THERMOCHEMICAL STUDIES OF CHEMICALLY VAPOR DEPOSITED AMORPHOUS SILICA.

Doped silica glasses (SiO//2-P//2O//5, SiO//2-GeO//2, SiO//2-GeO//2-P//2O//5, with dopant concentration of up to 20 mol %) are of wide use in the semiconductor industry either as dielectrics or as final passivation layers. One of the major methods of obtaining those glasses as thin films is Low Pressure Chemical Vapor Deposition (LPCVD). Two kinds of vitreous sample can be obtained from an LPCVD furnace, thin film and 'snow', the latter being a very reactive powder adhering to the furnace walls. Since there is a lack of basic thermodynamic, phase equilibrium and microstructural data for these doped glass systems, the authors have begun such studies with work on SiO//2 since it is the basis of all other doped glasses.