MAPPING OF RADIO-FREQUENCY PLASMA POTENTIAL THROUGHOUT A PARTICLE TRAPPING REGION USING AN EMISSIVE PROBE

This article describes the use of an emissive probe to map the time-in variant plasma potential in a rf generated plasma in a GEC Reference C ell. The mapping has been done throughout a region expected to trap co ntamination particles for four different geometric configurations of m aterials on the powered electrode of the GEC Cell. For one case, there is a potential maximum which is a trap for negatively charged particl es. For the other three cases, trapping can occur if a second force be sides the electrostatic force is present. We postulate that this is th e ion drag force. When particles are present in the system, the result ing particle clouds are observed using laser light scattering, and are superimposed of the maps. These clouds occur just where one would exp ect them to, given the electromagnetic force configuration exhibited b y the maps plus the supposition of the existence of an ion drag force. It is shown that, at the location of a cloud, the ion drag force is o f the right magnitude relative to the electrostatic force to permit tr apping of particles. (C) 1996 American Vacuum Society.