FUNDAMENTAL PROCESSES IN SPUTTERING OF RELEVANCE TO THE FABRICATION OF THIN-FILM SOLAR-CELLS

If thin film photovoltaic cells are to have a significant impact on U. S. electrical energy needs, facilities with production capabilities in the range of 25 - 50 Mw per year are required. The deposition sections in these facilities must provide large deposition areas, large storage of coating material and reasonable deposition rates. D. c. reactive sputtering using magnetron sources shows promise for meeting all three of these requirements for the deposition of both CuInSe//2 and amorphous hydrogenated silicon (a-Si:H). The question thus is whether films with properties suitable for fabricating high performance photovoltaic devices can be fabricated by reactive sputtering. This paper reviews several atomic level processes that occur during sputter deposition and that influence film properties. Attention is given to target processes that lead to the formation of selenide surface layers during CuInSe//2 reactive sputtering, and to substrate reactions which appear to control film properties in the CuInSe//2 case and to a degree in the a-Si:H case. Experiments which are under way to investigate the critical issues in CuInSe//2 and a-Si:H reactive sputtering are described.