Lithography apparatus, metronography system, and methods thereof

Abstract

The present invention provides a method for illuminating an object with sequential illumination shots, an illumination system, and a lithography apparatus. [Solution] The method includes illuminating a target structure with sequential illumination shots, directing the scattered beam from the target structure to an imaging detector, generating a detection signal using the imaging detector, and determining the properties of the target structure based on at least the detection signal. The integral time of each illumination shot in the sequential illumination shots is selected to reduce low-frequency errors.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the priority of U.S. Provisional Patent Application No. 63 / 129,714, filed on December 23, 2020, the entire disclosure of which is incorporated herein by reference.

[0002]

[0002] The present disclosure relates to a lithographic apparatus, for example a lithographic apparatus for irradiating an object with sequential illumination shots.

Background Art

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, also alternatively referred to as a mask or reticle, can be used to generate the circuit patterns to be formed on individual layers of the IC. This pattern can be transferred onto a target portion (e.g., including part of one or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed by imaging onto a layer of radiation - sensitive material (resist) provided on the substrate. Generally, one substrate includes a network of adjacent target portions onto which patterns are sequentially imparted. Conventional lithographic apparatuses include so - called steppers, where each target portion is irradiated by exposing the entire pattern onto the target portion in one go, and so - called scanners, where the substrate is scanned synchronously in a given direction (the "scan" direction) parallel or antiparallel to a given direction (the "scan" direction) while the pattern is scanned with a radiation beam in the given direction, thereby irradiating each target portion. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004]

[0004] Another lithography system is an interference lithography system in which there is no patterning device, and the light beam is split into two beams, and these two beams are made to interfere with a target portion of the substrate through the use of a reflection system. The interference forms a line on the target portion of the substrate.

[0005]

[0005] During a lithography operation, various processing steps may require that different layers be formed sequentially on the substrate. Therefore, it may be necessary to position the substrate with high precision relative to previously formed patterns. Generally, alignment marks are placed on the substrate to be aligned and positioned relative to a second object. A lithography apparatus may use an alignment device to detect the position of the alignment marks and to align the substrate using the alignment marks to ensure accurate exposure from the mask. Misalignment between alignment marks in two different layers is measured as an overlay error.

[0006]

[0006] Parameters of the patterned substrate are measured to monitor the lithography process. Parameters may include, for example, the overlay error between consecutive layers formed in or on the patterned substrate and the critical linewidth of the developed photosensitive resist. This measurement can be performed on the product substrate and / or on a dedicated metrology target. Various techniques exist for measuring the microstructure formed by the lithography process, including measuring multiple wavelengths simultaneously or sequentially. [Overview of the project]

[0007]

[0007] Using multiple wavelengths in the measurement is important for correcting mark asymmetry. Therefore, it is necessary to obtain the measurement using multiple wavelengths efficiently.

[0008]

[0008] In some embodiments, the method includes illuminating a target structure with sequential illumination shots, directing the scattered beam from the target structure to an imaging detector, generating a detection signal using the imaging detector, and determining the properties of the target structure based on at least the detection signal. The integral time of each illumination shot in the sequential illumination shots is selected to reduce low-frequency errors.

[0009]

[0009] In some embodiments, the system comprises an illumination system configured to illuminate a target structure with sequential illumination shots, a detection system configured to direct scattered beams from the target structure to an imaging detector, an imaging detector configured to generate a detection signal, and a processing circuit configured to determine the characteristics of the target structure based on at least the detection signal. The integral time of each illumination shot in the sequential illumination shots is selected to reduce low-frequency errors.

[0010]

[0010] Further features of the present disclosure, as well as the structure and operation of various embodiments, will be described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific embodiments described herein. Such embodiments are described herein for illustrative purposes only. Those skilled in the art will readily come up with further embodiments based on the teachings contained herein. [Brief explanation of the drawing]

[0011]

[0011] The accompanying drawings incorporated herein and forming part thereof illustrate and describe the disclosure, further illustrate the principles of the disclosure, and enable those skilled in the art to prepare and use the disclosure.

[0012] [Figure 1A]

[0012] A schematic diagram of a reflective lithography apparatus according to some embodiments is shown. [Figure 1B]

[0013] A schematic diagram of a transmissive lithography apparatus according to some embodiments is shown. [Figure 2]

[0014] Shows a more detailed schematic diagram of a reflective lithography apparatus according to some embodiments. [Figure 3]

[0015] Shows a schematic diagram of a lithography cell according to some embodiments. [Figure 4A]

[0016] Shows a schematic diagram of an alignment apparatus according to some embodiments. [Figure 4B]

[0016] Shows a schematic diagram of an alignment apparatus according to some embodiments. [Figure 5]

[0017] Shows a system according to some embodiments. [Figure 6]

[0018] Shows the spectrum of errors in stage position measurement (SPM) according to some embodiments. [Figure 7]

[0019] Shows the integration time and the corresponding transfer function for simultaneous and sequential illumination according to some embodiments. [Figure 8]

[0020] Shows the integration time for multiple measurement cases according to some embodiments. [Figure 9]

[0021] Shows the reproducibility error as a function of the number of shots within a certain period according to some embodiments. [Figure 10]

[0022] Shows sequential illumination shots according to some embodiments. [Figure 11]

[0023] Shows sequential illumination shots using multiple wavelengths according to some embodiments. [Figure 12]

[0024] Shows stacked illumination shots using multiple wavelengths according to some embodiments. [Figure 13]

[0025] Shows illumination shots with unequal intervals according to some embodiments. [Figure 14]

[0026] Shows the integration time for multiple measurement cases according to some embodiments. [Figure 15]

[0027] Shows the reproducibility error as a function of the number of apodized shots according to some embodiments. [Figure 16]

[0028] Shows a system according to some embodiments. [Figure 17]

[0029] Shows the sequential illumination shots of each channel of two or more channels of an inspection system according to some embodiments. [Figure 18]

[0030] Shows a flowchart of operations performed by a system according to some embodiments.

[0013]

[0031] The features of the present disclosure will become more apparent by reading the following detailed description while referring to the drawings that identify corresponding elements throughout with like reference numerals. In the drawings, generally, like reference numbers indicate identical, functionally similar, and / or structurally similar elements. Further, generally, the leftmost digit of a reference number identifies the drawing in which the reference number is first shown. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as being to scale.

Mode for Carrying Out the Invention

[0014]

[0032] This specification discloses one or more embodiments incorporating the features of the present disclosure. The one or more disclosed embodiments are provided as examples. The scope of the present disclosure is not limited to the one or more disclosed embodiments. The claimed features are defined by the claims appended to this specification.

[0015]

[0033] Where one or more embodiments are described herein, and where “one embodiment,” “a particular embodiment,” “exemplary embodiment,” etc. are used herein, it is understood that one or more embodiments described may include certain features, structures, or characteristics, but each embodiment may not necessarily include those features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, where certain features, structures, or characteristics are described in relation to a particular embodiment, it is understood that performing such features, structures, or characteristics in relation to other embodiments, whether expressly described or not, is within the knowledge of those skilled in the art.

[0016]

[0034] Spatially relative terms such as "beneath," "below," "lower," "above," "on," and "upper" can be used herein to facilitate the description of the relationship between one element or feature and one or more other elements or features, as shown in the figures. Spatially relative terms are intended to encompass various orientations of the device in use or operation, in addition to the orientation shown in the figures. The device may be oriented in other ways (it may be rotated 90 degrees or in other directions), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0017]

[0035] As used herein, the term "approximately" indicates a value of a given quantity that may vary based on a particular technique. Based on a particular technique, the term "approximately" may indicate a value of a given quantity that varies within a range of, for example, 10 to 30% of its value (e.g., ±10%, ±20%, or ±30% of its value).

[0018]

[0036] Embodiments of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure can also be implemented as instructions stored on a machine-readable medium that can 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 read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, propagating signals of electrical, optical, sound, or other forms (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain operations. However, such descriptions are merely for convenience, and such operations may actually be obtained from computing devices, processors, controllers, or other devices that perform firmware, software, routines, instructions, etc.

[0019]

[0037] Before detailing such embodiments, it would be useful to present illustrative environments in which embodiments of the present invention can be implemented.

[0020]

[0038] Exemplary lithography system

[0021]

[0039] Figures 1A and 1B show schematic diagrams of lithography apparatus 100 and lithography apparatus 100', respectively, in which embodiments of the present disclosure may be implemented. Lithography apparatus 100 and lithography apparatus 100' each include: an illumination system (illuminator) IL configured to adjust a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., mask table) MT connected to a first positioner PM configured to support a patterning device (e.g., a mask, reticle, or dynamic patterning device) MA and to precisely position the patterning device MA; and a substrate table (e.g., wafer table) WT connected to a second positioner PW configured to hold a substrate (e.g., a resist-coated wafer) W and to precisely position the substrate W. Lithography apparatus 100 and 100' also include a projection system PS configured to project the pattern applied to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (e.g., including one or more dies). In lithography apparatus 100, the patterning device MA and projection system PS are reflective. In lithography apparatus 100', the patterning device MA and projection system PS are transmissive.

[0022]

[0040] The illumination system IL may include various types of optical components, such as refractive, reflective, reflector-refracting, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling the radiant beam B.

[0023]

[0041] The support structure MT holds the patterning device MA in a manner that depends on conditions such as the orientation of the patterning device MA relative to a reference frame, the design of at least one of the lithography apparatuses 100 and 100', and whether or not the patterning device is held in a vacuum environment. The support structure MT can hold the patterning device MA using mechanical, vacuum, electrostatic, or other clamping techniques. The support structure MT may be, for example, a frame or a table, and may be fixed or movable as needed. By using sensors, the support structure MT can ensure that the patterning device MA is positioned in a desired location relative to, for example, the projection system PS.

[0024]

[0042] The term "patterning device" (MA) should be broadly interpreted to refer to any device that can be used to impart a pattern to the cross-section of a radiation beam B, for example, to generate a pattern on a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in the device that is generated on the target portion C to form an integrated circuit.

[0025]

[0043] The patterning device MA may be transmissive (as in the lithography apparatus 100' in Figure 1B) or reflective (as in the lithography apparatus 100 in Figure 1A). 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 masks, Levenson phase-shift masks, halftone phase-shift masks, and various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in a different direction. The tilted mirrors impart a pattern to the radiation beam B reflected by the matrix of small mirrors.

[0026]

[0044] As used herein, the term “projection system” PS may include any type of projection system, including refractive, reflective, magnetic, electromagnetic, electrostatic, or any combination thereof, that is appropriate for the exposure radiation used or other factors such as the use of immersion liquid or vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation because other gases may absorb too much radiation or electrons. Therefore, a vacuum environment may be provided throughout the beam path using vacuum walls and vacuum pumps.

[0027]

[0045] The lithography apparatus 100 and / or lithography 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 “multistage” machine, additional substrate tables WT may be used in parallel, or preparation steps may be performed on one or more other tables while one or more substrate tables WT are being used for exposure. In some situations, the additional tables may not be substrate tables WT.

[0028]

[0046] The lithography apparatus may be of a type that can cover at least a portion of the substrate with a liquid having a relatively high refractive index, such as water, to fill the space between the projection system and the substrate. The immersion liquid can also be applied to other spaces in the lithography apparatus, such as between the mask and the projection system. Immersion techniques are well known in the art to increase the numerical aperture of the projection system. As used herein, the term "immersion" does not mean submerging a structure such as a substrate in a liquid, but rather that a liquid is present between the projection system and the substrate during exposure.

[0029]

[0047] Referring to Figures 1A and 1B, the illuminator IL receives a radiated beam from the radiation source SO. For example, if the radiation source SO is an excimer laser, the radiation source SO and the lithography apparatus 100, 100' may be separate physical entities. In this case, the radiation source SO is not considered to constitute part of the lithography apparatus 100 or 100', and the radiated beam B passes from the radiation source SO to the illuminator IL via a beam delivery system BD (Figure 1B) equipped with, for example, appropriate guide mirrors and / or beam expanders. In other cases, for example, if the radiation source SO is a mercury lamp, the radiation source SO may be an integral part of the lithography apparatus 100, 100'. The radiation source SO and the illuminator IL, and the beam delivery system BD if required, are sometimes referred to as the radiation system.

[0030]

[0048] The illuminator IL may be equipped with an adjuster AD (Figure 1B) for adjusting the angular intensity distribution of the radiated beam. Generally, at least the outer and / or inner radial ranges of the intensity distribution at the pupil plane of the illuminator (generally referred to as "σ-outer" and "σ-inner," respectively) can be adjusted. In addition, the illuminator IL may be equipped with various other components such as an integrator IN and a capacitor CO (Figure 1B). The illuminator IL can be used to adjust the radiated beam B to obtain desired uniformity and intensity distribution in the beam cross-section.

[0031]

[0049] Referring to Figure 1A, the radiant beam B is incident on a patterning device (e.g., a mask) MA held in a support structure (e.g., a mask table) MT, and a pattern is applied by the patterning device. In the lithography apparatus 100, the radiant beam B is reflected from the patterning device (e.g., a mask) MA. After being reflected from the patterning device (e.g., a mask) MA, the radiant beam B passes through a projection system PS. The projection system PS focuses the radiant beam B onto a target portion C of the substrate W. With the help of a second positioner PW and a position sensor IF2 (e.g., an interference device, a linear encoder, or a capacitance sensor), the substrate table WT can be precisely moved (e.g., to position different target portions C in the path of the radiant beam B). Similarly, the patterning device (e.g., a mask) MA can be precisely positioned relative to the path of the radiant beam B using a first positioner PM and another position sensor IF1. The patterning device (e.g., mask) MA and the substrate W can be aligned using the mask alignment marks M1 and M2 and the substrate alignment marks P1 and P2.

[0032]

[0050] Referring to Figure 1B, the radiation beam B is incident on a patterning device (e.g., mask MA) held in a support structure (e.g., mask table MT), and is patterned by the patterning device. After crossing the mask MA, the radiation beam B passes through a projection system PS. The projection system PS focuses the beam onto a target portion C of the substrate W. The projection system has a pupil PPU conjugate to the illumination system pupil IPU. A portion of the radiation originates from the intensity distribution in the illumination system pupil IPU, crosses the mask pattern without being affected by diffraction in the mask pattern, and creates an image of the intensity distribution in the illumination system pupil IPU.

[0033]

[0051] The projection system PS projects an image MP' of the mask pattern MP. The image MP' is formed on a photoresist layer coated on the substrate W by a diffracted beam generated from the mask pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. From radiative diffraction in the array that is not zero-order diffraction, stimulated diffracted beams are generated whose direction is changed perpendicular to the lines. The non-diffracted beams (i.e., so-called zero-order diffracted beams) traverse the pattern without changing their propagation direction. The zero-order diffracted beams traverse the upper lens or upper lens group of the projection system PS, which is upstream of the conjugate pupil PPU of the projection system PS, to reach the conjugate pupil PPU. The portion of the intensity distribution on the plane of the conjugate pupil PPU related to the zero-order diffracted beam is an image of the intensity distribution of the illumination system pupil IPU of the illumination system IL. The aperture device PD is positioned, for example, in or substantially in the plane containing the conjugate pupil PPU of the projection system PS.

[0034]

[0052] The projection system PS is positioned by a lens or lens group L to capture not only the zero-order diffracted beam but also the first-order or higher-order diffracted beams (not shown). In some embodiments, dipole illumination can be used to image a line pattern extending perpendicular to the line, taking advantage of the resolution-enhancing effect of dipole illumination. For example, the first-order diffracted beam interferes with the corresponding zero-order diffracted beam at the wafer W level to produce an image of the line pattern MP with the highest possible resolution and process window (i.e., a combination of usable depth of focus and allowable exposure dose variation). In some embodiments, astigmatism can be reduced by providing an radiating pole (not shown) in the opposing quadrant of the illumination system pupil IPU. Furthermore, in some embodiments, astigmatism can be reduced by blocking the zero-order beam with a conjugate pupil PPU of the projection system associated with the radiating pole in the opposing quadrant. This is described in detail in U.S. Patent No. 7,511,799B2, issued March 31, 2009, which is incorporated herein by reference in its entirety.

[0035]

[0053] With the help of a second positioner PW and position sensor IF (e.g., an interference device, linear encoder, or capacitive sensor), the substrate table WT can be precisely moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, the mask MA can be precisely positioned relative to the path of the radiation beam B using the first positioner PM and another position sensor (not shown in Figure 1B) (e.g., after mechanical removal of the mask library or during scanning).

[0036]

[0054] Generally, the movement of the mask table MT can be achieved with the help of long-stroke modules (coarse positioning) and short-stroke modules (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate table WT can be achieved using long-stroke modules and short-stroke modules that form 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 or fixed only to short-stroke actuators. The mask MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks, as shown in the figure, occupy dedicated target areas, but may also be located in the space between target areas (known as scribe line alignment marks). Similarly, in situations where multiple dies are provided on the mask MA, the mask alignment marks may be placed between the dies.

[0037]

[0055] The mask table MT and patterning device MA may be located inside the vacuum chamber V. An in-vacuum robot IVR can be used to move the patterning device, such as a mask, inside and outside the vacuum chamber. Alternatively, if the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transport tasks, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for the smooth transfer of any payload (e.g., a mask) to a fixed kinematic mount at a relay station.

[0038]

[0056] The lithography apparatuses 100 and 100' shown in the figure can be used in at least one of the following modes.

[0039]

[0057] 1. In step mode, the support structure (e.g., mask table) MT and substrate table WT are kept essentially stationary, while the entire pattern applied to the radiation beam B is projected onto the target portion C in one pass (i.e., single static exposure). Next, the substrate table WT is moved in the X and / or Y directions so that another target portion C can be exposed.

[0040]

[0058] 2. In scan mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously, while the pattern applied to the radiation beam B is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., mask table) MT can be determined by the magnification (reduction) and image inversion characteristics of the projection system PS.

[0041]

[0059] 3. In another mode, the support structure (e.g., mask table) MT is held in a substantially stationary state, holding the programmable patterning device, and projects the pattern applied to the radiation beam B onto the target portion C while the substrate table WT is moved or scanned. A pulsed radiation source SO can be used, and the programmable patterning device is updated as needed each time the substrate table WT is moved or between consecutive radiation pulses during scanning. This operating mode is readily available for maskless lithography using programmable patterning devices such as programmable mirror arrays.

[0042]

[0060] Combinations and / or variations of the above-mentioned usage modes, or entirely different usage modes, can also be used.

[0043]

[0061] In a further embodiment, the lithography apparatus 100 includes an extreme ultraviolet (EUV) radiation source. The extreme ultraviolet radiation source is configured to generate an EUV radiation beam for EUV lithography. Generally, the EUV radiation source is configured within a radiation system, and a corresponding illumination system is configured to adjust the EUV radiation beam of the EUV radiation source.

[0044]

[0062] Figure 2 shows a lithography apparatus 100 in more detail, comprising a source collector apparatus SO, an illumination system IL, and a projection system PS. The source collector apparatus SO is constructed and positioned to maintain a vacuum environment within its enclosed structure 220. An EUV radiating plasma 210 can be formed by a discharge-generated plasma source. To generate EUV radiation, an extremely hot plasma 210 can be generated by a gas or vapor such as Xe gas, Li vapor, or Sn vapor, causing it to emit radiation in the EUV range of the electromagnetic spectrum. The extremely hot plasma 210 can be generated, for example, by generating at least an incompletely ionized plasma by discharge. For efficient radiation generation, a suitable gas or vapor, such as Xe, Li, Sn vapor, or any other suitable gas or vapor with a partial pressure of 10 Pa, for example, may be required. In some embodiments, an excited tin (Sn) plasma is supplied to generate EUV radiation.

[0045]

[0063] Radiation emitted from the high-temperature plasma 210 is delivered from the radiation source chamber 211 into the collector chamber 212 via an optional gas barrier or contaminant trap 230 (sometimes also called a contaminant barrier or foil trap) positioned within or behind the opening of the radiation source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further described herein includes at least a channel structure.

[0046]

[0064] The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing-incident collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation crossing the collector CO can be reflected by the grating spectral filter 240 and focused on a virtual source point IF. The virtual source point IF is generally called the intermediate focus, and the source collector device is arranged such that the intermediate focus IF is located in or near the aperture 219 of the closed structure 220. The virtual source point IF is an image of the radiation-emitting plasma 210. The grating spectral filter 240 is used in particular to suppress infrared (IR) radiation.

[0047]

[0065] Subsequently, the radiation traverses the illumination system IL. The illumination system IL may include a faceted field mirror device 222 and a faceted pupil mirror device 224, which are arranged to give the patterning device MA a desired angular distribution of the radiation beam 221 and a desired uniformity of radiation intensity in the patterning device MA. When the radiation beam 221 is reflected by the patterning device MA held by the support structure MT, a patterned beam 226 is formed, and this patterned beam 226 is imaged by the projection system PS onto a substrate W held by a wafer stage or substrate table WT via reflective elements 228, 229.

[0048]

[0066] In general, the illumination optical unit IL and projection system PS may contain more elements than those shown in the figure. The grating spectral filter 240 may be optionally present depending on the type of lithography apparatus. Furthermore, there may be more mirrors than those shown in Figure 2; for example, the projection system PS may have one to six additional reflective elements compared to those shown in Figure 2.

[0049]

[0067] The collector-type CO system shown in Figure 2 is presented as a nested collector having grazing-type reflectors 253, 254, and 255, as just one example of a collector (or collector mirror). The grazing-type reflectors 253, 254, and 255 are symmetrically arranged in the axial direction with respect to the optical axis O, and this type of collector-type CO system is suitably used in combination with a discharge-generating plasma source, often called a DPP source.

[0050]

[0068] Exemplary lithography cell

[0051]

[0069] Figure 3 shows a lithography cell 300, sometimes called a lithocell or cluster, according to some embodiments. A lithography apparatus 100 or 100' may constitute part of the lithography cell 300. The lithography cell 300 may also include one or more devices that perform pre-exposure and post-exposure processes 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 bake plate BK. A substrate handler, i.e., a robot RO, picks up the substrate from input / output ports I / O1 and I / O2, moves them between various process devices, and delivers them to the loading bay LB of the lithography apparatus 100 or 100'. These devices are often collectively called a track and are under the control of a track control unit TCU. The TCU itself is controlled by a monitoring and control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, these various devices can be operated to maximize throughput and processing efficiency.

[0052]

[0070] exemplary inspection device

[0053]

[0071] To control the lithography process to precisely position device features on a substrate, alignment marks are typically provided on the substrate, and the lithography apparatus includes one or more alignment devices and / or systems that must precisely measure the position of the marks on the substrate. These alignment devices are essentially position measuring devices. Various types of marks and various types of alignment devices and / or systems are known from various manufacturers at different times. The type of system widely used in current lithography apparatus is based on a self-referencing interferometer described in U.S. Patent No. 6,961,116 (den Boef et al.), which is incorporated entirely by reference herein. Generally, marks are measured separately to obtain the X and Y positions. Combined X and Y measurements may be performed using the technique described in U.S. Publication No. 2009 / 195768A (Bijnen et al.), which is also incorporated entirely by reference herein.

[0054]

[0072] Terms such as “inspection equipment” and “metrology equipment” may be used herein to refer to devices or systems (e.g., alignment equipment) used to inspect wafer alignment, for example, for measuring structural characteristics (e.g., overlay error, critical dimension parameters) or used in lithography equipment.

[0055]

[0073] Figure 4A shows a schematic cross-sectional view of a metronome 400 according to one embodiment. In some embodiments, the metronome 400 may be implemented as part of a lithography apparatus 100 or 100'. The metronome 400 may be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). The metronome 400 may be further configured to detect the position of alignment marks on the substrate and to use the detected position of the alignment marks to align the substrate with respect to the patterning device or other components of the lithography apparatus 100 or 100'. Such alignment of the substrate may ensure accurate exposure of one or more patterns on the substrate.

[0056]

[0074] In some embodiments, the metrology apparatus 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and an overlay calculation processor 432. The illumination system 412 may be configured to supply a narrowband electromagnetic radiation beam 413 having one or more passbands. In one example, one or more passbands may be in the wavelength spectrum from about 500 nm to about 900 nm. In another example, one or more passbands may be separate narrow passbands in the wavelength spectrum from about 500 nm to about 900 nm. The illumination system 412 may further be configured to provide one or more passbands having a substantially constant center wavelength (CWL) value over a long period of time (e.g., over the lifetime of the illumination system 412). Such a configuration of the illumination system 412 may help prevent deviations from the desired CWL value from the actual CWL value in the current alignment system. As a result, the use of a constant CWL value may improve the long-term stability and accuracy of the alignment system (e.g., metrologic device 400) compared to current alignment devices.

[0057]

[0075] In some embodiments, the beam splitter 414 may be configured to receive the radiating beam 413 and split the radiating beam 413 into at least two radiating subbeams. For example, as shown in Figure 4A, the radiating beam 413 may be split into radiating subbeams 415 and 417. The beam splitter 414 may further be configured to direct the radiating subbeam 415 toward a substrate 420 mounted on a stage 422. In one example, the stage 422 is movable along direction 424. The radiating subbeam 415 may be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 may be covered with a radiation-sensitive film. In some embodiments, the alignment mark or target 418 may have 180-degree (i.e., 180°) symmetry. In other words, when an 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 may be substantially identical to the unrotated alignment mark or target 418. The target 418 on the substrate 420 may be a resist layer grid containing bars formed from solid resist lines, a product layer grid, or a composite grid stack in an overlay target structure containing resist grids superimposed or alternating on the product layer grid. Alternatively, the bars may be etched into the substrate. This pattern may be sensitive to chromatic aberration in lithography projection equipment, particularly projection systems PL, and illumination symmetry and the presence of such aberrations may manifest as variations in the printed grid. In one example, an in-line method used in device manufacturing to measure line width, pitch, and critical dimensions utilizes a technique known as "scalculometry."For example, the scatterometry method is described in Raymond et al., "Multiparameter Grating Metrology Using Optical Scatterometry," J.Vac.Sci.Tech.B, Vol.15, no.2, pp.361-368 (1997) and Niu et al., "Specular Spectroscopic Scatterometry in DUV Lithography," SPIE, Vol.3677 (1999), both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by periodic structures in a target, and the resulting reflection spectrum at a given angle is detected. The structures that produce this reflection spectrum are reconstructed, for example, using Rigorous Coupled-Wave Analysis (RCWA) or by comparing them with a library of patterns derived by simulation. Thus, the grating is reconstructed using scatterometry data of a printed grating. Based on knowledge of the printing process and / or other scatometry processes, grid parameters such as line width and shape may be input into the reconstruction process performed by the processing unit (PU).

[0058]

[0076] In some embodiments, the beam splitter 414 may further receive the diffractive radiation beam 419 and, according to one embodiment, be configured to split the diffractive radiation beam 419 into at least two radiation subbeams. As shown in Figure 4A, the diffractive radiation beam 419 may be split into diffractive radiation subbeams 429 and 439.

[0059]

[0077] While the beam splitter 414 is shown directing the radiating subbeam 415 towards the alignment mark or target 418 and the diffracting radiating subbeam 429 towards the interferometer 426, the disclosure is not limited thereto. It will be apparent to those skilled in the art that other optical devices may be used to illuminate the alignment mark or target 418 on the substrate 420 and to obtain results similar to detecting an image of the alignment mark or target 418.

[0060]

[0078] As shown in Figure 4A, the interferometer 426 may be configured to receive a radiant subbeam 417 and a diffracted radiant subbeam 429 via a beam splitter 414. In an exemplary embodiment, the diffracted radiant subbeam 429 may be at least a portion of the radiant subbeam 415 that can be reflected from the alignment mark or target 418. In this embodiment, the interferometer 426 includes any suitable set of optical elements, for example, a combination of prisms that can be configured to form two images of the alignment mark or target 418 based on the received diffracted radiant subbeam 429. It should be understood that while high-quality images do not need to be formed, the features of the alignment mark 418 should be resolved. The interferometer 426 may further be configured to rotate one of these two images by 180° relative to the other of these two images, and to recombine the rotated and unrotated images interferometrically.

[0061]

[0079] In some embodiments, the detector 428 may be configured to receive the recombined image via an interferometer signal 427 when the alignment axis 421 of the metrologic apparatus 400 passes through the center of symmetry (not shown) of the alignment mark or target 418, and to detect interference resulting from the recombined image. Such interference may result from the alignment mark or target 418 being 180° symmetric, according to exemplary embodiments, causing the recombined images to interfere in a constructive or cancelative manner. Based on the detected interference, the detector 428 may further be configured to determine the position of the center of symmetry of the alignment mark or target 418, and thereby detect the position of the substrate 420. In one example, the alignment axis 421 may be aligned with a light beam perpendicular to the substrate 420 and passing through the center of the image rotation interferometer 426. The detector 428 may further be configured to estimate the position of the alignment mark or target 418 by implementing sensor characteristics and interacting with process variations of the wafer mark.

[0062]

[0080] In further embodiments, the detector 428 may determine the position of the alignment mark or the center of symmetry of the target 418 by performing one or more of the following measurements. 1. Measuring positional variations (positional shifts between colors) for various wavelengths. 2. Measuring positional variations for various orders (positional shifts between diffraction orders), and / or 3. Measure the positional variation (positional shift between polarizations) for various polarizations. For example, this data may be obtained using any type of alignment sensor, such as the SMASH (Smart Alignment Sensor Hybrid) sensor described in U.S. Patent No. 6,961,116, which employs a single detector and a self-reference interferometer using four different wavelengths and extracts the alignment signal in software, the ORION sensor, or Athena (Advanced Technology using High-order ENhancement of Alignment) described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector. All of these patents are incorporated herein by reference in their entirety.

[0063]

[0081] In some embodiments, the beam analyzer 430 may be configured to receive a diffracted radiation subbeam 439 and determine its optical state. The optical state may be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 may further be configured to determine the position of the stage 422 and correlate the position of the stage 422 with the position of the alignment mark or the center of symmetry of the target 418. Thus, the position of the alignment mark or the target 418, and consequently the position of the substrate 420, can be precisely determined with respect to the stage 422. Alternatively, the beam analyzer 430 may be configured to determine the position of the metronome 400 or any other reference element so that the center of symmetry of the alignment mark or the target 418 can be determined with respect to the metronome 400 or any other reference element. The beam analyzer 430 may be a point or imaging polarimeter with some form of wavelength band selectivity. In some embodiments, the beam analyzer 430 may be directly integrated into the metrology device 400, or, according to other embodiments, may be connected via several types of optical fibers, such as polarization-preserving single-mode, multimode, or imaging optical fibers.

[0064]

[0082] In some embodiments, the beam analyzer 430 may be further configured to measure overlay data between two patterns on the substrate 420. One of these patterns may be a reference pattern on a reference layer. The other pattern may be an exposed pattern on an exposure layer. The reference layer may be an etched layer already present on the substrate 420. The reference layer may be generated by a reference pattern exposed on the 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 exposed pattern exposed on the substrate 420 by the lithography apparatus 100 or 100'. The exposed pattern on the substrate 420 may correspond to the movement of the substrate 420 by the stage 422. In some embodiments, the measured overlay data may also indicate an offset between the reference pattern and the exposed pattern. The measured overlay data may be used as calibration data to calibrate the exposure pattern exposed by the lithography apparatus 100 or 100', which may result in minimizing the offset between the exposure layer and the reference layer after calibration.

[0065]

[0083] In some embodiments, the beam analyzer 430 may further be configured to determine a model of the product stack profile of the substrate 420, and may 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 products, such as alignment marks, target 418, and substrate 420, and may also include optical feature measurements induced by mark processing variations, which are a function of illumination variations. The product stack profile may also include product grating profiles, mark stack profiles, mark asymmetry information, etc. An example of the beam analyzer 430 is found in a metrology device known as Yieldstar®, manufactured by ASML in Veldhoven, 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 further be configured to process information relating to specific characteristics of the exposure pattern within its layers. For example, the beam analyzer 430 may process overlay parameters of the depicted image within its layer (an indicator of the positioning accuracy of the first layer relative to the previous layer on the substrate, or the positioning accuracy of the first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g., line width and its variation). Other parameters include image parameters related to the quality of the depicted image of the exposure pattern.

[0066]

[0084] In some embodiments, an array of detectors (e.g., sensor array 1006) may be connected to a beam analyzer 430, allowing for the possibility of accurate stack profile detection, as discussed below. For example, detector 428 may be an array of detectors. Several options are available for the detector array, namely a multimode fiber bundle, individual PIN detectors for each channel, or a CCD or CMOS (linear) array. Using a multimode fiber bundle allows for the separation of radiating elements for stability reasons. Individual PIN detectors offer a large dynamic range but may require separate preamplifiers. Therefore, the number of elements is limited. A CCD linear array provides a large number of elements that can be read out at high speed and is particularly useful when phase stepping detection is used.

[0067]

[0085] In some embodiments, as shown in Figure 4B, a second beam analyzer 430' may be configured to receive the diffracted radiation subbeam 429 and determine its optical state. The optical state may be a measure such as beam wavelength, polarization, or beam profile. The second beam analyzer 430' may be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430' may be configured to perform at least all the functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 422 with the position of the alignment mark or the center of symmetry of the target 418. Thus, the position of the alignment mark or the target 418, and consequently the position of the substrate 420, can be precisely known with respect to the stage 422. The second beam analyzer 430' may also be configured to determine the position of the metronome 400 or any other reference element so that the center of symmetry of the alignment mark or the target 418 can be known with respect to the metronome 400 or any other reference element. The second beam analyzer 430' may further be configured to determine the overlay data between the two patterns and the model of the product stack profile of the substrate 420. The second beam analyzer 430' may also be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement.

[0068]

[0086] In some embodiments, the second beam analyzer 430' may be directly integrated into the metrology device 400, or, according to other embodiments, may be connected via some type of optical fiber, such as polarization-preserving single-mode, multimode, or imaging. Alternatively, the second beam analyzer 430' and beam analyzer 430 may be combined to form a single analyzer (not shown) configured to receive both diffracted emission subbeams 429 and 439 and determine their optical states.

[0069]

[0087] In some embodiments, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 may be an overlay calculation processor. The information may include a model of the product stack profile constructed by the beam analyzer 430. Alternatively, the processor 432 may use the received information about product marks to construct a model of the product mark profile. In either case, the processor 432 constructs models of the stacked product and overlay mark profiles using or incorporating the model of the product mark profile. The stack model is then used to determine the overlay offset and minimize spectral effects on the overlay offset measurement. 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, alignment signals, associated position estimates, the pupil plane, the image plane, and the optical state of additional planes, the processor 432 may generate a basic correction algorithm. The pupil plane is the plane where the radial position of the radiation determines the angle of incidence and the angular position determines the azimuth angle of the radiation. The processor 432 may use its basic correction algorithm to characterize the metrology apparatus 400 based on wafer marks and / or alignment marks 418.

[0070]

[0088] In some embodiments, the processor 432 may be further configured to determine the position offset error of the printed pattern relative to the sensor estimate for each mark, based on information received from the detector 428 and the beam analyzer 430. This information may include product stack profiles, overlays of each alignment mark or target 418 on the substrate 420, critical dimensions, and focus measurements. The processor 432 may utilize a clustering algorithm to group marks into sets of similar, constant offset errors and generate an alignment error offset correction table based on this information. The clustering algorithm may be based on additional optical stacking processing information associated with each set of overlay measurements, position estimates, and offset errors. Overlays are calculated for multiple different marks, e.g., overlay targets with positive and negative biases around a programmed overlay offset. The target from which the smallest overlay is measured is used as the reference (because it is measured with the highest accuracy). From this measured small overlay and the known programmed overlay of its corresponding target, the overlay error may be estimated. Table 1 shows how this may be done. In the example shown, the smallest overlay measured was -1 nm. However, this is related to a target with a programmed overlay of -30 nm. As a result, the process is causing an overlay error of 29 nm.

[0071] [Table 1]

[0072] The minimum value may be considered a reference point, and an offset may be calculated between the measured overlay and the predicted overlay resulting from the programmed overlay. This offset determines the overlay error for each mark or set of marks with a similar offset. Thus, in the example in Table 1, the minimum measured overlay was -1 nm at the target location where the programmed overlay was 30 nm. The difference between the predicted and measured overlays at other targets is compared to this reference. Tables such as Table 1 may be obtained from marks and targets 418 under various lighting settings, and the lighting setting that yields the minimum overlay error, and its corresponding calibration coefficient, may be determined and selected. Subsequently, the processor 432 may group the marks into sets of similar overlay errors. The criteria for grouping the marks may be adjusted based on various process controls, e.g., different error ranges for different processes.

[0073]

[0089] In some embodiments, the processor 432 may verify that all or most elements of a group have similar offset errors and, based on its additional optical stack measurements, apply individual offset corrections from a clustering algorithm to each mark. The processor 432 may determine a correction value for each mark and feed back the correction value to the lithography apparatus 100 or 100' to correct overlay errors, for example, by supplying the correction value to the alignment apparatus 400.

[0074]

[0090] Figure 5 shows a system 500 according to some embodiments. In some embodiments, system 500 may represent a more detailed diagram of the inspection device 400 (Figures 4A and 4B). For example, Figure 5 shows a more detailed diagram of the lighting system 412 and its function. Unless otherwise noted, elements in Figure 5 that have similar reference numbers to elements in Figures 4A and 4B (e.g., reference numbers that share two rightmost digits) may have similar structures and functions.

[0075]

[0091] In some embodiments, system 500 comprises an illumination system 512, an optical system 510, a detector 528, and a processor 532. The illumination system 512 may comprise a radiation source 502, an optical fiber 504 (e.g., a multimode fiber), an optical element 506 (e.g., a lens or lens system), and a diffracting element 508 (e.g., a grating, an adjustable grating, etc.). The optical system 510 may comprise one or more of the optical elements 506, a blocking element 536, a reflecting element 538 (e.g., a spot mirror), a reflecting element 534, and an optical element 540 (e.g., an objective lens). Figure 5 shows an unrestricted depiction of system 500 for inspecting a target 518 (also referred to as the “target structure”) on a substrate 520. The substrate 520 is disposed on an adjustable stage 522 (e.g., a movable support structure). It should be understood that the structures depicted in the illumination system 512 and the optical system 510 are not limited to their depicted positions. For example, the diffracting element 508 may be located within the optical system 510. The location of the structure may change as needed, for example, according to the design of the modular assembly.

[0076]

[0092] In some embodiments, the radiation source 502 can generate radiation 516. The radiation 516 may be spatially incoherent. Because the output of the radiation source 502 may not be directed directly to the downstream optical structure, the optical fiber 504 can guide the radiation 516 to the downstream optical structure. The optical element 506 can guide or adjust the radiation 516 (e.g., focus, collimate, parallelize, etc.). The diffracting element 508 can diffract the radiation 516 to generate radiation beams 513 and 513' (also known as the first and second radiation beams). The radiation beam 513 may include a first non-zero diffraction order (e.g., +1st order) from the diffracting element 508. The radiation beam 513' may include a second non-zero diffraction order (e.g., -1st order) from the diffracting element 508, which is different from the first non-zero diffraction order. The diffracting element 508 may generate a zero-order beam (unsigned). The blocking element 536 can block the zero-order beam to enable dark-field measurements. A spot mirror directs the radiating beams 513 and 513' toward the target 518. The optical element 540 focuses the radiating beams 513 and 513' toward the target 518 so that the illumination spots of both beams overlap. The illumination spots may underfill or overfill the target 518.

[0077]

[0093] In some embodiments, the target 518 may include a diffracting structure (e.g., a grating shown in Figure 5). The target 518 may reflect, refract, diffract, or scatter radiation. For simplicity of discussion and without limitation, radiation interacting with the target will be referred to as scattered radiation throughout. The target 518 can scatter incident radiation, and the scattered radiation is represented by scattered radiation beams 519 and 519' (also called the first and second scattered radiation beams). Scattered radiation beam 519 may represent radiation from radiation beam 513 scattered by the target 518. Similarly, scattered radiation beam 519' may represent radiation from radiation beam 513' scattered by the target 518. The optical element 542 focuses the scattered radiation beams 519 and 519' so that they interfere with each other at the detector 528. The optical element 540 guides the radiation beams 513 and 513' to be incident on the target 518 at a non-zero incidence angle (e.g., off-axis). The detector 528 can generate a detection signal based on the reception of the scattered radiation beams 519 and 519'. The detector 528 may be an imaging detector (e.g., CCD, CMOS, etc.). In this scenario, the detection signal may include a digital or analog representation of the image, including the interference pattern, and is transmitted to the processor 532.

[0078]

[0094] In some embodiments, the processor 532 can analyze the detection signal to determine the characteristics of the target 518. It should be understood that the measurement process may differ depending on what characteristics of the target 518 are to be determined. For example, if the characteristic of the target 518 to be determined is the alignment position, the measurement is performed on the target 518 alone. In another example, if the characteristic of the target 518 to be determined is the overlay error, the measurement compares the target 518 with a second target. Overlay error determination is the process of comparing a first target (on a first manufacturing layer) with a second target (on a second manufacturing layer different from the first layer) to determine whether the first and second layers are properly superimposed on each other. The first and second targets may be manufactured, for example, stacked on top of each other or side by side. Other characteristics of the target 518 (e.g., line width, pitch, critical dimension) may be determined from the target 518 alone or in combination with another target. Furthermore, although the above description assumes that both radiation beams 513 and 513' are incident on target 518 (i.e., alignment measurement), embodiments may be envisioned in which the radiation beams are directed to another target, for example, to enable overlay error measurement. For example, radiation beams 513 and / or 513' may be duplicated (e.g., using a beam splitter) to be sent to another target.

[0079]

[0095] In some embodiments, the analysis performed by the processor 532 may be based on the fact that the target 518 has been irradiated by radiation beams 513 and 513' having different diffraction orders (e.g., +1 and -1) (e.g., alignment measurement). The analysis includes, for example, performing a mathematical fit to the moiré pattern (e.g., fitting a sine function along the pitch direction of the moiré pattern). Using the information inferred from the mathematical fit, the determined properties of the target 518 may be improved and more accurate. This technique reduces the effects of factors that degrade the accuracy of the measurement, such as finite-size effects, the presence of higher diffraction orders, and defects in the grating and optical components. It should be understood that the mathematical fit is performed on a still image. For example, a region of interest may be selected on the target 518, and / or weights may be assigned to the detected pixels to improve the accuracy and robustness of the measurement. This is described in detail in PCT / EP2019 / 072762, filed 27 August 2019, which is incorporated herein by reference in whole.

[0080]

[0096] In wafer alignment metrology, measuring multiple colors is important to compensate for mark asymmetry and / or to capture other anomalies. Some camera-based systems (e.g., System 500 or Yieldstar® in Figure 5) may measure colors sequentially. In some embodiments, sequential measurement of M types of colors means a shorter integration time per color (τ / M) compared to a simultaneous case (i.e., colors are measured simultaneously) at the same throughput. In some embodiments, the shorter integration time can make the sequential scheme more susceptible to wafer stage position errors (SPM errors).

[0081]

[0097] Figure 6 shows the error spectrum of SPM measurement according to some embodiments. As shown in Figure 600, the error at lower frequencies (0-500 Hz) is greater than the error at higher frequencies (above 1500 Hz).

[0082]

[0098] Figure 7 shows the integral time and corresponding transfer function for simultaneous and sequential illumination according to some embodiments. For example, Figure 700 shows the integral time for simultaneous illumination. In some embodiments, the integral time is 5 ms for each wavelength (each color). Figure 702 shows the integral time for sequential illumination. Sequential illumination involves illuminating the target structure with radiation at a first wavelength (i.e., a first illumination shot), followed by radiation at a second wavelength, and so on. In some embodiments, the integral time is 1 ms for each of the five wavelengths. In some embodiments, the total integral time for simultaneous and sequential illumination may be the same. Figure 704 shows the transfer function from stage error to measurement error for simultaneous illumination, and Figure 706 shows the transfer function for sequential illumination. For example, using simultaneous illumination, an integral time of 5 ms results in a transfer function that drops rapidly. In some embodiments, if the integral time is shorter (1 ms), the drop in the transfer function is considerably slower, which allows more of the low-frequency components (with larger errors) to be investigated.

[0083]

[0099] In some embodiments, as integration time decreases, the signal becomes increasingly susceptible to low-frequency errors in dynamic systems where resonances exist. Furthermore, multiple resonances may exist in the system.

[0084]

[0100] This specification describes methods and systems for optimizing high-speed sequential color / polarization illumination systems in which each color and / or polarization can be turned on multiple times in very short intervals so as to maximize robustness against mechanical dynamics.

[0085]

[0101] In some embodiments, the integral time associated with the first wavelength may be divided into multiple (N) measurement shots (or illumination shots). In some embodiments, an integral time of 1 ms may extend over the entire measurement time (e.g., 5 ms).

[0086]

[0102] Figure 8 shows the integral time for several measurement examples according to some embodiments. Figure 800 shows the integral time for simultaneous illumination. Figure 802 shows the transfer function for simultaneous illumination. Figure 804 shows the integral time for a single measurement (N=1). Figure 806 shows the corresponding transfer function for the case of N=1. Figure 808 shows the integral time for multiple measurements (N=5). An integral time of 1 ms can be divided into five measurement shots. Each measurement shot has an integral time shorter than 1 ms. Figure 810 shows the corresponding transfer function for the case of N=5. As shown in Figure 810, the transfer function decreases steeply at low frequencies, similar to the simultaneous case. Figure 812 shows the integral time for multiple measurements (N=10). The corresponding transfer function is shown in Figure 814.

[0087]

[0103] In some embodiments, repeated shots can result in a recovery of the transfer curve at inherently higher frequencies (e.g., about 800 Hz for N=5). The frequency at which recovery occurs can be adjusted by adjusting the number of divisions N. In some embodiments, the transfer function is adjusted so that frequencies with smaller errors shift to a larger region. Thus, the transfer function is less sensitive to SPM errors and / or other errors.

[0088]

[0104] Figure 9 shows the reproducibility error as a function of the number of shots within a certain period, according to one embodiment. Figure 900 shows the improvement in reproducibility error. For example, the reproducibility when N=10 is better than the reproducibility when N=1 (no division).

[0089]

[0105] In some embodiments, the time between shots may be used to illuminate the target structure with illumination shots (e.g., radiation) having other characteristics (e.g., different wavelengths and / or polarizations). In some embodiments, the integral time for each color may be divided in the same way and combined with one another.

[0090]

[0106] Figure 10 shows sequential (or combined) illumination shots according to some embodiments. In some embodiments, Figure 1000 shows a series of measurements using illumination shots having a first characteristic (e.g., at a first wavelength). In some embodiments, extending the measurements to other wavelengths (colors) is done by temporally shifting the other wavelengths. In some embodiments, Figure 1002 shows a series of measurements using illumination shots having various characteristics (e.g., various wavelengths). In some embodiments, the integral time associated with each wavelength may be divided into two or more integral times. A target structure (e.g., target structure 518 in Figure 5) is illuminated by a sequence of illumination shots. The sequence of illumination shots includes sequentially illuminating the target structure with radiation having various wavelengths and / or polarizations. In some embodiments, the target structure may be illuminated by a first illumination shot at a first wavelength 1004, followed by a second illumination shot at a second wavelength 1006, followed by a third illumination shot at a third wavelength 1008, followed by a fourth illumination shot at a fourth wavelength 1010, and then a fifth illumination shot at a fifth wavelength 1012. The sequence may then be repeated for the duration of the measurement. Therefore, the reproducibility error at each wavelength is reduced.

[0091]

[0107] In some embodiments, if the integration time of a single wavelength is divided into N=10 individual shots, each shot may have an integration time of 0.1 ms, which is sufficient for a camera frame rate of 10,000. In some embodiments, changing the wavelength of the radiated beam may be done using an acousto-optically tunable filter (AOTF) device (10 μs). In some embodiments, about 0.5 ms may be lost due to color switching.

[0092]

[0108] In some embodiments, the integral time associated with a first wavelength may extend to the measurement period, while other wavelengths are measured between multiple measurement shots associated with the first wavelength. In this way, only the measurement shot associated with the first wavelength is divided into multiple short-duration (fast) measurement (illumination) shots. Other wavelengths are measured between shots of the first wavelength. In some embodiments, data from a first measurement at the first wavelength may be used to investigate stage dynamics. Stage dynamics for a second wavelength may be interpolated from the stage dynamics determined at the first wavelength. For example, differences in various positions in the image obtained from illumination shots at the first wavelength may be used to interpolate errors due to stage dynamics at other wavelengths. In some embodiments, the repetition rate of the first wavelength may be twice the resonance in the system.

[0093]

[0109] Figure 11 shows sequential illumination shots using multiple wavelengths according to some embodiments. In some embodiments, a single color is diffused throughout the measurement period, and other colors are measured in between. As shown in Figure 1100, a first color may be divided into five measurement shots (i.e., shots 1102a, 1102b, 1102c, 1102d, and 1102e). A second illumination shot 1104 having a second characteristic is measured between shots 1102a and 1102b. A third illumination shot 1106 having a third characteristic may be measured between shots 1102b and 1102c. A fourth illumination shot 1108 having a fourth characteristic may be measured between shots 1102c and 1102d. In some embodiments, a fifth illumination shot 1110 having a fifth characteristic may be measured between shots 1102d and 1102e. In some applications, the second illumination shot 1104, the third illumination shot 1106, the fourth illumination shot 1108, and the fifth illumination shot 1110 may be at different wavelengths.

[0094]

[0110] In some embodiments, a reference illumination beam having a first characteristic (e.g., color 1) may be split into multiple measurement shots captured by a first detector. The remaining illumination characteristics (e.g., colors 2, 3, 4, 5, and 6) may be measured simultaneously by a second detector with the same integration time per measurement. In some embodiments, data from the diffused measurement (i.e., color 1) may be used to correct the other colors for any machine dynamics spectrum. In some embodiments, two images may be captured simultaneously. In some embodiments, the two images may be captured by a single detector using a dichroic filter and mirrors.

[0095]

[0111] In some embodiments, a reference illumination beam having the first characteristic may be illuminated from another reference. For example, if the sensor itself is deformed, another reference illumination (e.g., another reference mark, mirror) may be used next to the objective lens.

[0096]

[0112] In some embodiments, lighting fixtures with various characteristics may be stacked in pairs.

[0097]

[0113] Figure 12 shows stacked illumination shots using multiple wavelengths according to some embodiments. In some embodiments, two or more colors may alternate in a first part of the measurement time, and two different colors may alternate in a second part of the measurement time (e.g., the remaining part). In some embodiments, each illumination may be divided into two shots. In some embodiments, shot 1202 having a first characteristic (e.g., at a first wavelength) may alternate with shot 1204 having a second characteristic (e.g., at a second wavelength) during a first period. Then, shot 1206 having a third characteristic (e.g., at a third wavelength) may alternate with shot 1208 having a fourth characteristic (e.g., at a fourth wavelength). In some embodiments, the order of illumination shots may be shot 1202, shot 1204, shot 1202, shot 1204, shot 1206, shot 1208, shot 1206, and shot 1208.

[0098]

[0114] In one example, an integration time of 0.25 ms per shot may be used. The sequence may have a transfer curve dip at approximately 1 kHz. In some embodiments, 10 different characteristics (e.g., color, polarization) may be measured within an integration time of 5 ms. In some embodiments, a frame rate of 4000 fps is used for the detector 528 in Figure 5.

[0099]

[0115] In some embodiments, unequal spacing may be used. In some embodiments, the spacing between illumination shots may be optimized to remove spectral weights around a desired frequency (e.g., 1 kHz or other frequencies).

[0100]

[0116] Figure 13 shows illumination shots with unequal spacing according to some embodiments. As shown in Figure 1300, illumination shots 1302 may be unequally spaced. In other words, the time between two illumination shots 1302 may not be equal to the time between another two illumination shots 1302. In some embodiments, the binary pattern associated with shots 1302 (i.e., the distance between illumination shots) may be optimized so that the spectral weights are zero around a desired frequency (e.g., 1 kHz). In some embodiments, the binary pattern associated with shots 1302 is optimized so that the Fourier transform is proportional to the reciprocal of the SPM spectrum (larger when the SPM is low and smaller when the SPM is high). In some embodiments, illumination shots at different wavelengths may be irradiated between illumination shots 1302.

[0101]

[0117] In some embodiments, the intensity of each illumination shot may vary.

[0102]

[0118] Figure 14 shows the integral time for several measurement examples according to some embodiments. In some embodiments, each shot may be assigned a separate intensity as shown in Graphs 1402 and 1404. This allows for greater control over the shape of the resulting transfer function. Graph 1402 shows the measurement time for N=5. Graph 1404 shows the measurement time for N=10. Graphs 1402 and 1404 show a simple Gaussian envelope. Other envelopes may be used in some embodiments. Graphs 1406 and 1408 show the transfer functions corresponding to Graphs 1402 and 1404, respectively. In some embodiments, the zero crossing in the transfer function may be adjusted to be smoother. As shown in Graphs 1406 and 1408, the ripple around 1 kHz is attenuated compared to Graphs 810 and 814 (where a constant intensity is used for all illumination shots).

[0103]

[0119] In some embodiments, the intensity of the shot may be adjusted by an illumination system (e.g., illumination system 512 in Figure 5). However, this may reduce the number of captured photons. Therefore, there is a trade-off between the deterioration of reproducibility due to the reduction in photons and the improvement of reproducibility by suppressing positional errors (SPM noise) of the wafer stage.

[0104]

[0120] In some embodiments, the intensity of the shots may be adjusted during the analysis of the detection signal (i.e., in post-processing by the processor 532 in Figure 5). In some embodiments, all illumination shots may be directed at the target structure with equal intensity. In some embodiments, different weights may be assigned to individual shots during post-processing.

[0105]

[0121] In some embodiments, intensity switching may be performed in conjunction with color switching using an acousto-optically adjustable filter (AOTF) in approximately 10 μs.

[0106]

[0122] Figure 15 shows the repeatability error using apodized illumination shots according to some embodiments. Figure 1502 shows the improvement in repeatability over a 1 ms integration time when using apodization as a function of the number of shots within a given period. Figure 1504 shows the improvement over fixed intensity shots. For N=10, the intensity performance of apodization may be better than that of no apodization.

[0107]

[0123] Figure 16 shows a schematic diagram of system 1600 according to one embodiment. In some embodiments, system 1600 may represent a more detailed diagram of inspection device 400 (Figures 4A and 4B). For example, Figure 16 shows a more detailed diagram of lighting system 1612 and its function.

[0108]

[0124] In some embodiments, system 1600 comprises an illumination system 1602, an optical system 1604, a detector system 1606, and a processor 1608. Illumination system 1602 may comprise a radiation source 1610, a polarizer 1612, a phase difference plate 1614 (e.g., a waveplate), a first optical element 1616 (e.g., a lens or lens system), a reflecting element 1618 (e.g., an internal total internal reflection prism), a field diaphragm 1620, a second optical element 1622, a waveplate 1624, and an aperture diaphragm 1626. Optical system 1604 may comprise a reflecting element 1628 (e.g., a spot mirror) and an optical element 1630 (e.g., an objective lens). The reflecting element 1628 can function as a field diaphragm for zero-order diffraction radiation.

[0109]

[0125] Figure 16 shows a non-restrictive depiction of a system 1600 for inspecting a target 1632 (also referred to as the “target structure”) on a substrate 1634. The substrate 1634 is positioned on an adjustable stage 1636 (e.g., a movable support structure). It should be understood that the structures depicted within the illumination system 1602 and the optical system 1604 are not limited to their depicted positions. The positions of the structures may change as needed, for example, according to the design of a modular assembly.

[0110]

[0126] In some embodiments, target 1632 may include a diffracting structure. Target 1632 may reflect, refract, diffract, or scatter radiation. For simplicity and without limitation, radiation interacting with the target will be referred to as scattered radiation throughout. Scattered radiation may be focused by objective system 1630.

[0111]

[0127] The detector system 1606 may comprise a self-reference interferometer 1638 and one or more detectors. Scattered radiation may pass through the optical element 1630 and travel to the self-reference interferometer 1638.

[0112]

[0128] In one embodiment, a further beam splitter 1642 splits the optical signal into two paths A and B. One path may contain the sum of two rotational fields, and the other may contain the difference. Similarly, a beam splitter 1644 may split the optical signal into two paths C and D, each representing the sum and difference of rotational fields. The radiation from each path A, B, C, and D may be focused by corresponding lens assemblies 1646A, 1646B, 1646C, and 1646D. The radiation may then pass through apertures 1648A, 1648B, 1648C, or 1648D, which remove most of the radiation from outside the spot on the substrate. Lens assemblies 1646A, 1646B, 1646C, and 1646D may focus the radiation field into respective detectors 1650A, 1650B, 1650C, and 1650D. Each detector may provide a time-varying signal (e.g., a waveform) synchronized with the physical scanning operation between the system 1600 and the target structure 1632. The signals from the detectors may be processed by the processor 1608.

[0113]

[0129] In some embodiments, the system 1600 may be used to measure 12 different characteristics (e.g., color, polarization, and color and polarization) without adding an additional optical analog / digital board (OADB) channel.

[0114]

[0130] Figure 17 shows sequential illumination shots according to some embodiments. In some embodiments, a target structure having a mark pitch of 1.6 μm and a scan length of 24 μm (e.g., target 1632 in Figure 16) may use 30 signal periods. In some embodiments, three wavelengths (colors) may be used for each of the four channels of system 1600 (channels 1702, 1704, 1706, and 1708). Thus, each wavelength (e.g., wavelengths 1710a, 1710b, 1710c, 1710d, 1710e, 1710f, 1710g, 1710h, 1710i, 1710j, 1710k, and 1710l) may use 10 signal periods. In some embodiments, this may allow more colors to be measured using system 1600 without adding optical analog / digital board (OADB) channels. In some embodiments, the colors may be adjusted (e.g., between colors 1, 2, and 3).

[0115]

[0131] In some embodiments, the scan length may be less than 30 signal periods. In some embodiments, each measurement may correspond to a half-period. Therefore, 10 half-periods per wavelength may be used. Thus, each integral time may include a peak or trough of the signal. In some embodiments, the signals may be stitched together and synchronized.

[0116]

[0132] In some embodiments, the detection signals from each integration window are processed individually. In this case, the characteristics of the target structure may be determined based on the average of the detection signals.

[0117]

[0133] Figure 18 shows method steps for performing method 1800, which includes the functions described herein, according to some embodiments. Method 1800 in Figure 18 may be performed in any possible order, and not all steps need to be performed. Furthermore, the method steps in Figure 18 above reflect only examples of steps and are not limiting. That is, further method steps and functions may be conceivable based on the embodiments described with reference to Figures 1 to 17.

[0118]

[0134] Method 1800 includes illuminating the target structure with sequential illumination shots, as shown in step 1802. The integral time of each illumination shot in the sequential illumination shots is selected to minimize low-frequency errors. In other words, the integral may be selected to minimize the dependence of the detection signal on low-frequency errors. Method 1800 also includes directing the scattered beam from the target structure to an imaging detector, as shown in step 1804. Method 1800 further includes generating a detection signal using the imaging detector, as shown in step 1806. Method 1800 further includes determining the properties of the target structure based at least on the detection signal.

[0119]

[0135] Embodiments may be further described using the following clauses. 1. Illuminate the target structure with sequential illumination shots selected so that the integral time of each illumination shot reduces low-frequency errors. Directing the scattered beam from the target structure towards the imaging detector, To generate a detection signal using an imaging detector, A method comprising determining the characteristics of a target structure at least based on a detection signal. 2. The method of Clause 1, wherein the target structure is illuminated sequentially with illumination shots, the process comprising alternating in time radiation at a first wavelength and / or a first polarization with radiation at a second wavelength and / or a second polarization. 3. Irradiating the target structure sequentially with illumination shots, Dividing the integral time of radiation at the first wavelength into two or more integral times, Irradiating the target structure with illumination shots at a first wavelength for two or more integrated time intervals, and The method according to Clause 1, comprising irradiating a target structure with one or more illumination shots having different wavelengths between illumination shots at a first wavelength. 4. Each of the one or more illumination shots has an integral time longer than the integral time associated with the illumination shot at the first wavelength. The method of Clause 3, wherein each of the one or more illumination shots has a different wavelength from another illumination shot in the one or more illumination shots. 5. Illuminating the target structure sequentially with illumination shots, Dividing the integral time of radiation at the first wavelength into three or more integral times, This includes irradiating the target structure with a first illumination shot, a second illumination shot, and a third illumination shot at a first wavelength, The method of Clause 1, wherein the period between the first lighting shot and the second lighting shot is different from the period between the second lighting shot and the third lighting shot. 6. The sequential illumination shots are at the first wavelength, and the method further... Irradiating the target structure with radiation at a second wavelength, Directing the second scattered beam from the target structure towards the imaging detector, To generate a second detection signal using an imaging detector, and The method of Clause 1, which includes adjusting a second detection signal based on the detection signal. 7. The method of Clause 1, further comprising adjusting the intensity of each lighting shot in a sequential lighting shot so that the intensity of the sequential lighting shots is apodized with the envelope. 8. The method of Clause 7, wherein the adjustment is performed by a lighting system that generates sequential lighting shots. 9. The method of Clause 7, wherein the adjustment is performed by a processor acting on the detection signal. 10. A sequential illumination shot includes at least one set of illumination shots, the first set including illumination shots at various wavelengths. The method of Clause 1, wherein at least one set is repeated at least once in a sequential lighting shot. 11. Illuminate the target structure sequentially with a second set of illumination shots. Directing the scattered beam from the target structure associated with a second set of sequential illumination shots to another imaging detector, Using a different imaging detector to generate a different detection signal, and The method of Clause 1, further comprising determining the characteristics of a target structure based on at least one detection signal and another detection signal. 12. Illuminating the target structure sequentially with illumination shots, Illuminating the target structure with a series of illumination shots at multiple wavelengths, and The method of Clause 1, which includes repeating the illumination for the duration of the measurement. 13. An illumination system that illuminates a target structure with sequential illumination shots selected such that the integral time of each illumination shot reduces low-frequency errors, A detection system that directs a scattered beam from the target structure towards an imaging detector, An imaging detector that generates a detection signal, A system comprising a processing circuit that determines the characteristics of a target structure, at least based on a detection signal. 14. The system of Clause 13, wherein the lighting system alternates in time between emitting radiation at a first wavelength and / or a first polarization and emitting radiation at a second wavelength and / or a second polarization. 15. Lighting, The integral time of radiation at the first wavelength is divided into two or more integral times, The target structure is irradiated with two or more integrated time shots at the first wavelength, The system of Clause 13, wherein the target structure is irradiated with one or more illumination shots having different wavelengths between illumination shots at a first wavelength. 16. The system of Clause 15, wherein each of the one or more illumination shots has an integral time longer than the integral time associated with the illumination shot at a first wavelength, and each of the one or more illumination shots has a different wavelength from another illumination shot of the one or more illumination shots. 17. The sequential illumination shots are at the first wavelength. The lighting system further irradiates the target structure with radiation at a second wavelength, The detection system further directs a second scattered beam from the target structure towards the imaging detector. The imaging detector then generates a second detection signal, The system of clause 13, wherein the processing circuit further adjusts the second detection signal based on the detection signal. 18. The system of clause 13 further adjusts the detection signal so that the intensity weights of sequential illumination shots are apodized with the n envelope. 19. A sequential illumination shot includes at least one set of illumination shots, the first set including illumination shots at various wavelengths. The system of Clause 13, wherein at least one set is repeated at least once in a sequential lighting shot. 20. A lighting device for illuminating the pattern of a patterning device, A projection system that projects an image of a pattern onto a substrate, An illumination system that illuminates a target structure with sequential illumination shots selected so that the integral time of each shot reduces low-frequency errors, A detection system that directs a scattered beam from the target structure towards an imaging detector, An imaging detector that generates a detection signal, A lithography apparatus comprising a metrology system and a processing circuit that determines the characteristics of a target structure at least based on a detection signal.

[0120]

[0136] In some embodiments, irradiation includes alternating between emission at a first wavelength and / or a first polarization and emission at a second wavelength and / or a second polarization over time.

[0121]

[0137] In some embodiments, irradiation includes dividing the integral time of radiation at a first wavelength into two or more integral times, irradiating the target structure with illumination shots at the first wavelength for two or more integral times, and irradiating the target structure with one or more illumination shots having different wavelengths between the illumination shots at the first wavelength.

[0122]

[0138] In some embodiments, irradiation includes dividing the integral time of radiation at a first wavelength into three or more integral times, and irradiating the target structure with a first illumination shot, a second illumination shot, and a third illumination shot at the first wavelength. In some embodiments, the period between the first illumination shot and the second illumination shot is different from the period between the second illumination shot and the third illumination shot.

[0123]

[0139] Examples of commercially available alignment sensors include the SMASH®, ORION®, and ATHENA® manufactured by ASML of the Netherlands, as mentioned above. The structure and function of the alignment sensors are discussed with reference to Figure 4 and in whole in U.S. Patent No. 6,961,116 and U.S. Patent Publication No. 2009 / 195768, which are incorporated herein by reference.

[0124]

[0140] While this text specifically refers to the use of lithography equipment in the manufacture of ICs, it should be understood that the lithography equipment described herein has other applications. For example, these include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, LCDs, and thin-film magnetic heads. In light of these alternative applications, it will be recognized by those skilled in the art that where the terms “wafer” or “die” are used herein, they may be considered synonymous with the more general terms “substrate” or “target portion,” respectively. The substrates described herein may be processed before or after exposure using, for example, a track unit (usually a tool that coats a layer of resist onto the substrate and develops the exposed resist), a metronome unit, and / or an inspection unit. Where appropriate, the disclosure herein may be applied to the above and other substrate processing tools. Furthermore, the substrate may be processed multiple times, for example, to produce a multilayer IC, and therefore the term substrate as used herein may also refer to a substrate that already contains multiple processed layers.

[0125]

[0141] While the use of embodiments of this disclosure in the field of optical lithography has been particularly noted, it should be understood that this disclosure can be used in other fields, such as imprint lithography, depending on the context, and is not limited to optical lithography. In imprint lithography, a topography within a patterning device defines the pattern created on a substrate. The topography of the patterning device is imprinted into a resist layer supplied to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, and once the resist has cured, the pattern remains inside.

[0126]

[0142] It should be understood that the terms and technical descriptions in this specification are for illustrative purposes only and not for limitation, and therefore, the terms and technical descriptions in this disclosure should be interpreted by those skilled in the art in light of the teachings contained herein.

[0127]

[0143] Furthermore, as used herein, terms such as “radiation,” “beam,” “light,” and “illumination” include, for example, ultraviolet (UV) radiation (e.g., having wavelengths λ of 365, 248, 193, 157, or 126 nm), extreme ultraviolet (EUV) or soft X-ray radiation (e.g., wavelengths in the range of 5 to 20 nm, e.g., having a wavelength of 13.5 nm), or hard X-rays operating at less than 5 nm, as well as all types of electromagnetic radiation, including particulate beams such as ion beams or electron beams. Generally, radiation with wavelengths between about 400 and about 700 nm is considered visible radiation. Radiation with wavelengths between about 780 and about 3000 nm (or above) is considered IR radiation. UV refers to radiation with wavelengths between about 100 and 400 nm. In lithography, the term “UV” also usually applies to wavelengths that can be produced by mercury discharge lamps, namely the G-line at 436 nm, the H-line at 405 nm, and / or the I-line at 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation with wavelengths of approximately 100–200 nm. Deep UV (DUV) generally refers to radiation with wavelengths in the range of 126 nm–428 nm, and in some embodiments, excimer laser devices can generate DUV used in lithography equipment. For example, it should be recognized that radiation with wavelengths in the range of 5–20 nm is at least partly related to radiation having a certain wavelength band in the range of 5–20 nm.

[0128]

[0144] As used herein, the term “substrate” refers to a material on which a layer of material is added. In some embodiments, the substrate itself may be patterned, and the material added on top of it may also be patterned, or it may remain patternless.

[0129]

[0145] While this document specifically refers to the use of the apparatus and / or systems provided herein in the manufacture of ICs, it should be clearly understood that such apparatus and / or systems have many other possible applications. For example, they can be used in integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, LCD panels, thin-film magnetic heads, and the like. In light of these alternative applications, it will be recognized by those skilled in the art that where the terms “reticle,” “wafer,” or “die” are used herein, they may be replaced with the more general terms “mask,” “substrate,” and “target portion,” respectively.

[0130]

[0146] While specific embodiments of this disclosure have been described above, it will be understood that embodiments of this disclosure can be carried out in ways other than those described. The description is illustrative and not limiting. Therefore, it will be apparent to those skilled in the art that modifications to the described disclosure can be made without departing from the claims set forth below.

[0131]

[0147] It should be understood that the "Modes for Carrying Out the Invention" section, rather than the "Summary of the Invention" and "Abstract" sections, is intended to be used when interpreting the claims. The "Summary of the Invention" and "Abstract" sections may describe one or more exemplary embodiments as envisioned by the inventors, but may not describe all exemplary embodiments of this disclosure and therefore do not limit the scope of this disclosure and the accompanying claims in any way.

[0132]

[0148] The above has described the disclosure using functional components and their relationships that illustrate embodiments of specific functions. The boundaries of these functional components are arbitrarily defined in this specification for the sake of clarity. Alternative boundaries can be defined as long as the specific function and its relationships are adequately performed.

[0133]

[0149] The above-mentioned descriptions of specific embodiments fully illustrate the overall nature of this disclosure, and by applying knowledge of the art, such specific embodiments can be readily modified and / or adapted to various uses without excessive experimentation and without departing from the overall concept of the invention. Accordingly, such adaptations and modifications shall fall within the meaning and scope of equivalents of the disclosed embodiments based on the teachings and guidance presented herein.

[0134]

[0150] The scope and extent of the protected subject matter are not limited by any of the exemplary embodiments described above, but are defined solely by the claims and their equivalents.

Claims

1. The target structure is illuminated with sequential illumination shots, the integral time of each illumination shot is selected to reduce low-frequency errors. Directing the scattered beam from the target structure towards the imaging detector, To generate a detection signal using the aforementioned imaging detector, A method comprising determining the characteristics of the target structure based at least on the detection signal.

2. The method of claim 1, wherein sequentially irradiating the target structure with illumination shots includes alternately emitting radiation at a first wavelength and / or a first polarization and emitting radiation at a second wavelength and / or a second polarization in time.

3. The target structure is sequentially irradiated with illumination shots. Dividing the integral time of radiation at the first wavelength into two or more integral times, Irradiating the target structure with illumination shots at the first wavelength for two or more integrated time periods, and The method of claim 1, comprising irradiating the target structure with one or more illumination shots having different wavelengths between the illumination shots at the first wavelength.

4. Each of the one or more illumination shots has an integral time longer than the integral time associated with the illumination shot at the first wavelength. The method according to claim 3, wherein each of the one or more illumination shots has a different wavelength from another illumination shot of the one or more illumination shots.

5. The target structure is sequentially irradiated with illumination shots. Dividing the integral time of radiation at the first wavelength into three or more integral times, This includes irradiating the target structure with a first illumination shot, a second illumination shot, and a third illumination shot at the first wavelength, The method according to claim 1, wherein the period between the first illumination shot and the second illumination shot is different from the period between the second illumination shot and the third illumination shot.

6. The sequential illumination shots are at a first wavelength, and the method further, The target structure is irradiated with radiation at a second wavelength. Directing the second scattered beam from the target structure towards the imaging detector, To generate a second detection signal using the aforementioned image detector, and The method of claim 1, further comprising adjusting the second detection signal based on the detection signal.

7. The method of claim 1, further comprising adjusting the intensity of each illumination shot in the sequential illumination shot such that the intensity of the sequential illumination shot apodizes with the envelope.

8. The method of claim 7, wherein the adjustment is performed by a lighting system that generates sequential lighting shots.

9. The method of claim 7, wherein the adjustment is performed by a processor acting on the detection signal.

10. The sequential illumination shots include at least one set of illumination shots, the first set including illumination shots at various wavelengths, The method according to claim 1, wherein the at least one set is repeated once or more in the sequential illumination shot.

11. The target structure is sequentially irradiated with a second set of illumination shots. Directing the scattered beam from the target structure associated with the second set of sequential illumination shots to another imaging detector, To generate another detection signal using the aforementioned other imaging detector, and The method of claim 1, further comprising determining the characteristics of the target structure based on at least the detection signal and the other detection signal.

12. The target structure is sequentially irradiated with illumination shots. Illuminating the target structure with a series of illumination shots at multiple wavelengths, and The method of claim 1, comprising repeating the illumination for the duration of the measurement.

13. A lighting system that illuminates a target structure with sequential illumination shots selected so that the integral time of each illumination shot reduces low-frequency errors, A detection system that directs the scattered beam from the target structure towards an imaging detector, The imaging detector that generates a detection signal, A system comprising a processing circuit that determines the characteristics of the target structure at least based on the detection signal.

14. The lighting system according to claim 13, wherein the lighting system alternately emits radiation at a first wavelength and / or a first polarization in time with radiation at a second wavelength and / or a second polarization.

15. The aforementioned lighting, The integral time of radiation at the first wavelength is divided into two or more integral times, The target structure is irradiated for two or more integrated time intervals with illumination shots at the first wavelength. The system of claim 13, wherein the target structure is irradiated with one or more illumination shots having different wavelengths between the illumination shots at the first wavelength.

16. The system of claim 15, wherein each of the one or more illumination shots has an integral time longer than the integral time associated with the illumination shot at the first wavelength, and each of the one or more illumination shots has a different wavelength from another illumination shot of the one or more illumination shots.

17. The sequential illumination shots are at the first wavelength, The illumination system further irradiates the target structure with radiation at a second wavelength, The detection system further directs a second scattered beam from the target structure towards the imaging detector. The imaging detector further generates a second detection signal, The system according to claim 13, wherein the processing circuit further adjusts the second detection signal based on the detection signal.

18. The system of claim 13, wherein the processing circuit further adjusts the detection signal so that the intensity weights of the sequential illumination shots are apodized with the n envelope.

19. The sequential illumination shots include at least one set of illumination shots, the first set including illumination shots at various wavelengths, The system according to claim 13, wherein the at least one set is repeated once or more in the sequential illumination shot.

20. A lighting device for illuminating the pattern of a patterning device, A projection system for projecting the image of the aforementioned pattern onto a substrate, An illumination system that illuminates a target structure with sequential illumination shots selected so that the integral time of each shot reduces low-frequency errors, A detection system that directs the scattered beam from the target structure towards an imaging detector, The imaging detector that generates a detection signal, A lithography apparatus comprising a metrology system and a processing circuit that determines the characteristics of the target structure at least based on the detection signal.

Images