A reflector for EUV has additional multi-layers on the front surface of a base multilayer stack provided selectively to compensate for figure errors in the base multilayer stack or the substrate on which the multilayer stack is provided. A phase shift mask for EUV uses two multilayer stacks, one introducing a relatively phase shift and one introducing a relatively samll phase shift, to for contrasting regions of the mask.Electrical Engineering, Mathematics and Computer Scienc