A source of hyperthermal neutrals for materials processing

In this letter, we describe a unique method of producing hyperthermal neutrals for material processing. The hyperthermal neutrals are produced by accelerating ions across a sheath from a plasma onto a surface. On impact, the ions are neutralized and reflected with ∼ 50% of their incident energy. These neutrals then bounce off of additional surfaces prior to impacting the target. This unique multiple bounce system was developed for the following reasons: to reduce contamination from sputtered surface material, improve beam uniformity, and reduce UV radiation in the beam path. As a test of this method, we built a prototype beam source and used it to ash photoresist at rates up to 0.022 μm/min. These rates are consistent with a predicted neutral beam flux, 2 × 10¹⁴ cm^-2 s^-1. In addition, a simple model is used to indicate that this method is capable of producing economically acceptable ash rates. Comparisons with other neutral-beam production methods are made.