Silicon substrates and thermally grown oxide films were exposed to ClF3 gas at various temperatures between room temperature and 600℃. Above room temperature, the activation energy of the silicon etch rate is 0.18 eV. The activation energy of Si02 etch rate below 400℃ is estimated to be 0.12±0.01 eV. The obtained etch selectivity of silicon with respect to the Si02 is 100-300 between room temperature and 400℃. An enhanced etch rate is observed for the n-type silicon with low resistivity near room temperature. The CIF3 gas, which has appropriate vapor pressure, has useful properties not only for in-situ cleaning but also for micromachining of silicon-related materials.