The effect on surface passivation of the deposition power in plasma enhanced chemical vapour deposited silicon nitride

In this paper we present an investigation on the influence of RF power (PRF) on the passivating properties of silicon nitride (SiNx:H) in a direct plasma enhanced chemical vapour deposition (PECVD) system and found that PRF greatly affected the passivation quality. Minority carrier lifetime measurements revealed a monotonous decrease in effective lifetime from 470μs at 5.4 mW/cm2 to 103μs at 13.5 mW/cm2 above which the decrease was less pronounced. Capacitance-voltage measurements were performed using a bias from -15 V to 15 V at frequencies from 1kHz to 1MHz and showed strong dependence on frequency, suggesting a high concentration of
electronically active traps near the SiNx:H/Si interface for all values of PRF. Admittance spectroscopy measurements suggested an increasing number of shallow traps in the band gap with increasing PRF. We argue that increase in the number of traps with PRF that cause the decrease in minority carrier lifetime is due to ion bombardment of the Si surface during PECVD in combination with a reduced concentration of passivating Si-H bonds.