Measurement of contrast and critical dimensions using alignment sensors

Abstract

A method may include directing radiation toward at least two targets using an optical scanning system to generate a first portion and a second portion of scattered radiation. The first target may include a plurality of first grating line structures including a feature having a first offset value. The second target may include a plurality of second grating line structures including features having a second offset value. The method may include detecting a first portion and a second portion of scattered radiation, generating a first measurement signal indicative of a first target position based on a first bias feature, and generating a second measurement signal indicative of a second target position based on a second bias feature. The method may include analyzing effects of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the target set.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 404,585, filed on September 8, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to inspection systems, such as alignment systems, for measuring the position of targets in lithographic apparatus and systems. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device (which can be a mask or a reticle) can be used to generate a circuit pattern to be formed on an individual layer of an IC. The pattern can be transferred to a target portion (e.g., including a portion, one or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually via imaging onto a layer of radiation-sensitive material (photoresist or simply "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 simultaneously scanning the target portion parallel to or antiparallel to the scanning direction. The pattern can also be transferred from a patterning device to a substrate by imprinting the pattern onto the substrate.

[0005] During a lithography operation, different processing steps may require the sequential formation of different layers on a substrate. Therefore, it may be necessary to position the substrate with high precision relative to an existing pattern formed thereon. Typically, alignment marks are placed on the substrate to be aligned and positioned relative to a second object. The lithography apparatus may use an alignment device to detect the position of the alignment marks and align the substrate using the alignment marks to ensure accurate exposure from the mask. The misalignment between the alignment marks of two different layers is measured as overlay error.

[0006] In order to monitor the lithography process, the parameters of the patterned substrate are measured. For example, the parameters may include the overlay error between successive layers formed in or on the patterned substrate and the critical line width of the developed photoresist. The measurement can be performed on a product substrate and / or a dedicated measurement target. There are a variety of techniques for measuring the microstructures formed in the lithography process, including the use of scanning electron microscopes and various dedicated tools. A fast and non-invasive form of dedicated inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the surface of the substrate and the characteristics of the scattered or reflected beam are measured. By comparing the characteristics before and after the beam is reflected or scattered by the substrate, the characteristics of the substrate can be determined. For example, this can be achieved by comparing the reflected beam with data stored in a known measurement library associated with known substrate characteristics. A spectral scatterometer directs a broadband radiation beam onto a substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. In contrast, an angularly resolved scatterometer uses a monochromatic radiation beam and measures the variation of the scattered radiation intensity with angle.

[0007] Such optical scatterometers can be used to measure parameters such as the critical dimension of a developed photoresist or the overlay error (OV) between two layers formed in or on a patterned substrate. The properties of a substrate can be determined by comparing the properties of an irradiating beam before and after the beam is reflected or scattered by the substrate.

[0008] Inspection is an important aspect of any lithography process, used to determine sub-nanometer accuracy when printing device patterns on wafers. However, inspection measurements also add time to the manufacturing process, thereby reducing the number of manufactured devices that can be output by the lithography process in a given time frame. A lithography process can rely on a variety of inspection tools to meet different inspection requirements (e.g., overlay, alignment, critical dimensions, etc.). Some inspection tools are more complex and time-consuming than others. Summary of the invention

[0009] Therefore, it is desirable to increase manufacturing speed and throughput.For example, based on aspects described herein, the number of inspection tools required in a given lithography process can be reduced, and some inspection processes can be performed faster.

[0010] In some aspects, a method may include directing radiation toward a set of targets including a first target and a second target using an optical scanning system to generate a first portion and a second portion of scattered radiation. The first target may include a plurality of first grating line structures including a first bias feature having a first bias value. The second target may include a plurality of second grating line structures including a second bias feature having a second bias value different from the first bias value. Directing the radiation may include scanning the radiation over the set of targets. The method may also include detecting the first portion of the scattered radiation and the second portion of the scattered radiation using the optical scanning system. The method may also include generating a first measurement signal indicating a first position of the first target based on the first bias feature. The method may also include generating a second measurement signal indicating a second position of the second target based on the second bias feature. The method may also include analyzing the effects of the first bias value and the second bias value on the first position and the second position based on the first measurement signal and the second measurement signal to determine at least one characteristic of the set of targets.

[0011] In some aspects, a system may include an optical scanning system and a non-transitory computer readable medium. The optical scanning system may include a radiation source, an optical device, and a detection system. The radiation source may be configured to generate radiation. The optical device may be configured to direct the radiation toward a target set including a first target and a second target to generate scattered radiation from the target set. The optical scanning system may be configured to actuate to scan the radiation over the target set. The detection system may be configured to generate a first measurement signal indicating a first position of the first target based on the scattered radiation, and to generate a second measurement signal indicating a second position of the second target. The non-transitory computer readable medium may be configured to store instructions thereon, which, when executed by one or more computing devices, cause the one or more computing devices to perform an operation. The operation may include analyzing the first measurement signal and the second measurement signal. The first target may include a plurality of first grating line structures, the plurality of first grating line structures including a first bias feature, the first bias feature having a first bias value that affects the first measurement signal. The second target may include a plurality of second grating line structures, the plurality of second grating line structures including a second bias feature, the second bias feature having a second bias value that affects the second measurement signal. The second bias value may be different from the first bias value. The analyzing may include analyzing the effects of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the set of targets.

[0012] In some aspects, the lithographic apparatus may include an irradiation system, a projection system, an optical scanning system, and a non-transitory computer readable medium. The irradiation system may be configured to irradiate a pattern of a patterning device. The projection system may be configured to project an image of the pattern onto a substrate. The optical scanning system may include a radiation source, an optical device, and a detection system. The radiation source may be configured to generate radiation. The optical device may be configured to direct radiation toward a target set including a first target and a second target to generate scattered radiation from the target set. The optical scanning system may be configured to actuate to scan radiation over the target set. The detection system may be configured to generate a first measurement signal indicating a first position of the first target based on the scattered radiation, and to generate a second measurement signal indicating a second position of the second target. The non-transitory computer readable medium may be configured to store instructions thereon, which, when executed by one or more computing devices, cause one or more computing devices to perform an operation. The operation may include analyzing the first measurement signal and the second measurement signal. The first target may include a plurality of first grating line structures, the plurality of first grating line structures including a first bias feature, the first bias feature having a first bias value that affects the first measurement signal. The second target may include a plurality of second grating line structures, the plurality of second grating line structures including a second bias feature, the second bias feature having a second bias value that affects the second measurement signal. The second bias value may be different from the first bias value. The analysis may include analyzing the effects of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the target set.

[0013] In some aspects, a non-transitory computer readable medium is configured to store instructions thereon that, when executed by one or more computing devices, cause the one or more computing devices to perform operations. The operations may include analyzing a first measurement signal and a second measurement signal from an optical scanning system, the optical scanning system being configured to inspect a target set including a first target and a second target. The first measurement signal may indicate a first position of the first target based on scanning radiation on the first target. The first target may include a plurality of first grating line structures, the plurality of first grating line structures including a first bias feature, the first bias feature having a first bias value that affects the first measurement signal. The second measurement signal may indicate a second position of the second target based on scanning radiation on the second target. The second target may include a plurality of second grating line structures, the plurality of second grating line structures including a second bias feature, the second bias feature having a second bias value that affects the second measurement signal. The second bias value may be different from the first bias value. The analysis may include analyzing the effects of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the target set.

[0014] The following describes in detail the additional features of various aspects of the present disclosure with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific aspects described herein. These aspects are presented herein for illustrative purposes only. Based on the teachings contained herein, other aspects will be clear to those skilled in the relevant art. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable one skilled in the relevant art to make and use the aspects described herein.

[0016] Figure 1A A reflective lithography apparatus according to some aspects is shown.

[0017] Figure 1B A transmissive lithography apparatus according to some aspects is shown.

[0018] Figure 2 More details of a reflective lithography apparatus according to some aspects are shown.

[0019] Figure 3 A lithography cell according to some aspects is shown.

[0020] Figure 4A and Figure 4B An inspection apparatus according to some aspects is shown.

[0021] Figure 5A , Figure 5B , Figure 5C , Fig. 6A , Figure 6B and Figure 6C A grating line structure that can be implemented as an alignment target according to some aspects is shown.

[0022] Fig. 7A and Figure 7B Objectives according to some aspects are shown.

[0023] Figure 8 A graph showing alignment position measurements of different targets with different offset values ​​according to some aspects.

[0024] Fig. 9 1- Figure 8 The method of operation described.

[0025] Fig.10 A computer system 1000 is shown in accordance with some aspects.

[0026] Features of the present disclosure will become more apparent when the following detailed description is made in conjunction with the accompanying drawings, in which the same reference numerals identify corresponding elements throughout. In the accompanying drawings, the same reference numerals generally represent identical, functionally similar, and / or structurally similar elements. In addition, generally, the leftmost digit of a reference numeral indicates the figure in which the reference numeral first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be construed as scale drawings. DETAILED DESCRIPTION

[0027] The aspects described herein, and references in the specification to "one aspect," "aspect," "exemplary aspect," and "example aspect," etc., indicate that the described aspects may include specific features, structures, or characteristics, but each aspect does not necessarily include the specific features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same aspect. Furthermore, when specific features, structures, or characteristics are described in conjunction with aspects, it should be understood that it is within the knowledge of those skilled in the art to implement such features, structures, and characteristics in conjunction with other aspects, whether or not explicitly described.

[0028] For ease of description, spatially relative terms (such as "below," "beneath," "lower," "above," "upper," etc.) may be used herein to describe the relationship of one element or feature shown in the figures to another (multiple) element or (multiple) feature. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

[0029] The terms "about," "approximately," and the like may be used herein to indicate a value of a given quantity that may vary based on a particular technology. Based on a particular technology, the terms "about," "approximately," and the like may indicate a value of a given quantity that varies, for example, within 10%-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0030] Aspects of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the present disclosure may also be implemented as instructions stored on a computer-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 readable 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, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and such actions are generated by a computing device, a processor, a controller, or other device executing the firmware, software, routines, instructions, etc. The term "machine-readable medium" may be interchangeable with similar terms, such as "computer program product", "computer-readable medium", "non-transient computer-readable medium", etc. The term "non-transient" may be used to describe one or more forms of computer-readable media other than transient propagation signals.

[0031] Before describing these aspects in further detail, however, it is helpful to provide an example environment in which aspects of the present disclosure may be implemented.

[0032] Example Lithography System

[0033] Figure 1A and Figure 1B A lithographic apparatus 100 and a lithographic apparatus 100' are respectively shown in which aspects of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' each include: an illumination system (illuminator) IL, which is configured to condition a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask stage) MT, which is configured to support a patterning device (e.g., a mask, a reticle, or a dynamic patterning device) MA and is connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate stage (e.g., a wafer stage) WT, which is configured to hold a substrate (e.g., a resist-coated wafer) W and is connected to a second positioner PW configured to accurately position the substrate W. The lithographic apparatus 100 and 100' also have a projection system PS, which is configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion (e.g., including one or more dies) C of the substrate W. In the lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In the lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0034] The illumination system IL may include various types of optical components (such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components), or any combination thereof, for directing, shaping or controlling the radiation beam B.

[0035] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to the reference frame, the design of at least one of the lithographic apparatuses 100 and 100', and other conditions (such as whether the patterning device MA is held in a vacuum environment). The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT can, for example, be a frame or a table, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is in a desired position, for example relative to the projection system PS.

[0036] The term “patterning apparatus” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device created in the target portion C (which will form an integrated circuit).

[0037] The patterning device MA may be transmissive (e.g. Figure 1B lithographic apparatus 100') or reflective (e.g. Figure 1A 100). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. Examples of programmable mirror arrays employ a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by the matrix of small mirrors.

[0038] The term "projection system" PS may include any type of projection system (including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems), or any combination thereof, which is suitable for the exposure radiation used, or other factors, such as the use of an immersion liquid or the use of a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases may absorb excess radiation or electrons. Therefore, a vacuum environment may be provided to the entire beam path with the aid of vacuum walls and a vacuum pump.

[0039] The lithographic apparatus 100 and / or lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, additional substrate tables WT may be used in parallel, or preparatory steps may be performed on one or more tables while exposure is being performed using one or more other substrate tables WT. In some cases, the additional tables may not be substrate tables WT.

[0040] 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 (e.g., 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, for example, between the mask and the projection system. Immersion techniques for increasing the numerical aperture of the projection system are well known in the art. The term "immersion" as used herein does not imply that the structure (such as the substrate) must be immersed in the liquid. For example, during exposure, the liquid may be located between the projection system and the substrate.

[0041] refer to Figure 1A and Figure 1B The illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example when the source SO is an excimer laser. In this case, the source SO is considered not to form part of the lithographic apparatus 100 or 100', and the radiation beam B is delivered to the lithographic apparatus 100 or 100' by means of a beam delivery system BD ( Figure 1B In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example, when the source SO is a mercury lamp. The radiation system may include the source SO, the illuminator IL and / or the beam delivery system BD.

[0042] The illuminator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam ( Figure 1B 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 can be adjusted. Furthermore, the illuminator IL may include various other components (in Figure 1B In the embodiment of the present invention, there are two types of devices (integrators), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0043] refer to Figure 1A, 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 MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., a mask) MA. After reflecting from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometric measurement device, a linear encoder, or a capacitive sensor), the substrate table WT can be precisely moved (e.g., in order to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B. The patterning device (e.g., a mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0044] refer to Figure 1B , the radiation beam B is incident on a patterning device (e.g., mask MA) held on a support structure (e.g., mask table MT) and is patterned by the patterning device. After passing through the 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. The projection system has a pupil conjugate PPU relative to the illumination system pupil IPU. Portions of the radiation are emitted from the intensity distribution at the illumination system pupil IPU and pass through the mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0045] The projection system PS projects an image of a mask pattern MP onto a photoresist layer coated on a substrate W, wherein the image is formed by a diffraction beam generated from the marking pattern MP by radiation from an intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. The diffraction generation direction of radiation different from the zero-order diffraction at the array changes in a direction perpendicular to the line. The undiffracted beam (i.e., the so-called zero-order diffraction beam) passes through the pattern without any change in the propagation direction. The zero-order diffraction beam passes through the upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zero-order diffraction beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. For example, the aperture device PD is disposed at or substantially at a plane including the pupil conjugate PPU of the projection system PS.

[0046] The projection system PS is arranged to capture (e.g., using a lens or lens group L) a zero-order diffraction beam, a first-order diffraction beam, and / or a higher-order diffraction beam (not shown). In some aspects, dipole illumination for imaging a line pattern extending in a direction perpendicular to the line can be used to exploit the resolution enhancement effect of dipole illumination. For example, a first-order diffraction beam interferes with a corresponding zero-order diffraction beam at the level of the wafer W to create an image of the line pattern MP with the highest possible resolution and processing window (i.e., available depth of focus combined with tolerable exposure dose deviations). In some aspects, astigmatic aberrations can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. In addition, in some aspects, astigmatic aberrations can be reduced by blocking the zero-order beam in the pupil conjugate PPU of the projection system associated with the radiation poles in the opposite quadrant. This is described in more detail in US 7,511,799 B2, issued on March 31, 2009, which is incorporated herein by reference in its entirety.

[0047] With the aid of a second positioner PW and a position sensor IFD (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be precisely moved (e.g. to position a different target portion C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor ( Figure 1B ) can be used to accurately position the mask MA relative to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during scanning).

[0048] Typically, movement of the mask table MT can be achieved by 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 can be achieved 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 mask table MT may be connected to a short-stroke actuator or may be fixed. The mask MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as shown) occupy dedicated target portions, they may be located in the space between target portions (referred to as scribe line alignment marks). Similarly, where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0049] The mask table MT and the patterning device MA may be located in a vacuum chamber V, wherein an in-vacuum robot IVR may be used to move the patterning device (such as a mask) into and out of the vacuum chamber. Alternatively, when the mask table MT and the patterning device MA are located outside the vacuum chamber, an out-of-vacuum robot may be used for various transport operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots may be calibrated to smoothly transport any payload (e.g., a mask) to the fixed kinematic mount of the transport station.

[0050] The lithographic apparatuses 100 and 100' may be used in at least one of the following modes:

[0051] 1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT remain substantially stationary while an entire pattern imparted to the radiation beam B is projected at once onto a target portion C (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0052] 2. In scan mode, the support structure (e.g. mask table) MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de)magnification and image reversal characteristics of the projection system PS.

[0053] 3. In another mode, the support structure (e.g., mask table) MT remains 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 B is projected onto a target portion C. A pulsed radiation source SO may be employed, and the programmable patterning device 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.

[0054] Combinations and / or variations of the described modes of use or entirely different modes of use may also be employed.

[0055] In another aspect, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Typically, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0056] Figure 2The lithographic apparatus 100 is shown in more detail, and the lithographic apparatus 100 includes a source collector device SO, an irradiation system IL, and a projection system PS. The source collector device SO is constructed and arranged so that a vacuum environment can be maintained in a closed structure 220 of the source collector device SO. The EUV radiation emitting plasma 210 can be formed by a plasma source generated by a discharge. EUV radiation can be generated by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, wherein the EUV radiation emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation emitting plasma 210 is generated by, for example, a discharge that results in at least partially ionized plasma. In order to efficiently generate radiation, a partial pressure of Xe, Li, Sn vapor, or any other suitable gas or vapor, such as 10Pa, can be used. In some aspects, a plasma that excites tin (Sn) (e.g., via laser excitation) is provided to generate EUV radiation.

[0057] The radiation emitted by the EUV radiation emitting plasma 210 enters the collector chamber 212 from the source chamber 211 via an optional gas barrier or contaminant trap 230 (also referred to as a contaminant barrier or foil trap in some cases), which is located in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further referred to herein includes at least a channel structure.

[0058] The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation passing through the collector CO may be reflected off the grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is often referred to as an intermediate focus, and the source collector arrangement is arranged so that the intermediate focus INTF is located at or near an opening 219 in the enclosure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. The grating spectral filter 240 is particularly used to suppress infrared (IR) radiation.

[0059] The radiation then passes through the illumination system IL, which may include a faceted field mirror arrangement 222 and a faceted pupil mirror arrangement 224, which are arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA and a desired uniformity of radiation intensity at the patterning device MA. When the radiation beam 221 is reflected at the patterning device MA held by the support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by a wafer stage or substrate table WT.

[0060] There may typically be more elements than shown in the illumination optics unit IL and the projection system PS. A grating spectral filter 240 may optionally be present, depending on the type of lithographic apparatus. Figure 2 There may be more reflectors than those shown, for example Figure 2 Compared to what is shown, there may be one to six additional reflective elements in the projection system PS.

[0061] like Figure 2 As shown, the collector optics CO is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically around the optical axis O, and this type of collector optics CO is preferably used in conjunction with a discharge produced plasma source (commonly referred to as a DPP source).

[0062] Example Lithography Cell

[0063] Figure 3 A lithography unit 300, sometimes also referred to as a lithography unit or cluster, is shown according to some aspects. The lithography apparatus 100 or 100' may form part of the lithography unit 300. The lithography unit 300 may also include one or more devices for performing pre-exposure and post-exposure processing on the substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a baking plate BK. A substrate handler or robot RO picks up a substrate from input / output ports I / O1, I / O2, moves the substrate between different processing devices, and delivers it to a loading area LB of the lithography apparatus 100 or 100'. These devices (generally 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. Therefore, different devices can be operated to maximize yield and processing efficiency.

[0064] Example inspection device

[0065] In order to control the lithography process to accurately place the device features on the substrate, alignment marks are usually provided on the substrate, and the lithography apparatus includes one or more inspection devices for accurately positioning the marks on the substrate. These alignment devices are effective position measurement devices. Different types of marks and different types of alignment devices and / or systems are known from different times and different manufacturers. A system widely used in current lithography apparatus is based on the self-reference interferometer described in U.S. Patent No. 6,961,116 (den Boef et al.). Usually, the marks are measured separately to obtain the X and Y positions. However, the X and Y combined measurement can be performed using the technology described in U.S. Publication No. 2009 / 195768A (Bijnen et al.). The entire contents of these disclosures are incorporated herein by reference.

[0066] Figure 4A A cross section of an inspection apparatus 400 that can be implemented as part of a lithographic apparatus 100 or 100' is shown according to some aspects. In some aspects, the inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). The inspection apparatus 400 can also be configured to detect the position of alignment marks on the substrate and use the detected position of the alignment marks to align the substrate relative to the patterning device or other components of the lithographic apparatus 100 or 100'. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0067] The terms "inspection device", "measurement system", etc. may be used in this document to refer to, for example, equipment for measuring structural properties (e.g., overlay sensors, critical dimension sensors, etc.), equipment or systems for checking wafer alignment in a lithography device (e.g., alignment sensors), etc.

[0068] In some aspects, the inspection device 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a coverage calculation processor 432. The illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a wavelength spectrum between about 500 nm and about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a wavelength spectrum between about 500 nm and about 900 nm. The illumination system 412 may also be configured to provide one or more passbands having a substantially constant center wavelength (CWL) value over a long period of time (e.g., during the lifetime of the illumination system 412). As described above, such a configuration of the illumination system 412 may help prevent a deviation of an actual CWL value from a desired CWL value in a current alignment system. Thus, the use of a constant CWL value may improve the long-term stability and accuracy of an alignment system (e.g., the inspection device 400) compared to current alignment devices.

[0069] In some aspects, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. Figure 4AAs shown, the radiation beam 413 can be split into radiation sub-beams 415 and 417. The beam splitter 414 can also be configured to direct the radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along a direction 424. The radiation sub-beam 415 can be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 can be coated with a radiation sensitive film. In some aspects, the alignment mark or target 418 can have a one hundred and eighty degree (i.e., 180°) symmetry. That is, when the alignment mark or target 418 is rotated 180° around an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 can be substantially the same as the unrotated alignment mark or target 418. The target 418 on the substrate 420 can be (a) a resist layer grating comprising strips formed from solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interwoven on a product layer grating. Alternatively, the strips can be etched into the substrate. The pattern is sensitive to chromatic aberrations in the lithographic projection apparatus (particularly the projection system PL), and the illumination symmetry and the presence of such aberrations can manifest themselves in variations in the printed grating. One in-line method for measuring line width, pitch, and critical dimensions in device manufacturing utilizes a technique called "scatterometry". Scatterometry methods are described in "Multiparameter Grating Metrology Using Optical Scatterometry" by Raymond et al. (J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997)) and in "Specular Spectroscopic Scatterometry in DUV Lithography" by Niu et al. (SPIE, Vol. 3677 (1999)), which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by a periodic structure in the target, and the resulting reflection spectrum at a given angle is detected. For example, the structure that produces the reflection spectrum is reconstructed using rigorous coupled wave analysis (RCWA) or by comparison with a library of patterns derived by simulation. Therefore, the scatterometry data of the printed grating are used to reconstruct the grating. The parameters of the grating (such as line width and shape) can be input into the reconstruction process performed by the processing unit PU based on knowledge of the printing step and / or other scatterometry processes.

[0070] According to one aspect, in some aspects, the beam splitter 414 can also be configured to receive the diffracted radiation beam 419 and split the diffracted radiation beam 419 into at least two radiation sub-beams. The diffracted radiation beam 419 can be split into diffracted radiation sub-beams 429 and 439, such as Figure 4A shown.

[0071] It should be noted that although beam splitter 414 is shown as directing radiation sub-beam 415 toward alignment mark or target 418 and directing diffracted radiation sub-beam 429 toward interferometer 426, the present disclosure is not limited thereto. Other optical arrangements may be used to obtain similar results of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0072] like Figure 4A As shown, the interferometer 426 can be configured to receive the radiation sub-beam 417 and the diffracted radiation sub-beam 429 through the beam splitter 414. In an example aspect, the diffracted radiation sub-beam 429 can be at least a portion of the radiation sub-beam 415 that can be reflected from the alignment mark or target 418. In an example of this aspect, the interferometer 426 includes any suitable set of optical elements, such as a combination of prisms, that can be configured to form two images of the alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be understood that high quality images do not need to be formed. It is sufficient to resolve the features of the alignment mark 418. The interferometer 426 can also be configured to rotate one of the two images 180° relative to the other of the two images and interferometrically recombine the rotated and unrotated images.

[0073] In some aspects, the detector 428 can be configured to receive the reconstructed image via the interferometer signal 427 and detect interference caused by the reconstructed image when the alignment axis 421 of the inspection device 400 passes through the center of symmetry (not shown) of the alignment mark or target 418. According to example aspects, such interference may be due to the alignment mark or target 418 being 180° symmetrical and the reconstructed images interfering constructively or destructively. Based on the detected interference, the detector 428 can also be configured to determine the location of the center of symmetry of the alignment mark or target 418 and thereby detect the location of the substrate 420. According to one example, the alignment axis 421 can be aligned with a light beam that is perpendicular to the substrate 420 and passes through the center of the image rotation interferometer 426. The detector 428 can also be configured to estimate the location of the alignment mark or target 418 by implementing sensor characteristics and interacting with wafer marking process variations.

[0074] In another aspect, the detector 428 determines the location of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements:

[0075] 1. Measure the position change of various wavelengths (position shift between colors);

[0076] 2. Measuring the positional variation of the various orders (positional shifts between diffraction orders); and / or

[0077] 3. Measure the position change of various polarizations (position shift between polarizations).

[0078] This data can be acquired using any type of alignment sensor, for example, a SMASH (Smart Alignment Sensor Hybrid) sensor as described in U.S. Patent No. 6,961,116, which uses a self-referencing interferometer with a single detector and four different wavelengths, and the alignment signal is extracted in software; or Athena (Advanced Technology Using High-Order Enhanced Alignment) as described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated herein by reference in their entirety.

[0079] In some aspects, the beam analyzer 430 can be configured to receive and determine the optical state of the diffracted radiation sub-beam 439. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 can also be configured to determine the position of the stage 422 and correlate the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. Therefore, the position of the alignment mark or target 418 and therefore the position of the substrate 420 can be accurately known with reference to the stage 422. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection device 400 or any other reference element, so that the center of symmetry of the alignment mark or target 418 can be known with reference to the inspection device 400 or any other reference element. The beam analyzer 430 can be a point or imaging polarimeter with some form of wavelength band selectivity. In some aspects, according to other aspects, the beam analyzer 430 can be directly integrated into the inspection device 400, or connected via several types of optical fibers: polarization-maintaining single mode, multimode, or imaging.

[0080] In some aspects, the beam analyzer 430 may also be configured to determine coverage data between two patterns on the substrate 420. One of the patterns may be a reference pattern on a reference layer. Another pattern may be an exposure pattern on an exposure layer. The reference layer may be an etching layer already present on the substrate 420. The reference layer may be generated by a reference pattern exposed on a substrate by the lithography apparatus 100 and / or 100'. The exposure layer may be a resist layer exposed adjacent to the reference layer. The exposure layer may be generated by an exposure pattern exposed on the substrate 420 by the lithography apparatus 100 or 100'. The exposure pattern on the substrate 420 may correspond to the movement of the stage 422 to the substrate 420. In some aspects, the measured coverage data may also indicate an offset between the reference pattern and the exposure pattern. The measured coverage data may be used as calibration data to calibrate the exposure pattern exposed by the lithography apparatus 100 or 100' so that after calibration, the offset between the exposure layer and the reference layer may be minimized.

[0081] In some aspects, the beam analyzer 430 can also be configured to determine a model of a product stack profile of the substrate 420, and can be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement. The product stack profile includes information about the stacked product, such as alignment marks, the target 418, or the substrate 420, and can include optical feature measurements caused by variations in the marking process that vary with illumination variations. The product stack profile can also include a product raster profile, a mark stack profile, and mark asymmetry information. An example of a beam analyzer 430 is Yieldstar TM , which is manufactured by ASML of Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is incorporated herein by reference in its entirety. The beam analyzer 430 may also be configured to process information related to specific characteristics of the exposure pattern in the layer. For example, the beam analyzer 430 may process overlay parameters (an indication of the accuracy of positioning of a layer relative to the previous layer on the substrate, or an indication of the accuracy of positioning of a first layer with respect to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g., line width and its variation) of the image depicted in the layer. Other parameters are image parameters related to the quality of the depicted image of the exposure pattern.

[0082] In some aspects, a detector array (not shown) can be connected to the beam analyzer 430 and allow the possibility of precise stack profile detection as described below. For example, the detector 428 can be a detector array. For the detector array, there can be multiple options: a bundle of multimode optical fibers, discrete pin detectors for each channel, or a CCD or CMOS (linear) array. For stability reasons, the use of a bundle of multimode optical fibers enables any dissipative elements to be remotely located. Discrete PIN detectors provide a large dynamic range, but each requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays provide many elements that can be read out at high speed, and these elements are particularly interesting if phase-stepping detection is used.

[0083] In some aspects, the second beam analyzer 430' can be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, such as Figure 4BAs shown. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The second beam analyzer 430' can be the same as the beam analyzer 430. Alternatively, the second beam analyzer 430' can be configured to perform one or more functions of the beam analyzer 430, such as determining the position of the stage 422 and associating the position of the stage 422 with the position of the symmetry center of the alignment mark or target 418. Therefore, the position of the alignment mark or target 418 and therefore the position of the substrate 420 can be accurately known with reference to the stage 422. The second beam analyzer 430' can also be configured to determine the position of the inspection device 400 or any other reference element, so that the symmetry center of the alignment mark or target 418 can be known with reference to the inspection device 400 or any other reference element. The second beam analyzer 430' can also be configured to determine the overlay data between the two patterns and a model of the product stacking profile of the substrate 420. The second beam analyzer 430' can also be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement.

[0084] In some aspects, according to other aspects, the second beam analyzer 430' can be directly integrated into the inspection device 400, or can be connected via several types of optical fibers: polarization-maintaining single mode, multimode, or imaging. Alternatively, the second beam analyzer 430' and the beam analyzer 430 can be combined to form a single analyzer (not shown) that is configured to receive and determine the optical state of the two diffracted radiation sub-beams 429 and 439.

[0085] In some aspects, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 can be a coverage calculation processor. The information may include a model of the product stacking profile constructed by the beam analyzer 430. Alternatively, the processor 432 can use the received information about the product marking to construct a model of the product marking profile. In either case, the processor 432 uses or combines the model of the product marking profile to construct a model of the stacked product and the coverage mark profile. The stacking model is then used to determine the coverage offset and minimize the spectral impact of the coverage offset measurement. The processor 432 can create a basic correction algorithm based on the information received from the detector 428 and the beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signal, the related position estimate, and the optical state in the pupil, image and additional planes. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth of the radiation. The processor 432 can characterize the inspection device 400 with reference to the wafer mark and / or alignment mark 418 using the basic correction algorithm.

[0086] In some aspects, the processor 432 may also be configured to determine the printed pattern position offset error associated with the sensor estimate of each mark based on information received from the detector 428 and the beam analyzer 430. The information includes, but is not limited to, the product stacking profile, overlay measurement, critical dimension, and focus of each alignment mark or target 418 on the substrate 420. The processor 432 may group the marks into similar sets of constant offset errors using a clustering algorithm and create an alignment error offset correction table based on the information. The clustering algorithm may be based on overlay measurements, position estimates, and additional optical stacking process information associated with each set of offset errors. Overlays are calculated for multiple different marks, for example, overlay targets with positive and negative biases around the programmed overlay offsets. The target with the minimum coverage measured is used as a reference (because it is measured to have the best accuracy). Based on the measured small coverage and the known programmed coverage of its corresponding target, the overlay error can be inferred. Table 1 illustrates how this is performed. The minimum measured coverage in the example shown is -1nm. However, this is related to a target with a programmed coverage of -30nm. This process can introduce an overlay error of 29nm.

[0087]

[0088]

[0089] The minimum value can be considered as a reference point and relative to this, the offset between the measured coverage and the coverage expected due to the programmed coverage can be calculated. This offset determines the coverage error for each mark or set of marks with similar offsets. Therefore, in the example of Table 1, the minimum measured coverage is -1nm and at the target location, the programmed coverage is 30nm. The difference between the expected coverage and the measured coverage at other targets is compared with this reference. Tables such as Table 1 can also be obtained from the marks and targets 418 under different illumination settings, and the illumination settings and their corresponding calibration factors that result in the minimum coverage error can be determined and selected. After this, the processor 432 can group the marks into sets of similar coverage errors. The criteria for grouping marks can be adjusted based on different process controls, for example, different error tolerances for different processes.

[0090] In some aspects, the processor 432 can confirm that all or most members of the group have similar offset errors and apply individual offset corrections in the clustering algorithm to each mark based on its attached optical stack metric. The processor 432 can determine the correction for each mark and feed the correction back to the lithography apparatus 100 or 100' to correct errors in overlay, for example, by feeding the correction back into the inspection apparatus 400.

[0091] Example Check Target and Action

[0092] The terms "image contrast", "contrast", etc. may be used herein to refer to the quality of a printed feature. In lithography, the quality of a printed feature may be quantified using several metrics, such as local CDU ("LCDU"), line width roughness ("LWR"), normalized image logarithmic slope ("NILS"), etc. The term "contrast" may be used to include one or more of such metrics.

[0093] Conventional methods for measuring contrast may rely on expensive optional measurement hardware and are time-consuming, thereby reducing yield. In some aspects, the term "yield" can be used to characterize the rate of photolithography manufacturing. For example, yield can refer to the rate at which photolithography manufacturing is completed on a wafer, the rate at which a wafer clears a specific manufacturing step and moves to the next step, etc. Yield can be a performance indicator of a photolithography device. It is expected that the photolithography system outputs as many products as possible in the shortest possible time. Photolithography manufacturing can include several complex processes. Each part of the process may involve technical choices that balance quality (e.g., sub-nanometer accuracy, high yield) and disadvantages (e.g., slow manufacturing speed, cost). For example, in order to improve pattern transfer accuracy, photolithography can include checking printed marks on a substrate. This inspection can be used to determine the consistency of the printed pattern on the substrate, or to align the substrate to correctly receive a new pattern. However, the additional time of the inspection process can greatly affect the yield.

[0094] Measuring contrast across a wafer can be a desirable capability to include in a lithography tool. However, current methods for measuring contrast, such as electron beam methods, are too slow, too expensive, and too impractical to cover an entire wafer. Lack of image contrast quantification, calibration, and matching in deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography tools often results in avoidable parts swaps and unresolved problems.

[0095] Although lithography tools currently use a variety of inspection tools to complete various inspection tasks, inspection tools still lack contrast measurement capabilities. TM Tools such as SMASH are image-based scatterometer inspection tools that can resolve critical dimensions of printed structures. Image-based inspection involves analyzing resolved images of printed structures. Alignment sensors, on the other hand, use diffraction-based interferometry techniques, like SMASH described above, to analyze the modulation of the illumination signal from the target. From the analysis, the position of the target can be inferred. Conventional alignment sensors are not used to resolve critical dimensions and print quality because conventional alignment sensors are not optically designed to resolve images with sub-nanometer features. While it is possible to design such an alignment sensor for sub-nanometer image resolution (so that it can perform both alignment and image-based inspection), the cost and complexity of such a design is prohibitive.

[0096] However, in some aspects of the present disclosure, it is contemplated that a diffraction-based alignment sensor can have contrast and critical dimension measurement capabilities in a manner that overcomes image resolution limitations, for example, through clever use of specially designed targets and post-processing analysis. In this way, a lithography machine with a conventional alignment sensor can gain access to contrast and critical dimension capabilities that were previously unavailable. Furthermore, changing the target design and adding post-processing operations (e.g., software) can reduce cost and complexity compared to redesigning optical hardware, and can be faster than using other systems dedicated only to critical dimension and contrast.

[0097] Before describing the details of aspects of the present disclosure, it is beneficial to first consider an overview of how alignment measurements are performed. In some aspects, target 418 may be illuminated with illuminating radiation to generate scattered radiation. By designing target 418 as a diffraction element (e.g., a grating), the scattered radiation may have one or more diffraction orders (e.g., ±1, ±2, etc.). The diffraction orders may be collected and sent to detector 428 (or multiple detectors). Detector 428 may generate measurement information in the form of a signal (e.g., a measurement signal). The measurement signal may be analyzed by a processor to determine the relative position of target 418 (e.g., the wafer alignment position). For alignment measurements, detector 428 may be a single-unit detector (i.e., a single-pixel detector), a multi-pixel detector capable of resolving images (e.g., a camera), etc. By analyzing the total intensity on the detector, the alignment position may be extracted from the measurement signal (e.g., the measurement may work without resolving individual pixels, so a single-unit detector may be used). For example, alignment measurements may involve modulating the illumination (e.g., by scanning an illumination spot on target 418), and then analyzing the characteristics of the AC measurement signal generated by the detector (e.g., amplitude, phase, etc.). The alignment position of target 418 may be derived from characteristics of the AC measurement signal (eg, the phase of the signal).

[0098] Based on this method of extracting the diffraction target position, it can be inferred that the change in the diffraction characteristics of the alignment mark can be used to shift the "apparent" (measured) position of the alignment mark in a deterministic manner. The shift in the apparent position of the wafer can then be used to extract contrast and critical dimension information by analyzing the apparent position of the alignment measurement.

[0099] Figure 5A , Figure 5B and Figure 5CGrating line structures 502, 504, and 506 that can be implemented as alignment targets according to some aspects are shown, respectively. In some aspects, the grating line structure 502 can include a main structure 508 and a bias feature 510 (e.g., a first bias feature). In some aspects of the targets disclosed herein, the target can include an iteration of the grating line structure 502. In contrast, a conventional grating can include an iteration of the main structure 508, which can be iterated without the bias feature 510. In some aspects, the grating line structure 504 can include a main structure 512 and a bias feature 514 (e.g., a second bias feature). The grating line structure 506 can include a main structure 516 and a bias feature 518 (e.g., a third bias feature).

[0100] In some aspects, enumerated adjectives (e.g., "first," "second," "third," etc.) can be used to distinguish similar elements without establishing an order, hierarchy, or quantity (unless otherwise specified). For example, the terms "first biasing feature" and "second biasing feature" can be used in a manner similar to "i-th biasing feature" or "j-th biasing feature" to distinguish two biasing features without specifying a particular order or hierarchy. Furthermore, the elements in the figure are not limited to any particular enumerated adjectives. As a non-limiting example, biasing features 510, 514, and 518 can be referred to as a "sixth" biasing feature, a "first" biasing feature, and a "second" biasing feature, respectively.

[0101] According to some aspects, Figure 5B For the nominal case. In some aspects, the bias feature 514 can include a periodic feature with a pitch P and a zero bias (also referred to as a bias step size 0). The measured response resulting from the zero bias target can be defined as the ratio of the measured response to the nominal critical dimension CD nom Corresponding. The definition of zero bias (or any bias) can be achieved by, for example, performing a calibration process against a known reference or standard mark and applying the results to a post-processing analysis of subsequent measurements. In addition, the definition of the nominal measurement position of the target can also be achieved in this way to take into account any offset caused by the use of bias features in aligning the target. Diagram 522 shows the mass distribution corresponding to the grating line structure 504. In the figure, the center of gravity is represented as "CoG". The resulting center of gravity position is due to the mass being weighted more toward the main structure 512.

[0102] According to some aspects, Figure 5A In some aspects, bias feature 510 can include a periodic feature having a pitch P and a -1 bias (also referred to as a bias step -1). The measured response resulting from the -1 bias target can be referenced to a nominal critical dimension (e.g., CD nom -1 bias). In particular, with Figure 5B510 can have a smaller duty cycle compared to the nominal case of grating line structure 504, which reduces the width of bias feature 510. Graph 520 shows the mass distribution corresponding to grating line structure 502. The resulting center of gravity position is due to the mass being weighted according to the effect of the -1 bias. Compared to grating line structure 504 (nominal), the center of gravity of grating line structure 502 is shifted more to the left due to the smaller duty cycle of bias feature 510 resulting in a reduction in mass on the right side.

[0103] According to some aspects, Figure 5C In some aspects, bias feature 518 can include a periodic feature having a pitch P and a +1 bias (also referred to as a bias step +1). The measured response resulting from a +1 bias target can be referenced to a nominal critical dimension (e.g., CD nom +1 bias). In particular, with Figure 5B 518 can have a larger duty cycle compared to the nominal case of grating line structure 504, which increases the width of bias feature 518. Graph 524 shows the mass distribution corresponding to grating line structure 506. The resulting center of gravity position is due to the mass being weighted according to the effect of the +1 bias. Compared to grating line structure 504 (nominal), the center of gravity of grating line structure 506 is shifted more to the right due to the increased mass on the right side caused by the larger duty cycle of bias feature 518.

[0104] In some aspects, the grating line structure can be a structure that has been deposited onto a substrate wafer. For example, the grating line structure can be made from a photoresist that survives a photoresist development step. Conversely, the grating line structure can be a recess etched into a material. For example, the grating line structure can be made by etching a valley in the photoresist, the valley having the outline of the grating line structure. It should be understood that in the latter case, the mass distribution in graphs 520, 522, and 524 will be reversed to represent valleys rather than plateaus, and the center of gravity of the feature will be represented by a similar amount of negative space.

[0105] In some aspects, by utilizing fine bias features, the grating line structures 502, 504, and 506 can have a structural bias that causes a center of gravity shift of the grating line structures. As previously described, an optical system (such as an alignment sensor) is able to resolve the main structures 508, 512, and 516, but may not be able to resolve the bias features 510, 514, and 518 (and therefore cannot resolve contrast or critical dimensions). However, the center of gravity shift caused by different biases can be used to infer contrast and / or critical dimensions. Even if the alignment sensor cannot optically resolve the bias features 510, 514, and 518 due to their small size, the alignment position measurement can be sensitive to the shift in the center of gravity of the grating line structure caused by the bias features (resulting in an apparent position shift of the measured target). Since the center of gravity shift and the apparent position shift have a deterministic relationship, the size and quality of the bias features 510, 514, and 518 can be inferred by analyzing the apparent positions produced by two or more targets with different bias features.

[0106] In some aspects, the bias feature design is not limited to Figure 5A , Figure 5B and Figure 5C It will be appreciated that the principle of offsetting the centre of gravity may be implemented using other designs, such as Fig. 6A , Figure 6B and Figure 6C Those designs shown.

[0107] Fig. 6A , Figure 6B and Figure 6C 602, 604, and 606 are respectively shown, which can be implemented as an alignment target according to some aspects. In some aspects, the grating line structures 602, 604, and 606 can respectively include the same grating line structures as the grating line structures 502, 504, and 506 ( Figure 5A , Figure 5B and Figure 5C ) has similar structure and function. Therefore, unless otherwise specified, the description of the elements of FIG. 5 can also be applied to Fig. 6A , Figure 6B and Figure 6C The corresponding elements of the drawings (e.g., reference numerals that share the two rightmost digits) are not shown and will not be reintroduced in full detail. Fig. 6A , Figure 6B and Figure 6C The elements in may include body structures 608 , 612 , and 616 , offset features 610 , 614 , and 618 , and graphs 620 , 622 , and 624 .

[0108] In some aspects, the offset features 610, 614, and 618 can be aligned parallel to their respective main structures. Figure 5A , Figure 5B and Figure 5CThe offset features in 610, 614 and 618 are aligned perpendicular to their corresponding main structures. In other words, the pitch P of the offset features 610, 614 and 618 is parallel to the pitch of the main larger grating structure (whereas Figure 5A , Figure 5B and Figure 5C In a similar manner, the offset features 610, 614 and 618 can achieve an offset of the center of gravity of the grating line structure, as shown in the corresponding graphs 620, 622 and 624. The design of the offset feature is not limited to Figure 5A , Figure 5B , Figure 5C , Fig. 6A , Figure 6B and Figure 6C Other structural variations are contemplated (e.g., circles, dots, squares, arbitrary shapes, two-dimensional arrays, etc.) that achieve a shift in the center of gravity of the grating line structure based on deterministic biasing techniques, thereby achieving a shift in the target apparent position of the grating line structure disclosed herein.

[0109] Fig. 7A and Figure 7B Targets 726 and 728 are shown according to some aspects. In some aspects, targets 726 and 728 may include targets similar to reference Figure 5A , Figure 5B and Figure 5C Therefore, unless otherwise stated, the Figure 5B and Figure 5C The description of the elements can also be applied to Fig. 7A and Figure 7B The corresponding elements of FIG. 1 (e.g., reference numerals that share the two rightmost digits) will not be fully reintroduced in detail. Fig. 6A , Figure 6B and Figure 6C Other aspects of the structures and functions described, such as those of targets 726 and 728, are also contemplated.

[0110] In some aspects, a target 726 (e.g., a first target) may include a plurality of grating line structures 702 (e.g., a first grating line structure). The grating line structure 702 includes a main structure 708 (e.g., a first main structure) and a bias feature 710 (e.g., a first bias feature 710). The bias feature 710 may correspond to a case where the bias step is -1 (e.g., a first bias value; the bias value may be expressed in a ratio, a unit of length, etc.). A target 728 (e.g., a second target) may include a plurality of grating line structures 704 (e.g., a second grating line structure). The grating line structure 704 includes a main structure 712 (e.g., a second main structure) and a bias feature 714 (e.g., a second bias feature 710). The bias feature 714 may correspond to a case where the bias step is 0 (e.g., a second bias value; the bias value may be expressed in a ratio, a unit of length, etc.). It should be understood that a third target may include a design corresponding to a bias step of +1. It should also be understood that more target designs are contemplated for other bias step sizes (eg, -3, -2, +2, +3, etc.).

[0111] In some aspects, an alignment inspection system (e.g., inspection system 400 ( Figure 4A and Figure 4B )) inspect targets 726 and 728. For example, radiation can be directed toward targets 726 and 728 to generate first and second portions of corresponding scattered radiation. The scattered radiation can be detected (e.g., using detector 428 (Figure 4)). A first measurement signal can be generated. The first measurement signal can indicate the position of target 726 (e.g., a first position) based on the offset provided by bias feature 710. A second measurement signal can be generated. The second measurement signal can indicate the position of target 728 (e.g., a second position) based on the offset provided by bias feature 714. The measurement signals can be analyzed. In particular, the effects of the first bias value and the second bias value on the first position and the second position can be analyzed. Through the analysis, the contrast and / or critical dimension of the target can be determined. Two or more targets (e.g., using three targets to generate Figure 8 ).

[0112] Figure 8 A graph 800 of alignment position measurements of different targets with different bias values ​​is shown according to some aspects. In some aspects, the vertical axis of graph 800 can represent the apparent pattern displacement (APD) of the measured target. The horizontal axis of graph 800 can represent the bias value, which can be expressed in real units (e.g., nm) or arbitrary step sizes (e.g., -1 bias, +1 bias, 0 bias, etc.). Different data points can correspond to different targets with different bias values ​​(see FIG. 8 ). Fig. 7A and Figure 7B Some example goals are discussed).

[0113] In some aspects, data points 802, 804, and 806 can represent measurements of targets (e.g., a first set of targets) with bias values ​​of -1, 0, and +1, respectively. As a non-limiting example, three data points 802, 804, and 806 are shown, but it should be understood that aspects of the disclosure herein can work with two or more data points (e.g., four, five, six, or more data points, each associated with a different bias value). At least one determinable characteristic can be associated with the first set of targets. The characteristics of the second set of targets can be, for example, a critical dimension (e.g., a first critical dimension) and / or a contrast. In Figure 8 , the critical dimension pCD1 is associated with data point 804, corresponding to the zero bias target. Since the relationship between the bias value and the apparent position shift is deterministic, the analysis algorithm can be programmed to compare the measured alignment position (APD) and the bias value (e.g., comparing a 0 bias to a -1 bias, comparing a 0 bias to multiple non-zero biases, etc.). Given that conventional alignment sensors may not be able to resolve critical dimension structures, critical dimension estimation can still be performed by analyzing the shift in apparent position caused by different bias values ​​(e.g., adding a given amount of nanometer width to the biased feature can deterministically enhance the shift in apparent position). In addition, the analysis algorithm can use the slope (e.g., slope 803) of at least two of the data points 802, 804, and 804 to determine contrast (which, as previously described, is related to the quality of the printed feature).

[0114] In some aspects, data points 808, 810, and 812 may represent measurements of targets (e.g., a second set of targets) with bias values ​​of -1, 0, and +1, respectively. At least one determinable characteristic may be associated with the second set of targets. The characteristic of the second set of targets may be, for example, a critical dimension (e.g., Figure 8 802, 804, and 806 and the first set of targets, the second set of targets can be checked by an alignment sensor and an analysis algorithm can extract the critical dimension and / or contrast (e.g., based on slope 805). The scene depicted by data points 808, 810, and 812 can be a scene with poor contrast (e.g., a higher slope). Contrast can be a primary and important indicator of how well the printing device is actually working. When comparing measurements of two sets of identical bias targets, a higher slope can indicate that there is a problem with the exposure of the photoresist (e.g., underexposure or overexposure).

[0115] Fig. 9 1- Figure 8In some aspects, at step S902, a radiation source of an optical scanning system may be used to direct radiation toward a target set. Non-limiting examples of optical scanning systems may include inspection device 400 ( Figure 4A and Figure 4B ). As previously explained, the optical scanning system can scan the illumination spot on the grating target to determine the characteristics of the target, such as the alignment position. The optical scanning system can be, for example, a diffraction-based alignment sensor, etc. The scanning optical system can actuate parts of its hardware to achieve scanning. For example, the optical components of the optical scanning system can move relative to the target. In another example, the target (or target support platform) can move relative to the optical components of the scanning system. The target set can include a first target and a second target. For example, the target set can be targets 726 and 728 ( Fig. 7A and Figure 7B ). The first target may include a plurality of first grating line structures including a first bias feature having a first bias value to generate a first portion of scattered radiation. The second target may include a plurality of second grating line structures including a second bias feature having a second bias value different from the first bias value to generate a second portion of scattered radiation.

[0116] In some aspects, at step S904, the first and second portions of the scattered radiation can be detected at a detector of the optical scanning system. The detection can be performed by, for example, detector 428 ( Figure 4A and Figure 4B ). In step S906, a first measurement signal may be generated by the detector. The first measurement signal may indicate a first position of the first target based on the first bias feature. In step S908, a second measurement signal may be generated by the detector. The second measurement signal may indicate a second position of the second target based on the second bias feature. In step S910, based on the first measurement signal and the second measurement signal, the influence of the first bias value and the second bias value on the first position and the second position may be analyzed to determine at least one characteristic of the target set.

[0117] In some aspects, the at least one characteristic may include a critical dimension of the target set, a contrast ratio of the target set, or both. The analysis of step S910 may include analyzing an apparent shift of the first position based on the first bias value, analyzing an apparent shift of the second position based on the second bias value, or analyzing both. The method 900 may also include determining the critical dimension, the contrast ratio, or both based on the analysis of the apparent shift of the first position, the second position, or the first position and the second position.

[0118] In some aspects, the target set may include a third target. The target set may improve additional targets (e.g., two or more targets). The additional targets may help improve the accuracy of quantifying at least one characteristic of the target set. The additional targets may be implemented as described for the first and second targets (e.g., irradiating with radiation, generating a portion of scattered radiation, etc.).

[0119] In some aspects, the first biasing feature can include a periodic structure having a pitch and a first duty cycle. The second biasing feature can include a periodic structure having the same pitch but a second duty cycle different from the first duty cycle. In some aspects, the pitch can be oriented approximately perpendicular to the pitch of the first grating line structure (e.g., as Figure 5A , Figure 5B and Figure 5C In some aspects, the pitch can be oriented approximately parallel to the pitch of the first grating line structure (e.g., as shown in FIG. Fig. 6A , Figure 6B and Figure 6C shown).

[0120] In some aspects, the analysis may be performed using a processor of the lithographic apparatus.A computer readable medium may be used to store instructions that are executed by a processor to perform method steps.

[0121] Fig. 9 The method steps may be performed in any possible order, and it is not necessary to perform all steps. Fig. 9 The method steps of FIG. 1-1 only reflect examples of the steps and are not restrictive. Figure 8 Of the described aspects, additional method steps and functions are contemplated.

[0122] Fig.10 A computer system 1000 according to some aspects is shown. For example, various aspects and components therein may be implemented using the computer system 1000 or any other well-known computer system. For example, Fig. 9 The method steps may be implemented via the computer system 1000 .

[0123] In some aspects, computer system 1000 may include one or more processors (also referred to as central processing units or CPUs), such as processor 1004. Processor 1004 may be connected to a communication infrastructure or bus 1006.

[0124] In some aspects, one or more processors 1004 can each be a graphics processing unit (GPU). In some aspects, a GPU is a processor that is an electronic circuit specifically designed to process math-intensive applications. A GPU can have a parallel structure that is very efficient for processing large blocks of data in parallel, such as math-intensive data common in computer graphics applications, images, videos, etc.

[0125] In some aspects, the computer system 1000 may also include (multiple) user input / output devices 1003, such as a monitor, keyboard, pointing device, etc., which communicate with the communication infrastructure 1006 through (multiple) user input / output interfaces 1002. The computer system 1000 may also include a main memory 1008, such as a random access memory (RAM). The main memory 1008 may include one or more levels of cache. Control logic (i.e., computer software) and / or data are stored in the main memory 1008.

[0126] In some aspects, the computer system 1000 may also include one or more secondary storage devices or memories 1010. The secondary memory 1010 may include, for example, a hard disk drive 1012 and / or a removable storage device or drive 1014. The removable storage drive 1014 may be a floppy disk drive, a tape drive, an optical disk drive, an optical storage device, a tape backup device, and / or any other storage device / drive. The removable storage drive 1014 may interact with a removable storage unit 1018. The removable storage unit 1018 may include a computer-usable or readable storage device having computer software (control logic) and / or data stored thereon. The removable storage unit 1018 may be a floppy disk, a tape, an optical disk, a DVD, an optical storage disk, and / or any other computer data storage device. The removable storage drive 1014 reads from and / or writes to the removable storage unit 1018 in a well-known manner.

[0127] In some aspects, secondary memory 1010 may include other components, tools, or other methods for allowing computer system 1000 to access computer programs and / or other instructions and / or data. Such components, tools, or other methods may include, for example, a removable storage unit 1022 and an interface 1020. Examples of removable storage unit 1022 and interface 1020 may include a program cartridge and cartridge interface (such as found in video game devices), a removable storage chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage device and associated interface.

[0128] In some aspects, the computer system 1000 may also include a communication or network interface 1024. The communication interface 1024 enables the computer system 1000 to communicate and interact with any combination of remote devices, remote networks, remote entities (individually and collectively referred to as reference numeral 1028), etc. For example, the communication interface 1024 can allow the computer system 1000 to communicate with the remote device 1028 via a communication path 1026, which can be wired and / or wireless and can include any combination of a LAN, a WAN, the Internet, etc. Control logic and / or data can be transmitted to and from the computer system 1000 via the communication path 1026.

[0129] In some aspects, a non-transitory tangible device or article of manufacture including a non-transitory tangible computer usable or readable medium having control logic (software) stored thereon is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 1000, main memory 1008, secondary memory 1010, and removable storage units 1018 and 1022, and tangible articles of manufacture embodying any combination of the foregoing. When executed by one or more data processing devices (such as computer system 1000), such control logic causes such data processing devices to operate as described herein.

[0130] Based on the teachings contained in this disclosure, it will be clear to those skilled in the relevant art how to use the Fig.10 The aspects of the present disclosure may be made and used with data processing devices, computer systems, and / or computer architectures other than those shown. In particular, the aspects described herein may operate with software, hardware, and / or operating system implementations other than those described herein.

[0131] The embodiments may be further described using the following terms:

[0132] 1. A method comprising:

[0133] The radiation is directed toward a set of targets using an optical scanning system, the set of targets including a first target and a second target, wherein

[0134] The first target includes a plurality of first grating line structures, the plurality of first grating line structures including a first bias feature, the first bias feature having a first bias value to generate a first portion of scattered radiation,

[0135] The second target includes a second plurality of grating line structures including a second bias feature having a second bias value different from the first bias value to generate a second portion of the scattered radiation, and

[0136] said directing of said radiation comprises scanning said radiation over said set of targets;

[0137] detecting, using the optical scanning system, a first portion of the scattered radiation and a second portion of the scattered radiation;

[0138] generating a first measurement signal based on the first offset feature, the first measurement signal indicating a first position of the first target;

[0139] generating a second measurement signal based on the second offset feature, the second measurement signal indicating a second position of the second target; and

[0140] Based on the first measurement signal and the second measurement signal, the influence of the first offset value and the second offset value on the first position and the second position is analyzed to determine at least one characteristic of the target set.

[0141] 2. The method of clause 1, further comprising: determining the at least one characteristic, wherein the at least one characteristic comprises a critical dimension of the target set, a contrast of the target set, or the critical dimension and the contrast.

[0142] 3. A method according to clause 1, wherein analyzing the impact of the first bias value and the second bias value includes: analyzing the apparent offset of the first position based on the first bias value, analyzing the apparent offset of the second position based on the second bias value, or analyzing the apparent offset of the first position and the apparent offset of the second position.

[0143] 4. The method according to clause 3 further includes: determining a critical dimension, a contrast, or both the critical dimension and the contrast based on an analysis of an apparent shift of the first position, an apparent shift of the second position, or an apparent shift of the first position and an apparent shift of the second position.

[0144] 5. The method according to clause 1, wherein:

[0145] The target set includes a third target;

[0146] the third target comprising a third plurality of grating line structures, the third plurality of grating line structures comprising a third bias feature having a third bias value to generate a third portion of the scattered radiation;

[0147] The third bias value is different from the first bias value and the second bias value;

[0148] The method further comprises:

[0149] detecting a third portion of the scattered radiation; and

[0150] generating a third measurement signal based on the third offset feature, the third measurement signal indicating a third position of the third target;

[0151] The analysis is also based on the third measurement signal; and

[0152] The analyzing further includes analyzing an effect of the third bias value on the third position to determine the at least one characteristic.

[0153] 6. A method according to clause 1, wherein:

[0154] The first biasing feature comprises a periodic structure having a pitch and a first duty cycle;

[0155] The second biasing feature comprises a periodic structure having the pitch and a second duty cycle; and

[0156] The analysis is also based on a difference between the first duty cycle and the second duty cycle.

[0157] 7. The method of clause 6, wherein the pitch is oriented approximately perpendicular to a pitch of the first grating line structure.

[0158] 8. The method of clause 6, wherein the pitch is oriented approximately parallel to a pitch of the first grating line structure.

[0159] 9. The method according to clause 1, wherein:

[0160] The optical scanning system includes a diffraction-based alignment sensor;

[0161] The detecting includes detecting a first portion of the scattered radiation and a second portion of the scattered radiation using the diffraction-based alignment sensor.

[0162] 10. The method of clause 9, wherein the analyzing is performed by a processor of a lithographic apparatus.

[0163] 11. A system comprising:

[0164] Optical scanning system, including:

[0165] a radiation source configured to generate radiation;

[0166] an optical device configured to direct the radiation toward a set of targets to generate scattered radiation from the set of targets, the set of targets comprising a first target and a second target, wherein the optical scanning system is configured to actuate to scan the radiation over the set of targets;

[0167] A detection system, configured to:

[0168] generating a first measurement signal, the first measurement signal being indicative of a first position of the first target; and

[0169] generating a second measurement signal, the second measurement signal being indicative of a second position of the second target; and

[0170] A non-transitory computer readable medium configured to store instructions on the non-transitory computer readable medium, the instructions, when executed by one or more computing devices, causing the one or more computing devices to perform operations, the operations comprising:

[0171] The first measurement signal and the second measurement signal are analyzed, wherein

[0172] The first target includes a plurality of first grating line structures, the plurality of first grating line structures include a first bias feature, the first bias feature having a first bias value affecting the first measurement signal,

[0173] The second target includes a plurality of second grating line structures, the plurality of second grating line structures include a second bias feature, the second bias feature has a second bias value that affects the second measurement signal, and

[0174] The second offset value is different from the first offset value, and

[0175] The analyzing includes analyzing an effect of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the set of targets.

[0176] 12. A system according to clause 11, wherein the non-transitory computer-readable medium is further configured to store additional instructions so that the operation also includes: determining at least one characteristic, wherein the at least one characteristic includes a critical dimension of the target set, a contrast of the target set, or the critical dimension and the contrast.

[0177] 13. A system according to clause 11, wherein the non-transitory computer-readable medium is further configured to store additional instructions so that analyzing the effects of the first bias value and the second bias value includes: analyzing the apparent offset of the first position based on the first bias value, analyzing the apparent offset of the second position based on the second bias value, or analyzing the apparent offset of the first position and the apparent offset of the second position.

[0178] 14. A system according to claim 13, wherein the non-transitory computer-readable medium is also configured to store additional instructions so that the operation also includes: determining a critical dimension, a contrast, or the critical dimension and the contrast based on an analysis of an apparent offset of the first position, an apparent offset of the second position, or an apparent offset of the first position and an apparent offset of the second position.

[0179] 15. A system according to clause 11, wherein:

[0180] The target set includes a third target;

[0181] The scattered radiation includes radiation from the third target;

[0182] The detection system is further configured to generate a third measurement signal based on the scattered radiation, the third measurement signal being indicative of a third position of the third target;

[0183] The third target includes a plurality of third grating line structures, the plurality of third grating line structures include a third bias feature, the third bias feature has a third bias value that affects the third measurement signal;

[0184] The non-transitory computer readable medium is further configured to store additional instructions such that the analyzing further comprises analyzing an effect of the third bias value on the third position to determine the at least one characteristic; and

[0185] The third offset value is different from the first offset value and the second offset value.

[0186] 16. A system according to clause 11, wherein:

[0187] The non-transitory computer readable medium is further configured to store additional instructions such that the analyzing is based on a difference between the first duty cycle and the second duty cycle;

[0188] The first biasing feature comprises a periodic structure having a pitch and the first duty cycle; and

[0189] The second biasing feature includes a periodic structure having the pitch and the second duty cycle.

[0190] 17. The system of clause 16, wherein the pitch is oriented approximately perpendicular to a pitch of the first grating line structure.

[0191] 18. The system of clause 16, wherein the pitch is oriented approximately parallel to a pitch of the first grating line structure.

[0192] 19. The system of claim 11, wherein the inspection system is a diffraction-based alignment sensor.

[0193] 20. A lithographic apparatus comprising:

[0194] an illumination system configured to illuminate a pattern of the patterning device;

[0195] a projection system configured to project an image of the pattern onto a substrate;

[0196] Optical scanning system, including:

[0197] a radiation source configured to generate radiation;

[0198] an optical device configured to direct the radiation toward a set of targets to generate scattered radiation from the set of targets, the set of targets comprising a first target and a second target, wherein the optical scanning system is configured to actuate to scan the radiation over the set of targets; and

[0199] A detection system, configured to:

[0200] generating a first measurement signal, the first measurement signal being indicative of a first position of the first target; and

[0201] generating a second measurement signal, the second measurement signal being indicative of a second position of the second target; and

[0202] A non-transitory computer readable medium configured to store instructions on the non-transitory computer readable medium, the instructions, when executed by one or more computing devices, causing the one or more computing devices to perform operations, the operations comprising:

[0203] The first measurement signal and the second measurement signal are analyzed, wherein

[0204] the first measurement signal indicates a first position of the first target,

[0205] The first target includes a plurality of first grating line structures, the plurality of first grating line structures include a first bias feature, the first bias feature has a first bias value that affects the first measurement signal,

[0206] The second measurement signal comprises information about a second position of the second target,

[0207] The second target includes a plurality of second grating line structures, the plurality of second grating line structures include a second bias feature, the second bias feature has a second bias value that affects the second measurement signal,

[0208] The second offset value is different from the first offset value, and

[0209] The analyzing includes analyzing an effect of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the set of targets.

[0210] 21. A non-transitory computer readable medium configured to store instructions thereon, the instructions, when executed by one or more computing devices, causing the one or more computing devices to perform operations comprising:

[0211] analyzing a first measurement signal and a second measurement signal from an optical scanning system configured to inspect a set of targets including a first target and a second target, wherein

[0212] the first measurement signal indicates a first position of the first target based on the scanning radiation on the first target,

[0213] The first target includes a plurality of first grating line structures, the plurality of first grating line structures include a first bias feature, the first bias feature having a first bias value affecting the first measurement signal,

[0214] the second measurement signal indicates a second position of the second target based on the scanning radiation on the second target,

[0215] The second target includes a plurality of second grating line structures, the plurality of second grating line structures include a second bias feature, the second bias feature has a second bias value that affects the second measurement signal,

[0216] The second offset value is different from the first offset value, and

[0217] The analyzing includes analyzing an effect of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the set of targets.

[0218] The terms "radiation", "beam", "light", "irradiation", etc. may be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5 nm-100 nm, such as 13.5 nm), or hard X-rays operating at less than 5 nm, and particle beams, such as ion beams or electron beams. Generally, radiation with wavelengths between about 400 nm and about 700 nm is considered visible radiation; radiation with wavelengths between about 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation with wavelengths of about 100 nm to 400 nm. In lithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps: G line 436 nm; H line 405 nm; and / or I line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gases) refers to radiation having a wavelength of approximately 100 nm-200 nm. Deep ultraviolet (DUV) generally refers to radiation having a wavelength range of from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation for use within a lithographic apparatus. It should be understood that radiation having a wavelength in the range of, for example, 5 nm-20 nm refers to radiation having a particular wavelength band, at least a portion of which is within the range of 5 nm-20 nm.

[0219] Although some aspects of the present disclosure are described in the context of a lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel 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 can be considered as a specific example of the more general term "substrate" or "target portion", respectively. The substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a resist layer to a substrate and develops the exposed resist) and / or a measurement unit. Where applicable, the aspects disclosed herein can be applied to such and other substrate processing tools. In addition, the substrate can be processed multiple times, for example to create a multi-layer IC, so the term substrate used herein can also refer to a substrate that already contains multiple processing layers.

[0220] In addition, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, the topography in the patterning device defines the pattern created on the substrate. The topography of the patterning device can be pressed into a resist layer supplied to the substrate, and the resist is then cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist to leave a pattern therein.

[0221] It should be understood that the phrases or terms herein are for description rather than limitation, and thus the phrases or terms of this specification should be interpreted by those skilled in the relevant art based on the teachings herein.

[0222] The present disclosure has been described above with the aid of functional building blocks that illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined herein. As long as the specified functions and their relationships are properly performed, alternative boundaries can be defined. The above description of specific aspects will fully reveal the general nature of the present disclosure so that others can easily modify and / or adapt the various applications of these specific aspects by applying knowledge within the technical scope of the art without excessive experimentation and without departing from the overall concept of the present disclosure. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to be within the meaning and scope of equivalents of the disclosed aspects.

[0223] It should be understood that the Detailed Description section (rather than the Summary and Abstract sections) is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more aspects of the disclosure contemplated by the inventor, but not necessarily all aspects, and therefore, are not intended to limit the disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

1. A method comprising: The radiation is directed toward a set of targets using an optical scanning system, the set of targets including a first target and a second target, wherein The first target includes a plurality of first grating line structures, the plurality of first grating line structures including a first bias feature, the first bias feature having a first bias value to generate a first portion of scattered radiation, The second target includes a second plurality of grating line structures including a second bias feature having a second bias value different from the first bias value to generate a second portion of the scattered radiation, and said directing of said radiation comprises scanning said radiation over said set of targets; detecting, using the optical scanning system, a first portion of the scattered radiation and a second portion of the scattered radiation; generating a first measurement signal, the first measurement signal indicating a first position of the first target based on the first bias feature; generating a second measurement signal, the second measurement signal indicating a second position of the second target based on the second offset feature; as well as Based on the first measurement signal and the second measurement signal, the influence of the first offset value and the second offset value on the first position and the second position is analyzed to determine at least one characteristic of the target set.

2. The method according to claim 1, further comprising: The at least one characteristic is determined, wherein the at least one characteristic comprises a critical dimension of the set of objects, a contrast ratio of the set of objects, or both the critical dimension and the contrast ratio.

3. The method of claim 1 , wherein analyzing the impact of the first bias value and the second bias value comprises: The apparent shift of the first position is analyzed based on the first offset value, the apparent shift of the second position is analyzed based on the second offset value, or the apparent shift of the first position and the apparent shift of the second position are analyzed.

4. The method according to claim 3, further comprising: A critical dimension, a contrast ratio, or both the critical dimension and the contrast ratio are determined based on an analysis of the apparent shift of the first location, the apparent shift of the second location, or both the apparent shift of the first location and the apparent shift of the second location.

5. The method according to claim 1, wherein: The target set includes a third target; The third target includes a third plurality of grating line structures including a third bias feature having a third bias value to generate a third portion of scattered radiation; The third bias value is different from the first bias value and the second bias value; The method further comprises: detecting a third portion of the scattered radiation; as well as generating a third measurement signal, the third measurement signal indicating a third position of the third target based on the third offset feature; The analysis is also based on the third measurement signal; and The analyzing further includes analyzing an effect of the third offset value on the third position to determine the at least one characteristic.

6. The method according to claim 1, wherein: The first biasing feature comprises a periodic structure having a pitch and a first duty cycle; The second biasing feature comprises a periodic structure having the pitch and a second duty cycle; and The analysis is also based on a difference between the first duty cycle and the second duty cycle.

7. The method of claim 6, wherein the pitch is oriented approximately perpendicular to a pitch of the first grating line structure.

8. The method of claim 6, wherein the pitch is oriented approximately parallel to a pitch of the first grating line structure.

9. The method according to claim 1, wherein: The optical scanning system includes a diffraction-based alignment sensor; The detecting includes detecting a first portion of the scattered radiation and a second portion of the scattered radiation using the diffraction-based alignment sensor.

10. The method of claim 9, wherein the analyzing is performed by a processor of a lithographic apparatus.

11. A system comprising: Optical scanning system, including: a radiation source configured to generate radiation; an optical device configured to direct the radiation toward a set of targets to generate scattered radiation from the set of targets, the set of targets comprising a first target and a second target, wherein the optical scanning system is configured to actuate to scan the radiation over the set of targets; A detection system, configured to: generating a first measurement signal, the first measurement signal being indicative of a first position of the first target; and generating a second measurement signal, the second measurement signal being indicative of a second position of the second target; and A non-transitory computer readable medium configured to store instructions on the non-transitory computer readable medium, the instructions, when executed by one or more computing devices, causing the one or more computing devices to perform operations, the operations comprising: The first measurement signal and the second measurement signal are analyzed, wherein The first target includes a plurality of first grating line structures, the plurality of first grating line structures include a first bias feature, the first bias feature having a first bias value affecting the first measurement signal, The second target includes a plurality of second grating line structures, the plurality of second grating line structures include a second bias feature, the second bias feature has a second bias value that affects the second measurement signal, and The second offset value is different from the first offset value, and The analyzing includes analyzing an effect of the first bias value and the second bias value on the first position and the second position to determine at least one characteristic of the set of targets.

12. The system of claim 11, wherein the non-transitory computer readable medium is further configured to store additional instructions such that the operations further comprise: The at least one characteristic is determined, wherein the at least one characteristic comprises a critical dimension of the set of objects, a contrast ratio of the set of objects, or both the critical dimension and the contrast ratio.

13. The system of claim 11, wherein the non-transitory computer readable medium is further configured to store additional instructions such that analyzing the impact of the first bias value and the second bias value comprises: The apparent shift of the first position is analyzed based on the first offset value, the apparent shift of the second position is analyzed based on the second offset value, or the apparent shift of the first position and the apparent shift of the second position are analyzed.

14. The system of claim 13, wherein the non-transitory computer readable medium is further configured to store additional instructions such that the operations further comprise: A critical dimension, a contrast ratio, or both the critical dimension and the contrast ratio are determined based on an analysis of the apparent shift at the first location, the apparent shift at the second location, or both the apparent shift at the first location and the apparent shift at the second location.

15. The system of claim 11, wherein: The target set includes a third target; The scattered radiation includes radiation from the third target; The detection system is further configured to generate a third measurement signal based on the scattered radiation, the third measurement signal being indicative of a third position of the third target; The third target includes a plurality of third grating line structures, the plurality of third grating line structures include a third bias feature, the third bias feature has a third bias value that affects the third measurement signal; The non-transitory computer readable medium is further configured to store additional instructions such that the analyzing further comprises analyzing an effect of the third bias value on the third position to determine the at least one characteristic; and The third offset value is different from the first offset value and the second offset value.

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