| 摘要 |
PURPOSE:To contrive improvement in detection accuracy of a marking position by a method wherein a reflected electron is detected by scanning an electron beam on a mark, the mark signal obtained is converted into A/D, and a primary moment is calculated from the signal distribution of the value cumulated for a fixed period, thereby enabling to reduce the effect of noise. CONSTITUTION:The reflected electron obtained by scanning a mark 1 using an electron beam 2 is detected by a reflected electron detector 3. A mark signal 4 is converted into digital form at A/D, and supplied directly to subtracter 6 by delaying a fixed period or through the intermediary of a DL 7. At a subtracter 6, the output of the DL 7 is deducted from the output of the AD 5, supplied to a cumulative adding machine 8 and cumulatively added there, and then supplied to a primary moment computing circuit and a primary moment setting machine 10. Based on the value of signal distribution of cumulative adding output which is set on a setting machine 10 and the signal X showing the scanning position of an electron beam, the primary moment of the signal distribution is calculated by the circuit 9, and the result is supplied to a subtracter 11. The beam scanning distance d/2 of one half of the delayed period of DL 7 is deducted from the primary moment value by the subtracter 11, and the result is outputted as the center position information of the signal 4. |
