As semiconductor manufacturing moves towards smaller logic devices and thinner gate oxides, there is serious concern that pattern-dependent charging during plasma etching will impede progress by distorting etch profiles and by causing oxide breakdown. Simulations of the final overetch predict that the use of ultrathin oxides(⩽5 nm),combined with a low substrate potential, will actually eliminate notching by enabling electron tunneling from the substrate to decrease surface charging potentials at the bottom of high aspect ratio trenches. Comparison with published experimental results validates the simulations. ©1997 American Institute of Physics.