Lithographic apparatus and device manufacturing method
View Patent ↗A lithographic apparatus includes a support structure configured to hold a patterning device, the patterning device configured to pattern a beam of radiation according to a desired pattern, a substrate table configured to hold a substrate and a projection system configured to project the beam as patterned onto a target portion of the substrate. The lithographic apparatus further includes a polarization modifier disposed in a path of the beam. The polarization modifier comprises a material having a radially varying birefringence.
1. A lithographic apparatus, comprising:
a support structure configured to hold a patterning device, the patterning device configured to pattern a beam of radiation;
a substrate table configured to hold a substrate;
a projection system configured to project the beam as patterned onto a target portion of the substrate; and
a circular polarization modifier disposed in a path of the beam of radiation to modify a polarization state of the beam of radiation, the circular polarization modifier comprising a material with circular birefringence so as to increase a depth of focus of a lithographic process implemented by the apparatus.
2. The apparatus according to claim 1 , wherein the circular polarization modifier comprises a rotator having the following Jones matrix:
J
=
(
cos
β
-
sin
β
sin
β
cos
β
)
wherein β is a rotation angle.
3. The apparatus according to claim 2 , wherein
β
=
β
0
p
2
+
q
2
NA
2
where p and q are pupil coordinates, NA is a numerical aperture of the projection system, and β 0 is an angle of rotation at a rim of an aperture of the projection system.
4. The apparatus according to claim 2 , wherein the rotator is a space variant element configured to vary an amount of rotation of a polarization of the beam radially.
5. The apparatus according to claim 4 , wherein a thickness of the space variant element increases or decreases radially.
6. The apparatus according to claim 5 , wherein the space variant element is formed from a material comprising quartz.
7. The apparatus according to claim 2 , wherein the rotator comprises a first half-wave plate having a first axis and a second half-wave plate having a second axis, the first axis and the second axis enclosing a half angle that increases quadratically to a rim of an aperture of the projection system.
8. The apparatus according to claim 2 , wherein the rotator comprises an angular variant element in which the birefringence varies in a field plane and configured to vary an amount of rotation of a polarization of the beam with an angle of propagation of the beam.
9. The apparatus according to claim 8 , wherein the rotator comprises an optical element having a birefringent coating deposited thereon.
10. The apparatus according to claim 8 , wherein the rotator comprises an optical element formed of right-handed and left-handed chiral thin films.
11. The apparatus according to claim 1 , wherein, in use of the apparatus, a depth of focus is approximately doubled in size compared to a depth of focus obtained in a lithographic process performed with a lithographic apparatus without the polarization modifier.
12. The apparatus according to claim 1 , wherein, in use of the apparatus, a critical dimension of a printed feature on the substrate is substantially symmetrical around a best focus position.
13. The apparatus according to claim 1 , wherein the polarization modifier is disposed in a pupil plane of the projection system or in a vicinity of the pupil plane.
14. The apparatus according to claim 1 , wherein the polarization modifier is disposed between the patterning device and the projection system.
15. A lithographic apparatus comprising:
a support structure configured to hold a patterning device, the patterning device configured to pattern a beam of radiation;
a substrate table configured to hold a substrate;
a projection system configured to project the beam as patterned onto a target portion of the substrate; and
a polarization modifier disposed in a path of the beam of radiation to modify a polarization state of the beam of radiation, the polarization modifier comprising a material having a radially continuously varying birefringence,
wherein the polarization modifier comprises an angular variant element in which the birefringence varies in a field plane and configured to vary an amount of rotation of a polarization of the beam with an angle of propagation of the beam.
16. A method for manufacturing a device, comprising:
projecting a patterned beam of radiation through a circular polarization modifier to modify a polarization state of the beam of radiation, the polarization modifier comprising a material with circular birefringence so as to increase a depth of focus of a lithographic process implemented by the apparatus, onto a target portion of a substrate.
17. The method according to claim 16 , wherein the circular polarization modifier comprises a space variant element in which an amount of rotation of a polarization of the patterned beam varies radially.
18. The method according to claim 16 , wherein the circular polarization modifier comprises a first half-wave plate having a first axis and a second half-wave plate having a second axis, the first axis and the second axis enclosing a half angle that increases quadratically to a rim of an aperture of a projection system used to project the patterned beam.
19. The method according to claim 16 , wherein the circular polarization modifier comprises an angular variant element in which birefringence varies in a field plane and an amount of rotation of a polarization of the patterned beam varies with an angle of propagation of the patterned beam.
20. The method according to claim 16 , further comprising printing a feature on the substrate, wherein a critical dimension of the printed feature is substantially symmetrical around a best focus position.