Low temperature plasmaless etching of silicon dioxide film using chlorine trifluoride gas with water vapor

The etching characteristics of silicon dioxide (SiO₂) films using chlorine trifluoride (ClF₃) gas with water (H₂O) vapor, without using the gas discharge method, have been studied. When the sample was cooled to -50 °C, a high SiO₂ etching rate of 400 nm/mix was obtained. On the basis of in situ Fourier transform infrared spectroscopic analysis for the vapor phase and for the sample surface, the etching mechanism of the high SiO₂ etching rate was proposed. The mechanism consists of (i) adsorption of H₂O onto the sample surface at low temperatures, (ii) hydrogen fluoride ion (HF₂^-) formation by the reaction of hydrogen fluoride (HF) with H₂O, in which the HF is formed by the hydrolysis of ClF₃, (iii) silicon tetrafluoride (SiF₄) formation by the reaction of HF₂^- with Si in SiO₂ networks, and (iv) desorption of SiF₄ as a gas from the SiO₂ surface. It has been confirmed that low temperature plasmaless etching using a ClF₃/H₂O gas mixture is effective for the removal of SiO₂ films. In addition, the etch rate for polycrystalline silicon (poly-Si) can be controlled by changing the substrate temperature from 25 to -50 °C. This property allows for the sequential etching of native oxide and poly-Si films.