Porous silicon has been used in many applications such as light-emitting materials in optoelectronics, bone growth media, gas and humidity sensors, sacrificial layers in micromachining, surface texturization in photovoltaics or substrate material in mass spectrometry. Also it is important in the industries of solar cells and diffusion membrane. Formation of porous silicon can be carried out by chemical etching, photo-etching, stain etching in presence of oxidizing agent, metal-assisted etching and anodic etching.