Photomask reticle for use in projection exposure, and manufacturing methods therefor
View Patent ↗A photomask reticle for use in projection exposure to form a resist pattern on a workable film formed over a semiconductor substrate, includes a first area in which a light shield is formed, a second area formed around said first area, a third area formed around said second area; and a fourth area formed around said third area, the areas being formed over a substrate, a relationship between transmissivities of said areas being second area transmissivity>fourth area transmissivity>third area transmissivity>first area transmissivity.
1. A photomask reticle for use in projection exposure to form a resist pattern on a workable film formed over a semiconductor substrate, comprising:
a first area in which a light shield is formed;
a second area formed around said first area;
a third area formed around said second area; and
a fourth area formed around said third area, the areas being formed over a substrate, a relationship between transmissivities of said areas being second area transmissivity>fourth area transmissivity>third area transmissivity>first area transmissivity.
2. The reticle according to claim 1 , wherein said first area comprises:
a first part including dense patterns including a plurality of light shields which are formed adjacent to one another; and
a second part including an isolated pattern including one light shield, wherein said dense patterns and said isolated pattern are independently formed in positions apart from each other.
3. The reticle according to claim 1 , wherein a plurality of unresolved micro light shields are arranged in said third area and said fourth area.
4. The reticle according to claim 3 , wherein said plurality of unresolved micro light shields are randomly arranged.
5. The reticle according to claim 3 , wherein the shapes of said plurality of unresolved micro light shields as projected in the direction normal to the main face of said substrate include congruent shapes or similar shapes.
6. The reticle according to claim 3 , wherein a height of said plurality of unresolved micro light shields is less than a height of said light shield in said first area.
7. The reticle according to claim 3 , wherein said first area comprises a halftone including a plurality of light shields having an attenuated phase part not less than 3% but not more than 12% in transmissivity, and light rays passing through said plurality of light shields of said halftone and light rays passing through said second area are different in phase.
8. The reticle according to claim 3 , wherein said light shield in said first area comprises a plurality of light shields differing in transmissivity, and said plurality of light shields are arranged such that their transmissivity increases in a direction towards said second area.
9. A method of manufacturing the reticle for use in projection exposure according to claim 1 , comprising:
forming a light shield layer over said substrate;
forming a resist layer over said light shield layer;
forming, in said resist layer, a resist mask having patterns which form said first area, said third area and said fourth area; and
removing said resist layer after transferring said patterns formed by said resist mask to said light shield layer.
10. A method of manufacturing the reticle for use in projection exposure according to claim 1 , comprising:
forming a light shield layer over said substrate;
forming an intermediate mask layer over said light shield layer;
forming a resist layer over said intermediate mask layer;
forming, in said resist layer, a resist mask having patterns which form said first area, said third area and said fourth area;
removing said resist layer after transferring said patterns formed by said resist mask to said intermediate mask layer; and
removing said intermediate mask layer after further transferring to said light shield layer said patterns transferred to said intermediate mask layer.
11. The reticle according to claim 1 , wherein the third area comprises a plurality of randomly arranged micro light shields.
12. The reticle according to claim 1 , wherein the fourth area comprises a plurality of randomly arranged micro light shields, a number of the plurality of micro light shields in the third area being greater than a number of the plurality of micro light shields in the fourth area.
13. The reticle according to claim 12 , wherein a bottom of the plurality of micro light shields contacts the substrate and comprises a shape which is similar to a shape of a top of the plurality of micro light shields.
14. The reticle according to claim 1 , wherein the first area comprises a first part comprising a main pattern which includes the light shield, and a second part comprising a phase shifter formed around a periphery of the main pattern.
15. The reticle according to claim 14 , wherein light rays to be transmitted by the first and third areas has a first phase, and light rays to be transmitted by the second and fourth areas has a second phase which is different from the first phase.
16. The reticle according to claim 14 , wherein a phase of light rays passing through the first part of the first area has a difference of substantially half the wavelength from a phase of light rays passing through the second part of the first area.
17. The reticle according to claim 1 , wherein the fourth area comprises a plurality of randomly arranged micro light shields which are formed around an entire periphery of the third area.
18. A photomask reticle, comprising:
a first portion comprising a substrate and a light shield formed on the substrate, the first portion having a first transmissivity;
a second portion formed around the first portion and having a second transmissivity;
a third portion formed around the second portion and having a third transmissivity which is greater than the first transmissivity; and
a fourth portion formed around the third portion and having a fourth transmissivity which is greater than the third transmissivity and less than the second transmissivity.