Development and Characterization of a New Compact Microwave Radical Beam Source

Abstract

For plasma-assisted processing of future semiconductor devices, a new compact microwave plasma source has been specifically designed. The source is versatile in that plasma production is possible over a wide pressure range. Measured plasma parameters include electron densities in excess of 1011 cm-3 and low plasma potential (<10 V). Plasma chemistry was investigated by emission spectroscopy and the main excited species found was atomic oxygen radicals. In determining the absolute density of radical species, titration using NO2 gas was employed to correlate the oxygen atom density with the plasma operating conditions. At a microwave power of 300 W and a O2 partial pressure of 16.6 Pa oxygen atom densities in excess of 1.9×1015 cm-3 have been measured, which gives dissociation rates of O2 of approximately 20%. Effects of wall materials on the oxygen atom density were also investigated. Using a Teflon liner at high pressures provides a 37% increase in oxygen atom density due the lower recombination coefficient of Teflon compared to stainless steel.