111111
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`1111111111111111111111111111111111111111111111111111111111111
`US007295739B2
`
`c12) United States Patent
`Solarz
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,295,739 B2
`Nov. 13, 2007
`
`(54)
`
`COHERENT DUV ILLUMINATION FOR
`SEMICONDUCTOR WAFER INSPECTION
`
`(75)
`
`Inventor: Richard William Solarz, Danville, CA
`(US)
`
`6,845,204 B1 *
`6,944,382 B2 *
`7,006,221 B2 *
`2004/0258381 A1 *
`2005/0276556 A1 *
`
`112005 Broeng et a!. .............. 385/126
`.............. 385/123
`9/2005 Berkey et a!.
`................. 356/369
`2/2006 Wolf et a!.
`12/2004 Borrelli et al.
`. ............ 385/125
`12/2005 Williams et a!. ............ 385/123
`
`(73) Assignee: KLA-Tencor Technologies
`Corporation, Milpitas, CA (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 28 days.
`
`(21) Appl. No.: 111061,150
`
`(22) Filed:
`
`Feb. 18, 2005
`
`(65)
`
`Prior Publication Data
`
`US 2006/0083470 Al
`
`Apr. 20, 2006
`
`Related U.S. Application Data
`
`(60) Provisional application No. 60/620,814, filed on Oct.
`20, 2004.
`
`(51)
`
`Int. Cl.
`G02B 6102
`(2006.01)
`(52) U.S. Cl. ...................... 385/125; 385/122; 385/123;
`385/126; 359/285; 359/342; 359/334
`(58) Field of Classification Search ........ 385/125-126,
`385/123; 356/369; 372/3, 18; 362/551-582,
`362/608-634
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`111986 Chraplyvy ..................... 372/3
`H15 H *
`6,496,634 B1 * 12/2002 Levenson ................... 385/125
`6,822,978 B2 * 1112004 Kafka et al ................... 372/18
`
`OTHER PUBLICATIONS
`
`Benabid et a!. "Stimulated Raman Scattering in Hydrogen-Filled
`Hollow Core Photonic Crystal Fiber", Oct. 11, 2002, Science, vol.
`298. pp. 399-402.*
`F. Benabid, eta!., "Ultrahigh Efficiency Laser Wavelength Conver(cid:173)
`sion in a Gas-Filled Hollow Core Photonic Crystal Fiber by Pure
`Stimulated Rotational Raman Scattering in Molecular Hydrogen,"
`Physical Review Letters, vol. 93, No. 12, Sep. 17, 2004.
`
`(Continued)
`
`Primary Examiner-Brian Healy
`Assistant Examiner--Guy G Anderson
`(74) Attorney, Agent, or Firm-Smyrski Law Group, A P.C.
`
`(57)
`
`ABSTRACT
`
`An apparatus for inspecting a specimen, such as a semicon(cid:173)
`ductor wafer, is provided. The apparatus comprises a laser
`energy source, such as a deep ultraviolet (DUV) energy
`source and an optical fiber arrangement. The optical fiber
`arrangement comprises a core surrounded by a plurality of
`optical fibers structures used to frequency broaden energy
`received from the laser energy source into frequency broad(cid:173)
`ened radiation. The frequency broadened radiation is
`employed as an illumination source for inspecting the speci(cid:173)
`men. In one aspect, the apparatus comprises a central core
`and a plurality of structures generally surrounding the cen(cid:173)
`tral core, the plurality of fibers surround a hollow core fiber
`filled with a gas at high pressure, a tapered photonic fiber,
`and/or a spider web photonic crystalline fiber, configured to
`receive light energy and produce frequency broadened radia(cid:173)
`tion for inspecting the specimen.
`
`24 Claims, 4 Drawing Sheets
`
`250
`
`221
`
`I
`I
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`I
`I
`\
`
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`
`\
`
`\
`
`204
`
`' ' ' ' '--------
`
`~ 220
`
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`US 7,295,739 B2
`Page 2
`
`OTHER PUBLICATIONS
`
`F. Benabid, et al., "Stimulated Raman Scattering in Hydrogen-Filled
`Hollow-Core Photonic Crystal Fiber," Science, vol. 298, Oct. 11,
`2002, pp. 399-402.
`K. Saitoh, et al., "Leakage loss and group velocity dispersion in
`air-core photonic bandgap fibers," Optics Express, vol. 11, No. 23,
`3100, Nov. 17, 2003.
`J.C. Knight, et al., "Photonic Band Gap Guidance in Optical
`Fibers," SCIENCE, Nov. 20, 1998, vol. 282, pp. 1476-1478.
`M. Huebner, et al., "Fiber-Optic Systems in the UV-Region,"
`Biomedical Diagnostic, Guidance, and Surgical-Assist Systems II,
`Proceedings of SPIE vol. 3911 (2000), pp. 303-312.
`K.F. Klein, et a!., "UV-Fibers for Applications Below 200 NM,"
`Optical Fibers and Sensors for Medical Applications, Proceedings
`of SPIE vol. 4253 © 2001 SPIE, pp. 42-49.
`
`Ilko K. Ilev, et al., "Ultraviolet Broadband (190-450 nm) Nonlinear
`Frequency Conversion in Optical Fibers for Biomedical Use," US
`Food and Drug Administration, Center for Devices and Radiologi(cid:173)
`cal Health, HFZ-134, Rockville, MD 20857, © 2001 IEEE.
`S.O. Konorov, et a!., "Hollow-core photonic-crystal fibers opti(cid:173)
`mized for four-wave mixing and coherent anti-Stokes Raman scat(cid:173)
`tering,"Journal of Raman Spectroscopy, JRaman Spectrosc. 2003;
`34: 688-692.
`Liu Xiaoxia, et al., "Study of Silver Film Inside Silica Capillary,"
`International Symposium on Photonic Glass (ISPG 2002), SPIE vol.
`5061 © 2003 SPIE, pp. 254-258.
`
`* cited by examiner
`
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`U.S. Patent
`
`Nov. 13, 2007
`
`Sheet 1 of 4
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`US 7,295,739 B2
`
`1-:z w
`::::::li! w
`0 :z
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`w(cid:173)
`CD
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`u ..........
`1-
`0....
`0
`
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`U.S. Patent
`
`Nov. 13, 2007
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`Sheet 2 of 4
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`US 7,295,739 B2
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`00
`..... 0
`00 . . . . .
`0
`00
`0
`0
`0
`0
`
`FIG. 2A
`
`FIG. 28
`
`200
`
`210
`
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`U.S. Patent
`
`Nov. 13, 2007
`
`Sheet 3 of 4
`
`US 7,295,739 B2
`
`I
`I
`I
`I
`I
`I
`I
`I
`\
`\
`\
`\
`\
`\
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`\
`
`250
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`221
`
`202
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`\.
`\.
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`" " " .......
`
`....... ..._ ------
`
`FIG. 2C
`
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`U.S. Patent
`
`Nov. 13, 2007
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`Sheet 4 of 4
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`US 7,295,739 B2
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`US 7,295,739 B2
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`2
`ing on the application. Further, such an illuminator design
`that does not damage the wafer would be highly beneficial.
`It would be beneficial to provide a system overcoming
`these drawbacks present in previously known systems and
`provide an optical inspection system illumination design
`having improved functionality over devices exhibiting those
`negative aspects described herein.
`
`SUMMARY OF THE INVENTION
`
`1
`COHERENT DUV ILLUMINATION FOR
`SEMICONDUCTOR WAFER INSPECTION
`
`This application claims the benefit of U.S. Provisional
`Patent Application 60/620,814, filed Oct. 20, 2004, and
`entitled "Coherent DUV Sources for Semiconductor Wafer
`Inspection," inventors Yung-Ho Chuang, J. Joseph Arm(cid:173)
`strong, and Richard William Solarz.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`1. Field of the Invention
`The present invention relates generally to the field of
`illuminators, and more particularly to illuminators employed
`in the inspection of semiconductor wafers.
`2. Description of the Related Art
`Many optical systems provide an ability to inspect or
`image features on the surface of a specimen, such as
`inspecting defects on a semiconductor wafer or photomask.
`Certain advanced semiconductor defect inspection systems
`can detect defects on the order of 30 nm in size during a full
`inspection of a 300 mm diameter wafer.
`The demands of the semiconductor industry for wafer and
`photomask inspection systems exhibiting high throughput
`and improvements in resolution are ongoing. Successive
`generations of such inspection systems tend to achieve
`higher resolution by illuminating the wafer or reticle using
`light energy having increased wavelength and power. Highly
`detailed inspection can benefit from broadband illumination
`having high average power coherent radiation. Further,
`operation in the wavelength range of substantially 150 nm to
`500 urn can be beneficial in current wafer inspection
`arrangements.
`Previous illuminator designs tend to offer limited bright(cid:173)
`ness levels as measured in terms of watts/cm2 -str-um. Pre- 35
`vious designs for high power broadband illumination
`include mercury xenon lamps having power in the range of
`500 watts to 1000 watts, as well as brightness of approxi(cid:173)
`mately a few hundred W/cm2-str in the integrated wave(cid:173)
`length range of 150 nm to 500 nm. Proposals have been 40
`made to use cascaded arc lamp arrangements, thus providing
`brightness of roughly a few kw/cm2-str in the integrated
`wavelength range from 150 nm to 500 urn.
`Use of mercury xenon or cascaded arc lamps tends to be
`limited in that when used with very small sensor pixels and 45
`apertured illumination modes, they can be unable to be
`imaged with sufficient intensity to enable adequate operation
`of TDI sensors. Efficient light use in the presence of rela(cid:173)
`tively small pixel sizes requires focusing to match the
`radiation footprint to the sensor image area at the wafer 50
`plane. Mercury xenon and cascaded arc lamps tend to be
`limited in the average power at the wafer plane for small
`sensor pixels due to their limited brightness, particularly in
`imaging modes such as edge contrast, where as the name
`implies, the contrast of the edge of the wafer is examined 55
`and illumination and collection employ apertures to empha(cid:173)
`size edge scatter. Edge contrast modes and similar illumi(cid:173)
`nation modes tend to waste illumination radiation, and thus
`limit the average power available for inspection.
`In the semiconductor inspection enviroument, an illumi- 60
`nator or illuminating arrangement transmitting light with a
`high average power and brightness may provide benefits
`over previous types of illuminators. Such an illuminating
`arrangement operating at sufficient average power and
`brightness levels that can successfully operate in the pres- 65
`ence of TDI sensors and using an edge contrast mode may
`be preferable to other previous types of illuminators depend-
`
`According to one aspect of the present design, there is
`provided an apparatus for inspecting a specimen, such as a
`semiconductor wafer. The apparatus comprises a laser
`energy source and an optical fiber arrangement. The optical
`15 fiber arrangement comprises a core surrounded by a plurality
`of engineered features used to frequency broaden energy
`received from the laser energy source into frequency broad(cid:173)
`ened radiation. The frequency broadened high brightness or
`high spectral brightness radiation is employed as an illumi-
`20 nation source for inspecting the specimen.
`According to another aspect of the present design, there is
`provided an apparatus comprising a central core and a
`plurality of engineered features generally surrounding the
`central core, a tapered photonic fiber, and/or a spider web
`25 photonic crystalline fiber, configured to receive light energy
`and produce frequency broadened radiation for inspecting
`the specimen.
`These and other advantages of the present invention will
`become apparent to those skilled in the art from the follow-
`30 ing detailed description of the invention and the accompa(cid:173)
`nying drawings.
`
`DESCRIPTION OF THE DRAWINGS
`
`The present invention is illustrated by way of example,
`and not by way of limitation, in the figures of the accom(cid:173)
`panying drawings in which:
`FIG. 1 illustrates a general conceptual arrangement for the
`present design;
`FIG. 2A shows a sample solid core photonic crystalline
`fiber end view;
`FIG. 2B is an end view of a solid core cobweb or spider
`web fiber;
`FIG. 2C illustrates a more detailed hollow core fiber
`composed of a hollow core surrounded by a matrix of
`relatively fine silica webs, sometimes referred to as kagome'
`lattices; and
`FIG. 3 represents optical fiber having high pressure ves(cid:173)
`sels positioned on either end of the optical fiber.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`According to the present invention, there is provided a
`broadband illuminator transmitting high average power
`coherent radiation in the range of 150 nm to 500 nm, or
`portions thereof, for purposes of inspecting a semiconductor
`wafer. The present design may offer improvements over
`previously known broadband illumination designs.
`The present design employs optical fibers to frequency
`broaden the output of an input laser beam and uses fre(cid:173)
`quency broadened radiation as an illumination source in a
`brightfield inspection tool. FIG. 1 illustrates a general con(cid:173)
`ceptual arrangement for the present design. From FIG. 1,
`illuminator 101 may comprise a laser, such as a laser
`operating in the deep ultraviolet (DUV) range, where the
`illuminator provides light energy to optical fiber arrange-
`
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`US 7,295,739 B2
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`3
`ment 102. Light passes through optical fiber arrangement
`102 to optional optical arrangement 103 and to the surface
`of the specimen or semiconductor wafer 104.
`The illuminator 101 may be a mode locked or ultrafast
`UV pump laser operating at, for example, wavelengths of
`255 nm and/or 266 nm, or illuminator 101 may comprise a
`cw (continuous wave) laser operating at, for example, wave(cid:173)
`lengths of 266 nm or shorter. The optical fiber used in optical
`fiber arrangement 102 may include a hollow core fiber, a
`tapered photonic fiber, or a spider web photonic crystalline 10
`fiber. The optical fiber employed is used in a frequency
`conversion process. The result from the optical fiber
`arrangement 102 is an ultrawide band DUV light transmis(cid:173)
`sion, with sample DUV spectra ranging from 450 nm to 200
`nm in either a continuum or a series of Raman lines 15
`contained within the same region.
`Various fiber constructions may be employed in the
`optical fiber arrangement. FIG. 2A shows a sample solid
`core photonic crystalline fiber end view 200. FIG. 2B
`illustrates an end view of a solid core cobweb or spider web
`fiber 210. FIG. 2C illustrates a more detailed hollow core
`fiber 220 composed of a hollow core or core region 250
`surrounded by a matrix of relatively fine silica webs, some(cid:173)
`times referred to as kagome' lattices, where the lattice is
`surrounded by a solid structure. The hollow core fiber 220 is
`typically composed of two or more regions. Core region 250
`comprises a typically hollow core 221 of diameter a. Outside
`core region 250 is region b 202, which delineates or defines
`a collection of annularly distributed circular fiber elements
`such as element 222. Outside region b 202 is region c 203,
`which defines a further collection of distributed circular fiber
`elements such as element 223. The number of armular circles
`and annularly distributed circular fiber elements may repeat
`or include further versions, including as many as 20 or more
`such regions, with the final region being the solid region 204
`of collective mean diameter d. The term "string" may be
`employed here to describe the collection of similarly sized
`circles in a region. In the embodiment shown, all circles
`annularly distributed around region b 202, such as element
`202, represent a string of fibers of the same diameter. The 40
`regions shown are composed of one or more strings arranged
`around the previous inner region.
`While circles are shown in FIG. 2C, it is to be understood
`that near circular, or oval, or oddly shaped fibers may be
`employed in the fiber design. Generally any fiber and core 45
`shapes may be employed, and the shapes depicted in FIG.
`2C are not intended to be limiting in that regard.
`Each region may be defined using two parameters, A and
`d, where A is the center-to-center spacing of each circle in
`the string and d is the diameter of each hole or fiber in each 50
`string. The diameters of different strings may have similar
`sizes, or outer strings may have greater diameters than inner
`strings. In one embodiment, the hollow core fiber may have
`a ratio of d/A of greater than 0.7 in region b 202. In another
`embodiment, the ratio of d/A is in the range of0.95 or more 55
`in region b 202. Other regions, such as region c 203 and
`higher, may have similar ratios. In one embodiment, the
`fibers may have a spacing A in the range of approximately
`0.1 microns to approximately 0.5 microns for region b 202.
`The fibers such as element 221, element 222, and/or element 60
`223, may be constructed of glass, water and/or hydroxyl
`containing glass, ceramics, or other materials used to fab(cid:173)
`ricate fibers for the transmission of optical radiation. The
`fiber can have varying length, including from less than 1 em
`to more than tens or hundreds of kilometers.
`The construction and operation of strings of fibers is
`discussed in detail in various publications, including but not
`
`4
`limited to K. Saitoh and M. Koshiba, "Leakage loss and
`group velocity dispersion in air-core photonic bandgap
`fibers," Optics Express 3100, Vol. 11, No. 23, 17 Nov. 2003;
`F. Benabid et a!., "Stimulated Raman Scattering in Hydro(cid:173)
`gen-Filled Hollow-Core Photonic Crystal Fiber," Science,
`Vol. 298, pp. 399-402, 11 Oct. 2002; F. Benabid et a!.,
`"Ultrahigh Efficiency Laser Wavelength Conversion in a
`Gas-Filled Hollow Core Photonic Crystal Fiber by Pure
`Stimulated Rotational Raman Scattering in Molecular
`Hydrogen," Physical Review Letters, Vol. 93, No. 12, pp.
`123903-1 to 123903-4, 17 Sep. 2004. These references
`disclose the general construction of optical fibers with
`silica-air microstructures called photonic crystal fibers, or
`PCFs. One type of fiber guides light between a solid core and
`a cladding region containing multiple air holes. The second
`uses a perfectly periodic structure exhibiting a photonic
`bandgap effect at the operating wavelength to guide light in
`a low index core region. Each type of fiber guide may take
`different forms and use different fiber dimensions and vary-
`20 ing open or empty regions, wherein leakage losses may be
`reduced and dispersion properties altered depending on the
`air hole diameter and pitch of the air holes and or fibers
`employed. These references further discuss stimulated
`Raman scattering (SRS) using low-loss fiber, wherein stimu-
`25 lated Raman scattering may occur, thereby permitting pure
`conversion, in one example, to the rotational Stokes fre(cid:173)
`quency in a single pass configuration pnmped by a micro(cid:173)
`chip laser. The 2002 Benabid Science article discloses an
`experimental setup showing various beamsplitters, objec-
`30 tives, gas cells, bandpass color filters, a fast photodetector
`and an optical spectrum analyzer in addition to hollow core
`photonic crystal fiber (HC-PCF) employed to achieve effi(cid:173)
`cient SRS in hydrogen gas. The HC-PCF employed in the
`Benabid 2002 reference has a core diameter of 15 microme-
`35 ters, filled with hydrogen gas and pumped with a Q-switched
`single mode frequency doubled Nd:YAG (neodymium/yt(cid:173)
`trium alnminum garnet) laser operating at a wavelength of
`532 nm with a repetition rate of 20 Hz and a pulse duration
`of 6 ns.
`The term Raman or Raman mode refers to a form of
`vibrational or rotational molecular spectroscopy based on an
`inelastic light scattering process. Raman spectroscopy scat(cid:173)
`ters a laser photon or photon beam using a sample molecule.
`The result is a gain or loss of energy, resulting in a change
`of energy or wavelength for the irradiating photon or photon
`beam. The result is a gain or loss of energy typified by the
`rotational or vibrational structure in the molecule. In other
`words, the Raman effect arises when a photon is incident on
`a molecule and interacts with the polarizability of the
`molecule. The difference in energy between the incident
`photon and the Raman scattered photon is equal to the
`energy of a vibration of the scattering molecule. A plot of
`intensity of scattered light versus energy difference is called
`a Raman spectrum. Raman mode illumination techniques
`may be employed in the current design, typically using a gas
`or gaseous mixture as a medinm to change energy and/or
`wavelength of the illnminating or transmitted photon or
`photon beam.
`The present design employs a different laser, operating at
`a different frequency and in the deep ultraviolet (DUV)
`range and is used in the semiconductor wafer process.
`Photonic crystalline fiber may be employed, where the
`photonic crystalline fiber may be low dispersion in the pnmp
`radiation band and in regions extending up to 100 nm from
`65 either side of the pnmp band. The present design uses optical
`fibers, such as gas filled optical fibers, or photonic crystal(cid:173)
`line fibers to frequency broaden the output of an input laser
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`5
`beam between approximately 250 and 400 nm or, for
`example, between 170 and 270 nm. The frequency broad(cid:173)
`ened radiation may subsequently be used as an illumination
`source in a bright field semiconductor wafer inspection tool.
`When the design uses a hollow core optical fiber as optical
`fiber 102, the hollow core may be filled with gas at a
`relatively high pressure. The relatively high pressure may be
`within a range between a fraction of an atmosphere or
`fraction of one bar to many tens of atmospheres or many tens
`of bars. Such a high pressure gas may be a type of gas
`possessing active high frequency Raman modes, or alter(cid:173)
`nately a mixture of such gases. The high pressure gas may
`be a gas such as hydrogen, deuterium, methane, carbon
`dioxide, and so forth, and/or other Raman active gases.
`Other gases and gas mixtures may be employed. Raman
`modes to be either vibrational, rotational, or both vibrational
`and rotational. The high pressure gas used in said the hollow
`core fiber may be introduced to the fiber by a high pressure
`vessel positioned on either side of the fiber, such as at the
`fiber entrance and exit. FIG. 3 illustrates a fiber 301 includ(cid:173)
`ing high pressure vessels 302 and 303 positioned on either
`end of the fiber, as well as an entrance window 304 at the
`receiving end of the fiber for passage of the initial light beam
`into the end of the fiber from the ambient pressure of the
`atmosphere in the operating area. The high pressure vessel
`303 may include an exit window 305 for passage of the
`frequency broadened laser beam from the exit of the fiber
`301. The entrance window 304 and exit window 305 may
`either be blank substrates without coatings or antireflection
`coated at either the entrance window 304 for the initial laser
`beam and/or at the exit window 305 for the broadened laser
`exit radiation.
`The initial laser beam may be within an initial wavelength
`range in the deep ultraviolet range, such as from approxi(cid:173)
`mately 280 nm to 180 nm. The initial laser beam may be
`either continuous wave (cw), modelocked, q-switched or
`gain switched. The initial laser beam may be either polarized
`or unpolarized. Output broad band radiation from, for
`example, exit window 305 may have a total bandwidth in the
`range of approximately 40 nm or more. Typically such 40
`radiation may be between approximately 10 nm and 80 nm,
`where bandwidth is defined as the half power points of the
`longest and shortest wavelength features present. Such
`wavelength features may be known Raman bands, vibra(cid:173)
`tional or rotational, and the individual shortest and longest 45
`bands may include at least 5 percent of the total energy
`within the bandwidth. Alternately, the wavelength feature
`may not include a Raman band but rather may comprise the
`initial laser wavelength transmitted.
`Regarding dimensions of the fiber hollow core, such as 50
`hollow core 250, such a core may have a diameter enabling
`propagation of only a lowest fiber mode, or propagation of
`only a few low order modes. The hollow core, such as
`hollow core 250, may have a diameter consistent with
`propagating a beam having an M -squared value at the output 55
`is less than 50. M-squared represents the ratio of the laser
`beam's multimode diameter-divergence product to the ideal
`diffraction limited beam diameter-divergence product. A
`perfect beam will have an M-squared value of 1.0, while a
`poor quality beam may have an M-squared value of several 60
`hundred.
`The initial laser, such as illuminator 101, may be either
`diode pumped solid state laser, fundamental or harmonically
`upconverted, a frequency upconverted argon ion or krypton
`ion laser, a harmonically upconverted Er:fiber laser, a fre(cid:173)
`quency upconverted diode pumped atomic vapor laser, a
`harmonically converted Ti:S laser, an excimer laser, or any
`
`6
`other type of laser generally having a fundamental or
`upconverted wavelength in the range of between approxi(cid:173)
`mately 180 and 280 nm. Radiation may be obtained by
`delivering pump radiation of, for example, on the order of
`355 nm in wavelength, but wavelengths in the general range
`of between 250 and 400 nm. The pump source may provide
`from approximately 100 mw to 8 watts or higher, where the
`conversion efficiency of the pump radiation may be in the
`range of approximately 1 percent to approximately 70
`10 percent into broadband radiation. While photonic crystalline
`fiber has been disclosed as one embodiment, other bulk
`materials or waveguides may be employed as transmission
`media. If photonic crystalline fiber is employed, the fiber
`may or may not be constructed from UV resistant materials
`15 beyond those disclosed above.
`As a result, broadband radiation produces a higher bright(cid:173)
`ness format and can minimize the risk of light starvation.
`Radiation is coherent or of high partial coherence and thus
`has orders of magnitude greater brightness than previous
`20 broadband designs from sources such as arc lamps or
`cascade arcs. Radiation is developed at potentially signifi(cid:173)
`cantly shorter wavelengths
`The design presented herein and the specific aspects
`illustrated are meant not to be limiting, but may include
`25 alternate components while still incorporating the teachings
`and benefits of the invention, namely a specimen or semi(cid:173)
`conductor wafer inspection device employing light energy in
`the DUV spectrum via a photonic crystalline fiber or other
`fiber medium, arranged using a hollow core surrounded by
`30 strings of holes. While the invention has thus been described
`in connection with specific embodiments thereof, it will be
`understood that the invention is capable of further modifi(cid:173)
`cations. This application is intended to cover any variations,
`uses or adaptations of the invention following, in general,
`35 the principles of the invention, and including such depar(cid:173)
`tures from the present disclosure as come within known and
`customary practice within the art to which the invention
`pertains.
`
`What is claimed is:
`1. An apparatus for inspecting a specimen, comprising:
`a deep ultraviolet (DUV) laser energy source;
`an optical fiber arrangement comprising a core sur(cid:173)
`rounded by a first plurality of large substantially annu(cid:173)
`larly arranged optical fibers having substantially simi(cid:173)
`lar large cross sectional dimensions, surrounded by a
`second plurality of smaller optical structures having
`substantially similar small cross sectional dimensions,
`said first plurality of large substantially annularly
`arranged optical fibers and second plurality of small
`optical structures used to frequency broaden energy
`received from the laser energy source into frequency
`broadened DUV radiation;
`wherein the frequency broadened DUV radiation is
`employed as an illumination source for inspecting the
`specimen.
`2. The apparatus of claim 1, wherein the plurality of
`optical fibers-comprise at least one from a group compris-
`ing:
`a hollow core fiber;
`a tapered photonic fiber;
`a spider web photonic crystalline fiber; and
`a kagome' type hollow core photonic crystalline fiber.
`3. The apparatus of claim 2, wherein the hollow core fiber
`65 is composed of a hollow core surrounded by a matrix of fine
`silica webs, sometimes called kagome' lattices, wherein said
`fine silica webs are surrounded by a solid structure.
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`Energetiq Ex. 2073, page 9 - IPR2015-01277
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`US 7,295,739 B2
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`4. The apparatus of claim 2, wherein the hollow core fiber
`is filled with relatively high pressure gas.
`5. The apparatus of claim 1, wherein the first plurality of
`large substantially annularly arranged optical fibers com(cid:173)
`prise a collection of annularly distributed substantially cir(cid:173)
`cular shapes comprising fewer fibers than the second plu(cid:173)
`rality of optical fibers.
`6. The apparatus of claim 5, wherein the first plurality of
`large substantially annularly arranged optical fibers and
`second plurality of smaller optical structures further com- 10
`prise regions composed of one or more strings of concentric
`circular fibers, wherein each region comprises two defined
`parameters A and d where A is a center to center spacing of
`each circle in the string and d is the diameter of the hole in
`each string, wherein at least one region has a d/ A ratio of
`greater than approximately 0.7.
`7. The apparatus of claim 1, wherein said optical fibers
`comprise at least one from a group comprising glass, low
`water, hydroxyl containing glass, and ceramics.
`8. The apparatus of claim 1, wherein said DUV laser 20
`energy source comprises at least one from a group compris(cid:173)
`ing:
`a diode pumped solid state laser (fundamental);
`a diode pumped solid state laser (harmonically upcon-
`verted);
`a frequency upconverted argon ion laser;
`a frequency upconverted krypton ion laser;
`a harmonically upconverted Er:fiber laser;
`a frequency upconverted diode pumped atomic vapor
`laser;
`a harmonically converted Ti:S laser;
`an excimer laser;
`a first DUV laser whose fundamental wavelength lies
`between 180 and 280 urn; and
`a second DUV laser whose upconverted wavelength lies 35
`between 180 and 280 urn.
`9. An apparatus for broadening the frequency of deep
`ultraviolet (DUV) energy used for inspecting a specimen,
`comprising:
`a central core; and
`a plurality of substantially circular structures generally
`surrounding the central core, said plurality of substan(cid:173)
`tially circular structures comprising an inner group of
`large diameter, substantially annularly distributed
`fibers and an outer group of small diameter fibers,
`wherein the plurality of substantially circular structures
`comprise at least one from a group comprising:
`a hollow core fiber;
`a tapered photonic fiber;
`a spider web photonic crystalline fiber; and
`a kagome' type hollow core photonic crystalline fiber;
`wherein said plurality of fibers are configured to receive
`DUV light energy and produce frequency broadened
`DUV radiation for inspecting the specimen.
`10. The apparatus of claim 9, wherein the hollow core
`fiber is composed of a hollow core surrounded by a matrix
`of fine silica webs, sometimes called kagome' lattices,
`wherein said fine silica webs are surrounded by a solid
`structure.
`11. The apparatus of claim 9, wherein the hollow core
`fiber is filled with relatively high pressure gas.
`12. The apparatus of claim 9, wherein the inner group of
`large diameter, substantially annularly distributed fibers
`comprise a collection of annularly distributed circles of a 65
`predetermined collective diameter comprising predeter(cid:173)
`mined individual substantially circular large fiber diameters.
`
`8
`13. The apparatus of claim 12, wherein the outer group of
`small diameter fibers define a first region and comprise
`strings of concentric circles forming a second region
`arranged around the inner group of large diameter, substan(cid:173)
`tially annularly distributed fibers, wherein each region com(cid:173)
`prises two defined parameters A and d where A is a center
`to center spacing of each circle in the string and d is the
`diameter of the hole in each string, wherein at least one
`region has ad/A ratio of greater than approximately 0.7.
`14. The apparatus of claim 9, wherein said plurality of
`fibers comprise at least one from a group comprising glass,
`low water, hydroxyl containing glass, and ceramics.
`15. The apparatus of claim 11, wherein the relatively high
`pressure gas comprises at least one gas possessing active
`15 high frequency Raman modes.
`16. The apparatus of claim 15, wherein the high frequency
`Raman modes comprise at least one from a group compris(cid:173)
`ing vibrational Raman modes and rotational Raman modes.
`17. A broadband inspection device, comprising:
`a deep ultraviolet (DUV) light energy source; and
`an optical fiber arrangement comprising a core sur(cid:173)
`rounded by a plurality of optical fibers, said plurality of
`optical fibers comprising an inner group of large,
`substantially annularly distributed fibers and an outer
`group of small fibers, said plurality of optical fibers
`used to frequency broaden DUV energy received from
`the DUV light energy source into frequency broadened
`DUV radia