Highly selective isotropic gas-phase etching of SiO₂ using HF and methanol at temperatures –30 °C and lower

The gas-phase etching of SiO₂ was examined using HF and methanol vapor at temperatures below 0 °C and at low pressure. The etching rate of SiO₂ increased with decreasing temperature and showed a maximum around –30 °C. The obtained etching rate was a maximum of 40 nm min⁻¹ at plasma-enhanced chemical vapor deposition SiO₂. The etching rate of SiN examined for comparison was more than ten times smaller than that of SiO₂ under the same condition. As a result, the etching selectivity of SiO₂ to SiN was found to be over 20 at –40 °C. When utilizing a low temperature of less than –30 °C, gas-phase etching of SiO₂ showing a high etching rate and selectivity was achieved.