Porous silicon pore filling by metal electroplating

Abstract

Porous silicon can be used as an insulating material in Si devices and as a membrane for ion or molecule separation. Its recently demonstrated photo- and electro-luminescence properties may find novel applications in optoelectronics. Porous silicon has a large internal surface, and, with its pores filled with conducting materials, can form a capacitor with a high charge storage capacity. Recently, thin metal films have been electroplated on porous silicon substrates. These films were then detached and used as condenser microphone diaphragms. Electroplated metal films can also provide electrical contacts to an electro-luminescent porous silicon structure. In this paper, we report our TEM study of a copper electroplating process. We found that in such a process copper preferentially deposits from the bottom of the pore tips upward and fills the entire length of each pore as well as the horizontal side branches.Anodization of silicon was performed in an aqueous HF solution to form a porous layer. Silicon substrates used in this experiment were n-type, (l00)-oriented wafers with a doping concentration of 1017 cm−3 and p-type, (l00)-oriented wafers with a doping concentration of 1019 cm-3.