GB1355252A - Electron lenses of the magnetic field type - Google Patents

Abstract

1355252 Electron beam magnetic focusing apparatus HITACHI Ltd 10 May 1971 [13 May 1970] 14056/71 Heading H1D An electron lens for an electron microscope includes an annular exciting lens 5, a magnetic cover of an upper magnetic path member 3, a lower magnetic path member 4, and magnetic polepieces 1, 2, either formed as separate pieces or integrally with the members, in either case the poles being located within the central space defined by the annular coil a plurality of compensating coils 7 (e.g. with four coils as in Fig. 1b (not shown)) at least partially embedded in the lower polepiece or path member and separated by the cover or another part of the lens from the tubular beam space, with supply means for supplying compensating currents to the compensating coils and circuit means for adjusting the compensating currents whereby astigmatism and undesired deflection of an electron beam may be corrected. Spacer 6 is non-magnetic. In Fig. 1b opposite coils are in series opposition. Correction of astigmatism in any, rather than one direction, is by eight coils, Fig. Ic (not shown), and current through respective sets of four coils may be varied according to sine and cosine functions. Astigmatism correction in any direction may be attained by four coils as in Fig. 6b (not shown), respective sets subtending 45 degrees, the polepiece and magnetic path member being formed integrally, Fig. 6a (not shown). The coils may be embedded in the lower magnetic member 4 (Fig. 2, not shown) or mounted on the lower polepiece 2 (Figs. 3a, 3b, not shown) with protective tube (8). Figs. 4a, 4b (not shown) include four coils 7 at points as remote as possible from the beam and eight coils, similar to Fig. lc, may be included. The coil device 7 may also be mounted in the magnetic cover without being exposed to the beam (Figs. 5a, 5b, not shown). Connections from compensating coils to lens coil 5 may be as in Fig. 7 (not shown).