Generation of electron-beam produced plasmas and applications to surface modification

Abstract

NRL has developed a number of hollow cathodes to generate sheets of electrons culminating in a ‘Large Area Plasma Processing System’ (LAPPS) based on the electron-beam ionization process. Beam ionization is fairly independent of gas composition and produces low temperature plasma electrons (<0.5 eV in molecular gases) in high densities (10 9–10 12 cm −3). The present system consists of a pulsed planar plasma distribution generated by a magnetically collimated sheet of 2 kV electrons (<1 mA/cm 2) injected into a neutral background of processing gases (oxygen, nitrogen, sulfur hexafluoride, argon). Operating pressures range from 2–13 Pa with 150–165 Gauss magnetic fields for a highly localized plasma density of ∼10 11 cm −3. This plasma source demonstrated anisotropic removal rates of polymeric (photoresist) material and silicon with O 2 and Ar/O 2/SF 6 mixtures, respectively. In pure nitrogen, this same source showed a surface nitriding rate of ∼1 μm/h of plasma exposure time on austenitic stainless steel at 400 °C. Time-resolved in situ plasma diagnostics (Langmuir probes and mass spectrometry) of these pulsed plasmas are also shown to illustrate the general plasma characteristics.