Degradation of hydrogenated amorphous silicon passivation films caused by sputtering deposition

Abstract

The degradation of thin passivation films on silicon wafers after sputtering deposition with different process parameters has been investigated. Thin intrinsic amorphous silicon passivation films with different thicknesses and with different doped top layers were deposited on textured n-doped silicon wafers. The passivation quality was measured by microwave photoconduction decay lifetime measurements before and after the sputtering processes and also after an annealing process at 150 °C in air for 12 min. The degradation which was observed shows dependencies on the passivation film thickness, the deposition process parameters and the kind of the doped top layer. Some processes lead to a strong degradation of the passivation quality even after annealing. For others the initial passivation quality could be regained after annealing. The cause of the degradation was determined to be high energy plasma photons in the range of 300–375 nm.