On The Mechanism of the Anisotropic Dissolution of Silicon in Chlorine Containing Hydrofluoric Acid Solutions

Abstract

The wet-chem. acidic treatment of silicon wafer surfaces is important in photovoltaic, microelectronic and further industries. Recent works report on new mixts. for acidic anisotropic etching mixts. based on hydrofluoric acid HF and hydrochloric acid HCl with an added oxidant. The aim of this work was to get an insight into the reactions during the etching process of silicon in the system HF-HCl-Cl2. The etching mixts., gaseous reaction products, as well as the generated silicon surfaces were investigated by 19F, 29Si, and 35Cl NMR, ion chromatog. (IC), iodometric titrn., FT-IR spectroscopy, diffuse reflectance FT-IR spectroscopy (DRIFT) as well as SEM and energy dispersive x-ray spectroscopy (SEM-energy-dispersive x-ray anal.). A reaction scheme for the anisotropic dissoln. of silicon in chlorine contg. aq. HF-solns. is proposed, which involves dissolved Cl2 as the oxidizing agent, coordination of fluoride/chloride ions and formation of a hydrophilic surface. These steps are similar to the well known alk. anisotropic etching of silicon. [on SciFinder(R)]