Reaction kinetics during the thermal activation of the silicon surface passivation with atomic layer deposited Al2O3

The excellent surface passivation of crystalline silicon provided by Al2O3 requires always an activation by a thermal post-deposition treatment. In this work, we present an indirect study of the reaction kinetics during such thermal activation treatments for Al2O3 synthesized by atomic layer deposition. The study was performed for Al2O3 deposited at varying temperatures, which results in different micro-structures of the films and, in particular, different hydrogen concentrations. The effective carrier lifetime was measured sequentially as a function of the annealing time and temperature. From these data, the reaction rate Ract and the activation energy EA were extracted. The results revealed a rather constant EA in the range of 1.4 to 1.5 eV, independent of the deposition temperature. The reaction rate, however, was found to increase with decreasing deposition temperature, which correlates with an increasing amount of hydrogen being incorporated in the Al2O3 films. This is a strong indication for an interface hydrogenation that takes place during the thermal activation, which is limited by the amount of hydrogen provided by the Al2O3 layer.