Silicon oxide etching mechanism by hydrogen fluoride and methanol vapor mixture

Abstract We investigate mechanisms of silicon dioxide (SiO 2 ) etching involving hydrogen fluoride (HF) and a methanol (CH 3 OH) vapor mixture, particularly, the contributions of water (H 2 O) and CH 3 OH. H 2 O might come from the injected gases, chamber wall, and the SiO 2 films, but the amount is very small. Instead, during the etching process, two molecules of H 2 O are generated, which might affect SiO 2 etching. Considering no incubation time and stable etching rates by adding CH 3 OH, CH 3 OH could be a primary catalyst according to our investigations. Accordingly, we can suggest a SiO 2 etching mechanism by HF and CH 3 OH. The mixture gases of HF and CH 3 OH are exposed to the SiO 2 surface. When the HF and CH 3 OH pressures are high enough for condensation on the SiO 2 surface, a thin condensed layer is generated. Hydrogen fluoride can be easily soluble to the condensed layer, at which it is ionized causing the etching of SiO 2 . A high enough concentration of byproducts generates vapor silicon terafluoride and H 2 O, enabling etching to proceed.