Etching of thin SiO2 layers using wet HF gas

Abstract

The etching of SiO2 layers on silicon with HF/H2O vapor mixtures using a N2 gas flow as a carrier was studied. The differences between the etching process of SiO2 on silicon using HF in water solutions and the gaseous etching process were investigated using x-ray photoelectron spectroscopy analysis. The experiments focused on the removal of thin (native) oxide layers. It is shown that HF gas etching yields a good and reproducible removal of the suboxide (SiOx) interface layer. Various parameters influencing the etching process are discussed. In our experiments the HF-gas etch proved to be superior to the liquid-HF etch with respect to the removal of the SiOx layer. After the HF gas etching process a logarithmic regrowth of an oxide layer in air occurs at a rate of 0.2 to 0.3 nm/decade (time in hours). Flashing HF gas etched samples to 700 °C for 2–3 min under ultrahigh vacuum conditions results in complete removal of oxygen.