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
.