Multilayer-film mirrors for use in extreme UV optical systems, and methods for manufacturing such mirrors exhibiting improved wave aberrations
First Claim
1. An apparatus for removing one or more surficial layers of a multilayer film on a multilayer-film mirror so as to correct a reflection wave-front produced by the multilayer-film mirror, the multilayer film comprising multiple alternating layers of at least a first layer-material and a second layer-material having mutually different refractive indices with respect to a prescribed wavelength, the apparatus comprising:
- a layer-removal device situated and configured to remove at least a respective portion of one or more surficial layers of the multilayer film; and
an analysis device situated and configured to analyze at least one of the removed layer-materials.
1 Assignment
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Accused Products
Abstract
Methods are disclosed for correcting the wave aberrations of light reflected from multilayer-film mirrors as used in, e.g., optical systems as used for EUV lithography (EUVL) apparatus. Wave aberrations are corrected by addition and/or removal of one or more layers (typically layer-sets) to and from, respectively, the surface of the multilayer film of the mirror. In certain embodiments, layer-removal is monitored in situ by any of several techniques. In other embodiments, mirror substrates are processed to a prescribed shape precision and surface roughness, followed by formation of the multilayer film and assembly of the mirrors into the intended optical assembly. The wave aberration is measured at operating wavelength. If the measured wave aberration is not within specifications, then the mirrors are corrected individually by selective removal and/or addition of layer-set(s). The corrected mirrors are reassembled and re-tested as an optical assembly. This cycle is repeated as required. In other embodiments, the mirrors are corrected by removing layer-sets in layer-set increments, followed by re-formation, at less than normal layer thickness, of the layer of the material having the most impact on defining the reflection wave-front, until the desired layer thickness is achieved. In yet other embodiments, layer(s) are removed such that the resulting corrected reflection wave-front is smooth.
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Citations
115 Claims
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1. An apparatus for removing one or more surficial layers of a multilayer film on a multilayer-film mirror so as to correct a reflection wave-front produced by the multilayer-film mirror, the multilayer film comprising multiple alternating layers of at least a first layer-material and a second layer-material having mutually different refractive indices with respect to a prescribed wavelength, the apparatus comprising:
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a layer-removal device situated and configured to remove at least a respective portion of one or more surficial layers of the multilayer film; and
an analysis device situated and configured to analyze at least one of the removed layer-materials. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for removing one or more surficial layers of a multilayer film on a multilayer-film mirror so as to correct a reflection wave-front produced by the multilayer-film mirror, the multilayer film comprising multiple alternating layers of at least a first layer-material and a second layer-material formed at a prescribed period length on a reflective surface of a mirror substrate, the first and second layer-materials having mutually different refractive indices with respect to a prescribed wavelength of incident light, the method comprising:
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removing at least a respective portion of one or more surficial layers of the multilayer film; and
analyzing at least one of the removed layer-materials. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 99, 100, 108)
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24. A method for producing a multilayer-film mirror for use with a prescribed wavelength of incident light, the method comprising:
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forming a reflection surface on a mirror substrate;
forming a multilayer film on the reflection surface by forming a stacked laminate of multiple alternating layers of at least a first layer-material and a second layer-material at a prescribed period length suitable for rendering the reflection surface reflective to the incident light, the first and second layer-materials having mutually different refractive indices with respect to the prescribed wavelength;
measuring a profile of a reflected wave-front produced by reflection of the incident light from the multilayer film;
based on the measured profile of the reflected wave-front, directing a layer-removal force locally to the multilayer film so as to remove, at one or more specified locations on the multilayer film, at least a portion of a surficial layer of the multilayer film so as to reduce an aberration of the reflected wave-front;
detecting the respective layer-material removed from the specified location; and
based upon the detected removal of layer-material, controlling an amount of layer-material removed from the specified location to achieve a desired reduction of wave aberration of the reflected light. - View Dependent Claims (25, 26, 27, 28, 29, 101, 109)
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30. A method for manufacturing a reflective optical system for use with a prescribed operating wavelength of light, the method comprising:
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(a) forming a respective reflection surface on each of multiple mirror substrates;
(b) on each reflection surface, forming a respective multilayer film by forming a stacked laminate of multiple alternating layers of at least a first layer-material and a second layer-material at a prescribed period length suitable for rendering the respective reflection surface reflective to the incident wavelength, the first and second layer-materials having mutually different refractive indices with respect to the prescribed wavelength, thereby forming respective multilayer-film mirrors;
(c) assembling the multilayer-film mirrors into a housing for the optical system;
(d) measuring a wave aberration of the assembled optical system at the operating wavelength;
(e) from the measured wave aberration, computing respective wave-front corrections to be made to the constituent multilayer-film mirrors in the optical system;
(f) as required according to the computed respective wave-front corrections, selectively removing one or more layers from the multilayer-film surface of the respective multilayer-film mirrors so as to correct a reflective-surface profile of the multilayer-film mirror in a manner corresponding to the required respective wave-front correction; and
(g) sequentially repeating steps (e), (f), (c), and (d) as required until the wave aberration of the optical system does not exceed a predetermined specification. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46)
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47. A multilayer-film mirror, comprising:
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a mirror substrate defining a reflection surface;
a multilayer film formed on the reflection surface, the multilayer film defining an effective region intended to be a region from which light of a desired wavelength is reflected from the multilayer-film mirror; and
a coordinate-reference mark situated outside the effective region. - View Dependent Claims (48, 49, 50, 51, 52, 102, 110)
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53. A method for manufacturing a multilayer-film mirror, comprising:
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forming a first multilayer film on a surface of a mirror substrate, the first multilayer film having a prescribed period length and being formed by laminating multiple layer-sets each comprising alternating respective layers of at least two types of substances having mutually different refractive indices for a wavelength of light with which the mirror is to be used;
obtaining a profile of a reflected wave-front produced by reflection of the light from a surface of the first multilayer film, and identifying from the profile a wave aberration requiring reduction; and
based on the obtained profile, laminating to selected regions of the surface of the first multilayer film at least one layer-set of a second multilayer film, so as to correct the wave aberration. - View Dependent Claims (54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 103, 111)
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65. A method for manufacturing a multilayer-film mirror, comprising:
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forming a first multilayer film on a surface of a mirror substrate, the first multilayer film having a prescribed period length and being formed by laminating multiple layer-sets each comprising alternating respective layers of at least two types of substances having mutually different refractive indices for a wavelength of light with which the mirror is to be used;
obtaining a profile of a reflected wave-front produced by reflection of the light from a surface of the first multilayer film, and identifying from the profile a wave aberration requiring reduction; and
based on the obtained profile, (i) removing at least one layer-set from selected locations of the surface of the first multilayer film and (ii) laminating to selected regions of the surface of the first multilayer film at least one layer-set of a second multilayer film, so as to correct the wave aberration. - View Dependent Claims (66, 67, 68, 69, 70, 71, 72, 104, 112)
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73. A multilayer-film mirror, comprising:
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a mirror substrate defining a reflection surface;
a first multilayer film formed on the reflective surface, the first multilayer film having a prescribed period length and being formed by laminating multiple layer-sets each comprising alternating respective layers of at least two types of substances having mutually different refractive indices for a wavelength of light with which the mirror is to be used, the first multilayer film having a surface defining at least one location at which a respective portion of at least a topmost layer-set has been removed to reduce a wave aberration of light reflected from the multilayer-film mirror; and
a second multilayer film laminated to at least one selected location on the surface of the first multilayer film, the second multilayer film having a period length substantially equal to the period length of the first multilayer film to correct the reflected wave-front produced by the multilayer-film mirror. - View Dependent Claims (74, 75, 76, 77, 105, 113)
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78. A method for manufacturing a multilayer-film mirror, comprising:
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forming a multilayer film on a surface of a mirror substrate, the multilayer film having a prescribed period length and being formed by laminating multiple layer-sets each comprising respective alternating layers of at least a first substance and a second substance, the first substance exhibiting a relatively large difference in respective refractive index to EUV light relative to the refractive index of a vacuum, and the second substance exhibiting a relatively small difference in relative refractive index to EUV light relative to the refractive index of a vacuum;
obtaining a profile of a reflected wave-front produced by reflection of the light from a surface of the multilayer film, and identifying from the profile a wave aberration requiring reduction; and
based on the obtained profile, (i) removing at least one layer-set from at least one selected location on the surface of the multilayer film, so as to leave exposed at the selected location a next layer of the second material, and (ii) laminating to the exposed layer of the second material at the selected location an amount of the first material to a prescribed thickness that is less than a layer thickness of the first material in the multilayer film, so as to reduce the wave aberration. - View Dependent Claims (79, 80)
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81. A multilayer-film mirror, comprising:
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a mirror substrate defining a reflection surface;
a multilayer film formed on the reflection surface, the multilayer film having a prescribed period length and comprising multiple laminated layer-sets each comprising respective alternating layers of at least a first substance and a second substance, the first substance exhibiting a relatively large difference in respective refractive index to EUV light relative to the refractive index of a vacuum, and the second substance exhibiting a relatively small difference in relative refractive index to EUV light relative to the refractive index of a vacuum; and
the multilayer film having a surface including a processed region serving to reduce a wave aberration of the multilayer-film mirror by correcting a wave-front reflected from the multilayer film, the processed region including a void formed by selective removal of at least one surficial layer-set of the multilayer film in the region, and a partial-thickness layer of the first material formed on a surface of the second material, the partial-thickness layer having a thickness that is less than a layer thickness of the first material in the multilayer film. - View Dependent Claims (82, 83, 84, 85, 86)
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87. A method for manufacturing a multilayer-film mirror, comprising:
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forming a multilayer film on a surface of a mirror substrate, the multilayer film having a prescribed period length and being formed by laminating multiple layer-sets each comprising respective alternating layers of at least a first substance and a second substance, the first substance exhibiting a relatively large difference in respective refractive index to EUV light relative to the refractive index of a vacuum, and the second substance exhibiting a relatively small difference in relative refractive index to EUV light relative to the refractive index of a vacuum;
obtaining a profile of a reflected wave-front produced by reflection of the light from a surface of the multilayer film, and identifying from the profile a wave aberration requiring reduction; and
based on the obtained profile, at corresponding locations on a surface of the multilayer film, selectively removing at least one layer-set of the multilayer film in a manner yielding a smoothly connected corrected reflection wave-front. - View Dependent Claims (88, 89, 90, 91, 92, 106, 114)
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93. A multilayer-film mirror, comprising:
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a mirror substrate defining a reflection surface; and
a multilayer film formed on the reflective surface, the multilayer film having a prescribed period length and being formed by laminating multiple layer-sets each comprising respective alternating layers of at least two types of substances having mutually different refractive indices for a wavelength of light with which the mirror is to be used, the multilayer film having a surface defining at least one location at which a respective portion of at least a topmost layer-set has been removed to reduce a wave aberration of light reflected from the multilayer-film mirror, the at least top-most layer-set being removed to yield corresponding layer edges in the location that are configured to produce a smoothly connected corrected reflection wave-front. - View Dependent Claims (94, 95, 96, 97, 98, 107, 115)
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Specification