Computer generated hologram, exposure apparatus, and device fabrication method
The present invention provides a computer generated hologram which forms a light intensity distribution on a predetermined plane by giving a phase distribution to a wavefront of incident light, comprising an anisotropic layer whose refractive index with respect to linearly polarized light in a first direction is different from a refractive index of the anisotropic layer with respect to linearly polarized light in a second direction perpendicular to the linearly polarized light in the first direction, and an isotropic layer whose refractive index with respect to the linearly polarized light in the first direction is equal to a refractive index of the isotropic layer with respect to the linearly polarized light in the second direction.
1. A computer generated hologram which forms a light intensity distribution on a predetermined plane by giving a phase distribution to a wavefront of incident light, comprising
an anisotropic layer whose refractive index with respect to linearly polarized light in a first polarization direction is different from a refractive index of the anisotropic layer with respect to linearly polarized light in a second polarization direction perpendicular to the first polarization direction, and
an isotropic layer whose refractive index with respect to the linearly polarized light in the first direction is equal to a refractive index of the isotropic layer with respect to the linearly polarized light in the second direction,
wherein a first light intensity distribution formed on the predetermined plane by a linearly polarized light component in the first polarization direction of the incident light is made different from a second light intensity distribution formed on the predetermined plane by a linearly polarized light component in the second polarization direction of the incident light by giving different phase distributions to a wavefront of the linearly polarized light component in the first polarization direction of the incident light, and a wavefront of the linearly polarized light component in the second polarization direction of the incident light,
wherein the computer generated hologram includes a plurality of cells, and a thickness of the anisotropic layer and a thickness of the isotropic layer are set for each of the plurality of cells, and
wherein the number of thicknesses of the anisotropic layer is smaller than the number of thicknesses of the isotropic layer in the plurality of cells.
2. The hologram according to claim 1 , wherein the different phase distributions are given to the wavefront of the linearly polarized light component in the first polarization direction of the incident light, and the wavefront of the linearly polarized light component in the second polarization direction of the incident light by setting a refractive index of the anisotropic layer for each of a plurality of cells.
3. The hologram according to claim 1 , wherein a bonded plane between the anisotropic layer and the isotropic layer is a flat plane.
4. The hologram according to claim 1 , wherein a refractive index of the anisotropic layer with respect to the linearly polarized light in one of the first polarization direction and the second polarization direction is equal to a refractive index of the isotropic layer.
5. The hologram according to claim 1 , wherein the anisotropic layer is made of a birefringence material.
6. The hologram according to claim 5 , wherein the birefringence material has intrinsic birefringence.
7. The hologram according to claim 1 , wherein the anisotropic layer has a three-dimensional structure which generates structural birefringence.
8. An exposure apparatus comprising:
an illumination optical system configured to illuminate a reticle with light from a light source; and
a projection optical system configured to project a pattern of the reticle onto a substrate,
wherein the illumination optical system includes a computer generated hologram according to claim 1 .
9. The apparatus according to claim 8 , wherein the illumination optical system includes an optical element configured to convert the light which enters the computer generated hologram into non-polarized light.
10. The apparatus according to claim 8 , wherein
the illumination optical system includes a polarization state adjusting unit configured to adjust a polarization state of the light which enters the computer generated hologram, and
the polarization state adjusting unit adjusts an intensity ratio between the linearly polarized light component in the first polarization direction and the linearly polarized light component in the second polarization direction of the light which enters the computer generated hologram, thereby adjusting a ratio between light intensities of the first light intensity distribution and the second light intensity distribution.
11. A device fabrication method comprising steps of:
exposing a substrate using an exposure apparatus according to claim 8 ; and
performing a development process for the substrate exposed.
12. The hologram according to claim 1 , wherein
the plurality of cells include a first cell, a second cell, a third cell and a fourth cell,
the first cell and fourth cell do not shift a phase between the linearly polarized light component in the first polarization direction and the linearly polarized light component in the second polarization direction,
the second cell and the third cell shift a phase by u between the linearly polarized light component in the first polarization direction and the linearly polarized light component in the second polarization direction,
the thickness of the anisotropic layer in the first cell is equal to the thickness of the anisotropic layer in the fourth cell,
the thickness of the isotropic layer in the first cell is different from the thickness of the isotropic layer in the fourth cell,
the thickness of the anisotropic layer in the second cell is different from the thickness of the anisotropic layer in the third cell, and
the thickness of the isotropic layer in the second cell is different from the thickness of the isotropic layer in the third cell.
13. The hologram according to claim 1 , wherein
the plurality of cells include a first cell, a second cell, a third cell and a fourth cell,
the first cell and the fourth cell do not shift a phase between the linearly polarized light component in the first polarization direction and the linearly polarized light component in the second polarization direction,
the second cell and the third cell shift a phase by u between the linearly polarized light component in the first polarization direction and the linearly polarized light component in the second polarization direction,
the thickness of the anisotropic layer in the first cell is equal to the thickness of the anisotropic layer in the fourth cell,
the thickness of the isotropic layer in the first cell is different from the thickness of the isotropic layer in the fourth cell,
the thickness of the anisotropic layer in the second cell is equal to the thickness of the anisotropic layer in the third cell, and
the thickness of the isotropic layer in the second cell is different from the thickness of the isotropic layer in the third cell.