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Title: High-brightness limited-area thermionic electron sources for microscopy and lithography
Author: Chen, B. L. B.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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Electron Microscopy and Electron Beam Lithography Systems are widely used in industry and research. The ultimate performance of such systems is determined by the brightness of the source from which the electrons are derived, a higher brightness allowing greater resolution at a given probe current. In addition to brightness, lithographic systems frequently require high absolute current. This dissertation addresses theoretically and experimentally the formation and characteristics of electron beams with a brightness of 106A/cm2-sr or more using limited-area thermionic sources. The various emission mechanisms used in electron guns are described and the brightness of an electron source is discussed. Space charge limits the available current density in the gun region and the focused current in the drift space of an electron beam analyser. Two models for predicting the performance of limited-area-cathode guns are proposed and agree well with the experimental results. Taguchi's methodology is introduced to undertake a systematic optimal design of an electron gun using an electron optical program, the 'Source' program. The experimental and theoretical results indicate that the major limitation to the performance of limited-area-cathode guns lies in the gun structure, especially, the emitting radius of the cathode and the manner of cathode emission itself rather than the drift-space. A new gun structure will be required if a brightness of 108Amp/cm2-sr at 30 kV (or an equivalent figure at lower voltages) is to be achieved. On the other hand, the analysing section can be modified so that such a brightness value can be measured.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available