Patent GB-1304344-A (GB)
IPC: G01N23/225
Filed: 1969-02-01
Abstract: 1304344 Electron microscope J R BANBURY and W C NIXON 2 Feb 1970 [1 Feb 1969] 5855/69 Heading H1D In electron beam apparatus where in a finely focused electron beam impinges on the specimen surface S to be examined, the secondary electrons emitted are subjected to electrostatic and/or magnetic fields, for instance by polepiece P and electrostatic shield C, such that electrons of a given energy emerging in different directions are caused to diverge from one another over a greater solid angle than they would in the absence of such a field, the field accentuating the differences in the respective trajectories, and the entry window of detector D occupies only a fraction of the solid angle over which the electrons spread. The beam may be raster or line scanned and a two dimensional c.r.t. display formed, or the specimen may be moved, or both may be stationary while the specimen voltage or potential across a junction in it varied. Variations in secondary coefficient may be due to surface topography, bumps inclined away or toward the detector appearing dark or light respectively, changes in the nature of the material due to potential contrast (e.g. examination of semi-conductors, integrated circuits, and micro-circuit elements) or e.m. fields in or near the surface. Electron probe microanalysis in which primarily the resultant X-rays are analysed may also include means for constrast image production from secondary electrons. If the specimen surface is inclined to the beam the divergent will normally be away from the normal to the specimen. The divergent trajectories need not be continuously divergent, and the electrode potentials may be varied to change the operational mode. Shield C at 200 to 500 V for example need not be circular, member P could be an earthed shield covering the polepiece and the specimen covered by an earthed disc shield with an aperture to enhance predictability. Gauze G preceeding scintillator D may extend 60 to 120 degrees, e.g. 90 degrees and the major depth of the shield, normally metal. The gauze is preferably operationally adjustable to detect electrons over the selected axis length, by blanking off for instance, the signal representing particular energy direction combinations, and a velocity analyser may be included. D may be at several KV and connected to a photo-multiplier. Components may be C coated to reduce spurious emission due to back scattered primary electrons. Fig. 3 (not shown) is preferred for magnetic contrast variations with insulated grid or plate A at the polepiece, and other potentials as shown. B and E fields parallel to the specimen surface may be observed. Electric potential contrast may be monitored by the Fig. 4 (not shown) array. Electrode R may improve linearity between surface potential and detector signal and D.C. and A.C. voltages or microcircuits or circuit elements may be observed, e.g. stroboscopically. The beam may be incident up to 90 degrees, the detector shield system rotated, the beam entering through an apertured plate. Permanent or electromagnets may provide superposed B fields and two axially spaced toriodally wound electromagnets may replace shield C providing a wholly B field.