High-efficiency neutral-beam generation by combination of inductively coupled plasma and parallel plate DC bias

To avoid several kinds of radiation damage caused by charge build-up and by ultraviolet and X-ray photons during etching processes, we have developed a high-performance, neutral-beam etching system. The neutral-beam source co nsists of an inductively coupled plasma (ICP) source and top and bottom car bon parallel plates. The bottom carbon plate includes numerous apertures fo r extracting neutral beams from the plasma. By supplying a direct current ( DC) bias to the top plate, the generated ions are accelerated towards the b ottom plate. Most of them are efficiently converted into neutral atoms, eit her by neutralization in charge-transfer collisions with gas molecules duri ng the ion transport and with aperture sidewalls in the bottom plate, or by recombination with low-energy electrons near the end of the bottom plate. When the aperture diameter and aperture length were 1 mm and 10 mm, respect ively, the neutralization efficiency was almost 100% and the neutral flux d ensity was equivalent to 1.2-2.8 mA/cm(2). A neutral beam could thus be pro duced efficiently from the ICP source and the apertures in the bottom plate .