Reflective mask blank for EUV exposure, and reflective mask
A reflective mask blank includes a multilayer reflective film, and a pattern film to be partially etched when processing into a mask. The multilayer reflective film and the pattern film are placed on/above a substrate in this order from the substrate side. The pattern film includes an absorber film and a surface reflection enhancing film in this order from the substrate side. The relation of ((n−1) 2 +k 2 ) 1/2 >((n ABS −1) 2 +k ABS 2 ) 1/2 +0.03 is satisfied, n ABS and k ABS being a reflective index and an absorption coefficient of the absorber film at a wavelength of 13.53 nm, respectively, and n and k being a reflective index and an absorption coefficient of the surface reflection enhancing film at a wavelength of 13.53 nm, respectively.
1. A reflective mask blank which is a binary reflective mask blank comprising:
a multilayer reflective film which reflects EUV light; and
a pattern film to be partially etched when processing into a mask, the multilayer reflective film and the pattern film being placed on/above a substrate in this order from the substrate side;
wherein the pattern film includes an absorber film which absorbs EUV light and a surface reflection enhancing film in this order from the substrate side, the surface reflection enhancing film is directly laminated on the absorber film, and
the following relation is satisfied:
(( n− 1) 2 +k 2 ) 1/2 >(( n ABS −1) 2 +k ABS 2 ) 1/2 +0.03
wherein n ABS is a reflective index of the absorber film at a wavelength of 13.53 nm, k ABS is an absorption coefficient of the absorber film at a wavelength of 13.53 nm, n is a reflective index of the surface reflection enhancing film at a wavelength of 13.53 nm, and k is an absorption coefficient of the surface reflection enhancing film at a wavelength of 13.53 nm,
wherein the refractive index n of the surface reflection enhancing film is 0.95 or less, and
the pattern film has a thickness so that EUV light reflectance is 2% or less.
2. The reflective mask blank according to claim 1 , wherein film thickness d of the surface reflection enhancing film satisfies the following relation using the refractive index n:
13.53 nm/4 n× 0.5< d< 13.53 nm/4 n× 1.5.
3. The reflective mask blank according to claim 2 , wherein the film thickness d of the surface reflection enhancing film satisfies the following relation:
d< 1/10× d ABS
wherein d ABS is a film thickness of the absorber film.
4. The reflective mask blank according to claim 1 , wherein the surface reflection enhancing film is a ruthenium-based material film containing ruthenium.
5. The reflective mask blank according to claim 1 , wherein a protective film for protecting the multilayer reflective film is provided between the multilayer reflective film and the pattern film.
6. The reflective mask blank according to claim 1 , wherein a hard mask film to be removed when processing into a mask is provided on the pattern film.
7. The reflective mask blank according to claim 6 , wherein the hard mask film is selected from the group consisting of a tantalum-based material film containing a tantalum-based material, a chromium-based material film containing a chromium-based material, and a silicon-based material film containing a silicon-based material.
8. A binary reflective mask in which a pattern film of the reflective mask blank according to claim 1 has been patterned.
9. The reflective mask blank according to claim 1 , wherein the surface reflection enhancing film is a single film with uniform composition.
10. The reflective mask blank according to claim 1 , wherein the absorber film comprises a tantalum-based material.
11. The reflective mask blank according to claim 10 , wherein the tantalum-based material is TaN.
12. The reflective mask blank according to claim 1 , which comprises only a single surface reflection enhancing film with uniform composition.