Abstract: The mask includes a substrate formed of a material having a first index of refraction and a first level of transmittance to a wavelength of light with which the phase shift mask is designed for use. Second portions of the substrate are impregnated with a dopant species, leaving first portions of the substrate unaffected by the dopant species. The second portions of the substrate have a second index of refraction and a second level of transmittance to the wavelength of light. The first index of refraction is not equal to the second index of refraction. The second portions of the substrate shift a phase of the light relative to the first portions of the substrate and thereby increase an effective imaging resolution of the phase shift mask. In this manner, instead of using an etch process or a deposition process to form phase shifting regions of the mask, a doping processing is used instead. Most preferably, an ion implantation process is used.