A full phase shifting mask (FPSM) can be advantageously used in a damascene process for hard-to-etch metal layers. Because the FPSM can be used with a positive photoresist, features on an original layout can be replaced with shifters on a FPSM layout. Adjacent shifters should be of opposite phase, e.g. 0 and 180 degrees. In one embodiment, a dark field trim mask can be used with the FPSM. The trim mask can include cuts that correspond to cuts on the FPSM. Cuts on the FPSM can be made to resolve phase conflicts between proximate shifters. In one case, exposing two proximate shifters on the FPSM and a corresponding cut on the trim mask can form a feature in the metal layer. The FPSM and/or the trim mask can include proximity corrections to further improve printing resolution.