Source: http://www.google.com/patents/US20050111007?dq=5708422
Timestamp: 2017-09-23 02:41:36
Document Index: 693696602

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60']

Patent US20050111007 - Catoptric and catadioptric imaging system with pellicle and aperture-array ... - Google Patents
An interferometric system including: an interferometer that directs a measurement beam at an object point to produce a return measurement beam, focuses the return measurement beam to an image point in an image plane, and mixes the return measurement beam with a reference beam at the image point to form...http://www.google.com/patents/US20050111007?utm_source=gb-gplus-sharePatent US20050111007 - Catoptric and catadioptric imaging system with pellicle and aperture-array beam-splitters and non-adaptive and adaptive catoptric surfaces
Publication number US20050111007 A1
Application number US 10/948,959
Also published as US7095508, US7180604, US20060072204, US20060092429, WO2005031397A2, WO2005031397A3
Publication number 10948959, 948959, US 2005/0111007 A1, US 2005/111007 A1, US 20050111007 A1, US 20050111007A1, US 2005111007 A1, US 2005111007A1, US-A1-20050111007, US-A1-2005111007, US2005/0111007A1, US2005/111007A1, US20050111007 A1, US20050111007A1, US2005111007 A1, US2005111007A1
Inventors Henry Hill, Steven Hamann, David Fischer
Patent Citations (50), Referenced by (24), Classifications (31), Legal Events (1)
Catoptric and catadioptric imaging system with pellicle and aperture-array beam-splitters and non-adaptive and adaptive catoptric surfaces
US 20050111007 A1
14. The interferometric system of claim 1, wherein the beam splitter has an array of transmitting apertures formed therein and wherein said one set of rays travels along a path contacting on one end the beam splitter and on another end the concave reflecting surface and at least most of which passes through a gas or vacuum.
15. The interferometric system of claim 13, wherein the interferometer comprises an array of independently positionable reflecting elements forming the reflecting surface.
16. The interferometric system of claim 15, wherein the reflecting surface is positioned to receive the first set of rays and reflect the first set of rays back to the beam splitter, and wherein the beam splitter is positioned to reflect at least a portion of each ray received from the reflecting surface to the image point.
17. An imaging system for imaging an object point to an image point, the system comprising:
wherein the beam splitter has an array of transmitting apertures formed therein and wherein said one set of rays travels along a path contacting on one end the beam splitter and on another end the concave reflecting surface and at least most of which passes through a gas or vacuum.
18. The imaging system of claim 17, wherein the beam splitter is a self-supporting structure.
19. The imaging system of claim 17, wherein the beam splitter comprises a thin reflective layer in which the array of transmitting apertures are formed.
20. The imaging system of claim 19, wherein the thin reflective layer is highly reflective.
21. The imaging system of claim 19, wherein the thin reflective layer comprises aluminum.
22. The imaging system of claim 17, wherein the beam splitter comprises a pellicle on which the thin reflective layer is formed.
23. The imaging system of claim 17, wherein the beam splitter comprises a first pellicle and a second pellicle with the thin reflective layer sandwiched between the first and second pellicles.
24. The imaging system of claim 22, wherein the pellicle comprises a refractive material.
25. The imaging system of claim 24, wherein the refractive material is from the group consisting of UV grade fused silica, F—SiO2, CaF2, and LiF.
26. The imaging system of claim 17, wherein the beam splitter is a vertically oriented, planar structure.
27. The imaging system of claim 17, wherein the size of the apertures is larger than the wavelength of the light rays being imaged onto the image point.
28. The imaging system of claim 17, wherein the beam splitter comprises a grid of conducting wires which defines the array of transmitting apertures.
29. The imaging system of claim 17, wherein the reflecting surface is positioned to receive the first set of rays and reflect the first set of rays back to the beam splitter, and wherein the beam splitter is positioned to reflect at least a portion of each ray received from the reflecting surface to the image point.
30. The imaging system of claim 29, wherein the reflecting surface is substantially concentric with the object point.
31. The imaging system of claim 17, wherein the reflecting surface is positioned to receive the second set of rays and reflect the second set of rays back to the beam splitter, wherein the beam splitter is positioned to transmit at least a portion of each ray received from the reflecting surface to the image point.
32. The imaging system of claim 20, wherein the reflecting surface is substantially concentric with the image point.
33. The imaging system of claim 17, wherein the optical structure comprises an array of independently positionable reflecting elements forming said reflecting surface.
34. An imaging system for imaging an object point to an image point, the system comprising:
35. The imaging system of claim 34, wherein the array of independently positionable reflecting elements form corresponding portions of the Fresnel reflecting surface and wherein the corresponding portions of the reflecting surface have a common center of curvature and different radii of curvature.
36. The imaging system of claim 34 further comprising a plurality of position control elements, each of which is connected to a corresponding one of the reflecting elements in the array.
37. The imaging system of claim 36, wherein each of the position control elements of the plurality of position control elements comprises a transducer.
38. The imaging system of claim 37, wherein each transducer of the plurality of transducers controls a radial position of its corresponding reflecting element.
39. The imaging system of claim 37, wherein each transducer of the plurality of transducers controls an orientation of the corresponding reflecting element relative to an optical axis for that reflecting element.
40. The imaging system of claim 37 further comprising a servo control system which controls the plurality of transducers.
41. The imaging system of claim 34, wherein the reflecting surface is positioned to receive the first set of rays and reflect the first set of rays back to the beam splitter, and wherein the beam splitter is positioned to reflect at least a portion of each ray received from the reflecting surface to the image point.
42. The imaging system of claim 34, wherein the reflecting surface is positioned to receive the second set of rays and reflect the second set of rays back to the beam splitter, wherein the beam splitter is positioned to transmit at least a portion of each ray received from the reflecting surface to the image point.
43. An interferometric system comprising:
a detector system that generates an electrical interference signal from the mixed beam,
wherein the interferometer comprises a source for generating an input beam and an apodizing filter through which the input beams passes to generate a conditioned beam, and wherein the measurement beam is derived from the conditioned beam.
44. The interferometric system of claim 43, wherein the interferometer further comprises a focusing optic for focusing the measurement beam as a spot on the object.
45. The interferometric system of claim 43, wherein the apodizing filter comprises an aperture that is apodized.
46. The interferometric system of claim 43, wherein the apodizing filter comprises an aperture and a coating that has a transmission coefficient that depends on the position within the aperture.
47. An imaging system for imaging an object point to an image point, the system comprising:
48. An imaging system for imaging an object point to an image point, the system comprising:
49. The imaging system of claim 48, wherein each aperture in the array of transmitting apertures has a dimension in an azimuthal direction relative the central axis that is an increasing function of that apertures distance from the central axis.
A number of different applications of catadioptric imaging systems for far-field and near-field interferometric confocal and non-confocal microscopy have been described such as in commonly owned U.S. Pat. No. 6,552,852 (ZI-38) entitled “Catoptric And Catadioptric Imaging Systems” and No. 6,717,736 (ZI-43) entitled “Catoptric And Catadioptric Imaging Systems;” U.S. Provisional Patent Applications No. 60/447,254, filed Feb. 13, 2003, entitled “Transverse Differential Interferometric Confocal Microscopy,” (ZI-40); No. 60/448,360, filed Feb. 19, 2003, entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling,” (ZI-41); No. 60/448,250, filed Feb. 19, 2003, entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy,” (ZI-42); No. 60/442,982, filed Jan. 28, 2003, entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” (ZI-45); No. 60/459,425, filed Apr. 1, 2003, entitled “Apparatus and Method for Joint Measurement Of Fields Of Scattered/Reflected Orthogonally Polarized Beams By An Object In Interferometry,” (ZI-50); No. 60/485,507, filed Jul. 7, 2003, entitled “Apparatus And Method For High Speed Scan For Sub-Wavelength Defects And Artifacts In Semiconductor Metrology,” (ZI-52); No. 60/485,255, filed Jul. 7, 2003, entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution,” (ZI-53); No. 60/501,666, filed Sep. 10, 2003, entitled “Catoptric And Catadioptric Imaging Systems With Adaptive Catoptric Surfaces,” (ZI-54); No. 60/602,046, filed Aug. 16, 2004, entitled “Apparatus And Method For Joint And Time Delayed Measurements Of Components Of Conjugated Quadratures Of Fields Of Reflected/Scattered Beams By An Object In Interferometry,” (ZI-57); and U.S. Patent Applications No. 10/778,371, filed Feb. 13, 2004, entitled “Transverse Differential Interferometric Confocal Microscopy,” (ZI-40); No. 10/782,057, filed Feb. 19, 2004, entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling,” (ZI-41); No. 10/782,058, filed Feb. 19, 2004, entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy,” (ZI-42); No. 10/765,229, filed Jan. 27, 2004, entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” (ZI-45); No. 10/816,180, filed Apr. 1, 2004, entitled “Apparatus and Method for Joint Measurement Of Fields Of Scattered/Reflected or Transmitted Orthogonally Polarized Beams By An Object In Interferometry,” (ZI-50); No. 10/886,010, filed Jul. 7, 2004, entitled “Apparatus And Method For High Speed Scan For Sub-Wavelength Defects And Artifacts In Semiconductor Metrology,” (ZI-52); No. 10/886,157, filed Jul. 7, 2004, entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution,” (ZI-53); and No. t.b.d., filed Sep. 10, 2004, entitled “Catoptric And Catadioptric Imaging Systems With Adaptive Catoptric Surfaces,” (ZI-54). In addition, U.S. Patent Application (ZI-48) 10/218,201, entitled “Method for Constructing a Catadioptric Lens System,” filed Apr. 1, 2004 described one way to make some of these catadioptric lens systems. These patents, patent applications, and provisional patent applications are all by Henry A. Hill and the contents of each are incorporated herein in their entirety by reference.
A general description of embodiments incorporating the present invention will first be given for interferometer systems wherein either a N-dimensional bi- or quad-homodyne detection method is used where N is an integer. Referring to FIG. 1 a, an interferometer system is shown diagrammatically comprising an interferometer 10, a source 18, a beam-conditioner 22, a detector 70, an electronic processor and controller 80, and a measurement object shown as substrate 60. Source 18 generates input beam 20. The interferometer system shown in FIG. 1 a is for the case of an imaging system operating in a reflecting mode to measure properties of fields reflected/scattered by substrate 60. For the case of operation in a transmission mode, a portion of beam 24 split off as a measurement beam is incident on substrate 60 from the backside of substrate 60 such as shown diagrammatically in FIG. 3 a. Source 18 is preferably a pulsed source that generates beam 20 with a single frequency component. Beam 20 is incident on and exits beam-conditioner 22 as input beam 24 that has the one or more frequency components. Alternatively, source 18 generates beam 20 with two frequency components that may have different polarization states wherein input beam 24 has one or more frequency components for each of the different polarization states. The different frequency components of the measurement beam components of input beam 24 are coextensive in space, the different frequency components of the reference beam components of input beam 24 are coextensive in space, and the different frequency components of both the reference and measurement beam components have the same temporal window function. Further description of source 18 and beam-conditioner 22 is the same as the corresponding description in commonly owned U.S. Provisional Patent Application filed Aug. 16, 2004 (ZI-57) entitled “Apparatus and Method for Joint And Time Delayed Measurements of Components of Conjugated Quadratures of Fields of Reflected/Scattered and Transmitted/Scattered Beams by an Object in Interferometry” by Henry A. Hill of which the contents are herein incorporated in their entirety by reference.
The first imaging system 10A is a catadioptric imaging system such as described in cited U.S. Pat. No. 6,552,852 (ZI-38) and U.S. Pat. No. 6,717,736 (ZI-43); U.S. Provisional Patent Applications No. 60/447,254 (ZI-40), No. 60/448,360 (ZI-41), No. 60/448,250 (ZI-42), No. 60/442,982 (ZI-45), No. 60/459,425, (ZI-50), No. 60/485,255 (ZI-53), and No. 60/501,666 (ZI-54); U.S. Patent Applications No. 10/778,371 (ZI-40) entitled “Transverse Differential Interferometric Confocal Microscopy,” No. 10/782,057 (ZI-41) entitled “Longitudinal Differential Interferometric Confocal Microscopy,” No. 10/782,058 (ZI-42) entitled “Thin Film Metrology Using Interferometric Confocal Microscopy,” No. 10/765,229 (ZI-45) entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” and No. 10/816,180 (ZI-50) entitled “Apparatus and Method for Joint Measurement Of Fields Of Orthogonally Polarized Beams Scattered/Reflected By An Object In Interferometry;” and U.S. Patent Application filed Jul. 7, 2004 (ZI-53) entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution.” Catadioptric imaging system 10A is shown schematically in FIG. 1 c with adaptive reflective surfaces 42A-1, 42A-2, 42A-3, 42C-1, 42C-2, 42C-3, 46A-1, 46A-2, 46C-1, and 46C-2. The adaptive reflective surfaces with transducers and servo control signals are shown schematically in FIG. 1 d. Catadioptric imaging system 10A comprises catadioptric elements 40 and 44, beam-splitter 48, and convex lens 50. Surfaces 42A and 42C comprise a first single convex spherical surface and 46A and 46C comprise a second single convex spherical surface wherein the first and second convex spherical surfaces have the same nominal radii of curvature and the respective centers of curvature of the first and second convex spherical surfaces are conjugate points with respect to beam-splitter 48. Surfaces 42B and 46B are concave spherical surfaces with nominally the same radii of curvature. The centers of curvature of surfaces 42B and 46B are the same as the centers of curvature of the second and first convex spherical surfaces, respectively. The center of curvature of convex lens 50 is the same as the center of curvature of surfaces 42B and the second convex spherical surface.
The combination of a reflection and a transmission for each ray of the converging beams forming the interferometric conjugate image at center of curvature 60 substantially compensates for departure of properties of beam-splitter 48 from properties of an ideal beam-splitter. The compensation is demonstrated by Equation (3). Function T(θ)1/2R(θ)1/2 has a maximum at T(θ)=R(θ)=½ and has only a second order dependence on changes of the transmission/reflection properties, i.e., [T(θ)1/2−1/{square root}{square root over (2)}][R(θ)1/21/{square root}{square root over (2)}].
Adaptive reflective surfaces 42A-1, 42A-2, 42A-3, 42C-1, 42C-2, 42C-3, 46A-1, 46A-2, 46C-1, and 46C-2 and associated portions of refractive surfaces 42A, 42C, 46A, and 46C are separated by radial distances typically of the order of a few microns and form an asymmetric Fabry-Perot cavity. The asymmetric Fabry-Perot cavity comprises a rear mirror that has a high reflectivity and a front mirror as a partially reflecting dielectric interface and is an example of the Gires-Tournois etalon. The beam reflected by a Gires-Tournois etalon is to a high accuracy a purely phase-modulated beam. With a reflectivity of R=0.04 for the front mirror, the relationship between the phase shift introduced by the etalon and the optical path length of the etalon cavity is represented by a linear relationship with a cyclic error that is principally a small amplitude second harmonic cyclic error. The amplitude in phase produced by the second harmonic cyclic error is approximately 2{square root}{square root over (R)}=0.4 radians. In the first embodiment of the present invention, the effect of the cyclic errors is easily measured in an initialization phase of the first embodiment and subsequently compensated through control of the thickness of the cavities without any modulation of the intensity of the reflected beams.
The surface tolerances on portions of refractive surfaces 42A, 42C, 46A, and 46C associated with the adaptive reflective surfaces 42A-1, 42A-2, 42A-3, 42C-1, 42C-2, 42C-3, 46A-1, 46A-2, 46C-1, and 46C-2 are relaxed in the first embodiment as a result of two effects. The first of the two effects is that the net effect of an error in the surface figure of a refractive surface on a double transmission through the refractive surface is reduced relative to the effect of the same error in the surface figure of mirror on an internally reflected beam by a factor of n - 1 n ( 4 )
Each conjugate pair of adaptive reflective surfaces 42A-1, 42A-2, 42A-3, 42C-1, 42C-2, 42C-3, 46A-1, 46A-2, 46C-1, and 46C-2 have been described in terms of maximizing the corresponding portions of amplitudes of beams 26C and 26D [see discussion associated with respect to Equation (1)]. It is apparent on examination of Equation (1) that each of the conjugate pairs of adaptive reflective surfaces may also be used as an optical switch by adjusting the corresponding (p such that
When a plane section of substrate 60 that is being imaged by interferometer 10 of the first embodiment of the present invention is embedded below the surface of substrate 60, spherical aberrations will be introduced such as described in commonly owned U.S. Provisional Patent Application No. 60/444,707 (ZI-44) entitled “Compensation for Effects of Mismatch in Indices of Refraction at a Substrate-Medium Interface in Confocal and Interferometric Confocal Microscopy” and U.S. patent application Ser. No. 10/771,785 (ZI-44) entitled “Compensation for Effects of Mismatch in Indices of Refraction at a Substrate-Medium Interface in Confocal and Interferometric Confocal Microscopy” wherein both the provisional and non-provisional patent applications are by Henry A. Hill and the contents of which are herein incorporated in their entirety by reference. Aberrations may also be introduced by a pellicle beam-splitter or aperture-array beam-splitter. Certain of the aberrations are compensated in catadioptric imaging system 10A by changing the focal lengths of conjugate pairs of adaptive reflective surfaces 42A-1, 42A-2, 42C-1, 42C-2, 46A-1, 46A-2, 46C-1, and 46C-2. The focal lengths of the conjugate pairs of adaptive reflective surfaces are adjusted by changing the radial locations of the conjugate pairs of adaptive reflective surfaces 42A-1, 42A-2, 42C-1, 42C-2, 46A-1, 46A-2, 46C-1, and 46C-2.
The description of the considerations made in the selection of radii of curvature of the first single convex surface comprising surfaces 42A and 42C, the second single convex surface comprising surfaces 46A and 46C, concave surfaces 42B and 46B, the adaptive reflective surfaces 42A-1, 42A-2, 42A-3, 42C-1, 42C-2, 42C-3, 46A-1, 46A-2, 46C-1, and 46C-2 are that same as the description given for the selection of radii of corresponding optical surfaces in the third embodiment of the present invention and in the cited U.S. Provisional Patent Application No. 60/485,255 (ZI-53) and U.S. Patent Application filed Jul. 7, 2004 (ZI-53) entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution.” The description of the selection of the radius of curvature associated with element 50 is the same as the description of the selection of the corresponding optical surface in the third embodiment of the present invention and in the cited U.S. Provisional Patent Application No. 60/485,255 (ZI-53) except that the radius of curvature associated with element 50 are ½ of the radius of curvature of the corresponding optical surface in the third embodiment and in the cited U.S. Provisional Patent Application No. 60/485,255 (ZI-53).
The description of source 18 including a pulse mode of operation and beam-conditioner 22 is the same as the corresponding portions of the description given to the source and beam-conditioner in embodiments described in commonly owned U.S. Provisional Patent Application No. 60/442,858 (ZI-47) entitled “Apparatus and Method for Joint Measurements of Conjugated Quadratures of Fields of Reflected/Scattered Beams by an Object in Interferometry” and U.S. patent application Ser. No. 10/765,368 (ZI-47) entitled “Apparatus and Method for Joint Measurements of Conjugated Quadratures of Fields of Reflected/Scattered or Transmitted Beams by an Object in Interferometry” wherein the provisional and the non-provisional patent applications are by Henry A. Hill and the contents of which are herein incorporated in their entirety by reference and in cited U.S. Provisional Patent Application No. 60/485,255 (ZI-53), in cited U.S. Provisional Patent filed Aug. 16, 2004 (ZI-57) entitled “Apparatus and Method for Joint And Time Delayed Measurements of Components of Conjugated Quadratures of Fields of Reflected/Scattered and Transmitted/Scattered Beams by an Object in Interferometry,” and in cited U.S. Patent Application filed Jul. 7, 2004 (ZI-53) entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution.” The beam-conditioner 22 may comprise acousto-optic modulators.
The descriptions the of bi-homodyne and quad-homodyne detection methods of the first embodiment of the present invention are the same as corresponding portions of the descriptions given for the descriptions of bi-homodyne and quad-homodyne detection methods in the cited U.S. Provisional Patent Application Nos. 60/442,858 (ZI-47) and 60/485,255 (ZI-53) and in cited U.S. patent application Ser. No. 10/765,368 (ZI-47) and U.S. Patent Application filed Jul. 7, 2004 (ZI-53) wherein the homodyne detection methods are based on frequency encoding. The extension of the bi- and quad-homodyne detection methods to N-dimensional bi- and quad-homodyne detection methods based on a combination of frequency encoding and either amplitude or phase modulations or permutations is implemented in the first embodiment by the use of the conjugate pairs of adaptive reflective surfaces of catadioptric imaging system 10A as optical switches or as nt phase shifters, respectively. The extension of the bi- and quad-homodyne detection methods to N-dimensional bi- and quad-homodyne detection methods may also be based on a combination of frequency encoding, polarization encoding, and either amplitude or phase modulations or permutations. The description of bi- and quad-homodyne detection methods based on a combination of frequency and polarization encoding is the same as the corresponding description given in cited U.S. Provisional Patent Application No. 60/459,425 (ZI-50) and in cited U.S. Patent Application filed Apr. 4, 2004 (ZI-50) entitled “Apparatus and Method for Joint Measurement Of Fields Of Orthogonally Polarized Beams Scattered/Reflected By An Object In Interferometry.”
The N-dimensional bi- and quad-homodyne detection methods are homodyne detection methods that exhibit the same properties as the cited bi- and quad-homodyne detection methods with respect to making joint measurements of conjugated quadratures of fields: a joint measurement of a conjugated quadratures of fields is made in the bi- and quad-homodyne detection methods and joint measurements are made of N independent conjugated quadratures of fields in the N-dimensional bi- and quad-homodyne detection methods where N is an integer. The (i,k) electrical interference signal Σi,k, 1≦i≦N and 1≦k≦4, is written in terms of the contribution Si,j,k that corresponds to portion j of the N portions of electrical interference signal Σi,k associated with the conjugate pairs of adaptive reflective surfaces 42A-1, 42A-2, 42A-3, 42C-1, 42C-2, 42C-3, 46A-1, 46A-2, 46C-1, and 46C-2. The representation of Σi,k in terms of Si,j,k is expressed as Σ i , k = ∑ j = 1 N h ij S i , j , k , 1 ≤ i ≤ N , 1 ≤ k ≤ 4 ( 7 )
There are 4N values of electrical interference signal Σi,k measured for each spot in or on substrate 60 that is being imaged. The number of different values of the electrical interference signal Σi,k that is measured is 4 times the number of independent conjugated quadratures that are being measured because there are 2N independent components of conjugated quadratures measured and two measurements of electrical interference signal values are required for each independent component of conjugated quadratures. For further discussion, reference is made to the bi-homodyne detection method such as described in cited U.S. Provisional Patent Applications No. 60/442,858 (ZI-47) and in cited U.S. Patent Applications filed Jan. 27, 2004 (ZI-47) entitled “Apparatus and Method for Joint Measurements of Conjugated Quadratures of Fields of Reflected/Scattered and Transmitted Beams by an Object in Interferometry” and in commonly owned U.S. Provisional Patent Application No. 60/485,507 (ZI-52) and in commonly owned U.S. Patent Application filed Jul. 7, 2004 (ZI-52) and entitled “Apparatus And Method For High Speed Scan For Detection And Measurement of Properties of Sub-Wavelength Defects And Artifacts In Semiconductor And Mask Metrology” wherein conjugated quadratures of scattered/reflected or scattered/transmitted fields are obtained jointly with a set of four electrical interference signal values obtained for each spot on and/or in a substrate being imaged. The latter cited provisional and non-provisional applications are by Henry A. Hill and the contents of each are incorporated herein in their entirety by reference.
The contribution Si,j,k is represented for the bi-homodyne detection method within a scale factor by the formula S i , j , k = P i , k ∑ m = 1 2 { ξ i , k 2  A j , m  2 + ζ i , k 2  B j , m  2 + η i , k 2  C j , m  2 + ζ i , k η i , k 2  B j , m   C j , m  cos φ B j , m C j , m ɛ m , k + ξ i , k ζ i , k 2  A j , m   B j , m  cos φ A j , m B j , m ɛ m , k + ɛ m , k ξ i , k η i , k [ 1 - ( - 1 ) m ]  A j , m   C j , m  cos φ A j , m C j , m + ɛ m , k ξ i , k η i , k [ 1 + ( - 1 ) m ]  A j , m   C j , m  sin φ A j , m C j , m } ( 8 )
where coefficient Aj,m represents the amplitude of the reference beam corresponding to pulse (i,k) of input beam 24 and to the frequency component of the input beam 24 that has index m; coefficient Bj,m represents the amplitude of the background beam corresponding to reference beam Aj,m; coefficient Cj,m represents the amplitude of the return measurement beam corresponding to reference beam Aj,m; Pi,k represents the integrated intensity of the first frequency component of the input beam 24 pulse (i,k) of a sequence of 4N pulses; and an example set of values for εm,k are listed in Table 1. There are other set of values for εm,k that may be used in embodiments of the present invention wherein the other set of values for εm,k satisfy the conditions set out in subsequent Equations (9) and (10) herein.
single-homodyne detection operating in a non-scanning mode, the conjugate set of pinholes corresponds to a single pinhole and the conjugate set of four pixels corresponds to a single pixel. In a single-frequency single-homodyne detection operating in a non-scanning mode, the conjugate set of four pinholes comprise pinholes of pinhole array beam-splitter 12 that are conjugate to a spot in or on the substrate being imaged at different times during the scan.
An important requirement of εm,k is that ∑ k = 1 4 ɛ m , k = 0 , m = 1 , 2. ( 9 )
Another important requirement is that the εm,k are orthogonal over the range of m=1,2 for m≠m′ since εm,k and εm′,k are orthogonal over the range of k=1, 2, 3, 4, i.e., ∑ j = 1 4 ɛ m , j ɛ m ′ , j = 4 δ m , m ′ ( 10 )
A set of conditions that are used to derive the matrix elements hi,j for the phase modulation or permutation embodiment are that the values of hi,j are either ±1 and that ∑ j = 1 N h i , j h i ′ , j = N δ i , i ′ . ( 12 )
Three examples of matrices H=(hij) which meet the requirements of the N-dimensional bi- and quad-homodyne detection methods when using phase modulations or permutations are as follows: ( h ij ) = ( 1 1 1 - 1 ) , N = 2 ; ( 13 ) ( h ij ) = ( 1 1 1 1 1 - 1 1 - 1 1 1 - 1 - 1 1 - 1 - 1 1 ) , N = 4 ; ( 14 ) ( h ij ) = ( 1 1 1 1 1 1 1 1 1 - 1 1 - 1 1 - 1 1 - 1 1 1 - 1 - 1 1 1 - 1 - 1 1 - 1 - 1 1 1 - 1 - 1 1 1 1 1 1 - 1 - 1 - 1 - 1 1 - 1 1 - 1 - 1 1 - 1 1 1 1 - 1 - 1 - 1 - 1 1 1 1 - 1 - 1 1 - 1 1 1 - 1 ) , N = 8. ( 15 )
Note that the matrix for N=2p where p is an integer is generated from the matrix (hij) for N=2p-1 and the matrix (hij) for N=2, i.e., for each matrix element of (hij) for N=2, substitute the matrix (hij) for N=2p-1 multiplied by the respective matrix element of (hij) for N=2. This construction technique corresponds to the Sylvester construction [see Sylvester (1867)].
The conditions that are used to derive the matrix elements hi,j for the amplitude modulation or permutation embodiment are that the values of hi,j be equal to either 0 or 1 and that the selection of the designs yield the best signal-to-noise ratios. In this case, the values of the matrix elements hi,j are derived for example from a binary simplex code [see M. Harwit and N.J. A. Sloane, Hadamard Transform Optics (Academic, New York, 1979)]. Using sij to denote the matrix elements hi,j for the amplitude modulation or permutation, an example of a set of matrix elements sij of order 7 is ( s ij ) = ( 0 0 1 0 1 1 1 0 1 0 1 1 1 0 1 0 1 1 1 0 0 0 1 1 1 0 0 1 1 1 1 0 0 1 0 1 1 0 0 1 0 1 1 0 0 1 0 1 1 ) . ( 16 )
A first variant of the first embodiment of the present invention comprises the apparatus of the first embodiment and an additional beam conditioning of the measurement beam incident on substrate 60. In the first variant of the first embodiment, the measurement beam is focused to a small spot on substrate 60. The detector may comprise a single pixel detector or a linear array of pixels wherein the linear array of pixels correspond for example to angles of reflection/scattered radiation from substrate 60. The additional beam conditioning may comprise an imaging element 54G and an apodizing filter 54F as shown schematically in FIG. 1 g.
Measurement beam 24D is transmitted by imaging element 54G as measurement beam 24E subsequent to transmission by apodizing filter 54F. Measurement beam 24E is a converging beam that is focused to a spot on substrate 60. Apodizing filter 54F may comprise a simple aperture that has a transmission of 100% anywhere within the aperture. In this case, contribution of reflection/scattering by portions of substrate 60 lying outside of the focused spot will contribute to the signal generated by the detector according to the point transfer function of the aperture. For a circular aperture and a uniform beam amplitude across the aperture, the point transfer function is an Airy function [J1(x)/x] where J1 is a Bessel function of the first kind and order 1. For a square aperture, the transfer function will be the product of two sinc functions, i.e., (sin x/x)(sin y/y).
Field of View: the longitudinal separation between the sagittal and tangential surfaces Δz is given by the formula Δ z = 2 ρ 2 r 0 ( 17 )
where ρ is the radius of the field of view and r0 is the radius of the respective catoptric reflective surface of imaging system 10A. Defining the field of view as that radius ρ such that the longitudinal separation Δz is equal to the depth of focus, we have ρ = ( r 0 λ 2 ) 1 / 2 1 NA ( 18 )
where NA is the numerical aperture of catoptric imaging system 10A.
Associated with the convex refractive surfaces 242A, 242C, 246A, and 246C are adaptive reflective surfaces 242A-1, 242A-2, 242A-3, 242C-1, 242C-2, 242C-3, 246A-1, 246A-2, 246A-3, 246C-1, 246C-2, and 246C-3. The adaptive reflective surfaces 242A-1, 242A-2, 242A-3, 242C-1, 242C-2, 242C-3, 246A-1, 246A-2, 246A-3, 246C-1, 246C-2, and 246C-3 are shown schematically in FIG. 2 b and the adaptive reflective surfaces with associated transducers 3242A-1, 3242A-2, 3242A-3, 3242C-1, 3242C-2, 3242C-3, 3246A-1, 3246A-2, 3246A-3, 3246C-1, 3246C-2, and 3246C-3 are shown schematically in FIG. 2 c.
The description of the operation and different modes of operation of the third embodiment of the present invention with respect to the adaptive reflective surfaces is the same as corresponding portions of the description given for the operation and for the different modes of operation of adaptive reflective surfaces in the first embodiment and variant thereof of the present invention.
The sagittal field of catadioptric imaging system 210A is a flat field and the tangential field is also a flat field for a certain object field when the Petzval sum is zero, i.e., 2 ∑ j = 1 p - 1 ( 1 n j - 1 n j + 1 ) 1 r j + 1 n p 2 r p = 0 ( 19 )
where rj is the radius of curvature of surface j, rp is the radius of curvature of the mirror surface, and nj is the index of refraction of the media located on the beam incidence side of surface j such as shown diagrammatically in FIG. 2 d. The condition for the generation of an achromatic anastigmat at wavelength λc is accordingly given by the equation ∂ [ 2 ∑ j = 1 p - 1 ( 1 n j - 1 n j + 1 ) 1 r j + 1 n p 2 r p ] ∂ λ = 0. ( 20 )
For an example of an achromatic anastigmat design for deep UV operation, the media of elements 240, 244, 256, and 258 is selected as CaF2 and the media of concentric lenses 252 and 254 is selected as a UV grade fused silica. Other parameters of the example achromatic anastigmat design such as the radii of curvature of surfaces are listed in Table 1 for λc=250 nm. With this choice of media, the operation range is down to 170 nm. For the achromatic anastigmat design parameters listed in Table 2, the contribution of geometric ray tracing effects is ≲40 nm for an object field of 1.5 mm in diameter and a numerical aperture NA=0.970 in the object space just outside of the plane surface of plano convex lens 258.
A variant of catadioptric imaging system 210A is shown in FIG. 2 e wherein catadioptric imaging system 210A is an anastigmat that is not achromatic. The media of elements 240 and 244 may comprise CaF2, BaF2, or SrF2 for work down to 140 nm and UV grade fused silica for operation to 180 nm. The respective radii of the curvature for anastigmat design at λ=250 nm using CaF2 are listed in Table 2. For anastigmat design listed in Table 3, the contribution of geometric ray tracing effects is ≲40 nm for an object field of 1.5 mm and a numerical aperture NA=0.970 in the object space just outside of the plane surface of plano convex lens 258.
Fused Silica 1 1.507446 8.147
mm and a numerical aperture NA=0.970 in the object space just outside of the plane surface of piano convex lens 258.
Another form of catadioptric imaging system that may be used for catadioptric and catoptric imaging system 10 is the catadioptric imaging system such as described in commonly owned U.S. Provisional Patent Application No. 60/460,129 (ZI-51) entitled “Apparatus and Method for Measurement of Fields of Forward Scattered/Reflected and Backscattered Beams by an Object in Interferometry” and U.S. patent application Ser. No. 10/816,172 wherein both are by Henry A. Hill and the contents of which are herein incorporated in their entirety by reference.
The location of the object plane of catadioptric imaging system 210A shown diagrammatically in FIG. 2 f is outside of piano convex lens 258 and on the surface of substrate 60. The separation of the plane surface of plano convex lens 258 and the surface of substrate 60 is h. The object plane of catadioptric imaging system 210A may also be located in the interior of substrate 60 which is shown diagrammatically in FIG. 2 g. The spherical aberrations introduced by transmission through plane surfaces shown in FIGS. 2 f and 2 g are compensated in the third embodiment through the use of the conjugate adaptive reflective surfaces such as described in the first embodiment of the present invention.
The remaining description of the third embodiment of the present invention is the same as the corresponding portions of the descriptions of the first embodiment and variant thereof and second embodiment of the present invention and of the catadioptric imaging systems given in cited U.S. Provisional Patent Applications No. 60/485,507 (ZI-52) and No. 60/485,255 (ZI-53) and U.S. Patent Applications filed Jul. 7, 2004 (ZI-52) and entitled “Apparatus and Method for High Speed Scan for Subwavelength Defects in Semiconductor Metrology” and filed Jul. 7, 2004 (ZI-53) entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution.”
The location of the object plane of catadioptric imaging system 210A may also be on the plane surface of piano convex lens 258. In this case, the measurement beam can be arranged to probe substrate 60 as an evanescent field when h is of the order of λ/4. The third embodiment can change rapidly from using the evanescent field as a probe beam to using the non-evanescent fields as a probe beam by use of the high speed vertical scan feature of the present invention.
Referring to FIG. 3 b, mirror system 354B redirects and displaces measurement beam 324A such that measurement beam 324C is propagating in a plane displaced out of the plane of FIG. 3 b. Mirror system 354C displaces measurement beam 324C such that the transmitted measurement beam subsequently reflected by mirror 354D propagates in the plane of FIG. 3 b. The remaining description of the fifth embodiment of the present invention is the same as corresponding descriptions given for the first four embodiments of the present invention and corresponding descriptions given for embodiments given in cited U.S. Pat. No. 6,552,852 (ZI-38) and No. 10/366,651 (ZI-43); U.S. Provisional Patent Applications No. 60/447,254 (ZI-40), No. 60/448,360 (ZI-41), No. 60/448,250 (ZI-42), No. 60/442,982 (ZI-45), No. 60/459,425 (ZI-50), No. 60/485,255 (ZI-53), filed Jul. 7, 2003 (ZI-52) and entitled “Apparatus and Method for High Speed Scan for Subwavelength Defects in Semiconductor Metrology,” and filed Sep. 10, 2003 (ZI-54) entitled “Catoptric and Catadioptric Imaging Systems With Adaptive Catoptric Surfaces;” and U.S. Patent Applications No. 10/778,371 (ZI-40) entitled “Transverse Differential Interferometric Confocal Microscopy,” No. 10/782,057 (ZI-41) entitled “Longitudinal Differential Interferometric Confocal Microscopy,” No. 10/782,058 (ZI-42) entitled “Thin Film Metrology Using Interferometric Confocal Microscopy,” No. 10/765,229 (ZI-45) entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” and No. 10/816,180 (ZI-50) entitled “Apparatus and Method for Joint Measurement Of Fields Of Orthogonally Polarized Beams Scattered/Reflected By An Object In Interferometry;” and U.S. Patent Application filed Jul. 7, 2004 (ZI-53) entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution.”
Referring to FIG. 4 c, the locations and orientations of adaptive reflecting surfaces are controlled by transducers according to servo control signal 498. The description of servo control signal 498 is the same as the corresponding description of servo control signal 98 from servo controller 96 shown in FIG. 1 a. For each of the adaptive reflective surfaces 442A-1, 442A-2, 442A-3, 442C-1, 442C-2, 442C-3, 446A-1, 446A-2, 446A-3, 446C-1, 446C-2, and 446C-3, there are corresponding transducers 3442A-1, 3442A-2, 3442A-3, 3442C-1, 3442C-2, 3442C-3, 3446A-1, 3446A-2, 3446A-3, 3446C-1, 3446C-2, and 3446C-3, respectively. Each of the transducers comprises three transducers that can either change the radial position of a corresponding adaptive reflective surface or effect changes in the orientation of the corresponding adaptive reflective surface in two orthogonal planes. The two orthogonal planes intersect in a line that is parallel to the optical axis of the corresponding adaptive reflective surface. Certain of the transducers are located so as to not interfere with substrate 60 and are indicate as dashed lines in FIG. 4 c.
The working distance of interferometer 10 in FIG. 4 a can be increased for example by removing the adaptive reflective surfaces 446A-3, 446C-3, 442A-3, and 442C-3 at the expense of increasing the size of the central obstruction presented to beams reflected/scattered or transmitted by the catadioptric imaging system.
Referring to FIG. 4 a, when input beam 24 comprises coextensive reference and measurement beams, first and second portions of input beam 24 are reflected and transmitted, respectively, by beam-splitter mirror system 454A that comprises a non-polarizing beam-splitter as a measurement beam 424A and as reference beam 424B. When input beam 24 comprises non-coextensive reference and measurement beams, element 454A functions as a set of mirrors to reflect the measurement beam component of beam 24 as beam 424A and the reference beam component beam of 24 as reference beam 424A. Propagation of measurement beam 424A is in the plane of FIG. 4 a and is reflected by mirror 454B as measurement beam 424C. Propagation of reference beam 424B is displaced out of the plane of FIG. 4 a and directed toward mirror system 454D. Reference beam 424B exits mirror system 454D as reference beam 424D (see FIG. 4 b). Propagation of reference beam 424D is in the plane of FIG. 4 b and is incident on thin fluorescent layer 12. Output beam 434 shown in FIG. 4 a corresponds to output beam 34 shown in FIG. 1 a.
The function of beam-splitter 448 is the same as the function of beam-splitter 48 of the first embodiment of the present invention with respect generating complimentary beams 426E and 428E and complimentary beam 426F and 428F [see FIG. 4 f and the discussion associated with Equation (1)]. Beam-splitter 448 is shown schematically in Fib. 4 f and comprises two pellicles 448A and 448B and beam-splitting layer 448C. The refractive media, e.g., UV grade fused silica, F—SiO2, CaF2, or LiF, of pellicles 448A and 448B is selected to meet the transmission requirements of an end use application. The thickness d of pellicles 448A and 448B is selected to be small as practical in order to reduce optical aberrations introduced by the pellicles consistent with the pellicles being self supporting, meeting required flatness specifications, and meeting required uniformity of thickness specifications.
λΔx≳3(Δr cos θ)2, (21)
λΔx≳3w2, (22)
where Δx is an average path length of measurement and/or reference beams from beam-splitter 748 to the respective adaptive reflective surface, e.g., beams 426E, 426F, 428E, and 428F and adaptive reflective surfaces 442A-1, 442C-1, 446A-1, and 446C-1, respectively, shown in FIGS. 9 a and θ is a corresponding average angle of incidence at the beam-splitter. The radial and azimuthal dimensions for the apertures of the aperture array will generally be different for optimum performance of the beam-splitter. In addition, the radial and azimuthal dimensions of the apertures will generally be dependent on the angle of incidence θ of a beam, the radius of curvature r of a respective adaptive reflective surface, and h the spacing between beam-splitter 748 and the center of curvature of the respective adaptive reflective surface (see FIG. 9 a). Equations (21) and (22) can be written in terms of h and r explicitly for Δr and w with the results Δ r ≾ [ λ ( r - h sec θ ) 3 ] 1 / 2 sec θ , ( 23 ) w ≾ [ λ ( r - h sec θ ) 3 ] 1 / 2 , ( 24 )
respectively. The value of w starts off with a value of w≲[λ(r−h)/3]1/2 for θ=0 and decreases to a value of zero when θ reaches in maximum value of cos−1(h/r). The value of Δr also starts off at θ=0 with a value of Δr≲[λ(r−h)/3]1/2, e.g., Δr≲0.408(λr)1/2 for h=0.5r, then increases to a maximum value at θ≅42 degrees for the example h=0.5r, i.e. Δr≲0.444(λr)1/2, and then decreases to a value of zero when θ reaches the maximum value of cos−1 (h/r) which is 60 degrees for the example h=0.5r.
So, another important property of the sixth embodiment is a reduced optical path length in a refractive medium which is particularly important when working in the IR, UV, VUV, or EUV. The optical path length in a refractive medium in the sixth embodiment is approximately {fraction (1/10)} of the optical path length in a refractive medium for those embodiments that are not based on use of a thin beam-splitter. A consequence of the another important property is an extended range into the IR, UV, VUV and/or in the EUV for a given refractive medium.
An advantage of the variant of the sixth embodiment is the same as an advantage of the third embodiment of the present invention. The location of the object plane of catadioptric imaging system 410A may also be on the plane surface of piano convex lens 454. In this case, the measurement beam can be arranged to probe substrate 60 as an evanescent field when the spacing between plano convex lens 454 and substrate 60 is of the order of λ/4. The variant of the sixth embodiment can change rapidly from using the evanescent field as a probe beam to using the non-evanescent fields as a probe beam by use of the high speed vertical scan feature of the present invention.
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International Classification G02B17/08, G02B, G01J1/58, G01B9/02, G02B26/06
Cooperative Classification G01B9/02056, G01B9/02079, G01B9/02068, G01B9/02022, G01B2290/70, G01B9/02014, G01B9/02007, G03F7/7085, G01N21/9501, G01N21/8806, G01J1/58, G03F1/84, G03F9/7088, G02B26/06, G02B17/0808, G02B17/086
European Classification G03F1/84, G03F9/70M, G03F7/70P4, G02B17/08M1, G01B9/02, G02B17/08A1, G01J1/58, G02B26/06, G01N21/95A
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HILL, HENRY A.;HAMANN, STEVEN;FISCHER, DAVID;REEL/FRAME:015626/0275