Theoretical overview of the large-area plasma processing system (LAPPS)

A large-area plasma processing system (LAPPS) is under development at the Naval Research Laboratory. In the LAPPS, the plasma is generated by a sheet electron beam with voltages and current densities of the order of kilovolts and tens of milliamps per cm2. The plasma dimensions are a metre square by a few centimetres thick. The beam is guided by a magnetic field of 50-300 G. Since an electron beam of this type efficiently ionizes any gas, high electron densities of n~1012-1013 cm-3 are easily generated at 30-100 mTorr background pressure. In addition to large area and high electron density, the LAPPS has advantages for plasma processing. These include independent control of ion and free radical fluxes to the surface, very high uniformity, very low electron temperature (Te, {<}1 eV, but can be controllably increased to a desired value) and a geometry that is well suited for many applications. This paper sketches an initial theoretical overview of issues in the LAPPS and compares aspects of the theory to a preliminary experiment.