Study of the porous polycrystalline silicon formation process

Abstract

Electrochemical dissolution (in hydrofluoric acid) of p-type polycrystalline silicon layers deposited on crystalline silicon substrates has been studied. Some properties of the porous silicon (PS) layers obtained are described. The dissolution occurs via two processes that take place simultaneously, at close rates. The first one is the formation of macropores, which results in the development of a columnar structure; the second is the transformation of the columns into a mesoporous medium. The PS layers obtained have a smooth surface, a sufficiently high porosity and a high etching rate in aqueous KOH solutions, which is important for the use of PS as sacrificial layers. Valuable information on the process is obtained by in situ capacitance measurements during electrochemical dissolution.