Method for improving refractive index control in PECVD deposited a-SiN

1. A method for providing an amorphous silicon-based film deposited on a substrate, said method comprising:

providing gases consisting essentially of at least one volume of each of N 2 , SiH 4 and compensating He;

plasma enhanced chemical vapor depositing at least one layer of amorphous silicon-based film on said substrate using the gases; and

varying only a ratio of N 2 to SiH 4 and a flow volume of He so that said plasma enhanced chemical vapor depositing uses a substantially constant total flow volume of N 2 , SiH 4 and He whereby the index of refraction of the deposited at least one layer of amorphous silicon-based film is controlled.

2. The method of claim 1 , further comprising maintaining a substantially constant flow of one of said at least one volume of each of N 2 and SiH 4 .

3. The method of claim 2 , further comprising adjusting said at least one volume of He to maintain said substantially constant total flow volume of He, N 2 and SiH 4 .

4. The method of claim 1 , wherein the depositing said at least one layer of amorphous silicon-based film on said substrate comprises thermally-enhanced plasma enhanced chemical vapor deposition.

5. The method of claim 1 , wherein said amorphous silicon-based film deposited on the substrate forms at least one portion of a waveguide.

6. The method of claim 1 , wherein said amorphous silicon-based film deposited on a substrate forms at least one portion of an arrayed waveguide grating.

7. An amorphous silicon based waveguide on a substrate, comprising:

a waveguide core; and

at least one cladding;

wherein at least one of said core and said at least one cladding comprise a plasma enhanced chemical vapor deposited film characterized by plasma enhanced chemical vapor depositing onto the substrate using a flow volume consisting of at least one formation volume of each of N 2 , SiH 4 , and a compensating volume of He

wherein only a ratio of N 2 , to SiH 4 and a flow volume of He are varied and a substantially constant total flow volume of N 2 , SiH 4 and He is maintained during formation of the plasma enhanced chemical vapor deposited film whereby the index of refraction of the deposited film is controlled.

8. The waveguide of claim 7 , wherein said plasma enhanced chemical vapor deposition comprises a thermally enhanced, plasma enhanced chemical vapor deposition.

9. The waveguide of claim 7 , wherein said waveguide forms part of an arrayed waveguide grating.

10. An optical device, comprising:

a waveguide having at least one layer of amorphous silicon-based film,

wherein said at least one layer of amorphous silicon-based film is characterized by plasma enhanced chemical vapor deposition of the film using a flow volume consisting of at least one volume of each of N 2 , SiH 4 , and a compensating volume of He, wherein only a ratio of N 2 to SiH 4 and a flow volume of He are varied and a total flow volume of N 2 , SiH 4 and He is maintained substantially constant during formation of the plasma enhanced chemical vapor deposited film whereby the index of refraction of the deposited film is controlled.

11. The optical device of claim 10 , wherein the plasma enhanced chemical vapor depositing uses a substantially constant flow of one of said at least one volume of each of N 2 and SiH 4 during deposition of said at least one layer of amorphous silicon-based film.

12. The optical device of claim 11 , wherein said plasma enhanced chemical vapor depositing includes adjusting the least one volume of He to maintain a substantially constant total flow volume of said He, N 2 and SiH 4 .