Design and characterization of a planar magnetron glow discharge atom and ion source.

Abstract

A glow discharge device is described which uses a curved magnetic field passing through the surface of a planar cathode in order to trap electrons near the cathode surface. This results in significant reduction in plasma voltage, and stable plasma operation is achieved over an extended range of pressures and cathode current densities. Design features and performance data are presented for several configurations of this device. The magnetic field is generated by permanent magnets located directly behind the cathode surface. The plasma geometry is determined by the locus of greatest magnetic field strength, and has the form of a ring extending from the cathode surface to several millimeters from the surface. Plasma voltage vs. pressure data indicate that several modes of operation occur over the pressure range investigated. Pressure sensitivities of emission intensities from plasma support gas, cathodically sputtered species, continuum background, and residual-gas band systems also indicate the presence of different modes of operation, characterized by a shift to more energetic processes as the pressure is reduced. Emission from higher-energy neutral-atom and ion lines increase dramatically at the lowest pressures. Current sensitivities of emission intensities from plasma gas species are reduced by gas heating due to the sputtering process. The dependence of emission on current is greater for cathodically sputtered atoms and ions than for continuum background at low pressures. Atom/atom and ion/atom emission intensity ratios indicate a relative increase in higher-energy populations as the pressure is reduced. Calculated plasma excitation temperatures are representative of an ionizing plasma. Spatially resolved ion distributions measured by mass spectrometry at a number of pressures indicate a large radial inhomogeneity, with greatest ion signal located in the region of maximum field strength. Ionization is appreciable at all distances from the cathode at low pressures, and becomes more localized near the cathode as the pressure is increased. Ion signals show a dramatic increase as pressure is reduced.