Evanescent wave assist features for microlithography

Abstract

A method for improved imaging performance of a microlithography photomask is described. By providing sub resolution evanescent wave assist features in regions surrounding a main photomask feature, the coupling of the evanescent energy from these features can add to the transmission efficiency of the main feature. The photomask comprises a transparent substrate support member having at least a first and second surface, wherein said first surface is smooth and said second surface is patterned with a plurality of grooves; a film coating disposed over said plurality of groves, wherein said film coating has one or more openings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is disclosed with reference to the accompanying drawings, wherein:

FIG. 1 is an embodiment of the invention showing EWAFs on opposite sides of a main feature;

FIG. 2 shows the resulting impact on imaging of EWAFs;

FIG. 3 shows an embodiment of the invention with one pair of EWAFs inside a main feature opening;

FIG. 4 shows an embodiment of the invention with EWAFs on the back side of a mask;

FIG. 5 shows a near field transmission for a chromium oxide film;

FIG. 6 shows a near field transmission for a chromium nitride film;

FIG. 7 shows a near field transmission for a tantalum nitride film;

FIG. 8 shows a near field transmission for a chromium film; and

FIG. 9 shows a far field transmission for a chromium oxide film.

Claims

1. A photomask for projection lithography comprising: a transparent substrate support member having at least a first and second surface, wherein said first surface is smooth and said second surface is patterned with a plurality of grooves;a film coating disposed over said plurality of groves, wherein said film coating has one or more openings; andwherein transmission of irradiation through said one or more openings is enhanced by evanescent coupling between said plurality of grooves and said one or more openings.

2. The photomask of claim 1, wherein said film coating comprises a dielectric material.

3. The photomask of claim 1, wherein said film coating comprises a metallic material.

4. The photomask of claim 1, wherein said film coating comprises a metallic nitride material.

5. The photomask of claim 1, wherein said film coating comprises a dielectric nitride material.

6. The photomask of claim 1, wherein said film coating comprises a dielectric oxide material.

7. The photomask of claim 1, wherein said film coating comprises a metallic oxide material.

8. The photomask of claim 1, wherein said film coating comprises an oxi-nitride material.

9. The photomask of claim 1, wherein said film coating comprises a metallic oxi-nitride material.

10. The photomask of claim 1, wherein said film coating comprises chromium.

11. The photomask of claim 1, wherein said film coating comprises chromium oxide.

12. The photomask of claim 1, wherein said film coating comprises chromium nitride.

13. The photomask of claim 1, wherein said film coating comprises chromium oxynitride.

14. The photomask of claim 1, wherein said film coating comprises a nitride chosen from the group consisting of Ta, Mo, Ti, Cr, Nb, Ru, Rh, W, Zr, and Al.

15. The photomask of claim 1, wherein said film coating comprises an element chosen from group IVA, VA, and VIA.

16. The photomask of claim 1, wherein said film coating comprises an oxide chosen from the group consisting of Ta, Mo, Ti, Cr, Nb, Ru, Rh, W, Zr, and Al.

17. The photomask of claim 1, wherein at least one of said one or more openings is square.

18. The photomask of claim 1, wherein at least one of said one or more openings is rectangular.

19. The photomask of claim 1, wherein said one or more openings includes a plurality of contact holes.

20. The photomask of claim 1, wherein said plurality of groves have a depth between about lambda/(4n) and 4lambda/n, where lambda is defined as exposing radiation wavelength and n is defined as refractive index of said transparent substrate support.

21. The photomask of claim 1, wherein said plurality of groves have a pitch of about lambda/(4n) and 4lambda/n, where lambda is defined as exposing radiation wavelength and n is defined as refractive index of said transparent substrate support.

22. The photomask of claim 1, further comprising an absorber.

23. The photomask of claim 22, wherein said absorber has a depth between about 10 to 1000 nanometers.

24. A projection lithography imaging system comprising: an illumination system configured to produce radiation in the ultraviolet-visible spectral region;a projection system configured to produce an image;a photosensitized substrate to record said image;a photomask including one or more sub-resolution features and a main feature,wherein said photomask is configured to create an object for projection in said system; andwherein said one or more sub-resolution features produce an evanescent wave when irradiated by said illumination system.

25. The system of claim 24, wherein said evanescent wave enhances resolution of said main feature.

26. The system of claim 24, wherein said photomask includes a pattern chosen from the group consisting of a contact hole pattern, a space pattern, a line pattern, and an island pattern.

27. The system of claim 24, wherein said photomask further includes an absorber.

28. The system of claim 27, wherein said one or more sub-resolution features are disposed between said absorber and said photosensitized substrate.

29. The system of claim 24, wherein said photomask includes a front and a back.

30. The system of claim 29, wherein said one or more sub-resolution features are disposed on said back of said photomask.

31. The system of claim 27, wherein said one or more sub-resolution features are patterned into said absorber.

32. The system of claim 24, wherein said one or more sub-resolution features are disposed within said main feature.

33. A system for computing the steps of photomask design layout including evanescent wave assist features using a computer system comprising: a central processing unit for computation of evanescent wave assist feature placement solutions;a memory storing computer instructions for said computation of said evanescent wave assist feature placement solutions, wherein when said computer instructions are executed on the central processing unlit, they perform a process comprising the steps of:determining design parameters for one or more main features and one or more sub-resolution features, wherein said one or more sub-resolution features are designed to produce an evanescent wave when irradiated by an illumination source;optimizing said photomask for resolution enhancement; andgenerating evanescent wave assist feature placement solutions wherein an optimized photomask design is saved in a file which is used to create patterns on a imaged substrate.

34. The system of claim 33, wherein said design parameters are chosen from the group consisting of number, size, location, and shape.

35. The system of claim 33, wherein said optimized photomask design includes a pattern chosen from the group consisting of a contact hole pattern, a space pattern, a line pattern, and an island pattern.