Morphological Development from Uniform Microporous Structure to Macropore-Like Structure

INTRODUCTION Porous silicon can be formed by electrochemical anodization in HF solution below the critical current density. The size and shape of the pores vary depending on wafer resistivity, current density and solution composition. Pores are mainly classified into three groups according to the pore diameter, micropores ( 50 nm). The first macropore structure on p-type silicon was observed by Propst and Kohl in 1994 [1]. There are some reports that the nanoporous layer is covering or filling the macroporous layer [2]. In our previous work, the way to transform from nano to macroporous regimes was proposed [3]. When the nanoporous materials in the skeleton structure which is a macropore-like structure filled with a microporous body are completely dissolved, a macroporous structure appears. In the present work, the development from the skeleton structure to the macropore-like structure is studied.