US Patent 11854865 Selective etching process for SiGe and doped epitaxial silicon

The present disclosure relates to a fabricating procedure of a radio frequency device, in which a precursor wafer including active layers, SiGe layers, and a silicon handle substrate is firstly provided. Each active layer is formed from doped epitaxial silicon and underneath a corresponding SiGe layer. The silicon handle substrate is over each SiGe layer. Next, the silicon handle substrate is removed completely, and the SiGe layer is removed completely. An etch passivation film is then formed over each active layer. Herein, removing each SiGe layer and forming the etch passivation film over each active layer utilize a same reactive chemistry combination, which reacts differently to the SiGe layer and the active layer. The reactive chemistry combination is capable of producing a variable performance, which is an etching performance of the SiGe layer or a forming performance of the etch passivation film over the active layer.