Highly homogeneous silica coatings for optical and protective applications deposited by PECVD at room temperature in a planar uniform distributed electron cyclotron resonance plasma reactor.

Thin near-stoichiometric silica films were deposited by plasma-enhanced chemical vapour deposition (PECVD) using pure SiH4 and O-2 in a planar plasma reactor based on the proprietary uniform distributed electron cyclotron resonance (UDECR) technology. Samples were kept approximately at room temperature during the process. In the pressure range 0.1-0.4 Pa, dense (>5X10(10) cm(-3)) diffusion plasmas could be sustained very homogeneously over areas larger than 200 mmX200 mm. In conjunction with appropriate distributed gas injection set-up, extremely good layer uniformities were obtained, with no visible irisations for thicknesses of 0.1-6 mu m The reactor concept intrinsically lends itself to process scale-up which is even trivial along one dimension. The effects of gas flow rates and substrate r.f. bias were investigated, mainly by Fourier transform infrared absorption spectroscopy and spectroscopic ellipsometry ( 1.4-5.0 eV). The Si-H and O-H bond contents were found to be very low for all samples. For films deposited under sufficient ion bombardment energy, typical values for the refractive index at 2.0 eV (1.458) and the Si-O-Si stretching frequency (1075 cm(-1)) were very close to those obtained in the case of thermally grown silica, indicating an unusually dense microstructure for the as-deposited PECVD films grown at quasi-ambient temperature. Transparent protective coatings 3-5 mu m thick showing excellent abrasion resistance and weatherability could thus be deposited on metals and optical polymers.