Photomask blank and photomask

A photomask comprising a transparent substrate and a mask pattern formed thereon, said substrate comprising phase shift regions formed by etching the transparent substrate, and said mask pattern comprising transparent regions and light-shielding regions, and said mask pattern comprising

• an etch stop film disposed on the substrate, said etch stop film of single layer or multilayer construction being resistant to fluorine dry etching and removable by chlorine dry etching,
• a light-shielding film disposed contiguous to said etch stop film and consisting of a single layer or multiple layers composed of a material containing a transition metal and silicon, and
• an antireflective film disposed contiguous to said light-shielding film and consisting of a single layer or multiple layers, wherein
• said transition metal is at least one element selected
• from the group consisting of titanium, vanadium, cobalt, nickel, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, and
• an optical density OD of the combination of etch stop film, light-shielding film and antireflective film is at least 2.5.