| 摘要 |
An electron beam apparatus focusses an electron beam (1) onto a specimen (6) by means of an objective magnetic lens (2). In order to detect changes in the height of the specimen, a laser light beam (1) from a laser source (9) is incident on the specimen (6) and the reflected laser beam (11) is detected by a light detector (3). Any change in the height of the specimen (6) changes the path of the laser beam (11) to the detector (3). Therefore, by monitoring the detector (3), the focussing of the electron beam (1) on the specimen (6) can be controlled by varying the current to an excitation coil (31) of the objective magnetic lens (2) or by moving the specimen (6) via a mounting stage (10). At least one of the pole pieces (28,29) of the objective lens (2) is on the opposite side of the path of the laser beam to the source of the electron beam (1), so that the objective magnetic lens (2) may be close to the specimen (6), permitting a short focal length. Thus, the laser beam (11) may pass between the pole pieces (28,29). An optical microscope (39) may also be provided to permit the specimen (6) to be viewed. The viewing path of the optical microscope (39) extends through an opening (37A) in one or both of the pole pieces (28,29) of the objective magnetic lens (2). <IMAGE> |
