High Rate Deposition of SiOx and ZnO Coatings

The plasma-technological deposition of protective coatings on glass, metal and especially plastic materials is of increasing interest in the industry. However, many deposition processes do not meet the industrial demands for fast process time and scalability to large substrate areas of several square meters.

For this reason, IGVP has developed a process for high rate deposition by microwave plasma assisted chemical vapor deposition (MW-PECVD). The main goal here was the coating of polycarbonate (PC) with scratch-resistant SiO_x and UV-absorbing ZnO layers in order to be able to use the sensitive material outdoors as well, for example in architecture or in the automotive sector.

For the layer deposition on an area of 10*15 cm² an array of 4 Duo-Plasmalines is used, which produces a microwave plasma with high density and large volume. The gaseous monomers (hexamethyldisiloxane for SiO_x and diethylzinc for ZnO) flow together with oxygen through the plasma zone during the coating, where they are effectively dissociated by the microwave plasma, and finally combine on the substrate into solid transparent layers.

High deposition rates of up to 60 μm/min for SiO_x and 700 nm/min for ZnO can be achieved. Based on the coating parameters, the coating properties can be optimized with regard to transparency, UV absorption, abrasion resistance and adhesion. In this way, a layer structure of SiO_x and ZnO could be developed, which can exceed the scratch and UV protection of conventional clearcoats on polycarbonate.

Due to the good scalability of the Duo-Plasmaline, the deposition process for SiO_x could also be scaled up to a substrate area of 0.5 m², which also enables large-area coatings. The modular system consists of two side chambers and a coating unit, which is equipped with 2 Duo-Plasmalines with a length of 60 cm and a gas supply. During the process, the substrate passes through the coating unit and is continuously coated. Dynamic deposition rates of 3 μm*m/min can be achieved, which makes the process interesting for industrial applications.

In addition to the use as a scratch protection function, the SiO_x coatings were also successfully tested as corrosion protection layers, as electrical insulation layers and as barrier coatings against solvents.