(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2004/0114150 A1
`(43) Pub. Date:
`Jun. 17, 2004
`Wegmann et al.
`
`US 20040114150A1
`
`(54)
`
`(75)
`
`METHOD AND APPARATUS FOR
`DETERMINING THE INFLUENCING OF
`THE STATE OF POLARIZATION BY AN
`OPTICAL SYSTEM; AND AN ANALYSER
`
`Inventors: Ulrich Wegmann, Koenigsbronn (DE);
`Michael Hart], Munich (DE); Markus
`Mengel, Heidenheim (DE); Manfred
`Dahl, Lauchheim (DE); Helmut
`Haidner, Aalen (DE); Martin
`Schriever, Aalen (DE); Michael
`Totzeck, SchWaebisch Gmuend (DE)
`
`Correspondence Address:
`SUGHRUE MION, PLLC
`2100 PENNSYLVANIA AVENUE, N.W.
`SUITE 800
`WASHINGTON, DC 20037 (US)
`
`Assignee: CARL ZEISS SMT AG
`
`Appl. No.:
`
`10/628,431
`
`Filed:
`
`Jul. 29, 2003
`
`Foreign Application Priority Data
`
`(73)
`(21)
`(22)
`(30)
`
`Jul. 29, 2002
`
`(DE) ................................... .. 102 355 14.2
`
`Jan. 31, 2003 (DE) ................................... .. 103 04 822.7
`
`Publication Classi?cation
`
`(51) Int. Cl? ..................................................... .. G01B 9/02
`
`(52) Us. 01. .......................................... .. 356/491; 356/520
`
`(57)
`
`ABSTRACT
`
`A method and an apparatus for determining the in?uencing
`of the state of polarization of optical radiation by an optical
`system under test, Wherein radiation With a de?ned entrance
`state of polarization is directed onto the optical system, the
`exit-side state of polarization is measured, and the in?uenc
`ing of the state of polarization is determined by the optical
`system With the aid of evaluation of the exit state of
`polarization With reference to the entrance state of polariza
`tion. An analyser arrangement Which can be used for this
`purpose is also disclosed. The method and the apparatus are
`used, e.g., to determine the in?uencing of the state of
`polarization of optical radiation by an optical imaging
`system of prescribable aperture, the determination being
`performed in a pupil-resolved fashion.
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`Nikon Exhibit 1009 Page 1
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`Patent Application Publication Jun. 17, 2004 Sheet 1 0f 6
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`US 2004/0114150 A1
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`Patent Application Publication Jun. 17, 2004 Sheet 2 0f 6
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`US 2004/0114150 A1
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`Nikon Exhibit 1009 Page 3
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`Patent Application Publication Jun. 17, 2004 Sheet 3 0f 6
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`US 2004/0114150 A1
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`Nikon Exhibit 1009 Page 4
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`Patent Application Publication Jun. 17, 2004 Sheet 4 0f 6
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`US 2004/0114150 A1
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`Nikon Exhibit 1009 Page 5
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`

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`Patent Application Publication Jun. 17, 2004 Sheet 5 0f 6
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`US 2004/0114150 A1
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`Nikon Exhibit 1009 Page 6
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`Nikon Exhibit 1009 Page 7
`
`

`

`US 2004/0114150 A1
`
`Jun. 17, 2004
`
`METHOD AND APPARATUS FOR DETERMINING
`THE INFLUENCING OF THE STATE OF
`POLARIZATION BY AN OPTICAL SYSTEM; AND
`AN ANALYSER
`
`[0001] The following disclosure is based on German
`Patent Application No. 102 35 514.2 ?led on Jul. 29, 2002
`and German Patent Application No. 103 04 822.7 ?led on
`Jan. 31, 2003, Which are incorporated into this application
`by reference.
`
`BACKGROUND OF THE INVENTION
`
`[0002] 1. Field of the Invention
`
`[0003] The invention relates to a method for determining
`the in?uencing, caused by an optical system, of the state of
`polariZation of optical radiation to an aberration correction
`method and to an apparatus, suitable for carrying out such a
`method, and to a polariZation analyser arrangement Which
`can be used in the latter.
`
`[0004] 2. Description of the Related Art
`
`[0005] Various methods and apparatuses are knoWn Which
`can be used to determine hoW an optical system in?uences
`the state of polariZation of optical radiation. The term optical
`system is to be understood in this case as any arrangement
`of one or more optical components Which transmit and/or
`re?ect the incident optical radiation, in particular including
`lenses and objectives constructed thereWith. The term opti
`cal radiation is to be understood here as any desired elec
`tromagnetic radiation Which is applied to the optical system
`under test, for example visible light or UV radiation. Par
`ticularly Widely used are ellipsometry methods and ellip
`sometry apparatuses in diverse forms. In order to describe
`the state of polariZation and hoW it is in?uenced or changed
`by the optical system, use is made of suitable variables such
`as the Stokes parameters, the Muller matrix, the polariZation
`matrix and the Jones matrix. Reference may be made to the
`relevant literature for details in this regard.
`
`[0006] A method and an apparatus of the type mentioned
`at the beginning are disclosed in Patent Speci?cation US.
`Pat. No. 5,298,972. In this method and in this apparatus the
`in?uencing of the state of polariZation caused by an optical
`system is determined in an integral fashion, speci?cally by
`determining a single set of Stokes parameters, assigned to
`the optical system under test, and determining the Jones
`matrix resulting therefrom. The radiation is directed via a
`single-mode ?bre in each case onto the optical component
`and diverted by the latter, the result being to effect spatial
`beam ?ltering.
`
`[0007] It is also knoWn to utiliZe polariZation effects to
`produce polariZation images of objects. The Patent Speci?
`cation US Pat. No. 5,396,329 indicates a corresponding
`image recording system Which, in addition to an imaging
`optics, has an optical retarder, for example in the form of a
`compensator, and, doWnstream thereof, a linear polariZer
`Which are both arranged rotatively. Serving as image detec
`tion unit is, for example, an imaging camera, a CCD detector
`or a roW of individual detector elements. The computational
`evaluation is performed via the Stokes parameters and one
`Muller matrix for each polariZation-relevant component.
`
`[0008] The Patent Speci?cation US. Pat. No. 5,166,752
`discloses an ellipsometry system in Which a parallel entrance
`
`bundle is focused onto an optical system under test such that
`the individual rays are incident at various angles, and the
`light cone re?ected or transmitted by this optical system
`under test is refocused into a parallel exit beam. Serving as
`detector unit is a roW of individual detector elements Which
`are struck in each case by light rays Which originate from a
`narroW range of angles of incidence on the optical system
`under test. The aim of this is to permit simultaneous detec
`tion of the state of polariZation of light rays incident on the
`system under test at various angles of incidence Without an
`attendant requirement for a scanning detection operation.
`This ellipsometry system is used, in particular, to test optical
`materials for properties Which cause a change in state of
`polariZation, speci?cally the birefringence of an optical
`volumetric material in the case of transmission measure
`ment.
`[0009] As is knoWn, it is possible for the purpose of
`determining the image quality of optics Which image With
`high precision to make use of Wavefront sensors With the aid
`of Which deviations of the image-side Wavefronts from the
`ideal imaging behaviour can be determined very accurately.
`So-called shearing interferometers, for example, are in use
`for this purpose. AWavefront detection device based thereon
`is disclosed in Laid-Open Speci?cation DE 101 09 929 A1.
`This apparatus is also suitable, in particular, for determining
`the image quality of projection objectives of microlitho
`graphic projection exposure machines, and includes means
`for providing a Wavefront source, for example With an
`optical conductor and a perforated mask arranged at the
`output thereof, in the object plane of the optical imaging
`system under test and a diffraction grating in the image plane
`conjugate to the object plane. Connected doWnstream of the
`diffraction grating is a spatially resolving radiation detector,
`for example in the form of a CCD chip, an interposed optics
`imaging the interferogram produced by the diffraction grat
`ing onto the sensor surface of the detector. This type of
`Wavefront sensor technology can test the imaging system
`With the aid of the same radiation Which is used by the
`imaging system in its normal operation, and it can be
`integrated in one component With the imaging system. This
`type of Wavefront sensor is therefore also denoted as an
`operational interferometer (OI).
`[0010] In the German Patent Application 102 17 242.0,
`Which is not a prior publication, a measuring apparatus is
`described Which can, in particular, be such an OI apparatus
`and serves the purpose of interferometric measurement of an
`optical imaging system Which is used for imaging a useful
`pattern, provided on a mask, into the image plane, the mask
`being arranged in the object plane for this purpose. It is
`proposed to implement the Wavefront source from the inter
`ferometric measurement by means of a measuring pattern
`formed on the mask in addition to the useful pattern.
`[0011] A further method, used in practice, of Wavefront
`detection by high-precision imaging systems is represented
`by point diffraction interferometry, the basic principles of
`Which are described in the relevant specialist literature—see,
`for example, D. Malacara, “Optical Shop Testing”, Chapter
`3.7, John Wiley, NeW York, 1991. Speci?c discussions are
`provided in Patent Speci?cations US. Pat. No. 6,344,898 B1
`and US. Pat. No. 6,312,373, and in the Laid-Open Speci
`?cations JP 11-142291 and WO 02/42728.
`[0012] In the case of modern high-precision imaging sys
`tems of high numerical aperture, used as microlithographic
`
`Nikon Exhibit 1009 Page 8
`
`

`

`US 2004/0114150 A1
`
`Jun. 17, 2004
`
`projection objectives, for example, the in?uence of the
`imaging system on the state of polarization of the radiation
`used can scarcely be neglected any longer. Thus, for
`example, polariZation-induced effects on the image quality
`are produced by birefringence in the case of lenses made
`from calcium ?uoride such as are frequently used for short
`Wavelengths, and by polariZation effects at de?ecting mir
`rors. There is therefore a need to be able to determine the
`in?uencing of the state of polariZation of optical imaging
`systems of high aperture as Well as possible in quantitative
`terms, in order to draW conclusions on the polariZation
`dependent image quality.
`[0013] The invention is based on the technical problem of
`providing a novel method and a novel apparatus of the type
`mentioned at the beginning, as Well as a polariZation analy
`ser arrangement Which can be used in this case, With the aid
`of Which the in?uencing, caused by an optical system under
`test, of the state of polariZation of the radiation used and/or
`an aberration correction can be determined comparatively
`accurately such that they are also suitable, in particular, for
`determining the polariZation-induced in?uence on the imag
`ing quality very precisely in the case of optical imaging
`systems.
`
`SUMMARY OF THE INVENTION
`[0014] The invention solves this problem by providing a
`method for determining the in?uencing of the state of
`polariZation of optical radiation by an optical system under
`test, in Which entrance-side radiation With a de?ned entrance
`state of polarization is directed onto the optical system, the
`exit state of polariZation is measured by radiation emerging
`from the optical system, and the in?uencing of the state of
`polariZation by the optical system is determined by means of
`evaluating the measured exit state of polariZation With
`reference to the entrance state of polariZation, Wherein the
`in?uencing of the state of polariZation caused by an optical
`imaging system of prescribable aperture is determined With
`pupil resolution.
`[0015] In a further aspect the invention solves this prob
`lem by providing a method for image correction, Wherein the
`distortion of a pupil image by an optical imaging system of
`prescribable aperture is determined by means of optical
`computation or measurement acquisition or a combination
`of the tWo, and corrected compurationally. This image
`correction can be used in the method for determining the
`in?uencing of the state of polariZation of optical radiation by
`an optical system under test according to the present inven
`tion.
`
`[0016] The invention is further directed to an apparatus for
`determining the in?uencing of the state of polariZation of
`optical radiation by an optical system under test, having
`means for providing entrance-side radiation, directed onto
`the optical system, With a de?ned entrance state of polar
`iZation, polariZation detector means for measuring the exit
`state of polariZation of radiation emerging from the optical
`system, and an evaluation unit for determining the in?uenc
`ing of the state of polariZation by the optical system by
`means of evaluating the measured exit state of polariZation
`With reference to the entrance state of polariZation, Wherein
`the polariZation detector means are set up to measure the exit
`state of polariZation With pupil resolution, and the evaluation
`unit is set up to determine the in?uencing of the state of
`polariZation With pupil resolution.
`
`[0017] As a yet further aspect the present invention pro
`vides for a polariZation analyser arrangement comprising a
`periodic structure, a beam-shaping unit, a compensator
`polariZer unit, and a polariZation analyser element, in par
`ticular a polariZation beam splitter element.
`[0018] In addition the present invention provides for a
`polariZation analyser arrangement comprising a beam-shap
`ing unit, a compensator polariZer unit Which comprises a
`plurality of compensator elements Which are ?xedly
`arranged With directions of polariZation rotated relative to
`one another, and a polariZation analyser element, in particu
`lar a polariZation beam splitter element.
`[0019] The polariZation analyser arrangement of the
`present invention can be used as polariZation detector or
`polariZer means in the apparatus for determining the in?u
`encing of the state of polariZation of optical radiation by an
`optical system under test.
`[0020] The method and the apparatus according to the
`present invention may be used for testing optical imaging
`systems of prescribable aperture Whose in?uencing of the
`state of polariZation is determined With pupil resolution.
`Here, the term “With pupil resolution” is to be understood as
`an angle-resolved determination of this in?uencing of the
`state of polariZation over at least a portion of the pupil range,
`given by the aperture, of the optical imaging system.
`[0021] The determination of the in?uencing of the state of
`polariZation is therefore performed With pupil resolution for
`the individual coordinate points of the pupil range under
`consideration, and not as a purely integral measurement
`Without spatial resolution. This permits the optical imaging
`system to be tested With pupil resolution for possible optical
`aberrations Which are caused by the in?uencing of the state
`of polariZation. An important ?eld of application is testing of
`aberrations in the case of high-precision projection objec
`tives of microlithography projection exposure machines for
`Wafer exposure in the fabrication of semiconductor compo
`nents, Where very ?ne structures are to be transferred to a
`Wafer from a mask, for example With the aid of UV
`radiation.
`[0022] In a development of the method a de?ned entrance
`state of polariZation is provided in the object plane of the
`imaging system, and the exit state of polariZation is mea
`sured With pupil resolution Within a prescribable pupil range
`of the imaging system.
`[0023] A further development of the method provides as
`entrance-side radiation a spatially incoherent point light
`radiation emanating from the object plane of the imaging
`system. Suitable for this purpose is an apparatus Which is
`further developed according to the invention and comprises
`a perforated mask With one or more openings in the object
`plane of the imaging system and upstream ?rst polariZation
`means. The latter can include, in a development of the
`apparatus according to the invention, a polariZer unit and/or
`a compensator unit in serial arrangement, Which can be set
`to various spatial orientations. This can be implemented by
`using rotatable polariZers and/or compensators or using
`different optical channels, Which can be sWitched in, With
`preset polariZer/compensator units. In a further re?nement,
`the apparatus can include a diffusing screen in front of the
`?rst polariZation means.
`[0024] A further developed apparatus has as polariZation
`detector means a CCD detector and upstream second polar
`
`Nikon Exhibit 1009 Page 9
`
`

`

`US 2004/0114150 A1
`
`Jun. 17, 2004
`
`iZation means. The polarization detector means thus
`designed permit the simultaneous measurement, With pupil
`resolution, of the exit state of polariZation for all spatial
`coordinates of the pupil range under consideration in a
`single measuring operation Without the need for alterna
`tively possible scanning of the pupil range by a detector
`measuring in a punctiform fashion.
`
`[0025] The evaluation of the exit state of polariZation
`Within the inventive method may include a determination of
`the phase-reduced Jones matrix from an ellipsometric mea
`surement of the in?uencing of the state of polariZation.
`
`[0026] In a further embodiment of the inventive method
`the pupil-resolved, spatial characteristic of the exit-side
`Wavefront phase is determined by means of shearing inter
`ferometry or point-diffraction interferometry. In conjunction
`With a determination of the phase-reduced Jones matrix it is
`possible therefrom to determine the complete, pupil-re
`solved Jones matrix of the optical imaging system. In this
`case, the polariZation detector means of the apparatus car
`rying out the method have a corresponding shearing or
`point-diffraction interferometer unit in a corresponding
`development of the invention.
`
`[0027] In a further embodiment of the inventive method
`the radiation obtained on the exit side by shearing interfer
`ometry or point-diffraction interferometry is combined With
`a polariZation analysis for pupil-resolved determination of
`modulus and phase of the matrix elements of the Jones
`matrix.
`
`[0028] The image correction method of the invention
`alloWs to use a relatively simple, cost-effective detection
`side optics. The method is suitable in this case, both in
`conjunction With the inventive measures for determining the
`in?uencing of the state of polariZation by an optical system
`and, independently thereof, for any other applications in
`Which a correction of pupil image distortion is desirable. In
`particular, the method can also come into use in measure
`ment systems Which acquire Wavefronts such as the above
`mentioned OI system, including in system variants taking no
`account of in?uences of polariZation.
`
`[0029] The evaluation unit of the apparatus carrying out
`the method is, in an embodiment of the invention, appro
`priately designed for carrying out the method variants With
`determination of the phase-reduced or complete, pupil
`resolved Jones matrix.
`
`[0030] The polariZation analyser arrangement in accor
`dance With the invention is suitable, in particular, for use as
`polariZation detector means or polariZation preparation
`means in the determination according to the invention of the
`in?uencing of the state of polariZation of optical radiation by
`an optical system under test. In advantageous re?nements,
`the arrangement includes a beam-shaping optics composed
`of one or more spherical and/or aspheric refractive lenses,
`one or more diffractive lenses, one or more spherical and/or
`aspheric mirror elements, or a combination of the said
`optical elements. In one embodiment, there is located in
`front of the beam-shaping optics a periodic structure With
`the aid of Which it is possible, for example, to implement the
`measurement acquisition of a pupil image distortion.
`
`[0031] Depending on the requirements, it is possible to
`arrange the periodic structure such that it is coupled to a
`detector element, arranged after the polariZation analyser
`
`element, such that it moves laterally thereWith, or to hold the
`periodic structure and the detector element such that they
`can move relative to one another laterally Without such a
`coupling.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0032] Advantageous embodiments of the invention are
`illustrated in the draWings and described in more detail
`beloW. In the draWings:
`
`[0033] FIG. 1 shoWs a diagrammatic side vieW of a
`microlithography projection exposure machine having an
`assigned apparatus for determining the in?uencing of the
`state of polariZation by a projection objective by means of
`ellipsometric measurement,
`[0034] FIG. 2 shoWs an illustration of a microlithography
`projection exposure machine corresponding to FIG. 1, but
`having an apparatus variant for determining the in?uencing
`of the state of polariZation, Which includes a shearing
`interferometer unit,
`
`[0035] FIG. 3 shoWs a diagrammatic illustration for
`explaining tWo-beam interferometry in the Jones matrix
`calculus, as it forms a basis of the mode of operation of the
`apparatus in accordance With FIG. 2,
`
`[0036] FIG. 4 shoWs an illustration of a microlithography
`projection exposure machine corresponding to FIG. 2, but
`for an apparatus variant having additional polariZation
`analyser means on the exit side of the shearing interferom
`eter unit,
`
`[0037] FIG. 5 shoWs an illustration of a microlithography
`projection exposure machine corresponding to FIG. 2, but
`for an apparatus variant Which operates as a point-diffraction
`interferometer having additional polariZation analyser
`means,
`[0038] FIG. 6 shoWs a diagrammatic side vieW of a
`polariZation analyser arrangement Which can be used as
`polariZation detector means, for example in apparatuses of
`the type of FIGS. 1, 2, 4 and 5,
`
`[0039] FIG. 7 shoWs a side vieW corresponding to FIG. 6
`for a variant having an additional periodic structure for the
`purpose of measurement acquisition of the pupil distortion,
`
`[0040] FIG. 8 shoWs a side vieW corresponding to FIG. 7
`for a variant having tWo lenses,
`
`[0041] FIG. 9 shoWs a side vieW corresponding to FIG. 6
`for a variant Which contains a mirror element,
`
`[0042] FIG. 10 shoWs a side vieW corresponding to FIG.
`6 for a variant having a plurality of individual lambda/4
`polariZer elements Which are permanently arranged With
`directions of polariZation rotated relative to one another, and
`
`[0043] FIG. 11 shoWs a diagram of the angle of incidence
`as a function of the pupil for a typical optics of a polariZation
`analyser arrangement according to the type of FIGS. 6 to 10.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0044] FIG. 1 shoWs a diagram of the design of a microli
`thography projection exposure machine having an assigned
`apparatus for determining the in?uencing of the state of
`polariZation by the imaging part of the system. The projec
`
`Nikon Exhibit 1009 Page 10
`
`

`

`US 2004/0114150 A1
`
`Jun. 17, 2004
`
`tion exposure machine includes in the usual Way an illumi
`nating system 1 as that part of the system Which supplies the
`desired radiation, for example UV radiation in the Wave
`length region of about 248 nm or 193 nm, and a doWnstream
`projection objective 2 as imaging part of the system. The
`design, Which is so far conventional, is expanded by com
`ponents of an apparatus With the aid of Which the in?uenc
`ing, caused by the projection objective 2, of the state of
`polariZation of the optical radiation used is supplemented by
`a so-called numerical aperture (NA) measurement technol
`ogy With the aid of an ellipsometer function. This apparatus
`is speci?cally suitable for determining the phase-reduced
`Jones matrix in a spatially resolved fashion over the pupil
`range of the projection objective 2, in the case of Which an
`optical imaging system With a comparatively high aperture
`is involved.
`
`[0045] The apparatus includes betWeen the illuminating
`system 1 and projection objective 2 means for providing
`entrance-side radiation for the projection objective 2 With a
`de?ned entrance state of polariZation. These means include,
`one behind another in the beam path, a diffusing screen 3, a
`rotatable polariZer 4, a rotatable compensator 5 (optional), a
`spot lens and a so-called pinhole or perforated mask 7
`having one or more openings. Spatially incoherent radiation
`is provided to a suf?cient extent by the diffusing screen 3,
`Which is of a sufficiently strongly scattering design. The
`perforated mask 7 is arranged in the focal plane of the spot
`lens 6, Which is illuminated homogeneously to a very large
`extent and simultaneously forms the object plane of the
`projection objective 2. This yields a point light source,
`Which is incoherent spatially as far as possible, in the object
`plane. DoWnstream of the projection objective 2 is a micro
`scope objective 8 Whose focal plane coincides With the
`image plane of the projection objective 2 and has a numeri
`cal aperture Which is at least as large as that of the projection
`objective 2 under test. The microscope objective 8 thus
`images an object point in the plane of the perforated mask
`7 to in?nity, that is to say into a real parallel beam path. A
`sharp image of the intensity distribution of the parallel beam
`is produced on a detector element 10 by a suitable loW
`aperture relay optics 9, for example a 4f optics, the said
`detector element being, for example, a CCD chip or imaging
`camera.
`
`[0046] To this extent, the abovementioned components
`form an NA measurement apparatus With the aid of Which
`the transmission of the projection objective 2 can be deter
`mined in a spatially resolved fashion over the entire pupil
`range in conjunction With a knoWn, prescribed angle-depen
`dent emission of the spot lens/perforated mask unit 6, 7, and
`With a knoWn, prescribed angle-dependent transmission of
`the microscope/relay optics unit 8, 9. The emission distri
`bution of the illumination can be determined, for example,
`in advance by angularly variable scanning by means of a
`measuring diode suspended goniometrically. The micro
`scope unit can be calibrated by rear transillumination With
`the aid of a parallel beam of knoWn intensity distribution
`and, again, by scanning the focal aperture cone With a
`goniometric measuring apparatus. The scanning method
`With a goniometric measuring apparatus is certainly also
`possible per se for the testing, presently of interest, of the
`projection objective 2, but the advantage of the mode of
`procedure described here is that an apparatus thus calibrated
`
`can be used to measure many ?eld points of the projection
`objective 2 virtually simultaneously or in any case in a
`relatively short time.
`
`[0047] By adding suitable optical polariZation compo
`nents, this NA measuring apparatus reacquires an ellipsom
`eter function Which permits the phase-reduced Jones matrix
`for the projection objective 2 to be determined in a pupil
`resolved fashion. This purpose is served, ?rstly, by the
`rotatable polariZer 3 and the rotatable compensator 5 on the
`entrance or illuminating side of the projection objective 2
`and, secondly, by an exit-side rotatable compensator 11 and,
`doWnstream thereof, an exit-side polariZer 12 betWeen the
`relay optics 9 and the CCD detector 10. The calibration of
`the illuminating part 6, 7 and of the microscope unit 8 can
`be performed by goniometrically scanning the relevant
`aperture cone by means of a conventional ellipsometer unit.
`In this case, the associated parallel beam paths through the
`polariZer and compensator arrangement are prescribed as at
`least four linearly independently states of polariZation.
`
`[0048] Speci?cally, it is then possible to set consecutively
`on the illuminating side four different states of polariZation
`Which correspond to four linearly independent Stokes vec
`tors, and on the output side the resulting Stokes vectors of
`the radiation transmitted by the projection objective 2 can be
`measured. In accordance With knoWn relationships, the
`entrance-side and exit-side Stokes vectors yield the Muller
`matrix from Which, in turn, the phase-reduced Jones matrix
`can be derived, as is knoWn from the relevant literature.
`
`[0049] This evaluation is performed by an evaluation unit
`13, Which is shoWn only diagrammatically in FIG. 1
`coupled to the CCD detector 10 and is suitably designed for
`this purpose. The apparatus assigned to the projection expo
`sure machine With illuminating system 1 and projection
`objective 2 therefore permits a simultaneous tWo-dimen
`sional determination of the phase-reduced Jones matrix in a
`pupil-resolved fashion, that is to say the elements of the
`Jones matrix, and thus the polariZing property of the pro
`jection objective 2, are determined in a spatially resolved
`fashion over the pupil range of the high-aperture projection
`objective 2 as a function of the pupil coordinate.
`
`[0050] The in?uence of the projection objective 2 on the
`state of polariZation of the exposure radiation directed onto
`a Wafer can thereby be determined quickly and accurately. In
`the case of modern microlithographic projection objectives
`With a high numerical aperture, this in?uence is gaining in
`importance, for example because of birefringence effects in
`the calcium ?uoride lenses used for short Wavelengths, and
`because of polariZation effects oWing to de?ecting mirrors.
`The spatially resolved knoWledge of these in?uences of the
`projection objective on the state of polariZation of the
`radiation can then be used suitably for the purpose of
`obtaining a desired imaging/exposure behaviour of the pro
`jection exposure machine.
`
`[0051] FIG. 2 shoWs a variant of the arrangement of FIG.
`1, the same reference symbols being selected, for the sake of
`simplicity, for functionally identical elements, and it being
`possible to this extent to refer to the above description of the
`example of FIG. 1. In particular, the example of FIG. 2 is
`concerned With a microlithography projection exposure
`machine having an illuminating system 1 and projection
`objective 2 Whose polariZing property is under test With the
`
`Nikon Exhibit 1009 Page 11
`
`

`

`US 2004/0114150 A1
`
`Jun. 17, 2004
`
`aid of an assigned apparatus, the design between the illu
`minating system 1 and projection objective 2 corresponding
`to that of FIG. 1.
`[0052] As mentioned, the apparatus of FIG. 1 is used to
`determine the pupil-resolved Jones matrix in a phase-re
`duced fashion, that is to say up to a global phase term
`dependent on pupil location. The apparatus used in the
`exemplary embodiment of FIG. 2 is capable of determining
`this global phase term by means of a shearing interferometry
`measuring technique in conjunction With a de?ned entrance
`state of polariZation. Accordingly, this apparatus includes on
`the exit side of the projection objective 2 under test a
`shearing interferometer unit 14 to Which the CCD detector
`10 is connected. A suitably designed evaluation unit 13a is
`coupled to the latter.
`[0053] The shearing interferometer unit is of a conven
`tional design per se, for example as is described in the
`above-mentioned DE 101 09 929 A1 and in the prior
`German Patent Application 102 17 242.0, likeWise men
`tioned above, to Which reference can be made for further
`details. The required control and evaluation processes are
`implemented in the evaluation unit 13a, as is evident straight
`aWay to the person skilled in the art from the present
`description of the associated process steps. The basic tWo
`beam interferometry in the Jones matrix calculus is illus
`trated diagrammatically by Way of example in FIG. 3. This
`yields the exit-side radiation intensity for the superimposi
`tion of tWo ?elds Which are represented by an original Jones
`matrix T and a Jones matrix TA displaced by Ax, from the
`trace formation of a matrix product of the sum matrix T+TA
`by the entrance polariZation matrix Pin, and the hermite
`conjugate sum matrix (T+TQ+. If the original and the
`displaced Jones matrix T and TA, respectively, are knoWn up