The formation of a lithographic mask (100) is disclosed, where the mask (100) can be used in forming integrated circuits onto a semiconductor substrate. A layer of etch stop material (106) is sandwiched between first (102) and second (108) layers of transmissive material that are substantially transparent to lithographic light. The layer of etch stop material (106) serves as an etch stop when a circuit pattern is etched into the second layer of transmissive material (108). This allows the second layer of etch stop material (108) to be etched to a more precise depth thereby providing a desired phase shift and concurrently controlling critical dimension width.