| 摘要 |
PURPOSE:To facilitate alignment between optical systems thereby to permit an improvement in working efficiency, by providing a beam current detector. CONSTITUTION:A beam current detector constituted by a coil is provided at one or more arbitrary positions on the part of a beam transport path on the downstream side of a blanking electrode 21, and a beam is modulated by the blanking electrode 21, thereby making it possible to measure the beam current at the position where the beam current detector is provided without affecting the beam. For example, current detector coils 230a-230e are respectively disposed under apertures. The arrangement is such that whether or not the beam is intercepted by a projection lens aperture owing to, for example, the deflecting operation is judged simply by making comparison between the respective outputs of control circuit 28, 29 connected to the beam current detectors. |
