A new technique for laser photodetachment diagnostics of negative ions in processing plasmas using an open microwave resonator

It is common that plasmas for materials processing contain negative ions, the density of which is often much larger than the electron density. The existence of negative ions in the plasma has a substantial effect on the potential structure of the plasma and charged particle transport in the plasma; when the plasma is pulsed, the negative ions may reach the materials surface and directly affect surface processes. Thus, to understand the basic properties of processing plasmas, quantitative measurement of negative ion density is important. The authors and others employed a highly sensitive microwave cavity resonance technique for detecting electron density and systematically studied the behavior of negative ions in electronegative plasmas. In these studies plasmas were generated in a cylindrical microwave cavity by capacitive coupling of RF power (13.56 MHz) and the photodetached electron density was detected as the shift of the cavity resonance frequency (/spl sim/3.6 GHz).