Effect of aspect ratio on topographic dependent charging in oxide etching

Consideration is given to a wall conductance inside a trench in SiO2 expose d by plasma etching in order to predict the wall surface charging as a func tion of the aspect ratio. With a lack of surface conductance, physical and electrical etch stops occur in SiO2 trench etching at high aspect ratios du e to the difference of the velocity distribution between the electrons and the positive ions incident on the wafer. The sensitivity to the aspect rati o of the bottom charging potential decreases with the increasing surface el ectron conductance. The wall potential in the trench exposed to plasma etch ing in a pulsed operation is simulated in a simplified manner, and is predi cted to be decreased by massive negative ions instead of electrons in the o ff-phase.