Mass spectrometry of positive ions in capacitively coupled low pressure RF discharges in oxygen with water impurities

Abstract

A capacitively coupled RF oxygen discharge is studied by means of mass spectroscopy. Mass spectra of neutral and positive species are measured in the mid plane between the electrodes at different distances between plasma and mass-spectrometer orifice. In the case of positive ions, as expected, the largest flux originates from . However, a significant number of impurities are detected, especially for low input powers and larger distances. The most abundant positive ions (besides ) are , , and . In particular, for the case of hydrated hydronium ions (n = 1, 2) a surprisingly large flux (for low pressure plasma conditions) is detected. Another interesting fact concerns the ions. Despite the relatively high ammount of water impurities ions are present only in traces. The reaction mechanisms leading to the production of the observed ions, especially the hydrated hydronium ions are discussed.