STRUCTURAL CHARACTERIZATION OF PHOTOCHEMICALLY GROWN SILICON DIOXIDE FILMS BY ELLIPSOMETRY AND INFRARED STUDIES

Silicon dioxide films grown by photochemical vapor deposition at diffe rent deposition rates are investigated by ellipsometry and Fourier tra nsform infrared measurements. Disagreement in the variation of refract ive index with chamber pressure between thin and thick films is interp reted in terms of a deposition rate dependent buildup of internal stre ss in the film. Direct measurements of curvature show the presence of compressive stress in thick SiO2 films grown at chamber pressures > 60 0 mTorr. Infrared transmission measurements also indicate a change in the structural characteristics of films (probably induced by stress), with increasing deposition rate. Molecular model calculations show a d ecrease in the Si-O-Si bond angle as the growth pressure increases. Io n implantation seems to release the stress in these films as evidenced by the shift observed in the stretching mode frequency. The relative concentrations of H2O, SiOH, and SiH groups in these films and the eff ect of annealing on the strength of these modes are also discussed. Re flection infrared measurements at 60-degrees incidence reveal a disord er induced longitudinal-transverse optic pair at around 1200 cm-1.