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`EP 1 739 493 A1
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`EUROPEAN PATENT APPLICATION
`
`(43) Date of publication:
`03.01.2007 Bulletin 2007/01
`
`(21) Application number: 06253180.1
`
`(51) Int CL:
`GO3F 7/20 (2005'01)
`G013 11/00 (200501)
`
`6023 6/00 (2005'01)
`H01L 21/00 (200501)
`
`(22) Date of filing: 20.06.2006
`
`
`(84) Designated Contracting States:
`AT BE BG CH CY CZ DE DK EE ES FI FR GB GR
`HU IE IS IT LI LT LU LV MC NL PL PT RO SE SI
`SK TR
`Designated Extension States:
`AL BA HR MK YU
`
`- Den Boef, Arie, Jeffrey
`5581 NA Waaire (NL)
`- Corbeij, Wilhelmus, Maria
`5646 JK Eindhoven (NL)
`- Van der Laan, Hans
`5501 CL Veldhoven (NL)
`
`(30) Priority: 30.06.2005 US 170746
`
`(71 ) Applicant: ASML Netherlands BV
`5504 DR Veldhoven (NL)
`
`(74) Representative: Leeming, John Gerard
`J.A. Kemp & Co.,
`14 South Square,
`Gray’s Inn
`London WC1R 5.“ (GB)
`
`(72) Inventors:
`- Pellemans, Henricus, Petrus, Maria
`5506 CT Veldhoven (NL)
`
`
`(54) Metrology apparatus for lithography
`
`A metrology apparatus for measuring a param-
`(57)
`eter of a microscopic structure on a substrate (W), the
`apparatus comprising a supercontinuum light source (2)
`
`Fig. 6
`
`arranged to generate a measurement beam, an optical
`system (202) arranged to direct the measurement beam
`onto the substrate (W) and a sensor (205) for detecting
`radiation reflected and/or diffracted by the structure.
`
`
`
`Printed by Jouvc, 75001 PARIS (FR)
`
`EP1739493A1
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`EP 1 739 493 A1
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`2
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`Description
`
`[0001] The present invention relates to a metrology de-
`vice, in particular one that can be used in a lithographic
`apparatus, in a process apparatus or as a stand-alone
`device and a metrology method, in particular that can be
`used as part of a device manufacturing method.
`[0002] A lithographic apparatus is a machine that ap-
`plies a desired pattern onto a substrate, usually onto a
`target portion of the substrate. A lithographic apparatus
`can be used, for example, in the manufacture of integrat—
`ed circuits (ICs).
`In that instance, a patterning device,
`which is alternatively referred to as a mask or a reticle,
`may be used to generate a circuit pattern to be formed
`on an individual layer of the IC. This pattern can be trans-
`ferred onto a target portion (e.g. comprising part of, one,
`or several dies) on a substrate (e.g. a silicon wafer).
`Transfer ofthe pattern is typically via imaging onto a layer
`of radiation-sensitive material (resist) provided on the
`substrate.
`In general, a single substrate will contain a
`network of adjacent target portions that are successively
`patterned. Known lithographic apparatus include so-
`called steppers, in which each target portion is irradiated
`by exposing an entire pattern onto the target portion at
`one time, and so—called scanners, in which each target
`portion is irradiated by scanning the pattern through a
`radiation beam in a given direction (the “scanning“-direc-
`tion) while synchronously scanning the substrate parallel
`or anti-parallel to this direction. It is also possible to trans-
`fer the pattern from the patterning device to the substrate
`by imprinting the pattern onto the substrate.
`[0003] During and after various steps in the production
`of devices using lithographic methods, it is necessary to
`make measurements on the devices that have been pro-
`duced to assess whether the production process has pro-
`ceeded correctly. Such measurements are collectively
`referred to as metrology. In view of the scale of devices
`produced by lithography, metrology methods generally
`involve illuminating the device structure or ateststructure
`with a measurement beam and detecting the returning
`radiation. One such method is scatterometry, in particular
`angle-resolved scatterometry in which the spectrum of
`the radiation reflected by the structure under inspection
`is measured at different angles using a sensor such as
`a CCD in the pupil plane of an objective lens.
`[0004] The sensitivity and speed of operation of most
`metrology devices is limited by the radiation source used
`to generate the measurement beam. Presently available
`sources include: Xe lamps, which have a good, wide
`bandwidth but poor luminance and poor spatial coher-
`ence; SLED lasers, which have good luminance and spa-
`tial coherence but not a particularly wide bandwidth and
`are not capable of generating wavelengths below about
`400nm.
`
`It is desirable to provide a metrology apparatus
`[0005]
`with improved sensitivity and/or speed of operation.
`[0006] According to an aspect of the invention, there
`is provided a metrology apparatus for measuring a pa-
`
`rameter of a microscopic structure on a substrate, the
`apparatus comprising a supercontinuum light source ar-
`ranged to generate a measurement beam, an optical sys-
`tem arranged to direct the measurement beam onto the
`substrate and a sensor for detecting radiation reflected
`and/or diffracted by the structure.
`[0007] According to an aspect of the invention, there
`is provided a metrology method for measuring a param-
`eter of a microscopic structure formed on a substrate,
`the method comprising:
`
`illuminating the structure with radiation from a super—
`continuum light source; and
`detecting radiation returned from the structure using
`a sensor.
`
`[0008] According to an aspect of the invention, there
`is provided a lithographic apparatus arranged to transfer
`a pattern onto a substrate and comprising a metrology
`apparatus according to any one of claims 1
`to 12 for
`measuring a parameter of a microscopic structure on the
`substrate.
`
`[0009] According to an aspect of the invention, there
`is provided a process apparatus arranged to effect a proc—
`ess on a substrate and comprising a metrology apparatus
`according to any one of claims 1 to 12 for measuring a
`parameter of a microscopic structure on the substrate.
`[0010] According to an aspect of the invention, there
`is provided a device manufacturing method comprising:
`
`measuring a parameter of a microscopic structure
`formed on a first substrate, by:
`
`illuminating the structure with radiation from a
`supercontinuum light source; and
`detecting radiation returned from the structure
`using a sensor;
`transferring a pattern onto a second substrate
`using a lithographic process, a parameter of the
`lithographic process being determined on the
`basis of the measured parameter of the struc-
`ture.
`
`[0011] Embodiments of the invention will now be de-
`scribed, by way of example only, with reference to the
`accompanying schematic drawings in which correspond-
`ing reference symbols indicate corresponding parts, and
`in which:
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`Figure 1 depicts a lithographic apparatus according
`to an embodiment of the invention;
`Figure 2 depicts a scatterometer according to an em-
`bodiment of the invention;
`Figure 3 depicts a light source useable in a scatter-
`ometer according to an embodimentof the invention;
`Figure 4 depicts interference regions in a pupil plane
`of a scatterometer according to an embodiment of
`the invention;
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`EP 1 739 493 A1
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`Figure 5 depicts a scatterometer according to anoth—
`er embodiment of the invention;
`Figure 6 depicts a scatterometer according to yet
`another embodiment of the invention; and
`Figure 7 depicts a scatterometer according to still
`another embodiment of the invention.
`
`Figure 1 schematically depicts a lithographic
`[0012]
`apparatus used in one embodiment of the invention. The
`apparatus comprises:
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`-
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`-
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`an illumination system (illuminator) lL configured to
`condition a radiation beam B (e.g. UV radiation or
`DUV radiation).
`a support structure (e.g. a masktable) MT construct-
`ed to support a patterning device (e.g. a mask) MA
`and connected to a first positioner PM configured to
`accurately position the patterning device in accord-
`ance with certain parameters;
`a substrate table (e.g. a wafer table) WT constructed
`to hold a substrate (e.g. a resist-coated wafer) W
`and connected to a second positioner PWconfigured
`to accurately position the substrate in accordance
`with certain parameters; and
`a projection system (e.g. a refractive projection lens
`system) PS configured to project a pattern imparted
`to the radiation beam B by patterning device MA onto
`a target portion C (e.g. comprising one or more dies)
`of the substrate W.
`
`[0013] The illumination system may include various
`types of optical components, such as refractive, reflec-
`tive. magnetic. electromagnetic, electrostatic or other
`types of optical components. or any combination thereof.
`for directing. shaping. or controlling radiation.
`[0014] The support structure supports. i.e. bears the
`weight of, the patterning device.
`It holds the patterning
`device in a manner that depends on the orientation of
`the patterning device, the design of the lithographic ap-
`paratus, and other conditions, such as for example
`whether or not the patterning device is held in a vacuum
`environment. The support structure can use mechanical,
`vacuum. electrostatic or other clamping techniques to
`hold the patterning device. The support structure may be
`a frame or a table. for example. which may be fixed or
`movable as required. The support structure may ensure
`that the patterning device is at a desired position. for ex-
`ample with respect to the projection system. Any use of
`the terms “reticle” or “mask" herein may be considered
`synonymous with the more general term “patterning de-
`vice.“
`
`[0015] The term “patterning device“ used herein
`should be broadly interpreted as referring to any device
`that can be used to impart a radiation beam with a pattern
`in its cross-section such as to create a pattern in a target
`portion ofthe substrate. ltshould be noted thatthe pattern
`imparted to the radiation beam may not exactly corre-
`spond to the desired pattern in the target portion of the
`
`substrate, for example if the pattern includes phase—shift—
`ing features or so called assist features. Generally. the
`pattern imparted to the radiation beam will correspond
`to a particular functional layer in a device being created
`in the target portion, such as an integrated circuit.
`[0016] The patterning device may be transmissive or
`reflective. Examples of patterning devices
`include
`masks, programmable mirror arrays, and programmable
`LCD panels. Masks are well known in lithography, and
`include mask types such as binary. alternating phase-
`shift. and attenuated phase-shift. as well as various hy-
`brid mask types. An example of a programmable mirror
`array employs a matrix arrangement of small mirrors,
`each of which can be individually tilted so as to reflect an
`incoming radiation beam in different directions. The tilted
`mirrors impart a pattern in a radiation beam which is re-
`flected by the mirror matrix.
`[0017] The term “projection system“ used herein
`should be broadly interpreted as encompassing any type
`of projection system, including refractive, reflective, cat-
`adioptric. magnetic. electromagnetic and electrostatic
`optical systems. or any combination thereof. as appro-
`priate for the exposure radiation being used. or for other
`factors such as the use of an immersion liquid or the use
`of a vacuum. Any use of the term “projection lens“ herein
`may be considered as synonymous with the more gen-
`eral term “projection system“.
`[0018] As here depicted, the apparatus is of a trans-
`missive type (e.g. employing a transmissive mask). Al-
`ternatively. the apparatus may be of a reflective type (e.g.
`employing a programmable mirror array of a type as re-
`ferred to above. or employing a reflective mask).
`[0019] The lithographic apparatus may be of a type
`having two (dual stage) or more substrate tables (and/or
`two or more mask tables). In such “multiple stage“ ma-
`chines the additional tables may be used in parallel, or
`preparatory steps may be carried out on one or more
`tables while one or more other tables are being used for
`exposure.
`[0020] The lithographic apparatus may also be of a
`type wherein at least a portion of the substrate may be
`covered by a liquid having a relatively high refractive in-
`dex. e.g. water. so as to fill aspace between the projection
`system and the substrate. An immersion liquid may also
`be applied to other spaces in the lithographic apparatus.
`for example. between the mask and the projection sys-
`tem. Immersion techniques are well known in the art for
`increasing the numerical aperture of projection systems.
`The term “immersion“ as used herein does not mean that
`
`a structure, such as a substrate. must be submerged in
`liquid, but ratheronly meansthat liquid is located between
`the projection system and the substrate during exposure.
`[0021] Referring to Figure 1, the illuminator lL receives
`a radiation beam from a radiation source 80. The source
`
`and the lithographic apparatus may be separate entities.
`for example when the source is an excimer laser. In such
`cases. the source is not considered to form part of the
`lithographic apparatus and the radiation beam is passed
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`from the source SO to the illuminator IL with the aid of a
`
`beam delivery system BD comprising, for example, suit-
`able directing mirrors and/or a beam expander. In other
`cases the source may be an integral part of the litho-
`graphic apparatus, for example when the source is a mer-
`cury lamp. The source SO and the illuminator lL, together
`with the beam delivery system BD if required, may be
`referred to as a radiation system.
`[0022] The illuminator IL may comprise an adjusterAD
`for adjusting the angular intensity distribution of the ra-
`diation beam. Generally, at least the outer and/or inner
`radial extent (commonly referred to as o—outer and 6-
`inner, respectively) of the intensity distribution in a pupil
`plane of the illuminator can be adjusted. In addition, the
`illuminator IL may comprise various other components,
`such as an integrator IN and a condenser CO. The illu-
`minator may be used to condition the radiation beam, to
`have a desired uniformity and intensity distribution in its
`cross-section.
`
`[0023] The radiation beam B is incident on the pattern-
`ing device (e.g., mask MA), which is held on the support
`structure (e.g., mask table MT), and is patterned by the
`patterning device. Having traversed the mask MA, the
`radiation beam B passes through the projection system
`PS, which focuses the beam onto a target portion C of
`the substrate W. With the aid of the second positioner
`PW and position sensor IF (e.g. an interferometric device,
`linear encoder or capacitive sensor), the substrate table
`WT can be moved accurately, e.g. so as to position dif-
`ferent target portions C in the path of the radiation beam
`B. Similarly, the first positioner PM and another position
`sensor (which is not explicitly depicted in Figure 1) can
`be used to accurately position the mask MA with respect
`to the path of the radiation beam B, e.g. after mechanical
`retrieval from a mask library, or during a scan. In general,
`movement of the mask table MT may be realized with
`the aid of a long—stroke module (coarse positioning) and
`a short-stroke module (fine positioning), which form part
`ofthe first positioner PM. Similarly, movementof the sub-
`strate table WT may be realized using a long-stroke mod-
`ule and a short-stroke module, which form part of the
`second positioner PW.
`In the case of a stepper (as op-
`posed to a scanner) the mask table MT may be connected
`to a short-stroke actuator only, or may be fixed. Mask
`MA and substrate W may be aligned using mask align-
`ment marks M1, M2 and substrate alignment marks P1,
`P2. Although the substrate alignment marks as illustrated
`occupy dedicated target portions, they may be located
`in spaces between target portions (these are known as
`scribe-lane alignment marks). Similarly, in situations in
`which more than one die is provided on the mask MA,
`the mask alignment marks may be located between the
`dies.
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`[0024] The depicted apparatus could be used in at
`least one of the following modes:
`
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`
`1. In step mode, the masktable MT and the substrate
`table WT are kept essentially stationary, while an
`
`entire pattern imparted to the radiation beam is pro—
`jected onto a target portion C atone time (Le. a single
`static exposure). The substrate table WT is then
`shifted in the X and/or Y direction so that a different
`
`target portion C can be exposed. In step mode, the
`maximum size of the exposure field limits the size of
`the target portion C imaged in a single static expo-
`sure.
`
`2. In scan mode, the masktable MT andthe substrate
`table WT are scanned synchronously while a pattern
`imparted to the radiation beam is projected onto a
`target portion C (Le. asingle dynamic exposure). The
`velocity and direction of the substrate table WT rel—
`ative to the mask table MT may be determined by
`the (de-)magnification and image reversal charac-
`teristics of the projection system P8. In scan mode,
`the maximum size of the exposure field limits the
`width (in the non-scanning direction) of the target
`portion in a single dynamic exposure, whereas the
`length of the scanning motion determines the height
`(in the scanning direction) of the target portion.
`3. In another mode, the mask table MT is kept es-
`sentially stationary holding a programmable pattern-
`ing device, and the substrate table WT is moved or
`scanned while a pattern imparted to the radiation
`beam is projected onto a target portion C.
`In this
`mode, generally a pulsed radiation source is em-
`ployed and the programmable patterning device is
`updated as required after each movementofthe sub-
`strate table WT or in between successive radiation
`
`pulses during a scan. This mode of operation can be
`readily applied to maskless lithography that utilizes
`programmable patterning device, such as a pro-
`grammable mirror array of a type as referred to
`above.
`
`[0025] Combinations and/or variations on the above
`described modes of use or entirely different modes of
`use may also be employed.
`the
`[0026] A scatterometer of an embodiment of
`present invention is shown in Figure 2. Save for the light
`source, which is described further below, the scatterom-
`eter is the same as that described in US Patent Applica-
`tion 10/918,742,
`filed 16-8-2004, which document is
`hereby incorporated by reference. The light source 2 is
`focused using lens system L2 through interference filter
`30 and is focused onto substrate 6 via a microscope ob-
`jective lens L1 . The radiation is then reflected via partially
`reflective surface 34 into a CCD detector in the back pro—
`jected pupil plane 40 in orderto have the scatterspectrum
`detected. The pupil plane 40 is at the focal length of the
`lens system L1. A detector and high aperture lens are
`placed at the pupil plane. The pupil plane may be re-
`imaged with auxiliary optics since the pupil plane of a
`high-NA lens is usually located inside the lens.
`[0027] The pupil plane of the reflector light is imaged
`on the CCD detector with an integration time of, for ex-
`ample, 40 milliseconds per frame.
`In this way, a two-
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`dimensional angular scatter spectrum of the substrate
`targets is imaged on the detector. The detector may be,
`for example, an array of COD detectors or CMOS detec-
`tors. The processing of the spectrum gives a symmetrical
`detection configuration and so sensors can be made ro-
`tationally symmetrical. This allows the use of compact
`substrate tables because a target on the substrate can
`be measured at any rotational orientation relative to the
`sensor. All the targets on the substrate can be measured
`by a combination of a translation and a rotation of the
`substrate.
`
`[0028] A set of interference filters 30 is available to
`select a wavelength of interest in the range of, say, 405
`- 790 nm or even lower, such as 200 - 300 nm. Much
`longer wavelengths, e.g. about 1 .5p.m. The interference
`filter may be tunable rather than comprising a set of dif-
`ferent filters. A grating could be used instead of interfer-
`ence filters.
`
`[0029] The substrate 6 may have on it a grating. The
`grating may be printed such that after development, the
`bars are formed of solid resist lines. The bars may alter-
`natively be etched into the substrate. This pattern is sen-
`sitive to co matic aberrations in the lithographic projection
`apparatus, particularly the projection system PL, and il—
`lumination symmetry and the presence of such aberra—
`tions will manifest themselves in avariation in the printed
`grating. Accordingly, the scatterometry data ofthe printed
`gratings is used to reconstruct the gratings. The param-
`eters of the grating, such as line widths and shapes, may
`be input to the reconstruction process from knowledge
`ofthe printing step and/or other scatterometry processes.
`[0030]
`In an embodiment of the invention,
`the light
`source 2 comprises a so-called “supercontinuum“ light
`source, an example of which is shown in Figure 3. As
`shown in thatfigure, the lightsource2comprisesasource
`laser 21 whose output is fed into a non—linear fibre 22
`which mixes the light output by the source laser 21 in a
`non-linear manner so as to convert the relatively narrow
`input bandwidth into a much broader output bandwidth.
`The exact width of the broadband output from the non-
`linear fibre can be selected by selection of the type of
`source laser input, variation of the properties of the non-
`linear fibre and the length of fibre used. An output band-
`width of at least about 20nm, or at least about 200nm,
`with a lowest wavelength of less than about 400nm is
`suitable for use in the present invention.
`[0031] The non-linear fibre 22 may be a tapered fibre
`or a photonic bandgap fibre several centimeters to sev—
`eral kilometers in length. It can conveniently used to cou-
`ple the measurement beam to the desired location and
`can be arranged to emit in a nearly pure TEM00 mode
`enabling the beam to be focused on a very small spot on
`the substrate. Multimode fibres may also be used. Silicon
`waveguides and bulk materials may also be used in place
`of the non-linear fibre.
`
`Suitable source lasers include both continuous
`[0032]
`beam lasers and pulsed beam lasers, with pulse lengths
`from greater than 1 ns to less than 15 fs and repetition
`
`rates from less than 10 Hz to greater than 1 kHz. Exam—
`ples ofsuitable lasers are: erbium-doped fibre lasers, 0-
`switched lasers (e.g. Nd-Yag lasers), mode-locked la-
`sers and Raman fibre lasers.
`
`[0033] Theincreasedintensityoftheilluminationbeam
`obtained using a supercontinuum source increases sig-
`nal-to-noise ratios and allows a substantial increase in
`
`It
`measurement speed and/or measurement accuracy.
`also makes practicable measurements on latent marks
`in undeveloped resist. This facilitates in-line metrology,
`i.e.
`integration of the metrology sensor into the litho—
`graphic apparatus, potentially allowing reworking prior to
`development and/or corrections within a single batch. In
`other words, the metrology results can be used to adjust
`a parameter of a subsequent exposure on the same sub-
`strate (with or without reworking) or on a different sub-
`strate.
`
`In a particular embodiment of the invention, the
`[0034]
`spatial coherence of the beam generated by the super-
`continuum light source is used to generate interference
`fringes that can significantly increase sensitivity. This is
`shown in Figure 4. The objective lens L1 is set at a small
`defocus and arranged so that the zeroth and at least one
`of the first (in the illustrated arrangement both) diffraction
`orders produced by the test structure partially overlap in
`the pupil plane 40.
`In the overlapping region, indicated
`by hatching, interference fringes are formed. The occur-
`rence of fringes in this arrangement is described further
`in principles of Optical Disc Systems by G. Bouwhuis et
`al, Adam Hilger 1985 (ISBN 0-85274-785-3). For detec-
`tion purposes the interference pattern has several ad-
`vantages.
`i.e. when the
`in the small signal limit,
`[0035]
`Firstly,
`phase depth of the test structure is small and the first
`order beam is of low intensity, the contrast of the fringe
`pattern depends linearly on the phase depth and is there—
`fore higher than other detectors which have a quadratic
`dependence on phase depth.
`[0036]
`Secondly, the position of the fringes is depend-
`ent on the lateral offset of the test structure so that a
`
`scanning stage can be used to enable detection of the
`position of the mark and two marks in different layers can
`then be used to detect overlay.
`[0037]
`Thirdly, the fringe frequency depends on the
`defocus of the sensor with respect to the object lane of
`the test structure. The device can therefore be used to
`
`obtain depth information.
`[0038]
`Fourthly, by using a compound overlay mark
`(two gratings positioned above or near each other in two
`different layers) asymmetry between the two overlap ar-
`eas in the pupil plane 40 can be used for overlay detec-
`tion.
`
`[0039] The metrology device of embodiments of the
`invention can be incorporated into a lithographic appa-
`ratus, e.g. at the measurement station of a dual-stage
`apparatus, or a process device such as a PVD apparatus.
`[0040]
`In another particular embodiment of the inven-
`tion, shown in Figure 5, the speed of measurement of
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`the scatterometer can be substantially increased by syn—
`chronizing the output pulses of the supercontinuum light
`source to movement of a stage carrying the substrate.
`[0041] The scatterometer 101 is supplied with a pulsed
`measurement beam by supercontinuum light source 1 02
`and makes measurements of markers on a substrate W
`which is held on a table WT. The table WT is scanned
`
`underneath the scatterometer 101 by positioning device
`PW which is connected to a controller 103. Controller
`
`103 may either control the positioner PW to position the
`substrate table or may receive position information from
`a position measurement system (not shown) whilst the
`positioner is under the control of a separate controller.
`Either way, the controller is also connected to source 1 O2
`and controls source 102 to emit a pulse when the sub-
`strate W is in a position such that a marker is under the
`scatterometer.
`In this way “on-the-fly“ measurements
`can be taken much more quickly that prior art arrange-
`ments which required markers to be positioned underthe
`scatterometer and the substrate held still for long enough
`for a measurement to be taken.
`
`[0042] Yetanotherparticularembodimentoftheinven-
`tion comprises a scatterometer 200 of the spectroscopic
`reflectometer type, as shown in Figure 6. In this device,
`the supercontinuum light source 2 supplies a high—power,
`broadband, well-collimated beam which is directed to a
`beam splitter 201, which reflects the beam towards the
`substrate W to be measured. A microscope objective 202
`focuses the beam onto the substrate and collects the
`
`reflected light, directing it through beamsplitter 201 to a
`mirror 203, which reflects it to a grating 204. The grating
`204 disperses the light onto a detector 205, e.g. a cooled
`CCD array. The output of the CCD array is an spectrum
`of the reflected light, Le. a measurement of intensity as
`a function of wavelength, which can be used to deduce
`parameters of a structure on the substrate W, e.g. the
`linewidth of a grating, in a known manner, for example
`by comparison with a library of measurements form test
`structures or spectra calculated by simulation.
`[0043]
`Scatterometer 200 is similar to known scatter-
`ometer except for the use of a supercontinuum light
`source; known scatterometers ofthis type have used Hal-
`ogen or deuterium lamps, or both. Use of the supercon-
`tinuum light source increases the intensity of the incident
`beam, and hence the reflected light, allowing measure-
`ments to be taken more quickly. Scatterometer 200 may
`also be used in the system of Figure 5.
`[0044]
`Still a further particular embodiment of the in—
`vention is scatterometer 300, shown in Figure 7, which
`is of the spectroscopic ellipsometer type. In this device,
`the output of supercontinuum light source 2 is passed
`though a polarizer 301 so as to linearly polarize the beam,
`or clean up its polarization if already partially polarized.
`If the output of the supercontinuum light source 2 is al-
`ready sufficiently polarized, polarizer 301 may be omit-
`ted. The polarized beam is then passed through a rotating
`compensator 302, to enable adjustment of the polariza-
`tion direction, and is focused onto the substrate W to be
`
`inspected by lens 303. A collecting lens 304 collects the
`reflected light and directs it to a polarizing analyser 305,
`after which an optical fibre couples the light to a spectro-
`scope 307 and detector array 308, e.g. a cooled CCD
`array.
`[0045] The properties of the substrate W and the films
`or structures thereon, affectthe intensity and polarization
`state - linearly polarized light becomes elliptically polar-
`ized - of the reflected light differently at different wave-
`lengths. By rotating the analyser, the scatterometer can
`provide measurements of intensity and ellipticity as func-
`tions of wavelength, providing information to enable re—
`construction of structures on the substrate or deduction
`
`of parameters thereof, by known techniques.
`[0046] Again, scatterometer 300 is similar to known
`scatterometer except for the use of a supercontinuum
`lightsource; known scatterometers ofthis type have used
`Xe arc or deuterium lamps, or both. Use of the supercon-
`tinuum lightsource increases the intensity of the incident
`beam, and hence the reflected light, allowing measure-
`ments to be taken more quickly. Scatterometer 300 may
`also be used in the system of Figure 5.
`[0047] Although specific reference may be made in this
`text to the use of lithographic apparatus in the manufac—
`ture of ICS, it should be understood that the lithographic
`apparatus described herein may have other applications,
`such as the manufacture of integrated optical systems,
`guidance and detection patterns for magnetic domain
`memories,
`flat-panel displays,
`liquid-crystal displays
`(LCDs), thin-film magnetic heads, etc. The skilled artisan
`will appreciate that, in the context of such alternative ap-
`plications, any use of the terms “wafer“ or “die“ herein
`may be considered as synonymous with the more gen-
`eral terms “substrate" or "target portion“, respectively.
`The substrate referred to herein may be processed, be-
`fore or after exposure, in for example a track (a tool that
`typically applies a layer of resist to a substrate and de—
`velops the exposed resist), a metrology tool and/or an
`inspection tool. Where applicable, the disclosure herein
`may be applied to such and other substrate processing
`tools. Further, the substrate may be processed more than
`once, for example in order to create a multi-layer IC, so
`that the term substrate used herein may also refer to a
`substrate that already contains multiple processed lay-
`ers.
`
`[0048] Although specific reference may have been
`made above to the use of embodiments of the invention
`
`in the context of optical lithography, it will be appreciated
`that the invention may be used in other applications, for
`example imprint lithography, and where the context al-
`lows, is not limited to optical lithography. In imprint lithog-
`raphy a topography in a patterning device defines the
`pattern created on a substrate. The topography of the
`patterning device may be pressed into a layer of resist
`supplied to the substrate whereupon the resist is cured
`by applying electromagnetic radiation, heat, pressure or
`a combination thereof. The patterning device is moved
`out of the resist leaving a pattern in it after the resist is
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`cured.
`
`[0049] The terms “radiation“ and “beam“ used herein
`encompass all types of electromagnetic radiation, includ-
`ing ultraviolet (UV) radiation (e.g. having a wavelength
`of or about 365, 355, 248, 193, 157 or 126 nm) and ex-
`treme ultra-violet (EUV) radiation (e.g. having a wave-
`length in the range of 5-20 nm), as well as particle beams,
`such as ion beams or electron beams.
`
`[0050] The term "lens“, where the context allows, may
`refer to any one or combination of various types of optical
`components,
`including refractive, reflective, magnetic,
`electromagnetic and electrostatic optical components.
`[0051] While specific embodiments of the invention
`have been described above, it will be appreciated that
`the invention may be practiced otherwise than as de-
`scribed. For example, the invention may take the form of
`a computer program containing one or more sequences
`of machine-readable instructions describing a method as
`disclosed above, or a data storage medium (e.g. semi-
`conductor memory, magnetic or optical disk) having such
`a computer program stored therein.
`[0052] The de