High-Efficiency Low Energy Neutral Beam Generation Using Negative Ions in Pulsed Plasma

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Abstract
To prevent 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 many apertures for extracting neutral beams from the plasma. By supplying a positive or negative direct current (DC) bias to the top and bottom carbon plates in the pulsed SF6 plasma, the generated positive or negative ions are respectively accelerated towards the bottom plate. The negative ions are more efficiently converted 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 neutralization efficiency of negative ions was more than 98% and the neutral flux density was equivalent to 4 mA/cm2.