Ultrahigh vacuum surface analysis of silicon (100) treated in aqueous hydrofluoric acid and buffered hydrofluoric acid solutions

Abstract

X-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, and thermal desorption spectroscopy were used to study the surface chemistry of Si(100) after wet chemical treatments in dilute HF (1 vol%; pH 3) and buffered HF (15 vol% NH 4OH, 22 vol% HF, 63 vol% H 2O; pH 4). This study was performed in a combined ultrahigh vacuum-electrochemical chamber (UHV-EC) in which sample transfer occured under ultrapure conditions. After wet chemical treatments the Si(100) surface had both SiF and SiH species present, and upon rinsing, SiF was hydrolyzed to SiOH resulting in a lower concentration of SiF. Treatment in buffered HF produces SiF 4 as an etching product. Evidence for this comes from detection of adsorbed SiF - 5 following treatment and transfer to UHV. The ultraclean transfer method used in this study greatly reduces the amount of adsorbed hydrocarbons compared to previous studies involving sample transfer through laboratory air, and thereby allows a more thorough UHV analysis of the surface chemistry of wet etching.