Method for determining the value of a parameter of interest in a patterning process, device manufacturing method

Abstract

The present disclosure relates to determining a value of a parameter of interest for a patterning process. A plurality of calibration data units are acquired from a target during a metrology process. Each of at least two calibration data units represents detection radiation acquired during the metrology process using a different corresponding polarization setting, each polarization setting defining a polarization property of incident radiation for the metrology process and a polarization property of detection radiation for the metrology process. Calibration information about the metrology process is acquired using the calibration data units. Measurement data units representing detection radiation scattered from another target are acquired, the other target comprising a structure formed on a substrate or on another substrate using the patterning process. The value of the parameter of interest is determined using the measurement data units and the acquired calibration information.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of European patent application 18203837.2 filed on October 31, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present description relates to obtaining values ​​of parameters of interest of a patterning process, such as a patterning process using a lithographic apparatus as part of a device fabrication process. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of an integrated circuit (IC) or other device designed to function. In this case, a pattern forming device (alternatively referred to as a mask or reticle) can be used to generate a circuit pattern that is to be formed on a single layer of a device designed to function. The pattern can be transferred to a target portion (e.g., a portion including one or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned continuously. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once; and so-called scanners, in which each target portion is irradiated by scanning the pattern by a radiation beam in a given direction (the "scanning" direction) while synchronously scanning the substrate parallel or antiparallel to the direction. The pattern can also be transferred from the pattern forming device to the substrate by imprinting the pattern onto the substrate.

[0005] Multiple layers and / or features can be manufactured and processed using different manufacturing processes (e.g., deposition, lithography, etching, chemical mechanical polishing, and ion implantation). Multiple devices can be manufactured on multiple dies on a substrate and then separated into individual devices. The device manufacturing process can be considered a patterning process. The patterning process involves a pattern transfer step, such as optical and / or nanoimprint lithography using a lithography apparatus to provide a pattern on a substrate, and typically but optionally involves one or more related pattern processing steps, such as resist development by a developing apparatus, baking of the substrate using a baking tool, etching of the pattern by an etching apparatus, etc. In addition, the patterning process involves one or more metrology processes.

[0006] Metrology processes are used at various steps during the patterning process to monitor and / or control the process. For example, the metrology process is used to measure one or more characteristics of the substrate, such as the relative position (e.g., registration, overlay, alignment, etc.) or size (e.g., line width, critical dimension (CD), thickness, etc.) of features formed on the substrate during the patterning process, so that, for example, the performance of the patterning process can be determined based on the one or more characteristics. If one or more characteristics are unacceptable (e.g., outside a predetermined range of characteristics), one or more variables of the patterning process can be designed or changed, for example, based on the measurement of the one or more characteristics, so that the substrate manufactured by the patterning process has acceptable characteristics.

[0007] With the development of lithography and other patterning process technologies, the size of functional elements has been continuously reduced, while the number of functional elements (such as transistors) of each device has been steadily increasing for decades. At the same time, the requirements for precision in terms of overlay, critical dimension (CD), etc. have become increasingly stringent. Errors (such as overlay errors, CD errors, etc.) are inevitably generated in the patterning process. For example, imaging errors may be caused by optical aberrations, pattern forming device heating, pattern forming device errors and / or substrate heating, and can be characterized by, for example, overlay, CD, etc. Additionally or alternatively, errors may be introduced into other parts of the patterning process (such as etching, developing, baking, etc.), and similarly can be characterized by, for example, overlay, CD, etc. Errors may cause problems with device function, including the inability of the device to operate or one or more electrical problems in the functional device. Therefore, it is necessary to be able to characterize one or more of these errors and take steps to design, modify, control, etc. patterning processes to reduce or minimize one or more of these errors. Summary of the invention

[0008] According to one aspect, a method for determining a value of a parameter of interest for a patterning process is provided, the method comprising: acquiring a plurality of calibration data units, each calibration data unit representing detected radiation scattered from a corresponding target during a metrology process, the target comprising a structure formed on a substrate using a patterning process; wherein each calibration data unit of at least two calibration data units represents detected radiation acquired using a different corresponding polarization setting during the metrology process, each polarization setting defining a polarization property of incident radiation for the metrology process and a polarization property of detected radiation for the metrology process; acquiring calibration information about the metrology process using the calibration data units; acquiring a measurement data unit representing detected radiation scattered from another target, the other target comprising a structure formed on the substrate or on another substrate using the patterning process; and determining the value of the parameter of interest using the measurement data unit and the acquired calibration information.

[0009] According to one aspect, a method for determining a value of a parameter of interest for a patterning process is provided, the method comprising: acquiring a first pair of calibration data units, each calibration data unit representing detected radiation scattered from a target during a metrology process, the target comprising a structure formed on a substrate using a patterning process; acquiring a first calibration data unit in the first pair of calibration data units when the substrate is at a reference angular position; acquiring a second calibration data unit in the first pair of calibration data units when the substrate is rotated away from the reference angular position by a predetermined angle; acquiring first calibration information about the metrology process using the first pair of calibration data units; acquiring measurement data units representing detected radiation scattered from another target, the other target comprising a structure formed on the substrate using the patterning process or on another substrate; and determining the value of the parameter of interest using the measurement data units and the acquired first calibration information. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0011] Figure 1 An embodiment of a lithographic apparatus is schematically depicted;

[0012] Figure 2 An embodiment of a lithographic cell or cluster is schematically depicted;

[0013] Figure 3A is a schematic diagram of a metrology device for measuring a target using a first pair of illumination apertures providing certain illumination patterns according to an embodiment;

[0014] Figure 3B is a schematic diagram of the diffraction spectrum of a target for a given irradiation direction;

[0015] Figure 3C is a schematic diagram of a second pair of illumination apertures providing an additional illumination pattern for diffraction-based overlay measurement;

[0016] Figure 3D is a schematic diagram of a third pair of illumination apertures combining the first pair of apertures and the second pair of apertures to provide an additional illumination mode for diffraction-based overlay measurements;

[0017] Figure 4 The form of a plurality of periodic structure (e.g., a plurality of grating) targets and the contours of measurement points on a substrate are schematically depicted;

[0018] Figure 5 Schematic depiction of the use Figure 3A The device obtains Figure 4 An image of the target;

[0019] Figure 6 schematically depicts example metering devices and metering techniques;

[0020] Figure 7 An example metering device is schematically depicted;

[0021] Figure 8 The relationship between the irradiation point of the metering device and the metering target is shown;

[0022] Fig. 9 schematically depicts a process for deriving one or more variables of interest based on measured data;

[0023] Fig.10 An example metering device is schematically depicted;

[0024] Fig.11 An example method for determining a value of a parameter of interest is depicted;

[0025] Fig.12 depicts a first of two intensities required to obtain a value of polarization imbalance at a first angular position of a substrate;

[0026] Fig.13 depicts a second of two intensities required to obtain a value for polarization imbalance at a second angular position of the substrate;

[0027] Fig.14 is a flow chart depicting a method of determining focus error, wherein correction factors are obtained from measurements of an initial target at substrate rotation positions of 0 degrees and 90 degrees;

[0028] Fig.15 is a graph depicting simulated measurements of four substrates in sequence to illustrate a method of determining values ​​of parameters of interest for multiple targets taking into account drift using measurements of a reference target;

[0029] Fig.16 It is a depiction Fig.15 A flowchart of an example method of the type shown in ; and

[0030] Fig.17 A computer system is schematically depicted on which embodiments of the present disclosure may be implemented. DETAILED DESCRIPTION

[0031] Before describing the embodiments in detail, it is helpful to introduce an example environment in which the embodiments may be implemented.

[0032] Figure 1 A lithographic apparatus LA is schematically depicted. The apparatus comprises:

[0033] - an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation);

[0034] a support structure (e.g., mask table) MT constructed to support a patterning device (e.g., mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters;

[0035] a substrate table (e.g. wafer stage) WT configured to hold a substrate (e.g. resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters; and

[0036] - a projection system (e.g., a refractive projection lens system) PS, configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W, the projection system being supported on a reference frame (RF).

[0037] The illumination system may include various types of optical components for directing, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0038] The support structure supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions (such as, for example, whether the patterning device is held in a vacuum environment). The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure can be, for example, a frame or a table, which can be fixed or movable as desired. The support structure can ensure that the patterning device is in a desired position, for example relative to a projection system. Any use of the term "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device".

[0039] The term "patterning device" as used herein should be broadly interpreted as referring to any apparatus that can be used to impart a pattern in a target portion of a substrate. In an embodiment, the patterning device is any apparatus that can be used to impart a pattern to a cross-section of a radiation beam so as to produce a pattern in a target portion of a substrate. It should be noted that the pattern imparted to the radiation beam may not completely correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so-called assist features. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device produced in the target portion (such as an integrated circuit, etc.).

[0040] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam, which is reflected by the matrix of mirrors.

[0041] The term "projection system" as used herein should be broadly interpreted to cover any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, depending on the exposure radiation used or other factors, such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system".

[0042] The projection system PS has an optical transfer function that may be non-uniform, which affects the pattern imaged on the substrate W. For non-polarized radiation, this effect can be well described by two scalar diagrams that describe the transmission (apodization) and relative phase (aberration) of the radiation exiting the projection system PS as a function of its position in the pupil plane. These scalar diagrams (which may be referred to as transmission diagrams and relative phase diagrams) can be represented as linear combinations of a complete set of basis functions. A particularly convenient set is the Zernike polynomials, which form a set of orthogonal polynomials defined on the unit circle. The determination of each scalar diagram can involve determining the coefficients in such an expansion. Since the Zernike polynomials are orthogonal on the unit circle, the Zernike coefficients can be determined by calculating the inner product of the measured scalar diagram of each Zernike polynomial in turn and dividing it by the square of the norm of the Zernike polynomial.

[0043] The transmission diagram and the relative phase diagram are field and system dependent. That is, in general, each projection system PS will have a different Zernike expansion for each field point (i.e., for each spatial position in its image plane). The relative phase of the projection system PS in its pupil plane can be determined, for example, by projecting radiation from a point source in the object plane of the projection system PS (i.e., the plane of the pattern forming device MA) through the projection system PS and measuring the wavefront (i.e., the trajectory of points with the same phase) using a shearing interferometer. The shearing interferometer is a common path interferometer and therefore, advantageously, does not require an auxiliary reference beam to measure the wavefront. The shearing interferometer may comprise a diffraction grating (e.g., a two-dimensional grid) in the image plane of the projection system (i.e., the substrate table WT), and a detector arranged to detect an interference pattern in a plane conjugate with the pupil plane of the projection system PS. The interference pattern is related to the derivative of the phase of the radiation relative to the coordinates in the pupil plane in the shear direction. The detector may comprise an array of sensing elements (such as, for example, a charge coupled device (CCD)).

[0044] The projection system PS of the lithographic apparatus may not produce visible fringes, and therefore the accuracy of the determination of the wavefront may be enhanced using a phase stepping technique such as, for example, moving a diffraction grating. Stepping may be performed in the plane of the diffraction grating and in a direction perpendicular to the scanning direction of the measurement. The stepping range may be one grating period, and at least three (evenly distributed) phase steps may be used. Thus, for example, three scanning measurements may be performed in the y direction, each for a different position in the x direction. Such stepping of the diffraction grating effectively converts phase changes into intensity changes, so that phase information can be determined. The grating may be stepped in a direction perpendicular to the diffraction grating (z direction) to calibrate the detector.

[0045] The transmission (apodization) of the projection system PS in its pupil plane can be determined, for example, by projecting radiation through the projection system PS from a point source in the object plane of the projection system PS (i.e. the plane of the patterning device MA) and measuring the intensity of the radiation in a plane conjugate to the pupil plane of the projection system PS using a detector. The same detectors as used for measuring the wavefront to determine aberrations can be used.

[0046] The projection system PS may include multiple optical (e.g., lens) elements and may also include an adjustment mechanism AM configured to adjust one or more optical elements to correct aberrations (phase changes across the entire pupil plane of the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system in which its optical axis extends in the z-direction. The adjustment mechanism may be operable to perform any combination of the following: displacing one or more optical elements; tilting one or more optical elements; and / or deforming one or more optical elements. The displacement of the optical element may be in any direction (x, y, z, or a combination thereof). The tilting of the optical element typically occurs outside a plane perpendicular to the optical axis by rotating about an axis in the x and / or y direction, although rotation about the z-axis can be used for non-rotationally symmetric aspheric optical elements. The deformation of the optical element may include low-frequency shapes (e.g., astigmatism) and / or high-frequency shapes (e.g., free-form aspheric surfaces). The deformation of the optical element may be performed, for example, by applying a force on one or more sides of the optical element using one or more actuators and / or by heating one or more selected regions of the optical element using one or more heating elements. In general, it may not be possible to adjust the projection system PS to correct for apodization (variation of transmission across a pupil plane). When designing a patterning device (e.g., mask) MA for the lithographic apparatus LA, a transmission map of the projection system PS may be used. Using computational lithography techniques, the patterning device MA may be designed to at least partially correct for apodization.

[0047] As depicted here, the device is of the transmissive type (eg, employing a transmissive mask). Alternatively, the device may be of the reflective type (eg, employing a programmable mirror array of the type described above, or employing a reflective mask).

[0048] The lithographic apparatus may be of a type having two (dual stage) or more worktables (e.g. two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system which is not dedicated to the substrate, e.g. to facilitate measurement and / or cleaning etc.). In such a "multi-stage" machine, additional worktables may be used in parallel, or preparatory steps may be performed on one or more worktables while exposure is being carried out using one or more other worktables. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt etc.) measurements using a level sensor LS may be performed.

[0049] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as between the patterning device and the projection system. Immersion techniques are well known in the art and are used to increase the numerical aperture of the projection system. The term "immersion" as used herein does not imply that structures such as the substrate are necessarily submerged in the liquid, but only that the liquid is located between the projection system and the substrate during exposure.

[0050] refer to Figure 1 , the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In this case, the source is not considered to be part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL with the help of a beam delivery system BD including, for example, suitable guide mirrors and / or a beam expander. In other cases, for example when the source is a mercury lamp, the source may be an integral part of the lithographic apparatus. The source SO and the illuminator IL, and the beam delivery system BD if necessary, may be referred to together as a radiation system.

[0051] The illuminator IL may include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent (commonly referred to as outer σ and inner σ, respectively) of the intensity distribution in a pupil plane of the illuminator is adjustable. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0052] The radiation beam B is incident on a patterning device (e.g. a mask) MA held on a support structure (e.g. a mask table) MT and is patterned by the patterning device. After passing through the patterning device MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position sensor IF (e.g. an interferometer, a linear encoder, a two-dimensional encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, in order to position a different target portion C in the path of the radiation beam B. Similarly, the first positioner PM and the further position sensor (which is not in the projection system) can be used to position the substrate table WT. Figure 1The support structure MT may be used to accurately position the patterning device MA relative to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during scanning. Typically, movement of the support structure MT may be achieved 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 may be achieved using a long-stroke module and a short-stroke module which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to the short-stroke actuator only, or may be fixed. The patterning device MA and the substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks shown occupy dedicated target portions, they may be located in the spaces between target portions (these are referred to as scribe alignment marks). Similarly, where more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0053] The depicted device can be used in at least one of the following modes:

[0054] 1. In step mode, the support structure MT and the substrate table WT remain substantially stationary while the entire pattern imparted to the radiation beam is projected at once onto a target portion C (i.e. a single static exposure). The substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C that is imaged in a single static exposure.

[0055] 2. In scan mode, the support structure MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), while the length of the scanning movement determines the height of the target portion (in the scanning direction).

[0056] 3. In another mode, the support structure MT is kept substantially stationary to hold the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, a pulsed radiation source is typically employed and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography utilizing a programmable patterning device, such as a programmable mirror array of the type described above.

[0057] Combinations and / or variations of the above described modes of use or entirely different modes of use may also be employed.

[0058] like Figure 2 As shown in , the lithography apparatus LA may form part of a lithography cell LC, sometimes also referred to as a lithography cell or cluster, and also include apparatus for performing pre-exposure and post-exposure processes on a substrate. Typically, these include one or more spin coaters SC for depositing one or more resist layers, one or more developers DE for developing the exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler or robot RO picks up one or more substrates from input / output ports I / O1, I / O2, moves them between different processing apparatuses, and transfers them to a feed station LB of the lithography apparatus. These apparatuses (often collectively referred to as tracks) are under the control of a track control unit TCU, which itself is controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, the different apparatuses may be operated to maximize throughput and processing efficiency.

[0059] In order for the substrates exposed by the lithographic apparatus to be correctly and consistently exposed, the exposed substrates need to be inspected to measure or determine one or more characteristics, such as overlay (which may be, for example, between structures in an overlying layer, or between structures in the same layer that are separately provided to the layer by, for example, a double patterning process), line width, critical dimension (CD), focus shift, material properties, etc. Therefore, the manufacturing facility, in which the lithography machine LC is typically also located, comprises a measurement system MET that receives some or all substrates W that have been processed in the lithography unit. The measurement system MET may be part of the lithography machine LC, for example it may be part of the lithography apparatus LA.

[0060] The measurement results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, the exposure of subsequent substrates may be adjusted (particularly if the inspection can be performed as soon as possible and fast enough so that one or more other substrates in the batch are still to be exposed), and / or the subsequent exposure of the exposed substrate may be adjusted. Furthermore, already exposed substrates may be stripped and reprocessed to improve yield, or discarded to avoid further processing of substrates known to be defective. In the case where only some target portions of the substrate are defective, further exposures may be performed only on the good target portions.

[0061] In the measurement system MET, the measurement device is used to determine one or more properties of the substrate, in particular to determine how one or more properties vary from one substrate to another or between different layers of the same substrate. The metrology device may be integrated into the lithography apparatus LA or the lithography cell LC, or may be a stand-alone device. In order to be able to perform fast measurements, it is necessary for the metrology device to measure one or more properties in the exposed resist layer immediately after exposure. However, the contrast of the latent image in the resist is low, there is only a small difference in refractive index between the parts of the resist exposed to the radiation and the parts of the resist not exposed to the radiation, and not all metrology devices have sufficient sensitivity to make useful measurements of the latent image. Therefore, the measurement can be performed after a post-exposure bake step (PEB), which is usually the first step performed on the exposed substrate and increases the contrast between the exposed and unexposed parts of the resist. At this stage, the image in the resist can be called a semi-latent image. Measurements can also be performed on the resist image after development (when the exposed or unexposed parts of the resist have been removed), and can also be performed after a pattern transfer step (such as etching). The latter possibility limits the possibilities for reworking defective substrates but can still provide useful information.

[0062] To achieve metrology, one or more targets may be provided on the substrate. In an embodiment, the target is specially designed and may include a periodic structure. In an embodiment, the target is a part of a device pattern, such as a periodic structure of the device pattern. In an embodiment, the device pattern is a periodic structure of a memory device (e.g., a bipolar transistor (BPT), a bit line contact (BLC), etc. structure).

[0063] In an embodiment, the target on the substrate may include one or more one-dimensional periodic structures (e.g., gratings) that are printed such that after development, the periodic structural features are formed by solid resist lines. In an embodiment, the target may include one or more two-dimensional periodic structures (e.g., gratings) that are printed such that after development, the one or more periodic structures are formed by solid resist columns or vias in the resist. The bars, columns, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0064] In an embodiment, one of the parameters of interest in the patterning process is overlay. Overlay can be measured using a dark field scattering method, in which the zero-order diffraction (corresponding to specular reflection) is blocked and only high orders are processed. Examples of dark field metrology can be found in PCT patent application publications WO 2009 / 078708 and WO 2009 / 106279 (the entire contents of which are incorporated herein by reference). Further developments of the technology are described in U.S. Patent Application Publications US2011-0027704, US2011-0043791, and US2012-0242970 (the entire contents of which are incorporated herein by reference). Diffraction-based overlay using dark field detection of diffraction orders can perform overlay measurements on smaller targets. These targets can be smaller than the irradiation point and can be surrounded by device product structures on the substrate. In an embodiment, multiple targets can be measured in one radiation capture.

[0065] Figure 3A A metrology device suitable for measuring, for example, overlay in an embodiment is schematically shown in FIG. Figure 3B Target T (comprising a periodic structure such as a grating) and the diffracted rays are shown in more detail in . The metrology apparatus may be a stand-alone device or may be incorporated into the lithographic apparatus LA, for example at a measuring station or into the lithography cell LC. An optical axis having a number of branches in the overall apparatus is indicated by a dashed line O. In the apparatus, radiation emitted by an output 11 (e.g. a light source such as a laser or a xenon lamp or an opening connected to the light source) is directed via a lens 15 onto a substrate W by an optical system comprising lenses 12, 14 and an objective lens 16. The lenses are arranged in a dual sequence of a 4F arrangement. A different lens arrangement may be used as long as it still provides an image of the substrate onto the detector.

[0066] In an embodiment, the lens arrangement allows access to an intermediate pupil plane for spatial frequency filtering. Thus, the angular range of radiation incident on the substrate can be selected by defining a spatial intensity distribution in a plane presenting the spatial spectrum of the substrate plane (here referred to as the (conjugate) pupil plane). In particular, this can be done, for example, by inserting an aperture plate 13 of suitable form between lenses 12 and 14 in a plane that is a back-projected image of the objective lens pupil plane. In the example shown, the aperture plate 13 has different forms marked as 13N and 13S, thereby allowing different illumination modes to be selected. The illumination system in this example forms an off-axis illumination mode. In a first illumination mode, the aperture plate 13N provides off-axis illumination from a direction designated as "north" for descriptive purposes only. In a second illumination mode, the aperture plate 13S is used to provide similar illumination, but from the opposite direction marked as "south". Other illumination modes are also possible by using different apertures. The rest of the pupil plane is ideally dark, because any unnecessary radiation outside the desired illumination mode may interfere with the desired measurement signal.

[0067] like Figure 3B As shown in , the target T is placed together with the substrate W substantially perpendicular to the optical axis O of the objective lens 16. The irradiation ray I incident on the target T from a specific angle offset from the axis O produces a zero-order ray (solid line 0) and two first-order rays (dotted chain line +1 and double-dotted chain line -1). In the case of overfilling of the small target T, these rays are only one of many parallel rays covering the area of ​​the substrate (including the metrology target T and other features). Since the hole in the plate 13 has a finite width (useful radiation must be allowed), the incident ray I will actually occupy a certain angle range, and the diffracted rays 0 and +1 / -1 will be slightly spread out. According to the point spread function of the small target, each +1 and -1 order will be further expanded within a specific angle range, rather than a single ideal ray as shown. Note that the spacing and irradiation angle of the periodic structure can be designed or adjusted so that the first-order rays entering the objective lens are closely aligned with the central optical axis. Figure 3A and 3B The rays shown in φ are somewhat off-axis, just to make them easier to distinguish in the figure. At least the 0th and +1st orders diffracted by the target on the substrate W are collected by the objective lens 16 and directed back through the prism 15.

[0068] return Figure 3A , a first illumination mode and a second illumination mode are shown by specifying diametrically opposed holes labeled as north (N) and south (S). When the incident ray I comes from the north side of the optical axis, that is, when the first illumination mode is applied using aperture plate 13N, the +1 diffraction ray labeled as +1 (N) enters objective lens 16. In contrast, when the second illumination mode is applied using aperture plate 13S, the -1 diffraction ray (labeled as 1 (S)) is the ray that enters lens 16. Therefore, in an embodiment, by measuring the target twice under certain conditions (for example, after rotating the target or changing the illumination mode or changing the imaging mode) to obtain the -1 and +1 diffraction order intensities, respectively, a measurement result can be obtained. Comparing these intensities for a given target provides a measure of the asymmetry in the target, and the asymmetry in the target can be used as an indicator of a parameter (for example, overlay) of a lithography process. In the above case, the illumination mode is changed.

[0069] The beam splitter 17 splits the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 forms a diffraction spectrum (pupil plane image) of the target on a first sensor 19 (e.g., a CCD or CMOS sensor) using the zero-order and first-order diffracted beams. Each diffraction order arrives at a different point on the sensor so that image processing can compare and contrast the orders. The pupil plane image captured by the sensor 19 can be used to focus a metrology device and / or normalize intensity measurements. The pupil plane image can also be used for other measurement purposes, such as reconstruction, as further described below.

[0070] In the second measurement branch, the optical systems 20, 22 form an image of the target on the substrate W of the sensor 23 (e.g., a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is set in a plane conjugate with the pupil plane of the objective lens 16. The aperture stop 21 is used to block the zero-order diffraction beam so that the image of the target formed on the sensor 23 is formed by the -1 or +1 order beam. Data about the image measured by the sensors 19 and 23 are output to the processor and controller PU, and the functions of the processor and controller PU will depend on the specific type of measurement performed. Note that the term "image" is used in a broad sense. If only one of the -1 and +1 orders is present, an image of periodic structural features (e.g., grating lines) will not be formed.

[0071] The specific forms of aperture plate 13 and aperture stop 21 shown in FIG3 are examples only. In another embodiment, coaxial illumination of the target is used, and an aperture stop with an off-axis aperture is used to pass substantially only one first order diffracted radiation to the sensor. In other embodiments, second, third and higher order beams (not shown in FIG3 ) may be used in the measurement instead of or in addition to the first order beam.

[0072] To adapt the illumination to these different types of measurements, the aperture plate 13 may include multiple hole patterns formed around a disk that rotates to place the desired pattern in place. Note that aperture plates 13N or 13S are used to measure periodic structures of a target oriented in one direction (X or Y, depending on the setup). To measure orthogonal periodic structures, target rotations of 90° and 270° can be achieved. Figure 3C and Figure 3D Different orifice plates are shown in FIG. Figure 3C Two other types of off-axis illumination modes are shown. Figure 3C In the first illumination mode of , aperture plate 13E provides off-axis illumination from a direction designated as "East" relative to the previously described "North" for descriptive purposes only. Figure 3C In a second illumination mode, aperture plate 13W is used to provide similar illumination, but from the opposite direction marked "West". Figure 3D Two other types of off-axis illumination modes are shown. Figure 3D In a first illumination mode, aperture plate 13NW provides off-axis illumination from directions designated as "North" and "West" as previously described. In a second illumination mode, aperture plate 13SE is used to provide similar illumination, but from opposite directions labeled as "South" and "East" as previously described. The use of these and many other variations and applications of the apparatus are described in, for example, the previously disclosed patent application publications mentioned above.

[0073] Figure 4An example composite metrology target T formed on a substrate is depicted. The composite target comprises four periodic structures (gratings in this case) 32, 33, 34, 35 positioned closely together. In embodiments, the periodic structure layout can be made smaller than the measurement spot (i.e., the periodic structure layout is overfilled). Thus, in embodiments, the periodic structures are positioned closely enough together that they are all within the measurement spot 31 formed by the illumination beam of the metrology device. Thus, in this case, all four periodic structures are illuminated simultaneously and imaged simultaneously on the sensors 19 and 23. In an example dedicated to overlay measurement, the periodic structures 32, 33, 34, 35 are themselves composite periodic structures (e.g., composite gratings) formed by overlaying periodic structures, i.e., the periodic structures are patterned in different layers of a device formed on a substrate W, and at least one periodic structure in one layer is overlaid with at least one periodic structure in another layer. The outer dimensions of such a target may be within 20 μm x 20 μm or within 16 μm x 16 μm. Furthermore, all periodic structures are used to measure the overlay between a specific pair of layers. To facilitate the target being able to measure more than one pair of layers, the periodic structures 32, 33, 34, 35 may have overlay offsets with different offsets to facilitate measuring the overlay between different layers in which different portions of the composite periodic structure are formed. Thus, all periodic structures for a target on a substrate will be used to measure one pair of layers, and all periodic structures for another identical target on a substrate will be used to measure another pair of layers, wherein the different offsets facilitate distinguishing the layer pairs.

[0074] return Figure 4 As shown in the figure, the orientation of periodic structures 32, 33, 34, 35 can also be different, so as to diffract incident radiation along the X and Y directions. In one example, periodic structures 32 and 34 are X-direction periodic structures with offsets +d, -d, respectively. Periodic structures 33 and 35 can be Y-direction periodic structures with offsets +d and -d, respectively. Although four periodic structures are shown, another embodiment can include a larger matrix to obtain the required accuracy. For example, a 3x 3 array of nine composite periodic structures can have offsets -4d, -3d, -2d, -d, 0, +d, +2d, +3d, +4d. The individual images of these periodic structures can be identified in the image captured by the sensor 23.

[0075] Figure 5 Shows that you can use Figure 3D The orifice plate 13NW or 13SE is used in the device of FIG. 3 Figure 435. Although the sensor 19 cannot resolve different individual periodic structures 32 to 35, the sensor 23 can. The dark rectangle represents the field of the image on the sensor in which the illumination point 31 on the substrate is imaged into the corresponding circular area 41. Therein, the rectangular areas 42 to 45 represent the images of the periodic structures 32 to 35. The target can be placed in the device product function, rather than in or in addition to the scribe lanes. If the periodic structure is located in the device product area, the device features may also be visible at the periphery of the image field. The processor and controller PU use pattern recognition to process these images to identify individual images 42 to 45 of the periodic structures 32 to 35. In this way, it is not necessary to align the image very accurately at a specific position within the sensor frame. The productivity of the measuring device is improved as a whole.

[0076] Once the individual images of the periodic structure have been identified, the intensities P1 to P4 of these individual images can be measured, for example, by averaging or summing the selected pixel intensity values ​​within the identified area. The intensities and / or other properties of the images can be compared to each other. These results can be combined to measure different parameters of the lithography process. Overlay performance is an example of such a parameter.

[0077] In an embodiment, one of the parameters of interest for the patterning process is feature width (eg, CD). Figure 6 A highly schematic example metrology device (e.g., scatterometer) capable of achieving feature width determination is depicted. It comprises a broadband (white light) radiation projector 2 that projects radiation onto a substrate W. The redirected radiation is passed to a spectrometer detector 4, which measures a spectrum 10 (intensity as a function of wavelength) of the specularly reflected radiation, as shown, for example, at the bottom left in the diagram. From this data, the structure or profile that gave rise to the detected spectrum can be reconstructed by a processor PU, for example by rigorous coupled wave analysis and nonlinear regression, or by comparison with a library of simulated spectra, such as Figure 6 . Typically, for reconstruction, the general form of the structure is known and some variables are assumed from knowledge of the process for manufacturing the structure, leaving only some structural variables to be determined from the measurement data. Such a metrology device can be configured as a normal incidence metrology device or an oblique incidence metrology device. In addition to measuring parameters by reconstruction, angle-resolved scattering can also be used to measure the asymmetry of features in products and / or resist patterns. A special application of asymmetric measurements is for overlay measurements, where the target includes a set of periodic features superimposed on another set of periodic features. The concept of asymmetric measurement performed in this manner is described in U.S. Patent Application Publication US2006-066855 (the entire contents of which are incorporated herein).

[0078] Figure 7An example of a metrology device 100 suitable for use with embodiments of the invention disclosed herein is shown. The operating principles of metrology devices of this type are explained in more detail in U.S. Patent Application Nos. US 2006-033921 ​​and US 2010-201963 (incorporated herein by reference in their entirety). An optical axis having multiple branches throughout the device is indicated by a dashed line O. In the device, radiation emitted by a source 110 (e.g., a xenon lamp) is directed onto a substrate W by an optical system comprising a lens system 120, an aperture plate 130, a lens system 140, a partially reflective surface 150, and an objective lens 160. In an embodiment, these lens systems 120, 140, 160 are arranged in a dual sequence of a 4F arrangement. In an embodiment, the lens system 120 is used to collimate the radiation emitted by the radiation source 110. If desired, different lens arrangements may be used. The angular range of the radiation incident on the substrate may be selected by defining a spatial intensity distribution in a plane presenting a spatial spectrum of the substrate plane. In particular, this can be done by inserting an aperture plate 130 of suitable form between the lenses 120 and 140 in a plane that is a back-projected image of the pupil plane of the objective. By using different apertures, different intensity distributions (e.g., annular, dipole, etc.) can be achieved. The angular distribution of the illumination in radial and peripheral directions as well as properties such as the wavelength, polarization and / or coherence of the radiation can be adjusted to obtain the desired result. For example, one or more interference filters 135 can be provided between the light source 110 and the partially reflecting surface 150 (see Fig. 9 ) to select a wavelength of interest in the range of, for example, 400 nm to 900 nm or less (such as 200 nm to 300 nm). The interference filter may be tunable, rather than comprising a set of different filters. A grating may be used instead of an interference filter. In an embodiment, one or more polarizers 175 (see Fig. 9 ) to select the polarization of interest. The polarizer may be adjustable rather than comprising a set of different polarizers.

[0079] like Figure 7 As shown in FIG. 1 , the target T is placed together with the substrate W perpendicular to the optical axis O of the objective lens 160. Therefore, the radiation from the source 110 is reflected by the partially reflective surface 150 and is focused via the objective lens 160 into an illumination point S on the target T on the substrate W (see FIG. 1 ). Figure 8 ). In an embodiment, objective lens 160 has a high numerical aperture (NA), ideally at least 0.9 or at least 0.95. Immersed metering devices (using relatively high refractive index liquids, such as water) can even have a numerical aperture greater than 1.

[0080] The illumination light 170, 172 focused from a specific angle off axis O to the illumination point produces diffracted light 174, 176. It should be remembered that these rays are only one of many parallel rays covering the area of ​​the substrate (including the target). Every element within the illumination point is within the field of view of the metrology device. Since the hole in plate 130 has a finite width (which must allow for a useful amount of radiation), the incident rays 170, 172 will actually occupy a certain range of angles, and the diffracted rays 174, 176 will be somewhat spread out. Depending on the point spread function of a small target, each diffraction order is further spread out over a certain range of angles, rather than being a single ideal ray as shown.

[0081] At least the 0th order diffracted by the target on the substrate W is collected by the objective lens 160 and directed back through the partially reflective surface 150. The optical element 180 provides at least a portion of the diffracted beam to the optical system 182, which forms a diffraction spectrum (pupil plane image) of the target T on the sensor 190 (e.g., CCD or CMOS sensor) using the zeroth order and / or the first order diffracted beam. In an embodiment, an aperture 186 is provided to filter out certain diffraction orders, thereby providing a specific diffraction order to the sensor 190. In an embodiment, the aperture 186 allows substantially or mainly only zeroth order radiation to reach the sensor 190. In an embodiment, the sensor 190 can be a two-dimensional detector so that a two-dimensional angular scattering spectrum of the substrate target T can be measured. The sensor 190 can be an array of, for example, CCD or CMOS sensors, and can use, for example, an integration time of 40 milliseconds per frame. The sensor 190 can be used to measure the intensity of the redirected radiation at a single wavelength (or a narrow wavelength range), to measure the intensity individually at multiple wavelengths, or to measure the integrated intensity in a specific wavelength range. Furthermore, the sensor may be used to measure the intensity of radiation having transverse magnetic polarization and / or transverse electric polarization and / or the phase difference between transverse magnetic polarization radiation and transverse electric polarization radiation, respectively.

[0082] Optionally, the optical element 180 provides at least a portion of the diffracted beam to the measurement branch 200 to form an image of the target on the substrate W on the sensor 230 (e.g., a CCD or CMOS sensor). The measurement branch 200 can be used for various auxiliary functions, such as focusing the metrology device (i.e., bringing the substrate W into focus with the objective lens 160) and / or for the above-mentioned reference FIGS. Figure 5 Dark-field imaging described.

[0083] In order to provide a customized field of view for gratings of different sizes and shapes, an adjustable field stop 300 is provided in the path from the source 110 to the objective 160 within the lens system 140. The field stop 300 contains an aperture 302 and is located in a plane conjugate to the plane of the target T, so that the illumination point is an image of the aperture 302. The image can be scaled according to the magnification factor, or the aperture and illumination point can have a 1:1 size relationship. In order to adapt the illumination to different types of measurements, the aperture plate 300 can include a plurality of hole patterns formed around a disk that rotates to place the desired pattern in place. Alternatively or additionally, a set of plates 300 can be provided and interchanged to achieve the same effect. Additionally or alternatively, a programmable aperture stop device such as a deformable mirror array or a transmissive spatial light modulator can also be used.

[0084] Typically, the target will be aligned with its periodic structural features parallel to the Y-axis or the X-axis. With respect to its diffraction properties, a periodic structure having features extending in a direction parallel to the Y-axis has periodicity in the X-direction, while a periodic structure having features extending in a direction parallel to the X-axis has periodicity in the Y-direction. In order to measure the performance in both directions, two types of features are typically provided. Although reference will be made to lines and spaces for simplicity, the periodic structure does not have to be formed by lines and spaces. Moreover, each line and / or the space between the lines may be a structure formed by smaller substructures. In addition, the periodic structure may be formed periodically in two dimensions at a time, for example, in the case where the periodic structure includes columns and / or through holes.

[0085] Figure 8 A plan view of an example target T is shown and Figure 7 The range of the illumination point S in the device of FIG. 1 is 1. In order to obtain a diffraction spectrum that is not disturbed by surrounding structures, in an embodiment, the target T is a periodic structure (e.g., a grating) that is larger than the width (e.g., diameter) of the illumination point S. The width of the point S can be smaller than the width and length of the target. In other words, the target is "underfilled" by the illumination, and the diffraction signal is essentially free of any signal such as product features from outside the target itself. This can simplify the mathematical reconstruction of the target because it can be treated as an infinite target.

[0086] Fig. 9 An example process of determining values ​​of one or more variables of interest for a target pattern 30' based on measurement data acquired using metrology is schematically depicted.The radiation detected by the detector 190 provides a measured radiation distribution 108 for the target 30'.

[0087] For a given target 30', a radiation distribution 208 can be calculated / simulated from a parameterized mathematical model 206 using, for example, a numerical Maxwell solver 210. The parameterized mathematical model 206 shows example layers of various materials that make up the target and are associated with the target. The parameterized mathematical model 206 can include one or more variables of features and layers of a portion of the target under consideration, which can be changed and derived. As shown in Figure 9, the one or more variables can include the thickness t of one or more layers, the width w (e.g., CD) of one or more features, the height h of one or more features, the sidewall angle α of one or more features, and / or the relative position between features (herein considered as overlay). Although not shown, the one or more variables can also include, but are not limited to, the refractive index (e.g., real or complex refractive index, refractive index tensor, etc.) of one or more layers, the extinction coefficient of one or more layers, the absorptivity of one or more layers, the resist loss during the development process, the foothold of one or more features, and / or the line edge roughness of one or more features. One or more values ​​of one or more parameters of a one-dimensional periodic structure or a two-dimensional periodic structure (such as the value of a width, length, shape, or three-dimensional profile feature) can be input into the reconstruction process from the knowledge of the patterning process and / or other measurement processes. For example, the initial values ​​of the variables may be those expected values ​​of one or more parameters of the target being measured, such as values ​​of CD, spacing, etc.

[0088] In some cases, the target may be divided into multiple instances of a unit cell. To help simplify the calculation of the radiation distribution of the target in such cases, the model 206 may be designed to perform calculations / simulations using a unit cell of the structure of the target, where the unit cell is repeated as an instance across the entire target. Thus, the model 206 may perform calculations using one unit cell and replicate the results to fit the entire target using appropriate boundary conditions in order to determine the radiation distribution of the target.

[0089] Additionally or alternatively to calculating the radiation distribution 208 at reconstruction time, a plurality of radiation distributions 208 may be pre-calculated for a plurality of variations of the variable of the target portion under consideration to create a library of radiation distributions for use at reconstruction time.

[0090] Then, at 212, the measured radiation distribution 108 is compared to the calculated radiation distribution 208 (e.g., calculated around the time or obtained from a library) to determine a difference between the two. If a difference exists, the values ​​of one or more variables of the parameterized mathematical model 206 may be changed, a new calculated radiation distribution 208 (e.g., calculated or obtained from a library) may be obtained, and compared to the measured radiation distribution 108 until there is a sufficient match between the measured radiation distribution 108 and the radiation distribution 208. At this point, the values ​​of the variables of the parameterized mathematical model 206 provide a good or best match to the geometry of the actual target 30'. In an embodiment, a sufficient match exists when the difference between the measured radiation distribution 108 and the calculated radiation distribution 208 is within a tolerance threshold.

[0091] As described above, one or more parameters of interest (such as CD and / or overlay) can be determined from the structure of a target (e.g., a diffraction target within a product pattern or a diffraction target specifically designed for measurement and separated from the device pattern) by illuminating the target, collecting redirected radiation from the structure using an objective, and detecting the redirected radiation by a pupil detector in the Fourier plane of the objective. Such measured pupil can be processed using, for example, an inference method to derive a signal component therefrom, which is combined with an appropriate set of weights to produce, for example, an overlay value. Additionally or alternatively, such as with respect to Fig. 9 The method described can use this measured pupil to determine, for example, the CD.

[0092] In an embodiment, the radiation used to illuminate the target is linearly polarized electromagnetic radiation. Linear polarization confines the electric field of the electromagnetic radiation to a single plane along the propagation direction. In an embodiment, for convenience herein, a first type of linear polarization in a first direction perpendicular to the propagation direction is designated as "H" or horizontal linear polarization, and for convenience herein, a second type of linear polarization in a second direction orthogonal to the second direction and perpendicular to the propagation direction is designated as "V" or vertical linear polarization. Of course, the radiation does not have to be vertical or horizontal. The first linear polarization can be p-polarization and the second linear polarization can be s-polarization. Of course, the first linear polarization and the second linear polarization can be labeled with other labels.

[0093] Diffractive structures (e.g., diffraction gratings) and other similar complex structures change the polarization state of the impinging radiation. Therefore, in an embodiment, the optical properties of an object including the structure under investigation can be characterized by the following reflectivity matrix:

[0094]

[0095] where R is the reflectivity and the subscripts correspond to the applicable linear polarizations. In particular, the first index of the subscript refers to the polarization state of the radiation emerging from the target and the second index of the subscript refers to the polarization state of the incident radiation impinging on the target. For example, R HV Refers to the reflectivity from V polarized illumination to H polarization. Each element of this matrix depends on the wavelength as well as the polarity and azimuth of the incidence. Of course, these structures can be characterized by a reflectivity matrix based on s polarization and p polarization, etc. In addition, although embodiments are described herein in terms of reflectivity, different or additional optical properties than reflectivity can be used, which can be determined in similar aspects at different illumination polarizations and exit polarizations. In addition, although embodiments are described herein in terms of two different types of linear polarizations, more than two types of linear polarizations can be used.

[0096] In a metrological setup, the observable of the detector can be the total reflected intensity. That is, the detection is not polarization sensitive. Thus, if the illumination is H-polarized, the detected intensity is proportional to:

[0097] |R HH | 2 +|R VH | 2

[0098] If the illumination is V polarized, the detected intensity is proportional to:

[0099] |R VV | 2 +|R HV | 2

[0100] However, it is expected that different polarization channels (i.e. different elements of the reflectivity matrix) carry different information about parameters of interest such as CD and / or overlay. Therefore, in embodiments, it is advantageous to detect H linearly polarized and V linearly polarized radiation emerging from the target, for example to decorrelate more profile parameters (e.g. as part of an inference method) and to increase sensitivity to them, respectively. Therefore, in embodiments, with the selected R HH , R VH , R VV and R HV A combination of at least two associated values ​​of (or additional or different optical properties as described above) is used to derive a parameter of interest (e.g., overprint, CD, etc.). It should be understood that the combination may be used to derive a single value of the parameter of interest. HH , R VH , R VV and R HV In an alternative embodiment, only RVH and R HV The corresponding values ​​are used to derive the parameters of interest.

[0101] Fig.10 Schematically depicts an example metrology device for enabling detection of H polarization and V polarization emitted from a target, respectively, according to an embodiment. Figure 7 The metrology device is similar to that of R , but with some changes. Specifically, in an embodiment, the metrology device includes a cross-polarization element 192 before the pupil sensor 190 to separate the exit polarization state of the radiation into a first portion 196 having a first linear polarization and a second portion 198 having a different second linear polarization. The cross-polarization element 192 provides for measuring the polarization state of the radiation respectively related to R by applying horizontal linear polarization radiation to the target and applying vertical linear polarization radiation to the same target. HH , R VH , R VV and R HV Associated values ​​(such as |R HH | 2 、|R VH | 2 、|R VV | 2 and |R HV | 2 ) capability. Therefore, for H polarization, the cross-polarization element 192 enables the outgoing V and H polarizations to be measured separately, thereby obtaining |R VH | 2 and |R HH | 2 Similarly, for V polarization, the cross-polarization element 192 enables the outgoing V and H polarizations to be measured separately, thereby obtaining |R VV | 2 and |R HV | 2 .

[0102] In an embodiment, different polarizations may be provided alternately to the target. For example, in an embodiment, source 110 may alternately provide temporal H and V polarizations. In an embodiment, a polarization element in the optical path between source 110 and the target may be used to alternately provide temporal H and V polarizations (e.g., using polarizer 175 as shown in FIG. 9 , which is Figure 7 and Fig.10 , can be similarly arranged between the source 110 and the objective lens 160).

[0103] In an embodiment, a plurality of illumination points may be provided in parallel, one or more of which have H polarization and one or more other of which have V polarization. Thus, in an embodiment with two illumination points and one illumination point with V polarization and the other illumination point with H polarization, the cross-polarization element 192 may separate the polarization of each illumination point separately to measure four sets of linear polarizations: V-polarized exit radiation from the target for V illumination, H-polarized exit radiation from the target for V illumination, V-polarized exit radiation from the target for H illumination, and H-polarized exit radiation from the target for H illumination.

[0104] In embodiments, the cross polarization element 192 may be arranged differently. For example, it may be arranged in a polarizing beam splitter type, where a particular linear polarization passes through a beam splitting surface in a first direction toward one sensor 190 in the first direction, and an orthogonal linear polarization is reflected from the beam splitting surface in a second direction substantially orthogonal to the first direction to another sensor 190 in the second direction. Other arrangements are possible, including other beam steering components.

[0105] However, cross-polarization detection alone is insensitive to the phase of the reflection coefficient, since only its absolute value is measured. To be able to measure at least some relative phase, a retarder 194 (e.g., a quarter-wave plate) is placed before the cross-polarization element 192. In this retarder 194 and cross-polarization element 192 configuration, the two output intensity channels of the H-polarized illumination of the target are:

[0106]

[0107] And the two output intensity channels of V-polarized illumination of the target are:

[0108]

[0109] The interference term carries information about the relative phase between the diagonal and off-diagonal channels of the reflectivity matrix.

[0110] Thus, a metrology device capable of performing a metrology process with a plurality of different polarization settings may be provided. Each polarization setting defines the polarization properties of incident radiation (which may be referred to as incident radiation channel) for the metrology process. Each polarization setting also defines the polarization properties of detected radiation (which may be referred to as detected radiation channel) for the metrology process.

[0111] In the above reference Fig.10In the described metrology process, examples of polarization properties of the incident radiation channel include H (or horizontal linear polarization) and V (vertical linear polarization). Other polarization properties are also possible, including s-polarization and p-polarization. In an embodiment, the polarization property of the incident radiation channel is defined by a polarizer disposed between the source 110 and the target T.

[0112] In the above reference Fig.10 In the described metrology process, examples of polarization properties of the detection radiation channel include H (or horizontal linear polarization) and V (vertical linear polarization). Other polarization properties are also possible, including s-polarization and p-polarization. In an embodiment, the polarization property of the detection radiation channel is defined by a polarizer disposed between the target T and the sensor 190, 230 for detecting radiation scattered from the target T.

[0113] Therefore, four examples of different polarization settings include: incident = H, detection = H (which can be called HH or H / H); incident = H, detection = V (which can be called HV or H / V); incident = V, detection = H (which can be called VH or V / H); incident = V, detection = V (which can be called V / V or VV).

[0114] A variety of other settings can be used during metering. These include:

[0115] a. A setting that defines which diffraction order (e.g., zeroth order, +1st order, or -1st order) is detected from a periodic structure in the target T;

[0116] b. Define the setting of the deviation (e.g., +d or -d or any other deviation) in the periodic structure in the target T;

[0117] c. Setting of the direction of periodicity of the periodic structure in the target T (eg, the X-direction periodic structure or the Y-direction periodic structure).

[0118] Comparisons between measurements obtained using metrology procedures with different settings are subject to errors due to undesirable differences in conditions, such as differences in optical path lengths and / or optical components such as optical fibers. These errors may result in intensity asymmetries between scattered radiation from equal and opposite diffraction orders not caused by the target T and / or polarization imbalances between scattered radiation corresponding to different polarization settings not caused by the target T (e.g., resulting in differences in intensity or intensity distributions).

[0119] Errors that result in an intensity asymmetry between scattered radiation from equal and opposite diffraction orders may be referred to as sensor asymmetry and are denoted δ in the following. Polarization imbalance is referred to as θ in the following.

[0120] In the example case where the target T is a multi-periodic structure target, wherein the multi-periodic structure target includes four periodic structures (gratings) with different deviations and orientations, such as Figure 4 As depicted in , and the target T is rotated to different positions (e.g., the angular position is 0, 90, 180, or 270 degrees), the effects of δ and θ on the detection intensity can be expressed as linear perturbations as follows:

[0121]

[0122] The intensity I on the left side of the equation represents the intensity I for a given target site St1 to St4 (see Fig.12 and 13 ), polarization setting (e.g., H / H, H / V, V / H, or V / V), wedge order (limiting the received diffraction orders), and substrate angular position (e.g., 0 degrees, 90 degrees, 180 degrees, or 270 degrees) measured using a metrology process.

[0123] The intensity I on the right side of the equation represents the intensity that would be acquired if both δ and θ were zero and is defined relative to the properties of the target T. This intensity I is a function of the direction of the periodicity of the periodic structure at the relevant target sites St1 to St4 (called the grating direction, such as X or Y), the deviation of the periodic structure at the relevant target sites St1 to St4 (e.g., +d or -d or any other deviation), the grating order (defining the diffraction order corresponding to the wedge order, such as +1 or -1), and the polarization setting relative to the periodic structure at the relevant target sites St1 to St4. The combination of the target sites St1 to St4 and the angular position of the substrate defines the periodic structure being analyzed.

[0124] In an embodiment, different combinations of settings (e.g., different grating directions, deviations, orders, polarization settings, and angular positions) produce 128 measured intensities and 128 corresponding equations. These equations can be solved to derive values ​​for δ and θ. If there are more degrees of freedom (e.g., more possibilities for one or more of the grating directions, deviations, orders, polarization settings, and angular positions), more equations can be obtained and solved to produce values ​​for δ and θ. For example, there will typically be two possible deviations (e.g., +d and -d), but other deviations or continuous deviations can be used, which can be addressed by measuring additional intensities to solve additional equations and / or by interpolation techniques.

[0125] In an embodiment, Fig.11 As schematically depicted in , based on the above analysis, a method for determining the value of a parameter of interest of a patterning process is provided.

[0126] In step S1, a plurality of calibration data units 60 are obtained from a metrology process S0. The metrology process S0 may be obtained using, for example, the calibration data units 60 described above with reference to FIG. Figure 6 , Figure 7 and Fig. 9 The calibration data unit 60 may be performed by any metrology device described. Each calibration data unit 60 represents detected radiation scattered from a corresponding target T during the metrology process. The corresponding target T may be the same target for at least a subset of the calibration data units 60, or may be a different target for at least a subset of the calibration data units 60. As described above, the target T comprises a structure formed on a substrate W using a patterning process (e.g., forming part of a photolithography manufacturing process). In an embodiment, the target T comprises a plurality of periodic structure targets, such as Figure 4 In an embodiment, the target T comprises periodic structures in different layers for measuring overlay.

[0127] The metrology process is performed by a metrology device capable of applying a plurality of different polarization settings. In an embodiment, each of the at least two calibration data units 60 represents detection radiation acquired using a different corresponding polarization setting during the metrology process (i.e., a different combination of polarization properties of the incident and detected radiation channels).

[0128] In steps S2 and S3, calibration information about the metrology process is acquired using the calibration data unit 60 acquired in step S1. As described in further detail below, the calibration information may include information about polarization imbalance θ (step S2) and optionally about sensor asymmetry δ (step S3).

[0129] In step S4, measurement data units are acquired representing detection radiation scattered from a further target T. The further target T may include structures formed on the same substrate W as the substrate W used to acquire the one or more calibration data units 60, or may include structures formed on a further substrate W. The further target T is formed using the same patterning process as the one or more targets T used to acquire the calibration data units 60.

[0130] Each calibration data unit 60 and each measurement data unit may include various representations of the detection radiation in the pupil plane, including, for example, the detection radiation intensity, the detection radiation phase, the detection radiation intensity distribution, or the detection radiation phase distribution. Alternatively or additionally, each calibration data unit 60 and each measurement data unit includes the detection radiation intensity, the detection radiation phase, the detection radiation intensity distribution, or the detection radiation phase distribution in the image plane.

[0131] In step S5, the value of the parameter of interest is determined using the measurement data units acquired in step S4 and the calibration information acquired in step S2 and optionally in step S3. The calibration information may for example be used to reduce the effects of polarization imbalance and / or sensor asymmetry (as described above).

[0132] Various parameters of interest may be determined in step S5. In an embodiment, the structure comprises a multilayer structure, and the parameters of interest comprise overlay errors between two or more different layers in the multilayer structure. Alternatively or additionally, the parameters of interest may comprise focus errors, critical dimensions, or any other parameters of interest relevant to controlling a patterning process.

[0133] In an embodiment, the different polarization settings used to acquire the calibration data unit 60 include at least a first polarization setting and a second polarization setting. In an embodiment, the incident radiation of the first polarization setting is polarized differently (e.g., orthogonally) than the incident radiation of the second polarization setting, and the detected radiation of the first polarization setting is polarized differently (e.g., orthogonally) than the detected radiation of the second polarization setting.

[0134] In this type of embodiment, a calibration information unit is obtained using a pair of calibration data units 60. In an embodiment, the calibration information unit comprises values ​​of polarization imbalance θ for a specific subset of metrology process settings.

[0135] The first calibration data unit 60 of the pair of calibration data units 60 is acquired using a first polarization setting with the substrate W in a reference angular position. The second calibration data unit 60 of the pair of calibration data units 60 is acquired using a second polarization setting with the substrate W rotated by a predetermined angle (e.g., 90 degrees) relative to the reference angular position. In an embodiment, the predetermined angle is equal to the angle between the polarization direction of incident radiation of the first polarization setting and the polarization direction of incident radiation of the second polarization setting (e.g., 90 degrees). In an embodiment, the predetermined angle is equal to the angle between the polarization direction of detected radiation of the first polarization setting and the polarization direction of detected radiation of the second polarization setting.

[0136] Thus, a pair of calibration data elements 60 may be acquired at angular positions of the substrate W that are separated by an angular amount that is the same as the angular separation between polarizations in the incident and / or detected radiation. In the specific examples described herein, the predetermined angle is 90 degrees, but other angles are possible, including, for example, 45 degrees. Thus, the target T may be subjected to a metrology process that is nominally identical in terms of the polarization directions of the incident and detected radiation channels relative to the target T, but that is implemented by the metrology apparatus using different polarization settings. The inventors have found that this provides a sensitive measure of the polarization imbalance θ.

[0137] In an embodiment, by Figure 4 The polarization imbalance θ is obtained by deriving the normalized difference between the measured intensities of the target T after the substrate is rotated 90 degrees in a multi-periodic structure target of the type depicted in FIG (having four periodic structures 32 to 35). For a general metrology setup, this can be expressed as follows:

[0138]

[0139] Wherein "HV" and "VH" indicate that the polarization settings of the two acquired intensities are always relative (for example, H / H and V / V, H / V and V / H, V / H and H / V, or V / V and H / H), "SiteN" and "SiteN-1" indicate that the position change of the periodic structure 32-35 caused by the rotation of the substrate W is taken into account, "WR" indicates the reference angular position of the substrate, and "θ+90°" indicates the reference angular position +90 degree rotation.

[0140] An example implementation of the above equation is Fig.11 and Fig.12 is shown in and described by the following equation:

[0141]

[0142] in represents the θ value corresponding to the combination of metrology process settings, where the +1 diffraction order of the positive X-direction periodic structure is measured using a polarization setup, where the incident and detected radiation channels are co-polarized and at 0 degrees relative to the direction of periodicity of the periodic structure.

[0143] By exporting Fig.12 The intensity shown in With Fig.13 The intensity shown in The normalized difference between them can be used to obtain the value of θ in this case.

[0144] Fig.12 (Left) Target T is depicted at an angular position of 0 degrees on substrate W. Stations 1 to 4 are labeled St1, St2, St3, and St4, respectively. Fig.12 (Right) The polarization setup shown acquires intensity from the X-direction periodic structure 32 with a deviation of +d and located at St1. The polarization setup is such that the polarization property of the incident radiation channel 51 is H and the polarization property of the detection radiation channel 52 is also H. Therefore, in this example, the incident and detection radiation channels are co-polarized and parallel to the direction of the periodicity of the X-direction periodic structure 32.

[0145] Fig.13 (Left) depicts the substrate W at a 90 degree angle (counterclockwise rotation) Fig.11 The target T. Sites 1 to 4 are labeled St1, St2, St3 and St4 respectively. The periodic structure 32 with a deviation of +d has been moved from St1 to St4, and the X-direction periodic structure has become a Y-direction periodic structure. Fig.13(right) The polarization setup depicted in Figure 1 acquires intensity from the Y-direction periodic structure 32 at St4. The polarization setup is such that the polarization property of the incident radiation channel 51 is V and the polarization property of the detection radiation channel 52 is also V. Therefore, the incident and detection radiation channels are still co-polarized and are still parallel to the direction of the periodicity of the periodic structure 32 (although now parallel to the Y direction rather than the X direction).

[0146] From the perspective of periodic structure 32, for Fig.12 The measurement process performed in Fig.13 The polarization properties of the incident radiation channel 51 and the detected radiation channel 52 are identical for the metrology process performed in θ (i.e., parallel to the direction of the periodicity of the periodic structure 32). Therefore, any non-zero value of θ can be a measure of polarization imbalance.

[0147] References Fig.12 and 13 The described embodiment belongs to a class of embodiments in which a first calibration data unit of a first pair of calibration data units is acquired with the substrate in a reference angular position (eg, Fig.12 ) and obtaining the second calibration data unit in the first pair of calibration data units when the substrate is rotated away from the reference angular position by a predetermined angle. In some embodiments, the predetermined angle is 90 degrees (e.g., Fig.13 ), but other angles such as tilt angles may be used. The calibration data unit is used to obtain first calibration information, which may then be used to determine the value of the parameter of interest with improved accuracy. Fig.11 and Fig.12 In the described embodiments, the first calibration information includes information about the polarization imbalance θ. This is achieved by arranging a first calibration data unit to be acquired using a first polarization setting and a second calibration data unit to be acquired using a second polarization setting. The angle between the polarization direction of the incident radiation of the first polarization setting and the polarization direction of the incident radiation of the second polarization setting is equal to a predetermined angle (e.g., 90 degrees), or the angle between the polarization direction of the detected radiation of the first polarization setting and the polarization direction of the detected radiation of the second polarization setting is equal to a predetermined angle (e.g., 90 degrees). The general method of using measurements of the substrate at 0 degrees and a predetermined angle away from 0 degrees (e.g., 90 degrees) can be used to determine other types of calibration information without necessarily requiring the use of different polarization settings.

[0148] In some embodiments, the above method is used to determine calibration information for correcting measurements of a parameter of interest in a patterning process for forming a structure on a substrate. In an embodiment, the method is used to determine calibration information for correcting measurements of a focus error. For the case of correcting measurements of a focus error, Fig.14The flowchart of FIG. 1 illustrates a method.

[0149] In steps S11 and S13, metrology measurements are performed on a target including the first periodic structure 32 and the second periodic structure 33. Between steps S11 and S13, in step S12, the substrate is rotated by a predetermined angle (e.g., 90 degrees). The calibration data units obtained from steps S11 and S13 are used to obtain calibration information in the form of correction factors in step S14. The target may, for example, take the above-mentioned Fig.11 and Fig.12 The first periodic structure 32 is oriented at a predetermined angle (eg, 90 degrees) relative to the second periodic structure 33. In an embodiment, the first periodic structure 32 and the second periodic structure 33 are gratings having the same pitch.

[0150] The method includes acquiring a first pair of calibration data units. Each calibration data unit represents detected radiation scattered from a target during a metrology process. The target is a structure formed on a substrate using a patterning process. A first calibration data unit in the first pair of calibration data units is acquired when the substrate is in a reference angular position (in step S11). A second calibration data unit in the first pair of calibration data units is acquired when the substrate is rotated away from the reference angular position by a predetermined angle (e.g., 90 degrees) (in step S13). The first calibration data unit and the second calibration data unit in the first pair of calibration units are acquired from a first periodic structure 32. First calibration information about the metrology process is acquired using the first pair of calibration data units (in step S14). The first calibration information may include a first correction factor.

[0151] The method further includes acquiring a second pair of calibration data units. Each calibration data unit represents detected radiation scattered from the target during the metrology process. When the substrate is at a reference angular position, a first calibration data unit in the second pair of calibration data units is acquired from the second periodic structure 33 (in step S11). When the substrate is at a predetermined angle (e.g., 90 degrees) from the reference angular position, a second calibration data unit in the second pair of calibration data units is acquired from the second periodic structure 33 (step S13). Second calibration information about the metrology process is acquired using the second pair of calibration data units (in step S14). The second calibration information may include a second correction factor.

[0152] In step S15, another target is measured to obtain a measurement data unit. The measurement data unit represents the detection radiation scattered from the other target. The other target includes a structure formed on a substrate or on another substrate using a patterning process. In an embodiment, the other target includes a first periodic structure 32 and a second periodic structure 33 oriented at a predetermined angle (e.g., 90 degrees) relative to each other. The first periodic structure 32 and the second periodic structure 33 may have the same form as the first periodic structure 32 and the second periodic structure 33 of the target for obtaining the first calibration information and the second calibration information in step S14 (e.g., including gratings with the same spacing). In step S16, the value of the parameter of interest is obtained using the measurement data unit and the first calibration information and the second calibration information obtained in step S14. In an embodiment, the determination of the parameter of interest includes determining a focus error. The parameter of interest (e.g., a focus error) is determined based on the measurement data unit including the first data and the second data. The first data represents the detection radiation scattered from the first periodic structure 32. The second data represents the detection radiation scattered from the second periodic structure 33. Determination of a parameter of interest (eg, focus error) includes applying a first correction factor to the first data and applying a second correction factor to the second data.

[0153] In an embodiment, the first data represents a first sum of the intensities of the +1 and -1 diffraction orders of radiation from the first periodic structure 32. The second data represents a second sum of the intensities of the +1 and -1 diffraction orders of radiation from the second periodic structure 33. The first data and the second data may be acquired using a dark field imaging mode. Determination of a parameter of interest (e.g., focus error) includes determining a difference between the first sum and the second sum after applying a correction factor to the first data and the second data.

[0154] The above method is particularly effective for determining focus error because it has been found that periodic structures (e.g., first periodic structure 32 and second periodic structure 33) that are oriented differently relative to each other (e.g., 90 degrees relative to each other) and have the same spacing have different responses to certain types of aberrations (e.g., aberrations proportional to astigmatism, such as Z5). This causes the difference between the sum of the +1 and -1 diffraction orders from one periodic structure (e.g., first periodic structure 32) and the sum of the +1 and -1 diffraction orders from another periodic structure (e.g., second periodic structure 33) to be correlated with (e.g., varies monotonically with) the focus of the lithographic apparatus used to form the periodic structure. Therefore, a calibration curve can be derived so that the focus error can be derived from the measurement of the difference between the two sums of +1 and -1 diffraction orders of different periodic structures. In an embodiment, the method also includes forming the target and the further target using a patterning process with intentionally applied astigmatism to enhance the correlation between the focus error and the difference between the first sum and the second sum.

[0155] Without the first and second correction factors, the measured first and second sums will be affected by sensor asymmetries caused by the lens and other optical components of the metrology device. Since the first periodic structure 32 and the second periodic structure 33 scatter light in different directions (perpendicular to the orientation of the periodic structures), the light will pass along different optical paths in the metrology device. Therefore, the measured +1 and -1 diffraction orders of the first periodic structure 32 will be affected by different sensor asymmetries compared to the measured +1 and -1 diffraction orders of the second periodic structure 33. As a result, the difference between the first and second sums will be affected by sensor asymmetry, which may be different for different metrology devices.

[0156] When the predetermined angle is 90 degrees, the above reference Fig.14 The method described takes advantage of the fact that a 90 degree rotation of the substrate causes the first periodic structure 32 and the second periodic structure 33 to rotate into one another's orientation (e.g. horizontal to vertical, vertical to horizontal). Thus, scattered radiation from one of the periodic structures at 90 degrees to the substrate will follow the same optical path as scattered radiation from the other periodic structure at 0 degrees to the substrate. If the first correction factor and the second correction factor are denoted as ω, respectively V (considering the direction of the first periodic structure to be “vertical”) and ω H (the direction of the second periodic structure is considered to be "horizontal"), then its expression can be as follows:

[0157] and Among them I V0is the total diffraction intensity (of the first-order component) from the first periodic structure 32 when the substrate is rotated 0 degrees, I V90 is the diffraction intensity (of the first-order component) from the first periodic structure 32 when the substrate is rotated 90 degrees, I H0 is the diffraction intensity (of the first-order component) from the second periodic structure 33 when the substrate is rotated 0 degrees, I H90 is the diffraction intensity (of the first-order component) from the second periodic structure when the second substrate is rotated 90 degrees.

[0158] The corrected value of the diffraction intensity from the first periodic structure 32 It is given by the following expression:

[0159]

[0160] The corrected value of the diffraction intensity from the second periodic structure 33 It is given by the following expression:

[0161]

[0162] The above described method allows accurate and reliable measurement of focus error with minimal variations between different metrology devices and without the need to perform measurements at multiple rotational positions of the substrate (other than the initial need to acquire the first and second correction factors).

[0163] In an embodiment, a calibration information unit (e.g., a value of polarization imbalance θ for a particular subset of metrology process settings) is acquired at each of at least two different reference angular positions for each of at least one pair of calibration data units 60. In an embodiment, the different reference angular positions include at least two angular positions separated from each other by 180 degrees. Thus, for example, a first calibration information unit may be acquired using a pair of calibration data units 60 acquired with the substrate W at 0 degrees and 90 degrees, and a second calibration information unit may be acquired using a pair of calibration data units 60 acquired with the substrate W at 180 degrees and 270 degrees. As described below, calibration data units 60 acquired at angular positions of the substrate W separated from each other by 180 degrees may also be used to derive information about the sensor asymmetry δ.

[0164] Although the examples described herein involve example angular positions of the substrate W and polarization directions that are multiples of 90 degrees, the value of the polarization imbalance θ can be derived (using trigonometry) from the same measurement for any polarization angle in the incident radiation channel and any polarization angle in the detected radiation channel.

[0165] In an embodiment, a calibration information unit (e.g., a value of polarization imbalance θ) is obtained for each of a plurality of pairs of calibration data units 60, each pair of calibration data units 60 being obtained using a periodic structure 32 to 35 having a different corresponding deviation (e.g., +d or -d). As described above, each deviation may represent an intentionally applied nominal offset (e.g., +d or -d) between different layers of the periodic structure 32 to 35.

[0166] In an embodiment, the calibration information elements (e.g., values ​​of polarization imbalance θ) are averaged over different values ​​of the metrology process settings. For example, the calibration information elements may be averaged over different deviations and / or different reference angular positions of the substrate W. Such averaging may reduce negative effects caused by unwanted inhomogeneities of the radiation spots used to illuminate the target T during the metrology process.

[0167] In an embodiment, a calibration data unit 60 is acquired for each of a plurality of different orientations of the target T, e.g., for one orientation of the target T, the periodicity of the periodic structures 32 to 35 in the target T is parallel to X, and for another orientation of the target T, the periodicity of the periodic structures 32 to 25 in the target T is parallel to Y. For each different orientation, at least one separate calibration information unit (e.g., a value of the polarization imbalance θ) is acquired.

[0168] In an embodiment, calibration data units 60 are acquired for each of a plurality of different diffraction orders of radiation scattered from the target T, e.g. +1 and -1. For each different diffraction order, at least one separate calibration information unit (e.g. a value of polarization imbalance θ) is acquired.

[0169] In an embodiment, a calibration data unit 60 is acquired for each of a plurality of different polarization settings relative to the target, for example: 1) the incident and detected radiation are co-polarized and parallel to the direction of the periodicity of the periodic structure in the target T; 2) the incident and detected radiation are cross-polarized and the incident radiation is polarized parallel to the direction of the periodicity of the periodic structure in the target T; 3) the incident and detected radiation are cross-polarized and the detected radiation is polarized parallel to the direction of the periodicity of the periodic structure in the target T; and 4) the incident and detected radiation are co-polarized orthogonally to the direction of the periodicity of the periodic structure in the target T. In an embodiment, for each different polarization setting relative to the target T, at least one separate calibration information unit (e.g., a value of polarization imbalance θ) is acquired.

[0170] In an embodiment, determining the value of the parameter of interest from the measurement data units in step S5 comprises selecting one or more individual calibration information units (e.g. one or more values ​​of polarization imbalance θ) according to the configuration of the metrology process used to acquire the measurement data units (e.g. so that the selected calibration information units appropriately represent the conditions under which the measurement data units were acquired and thus optimally correct errors such as polarization imbalance θ and / or sensor asymmetry δ).

[0171] The value of sensor asymmetry δ can be obtained using a similar approach as discussed above for polarization imbalance θ. Figure 4 δ is solved by deriving the normalized difference between the measured intensities of the target after a 180 degree substrate rotation for a target of the type depicted in FIG. 1 (having four periodic structures 32-35). For a general metrology setup, this can be expressed as follows:

[0172]

[0173] Wherein "HV" indicates that the polarization setting between the two acquired intensities is always the same (for example, H / H and H / H, H / V and H / V, V / H and V / H or V / V and V / V), "SiteN" and "SiteN+2" indicate that the position change of the periodic structure 32-35 caused by the rotation of the substrate W is taken into account, and "WR" indicates the reference angular position of the substrate. "WR+180" indicates a rotation of +180 degrees from the reference angular position, and "±1" and " 1" means that the two intensity diffraction orders acquired are always opposite (e.g., +1 and -1 or -1 and +1).

[0174] An example implementation of the above equation is described by the following equation:

[0175]

[0176] in represents the δ value corresponding to the metrology process setup combination, where a positively polarized X-direction periodic structure is measured using a polarization setup, where the incident and detected radiation channels are co-polarized and at 0 degrees relative to the direction of periodicity of the periodic structure.

[0177] In an embodiment, 32 separate solutions for the delta coverage can be found: 2 directions of the periodic structure (e.g., parallel to X and Y), 2 deviations (e.g., +d and -d), 4 polarization settings relative to the target, and 2 reference angular positions of the substrate (e.g., 0 degrees and 90 degrees). Averaging can be done over the different deviations and / or reference angular positions to reduce the impact of illumination point non-uniformity and improve accuracy. In other embodiments, there may be fewer or more separate solutions for delta, depending on the number of available degrees of freedom. For example, if more than four polarization settings are available (e.g., where a greater number of different polarization directions are available), there may be a correspondingly greater number of separate solutions for delta.

[0178] The properties of the patterning process may vary over time, resulting in variations in defects such as polarization imbalance θ and / or sensor asymmetry δ. Such drift may occur, for example, due to temperature variations of the optical components of the lithographic apparatus LA. For example, absorption of radiation in the objective lens may result in heating and stress-induced birefringence.

[0179] Frequent updating of calibration information (e.g., to repeatedly update the values ​​of polarization imbalance θ and / or sensor asymmetry δ) can reduce the effects of drift, but the time wasted in making the necessary measurements can negatively impact throughput. The following embodiments provide methods for reducing the effects of drift while allowing the overall process to be kept at an acceptable level.

[0180] Fig.15 is a graph depicting simulated measurements on a group (batch) of four substrates W1 to W4 for illustrating an exemplary method. In this embodiment, measurements are performed over a measurement time window from t0 to t4. The target on substrate W1 is measured between t0 and t1, the target on substrate W2 is measured between t1 and t2, the target on substrate W3 is measured between t2 and t3, and the target on substrate W4 is measured between t3 and t4. The vertical axis represents the measurement drift of the overlay OV, which is an example of a parameter of interest that can drift over time. The horizontal axis represents time, and in the example shown, the measurement time window extends for approximately 80 minutes. The solid circles represent measurements performed on targets with relatively low stacking sensitivity. The hollow circles represent measurements performed on targets with higher stacking sensitivity. The curves above and below the horizontal line of overlay OV=0 correspond to measurements performed on the substrate at 0 and 180 degree rotation positions, respectively. It can be seen that the overlay OV varies significantly over time throughout the measurement time window, and in this example, the maximum deviation is approximately 0.2nm.

[0181] Fig.16 is a flow chart depicting an example method for determining the value of a parameter of interest while taking drift into account. The method is applicable to measurements made over a long period of time on multiple targets and multiple substrates, such as Fig.15Described in.

[0182] In step S21, calibration information is obtained from the target. The calibration information may include information about polarization imbalance θ and / or sensor asymmetry δ, and may be obtained using any of the methods described above (e.g., by executing the above reference Fig.11 Steps S0 to S2 or S0 to S3 described above) or other methods are used to obtain. Fig.15 In the example shown, the calibration information may be obtained from a measurement performed at time 61 shortly after t0. Fig.11 The measurement is performed as described in step S0.

[0183] from Fig.16 The method also includes, during a measurement period (in Fig.15 A measurement data unit (representing detected radiation scattered from the target) is acquired for each of the N additional targets (represented by solid and hollow circles in FIG. 1 ). The acquisition of the measurement data unit for each additional target may be performed using any of the methods described above (e.g., as described in reference to FIG. 1 ). Fig.11 The method further comprises acquiring measurement data units at M different times within a measurement time period for a single fixed reference target. M is typically less than N. In an embodiment, the measurement data units for the reference target are acquired once for each substrate processed. Fig.15 In an example of , measurement data units for a reference target may be acquired at a frequency of once for each substrate processed, for example, at the start of measurement of the substrate (e.g., shortly after time t1, t2, t3, and t4). The reference target is ideally configured to be as similar as possible to the N additional targets (e.g., having the same spacing), and is ideally measured using the same optical settings as the N additional targets (e.g., at the same wavelength). The value of the parameter of interest is determined for each of the one or more additional targets (e.g., overlay) using the measurement data units acquired for the target, the acquired calibration information, and the measurement data acquired from one or more measurements of the reference target. The measurement data units provide nominal information about the value of the parameter of interest. The calibration information provides a first correction level for the value of the parameter of interest. The one or more measurements of the reference target allow the correction provided by the calibration information to be improved by taking into account drift. It is expected that the one or more measurements of the reference target are related to drift because the properties of the reference target are expected to remain constant over time.

[0184] follow Fig.16 In the example flow, in step S22, acquisition of measurement data units is performed for each additional target on the first substrate W1. After step S22, in step S23, measurement data units are acquired for the reference target (e.g., Fig.15t1 in ). After step S23, in step S24, acquisition of measurement data units is performed for each additional target on the second substrate W2. Steps S23 and S24 are repeated until the penultimate substrate W3 of the batch (in the present example, substrate W3) has been processed. In this example, the additional targets of substrates W2 and W3 are therefore measured, and the reference target is measured between them at t2. In this embodiment, the method then continues to step S25, in which calibration information is acquired from the target on the last substrate W4. The calibration information may include information about the polarization imbalance θ and / or the sensor asymmetry δ, and may be acquired using any of the methods described above (e.g., by performing the above reference Fig.11 The steps S0 to S2 or S0 to S3) or other methods are used to obtain. Fig.15 In the example shown, the measurement performed from time point 62 shortly after t3 (eg, as described above with reference to Fig.11 The calibration information is obtained in step S0 of the method. After step S25, in step S26, the acquisition of measurement data units of additional targets is performed for additional targets of the last substrate W4. In step S27, the value of the parameter of interest is determined for each of the one or more additional targets using the measurement data units acquired for the target, the calibration information acquired, and the measurement data acquired from one or more measurements of the reference target. In the example shown, the method may involve repeating the step of acquiring multiple calibration data units (to acquire calibration information) at least once during the measurement time period (for example, at time point 62) to acquire updated calibration information. The updated calibration information can then be used to perform the determination of the value of the parameter of interest for one or more additional targets in step S27.

[0185] Measurements and calibration information on a reference target (e.g., as acquired using measurements at time points 61 and 62) allow drift in the patterning process to be effectively accounted for with minimal throughput loss. The information provided by the measurements of the reference target and the calibration information can be used in a variety of ways. In some embodiments, the measurements and calibration information on the reference target provide correction data that can be used to correct nominal values ​​of parameters of interest (e.g., overlay). The correction data can include information about expected drifts of characteristics such as polarization imbalance θ and / or sensor asymmetry δ as a function of time. The calibration information acquired at time point 61 provides initial values ​​of polarization imbalance θ and / or sensor asymmetry δ, and the measurements on the reference target then provide information about how the polarization imbalance θ and / or sensor asymmetry δ changes over time. Alternatively or additionally, as Fig.15As shown in FIG. 6 , the correction data may be provided as a predicted curve 63 of the apparent drift of the contribution to the measured value of the parameter of interest (e.g., the drift of the contribution to the overlay OV) resulting from the drift of one or more properties of the patterning process (see FIG. 6 ). Fig.15 ). Here, an initial value of the drift may be determined from the calibration information acquired at point 61 (e.g., by determining the polarization imbalance θ and / or the sensor asymmetry δ), and subsequent measurements on a reference target provide information about how the expected drift changes over time. Subsequent measurements on a reference target provide information about the expected form of curve 63. In embodiments where calibration information is acquired at two points in time, for example, for a first substrate W1 and a last substrate W4 in a batch of substrates (e.g., at Fig.15 61 and 62 in the figure), the measurements on the reference target can be used to interpolate between the calibration information obtained at the two time points and / or to extrapolate to one or both time points (e.g., Fig.15 The step of determining the value of the parameter of interest for each additional target may comprise calculating the parameter of interest in the usual manner and then applying a correction from the correction data to obtain an improved value of the parameter of interest. A separate individual correction may be applied to each additional target.

[0186] The above method uses measurements on a reference target to monitor drift of properties such as polarization imbalance θ and / or sensor asymmetry δ, for example, by interpolation and / or extrapolation based on calibration information acquired at one or more points in time. In an alternative approach, the interpolation and / or extrapolation may be replaced by determining how the calibration information relates to one or more other parameters of the lithographic apparatus or target that can be measured and used to update the calibration information to account for the drift.

[0187] As an alternative or in addition to the above-described method of correcting drift, one or more pre-calibration curves may be derived and used to at least partially correct drift. The pre-calibration curves may be derived by computational modeling or calibration measurements, and the pre-calibration curves may take into account the effects of various factors on polarization imbalance θ and / or sensor asymmetry δ, including one or more of: changes over time only (e.g., a scenario in which the lithography apparatus LA is idle); changes in input air temperature (e.g., acquired via a sensor); and changes in objective lens temperature (e.g., acquired via a sensor).

[0188] refer to Fig.16, a computer system 3200 is shown. The computer system 3200 includes a bus 3202 or other communication mechanism for conveying information and a processor 3204 (or multiple processors 3204 and 3205) coupled to the bus 3202 for processing information. The computer system 3200 also includes a main memory 3206, such as a random access memory (RAM) or other dynamic storage device, which is coupled to the bus 3202 for storing information and instructions to be executed by the processor 3204. The main memory 3206 can also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor 3204. The computer system 3200 also includes a read-only memory (ROM) 3208 or other static storage device coupled to the bus 3202 for storing static information and instructions for the processor 3204. A storage device 3210, such as a magnetic disk or optical disk, is provided and coupled to the bus 3202 for storing information and instructions.

[0189] The computer system 3200 can be coupled to a display 3212 via the bus 3202, such as a cathode ray tube (CRT) or a flat panel display or a touch panel display for displaying information to a computer user. An input device 3214 including alphanumeric keys and other keys is coupled to the bus 3202 for communicating information and command selections to the processor 3204. Another type of user input device is a cursor control 3216, such as a mouse, trackball, or cursor direction keys, which is used to communicate direction information and command selections to the processor 3204 and to control cursor movement on the display 3212. The input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), to allow the device to specify a position in a plane. A touch panel (screen) display can also be used as an input device.

[0190] The computer system 3200 may be adapted to function as a processing unit herein in response to the processor 3204 executing one or more sequences of one or more instructions contained in the main memory 3206. Such instructions may be read into the main memory 3206 from another computer-readable medium, such as a storage device 3210. The execution of the sequence of instructions contained in the main memory 3206 may cause the processor 3204 to perform the processes described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequence of instructions contained in the main memory 3206. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Therefore, the embodiments are not limited to any particular combination of hardware circuitry and software.

[0191] As used herein, the term "computer-readable medium" refers to any medium that participates in providing instructions to processor 3204 for execution. Such medium can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device 3210. Volatile media include dynamic memory, such as main memory 3206. Transmission media include coaxial cables, copper wires, and optical fibers, including wires that constitute bus 3202. Transmission media can also take the form of sound waves or light waves, such as sound waves or light waves generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tapes, any other physical media with hole patterns, RAMs, PROMs and EPROMs, FLASH-EPROMs, any other storage chips or boxes, carriers described below, or any other media from which a computer can read.

[0192] Various forms of computer readable media may be involved in transmitting one or more sequences of one or more instructions to the processor 3204 for execution. For example, the instructions may initially be carried on a disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system 3200 may receive the data over the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to the bus 3202 may receive the data carried in the infrared signal and place the data on the bus 3202. The bus 3202 carries the data to the main memory 3206, from which the processor 3204 retrieves and executes the instructions. The instructions received by the main memory 3206 may optionally be stored on the storage device 3210 before or after being executed by the processor 3204.

[0193] The computer system 3200 may also include a communication interface 3218 coupled to the bus 3202. The communication interface 3218 provides a two-way data communication coupled to a network link 3220 connected to a local area network 3222. For example, the communication interface 3218 may be an integrated services digital network (ISDN) card or a modem for providing a data communication connection with a corresponding type of telephone line. As another example, the communication interface 3218 may be a local area network (LAN) card for providing a data communication connection with a compatible LAN. A wireless link may also be implemented. In any such implementation, the communication interface 3218 sends and receives electrical, electromagnetic or optical signals carrying digital data streams representing various types of information.

[0194] The network link 3220 typically provides data communication through one or more networks to other data devices. For example, the network link 3220 can provide a connection through a local network 3222 to a host computer 3224 or to data equipment operated by an Internet Service Provider (ISP) 3226. The ISP 3226 in turn provides data communication services through a global packet data communication network, now commonly referred to as the "Internet" 3228. Both the local network 3222 and the Internet 3228 use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on the network link 3220 and through the communication interface 3218, which carry the digital data to and from the computer system 3200, are exemplary forms of carrier waves that transport the information.

[0195] The computer system 3200 can send messages and receive data, including program code, through the network, network link 3220 and communication interface 3218. In the Internet example, server 3230 may transmit the requested code for the application program through Internet 3228, ISP 3226, local network 3222 and communication interface 3218. According to one or more embodiments, one such downloaded application provides methods such as those disclosed herein. The received code can be executed by processor 3204 when received, and / or stored in storage device 3210 or other non-volatile storage for later execution. In this way, computer system 3200 can obtain application code in the form of a carrier wave.

[0196] Embodiments of the present disclosure may take the form of a computer program containing one or more machine-readable instruction sequences describing the methods disclosed herein, or a data storage medium (e.g., a semiconductor memory, a magnetic disk, or an optical disk) in which such a computer program is stored. In addition, the machine-readable instructions may be embodied in two or more computer programs. The two or more computer programs may be stored on one or more different memories and / or data storage media.

[0197] Further embodiments according to the invention are described in the following numbered clauses:

[0198] 1. A method for determining a value of a parameter of interest of a patterning process, comprising:

[0199] acquiring a plurality of calibration data units, each calibration data unit representing detected radiation scattered from a corresponding target during a metrology process, the target comprising a structure formed on a substrate using the patterning process;

[0200] wherein each calibration data unit of at least two of the calibration data units represents detection radiation acquired using a different corresponding polarization setting during the metrology process, each polarization setting defining a polarization property of incident radiation for the metrology process and a polarization property of detection radiation for the metrology process;

[0201] using the calibration data unit to obtain calibration information about the metrology process;

[0202] acquiring measurement data units representing detected radiation scattered from a further target comprising a structure formed on the substrate or on a further substrate using the patterning process; and

[0203] The value of the parameter of interest is determined using the measurement data unit and the acquired calibration information.

[0204] 2. A method according to clause 1, wherein:

[0205] The different polarization settings used to obtain the calibration data unit include at least a first polarization setting and a second polarization setting; and

[0206] The incident radiation of the first polarization setting is polarized differently than the incident radiation of the second polarization setting.

[0207] 3. The method of clause 2, wherein the incident radiation of the first polarization setting is polarized orthogonally to the incident radiation of the second polarization setting.

[0208] 4. A method according to clause 2 or 3, wherein the detection radiation of the first polarisation setting is polarised differently than the detection radiation of the second polarisation setting.

[0209] 5. A method according to clause 4, wherein the detection radiation of the first polarisation setting is polarised orthogonally to the detection radiation of the second polarisation setting.

[0210] 6. A method according to any one of clauses 2 to 5, wherein:

[0211] Using a pair of calibration data units to obtain a calibration information unit;

[0212] A first calibration data unit of the pair of calibration data units is acquired using the first polarization setting with the substrate in a reference angular position; and

[0213] The second calibration data unit of the pair of calibration data units is acquired using the second polarization setting with the substrate rotated away from the reference angular position by a predetermined angle.

[0214] 7. A method according to clause 6, wherein the predetermined angle is equal to the angle between the polarization direction of the incident radiation of the first polarization setting and the polarization direction of the incident radiation of the second polarization setting.

[0215] 8. A method according to clause 6 or 7, wherein the predetermined angle is equal to the angle between the polarization direction of the detection radiation of the first polarization setting and the polarization direction of the detection radiation of the second polarization setting.

[0216] 9. A method according to any one of clauses 6 to 8, wherein the predetermined angle is equal to 90 degrees.

[0217] 10. A method according to any of clauses 6 to 9, wherein a calibration information unit is obtained for each reference angular position of a plurality of different reference angular positions.

[0218] 11. The method of clause 10, wherein the different reference angular positions comprise at least two angular positions that are 180 degrees apart from each other.

[0219] 12. A method according to any one of clauses 6 to 11, wherein:

[0220] at least a subset of the calibration information units includes a calibration information unit for each pair of calibration data units in a plurality of pairs of calibration data units, each pair of the plurality of pairs of calibration data units being obtained using a periodic structure having a respective deviation that is different relative to each other pair; and

[0221] Each deviation represents an intentionally imposed nominal offset between different layers of the periodic structure.

[0222] 13. The method according to any of clauses 10 to 12, wherein the obtaining of the calibration information comprises averaging two or more of the calibration information units.

[0223] 14. A method according to any one of clauses 6 to 13, wherein:

[0224] acquiring a unit of calibration data for each of a plurality of different orientations of the target; and

[0225] For each of the different orientations, at least one separate calibration information unit is obtained.

[0226] 15. A method according to any one of clauses 6 to 14, wherein:

[0227] acquiring a calibration data unit for each of a plurality of different diffraction orders of the radiation scattered from the target; and

[0228] For each of the different diffraction orders, at least one separate calibration information unit is acquired.

[0229] 16. A method according to any one of clauses 6 to 15, wherein:

[0230] acquiring a calibration data unit for each of a plurality of different polarization settings relative to the target; and

[0231] At least one separate calibration information unit is acquired for each of the different polarization settings relative to the target.

[0232] 17. A method according to any one of clauses 14 to 16, wherein the determination of the value of the parameter of interest from the measurement data unit comprises: selecting one or more calibration information units from the separate calibration information units according to the configuration of the metrology process used to obtain the measurement data unit.

[0233] 18. A method according to any of the preceding clauses, wherein each calibration data unit comprises or is derived from:

[0234] the detected radiation intensity in a pupil plane, the detected radiation phase in a pupil plane, the detected radiation intensity distribution in a pupil plane, or the detected radiation phase distribution in a pupil plane; or

[0235] The detected radiation intensity in the image plane, the detected radiation phase in the image plane, the detected radiation intensity distribution in the image plane, or the detected radiation phase distribution in the image plane.

[0236] 19. A method according to any of the preceding clauses, wherein each measurement data unit comprises or is derived from:

[0237] the detected radiation intensity in a pupil plane, the detected radiation phase in a pupil plane, the detected radiation intensity distribution in a pupil plane, or the detected radiation phase distribution in a pupil plane; or

[0238] The detected radiation intensity in the image plane, the detected radiation phase in the image plane, the detected radiation intensity distribution in the image plane, or the detected radiation phase distribution in the image plane.

[0239] 20. A method according to any of the preceding clauses, wherein:

[0240] The step of acquiring a measurement data unit is performed for each of the further N targets during the measurement time period;

[0241] The step of acquiring measurement data units is also performed at M different times during the measurement time period for a single fixed reference target, wherein M is less than N; and

[0242] The value of the parameter of interest is determined as follows: for each of one or more of the further targets, using the measurement data units acquired for that target, the acquired calibration information and the measurement data acquired from one or more of the measurements of the reference target.

[0243] 21. The method of clause 20, further comprising repeating the step of acquiring a plurality of calibration data units at least once during the measurement period to acquire updated calibration information, wherein:

[0244] The determining of the value of the parameter of interest for one or more of the further targets is performed using the updated calibration information.

[0245] 22. A method according to any of the preceding clauses, wherein the structure comprises a multi-layer structure and the parameter of interest comprises an overlay error between two or more different layers in the multi-layer structure.

[0246] 23. A method according to any of the preceding clauses, wherein the parameter of interest comprises focus error or critical dimension.

[0247] 24. A method of determining a value of a parameter of interest of a patterning process, comprising:

[0248] acquiring a first pair of calibration data units, each calibration data unit representing detected radiation scattered from a target during a metrology process, the target comprising a structure formed on a substrate using the patterning process;

[0249] The first calibration data unit of the first pair of calibration data units is acquired with the substrate in a reference angular position;

[0250] The second calibration data unit of the first pair of calibration data units is acquired with the substrate rotated away from the reference angular position by a predetermined angle;

[0251] using the first pair of calibration data units to obtain first calibration information about the metrology process;

[0252] acquiring measurement data units representing detected radiation scattered from a further target comprising a structure formed on the substrate or on a further substrate using the patterning process; and

[0253] The value of the parameter of interest is determined using the measurement data unit and the acquired first calibration information.

[0254] 25. A method according to clause 24, wherein:

[0255] The first calibration data unit is acquired using a first polarization setting during the metrology process;

[0256] The second calibration data unit is acquired during the metrology process using a second polarization setting different from the first polarization setting;

[0257] Each polarization setting defines polarization properties of incident radiation for the metrology process and polarization properties of detected radiation for the metrology process; and one or both of the following are satisfied:

[0258] an angle between a polarization direction of incident radiation of the first polarization setting and a polarization direction of incident radiation of the second polarization setting being equal to the predetermined angle; and

[0259] The angle between the polarization direction of the detection radiation of the first polarization setting and the polarization direction of the detection radiation of the second polarization setting is equal to the predetermined angle.

[0260] 26. A method according to clause 24 or 25, wherein:

[0261] The target includes a first periodic structure and a second periodic structure, the first periodic structure being oriented at the predetermined angle relative to the second periodic structure; and

[0262] The first calibration data unit and the second calibration data unit of the first pair of calibration units are obtained from the first periodic structure.

[0263] 27. The method according to clause 26, further comprising:

[0264] acquiring a second pair of calibration data units, each calibration data unit representing detected radiation scattered from the target during the metrology process;

[0265] A first calibration data unit of the second pair of calibration data units is acquired from the second periodic structure when the substrate is in the reference angular position;

[0266] The second calibration data unit of the second pair of calibration data units is acquired from the second periodic structure when the substrate is at the predetermined angle from the reference angular position; and

[0267] The second pair of calibration data units is used to obtain second calibration information about the metrology process.

[0268] 28. A method according to clause 27, wherein:

[0269] said further target comprising a first periodic structure and a second periodic structure oriented at said predetermined angle relative to each other;

[0270] The determination of the parameter of interest uses a measurement data unit comprising first data representing detection radiation scattered from the first periodic structure and second data representing detection radiation scattered from the second periodic structure; and

[0271] The determining of the parameter of interest comprises applying a correction factor to the first data based on the first calibration information and applying a correction factor to the second data based on the second calibration information.

[0272] 29. A method according to clause 28, wherein:

[0273] The first data represents a first sum of intensities of a +1 diffraction order and a -1 diffraction order of radiation from the first periodic structure;

[0274] The second data represents a second sum of intensities of the +1 diffraction order and the -1 diffraction order of radiation from the second periodic structure; and

[0275] The determining of the parameter of interest comprises determining a difference between the first sum and the second sum after applying the correction factor to the first data and the second data.

[0276] 30. A method according to any of clauses 24 to 29, wherein the parameter of interest comprises a focus error.

[0277] 31. A method according to clause 30, wherein the target and the further target are formed using a patterning process having intentionally applied astigmatism to enhance the correlation between the focus error and the difference between the first sum and the second sum.

[0278] 32. A method according to any one of clauses 24 to 31, wherein the predetermined angle is 90 degrees.

[0279] 33. A device manufacturing method comprising:

[0280] forming a structure on the substrate using a patterning process, wherein the patterning process forms part of a photolithographic manufacturing process;

[0281] performing a method according to any preceding clause to determine a value of a parameter of interest of the patterning process; and

[0282] The patterning process is adjusted based on the determined value of the parameter of interest.

[0283] Although specific reference may be made herein to the use of metrology devices in the manufacture of ICs, it should be understood that the metrology devices and processes 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 heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any use of the term "wafer" or "die" herein is considered to be synonymous with the more general term "substrate" or "target portion", respectively. The substrate referred to herein may be processed before or after exposure, such as in a track (a tool that typically applies a layer of resist on a substrate and develops the exposed resist), a metrology tool, and / or one or more other tools. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, a substrate may be processed more than once, such as for the manufacture of a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already contains multiple processed layers.

[0284] Although specific reference may have been made above to the use of embodiments of the present disclosure in the context of optical lithography, it should be understood that the present disclosure may be used in other applications, such as nanoimprint lithography, and is not limited to lithography where the context permits. In the case of nanoimprint lithography, the patterning device is an imprint template or mold.

[0285] As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365, 355, 248, 193, 157, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 to 20 nm), as well as particle beams (such as ion beams or electron beams).

[0286] The term "lens," where the context permits, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.

[0287] Reference herein to correction or rectification of an error includes eliminating the error or reducing the error to within a tolerance range.

[0288] As used throughout this application, the word "may" is used in a permissive sense (i.e., indicating that it is possible) rather than a mandatory sense (i.e., must). The words "include", "including", and "includes" and the like mean, but are not limited to. As used throughout this application, unless the content clearly indicates otherwise, the singular forms "a", "an", and "the" include plural indicators. Thus, for example, references to "an" or "an" elements include combinations of two or more elements, although other terms and phrases, such as "one or more", are used for one or more elements. Unless otherwise indicated, the term "or" is non-exclusive, i.e., includes "and" and "or". Terms describing conditional relationships (e.g., "in response to X, Y," "when X, Y," "if X, then Y," "when X, Y," etc.) include causal relationships where the antecedent is a necessary causal condition, the antecedent is a sufficient causal condition, or the antecedent is a contingent causal condition of the effect, e.g., "state X occurs when condition Y is acquired" is a generic term for "X occurs only when Y" and "X occurs when Y and Z." Such conditional relationships are not limited to consequences occurring immediately after the antecedent is acquired, as some consequences may be delayed, and in conditional statements, antecedents are related to their consequences, e.g., the antecedent is related to the likelihood of the consequence occurring. Unless otherwise indicated, a statement in which multiple properties or functions are mapped to multiple objects (e.g., one or more processors that perform steps A, B, C, and D) includes both that all such properties or functions are mapped to all such objects and that a subset of the properties or functions are mapped to a subset of the properties or functions (e.g., both that all processors perform steps AD and that processor 1 performs step A, processor 2 performs step B and part of step C, and processor 3 performs part of step C and step D). In addition, unless otherwise indicated, a statement that a value or action is "based on" another condition or value includes both that the condition or value is the only factor and that the condition or value is one of multiple factors. Unless otherwise indicated, a statement that "each" instance of a set has a property should not be read as excluding the case where some otherwise identical or similar members of the larger set do not have the property, i.e., each does not necessarily mean every one.

[0289] To the extent that certain U.S. patents, U.S. patent applications, or other materials (e.g., articles) are incorporated by reference, the text of such U.S. patents, U.S. patent applications, and other materials is incorporated by reference only to the extent that there is no conflict between such materials and the statements and drawings presented herein. In the event of such a conflict, any such conflicting text in such incorporated by reference U.S. patents, U.S. patent applications, and other materials is not expressly incorporated by reference herein.

[0290] The above description is intended to be illustrative rather than limiting. It will therefore be apparent to those skilled in the art that modifications may be made to the present disclosure as described without departing from the scope of the claims set forth hereinafter.

Claims

1. A method for determining a value of a parameter of interest of a patterning process, comprising: acquiring a plurality of calibration data units, each calibration data unit representing detected radiation scattered from a corresponding target during a metrology process, the target comprising a structure formed on a substrate using the patterning process; wherein each calibration data unit of at least two of the calibration data units represents detection radiation acquired using a different corresponding polarization setting during the metrology process, each polarization setting defining a polarization property of incident radiation for the metrology process and a polarization property of detection radiation for the metrology process; using the calibration data unit to obtain calibration information about the metrology process; acquiring measurement data units representing detected radiation scattered from a further target comprising a structure formed on the substrate or on a further substrate using the patterning process; as well as The value of the parameter of interest is determined using the measurement data unit and the acquired calibration information.

2. The method according to claim 1, wherein: The different polarization settings for acquiring the calibration data unit include at least: a first polarization setting and a second polarization setting; and The incident radiation of the first polarization setting is polarized differently than the incident radiation of the second polarization setting. 3 . The method of claim 2 , wherein the incident radiation of the first polarization setting is polarized orthogonally to the incident radiation of the second polarization setting. 4 . The method according to claim 2 , wherein the detection radiation of the first polarization setting is polarized differently than the detection radiation of the second polarization setting. 5 . The method of claim 4 , wherein the detection radiation of the first polarization setting is polarized orthogonally to the detection radiation of the second polarization setting.

6. The method according to claim 2, further comprising: Using a pair of calibration data units to obtain a calibration information unit; A first calibration data unit of the pair of calibration data units is acquired using the first polarization setting with the substrate in a reference angular position; as well as The second calibration data unit of the pair of calibration data units is acquired using the second polarization setting with the substrate rotated away from the reference angular position by a predetermined angle.

7. The method of claim 6, wherein the predetermined angle is equal to the angle between the polarization direction of the incident radiation of the first polarization setting and the polarization direction of the incident radiation of the second polarization setting.

8. A method according to claim 6 or 7, wherein the predetermined angle is equal to the angle between the polarization direction of the detection radiation of the first polarization setting and the polarization direction of the detection radiation of the second polarization setting.

9. The method of claim 6, wherein the predetermined angle is equal to 90 degrees.

10. The method of claim 6, wherein a calibration information unit is obtained for each reference angular position of a plurality of different reference angular positions. The method of claim 10 , wherein the different reference angular positions include at least two angular positions separated from each other by 180 degrees.

12. The method according to claim 10, wherein: at least a subset of the calibration information units includes a calibration information unit for each pair of calibration data units in a plurality of pairs of calibration data units, each pair of the plurality of pairs of calibration data units being obtained using a periodic structure having a respective deviation that is different relative to each other pair; as well as Each deviation represents an intentionally imposed nominal offset between different layers of the periodic structure.

13. The method according to any one of claims 10 to 12, wherein the obtaining of the calibration information comprises: Two or more of the calibration information units are averaged.

14. The method according to claim 6, wherein: acquiring a unit of calibration data for each of a plurality of different orientations of the target; and For each of the different orientations, at least one separate calibration information unit is obtained.

15. The method of claim 6, wherein: acquiring a calibration data unit for each of a plurality of different diffraction orders of the radiation scattered from the target; and For each of the different diffraction orders, at least one separate calibration information unit is acquired.

16. The method according to claim 6, wherein: acquiring a calibration data unit for each of a plurality of different polarization settings relative to the target; and At least one separate calibration information unit is acquired for each of the different polarization settings relative to the target.

17. The method according to any one of claims 14 to 16, wherein the determination of the value of the parameter of interest from the measurement data unit comprises: One or more of the separate calibration information units are selected depending on a configuration of the metrology process used to obtain the measurement data unit.

18. The method of claim 1, wherein each calibration data unit comprises or is derived from: the detected radiation intensity in a pupil plane, the detected radiation phase in a pupil plane, the detected radiation intensity distribution in a pupil plane, or the detected radiation phase distribution in a pupil plane; or The detected radiation intensity in the image plane, the detected radiation phase in the image plane, the detected radiation intensity distribution in the image plane, or the detected radiation phase distribution in the image plane.

19. The method of claim 1, wherein each measurement data unit comprises or is derived from: the detected radiation intensity in a pupil plane, the detected radiation phase in a pupil plane, the detected radiation intensity distribution in a pupil plane, or the detected radiation phase distribution in a pupil plane; or The detected radiation intensity in the image plane, the detected radiation phase in the image plane, the detected radiation intensity distribution in the image plane, or the detected radiation phase distribution in the image plane.

20. The method of claim 1, wherein: The step of acquiring a measurement data unit is performed for each of the other N targets during the measurement time period; The step of acquiring measurement data units is also performed at M different times during the measurement time period for a single fixed reference target, where M is less than N; as well as The value of the parameter of interest is determined as follows: for each of one or more of the further targets, using the measurement data units acquired for that target, the acquired calibration information, and the measurement data acquired from one or more of the measurements of the reference target.

21. The method according to claim 20, further comprising: The step of acquiring a plurality of calibration data units is repeated at least once during the measurement time period to acquire updated calibration information, wherein: The determining of the value of the parameter of interest for one or more of the further targets is performed using the updated calibration information.

22. The method of claim 1, wherein the structure comprises a multi-layer structure and the parameter of interest comprises an overlay error between two or more different layers in the multi-layer structure.

23. The method of claim 1, wherein the parameter of interest comprises focus error or critical dimension.

24. A method of determining a value of a parameter of interest of a patterning process, comprising: acquiring a first pair of calibration data units, each calibration data unit representing detected radiation scattered from a target during a metrology process, the target comprising a structure formed on a substrate using the patterning process; The first calibration data unit of the first pair of calibration data units is acquired with the substrate in a reference angular position; The second calibration data unit of the first pair of calibration data units is acquired with the substrate rotated away from the reference angular position by a predetermined angle; using the first pair of calibration data units to obtain first calibration information about the metrology process; acquiring measurement data units representing detected radiation scattered from a further target comprising a structure formed on the substrate or on a further substrate using the patterning process; as well as The value of the parameter of interest is determined using the measurement data unit and the acquired first calibration information.

25. The method of claim 24, wherein: The first calibration data unit is acquired using a first polarization setting during the metrology process; The second calibration data unit is acquired during the metrology process using a second polarization setting different from the first polarization setting; Each polarization setting defines a polarization property of incident radiation for said metrology process and a polarization property of detected radiation for said metrology process; And one or both of the following are met: an angle between a polarization direction of incident radiation of the first polarization setting and a polarization direction of incident radiation of the second polarization setting being equal to the predetermined angle; and The angle between the polarization direction of the detection radiation of the first polarization setting and the polarization direction of the detection radiation of the second polarization setting is equal to the predetermined angle.

26. The method according to claim 24 or 25, wherein: The target includes a first periodic structure and a second periodic structure, the first periodic structure being oriented at the predetermined angle relative to the second periodic structure; as well as The first calibration data unit and the second calibration data unit of the first pair of calibration units are obtained from the first periodic structure.

27. The method according to claim 26, further comprising: acquiring a second pair of calibration data units, each calibration data unit representing detected radiation scattered from the target during the metrology process; A first calibration data unit of the second pair of calibration data units is acquired from the second periodic structure when the substrate is in the reference angular position; The second calibration data unit of the second pair of calibration data units is acquired from the second periodic structure when the substrate is at the predetermined angle from the reference angular position; as well as The second pair of calibration data units is used to obtain second calibration information about the metrology process.

28. The method of claim 27, wherein: said further target comprising a first periodic structure and a second periodic structure oriented at said predetermined angle relative to each other; said determination of said parameter of interest uses a measurement data unit comprising first data representing detection radiation scattered from said first periodic structure and second data representing detection radiation scattered from said second periodic structure; and The determining of the parameter of interest includes applying a correction factor to the first data based on the first calibration information and applying a correction factor to the second data based on the second calibration information.

29. The method of claim 28, wherein: The first data represents a first sum of intensities of a +1 diffraction order and a -1 diffraction order of radiation from the first periodic structure; The second data represents a second sum of the intensities of the +1 diffraction order and the -1 diffraction order of radiation from the second periodic structure; as well as The determining of the parameter of interest comprises determining a difference between the first sum and the second sum after applying the correction factor to the first data and the second data.

30. The method of claim 29, wherein the parameter of interest comprises focus error.

31. A method according to claim 30, wherein the target and the further target are formed using a patterning process having intentionally applied astigmatism to enhance the correlation between the focus error and the difference between the first sum and the second sum.

32. The method of claim 24, wherein the predetermined angle is 90 degrees.

33. A device manufacturing method comprising: forming a structure on the substrate using a patterning process, wherein the patterning process forms part of a photolithographic manufacturing process; performing a method according to any preceding claim to determine a value of a parameter of interest of the patterning process; as well as The patterning process is adjusted based on the determined value of the parameter of interest.

Images