PURPOSE: To provide the projection mask which compensates variation in the height of the surface of a wafer.

CONSTITUTION: The projection mask 22 receives fixed-wavelength coherent radiant light 30 at least partially. The mask has (a) an opaque area which cuts off part of the radiant light and (b) a transparent area which transmits part of the radiant light. The transparent area is varied in thickness so as to locally adjust the focus of the transmitted radiant light 36 so that the transmitted radiant light passes through different parts of the transparent area at ≥3, preferably, ≥4 discrete phase angles. As main application, the focus position changes locally according to the style of structures 26 and 28 supplied with the transmitted radiant light when a pattern is formed on the structures. Consequently, the depth of focus increases.