A COMPARISON OF SIO2 THIN-FILM UVCVD RATES AND MECHANISMS FROM SIH4/O2 AND SIH4/N2O PRECURSOR GASES BY SURFACE-SENSITIVE INFRARED-SPECTROSCOPY

With the help of a surface-sensitive multiple internal reflection technique, we have been able to measure photodeposition rates of silica with a low-pressure mercury lamp down to room temperature. At such a temperature, the deposition rates with O2 or N2O as the oxidizing precursor are equal. While the oxygen-induced photodeposition rate increases rapidly with temperature in the O2 system, it saturates at a low value, for a temperature higher than 100-degrees-C in the N2O system. In the first case the surface is covered with hydroxyl groups, adsorbed water, mono- and dihydride species. In the second case we reveal an almost water- and hydroxyl-free bulk and surface material, and the presence of few nitrogen-containing species. These features make the silica films prepared in this latter way an interesting material for various technological processes.