Quantitative comparison of simulated and experimental silver crystal formation at the interface of silver thick film contacts on n-type silicon

We present results from a study of the nanostructure of silver thick film contact interfaces on n-type Si-(111) and Si- (100). At the interface of such contacts silver crystals grow in pits, which form during contact formation. They carry the current across the interface and hence determine the contact resistance, which is an efficiency limiting parameter of silicon solar cells. The size and shape of the silver crystals is governed by the pits in the silicon surface, because the crystals only emerge in these pits. Consequently, being able to predict pit characteristics in dependence of contact processing parameters will enable the prediction of the crystal size and coverage, which influences the contact resistance. In the present work, we investigate these pits experimentally by scanning electron microscopy. We are the first to simulate the pit formation at a silver thick film contact interface based on the removal probability of silicon surface atoms. For this purpose, an existing model, which was originally designed to describe the mechanism of wet chemical etching of silicon, is modified to match our interface conditions. Our simulations lead to a consistent and quantitative correct description of all experimental data. The simulations enable to predict pit formation for arbitrary contact formation process parameters like temperature or duration for silver thick film contacts on n-type silicon.