Plasma etching optimization of oxideitride/oxide interpolydielectric breakdown time in flash memory devices

摘要

The breakdown time of flash memory oxideitride/oxide (ONO) layerntbd under positive constant current stressing has been foundnto be closely related to the cumulative extent of (over)etch of thentungsten silicide, control polysilicon, and ONO layers, i.e.,nΣ(ΛOE). An empirical first-order relation between tbdn and Σ(ΛOE) has been derived to facilitate the plasmanetch recipe optimization. This has led to a four-fold increase in thenaverage tbd across a 200-mm wafer to 208 s. More importantly,nthe spread in tbd has been tightened to ~5%, which is downnfrom ~54%