Phase-shift photomask-blank, phase-shift photomask and fabrication method thereof

A method of fabricating a phase-shift mask blank, comprising:

• depositing a phase-shift multilayer film including a stack of n layers made of a metal silicide compound on a substrate by sputtering;
• and
• performing an oxidation processing on the top surface of said phase-shift multilayer film to form a stabilized oxide layer,
• wherein said film deposition by sputtering is performed using power applied to a plurality of targets of different compositions of a metal and silicon constituting said metal silicide, and the power applied to each of said plurality of targets is determined in such a manner that the differences in metal content and silicon content between an m-th layer from the substrate in the phase-shift multilayer film and an (m+1) -th layer are both equal to or less than 5 mole %, and the differences in power applied to the plurality of targets between an m-th layer from the substrate in the phase-shift multilayer film and an (m+1) -th layer are equal to or less than 30% of the maximum of the power applied to the plurality of targets, and
• said oxidation processing is performed in such a manner that the metal content of a surface area of said stabilized oxide layer is equal to or less than one third (in molar ratio) of the metal content of a layer containing the largest amount of metal in said phase-shift multilayer film (where n is an integer equal to or more than 2, and m is an integer falling within a range of 1≦m ≦(n−1)).