Soft x-ray reduction camera for submicron lithography

• US 5,003,567 A
• Filed: 02/09/1989
• Issued: 03/26/1991
• Est. Priority Date: 02/09/1989
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Hawryluk, Andrew M., Seppala, Lynn G.
• Primary Examiner(s): Fields, Carolyn E.
• Assistant Examiner(s): Porta, David P.
• Application Number:
  US07/308,332
• Time in Patent Office: 775 Days
• Field of Search: 378/34, 378/35, 378/84, 378/85, 378/145, 250/492.2, 355/67, 355/53
• US Class Current: 378/34
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: G02B 17/0621 off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements
• CPC Class Codes: G03F 7/2039 X-ray radiation
• CPC Class Codes: G03F 7/70033 by plasma extreme ultraviolet [EUV] sources
• CPC Class Codes: G03F 7/70233 Optical aspects of catoptric systems, i.e. comprising only reflective elements, e.g. extreme ultraviolet [EUV] projection systems

Abstract

Soft x-ray projection lithography can be performed using x-ray optical components and spherical imaging lenses (mirrors), which form an x-ray reduction camera. The x-ray reduction is capable of projecting a 5x demagnified image of a mask onto a resist coated wafer using 4.5 nm radiation. The diffraction limited resolution of this design is about 135 nm with a depth of field of about 2.8 microns and a field of view of 0.2 cm². X-ray reflecting masks (patterned x-ray multilayer mirrors) which are fabricated on thick substrates and can be made relatively distortion free are used, with a laser produced plasma for the source. Higher resolution and/or larger areas are possible by varying the optic figures of the components and source characteristics.

Claims

1. Apparatus for performing soft x-ray projection lithography with soft x-rays of a preselected wavelength comprising:

a reflecting x-ray mask comprising a substrate and a patterned x-ray multilayer mirror formed on the substrate;

substantially normal incidence reflective x-ray imaging means positioned after the mask for projecting an image of the x-ray mask onto an image plane, said imaging means being reflective at the preselected wavelength at substantially normal incidence;

wherein the mask substrate is curved to produce a substantially flat field curvature at the image plane.

2. The apparatus of claim 1 wherein the x-ray imaging means comprises:

a primary mirror having a multilayer x-ray reflecting convex surface;

a secondary mirror having a multilayer x-ray reflecting concave surface;

the primary and secondary mirrors being optically aligned in a spaced relationship so that x-rays incident from the mask at substantially normal incidence to the primary mirror are reflected from the primary mirror to the secondary mirror to the image plane.

3. The apparatus of claim 1 further comprising an x-ray source positioned so that x-rays from the source are incident on the mask.

4. The apparatus of claim 3 wherein the x-ray source is a layer produced plasma source.

5. The apparatus of claim 3 further comprising a near normal incidence, reflection condenser means optically aligned with the source and mask to provide substantially uniform illumination of the mask by the source.

6. The apparatus of claim 1 wherein the mask has a mask contrast of greater than about 100:

1.

7. The apparatus of claim 1 wherein the multilayer mirror is selected from C/Cr, Mo/Si, and B/Ru multilayer mirrors.

8. The apparatus of claim 2 wherein the primary and secondary mirrors are substantially spherical.

9. The apparatus of claim 2 wherein the primary and secondary mirrors are substantially aspherical.

10. The apparatus of claim 1 wherein the imaging means has a demagnification in the range of about 1-10X.

11. The apparatus of claim 2 wherein the primary and secondary mirrors are coated with a multilayer selected from a Cr/C, Mo/Si, and B/Ru.

12. The apparatus of claim 3 wherein the source produces x-rays with a wavelength of about 2 nm to about 250 nm.

13. Apparatus for soft x-ray projection lithography with x-rays of a preselected wavelength in the range of 2 nm to 150 nm, comprising:

a reflecting x-ray mask comprising a substrate and a patterned x-ray multilayer mirror formed on the substrate;

a substantially spherical primary mirror having a multilayer x-ray reflecting convex surface having a reflectivity at the preselected wavelength at substantially normal incidence;

a substantially spherical secondary mirror having a multilayer x-ray reflecting concave surface having a reflectivity at the preselected wave length at substantially normal incidence;

the mask, primary mirror and secondary mirror being positioned in a fixed off-axis relationship so that x-rays reflecting by the mask are incident on and reflected by the primary mirror to the secondary mirror and from the secondary mirror to an image plane to project an image of the mask onto the image plane;

wherein the mask substrate is curved to produce a substantially flat field at the image plane.

14. The apparatus of claim 13 further comprising a soft x-ray source positioned in a fixed relationship relative to the mask so that x-rays are incident on the mask.

15. The apparatus of claim 13 wherein the primary and secondary mirrors have a common center of curvature.

16. The apparatus of claim 15 further comprising a pupil placed in the optical path between the secondary mirror and image plane and in the same plane as the common center of curvature of the mirrors.

17. The apparatus of claim 15 further comprising condenser means aligned with the source and mask to provide substantially uniform x-ray illumination of the mask by the source.

18. The apparatus of claim 13 having a demagnification of about 1×

10x.

19. The apparatus of claim 13 wherein the mask, primary mirror and secondary mirror are formed of a plurality of alternating layer pairs selected from carbon/chromium, molybdenum/silicon, and boron/ruthenium.

20. The apparatus of claim 14 wherein the x-ray source comprises a laser produced plasma source.

21. Method for performing x-ray projection lithography, comprising:

forming an x-ray mask with a substrate and a patterned x-ray multilayer mirror on the substrate;

directing a beam of soft x-rays of a preselected wavelength from as source onto the x-ray mask;

reflecting the x-rays from the mask;

imaging x-rays from the mask onto an image plane by an imaging means having a reflectivity at the preselected wavelength at substantially normal incidence;

wherein the mask substrate is curved to produce a substantially flat field at the image plane.

22. Method of claim 21 further comprising imaging the x-rays from the mask onto an image plane by reflecting the x-rays from the mask from a substantially spherical primary mirror to a substantially spherical secondary mirror to the image plane.

23. Method of claim 22 further comprising positioning the primary mirror and secondary mirror to produce an image demagnification of 1-10x.

24. Method of claim 22 further comprising forming the primary mirror with a multilayer x-ray reflecting convex surface and the secondary mirror with a multilayer x-ray reflecting concave surface, the convex and concave reflecting surfaces having a reflectivity at the preselected wavelength at substantially normal incidence.

25. Method of claim 21 further comprising producing a substantially uniform illumination of the mask.

26. A reflection mask, comprising:

a curved substrate;

a patterned multilayer mirror formed on the substrate.

27. The mask of claim 26 wherein the substrate is curved to produce a substantially flat field curvature at an image plane when the mask is imaged onto the image plane by an imaging means positioned after the mask.

28. The mask of claim 26 wherein the mask has a mask contrast of greater than about 100:

1.

29. The mask of claim 26 wherein the multilayer mirror is selected from C/Cr, Mo/Si, and B/Ru multilayer mirrors.

30. The mask of claim 26 wherein the patterned multilayer mirror comprises micron width-lines with a height of about 0.2-0.4 microns.

31. The mask of claim 26 wherein the patterned multilayer mirror is reflective at a wavelength in the range of about 2 nm to about 250 nm.

32. The mask of claim 26 wherein the patterned multilayer mirror is reflective at a wavelength in the range of about 4.5 nm to about 13 nm.

33. The mask of claim 26 wherein the patterned multilayer mirror comprises up to about 200 layer pairs of alternating high refractive index and low refractive index layers.