Manifold use of growth substrate in the porous silicon-layer transfer-process

The number of process cycles that the same monocrystalline Si growth substrate wafer can be used is an important issue when applying layer transfer processes to photovoltaics. Together with the thickness of the epitaxial layer this number controls the Si consumption. The nine-fold application of the porous silicon (PSI) process to the same 4" silicon wafer is demonstrated. The electronic quality of the epitaxial layer is maintained. During this nine-fold use the average consumption of Si from the substrate wafer is 46 μm per cycle. With an improved processing sequence the Si consumption per cycle is reduced to only 12 μm.