ASPECT-RATIO-DEPENDENT CHARGING IN HIGH-DENSITY PLASMAS

The effect of aspect ratio (depth/width) on charge buildup in trenches during plasma etching of polysilicon-on-insulator structures is studi ed by Monte Carlo simulations. Increased electron shadowing at larger aspect ratios reduces the electron current to the trench bottom. To re ach a new charging steady state, the bottom potential must increase, s ignificantly perturbing the local ion dynamics in the trench: the defl ected ions bombard the sidewall with larger energies resulting in seve re notching. The results capture reported experimental trends and reve al why the increase in aspect ratio that follows the reduction in crit ical device dimensions will cause more problems unless the geometry is scaled to maintain a constant aspect ratio. (C) 1997 American Institu te of Physics.