BORON-DIFFUSION IN AMORPHOUS SILICA FILMS

The diffusion coefficients of boron in amorphous silica (SiO2) films h ave been determined over the temperature range from 1173 to 1373 K. Th e SiO2 films were prepared by thermal oxidation of silicon substrates. Boron was incorporated into the SiO2 films from boron vapor, the pres sures of which were varied between 5.5 X 10(-18) and 7.2 X 10(-13) Pa. The diffusion coefficients were calculated from boron concentration p rofiles in the SiO2 films measured using secondary ion mass spectromet ry: D-B/m(2) s(-1) = 1.88 X 10(-12) exp (-205,000/RT), where R is 8.31 J K-1 mol(-1). The diffusion coefficients were not dependent upon bor on vapor pressures, i.e., the boron concentrations at the film surface . The discussion on the activation energy and chemical state analysis using x-ray photoelectron spectroscopy offer the mechanism that boron diffuses through the silicon sites in the network of SiO2.