| 摘要 |
PURPOSE:To minimize error and mark damage due to electron beam scanning operation by a method wherein mark signals are set up to attain to the level of the mark signals specified by mark position detecting circuit by an amplifying circuit set up in processing circuit. CONSTITUTION:A mark 2 provided on a specimen is scanned by electron beams 1 to detect reflecting electrons. The output of a detector 3 is multiplying DA converted 4 to be transmitted to a level control circuit 5 while the maximum and minimum values of the output from the circuit 5 are memorized by the maximum and minimum value detecting circuit 7. An AD converter built-in a mark position detecting circuit 11 is provided with the reference value to attain to the maximum value 8 of the circuit 7 by changing a DA converter 16 in the circuit 5. Likewise, an AD converter in the circuit 11 is provided with the reference value by turning switches S2 and S3 respectively OFF and ON changing the converter 16 in the circuit 5 to attain to the minimum value 9. |
