Passivation of n $^{+}$ -Type Si Surfaces by Low Temperature Processed SiO $_{2}$ /Al

The surface passivation of SiO₂/Al ₂O₃ stacks prepared at low process temperatures was investigated on phosphorous diffused n⁺-type Si surfaces with a broad range of sheet resistances. Two kinds of SiO₂ films were prepared, the first with plasma-enhanced chemical vapor deposition (PECVD) and the second in a wet chemical process. After atomic layer deposition of the Al₂O₃ capping layer, the resulting SiO₂/Al₂O₃ stacks differ in the polarity of their fixed charge density, i.e., the PECVD SiO₂ stacks had a positive and the wet chemically grown SiO₂ stacks a negative fixed charge density. The PECVD SiO₂/Al₂O₃ stacks resulted in a high surface passivation over a broad range of sheet resistances whereas the wet chemically grown SiO₂ stacks were only feasible for diffused surfaces with low sheet resistances (<; 100 Ω/□). By corona charging experiments, it was established that the field effect based on a negative fixed charge density was the reason for the loss in surface passivation in the specific range of diffused surfaces.