Halftone phase shift mask blank and halftone phase shift mask

A halftone phase shift mask blank comprising a transparent substrate and a halftone phase shift film thereon having a phase shift of 150° to 200° and a transmittance of 3% to 30% with respect to light of wavelength up to 200 nm, wherein

• said halftone phase shift film is a single layer or a multilayer film, each layer comprising silicon and nitrogen and oxygen, when the halftone phase shift film is a single layer, the overall single layer is composed of a silicon base material, or when the halftone phase shift film is a multilayer film, at least 60% of its thickness is composed of a silicon base material, said silicon base material having a total content of silicon, nitrogen and oxygen of at least 90 at %, a silicon content of 30 to 70 at %, a total content of nitrogen and oxygen of 30 to 60 at %, an oxygen content of up to 2 at %, and a transition metal content of 0.01 to 0.9 at %, and
• said halftone phase shift film has a thickness of up to 70 nm.