Patent ID: 9644955
Date: 2017-05-09
CPC Classifications: G01B,H01J,H01L

Claim:
1. A scanning electron beam device, comprising: an electron source; a deflector for deflecting an electron beam emitted from the electron source; an objective lens for converging the electron beam; a stage configured to support a wafer on which the electron beam is radiated, wherein one selected from the stage and the objective lens can be raised and lowered; a retarding electrode on the stage; and a controller performs rough focus adjustment, in response to a variation in height of the wafer, using mechanical focusing that is performed by raising/lowering the stage or the objective lens, wherein the scanning electron beam devices acquires a scanning electron image of the wafer by radiating the electron beam onto the wafer and detecting secondary electrons generated from the wafer, wherein, in a first acceleration-voltage region having a first acceleration voltage for the electron beam, the controller further performs, in addition to the rough focus adjustment, a first precise focus adjustment responding to the variation in the height of the wafer using electromagnetic focusing that is performed by adjusting an excitation current for the objective lens; and wherein, in a second acceleration-voltage region having a second acceleration voltage for the electron beam greater than the first acceleration voltage, the controller further performs, in addition to the rough focus adjustment, a second precise focus adjustment through (i) a first electrostatic focusing that is performed by adjusting a retarding voltage applied to the retarding electrode, (ii) a second electrostatic focusing that is performed by adjusting a boosting voltage applied to a boosting electrode, or (iii) a third electrostatic focusing that is performed by adjusting an initial acceleration voltage for the electron source.