Moisture Instability of Borophosphosilicate Glass and the Effects of Thermal Treatment

Borophosphosilicate glass films deposited by tetraethoxysilane‐ozone chemical vapor deposition are highly susceptible to atmospheric moisture absorption. Moisture diffuses into these oxides through the exposed surface and incorporates itself as surface adsorbed water, silanol, and phosphorous dihydroxide. Thermal treatments dehydrate the glass matrix by ( i ) driving off surface adsorbed water, ( ii ) causing pairs of silanol groups to react to form silicon dioxide, and ( iii ) causing doubly hydroxylated phosphorous atoms to form phosphorous‐oxygen double bonds. The residual stress and thickness of as‐deposited films change rapidly over time due to the moisture instability whereas these properties are stable in furnace densified films. Films treated under various rapid thermal processing conditions (temperatures from 700 to 900°C and times from 10 to 50 s) are chemically similar to each other but have different physical properties depending on the specific conditions of the cure. The degree of chemical and physical change that takes place in these films over time also depends on the specific cure conditions. Phosphorous hydration plays an important role in these changes which correlate more strongly with the cure temperature than the cure time. For all of the cure conditions studied, the postcure film density is a consistently good predictor of the subsequent film stability.