24 June 1993 Optimization of low-voltage electron optics
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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.
© (1993) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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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