| 摘要 |
PURPOSE:To achieve accurate alignment of beam by preventing partial cut of beam through limiting aperture. CONSTITUTION:An aligning aperture mask 21, an aligning deflection coil 22, a reflected electron detector 23, etc. are employed to detect the edge position of the aperture 21a of aperture mask 21 thus to measure the coordinates of intermediate point and to align the electron beam highly accurately to the center of aperture. When compared with the case employing a limiting aperture mask, the beam is never cut partially by the aperture mask to prevent variation of beam current or uneven beam current density. While since the scattered electrons are never charged up. stability of beam is improved.
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