 3, Mar. 1993.
J.W. Goodman, Introduction to Fourier Optics, McGraw-Hill, San Fran., 1968.
C.G. Bernhard, “Structural and functional adaptation in a visual system.”, Endeavor, 26
Optical Switch Corporation
Wu Shean C.
LandOfFree
Process for modulating interferometric lithography patterns... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for modulating interferometric lithography patterns..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for modulating interferometric lithography patterns... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2530113