Sputtering of silicon thin films for passivated contacts

Abstract

We investigate SiOx/poly-Si layer stacks produced by sputter deposition of silicon for use as charge carrier selective passivated contacts. Excellent passivation quality with implied open circuit voltages up to 735 mV and Jo = (5.2 ± 0.8) fA/cm2 are demonstrated for n+ doped poly-Si on 1-5 Ωcm saw-damage etched n-type CZ wafers. Layers of intrinsic a-Si with a thickness of 100 nm have been deposited on a wet chemically grown SiOx layer. Subsequently, a tube furnace process was used for doping the layers by POCl3 diffusion and simultaneous solid phase crystallization to poly-Si. All layers remain free of blistering after all process steps, including PECVD SiNx deposition for hydrogenation and a thermal treatment mimicking the contact firing process of screen printed solar cells. The influence of different deposition conditions, as well as diffusion and annealing parameters on the passivation quality are discussed and layers produced with different sputter platforms, including a lab-type device and an industrially relevant inline tool with rotatable magnetrons, are compared.