Mechanistic study of borosilicate glass growth by low-pressure chemical vapor deposition from tetraethylorthosilicate and trimethylborate
A reaction mechanism and film morphology as a function of reactor conditions and post growth thermal annealing for borosilicate glass (BSG), (SiO2)x(B2O3)1−x, films deposited from tetraethylorthosilicate (TEOS), trimethylborate (TMB), and oxygen (O2) precursors by low-pressure chemical vapor deposition (LPCVD) was determined. An empirically derived reaction model for BSG film growth is proposed that predicts the growth rate and composition of BSG films up to 70 mole% B2O3. The BSG reaction model includes a strongly adsorbed TEOS-derived intermediate that forms SiO2 and a direct surface reaction of TMB, in O2, to form B2O3. This model is supported by growth rate and mass spectroscopic data. The BSG film morphology, investigated using atomic force microscopy, was found to have a root-mean-square roughness of 0.5 nm, with the precise film morphology being a function of reactor conditions. The BSG film roughness increases with film thickness, temperature, and boron content. Thermal annealing of the films in a water-free environment leads to planarization of the BSG governed by the film composition and anneal temperature.