Optically semitransmissive film, photomask blank and photomask, and method for designing optically semitransmissive film

Abstract

The present invention provides an optically semitransmissive film that has a near-zero phase shift, has a desired transmissivity, and is relatively thin; a novel phase-shift mask that uses the optically semitransmissive film; a photomask blank that can [be used to] manufacture the phase-shift mask; and a method for designing the optically semitransmissive film. The film is formed on a translucent substrate and transmits a portion of light having a desired wavelength λ, wherein the film has at least one phase-difference reduction layer that fulfills the following functions. Specifically, the phase-difference reduction layer is a layer that has a refractive index n and a thickness d that satisfy the expression 0<d≦λ(2(n−1)), and is a layer in which the value Δθ (hereinafter referred to as phase difference Δθ (units: degrees)) obtained by subtracting the phase of light (hereinafter referred to as layer-referenced light) in the absence of a layer from the phase of light (hereinafter referred to as layer-transmitted light) transmitted through a layer is less than the value Δθ=(360/λ)×(n−1)×d (hereinafter referred to as the phase difference Δθ(units: degrees)) calculated based on the difference in the optical distance between the layer-transmitted light and the layer-referenced light.