Phase shift mask blank and phase shift mask

A phase shift mask blank comprising a substrate, and a phase shift film thereon, the phase shift film composed of a material containing silicon and nitrogen and free of a transition metal, wherein

• the phase shift film has a phase shift of 170° to 190° and a transmittance of 4% to 8%, with respect to exposure light of KrF excimer laser, and a thickness of 85 to 90 nm,
• the phase shift film comprises at least one compositionally graded layer having a composition continuously varying in a thickness direction, and a refractive index n and an extinction coefficient k, with respect to the exposure light, varying in the thickness direction, and
• the compositionally graded layer has a difference between a maximum refractive index n(H) and a minimum refractive index n(L) of up to 0.40, and a difference between a maximum extinction coefficient k(H) and a minimum extinction coefficient k(L) of up to 1.5.