PECVD - PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION
Quite often vacuum PECVD appears to be first choice when it comes to scratch resistant coatings on soft flexible substrate materials or where surfaces need to be hydrophilic or hydrophobic. As a representative example for the wide range of possible PECVD applications s scratch resistant layers on a soft polymer like polycarbonate can effectively be produced in a plasma discharge by adding a silicon containing compound like HMDSO vapour and oxygen. Quartz like layers can thus be deposited at rates of several hundred nanometers per second under certain conditions.
By employing the so called remote plasma process (plasma discharge is not in direct contact with the substrate but some distance like 20 to 50 cm away) very uniform, homogenous and amorphous quartz layers can be deposited showing a silicon to oxygen stoichiometry of 1:2, resembling pure quartz, as shown in the XPS spectrum below.
The decisive advantage of vacuum processes lies in the fact that the atomic consistency of the deposited films can vary over a wide range. Just by changing the HMDSO/oxygen mixture and/or the plasma discharge power level, the deposited quartz like layers could lose their brittleness without losing their anti-scratch properties. This behaviour is extremely important for the coating of polymer foil.
The above infrared spectra impressively demonstrate that the surplus of oxygen in such a plasma discharge burns off almost all organic molecule fragments and leaves almost pure silicon dioxide while organic fragments can be found in the layers produced under oxygen deficiency.