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 consists of an inductively coupled plasma (ICP) source and top and bottom carbon parallel plates. The bottom carbon plate includes numerous apertures for extracting neutral beams from the plasma. By supplying a direct current (DC) bias to the top plate, the generated ions are accelerated towards the bottom plate. Most of them are efficiently converted into neutral atoms, either by neutralization in charge-transfer collisions with gas molecules during 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, respectively, the neutralization efficiency was almost 100% and the neutral flux density was equivalent to 1.2-2.8 mA/cm² . A neutral beam could thus be produced efficiently from the ICP source and the apertures in the bottom plate.