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 degreesC, a high SiO2 etching rate of 400 nm/min was obtained. On the basis of in situ Fourier transform infrared spectroscopic analysis fur the vapor phase and for the sample surface, the etching mechanism of the high SiO2 etching rate was proposed. The mechanism consists of ii) adsorption of H2O onto the Sample surface at low temperatures, iii) 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 (ir) 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. Tn addition, the etch rate for polycrystalline silicon (poly-Si) can he controlled by changing the substrate temperature from. 25 to -50 degreesC. This property allows for the sequential etching of native oxide and poly-Si films.