Degradation of Surface Passivation and Bulk in p-Type Monocrystalline Silicon Wafers at Elevated Temperature

Abstract

The surface passivation quality and the bulk lifetime of boron-doped p-type Czochralski silicon wafers were studied in response to dark annealing at 175 °C, using in situ effective lifetime measurements. We investigated non-fired and fired silicon nitride (SiNx), aluminum oxide (AlOx) capped with SiNx, and thermally-grown silicon oxide (SiO2). Modulation in surface passivation quality and bulk lifetime was detected only in cases where hydrogen is assumed to be released into the silicon wafer from the dielectric (AlOx/SiNx stack and fired SiNx layer). Interestingly, the degradation of both the surface and the bulk were followed by a recovery. It is also interesting to note that the changes in the surface and the bulk seem to be related, as the surface degradation starts when the initial bulk degradation ends. This study indicates a possible involvement of hydrogen in both the degradation and the recovery processes. The evolution of the effective lifetime as a function of time is similar to that reported for carrier-induced degradation in multicrystalline wafers; however, occurring on a different time scale. Hence, these findings may also be valuable for investigation of other degradation mechanisms in different silicon materials.