MECHANISM OF (111)SILICON ETCHING IN HF-ACETONITRILE

The electrochemical oxidation-dissolution of (111) silicon has been in vestigated in HF-acetonitrile (MeCN) solutions. Four electrons per sil icon were observed per oxidized silicon. Current doubling (quantum eff iciency of 2.2) was observed for the photo-oxidation of n-Si. Unlike t he etching of (111) silicon in aqueous HF solutions, no pores were for med in HF-MeCN. The etching of (111) silicon in HF-MeCN resulted in th e formation of triangular pits defined by the (111) planes. A mechanis m for the etching is proposed where steric hindrance of the surface te rminated hydrogens induces bond strain and enhances the chemical react ivity. The mechanism also accounts for the formation of pores in (100) silicon, and the formation of a highly branched microporous structure when silicon is etched in an aqueous solution.