Photomask and method of structuring a photoresist by double exposure with imaging auxiliary structures and different exposure tools
View Patent ↗A method for structuring photoresists and a corresponding photolithography mask utilize a principal structure and an auxiliary structure. In addition to the principal structure to be imaged, the photomask has an imaging auxiliary structure, which improves the imaging of the principal structure. The portions of the imaging auxiliary structure in the photoresist are exposed in a second exposure step and thereby likewise changed into a form that is soluble in a developer. Only the principal structure remains on the substrate after development.
1. A method of structuring a photoresist, which comprises:
providing a photoresist for at least a semidense structure on a substrate;
performing a first exposure by exposing the photoresist with a first photomask imaging a principal structure and an imaging auxiliary structure, for improved imaging of the principal structure, onto the photoresist to thereby cause a chemical differentiation of the photoresist between exposed and unexposed regions; and
subsequently performing a second exposure with a second photomask imaging the imaging auxiliary structure on the photoresist but not imaging the principal structure on the photoresist to thereby cause a chemical modification of the photoresist only in imaged portions of the imaging auxiliary structure; and
developing the photoresist with a developer such that only the principal structure is retained on the substrate.
2. The method according to claim 1 , which comprises carrying out the first exposure and the second exposure under mutually different conditions.
3. The method according to claim 2 , which comprises fashioning the mutually different conditions by carrying out the first exposure with a first exposure device and carrying out the second exposure with a second exposure device having a different numerical aperture than the second exposure device.
4. The method according to claim 3 , wherein the first exposure device has a greater numerical aperture than the second exposure device.
5. The method according to claim 2 , which comprises fashioning the mutually different conditions by carrying out the first exposure with exposure radiation having a wavelength different from an exposure radiation of the second exposure.
6. The method according to claim 5 , wherein the radiation used for the first exposure has a shorter wavelength than the radiation used for the second exposure.
7. The method according to claim 2 , wherein the first photomask and the second photomask are masks of a different mask type.
8. The method according to claim 7 , wherein the mask type is selected from the group consisting of chrome masks, halftone phase shift masks, and alternating phase shift masks.
9. The method according to claim 1 , which comprises performing a baking step after the first exposure, and subsequently carrying out the second exposure.
10. The method according to claim 1 , which comprises, after the first exposure, performing an intermediate development of the photoresist with a developer such that the principal structure and the auxiliary structure remain on the substrate.
11. A method of structuring a photoresist, which comprises:
providing a photoresist for at least a semidense structure on a substrate;
performing a first exposure by exposing the photoresist with a first photomask imaging a principal structure and an imaging auxiliary structure, for improved imaging of the principal structure, onto the photoresist to thereby cause a chemical differentiation of the photoresist between exposed and unexposed regions; and
subsequently performing a second exposure by exposing the photoresist with a second photomask imaging the imaging auxiliary structure on the photoresist but not substantially imaging the principal structure on the photoresist, to thereby cause a chemical modification of the photoresist only in imaged portions of the imaging auxiliary structure; and
developing the photoresist to develop only the principal structure on the substrate.
12. The method according to claim 11 , which comprises carrying out the first exposure and the second exposure under mutually different conditions.