Improvement of transport parameters in solar grade monocrystalline silicon by application of a sacrificial porous silicon layer

Gettering impurities away from device active regions has already become an integral part of manufacturing integrated circuits (IC) using Czockralski (Cz) Si wafers. The possibility of gettering impurities from solar grade silicon was studied. The aim of this study is to investigate the effect of gettering unwanted impurities from solar grade silicon wafers on their electronic properties by using a porous silicon (PS) sacrificial layer combined with an Infrared heat treatment processing in N2 or O2 atmospheres. This process enables to concentrate unwanted impurities in an inactive region (i.e. the PS layer) close to the surface and to remove them by dissolving the PS layer. Capacity–Voltage (C–V) impedancemetry, Hall effect and light beam induced current measurements were used to determine the majority carrier density, the carrier mobility and the minority carrier diffusion length (Ld) of the Si wafer, respectively. Heat treatments in both N2 and O2 ambient lead to a decrease of the Si wafer majority carrier density together with an enhancement of the carrier mobility and the minority carrier diffusion length, nevertheless better results were obtained in O2 atmosphere. These results give evidence of the effectiveness of using PS for an efficient gettering effect in solar grade monocrystalline Si.