SiC formation and influence on the morphology of polycrystalline silicon thin films on graphite substrates produced by zone melting recrystallization

Polycrystalline silicon thin films for photovoltaic applications are produced by a zone melting recrystallization process by means of a line electron beam. During this process carbon atoms of the graphite substrate dissolve in the silicon melt. Because of the high temperatures in the molten silicon, molecular silicon carbide is formed. It crystallizes at the melt interfaces to the vacuum and the graphite substrate by a heterogeneous nucleation. Cubic SiC crystals (beta-SIC) grow up to sizes of 700 nm. The morphology of the silicon layer is significantly influenced by the crystals at the Si-vacuum interface, since they assemble in a net-like structure. In this solid lid cracks may form followed by a deformation of the surface (clod shape). Utilizing this effect e.g. the surface roughness of the polycrystalline silicon thin film can be reduced and favorable conditions are obtained for a succeeding liquid phase epitaxy process (LPE) to grow the active layer of the cell. (C) 1998 Elsevier Science S.A. All rights reserved.