| 摘要 |
PURPOSE:To provide a charged-beam optical mirror tube which can restrict the dimensional error caused by the vertical movement of a sample surface within the tolerance, and which can extend the scanning visual-field. CONSTITUTION:The deflection amount of a beam-returning-back deflector 3 is regulated so that the deflection center (P) of the deflector 3 is located above an objective lens 1. Owing to the above constitution, an electron beam, after being deflected by beam-positioning deflectors 4 and 5 and becoming incident upon an objective lens 1 at an angle of theta, is returned back by means of the deflector 3, and becmoes incident upon a sample surface 2 at an angle slightly smaller than 90 deg.. Therefore, a beam location (S2) on the sample surface 2 is positioned apart from the optical axis by a distance (r2). As a result, the deflection value of the beam at the sample surface 2 can be made large, that is to say, the area of the scanning visual-field can be made large. Besides, the picturing accuracy can be maintained within the tolerance even when the surface 2 moves up and down. |
