Ion-ion plasmas from discharges based on electron beam ionization

Abstract

Summary form given only, as follows. Use of both positive and negative ions in plasma processing of materials has been shown to be advantageous in terms of better feature evolution and control. The formation of these ion-ion plasmas is dictated by electron attachment to the neutral gas, which is enhanced at low electron temperatures. Thus, ion-ion plasmas are usually formed in the afterglow of a pulsed plasma as the electron temperature drops during the plasma decay. Discharges produced by electron-beams inherently have low electron temperatures (<1 eV in molecular gases), and therefore are good candidates to form ion-ion plasmas continuously. Using simple Langmuir probes, we have studied the electronegative gases O/sub 2/ and SF/sub 6/ which have very different attachment cross sections resulting in very different ionic species. Analysis of temporally resolved plasma characteristics deduced from these measurements will be presented for pure O/sub 2/ and Ar/SF/sub 6/ mixtures with mixture fractions varying from 0-100%. Oxygen discharges show no noticeable negative ion contribution during the active or afterglow. In contrast, SF/sub 6/ discharges demonstrate ion-ion plasma characteristics in the active glow and are completely ion-ion in the afterglow. Comparison between these discharges with accepted cross sections and production mechanisms will also be presented.