Control of dissociation by varying oxygen pressure in noble gas admixtures for plasma processing

The electron density, electron temperature, and atomic oxygen density are measured in mixtures of oxygen and noble gas discharges as a function of the input power and the oxygen partial pressure. The atomic oxygen density is measured by both actinometry and appearance mass spectrometry and plasma density and electron temperature are monitored with Langmuir probes. The background noble gas determines the electron density and temperature as long as the partial pressure of oxygen remains small. The dissociated atomic neutral oxygen density is highest in $O2∕Xe$ mixtures and lowest in $O2∕He$ mixtures, increases with electron density, and decreases with electron temperature. Estimates of the dominant source and sink rates of atomic oxygen are used to explain these results using a simple zero-dimensional dissociation kinetics and transport model. The use of noble gas/oxygen mixtures allows for a larger range of atomic oxygen density and ion density than in pure oxygen plasmas, and also allows for independent control of the ion density and the atomic oxygen density.