Correction of astigmatism in electron beam instruments

Details Correction of astigmatism in electron beam instruments Correction of astigmatism in electron beam instruments

1983-06-16

1986-01-28

Smith, Alfred E.

Radiant energy

With charged particle beam deflection or focussing

With detector

250396R, 250310, 250311, H01J 312

Patent

active

045673691

ABSTRACT:
An electron beam instrument having an objective lens coil 14 and stigmator coils 18 has its astigmatism corrected for by measurement of the contrast in the final image. The currents through the objective lens and the stigmator coils are adjusted in sequence iteratively to optimize the contrast.
The optimum contrast may be either a maximum contrast or a minimum contrast depending on the nature of the instrument and its mode of operation. Measurement of contrast may be made by measuring the magnitudes of successive points of an image and calculating the variance. Alternatively two measurements of magnitude at each point of an image may be made and the covariance calculated.

REFERENCES:
patent: 4038543 (1977-07-01), Krisch et al.
patent: 4180738 (1979-12-01), Smith et al.
patent: 4231065 (1980-10-01), Fitch et al.
Harris, "Constant Variance Enhancement . . .", Applied Optics, vol. 16, No. 5, May 1977, pp. 1268-1271.

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