Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1999-10-21
2004-06-22
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S396000, C430S005000, C430S022000
Reexamination Certificate
active
06753131
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to optical devices, and more particularly to an elastomeric, transparent element having a diffracting surface for use as a near-field, contact-mode phase mask for photolithography, a sensor of physical force, and a visual display device. The invention also relates generally to the optical patterning of surfaces via photolithography, and more particularly to photolithography in which a surface of photoresist is contoured and alters light in a manner such that the photoresist is developed according to a pattern without the use of an auxiliary mask.
BACKGROUND OF THE INVENTION
Differences in phase of electromagnetic radiation can be produced by varying the path that light follows, either by passage of light through media of differing refractive index, or reflection from a corrugated surface and by interaction of light with diffraction gratings. Phase differences of light have been exploited for a variety of uses including sensors, apparatus for photolithography, and optical displays. A brief description of several examples of such uses follows.
Sensors and modulators based on changes in optical properties corresponding to changes in electric, magnetic, and acoustic fields are known. Micron-scale modulators that involve mechanical deformation of suspended beams, mirrors, and Fabry-Perot cavities are under development for applications in fiber optic communications and displays. See, for example, Leeson, et al., “Design and Fabrication of Planar, Resonant, Franz-Keldysh Optical Modulators”,
Electron. Lett
., 24, 1546-1547 (1988); Solgaard, et al., “Deformable Grating Optical Modulator”,
Optics Letters
, 17 (9), 688-690 (1992); Feather, et al., “Micromirrors and Digital Processing”,
Photonics Spectra
, 118-124 (May, 1995).
Yamamoto, et al., in “Direct Measurement of Piezoelectric Strain Using a Diffraction Grating”,
J. Am. Cer. Soc
., 70, 8, 557-561 (August, 1987), describe application of a large DC electric field to a sample to induce strain in the sample in a direction parallel to a surface having a grating relief structure, and determination of the strain by detection of a change in wavelength of light in the diffraction pattern produced by the grating.
Boone, P. M., in an article entitled “A Method for Directly Determining Surface Strain Fields Using Diffraction Gratings”,
Experimental Mechanics
, 481-489 (November, 1971), describes determination of the strain distribution at the surface of a solid body to which stress is applied by analyzing diffraction phenomena of a grating applied to the body.
Sciammarella, et al., in “Two New Optical Techniques to Measure Strain”,
Experimental Mechanics
, 311-316 (August, 1974), describe determination of strain in an article to which stress is applied by engraving a grating into a surface of the article and determining a change in angle of a particular diffracted beam with the grating surface corresponding to a change in pitch of the grating resulting from strain. See also Olivaries-Perez, et al., “Dynamic Holographic Gratings With Photoresist”,
Applied Optics
, 34 (25), 5577 (1995).
Post, et al., in “High-Sensitivity Moiré Interferometry—A Simplified Approach”,
Experimental Mechanics
, 100-104 (March, 1981) report a Moiré Interferometry arrangement in which a collimated beam is incident upon a phase-type reflection grating on a specimen, the specimen is deformed, and determination is made of deformation parallel to the grating surface corresponding to a shift in wavelength of light diffracted at the grating.
Photolithographic techniques have exploited phase-shifts of light produced by masks. Toh, et al., in “Chromeless Phase-Shifted Masks: A New Approach to Phase-Shifting Masks” SPIE volume 1496, Tenth Annual Symposium On Microlithography, 27-53 (1990); and Tanaka, et al., in “A Novel Optical Lithography Technique Using the Phase-Shifter Fringe”,
Japanese Journal of Applied Physics
, 30 (5), 1131-1136 (1991) report a phase-edge photolithography method in which a transparent mask induces abrupt changes of the phase of light used for exposure of photoresist, causing optical attenuation at those phase-shifted locations. Very small features can be created in photoresist according to the technique, but an arrangement of imaging optics must be positioned between the phase mask and the photoresist. The requirement of optics in projection onto the photoresist limits the area of photoresist that can be patterned in a single exposure, and the technique requires precise positioning of the resist at the image plane.
The techniques discussed above involving diffraction and phase-shifting of light for a variety of purposes all involve relatively complicated and expensive optics and/or involve measurement of a change in wavelength of light associated with a shift in a fringe pattern of a diffraction grating, which itself can require relatively complicated optics for detection.
Photolithography is a procedure in which a material called photoresist is placed on a surface and exposed to electromagnetic radiation in a pattern such that certain portions of the photoresist are exposed to the radiation and certain portions are not exposed. Depending upon the particular type of photoresist used, the exposed portions or the unexposed portions are removed chemically, which exposes the surface in a pattern identical to or complementary to the pattern of electromagnetic radiation. Exposed portions of the underlying surface then can be etched away, or portions can be plated on the underlying surface, in a pattern dictated by the pattern of photoresist. This technique has been widely used in fabrication of many small-scale devices, especially microelectronic devices.
To expose photoresist to electromagnetic radiation in a specific pattern, two general techniques have been used. One has involved “writing” into the photoresist with a beam of electromagnetic radiation such as a laser beam or an electron beam. Another widely-used technique involves exposing the photoresist to electromagnetic radiation through a mask. Amplitude masks and phase-shifting masks are known for use in this technique.
Although photolithography is a well-developed field, most techniques require relatively complicated and expensive apparatus. Accordingly, there is a general need to provide simplified, inexpensive, photolithographic techniques and devices for optical displays, sensors, and photolithographic masks that are relatively simple and inexpensive to fabricate and use.
SUMMARY OF THE INVENTION
The present invention provides a contact phase mask for use in photolithography. The phase mask can be used in combination with a surface, such as a surface of photoresist, to which phase-shifted radiation advantageously is applied, can include a surface conformable to the surface that receives the radiation. The mask has a first portion, having a first refractive index, positionable against a surface to receive radiation and allows for a medium having a second, different refractive index to reside adjacent the first portion, and also adjacent the surface that receives phase-shifted radiation. The phase mask can be used in combination with a system including a stage for positioning a sample including a layer of photoresist. The system is free of optical elements positionable between the mask and the photoresist.
The present invention also provides techniques involving photoreactions at surfaces, articles for use in surface photoreactive procedures, and methods of making these articles.
According to one aspect, the invention provides a method for exposing a surface to electromagnetic radiation through a phase mask. The method involves placing a surface of a phase mask in contact with a surface of an article to be exposed, and exposing the surface to electromagnetic radiation through the phase mask. The phase mask can include a contoured surface.
In one embodiment, the invention provides a method of using a phase-shifting article. The method is used in conjunction with a surface of an article to be exposed to electromagnetic radiation, and in
Breen Tricia Lynn
Jackman Rebecca J.
Paul Kateri E.
Rogers John A.
Schueller Olivier J. A.
Huff Mark F.
Mohamedulla Saleha R.
Wolf Greenfield & Sacks P.C.
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