Effect of a post-deposition anneal on Al2O3/Si interface properties

While Al₂O₃ has been proven to provide an excellent level of surface passivation on all sorts of p-type doped silicon surfaces, the passivation mechanism of this layer and especially the influence of the post-deposition anneal on the Al₂O₃/Si interface properties is not yet completely understood. A great increase in the surface passivation is observed after a post-deposition anneal, i.e. a post-deposition anneal is mandatory to activate the surface passivation. Thus, the influence of this anneal on the interface properties, density of negative fixed charges Q_f and density of interface traps D_it, will be investigated and correlated to the measured minority carrier lifetime. In the case of plasma enhanced ALD, Q_f is already high in the as-deposited state and the annealing process only has a minor effect on Q_f (Q_f increases by 20-50 %, depending on the annealing temperature). The D_it however is strongly reduced by the post-deposition anneal, decreasing by two orders of magnitude. This large reduction in D_it is a prerequisite for benefiting from the strong field effect induced by the high density of negative charges of the Al₂O₃.