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Germanium silicon oxynitride high index films for planar waveguides
| Details |
Inventors: Akwani, Ikerionwu Asiegbu; Bellman, Robert Alan; Grandi, Thomas Paul; Sachenik, Paul Arthur;
Assignee: Corning Incorporated (Corning, NY)
Primary Examiner: Ullah; Akm E.
Assistant Examiner:
Attorney, Agent or Firm: Price, Heneveld, Cooper, DeWitt & Litton
A composition represented by the formula Si.sub.1-x Ge.sub.x O.sub.2(1-y) N.sub.1.33y, wherein x is from about 0.05 to about 0.6 and y is from about 0.14 to about 0.74 exhibits properties highly suited for use in fabricating waveguides for liquid crystal based optical devices. In particular, the compositions have an index of refraction of from about 1.6 to about 1.8 for light at a wavelength of 1550 nm, and/or a coefficient of thermal expansion of from about 2.5.times.10.sup.-6.degree. C.sup.-1 to about 5.0.times.10.sup.-6.degree. C..sup.-1. The compositions also have inherently low hydrogen content, and a high hydrogen permeability which allows better hydrogen removal by thermal annealing to provide a material which exhibits low optical losses and better etching properties than alternative materials. |
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DETAILED DESCRIPTION The invention overcomes the problems inherent with high index silicon oxynitride films formed by chemical vapor deposition, and provides a commercially viable method of fabricating a high refractive index waveguide material.
More specifically, the invention provides a germanium silicon oxynitride material having an inherently lower hydrogen content as deposited than silicon oxynitride; a higher hydrogen permeability than silicon oxynitride, which facilitates hydrogen removal; and a coefficient of thermal expansion which closely matches the coefficient of thermal expansion for silicon.
These properties are extremely useful for fabricating optical devices based on total internal reflectance of liquid crystals.
In accordance with one aspect of the invention, a composition represented by the formula Si.
sub.
1-x Ge.
sub.
x O.
sub.
2(1-y) N.
sub.
1.
33y is provided wherein x is from about 0.
05 to about 0.
6 and y is from about 0.
14 to about 0.
74.
Such compositions exhibit a relatively high index of refraction, and a coefficient of thermal expansion which closely matches the coefficient of thermal expansion for silicon.
In accordance with another aspect of the invention, the germanium silicon oxynitride composition has an index of refraction of from about 1.
6 to about 1.
8 for light at a wavelength of 1550 nm.
In accordance with another aspect of the invention, the germanium silicon oxynitride composition has a coefficient of thermal expansion of from about 2.
5.
times.
10.
sup.
-6.
degree.
C.
.
sup.
-1 to about 5.
0.
times.
10.
sup.
-6.
degree.
C.
.
sup.
-1.
In another aspect of the invention, a germanium silicon oxynitride film is deposited on a silicon substrate.
The germanium silicon oxynitride film has an index of refraction of from about 1.
6 to about 1.
8 for light at a wavelength of 1550 nm, and a coefficient of thermal expansion of from about 2.
5.
times.
10.
sup.
-6.
degree.
C.
.
sup.
-1 to about 5.
0.
times.
10.
sup.
-6.
degree.
C.
.
sup.
-1.
In accordance with a further aspect of the invention, a germanium silicon oxynitride film deposited on a silicon substrate is represented by the formula Si
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