Throughout the last years strong efforts have been made to use Al-doped ZnO films on glass as substrates for amorphous or amorphous/microcrystalline silicon solar cells. The material promises better performance at low cost especially because ZnO:Al can be roughened in order to enhance the light scattering into the cell.

The deposition of high quality films by magnetron sputtering or alternative methods such as PLD or LPCVD has been reported repeatedly. Nevertheless the transfer to large areas is accompanied by technological difficulties. One of the most promising candidates for large area deposition of ZnO:Al is reactive magnetron sputtering of Al-doped Zn targets. Despite the need for harsh process control the possible advantages such as high deposition rates and low target cost seem to outweigh the problems.

At Fraunhofer IST the reactive magnetron sputtering process has been optimised in order to meet the requirements for front contacts in thin film silicon solar cells. The most crucial points in this respect are high transmittance in the visible and near-infrared, a reasonable sheet resistance and the etching behaviour. It will be shown how the ZnO material properties can be influenced by choosing adequate deposition conditions and what effects are observed in terms of cell performance.

The developed processes are subsequently scaled up on the In-Line coater A700V at Fraunhofer IST. A-Si/µc-Si tandem modules on 30 x 30 cm² substrates reached initial efficiencies of up to 9.8 %.

In order to provide a sufficient wear protection on tools which finally supports to increase productivity in manufacturing processes, the substrates can be coated with hard material layers. Because of its high hardness and oxygen resistance Titanium-Aluminium-Nitride (TiAlN)- hard material coatings have been applied usually for high speed cutting and minimal lubrication applications.

In the past many attempts to increase the performance of TiAlN- coatings had been carried out. One approach e.g. was the optimisation of the Al- content in TiAlN- thin films. The performance of the coating increases with aluminium content until a maximum value is reached when the structure changes from face centred cubic (fcc) to body centred cubic (bcc).

The aluminium content can be modified by the target material composition itself as well as by process parameters. E.g. it is well-known that through decreasing substrate voltage (BIAS) the Al- content in TiAlN coating is increased.

In the standard hard material coating process of the DREVA 600 coating plant two hollow cathode (HC -) plasma sources are being used for the in-situ pre-treatment of the substrates i.e. for electron impact heating and Ar- ion etching. Six vacuum arc (VARC-) sources provided as metal evaporation sources operate in the subsequent reactive thin film deposition process.

Thus, both hollow cathode plasma sources of the DREVA 600 are completely integrated into the deposition process itself. By means of optical emission spectroscopy (OES-) measurements it can be demonstrated that the additional hollow cathode plasma provides an increase of excitation and ionisation degree of the evaporated aluminium in the new TiAlN deposition process. Results, how effectively this additional HC- plasma influences the TiAlN-thin film properties will be shown.

The main challenges in capacitor web coating are the decreasing web thickness, the increasing conductivity and the competition for higher web speeds, i.e. higher productivity. All trends require a better transfer of the heat of condensation from the evaporated material to the coating drum in order to prevent thermal damage to the web. Applying a bias voltage to the web after the actual coating is used in most of today´s coaters, but is limited by the break through voltage of the web itself. Furthermore, pinholes cause a frequent collapse of the bias and the corresponding enhanced heat transfer, which results in patches of thermally damaged web or ultimately in web tear.

Modern coaters use an elaborate system of charge management of the web throughout the coating system. A pre treatment station neutralizes the (changing) inherent static charge on the web and creates a steady ground state of the web from the unwinder. At the same time a surface modification of the web can be performed to promote adhesion. A scanning electron beam then applies a very high, but immobile (static) charge before coating. The resulting difference in potential between web and coating drum is an order of magnitude higher than conventional bias and results in a much higher adhesion force of the web to the drum. In consequence, the heat transfer from web to the drum is enhanced during the entire time of contact to the coating drum. This allows coating of thinner web at higher speeds with higher thickness. Finally, a post treatment station assures the complete discharge of the web on the rewinder.

This paper explains the principle of electron beam bias, quantitatively compares the electrical forces at work and the experimental results of web coating with traditional and electron beam bias systems. The necessary hardware is explained and production data are discussed.