Photo-induced preferential anodization for fabrication of monocrystalline micromechanical structures

Photo-induced preferential anodization (PIPA) for fabrication of monocrystalline micromechanical structures is presented. P-type silicon formed in an n-type substrate is preferentially anodized in an aqueous solution of hydrofluoric acid under illumination. This technology is based on anodization and the photovoltaic effect. In experiments, dependence on light intensity, HF concentration, and the ratio of the pn-junction area to the entrance area of the HF solution was investigated. It was found that porous silicon conditions depend on light intensity and HF concentration and that anodic current density provided by a pn-junction is the most important factor for controlling PIPA. A monocrystalline microbridge structure 1 mu m thick, 20 mu m wide, and 300 mu m long was formed using this technology. >