Remote microwave PECVD for continuous, wide-area coating under atmospheric pressure

In order to establish economic coating technologies for mass-produced materials, the widely used, microwave plasma-enhanced (PE) CVD technology has been extended to atmospheric pressure operation. Microwave plasma activation substantially widens the range of potential applications compared to conventional atmospheric CVD, because it is capable of processing temperature-sensitive substrates. A cylinder-type microwave cavity was scaled-up to different working diameters. The half-meter range has already been achieved, and further scale-up potential can be demonstrated. The microwave source offers access to a spatially extended, homogeneous, stable, non-thermal plasma, even in the downstream region. A range of gases can be used for plasma excitation, and the emanating plasma is clean because there is negligible wall interaction. Fluid dynamics modeling was used as a tool for both reactor design and process optimization. In-situ process characterization was provided by spectroscopic methods (optical emission spectra (OES), Fourier-transform infrared (FTIR)) and a range of atomic and molecular intermediates, precursor fragments, and reaction products were identified. A deep precursor fragmentation occurs in the remote plasma region leading to inorganic layer materials. Silica layers were deposited on stainless steel and glass. Deposition rates were in the range 15-100 nm s-1 (static) and 0.3-2.0 nm m s-1 (dynamic). Layer properties were determined by spectroscopic ellipsometry and FTIR reflectance spectroscopy, elastic recoil detection analysis (ERDA), and nano-indentation. The optical properties and the network structure of the silica layers on both substrates are close to bulk silica.