| 摘要 |
PURPOSE: To make the image plane of a projection optical system exactly coincident with the surface of a wafer by a method wherein the focal point of the projection optical system is detected by an automatic focusing system, and the surface of the substrate is positioned at the position of an image plane on the basis of the detected focal point. CONSTITUTION: In an automatic focal point detection optical system, an illuminating system is made to illuminate a focusing mark 30 on a reticule 1 and its vicinity with light which is of the same wavelength with exposure light and extracted from a light exposure illuminating system 7 through a light guiding fiber 13. A reflected light returning from a reference plane mirror 6 through the intermediary of the reticule 1 is detected in volume by a photodetection 22 of a photodetective system. The focal point of a projection lens detected by the output signal of the photodetector 22 is made to serve as the reference point of an off-axis automatic focus detection system. The printing optimal position of a wafer is determined on the basis of the above reference point taking offsets such as the thickness of a coating on the wafer, a level difference and the like into consideration. By this setup, the image plane of a projection optical system is made exactly coincident with the plane of a wafer. |
