The effect of topographical local charging on the etching of deep-submicron structures in SiO₂ as a function of aspect ratio

Physical and electrical influences on plasma etching on the inside of a microtrench in SiO₂ were numerically investigated using Monte Carlo simulation of ions and electrons with the aid of surface charge continuity and Poisson's equation. When the aspect ratio is greater than seven, the bottom is charged up to a potential sufficient to prevent the influence of all the incident ions, with a realistic initial energy of 300 eV for SiO₂ etching within the period required for monolayer stripping, resulting in etch stop. The cause of etch stop is purely the result of the electrical local charging due to the topography of the trench, and of the initial conditions for incident charged particles. The etch stop caused by a cw plasma will be disorganized or prevented within a short time by the aid of ion-ion plasma in an afterglow phase.