Al2O3 and TiO2 deposited by atomic layer deposition are evaluated as etch masks for dry etch processes in an inductively coupled plasma reactor using the Bosch process. In the inductively coupled plasma chamber during deep silicon etching, because of the chemical nature of the etch process and the inert nature of Al2O3, the result is exceptional selectivity for silicon over as-deposited Al2O 3, particularly at relatively low bias and high pressures used for through-wafer etching. TiO2 is less resistant and appears to suffer more from chemical attack. In both cases, etch rate increases slowly with increasing rf bias. However, there is a sharp discontinuity in the etch rate of Al2O3 when the bias power is operated in a pulsed low-frequency mode. This is thought to be due to increased sputtering from heavier ions. Preliminary studies indicate the etching conditions for Al 2O3 may be extended into a dielectric etch regime requiring more study.