Requirements of neutral beam source regarding gas pressure and neutral angle for nanoscale etching

Abstract

Neutral beam etching is proposed as a candidate process for reducing plasma-process-induced damage (PPID) in nanoscale devices. The requirements of neutral beam properties for high-performance etching are investigated using a two-dimensional particle code. The neutral beam is generated using a plasma-source ion gun and low-angle reflectors. Neutral fluxes from both the neutral beam source and background gases are calculated as functions of gas pressure. The optimal pressure regime which is related to the rate of sidewall etching is suggested. In three-dimensional charge-up simulations, it is observed that the etching rate decreases with decreasing trench size due to the surface charging effect. However, a smaller reduction in the etching rate is observed experimentally in neutral beam etching. The influence of the neutral angle distribution on the etching rate is investigated using a Poisson random variable model. A low directional ratio of the neutral angle results in a low etching rate and a large decrease in etching rate as trench width decreases. Therefore, a pressure of less than 0.5 mTorr and a directional ratio of neutral angle higher than 50% are required for high-performance neutral beam etching.