Etch characteristics of Si1−xGex films in HNO3:H2O:HF

The etch characteristics of Si1−xGex films in HNO3:H2O:HF were examined. The etch rate ratio (etch selectivity) between Si1−xGex and Si escalated with the growth of HNO3 concentration at low concentration level, and when the HNO3 concentration exceeded a critical level the etch selectivity descended with higher HNO3 concentration. The dependence of etch selectivity on the HNO3 concentration was due to the higher critical HNO3 concentration for etching Si than that for etching Si1−xGex. Since the Ge-Ge bond energy was weaker than that of Si-Si and Si-Ge, the Ge atoms were oxidized preferentially once the HNO3 composition exceeded the critical concentration of etching Si1−xGex, which was manifested by the XPS spectra of Si1−xGex etched in HNO3:H2O:HF. When the HNO3 volume rose to another critical value, the significant growth of the Si etch rate lowered the etch selectivity. Although both the etch rates of Si1−xGex and Si dropped with lower HF concentration, the etch rate ratio of Si1−xGex to Si boosted remarkably due to the water-soluble characteristics of GeO2.