| 摘要 |
PURPOSE:To automate level compensation and to perform always stable mark detection, by scanning a substrate to extract an offset level by the electron beam before the mark detection, and feeding back said level to an amplifier of the mark detecting signal. CONSTITUTION:The mark position provided on the substrate is scanned by the electron beam. A signal from a reflected electron detector 6 is amplified to obtain positioning data. A switch 5 is provided between the amplifier 1 of the detecting device and an output terminal 8. The substrate is scanned to detect the different states of the surface at various machining stages before the mark is scanned. Said amplified signal is fed back to the amplifier 1 through the swtich 5, AD converter 4, a registor 3, and a DA converter 2, so that the signal output (the detected signal at the offset level) besed on the surface state becomes a zero level. In this constitution, the offset level compensation at every machining stage can be automatically performed, and the mark detection can be performed at the constant signal level. Therefore the positioning accuracy and the reliability can be improved. |
