| 摘要 |
PROBLEM TO BE SOLVED: To provide a charged-particle beam measuring method which enables the focused state of a focusing beam to be measured accurately without being affected by noise components. SOLUTION: An electron beam is scanned across a knife edge member in a detector 27. A signal obtained from the detector 27 through this scan is supplied to a computing circuit 29 via an A/D converter 28. The computing circuit 29 subtracts half of an initial value from data, converts it to an absolute value, and performs addition. This operation is performed as the excitation of an objective lens 14 is changed plural times. From the peak position of the resulting curve of foci and the added value of currents, an optimum focus value is obtained. Once a just-in-focus position is calculated, that value is supplied to a control CPU 17 from the computing circuit 29. The control CPU 17 controls an objective lens control circuit 22 based on the signal from the computing circuit 29, and supplies an exciting current that achieves a just-in-focus state to the objective lens 14. |
