Patent ID: 10928721

Abstract:
To provide a reflective mask blank for EUV lithography which is excellent in flatness, whereby the deterioration of the overlay accuracy at the time of pattern transfer can be relatively easily corrected, and the deterioration of the overlay accuracy due to the flatness is small.A reflective mask blank for EUVL, which is a reflective mask blank for EUV lithography having a reflective layer for reflecting EUV light and an absorber layer for absorbing EUV light formed in this order on the main surface of a substrate and having a conductive film formed on the rear surface opposite to the main surface, of the substrate, wherein when the shapes of quality-guaranteed regions of the main surface and the rear surface of the reflective mask blank for EUVL are measured by a laser interferometer, and the measured values obtained are fitted to quadratic function, the proportion of the quadratic function components is at least 35%, and the flatness at the quality-guaranteed regions of the main surface and the rear surface is at most 600 nm.