Nickel Selective Etching Studies for Self-Aligned Silicide Process in Ge and SiGe-Based Devices

The limitations of the H2SO4/H2O2/H2O mixture (diluted SPM chemistry) as a reagent for the nickel selective etching step of the salicidation process when silicon is replaced by silicon- germanium alloys or pure germanium is investigated. When the Ge content in SiGe is higher than 30%, SPM is not suitable anymore due to the high etch rate of the germanosilicide layer. This high etch rate is related to the poor stability of the Ge oxide in aqueous solutions. For Ge contents above 30%, H2SO4 96% is proposed as a selective etching reagent instead of SPM. With this chemistry, a very high Ni/NiSiGe selectivity and a good Ni/NiGe selectivity are obtained, since only 10% of the germanide layer is attacked while the Ni layer is completely removed.