OBSERVATION OF DEFECTS IN THERMAL OXIDES OF POLYSILICON BY TRANSMISSION ELECTRON-MICROSCOPY USING COPPER DECORATION

Copper decoration followed by transmission electron microscopy (TEM) o bservation is proposed for identifying defects in thermal oxides of po lysilicon films. This method uses copper decoration to detect the loca tion of defects in the oxide, and sample thinning for TEM observation. The advantage of copper decoration is that the electronic current nee ded for defect detection is very small, so it does not change the orig inal oxide-defect structure. TEM and scanning electron microscope obse rvations revealed that the defects are polygonal voids located on the polysilicon grain boundary. The diameter of a void was typically 70 nm . A stress-induced migration of silicon atoms along grain boundaries m ay be related to the formation of the voids. A model for defect format ion is presented.