P-type Crystalline Silicon Surface Passivation Using Silicon Oxynitride/SiN Stack for PERC Solar Cell Application

Abstract

Silicon nitride layers have been long used as front side passivation layers for n-type silicon substrates. Here we explore the passivation property of silicon oxynitride (SiON) and silicon oxynitride/silicon nitride stacks, instead of SiO₂, on p-type silicon wafers for back-surface passivation. SiON and SiON/SiN stacks can be deposited at low temperatures with very high deposition rates compared to SiO₂. Since SiN and SiON form an inversion layer at the interface when contacted with p-type silicon, these dielectric layers are not ideal for passivating p-type substrates but the commercial benefits of these dielectric layers in terms of low thermal budget and high deposition rates motivated us to look deeper into the passivation properties of these dielectric layers by using capacitance–voltage and carrier lifetime measurements. Different types of charges like fixed charge, mobile charge, and interface charge have been calculated using “MOS capacitor” like structures with SiON and SiON/SiN stack as insulating layers. These results indicate that the interface charge dictates the passivation quality of these dielectric layers.