Photomask blank, photomask and fabrication method thereof
View Patent ↗A light-shielding film for exposure light is formed on one principal plane of a transparent substrate made of quartz or the like that serves as a photomask substrate. The light-shielding film can serve not only as the so-called “light-shielding film” but also as an anti-reflection film. In addition, the light-shielding film has a total thickness of 100 nm or less, 70% or more of which is accounted for by the thickness of a chromium compound that has an optical density (OD) per unit thickness of 0.025 nm −1 for light having a wavelength of 450 nm. In the case where the photomask blank is used for fabricating a mask designed for ArF exposure, the thickness and composition of the light-shielding film are selected in such a manner that the OD of the light-shielding film is 1.2 to 2.3 for 193 or 248 nm wavelength light.
1. A photomask blank comprising:
a transparent substrate; and
a light-shielding film for exposure light formed on the transparent substrate,
characterized in that said light-shielding film has a total thickness of 100 nm or less, 70% or more of which is accounted for by the thickness of a chromium compound that has an optical density (OD) per unit thickness of 0.025 nm −1 or less for light having a wavelength of 450 nm.
2. The photomask blank according to claim 1 , characterized in that 70% or more of the total thickness of said light-shielding film is accounted for by the thickness of a chromium compound that has a chromium content of 50 atomic % or less in terms of atomic ratio.
3. The photomask blank according to claim 1 , characterized in that said light-shielding film comprises a chromium-metal film having a chromium content of 50 atomic % or more in terms of atomic ratio and a first and a second chromium-compound film having a chromium content of 50 atomic % or less in terms of atomic ratio, and
said chromium-metal film is disposed between said first chromium-compound film and said second chromium-compound film.
4. The photomask blank according to claim 1 , characterized in that said light-shielding film comprises a first and a second chromium-metal film having a chromium content of 50 atomic % or more in terms of atomic ratio and a first, a second and a third chromium-compound film having a chromium content of 50 atomic % or less in terms of atomic ratio, and
said first chromium-metal film is disposed between said first chromium-compound film and said second chromium-compound film, and said second chromium-metal film is disposed between said second chromium-compound film and said third chromium-compound film.
5. The photomask blank according to claim 1 , characterized in that said light-shielding film has a reflectance of 30% or less for light having a wavelength of 250 nm to 270 nm.
6. The photomask blank according to claim 1 , characterized in that the optical density (OD) of said light-shielding film is 2.5 to 3.5 for light having a wavelength of 193 nm.
7. The photomask blank according to claim 1 , characterized in that the optical density (OD) of said light-shielding film is 2.5 to 3.5 for light having a wavelength of 248 nm.
8. The photomask blank according to claim 1 , characterized in that said light-shielding film is a multilayer film that contains a stack of a plurality of layers having different optical characteristics, and the uppermost layer of the multilayer film has an extinction coefficient (k) of 1.0 to 1.5 for light having a wavelength of 193 nm.
9. The photomask blank according to claim 1 , characterized in that said light-shielding film is a multilayer film that contains a stack of a plurality of layers having different optical characteristics, a primary constituent material of the uppermost layer of the multilayer film is chromium oxide, chromium nitride or chromium oxynitride, and the percentage contents (atomic %) of oxygen, nitrogen and carbon in the film at depths of 0.5 to 1.0 nm from the surface of said uppermost layer are related according to the oxygen content>nitrogen content>carbon content.
10. The photomask blank according to claim 1 , characterized in that said light-shielding film is a multilayer film that contains a stack of a plurality of layers, and the uppermost layer of the multilayer film has a thickness of 10 to 40 nm.
11. A half-tone phase-shift mask blank comprising:
a transparent substrate;
a translucent film having a predetermined phase-shift capability and a predetermined transmittance for exposure light formed on the transparent substrate; and
a light-shielding film formed on the translucent film,
characterized in that said translucent film has a region that contains both silicon (Si) and molybdenum (Mo), and said light-shielding film has a thickness of 60 nm or less, 70% or more of which is accounted for by the thickness of a chromium compound that has an optical density (OD) per unit thickness of 0.025 nm −1 or less for light having a wavelength of 450 nm.
12. The photomask blank according to claim 11 , characterized in that 70% or more of the total thickness of said light-shielding film is accounted for by the thickness of a chromium compound that has a chromium content of 50 atomic % or less in terms of atomic ratio.
13. The photomask blank according to claim 11 , characterized in that said light-shielding film comprises a chromium-metal film having a chromium content of 50 atomic % or more in terms of atomic ratio and a first and a second chromium-compound film having a chromium content of 50 atomic % or less in terms of atomic ratio, and
said chromium-metal film is disposed between said first chromium-compound film and said second chromium-compound film.
14. The photomask blank according to claim 11 , characterized in that said light-shielding film comprises a first and a second chromium-metal film having a chromium content of 50 atomic % or more in terms of atomic ratio and a first, a second and a third chromium-compound film having a chromium content of 50 atomic % or less in terms of atomic ratio, and
said first chromium-metal film is disposed between said first chromium-compound film and said second chromium-compound film, and said second chromium-metal film is disposed between said second chromium-compound film and said third chromium-compound film.
15. The photomask blank according to claim 11 , characterized in that said light-shielding film has a reflectance of 30% or less for light having a wavelength of 250 nm to 270 nm.
16. The photomask blank according to claim 11 , characterized in that the optical density (OD) of said light-shielding film is 2.5 to 3.5 for light having a wavelength of 193 nm.
17. The photomask blank according to claim 11 , characterized in that the optical density (OD) of said light-shielding film is 2.5 to 3.5 for light having a wavelength of 248 nm.
18. The photomask blank according to claim 11 , characterized in that said light-shielding film is a multilayer film that contains a stack of a plurality of layers having different optical characteristics, and the uppermost layer of the multilayer film has an extinction coefficient (k) of 1.0 to 1.5 for light having a wavelength of 193 nm.
19. The photomask blank according to claim 11 , characterized in that said light-shielding film is a multilayer film that contains a stack of a plurality of layers having different optical characteristics, a primary constituent material of the uppermost layer of the multilayer film is chromium oxide, chromium nitride or chromium oxynitride, and the percentage contents (atomic %) of oxygen, nitrogen and carbon in the film at depths of 0.5 to 1.0 nm from the surface of said uppermost layer are related according to the oxygen content>nitrogen content>carbon content.
20. The photomask blank according to claim 11 , characterized in that said light-shielding film is a multilayer film that contains a stack of a plurality of layers, and the uppermost layer of the multilayer film has a thickness of 10 to 30 nm.