An electron-beam microcolumn with improved resolution, beam current, and stability

We have built and tested a 1 keV electron-beam microcolumn that focuses 1 nA of beam current into a 10 nm full width half-maximum beam diameter at a working distance of 1 mm. The electron source is a miniaturized Zr/O/W Schottky field emitter with 150 mu A/sr angular emission current density operating at about 1800 K at a distance of only 100 mu m from a silicon membrane extractor electrode, The actual microcolumn is 3.5 mm long assembled mainly from silicon membrane electrodes. Improved einzel lens design and fabrication allowed the operation of this beam focusing element in the accelerating mode. Spherical and chromatic aberrations were reduced by factors of about 2-3, respectively, as compared to he retarding lens mode. Excellent beam current stability with less than 1% variation over several hours has been observed. (C) 1995 American Vacuum Society.