Patent US6249351B1 successfully refreshed from Google Patents.
US6249351B1
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US
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Grazing incidence interferometer and method
Assignee: Zygo Corp
•
Filing: 1999-06-03
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Granted: 2001-06-19
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Expires: 2019-06-03
Abstract
Abstract A two-beam interferometer illuminates a sample surface with light at grazing incidence angles for the purpose of analyzing a surface characteristic such as surface topography. The interferometer includes a diffractive-optic beam splitter, which separates an incoming light beam into measurement and reference beams and a diffractive-optic beam combiner, which produces an output beam by interfering portions of the reference beam with reflected portions of the measurement beam. Those portions of the reference wavefront and the measurement wavefront that interfere originate from substantially the same portion of the initial illumination wavefront.
Inventors
- 👤 Peter de Groot
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 19:42
CPC Classifications
G; G01; G01B; G01B11/00; G01B11/30; G01B9/00; G01B9/02; G01B9/02001; G01B9/02002; G01B9/02004; G01B9/02015; G01B9/02017; G01B9/02021; G01B9/02022; G01B9/02034; G01B9/02038; G01B9/02039; G01B9/0209; G01B2290/00; G01B2290/30
Claims Analysis
Total Claims: 92
Claim 1
Independent Claim
109 words
A two-beam grazing incidence interferometer for analyzing a surface of a sample, comprising: a diffractive-optic beam splitter to use amplitude division to separate at least a portion of an initial wavefront generated by a light source into a reference wavefront and a measurement wavefront; a diffractive-optic beam combiner located to generate an output wavefront by interfering portions of the reference wavefront with portions of the measurement wavefront, the portions of the measurement wavefront having undergone a reflection from the sample surface only once and at a grazing angle, the interfering portions of the reference and the measurement wavefronts originating from substantially the same portions of the initial illumination wavefront.
Claim 2
Dependent Claim
109 words
A two-beam grazing incidence interferometer for analyzing a surface of a sample, comprising: a diffractive-optic beam splitter to use amplitude division to separate at least a portion of an initial wavefront generated by a light source into a reference wavefront and a measurement wavefront; a diffractive-optic beam combiner located to generate an output wavefront by interfering portions of the reference wavefront with portions of the measurement wavefront, the portions of the measurement wavefront having undergone a reflection from the sample surface only once and at a grazing angle, the interfering portions of the reference and the measurement wavefronts originating from substantially the same portions of the initial illumination wavefront.
Claim 3
Dependent Claim
20 words
The interferometer of claim 1 , further comprising: an illumination system including the light source to generate the initial wavefront.
Claim 4
Dependent Claim
29 words
The interferometer of claim 2 , further comprising: an image forming system to form from the output wavefront an image of the sample surface, said image displaying interference fringes.
Claim 5
Dependent Claim
23 words
The interferometer of claim 3 , wherein at least one of the diffractive-optic beam splitter and diffractive-optic beam combiner is a transmission device.
Claim 6
Dependent Claim
24 words
The interferometer of claim 3 , wherein at least one of the diffractive-optic beam splitter and the diffractive-optic beam combiner is a reflection device.
Claim 7
Dependent Claim
23 words
The interferometer of claim 3 , wherein at least one of the diffractive-optic beam splitter and diffractive-optic beam combiner is an acousto-optic modulator.
Claim 8
Dependent Claim
35 words
The interferometer of claim 3 , wherein at least one of the diffractive-optic beam splitter and diffractive-optic beam combiner is constructed to suppress diffraction orders not producing either the reference wavefront or the measurement wavefront.
Claim 9
Dependent Claim
31 words
The interferometer of claim 3 , wherein the reference wavefront and the measurement wavefront are the first-order diffracted wavefronts emanating from the diffractive-optic beam splitter when illuminated by the initial wavefront.
Claim 10
Dependent Claim
41 words
The interferometer of claim 3 , wherein the combiner is located to recombine the measurement wavefront and the reference wavefront after each beam undergoes at least one wavefront inversion and with the number of inversions of each beam equal modulo two.
Claim 11
Dependent Claim
49 words
The interferometer of claim 3 , wherein the diffractive-optic beam splitter and combiner are located to produce fringes having separations defined by an equivalent wavelength equal to the wavelength of the source divided by the cosine of an angle of incidence of the measurement wavefront on the sample surface.
Claim 12
Dependent Claim
41 words
The interferometer of claim 10 , wherein the beam splitter and recombiner are adapted recombine the measurement and reference beams in response to the reference beam being reflected off the sample at an angle at least as large as 75 degrees.
Claim 13
Dependent Claim
24 words
The interferometer of claim 10 , wherein the splitter is configured to produce an equivalent wavelength independent of the wavelength of the light source.
Claim 14
Dependent Claim
21 words
The interferometer of claim 12 , wherein the diffractive-optic beam splitter and the diffractive-optic beam combiner are substantially identical linear gratings.
Claim 15
Dependent Claim
34 words
The interferometer of claim 1 , wherein the diffractive-optic beam splitter and the diffractive-optic beam combiner have areas smaller than one half the area of sample surfaces that the interferometer is adapted to analyze.
Claim 16
Dependent Claim
18 words
The interferometer of claim 1 , further comprising: a reference mirror for redirecting and inverting the reference wavefront.
Claim 17
Dependent Claim
32 words
The interferometer of claim 3 , further comprising: a reference mirror for redirecting and inverting the reference wavefront; and a fold mirror for redirecting both the measurement wavefront and the reference wavefront.
Claim 18
Dependent Claim
22 words
The interferometer of claim 16 , wherein the diffractive-optic beam splitter and the diffractive-optic beam combiner belong to a single diffractive-optic element.
Claim 19
Dependent Claim
19 words
The interferometer of claim 1 , wherein the diffractive-optic beam splitter and the diffractive-optic beam combiner are cylindrical gratings.
Claim 20
Dependent Claim
19 words
The interferometer of claim 18 , further comprising: a cylindrical reference mirror for redirecting and inverting the reference wavefront.
Claim 21
Dependent Claim
19 words
The interferometer of claim 19 , wherein the diffractive-optic beam splitter and the diffractive-optic beam combiner are axicon gratings.
Claim 22
Dependent Claim
21 words
The interferometer of claim 3 , wherein the image forming system further comprises a viewing screen located to display the image.
Claim 23
Dependent Claim
28 words
The interferometer of claim 21 , wherein the viewing screen is oriented at an oblique angle with respect to an axis defined by the beam splitter and recombiner.
Claim 24
Dependent Claim
16 words
The interferometer of claim 22 , further comprising: an electronic camera directed towards the viewing screen.
Claim 25
Dependent Claim
16 words
The interferometer of claim 1 , further comprising: an electronic camera located to view the image.
Claim 26
Dependent Claim
85 words
The interferometer of claim 3 , further comprising: first and second reference mirrors for redirecting first and second portions of the reference wavefront; and wherein the beam splitter is adapted to direct the first and second portions of the reference wavefront in diverging directions and to direct first and second portions of the measurement wavefront in divergent directions; and wherein the beam combiner interferes the first and second portions of the reference wavefront with the respective first and second reflected portions of the measurement wavefront.
Claim 27
Dependent Claim
26 words
The interferometer of claim 15 , further comprising: an actuator to change the difference between optical path lengths traversed by the reference and the measurement wavefronts.
Claim 28
Dependent Claim
13 words
The interferometer of claim 26 , wherein the actuator comprises a piezo-electric crystal.
Claim 29
Dependent Claim
23 words
The interferometer of claim 27 , wherein the actuator is located to displace the sample in a direction substantially perpendicular the sample surface.
Claim 30
Dependent Claim
19 words
The interferometer of claim 27 , wherein the actuator is located to displace an optical element of the interferometer.
Claim 31
Dependent Claim
37 words
The interferometer of claim 27 , further comprising: an electronic camera for converting the interference fringes into electronic signals; and a computer to perform phase shifting interferometry on the sample surface with the actuator and electronic camera.
Claim 32
Dependent Claim
11 words
The interferometer of claim 3 , wherein the source is monochromatic.
Claim 33
Dependent Claim
50 words
The interferometer of claim 31 , wherein the source is a wavelength tunable source; and a reference mirror for redirecting and inverting the reference wavefront and for producing path length differences of more than a few wavelengths between interfering portions of the reference and the measurement wavefronts at the combiner.
Claim 34
Dependent Claim
41 words
The interferometer of claim 32 , wherein the image forming system further comprises: an electronic camera for converting the interference fringes into electronic signals; and a computer control for performing phase shifting interferometry using the tunable source and the electronic camera.
Claim 35
Dependent Claim
14 words
The interferometer of claim 3 , wherein the source is a spectrally broadband source.
Claim 36
Dependent Claim
58 words
The interferometer of claim 3 , wherein the source is an extended source that produces divergent rays in the illumination beam; and a reference mirror for redirecting and inverting the reference wavefront and for producing path length differences of not more than a few wavelengths between interfering portions of the reference and the measurement wavefronts at the combiner.
Claim 37
Dependent Claim
39 words
The interferometer of claim 35 , further comprising: an actuator for changing an optical path length traversed by one of the reference wavefront and the measurement wavefront; and an electronic camera for converting the interference fringes into electronic signals.
Claim 38
Dependent Claim
13 words
The interferometer of claim 36 , wherein the actuator comprises a piezo-electric crystal.
Claim 39
Dependent Claim
13 words
The interferometer of claim 36 , wherein the actuator includes a motor-driven stage.
Claim 40
Dependent Claim
21 words
The interferometer of claim 36 , wherein the actuator is oriented to displace the sample substantially perpendicular to the sample surface.
Claim 41
Dependent Claim
19 words
The interferometer of claim 36 , wherein the actuator is located to displace an optical element of the interferometer.
Claim 42
Dependent Claim
31 words
The interferometer of claim 36 , further comprising: a computer control configured to perform fringe contrast-scanning interferometry using the actuator and the electronic camera to measure topography of the sample surface.
Claim 43
Dependent Claim
96 words
A two-beam grazing incidence interferometer for analyzing a surface of a sample, comprising: a birefringent beam splitter for separating an initial wavefront produced by a light source into reference and measurement wavefronts; and a birefringent beam combiner, located to generate an output wavefront by interfering corresponding portions of the reference and the measurement wavefronts, the portions of the measurement wavefront being reflected off the sample surface only once and at a grazing angle, each pair of corresponding portions of the reference and the measurement wavefronts originating from substantially the same portion of the initial illumination wavefront.
Claim 44
Dependent Claim
96 words
A two-beam grazing incidence interferometer for analyzing a surface of a sample, comprising: a birefringent beam splitter for separating an initial wavefront produced by a light source into reference and measurement wavefronts; and a birefringent beam combiner, located to generate an output wavefront by interfering corresponding portions of the reference and the measurement wavefronts, the portions of the measurement wavefront being reflected off the sample surface only once and at a grazing angle, each pair of corresponding portions of the reference and the measurement wavefronts originating from substantially the same portion of the initial illumination wavefront.
Claim 45
Dependent Claim
20 words
The interferometer of claim 42 , further comprising: an illumination system comprising the light source to generate the initial wavefront.
Claim 46
Dependent Claim
29 words
The interferometer of claim 43 , further comprising: an optical imaging system to form an image of the sample surface from the output wavefront, said image displaying interference fringes.
Claim 47
Dependent Claim
22 words
The interferometer of claim 44 , wherein one of the birefringent beam splitter and the birefringent beam combiner comprises a Wollaston prism.
Claim 48
Dependent Claim
23 words
The interferometer of claim 44 , wherein the birefringent beam combiner further comprises a polarization analyzer to mix the reference and measurement wavefronts.
Claim 49
Dependent Claim
23 words
The interferometer of claim 44 , wherein the splitter is adapted to produce the reference wavefront and the measurement wavefront with orthogonal polarizations.
Claim 50
Dependent Claim
31 words
The interferometer of claim 44 , wherein the recombiner is located to recombine light from the measurement wavefront reflected by the sample surface at an angle of at least 75 degrees.
Claim 51
Dependent Claim
24 words
The interferometer of claim 42 , wherein the splitter and the combiner are located to be substantially smaller in area than the sample surface.
Claim 52
Dependent Claim
18 words
The interferometer of claim 42 , further comprising: a reference mirror for redirecting and inverting the reference wavefront.
Claim 53
Dependent Claim
32 words
The interferometer of claim 44 , further comprising: a reference mirror for redirecting and inverting the reference wavefront; and a fold mirror for redirecting both the measurement wavefront and the reference wavefront.
Claim 54
Dependent Claim
26 words
The interferometer of claim 51 , wherein both the birefringent optic beam splitter and the birefringent optical beam combiner are portions of a single optical element.
Claim 55
Dependent Claim
21 words
The interferometer of claim 44 , wherein the optical imaging system further comprises a viewing screen positioned to produce the image.
Claim 56
Dependent Claim
25 words
The interferometer of claim 53 , wherein the viewing screen is oriented at an oblique angle to an axis from the splitter to the combiner.
Claim 57
Dependent Claim
21 words
The interferometer of claim 53 , wherein the optical imaging system further comprises an electronic camera directed at the viewing screen.
Claim 58
Dependent Claim
20 words
The interferometer of claim 44 , wherein the optical imaging system further comprises an electronic camera for viewing the image.
Claim 59
Dependent Claim
80 words
The interferometer of claim 44 , further comprising: first and second reference mirrors for redirecting first and second portions of the reference wavefront, the first and second portions being directed in diverging directions; and wherein the beam splitter is adapted to direct the first and second portions of the reference wavefront in different directions; and wherein the beam combiner interferes the first and second portions of the reference wavefront with respective first and second reflected portions of the measurement wavefront.
Claim 60
Dependent Claim
22 words
The interferometer of claim 57 , wherein the first and second reflected portions are reflected off opposite sides of a planar sample.
Claim 61
Dependent Claim
28 words
The interferometer of claim 44 , further comprising: an actuator located to change the optical path length traversed by one of the reference wavefront and the measurement wavefront.
Claim 62
Dependent Claim
13 words
The interferometer of claim 59 , wherein the actuator includes a piezo-electric crystal.
Claim 63
Dependent Claim
23 words
The interferometer of claim 59 , wherein the actuator is oriented to displace the sample in a direction substantially perpendicular the sample surface.
Claim 64
Dependent Claim
19 words
The interferometer of claim 59 , wherein the actuator is located to displace an optical element of the interferometer.
Claim 65
Dependent Claim
41 words
The interferometer of claim 59 , further comprising: an electronic camera located to view the interference fringes and configured to produce electronic signals therefrom; and a computer control configured to perform phase shifting interferometry using the actuator and the electronic camera.
Claim 66
Dependent Claim
34 words
The interferometer of claim 50 , wherein the reference mirror and combiner are configured to recombine the measurement and reference surfaces after traveling over optical paths differing by more than about two equivalent wavelengths.
Claim 67
Dependent Claim
11 words
The interferometer of claim 64 , wherein the source is monochromatic.
Claim 68
Dependent Claim
19 words
The interferometer of claim 64 , wherein the source is a tunable to change the wavelength of emitted light.
Claim 69
Dependent Claim
41 words
The interferometer of claim 66 , further comprising: an electronic camera for converting the interference fringes into electronic signals; and a computer control to perform phase shifting interferometry using the tunable source and the electronic camera to measure the sample surface.
Claim 70
Dependent Claim
35 words
The interferometer of claim 50 , wherein the reference mirror and combiner are configured to recombine portions of the measurement and reference surfaces traveling over optical paths differing by less than about three equivalent wavelengths.
Claim 71
Dependent Claim
13 words
The interferometer of claim 68 , wherein the source is a broadband source.
Claim 72
Dependent Claim
13 words
The interferometer of claim 68 , wherein the source is an extended source.
Claim 73
Dependent Claim
23 words
The interferometer of claim 43 , wherein the source is configured to produce the illumination beam being one of spectrally broadband and non-collimated.
Claim 74
Dependent Claim
13 words
The interferometer of claim 71 , wherein the source is an extended source.
Claim 75
Dependent Claim
40 words
The interferometer of claim 71 , further comprising: an actuator to change the optical path length traversed by one of the reference wavefront and the measurement wavefront; and an electronic camera directed to convert the interference fringes into electronic signals.
Claim 76
Dependent Claim
13 words
The interferometer of claim 73 , wherein the actuator comprises a piezo-electric crystal.
Claim 77
Dependent Claim
13 words
The interferometer of claim 73 , wherein the actuator comprises a motor-driven stage.
Claim 78
Dependent Claim
24 words
The interferometer of claim 73 , wherein the actuator is located to displace the sample in a direction substantially perpendicular to the sample surface.
Claim 79
Dependent Claim
19 words
The interferometer of claim 73 , wherein the actuator is located to displace an optical element of the interferometer.
Claim 80
Dependent Claim
29 words
The interferometer of claim 73 , further comprising: a computer control to perform fringe contrast scanning interferometry using the actuator and the electronic camera to measure the sample surface.
Claim 81
Independent Claim
79 words
A method for performing interferometry with light reflected off a sample at a grazing angle, said method comprising: splitting an incoming wavefront into first and second beams; reflecting portions of the second beam off of the sample surface at a grazing angle; and intefering portions of the first beam with the portions of the second beam by combining the portions of the first and second beams which have the relative wavefront relation of the two beams leaving the splitter.
Claim 82
Independent Claim
79 words
A method for performing interferometry with light reflected off a sample at a grazing angle, said method comprising: splitting an incoming wavefront into first and second beams; reflecting portions of the second beam off of the sample surface at a grazing angle; and intefering portions of the first beam with the portions of the second beam by combining the portions of the first and second beams which have the relative wavefront relation of the two beams leaving the splitter.
Claim 83
Dependent Claim
24 words
The method of claim 79 , wherein the splitting includes diffractively splitting the wavefront of the incoming beam into the first and second beams.
Claim 84
Dependent Claim
29 words
The method of claim 79 , wherein the interfering recombines portions of the wavefronts of the first and second beams originating in the same portion of the incoming beam.
Claim 85
Dependent Claim
27 words
The method of claim 79 , wherein the reflected beam is directed at more than 75 degrees from the direction of the normal to the sample surface.
Claim 86
Dependent Claim
34 words
The method of claim 79 , wherein the act of interfering includes interfering portions of the two beams that have traveled over path lengths that differ by less than several wavelengths of light therein.
Claim 87
Dependent Claim
17 words
The method of claim 79 , further comprising: forming white-light fringes with light from the interfering beams.
Claim 88
Dependent Claim
51 words
The method of claim 84 , further comprising: moving the sample to a new location; and repeating the acts of splitting, reflecting, interfering and forming on the sample surface at the new location, the new location enabling new features on the sample surface to reflect light that generates new white-light fringes.
Claim 89
Dependent Claim
97 words
An interferometer to analyze light reflected from a sample surface at a grazing angle, said interferometer comprising: an optical element to form first and second beams by respectively reflecting and transmitting portions of an incoming beam; at least one reflector to redirect a portion of the second beam back towards the optical element which combines the first beam and the reflected back portion of the second beam without a relative wavefront inversion, the portion of the second beam having reflected off the sample surface only once before being combined with the first beam at the optical element.
Claim 90
Dependent Claim
97 words
An interferometer to analyze light reflected from a sample surface at a grazing angle, said interferometer comprising: an optical element to form first and second beams by respectively reflecting and transmitting portions of an incoming beam; at least one reflector to redirect a portion of the second beam back towards the optical element which combines the first beam and the reflected back portion of the second beam without a relative wavefront inversion, the portion of the second beam having reflected off the sample surface only once before being combined with the first beam at the optical element.
Claim 91
Dependent Claim
15 words
The interferometer of claim 86 , wherein the optical element is a partially silvered mirror.
Claim 92
Dependent Claim
22 words
The interferometer of claim 86 , wherein the grazing angle is at least 75 degrees from a normal to the sample surface.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2004-06-18 | 2004-12-18 | 2005-06-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2008-06-18 | 2008-12-18 | 2009-06-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2012-06-18 | 2012-12-18 | 2013-06-19 | $7700.00 | Window Closed / Lapsed |