Control of Selectivity between SiGe and Si in Isotropic Etching Processes

The selectivity between SiGe and Si has been investigated in chemical dry etching. Starting from a pure CF 4 process that etches SiGe with a good selectivity to Si, the modification of the gas mixture was studied with the aim of understanding the way these materials are etched in the presence of O 2 , N 2 and/or CH 2 F 2 . Passivation phenomena were used to show that invert selectivities can be obtained. Their combination leads to ultrahigh Si:SiGe selectivity.