Improved Silicon Surface Passivation of APCVD Al₂O₃ by Rapid Thermal Annealing

Short-duration post-deposition thermal treatments at temperatures above those normally used for annealing activation have the potential to further improve the already excellent passivation of crystalline silicon (c-Si) achieved by Al₂O₃, but have so far received little attention. In this work we investigate the influence of rapid thermal annealing (RTA) on the surface passivation of c-Si by Al₂O₃ deposited by atmospheric pressure chemical vapour deposition (APCVD) as a function of RTA peak temperature between 500 and 900 °C, and for Al₂O₃ deposition temperatures between 325 and 440 °C. The saturation current density J₀ of undiffused p-type surfaces is observed either to increase or decrease following RTA depending on the Al₂O₃ deposition temperature and the RTA peak temperature. The optimum deposition temperature depends on the post-deposition thermal processing to be applied. Films deposited at lower temperatures provide worse passivation after low temperature heat treatment, but maintain this passivation better at higher RTA temperatures. An exceptionally low J₀ of 7 fA cm^-2, due to the combination of a very low interface state density D_it and unusually high negative fixed charge density Q_f, is achieved by the use of a short 500-550 °C RTA combined with optimised deposition conditions.