PACVD SiOx Coatings Deposited with Microwave Technology

SiOx thin films are widely spread in various applications, such as semiconductor manufacturing, glass industry, sensors, decorative coatings. The interest in them comes from their optical transparency,  diffusion, electrical and thermal barrier properties,  high surface hardness and chemical inertness. The last makes them very good corrosion protection coatings. For many applications, they are deposited by sputtering, either reactively from a silicon target and oxygen gas or directly from SiO₂ target. In both cases, there are serious drawbacks. In the first case, a complicated control circuit is needed to keep the process in the desired operating conditions. In the second case, rf-sputtering must be used, which brings higher equipment costs , lower deposition rate and problems with the coating uniformity in large–scale coaters. Sputtering inevitably introduces also point defects that may corrupt barrier and anticorrosion properties.

In this study, a  PACVD method,  based on microwave generated plasma in a commercial PVD machine, is presented. The method improves by a factor of two the deposition rate in comparison to magnetron sputtering and does not require sophisticated control mechanisms. The SiOx films are deposited from two precursors in the presence of oxygen on various types of substrates – glass, silicon wafers, high-speed steel and  100Cr6 steel. The results include the optical, electrical and corrosion protective properties of the SiOx films as a function of the gas mixture ratio, precursor type and the main process parameters. The method allows also for coatings with tunable hydrophobicity in a wide range – water contact angles between 40° and 120°. The transition from SiOx to stoichiometric SiO₂ films as a function of the process conditions is illustrated by means of dielectric constant measurements and compositional analysis with ToF-SIMS and SEM-EDX techniques.