PURPOSE: To expand such a range of phase shifter film thicknesses as to impart a permissible phase difference and to solve the various problems associated with phase deviations and fluctuations by determining the refractive index at the exposing wavelength of a transparent material so as to satisfy a specific relation.

CONSTITUTION: The refractive index n1 at the exposing wavelength of the phase shifter is so determined as to satisfy at least the relation m1/(m1-1)x0.98≤n1≤m1/(m1-1)x1.02 (where m1 is ≥2 natural number). The relation between the phase difference introduced by the phase shifter of the mask and the film thickness of the phase shifter is as shown in Fig. when calculated. The permissible range of the film thickness is expanded by using the condition at the point a if the permissible ranges δ da and δ db of the film thicknesses of the case the condition to attain 180° phase difference exists at the point a and the case the condition exists at the point b deviated from the point a are compared. The permissible range of the film thickness of the phase shifter is expanded in this way and the various problems, such as deterioration of optical images, occurring in the phase deviations or fluctuations are solves.