Analysis of ion-implanted amorphous and polycrystalline silicon films as diffusion sources for ultrashallow junctions

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Abstract
This paper discusses the diffusion of As, P, and B in amorphous and polycrystalline silicon‐on‐single‐crystal silicon systems during rapid thermal annealing and furnace annealing. It is found that the changes of microstructure during annealing play a major role in determining the diffusion profiles in the substrate as well as in the polycrystalline silicon layer. For As or P doping, a drive‐in diffusion results in a much larger grain microstructure for as‐deposited amorphous silicon than for as‐deposited polycrystalline silicon, which leads to the formation of shallower junctions in the substrate for the first case. For B doping, there is little difference in the final microstructure and junction depth between the two cases. At high anneal temperatures, the native interfacial oxide breaks up, causing epitaxial realignment of the polycrystalline silicon film and subsequent enhanced diffusion in the substrate.