Lithographic apparatus, device manufacturing method, and device manufactured thereby
View Patent ↗In a lithographic projection apparatus, a grating spectral filter is used to filter an EUV projection beam. The grating spectral filter is preferably a blazed, grazing incidence, reflective grating. Cooling channels may be provided in or on the rear of the grating spectral filter. The grating spectral filter may be formed of a material effectively invisible to the desired radiation.
1. A radiation source apparatus comprising:
a radiation source unit configured to supply radiation of desired wavelengths and radiation of undesired wavelengths; and
a grating spectral filter configured to diffract said radiation of desired wavelengths into a zeroth-order beam to form a projection beam of radiation and to diffract said radiation of undesired wavelengths away from said radiation of desired wavelengths.
2. A radiation source apparatus according to claim 1 wherein said grating spectral filter comprises a blazed grating.
3. A radiation source apparatus according to claim 2 wherein said grating spectral filter has a blazing angle less than about 2.5°.
4. A radiation source apparatus according to claim 2 wherein said grating spectral filter has a line density in the range of from 200 to 700 lines per mm.
5. A radiation source apparatus according to claim 1 wherein said grating spectral filter is a laminar grating.
6. A radiation source apparatus according to claim 1 wherein said grating spectral filter is configured to allow said radiation of said desired wavelengths to pass therethrough without substantially changing said radiation of said desired wavelengths.
7. A radiation source apparatus according to claim 6 wherein said grating spectral filter is substantially formed of a material that allows said radiation of said desired wavelengths to pass therethrough without substantially changing said radiation of said desired wavelengths.
8. A radiation source apparatus according to claim 7 wherein said grating spectral filter is substantially formed of a material having a refractive index close to unity at said desired wavelengths.
9. A radiation source apparatus according to claim 8 wherein said grating spectral filter comprises silicon.
10. A radiation source apparatus according to claim 1 further comprising a cooling element provided in thermal contact with said grating spectral filter.
11. A radiation source apparatus according to claim 10 wherein said cooling element comprises coolant channels.
12. A radiation source apparatus according to claim 11 further comprising a cooling system for passing coolant fluid through said coolant channels.
13. A radiation source apparatus according to claim 1 wherein said grating spectral filter is a reflective filter.
14. A radiation source apparatus according to claim 1 wherein said grating spectral filter is a grazing incidence reflector.
15. A radiation source apparatus according to claim 13 wherein said grating spectral filter is integral with an optical element of said radiation source apparatus.
16. A radiation source apparatus according to claim 1 wherein said radiation of desired wavelengths has an approximate wavelength selected from the group comprising: 365 nm, 248 nm, 193 nm, 157 nm, 126 nm, from 8 nm to 20 nm and from 9 nm to 16 nm.
17. A radiation source apparatus according to claim 1 wherein said radiation source unit is a laser-produced, or discharge, plasma radiation source.
18. A radiation source apparatus according to claim 1 wherein a portion of said radiation of undesired wavelengths is diffracted by said grating spectral filter onto a structure selected from the group comprising: a heat sink, an aperture, a diaphragm, a beam dump, and combinations thereof.
19. A radiation source apparatus according to claim 1 , wherein said grating spectral filter is configured to reflect said radiation of desired wavelengths to form the projection beam of radiation.
20. A radiation source apparatus according to claim 1 , wherein substantially no radiation of undesired wavelengths is diffracted into the zeroth-order beam.
21. A lithographic projection apparatus comprising:
a radiation source apparatus comprising a radiation source unit configured to supply radiation of desired wavelengths and a grating spectral filter configured to diffract said radiation of desired wavelengths into a zeroth-order beam to form a projection beam of radiation and to diffract radiation of undesired wavelengths supplied by said radiation source unit away from said radiation of desired wavelengths;
a support structure configured to support a patterning structure, the patterning structure being constructed and arranged to pattern the projection beam according to a desired pattern;
a substrate table configured to hold a substrate; and
a projection system configured to project the patterned beam onto a target portion of the substrate.