Formation Mechanism of Porous Silicon Layer by Anodization in

The mechanism of formation of porous silicon layer (PSL) has been studied according to the following experimental results. PSL is formed by the local dissolution of silicon which occurs only at the base of the pores. The HF concentration f the electrolyte in the pores of PSL is constant during anodiza-tion and the anodic reaction in the pores proceeds uniformly in the thickness direction. The dissolution of silicon in the pores is the results of the divalent and the tetravatent reactions of silicon with HF, without the disproportionation reaction. The insoluble surface porous film (SPF) exists at the surface of PSL and the silicic acid is formed in PSL. A model of forming PSL is proposed, with emphasis being placed on the anodic reaction and the local dissolution of silicon which is initiated by SPF and is promoted by the hindrance layers composed of the sJ_licic acid. The anodization of silicon in hydrofluoric acid solu-tion has been studied by many investigators. Thes