A mask blank including a light shielding film pattern having high ArF light fastness.
The light shielding film is on a transparent substrate. In the mask blank, the light shielding film is a single layer film formed of a material containing silicon and nitrogen, and the light shielding film has an optical density to an ArF excimer laser exposure light of 2.5 or more, a surface reflectance to the exposure light of 40% or less, a back-surface reflectance to the exposure light of 40% or less, a transmittance to a light having a wavelength of 900 nm of 50% or less, an extinction coefficient to a light having a wavelength of 900 nm of 0.04 or more, and a thickness of 60 nm or less.