Method of removing assist features utilized to improve process latitude

1. A method of transferring a lithographic pattern onto a substrate by use of a lithographic apparatus, said method comprising the steps of:

defining features to be printed on said substrate;

determining which of said features require assist features to be disposed adjacent thereto in order for said features to be printed within defined resolution limits;

generating a mask containing said features to be printed and said assist features;

performing a first illumination process so as to print said features on said substrate, said first illumination process resulting in the partial printing of said assist features on said substrate, said first illumination process including a dipole illumination of said substrate; and

performing a second illumination process so as to reduce the amount of said assist features printed on said substrate; said second illumination process comprising the step of performing a quadrapole illumination.

2. The method of transferring a lithographic pattern onto a substrate according to the method of claim 1 , wherein said second illumination process comprises a QUASAR™ illumination.

3. The method of transferring a lithographic pattern onto a substrate according to the method of claim 1 , wherein the sequence in which said first illumination process and said second illumination process are performed is interchangeable.

4. The method of transferring a lithographic pattern onto a substrate according to the method of claim 1 , wherein said dipole illumination includes performing a first exposure of said substrate utilizing a x-dipole illumination, and a second exposure of said substrate utilizing a y-dipole illumination.

5. The method of transferring a lithographic pattern onto a substrate according to the method of claim 1 , wherein said second illumination process utilizes a mask having a pattern formed therein, which is a biased negative of a pattern defined by the assist features contained in said mask.

6. The method of transferring a lithographic pattern onto a substrate according to the method of claim 1 , wherein substantially all of said assist features printed on said substrate as a result of said first illumination process are removed from said substrate by said second illumination process.

7. The method of transferring a lithographic pattern onto a substrate according to the method of claim 1 , wherein said assist features include assist features aligned in a first direction and assist features aligned in a second direction, said first direction and said second direction being orthogonal to one another.

8. The method of transferring a lithographic pattern onto a substrate according to the method of claim 7 , wherein said second illumination process substantially removes both said assist features aligned in said first direction and said assist features aligned in said second direction.

9. A device manufacturing method comprising the steps of:

providing a substrate that is at least partially covered by a layer of radiation sensitive material;

providing a projection beam of radiation using a radiation system;

using patterning means to endow the projection beam with a pattern in its cross-section, said patterning means includes features to be printed on said substrate and assist features disposed adjacent at least one of said features to be printed, said assist features performing optical proximity correction;

projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material including a first illumination process so as to print said features on said substrate, said first illumination process resulting in the partial printing of said assist features on said substrate, said first illumination process including a dipole illumination of said substrate; and

performing a second illumination process so as to reduce the amount of said assist features printed on said substrate; said second illumination process comprising the step of performing a quadrapole illumination.

10. The device manufacturing method of claim 9 , wherein said second illumination process comprises a QUASAR™ illumination.

11. The device manufacturing method of claim 9 , wherein the sequence in which said first illumination process and said second illumination process are performed is interchangeable.

12. The device manufacturing method of claim 9 , wherein said dipole illumination includes performing a first exposure of said substrate utilizing a x-dipole illumination, and a second exposure of said substrate utilizing a y-dipole illumination.

13. The device manufacturing method of claim 9 , wherein said second illumination process utilizes a mask having a pattern formed therein, which is a biased negative of a pattern defined by the assist features contained in said mask.

14. The device manufacturing method of claim 9 , wherein substantially all of said assist features printed on said substrate as a result of said first illumination process are removed from said substrate by said second illumination process.

15. The device manufacturing method of claim 9 , wherein said assist features include assist features aligned in a first direction and assist features aligned in a second direction, said first direction and said second direction being orthogonal to one another.

16. The device manufacturing method of claim 15 , wherein said second illumination process substantially removes both said assist features aligned in said first direction and said assist features aligned in said second direction.