High purity deposition of silicon layers with rates > to 300 nm/s

High rate silicon vacuum deposition by electron beam evaporation is very attractive because of economic reasons as well as because of the high layer purity. Both are urgently needed for many silicon thin film applications, including silicon thin film photovoltaics. In the investigations described here, two different axial e-beam gun/crucible setups were applied, a water-cooled crucible setup and a crucible-free setup. For both setups the size of the melting bath is analyzed, limiting the adaptable electron beam power. Static deposition rates > 300 nm/s are demonstrated, which allow deposition costs as low as 0.03 e/WP for a 15 mm silicon layer on a 200 mm x 200 mm glass substrate for thin-film photovoltaic (PV) application. This is substantial lower than the 0.17 e/WP silicon wafer cost forecast for 2018 [1]. The high rate deposition process also offers new opportunities for the production of thick silicon layers as functional layers. First results for 8 EL 180 mm thick silicon layers are demonstrated. The iron and copper impurities of layers were below the detection limit of D-SIMS measurements and fulfill the purity demands 5.1014 atoms/cm3 for iron and 3.1014 atoms/cm3 for copper formulated by Hofstetter et al. [2] for high effective solar cells.