High-efficiency low energy neutral beam generation using negative ions in pulsed plasma

To prevent several kinds of radiation damage caused by charge build-up and by ultraviolet and X-ray photons during etching processes, we have develope d a high-performance, neutral-beam etching system. The neutral-beam source consists of an inductively coupled plasma (ICP) source and top and bottom c arbon parallel plates. The bottom carbon plate includes many apertures for extracting neutral beams from the plasma. By supplying a positive or negati ve direct current (DC) bias to the top and bottom carbon plates in the puls ed SF6 plasma, the generated positive or negative ions are respectively acc elerated towards the bottom plate. The negative ions are more efficiently c onverted into neutral atoms in comparison with the positive ions, either by neutralization in charge-transfer collisions with gas molecules during the ion transport or with aperture sidewalls in the bottom plate. The neutrali zation efficiency of negative ions was more than 98% and the neutral flux d ensity was equivalent to 4 mA/cm(2).