24 June 1993 Optimization of low-voltage electron optics
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Abstract
In a previous paper we described a miniature unity-magnification system that employed magnetic focusing solely and indicated that a minimum beam diameter of about 150 angstroms should be possible at 100 V. However, such a system has proved difficult to realize in practice because of the difficulty of providing a suitable beam extraction system for the field emission source. The scanning tunneling microscope has proven capable of high-resolution patterning at ultra-low energy (< 100 eV), but the sensitivity of electron-beam resists tends to drop at these energies. Here we describe a variety of alternative designs that appear to be more practical. One possible configuration, an acceleration/retardation system with superposed magnetic field, should allow us to obtain a minimum beam diameter of about 100 angstroms at 200 V. In another configuration which we have implemented experimentally, we employ a standard commercial SEM as our source and introduce a confined magnetic lens as the final focusing element. The magnetic field is provided by a NdFeB permanent magnet, which allows for reasonably high field strength (0.6 - 0.8 T) and compact size. This system offers an effective means of extending the range of operation of any SEM to low energies.
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Laurence S. Hordon, Laurence S. Hordon, Zhirong Huang, Zhirong Huang, Raymond Browning, Raymond Browning, Nadim I. Maluf, Nadim I. Maluf, Roger Fabian W. Pease, Roger Fabian W. Pease, } "Optimization of low-voltage electron optics", Proc. SPIE 1924, Electron-Beam, X-Ray, and Ion-Beam Submicrometer Lithographies for Manufacturing III, (24 June 1993); doi: 10.1117/12.146530; https://doi.org/10.1117/12.146530
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