Patent ID: 7754286

Claim:
A method of forming a silicon dioxide film on a silicon substrate, comprising: a wet oxidation step of thermal oxidizing the surface of the silicon substrate using water vapor to form a silicon dioxide film having a thickness of 2 μm thereon, a deposition step of depositing epitaxial silicon on said silicon dioxide film formed on said silicon substrate to obtain a deposited epitaxial silicon film; and a thermal oxidation step of oxidizing said deposited epitaxial silicon film by heat in an electric furnace to convert it into a silicon dioxide film, wherein said deposition step and said thermal oxidation step are repeated a plural number of times until a resulting silicon dioxide film on the silicon substrate has a thickness for an optical waveguide, said thickness being not smaller than ten and several microns, a film growing rate of said epitaxial silicon film is 1.06 μm/min, a surface roughness of said epitaxial silicon film is 0.15 nm, and a thickness of said epitaxial silicon film formed during each repetition of said deposition step is not larger than 5 μm.