Parameter space map of an electron cyclotron resonance plasma in a compact chamber

Abstract

Ion current density measurements were made in an electron cyclotron resonance (ECR) plasma reactor for both argon and oxygen discharges. Spatial changes in the ion current density were also recorded across the reactor diameter for changes in pressure and power. These measurements revealed a minimum in the ion current density on the reactor axis. This observation has been explained as a consequence of the shape of the ECR region, which, in turn, is dependent on the mode of coupling. Current density measurements were made as a function of reactor pressure and microwave power for two different axial locations in the system. A Langmuir probe was also used at these two locations to measure the electron temperature as a function of these process conditions. It was observed that the ion current density and/or plasma density measured downstream from the ECR zone, increased significantly in the low-pressure/high-microwave power region. Results from this region of the operating parameter space have not previously been reported. Further existing models do not predict this observed increase in plasma density or ion current density. It has been proposed that a rarefication of the gas in the ECR region, as a result of gas heating, has acted to increase the outward diffusion of electrons from the ECR zone and, thus, has increased the ambipolar diffusion of ions to the downstream location. This proposal has been partially validated by experimental results in which the ion energy was measured as a function of reactor pressure and gas flow rate. The shape of the oxygen parameter space map differs significantly from that for Ar. The principal reasons for these changes are a number of different inelastic electron scattering mechanisms which effect the transport electrons out of the ECR zone and through ambipolar diffusion also the transport of ions. The second factor is the production of negative ionic species which varies with reactor pressure and, thus, T/sub e/.