US Patent 7232629 Method of forming and testing a phase shift mask

A surface of a mask substrate is divided into a main field region and a blank periphery region surrounding the main field region. A first pattern, at least one second pattern and at least one third pattern are formed within the main field region to form a phase shift mask (PSM). By using the PSM, a pattern transferring process is performed to transfer the first pattern, the second pattern and the third pattern to a semiconductor wafer. Finally, by using the second and third patterns transferred to the semiconductor wafer, a PSM test is performed.