Plasma and surface diagnostics during plasma-enhanced chemical vapor deposition of SiO₂ from SiH₄/O₂/Ar discharges

Factors affecting the SiOH incorporation into SiO₂ films during plasma-enhanced chemical vapor deposition were studied using in-situ attenuated total reflection Fourier transform infrared spectroscopy, optical emission actinometry, and Langmuir probe measurements. The silane-to-oxygen ratio, R, in the process gas mixture determines the chemical nature of the substrate surface and the incorporation rate of SiOH and SiH into the film. The oxide surface and the film are hydroxyl rich during deposition with SiH₄-to-O₂ ratio below 0.7. Silicon hydrides are observed on the surface and in the film when R exceeds 0.7. The SiOH concentration in the film correlated well with SiH concentration above the substrate surface, which is representative of the silane fragment (SiH_x) flux arriving at the surface of the growing film. High O flux compared to SiH_x flux results in immediate oxidation of the silane fragments adsorbed onto the surface which leads to OH rich surface and SiOH incorporation. As the SiH_x flux relative to O flux increases, the reaction of silane fragments with surface SiOH reduces the SiOH coverage on the surface and the SiOH incorporation rate into the film.