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    公开号:NL2012996A
    申请号:NL2012996
    申请日:2014-06-13
    公开日:2015-01-06
    发明作者:Richard Quintanilha
    申请人:Asml Netherlands Bv；
    IPC主号:
    专利说明:

    INSPECTION APPARATUS AND METHOD, LITHOGRAPHICAPPARATUS, LITHOGRAPHIC PROCESSING CELL AND DEVICEMANUFACTURING METHOD
    FIELD
    The present invention relates to apparatus and methods for determiningproperties in microstructures usable, for example, in the manufacture of devices bylithographic techniques.
    BACKGROUND A lithographic apparatus is a machine that applies a desired pattern onto asubstrate, usually onto a target portion of the substrate. A lithographic apparatus canbe used, for example, in the manufacture of integrated circuits (ICs). In that instance,a patterning device, which is alternatively referred to as a mask or a reticle, may beused to generate a circuit pattern to be formed on an individual layer of the IC. Thispattern can be transferred onto a target portion (e.g., comprising part of, one, orseveral dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typicallyvia imaging onto a layer of radiation-sensitive material (resist) provided on thesubstrate. In general, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire patternonto the target portion at one time, and so-called scanners, in which each targetportion is irradiated by scanning the pattern through a radiation beam in a givendirection (the “scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible to transfer the pattern fromthe patterning device to the substrate by imprinting the pattern onto the substrate.
    In order to monitor the lithographic process, parameters of the patternedsubstrate are measured. Parameters may include, for example, the overlay errorbetween successive layers formed in or on the patterned substrate and criticallinewidth of developed photosensitive resist. This measurement may be performed ona product substrate and/or on a dedicated metrology target. There are varioustechniques for making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes andvarious specialized tools. A fast and non-invasive form of specialized inspection toolis a scatterometer in which a beam of radiation is directed onto a target on the surfaceof the substrate and properties of the scattered or reflected beam are measured. Bycomparing the properties of the beam before and after it has been reflected orscattered by the substrate, the properties of the substrate can be determined. This canbe done, for example, by comparing the reflected beam with data stored in a library ofknown measurements associated with known substrate properties. Two main types ofscatterometer are known. Spectroscopic scatterometers direct a broadband radiationbeam onto the substrate and measure the spectrum (intensity as a function ofwavelength) of the radiation scattered into a particular narrow angular range.Angularly resolved scatterometers use a monochromatic radiation beam and measurethe intensity of the scattered radiation as a function of angle.
    In lithographic processes, it is necessary frequently to make measurements ofthe structures created, e.g., for process control and verification. Various tools formaking such measurements are known, including scanning electron microscopes,which are often used to measure critical dimension (CD) Various forms ofscatterometers have been developed for use in the lithographic field. These devicesdirect a beam of radiation onto a target and measure one or more properties of thescattered radiation - e.g., intensity at a single angle of reflection as a function ofwavelength; intensity at one or more wavelengths as a function of reflected angle; orpolarization as a function of reflected angle - to obtain a "spectrum" from which aproperty of interest of the target can be determined. Determination of the property ofinterest may be performed by various techniques: e.g., reconstruction of the targetstructure by iterative approaches such as rigorous coupled wave analysis or finiteelement methods; library searches; and principal component analysis. In this type ofmeasurement devices measurements information is collected in the pupil plane of themeasurement branch.
    Properties of gratings, such as overlay or CD, can also be measured in animage plane of the measurement branch of a measurement device. This is the case forAngle Resolved Imaging Microscopy (ARIM). In the ARIM method light is directedto the target under a certain angle of incidence (AOI) resulting in a measured image.After this measurement the angle of incidence is modified and another measurementtakes place using light that is incident on the target with the modified angle. The images that are captured in this way can be used for reconstruction of the measuredtarget. The ARfM method enables to measure relatively small targets.
    SUMMARY
    According to an aspect of the present invention, there is provided an apparatusfor determining a property of a target on a substrate, the apparatus comprising: anillumination system configured to provide radiation; an optical system comprising anobjective, and configured to illuminate the target via the objective with two or moreillumination beams; an optical device configured to separately redirect diffractionorders resulting from the illumination of the target with the two or more illuminationbeams; one or more detectors in an image plane, the one or more detectors configuredto measure one or more properties of the separately redirected diffraction orders; aprocessor configured to determine the property of the target using the measured oneor more properties of the separately redirected diffraction orders.
    According to another aspect of the present invention, there is provided amethod of determining a property of a target on a substrate, the method comprisingilluminating the target via an objective with radiation of two or more illuminationbeams, separately redirecting zero diffraction orders of radiation scattered from saidsubstrate; measuring one or more properties of the separately redirected zerodiffraction orders using one or more detectors; and determining the property of thetarget using the measured one or more properties of the separately redirected zerodiffraction orders.
    According to another aspect of the present invention, there is provided alithographic apparatus comprising: an illumination system arranged to illuminate apattern; a projection system arranged to project an image of the pattern on to asubstrate; and an inspection apparatus for determining a property of a target on asubstrate. The inspection apparatus comprising: an illumination system configured toprovide radiation; an optical system comprising an objective, and configured toilluminate the target via the objective with two or more illumination beams; an opticaldevice configured to separately redirect diffraction orders resulting from theillumination of the target with the two or more illumination beams; one or moredetectors in an image plane, the one or more detectors being configured to measureone or more properties of the separately redirected diffraction orders; a processor configured to determine the property of the target using the measured one or moreproperties of the separately redirected diffraction orders.
    According to another aspect of the present invention, there is provided alithographic cell comprising: a coater arranged to coat substrates with a radiationsensitive layer; a lithographic apparatus arranged to expose images onto the radiationsensitive layer of substrates coated by the coater; a developer arranged to developimages exposed by the lithographic apparatus; and an inspection apparatus fordetermining a property of a target on a substrate. The inspection apparatus comprisingan illumination system configured to provide radiation; an optical system comprisingan objective, and configured to illuminate the target via the objective with two ormore illumination beams; an optical device configured to separately redirectdiffraction orders resulting from the illumination of the target with the two or moreillumination beams; one or more detectors in an image plane, the one or moredetectors being configured to measure one or more properties of the separatelyredirected diffraction orders; a processor configured to determine the property of thetarget using the measured one or more properties of the separately redirecteddiffraction orders.
    According to another aspect of the present invention, there is provided adevice manufacturing method comprising: using a lithographic apparatus to form apattern on a substrate; and determining a value related to a parameter of the patternby: providing radiation; illuminating the target via an objective with the radiation oftwo or more illumination beams; separately redirecting zero diffraction orders ofradiation scattered from said substrate; measuring one or more properties of theseparately redirected zero diffraction orders using one or more detectors; anddetermining the value related to a parameter of the pattern using the measured one ormore properties of the separately redirected zero diffraction orders.
    Further features and advantages of the invention, as well as the structure andoperation of various embodiments of the invention, are described in detail below withreference to the accompanying drawings. It is noted that the invention is not limited tothe specific embodiments described herein. Such embodiments are presented hereinfor illustrative purposes only. Additional embodiments will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.
    BRIEF DESCRIPTION OF THE DRAWINGS
    Embodiments of the invention will now be described, by way of example only,with reference to the accompanying schematic drawings in which correspondingreference symbols indicate corresponding parts, and in which:
    Figure 1 depicts a lithographic apparatus;
    Figure 2 depicts a lithographic cell or cluster;
    Figure 3 depicts a first scatterometer;
    Figure 4 depicts a second scatterometer;
    Figure 5 depicts an embodiment of the invention.
    Figure 6 illustrates light rays having different angles of incidence on thesubstrate;
    Figure 7 illustrates two light beams incident on the target grating on thesubstrate and the resulting scattered diffraction orders;
    Figure 8 illustrates the scanning of a quadruple across the illumination pupil;and
    Figure 9 illustrates another embodiment of the present invention.
    The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken in conjunction withthe drawings, in which like reference characters identify corresponding elementsthroughout. In the drawings, like reference numbers generally indicate identical,functionally similar, and/or structurally similar elements. The drawing in which anelement first appears is indicated by the leftmost digit(s) in the correspondingreference number.
    DETAILED DESCRIPTION
    This specification discloses one or more embodiments that incorporate thefeatures of this invention. The disclosed embodiment(s) merely exemplify theinvention. The scope of the invention is not limited to the disclosed embodiment(s).The invention is defined by the clauses appended hereto.
    The embodiment(s) described, and references in the specification to "oneembodiment", "an embodiment", "an example embodiment", etc., indicate that theembodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, orcharacteristic. Moreover, such phrases are not necessarily referring to the sameembodiment. Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is understood that it is within theknowledge of one skilled in the art to effect such feature, structure, or characteristic inconnection with other embodiments whether or not explicitly described.
    Embodiments of the invention may be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the invention may also beimplemented as instructions stored on a machine-readable medium, which may beread and executed by one or more processors. A machine-readable medium mayinclude any mechanism for storing or transmitting information in a form readable by amachine (e.g., a computing device). For example, a machine-readable medium mayinclude read only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; electrical, optical,acoustical or other forms of propagated signals, and others. Further, firmware,software, routines, instructions may be described herein as performing certain actions.However, it should be appreciated that such descriptions are merely for convenienceand that such actions in fact result from computing devices, processors, controllers, orother devices executing the firmware, software, routines, instructions, etc.
    Before describing such embodiments in more detail, however, it is instructiveto present an example environment in which embodiments of the present inventionmay be implemented.
    Embodiments of the present invention use a plurality of wavelengths (inparallel with a broadband light source or in series using a tunable monochromaticlight source) and detecting intensity for different wavelengths for spatially separateddiffraction orders.
    Figure 1 schematically shows a lithographic apparatus LAP including a sourcecollector module SO according to an embodiment of the invention. The apparatuscomprises: an illumination system (illuminator) IL configured to condition a radiationbeam B (e.g., EUV radiation); a support structure (e.g., a mask table) MT constructedto support a patterning device (e.g., a mask or a reticle) MA and connected to a firstpositioner PM configured to accurately position the patterning device; a substratetable (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist-coatedwafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g., a reflective projection system) PSconfigured to project a pattern imparted to the radiation beam B by patterning deviceMA onto a target portion C (e.g., comprising one or more dies) of the substrate W.
    The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types ofoptical components, or any combination thereof, for directing, shaping, or controllingradiation.
    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 thepatterning device, the design of the lithographic apparatus, and other conditions, suchas for example whether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. The support structuremay ensure that the patterning device is at a desired position, for example with respectto the projection system. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”
    The term “patterning device” used herein should be broadly interpreted asreferring to any device that can be used to impart a radiation beam with a pattern in itscross-section such as to create a pattern in a target portion of the substrate. It shouldbe noted that the pattern imparted to the radiation beam may not exactly correspond tothe desired pattern in the target portion of the substrate, for example if the patternincludes phase-shifting features or so called assist features. Generally, the patternimparted to the radiation beam will correspond to a particular functional layer in adevice being created in the target portion, such as an integrated circuit.
    The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, and programmableLCD panels. Masks are well known in lithography, and include mask types such asbinary, alternating phase-shift, and attenuated phase-shift, as well as various hybridmask types. An example of a programmable mirror array employs a matrixarrangement of small mirrors, each of which can be individually tilted so as to reflectan incoming radiation beam in different directions. The tilted mirrors impart a patternin a radiation beam, which is reflected by the mirror matrix.
    The term “projection system” used herein should be broadly interpreted asencompassing any type of projection system, including refractive, reflective,catadioptric, magnetic, electromagnetic and electrostatic optical systems, or anycombination thereof, as appropriate for the exposure radiation being used, or for otherfactors such as the use of an immersion liquid or the use of a vacuum. Any use of theterm “projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.
    As here depicted, the apparatus is of a transmissive type (e.g., employing atransmissive mask). Alternatively, the apparatus may be of a reflective type (e.g.,employing a programmable mirror array of a type as referred to above, or employinga reflective mask).
    The lithographic apparatus may be of a type having two (dual stage) or moresubstrate tables (and/or two or more mask tables). In such “multiple stage” machinesthe additional tables may be used in parallel, or preparatory steps may be carried outon one or more tables while one or more other tables are being used for exposure.
    The lithographic apparatus may also be of a type wherein at least a portion ofthe substrate may be covered by a liquid having a relatively high refractive index, e.g.,water, so as to fill a space between the projection system and the substrate. Animmersion liquid may also be applied to other spaces in the lithographic apparatus, forexample, between the mask and the projection system. Immersion techniques are wellknown 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, mustbe submerged in liquid, but rather only means that liquid is located between theprojection system and the substrate during exposure.
    Referring to Figure 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may be separateentities, for example when the source is an excimer laser. In such cases, the source isnot considered to form part of the lithographic apparatus and the radiation beam ispassed from the source SO to the illuminator IL with the aid of a beam deliverysystem BD comprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of the lithographicapparatus, for example when the source is a mercury lamp. The source SO and theilluminator IL, together with the beam delivery system BD if required, may bereferred to as a radiation system.
    The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least the outer and/or innerradial extent (commonly referred to as σ-outer and σ-inner, respectively) of theintensity distribution in a pupil plane of the illuminator can be adjusted. In addition,the illuminator TL may comprise various other components, such as an integrator INand a condenser CO. The illuminator may be used to condition the radiation beam, tohave a desired uniformity and intensity distribution in its cross-section.
    The radiation beam B is incident on the patterning device (e.g., mask MA),which is held on the support structure (e.g., mask table MT), and is patterned by thepatterning device. Having traversed the mask MA, the radiation beam B passesthrough the projection system PL, which focuses the beam onto a target portion C ofthe substrate W. With the aid of the second positioner PW and position sensor IF(e.g., an interferometric device, linear encoder, 2-D encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g., so as to position different targetportions C in the path of the radiation beam B. Similarly, the first positioner PM andanother position sensor (which is not explicitly depicted in Figure 1) can be used toaccurately 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, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, which form part of thesecond positioner PW. In the case of a stepper (as opposed to a scanner) the masktable MT may be connected to a short-stroke actuator only, or may be fixed. MaskMA and substrate W may be aligned using mask alignment marks Ml, M2 andsubstrate alignment marks PI, P2. Although the substrate alignment marks asillustrated occupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks). Similarly, insituations in which more than one die is provided on the mask MA, the maskalignment marks may be located between the dies.
    The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e., a single static exposure). Thesubstrate table WT is then shifted in the X and/or Y direction so that a different targetportion C can be exposed. In step mode, the maximum size of the exposure fieldlimits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the mask table MT and the substrate table WT are scannedsynchronously while a pattern imparted to the radiation beam is projected onto atarget portion C (i.e., a single dynamic exposure). The velocity and direction of thesubstrate table WT relative to the mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PL. In scanmode, the maximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereas the length of thescanning motion determines the height (in the scanning direction) of the targetportion. 3. In another mode, the mask table MT is kept essentially stationary holding aprogrammable patterning device, and the substrate table WT is moved or scannedwhile a pattern imparted to the radiation beam is projected onto a target portion C. Inthis mode, generally a pulsed radiation source is employed and the programmablepatterning device is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode of operationcan be readily applied to maskless lithography that utilizes programmable patterningdevice, such as a programmable mirror array of a type as referred to above.
    Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.
    As shown in Figure 2, the lithographic apparatus LA forms part of alithographic cell LC, also sometimes referred to a lithocell or cluster, which alsoincludes apparatus to perform pre- and post-exposure processes on a substrate.Conventionally these include spin coaters SC to deposit resist layers, developers DEto develop exposed resist, chill plates CH and bake plates BK. A substrate handler, orrobot, RO picks up substrates from input/output ports I/Ol, 1/02, moves thembetween the different process apparatus and delivers then to the loading bay LB of thelithographic apparatus. These devices, which are often collectively referred to as thetrack, are under the control of a track control unit TCU which is itself controlled bythe supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatus can be operated tomaximize throughput and processing efficiency.
    In order that the substrates that are exposed by the lithographic apparatus areexposed correctly and consistently, it is desirable to inspect exposed substrates tomeasure properties such as overlay errors between subsequent layers, line thicknesses,critical dimensions (CD), etc. If errors are detected, adjustments may be made toexposures of subsequent substrates, especially if the inspection can be done soon andfast enough that other substrates of the same batch are still to be exposed. Also,already exposed substrates may be stripped and reworked - to improve yield - ordiscarded, thereby avoiding performing exposures on substrates that are known to befaulty. In a case where only some target portions of a substrate are faulty, furtherexposures can be performed only on those target portions which are good.
    An inspection apparatus is used to determine the properties of the substrates,and in particular, how the properties of different substrates or different layers of thesame substrate vary from layer to layer. The inspection apparatus may be integratedinto the lithographic apparatus LA or the lithocell LC or may be a stand-alone device.To enable most rapid measurements, it is desirable that the inspection apparatusmeasure properties in the exposed resist layer immediately after the exposure.However, the latent image in the resist has a very low contrast - there is only a verysmall difference in refractive index between the parts of the resist which have beenexposed to radiation and those which have not - and not all inspection apparatus havesufficient sensitivity to make useful measurements of the latent image. Thereforemeasurements may be taken after the post-exposure bake step (PEB) which iscustomarily the first step carried out on exposed substrates and increases the contrastbetween exposed and unexposed parts of the resist. At this stage, the image in theresist may be referred to as semi-latent. It is also possible to make measurements ofthe developed resist image - at which point either the exposed or unexposed parts ofthe resist have been removed - or after a pattern transfer step such as etching. Thelatter possibility limits the possibilities for rework of faulty substrates but may stillprovide useful information.
    Figure 3 depicts a scatterometer which may be used in the present invention. Itcomprises a broadband (white light) radiation projector 2 which projects radiationonto a substrate W. The reflected radiation is passed to a spectrometer detector 4,which measures a spectrum 10 (intensity as a function of wavelength) of the specular reflected radiation. From this data, the structure or profile giving rise to the detectedspectrum may be reconstructed by processing unit PU, e.g., by Rigorous CoupledWave Analysis and non-linear regression or by comparison with a library of simulatedspectra as shown at the bottom of Figure 3. In general, for the reconstruction thegeneral form of the structure is known and some parameters are assumed fromknowledge of the process by which the structure was made, leaving only a fewparameters of the structure to be determined from the scatterometry data. Such ascatterometer may be configured as a normal-incidence scatterometer or an oblique-incidence scatterometer.
    Another scatterometer that may be used with the present invention is shown inFigure 4. In this device, the radiation emitted by radiation source 2 is collimated usinglens system 12 and transmitted through interference filter 13 and polarizer 17,reflected by partially reflected surface 16 and is focused onto substrate W via amicroscope objective lens 15, which has a high numerical aperture (NA), e.g., at least0.9 or at least 0.95. Immersion scatterometers may even have lenses with numericalapertures over 1. The reflected radiation then transmits through partially reflectingsurface 16 into a detector 18 in order to have the scatter spectrum detected. Thedetector may be located in the back-projected pupil plane 11, which is at the focallength of the lens system 15, however the pupil plane may instead be re-imaged withauxiliary optics (not shown) onto the detector. The pupil plane is the plane in whichthe radial position of radiation defines the angle of incidence and the angular positiondefines azimuth angle of the radiation. Alternatively, the detector can be located at animage plane. In one example, the detector is a two-dimensional detector so that a two-dimensional angular scatter spectrum of a substrate target 30 can be measured. Thedetector 18 may be, for example, an array of CCD or CMOS sensors, and may use anintegration time of, for example, 40 milliseconds per frame. A reference beam is often used for example to measure the intensity of theincident radiation. To do this, when the radiation beam is incident on the beam splitter16 part of it is transmitted through the beam splitter as a reference beam towards areference mirror 14. The reference beam is then projected onto a different part of thesame detector 18 or alternatively on to a different detector (not shown). A set of interference filters 13 is available to select a wavelength of interest inthe range of, say, 405 - 790 nm or even lower, such as 200 - 300 nm. The interference filter may be tunable rather than comprising a set of different filters. A grating couldbe used instead of interference filters.
    The detector 18 may measure the intensity of scattered light at a singlewavelength (or narrow wavelength range), the intensity separately at multiplewavelengths or integrated over a wavelength range. Furthermore, the detector mayseparately measure the intensity of transverse magnetic- and transverse electric-polarized light and/or the phase difference between the transverse magnetic- andtransverse electric-polarized light.
    Using a broadband light source (i.e., one with a wide range of lightfrequencies or wavelengths - and therefore of colors) is possible, which gives a largeetendue, allowing the mixing of multiple wavelengths. The plurality of wavelengthsin the broadband each has a bandwidth of Δλ and a spacing of at least 2 Δλ (i.e., twicethe bandwidth). Several “sources” of radiation can be different portions of anextended radiation source which have been split using fiber bundles. In this way,angle resolved scatter spectra can be measured at multiple wavelengths in parallel. A3-D spectrum (wavelength and two different angles) can be measured, which containsmore information than a 2-D spectrum. This allows more information to be measuredwhich increases metrology process robustness.
    The target 30 on substrate W may be a 1-D grating, which is printed such thatafter development, the bars are formed of solid resist lines. The target 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solidresist pillars or vias in the resist. The bars, pillars or vias may alternatively be etchedinto the substrate. This pattern is sensitive to chromatic aberrations in the lithographicprojection apparatus, particularly the projection system PL, and illuminationsymmetry and the presence of such aberrations will manifest themselves in a variationin the printed grating. Accordingly, the scatterometry data of the printed gratings isused to reconstruct the gratings. The parameters of the 1-D grating, such as linewidths and shapes, or parameters of the 2-D grating, such as pillar or via widths orlengths or shapes, may be input to the reconstruction process, performed byprocessing unit PU, from knowledge of the printing step and/or other scatterometryprocesses.
    As described above, the target is on the surface of the substrate. This targetwill often take the shape of a series of lines in a grating or substantially rectangularstructures in a 2-D array. The purpose of rigorous optical diffraction theories in metrology is effectively the calculation of a diffraction spectrum that is reflected fromthe target. In other words, target shape information is obtained for CD (criticaldimension) uniformity metrology. CD uniformity is a measurement of the uniformityof the grating on the spectrum to determine how the exposure system of thelithographic apparatus is functioning. Specifically, CD, or critical dimension, can bethe width of the object that is "written" on the substrate and is the limit at which alithographic apparatus is physically able to write on a substrate.
    The present invention relates to embodiments of apparatus for determiningcritical dimensions (CD) of periodic targets, such as gratings,
    Figure 5 illustrates an inspection apparatus according to an embodiment of thepresent invention. With reference to Figure 5, a broadband light source 702 provides anarrow pencil beam of white light, providing a plurality of wavelengths of radiation.The plurality of wavelengths are thus provided simultaneously, for fast measurementby the apparatus. In another embodiment, a tunable light source provides differentwavelengths at different times. The light source 702 may, for example, be a white-light laser or a Xenon lamp. The illumination pupil 706 at the exit of the illuminatorhas one spot 708. The pencil beam is sent through a device 710. For example, thedevice 710 comprises number of (e.g., four) apertures. The illumination pupil plane714 that exits the device 710 is illuminated with four identical white-light sources716, 716', 716” and 716”’ This provides a well-defined angle of incidence ofillumination across the target that facilitates grating reconstruction. For this reason,the extent of the point sources is kept small. The position of the white-light sources716, 716', 716” and 716”’ can be chosen differently than in a square shape. Forinstance, any configuration wherein one white-light source is positioned in each pupilquadrant would be accurate. Also, the invention is not limited to the usage of fourwhite-light sources. Also any other number (e.g., eight) of white-light sources wouldbe accurate.
    Lenses LI and L2 form a double-telecentric system that image theillumination pupil into the pupil plane of the high-NA (numerical aperture) lens L3.This objective lens L3 illuminates the target 30 which may be a small grating that issurrounded by an unknown product pattern. Lenses LI, L2 and L3 thus form anoptical system that illuminates the target via the objective. The illumination spot onthe wafer is normally chosen much larger than the grating. Typical values are, forexample, a spot diameter of 30 μπι projected on the wafer and grating size of 10x10 μιη2. The embodiment will still work when the illumination spot is smaller than thegrating, for example with a relatively large grating in a scribe lane.
    Figure 6 illustrates light rays incident on the substrate as a result from two ofthe four white-light sources (i.e., 716 and 716”)· The solid arrows represent light rayscoming from point 716 in the illumination plane 714. The dashed arrows representlight rays coming from point 716” in the illumination plane 714. As can be seen, theangle of incidence of the lights rays coming from point 716 is different than the angleof incidence of the light rays coming from 716”. The substrate W has a target grating30 surrounded by product areas 802. The illumination beam thus overfills the targetgrating 30. Figure 7 illustrates two light beams incident on the target grating 30 onthe substrate W and the resulting scattered diffraction orders. The solid arrow 902represents a light ray coming from point 716 in the illumination plane 714. The solidarrows -1, 0 and +1 represent the scattered negative first order, zeroth order andpositive first order diffracted beams respectively originating from the incident beam902. The dashed arrow 902” represents a light ray coming from point 716”in theillumination plane 714. The dashed arrows -1', 0' and +Γ represent the scatterednegative first order, zeroth order and positive first order diffracted beams respectivelyoriginating from the incident beam 902'. Each of the scattered beams has a band ofwavelengths of light because a white light source is used. For measuring properties,such as critical dimension, of target grating 30 in particular the zero order diffractedbeams are of interest. It can be seen in figure 7 that the zero order beams 0 and 0”each reflect from the grating target 30 under a different angle. The same holds for thezero order beams as a result of lights rays coming from points 716’ and 716’” (notdepicted is figures 6 and 7). The angle of reflection depends on the position of thecorresponding white-light source in the respective quadrant of the illumination pupil.The shape of the grating will affect the zeroth orders as a result of which criticaldimensions (CD) can be measured.
    Because different positions in the illumination pupil of the white-light sourcesresult in different angles of incidence, the angles of incidence can be chosen that arethe most sensitive for the to be measured properties of the target grating 30. In otherwords, the zero order information that an increased sensibility for certaincharacteristics, such as CD, of the target grating 30 can be selected according to thepresent invention.
    With reference again to Figure 5, the light that is scattered by the targetgrating 30 and the surrounding product area is collimated by lens L3 and the doubletelecentric system L3 and L4 make a magnified image of the grating and productenvironment on the field stop FS. The field stop FS is placed at the image plane of theobjective lens L3. The purpose of the field stop FS is to limit the spatial extent of theintermediate image and to suppress stray light in the detection optics. The spatial filterthus spatially filters radiation scattered from a surface of the substrate adjacent to thetarget to select radiation scattered by the target.
    Lenses L4 and L5 re-image the pupil plane PP of the scattered light onto anachromatic quadrature wedge QW. This image 718 of the pupil plane has the zerodiffraction orders resulting from the incident beams 716, 716’, 716” and 716”’. Thequadrature wedge QW redirects the light in the four quadrants of the pupil plane 718in four different directions. Thus the quadrature wedge QW is an optical deviceconfigured to separately redirect diffraction orders of radiation scattered from thesubstrate. The quadrature wedge QW may comprise four wedges. As a result of thequadrature wedge QW, lens L6 produces, in the image plane IP, four spatiallyseparated sub images 720 of the light that is transmitted by the aperture stop FS. Eachof the four sub images 720 are the width WFS of the field stop FS. The central squarein each sub-image represents the target grating and is surrounded by the productcircuitry. Although the target grating is shown as a square, it may have another shape,such as a rectangle. The images 720 comprise the zeroth order images 0, 0’, 0” andO'” resulting from respectively incident beams 716, 716’, 716” and 716’”. Theskilled person will appreciate that the arrangement of each of the four sub images inthe image plane will depend on the wedge arrangement. Other arrangement of the subimages can therefore be achieved using different relative orientation of the wedgesand/or one or more lenses L6. Furthermore, the sub images need not be arranged onthe same plane.
    As white light is used, the quadrature wedge is achromatic otherwise theimage shift would become color-dependent. Achromatic wedges can be made intransmission but reflective wedges are also suitable since they are intrinsicallyachromatic.
    Four multimode detection fibers MF are now used to capture the zero orderintensity components. Thus the fibers are a capturing device configured to capture oneor more of the separately redirected zero diffraction orders. This is “selected area” detection that suppresses light from the product environment. The position of thefibers relative to the lenses is configured to capture the selected area of each subimage 720 corresponding to the target grating. Optionally, piezo micro manipulatorsmay be used for a dynamic adjustment in the sensor.
    Multimode fibers typically have core diameters of 200 μηι and this diameter issmaller than the image of the grating in order to select light scattered by the grating inpreference to that scattered by the surrounding product area. If the grating has a lengthof 10 μηι then the magnification of the lens system L3, L4, L5 and L6 in thisembodiment is at least 40.
    The wedge angle is sufficiently large to allow a complete separation of thefour sub images 720. If the separation is too small the images will overlap causingcrosstalk from the product area into the grating area.
    The broadband light that is captured by the detection fibers is sent to fourspectrometers (S1-S4) that are nominally identical. These four spectrometerssimultaneously and in parallel measure the intensities of the four zero diffractionorders as a function of the wavelength. For example, a typical wavelength range couldbe 400 - 800 nm with a spectral resolution of 5 nm. This yields 80 pixels perspectrum so a grand total of about 320 samples. This measurement at the plurality ofthe wavelengths λ in the broadband light source can be acquired with very shortacquisition times which enables high throughput. Because several (in thisembodiment four) zero diffraction orders can be measured simultaneously and thezero diffraction orders result from incident beams with different angles of incidence(AOI), the throughput of the measurement is improved.
    The set of measured spectra can now be used in processor PU to calculate aproperty, such as CD, of the target grating. Instead of using a white-light source, asingle wavelength source can be used. The single wavelength source may be tunableor switchable to provide a plurality of wavelengths. For each single wavelength animage is projected on a detector such as a CCD camera which measures the intensitiesof the images formed by the four zero orders. In such an embodiment a patternrecognition software module executing on the processing unit PU is used to identifythe area where the grating images are located and to extract the intensities zero ordersat a particular wavelength. The wavelength is thus adjusted and the measurements are repeated in series to determine the intensities of the four zero orders a plurality of thesingle wavelengths.
    It is also possible to make a more complex illumination associated with amulti-wedges prism. For instance, this method can be easily extended to 8 wedgesprism associated with an octupole illumination. This will enable an improvement ofthe throughput by a factor of 8 (and will limit the number of scans). It is in principlefeasible to develop special multi-wedges and multi-poles illumination to avoid anyscanning and perform the acquisition of all required data in one single measurement.A priori this will require a large CCD array to fit all images.
    More measurement information can be obtained if the illumination is scannedin the illumination pupil plane. Figure 8 shows an example in case of quadrupleillumination. Four illumination beams can be created by a single aperture in eachpupil quadrant. The position of the four apertures can be of course chosen differentlythan in a square shape. The scanning of the quadruple can be done by a tilting mirrorplaced in the illumination field stop of the tool which will enable to scan the pupilwith the quadruple. Another option is having a set of different quadruple in the wheelplaced in the entrance pupil of the tool, or scanning the entrance pupil with thequadruple using the apertures holder wheel place in the entrance pupil of the tool.
    Although the measurement and modeling of intensity of diffracted light as afunction of frequency is described with reference to Figure 5, embodiments of thepresent invention also include the measurement and modeling of the polarization stateas a function of frequency using suitable ellipsometric or polarimetric techniques.
    In an alternative embodiment, instead of using a white-light source a singlewavelength source is used. The single wavelength source may be tunable orswitchable to provide a plurality of wavelengths, and the sub images 720 are projectedon a detector such as a CCD camera which measured the intensities of the imagesformed be the several 0th diffraction orders. In such an embodiment a patternrecognition software module can be used to identify the area where the sub images720 are located and to extract the intensities of the several 0th diffraction orders. A further improvement of the throughput can be achieved when a broadbandsource 702 is used and spectrometers S1-S4 are used that measure information at aplurality of wavelengths λ simultaneously (see Figure 9). In Figure 9 the samereferences are used as in figure 5. In such a configuration it will not be required toacquire many images as function of the AOI. For instance, if a spectrometer S has a spectral resolution of 5 nm and a broadband source 702 is used with a range of 400nm to 750 nm that will result for each AOI to 70 measurement points. The wavelengthdependent zero order intensities measured by the respective spectrometers S1-S4 aredepicted at the lower part of Figure 9. A multimode detection fiber MF is used to capture the several (in this casefour) 0th order intensities. The multimode detection fiber MF may also function as a“selective area” detector. This ensures partially that light from the targets environmentis suppressed. The fibers in the multimode fiber MF may for instance have a corefrom 200pm to 2 mm although also other measures are possible. In general,depending of the tool magnification and the target size in the image the properdiameter core will be chosen. Different type of Fourier filtering can be used. Thethroughput can be increased by the use of achromatic wedge associated 4 opticalfibers as detector and a quadruple in the illumination entrance pupil of the tool. Thatwill enable to measure simultaneously 4 different angles of incidence.
    The inspection apparatus and method of inspection embodiments describedherein may be used in methods of device manufacturing and may be incorporated intolithographic apparatuses and lithographic processing cells.
    Although specific reference may be made in this text to the use of inspectionapparatus in the manufacture of ICs, it should be understood that the inspectionapparatus described herein may have other applications, such as the manufacture ofintegrated optical systems, guidance and detection patterns for magnetic domainmemories, flat-panel displays, liquid-crystal displays (LCDs), thin film magneticheads, etc.. The skilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may be considered assynonymous with the more general terms “substrate” or “target portion", respectively.The substrate referred to herein may be processed, before or after exposure, in forexample a track (a tool that typically applies a layer of resist to a substrate anddevelops the exposed resist), a metrology tool and/or an inspection tool. Whereapplicable, the disclosure herein may be applied to such and other substrateprocessing tools. Further, the substrate may be processed more than once, for examplein order to create a multi-layer IC, so that the term substrate used herein may alsorefer to a substrate that already contains multiple processed layers.
    Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprintlithography, and where the context allows, is not limited to optical lithography. Inimprint lithography a topography in a patterning device defines the pattern created ona substrate. The topography of the patterning device may be pressed into a layer ofresist supplied to the substrate whereupon the resist is cured by applyingelectromagnetic radiation, heat, pressure or a combination thereof. The patterningdevice is moved out of the resist leaving a pattern in it after the resist is cured.
    The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g., having awavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet(EUV) radiation (e.g., having a wavelength in the range of 5-20 nm), as well asparticle beams, such as ion beams or electron beams.
    The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractive, reflective,magnetic, electromagnetic and electrostatic optical components.
    While specific embodiments of the invention have been described above, itwill be appreciated that the invention may be practiced otherwise than as described.For example, the invention may take the form of a computer program containing oneor more sequences of machine-readable instmctions describing a method as disclosedabove, or a data storage medium (e.g., semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein.
    The descriptions above are intended to be illustrative, not limiting. Thus, itwill be apparent to one skilled in the art that modifications may be made to theinvention as described without departing from the scope of the clauses set out below.
    It is to be appreciated that the Detailed Description section, and not theSummary and Abstract sections, is intended to be used to interpret the clauses. TheSummary and Abstract sections may set forth one or more but not all exemplaryembodiments of the present invention as contemplated by the inventor(s), and thus,are not intended to limit the present invention and the appended clauses in any way.
    The present invention has been described above with the aid of functionalbuilding blocks illustrating the implementation of specified functions andrelationships thereof. The boundaries of these functional building blocks have beenarbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof areappropriately performed.
    The foregoing description of the specific embodiments will so fully reveal thegeneral nature of the invention that others can, by applying knowledge within the skillof the art, readily modify and/or adapt for various applications such specificembodiments, without undue experimentation, without departing from the generalconcept of the present invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of the disclosedembodiments, based on the teaching and guidance presented herein. It is to beunderstood that the phraseology or terminology herein is for the purpose ofdescription and not of limitation, such that the terminology or phraseology of thepresent specification is to be interpreted by the skilled artisan in light of the teachingsand guidance.
    The breadth and scope of the present invention should not be limited by any ofthe above-described exemplary embodiments, but should be defined only inaccordance with the following clauses and their equivalents. Other aspects of theinvention are set-out as in the following numbered clauses: 1. An apparatus for determining a property of a target on a substrate, the apparatuscomprising: - an illumination system configured to provide radiation; - an optical system comprising an objective, and configured to illuminate the targetvia the objective with two or more illumination beams; - an optical device configured to separately redirect diffraction orders resulting fromthe illumination of the target with the two or more illumination beams; - one or more detectors in an image plane, the one or more detectors being configuredto measure one or more properties of the separately redirected diffraction orders; - a processor configured to determine the property of the target using the measuredone or more properties of the separately redirected diffraction orders. 2. The apparatus of clause 1, wherein the two or more illumination beams are not point-mirrored with respect to a pupil plane of the objective. 3. The apparatus of clause 1 or clause 2, wherein the optical device is configured toseparate diffraction orders of radiation scattered from said substrate resulting fromeach of the two or more illumination beams. 4. The apparatus of any of the preceding clauses, wherein the diffraction orders are zerodiffraction orders. 5. The apparatus of clause 4, wherein the optical device is configured to project theseparated diffraction orders onto the one or more detectors to form spatially separatedimages of the target arising from different separated diffraction orders. 6. The apparatus of any previous clause, wherein the illumination system comprises abroadband light source. 7. The apparatus of any previous clause, wherein the illumination system comprises atunable single-wavelength light source. 8. The apparatus of any previous clause, wherein the apparatus is configured toilluminate the target with four illuminations beams and the optical device comprisesfour wedges configured to separately redirect radiation from each of four quadrants. 9. The apparatus of any previous clause, wherein the optical device is achromatic. 10. The apparatus of any previous clause, further comprising a capturing deviceconfigured to capture one or more of the separately redirected diffraction orders. 11. The apparatus of clause 10, wherein the capturing device comprises one or moreoptical fibers. 12. The apparatus of any previous clause, wherein the measured properties comprise theintensity. 13. The apparatus of any previous clause, wherein the one or more detectors comprises aspectrometer. 14. The apparatus of clause 13, wherein the spectrometer is configured to measure one ormore properties of the separately redirected diffraction orders at a plurality ofwavelengths simultaneously. 15. A method of determining a property of a target on a substrate, the method comprising:illuminating the target via an objective with radiation of two or more illumination beams; separately redirecting zero diffraction orders of radiation scattered from saidsubstrate; measuring one or more properties of the separately redirected zero diffraction ordersusing one or more detectors; and determining the property of the target using the measured one or more properties ofthe separately redirected zero diffraction orders. 16. A lithographic apparatus comprising: an illumination system arranged to illuminate a pattern; a projection system arranged to project an image of the pattern on to a substrate; andan inspection apparatus for determining a property of a target on a substrate, theinspection apparatus comprising: - an illumination system configured to provide radiation; - an optical system comprising an objective, and configured to illuminate thetarget via the objective with two or more illumination beams; - an optical device configured to separately redirect diffraction orders resultingfrom the illumination of the target with the two or more illumination beams; - one or more detectors in an image plane, the one or more detectors beingconfigured to measure one or more properties of the separately redirected diffractionorders; - a processor configured to determine the property of the target using themeasured one or more properties of the separately redirected diffraction orders. 17. A lithographic cell comprising: a coater arranged to coat substrates with a radiation sensitive layer;a lithographic apparatus arranged to expose images onto the radiation sensitive layerof substrates coated by the coater; a developer arranged to develop images exposed by the lithographic apparatus; andan inspection apparatus for determining a property of a target on a substrate, theinspection apparatus comprising: - an illumination system configured to provide radiation; - an optical system comprising an objective, and configured to illuminate thetarget via the objective with two or more illumination beams; - an optical device configured to separately redirect diffraction orders resultingfrom the illumination of the target with the two or more illumination beams; - one or more detectors in an image plane, the one or more detectors beingconfigured to measure one or more properties of the separately redirected diffractionorders; - a processor configured to determine the property of the target using themeasured one or more properties of the separately redirected diffraction orders. 18. A device manufacturing method comprising: using a lithographic apparatus to form a pattern on a substrate; anddetermining a value related to a parameter of the pattern by: providing radiation; illuminating the target via an objective with the radiation of two or moreillumination beams; separately redirecting zero diffraction orders of radiation scattered from saidsubstrate; measuring one or more properties of the separately redirected zero diffractionorders using one or more detectors; and determining the value related to a parameter of the pattern using the measuredone or more properties of the separately redirected zero diffraction orders.
    权利要求:
    Claims (1)
    [1]
    A lithography device comprising: an exposure device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being able to apply a pattern in a cross-section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.
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    法律状态:
    2015-04-15| WDAP| Patent application withdrawn|Effective date: 20150108 |
    2015-04-22| WDAP| Patent application withdrawn|Effective date: 20150108 |
    优先权:
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    US201361842430P| true| 2013-07-03|2013-07-03|
    US201361842430|2013-07-03|
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