Scanning thermionic emission imaging of cathode surfaces

Peter B. Sewell; Victor Katsap; Warren K. Waskiewicz

doi:10.1117/12.370122

15 November 1999 Scanning thermionic emission imaging of cathode surfaces

Peter B. Sewell, Victor Katsap, Warren K. Waskiewicz

Proceedings Volume 3777, Charged Particle Optics IV; (1999) https://doi.org/10.1117/12.370122
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

Abstract

The evaluation of the thermionic emission characteristics of a variety of cathode technologies that may have application in the SCALPEL (Scattering with Angular Limitation Projection Electron-beam Lithography) instrument, has been conducted in a modified Scanning Electron Microscope. The thermionic emission image of the source, projected along the column axis by the electrostatic immersion lens of the gun, is analyzed by scanning this image across the entrance aperture of the column by driving the normal alignment coils with the scan drive electronics. The technique may be referred to as Scanning Thermionic Emission Electron Microscopy (STEEM). With this technique, the projected image of the cathode, the cross- over(s) and the cathode surface itself may be imaged by adjusting the focal length of the double condenser lens of the SEM. Images of 0.84 mm diameter cathodes in various forms, including polycrystalline Ta, coated polycrystalline cathodes and single crystal Ta have been examined at a range of magnifications. In addition to operation of the gun with a single large diameter Wehnelt aperture (2.5 mm), cathodes have been studied when located behind a fine mesh in the Wehnelt aperture. Multiple cross-overs with associated beams overlapping further along the axis of the instrument are observed. Single crystal Ta cathodes have been shown to provide the extremely uniform emission in the temperature limited mode, that is required for the effective operation of the SCALPEL technique.

Citation Download Citation

Peter B. Sewell, Victor Katsap, and Warren K. Waskiewicz "Scanning thermionic emission imaging of cathode surfaces", Proc. SPIE 3777, Charged Particle Optics IV, (15 November 1999); https://doi.org/10.1117/12.370122

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