| 摘要 |
PURPOSE:To automatically converge the particle flux onto a specimen, by detecting optimal upper and lower positions for each axis where the derivative of image signal becomes maximum, then positioning the face of specimen at the intermediate position of them. CONSTITUTION:The specimen 2 is lifted in step by up/down movement driver 8 and the face of specimen is repeatedly scanned by electron beam 1 in both X and Y directions at each step, then the detector 4 detcts the secondary electron 3 and outputs as imags signal. Said signal is stored in X and Y axis image signal memories 16, 17 for each scanning axis, and used at differentiating section 18 for selecting the representative derivative in each step. Then max. differential signal position detector 21 detects the position, for each scanning axis, corresponding with max. value of representative derivative, then optimal upper/lower position detector 22 calculates the optimal position of specimen and the drive section 8 brings the specimen 2 to optimal position. |
