| 摘要 |
PURPOSE:To contrive to improve the reproducibility by making accurate the control of the line width of patterns to be exposed, by a method wherein the amount of variation (amount of focal variation) of the image formation surface of the projection optical system which is generated by the variation in refractive index of air caused by the fluctuation in atmospheric pressure is detected and offset to correct by the amount of variation. CONSTITUTION:When a reticle R is illuminated, the pattern image in a pattern region Pr forms on the forming plane FP of a projection lens 2. A projector 20 as a focal detector that detects the gap between the lens 2 and a wafer W obliquely projects the slit light image forming on the forming plane FP, and a photo receptor 21 receives the reflected light of the slit light image from the wafer W located on the forming plane FP and then detects its position in the Z direction, with the result that the surface of the wafer W is adjusted at such a level that a focal signal indicates focal agreement. On the other hand, a pressure sensor 30 which detects the atmospheric pressure in terms of absolute values is provided, and the amount of focal variation is calculated by a control circuit 22. A correction control unit which feeds an off-set signal OFS correcting a level, detected as focal agreement by the focal detector, by the calculated amount of variation to said detector is provided, and the focal variation of the projection optical system caused by the variation in refractive index of air is corrected.
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