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-enhance d chemical vapour deposition (PECVD) using pure SiH4 and O-2 in a plan ar plasma reactor based on the proprietary uniform distributed electro n cyclotron resonance (UDECR) technology. Samples were kept approximat ely 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 conjunctio n with appropriate distributed gas injection set-up, extremely good la yer uniformities were obtained, with no visible irisations for thickne sses of 0.1-6 mu m The reactor concept intrinsically lends itself to p rocess scale-up which is even trivial along one dimension. The effects of gas flow rates and substrate r.f. bias were investigated, mainly b y 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 ve ry close to those obtained in the case of thermally grown silica, indi cating an unusually dense microstructure for the as-deposited PECVD fi lms grown at quasi-ambient temperature. Transparent protective coating s 3-5 mu m thick showing excellent abrasion resistance and weatherabil ity could thus be deposited on metals and optical polymers.