Hairpin probe assisted saturation current ratio method to determine plasma electronegativity

The saturation current ratio (SCR) method is considered to be one of the simplest methods to determine plasma electronegativity in electronegative discharges using a Langmuir probe (LP). 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 LP 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 LP. These measurements are further integrated with the standard SCR method to deduce the plasma electronegativity in an oxygen plasma.