Radiant energy – With charged particle beam deflection or focussing – Magnetic lens
Patent
1992-09-14
1993-11-23
Dzierzynski, Paul M.
Radiant energy
With charged particle beam deflection or focussing
Magnetic lens
250310, H01J 3721
Patent
active
052647030
ABSTRACT:
An electron beam instrument typified by a scanning electron microscope. The instrument does not suffer from defocus if the accelerating voltage is varied. The instrument has an objective lens, an electron gun emitting an electron beam, a control unit, an accelerating voltage-setting portion, first and second reference voltage sources. The control unit digitizes the accelerating voltage set by the accelerating voltage-setting portion and applies the digital voltage to the two reference voltage sources. The first voltage source consists of a first ROM and a first D/A converter. Similarly, the second voltage source consists of a second ROM and a second D/A converter. A signal V.sub.ref1 indicating the optimum objective lens current at a first working distance is stored in the first ROM. A signal .DELTA.V indicating the difference between the optimum objective lens current at a second working distance and the optimum objective lens current at the first working distance is stored in the second ROM. The output voltage from the second voltage source is applied to one end of a variable resistor acting as a focus-adjusting means. The first reference voltage is applied to one input terminal of an adder. The output voltage from the variable resistor is applied to the other input terminal of the adder. The output voltage from the adder can be varied from V.sub.ref1 (V.sub.H1) to V.sub.ref1 (V.sub.H1)+.DELTA.V(V.sub.H1) by adjusting the movable contact of the variable resistor. Hence, the focus can be adjusted.
REFERENCES:
patent: 4393309 (1983-07-01), Norioka
patent: 5130540 (1992-07-01), Yamada
patent: 5187371 (1993-02-01), Matsui et al.
patent: 5225676 (1993-07-01), Matsuya
Harasawa Kiyoshi
Shibano Akira
Dzierzynski Paul M.
Jeol Ltd.
Nguyen Kiet T.
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