The Effect of SiN_x:H Stoichiometry on Electrical and Chemical Passivation of Al₂O₃/SiN_x:H Stack Layer on p-type Silicon Wafers

In this paper, we report on the influence of SiNx:H stoichiometry on Al2O3/SiNx:H passivation stacks. We analyze the fabricated dielectric layers with four methods: FTIR, C-V, PCD and EQE. SiNx:H with a lower refractive index (SiN1) is poorer in H content than the one with a higher refractive index (SiN2) according to FTIR peaks. The calculated fixed charge density of the non-fired SiN1 layer is larger than SiN2; however, Al2O3 layer has the greatest magnitude but in negative polarity. The charge density of the Al2O3/SiN1 stack increases in magnitude with an increase in peak firing temperature while the Al2O3/SiN2 stack shows a decrease in magnitude. Al2O3/SiN1 stack resists a higher peak temperature during the fast-firing process with a relatively small reduction in iV(oc) values on symmetrically etched p-Si wafers due to the relatively lower H content of SiN1. Our results suggest that the chemical passivation of Si is more pronounced than the field effect passivation. We also investigate the effect of SiNx:H on the PERC solar cells with Al2O3/SiN1 and Al2O3/SiN2 stacks. The EQE results measured on the fabricated PERC cells demonstrate that the IR response is better for the PERC solar cells with Al2O3/SiN1 rear stack passivation implying enhanced passivation.