| 摘要 |
PURPOSE:To prevent variance of a focal point from operator to operator by employing a control means for changing objective lens exciting current synchronously with a Y deflection control signal and detecting the focal point based on a picture signal obtained at the time of changing the exciting current with the control means. CONSTITUTION:Employing a control means for changing an objective lens exciting current synchronously with a Y-direction control signal, a focal point is detected based on a picture signal obtained at the time of changing the exciting current with the control means. The control means consists of an objective lens exciting current source 12, an adder 13, and a switch 10b. Since the objective lens exciting current can be changed synchronously with electron beam scanning over a sample 5 of with an observation display, pictures of focal points continuously changing before and after the exact focal point can be displayed. This makes it possible to visualize the condition of the sample image being out of focus due to the changes in the objective lens exciting current. As a result it is possible to reduce variance in detecting the exact focal point from operator to operator.
|
