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 postdeposition anneal is mandatory to activate the surface passivation. Thus, the influence of this anneal on the interface properties, density of negative fixed charges Qf and density of interface traps Dit, will be investigated and correlated to the measured minority carrier lifetime. In the case of plasma enhanced ALD, Qf is already high in the as-deposited state and the annealing process only has a minor effect on Qf (Qf increases by 20-50 %, depending on the annealing temperature). The Dit however is strongly reduced by the post-deposition anneal, decreasing by two orders of magnitude. This large reduction in Dit is a prerequisite for benefiting from the strong field effect induced by the high density of negative charges of the Al2O3.