PURPOSE: To carry out exposure processing in a short period of time and to prevent generation of divergence of focus by specifying constituting material of a projection lens which projects a photomask image and average value of energy of i-rays to be absorbed.
CONSTITUTION: In a projection lens on which the image of the photomask which is irradiated by a beam from the beam source consisting of a short arc type mercury vapor lamp is projected, only the i-rays or i-rays and mercury vapor lamp beam whose spectrum is on the longer wave length side of the i-rays make incidence. This projection lens is constituted from glass material whose absorption rate of i-rays is under 20%, and the average value of energy of the absorbed i-rays is within 1W. Therefore, the image of a circuit pattern can be surely exposed at a high resolution utilizing the i-rays discharged from the mercury vapor lamp effectively, and by utilizing the i-rays and the beam on the longer wave length side of the i-rays, the illuminance on a projected surface is heightened. Thus, the efficiency of exposure processing is improved and the generation of divergence of the focus can be prevented.