Photomask blank
A photomask blank includes a chromium-based material film as a light-shielding film, wherein the chromium-based material film has an optical density per unit thickness at a wavelength of 193 nm of at least 0.050/nm, and the chromium-based material film has a tensile stress or compressive stress corresponding to an amount of warp of up to 50 nm. The present invention provides a photomask blank having a thin film of chromium-based material which is lowered in film stress while retaining a high optical density per unit film thickness. This enables high-accuracy patterning of a chromium-based material film.
1. A photomask blank comprising:
a quartz substrate; and
a chromium-based material film formed on the quartz substrate, wherein
the chromium-based material film is a light-shielding film,
the chromium-based material film comprises at least one selected from the group consisting of nitrogen, oxygen, carbon and hydrogen,
the chromium-based material film has an optical density per unit film thickness at a wavelength of 193 nm of at least 0.050/nm, and
when the chromium-based material film is formed on a quartz substrate having 152 mm square dimensions and 6.35 mm in thickness, and subjected to a heat treatment at a temperature of at least 150° C. for a time of at least 10 minutes, the chromium-based material film has a tensile stress or compressive stress corresponding to an amount of warp of up to 50 nm.
2. The photomask blank of claim 1 , wherein the amount of warp is up to 30 nm.
3. The photomask blank of claim 1 , wherein the optical density per unit film thickness is at least 0.054/nm.
4. The photomask blank of claim 1 , wherein the chromium-based material film has a thickness of in a range of 4 nm to 50 nm.
5. The photomask blank of claim 1 , wherein the temperature of the heat treatment is up to 300° C.
6. The photomask blank of claim 1 , wherein the chromium-based material film is a CrN film.
7. The photomask blank of claim 1 , wherein the chromium-based film is a monolayer film.
8. The photomask blank of claim 6 , wherein the CrN film has a chromium content of 70 to 90 atom % and a nitrogen content of 10 to 30 atom %.
9. The photomask blank of claim 1 , wherein the chromium-based film is a multilayer film.