Cryogenic etching of a-Si, SiO 2 , and Si 3 N 4 materials by CHF 3 /Ar inductively coupled plasma is investigated in a range of temperature from −140 to +20 °C. Samples of the three different materials are placed together on the same silicon carrier wafer. Depending on the experimental conditions, etching or deposition regimes were obtained on the samples. The thickness variation was measured by spectroscopic ellipsometry. A process window between −120 and −80 °C was found in which the Si 3 N 4 surface is etched while CF x deposition is obtained on a-Si and SiO 2 surfaces, resulting in the infinite etching selectivity of Si 3 N 4 to the other materials. At high enough self-bias (−120 V) and very low temperature (<−130 °C), Si 3 N 4 etch is reduced down to a very low value, while a-Si and SiO 2 are still being etched, which inverses the selectivity between Si 3 N 4 and the two other materials. EDX analyses of a Si 3 N 4 /a-Si/SiO 2 layer stack after the same etching process carried out at 20 and −100 °C confirm the presence of carbon and fluorine on a-Si at low temperature, showing the effect of the low temperature to switch from the etching to deposition regime on this material.