Phase grating for mask inspection system
Spectral Purity Filters, or SPFs, are disclosed. Such SPFs are designed to block out the 1030 nm drive laser and other undesired out of band light in a EUV mask inspection system. Different phase grating configurations for near normal incidence and grazing incidence are provided in the present disclosure and are configured specifically for EUV mask inspection.
1. A phase grating on a mirror, comprising:
a substrate;
a plurality of continuous base bilayers positioned on the substrate; and
a plurality of gratings positioned on the plurality of continuous base bilayers, wherein a depth of the plurality of gratings is approximately (laser wavelength)/4/cos(angle of incidence).
2. The phase grating of claim 1 , wherein the continuous base bilayers and the plurality of gratings are formed using at least one of: Mo/Si bilayers, Ru/Si bilayers, Ru/C bilayers, Mo/C bilayers, Mo/C bilayers, Si/C bilayers, La/B bilayers, La/B4C bilayers, Ru/B4C bilayers, Ti/B4C bilayers, LaN/B4C bilayers or LaN/B bilayers.
3. The phase grating of claim 1 , wherein each of the plurality of gratings is formed using between 10 and 200 bilayers.
4. The phase grating of claim 1 , wherein the gratings are arranged in at least one of: a parallel manner, a radial manner, an off-axis radial manner, a combination of different parallel sections, a combination of different radial sections, or a combination of parallel and radial sections.
5. The phase grating of claim 1 , wherein a pitch of the plurality of gratings is a predetermined value between 5 and 1000 um.
6. The phase grating of claim 1 , wherein a duty ratio of the gratings is a predetermined value between 0.7 and 1.5.
7. The phase grating of claim 1 , wherein the depth of the gratings is between 100 and 600 nm.
8. The phase grating of claim 1 , further comprising:
a coating containing at least one of: Ru, C, Pt, Pd, Au, Nb, Nb2O5, SiO2, TiO2 or RuO2 deposited on each of the plurality of gratings.
9. A phase grating on a mirror, comprising:
a substrate;
a continuous Ru base layer positioned on the substrate, the continuous Ru base layer having a thickness of at least approximately 50 nm; and
a plurality of Ru gratings positioned on the continuous Ru base layer, wherein a depth of the gratings is determined based on an angle of incidence.
10. The phase grating of claim 9 , wherein the Ru gratings are arranged to be approximately parallel to planes of incidence.
11. The phase grating of claim 9 , wherein a pitch of the gratings is between 5 and 1000 um.
12. The phase grating of claim 9 , wherein a duty ratio of the gratings is between 0.7 and 1.5.
13. The phase grating of claim 9 , wherein the depth of the gratings is between 300 and 5000 nm.
14. A mirror, comprising:
a substrate, the substrate having a grated surface defining a plurality of gratings, wherein each of the plurality of gratings having a depth of approximately (laser wavelength)/4/cos(angle of incidence), a pitch of the gratings is a predetermined value between 5 and 1000 um, and a duty ratio of the gratings is a predetermined value between 0.7 and 1.5; and
a coating layer deposited on the reflective substrate, the coating layer covering the entirety of the grated surface.
15. The mirror of claim 14 , wherein the laser wavelength is in a range between 500 and 2000 nm.
16. The mirror of claim 14 , wherein the angle of incidence is between 0 and 30 degrees.
17. The mirror of claim 16 , wherein the coating layer is formed using between 10 and 200 bilayers formed using at least one of: Mo/Si bilayers, Ru/Si bilayers, Ru/C bilayers, Mo/C bilayers, Mo/C bilayers, Si/C bilayers, La/B bilayers, La/B4C bilayers, Ru/B4C bilayers, Ti/B4C bilayers, LaN/B4C bilayers or LaN/B bilayers.
18. The mirror of claim 16 , wherein the gratings are arranged in at least one of: a parallel manner, a radial manner, an off-axis radial manner, a combination of different parallel sections, a combination of different radial sections, or a combination of parallel and radial sections.
19. The mirror of claim 14 , wherein the angle of incidence is between 66 and 86 degrees.
20. The mirror of claim 19 , wherein the coating layer is formed using Ru.
21. The mirror of claim 19 , wherein the gratings are arranged to be parallel to planes of incidence.
22. A mask inspection system, comprising:
a laser configured for driving an EUV light source;
a collector configured for collecting the EUV light and delivering the EUV light via an illumination module to an EUV mask;
a light sensor configured for receiving imaging of the EUV mask;
wherein the collector and the illumination module each includes at least one mirror, said at least one mirror having phase grating to suppress undesired radiations;
wherein if an angle of incidence to said at least one mirror is between 0 and 30 degrees, said phase grating includes a plurality of gratings each having a depth of approximately (laser wavelength)/4/cos(angle of incidence).
23. The mask inspection system of claim 22 , wherein each of the plurality of gratings is formed using at least one of: Mo/Si bilayers, Ru/Si bilayers, Ru/C bilayers, Mo/C bilayers, Mo/C bilayers, Si/C bilayers, La/B bilayers, La/B4C bilayers, Ru/B4C bilayers, Ti/B4C bilayers, LaN/B4C bilayers or LaN/B bilayers.
24. The mask inspection system of claim 22 , wherein the laser is in a wavelength range between 500 and 2000 nm.
25. The mask inspection system of claim 22 , wherein if the angle of incidence to said at least one mirror is between 0 and 30 degrees, the gratings are arranged in at least one of: a parallel manner, a radial manner, an off-axis radial manner, a combination of different parallel sections, a combination of different radial sections, or a combination of parallel and radial sections.
26. The mask inspection system of claim 22 , wherein if the angle of incidence to said at least one mirror is between 66 and 86 degrees, said phase grating includes a plurality of Ru gratings arranged to be parallel to planes of incidence.
27. The mask inspection system of claim 22 , wherein a pitch of the gratings is a predetermined value between 5 and 1000 um, and a duty ratio of the gratings is a predetermined value between 0.7 and 1.5.
28. The mask inspection system of claim 22 , wherein the phase grating is configured to simultaneously suppress laser and UV light.
29. The mask inspection system of claim 22 , wherein said at least one mirror is further configured to have at least two types of phase gratings.
30. The mask inspection system of claim 22 , wherein the light sensor is coated with a thin film coating.
31. The mask inspection system of claim 30 , wherein the thin film coating on the light sensor includes at least one of: Be and Zr.
32. A phase grating on a mirror, comprising:
a substrate;
a plurality of continuous base bilayers positioned on the substrate; and
a plurality of gratings positioned on the plurality of continuous base bilayers, wherein each of the plurality of gratings is formed using a number of bilayers, wherein a depth of the plurality of gratings is approximately (laser wavelength)/4/cos(angle of incidence).
33. The phase grating of claim 32 , wherein each of the number of gratings includes between 10 and 200 bilayers, and wherein the continuous base bilayers and the plurality of gratings are formed using at least one of: Mo/Si bilayers, Ru/Si bilayers, Ru/C bilayers, Mo/C bilayers, Mo/C bilayers, Si/C bilayers, La/B bilayers, La/B4C bilayers, Ru/B4C bilayers, Ti/B4C bilayers, LaN/B4C bilayers or LaN/B bilayers.
34. The phase grating of claim 32 , wherein a pitch of the gratings is a predetermined value between 5 and 1000 um.
35. The phase grating of claim 32 , wherein a duty ratio of the gratings is a predetermined value between 0.7 and 1.5.
36. The phase grating of claim 32 , wherein the laser wavelength is in a range between 500 and 2000 nm.
37. The phase grating of claim 32 , further comprising:
a coating containing at least one of: Ru, C, Pt, Pd, Au, Nb, Nb2O5, SiO2, TiO2 or RuO2 deposited on each of the number of gratings.