Formation of metal contacts to silicon germanium layers with etch resistive cap layers

Abstract

Cap layers are formed on silicon germanium (SiGe) source/drain regions to provide etch resistance to processing steps that can occur in a semiconductor manufacturing process between formation of the SiGe source/drain regions and metal contact formation. The cap layers comprise boron and are thin (e.g., 2 nm or less) to provide for a low metal contact resistance. The atomic concentration of boron in the second layer is in a range of about 0.2-20%. In addition to providing etch resistance, the cap layer provides for a thermally stable contact resistance as the cap layer can prevent or limit the creation of voids in the SiGe layer by preventing or limiting the diffusion of germanium from the SiGe layer into the metal in subsequent annealing and other high-temperature processing steps.