Modeling and Characterization of Gas‐Phase Etching of Thermal Oxide and TEOS Oxide Using Anhydrous HF and CH 3 OH

Abstract

We propose a model for a gas‐phase etching of silicon dioxide using anhydrous HF gas and methanol vapor on the basis of its mechanism and characteristics which were reported by previous researchers. Here, the etch reaction rate was assumed to be determined by the formation step of resulting from the ionization reaction between HF and adsorbed physcially on the oxide surface. The validity of this etch model was confirmed by the experimental data obtained from etching thermal oxide and tetraethylorthosilicate (TEOS) oxide at various etching conditions: HF partial pressure of 2 to 35 Torr, partial pressures of 0.3 to 4.5 Torr, and wafer temperatures of 25 to 75°C. It was shown that the gas‐phase etching of the oxides could be well characterized by the behaviors of physical adsorptions for HF and molecules on the oxides, which were expected from the Brunauer‐Emmett‐Teller (BET) equation with the values of parameters in the etch model. Also, it was shown that the etch selectivities between the thermal oxide and the TEOS were mainly dependent on the wafer temperature and the reactant partial pressures, and could be in the range of 2 to 30 according to the etching conditions in the gas‐phase regime.