This paper presents an analytical model for inhomogeneous, partially-magnetized electronegative plasma. It is shown that the radial potential of the plasma can be related to the electronegativity parameter α = nv/ne, the positive ion density, and the electron temperature distribution inside the plasma system. Using this expression, the electronegativity parameter has been determined in an oxygen plasma produced by a 13.56 MHz capacitive coupled radio-frequency discharge, and it is shown that the negative ion parameter obtained using this model is in good qualitative agreement with the saturation current ratio technique based on the cylindrical Langmuir probe.

The saturation current ratio method is considered as one of the simplest methods to determine plasma electronegativity in electronegative discharges using a Langmuir probe. However, its accuracy is susceptible to errors incurred in the estimation of electron and positive ion saturation currents from the ampere-voltage characteristics obtained by a cylindrical Langmuir probe and partly due to errors in estimating the positive ion flux at the sheath boundary. In spite of its wide use, these underlying limitations and their remedies have not been adequately investigated. In this paper, we address the above problems by involving a DC biased hairpin resonator probe to determine the plasma potential and sheath area correction factor for a cylindrical Langmuir probe. These measurements are further integrated with the standard saturation current ratio method to deduce the plasma electronegativity in an oxygen plasma.

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