Thin film sol-gel derived glass
Thermally-assisted organometallic sol-gel derived glasses have been found to permit fabrication of thin films sufficiently thin for telecom components. Inclusion of a photosensitizer in the film permits light of controlled intensity to modify refractive indices in the film to form useful structures.
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This application is a continuation of U.S. patent application Ser. No. 09/574,841, filed May 19, 2000, which is hereby incorporated by reference in its entirety.
This application is also related to a companion application Ser. No. 09/574,840, filed on May 19, 2000, and assigned to the assignee of the present application.
FIELD OF INVENTIONThis invention relates to a process for producing photosensitive thin films of sol-gel derived glass and to such films of a thickness useful for integrated optic devices produced thereby.
BACKGROUND OF THE INVENTIONThe doctoral thesis by the application herein entitled “Photolithography of Integrated Optic Devices in Porous Glass,” City University of New York, 1992, describes an organometallic system of inclusions in a thermally-assisted, porous glass bulk material. The process for fabricating the glass requires introduction of a photosensitizer, exposure to light through a mask and two heat treatments. The doctoral thesis states that sol-gel techniques can be used to make the porous glass bulk material.
BRIEF DESCRIPTION OF THE INVENTIONThe invention is based on the realization that the porous glass techniques for bulk materials using thermally assisted, organometallic, sol-gel derived glass can be extended to thin films suitable for telecom components and virtually free of lateral shrinkage. Consequently, a variety of highly desirable integrated optic components can be made by such a technique. Specifically, a technique for the photolithographic fabrication of integrated optic structures in thin films of photosensitive sol-gel glasses is described here. This technique involves the formation of a photosensitive sol-gel thin film including an organometallic photosensitizer, on a suitable substrate (glass, silicon, or any other support material). Next, the photosensitive film is exposed to white or ultraviolet light inducing a photochemical reaction in the photosensitive sol-gel glass network with the end photoproduct being a metal oxide. The photodeposited metal oxide is permanently bound to the sol-gel film glass network as a glass modifier during a heat treatment process, which in turn induces a permanent refractive index increase in the glass. The refractive index increase is dependent on the concentration of the photosensitizer and on the light energy used in the exposure process. Therefore, a spatially varying light intensity during exposure results in a spatially varying refractive index profile. This refractive index profile induced in the film can be designed to guide light.
Exposure of the photosensitive sol-gel film to white or ultraviolet light induces the unbinding of the metal from the photoliabile moiety component of the photosensitizer followed by the binding of the metal to the sol-gel film. The exposed regions of the sol-gel film are converted to a metal oxide silica film by first and second step heatings at a low temperature and high temperature, respectively. The low temperature drives out the unexposed (unbound) photosensitizer and the unbound photolabile moiety. The higher temperature step unbinds the organic component from the bound photosensitizer and drives it off. This step also permanently binds the metal to the silica film forming a metal oxide glass modifier. If the sol-gel film is deposited on a glass or silicon substrate, a metal oxide doped silica region of Si—O-M-O—Si is formed in the exposed regions acting as a glass modifier which in turn modifies the refractive index. The unexposed photosensitizer is driven off during the heat treatment steps. Since no material is removed from the sol-gel film in this process, as in the case of prior-art processes, the resulting top surface is planar, thus leading to a simpler process for producing devices and for achieving increased lifetime of resulting devices.
BRIEF DESCRIPTION OF THE DRAWINGS
Specifically,
Block 33 of
The concentration of photodeposited metal oxide determines the index of refraction of the exposed region which can be made relatively high compared to that of adjacent regions. If we visualize region 44 extending away from the view as indicated by the broken lines in
In one specific embodiment, a sol-gel film 1-10 microns thick was formed on a silicon substrate 1 cm×0.5 cm×0.1 cm thick with a SiO2 surface layer<2 microns thick thereon. The sol-gel film included Sn (M) 2%, 1 (X) 2%, and (CH3)3 (R) 2%. Region 44 has a width of 10 microns, exposed to light with a wavelength of 254 nm for 30 minutes. The exposed region had an index of refraction of 1.55 and the unexposed regions had indices of refraction of 1.45. The film has a thickness of 1-10 microns after processing and has unchanged lateral dimensions.
In another embodiment, a sol-gel film 1-10 microns thick was formed on a glass substrate 1 cm×0.5 cm×0.1 cm thick. The sol-gel film included Ti (M) 2%, Cl (X) 4%, and Cp (R) 4% where Cp is cyclopentadienyl. Region 44 has a width of 10 microns, exposed to light with a wavelength of 514 nm for 120 minutes. The exposed region had an index of refraction of 1.75 and the unexposed region had indices of refraction of 1.45. The film had an final thickness of 1-10 microns with the lateral dimensions thereof being unchanged.
Claims
1. A glass thin film derived from a thin film of photosensitive sol-gel doped with an organometallic photosensitizer, said organometallic photosensitizer having a formula R-M-X, where X is a photolabile moiety, M is a metal, and R is a volatile organic compound, wherein said thin film of photosensitive sol-gel has a thickness in excess of one micron.
2. A thin film as in claim 1, said film being formed on a substrate having a surface including silicon and oxygen.
3. A thin film as in claim 2 wherein said surface comprises SiO2 and is a silica enriched thin layer on a silicon substrate.
4. A thin film as in claim 1, said film being formed on a glass substrate.
5. A thin film as in claim 1, wherein R is taken from a class of low-volatile organic molecules consisting of CH3, CH3—CH2, CH3—CH2—CH2, and Cp, M is a metal taken from a class consisting of metals in Groups IVA, IVB, and VIB, transition metals and rare earth metals, and X is a photolabile moiety taken from a class consisting of halogens and carbonyls.
6. A thin film as in claim 3 where R comprises CH3, M comprises Sn, and X comprises I.
7. A thin film as in claim 3 wherein R comprises cyclopentadienyl.
8. A thin film as in claim 3 wherein M comprises Ti.
9. A thin film as in claim 3 wherein X comprises Cl.
10. A thin film as in claim 4 wherein R comprises CH3.
11. A thin film as in claim 4 wherein M comprises Pb.
12. A thin film as in claim 4 wherein X comprises Cl.
13. A thin film as in claim 2 including thereon a mask opaque to light in the UV and visible ranges.
14. A thin film of sol-gel derived glass on a silica substrate, said film including at least one metal oxide doped silica region of Si—O-M-O—Si with adjacent regions of SiO2, where M is a metal, said film having a thickness substantially in excess of one micron and being free of cracks and lateral shrinkage, and wherein said metal oxide is photodeposited from an organometallic photosensitizer included in the sol-gel used to form said film.
15. A method for forming a photosensitive sol-gel film including regions of different indices of refraction, said method comprising the steps of forming a photosensitive sol-gel film including an organometallic photosensitizer on a silica substrate, exposing said film through a mask to light of a wavelength and for a time for unbinding different amounts of metal constituents and of said sensitizer in different sections along at least a first channel thereof, exposing said film to heat at a first temperature and for a time to drive off the unbound sensitizer and to bind the metal constituents of said sol-gel film, and exposing said layer to heat at a second temperature higher than said first temperature for a time to unbind and drive off the organic constituents of said sol-gel film.
Type: Application
Filed: Apr 19, 2005
Publication Date: Feb 23, 2006
Applicant: Optinetrics, Inc. (Torrance, CA)
Inventor: Edgar Mendoza (Redondo Beach, CA)
Application Number: 11/110,372
International Classification: C03B 8/00 (20060101); B32B 17/06 (20060101); B32B 19/00 (20060101);