  A two dimensional electrostatic Particle-in-Cell simulation code is developed
to investigate anisotropy of ions in a trench geometry for plasma etching. The
numerical simulation results suggest that if the trench width is larger than
Debye length scale, anisotropy can be lost due to potential development across
the trench. Furthermore, the effects of ion charge build up on the trench
bottom is investigated, which can degrade the anisotropy.
