Plasma charging defect characterization, inspection, and monitors in poly-buffered STI

In this paper, the mechanism, inspection, and inline monitor of plasma charging defects found in an active area (AA) corner and edge using a poly-buffer (PB) STI process is reported. These defects are formed by the arcing (or discharging) through weak spots of pad-oxide between the poly-buffer layer and substrate as resulting from the charging of poly buffer layer during reverse-AA oxide etching. Such defect formation is found to be strongly enhanced by the magnetic field used in oxide etchers but not related to etch rate and plasma density. The defect inspection on patterned wafers is found to be strongly correlated to the flat-band voltage (V_fb) and to a lesser extent to oxide charge (Q_tot) degradation on in-line unpatterned oxide wafers. Therefore, the shift of V_tb and Q_tot on unpatterned wafers can be effective inline monitors for plasma charging damage during reverse-AA etching in PB-STI process.