Effect of films thickness and hydrogen annealing on passivation performance of plasma ALD based Hafnium oxide films

Abstract

We investigate the silicon surface passivation property of Plasma Atomic Layer Deposited (PALD) hafnium oxide (HfOx) thin films and study its dependence on silicon (Si) doping type, film thickness, and post-deposition annealing conditions. Our results demonstrate that as-deposited HfOx films exhibit poor passivation quality that can be improved by performing post-deposition annealing at 450℃ in hydrogen ambient. We demonstrate that the films can effectively passivate p-Si surfaces as compared to n-Si, where the surface passivation quality of the films improves with increasing film thickness for both silicon doping type. The best performance with minority carrier lifetime of 1.7 ms, corresponding surface recombination velocity (SRV) ~10 cm/s, is achieved for HfOx films thickness ~23 nm deposited on the p-Si substrate. The Capacitance-Voltage (C-V) measurements give an insight into the passivation mechanism of the studied films. Field effect passivation is found to be an important passivation mechanism in plasma ALD deposited HfOx films, as revealed by C-V measurements. The films are also characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), which reveals the chemical passivation provided by hydrogen ambient annealing. Overall, the impact of hafnium oxide film thickness and hydrogen ambient annealing conditions on silicon surface passivation is investigated. Our findings will help in utilizing plasma ALD process based hafnium oxide films for silicon solar cell device application.