Photomask blank, photomask, and method for manufacturing photomask blank

1. A photomask blank for producing a photomask to which an ArF excimer laser light is applied, wherein:

a light-shielding film is provided on a light transmissive substrate;

the light-shielding film has a laminated structure in which a back-surface antireflection layer, a light-shielding layer and a front-surface antireflection layer are laminated in this order from the side close to the light transmissive substrate;

the thickness of the entire light-shielding film is 60 nm or less;

the back-surface antireflection layer is made of a film containing a metal and has a first etching rate;

the front-surface antireflection layer is made of a film containing a metal and has a third etching rate;

the light-shielding layer is made of a film containing the same metal as that contained in the back-surface antireflection layer or the front-surface antireflection layer and has a second etching rate that is lower than the first etching rate and the third etching rate; and

the thickness of the light-shielding layer is 30% or less of the thickness of the entire light-shielding film.

2. The photomask blank according to claim 1 , wherein the thickness of the light-shielding layer is 40% or less of the thickness of the back-surface antireflection layer.

3. The photomask blank according to claim 1 , wherein the thickness ratio of the light-shielding layer to the front-surface antireflection layer is 1.0:0.7 to 1.0:7.0.

4. The photomask blank according to claim 1 , wherein the thickness of the light-shielding layer is 0.5% or more of the thickness of the entire light-shielding film.

5. The photomask blank according to claim 1 , wherein: the thickness of the back-surface antireflection layer is 23 to 33 nm; the thickness of the light-shielding layer is 2 to 6 nm; and the thickness of the front-surface antireflection layer is 11 to 17 nm.

6. The photomask blank according to claim 1 , wherein:

the optical density of the entire light-shielding film is 1.8 to 3.1;

the ratio of the optical density of the light-shielding layer to the sum of the optical densities of all the antireflection layers is 1:5 to 1:19; and

the antireflection layers are made of a film containing the same metal as that contained in the light-shielding layer, N and O, wherein the sum of the content of N and the content of O is 40 to 65 atomic %.

7. The photomask blank according to claim 1 , wherein: the optical density per unit film thickness of the antireflection layers is 0.04 nm −1 or less; and the optical density per unit film thickness of the light-shielding layer is 0.05 nm −1 or more.

8. The photomask blank according to claim 1 , wherein:

the optical density of the back-surface antireflection layer is 1.1 to 1.3;

the optical density of the light-shielding layer is 0.1 to 0.3; and

the optical density of the front-surface antireflection layer is 0.4 to 0.6.

9. The photomask blank according to claim 1 , wherein:

the sum of the content of N and the content of O in the back-surface antireflection layer is 40 to 55 atomic %;

the sum of the content of N and the content of O in the light-shielding layer is 30 atomic % or less; and

the sum of the content of N and the content of O in the front-surface antireflection layer is 45 to 65 atomic %.

10. The photomask blank according to claim 1 , wherein:

the optical density per unit film thickness of the back-surface antireflection layer is 0.03 to 0.04 nm −1 ; and

the optical density per unit film thickness of the light-shielding layer is 0.05 to 0.06 nm −1 .

11. The photomask blank according to claim 1 , wherein:

in the back-surface antireflection layer, the metal content is 25 to 50 atomic %, the sum of the content of N and the content of O is 35 to 65 atomic %, and the optical density is 1.1 to 1.3;

the light-shielding layer comprises the metal and N, wherein the metal content is 50 to 90 atomic %, the thickness is 2 to 6 nm, and the optical density is 0.1 to 0.3; and

in the front-surface antireflection layer, the metal content is 25 to 50 atomic %, the sum of the content of N and the content of O is 45 to 65 atomic %, and the optical density is 0.4 to 0.6.

12. The photomask blank according to claim 1 , wherein:

in the back-surface antireflection layer, the content of Cr is 30 to 40 atomic %, the sum of the content of N and the content of O is 40 to 55 atomic %, and the optical density is 1.1 to 1.3;

in the light-shielding layer, the content of Cr is 50 to 90 atomic %, the content of N is 3 to 25 atomic %, and the optical density is 0.1 to 0.3; and

in the front-surface antireflection layer, the content of Cr is 30 to 40 atomic %, the sum of the content of N and the content of O is 50 to 60 atomic %, and the optical density is 0.4 to 0.6.

13. The photomask blank according to claim 1 , wherein the etching rates of the back-surface antireflection layer, the light-shielding layer and the front-surface antireflection layer have the following relationship:

Second etching rate<First etching rate≦Third etching rate.

14. The photomask blank according to claim 1 , wherein:

a phase shifter film is provided between the light transmissive substrate and the light-shielding film; and

the thickness of the entire light-shielding film is 50 nm or less.

15. A photomask, which is produced using the photomask blank according to claim 1 .