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....http://www.google.com.au/patents/US7659042?utm_source=gb-gplus-sharePatent US7659042 - Full phase shifting mask in damascene process
