Plasma charging damage on silicon surface during reverse-AA oxide etching in poly-buffered STI (PB-STI) isolation process

Plasma induced defects (or pits) are found in the active area near the corner and boundary of trench after reverse-active area (AA) etching in a poly buffered STI (PB-STI) process. The defect mechanism is demonstrated in this paper as related to the charging of the poly buffer layer and subsequent arcing at weak points (between poly buffer layer and AA) through pad-oxide during R-AA etching. Such arcing and defect generation is strongly enhanced by magnetic fields and not related to etching rate or plasma density.