A halftone phase shift mask blank for use in manufacturing a halftone phase shift mask comprises a transparent substrate, a light transmitting portion formed on the substrate for transmitting an exposure light beam, a phase shifter portion formed on the substrate for transmitting a part of the exposure light beam as a transmitted light beam and for shifting a phase of the transmitted light beam by a predetermined amount, and a phase shifter film for forming the phase shifter portion. The halftone phase shift mask has an optical characteristic such that light beams passing through the light transmitting portion and through the phase shifter portion cancel each other in the vicinity of a boundary portion therebetween, thereby maintaining and improving an excellent contrast at a boundary portion of an exposure pattern to be transferred onto the surface of an object to be exposed. The phase shifter film comprises a film containing silicon, oxygen, and nitrogen as main components and an etching stopper film formed between the film and transparent substrate.