Adjustment of a measuring device or measurement performed by the measuring device based on the characteristics of the object being measured

Abstract

A method for adjusting a measurement device is disclosed herein, the method comprising: spatially dividing an intensity distribution in a pupil plane of the measurement device into a plurality of pixels; and reducing the effect of structural asymmetry in a target on a measurement of the target by the measurement device by adjusting the intensity of the plurality of pixels using a computer.

Description

[0001] This application is a divisional application of the international application PCT / EP2016 / 079105, which entered the Chinese national phase on November 29, 2016 and has application number 201680081810.1.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Application No. 62 / 268,974, filed December 17, 2015, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present disclosure relates to the adjustment of measurements made in electronic device processing based on characteristics of a measured target. Background Art

[0005] A lithographic apparatus is a machine that applies a desired pattern to a substrate, typically a target portion of a substrate. For example, a lithographic apparatus may be used to manufacture an integrated circuit (IC). In this case, a pattern forming device, alternatively referred to as a mask or reticle, may be used to generate a circuit pattern to be formed on a single layer of an integrated circuit. The pattern may be transferred to a target portion (e.g., including a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). Typically, the transfer of the pattern is performed by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned in succession. Known lithographic apparatus 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 along a given direction (the "scanning" direction) while scanning the substrate in a direction parallel or antiparallel to the direction by a radiation beam. In addition, the pattern can be transferred from the pattern forming device to the substrate by imprinting the pattern onto the substrate.

[0006] During lithography, it is often desirable to make measurements of the structures produced, for example for process control and verification. Various tools are known for making such measurements, including scanning electron microscopes (SEMs), which are commonly used to measure critical dimensions (CDs), and specialized tools for measuring the overlay of lithographic equipment (the accuracy of alignment of two layers in a device). Recently, various forms of scatterometers have been developed for use in the field of lithography. These devices direct a radiation beam onto a target and measure one or more properties of the scattered radiation—such as intensity as a function of wavelength at a single reflection angle, intensity as a function of reflection angle at one or more wavelengths, or polarization as a function of reflection angle to obtain a "spectrum"—from which properties of interest of the target can be determined. Confirmation of properties of interest can be performed using various techniques, such as reconstructing the target by iterative methods such as rigorous coupled wave analysis (RWCA) or finite element methods, library searches, and principal component analysis.

[0007] The targets used by conventional scatterometers are relatively large (e.g. 40 μm x 40 μm), with the grating and measurement beam producing a spot that is smaller than the grating (i.e. the grating is not filled). This simplifies the mathematical reconstruction of the target, since it can be considered to be infinite. However, in order to reduce the size of the targets to, for example, 10 μm x 10 μm or smaller, so that they can be positioned in product features rather than in scribes, metrology has been proposed in which the grating is made smaller than the measurement spot (i.e. the grating is overfilled). Typically, such targets are measured using dark-field scatterometry, in which the zeroth order of diffraction (corresponding to specular reflection) is blocked and only the higher orders are processed.

[0008] Diffraction-based overlay (DBO) using dark field detection of the first diffraction order enables overlay measurements of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by product structures on the wafer. Multiple targets can be measured in one image. In known measurement techniques, overlay measurements are obtained by measuring the target twice under certain conditions while rotating the target or changing the illumination mode or imaging mode to separately obtain the -1st diffraction order intensity and the +1st diffraction order intensity. These intensities are compared for a given grating, thereby providing a measure of the asymmetry in the grating.

[0009] One approach to improving measurement accuracy is better control at the design stage of an overlay metrology target that is compatible with known illumination patterns and other program constraints, thereby minimizing structural asymmetries in the target by design. The present disclosure addresses an alternative approach in which illumination is controlled to counteract the effects of asymmetries in overlay measurements even if structural asymmetries exist in the target. In other words, measurement accuracy is improved by taking advantage of the flexibility in reconfiguring illumination according to embodiments of the present disclosure rather than changing the target design. Summary of the invention

[0010] A method for adjusting a measurement device is disclosed herein, the method comprising: spatially dividing an intensity distribution in a pupil plane of the measurement device into a plurality of pixels; and reducing the effect of structural asymmetry in a target on a measurement of the target by the measurement device by adjusting the intensity of the plurality of pixels using a computer.

[0011] A method of adjusting a measurement device is disclosed herein. The method includes adjusting a parameter of the measurement device or a parameter of a measurement of the target by the measurement device based on a characteristic of the target.

[0012] A method is disclosed herein, comprising: setting a parameter of a measurement device or a parameter of a measurement of a target by the measurement device to a value adjusted based on a characteristic of the target; and measuring the target using the measurement device.

[0013] A method is disclosed herein, the method comprising: setting a characteristic of a target to a value, adjusting a parameter of a metrology device or a parameter of a measurement of the target by the metrology device based on the value; and manufacturing the target on a substrate.

[0014] A computer program product is disclosed herein, the computer program product comprising a non-transitory computer-readable medium having instructions thereon, the instructions implementing any of the above methods when executed by a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] These and other aspects and features of the present disclosure will become apparent to those of ordinary skill in the art after reviewing the following description of specific embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0016] Figure 1 depicts a lithographic apparatus according to an embodiment of the present disclosure;

[0017] Figure 2A shows a schematic diagram of a dark field scatterometer using a first pair of illumination apertures for measuring a target according to an embodiment of the present disclosure;

[0018] Figure 2B Details of the diffraction spectrum of the target grating for a given illumination direction are shown;

[0019] Figure 3A A cross-sectional view of the grating is depicted;

[0020] FIG. 3B to FIG. 3D Describes the principle of overlay measurement between two perpendicular layers of a grating using diffraction-based scatterometry;

[0021] 4A to 4F10 shows the various stages of illumination shaping by aperture and pupil filters, respectively, according to an embodiment of the present disclosure;

[0022] Figure 5 A target having a multi-layer memory structure for evaluating the effect of illumination optimization according to an embodiment is shown;

[0023] FIG. 6A to FIG. 6B An example of lithographic process-induced asymmetry in a target structure is shown;

[0024] Figure 7 A table listing the results of overlap sensitivity calculations for various illumination polarizations is shown (Table I);

[0025] Figures 8 to 10 shows the change of the irradiation shape according to the optimization algorithm disclosed in the present disclosure;

[0026] Figures 11 to 14 shows various mathematical functions plotted relative to the number of iterations used in the optimization algorithms disclosed in the present disclosure;

[0027] Fig.15 Schematically shows a process for a method according to an embodiment;

[0028] Fig.16 The flowchart for the method according to the embodiment is schematically shown. DETAILED DESCRIPTION

[0029] This specification discloses one or more embodiments that include features of the present disclosure. The disclosed embodiments merely illustrate the concepts of the present invention. The scope of the present disclosure is not limited to the disclosed embodiments. The present disclosure is defined by the appended claims. Although the described embodiments and references to "one embodiment," "embodiment," "exemplary embodiment," etc. in this specification indicate that the described embodiments may include specific features, structures, or characteristics, each embodiment may not necessarily include the specific features, structures, or characteristics. Furthermore, these terms do not necessarily refer to the same embodiment. In addition, when specific features, structures, or characteristics are described in conjunction with an embodiment, it should be understood that it is within the knowledge of a technician in the field to implement such features, structures, or characteristics in other embodiments, regardless of whether other embodiments are explicitly described.

[0030] The embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. The embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include: a read-only memory (ROM); a random access memory (RAM); a disk storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, firmware, software, programs, instructions may be described herein as performing certain actions. However, it should be understood that these descriptions are for convenience only, and that these actions are actually caused by a computing device, a processor, a controller, or other devices that execute firmware, software, programs, instructions, etc.

[0031] However, before describing these embodiments in greater detail, it is instructive to present an exemplary environment in which embodiments of the present disclosure may be implemented.

[0032] Figure 1 A lithographic apparatus LA is schematically depicted. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation), a patterning device support or support structure (e.g. mask table) MT configured 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, a substrate table (e.g. wafer stage) WT configured to hold a substrate (e.g. a wafer coated with an anti-contact agent) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PS configured to project a 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.

[0033] The illumination optics system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape or control radiation.

[0034] The patterning device support holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions (e.g., whether the patterning device is held in a vacuum environment). The patterning device support may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The patterning device support may be, for example, a frame or table that may be fixed or movable as desired. The patterning device support may 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."

[0035] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to produce a pattern in a target portion of the substrate. It should be noted that, for example, if the pattern imparted to the radiation beam includes phase-shifting features or so-called assist features, the pattern may not exactly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in the device (such as an integrated circuit) produced in the target portion.

[0036] 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 masks, alternating phase-shift masks, and attenuated phase-shift masks, as well as various hybrid mask types.

[0037] An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam which is reflected by the mirror matrix.

[0038] The term "projection system" as used herein should be interpreted broadly to cover any type of projection system suitable for the exposure radiation used or for other factors such as the use of an immersion liquid or the use of a vacuum, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system".

[0039] As depicted herein, the device is of the transmissive type (eg, using a transmissive mask). Alternatively, the device may be of the reflective type (eg, using a programmable mirror array of the type mentioned above, or using a reflective mask).

[0040] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such a "multi-stage" machine, the extra tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

[0041] 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, so as 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 the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of the projection system. The term "immersion" as used herein does not mean that structures such as the substrate are necessarily immersed in the liquid, but only means that the liquid is located between the projection system and the substrate during exposure.

[0042] refer to Figure 1 , the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source is an excimer laser, the source and the lithographic apparatus may be separate entities. In this case, the source is not considered to form part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directional 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 provided, may be referred to together as a radiation system.

[0043] The illuminator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent of the intensity distribution in a pupil plane of the illuminator (commonly referred to as σ-outer and σ-inner, respectively) may be adjusted. The intensity distribution in the pupil plane is referred to elsewhere in this specification as the "illumination beam". Additionally, 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 so as to have a desired uniformity and intensity distribution in its cross-section.

[0044] The radiation beam B is incident on a patterning device (e.g. a mask) MA held on a patterning device support (e.g. a mask table MT) and is patterned by the patterning device. After passing through the patterning device (e.g. a mask) 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 interferometric device, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be precisely 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 a further position sensor (in Figure 1 The image forming device (not explicitly shown in FIG. 1 ) can be used to accurately position the patterning device (e.g. mask) MA relative to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during scanning.

[0045] Typically, movement of the patterning device support (e.g. mask table) MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) forming part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module forming part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the patterning device support (e.g. mask table) MT may be connected to a short-stroke actuator only, or may be fixed.

[0046] Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the pattern forming device (e.g., mask) MA and substrate W. Although the substrate alignment marks shown occupy dedicated target portions, they can be located in the space between target portions (these marks are called scribe alignment marks). Similarly, in the case where more than one tube core is set on the pattern forming device (e.g., mask) MA, the mask alignment marks can be located between the tube cores. Small alignment marks can also be included in the tube core in the device feature, in which case it is necessary to make the mark as small as possible and do not require any imaging or program conditions that are different from adjacent features. The alignment system for detecting alignment marks is further described below.

[0047] The depicted device can be used in at least one of the following modes:

[0048] 1. In step mode, the entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure) while the patterning device support (e.g. mask table) MT and the substrate table WT are held substantially stationary. Next, the substrate table WT is shifted in the X and / or Y direction to enable a different target portion C to be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

[0049] 2. In scan mode, the patterning device support (e.g. mask table) 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 patterning device support (e.g. mask table) MT may be determined by the (or less) 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 the non-scanning direction) in a single dynamic exposure, while the length of the scanning motion determines the height of the target portion (in the scanning direction).

[0050] 3. In another mode, the patterning device support (e.g. mask table) MT holding the programmable patterning device is kept substantially stationary 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 used 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 is readily applicable to maskless lithography using a programmable patterning device such as a programmable mirror array of the type described above.

[0051] Additionally, combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0052] Figure 2A A dark field measurement device suitable for use in embodiments of the present disclosure is shown, but the present disclosure is not limited to dark field scattering measurement. Figure 2A In the example shown, a target grating T is illuminated and the rays diffracted from the grating are collected for measurement. Figure 2B The dark field metrology equipment may be a separate device or incorporated, for example, in a metrology station or lithography cell. Figure 1In the lithographic apparatus LA shown. The optical axis with multiple branches running through the apparatus is represented by a dotted line O. In the apparatus, the light emitted by a source 11 (e.g. a xenon lamp) is directed to a substrate W via a beam splitter 15 by an optical system comprising lenses 12, 14 and an objective lens 16. These lenses are configured in a double order of a 4F arrangement. Different lens arrangements can be used, with the restriction that the lens arrangement still provides a substrate image to the detector and simultaneously allows access to the intermediate pupil plane for spatial frequency filtering. Therefore, the angular range of radiation incident on the substrate can be selected by defining the 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 accomplished by inserting an aperture plate 13 of appropriate form between lenses 12 and 14 in a plane that is a back-projected image of the objective lens pupil plane. In the illustrated example, the aperture plate 13 has different forms, labeled 13N and 13S, allowing different illumination modes to be selected. The illumination system in this example forms an off-axis illumination mode. In a first illumination mode, aperture plate 13N provides off-axis from a direction designated (for purposes of description only) as "North". In a second illumination mode, aperture plate 13S is used to provide similar illumination, but from an opposite direction labeled "South". Other illumination modes are possible by using different apertures. The remainder of the pupil plane is desirably dark because any unwanted light outside the desired illumination mode will interfere with the desired measurement signal.

[0053] like Figure 2B As shown, the target grating T is placed so that the substrate W is perpendicular to the optical axis O of the objective lens 16. The illumination ray I that impinges on the grating T at an angle offset from the axis O produces a zeroth order component of illumination (solid line O) and two first order components of illumination (dash-dotted line +1 and dash-dotted line -1). It should be remembered that in the case of a small overfilled target grating, these illumination rays are only one of many parallel rays that cover the substrate area including the measurement target grating T and other features. Since the aperture in the plate 13 has a finite width (necessary to receive a useful amount of light), the incident ray I will actually occupy a range of angles, and the 0th order and +1 / -1 order diffracted rays will be slightly spread out. Depending on the point spread function of the small target, each order +1 and -1 will be further spread out over a range of angles, rather than a single ideal ray as shown. It should be noted that the grating pitch and the illumination angle can be designed or adjusted so that the first order rays entering the objective are closely aligned with the central optical axis. Figure 2A and Figure 2B The rays shown are shown slightly off-axis purely to make them easier to distinguish in the figure.

[0054] At least the 0th order and the +1st or -1st order diffracted by the target on the substrate W are collected by the objective lens 16 and directed back through the beam splitter 15. Figure 2A , both the first illumination mode and the second illumination mode are illustrated by indicating diametrically opposite apertures labeled North (N) and South (S). In other embodiments, East (E) and West (W) labels may be used depending on the position of the aperture. 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-order diffracted ray labeled +1 (N) enters objective lens 16. Conversely, when the second illumination mode is applied using aperture plate 13S, the -1-order diffracted ray (labeled -1 (S)) is the diffracted ray that enters lens 16.

[0055] The second beam splitter 17 divides the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 uses the zeroth order diffracted beam and the first order diffracted beam to form a diffraction spectrum (pupil plane image) of the target on a first sensor 19 (e.g., a CCD or CMOS sensor). Each diffraction order is incident on a different point on the sensor, so that image processing can compare and contrast multiple orders. The pupil plane image captured by the sensor 19 can be used to focus the metrology device and / or normalize the intensity measurement of the first order beam.

[0056] In the second measurement branch, the optical systems 20, 22 form an image of the target on the substrate W on a sensor 23 (e.g. a CCD or CMOS sensor). In the second measurement branch, an aperture 21 is provided in a plane conjugate to the pupil plane. The aperture 21 is used to block the zeroth order diffraction beam so that the image of the target formed on the sensor 23 is formed only by the -1 or +1 first order beam. The image captured by the sensors 19 and 23 is output to an image processor and controller PU, the functions of which will depend on the specific type of measurement being performed. It should be noted that the term "image" is used here in a broad sense. Therefore, if only one of the -1 order and the +1 order is present, then by the same token no image of the grating lines will be formed.

[0057] Figure 2A The particular forms of aperture plate 13 and field stop 21 shown are purely exemplary. In another embodiment of the present disclosure, 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 light to the sensor. In still other embodiments, second, third and higher order beams ( Figure 2B ) may be used in the measurement instead of or in addition to the first order beam.

[0058] To adapt the illumination to these different types of measurements, the aperture plate 13 may include a plurality of aperture patterns formed around a disk that rotates to position the desired pattern. Alternatively or in addition, a set of plates 13 may be provided and swapped to achieve the same effect. A programmable illumination device such as a deformable mirror array or a transmissive spatial line of sight modulator (SLM) may also be used. A moving mirror or prism may be used as another means for adjusting the illumination pattern.

[0059] As explained with respect to the aperture plate 13, the selection of the diffraction orders for imaging can alternatively be achieved by changing the pupil diaphragm 21 or by replacing the pupil diaphragm with a different pattern or by replacing the fixed field diaphragm with a programmable SLM. In this case, the illumination side of the measuring optical system can remain constant, while the imaging side has a first mode and a second mode. Therefore, in the present disclosure, there are actually three types of measurement methods, each with its own advantages and disadvantages. In one method, the illumination mode is changed to measure different orders. In another method, the imaging mode is changed. In a third method, the illumination mode and the imaging mode remain unchanged, but the target is rotated 180 degrees. In each case, the desired effect is the same, namely for selecting the first part and the second part of the non-zero order diffracted radiation that are symmetrically opposite to each other in the diffraction spectrum of the target. In principle, the desired selection of the orders can be obtained by changing the illumination mode and the imaging mode simultaneously, but this is likely to bring disadvantages without advantages, so it will not be discussed further.

[0060] Although the optical system used for imaging in this example has a wide entrance pupil defined by the field stop 21, in other embodiments or applications, the entrance pupil size of the imaging system itself may be small enough to be defined to the desired order and thus also serve as a field stop.

[0061] Typically, the target grating will be aligned with its grating lines running north-south or east-west. That is, the grating will be aligned in the X-direction or the Y-direction of the substrate W. It should be noted that the aperture plate 13N or 13S can be used to measure gratings oriented in one direction only (X or Y, depending on the setting). For measuring orthogonal gratings, target rotations of up to 90° and 270° may be implemented. As already mentioned, an off-axis aperture may be provided in the field stop 21 rather than in the illumination aperture plate 13. In this case, the illumination will be coaxial.

[0062] Additional aperture plates can be used to combine the illumination modes described above. If the crosstalk between these different diffraction signals is not too large, measurements of both the X-grating and the Y-grating can be performed without changing the illumination mode.

[0063] As mentioned above, the measurement target often takes the form of one or more gratings. The gratings can be placed in the scribe line or in the product area. If the grating is located in the product area, product features can also be seen in the periphery of the image field. The image processor and controller PU use pattern recognition to process these images to identify separate images when multiple gratings are used.

[0064] Although the target structures described above are metrology targets specifically designed and formed for the purpose of metrology, in other embodiments, properties of a target that is a functional component of a device formed on a substrate may be measured. Many devices have regular grating-like structures. The terms "target grating" and "target structure" as used herein do not require that the structure has been specifically provided for the measurement being performed.

[0065] In association with a physical grating structure of a target implemented on a substrate and a pattern forming device, an embodiment may include a computer program comprising one or more sequences of machine-readable instructions describing a method of generating a target on a substrate, measuring a target on a substrate and / or analyzing the measurements to obtain information about a lithographic process. The computer program may be executed, for example, in a unit PU in the apparatus of FIG. 2 and / or in a control unit in the lithographic apparatus. A data storage medium (e.g., a semiconductor memory, a magnetic disk or an optical disk) having the computer program stored thereon may also be provided. In the case of, for example, Figure 2A In the case where existing measurement equipment of the type shown is already in production and / or in use, the present disclosure can be implemented by providing an updated computer program product for causing a processor to perform the method described in the present disclosure and calculate the exposure dose accordingly. The program can be configured to control the optical system, substrate support, etc. as required to perform steps for measuring a plurality of suitable target structures.

[0066] Figure 3A A cross-sectional view of a standard single-layer grating pattern is shown. Figure 3A In , a limited section of only five periods of the grating is shown. The grating period is Pd, the horizontal line width of a single grating line is w1, and the vertical thickness of each grating line is t. In the complete grating, the pattern can be repeated in the vertical direction (z-axis) and the horizontal direction (x-axis) or the lateral direction (y-axis). Figure 3A The grating pattern in may include, for example, a chrome pattern on a reticle. The parameters Pd, w1, and t, along with other parameters, may be used to describe aspects of the grating.

[0067] Although the grating segments can be on the same device layer and used for same-layer alignment and / or image stitching purposes, FIG. 3B to FIG. 3DIt is shown how a grating-based metrology structure can be used to measure the overlay and / or alignment between two different layers in an electronic device. A first grating G1 is on layer 1, and a second grating G2 is on layer 2, where the two layers mimic device layers in an actual device to be manufactured (also referred to as a "product"). The device may have a first pattern in layer 1 and a second pattern in layer 2, and the overlay and / or alignment between those two patterns is of interest. Figure 3B shows an overlap with a deviation or bias in the negative direction (along the horizontal x-axis), and Figure 3D The overlap is shown with a deviation or bias in the positive direction (along the x-axis). The x-axis is also referred to as the overlap direction. Figure 3C The ideal case is shown where there is no overlay error between G1 and G2 because they are perfectly aligned (along the vertical z direction). Those skilled in the art will appreciate that the designer may intentionally add a positive deviation or bias or a negative deviation or bias along the x direction for measurement and image matching purposes, and measure the effect of the deviation or bias by measuring the change in the intensity (I) of the diffracted beam. Here, only the zeroth, +1st and -1st order diffracted beams are shown for simplicity, and higher order beams are not shown.

[0068] In diffraction-based metrology equipment (such as ASML's YieldStar), the illumination intensity distribution can be adjusted by adding a spatial light modulator (SLM) to the illumination. The SLM imposes some form of spatially varying intensity and / or modulation on the radiation beam. The SLM may include a physical mechanism, such as a programmable mirror array, a programmable LCD panel, etc., or a computer representation thereof. Adding an SLM enables free-form illumination. The intensity distribution in the pupil plane of the illumination is represented in the analog domain by a spatial pixel array, where each pixel or group of pixels can be independently adjusted to achieve various configurations of illumination, depending on the desired lithographic imaging performance. Adding an SLM helps reduce stray light in the system and can reduce the impact of mark asymmetry on overlay measurements. The term "mark" is used here to include a pattern in the design layout used as a measurement target. The mark can be part of a circuit, or a specific measurement mark placed in the scribe line of the wafer. The present disclosure assumes that the mark is not changed, but the illumination configuration is changed to offset the impact of process-induced structural asymmetry in the mark. By appropriately selecting the pixels in the illumination pupil, the effects of mark asymmetry can be reduced without affecting the contrast (ie, detectability) of the mark.

[0069] Specifically, the present disclosure focuses on the feasibility of adjusting the parameters of the measurement device (e.g., controlling the illumination) to improve the quality of the measurement (e.g., overlap detectability and measurement accuracy). Both the illumination (i.e., "source") and the overlap measurement target (i.e., "marker") can be optimized to improve the measurement accuracy ("source-marker optimization"). Here, the term "source" broadly includes both the radiation source and the illumination adjustment optics included in the radiation system. The present disclosure provides an illumination optimization algorithm for a given overlap measurement target, including free-form illumination optimization. Specifically, the present disclosure describes the selection of illumination points that are particularly useful for eliminating stray light, generating optical signals of sufficient intensity for detection and analysis, providing markings and improved contrast, and reducing sensitivity to process variations. The source is not the only parameter that can be adjusted based on the characteristics of the target. Any other parameter of the measurement device or measurement can be adjusted.

[0070] There are regions of the illuminated pupil that do not produce ±1 order information. Those regions only add the zeroth order. Although the zeroth order is filtered, regions of the pupil do produce stray light by "spillover" into the ±1 order regions through reflections in the optics. Using a simple geometry, these 0th order regions of illumination are eliminated. The location of such 0th order regions is pitch and wavelength dependent. Therefore, a spatial light modulator (SLM) or similar device is needed to vary the illumination.

[0071] The imaging conditions in the lithographic apparatus may be made similar to those of existing diffraction-based metrology apparatus such as the YieldStar manufactured by ASML.In a non-limiting exemplary configuration, the illumination may have a numerical aperture (NA) of 0.95. Figure 4A An illumination pupil with a standard quadrant aperture in a lithographic apparatus is shown. In metrology equipment, quadrant apertures are not usually present. The pupil of the objective is imaged via four wedges to redirect the zeroth order signal away from the sensor. In contrast, lithographic apparatus use pupil filters with various shapes. One of the advantages of the present disclosure is that when performing illumination optimization in the analog domain, any shape of the aperture and pupil filter can be assumed to mimic the actual configuration of the illumination pupil of a lithographic apparatus.

[0072] Figure 4B An exemplary illumination shape at the entrance pupil of an objective lens in a metrology device is shown. The zeroth order illumination passes through the upper right quadrant and the lower left quadrant of the pupil, as shown in FIG. Figure 4B By using Figure 4C A pupil filter, such as the one shown, blocks most of the zeroth order radiation while allowing the +1st and -1st order radiation to pass through to the objective. Figure 4D The shape of the illumination at the exit pupil of the objective is shown. Figure 4E The non-utilized area of ​​the illumination is shown. Figure 4Fshows a better choice of illumination pupil shape (compared to Figure 4A The standard quadrant aperture shown), wherein the exit pupil of the objective will be optimized to produce better results in counteracting the negative effects of structural asymmetries in the objective, which is the main goal of the present disclosure.

[0073] To achieve reduced sensitivity to lithography process variations, simulations are performed on various target designs that mimic actual devices. Exemplary devices include, but are not limited to: dynamic random access memory (DRAM), buried word line (bWL) layer, DRAM bit line (BL) layer, logic metal layer (M1), and DRAM storage node (SN) layer.

[0074] In an embodiment, using an exemplary circuit pattern for a DRAM storage node (SN), it is determined which pupil pixels will have reduced sensitivity to asymmetry induced by process variations. A metrology target (“mark”) is made to replicate the DRAM SN layer pattern (e.g., Figure 5 This is because this pattern is known to have overlapping sensitivity to process-induced structural asymmetries. Figure 5 In the structure shown, the grating pitch is 500 nm, the critical dimension of the top layer is 250 nm, and the illumination wavelength is 550 nm. Figure 4F The illumination pupil shape shown is used as the initial condition for illumination optimization. In the exemplary device structure 500, a resist layer 504 is used to pattern the top metal layer 502. An anti-reflective coating 506, a carbon layer 508, and an interlayer dielectric (ILD) separate the top layer from a buried storage node layer 514 made of tungsten. The substrate layer 512 is made of silicon. Those skilled in the art will appreciate that the scope of the present disclosure is not limited by the materials used in the device structure.

[0075] In addition to reducing sensitivity to process variations, the marker also needs to have sufficient diffraction efficiency (DE) and stack sensitivity (SS), so enough illumination pupil pixels are needed to reconfigure the illumination shape to study the impact of specific asymmetries. DE is a target design parameter representing the average intensity, and SS is related to DE. DE is expressed as:

[0076]

[0077] In this equation, I represents intensity, p in the subscript represents +1-order diffraction component, m in the subscript represents -1-order diffraction component, pb in the subscript represents positive deviation or bias, and nb in the subscript represents negative deviation or bias. For example, I p_pb Refers to the intensity of the +1st order diffraction component with positive deviation or bias.

[0078] The method first examines the gradient of intensity to verify that a certain illumination configuration can minimize the effect of asymmetry. An asymmetry parameter q is defined. The following equation establishes the degree of dependence of parameter q on overlap.

[0079] Define the overlapping OV as:

[0080] in,

[0081] Here, A is the asymmetry response and K is a mathematical constant representing the overlay error.

[0082] In this equation, d is the overlay deviation or bias. K represents the contrast in the target image due to the overlay error. The overlay deviation or bias d can be in the positive or negative direction, such as in Figure 3B and Figure 3D As shown. Stacking sensitivity (SS) is defined as K / DE and is a key performance indicator (KPI) for target design. One of the goals of target design is to maximize SS. When A becomes zero, the overlay error due to asymmetry becomes zero.

[0083] The algorithm for optimizing illumination pixel by pixel for known asymmetry in the target is based on calculating where the overlap is most sensitive to the asymmetry parameter q. The OV gradient is expressed with respect to the asymmetry parameter q as:

[0084]

[0085] At a pixel, the intensity can usually be expressed as I x (where x is alternately p_pb, m_pb, p_nb, and m_nb):

[0086]

[0087] Here, σ represents the coordinates of the illumination pupil and ρ represents the convolution coordinates of the convolution kernel ε. The convolution kernel is a function related to the finite spot of the measurement or to the finite size of the measurement mark. align represents the pupil of the camera, and P obj Represents the pupil filter in the exit pupil of the objective. s I represents the intensity of the irradiation (a parameter optimized for minimum sensitivity to process asymmetries or for maximum K). RCWArepresents the intensity as calculated, for example, by rigorous coupled wave analysis (RCWA), a semi-analytical method in computational electromagnetics applied to solve diffraction scattering from a measurement target having a periodic structure such as described herein. The intensity gradient is expressed with respect to the asymmetry parameter q as:

[0088] Intensity gradient and irradiation intensity I from RCWA s q is irrelevant. Therefore, the intensity gradient can be pre-computed for fast optimization. To optimize the overlap sensitivity to the parameter q, the following second-order derivative equation is used to express the relative illumination gradient:

[0089]

[0090] Approximately Compared with the above situation, The full equation for does not result in additional computation time.

[0091] The next step is to define a cost function (CF) for the irradiation. The CF is a mathematical function to be optimized in order to obtain an optimized irradiation. The cost function has an asymmetry parameter q as a variable. The goal of the optimization problem is to minimize the cost function, which is expressed as the following equation:

[0092]

[0093] is the constraint used in the above minimization equation, where β is a fixed (non-floating) parameter and α is a floating parameter. In the above equation, let the overlap sensitivity The norm of (denoted as n in the above equation) is minimized. The number of parameters used to optimize the overall irradiation is m (i.e., i=1, 2, ..., m). Examples of asymmetry parameters are asymmetry of sidewall angles (aSWA), floor tilt, etch depth, etc. FIG. 6A to FIG. 6B A target structure with a top grating layer G1 and a bottom grating layer G2 is shown, wherein the structural asymmetry is shown in an exaggerated manner for illustrative purposes. Fig. 6A It is schematically shown that there is a difference between the side wall angle about wall 601 and the side wall angle about wall 602. The side wall angle difference (ΔSWA) yields the aSWA parameter. Figure 6B The floor 610 is schematically shown to be tilted in the bottom grating layer. This asymmetry generates the bottom plate tilt parameter. Figure 5For the DRAM SN layer device shown, the overlay sensitivity due to process variations was studied for the bottom tungsten layer 514 for three illumination polarizations: transverse electric (TE), transverse magnetic (TM), and a combination of these two polarizations (BP). The results are tabulated and shown in Figure 7 Those skilled in the art will appreciate that in addition to polarization, the wavelength of the illumination source may also be varied, although this is not specifically described in the exemplary embodiments herein.

[0094] In the cost function minimization problem, α is a polarization mixing parameter to exploit the sensitivities due to TE polarization and TM polarization according to the following equation:

[0095]

[0096] In the above equations, α = 0.5 for BP, α = 1 for TE polarization, and α = 0 for TM polarization. α can also be optimized to minimize sensitivity to process asymmetry. The optimization constraints are recalculated as x, which is generally expressed as -b The barrier function is related to the stacking sensitivity (SS) of a particular device structure. The barrier function is used in optimization to represent the constraint of being less than (or greater than) the Heaviside function. The barrier function has a continuous gradient, while the Heaviside function does not have a continuous gradient. For example, in the standard source-mask optimization (SMO) program Tachyon provided by ASML, the barrier function uses the value of x -3 The hard constraint is b = 3. Usually, the barrier function is expressed as:

[0097]

[0098] Here, μ is a fixed parameter for the weight of the barrier function in Equation 11 compared to the unconstrained minimization in Equation 9. If m is large, the barrier function has a smaller weight (due to the negative sign) compared to the unconstrained minimization. In a non-limiting example, the values ​​of α, μ, and b may be equal to 0.5, 1, and 1, respectively.

[0099] The following equation represents the auxiliary cost function to be minimized, which is the original cost function in Equation 9 modified by the barrier function in Equation 11:

[0100]

[0101] To minimize the auxiliary cost function, the gradient of the auxiliary cost function needs to be zero.

[0102]

[0103] Since no overlay sensitivity (e.g., Figure 7 ), the root mean square (rms) asymmetry due to process variation is simplified in terms of two asymmetry parameters aSWA and floor tilt:

[0104]

[0105] CF is the unconstrained cost function in Equation 9, or the auxiliary cost function of Equation 11 constrained by the barrier function. Simulations have shown that the value of asymmetry CF is reduced from 1.56 for the initial configuration of the illumination to 1.22 for the illumination optimized for structural asymmetry, i.e., a 12% improvement is achieved by embodiments of the present disclosure. Although the percentage improvement varies depending on the target structure, improvements of at least 5% to 50% are routinely seen in experimental results. Figure 8 It is shown that when the algorithm of the present disclosure is used to minimize the unconstrained cost function CF Figure 5 Figure 2 shows the final illumination configuration of the device DRAM SN layer structure. Fig. 9 The spatial distribution of the barrier function B is shown, where the stack sensitivity SS>0.1. Fig.10 The final illumination configuration after the final iteration of the optimization algorithm is shown.

[0106] Fig.11 A graph of overlap sensitivity versus the asymmetry parameter aSWA is shown, showing that as the number of iterations increases and the corresponding shot shape changes, the sensitivity to aSWA decreases.

[0107] exist Fig.12 In the figure, the first-order derivative function is depicted. The relationship with the number of iterations, the results are represented by circles. Fig.12 The second-order derivative is also shown It is depicted as a triangle. Since the second-order derivative The value of is almost zero, that is, the gradient of the first-order derivative does not change mathematically with the number of iterations, so it can be calculated only by the first-order derivative. To approximate overlap sensitivity

[0108] Fig.13 Depicts the relationship between the value of K and the number of iterations, Fig.14 Depicted The relationship between the number of iterations. The illuminated pixels are adjusted so that the asymmetry A decreases. K decreases with the number of iterations, and The decrease of is faster than the increase of 1 / K. Therefore, the overlap sensitivity The results demonstrate that the sensitivity of the overlay measurement to process-induced structural asymmetries can be reduced by adjusting the illumination shape on a pixel-by-pixel basis.

[0109] Some of the features and advantages of the present optimization technique, among others, are that the removal of zero-order light can be accomplished quickly with simple geometric constraints; and most device structures are not limited by the minimum stack sensitivity barrier function B. In one embodiment, the illumination optimization is based on maximizing K, rather than reducing A in one embodiment. The asymmetry response A is independent of the angle in the alignment camera. In an alternative embodiment, the illumination optimization can be based on a reduction in sensitivity in A, rather than an increase in K. Furthermore, in an embodiment, the response in the pupil plane can be examined in addition to the image plane, because the pupil plane has more information about the asymmetry.

[0110] Fig.15 Schematically illustrated is a flow for a method according to an embodiment. In 1510, the intensity distribution in the pupil plane of the measurement device is spatially divided into a plurality of pixels. In 1520, the influence of the structural asymmetry in the target on the measurement of the target by the measurement device is reduced by adjusting the intensity of the plurality of pixels using a computer. The pupil plane may be an illumination pupil or a detection pupil. The measurement may measure overlap, focus, aberration, or a combination thereof. The structural asymmetry may include one or more of the following: a difference in side wall angle (SWA), a bottom plate tilt, and an etching depth. Adjusting the intensity may include calculating a cost function that represents the effect and is a function of the intensity. The cost function may represent the contrast of the image of the target. Adjusting the intensity may include finding a value that minimizes or maximizes the intensity of the cost function locally or globally. The cost function may be constrained. In optional 1530, one or more pixels are identified from the plurality of pixels, wherein the one or more pixels do not contribute to the signal used by the measurement device in the measurement, or wherein the contribution of the one or more pixels to the signal is below a threshold. In optional 1540, the intensity at the identified one or more pixels is adjusted. The measurement may be an overlay measurement, and the one or more pixels do not contribute to a diffraction order used in the overlay measurement. The diffraction order may be a +1 diffraction order or a -1 diffraction order. Reducing the effect of structural asymmetry may include adjusting polarization at the pixel. Reducing the effect of structural asymmetry may include adjusting bandwidth at the pixel. Reducing the effect of structural asymmetry may include adjusting wavelength at the pixel.

[0111] Fig.16A flow for a method according to an embodiment is schematically shown. In 1610, a parameter of a measurement device or a parameter of a measurement of the target by the measurement device is adjusted based on the characteristics of the target. The measurement can be selected from the group consisting of: overlapping measurement, focusing measurement, aberration measurement and a combination thereof. The parameter can be selected from the group consisting of: intensity at the illumination pupil of the measurement device, polarization at the illumination pupil of the measurement device, wavelength at the illumination pupil of the measurement device, bandwidth at the illumination pupil of the measurement device, intensity at the detection pupil of the measurement device, polarization at the detection pupil of the measurement device, wavelength at the detection pupil of the measurement device, bandwidth at the detection pupil of the measurement device and a combination thereof. For example, the aperture on the optical path can be used to adjust the intensity at the detection pupil or the source pupil. The parameter can be a characteristic of the projection optics of the measurement device or a characteristic of the source of the measurement device. Adjusting the parameter can affect the quality of the measurement. The quality can be the detectability of the target, the accuracy of the measurement or the robustness of the measurement. Adjusting the parameter can include calculating a cost function that represents the quality and is a function of the parameter. The cost function may represent the contrast of the image of the target. Adjusting the parameters may include finding values ​​of the parameters that minimize or maximize the cost function locally or globally. The cost function is constrained. Adjusting the parameters may include iteratively calculating the cost function and adjusting the parameters until a termination criterion is met. The cost function may be a function of a characteristic of the target. In optional 1620, the characteristic of the target is adjusted. In optional 1630, the adjusted parameters associated with the characteristic of the target are stored. The characteristic of the target may include the location of the target on the substrate.

[0112] The present invention can be further described using the following terms:

[0113] 1. A method for adjusting a measurement device, the method comprising:

[0114] spatially dividing the intensity distribution in a pupil plane of the measurement device into a plurality of pixels;

[0115] By adjusting the intensities of the plurality of pixels using a computer, the effect of structural asymmetries in the target on measurements of the target by the metrology device is reduced.

[0116] 2. A method as described in clause 1, wherein the pupil plane is an illumination pupil or a detection pupil.

[0117] 3. A method as described in any of clauses 1 to 2, wherein the measurement measures overlay, focus, aberration or a combination thereof.

[0118] 4. The method of any one of items 1 to 3, wherein the structural asymmetry comprises one or more of: a difference in side wall angle (SWA), floor tilt, and etch depth.

[0119] 5. A method as described in any of clauses 1 to 4, wherein adjusting the intensity includes calculating a cost function, which is representative of the impact and is a function of the intensity.

[0120] 6. A method as described in clause 5, wherein the cost function represents the contrast of the image of the target.

[0121] 7. A method as described in clause 5, wherein adjusting the intensity further comprises: finding a value of the intensity that minimizes or maximizes the cost function locally or globally.

[0122] 8. A method as described in clause 5, wherein the cost function is constrained.

[0123] 9. The method according to any one of items 1 to 8, further comprising:

[0124] identifying one or more pixels from the plurality of pixels, wherein the one or more pixels do not contribute to a signal used by the metrology device in the measurement, or wherein a contribution of the one or more pixels to the signal is below a threshold; and

[0125] The intensity at the identified one or more pixels is adjusted.

[0126] 10. The method of clause 9, wherein the measurement is an overlay measurement and the one or more pixels do not contribute to a diffraction order used in the overlay measurement.

[0127] 11. The method of item 10, wherein the diffraction order is a +1 diffraction order or a -1 diffraction order.

[0128] 12. A method as described in any of items 1 to 11, wherein reducing the impact of the structural asymmetry further comprises adjusting the polarization at the pixel.

[0129] 13. A method as described in any of items 1 to 12, wherein reducing the impact of the structural asymmetry further comprises adjusting the bandwidth at the pixel.

[0130] 14. The method of any one of clauses 1 to 13, wherein reducing the effect of the structural asymmetry further comprises adjusting the wavelength at the pixel.

[0131] 15. A computer program product comprising a non-transitory computer readable medium having instructions thereon, the instructions, when executed by a computer, implementing a method comprising:

[0132] spatially dividing the intensity distribution in a pupil plane of the measurement device into a plurality of pixels;

[0133] By adjusting the intensities of the plurality of pixels using a computer, the effect of structural asymmetries in the target on measurements of the target by the metrology device is reduced.

[0134] 16. A computer program product as described in clause 15, wherein the pupil plane is an illumination pupil or a detection pupil.

[0135] 17. A computer program product as described in any of clauses 15 to 16, wherein the measurement measures overlay, focus, aberration or a combination thereof.

[0136] 18. The computer program product of any of clauses 15 to 16, wherein the structural asymmetry comprises one or more of: a difference in side wall angle (SWA), floor tilt, and etch depth.

[0137] 19. A computer program product as described in any of clauses 15 to 18, wherein adjusting the intensity includes calculating a cost function, the cost function representing the impact and being a function of the intensity.

[0138] 20. A computer program product as described in clause 19, wherein the cost function represents the contrast of the image of the object.

[0139] 21. A computer program product as described in clause 19, wherein adjusting the strength further comprises: finding a value of the strength that minimizes or maximizes the cost function locally or globally.

[0140] 22. A computer program product as described in clause 19, wherein the cost function is constrained.

[0141] 23. A computer program product as described in any of items 15 to 22, further comprising: identifying one or more pixels from the plurality of pixels, wherein the one or more pixels do not contribute to a signal used by the measurement device in the measurement, or wherein the contribution of the one or more pixels to the signal is below a threshold; and

[0142] The intensity at the identified one or more pixels is adjusted.

[0143] 24. A computer program product as described in clause 23, wherein the measurement is an overlay measurement and the one or more pixels do not contribute to the diffraction orders used in the overlay measurement.

[0144] 25. A computer program product as described in clause 24, wherein the diffraction order is a +1st diffraction order or a -1st diffraction order.

[0145] 26. The computer program product of any of clauses 15 to 25, wherein reducing the effect of the structural asymmetry further comprises adjusting polarization at the pixel.

[0146] 27. A computer program product as described in any of clauses 15 to 26, wherein reducing the impact of the structural asymmetry further comprises adjusting the bandwidth at the pixel.

[0147] 28. The computer program product of any of clauses 15 to 27, wherein reducing the effect of the structural asymmetry further comprises adjusting the wavelength at the pixel.

[0148] 29. A method of adjusting a measurement device, the method comprising:

[0149] A parameter of the metrology device or a parameter of a measurement of the target by the metrology device is adjusted based on a characteristic of the target.

[0150] 30. The method of clause 29, wherein the measurement is selected from the group consisting of: a measurement of overlap, a measurement of focus, a measurement of aberration, and combinations thereof.

[0151] 31. A method as described in any of items 29 to 30, wherein the parameter is selected from the group consisting of: intensity at the illumination pupil of the measurement device, polarization at the illumination pupil of the measurement device, wavelength at the illumination pupil of the measurement device, bandwidth at the illumination pupil of the measurement device, intensity at the detection pupil of the measurement device, polarization at the detection pupil of the measurement device, wavelength at the detection pupil of the measurement device, bandwidth at the detection pupil of the measurement device, and combinations thereof.

[0152] 32. The method of any of clauses 29 to 31, wherein the parameter is a property of the projection optics of the metrology device or a property of a source of the metrology device.

[0153] 33. A method as described in any of clauses 29 to 32, wherein adjusting the parameter affects the quality of the measurement.

[0154] 34. A method as described in clause 33, wherein the quality is the detectability of the target, the accuracy of the measurement or the robustness of the measurement.

[0155] 35. A method as described in clause 33, adjusting the parameter includes calculating a cost function, which is representative of the quality and is a function of the parameter.

[0156] 36. A method as described in clause 35, wherein the cost function represents the contrast of the image of the target.

[0157] 37. A method as described in clause 35, wherein adjusting the parameter further comprises: finding a value of the parameter that minimizes or maximizes the cost function locally or globally.

[0158] 38. A method as described in clause 35, wherein the cost function is constrained.

[0159] 39. A method as described in clause 35, wherein adjusting the parameters includes: iteratively calculating the cost function and adjusting the parameters until a termination criterion is met.

[0160] 40. A method as described in clause 35, wherein the cost function is a function of a characteristic of the target.

[0161] 41. The method of any one of clauses 29 to 40, further comprising: adjusting a characteristic of the target.

[0162] 42. A method as described in any of clauses 29 to 41, further comprising: storing adjusted parameters associated with characteristics of the target.

[0163] 43. A method as described in any of items 29 to 42, wherein the characteristic of the target includes the location of the target on the substrate.

[0164] 44. A method comprising:

[0165] setting a parameter of a measurement device or a parameter of a measurement of a target by the measurement device to a value adjusted based on a characteristic of the target;

[0166] The target is measured using the measurement equipment.

[0167] 45. A method comprising:

[0168] setting a characteristic of a target to a value based on which a parameter of a measurement device or a parameter of a measurement of the target by the measurement device is adjusted;

[0169] The target is fabricated on a substrate.

[0170] 46. ​​A computer program product comprising a non-transitory computer readable medium having instructions thereon, the instructions, when executed by a computer, performing a method comprising:

[0171] A parameter of the metrology device or a parameter of a measurement of the target by the metrology device is adjusted based on a characteristic of the target.

[0172] 47. The computer program product of clause 46, wherein the measurement is selected from the group consisting of: a measurement of overlap, a measurement of focus, a measurement of aberration, and a combination thereof.

[0173] 48. A computer program product as described in any of items 46 to 47, wherein the parameter is selected from the group consisting of: intensity at the illumination pupil of the measurement device, polarization at the illumination pupil of the measurement device, wavelength at the illumination pupil of the measurement device, bandwidth at the illumination pupil of the measurement device, intensity at the detection pupil of the measurement device, polarization at the detection pupil of the measurement device, wavelength at the detection pupil of the measurement device, bandwidth at the detection pupil of the measurement device and combinations thereof.

[0174] 49. A computer program product as described in any of clauses 46 to 48, wherein the parameter is a characteristic of the projection optics of the metrology device or a characteristic of a source of the metrology device.

[0175] 50. A computer program product as described in any of clauses 46 to 49, wherein adjusting the parameter affects the quality of the measurement.

[0176] 51. A computer program product as described in clause 50, wherein the quality is the detectability of the target, the accuracy of the measurement or the robustness of the measurement.

[0177] 52. A computer program product as described in clause 50, wherein adjusting the parameter includes: calculating a cost function that represents the quality and is a function of the parameter.

[0178] 53. A computer program product as described in clause 50, wherein the cost function represents the contrast of the image of the object.

[0179] 54. A computer program product as described in clause 50, wherein adjusting the parameter further comprises: finding a value of the parameter that minimizes or maximizes the cost function locally or globally.

[0180] 55. A computer program product as described in clause 50, wherein the cost function is constrained.

[0181] 56. A computer program product as described in clause 50, wherein adjusting the parameters includes: iteratively calculating the cost function and adjusting the parameters until a termination criterion is met.

[0182] 57. A computer program product as described in clause 50, wherein the cost function is a function of a characteristic of the target.

[0183] 58. A computer program product as described in any of clauses 46 to 57, wherein the method further comprises adjusting a characteristic of the target.

[0184] 59. A computer program product as described in any of clauses 46 to 58, wherein the method further comprises: storing adjusted parameters associated with characteristics of the target.

[0185] 60. A computer program product as described in any of clauses 46 to 59, wherein the characteristic of the target includes the location of the target on a substrate.

[0186] 62. A computer program product comprising a non-transitory computer readable medium having instructions thereon, the instructions, when executed by a computer, performing a method comprising:

[0187] setting a parameter of a measurement device or a parameter of a measurement of a target by the measurement device to a value adjusted based on a characteristic of the target;

[0188] The target is measured using the measurement equipment.

[0189] 63. A computer program product comprising a non-transitory computer readable medium having instructions thereon, the instructions, when executed by a computer, performing a method comprising:

[0190] setting a characteristic of a target to a value based on which a parameter of a measurement device or a parameter of a measurement of the target by the measurement device is adjusted;

[0191] The target is fabricated on a substrate.

[0192] It will be appreciated by those skilled in the art that additional steps may be added to the process flow without departing from the scope of the present disclosure, and / or some of the steps shown in the flow chart may be replaced by steps specific to a certain lithography process. The above description is intended to be illustrative and exemplary, rather than restrictive. Therefore, it will be apparent to those skilled in the art that modifications may be made to the described embodiments of the invention without departing from the scope of the claims set forth below.

Claims

1. A non-transitory computer readable medium having instructions, the instructions being configured to, when executed by a computer system, cause the computer system to perform a method of adjusting a measurement device, the method comprising: A parameter of a metrology device used to measure a target or a parameter of a measurement of a target by the metrology device is set or adjusted to a value based on a characteristic of the target, including a structural asymmetry within the target or a value representing the position of the target on a substrate.

2. The medium of claim 1, wherein the measurement is selected from one or more of: a measurement of overlay, a measurement of focus and / or a measurement of aberration.

3. A medium according to claim 1, wherein the parameter is one or more selected from the following: intensity at the illumination pupil of the measurement device, polarization at the illumination pupil of the measurement device, wavelength at the illumination pupil of the measurement device, bandwidth at the illumination pupil of the measurement device, intensity at the detection pupil of the measurement device, polarization at the detection pupil of the measurement device, wavelength at the detection pupil of the measurement device and / or bandwidth at the detection pupil of the measurement device. 4 . The medium according to claim 1 , wherein the parameter is a property of the projection optics of the metrology device and / or a property of the radiation illumination of the metrology device.

5. The medium of claim 1, wherein the adjusting or setting the parameter affects a quality of the measurement of the target.

6. The medium of claim 5, wherein the quality refers to detectability of the target, precision of the measurement and / or robustness of the measurement.

7. The medium of claim 5, wherein said adjusting or setting said parameter comprises: A cost function is calculated that represents the quality and is a function of the parameters.

8. The medium of claim 7, wherein the cost function represents a contrast of an image of the object.

9. The medium of claim 7, wherein said adjusting or setting said parameter further comprises: Values ​​of the parameters are found that minimize or maximize the cost function locally or globally.

10. The medium of claim 7, wherein the cost function is constrained.

11. The medium of claim 7, wherein the cost function is a function of the characteristic of the target.

12. The medium of claim 1, further comprising adjusting the characteristic of the target.

13. The medium of claim 1, wherein the characteristic of the target comprises a value representing a location of the target on a substrate.

14. The medium of claim 1, wherein the characteristic of the target comprises a structural asymmetry within the target.

15. A method for adjusting a measurement device, the method comprising: A parameter of a metrology device used to measure a target or a parameter of a measurement of a target by the metrology device is set or adjusted to a value based on a characteristic of the target, including a structural asymmetry within the target or a value representing the position of the target on a substrate.

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