| 摘要 |
PURPOSE:To ease to compensate astigmatism, by furnishing a mean of scanning electron ray repeating several rounds at the same point on a sample during one scanning of a cathode ray tube, and forming plural sample images of different astigmatisms in one picture image. CONSTITUTION:An electron ray 2 is scanned two-dimensionally on a sample 5 by deflection coils 12X and 12Y, and the secondary electron 6 is detected and its sample image is displayed on a cathode ray tube 9. In this case, while deflection power supplies 10X and 10Y are furnished to give their signals to the tube 9 to be deflected, a deflection current with a frequency of several times is given to the coils 12X and 12Y through signal processing circuits 11X and 11Y, and moreover, an astigmatism compensating system 14 is controlled through moderation signal generating circuits 18X and 18Y. Therefore, plural sample images of different astigmatisms, in the same field of view, can be formed in a picture, which are compared to examine to select the best sample image. By this procedure, astigmatism compensation can be easily performed. |
