Infrared study of chemistry of Si surfaces in etching solution

The chemistry of Si(100) and (111) surfaces during immersion in dilute hydrofluoric acid (HF) solution was investigated ‘in-situ’ and in real time using infrared absorption spectroscopy in the multiple internal reflection geometry. We demonstrate that in dilute HF solution, Si surfaces are not perfectly terminated by hydrogen, but is covered in part with hydrogen-associated Si fluorides, such as SiH2(SiF) and SiH2F2. We find the hydrogen coverage of the surface in dilute HF solution depends on the HF concentration of the solution. It is shown that rinsing in water following HF treatment leads to complete hydrogen termination of the surface. The present results suggest that hydrogen-associated Si fluorides are involved in the etching of Si crystal surfaces.