| 摘要 |
PURPOSE:To enable any focus shift due to heat absorption in case of exposure to be corrected by a method wherein the outputs of a circuit processing output signals of an image sensing element detecting a part of image projected on a wafer are converted into electric signals to control a wafer driving system. CONSTITUTION:A part of mask pattern projected and image-formed on a wafer 4 is detected by an image sensing element 6 for image signals to be converted into frequency using a processing circuit 7 while specified component only is separated to be converted into electric signals further using a control circuit 8 for driving a wafer driving system 5. When the wafer 4 is subjected to a focussing shift, especially the intensity of frequency components in the image signals notably declines. Therefore, when the signals decline, the wafer driving system 5 is driven by the control circuit 8 to shift the wafer 4 to the position maximizing the signal intensity. Thus, the focus correction with high accuracy can be assured. |
