Effect of aspect ratio on topographic dependent charging in oxide etching

Consideration is given to a wall conductance inside a trench in SiO₂ exposed by plasma etching in order to predict the wall surface charging as a function of the aspect ratio. With a lack of surface conductance, physical and electrical etch stops occur in SiO₂ trench etching at high aspect ratios due to the difference of the velocity distribution between the electrons and the positive ions incident on the wafer. The sensitivity to the aspect ratio of the bottom charging potential decreases with the increasing surface electron conductance. The wall potential in the trench exposed to plasma etching in a pulsed operation is simulated in a simplified manner, and is predicted to be decreased by massive negative ions instead of electrons in the off-phase.