The Mechanism of Surface Passivation Degradation in SiO₂/SiNx Stack Under Light and Elevated Temperature

In this article, a significant degradation of the surface passivation was observed in Czochralski silicon (Cz-Si) lifetime samples using effective lifetime measurements during 1 sun illuminated treatment at 130 °C–175 °C. The samples are passivated by plasma-enhanced chemical vapor deposited silicon nitride (SiNx) and thermally grown silicon oxide (SiO2). Samples showed strong variations in the kinetics of the surface passivation degradation depending on the passivation stacks, phosphorus diffusion, and bulk doping. Recovery of the surface passivation was only observed on samples passivated by a single silicon nitride layer. To further investigate the observed behavior, corona charging capacitance-voltage measurements were performed. It is shown that surface degradation arises from a combination of changes in interface defect density (Dit) and fixed charge density (Qf). We show that two separate degradation channels contribute to the degradation in surface passivation, where the fixed charge density continuously declines, while the interface defect density increases to a maximum and subsequently decreases. The decrease in interface defect density leads to a recovery of surface passivation.