High-current pulse sources of broad beams of gas and metal ions for surface treatment

This paper reviews the experimental study, development, and improvement of various types of processing ion sources undertaken in association with the joint program performed in recent years by the Institute of Electrophysics and the Institute of High-Current Electronics of the Russian Academy of Sciences. The beam parameters (type and energy of ions, current density, cross-sectional area of the beam, permissible content of impurities, etc.) should meet the requirements of particular ion beam treatment conditions, while the ion source itself should be simple and reliable in operation. Technical and service characteristics of the developed ion sources permit their use for ion-beam modification of materials, preparation of surfaces and ion-assisted deposition of thin films, and in some other applications. The sources under consideration employ high-current glow discharges with a hollow cathode or in crossed electric and magnetic fields, and low-pressure are discharges and vacuum are. Cold cathodes enhance reliability of the ion sources when they work at a high residual gas pressure or in the reactive gas media. The repetitive pulse mode of the plasma and beam generation provides optimum conditions for stable operation of the discharge, control of the average beam current over a wide range, and formation of homogeneous large-cross-section beams. The paper describes techniques used to realize high-current discharges at a reduced pressure, methods for producing a stable, dense and homogeneous plasma in a large volume, techniques of formation of large-cross-section homogeneous beams, and also findings on the mass-charge composition of the plasma and beams produced. Some design versions of the sources are given. At voltages from 10 to 100 kV, the pulse duration of 10 to 1000 mu s, and the pulse repetition rate of 1 to 500 Hz these sources provide the current density of similar to 1-10 mA/cm(2) in beams having the cross-sectional area of a few hundreds of square centimeters. The achieved parameters of the sources permit their use both in commercial and research applications. The use of these sources for modification of surface properties of materials has been exemplified. (C) 2000 Elsevier Science B.V. All rights reserved.