Effect of wafer resistivity and HF concentration on the formation of vertically aligned porous silicon

In this study, the mechanism of vertically aligned porous silicon formation was examined. Silicon wafers with various resistivities and electrolytes containing different HF concentrations were used to explain porous silicon formation by the reaction at the silicon/electrolyte interface. Total pore volume increased proportionally to the current applied and anodization time. As the concentration of HF increased, pore depth and total pore volume formed in silicon anodization increased, then decreased beyond the optimum point. At a given applied current, total pore volume formed by anodization increased with an increase in resistivity of silicon wafer, but then decreased. From the mechanism of silicon etching and schematic isoetch contour of silicon suggested in this study, it is concluded that the formation of porous silicon is determined by an accumulation of F− near the silicon/electrolyte interface in silicon anodization.