Thermochemical and Spectroscopic Studies of Chemically Vapor‐Deposited Amorphous Silica

Abstract

Two k inds of low pressure CVD SiO2 samples, heterogeneous fi lm and homogeneous "snow, " have been col lected on stainless steel substrates at three di f ferent deposi t ion temperatures: 523, 643, and 703 K. They have been character-ized thermodynamica l ly by t ransposed temperature drop and h igh temperature solut ion calor imetry. Both film and "snow " samples are metastab le-- in terms of entha lpy relative to bu lk SiO2 g lass--by up to 101 k J- too l- '. The excess entha lpy increases with decreas ing deposi t ion temperature and is larger for "snows " than for films. On anneal ing at h igh temperatures, it gradual ly disappears. IR and Raman spectroscopies indicate that both Si-H and St-OH species are present in the as-deposited samples but d isappear upon anneal ing. All as-deposited samples have densit ies comparab le to bu lk SiO ~ glass, i.e., between 2.0 and 2.2 g-cm-:~. Annea l ing tends to increase the densi ty of all samples. Var ious doped silica glasses (SiO2-P~O5, SiO.,-B,O:,,. SiO.,-As~O:, etc., w i th dopant concentrat ions of up to 20 mole percent) are widely used in the semiconductor indust ry e i ther as dielectr ics (1) or as final pass ivat ion layers (2, 3). One of the major methods of obta in ing these glasses as th in fi lms is low pressure chemical vapor deposi t ion