Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-02-18
2003-05-13
Marcheschi, Michael (Department: 1755)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S346000, C430S296000, C430S013000, C430S325000, C430S321000, C430S322000, C430S323000, C501S013000, C501S056000, C501S065000, C501S067000, C501S069000, C501S072000
Reexamination Certificate
active
06562523
ABSTRACT:
BACKGROUND OF THE INVENTION
U.S. Pat. Nos. 4,567,104; 4,670,366; 4,894,303; and 5,078,771 and 5,285,517, all of inventions of Che-kuang Wu, described High Energy Beam Sensitive glass (HEBS-glass) articles exhibiting insensitivity and/or inertness to actinic radiation, the HEBS-glass articles which are darkened and/or colored within a thin surface layer of about 0.1-3 &mgr;m upon exposure to a high energy beam, electron beam, and ion beams in particular, without a subsequent development step, and which need no fixing to stabilize the colored image, since both the recorded image and the glass article are insensitive to radiation in the spectral range of uv and longer wavelengths. These patents are concerned with Ag+ ion-exchanged glass articles having base glass within alkali metal silicate composition fields containing at least one of the oxides of transition metals which have one to four d-electrons in an atomic state. The base glass composition can be varied widely, spontaneous reduction as well as photo-reduction of Ag+ ions are inhibited and/or eliminated due to the presence of said transition metal oxides in the glass article. The HEBS-glass is suitable for use as recording and archival storage medium and as phototools. The recorded images and/or masking patterns are up-datable, can be any single color seen in the visible spectrum, and is erasable by heat at temperatures above about 200° C. Heat erasure mode of recording in the high energy beam darkened glass article using a high intensity light beam, focused laser beam in particular, was also described.
Diffractive optics technology is maturing see for example, the publication by C. W. Chen and J. S. Anderson, “Imaging by diffraction: grating design and hardware results,” in Diffractive and Miniaturized Optics, S. H. Lee, ed., Vol. CR49 of SPIE Critical Reviews Series (Society of Photo-Optical Instrumentation Engineers,. Bellingham, Wash., 1993) pp. 77-97. Diffractive Optical Elements (DOE's) of various designs have been found useful for improving the design and performance of optical systems. Instead of using the binary method, such as described in “Binary Optics Technology: The Theory and Design of Multi-level Phase Diffractive Optical Elements” by G. J. Swanson of MIT, documented in MIT Tech. Rep. 854. (MIT, Cambridge, Mass., 1989), a cost-effective way of fabricating large numbers of DOE's in the shortest possible turnaround time has become increasingly important. Gray scale mask fabrication methods offer these features by drastically reducing the amount of processing steps involved to generate a multilevel and monolithic DOE. Currently multiplexing schemes exist to fabricate a quasi-gray-scale mask by changing the number of area of openings in a binary mask (similar to the halftone method) or by photographic emulsions. These approaches were described by Y. Opplinger etal in Microelcetron Eng. 23, 449-454 (1994) and by H. Anderson etal in Appl. Opt. 29, 4259-4267 (1990). Other methods of fabrication of gray-scale masks involve the cumberstone task of multiple binary exposures and following evaporation steps such as described by W. Daschner, etal in J. Vac. Sci. Technol. B 13, 2729-2731 (1995). The High Energy Beam Sensitive (HEBS) glass of the present invention offers the advantage of a one-step fabrication of a true gray-scale masks.
SUMMARY OF THE INVENTION
Since there is no graininess, HEBS-glass is capable of resolution to molecular dimensions. HEBS-glass turns dark instantaneously upon exposure to an electron beam, the more electron dosage the more it darkens. Therefore, HEBS-glass is ideally suited for making gray level masks. HEBS-glass gray level masks can be written with an e-beam writer using a 0.1 &mgr;m addressing grid size. Every 0.1 &mgr;m spot in the 5″×5″ HEBS-glass plate acquires a predetermined transmittance value ranging from 100 percent down to less than 0.1 percent upon e-beam patterning with a predetermined dosage for each address. A gray level mask made of HEBS-glass do not rely on a half tone method. Therefore, it is a true gray level mask.
It is the objective of the present invention to design HEBS-glass compositions so that the HEBS-glass gray level mask of the present invention facilitates new designs and low cost manufacturing processes for high-performance diffractive optics; asymmetric, irregularly shaped microlens arrays; and general three dimensional surfaces.
Application of the HEBS-glass of the present invention include micro-optical devices, microelectrical devices, micro-opto-electromechanical devices, integrated optical devices, two-dimensional fanout gratings, optical interconnects, fiber pigtailing, diffractive optical elements, refractive microlens arrays, microprism arrays, micromirror arrays and Bragg grating.
The essential properties of a HEBS-glass gray level mask which is necessary for the fabrication of general three dimensional microstructures are;
1. A mask pattern or image is grainiless even when observed under optical microscope at 1000× or at higher magnifications.
2. The HEBS-glass is insensitive and/or inert to photons in the spectral ranges employed in photolithographic processes, and is also insensitive and/or inert to visible spectral range of light so that a HEBS-glass mask blank and a HEBS-glass mask are permanently stable under room lighting conditions.
3. The HEBS-glass is sufficiently sensitive to electron beam exposures, so that the cost of making a mask using an e-beam writer is affordable for many applications.
4. The e-beam induced optical density is a unique function of, and is a very reproducible function of electron dosages for one or more combinations of the parameters of an e-beam writer. The parameters of e-beam writers include beam acceleration voltage, beam current, beam spot size and addressing grid size.
The essential properties No. 1 and No. 2 are properties of HEBS-glasses described in the US patents listed above. However, HEBS-glass compositions having a better e-beam sensitivity is in general more sensitive to photon energy as well.
It is the objective of the present invention to optimize HEBS-glass composition so that the HEBS-glass of the present invention is sufficiently sensitive to electron beam and that the cost of writing a gray level mask is affordable for many applications, and yet HEBS-glass of the present invention is totally inert to actinic radiation of 436 nm and longer wavelengths and has no sensitivity to actinic radiation at 365 nm for practical purposes eg. no significant darkening for 1,000,000 exposures in I-line steppers.
It has been determined that with a given value of e-beam exposure dosage the e-beam induced optical density in HEBS-glass is a function of beam acceleration voltage, of beam spot size, of beam current and of addressing grid size. Therefore, it is another objective of the present invention to design e-beam write schemes such that the essential properties No. 3 and No. 4 of a HEBS-glass gray level mask are both fulfilled.
The present invention is directed to a gray scale mask comprising a transparent High Energy Beam Sensitive-glass (HEBS-glass) having at least one gray scale zone with a plurality of gray scale levels, each gray scale level having a different optical density, the High Energy Beam Sensitive-glass in bodies of 0.090 inch cross section will exhibit the following properties:
(a) transmittance of more than 88% at 436 nm; and
(b) upon exposure to an electron beam using an electron beam pattern generator operated with a write scheme having a value of acceleration voltage selected from 20 to 30 kV, an addressing grid size of from 0.1 to 0.4 micrometer, and a value of beam current selected from 25 to 250 na, an electron beam darkening sensitivity in the linear portion of the sensitivity curve, of at least 2.454 unit of optical density value in the spectral range of 365 nm to 630 nm per electron dosage unit of milli coulomb/cm
2
, said HEBS-glass having a base glass composition consisting essentially on the mole % oxide basis 11.4 to 17.5% of one or mor
Wu Che-Kuang
Wu Laurie Ann
Canyon Materials, Inc.
Fish & Richardson P.C.
Marcheschi Michael
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