Low temperature, plasma assisted oxidation of amorphous Si

A preliminary study of plasma assisted oxidation of amorphous, hydrogenated Si (a-Si:H) has been carried out using a microwave frequency, electron cyclotron resonance excited reactor. A 'constant current through the substrate' mode was used. Films up to several tens of nm were obtained at room temperature in a time of much less than 60 min. The growth kinetics of the SiO2 on amorphous and crystalline Si substrates were similar and followed the predictions of a constant current, field assisted diffusion model. Infrared absorption spectroscopy on as-grown and chemically etched SiO2 films suggests that they differ and are inhomogeneous compared to thermal oxides. The differences are attributed to a network having a smaller Si-O-Si bridging bond angle than that for thermal SiO2 rather than density or stoichiometric differences. The latter has been confirmed by X-ray photoelectron spectroscopy measurements. Surface roughness in the form of macroscopic bubbles and peeling was observed in samples of a-Si:H following oxidation. This phenomenon, which we attribute to the release and nucleation of the H in the films, may severely limit the applicability of the method for producing low temperature oxides on a-Si. (C) 1997 Elsevier Science B.V.