Method and apparatus for controlling the objective lens in a sca

Details Method and apparatus for controlling the objective lens in a sca Method and apparatus for controlling the objective lens in a sca

1981-09-03

1983-07-12

Smith, Alfred E.

Radiant energy

With charged particle beam deflection or focussing

Magnetic lens

250396ML, 250310, 250311, G21K 108, G21K 510, H01J 314

Patent

active

043933092

ABSTRACT:
The relation between the focusing distance (D) of the objective lens and the excitation current (I) of the objective lens is stored in a data memory. The initial focusing distance (D.sub.o) corresponding to the optimum excitation current is determined as a result of the focusing adjustment operation. Thereafter, the change (.DELTA.D) in the focusing distance due to the specimen shift along the optical axis of the objective lens is detected. The magnitude of the excitation current corresponding to the focusing distance (D.sub.o +.alpha.D) is read from said memory and a current of that magnitude is supplied to the objective lens.

REFERENCES:
patent: 3715582 (1973-02-01), Akahori et al.
patent: 3842236 (1974-10-01), Von Walter

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