Surface passivation of crystalline silicon wafer via hydrogen plasma pre-treatment for solar cells

Abstract

The carrier lifetime of crystalline silicon wafers that were passivated with hydrogenated silicon nitride (SiN x :H) films using plasma enhanced chemical vapor deposition was investigated in order to study the effects of hydrogen plasma pre-treatment on passivation. The decrease in the native oxide, the dangling bonds and the contamination on the silicon wafer led to an increase in the minority carrier lifetime. The silicon wafer was treated using a wet process, and the SiN x :H film was deposited on the back surface. Hydrogen plasma was applied to the front surface of the wafer, and the SiN x :H film was deposited on the hydrogen plasma treated surface using an in-situ process. The SiN x :H film deposition was carried out at a low temperature (<350 °C) in a direct plasma reactor operated at 13.6 MHz. The surface recombination velocity measurement after the hydrogen plasma pre-treatment and the comparison with the ammonia plasma pre-treatment were made using Fourier transform infrared spectroscopy and secondary ion mass spectrometry measurements. The passivation qualities were measured using quasi-steady-state photoconductance. The hydrogen atom concentration increased at the SiN x :H/Si interface, and the minority carrier lifetime increased from 36.6 to 75.2 μs. The carbon concentration decreased at the SiN x :H/Si interfacial region after the hydrogen plasma pre-treatment.