| 摘要 |
PURPOSE:To accurately detect the defocusing of a projection lens on the surface of a wafer by converging light beams from masks which are generated by light irradiation on wafer marks formed on the wafer and causing them to interfere with each other, and detecting the reflected and diffracted light. CONSTITUTION:Mask marks 11 and 12 provided on a mask 10 at a specific distance l are irradiated with 1st and 2nd light beams and the two diffracted light beams generated by the marks 11 and 12 are converged on a mark 31 on a wafer 30 through a projection lens 20 to interfere with each other; and the diffracted light from the mark 31 is detected to obtain a 1st optical heterodyne detection signal of frequency (f1-f2), and the position shift between the mark and wafer can be detected. Further, while the position shift is corrected, one mark 12 of the mask 10 is irradiated with a 3rd light beam and an intermediate point between the marks 11 and 12 is irradiated with a 4th light beam; and the diffracted light from the mark 12 and the 4th light beam are converged on the mark 31 through a lens 20 to interfere with each other and thus a 2nd optical heterodyne detection signal of frequency (f1-f2) is obtained to detect the defocusing on the wafer surface. |
