Design of a Compact Negative Metal Ion Beam Source for Surface Studies
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ABSTRACT A compact negative metal ion beam source for direct low energy metal ion beam depositions studies in ultra high vacuum (UHV) environment, has been developed. The ion source is based on SKION's Solid State Ion Beam Technology. The secondary negative metal ion beam is effectively produced by primary cesium positive ion bombardment (negative ion yield varies from 0.1-0.5 for carbon). The beam diameter is in the range of 0.2-~3.0 cm depending on the focusing and ion beam energy. The ion source produces negative ion currents of about 0.8 rnA/cm 2 . The energy spread of the ion beam is less then ±5% of the ion beam energy. The energy of negative metal ion beam can be independently controlled in the range of 10-300 eV. Due to the complete solid state ion technology , the source can be operated while maintaining chamber pressures of less then 10.10 Torr. INTRODUCTION Direct metal ion beam process is currently being studied intensively as a new approach to the synthesis and the modification of materials, particularly using relatively low ion beam energies(10-300 eV). Many promising features of negative ion process have been demonstrated. [1-3] Most ion sources use a gas discharge or plasma generated ion source. These sources could be limited by one or more of the following factors: high working pressure, low flux, complicated apparatus, impurities, poor energy control, or inability to operate in the low energy region (10-300 eV). A compact negative metal ion source was developed by utilizing a solid state cesium ion source (SKION, CS02 cesium ion gun) as a primary ion source. Direct cesium ion bombardment from the solid state ion source can effectively produce negative ion beams with a negative ion yield of 0.1-0.5. [4,5] The source is very compact, reliable and high-flux, as compared to other types of negative ion sources. A schematic diagram of the negative metal ion source is shown in Figure 1. Design aspects of the ion source are presented in this paper. The ion source would be useful in studies where accurate control of the ion beam energy and current is needed in a high vacuum environment. SKION and Stevens Institute of Technology are currently using the ion source for several research projects such as: formation of amorphous diamond films and surface modification for homo- or hetero-epitaxial diamond films. [6] DESIGN OF ION SOURCE AND OPTIC SYSTEM A. Primary Cesium Ion Source The primary cesium ion source consists of a cylindrical solid state cesium ion source heated by a tungsten filament, [7,8] an electrode system and deflecting plates. The primary Cs' ion cur623
Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
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Primary Cs ion source 1. Cesium Modenite Solid Electrolyte 2. Beam Forming Electrode 3. Extracting Electrode Secondary
M ion source
4. Deflecting Electrode 5. Metal Target
6. Beam Forming Electrode 7. Extracting Electrode Optic system Einzel Lens ( 8-10 ) Aperture ( 11 )
0 0
. 1
2 inc,h
2 inches
Figure 1. Schematic diagram of the compact negative metal ion source
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