New steps towards large area plasma activated EB-PVD
In the beginning, EB-PVD (electron beam physical vapour deposition) of aluminium on strip steel was introduced as corrosion protection. Meanwhile, various metallic and oxide layer stacks on strip steel are applied in the car production industries in order to improve corrosion protection, welding ability, wear resistance and adhesion of organic top coatings. Double sided copper coating of strip steel by EB-PVD is industrially introduced with the aim to obtain solderable surfaces for pipe soldering of high pressure pipes of refrigerator systems and brake lines. Recently, aluminium coatings on steel based alloys are applied in the production of metal supported catalytic converters. High resistance coatings like SiO2 on stainless steel are applied as protection layers between the back contact of thin film solar cells and the bearing flexible metallic substrate. Thus, EB-PVD is well established as a large area coating technology. Reactive EB-PVD allows the deposition of some important compounds. Although EB-PVD is a superior coating technology regarding highest deposition rates, its successful industrial application in some cases depends on a further improvement of layer properties. Plasma activated EB-PVD is a process combination which allows to increase density, hardness, refractive index and other properties of the coatings. One possibility of plasma activation concerning the electron beam evaporation process is the ignition of a spotless arc discharge on the EB heated evaporant which is well known as the SAD (spotless arc activated deposition) process. This process, in which an anode near the crucible is applied in order to ignite a spotless arc onto the electron beam heated evaporant in the crucible, has been extended for the first time to large area dimensions. Reactive large area SAD of titanium dioxide has been carried out at deposition rates of up to 70 nm/s. Results of these investigations will be presented. Advantages of the process include high plasma densities with an ionisation degree of up to 60 %, less expensive additional equipment in the process surrounding of the EB evaporator compared to other plasma generation tools, and coinciding position of the arc on the evaporant with the location of the electron beam generated vapour source. The dynamic deposition rate of titanium dioxide achieved approximately 1000 nm.m/min. Expensive titanium suboxides as evaporant can be replaced by low cost titanium. Latest experiments showed that the SAD process can be extended to large area technology with no limitations with respect to substrate width. Thus, the way into industrial application is open. Applications of titanium and titanium compounds in the finishing industries are tabulated, where SAD may be applied in the near future.