Mask blank, method of manufacturing imprint mold, method of manufacturing transfer mask, method of manufacturing reflective mask, and method of manufacturing semiconductor device

A mask blank comprising:

• a substrate;
• and
• a hard mask film formed on the substrate, wherein
• the hard mask film is a single layer film having a composition gradient portion formed on a surface of the hard mask film that faces away from the substrate and in a region adjacent to the surface,
• the hard mask film is made of a material containing chromium, oxygen, and carbon with a total content of chromium, oxygen, and carbon being 95 atomic % or more,
• a part of the hard mask film excluding the composition gradient portion has a chromium content of 50 atomic % or more,
• a ratio of a carbon content [atomic %] divided by a total content [atomic %] of chromium, carbon, and oxygen in the part of the hard mask film excluding the composition gradient portion is 0.1 or more,
• a ratio of a carbon content [atomic %] divided by a total content [atomic %] of chromium and carbon in the part of the hard mask film excluding the composition gradient portion is 0.14 or more, and
• a content of nitrogen in the hard mask film is equal to or less than a detection limit value in composition analysis of X-ray photoelectron spectroscopy.