Downstream Etching of Si and SiO₂ Employing CF₄/O₂ or NF₃/O₂ at High Temperature

Abstract

The downstream etching reaction of Si and SiO 2 employing CF 4 /O 2 or NF 3 /O 2 gas mixtures at high temperature has been studied. The Si etch rate of CF 4 /O 2 downstream etching increases with increasing temperature reaching a maximum value around 15% O 2 concentration; the amount of decrease in the SiO 2 etch rate at higher temperatures and O 2 concentrations is small. Accordingly, a reversal in Si/SiO 2 selectivity is observed at 80% O 2 concentration in the temperature range from 100°C to 400°C, but it is not found in the NF 3 /O 2 case. As a result, the reversal is ascribed to F atoms involving silicon-oxide film formation on a Si surface.