Optical beam transformation system and illumination system comprising an optical beam transformation system

{
  "publication_number": "US2006146384A1",
  "country": "US",
  "kind": "A1",
  "title": "Optical beam transformation system and illumination system comprising an optical beam transformation system",
  "abstract": "An optical beam transformation system, which can be designed to be utilized in an illuminating system of a microlithograpic projection exposure apparatus, has a sequence of optical elements arranged along an optical axis of the optical beam transformation system and designed for transforming an entrance light distribution striking an entrance surface of the optical beam transformation system into an exit light distribution emerging from an exit surface of the optical beam transformation system by radial redistribution of light intensity. The optical elements include at least one transformation element causing a radial redistribution of light intensity and having at least one transformation surface inclined to the optical axis and causing a polarization-selective reflection of a light distribution incident on the transformation surface according to an efficiency symmetry characteristic for the transformation surface. The optical elements further include at least one optical compensation element effecting a spatially dependent compensation of transmission inhomogeneties caused by the polarization-selective reflection at the transformation surface according to a compensation symmetry adapted to the efficiency symmetry of the transformation surface. Axicon elements with axicon surfaces may be used as transformation elements.",
  "claims": [
    "1. An optical beam transformation system comprising: a sequence of optical elements arranged along an optical axis of the optical beam transformation system and designed for transforming an entrance light distribution striking an entrance surface of the optical beam transformation system into an exit light distribution emerging from an exit surface of the optical beam transformation system by radial redistribution of light intensity; the optical elements including at least one transformation element causing a radial redistribution of light intensity and having at least one transformation surface inclined to the optical axis and causing a polarization-selective reflection of a light distribution incident on the transformation surface according to an efficiency symmetry characteristic for the transformation surface; the optical elements further including at least one optical compensation element effecting a spatially dependent compensation of transmission inhomogeneties caused by the polarization-selective reflection of the transformation surface according to a compensation symmetry adapted to the efficiency symmetry of the transformation surface. 2. The optical beam transformation system according to claim 1, wherein the optical beam transformation system includes a first transformation element with a first transformation surface inclined to the optical axis, and at least one second transformation element with a second transformation surface inclined to the optical axis; and at least one intermediate surface arranged between the first transformation surface and the second transformation surface. 3. The optical beam transformation system according to claim 2, wherein all the transformation surfaces and the intermediate surface have a deflecting action on rays passing through the beam transformation system, whereby a distribution of an overall radial redistribution functionality of the optical beam transformation system over more than two optical surfaces is obtained such that a polarization-varying effect of the first and second transformation surfaces is at least partially compensated by the intermediate surface. 4. The optical beam transformation system according to claim 1, wherein, for all optical surfaces of the optical beam transformation system, including the transformation surface, an incident angle, occurring on the respective surfaces, of the penetrating radiation is at an angular spacing of at least 10° from the associated Brewster angle. 5. The optical beam transformation system according to claim 1, wherein, at all locations of the transformation surface, local inclination angles of the penetrating radiation are smaller than 30° with reference to a radial plane perpendicular to the optical axis. 6. The optical beam transformation system according to claim 1, wherein at least one of the transformation surfaces is conical. 7. The optical beam transformation system according to claim 1, wherein at least one of the transformation surfaces has the form of a multifaceted pyramid face having at least two pyramid facets inclined to the optical axis, the pyramid face having an n-fold radial symmetry about the optical axis, n being the number of the pyramid facets. 8. The optical beam transformation system according to claim 7, wherein more than four pyramid facets are provided. 9. The optical beam transformation system according to claim 1, wherein at least one transformation surfaces is a quasi-conical optical surface curved about a plurality of axes and having a first curvature, running in the circumferential direction, and a second curvature which lies in a plane of curvature containing the optical axis. 10. The optical beam transformation system according to claim 2, wherein all the transformation surfaces and the intermediate surface are conical or pyramidal axicon surfaces. 11. The optical beam transformation system according to claim 1, wherein the optical beam transformation system includes a first transformation element with a first transformation surface inclined to the optical axis, and at least one second transformation element with a second transformation surface inclined to the optical axis, wherein an axial spacing between the first transformation element and the second transformation element is adjustable. 12. The optical beam transformation system according to claim 1, wherein at least one transformation element is assembled from a plurality of separate individual elements arranged about the optical axis of the beam transformation system. 13. The optical beam transformation system according to claim 12, wherein at least one of the individual elements is mounted movably in such a way that it can be tilted about an axis perpendicular to a radial direction of the optical axis. 14. The optical beam transformation system according to claim 1, wherein the optical beam transformation system includes a first transformation element with a first transformation surface inclined to the optical axis, and at least one second transformation element with a second transformation surface inclined to the optical axis, wherein a polarization rotator for rotating the polarization of the penetrating light by approximately 90° is arranged between the first and the second transformation element. 15. The optical beam transformation system according to claim 14, wherein the polarization rotator comprises an optical delay system which effects a delay of half a wavelength or an odd multiple of half a wavelength between two mutually perpendicular states of polarization. 16. The optical beam transformation system according to claim 1, wherein at least one transformation element is mounted rotatably about the optical axis. 17. The optical beam transformation system according to claim 1, comprising: a first transformation element with a first transformation surface inclined to the optical axis, and at least one second transformation element, arranged downstream of the first transformation element, with a second transformation surface inclined to the optical axis; and an optical compensation element effective as a polarization-influencing optical element arranged in the light direction upstream of the first transformation surface and designed such that rays striking the transformation surfaces are polarized approximately perpendicular or approximately parallel to the respective incidence plane of rays on the first transformation surface. 18. The optical beam transformation system according to claim 17, wherein the optical compensation element has a compensation efficiency adapted to the efficiency symmetry of the transformation optical elements such that the optical beam transformation system operates in a substantially polarization-maintaining fashion, whereby each ray downstream of the optical beam transformation system has approximately the same polarization state as the same ray had upstream of the optical beam transformation system. 19. The optical beam transformation system according to claim 17, wherein the two transformation surfaces are conical in order to produce an annular illumination distribution. 20. The optical beam transformation system according to claim 17, wherein rays downstream of the optical compensation element effective as a polarization-influencing optical element are polarized one of radially and tangential in relation to an optical axis. 21. The optical beam transformation system according to claim 17, wherein the two transformation surfaces in each case comprise a number of pyramidally arranged segments for producing a multipole illumination. 22. The optical beam transformation system according to claim 21, wherein rays that strike a segment are linearly polarized parallel to a plane that is perpendicular to this segment and that contains the direction of the maximum surface gradient of this segment. 23. The optical beam transformation system according to claim 21, wherein rays that strike a segment are linearly polarized perpendicular to a plane that is perpendicular to this segment and that contains the direction of the maximum surface gradient of this segment. 24. The optical beam transformation system according to claim 17, wherein the optical compensation element effective as a polarization-influencing optical element comprises a first raster arrangement of half-wave plates whose principal axes are oriented such that rays striking the transformation surfaces are polarized approximately perpendicular or approximately parallel to the respective incidence plane of the rays. 25. The optical beam transformation system according to claim 17, wherein a second optical compensation element effective as a polarization-influencing optical element is arranged in the light direction downstream of the second transformation element and is designed in such a way that the rays in the light direction downstream of the second optical compensation element exhibit a prescribed polarization distribution. 26. The optical beam transformation system according to claim 25, wherein the second optical compensation element comprises a second raster arrangement of half-wave plates whose principal axes are oriented in such a way that the prescribed polarization distribution is produced. 27. The optical beam transformation system according to claim 17, wherein the optical beam transformation system is adapted to the polarization state of the radiation upstream of the optical beam transformation system such that the rays are one of linearly polarized parallel to a direction perpendicular to an optical axis and circularly polarized in the light direction downstream of the optical beam transformation system. 28. The optical beam transformation system according to claim 17, wherein the optical beam transformation system is adapted to the polarization state of the radiation upstream of the optical beam transformation system such that for each ray the polarization state in the light direction downstream of the optical beam transformation system is approximately the same as in the light direction upstream of the optical beam transformation system. 29. The optical beam transformation system according to claim 1, wherein the optical compensation element has a compensation efficiency adapted to the efficiency symmetry of the optical transformation elements such that the optical beam transformation system operates in a substantially polarization-maintaining fashion, whereby each ray downstream of the optical beam transformation system has approximately the same polarization state as the same ray had upstream of the optical beam transformation system. 30. The optical beam transformation system according to claim 1, wherein the compensation element has an anisotropic transmission according to a non-uniform spatial distribution of transmittance adapted to substantially reduce spatial transmission non-uniformities effected by the transformation element. 31. The optical beam transformation system according to claim 1, wherein the compensation element is effective for spatially dependent compensation of transmission inhomogeneities of an transformation element caused by polarization-selective reflection at the transformation surface, the compensation element acting on the incident radiation having with reference to the optical axis an essentially two-fold radially symmetrical efficiency characteristic in the case of which a first efficiency in the region around a first direction (x) running perpendicular to the optical axis is significantly higher or lower than a second efficiency in the region of a second direction (y) running perpendicular to the first direction and to the optical axis. 32. The optical beam transformation system according to claim 30, wherein the compensation element is arranged azimuthally in such a way relative to the transformation element that a light beam that passes through a region of relatively low transmission at the transformation element passes through a region of relatively high transmission in the region of the compensation element, and vice versa. 33. The optical beam transformation system according to claim 30, wherein the compensation element acts on the incident radiation with a substantially elliptic efficiency characteristic with reference to the optical axis. 34. The optical beam transformation system according to claim 30, wherein the optical compensation element has an n-fold radial compensation symmetry adapted to an n-fold efficiency symmetry of the transformation optical element, where n is an integer number with n≧2. 35. The optical beam transformation system according to claim 1, wherein at least one optical surface of the optical beam transformation system is occupied by an optical compensation coating effective as a compensation element for the spatially dependent compensation of the transmission inhomogeneities caused by polarization-selective reflection at the transformation surface. 36. The optical beam transformation system according to claim 35, wherein the compensation coating is designed such that with reference to transmission losses it essentially produces in a spatially resolving fashion an effect that is reciprocal to that of an uncoated transformation surface. 37. The optical beam transformation system according to claim 35, wherein at least one compensation coating is a multilayer interference layer system having alternating high-index and low-index dielectric individual layers with an azimuthally varying transmission efficiency. 38. The optical beam transformation system according to claim 35, wherein at least one compensation coating is a gray filter layer with an azimuthally varying transmission efficiency. 39. The optical beam transformation system according to claim 1, wherein at least one transformation element is an axicon element and the transformation surface is an axicon surface. 40. The optical beam transformation system according to claim 39, wherein the axicon surface is a conical surface. 41. The optical beam transformation system according to claim 39, wherein the axicon surface is formed as a multifaceted pyramid having at least two pyramid facets inclined to the optical axis. 42. The optical beam transformation system according to claim 39, wherein the axicon surface is a quasi-conical optical surface curved about a plurality of axes and having a first curvature, running in the circumferential direction, and a second curvature which lies in a plane of curvature containing the optical axis. 43. Axicon system for transforming an entrance light distribution striking an entrance surface of the axicon system into an exit light distribution emerging from an exit surface of the axicon system by radial redistribution of light intensity, having: an optical axis; a first axicon element with at least one first axicon surface; at least one second axicon element with at least one second axicon surface; and at least one intermediate surface arranged between the first axicon surface and the second axicon surface. 44. Axicon system according to claim 43, in which the intermediate surface is a further axicon surface. 45. Axicon system according to claim 43, in which the intermediate surface is a substantially planar or substantially spherical optical surface arranged in the light path downstream of an axicon surface. 46. Axicon system according to claim 43, in which incident angles of penetrating radiation which are in the vicinity of the Brewster angle do not occur on any of the axicon surfaces. 47. Axicon system according to claim 43, in which, for all axicon surfaces, an incident angle, occurring on the axicon surfaces, of the penetrating radiation is at an angular spacing of at least 10° from the associated Brewster angle. 48. Axicon system according to claim 43, in which, at all locations of the axicon surfaces, local inclination angles are smaller than 30° with reference to a radial plane perpendicular to the optical axis. 49. Axicon system according to claim 43, in which at least one of the axicon surfaces is conical. 50. Axicon system according to claim 43, in which at least one of the axicon surfaces has the form of a multifaceted pyramid face having at least two pyramid facets inclined to the optical axis. 51. Axicon system according to claim 50, in which more than four pyramid facets are provided. 52. Axicon system according to claim 43, in which at least one axicon surface is a quasi-conical optical surface curved about a plurality of axes and having a first curvature, running in the circumferential direction, and a second curvature which lies in a plane of curvature containing the optical axis. 53. Axicon system according to claim 43, which is designed such that light beams of the penetrating light, at each axial position between the entrance surface and the exit surface of the axicon system, run at an angle to the optical axis such that no region with a substantially parallel beam path is present between the entrance surface and exit surface. 54. Axicon system according to claim 43, in which an axial spacing between the first axicon element and the second axicon element is, preferably infinitely, adjustable. 55. Axicon system according to claim 43, in which at least one axicon element is assembled from a plurality of separate individual elements arranged about the optical axis of the axicon system. 56. Axicon system according to claim 55, in which at least one of the individual elements is mounted movably in such a way that it can be tilted about an axis perpendicular to a radial direction of the optical axis. 57. Axicon system according to claim 43, in which a polarization rotator for rotating the polarization of the penetrating light by approximately 90° is arranged between the first and the second axicon element. 58. Axicon system according to claim 57, in which the polarization rotator comprises an optical retardation system which effects a retardation of half a wavelength or an odd multiple of half a wavelength between two mutually perpendicular states of polarization. 59. Axicon system according to claim 58, in which the optical retardation system comprises two optical retardation elements which in each case effect a retardation of half a wavelength or an odd multiple thereof between two mutually perpendicular states of polarization, a first optical retardation element having a first fast axis, and the second optical retardation element having a second fast axis, and the first and the second fast axes enclosing an angle of 45°±5°. 60. Axicon system according to claim 57, in which the polarization rotator is arranged directly between an axicon surface of an upstream axicon element and an axicon surface of a downstream axicon element. 61. Axicon system according to claim 60, in which the polarization rotator has a double-axicon shape. 62. Axicon system according to claim 57, in which the polarization rotator is arranged directly between a substantially planar exit surface of an upstream axicon element and a substantially planar entrance surface of a downstream axicon element. 63. Axicon system according to claim 62, in which the polarization rotator has a plane-parallel shape. 64. Axicon system according to claim 43, in which at least one axicon element is mounted rotatably about the optical axis. 65. Axicon system according to claim 43, in which the at least one axicon element is designed as one of a diffractive and refractive and reflective element. 66. Illuminating system for an optical device, comprising at least one axicon system according to claim 43. 67. Illuminating system according to claim 66, wherein the optical device is a projection exposure apparatus for microlithography. 68. Illuminating system according to claim 67, which has at least one light mixer arranged downstream of the axicon system. 69. Microlithographic projection exposure apparatus comprising: a light source; an illuminating system in accordance with claim 66; and a projection objective. 70. Microlithographic projection exposure apparatus according to claim 69, in which the light source is designed for outputting linearly polarized light, and the projection objective is a catadioptric projection objective. 71. Microlithographic projection exposure apparatus according to claim 70, in which with the catadioptric projection objective has a polarization-selective physical beam splitter. 72. An illuminating system for a microlithography projection exposure apparatus comprising: an axicon module for producing an illumination distribution having a central intensity minimum, the axicon module comprising a first axicon element with a first axicon surface, and a second axicon element, assigned to the first axicon element, with a second axicon surface; and a first polarization-influencing optical element arranged in the light direction upstream of the first axicon element and designed in such a way that rays striking the axicon surfaces are polarized approximately perpendicular or approximately parallel to the respective incidence plane of the rays. 73. The illuminating system as claimed in claim 72, wherein the two axicon surfaces are conical in order to produce an annular illumination distribution. 74. The illuminating system as claimed in claim 73, wherein rays downstream of the first polarization-influencing optical element are polarized radially in relation to an optical axis (OA). 75. The illuminating system as claimed in claim 73, wherein rays downstream of the first polarization-influencing optical element are polarized tangential to an optical axis. 76. The illuminating system as claimed in claim 72, wherein the two axicon surfaces in each case comprise a number of pyramidally arranged segments for producing a multipole illumination. 77. The illuminating system as claimed in claim 76, wherein rays that strike a segment are linearly polarized parallel to a plane that is perpendicular to this segment and that contains the direction of the maximum surface gradient of this segment. 78. The illuminating system as claimed in claim 77, wherein rays that strike a segment are linearly polarized perpendicular to a plane that is perpendicular to this segment and that contains the direction of the maximum surface gradient of this segment. 79. The illuminating system as claimed in claim 72, wherein the first polarization-influencing optical element comprises a first raster arrangement of half-wave plates whose principal axes are oriented in such a way that rays striking the axicon surfaces are polarized approximately perpendicular or approximately parallel to the respective incidence plane of the rays. 80. The illuminating system as claimed in claim 79, wherein the first raster arrangement (615, 915) is joined in an optically seamless fashion, in particular wrung, to the first axicon element. 81. The illuminating system as claimed in claim 72, wherein the rays upstream of the first polarization-influencing optical element are linearly polarized parallel to a direction that is perpendicular to an optical axis. 82. The illuminating system as claimed in claim 72, wherein the rays upstream of the first polarization-influencing optical element are circularly polarized. 83. The illuminating system as claimed in claim 82, wherein the first polarization-influencing optical element comprises a quarter-wave plate that is arranged in the light direction upstream of the raster arrangement of half-wave plates. 84. The illuminating system as claimed in claim 72, wherein a second polarization-influencing element is arranged in the light direction downstream of the axicon module and is designed in such a way that the rays in the light direction downstream of the second polarization-influencing element exhibit a prescribed polarization distribution. 85. The illuminating system as claimed in claim 84, wherein the second polarization-influencing optical element comprises a second raster arrangement of half-wave plates whose principal axes are oriented in such a way that the prescribed polarization distribution is produced. 86. The illuminating system as claimed in claim 85, wherein the second raster arrangement is joined in a seamless fashion to the second axicon element. 87. The illuminating system as claimed in claim 84, wherein the rays are linearly polarized parallel to a direction perpendicular to an optical axis in the light direction downstream of the second polarization-influencing element. 88. The illuminating system as claimed in claim 84, wherein the rays are circularly polarized in the light direction downstream of the second polarization-influencing element. 89. The illuminating system as claimed in claim 88, wherein the second polarization-influencing optical element comprises a second raster arrangement of half-wave plates whose principal axes are oriented in such a way that the prescribed polarization distribution is produced and wherein the second polarization-influencing optical element comprises a quarter-wave plate that is arranged in the light direction downstream of the raster arrangement of half-wave plates. 90. The illuminating system as claimed in claim 84, wherein for each ray the polarization state in the light direction downstream of the second polarization-influencing element is approximately the same as in the light direction upstream of the first polarization-influencing element. 91. A microlithography projection exposure apparatus comprising an illuminating system as claimed in claim 72 for the purpose of illuminating a pattern-bearing mask, and an objective that images the pattern-bearing mask onto a photosensitive substrate. 92. A method for producing semiconductor components with the aid of a microlithography projection exposure apparatus as claimed in claim 91. 93. An axicon system for transforming an entrance light distribution striking an entrance surface of the axicon system into an exit light distribution emerging from an exit surface of the axicon system by radial redistribution of the light intensity, comprising: an optical axis; at least one axicon element with at least one axicon surface; and compensation means for spatially dependent compensation of transmission inhomogeneities of the axicon system caused by polarization-selective reflection at the axicon surface, the compensation means that act on the incident radiation having with reference to the optical axis an essentially two-fold radially symmetrical efficiency characteristic in the case of which a first efficiency in the region around a first direction (x) running perpendicular to the optical axis is significantly higher or lower than a second efficiency in the region of a second direction (y) running perpendicular to the first direction and to the optical axis. 94. The axicon system as claimed in claim 93, wherein the compensation means is arranged azimuthally in such a way relative to the axicon element that a light beam that passes through a region of relatively low transmission at the axicon element passes through a region of relatively high transmission in the region of the compensation means, and vice versa. 95. The axicon system as claimed in claim 93, wherein the compensation means that act on the incident radiation have a substantially elliptic efficiency characteristic with reference to the optical axis. 96. The axicon system as claimed in claim 93, wherein at least one optical surface of the axicon system is occupied by an optical compensation coating for the spatially dependent compensation of the transmission inhomogeneities caused by polarization-selective reflection at the axicon surface. 97. The axicon system as claimed in claim 96, wherein the compensation coating is designed such that with reference to transmission losses it essentially produces in a spatially resolving fashion an effect that is reciprocal to that of an uncoated axicon system. 98. The axicon system as claimed in claim 96, wherein at least one compensation coating is a multilayer interference layer system having alternating high-index and low-index dielectric individual layers with an azimuthally varying transmission efficiency. 99. The axicon system as claimed in claim 96, wherein at least one compensation coating is a gray filter layer with an azimuthally varying transmission efficiency. 100. The axicon system as claimed in claim 96, wherein the compensation coating has an azimuthal variation of its thickness that preferably exhibits azimuthally a complete two-fold sinusoidal course. 101. The axicon system as claimed in claim 96, wherein the compensation coating has an azimuthal variation in layer composition. 102. The axicon system as claimed in claim 96, wherein the axicon element has a further surface and only the axicon surface of an axicon element is occupied by a compensation coating. 103. The axicon system as claimed in claim 96, wherein the axicon element has a further surface and only the further surface is occupied by a compensation coating. 104. The axicon system as claimed in claim 96, wherein the axicon element has a further surface, and both the axicon surface and the further surface are occupied by a compensation coating, the spatial distributions of the efficiencies of the compensation coatings being coordinated with one another such that a compensation effect is produced. 105. The axicon system as claimed in claim 93, which comprises a first axicon element with a first axicon surface, and at least one second axicon element with a second axicon surface, wherein the axial distance between the axicon surfaces is variable. 106. The axicon system as claimed in claim 93, which is assigned at least one further optical component that exhibits a transmission non-uniformity with an elliptic transmission function, wherein that transmission function is spatially complementary to the axicon element or to the axicon system. 107. The axicon system as claimed in claim 106, wherein the further optical component is a rod integrator of rectangular cross section and different edge lengths. 108. An illuminating system for an optical device comprising at least one axicon system as claimed in claim 93. 109. The illuminating system as claimed in claim 108, wherein the optical device is a projection exposure apparatus for microlithography, 110. The illuminating system as claimed in claim 108 comprising a light source for outputting linearly polarized light with a preferred polarization direction and at least one rod integrator, arranged upstream or downstream of the axicon system, of rectangular cross section and different edge lengths, wherein the rod integrator is rotated with reference to the preferred polarization direction in such a way that the preferred polarization direction is aligned obliquely to the lateral surfaces of the rod integrator at an angle of approximately 45°. 111. A microlithography projection exposure apparatus comprising: a light source; an illuminating system as claimed in claim 108; and a projection objective. 112. The microlithography projection exposure apparatus as claimed in claim 111, wherein the light source is designed for outputting linearly polarized light, and the projection objective is a catadioptric projection objective. 113. The microlithography projection exposure apparatus as claimed in claim 112, wherein the catadioptric projection objective includes a polarization-selective physical beam splitter."
  ],
  "description_excerpt": "This application is a continuation-in-part application of international patent application PCT/EP2003/009613 filed on Aug. 29, 2003, and claiming priority from German patent application DE 103 22 375.4 filed on May 13, 2003; this application is also a continuation-in-part application of international patent application PCT/EP2004/004004 filed on Apr. 16, 2004, and claiming priority from German patent application DE 103 21 598.0 filed on May 13, 2003; and this application is also a continuation-in-part application of international patent application PCT/EP2004/004874 filed on May 7, 2004, and claiming priority from German patent application DE 103 22 376.2 filed on May 13, 2003. Priority is claimed from German patent application DE 103 22 375.4 filed on May 13, 2003, German patent application DE 103 21 598.0 filed on May 13, 2003 and German patent application DE 103 22 376.2 filed on May 13, 2003. The complete disclosures of the international and German patent applications are incorporated into this application by reference.\n\n1. Field of the Invention\n\nThe invention relates to an optical beam transformation system for transforming an entrance light distribution striking an entrance surface of the optical beam transformation system into an exit light distribution emerging from an exit surface of the optical beam transformation system by radial redistribution of light intensity, as well as to an illuminating system for an optical device which includes at least one such optical beam transformation system. The optical device including the illuminating system may be a projection exposure apparatus for microlithography.",
  "cpc": [
    "G03F 7/70183",
    "G02B 27/09",
    "G02B 27/0927",
    "G02B 27/0944",
    "G02B 27/095",
    "G02B 27/0977",
    "G02B 5/32",
    "G03F 7/70108",
    "G03F 7/70566"
  ],
  "ipc": [
    "G03H 1/08",
    "F21V 9/14",
    "G02B 27/28",
    "G02B 5/30",
    "G03B 27/72"
  ],
  "assignees": [
    "Carl Zeiss SMT GmbH"
  ],
  "inventors": [
    "Joerg Schultz",
    "Markus Deguenther",
    "Markus Brotsack",
    "Gerhard Fuerter",
    "Wolfgang Singer",
    "Manfred Maul",
    "Alexander Kohl",
    "Damian Fiolka"
  ],
  "filing_date": "2005-11-14",
  "publication_date": "2006-07-06",
  "priority_date": "2003-05-13",
  "application_number": "US-27197605-A",
  "family_id": "36640065",
  "cited_by_count": 128,
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}