Plasma and surface diagnostics during plasma-enhanced chemical vapor deposition of SiO2 from SiH4/O-2/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 him are hydroxyl rich during deposition with SiH4-to-O-2 ratio below 0.7. Silicon hydrides are observed on the surface and in the him when R exceeds 0.7. The SiOH concentration in the film correlated well with SM concentration above the substrate surface, which is representative of the silane fragment (SiHx) flux arriving at the surface of the growing film. High O flux compared to SiHx flux results in immediate oxidation of the silane fragments adsorbed onto the surface which leads to OH rich surface and SiOH incorporation. As the SiHx 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.