Plasma etching optimization of oxide/nitride/oxide interpoly dielectric breakdown time in flash memory

The breakdown time of flash memory oxide/nitride/oxide (ONO) layer t sub(bd) under positive constant current stressing has been found to be closely related to the cumulative extent of (over)etch of the tungsten silicide, control polysilicon, and ONO layers, i.e., capital sigma ( Lambda OE). An empirical first-order relation between t sub(bd) and capital sigma ( Lambda OE) has been derived to facilitate the plasma etch recipe optimization. This has led to a four-fold increase in the average t sub(bd) across a 200-mm wafer to 208 s. More importantly, the spread in t sub(bd) has been tightened to approx. 5%, which is down from approx. 54%.