Selective Etching of Native Silicon Oxide in Preference to Silicon Oxide and Silicon

An in-situ dry clean which removes native SiO _x and flowable oxide but does not etch the underlying silicon, thermal SiO ₂ or SiN _x , is reported. This process utilized a remote NF ₃ /NH ₃ /Ar plasma, and the selectivity was studied as a function of temperature and time. Under the optimized conditions, the native SiO _x on Si was removed after~15 seconds of plasma exposure whereas the etching of as-sputtered SiO ₂ was zero within this time period. Selectivity on a nanometer scale was confirmed by TEM of a patterned Si wafer showing that the optimized dry clean removed flowable SiO ₂ but does not etch Si and leaves SiNx/thermal SiO ₂ fins undamaged. Furthermore, this cleaning procedure was used to remove the native oxide on a SiGe-based patterned sample containing SiO ₂ /SiN _x films in preparation for MoSi _x atomic layer deposition (ALD). The selectivity between two types of silica relied on defective or weak Si-O bonds in native SiO _x compared to SiO ₂ .