In situ infrared characterization of the silicon surface in hydrofluoric acid

The surface of silicon in hydroflouric acid (HF) is coated with covalently attached hydrogen (SiHx groups, with x=1,2,3), with probably a very small concentration of SiF bonds. In contrast with a recent claim by Niwano et al. [J. Appl. Phys. 79, 3708 (1996)], we show that the concentration of SiF bonds is as yet beyond infrared detection limits. Our analysis indicates that the band at 2230 cm−1 observed by these authors actually arises from electrolyte absorption.