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  • 专利说明
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    • 专利摘要:
    A metrology system includes a radiation source configured to generate measurement radiation having a plurality of temporally separated different wavelengths, an optical system configured to direct the measurement radiation towards a substrate and a detector. The detector is configured to receive output radiation comprising the plurality of temporally separated different wavelengths. The metrology system further comprises a processor operable to determine a measurement parameter from the output radiation.
    公开号:NL2020598A
    申请号:NL2020598
    申请日:2018-03-16
    公开日:2018-10-24
    发明作者:Fredrik Friso Klinkhamer Jacob
    申请人:Asml Netherlands Bv；
    IPC主号:
    专利说明:

    FIELD [00011 The present disclosure relates to metrology systems that may be used, for example, in a lithographic apparatus.
    BACKGROUND [0002] A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g., comprising part of, one or several dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to tills direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. Another lithographic system is an interferometric lithographic system where there is no patterning device, but rather a light beam is split into two beams, and the two beams are caused to interfere at a target portion of substrate tlirough the use of a reflection system. The interference causes lines to be formed on at the target portion of the substrate.
    [0003] During lithographic operation, different processing steps may require different layers to be sequentially formed on the substrate. Accordingly, it may be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus may use a metrology system for detecting positions of the alignment marks (e.g., X and Y position) and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. The metrology system may be used to determine a height of a wafer surface in the Z direction.
    [0004] Alignment systems typically have their own illumination system. The signal detected from the illuminated alignment marks may be dependent on how well the wavelengths of the illumination system are matched to the physical or optical characteristics of the alignment marks, or physical or optical characteristics of materials in contact with or adjacent to the alignment marks. The aforementioned characteristics may vary depending on the processing steps used. Alignment systems may offer a wide band radiation beam having a set of discrete, relatively narrow passbands in order to maximize the quality and intensity of alignment mark signals detected by the alignment system. However, present systems are limited in the number of these passbands (colors) which it is practically possible to implement. The greater number of colors, the greater the information available for a measurement.
    SUMMARY [00051 Accordingly, there is a need for improving long term accuracy and stability of measurements in a metrology system.
    [00061 More specifically, it would be desirable to increase the number of different colors or wavelengths available for measurement by a metrology system.
    [0007] According to an embodiment, a metrology system comprises: a radiation source configured to generate measurement radiation having a plurality of temporally separated different wavelengths; tin optical system configured to direct the measurement radiation towards a substrate; a detector configured to receive output radiation, resulting from scattering (e.g., diffraction and/or reflection) of the measurement radiation by a structure on the substrate, the output radiation comprising said plurality of temporally separated wavelengths; and a processor operable to determine a measurement parameter from the output radiation.
    [0008] In an embodiment the radiation source is operable to scan through said plurality of temporally separated different wavelengths. In a further embodiment the radiation source is operable to scan through a sequence of different narrow wavelength bands. In a yet further embodiment, each wavelength band is narrower than 1 nm.
    [0009] In an embodiment the radiation source is operable to scan through the plurality of temporally separated wavelengths a plurality of times during a measurement period. In an embodiment the scan frequency for scanning through the plurality of temporally separated wavelengths is greater than 50 kHz, preferably greater than 100 kHz.
    [0010] In an embodiment the metrology system is operable to perform a color calibration step comprising: performing a measurement of said structure using said plurality of temporally separated wavelengths so as to determine a measurement response of the structure for each of said plurality of temporally separated different wavelengths; determining from said measurement response, a subset of said plurality of temporally separated different wavelengths which is optimized for said structure. In a further embodiment the metrology system is further operable to only use said subset of said plurality of temporally separated different wavelengths in performing measurements of the structure during production when determining said measurement parameter.
    [0011] In an embodiment the number of temporally separated different wavelengths is greater than 20.
    [0012] In an embodiment the smallest of the plurality of temporally separated different wavelengths is 500nm or smaller and the largest of the plurality of temporally separated different wavelengths is 900nm or larger.
    [0013] In an embodiment the radiation source comprises at least one tunable laser. In a further embodiment the radiation source comprises a plurality of tunable lasers, each generating measurement radiation in a different sub-range of said range of wavelengths.
    [0014] In an embodiment the processor is operable to temporally separate measurement data obtained from the output radiation according to said temporally separated different wavelengths. In a further embodiment the processor is operable to determine said measurement parameter from measurement data relating to at least one of said temporally separated different wavelengths. In another embodiment the processor is operable to determine which one or more of said temporally separated different wavelengths shows the best measurement response when measuring a structure, and use the measurement data relating to the one or more temporally separated different wavelengths which shows the best measurement response in determining said measurement parameter. In yet another embodiment the processor is operable to determine a combination of one or more of said temporally separated different wavelengths which minimizes the effect of asymmetry in a target being measured by the metrology device, on a measurement of the target. In yet another embodiment the processor is operable to determine from said measurement data, the relationship describing the variation of measurement response with wavelength when measuring a target, for a particular target and/or the stack in which it is comprised.
    [0015] In an embodiment said measurement parameter is one or more of: overlay, focus and a physical dimension of a structure on the substrate.
    [0016] In an embodiment said metrology device is an alignment device for determining the position of a substrate holder with reference to a reference structure in a lithographic apparatus and said measurement parameter is the position of the substrate holder.
    [0017] In an embodiment the metrology system comprises an interferometer configured to receive scattered radiation having been diffracted from a target on the substrate and to produce said output radiation from interference between the scattered radiation.
    [0018] In another embodiment, a lithographic apparatus is provided, comprising: an illumination system configured to illuminate a pattern of a patterning device; a projection system configured to project an image of the pattern onto a target portion of a substrate; and a metrology system of the first aspect.
    [0019] In yet another embodiment, a method of measuring a structure on a substrate comprises:
    generating measurement radiation having a plurality of temporally separated different wavelengths; directing the measurement radiation towards a substrate; detecting the output radiation, resulting from scattering of the measurement radiation by a structure on the substrate, the output radiation comprising said plurality of temporally separated wavelengths; and determining a measurement parameter from the output radiation.
    [0020] In an embodiment the generating step comprises scanning through said plurality of temporally separated different wavelengths. In a further embodiment said scanning comprises scanning through a sequence of different narrow wavelength bands. In an embodiment each wavelength band is narrower than lnm.
    [0021] In an embodiment the method comprises scanning through the plurality of temporally separated different wavelengths a plurality of times during a measurement period.
    [0022] In an embodiment the scan frequency for scanning through the plurality of temporally separated different wavelengths is greater than 50 kHz, or greater than 100 KHz.
    [0023] In an embodiment the method comprises performing an initial color calibration step comprising performing a measurement of said structure using said plurality of temporally separated different wavelengths so as to determine a measurement response of the structure for each of said plurality of temporally separated different wavelengths, and determining from said measurement response, a subset of said plurality of temporally separated different wavelengths which is optimized for said structure. In a further embodiment the method further comprises only using said subset of said plurality of temporally separated different wavelengths in performing measurements of the structure during production when determining said measurement parameter.
    [0024] In an embodiment the method comprises temporally separating measurement data obtained from the output radiation according to said temporally separated different wavelengths. In a further embodiment the method comprises determining said measurement parameter from measurement data relating to at least one of said temporally separated different wavelengths. In another embodiment, the method comprises determining which one or more of said temporally separated different wavelengths shows the best measurement response when measuring a structure, and using the measurement data relating to the one or more temporally separated different wavelengths which shows the best measurement response in determining said measurement parameter. In yet another embodiment the method further comprises determining a combination of one or more of said temporally separated different wavelengths which minimizes the effect of asymmetry in a target being measured, on a measurement of the target. In another embodiment the method comprises determining from said measurement data, the relationship describing the variation of measurement response with wavelength when measuring a target, for a particular target and/or the stack in which it is comprised.
    [0025] In an embodiment the method comprises determining the position of a substrate holder with reference to a reference structure in a lithographic apparatus and said measurement parameter is the position of the substrate holder.
    [0026] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant artfs) based on the teachings contained herein.
    BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES [0027] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.
    [0028] Figure lisa schematic illustration of a reflective lithographic apparatus according to an embodiment;
    [0029] Figure 2 is a schematic illustration of a transmissive lithographic apparatus according to an embodiment;
    [0030] Figure 3 is a schematic illustration of a lithographic cell, according to an embodiment;
    and [0031] Figure 4 is a schematic illustration of a metrology system, according to an embodiment.
    [0032] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.
    DETAILED DESCRIPTION [0033] This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the clauses appended hereto.
    [0034] The embodiment(s) described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment/s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
    [0035] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention may be implemented.
    [0036] Figures 1 and 2 are schematic illustrations of a lithographic apparatus 100 and lithographic apparatus 100', respectively, in which embodiments of the present invention may be implemented. Lithographic apparatus 100 and lithographic apparatus 100' each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100' also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.
    [0037] The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.
    [0038] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus 100 and 100', and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable, as required. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection sy stem PS.
    [0039] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.
    [0040] The patterning device MA may be transmissive (as in lithographic apparatus 100' of Figure
    2) or reflective (as in lithographic apparatus 100 of Figure 1). Examples of patterning devices MA include reticles, 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 hybrid 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 the radiation beam B which is reflected by a matrix of small mirrors.
    [0041] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.
    [0042] Lithographic apparatus 100 and/or lithographic apparatus 100' can be of a type having two (dual stage) or more substrate tables WT (and/or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be earned out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.
    [0043] Referring to Figures 1 and 2, the illuminator IL receives a radiation beam front a radiation source SO. The source SO and the lithographic apparatus 100, 100' can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in Figure 2) including, for example, suitable directing mirrors and/or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100'—for example when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, can be referred to as a radiation system.
    [0044] The illuminator IL can include an adjuster AD (in Figure 2) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as “σ-outer” and “σ-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in Figure 2), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.
    [0045] Referring to Figure 1, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner
    PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.
    [0046] Referring to Figure 2, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, 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. The projection system has a pupil PPU conjugate to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at a mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.
    [0047] With the aid of the second positioner PW and position sensor IF (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in Figure 2) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).
    [0048] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner P W. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator only or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (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 can be located between the dies.
    [0049] Mask table MT and patterning device MA can be in a vacuum chamber, where an invacuum robot 1VR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to the invacuum robot 1VR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.
    [0050] The lithographic apparatus 100 and 100' can be used in at least one of the following modes:
    [0051] 1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., 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.
    [0052] 2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.
    [0053] 3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.
    [0054] Combinations and/or variations on the described modes of use or entirely different modes of use can also be employed.
    [0055] In a further embodiment, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.
    [0056] Figure 3 at 200 shows the lithographic apparatus 100, 100’ in the context of an industrial production facility for semiconductor products. Within the lithographic apparatus (or “litho tool” 200 for short), the measurement station MEA is shown at 202 and the exposure station EXP is shown at 204. A control unit LACU is shown at 206. Within the production facility, apparatus 200 forms part of a “litho cell” or “litho cluster” that contains also a coating apparatus 208 for applying photosensitive resist and other coatings to substrate W for patterning by the apparatus 200. At the output side of apparatus 200, a baking apparatus 210 and developing apparatus 212 are provided for developing the exposed pattern into a physical resist pattern.
    [0057] Once the pattern has been applied and developed, patterned substrates 220 are transferred to other processing apparatuses such as are illustrated at 222, 224, 226. A wide range of processing steps are implemented by various apparatuses in a typical manufacturing facility. For the sake of example, apparatus 222 in this embodiment is an etching station, and apparatus 224 performs a postetch annealing step. Further physical and/or chemical processing steps are applied in further apparatuses, 226, etc.. Numerous types of operation can be required to make a real device, such as deposition of material, modification of surface material characteristics (oxidation, doping, ion implantation etc.), chemical-mechanical polishing (CMP), and so forth. The apparatus 226 may, in practice, represent a series of different processing steps performed in one or more apparatuses.
    [0058] As is well known, the manufacture of semiconductor devices involves many repetitions of such processing, to build up device structures with appropriate materials and patterns, layer-by-layer on the substrate. Accordingly, substrates 230 arriving at the litho cluster may be newly prepared substrates, or they may be substrates that have been processed previously in this cluster or in another apparatus entirely. Similarly, depending on the required processing, substrates 232 on leaving apparatus 226 may be returned for a subsequent patterning operation in the same litho cluster, they may be destined for patterning operations in a different cluster, or they may be finished products to be sent for dicing and packaging.
    [0059] Each layer of the product structure requires a different set of process steps, and the apparatuses 226 used al each layer may be completely different in type. Further, even where the processing steps to be applied by the apparatus 226 are nominally the same, in a large facility, there may be several supposedly identical machines working in parallel to perform the step 226 on different substrates. Small differences in set-up or faults between these machines can mean that they influence different substrates in different ways. Even steps that are relatively common to each layer, such as etching (apparatus 222) may be implemented by several etching apparatuses that are nominally identical but working in parallel to maximize throughput. In practice, moreover, different layers require different etch processes, for example chemical etches, plasma etches, according to the details of the material to be etched, and special requirements such as, for example, anisotropic etching.
    [0060] The previous and/or subsequent processes may be performed in other lithography apparatuses, as just mentioned, and may even be performed in different types of lithography apparatus. For example, some layers in the device manufacturing process which are very demanding in parameters such as resolution and overlay may be performed in a more advanced lithography tool than other layers that are less demanding. Therefore some layers may be exposed in an immersion type lithography tool, while others are exposed in a ‘dry’ tool. Some layers may be exposed in a tool working at DUV wavelengths, while others are exposed using EUV wavelength radiation.
    [0061] Also shown in Figure 3 is a metrology apparatus 240 which is provided for making measurements of parameters of the products at desired stages in the manufacturing process. A common example of a metrology station in a modem lithographic production facility is a scatterometer, for example an angle-resolved scatterometer or a spectroscopic scatterometer, and it may be applied to measure properties of the developed substrates at 220 prior to etching in the apparatus 222. Using metrology apparatus 240, it may be determined, for example, that important performance parameters such as overlay or critical dimension (CD) do not meet specified accuracy requirements in the developed resist. Prior to the etching step, the opportunity exists to strip the developed resist and reprocess the substrates 220 through the litho cluster. As is also well known, the metrology results from the apparatus 240 can be used to maintain accurate performance of the patterning operations in the litho cluster, by making small adjustments over time, thereby minimizing the risk of products being made out-ofspecification, and requiring re-work. Of course, metrology apparatus 240 and/or other metrology apparatuses (not shown) can be applied to measure properties of the processed substrates 232. 234, and incoming substrates 230.
    [0062] Figure 4 illustrates a schematic of a cross-sectional view of a metrology system 400 that can be implemented as a part of lithographic apparatus 100 or 100', according to an embodiment. In an example of this embodiment, metrology system 400 may be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Metrology system 400 may be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithography apparatus 100 or 100' using the detected positions of the alignment marks. Such alignment of the substrate may ensure accurate exposure of one or more patterns on the substrate.
    [0063] According to an embodiment, metrology system 400 may include ail illumination system 412, a reflector 414, an interferometer 426, a detector 428, and an analyzer 430, according to an example of tills embodiment. Illumination system 412 may be configured to provide (electromagnetic) measurement radiation 413. Reflector 414 may be configured to receive measurement radiation 413 and direct measurement radiation 413 towards substrate 420 as beam 415, according to an embodiment. Reflector 414 may be a mirror or dichromatic mirror. In one example, stage 422 is moveable along direction 424. Radiation 415 may be configured to illuminate an alignment mark or a target 418 located on substrate 420. In another example, radiation 415 is configured to reflect from a surface of substrate 420. Alignment mark or target 418 may be coated with a radiation sensitive film in an example of this embodiment. In another example, alignment mark or target 418 may have one hundred and eighty degree symmetry. That is, when alignment mark or target 418 is rotated one hundred and eighty degrees about an axis of symmetry perpendicular to a plane of alignment mark or target 418, rotated alignment mark or target 418 may be substantially identical to an un-rotated alignment mark or target 418.
    [0064] As illustrated in Figure 4, interferometer 426 may be configured to receive radiation 417. Radiation 419 may be scattered (e.g., diffracted and/or refracted from an alignment mark or target 418, or reflected from a surface of substrate 420), and is received at interferometer 426 as radiation 417. Interferometer 426 comprises any appropriate set of optical-elements, for example, a combination of prisms that may be configured to form two images of alignment mark or target 418 based on the received radiation 417. It should be appreciated that a good quality image need not be formed, but that the features of alignment mark 418 should be resolved. Interferometer 426 may be further configured to rotate one of the two images with respect to the other of the two images one hundred and eighty degrees and recombine the two images interferometiically.
    [0065] In an embodiment, detector 428 may be configured to receive the recombined image 427 and detect an interference as a result of the recombined image 427 when alignment axis 421 of metrology system 400 passes through a center of symmetry (not shown) of alignment mark or target
    418. Such interference may be due to alignment mark or target 418 being one hundred and eighty degree symmetrical, and the recombined image 427 interfering constructively or destructively, according to an example embodiment. Based on the detected interference, detector 428 may be further configured to determine a position of the center of symmetry of alignment mark or target 418 and consequently, detect a position of substrate 420. According to an example, alignment axis 421 may be aligned with an optical beam perpendicular to substrate 420 and passing through a center of image rotation interferometer 426. In another example, detector 428 is configured to receive the recombined image 427 and detect an interference of light being reflected off a surface of substrate 420.
    [0066] In a further embodiment, analyser 430 may be configured to receive signal 429 including information of the determined center of symmetry. Analyser 430 may be further configured to determine a position of stage 422 and correlate the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and consequently, the position of substrate 420 may be accurately known with reference to stage 422. Alternatively, analyser 430 may be configured to determine a position of metrology system 400 or any other reference element such that the center of symmetry of alignment mark or target 418 may be known with reference to metrology system 400 or any other reference element. Analyser 430 may be comprised as (or part of) control unitLACU of Figure 3.
    [0067] It should be noted that even though reflector 414 is shown to direct radiation 413 towards alignment mark or target 418 as radiation 415, the disclosure is not so limiting. It would be apparent to a person skilled in the relevant art that other optical arrangements may be used to obtain the similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418. Reflector 414 may direct the illumination in a direction normal to the surface of substrate 420, or at an angle.
    [0068] It is known that measurements using a metrology device, such as the metrology device or alignment sensor 400 illustrated, may be influenced by the stack overlaying, forming part of and/or beneath the mark or target being measured and also by process asymmetry in the mark. More specifically, the stack may respond differently to different wavelengths (or polarizations) of measurement radiation resulting in large reflectivity variation over different wavelengths. As such, a plot of received intensity at the detector 428 for light diffracted from an alignment mark as a function of wavelength of the measurement radiation 413 (e.g., a swing curve) will show that there is very large variation in the received intensity over the different wavelengths. Furthermore different stacks respond differently, such that the swing curve will be very different for alignment marks measured through different stacks. Additionally, process asymmetry in an alignment mark (e.g., un-designed and undesired asymmetry in the mark which is typically designed to be a symmetrical grating, for example) results in an apparent measured positional shift of the alignment mark.
    [0069] To mitigate these issues, it is known to use a multi-band measurement radiation source outputting measurement radiation in a plurality (e.g., four) colors. Tins increases the chance that there will be at least one color which shows a satisfactory reflectivity response for measurement of a target through a specific stack. Multiple colors also mean that the effect of mark asymmetry can be mitigated as the measurement response will be different for the different wavelengths, and therefore a measurement recipe (combination of wavelengths and polarizations) can be determined which is least affected by the mark asymmetry.
    [0070] However, the swing curve for a particular stack may show a number of troughs (wavelengths for which received intensity is very low indicating low reflectivity), and it is possible that each of the wavelength bands of the measurement radiation coincides with one of these troughs. If this occurs, no valid alignment measurement will be possible (wafer reject) as there will be insufficient measured intensity at any of the available wavelengths. Additionally, some of the wavelength bands may have a finite bandwidth, and where one of these bands are centered on a steep slope of the swing curve, one side of the band will be reflected more than the other; since the two sides go through different parts of the objective lens they will therefore be subject to different aberrations. This results in an alignment bias.
    [0071] Another issue with simultaneous measurement with multiple wavelengths is that a demultiplexer is required to separate the colors for processing. This can be a high cost component, particularly where there are a large number (e.g., 10 or more) of different colors.
    [0072] It is therefore proposed that different wavelengths of the measurement radiation are separated in the time domain, which is also named temporal wavelength separation. In such a proposal, illumination system 412 scans through the different wavelengths over time. This is indicated in Figure 4 by the plot 431 of intensity against time for the measurement radiation 413 output from illumination system 412. This shows the illumination sy stem 412 scanning one or more times through a plurality of different wavelengths (each represented by a spike of different dashed line form) over time, in this case n different wavelengths. The scanning through the plurality of n different wavelengths by the radiation source is described in the following example. A first wavelength is provided, at time tl, after which a second wavelength is provided at a time t2, which is temporally separated from time tl by a selected time period. After the second wavelength is provided, a third wavelength is provided at time t3, which is temporally separated from and following time t2 by a selected time period. This is repeated until a n13’ wavelength is provided at a time tn, which is temporally separated from and after the previous (nl)th wavelength by a selected amount of time. Then, in an embodiment, the scanning through the n different wavelengths begins again, and the first wavelength is provided again at a certain time period after the nlh wavelength was provided. The scanning through the plurality of different wavelengths may be repeated any number of times. It should be noted that at least two of the first, second, third,...nlh wavelengths are different with respect to each other. In an embodiment all wavelengths of the plurality of n wavelengths are different with respect to each other. A corresponding plot 432 relating to the intensities of the recombined image 427 following modulation by measurement of an alignment mark is also shown. Each modulated color (spike) comprises information on alignment, reflectivity and mark asymmetry. All colors are captured by detector 428. The separation of these colors can now be performed in the time domain, as indicated by plots 433, e.g., by analyser 430 or control unit LACU or other processor. No demultiplexer is required. Further processing of one or more of the separated color signals can then be performed to determine alignment position and/or mark asymmetry etc..
    [0073] In a specific embodiment, the bandwidth of each wavelength may be small (e.g., less than lnm bandwidth). In a specific embodiment, the scan speed over the full wavelength range (n wavelengths) may be greater than 50 kHz, and more specifically in the region of 100 kHz; this may provide about 10 samples at each wavelength per measurement period of the alignment mark, hi a specific embodiment, the number of wavelengths n may be greater than 20, greater than 30 or greater than 40.
    [0074] Preferably, the illumination system 412 may comprise a radiation source (e.g., laser source) having a tunable wavelength of sufficient range (e.g., 500nm to 900nm), sufficient power per pulse and sufficiently fast scanning. A narrow linewidth may also be preferred. Such a radiation source may comprise a tunable laser. Examples of a suitable tunable laser may be found in sensor interrogators for communications, which also require fast scanning capability. It is also possible (e.g., where a laser of sufficient range is unavailable) to use two or more t unable lasers, each operating in a sub-band of the required wavelength band, thereby dividing the required range between the two or more tunable lasers. [0075] If no radiation source is available which has sufficiently fast scanning (e.g., approximately 100kHz, then in an embodiment a color (or wavelength) calibration is proposed. It is proposed that such a color calibration is performed (e.g., once) for each measured mark/target/stack (e.g., per alignment mark/stack design). In such a color calibration step, an alignment mark (or other target as applicable) is measured using all available wavelengths (optionally all wavelength/polarization combinations). A swing curve can then be determined, from which a subset of available colors (e.g., between 8 or 12, more specifically 10, different colors) is identified which is optimized for that alignment mark. These may be the colors (or color/polarization combinations) which show the best measurement response (e.g., greatest reflectivity). In such an embodiment, it is proposed that measurements of the corresponding alignment mark or stack (or all measurements with that alignment mark/stack design) during production are performed with the subset of wavelengths (colors) optimized for that mark/stack.
    [0076] There tire a number of advantages in temporally septirating different wavelengths of measurement radiation for a metrology device. Such a concept allows more wavelengths to be used in a measurement and therefore greatly increases the probability that some of the wavelengths will be at, or sufficiently near, an intensity peak of the swing curve, reducing risk of failed alignment. It is also possible to ensure that the separate wavelengths can have a small bandwidth, making them less prone to alignment error resultant from wavelength dependent reflectivity in a single capture. By contrast, creating optical filters with sufficiently small bandwidth is very difficult or not possible. Additionally, the greater number of wavelengths means there is more information available. This means that alignment measurement and/or mark asymmetry correction can be more accurate. For example, by creating a linear combination of the available wavelengths, a recipe can be created which minimizes the effect of mark asymmetry. The more wavelengths available, the better such a correction scheme will work. It also provides the opportunity to construct a swing curve from an (in-line) measurement, increasing further the amount of information on available on the process. Finally, the metrology device no longer requires a demultiplexer to separate the wavelengths spatially.
    [0077] The metrology system 400 is shown and described as an alignment system (e.g., measuring x-y position of features on a substrate) where the light is directed towards a substrate in substantially normal direction to a surface of the substrate, and the diffracted light is collected. In another example, the light may be directed at an angle above the substrate surface, and the diffracted light is collected. The metrology system may alternatively be a height sensor (e.g., measuring z position of features on, or the surface of, the substrate). When used as height sensors, the metrology system uses light incident at an angle above the surface of the substrate and collect the reflected light rather than diffraction. In yet another example, the metrology system 400 may be a metrology system for making periodic measurements of formed structures (e.g., of overlay, focus or critical dimension), from which corrections may be determined and fed back to the lithographic system, such as metrology system MET 240 of Figure 3.
    [0078] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture 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 applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops 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 layers.
    [0079] Although specific reference may have been made above to the use of embodi ments 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 allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. Dae 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 cured.
    [0080] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.
    [0081] In the embodiments described herein, the terms 'lens” and “lens element,” where the context allows, can refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.
    [0082] Further, the terms “radiation,” “beam,” and “light” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (for example, having a wavelength λ of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-20 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and/or, 1-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in an embodiment, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.
    [0083] The term “substrate” as used herein generally describes a material onto which subsequent material layers are added. In embodiments, the substrate itself may be patterned and materials added on top of it may also be patterned, or may remain without patterning.
    [0084] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention.
    [0085] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the clauses. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments 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.
    [0086] The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description.
    Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.
    [0087] The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.
    [0088] The breadth and scope of the present invention should not be limited by any of the abovedescribed exemplary embodiments, but shotdd be defined only in accordance with the following clauses and their equivalents. Other aspects of the invention are set out as in the following numbered clauses:
    1. A metrology system, comprising:
    a radiation source configured to generate measurement radiation having a plurality of temporally separated different wavelengths;
    an optical system configured to direct the measurement radiation towards a substrate;
    a detector configured to receive output radiation, resulting from scattering of the measurement radiation by a structure on the substrate, the output radiation comprising said plurality of temporally separated different wavelengths; and a processor operable to determine a measurement parameter from the output radiation.
    2. A metrology system as described in clause 1, wherein the radiation source is operable to scan through said plurality of temporally separated different wavelengths.
    3. A metrology system as described in clause 2, wherein the radiation source is operable to scan through a sequence of different narrow wavelength bands.
    4. A metrology system as described in clauses 2 or 3, wherein the radiation source is operable to scan through the plurality of temporally separated wavelengths a plurality of times during a measurement period.
    5. A metrology system as described in any preceding clause, wherein the radiation source comprises a plurality of tunable lasers, each generating measurement radiation in a different sub-range of said range of wavelengths.
    6. A metrology system as described in any preceding clause, wherein the processor is operable to temporally separate measurement data obtained from the output radiation according to said temporally separated different wavelengths.
    7. A metrology system as described in clause 6, wherein the processor is operable to determine said measurement parameter from measurement data relating to at least one of said temporally separated different wavelengths.
    8. A metrology system as described in any preceding clause wherein said measurement parameter is one or more of: overlay, focus and a physical dimension of a structure on the substrate.
    9. A metrology system as described in any of clauses 1 to 8, wherein said metrology device is iin alignment device for determining the position of a substrate holder with reference to a reference structure in a lithographic apparatus and said measurement parameter is the position of the substrate holder.
    10. A lithographic apparatus, comprising:
    an illumination system configured to illuminate a pattern of a patterning device;
    a projection system configured to project an image of the pattern onto a target portion of a substrate; and a metrology system as described in any preceding clause.
    11. A method of measuring a structure on a substrate, comprising:
    generating measurement radiation having a plurality of temporally separated different wavelengths;
    directing the measurement radiation towards a substrate;
    detecting the output radiation, resulting from scattering of the measurement radiation by a structure on the substrate, the output radiation comprising said plurality of temporally separated different wavelengths: and determining a measurement parameter from the output radiation.
    12. A method as described in clause 11, wherein the generating step comprising scanning through said plurality of temporally separated different wavelengths.
    13. A method as described in clauses 11 or 12 comprising performing an initial color calibration step comprising:
    performing a measurement of said structure using said plurality of temporally separated different wavelengths so as to determine a measurement response of the structure for each of said plurality of temporally separated different wavelengths;
    determining from said measurement response, a subset of said plurality of temporally separated different wavelengths which is optimized for said structure.
    14. A method as described in any of clauses 11 to 13, comprising temporally separating measurement data obtained from the output radiation according to said temporally separated different wavelengths.
    15. A method as described in clause 14, comprising:
    determining which one or more of said temporally separated different wavelengths shows the best measurement response when measuring a structure; and using the measurement data relating to the one or more temporally separated different wavelengths which shows the best measurement response in determining said measurement parameter.
    权利要求:
    Claims (1)
    [1]
    CONCLUSION
    A lithography apparatus comprising:
    an illumination device adapted to provide a radiation beam;
    a carrier constructed for supporting a patterning device, which patterning device is in
    5 is capable of applying 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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    引用文献:
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    EP17166853|2017-04-18|
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