Characterization of a microwave plasma by in situ diagnostics

Abstract

An efficient microwave plasma source has been developed in our institute. Essentially, the microwave power is coupled to the plasma by slot antennae (SLAN) which are positioned on the inner side of an annular waveguide. The source has been operated with a wide variety of different working conditions and process gases, but this study focuses on argon and nitrogen. Microwave powers of up to 2 kW have been applied and the pressure varied between 1 and 1000 Pa. The plasma parameters have been determined either in the chamber itself or in a downstream zone. We report on spatially resolved single and double Langmuir probe measurements using a computer-driven fast acquisition system. In the plasma chamber, ion densities in excess of 10 12 cm −3 could be achieved. The electron temperature generally remains between 1 and 3 eV. Two different plasma regimes have been identified when the pressure is increased. Optical emission spectroscopic measurements using the Argon I line at 811.5 nm are discussed and the results compared with the electrical measurements. For a nitrogen plasma, molecular band spectra are obtained which were only partly resolved. With the choice of suitable spectral ranges, vibrational temperatures of some nitrogen states were determined, resulting in T vib = 7100 K. As a complementary diagnostic method, we have used laser-induced fluorescence. From a rotational band analysis of the (0,0) band of the first negative system ( B 2 Σ u + → X 2 Σ g +) of the nitrogen ion N 2 +, a rotational temperature of T rot = 770 K has been determined.