Mask for EUV lithography, EUV lithography system and method for optimising the imaging of a mask
A mask ( 105 ) for EUV lithography includes a substrate ( 107 ), a multi-layer coating ( 108 ) applied to the substrate ( 107 ) and a mask structure ( 109 ) which is applied to the multi-layer coating ( 108 ) and which has an absorber material, the mask structure ( 109 ) having a maximum thickness of less than 100 nm, preferably not exceeding a maximum thickness of 30 nm, particularly preferably 20 nm, in particular 10 nm. Also disclosed is an EUV lithography system having such a mask ( 105 ) and a method for optimizing the imaging of such a mask ( 105 ).
1. A mask for extreme ultraviolet (EUV) lithography comprising:
a substrate,
a multi-layer coating applied to the substrate, and
a mask structure applied to the multi-layer coating and which has an absorber material,
wherein the mask structure has a maximum thickness of less than 100 nm, and
wherein the multi-layer coating has an optical design which comprises a positionally-dependent variation of a thickness of a first layer of the multi-layer coating which is dependent on a pitch of the mask structure, and
wherein the optical design comprises a positionally-dependent variation of a thickness of a second layer of the multi-layer coating that is dependent on the pitch of the mask structure.
2. The mask according to claim 1 , wherein the positionally-dependent variation of the optical design of the multi-layer coating comprises a positionally-dependent change in thickness (D(X,Y)) of the multi-layer coating.
3. The mask according to claim 1 , wherein an optical design of the mask structure is adapted to the optical design of the multi-layer coating which comprises the positionally-dependent variation of the first layer.
4. The mask according to claim 1 , wherein a thickness (d) of the mask structure varies in a positionally-dependent manner in dependence on at least one of: a pitch (p) of the mask structure and an optical design of the multi-layer coating which comprises a positionally-dependent variation.
5. The mask according to claim 1 , wherein the mask structure has at least one absorber structure having a structural width (b(Z)) which varies in a thickness direction (Z) of the mask.
6. The mask according to claim 5 , wherein at least one flank of the absorber structure has a flank angle (α 1 , α 2 ) which is different from 90°.
7. The mask according to claim 6 , wherein the flank angle (α 1 , α 2 ) is between 70° and 88° or between 92° and 110°.
8. The mask according to claim 1 , wherein the absorber material of the mask structure has an absorption coefficient of more than 0.05.
9. The mask according to claim 8 , wherein the absorber material of the mask structure has an absorption coefficient of more than 0.08 at a wavelength of 13.5 nm.
10. The mask according to claim 1 , wherein the absorber material is selected from the group consisting of: Pt, Zn, Au, NiO, Ag 2 O, Ir and Fe.
11. The mask according to claim 1 , wherein the absorber material is selected from the group consisting of: SnO 2 , Co, Ni 8 Cr 2 , SnO and Cu.
12. The mask according to claim 1 , wherein the absorber material is selected from the group consisting of: Ag, Ac, Te, CsI and Sn.
13. The mask according to claim 1 , wherein the absorber material is selected from the group consisting of: Ni, Ag and ZnTe.
14. The mask according to claim 1 , wherein the multi-layer coating comprises a cover layer that is chemically and structurally compatible with the absorber material of the mask structure.
15. An EUV lithography system comprising:
a mask according to claim 1 , an illumination system configured and positioned to illuminate the mask with illumination light and an objective lens configured and positioned to image the mask onto a substrate.
16. The EUV lithography system according to claim 15 , wherein a thickness (d) of at least one absorber structure of the mask structure deviates by no more than 1.5 nm from a thickness (d C,MAX , d T,MIN ) at which at least one imaging characteristic value of the EUV lithography system has a minimum (d T,MIN ) or a maximum (d C,MAX ).
17. The EUV lithography system according to claim 16 , which is configured to operate the mask at a chief ray angle of at least 5°.
18. The EUV lithography system according to claim 15 , wherein at least one absorber structure of the mask structure has a structural width (b(Z)) which varies in a thickness direction (Z) of the mask and which improves at least one imaging characteristic value of the EUV lithography system a relative to an absorber structure having a structural width (b) which is constant in the thickness direction (Z).
19. The EUV lithography system according to claim 15 , wherein the multi-layer coating has an optical design which comprises a positionally-dependent variation and which improves at least one imaging characteristic value of the EUV lithography system relative to a multi-layer coating having an optical design which is not dependent on position.
20. The EUV lithography system according to claim 15 ,
wherein the multi-layer coating has an optical design which comprises a positionally-dependent variation which is dependent on the mask structure, and
wherein an optical design of the mask structure is adapted to the optical design of the multi-layer coating which comprises the positionally-dependent variation.
21. The EUV lithography system according to claim 15 , wherein the multi-layer coating has, in at least a part-region of the mask, a thickness at which at least one imaging characteristic value of the EUV lithography system is improved relative to a further multi-layer coating having a thickness at which the reflectivity (R) of the further multi-layer coating is optimised for the incidence angle range of the EUV lithography system.
22. The EUV lithography system according to claim 15 , which has, during the imaging of the mask, a telecentricity error between −0.5 mrad and 0.5 mrad.
23. The EUV lithography system according to claim 15 , wherein the objective lens has a numerical aperture of 0.2 or more.
24. The EUV lithography system according to claim 15 , wherein the imaging characteristic value is a telecentricity error or an image contrast.
25. The EUV lithography system according to claim 15 , which has, during the imaging of the mask, a telecentricity error between −0.1 mrad and 0.1 mrad.
26. The EUV lithography system according to claim 15 , wherein the objective lens has a numerical aperture of 0.5 or more.
27. The EUV lithography system according to claim 15 , wherein the pitch of the mask structure comprises a variation in the pitch.
28. The mask according to claim 1 , wherein the maximum thickness of the multi-layer coating is no more than 10 nm.
29. The mask according to claim 1 , wherein the positionally-dependent variation of the thickness of the first layer varies between a first thickness and a second thickness, and wherein the first thickness is greater than zero and the second thickness is greater than zero.
30. The mask according to claim 1 , wherein the pitch of the mask structure comprises a variation in the pitch.