Contains reports on two research projects.Joint Services Electronics Program (Contract DAAB07-75-C-1346

Coleman, John W.

Graham, Michael R.

Jacobsen, Edward H.

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II. ELECTRON OPTICSAcademic and Research StaffProf. John G. KingDr. John W. ColemanDr. Edward H. JacobsenGraduate StudentsMichael R. GrahamRichard W. Sheppe, Jr.A. ELECTROSTATIC ELECTRON LENSES JSEPJoint Services Electronics Program (Contract DAAB07-75-C-1346)Edward H. JacobsenDuring the past year we have developed and explored an analytic method forexpressing the electrical potential as a continuous function of position in a cylindricallysymmetric lens. Using this method, we partition the lens into appropriate cells and thenselect the proper Bessel-Fourier series to express the solution in each cell. Eachsolution is made to join smoothly to its neighbor along the cell partitions, and to satisfythe outer boundary conditions. By this procedure it is easy to estimate the relative pre-cision and convergence of each solution. Moreover, in contrast to numerical methods,this method affords a high degree of flexibility, in that variation of the lens parametersdoes not require major changes in the computer program for calculating electron trajec-tories. Details of this analysis are given elsewhere. 1Recent application of this analysis to an einzel lens reveals that significant reductionin spherical aberration can be achieved by a system of three flat, electron-transparentfoils (at ground potential and perpendicular to the axis) and two annular rings (onebetween each of the foils, at potentials VI and V2). In this doublet system a parallelbeam, entering a converging lens and exiting a diverging lens, can be brought to apoint focus for cone half-angles up to approximately 0. 1 radian. It appears that furtherimprovements can be realized by altering the symmetry, as regards the thickness andspacing of the annular rings along the axis and the cross-sectional shapes.While we intend to explore these possibilities, a practical problem arises, in that itis necessary to calculate first a number of trajectories for a given lens configuration,alter the lens parameters, and then recalculate the trajectories so as to evaluate theproperties of the modified lens. Although this procedure is straightforward, it is clumsyand expensive of machine time, since it is often difficult to intuit changes in the lensparameters which will render improved optical performance. Hence, it is highly desir-able to develop an analytical method by which one can be guided to the optical propertiesdirectly from the potential. We have considered some possibilities for executing a JSEPPR No. 118(II. ELECTRON OPTICS)JSEP hybrid procedure, partly analytical and partly numerical, which should facilitate theevaluation of the electron optical properties from a given potential, and we expect toreport on these in the future.In parallel with the analysis of flat einzel lenses, we have also been exploring theelectron optical properties of lenses bounded by hyperbolic surfaces which generate aninterior potential of the form V(r, z) = Ar 2 + Bz 2 . These systems exhibit optical prop-erties that are superior to those of any of the einzel lenses we have examined thus far,a feature not unexpected in the light of work by previous investigators.2 However, therearises the practical difficulty of providing curved (electron-transparent) foil boundingsurfaces, since the elimination of entrance and exit apertures is essential to the improvedoptical properties of such a lens. On the basis of recent studies using perturbation meth-ods, it appears that it may be possible to employ flat foils over a very limited and axiallycentered region of the bounding surfaces without seriously degrading the optical proper-ties. Moreover, small degradations in the optical properties can be offset by alteringslightly the shape of the boundaries and by using a converging-diverging doublet system.We intend to explore these systems at length and discuss the results in a subsequentreport.References1. N. D. Wittels and E. H. Jacobsen, "Bessel-Fourier Series Solutions for Cylindri-cally Symmetric Electrostatic Lens Potentials," J. Appl. Phys. 47, 2716-2723(1976).2. A. Septier, in V. E. Cosslett and R. Barer (Eds.), Advances in Optical and ElectronMicroscopy, Vol. I (Academic Press, Inc., New York, 1966), p. 204.B. HIGH-RESOLUTION HIGH-CONTRAST ELECTRON OPTICS: PROGRESSREPORT ON AUGER ELECTRON MICROSCOPE (AEM)Joint Services Electronics Program (Contract DAAB07-75-C-1346)John W. Coleman, Michael R. GrahamThe assembly of the final AEM is under way, with all major engineering design forthe system now completed. The three vacuum systems are under construction: the low-vacuum system is already pumping and the remaining parts of the two other systems arecompletely designed and on order. The 48 high-voltage feedthroughs have been designedand are also on order. A commercially available suitable image intensification systemof the channeltron-array type has been located. Full AEM assembly is on our schedule.We plan to use simulated specimens by September 1976 and real Auger emitting speci-mens by December 1976.JSEP Our goal is to extend by three orders of magnitude the resolution and sensitivityPR No. 118(II. ELECTRON OPTICS)attainable in depth profiles of impurities in Si and GaAs. In particular, we are inter- JSEPested in the sharpness of boundaries that isolate low-refractive-index components fromhigh-refractive-index components in integrated optic devices and separate regionsof different doping in integrated electronic circuit structures. By studying depth pro-files of these materials at levels heretofore unattainable, we shall facilitate device min-iaturization, which enhances speed of operation and reliability and reduces cost perfunction. JSEPPR No. 118

Electron Optics

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Electron Optics

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