Patent ID: 7651823

Claim:
A photomask blank for manufacturing a phase-shift mask, comprising an optically semitransmissive film which is formed on a transparent substrate and which transmits a portion of light having a desired wavelength λ, wherein the optically semitransmissive film comprises one or more layers, and has a refractive index n and a thickness d that satisfy the expression 0<d≦λ(2(n−1)) of an exposure light of wavelength λ; and at least one of the layers is a phase-difference reduction layer in which a phase difference Δθ 1 (hereinafter referred to as phase difference Δθ 1 (units: degrees)), wherein the phase difference Δθ 1 obtained by subtracting a phase of light (hereinafter referred to as layer-referenced light) in the absence of the phase-difference reduction layer from a phase of light (hereinafter referred to as layer-transmitted light) transmitted through the phase-difference reduction layers, is less than a calculated phase difference Δθ 0 =(360/λ)×(n−1)×d (hereinafter referred to as the phase difference Δθ 0 (units: degrees)) calculated based on the difference in an optical distance between the layer-transmitted light and the layer-referenced light.