Isotropic etching of SiGe alloys with high selectivity to similar materials

An isotropic etching process was developed in order to remove the sacrificial SiGe layer in Si/SiGe/Si stacks and thus obtain a cavity between the Si layers. This process is shown to be selective versus silicon as long as some SiGe remains, but the Si etch rate increases suddenly when the SiGe disappears. A mechanism based on the preferential action of fluorine species is proposed. It is corroborated by the results obtained on advanced electrical devices.