Plasma charging defect inspection and monitors in poly-buffered STI

Plasma induced defects (or pits) are found in the active area near corner and boundary of the trench after reverse-AA etching in the poly-buffered shallow trench isolation (PB-STI) process. The root cause of the formation of these defects is the arcing (or discharging) at weak spots between the poly and pad-oxide due to charging of the poly films during reverse AA oxide etching. Such arcing is found to be strongly enhanced by the magnetic field used during reverse AA oxide etching. In this paper, the inspection of plasma charging defects (pits) of patterned wafers are found to be strongly correlated to the flat-band voltage (Vfb) degradation as monitored by an un-patterned wafer. The magnetic field during oxide etching results in more charging defects and faster positive charge built-up in the oxide.