Photomask and pattern formation method using the same

1. A photomask comprising:

a transparent substrate having a transparent property against exposing light,

a semi-light-shielding portion formed on the transparent substrate;

an opening formed in the semi-light-shielding portion; and

a light-shielding portion formed on the transparent substrate and surrounding the opening, wherein:

the semi-light-shielding portion transmits the exposing light in an identical phase with respect to the opening, and

the light-shielding portion has a width not more than a maximum width with which an unexposed region is not formed by the exposing light having passed through the opening and diffracting at an edge of the opening to round to a back of the light-shielding portion.

2. The photomask of claim 1 , wherein the light-shielding portion is disconnected at a corner of the opening.

3. The photomask of claim 2 , wherein each disconnected part of the light-shielding portion has a length shorter than a corresponding side of the opening.

4. The photomask of claim 1 , wherein the light-shielding portion has a width not less than a minimum width with which light intensity of a side lobe caused by diffraction, at an edge of the opening, of the exposing light having passed through the opening is not sufficient for sensitizing a resist.

5. The photomask of claim 1 , wherein:

the photomask is designed for a specific reduction projection optical system, and is included in such a system along with an exposure apparatus, and

the light-shielding portion of the photomask has a width not less than (0.12×λ/NA)×M, where λ is a wavelength of the exposing light, NA is numerical aperture of a reduction projection optical system of an aligner and M is a reduction ratio of the reduction projection optical system.

6. The photomask of claim 1 , wherein:

the photomask is designed for a specific reduction projection optical system, and is included in such a system along with an exposure apparatus, and

the light-shielding portion of the photomask has a width not more than (1.74×λ/NA)×M, where λ is a wavelength of the exposing light, NA is numerical aperture of a reduction projection optical system of an aligner and M is a reduction ratio of the reduction projection optical system.

7. The photomask of claim 1 , wherein the light-shielding portion is in contact with the opening.

8. The photomask of claim 1 , wherein a part of the semi-light-shielding portion is present between the opening and the light-shielding portion.

9. The photomask of claim 8 , wherein:

the photomask is designed for a specific reduction projection optical system, and is included in such a system along with an exposure apparatus, and

the part of the semi-light-shielding portion of the photomask present between the opening and the light-shielding portion has a width not more than (0.10×λ/NA)×M, where λ is a wavelength of the exposing light, NA is numerical aperture of a reduction projection optical system of an aligner and M is a reduction ratio of the reduction projection optical system.

10. A pattern formation method using the photomask of claim 1 , the method comprising steps of:

(a) forming a resist film on a substrate;

(b) irradiating the resist film with the exposing light through the photomask; and

(c) patterning the resist film by developing the resist film having been irradiated with the exposing light.

11. The pattern formation method of claim 10 , wherein an ArF excimer laser is used as an exposing light source in the step (b).

12. The pattern formation method of claim 11 , wherein an immersion exposure process is employed in the step (b).

13. The pattern formation method of claim 12 , wherein the step (a) includes coating of the resist film with a top coat.