WO2018034908A1 - System and method for generating multi-channel tunable illumination from a broadband source - Google Patents

System and method for generating multi-channel tunable illumination from a broadband source Download PDF

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Publication number
WO2018034908A1
WO2018034908A1 PCT/US2017/046084 US2017046084W WO2018034908A1 WO 2018034908 A1 WO2018034908 A1 WO 2018034908A1 US 2017046084 W US2017046084 W US 2017046084W WO 2018034908 A1 WO2018034908 A1 WO 2018034908A1
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WO
WIPO (PCT)
Prior art keywords
channel
filter
spectral
illumination
filtering
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
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PCT/US2017/046084
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English (en)
French (fr)
Inventor
Andy HILL (Andrew)
Amnon Manassen
Ohad Bachar
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KLA Corp
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KLA Tencor Corp
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Publication date
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Priority to SG11201900804WA priority Critical patent/SG11201900804WA/en
Priority to CN201780050429.3A priority patent/CN109564157B/zh
Priority to KR1020197007076A priority patent/KR102265871B1/ko
Priority to JP2019508928A priority patent/JP6782834B2/ja
Publication of WO2018034908A1 publication Critical patent/WO2018034908A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/255—Details, e.g. use of specially adapted sources, lighting or optical systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
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    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
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    • G—PHYSICS
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    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J2001/4247—Photometry, e.g. photographic exposure meter using electric radiation detectors for testing lamps or other light sources
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    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
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    • G01J2003/069—Complex motion, e.g. rotation of grating and correcting translation
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    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/12—Generating the spectrum; Monochromators
    • G01J2003/1213—Filters in general, e.g. dichroic, band
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    • G01J3/12—Generating the spectrum; Monochromators
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    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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Definitions

  • the present disclosure relates generally to broadband illumination sources, and, more particularly, to generating multiple illumination spectra from a single broadband illumination source.
  • Tunable light sources may provide illumination tuned to one or more select wavelengths within a given spectral range.
  • typical tunable light sources may suffer from a limited capacity to independently and precisely modify the total intensity, spectral power, and/or polarization of multiple spectral regions of a tuned illumination beam. Therefore, it would be desirable to provide a system and method for curing defects such as those of the identified above.
  • the system includes an illumination source to generate an illumination beam.
  • the system includes a multi-channel spectral filter.
  • the multi-channel spectral filter includes two or more filtering channels including two or more channel beam paths.
  • the two or more filtering channels filter illumination propagating along the two or more channel beam paths based on two or more spectral transmissivity distributions.
  • the multi-channel spectral filter includes a channel selector to direct at least a portion of the illumination beam into at least one selected filtering channel of the two or more filtering channels to filter the at least a portion of the illumination beam based on a selected spectral transmissivity distribution of the two or more spectral transmissivity distributions.
  • the multichannel spectral filter includes at least one beam combiner to combine illumination from the two or more filtering channels to a single optical column.
  • the system includes a focusing element to direct illumination from the single optical column to a sample.
  • the system includes at least one detector to capture radiation from the sample.
  • a multi-channel spectral filter is disclosed, in accordance with one or more illustrative embodiments of the present disclosure.
  • the multi-channel spectral filter includes two or more filtering channels including two or more channel beam paths.
  • the two or more filtering channels filter illumination propagating along the two or more channel beam paths based on two or more spectral transmissivity distributions.
  • the multi-channel spectral filter includes a channel selector to direct at least a portion of an illumination beam into at least one selected filtering channel of the two or more filtering channels to filter the at least a portion of the illumination beam based on a selected spectral transmissivity distribution of the two or more spectral transmissivity distributions.
  • a multi-channel illumination source is disclosed, in accordance with one or more illustrative embodiments of the present disclosure.
  • the multi-channel illumination source includes a broadband illumination source configured to generate an illumination beam.
  • the multi-channel illumination source includes a multi-channel spectral filter.
  • the multi-channel spectral filter includes two or more filtering channels including two or more channel beam paths.
  • the two or more filtering channels filter illumination propagating along the two or more channel beam paths based on two or more spectral transmissivity distributions.
  • the multi-channel spectral filter includes a channel selector configured to direct at least a portion of the illumination beam into at least one selected filtering channel of the two or more filtering channels to filter the at least a portion of the illumination beam based on a selected spectral transmissivity distribution of the two or more spectral transmissivity distributions.
  • FIG. 1A is a conceptual view of a multi-channel illumination source including a multichannel tunable spectral filter and a broadband illumination source having a broad spectrum, in accordance with one or more embodiments of the present disclosure.
  • FIG. 1 B is a conceptual view of a multi-channel tunable spectral filter in which channel beams are further split into multiple output illumination beams, in accordance with one or more embodiments of the present disclosure.
  • FIG. 1 C is a conceptual view of a multi-channel tunable spectral filter having two channel beams in which the two channels are combined into a combined output illumination beam, in accordance with one or more embodiments of the present disclosure.
  • FIG. 1 D is a conceptual view of a multi-channel tunable spectral filter in which a combined output illumination beam is further split into multiple output illumination beams, in accordance with one or more embodiments of the present disclosure.
  • FIG. 2 is a conceptual view of a multi-channel illumination source illustrating an expanded view of an intensity modulator, in accordance with one or more embodiments of the present disclosure.
  • FIG. 3A is a conceptual view of a multi-channel illumination source illustrating a tunable filter including filter changers, in accordance with one or more embodiments of the present disclosure.
  • FIG. 3B is a diagram illustrating the spectral transmissivity of a first spectral filter, in accordance with one or more embodiments of the present disclosure.
  • FIG. 3C is a diagram illustrating the spectral transmissivity of a second spectral filter, in accordance with one or more embodiments of the present disclosure.
  • FIG. 3D is a diagram illustrating the spectral transmissivity of the first spectral filter of
  • FIG. 3B cascaded with the second spectral filter of FIG. 3C, in accordance with one or more embodiments of the present disclosure.
  • FIG. 4 is a schematic diagram of three filter changers containing spectral filters suitable for spectrally filtering a channel beam to include a narrow-band spectral profile that is tunable within three spectral windows, in accordance with one or more embodiments of the present disclosure.
  • FIG. 5 is a conceptual view of a multi-channel illumination source illustrating a tunable filter including angularly-tunable spectral filters, in accordance with one or more embodiments of the present disclosure.
  • FIG. 6 is a conceptual view of a multi-channel illumination source illustrating a tunable filter including linearly-tunable spectral filters, in accordance with one or more embodiments of the present disclosure.
  • FIG. 7 is a conceptual view of a tunable filter including a double-grating monochromator with a spatial filter, in accordance with one or more embodiments of the present disclosure.
  • FIG. 8 is a conceptual view of a metrology system including a multi-channel illumination source, in accordance with one or more embodiments of the present disclosure.
  • FIG. 9 is a conceptual view of a multi-beam metrology system including a multi-channel illumination source with a multi-channel tunable spectral filter, in accordance with one or more embodiments of the present disclosure.
  • Embodiments of the present disclosure are directed to a multi-channel tunable spectral filter.
  • a multichannel tunable spectral filter may separate an input illumination beam into one or more channels such that each channel beam may have an independently modifiable spectral distribution, total intensity, and/or polarization.
  • a multi-channel tunable spectral filter may tune the spectrum of an incident beam of illumination by directing portions of the illumination beam through one or more filtering channels.
  • Additional embodiments are directed to a multi-channel tunable filter in which channel beams (e.g.
  • Additional embodiments are directed to a multichannel tunable filter in which two or more channel beams are combined to form a combined output illumination beam. Additional embodiments are directed to a multichannel illumination source including a broadband illumination source and a multichannel tunable spectral filter. Further embodiments are directed to a metrology system including a multi-channel illumination source.
  • a typical spectral filter may modify the spectrum of incident illumination (e.g. electromagnetic radiation, or the like) by reducing the spectral power of select wavelengths relative to others.
  • a spectral transmittance of a spectral filter may describe the transmittance (e.g. from 0% to 100%, 0 to 1 , or the like) of illumination as a function of wavelength. It is noted that transmittance may refer to illumination passed by the filter through transmission and/or reflection.
  • a typical spectral filter may include, but is not limited to, one or more wavelength-dependent filters, one or more spectral filters or one or more spatial filters located in a lens Fourier plane in which the spectral content is spatially distributed.
  • a tunable spectral filter may selectively modify the spatial transmittance as a function of wavelength such that the spectrum of incident illumination may be dynamically tuned.
  • a tunable spectral filter may selectively modify the spectral power (e.g. the power per unit wavelength) of illumination.
  • a tunable spectral filter may modify the spectral transmittance by a variety of methods such as, but not limited to, replacing a spectral filter having a fixed spectral transmissivity with another (e.g. via a filter changer, or the like), adjusting the position and/or angle of a spectral filter having an orientation-dependent spectral transmissivity, or translating one or more spatial filtering elements.
  • a tuning speed at which the spectral transmissivity of a tunable spectral filter may be modified may be highly dependent on the components of the tunable filter. In many cases, the switching speed may be dependent on the speed at which one or more elements may be physically translated.
  • Some embodiments of the present disclosure are directed to a multi-channel tunable spectral filter having multiple spectral filtering channels and a channel selector.
  • the spectral filtering channels may have differing spectral transmissivities that may be generated based on any spectral filtering technique known in the art.
  • a spectrum of an incident illumination beam may be tuned by dynamically selecting which filtering channel or channels portions of the illumination beam propagate through. Accordingly, a switching speed at which a channel selector may selectively direct portions of the illumination beam between channels may be faster than a tuning speed of a single tunable spectral filter.
  • a multi-channel tunable spectral filter described in accordance with embodiments of the present disclosure may provide one or more channel beams having different spectral content.
  • each filtering channel provides a separate channel beam as an output beam from the multi-channel tunable spectral filter.
  • the channel beams from multiple spectral channels are combined into a combined output beam.
  • a single-output multi-channel tunable spectral filter having multiple filtering channels with different spectral transmissivities may, but is not required to, dynamically tune the spectrum of an illumination beam by selectively switching the full power of the illumination beam between the multiple filtering channels.
  • Additional embodiments of the present disclosure are directed to a multichannel tunable spectral filter in which the spectral transmissivity of the filtering channels may be tuned.
  • a channel including a tunable band-pass filter may, but is not required to, dynamically modify the central wavelength of passed illumination, a low-pass cutoff wavelength, a high-pass cutoff wavelength, a spectral bandwidth, a sharpness of a transition between passed wavelengths and filtered wavelengths, or the like. It is noted that the switching time associated with distributing illumination between filtering channels may be faster than the tuning time of a filtering channel.
  • a multi-channel tunable spectral filter with independently tunable filtering channels may provide a flexible platform for rapid switching between different spectral transmissivities.
  • a multi-channel tunable spectral filter may direct illumination from an illumination beam through one or more filtering channels while simultaneously modifying the spectral transmissivity of one or more additional tuning channels. Accordingly, the multi-channel tunable spectral filter may subsequently direct illumination from the illumination beam to the one or more additional filtering channels without a time delay associated with tuning a particular filtering channel.
  • a multi-channel tunable spectral filter may enable rapid tuning of the spectrum of an incident illumination beam using any spectral tuning method within each channel (e.g. fixed spectral transmissivity in filtering channels, relatively slowly tunable spectral transmissivity of filtering channels, or the like).
  • each channel of a multi-channel tunable spectral filter may provide, but is not required to provide, rapid modification the spectral content of filtered illumination, a stable spectrum of filtered illumination, minimal loss of spectral power within a desired spectral range for passed illumination, maximal attenuation of spectral power within an undesired spectral range for rejected illumination, a sharp transition between passed wavelengths and rejected wavelengths of illumination, a high tunable spectral resolution (e.g. an ability to selectively modify the spectral power of a narrow wavelength range, or the like), and/or a minimal perturbation of the phase distribution of the filtered illumination.
  • a high tunable spectral resolution e.g. an ability to selectively modify the spectral power of a narrow wavelength range, or the like
  • a multi-channel illumination source including a multi-channel tunable spectral filter may provide one or more beams of illumination with independently tuned spectral content (e.g. with a tunable spectral bandwidth of illumination, the central wavelength of the pass-band, or the like) to be directed to a sample.
  • a metrology system including a multichannel illumination source with independent spectral control for each channel may illuminate a sample with selectively controlled spectra over a broad continuous range of wavelengths.
  • the multi-channel illumination source may illuminate the sample with illumination from each channel simultaneously or sequentially.
  • the multi-channel illumination source may illuminate different portions of a sample (e.g. different cells of a metrology target, or the like) with different channels of illumination.
  • a multi-channel illumination source may enable optimization of multiple illumination profiles (e.g. multiple spectral profiles) for different cells of a metrology target.
  • FIG. 1A is a conceptual view of a multi-channel illumination source 100 including a multi-channel tunable spectral filter 101 and a broadband illumination source 102 having a broad spectrum (e.g. a range of wavelengths of illumination), in accordance with one or more embodiments of the present disclosure.
  • the broadband illumination source 102 generates an illumination beam 104.
  • the broadband illumination source 102 may include any type of illumination source suitable for providing an illumination beam 104 having a large range of wavelengths.
  • the broadband illumination source 102 is a laser source.
  • the broadband illumination source 102 may include, but is not limited to, a broadband laser source, a supercontinuum laser source, a white light laser source, or the like.
  • the broadband illumination source 102 may provide an illumination beam 104 having high coherence (e.g. high spatial coherence and/or temporal coherence).
  • the broadband illumination source 102 includes a laser-sustained plasma (LSP) source.
  • the broadband illumination source 102 may include, but is not limited to, a LSP lamp, a LSP bulb, or a LSP chamber suitable for containing one or more elements that, when excited by a laser source into a plasma state, may emit broadband illumination.
  • the broadband illumination source 102 includes a lamp source.
  • the broadband illumination source 102 may include, but is not limited to, an arc lamp, a discharge lamp, an electrode-less lamp, or the like.
  • the broadband illumination source 102 may provide an illumination beam 104 having low coherence (e.g. low spatial coherence and/or temporal coherence).
  • the broadband illumination source 102 may further produce broadband illumination with any temporal profile.
  • the broadband illumination source 102 may produce a continuous illumination beam 104, a pulsed illumination beam 104, or a modulated illumination beam 104.
  • the illumination beam 104 may be delivered from the broadband illumination source 102 via free-space propagation or guided light (e.g. an optical fiber, a light pipe, or the like).
  • a multi-channel tunable spectral filter 101 includes a channel selector 106 to separate the illumination beam 104 into two or more channel beams 108 (e.g. portions of the illumination beam propagating along any of the two or more filtering channels.
  • one or more channels of the multichannel tunable spectral filter 101 include an intensity modulator 1 10 to control the intensity of the channel beam 108.
  • one or more channels of the multi-channel tunable spectral filter 101 include a tunable filter 1 12 to control the spectral content of the channel beam 108.
  • the multi-channel tunable spectral filter 101 includes a controller 1 14 communicatively coupled to at least one of the intensity modulator 1 10 or the tunable filter 1 12.
  • the controller 1 14 may provide one or more signals to one or more components of the intensity modulator 1 10 and/or the tunable filter 1 12 to tune the intensity and/or spectral content of each of the channel beams 108.
  • each of the channel beams 108 are provided as output illumination beams 1 16. Accordingly, output illumination beams 1 16 may be provided to an external system (e.g. an illumination source, a metrology system, or the like).
  • the controller 1 14 includes one or more processors 126.
  • the one or more processors 1 18 are configured to execute a set of program instructions maintained in a memory medium 120, or memory.
  • the controller 1 14 may include one or more modules containing one or more program instructions stored in the memory medium 120 executable by the one or more processors 1 18.
  • the one or more processors 1 18 of a controller 1 14 may include any processing element known in the art. In this sense, the one or more processors 1 18 may include any microprocessor-type device configured to execute algorithms and/or instructions.
  • the one or more processors 1 18 may consist of a desktop computer, mainframe computer system, workstation, image computer, parallel processor, or any other computer system (e.g., networked computer) configured to execute a program configured to operate the multi-channel tunable spectral filter 101 , as described throughout the present disclosure. It is further recognized that the term "processor” may be broadly defined to encompass any device having one or more processing elements, which execute program instructions from a non-transitory memory medium 120.
  • controller 1 14 may be formed from a single component or multiple components. It is further noted herein that the multiple components of the controller 1 14 may be housed in a common housing or within multiple housings. In this way, any controller or combination of controllers may be separately packaged as a module suitable for integration into the multi-channel tunable spectral filter 101 .
  • the memory medium 120 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 1 18.
  • the memory medium 120 may include a non-transitory memory medium.
  • the memory medium 120 may include, but is not limited to, a read-only memory, a random access memory, a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid state drive and the like. It is further noted that memory medium 120 may be housed in a common controller housing with the one or more processors 1 18. In one embodiment, the memory medium 120 may be located remotely with respect to the physical location of the one or more processors 1 18 and controller 1 14.
  • the one or more processors 1 18 of controller 1 14 may access a remote memory (e.g., server), accessible through a network (e.g., internet, intranet and the like). Therefore, the above description should not be interpreted as a limitation on the present invention but merely an illustration.
  • the multi-channel tunable spectral filter 101 includes one or more steering mirrors 122 to direct the paths of the channel beams 108a,b.
  • the channel selector 106 may be any optical element or set of optical elements suitable for directing the illumination beam 104 into two or more channel beams 108.
  • the channel selector 106 may include one or more beamsplitters 1 19.
  • the channel selector 106 may include one or more dichroic mirrors.
  • the channel selector 106 separates the illumination beam 104 such that generated channel beams 108 have the same spectra.
  • the channel selector 106 may include one or more beamsplitters (e.g. beamsplitters 1 19, or the like) to separate the illumination beam 104 without modifying the spectral content of the illumination beam 104.
  • the channel selector 106 may separate the illumination beam 104 such that the generated channel beams 108 may have distinct spectra.
  • the channel selector 106 may include one or more dichroic mirrors to selectively reflect a first portion of the illumination beam 104 to generate a first channel beam 108 having a first spectrum and transmit a second portion of the illumination beam 104 to generate a second channel beam 108 having a second spectrum.
  • the channel selector 106 may include polarization-sensitive optical elements and/or polarization insensitive elements.
  • the channel selector 106 may include a series of two or more beam separating elements (e.g. beamsplitters, dichroic mirrors, or the like) to generate three or more channel beams 108.
  • a channel selector 106 configured to generate four channel beams may include three cascaded beam separating elements such that a first beam separating element may separate the illumination beam 104 into a first channel beam and a first intermediate beam, a second beam separating element may separate the first intermediate beam into a second channel beam and a second intermediate beam, and the third beam separating element may separate the second intermediate beam into a third channel beam and a fourth channel beam.
  • a channel selector 106 may generate any number of channel beams 108.
  • the channel selector 106 includes one or more routing elements to selectively direct the illumination beam into one of multiple available channels.
  • each channel may be configured to provide a unique spectral distribution (e.g. via a unique configuration of a tunable filter 1 12, or the like).
  • the one or more routing elements may control the channel the illumination beam 104 is directed to and thus provide rapid switching of the spectral distribution of the output illumination beam 1 16.
  • the one or more routing elements may include any optical and/or mechanical elements suitable for directing an illumination beam 104 such as, but not limited to, an acousto-optic modulator, an electro-optic modulator, a galvanometer mirror, or a piezo-electric mirror.
  • the intensity of the illumination beam 104 may be divided between the channel beams 108 according to any ratio.
  • each of the channel beams 108 exhibits the same intensity.
  • the channel selector 106 may include a beamsplitter having a 50/50 intensity ratio to generate two channel beams 108 having the same intensity.
  • the channel selector 106 may include a first beamsplitter to generate a first channel beam 108 having one third of the intensity of the illumination beam 104 and two thirds of the intensity of the illumination beam 104 in an intermediate beam.
  • the channel selector 106 may include a second beamsplitter having a 50/50 intensity ratio to split the intermediate beam into a second channel beam 108 and a third channel beam 108 such that the three channel beams 108 each have one third of the intensity of the illumination beam 104.
  • each of the channel beams 108 exhibits a different intensity.
  • the multi-channel tunable spectral filter 101 includes polarization-controlling optical elements.
  • the multi-channel tunable spectral filter 101 may include, but is not required to include, one or more polarizers, one or more waveplates, or one or more electro-optic cells (e.g. Pockels cells, or the like).
  • the channel selector 106 may include a polarization rotator 124 (e.g. a waveplate, an electro-optical cell, or the like) in the path of the illumination beam 104.
  • the channel selector 106 may include one or more polarized beamsplitters (e.g. beamsplitters 1 19, or the like).
  • different channel beams 108 may be associated with different polarizations and the relative intensity of the channel beams 108 may be controllable by adjusting the polarization angle of the illumination beam 104 with the polarization rotator 124 with respect to the orientation of the polarized beam splitter.
  • one or more channels of the multi-channel tunable spectral filter 101 may include a polarization rotator to adjust the polarization of a channel beam 108.
  • the multi-channel tunable spectral filter 101 may include one or more polarization-based intensity modulators.
  • a polarization-based intensity modulator may include a polarization controller and a polarizer.
  • the multi-channel tunable spectral filter 101 may include polarization-controlling elements in any beam path to selectively control the polarization of any beam such as, but not limited to, the illumination beam 104 from the broadband illumination source 102, any channel beam 108, or any output illumination beam 1 16.
  • polarization-sensitive optical elements may be mounted in rotatable mounts such that the orientations of the polarization-sensitive optical elements may be selectively controllable (e.g. via control signals from the controller 1 14, through manual adjustment by a user, or the like).
  • the output illumination beams 1 16 may be provided by the multi-channel tunable spectral filter 101 by any method known in the art.
  • one or more output illumination beams 1 16 are provided as a free-space illumination beam.
  • one or more output illumination beams 1 16 are fiber-coupled.
  • one or more output illumination beams 1 16 may be coupled to a single-mode fiber.
  • spatially coherent output illumination beams 1 16 e.g. provided by a spatially-coherent broadband illumination source 102
  • one or more output illumination beams 1 16 may be coupled to a multi-mode fiber.
  • FIG. 1 B is a conceptual view of a multi-channel tunable spectral filter 101 in which channel beams 108 are further split into multiple output illumination beams 1 16, in accordance with one or more embodiments of the present disclosure.
  • the multi-channel tunable spectral filter 101 includes an output polarization rotator 126 and an output beam separator 128 for each channel beam 108.
  • each channel beam 108 may be further split into multiple output illumination beams 1 16 having independently-adjustable intensity. Further, each output illumination beam 1 16 may be independently provided to an external system (e.g. to illuminate multiple locations of a sample, or the like).
  • a multi-channel tunable spectral filter 101 includes an adjustable polarizer (not shown) in the beam path of one or more channel beams 108 to selectively adjust the polarization of a channel beam 108.
  • an adjustable polarizer may be placed prior to a polarizing beamsplitter to selectively control the intensity ratio of output illumination beams 1 16.
  • the multi-channel tunable spectral filter 101 may provide any channel as an output illumination beam 1 16. Further, two or more channels of the multi-channel tunable spectral filter 101 may be combined into a single output illumination beam 1 16.
  • FIG. 1 C is a conceptual view of a multi-channel tunable spectral filter 101 having two channel beams 108a,b in which the two channels are combined into a combined output illumination beam 1 16, in accordance with one or more embodiments of the present disclosure.
  • the multi-channel tunable spectral filter 101 includes a beam combiner 130 to combine the two channel beams 108a,b.
  • the beam combiner 130 may be any optical element or set of optical elements suitable for combining the channel beams 108a,b into a combined output illumination beam 1 16.
  • the channel selector 106 may include, but is not limited to, one or more beamsplitters or one or more dichroic mirrors.
  • the beam combiner 130 may include polarizing and/or non-polarizing optical elements.
  • the channel selector 106 and the beam combiner 130 are formed from non-polarized beam splitters. Accordingly, the channel beams 108a,b may have the same polarization.
  • the channel selector 106 and the beam combiner 130 include polarized beamsplitters.
  • the channel selector 106 may separate the illumination beam 104 into two orthogonally-polarized channel beams 108a,b. Further, the beam combiner 130 may combine the orthogonally-polarized channel beams 108a,b into a single output illumination beam 1 16.
  • FIG. 1 D is a conceptual view of a multi-channel tunable spectral filter 101 in which a combined output illumination beam 1 16 is further split into multiple output illumination beams 1 16, in accordance with one or more embodiments of the present disclosure.
  • the multi-channel tunable spectral filter 101 includes an output polarization rotator 126 and an output beam separator 128 in the beam path of a combined output illumination beam 1 16.
  • the combined output illumination beam 1 16 may be further split into multiple output illumination beams 1 16 having independently-adjustable intensity.
  • each output illumination beam 1 16 may be independently provided to an external system (e.g. to simultaneously illuminate multiple locations of a sample, or the like).
  • FIG. 2 is a conceptual view of a multi-channel tunable spectral filter 101 illustrating an expanded view of an intensity modulator 1 10, in accordance with one or more embodiments of the present disclosure.
  • An intensity modulator 1 10 may include any optical element or combination of optical elements suitable for modifying the intensity of one or more channel beams 108.
  • An intensity modulator 1 10 in the path of a channel beam 108 may include a shutter to selectively block one or more channel beams 108.
  • a first intensity modulator 1 10a includes a first shutter 202 to selectively block a first channel beam 108a.
  • a second intensity modulator 1 10b includes a second shutter 204 to selectively block a second channel beam 108b.
  • a shutter may include any type of shutter known in the art for selectively blocking a channel beam including, but not limited to, a mechanical shutter, an acousto-optic shutter, or an electro-optic shutter.
  • a shutter may be communicatively coupled with the controller 1 14.
  • an intensity modulator 1 10 in the path of a channel beam 108 may include an intensity filter.
  • the first intensity modulator 1 10a includes a first intensity filter 206a.
  • the second intensity modulator 1 10b includes a second intensity filter 208.
  • an intensity filter may include any type of optical element or set of optical elements suitable for selectively attenuating the spectral power of one or wavelengths of a channel beam 108.
  • an intensity filter may include one or more neutral density filters to attenuate the intensity of all wavelengths of a channel beam 108 by the same degree.
  • an intensity filter includes an adjustable neutral density filter.
  • the intensity filter may be communicatively coupled with the controller 1 14.
  • the controller 1 14 may selectively control the intensity of each channel beam 108.
  • the intensity filter may include one or more filter changers (e.g. filter wheels, or the like) having a set of neutral density filters.
  • a filter changer may include two or more filter mounts arranged such that filters secured to the filter mounts may be selectively placed in the path of a channel beam 108.
  • the intensity of a channel beam 108 may be adjusted by selectively controlling the number and optical density of the neutral density filters placed in the path of the channel beam 108.
  • the intensity filter may include a gradient filter in which the transmissivity (or reflectivity) of the intensity filter may vary in a gradient pattern as a function of position on the intensity filter.
  • the intensity filter may include a linear gradient filter mounted to a linearly actuatable translation stage (e.g. coupled to the controller 1 14) such that the intensity of a channel beam 108 may be controllable by actuating the linear position of the linear gradient filter with respect to the channel beam 108.
  • the intensity filter includes a polarization controller and a polarizer.
  • the intensity filter may be a circular gradient filter mounted to a rotational stage (e.g. rotational stage 210 or rotational stage 212) in which the transmissivity (or reflectivity) of the intensity filter may be controllable by actuating the rotational position of the intensity filter with respect to the channel beam 108.
  • a rotational stage e.g. rotational stage 210 or rotational stage 212
  • the transmissivity (or reflectivity) of the intensity filter may be controllable by actuating the rotational position of the intensity filter with respect to the channel beam 108.
  • the multi-channel tunable spectral filter 101 may include an intensity modulator in the beam path of any output illumination beam 1 16 (e.g. output illumination beams 1 16 illustrated in FIG. 1 B, FIG. 1 D, or the like).
  • the intensity of any output illumination beam 1 16 may be selectively adjusted from completely blocked to fully transmitted.
  • a tunable filter 1 12 may include any optical element or combination of optical elements suitable for modifying the spectral content of one or more channel beams 108.
  • the tunable filter 1 12 includes a spectral filter to selectively attenuate one or more wavelengths of a channel beam 108.
  • the tunable filter 1 12 may include a low-pass filter to attenuate wavelengths above a cutoff wavelength, a high-pass filter to attenuate wavelengths below a cutoff wavelength, a band-pass filter to pass a defined spectral bandwidth of illumination and attenuate wavelengths outside of a select band of wavelengths, a band- reject filter to attenuate wavelengths within a select band of wavelengths, or the like.
  • the tunable filter 1 12 may include any type of spectral filter known in the art suitable for modifying the spectral content of a channel beam 108.
  • the tunable filter 1 12 may include, but is not required to include, a thin film spectral filter formed from one or more stacked layers.
  • the tunable filter 1 12 may include reflective spectral filters or transmissive spectral filters.
  • a spectral filter may be formed from a single optical element or a combination of optical elements.
  • the tunable filter 1 12 includes one or more tunable spectral filters in the optical path of at least one channel beam 108.
  • the spectral transmissivity of the filter e.g. one or more cutoff wavelengths, one or more transmissivity values, or the like
  • the tunable filter 1 12 includes one or more discrete (e.g. non-tunable) spectral filters in the optical path of at least one channel beam 108.
  • the spectral transmissivity of the filter e.g.
  • FIG. 3A is a conceptual view of a multi-channel tunable spectral filter 101 illustrating a tunable filter 1 12 including spectral filters secured in filter changers, in accordance with one or more embodiments of the present disclosure.
  • a first tunable filter 1 12a may include a first filter changer 302 and a second filter changer 304 to secure spectral filters to modify the spectral properties of a first channel beam 108a.
  • a second tunable filter 1 12b may include a third filter changer 306 and a fourth filter changer 308 to secure spectral filters to modify the spectral properties of a second channel beam 108b.
  • the spectrum of each channel beam 108a,b may be adjusted by selectively controlling the number and spectral transmissivity of the spectral filters within the filter changers placed in the path of the channel beams 108a, b.
  • the filter changers e.g. filter changers 302-308) are adjustable such that one or more spectral filters may be selectively placed in the paths of each channel beam 108a,b.
  • the filter changers 302-308 may secure any type of spectral filter such as, but not limited to, a low-pass filter, a high-pass filter, a band-pass filter, or a band-reject filter.
  • cascading two or more spectral filters may provide superior performance relative to a single spectral filter.
  • a tunable filter 1 12 e.g. tunable filter 1 12a,b as illustrated in FIG. 3A
  • cascaded spectral filters having overlapping pass bands may exhibit a higher suppression ratio (e.g. a ratio of a transmittance of blocked wavelengths to a transmittance of passed wavelengths, or the like) than any of the constituent spectral filters individually.
  • the performance criteria of any particular spectral filter may be relaxed, while maintaining a desired level of suppression of wavelengths outside of a desired passband.
  • the fabrication demands e.g. complexity of fabrication, number of coatings, cost of fabrication, or the like
  • the fabrication demands of a wideband band-pass filter may be less stringent than the fabrication demands of a narrowband band-pass filter.
  • the fabrication demands of a filter in which a desired suppression ratio must be held for a large range of wavelengths outside the passband may be more stringent than the fabrication demands of a filter in which a desired suppression ratio must be held for a narrow range of wavelengths outside the passband.
  • FIGS. 3B through 3D are diagrams illustrating the spectral transmissivity of a tunable filter including two cascaded spectral filters.
  • FIG. 3B is a diagram 310 illustrating the spectral transmissivity of a first spectral filter (e.g. mounted in the first filter changer 302, the third filter changer 306, or the like), in accordance with one or more embodiments of the present disclosure.
  • the first spectral filter includes a wide-band band-pass filter to pass wavelengths between a first wideband cutoff wavelength 312 and a second wideband cutoff wavelength 314 (e.g. defining a passband of wavelengths passed by the first spectral filter).
  • the first spectral filter may pass wavelengths within the passband with a first wideband transmissivity 316 and may pass wavelengths outside of the passband with a second wideband transmissivity 318.
  • a suppression ratio of the first spectral filter may correspond to a ratio of the second wideband transmissivity 318 to the first wideband transmissivity 316.
  • the first spectral filter provides a relatively high suppression ratio over a large range of wavelengths outside the passband.
  • FIG. 3C is a diagram 320 illustrating the spectral transmissivity of a second spectral filter (e.g. mounted in the second filter changer 304, the fourth filter changer 308, or the like), in accordance with one or more embodiments of the present disclosure.
  • the second spectral filter includes a narrow-band band-pass filter to pass wavelengths between a first narrow-band cutoff wavelength 322 and a second narrow-band cutoff wavelength 324 (e.g. defining a passband of wavelengths passed by the second spectral filter).
  • the second spectral filter may pass wavelengths within the passband with a first narrowband transmissivity 326 and may pass wavelengths outside of the passband with a second narrowband transmissivity 328.
  • a suppression ratio of the second spectral filter may correspond to a ratio of the second wideband transmissivity 318 to the first wideband transmissivity 316.
  • FIG. 3D is a diagram 330 illustrating the spectral transmissivity of the first spectral filter cascaded with the second spectral filter (e.g. as illustrated in FIG. 3A), in accordance with one or more embodiments of the present disclosure.
  • the cascaded spectral filters may pass wavelengths within a passband defined by the first narrowband transmissivity 326 and the second narrow-band cutoff wavelength 324.
  • the transmissivity 332 of the cascaded spectral filters may be a combination (e.g. a multiplicative combination) of the first wideband transmissivity 316 and the first narrowband transmissivity 326.
  • the tunable filter 1 12 may have a high suppression ratio over a relatively large range of wavelengths. Further, as illustrated in FIGS. 3B and 3C, it may be the case that a desired performance of the tunable filter 1 12 may be achieved using the cascaded first and second spectral filters in such a way that the fabrication demands on each of the first and second spectral filters are reduced relative to a tunable filter 1 12 having a single spectral filter with the same performance characteristics. For example, as illustrated in FIGS. 3B and 3C, the first spectral filter may exhibit a high suppression ratio over a large range of wavelengths outside of the passband, but may exhibit a wide passband. Further, the second spectral filter may exhibit a narrow passband, but may exhibit a lower suppression ratio for wavelengths outside of the passband of the first spectral filter.
  • FIG. 4 is a schematic diagram of three filter changers containing spectral filters suitable for spectrally filtering a channel beam 108 to include a narrow-band spectral profile that is tunable within three spectral windows, in accordance with one or more embodiments of the present disclosure.
  • a tunable filter 1 12 having three filter changers with eight filter mounts each provides narrowband spectral filtering of a channel beam 108 with eighteen selectable center wavelengths.
  • the tunable filter 1 12 includes a first filter changer 402, a second filter changer 404, and a third filter changer 406.
  • each filter changer 402-406 includes eight filter mounts suitable for securing a spectral filter.
  • the first filter changer 402 may include filter mounts 408-422
  • the second filter changer 404 may include filter mounts 424-438
  • the third filter changer 406 may include filter mounts 440-454.
  • each filter changer includes an open mount in which no filter is mounted.
  • a channel beam 108 may selectively pass through each filter changer without spectral modification.
  • filter mounts 408, 424, and 440 may be open mounts.
  • the tunable filter 1 12 provides narrowband spectral filtering using a wideband band-pass filter cascaded with a narrowband band-pass filter (e.g. as illustrated in FIGS. 3B through 3D).
  • filter mount 422 may include a wideband band-pass filter having a first passband (e.g. a red passband)
  • filter mount 438 may include a wideband band-pass filter having a second passband (e.g. a green passband
  • filter mount 454 may include a wideband band-pass filter having a third passband (e.g. a blue passband).
  • filter mounts 426-436 may include narrowband band-pass filters with center wavelengths within the first passband.
  • a channel beam 108 may be tuned to a wavelength within the first passband by setting the first filter changer 402 to filter mount 422, the second filter changer 404 to any of filter mounts 426-436, and the third filter changer 406 to filter mount 408 (e.g. open).
  • Filter mounts 442-452 may include narrowband band-pass filters with center wavelengths within the second passband.
  • a channel beam 108 may be tuned to a wavelength within the second passband by setting the first filter changer 402 to filter mount 408 (e.g. open), the second filter changer 404 to 438, and the third filter changer 406 to any of filter mounts 442-452.
  • Filter mounts 410-420 may include narrowband band-pass filters with center wavelengths within the third passband.
  • a channel beam 108 may be tuned to a wavelength within the third passband by setting the first filter changer 402 to any of filter mounts 410-420, the second filter changer 404 to 424 (e.g. open), and the third filter changer 406 to filter mount 454.
  • the tunable filter 1 12 may include band-pass filters in any region of the spectrum including, but not limited to, ultraviolet wavelengths, visible wavelengths, or infrared wavelengths.
  • a tunable filter 1 12 may include angularly-tunable spectral filters in which one or more filtering characteristics (e.g. a cutoff wavelength, a center wavelength, a transmissivity value, or the like) may be tuned according to the angle of incidence of a channel beam 108.
  • angularly-tunable spectral filters may include any type of spectral filter such as, but not limited to, a low-pass filter, a high-pass filter, a band-pass filter, or a band-reject filter.
  • a filter mount e.g. a single filter mount, a filter changer, or the like
  • a first tunable filter 1 12a may include a low-pass filter in a first filter mount 502 secured on a first rotation stage 504 and a high-pass filter in a second filter mount 506 secured on a second rotational stage 508.
  • a second tunable filter 1 12b may include a low-pass filter in a third filter mount 510 secured on a third rotation stage 512 and a high-pass filter in a fourth filter mount 514 secured on a fourth rotational stage 516.
  • a tunable filter 1 12 may include linearly-tunable spectral filters in which one or more filtering characteristics (e.g. a cutoff wavelength, a center wavelength, a transmissivity value or the like) may be tuned according to the linear position of a channel beam 108 on the filter.
  • a linearly-tunable spectral filter may include one or more thin films having a wedge profile such that a thickness may vary across the length of the filter.
  • linearly-tunable spectral filters may include any type of spectral filter such as, but not limited to, a low-pass filter, a high-pass filter, a band-pass filter, or a band-reject filter.
  • FIG. 6 is a conceptual view of a multi-channel tunable spectral filter 101 illustrating a tunable filter 1 12 including linearly-tunable spectral filters, in accordance with one or more embodiments of the present disclosure.
  • a filter mount e.g. a single filter mount, a filter changer, or the like
  • a first tunable filter 1 12a may include a low-pass filter in a first filter mount 602 secured on a first linear stage 604 and a high-pass filter in a second filter mount 606 secured on a second linear stage 608.
  • a second tunable filter 1 12b may include a low-pass filter in a third filter mount 610 secured on a third linear stage 612 and a high-pass filter in a fourth filter mount 614 secured on a fourth linear stage 616.
  • FIG. 7 is a conceptual view of a tunable filter 1 12 including a double-grating monochromator with a spatial filter, in accordance with one or more embodiments of the present disclosure.
  • a tunable filter 1 12a,b includes a first dispersive element 702a, b to spectrally disperse a channel beam (e.g. channel beam 108a or channel beam 108b), a filtering element 704a, b to operate as a spatial filter, and a second dispersive element 706a, b to spectrally recombine the channel beam to form a spectrally-filtered channel beam.
  • a channel beam e.g. channel beam 108a or channel beam 108b
  • a filtering element 704a, b to operate as a spatial filter
  • a second dispersive element 706a, b to spectrally recombine the channel beam to form a spectrally-filtered channel beam.
  • the second dispersive element 706a, b may remove the dispersion introduced by the first dispersive element 702a, b.
  • a spectral transmittance of the tunable filter 1 12a,b may be related to a spatial transmittance of the filtering element 704a, b.
  • the first dispersive element 702a, b may be any type of dispersive element known in the art suitable for introducing spectral dispersion into the channel beam (e.g. channel beam 108a or channel beam 108b).
  • the first dispersive element 702a, b may introduce dispersion into the channel beam through any mechanism such as, but not limited to, diffraction or refraction.
  • the first dispersive element 702a, b may be formed from transmissive and/or reflective optical elements.
  • the first dispersive element 702a, b includes a dynamically-generated diffraction grating.
  • a diffraction grating may be dynamically generated in a substrate material (e.g. a transparent optical material).
  • the dispersive characteristics of the first dispersive element 702a, b may be dynamically modified in order to tune the multi-channel tunable spectral filter 101 by adjusting the physical characteristics of the dynamically-generated diffraction grating. For example, the period or the modulation depth of a dynamically-generated diffraction grating may be adjusted (e.g. via the controller 1 14) to control the value of dispersion (e.g.
  • the modulation depth of the dynamically-generated diffraction grating may be adjusted (e.g. via the controller 1 14) to control the efficiency of dispersion (e.g. an efficiency value at which particular wavelengths of illumination is diffracted).
  • the first dispersive element 702a, b may include, but is not limited to, an acousto-optic modulator on an electro-optic modulator.
  • a tunable filter 1 12 e.g. tunable filter 1 12a,b
  • the first dispersive element 702a, b includes an acousto-optic modulator consisting of a solid medium coupled with a transducer configured to generate ultrasonic waves that propagate through the solid medium.
  • Properties of the solid medium such as, but not limited to, the refractive index may be modified by the propagating ultrasonic waves such that a channel beam is diffracted upon interaction with the solid medium.
  • ultrasonic waves may propagate through the solid medium at the velocity of sound in the medium and have a wavelength related to the frequency of the drive signal as well as the velocity of sound in the solid medium. Accordingly, a modulation frequency and/or a modulation strength of a transducer may be dynamically adjusted to modify the physical characteristics of the dynamically- generated diffraction grating and the corresponding dispersive properties of the first dispersive element 702a, b.
  • the tunable filter 1 12a,b includes a first optical element 708a, b (e.g. one or more lenses, or the like) to focus the spectrally-dispersed channel beam (e.g. channel beam 108a or channel beam 108b) to a focal plane 710a,b such that the spectrum of the channel beam may be spatially distributed across the focal plane 710a,b.
  • the focal plane 710a,b may correspond to a diffraction plane of the multi-channel tunable spectral filter 101 .
  • a "position" within the focal plane 710a,b may correspond to light from the channel beam exiting the first dispersive element 702a, b at a particular angle and thus a particular wavelength of illumination of the channel beam.
  • a first dispersive element 702a, b including a diffraction grating may diffract each wavelength of illumination of the channel beam at a different angle, whereupon each wavelength of illumination of the channel beam may be focused to a different location in the focal plane 710a,b.
  • the filtering element 704a, b of the multi-channel tunable spectral filter 101 is located at the focal plane 710a,b.
  • the filtering element 704a, b may spatially filter the spectrally-dispersed channel beam (e.g. channel beam 108a or channel beam 108b).
  • the filtering element 704a, b may have a spatial transmittance describing the transmittance of illumination (e.g. illumination of any wavelength) as a function of position. Accordingly, the spectral power of each wavelength of illumination of the channel beam may be modified according to the spatial transmittance of the filtering element 704a, b.
  • the spectral transmittance of the multi-channel tunable spectral filter 101 may be controllable through the spatial transmittance of the filtering element 704a, b.
  • the filtering element 704a, b may pass a select wavelength (or wavelength range) of the channel beam.
  • the filtering element 704a, b may, but is not required to, have a shape corresponding to the shape of the focal plane 710a,b.
  • a filtering element 704a, b may have a curved shape to match a focal plane 710a,b including a curved surface (e.g. as determined by the first dispersive element 702a, b and/or the first optical element 708a, b).
  • the multi-channel tunable spectral filter 101 includes a second optical element 712a,b (e.g. one or more lenses, or the like) to collect the spectrally-dispersed illumination passed by the filtering element 704a, b.
  • the second optical element 712a,b may collect at least a portion of the spectrally dispersed and filtered channel beam from the filtering element 704a, b.
  • the second optical element 712a,b may direct the collected spectrally dispersed and filtered illumination beam 104 to the second dispersive element 706a, b.
  • the second dispersive element 706a, b spectrally combines the spectrally dispersed and filtered channel beam 108 to remove the spectral dispersion introduced by the first dispersive element 702a, b.
  • a channel beam e.g. channel beam 108a or channel beam 108b
  • the dispersive characteristics of the second optical element 712a,b may be configured to counteract the dispersion induced by the first dispersive element 702a, b.
  • the first optical element 708a, b and the second optical element 712a,b form an optical relay system.
  • the first optical element 708a, b and the second optical element 712a,b may generate an image of the distribution of the channel beam on the first dispersive element 702a, b at the second dispersive element 706a, b.
  • the multi-channel tunable spectral filter 101 may minimally affect the properties of the channel beam such as, but not limited to, the divergence (e.g. degree of collimation), spatial coherence, or brightness (e.g. of the passed wavelengths), which may facilitate the integration of the multi-channel tunable spectral filter 101 into any system (e.g. a metrology system, or the like).
  • the filtering element 704a, b may have any spatial transmittance distribution in order to provide any filtering operation known in the art. Accordingly, the multi-channel tunable spectral filter 101 may operate as any type of spectral filter such as, but not limited to, a low-pass filter, a high-pass filter, a band-pass filter, or a notch-filter.
  • the multi-channel tunable spectral filter 101 may be utilized as a part of an external optical system.
  • FIG. 8 is a conceptual view of a metrology system 800 (e.g. a microscope, an imaging scatterometer, an angular resolved scatterometer, or the like) including a multi-channel illumination source 100, in accordance with one or more embodiments of the present disclosure.
  • a multi-channel illumination source 100 including a multi-channel tunable spectral filter 101 may provide a tunable illumination source for the metrology system 800.
  • the metrology system 800 includes an objective lens 802 configured to direct the beam of illumination 804 to a sample 806 along an illumination pathway 808.
  • the metrology system 800 is configured in epi-mode with a beamsplitter 810 such that the objective lens 802 both directs the beam of illumination 804 to the sample 806 and collects illumination from the sample 806 at a normal angle.
  • the metrology system 800 includes one or more illumination optics along a collection pathway 812 to receive radiation emanating from the sample 806 (e.g. reflected, scattered, and/or diffracted portions of the illumination beam 804, radiation emitted by the sample 806, or the like) and direct the collected radiation to a detector 814.
  • the beam of illumination 804 of the metrology system 800 includes any number of tunable illumination beams provided by the multi-channel tunable spectral filter 101 .
  • the beam of illumination 804 may include any number of output illumination beams 1 16 from the multi-channel tunable spectral filter 101 (e.g. channel beams 108, combined output illumination beams 1 16, or the like).
  • each output illumination beam 1 16 provided by the multi-channel tunable spectral filter 101 may have selectively adjustable properties such as, but not limited to, spectral content, intensity, or polarization.
  • the metrology system 800 may utilize tunable output illumination beams 1 16 provided by the multi-channel tunable spectral filter 101 to illuminate the sample 806.
  • the metrology system 800 may direct the tunable output illumination beams 1 16 to multiple portions of the sample 806 (e.g. multiple cells of a metrology target, or the like). Further, the metrology system 800 may direct the tunable output illumination beams 1 16 to the sample 806 simultaneously or sequentially.
  • the multi-channel tunable spectral filter 101 may efficiently tune the output illumination beams 1 16 (e.g. modify the spectral content of the output illumination beams 1 16) for efficient measurements.
  • a multichannel tunable spectral filter 101 including a double grating monochromator formed from acousto-optical modulators may efficiently tune a spatially coherent broadband source such as, but not limited to, a supercontinuum laser source.
  • the metrology system 800 includes multi-channel tunable spectral filter 101 to produce two independently tunable channel beams 108 as output illumination beams 1 16.
  • the metrology system 800 includes a beam combiner 816 to combine the output illumination beams 1 16 into a single beam of illumination 804.
  • the illumination pathway 808 of the metrology system 800 includes a set of illumination optical elements 818 to direct the beam of illumination 804 to the sample 806.
  • the set of illumination optical elements 818 may include an optical relay to relay an illumination pupil 820 to the objective lens 802.
  • the objective lens 802 may illuminate the sample 806 with any distribution of illumination from the beam of illumination 804 including, but not limited to, critical illumination or Kohler illumination.
  • the illumination pathway 808 may include an illumination field stop 822 to adjust the spatial extent of the beam of illumination 804 in a field plane.
  • the collection pathway 812 includes a set of collection optical elements 824 to direct illumination from the sample 806 to the detector.
  • the set of collection optical elements 824 may include an optical relay to relay a desired distribution of illumination from the objective lens 802 to the detector 814.
  • the set of collection optical elements 824 may relay an image of the sample 806 to the detector 814.
  • the set of collection optical elements 824 may relay an image of a pupil plane (e.g. a back focal plane of the objective lens 802) to the detector 814.
  • the metrology system 800 may detect the angular distribution of radiation from the sample 806.
  • FIG. 9 is a conceptual view of a multi-beam metrology system 900 including a multi-channel illumination source 100 with a multi-channel tunable spectral filter 101 , in accordance with one or more embodiments of the present disclosure.
  • a multi-channel illumination source 100 provides two output illumination beams 1 16a,b having different spectra.
  • the metrology system 900 includes a beam combiner 902 to collect the output illumination beams 1 16a,b to a single optical column.
  • the beam combiner 902 may include a beamsplitter.
  • beam combiner 902 may direct the output illumination beams 1 16 to a single objective lens 904.
  • the two output illumination beams 1 16 provided by the multi-channel illumination source 100 may be directed to a sample 906.
  • the two output illumination beams 1 16a,b may be directed to the same position on the sample 906. In another embodiment, the two output illumination beams 1 16a,b may be directed to different positions on the sample 906.
  • the metrology system 900 may include a beam scanner 908 to deflect one output illumination beam with respect to the other (e.g. output illumination beam 1 16b with respect to output illumination beam 1 16a) such that the two output illumination beams 1 16a,b may be directed to different positions of the sample 906 within the field of view of the objective lens 904.
  • the beam scanner 908 may be any element known in the art suitable for deflecting one output illumination beam with respect to the other such as, but not limited to, a reflective element with adjustable tip, tilt, and/or position (e.g. mounted on an adjustable actuator controlled by the controller 1 14, or the like) or a galvanometric mirror.
  • the metrology system 900 may include a scatterometry-based overlay metrology system in which the two output illumination beams 1 16a,b may be directed to two scatterometry metrology targets for simultaneous measurement.
  • the metrology system 900 includes two detectors 910a,b positioned to capture radiation emanating from the sample 906 from the two positions illuminated by the output illumination beams 1 16a,b.
  • the objective lens 904 may simultaneously direct illumination to the sample 906 and collect radiation emanating from the sample 906.
  • the metrology system 900 may be configured to capture pupil images associated with radiation emanating from the sample 906 (e.g. associated with the angular distribution of radiation from the sample 906).
  • the metrology system 900 may include one or more optical elements 912a,b to relay a pupil plane (e.g. a back focal plane of the objective lens 904 to the detectors 910a,b.
  • the metrology system 900 may include additional elements (e.g. spatial filters 914a,b, or the like) to condition the illumination collected by the objective lens 904.
  • the metrology system 900 may be configured to capture images of the sample 906 (e.g. a surface of the sample 906).
  • the metrology system 900 may include one or more beamsplitters 916a,b to facilitate the simultaneous illumination of and detection of radiation from the sample 906.
  • the one or more detectors may include any detector known in the art.
  • a detector may include, but are not limited to, a CCD detector, a photodiode, an avalanche photodiode (APD) and/or or a photomultiplier tube (PMT). It is further noted that a detector may be a multi-channel detector configured to simultaneously detect signals from multiple detection regions on a sample.
  • any two components so associated can also be viewed as being “connected”, or “coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “couplable”, to each other to achieve the desired functionality.
  • Specific examples of couplable include but are not limited to physically interactable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interactable and/or logically interacting components.

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KR1020197007076A KR102265871B1 (ko) 2016-08-17 2017-08-09 광대역 소스로부터 다중 채널 조정 가능한 조명을 생성하는 시스템 및 방법
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CN113924474A (zh) * 2019-05-23 2022-01-11 东京毅力科创株式会社 使用高光谱成像的半导体过程的光学诊断

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CN109564157B (zh) 2022-06-17
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US20180052099A1 (en) 2018-02-22
SG11201900804WA (en) 2019-03-28
US10371626B2 (en) 2019-08-06
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JP6782834B2 (ja) 2020-11-11
CN109564157A (zh) 2019-04-02

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