New fabrication method for multicrystalline silicon layers on graphite substrates suited for low-cost thin film solar cells

A new method for the fabrication of a columnar, multicrystalline silicon layer on a graphite substrate is presented. This method basically involves three process steps: (1) Deposition of a thin (3-5 μm) silicon layer, (2) zone melting recrystallization of this layer with a line electron beam as the heat source to form a multicrystalline seed layer, and (3) thickening of the seed layer by high temperature, epitaxial chemical vapour deposition (CVD) to a thickness of 20-40 μm. The recrystallization leads to (110)[112]-textured silicon seed layers if sufficiently high scan velocities are applied. The degree of deviation from the ideal (110)[112]-texture increases with decreasing scan velocity. The doping level of the seed layer is found to be only weakly affected by the zone melting recrystallization. The epitaxial layer grown on top of the seed layer exhibits a columnar grain structure.