Organic/inorganic thin films deposited from diethoxydimethylsilane by plasma enhanced chemical vapor deposition

Abstract

Thin a-SiO x C y H z films were deposited from diethoxydimethylsilane in a radio-frequency plasma polymerization process. The plasma deposition and the film properties were characterized with respect to the deposition rate evaluated from scanning electron microscopy observations, the film refractive index determined by spectroscopic ellipsometry and the film density measured by X-ray reflectometry. The layer chemical structure was investigated by Fourier-transform infrared spectroscopy analysis, 29Si solid-state nuclear magnetic resonance technique, and X-ray photoelectron spectroscopy measurements. The film growth rate exhibits a typical evolution as a function of the process parameters and appears to be dependent on the nature of the substrate. We are able to correlate the structure of the films obtained with the important composite parameter V/ P p (RF voltage V over the monomer partial pressure P p) characterizing the input energy per unit mass of monomer. Chemical analysis spectra show that the concentration of [(CH 3) 2–Si(–O) 2] silicon environment increases with lowering the V/ P p ratio; at very low V/ P p values, plasma polymers are close to polydimethylsiloxane. By contrast, the thin layers contain a high [SiO 4] concentration, characteristic of SiO 2, when V/ P p increases. Moreover, increasing V/ P p results in higher C/Si and O/Si ratios while the film's density and refractive index also rise.