Lithographic apparatus, spectral purity filter and device manufacturing method
A lithographic apparatus for patterning a beam of radiation and projecting it onto a substrate, comprising at least two spectral purity filters configured to reduce the intensity of radiation in the beam of radiation in at least one undesirable range of radiation wavelength, wherein the two spectral purity filters are provided with different radiation filtering structures from each other.
1. A lithographic apparatus configured to pattern a beam of radiation and project the beam of radiation onto a substrate, comprising:
a first spectral purity filter configured to reduce the intensity of radiation in the beam of radiation in at least one first undesirable range of radiation wavelengths; and
a second spectral purity filter configured to reduce the intensity of radiation in the beam of radiation in at least one second undesirable range of radiation wavelengths that is different than the at least one first undesirable range of radiation wavelengths;
wherein the first spectral purity filter and the second spectral purity filter are provided with different radiation filtering structures from each other;
wherein the first spectral purity filter is a grating spectral purity filter, comprising:
a first multilayer stack of alternating layers, configured to reflect radiation of a first wavelength in a first direction relative to the first multilayer stack; and
a first plurality of recesses in a top side of the first multilayer stack, the first plurality of recesses configured to form a grating arranged such that radiation of a second wavelength is reflected in a second direction relative to the first multilayer stack that is different from the first direction; and
wherein the second spectral purity filter is a second grating spectral purity filter comprising:
a second plurality of recesses, smaller than the first plurality of recesses, formed on the top side of the first multilayer stack between the recesses of the first plurality of recesses and in a lower surface of the recesses of the first plurality of recesses; and
wherein the second plurality of recesses are configured such that radiation of a third wavelength is reflected in a third direction relative to the first multilayer stack that is different from the first direction.
2. The lithographic apparatus of claim 1 , wherein the first spectral purity filter is configured to reduce the intensity of infrared radiation in the beam of radiation; and the first spectral purity filter is arranged within the radiation beam path closer to a source of radiation that provides the beam of radiation than the second spectral purity filter is to the source of radiation.
3. The lithographic apparatus of claim 1 , wherein the lithographic apparatus further comprises a radiation system that provides the beam of radiation; and
the first spectral purity filter is formed on a reflective surface of at least part of a collector in the radiation system.
4. The lithographic apparatus of claim 1 , wherein the first plurality of recesses have a depth of between approximately 1.5 μm to 3 μm.
5. The lithographic apparatus of claim 4 , wherein the depth is approximately 2.65 μm.
6. The lithographic apparatus of claim 1 , wherein the second plurality of recesses have a depth of between approximately 25 nm to 75 nm.
7. The lithographic apparatus of claim 6 , wherein the depth is approximately 50 nm.
8. The lithographic apparatus of claim 1 , wherein the second plurality of recesses have a cross-section that is one of substantially rectangular and substantially triangular.
9. The lithographic apparatus of claim 1 , wherein the second spectral purity filter is a grating filter.
10. A device manufacturing method comprising:
patterning a beam of radiation and projecting the beam of radiation onto a substrate;
using a first spectral purity filter to reduce the intensity of radiation in the beam of radiation in at least one first undesirable range of radiation wavelengths; and
using a second spectral purity filter to reduce the intensity of radiation in the beam of radiation in at least one second undesirable range of radiation wavelengths that is different than the at least one first undesirable range of radiation wavelengths;
wherein the first spectral purity filter and second spectral purity filter are provided with different radiation filtering structures from each other,
wherein the first spectral purity filter is a grating spectral purity filter comprising:
a multilayer stack of alternating layers, configured to reflect radiation of a first wavelength in a first direction relative to the multilayer stack; and
a first plurality of recesses in a top side of the multilayer stack, the first plurality of recesses configured to form a grating arranged such that radiation of a second wavelength is reflected in a second direction relative to the multilayer stack that is different from the first direction; and
wherein the second spectral purity filter comprises a second plurality of recesses, smaller than the first plurality of recesses, formed on the top side of the multilayer stack between the recesses of the first plurality of recesses and in a lower surface of the recesses of the first plurality of recesses,
wherein the second plurality of recesses are configured to form at least one second grating arranged such that radiation of a third wavelength is reflected in a third direction relative to the multilayer stack that is different from the first direction.
11. A spectral purity filter, comprising:
a multilayer stack of alternating layers, configured to reflect radiation of a first wavelength in a first direction relative to the multilayer stack; and
a first plurality of recesses in a top side of the multilayer stack, the first plurality of recesses configured to form a first grating arranged such that radiation of a second wavelength is reflected in a second direction relative to the multilayer stack that is different from the first direction;
characterized by a second plurality of recesses, smaller than the first plurality of recesses, formed on the top side of the multilayer stack between the recesses of the first plurality of recesses and in a lower surface of the recesses of the first plurality of recesses, the second plurality of recesses configured to form at least one second grating arranged such that radiation of a third wavelength is reflected in a third direction relative to the multilayer stack that is different from the first direction.
12. The spectral purity filter of claim 11 , wherein the first plurality of recesses have a depth of between approximately 1.5 μm to 3 μm.
13. The spectral purity filter of claim 12 , wherein the depth is approximately 2.65 μm.
14. The spectral purity filter of claim 11 , wherein the second plurality of recesses have a depth of between approximately 25 nm to 75 nm.
15. The spectral purity filter of claim 14 , wherein the depth is approximately 50 nm.
16. The spectral purity filter of claim 11 , wherein the second plurality of recesses have a cross-section that is one of substantially rectangular and substantially triangular.
17. The spectral purity filter of claim 11 , wherein the second and third directions are substantially the same.