Multi-channel lock-in camera for multi-parameter sensing in lithography processes

Abstract

The metrology system may include an illumination system, a camera, and an analyzer system. The illumination system transmits illumination toward a target. The illumination has a plurality of illumination parameters associated with a corresponding plurality of modulation frequencies. The camera receives scattered illumination from the target and generates, for each pixel of the camera, a measurement signal encoded with a signature of the plurality of modulation frequencies. The analyzer system, for each pixel of the camera, demodulates the measurement signal based on the plurality of modulation frequencies and outputs the phase, amplitude, or phase and amplitude of a demodulated component of the measurement signal corresponding to the modulation frequency.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to U.S. Patent Application No. 63 / 477,929, filed December 30, 2022, and U.S. Patent Application No. 63 / 509,432, filed June 21, 2023, both of which are incorporated herein by reference in their entireties.

[0002] FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to inspection sensors, such as alignment and scatterometry sensors, used in connection with lithography processes. [Background technology]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, patterning devices, often referred to as masks or reticles, can be used to generate a circuit pattern that will be formed in an individual layer of the IC. This pattern can be transferred onto the target portion (e.g. comprising part of a die, one die or several dies) on the substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (photoresist or simply "resist") provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the radiation beam in a given direction (the "scan" direction) while the target portion is synchronously scanned parallel or anti-parallel to the given direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithography operations, different layers may need to be formed sequentially on a substrate by different processing steps. Therefore, it may be necessary to position the substrate with high precision relative to previous patterns formed on the substrate. Typically, alignment marks are placed on the substrate to be aligned and positioned relative to a second object. Lithography apparatuses can use alignment devices to detect the positions of the alignment marks and to align the substrate with the alignment marks to ensure accurate exposure from the mask. Misalignment between alignment marks of two different layers is measured as an overlay error.

[0005] To monitor the lithography process, parameters of the patterned substrate are measured. These parameters may include, for example, the overlay error between successive layers formed within or on the patterned substrate and the critical linewidth of the developed photosensitive resist. These measurements can be performed on the product substrate and / or on dedicated metrology targets. There are various techniques for measuring the microstructures formed in the lithography process, including the use of scanning electron microscopes and various specialized tools. One fast, non-invasive form of specialized inspection tool is a scatterometer, in which a beam of radiation is transmitted to a target on the substrate surface and the properties of the scattered or reflected beam are measured. Comparing the beam properties before and after reflection or scattering by the substrate can reveal properties of the substrate. This can be done, for example, by comparing the reflected beam to data stored in a library of known measurements associated with known substrate properties. A spectroscopic scatterometer transmits a broadband beam of radiation to the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered within a specific, narrow angular range. In contrast, an angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0006]

[0006] Such optical scatterometers can be used to measure parameters such as the critical dimensions of a developed photosensitive resist or the overlay error (OV) between two layers formed in or on a patterned substrate. By comparing the properties of the illumination beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be revealed.

[0007]

[0007] Lithography systems are limited in the number of manufactured devices they can output within a given time frame. Faster lithography manufacturing is desired, which drives the advancement of faster inspection technologies. Optical inspection of targets on a wafer can be performed using multiple photon wavelengths. A given wavelength can provide information about the target that may not be readily apparent at another wavelength. Using multiple parameters, such as multiple wavelengths, during inspection can be time-consuming and slow down lithography manufacturing speeds. Summary of the Invention

[0008]

[0008] Therefore, it is desirable to improve multi-parameter inspection techniques to increase manufacturing speed and throughput.

[0009]

[0009] In some aspects, a metrology system can include an illumination system, a camera, and an analyzer system. The illumination system is configured to transmit illumination toward a target. The illumination has a plurality of illumination parameters associated with a corresponding plurality of modulation frequencies. The camera is configured to receive scattered illumination from the target. The camera is further configured to generate, for each pixel of the camera, a measurement signal encoded with a signature of the plurality of modulation frequencies. The analyzer system is configured, for each pixel of the camera, to demodulate the measurement signal based on the plurality of modulation frequencies. The analyzer system is further configured to output a phase, an amplitude, or a phase and an amplitude of a demodulated component of the measurement signal corresponding to the modulation frequency.

[0010] In some aspects, the lithographic apparatus comprises an illumination source, a projection system, and a metrology system. The illumination source is configured to illuminate a pattern on a patterning device. The projection system is configured to project an image of the pattern onto a substrate. The metrology system can comprise an illumination system, a camera, and an analyzer system. The illumination system is configured to transmit illumination towards a target. The illumination has a plurality of illumination parameters associated with a corresponding plurality of modulation frequencies. The camera is configured to receive scattered illumination from the target. The camera is further configured to generate, for each pixel of the camera, a measurement signal encoded with signatures of the plurality of modulation frequencies. The analyzer system is configured, for each pixel of the camera, to demodulate the measurement signal based on the plurality of modulation frequencies. The analyzer system is further configured to output a phase, an amplitude, or a phase and amplitude of a demodulated component of the measurement signal corresponding to the modulation frequency.

[0011]

[0011] The present disclosure 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 presented herein for illustrative purposes only.Based on the teachings contained herein, additional embodiments will be apparent to those skilled in the art. [Brief explanation of the drawings]

[0012]

[0012] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate the present disclosure and, together with the description, serve to explain the principles of the present disclosure and to enable those skilled in the art to make and use the aspects described in this specification.

[0013] [Figure 1A] 1 illustrates a reflective lithographic apparatus according to some embodiments. [Figure 1B]

[0014] 1 illustrates a transmissive lithographic apparatus according to some embodiments. [Figure 2]

[0015] 1 illustrates details of a reflective lithographic apparatus according to some embodiments. [Figure 3]

[0016] 1 illustrates a lithographic cell according to some embodiments. [Figure 4A]

[0017] 1 illustrates an inspection apparatus according to some embodiments. [Figure 4B] 1 illustrates an inspection apparatus according to some embodiments. [Figure 5A]

[0018] 1 illustrates a signal that may be received at a lock-in detector, in accordance with some aspects. [Figure 5B] 1 illustrates a signal that may be received by a lock-in detector, in accordance with some aspects. [Figure 5C] 1 illustrates a signal that may be received by a lock-in detector, in accordance with some aspects. [Figure 5D] 1 illustrates a signal that may be received by a lock-in detector, in accordance with some aspects. [Figure 6]

[0019] 1 illustrates an inspection apparatus according to some embodiments. [Figure 7]

[0020] 1 illustrates a flow diagram of a detector according to some embodiments. [Figure 8]

[0021] 1 illustrates a flow diagram of a detection system according to some embodiments. [Figure 9]

[0021] A flow diagram of a detection system according to some embodiments is shown. [Figure 10]

[0022] 1 illustrates a detector according to some embodiments. [Figure 11A]

[0023] 1 illustrates a pupil plane through which an illumination beam propagates, according to some aspects. [Figure 11B] 1 illustrates a pupil plane through which an illumination beam propagates, according to some aspects. [Figure 12]

[0024] 1 illustrates a computer system according to some aspects. [Figure 13]

[0025] 1 illustrates a flow diagram of operations that may be used and performed by a detection system, according to some aspects. [Figure 14]

[0025] A flow diagram of operations that can be used and performed by a detection system according to some aspects is shown.

[0014]

[0026] Features of the present disclosure will become more apparent from the following detailed description when read in conjunction with the drawings. Like reference symbols identify corresponding elements throughout the drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Furthermore, the left-most digit(s) of a reference number generally identify the figure in which that reference number first appears. Unless otherwise indicated, the figures provided throughout this disclosure should not necessarily be construed as being drawn to scale. DETAILED DESCRIPTION OF THE INVENTION

[0015]

[0027] References herein to the embodiments described herein, as well as to "one embodiment," "an embodiment," "exemplary embodiment," "example embodiment," and the like, indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments necessarily include that particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it will be understood that it is within the knowledge of one of ordinary skill in the art to achieve that particular feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0016]

[0028] For ease of description, spatially relative terms such as "beneath," "below," "lower," "above," "on," "upper," and the like may be used herein to describe the relationship of one element or feature shown in the figures to one or more other elements or features. 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 in other orientations (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be similarly interpreted accordingly.

[0017]

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

[0018]

[0030] Aspects of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the present disclosure may also be implemented as instructions stored on a computer-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (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 actions. However, it will be appreciated that such description is merely for convenience and that such actions result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc. The term "machine-readable medium" may be interchangeable with similar terms, such as "computer program product," "computer-readable medium," and "non-transitory computer-readable medium." The term "non-transitory" may be used herein to characterize one or more forms of computer-readable medium other than transitory, propagating signals.

[0019]

[0031] However, before describing such aspects in further detail, it is beneficial to present an exemplary environment in which aspects of the present disclosure can be implemented.

[0020]

[0032] Exemplary Lithography System

[0021]

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

[0022]

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

[0023]

[0035] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to a reference frame, the design of at least one of lithographic apparatuses 100 and 100′, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may, for example, be a frame or a table, and may be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

[0024]

[0036] The term "patterning device" MA should be interpreted broadly as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0025]

[0037] Patterning device MA can be transmissive (lithographic apparatus 100′ in FIG. 1B) or reflective (lithographic apparatus 100 in FIG. 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, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam B in different directions. The tilted mirrors impart a pattern to a radiation beam B that is reflected by the small mirror matrix.

[0026]

[0038] The term "projection system" PS may encompass any type of projection system, including refractive optical systems, catadioptric systems, magnetic optical systems, electromagnetic optical systems, and electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and other factors such as the use of an immersion liquid or a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases may be too absorbing of the radiation or electrons. Therefore, a vacuum environment may be provided throughout the beam path using a vacuum wall and vacuum pumps.

[0027]

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

[0028]

[0040] The lithographic apparatus may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system and the substrate. Immersion liquid may also be provided to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. As used herein, the term "immersion" does not imply that a structure, such as a substrate, must be submerged in liquid. For example, a liquid may be located between the projection system and the substrate during exposure.

[0029]

[0041] 1A and 1B, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example if the radiation source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B is passed from the source SO to the illuminator IL using a beam delivery system BD (FIG. 1B), which may include, for example, appropriate directing mirrors and / or beam expanders. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example if the radiation source SO is a mercury lamp. The radiation system may include the radiation source SO, the illuminator IL, and / or the beam delivery system BD.

[0030]

[0042] The illuminator IL may include an adjuster AD (FIG. 1B) for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may include various other components (FIG. 1B), such as an integrator IN and a condenser CO. The illuminator IL may be used to adjust the radiation beam B so that it has a desired uniformity and intensity distribution in its cross-section.

[0031]

[0043] Referring to FIG. 1A, a radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. A second positioner PW and a position sensor IF2 (e.g., an interferometric device, a linear encoder, or a capacitive sensor) can be used to accurately move the substrate table WT (e.g., to position various target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. The patterning device (e.g., mask) MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0032]

[0044] Referring to Figure 1B, a radiation beam B is incident on a patterning device (e.g., mask MA), which is held on a support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. A portion of the radiation emanates from the intensity distribution in the illumination system pupil IPU and traverses the mask pattern without being subjected to diffraction at the mask pattern, producing an image of the intensity distribution in the illumination system pupil IPU.

[0033]

[0045] The projection system PS projects an image of the mask pattern MP onto a photoresist layer coated on the substrate W. This image is formed by diffracted beams generated from the mask pattern MP by radiation from the intensity distribution. For example, the mask pattern MP can include an array of lines and spaces. Diffraction of radiation other than the zeroth-order diffraction at the array generates redirected diffracted beams whose direction is changed perpendicular to the lines. The non-diffracted beams (i.e., so-called zeroth-order diffracted beams) traverse the pattern without changing their propagation direction. The zeroth-order diffracted beams traverse the upper lens or upper lens group of the projection system PS upstream of the pupil conjugate PPU of the projection system PS and reach the pupil conjugate PPU. The portion of the intensity distribution associated with the zeroth-order diffracted beam in the plane of the pupil conjugate PPU is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. For example, an aperture device PD is located at or substantially at the plane containing the pupil conjugate PPU of the projection system PS.

[0034]

[0046] The projection system PS is positioned (e.g., using a lens or lens group L) to capture the zeroth-order diffracted beam, the first-order diffracted beam, and / or higher-order diffracted beams (not shown). In some embodiments, the resolution-enhancing effect of dipole illumination can be exploited by using dipole illumination to image a line pattern extending in a direction perpendicular to the line. For example, a first-order diffracted beam interferes with a corresponding zeroth-order diffracted beam at the level of the wafer W to generate an image of the line pattern MP with the highest possible resolution and process window (e.g., usable depth of focus combined with an acceptable exposure dose deviation). In some embodiments, astigmatism can be reduced by providing radiation poles (not shown) in opposing quadrants of the illumination system pupil IPU. Furthermore, in some embodiments, astigmatism can be reduced by blocking the zeroth-order beam at the projection system pupil conjugate PPU associated with the radiation poles in the opposing quadrants. This is described in more detail in U.S. Patent No. 7,511,799 B2, issued March 31, 2009, which is incorporated herein by reference in its entirety.

[0035]

[0047] The second positioner PW and a position sensor IFD (e.g. an interferometric device, a linear encoder or a capacitive sensor) may be used to accurately move the substrate table WT (e.g. to position various target portions C in the path of the radiation beam B). Similarly, the first positioner PM and a further position sensor (not shown in FIG. 1B) may be used to accurately position the mask MA with respect to the path of the radiation beam B (e.g. after mechanical retrieval from a mask library or during a scan).

[0036]

[0048] In general, movement of the mask table MT may be realized using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks (as illustrated) occupy dedicated target portions, but they may also be located in spaces between the target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0037]

[0049] The mask table MT and patterning device MA may be located within a vacuum chamber V. In that case, an in-vacuum robot IVR can be used to move the patterning device, such as a mask, in and out of 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 can be calibrated to smoothly move any payload (e.g., a mask) to a fixed kinematic mount in a transfer station.

[0038]

[0050] Lithographic apparatus 100 and 100' can be used in at least one of the following modes:

[0039]

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

[0040]

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

[0041]

[0053] 3. In another mode, the support structure (e.g. mask table) MT holds a programmable patterning device and is kept substantially stationary, while the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be used, updating the programmable patterning device as required with each movement of the substrate table WT, or between successive radiation pulses during a scan. This mode of operation is readily applicable to maskless lithography using a programmable patterning device, such as a programmable mirror array.

[0042]

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

[0043]

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

[0044]

[0056] 2 shows lithographic apparatus 100 in more detail, including a source collector apparatus SO, an illumination system IL, and a projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained within an enclosure 220 of the source collector apparatus SO. The EUV radiation-emitting plasma 210 can be formed by a discharge-produced plasma source. In some embodiments, an excited (e.g., laser-excited) plasma of tin (Sn) is provided to generate the EUV radiation.

[0045]

[0057] Radiation emitted by the EUV radiation-emitting plasma 210 is delivered from the source chamber 211 into the collector chamber 212 through an optional gas barrier or contaminant trap 230 (sometimes also referred to as a contaminant barrier or foil trap) positioned in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further illustrated herein includes at least a channel structure.

[0046]

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

[0047]

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

[0048]

[0060] In general, there may be more elements in the illumination optics unit IL and the projection system PS than are shown. A grating spectral filter 240 may optionally be present, depending on the type of lithographic apparatus. Furthermore, there may be more mirrors than are shown in Figure 2. For example, there may be one to six additional reflective elements in the projection system PS compared to what is shown in Figure 2.

[0049]

[0061] 2 is shown as a nested collector with grazing incidence reflectors 253, 254, and 255, as just one example of a collector (or collector mirror). Grazing incidence reflectors 253, 254, and 255 are arranged axially symmetrically about optical axis O, and this type of collector optic CO is suitable for use in combination with a discharge-produced plasma source, often referred to as a DPP source.

[0050]

[0062] Exemplary Lithography Cell

[0051]

[0063] FIG. 3 illustrates a lithography cell 300, sometimes referred to as a lithocell or cluster, according to some embodiments. Lithography apparatus 100 or 100′ may form a portion of lithography cell 300. Lithography cell 300 may also include one or more devices that perform pre-exposure and post-exposure processes on a substrate. Conventionally, these may include a spin coater SC that deposits a resist layer, a developer DE that develops exposed resist, a chill plate CH, and a bake plate BK. A substrate handler or robot RO retrieves substrates from input / output ports I / O1, I / O2, moves them between various process tools, and delivers them to a loading bay LB of lithography apparatus 100, 100′. These devices, often collectively referred to as a track, are under the control of a track control unit TCU. The TCU is itself controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, these various tools can be operated to maximize throughput and processing efficiency.

[0052]

[0064] Exemplary Inspection Equipment

[0053]

[0065] To control the lithography process to accurately place device features on the substrate, alignment marks are typically provided on the substrate, and the lithography apparatus includes one or more inspection devices for accurately positioning the marks on the substrate. These alignment devices are essentially position measurement devices. Various types of marks and alignment devices and / or systems are known from different eras and different manufacturers. A type of system widely used in current lithography apparatus is based on self-referencing interferometers, such as those described in U.S. Pat. No. 6,961,116 (den Boef et al.). Typically, marks are measured separately to obtain X and Y positions. However, combined X and Y measurements can be performed using techniques described in U.S. Patent Publication No. 2009 / 195768A (Bijnen et al.). The entire contents of both of these disclosures are incorporated herein by reference.

[0054]

[0066] 4A shows a cross-sectional view of an inspection apparatus 400 that can be implemented as part of lithographic apparatus 100 or 100′, according to some embodiments. In some embodiments, inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device) MA. Inspection apparatus 400 can be further configured to detect positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate with respect to the patterning device or other components of lithographic apparatus 100 or 100′. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0055]

[0067] Terms such as "inspection apparatus," "metrology system," and the like may be used herein to refer to, for example, devices used to measure characteristics of structures (e.g., overlay sensors, critical dimension sensors, etc.), devices or systems used in lithography apparatus to inspect the alignment of wafers (e.g., alignment sensors), and the like.

[0056]

[0068] In some embodiments, the inspection 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 provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a wavelength spectrum of about 500 nm to about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a wavelength spectrum of about 500 nm to about 900 nm. The illumination system 412 may further be configured to provide one or more passbands with a substantially constant center wavelength (CWL) value over an extended period of time (e.g., the lifetime of the illumination system 412). Configuring the illumination system 412 in this manner may help prevent the actual CWL value from shifting from the desired CWL value in current alignment systems, as discussed above. Additionally, as a result, using a constant CWL value can improve the long-term stability and accuracy of an alignment system (eg, inspection tool 400) compared to current alignment tools.

[0057]

[0069] In some embodiments, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, as shown in FIG. 4A , radiation beam 413 can be split into radiation sub-beams 415 and 417. Beam splitter 414 can be further configured to direct radiation sub-beam 415 to a substrate 420 disposed on a stage 422. In one example, stage 422 is movable along direction 424. Radiation sub-beam 415 can be configured to illuminate an alignment mark or target 418 positioned on substrate 420. Alignment mark or target 418 can be coated with a radiation-sensitive film. In some embodiments, alignment mark or target 418 can have 180-degree (i.e., 180°) symmetry. That is, if the alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 can be substantially identical to the unrotated alignment mark or target 418. The target 418 on the substrate 420 can be (a) a resist layer grating consisting of bars formed with solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure consisting of a resist grating superimposed or interleaved on a product layer grating. Alternatively, the bars can be etched into the substrate. This pattern is sensitive to chromatic aberrations and illumination symmetry in the lithographic projection apparatus, particularly the projection system PL, and the presence of such aberrations will manifest as variations in the printed grating. One in-line method used in device fabrication to measure line widths, pitches, and critical dimensions utilizes a technique known as “scatterometry.”Scatterometry methods are 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 scatterometry, light is reflected by periodic structures within a target, and the resulting reflectance spectrum at a given angle is detected. The structure that generated the reflectance spectrum is reconstructed, for example, using rigorous coupled wave analysis (RCWA) or by comparison with a library of simulated patterns. Thus, scatterometry data from the printed grating is used to reconstruct the grating. Grating parameters, such as linewidth and shape, can be input to the reconstruction process, which is performed by the processing unit PU with knowledge of the printing step and / or other scatterometry processes.

[0058]

[0070] In some embodiments, beam splitter 414 may be further configured to receive diffracted radiation beam 419 and split diffracted radiation beam 419 into at least two radiation sub-beams, according to one embodiment. As shown in Figure 4A, diffracted radiation beam 419 may be split into diffracted radiation sub-beams 429 and 439.

[0059]

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

[0060]

[0072] As shown in Figure 4A, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 via beam splitter 414. In an exemplary embodiment, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In one example of this embodiment, interferometer 426 includes any suitable set of optical elements, such as a combination of prisms that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It will be appreciated that forming good quality images is not required; it may be sufficient to be able to resolve features of alignment mark 418. Interferometer 426 can further be configured to rotate one of the two images by 180° relative to the other, and to interferometrically recombine the rotated and un-rotated images.

[0061]

[0073] In some embodiments, when the alignment axis 421 of the inspection apparatus 400 passes through the center of symmetry (not shown) of the alignment mark or target 418, the detector 428 can be configured to receive the recombined image via the interferometer signal 427 and detect interference as a result of this recombined image. According to an exemplary embodiment, such interference can result from the alignment mark or target 418 being 180° symmetric, causing the recombined images to interfere constructively or destructively. Based on the detected interference, the detector 428 can be further configured to determine the location of the center of symmetry of the alignment mark or target 418 and thereby detect the position of the substrate 420. According to one example, the alignment axis 421 can be aligned with an optical beam perpendicular to the substrate 420 and pass through the center of the image rotation interferometer 426. The detector 428 can be further configured to estimate the position of the alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0062]

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

[0063]

[0075] 1. Measure the positional variation for different wavelengths (positional shift between colors).

[0064]

[0076] 2. Measure the positional variation for different orders (positional shift between diffraction orders).

[0065]

[0077] 3. Measure the position variation for different polarizations (position shift between polarizations).

[0066]

[0078] This data can 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 utilizes a self-referencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or the Athena (Advanced Technology using High order ENhancement of Alignment) sensor described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated herein by reference in their entirety.

[0067]

[0079] In some embodiments, the beam analyzer 430 can be configured to receive the diffracted radiation sub-beam 439 and determine its optical state. The optical state can be a measure of beam wavelength, polarization, or beam profile. The beam analyzer 430 can also be configured to determine the position of the stage 422 and correlate the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418 relative to the stage 422, and therefore the position of the substrate 420, can be precisely known. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection tool 400 or any other reference element, such that the center of symmetry of the alignment mark or target 418 relative to the inspection tool 400 or any other reference element can be known. The beam analyzer 430 can be a point or imaging polarimeter with some form of wavelength band selectivity. In some embodiments, the beam analyzer 430 can be directly integrated into the inspection tool 400, or, according to other embodiments, can be connected via some type of optical fiber, such as a polarization-maintaining single-mode, multimode, or image optical fiber.

[0068]

[0080] In some embodiments, the beam analyzer 430 can be further configured to determine overlay data between two patterns on the substrate 420. One of these patterns can be a reference pattern on the reference layer. The other pattern can be an exposure pattern on the exposed layer. The reference layer can be an etched layer already present on the substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by the lithographic apparatus 100 and / or 100′. The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on the substrate 420 by the lithographic apparatus 100 or 100′. The exposure pattern on the substrate 420 can correspond to movement of the substrate 420 by the stage 422. In some embodiments, the measured overlay data can also indicate an offset between the reference pattern and the exposed pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus 100 or 100', thereby minimizing the offset between the exposed layer and the reference layer after calibration.

[0069]

[0081] In some embodiments, the beam analyzer 430 can be further configured to determine a model of the product stack profile of the substrate 420 and measure the overlay, critical dimension, and focus of the target 418 in a single measurement. The product stack profile includes information about the laminated product, such as the alignment mark, the target 418, or the substrate 420, and can include mark process variation-induced optical signature metrology, which is a function of illumination variations. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. One example of a beam analyzer 430 is the Yieldstar™ manufactured by ASML (Veldhoven, The Netherlands) and described in U.S. Patent No. 8,706,442, which is incorporated herein by reference in its entirety. The beam analyzer 430 can be further configured to process information related to specific characteristics of the exposure pattern within that layer. For example, the beam analyzer 430 may process overlay parameters (a measure of the accuracy of positioning of a layer relative to a previous layer on the substrate, or the accuracy of positioning of a first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters of the image written within a layer (e.g., line width and its variation). Other parameters are image parameters related to the quality of the written image of the exposure pattern.

[0070]

[0082] In some embodiments, a detector array (not shown) can be connected to the beam analyzer 430, allowing for accurate stack profile detection, as discussed below. For example, the detector 428 can be a detector array. Several options for the detector array are possible, including a bundle of multimode fibers, discrete pin detectors per channel, or a CCD or CMOS (linear) array. Using a bundle of multimode fibers allows any dissipative elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range, but each requires a separate preamplifier, thus limiting the number of elements. A CCD linear array offers many elements that can be read out at high speed, making it particularly interesting when phase-stepping detection is used.

[0071]

[0083] In some embodiments, as shown in FIG. 4B , a second beam analyzer 430′ can be configured to receive the diffracted radiation sub-beam 429 and determine its optical state. The optical state can be a measurand of beam wavelength, polarization, or beam profile. The second beam analyzer 430′ can be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430′ can be configured to perform one or more of 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 center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418 relative to the stage 422, and therefore the position of the substrate 420, can be precisely known. The second beam analyzer 430′ can also be configured to determine the position of the inspection apparatus 400 or any other reference element, so that the center of symmetry of the alignment mark or target 418 relative to the inspection apparatus 400 or any other reference element can be known. The second beam analyzer 430′ can be further configured to determine overlay data between the two patterns and a model of the product stack profile on the substrate 420. The second beam analyzer 430′ can also be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement.

[0072]

[0084] In some embodiments, the second beam analyzer 430' may be directly integrated into the inspection apparatus 400, or according to other embodiments, may be connected via some type of optical fiber, such as a polarization-maintaining single-mode, multimode, or image optical fiber. Alternatively, the second beam analyzer 430' and the beam analyzer 430 may be combined to form a single analyzer (not shown) configured to receive both diffracted radiation sub-beams 429 and 439 and determine their optical states.

[0073]

[0085] In some embodiments, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 can be an overlay calculation processor. The information can include a model of the product stack profile constructed by the beam analyzer 430. Alternatively, the processor 432 can construct the model of the product mark profile using received information about the product marks. In either case, the processor 432 uses or incorporates the model of the product mark profile to construct a model of the stacked product and overlay mark profile. The stack model is then used to determine the overlay offset and minimize the spectral effects on the overlay offset measurement. The processor 432 can generate a basic correction algorithm based on the information received from the detector 428 and the beam analyzer 430. This information includes, but is not limited to, the optical state of the illumination beam, the alignment signal, associated position estimates, and the optical state at the pupil plane, image plane, and additional planes. The pupil plane is the plane where the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. The processor 432 can use basic correction algorithms to characterize the inspection tool 400 with reference to the wafer marks and / or alignment marks 418 .

[0074]

[0086] In some embodiments, the processor 432 can be further configured to determine the printed pattern position offset error relative to the sensor estimate at each mark based on information received from the detector 428 and the beam analyzer 430. This information includes, but is not limited to, the product stack profile, overlay measurements, critical dimensions, and focus of each alignment mark or target 418 on the substrate 420. The processor 432 can use a clustering algorithm to group the marks into sets of similar constant offset errors and generate an alignment error offset correction table based on the information. The clustering algorithm can be based on the overlay measurements, position estimates, and additional optical stack process information associated with each offset error set. Overlay is calculated for multiple different marks, for example, for overlay targets with positive and negative biases centered around a programmed overlay offset. The target measuring the smallest overlay is considered a reference (since it is measured with the highest accuracy). From this measured small overlay and from the known programmed overlay of the corresponding target, the overlay error can be inferred. Table 1 shows how this can be done. The minimum measured overlay in the example shown is -1 nm. However, the associated programmed overlay of the target is -30 nm. The process may have introduced an overlay error of 29 nm.

[0075] [Table 1]

[0076]

[0087] The minimum value can be considered a reference point, against which the offset between the measured overlay and that expected by the programmed overlay can be calculated. This offset determines the overlay error for each mark or set of marks with a similar offset. Thus, in the example of Table 1, at a target location with a programmed overlay of 30 nm, the minimum measured overlay is −1 nm. The difference between the predicted and measured overlay for other targets is compared to this reference. Also, a table like Table 1 can be obtained from the marks and targets 418 under various illumination settings. The illumination setting that produces the minimum overlay error and its corresponding calibration factor can be determined and selected. After this, the processor 432 can group the marks into sets with similar overlay errors. The criteria for grouping the marks can be adjusted based on different process controls, such as different error tolerances for different processes.

[0077]

[0088] In some embodiments, processor 432 can apply an individual offset correction from a clustering algorithm to each mark based on additional optical stack metrology, ensuring that all or most of the members of a group have similar offset errors. Processor 432 can determine a correction for each mark and feed the correction back to lithographic apparatus 100 or 100′ to correct for overlay errors, for example, by providing the correction to inspection apparatus 400.

[0078]

[0089] Exemplary Multi-Channel Lock-In Camera for Inspection Apparatus

[0079]

[0090] Market demands are driving the need for faster lithographic manufacturing of electronic chips (e.g., integrated circuits). However, to ensure that electronic chip devices are printed accurately, inspection systems such as those described above can be used to ensure that device manufacturing meets manufacturing tolerances.

[0080]

[0091] The term "throughput" is generally understood as the amount of material or articles passing through a system or process. In some aspects, the term "throughput" can be used to characterize lithographic manufacturing rates. For example, throughput can represent the rate at which lithographic manufacturing is completed for wafers, the rate at which wafers clear a particular manufacturing step and move on to the next step, etc. Throughput can be a performance marker for a lithographic apparatus. It is desirable for a lithographic system to output as many products as possible in as short a time as possible. Lithographic manufacturing can include several complex processes. Each part of the process can involve a trade-off between quality (e.g., sub-nanometer accuracy, high yield) and drawbacks (e.g., slower manufacturing speed, cost). Even small lithographic errors in circuit printing can result in non-conforming device behavior (e.g., defective devices). To improve pattern transfer accuracy, lithography can include inspection of marks printed on a substrate. Inspection can be used to verify the conformance of a pattern printed on a substrate or to align a substrate to properly receive a new pattern. However, the added time of the inspection process can adversely affect throughput.

[0081]

[0092] In some embodiments, optical inspection of targets on a wafer can be performed using illumination of multiple colors (or wavelengths). A given wavelength can provide information about the target that may not be readily apparent at another wavelength. As used herein, concepts such as "multiple wavelengths," "multiple photon frequencies," and "multiple parameter values" can be used to characterize narrow band values ​​of related properties or parameters. In a non-limiting example of a wavelength parameter, a first wavelength can be characterized as including a narrow band of wavelengths centered around a first central wavelength. A second wavelength can similarly be characterized as including a narrow band of wavelengths centered around a second central wavelength. Characterizing a first wavelength as different from a second wavelength can be interpreted as the first central wavelength being different from the second central wavelength.

[0082]

[0093] In some embodiments, enumerated adjectives (e.g., "first," "second," "third," etc.) can be used to distinguish between elements that share similarities, but do not dictate an order, hierarchy, or quantity (unless otherwise indicated). For example, the terms "first wavelength" and "second wavelength" can be used in the same way as "i wavelength" and "j wavelength" to distinguish between two moieties, but do not specify a particular order, hierarchy, or quantity. Furthermore, the elements in the figures are not limited to any particular enumerated adjective.

[0083]

[0094] In some embodiments, detector 428, beam analyzer 430, and / or beam analyzer 430′ (FIGS. 4A and 4B) can comprise an image-based detector (e.g., a camera). The camera can include multiple pixels to resolve the image (e.g., a charge-coupled device (CCD) camera). Commercially available cameras can typically be optimized for the human viewing experience (e.g., red-green-blue (RGB) color sensitivity). To achieve RGB sensitivity, commercially available cameras can implement color filters at each pixel. Specifically, a given pixel of the camera can be sensitive to a particular color (e.g., one pixel can have a red filter, the next pixel a green filter, the pixel after this one a blue filter, and this pattern is repeated for all pixels; other arrangements are possible).

[0084]

[0095] In some embodiments, color cameras such as those described above can present challenges for inspection sensors intended for use in lithography processes. For example, commercially available cameras may be inappropriate for lithography inspection because such inspections are performed using four or more wavelengths. Lithography inspections may use wavelengths outside the visible RGB range that are not covered by typical cameras. Lithography inspections are also concerned with signal-to-noise ratio (SNR).

[0085]

[0096] Furthermore, as inspection times are shortened to increase lithography throughput, the number of photons collected by the detector becomes an increasingly important factor. A drawback of color cameras with pixel filters is that a subset of all pixels may be limited to one specific color and not respond to photons of different colors. In other words, pixels that respond to green wavelengths reject photons with non-green wavelengths (the rejected photons are wasted). As a workaround, the deficiency of pixel color filters can be ameliorated by using a monochromatic camera, allowing the camera to accept all photons regardless of wavelength. However, this means that illumination can be provided by sequential wavelength stepping (e.g., first using far-infrared, then near-infrared, then red, then green, etc.) to enable color signals to be distinguished from one another. However, this can increase inspection times and unnecessarily reduce throughput.

[0086]

[0097] Embodiments disclosed herein enable simultaneous detection of multiple wavelengths using a monochromatic camera. Furthermore, embodiments disclosed herein are not limited to detecting multiple wavelengths, but are applicable to simultaneously detecting multiple settings of an adjustable parameter, multiple values ​​of a parameter that may have more than one value, or permutations of settings or values ​​of two or more parameters (e.g., 12 wavelengths, 10 wavelengths, 2 polarizations, 5 wavelengths at one polarization and 5 wavelengths at another polarization, 4 angles of incidence, etc.). For simplicity of discussion, embodiments are described in terms of wavelength and one pixel, but it will be appreciated that wavelength is just one possible parameter and that one pixel is one of many pixels in a camera.

[0087]

[0098] Before describing the implementation of lock-in in image-based inspection, it is useful to first present some general aspects of lock-in detection techniques.

[0088]

[0099] In some embodiments, lock-in detection can utilize the principles of a lock-in amplifier to provide highly sensitive detection and selective filtering of weak or noisy signals, improving SNR. Lock-in amplifier techniques can provide increased accuracy, faster detection times, and reduced noise when performing optical measurements such as alignment position sensing and multi-angle scatterometry. Lock-in detection can utilize homodyne (single frequency) detection, heterodyne (multiple frequency) detection, and other well-known variants and optimizations. For simplicity of discussion, embodiments disclosed herein are described using one frequency per lock-in channel (e.g., one modulation frequency per channel), but it should be understood that embodiments of the present disclosure using other well-known lock-in detection mechanisms are also contemplated.

[0089]

[0100] In some embodiments, single channel lock-in detection can operate by detecting signals with any number of frequency components. The lock-in detector can be given a specific frequency to search for. The lock-in detector then detects the specified modulation frequency f S All frequency components except for those with (the signal of interest) can be removed. The graph in Figure 5A illustrates a composite signal 502 that may be received by a lock-in detector, according to some embodiments.

[0090]

[0101] It should be noted that the graphs of Figures 5A, 5B, 5C, and 5D have a vertical axis representing signal amplitude and a horizontal axis representing time.

[0091]

[0102] In some embodiments, the composite signal 502 may have multiple frequency components (in the non-limiting example of FIG. 5A, there are three frequency components f, f, and f, plus noise. Typically, noise covers a frequency range, but for simplicity, f noise represents the noise frequency range). noiseThe components are visible as random jagged spikes of signal in the composite signal 502. Figure 5B shows a signal 504 corresponding to the f1 component. Figure 5C shows a signal 506 corresponding to the f2 component. Figure 5D shows a signal 508 corresponding to the f3 component.

[0092]

[0103] A desirable aspect of lock-in detection is that the detection technique detects non-f i The desired f while suppressing the component i For example, if a lock-in detector is configured to detect a signal at frequency f (signal 504), the lock-in detector can lock onto components f, f, and f of composite signal 502. noise The lock-in detector can essentially ignore the f component and lock onto the embedded signal 504. Thus, it can extract the amplitude I and phase φ of the f component from the composite signal 502. Similarly, the lock-in detector can extract the f component (which returns amplitude I and phase φ), the f component (which returns amplitude I and phase φ), or any f n It can be configured to lock onto the component.

[0093]

[0104] Extending this concept to multi-channel lock-in detection, each channel is driven by a distinct modulation frequency (f1, f2, f3, ..., f n ) can be configured to be highly sensitive to received signals of mixed frequencies. When a mixed-frequency signal is received, each detection channel can lock onto a corresponding frequency component of the signal while rejecting non-corresponding frequency components. This allows for the extraction of the amplitude and phase of each frequency component of the received signal.

[0094]

[0105] 6 illustrates an inspection apparatus 600 according to some embodiments. In some embodiments, features of inspection apparatus 600 can be implemented in inspection apparatus 400 (FIGS. 4A and / or 4B) to enable simultaneous multi-channel detection while using the structures described with reference to FIGS. 4A and / or 4B.

[0095]

[0106] In some embodiments, inspection apparatus 600 may include an illumination system 602 (or radiation source branch, illumination source branch, illumination branch, etc.), a detection system 604 (or detection branch, etc.), and an optical system 606.

[0096]

[0107] In some embodiments, illumination system 602 may include illumination source 608, modulator 610, and combiner 612. Illumination source 608 may include source elements 608-1 through 608-n (e.g., a first source element, a second source element, ..., an nth source element). Modulator 610 may include modulator elements 610-1 through 610-n (e.g., a first modulator element, a second modulator element, ..., an nth modulator element).

[0097]

[0108] In some embodiments, the detection system 604 may include a detector 614 and an analyzer 616 (it will be appreciated that a camera may have multiple analyzers 616 (e.g., one analyzer for each pixel), although a strict one-to-one correspondence is not required; see FIG. 9 ). The analyzer 616 may include analyzer elements 616-1 through 616-n (e.g., a first analyzer element, a second analyzer element, ..., an nth analyzer element). The analyzer elements 616-1 through 616-n may operate in the digital domain. It will be appreciated that portions of the optical system 606 may belong to the illumination system 602, the detection system 604, or both. For example, the optical system 606 may include an objective that collects scattered illumination from a target 618 disposed on a substrate 620. The optical system may include a beam splitter 414 (FIGS. 4A and 4B) that directs illumination from the illumination system 602 toward a target 618 and directs illumination scattered from the target 618 toward a detector 614.

[0098]

[0109] In some embodiments, the illumination system 602 and the detection system 604 can operate together to provide a lock-in detection function. The inspection system 600 can also include a reference system 622. The reference system 622 can act as a master clock and provide timing information (e.g., a master frequency, a modulation frequency, a tick count, etc.) to the illumination system 602 and the detection system 604. The modulation frequency can be based on the master frequency (e.g., a subharmonic of the master frequency). In one example, the timing information can be provided in the form of a periodic signal (e.g., a step function of a given frequency).

[0099]

[0110] In some embodiments, source elements 608-1 through 608-n respectively correspond to photon wavelengths λ through λ. n (e.g., a first wavelength, a second wavelength, ..., nth wavelength). Source elements 608-1 through 608-n can be coupled to modulator elements 610-1 through 610-n, respectively. Based on a master frequency, modulator elements 610-1 through 610-n can couple to wavelengths λ1 through λ2, respectively. n Lighting with frequencies f1 to f n (e.g., first frequency, second frequency, ..., nth frequency). This logic is n Lighting at frequency f n This applies to all combinations of sources and modulator elements up to modulator element 610-n, which can be modulated at frequencies f1 to f2. n Each of the ( ) can define a channel (eg, channels 1 to n, thus multi-channel).

[0100]

[0111] As alluded to above, modulation is not limited to wavelength, but may also be related to other illumination parameters or combinations of illumination parameters, for example, a first parameter may be related to illumination of a first polarization (and / or wavelength and / or angle of incidence), a second parameter may be related to illumination of a second polarization (and / or wavelength and / or angle of incidence), etc.

[0101]

[0112] In some embodiments, combiner 612 can combine differently parameterized illumination from source elements 608-1 through 608-n to generate illumination beam 624, which includes a mix of illumination parameters (various wavelengths, polarizations, incidence angles, etc.). Optical system 606 can direct illumination beam 624 toward target 618, which can scatter photons from illumination beam 624. The scattered illumination can be collected by optical system 606 and directed to detector 614 as scattered illumination 626. A desirable feature is that the parameterization of illumination beam 624 need not be sequential in time. All different parameters of illumination beam 624 can overlap in time (e.g., be simultaneous). This also applies to scattered illumination 626. A lock-in function in the detection branch can perform demodulation so that illumination with different illumination parameters can be distinguished. Demodulation can be defined as the process by which a modulated signal is extracted from its carrier signal.

[0102]

[0113] In some embodiments, detector 614 may include a camera. The camera may receive timing information (e.g., a master periodic reference signal having a master frequency) from reference system 622. It is desirable to have a camera with a very high sampling rate so that the true shape of the detected composite signal can be faithfully reproduced or sufficiently approximated.

[0103]

[0114] As mentioned above, this discussion focuses on a single pixel of detector 614, but it should be understood that other pixels may function similarly. The pixels of detector 614 may have a monochromatic response; that is, the pixel responds to each received photon regardless of parameterization (e.g., pixels are not rejected based on color, unlike the concept of a color camera with color filters). Each pixel may be, for example, a quantum image sensor (QIS), which is a photon-counting image sensor. Other types of pixelated sensors are also contemplated. Each pixel may generate a measurement signal 628 based on the amount of photons received. In some embodiments, as photons of scattered illumination 626 are received at a pixel of detector 614, the resulting measurement signal 628 from the pixel may be a composite signal. The illumination beam 624 may be modulated at modulation frequencies f1 through f2. n The effect of encoding the composite measurement signal 628 with modulation frequencies f1 to f n The composite measurement signal 628 thus contains information of different parameterizations provided by the illumination branches and the effects of interaction with the target 618 (e.g., the parameters can be multiple wavelengths, multiple wavelengths at one polarization, multiple wavelengths at another polarization, multiple angles of incidence, etc.). A non-limiting example of a composite signal (with three parameters) is shown in composite signal 502 (FIG. 5A).

[0104]

[0115] In some embodiments, analyzer elements 616-1 through 616-n can be used to demodulate measurement signal 628 into different channels 1 through n. Each channel provides the amplitude and phase of each frequency component (i.e., I and φ, I and φ, ..., I n and φ n) for all n parameter settings (e.g., wavelength, polarization, incident light, etc.). n ) and / or phase φ n In one non-limiting example of a four-wavelength measurement, the output of a multi-channel lock-in camera can be used to generate four images (one for each wavelength) of intensities I, I, I, and I from each pixel, and / or four images of phases φ, φ, φ, and φ from each pixel.

[0105]

[0116] In some aspects, photons are not intentionally rejected by the detector 614, allowing for efficient use of the entire intensity provided by the illumination source (as opposed to intentional color rejection by color filters in a color camera). Furthermore, because illumination with different parameters can overlap in time, this non-sequential aspect of the measurement technique allows for much faster inspection of one or more lithography targets 618 and a higher SNR due to the mechanism that does not reject photons.

[0106]

[0117] FIG. 7 shows a flow diagram of a detector 714 according to some embodiments. In some embodiments, the detector 714 may include similar structure and functionality to the detector 614 described with reference to FIG. 6. Accordingly, unless otherwise indicated, descriptions of elements in FIG. 6 are also applicable to corresponding elements in FIG. 7 (e.g., reference numbers share the rightmost two digits) and will not be reintroduced in detail. Such elements in FIG. 7 may include a scattered illumination 726 and a measurement signal 728. Structure and functionality can be inferred from descriptions of similar elements in FIG. 6.

[0107]

[0118] In some embodiments, the detector 714 can be a camera (e.g., a QIS camera). A QIS camera can have several desirable characteristics (e.g., high readout speed and low additive noise). The detector 714 can include pixels 730, a sample clock 732, a comparator 734, and a counter 736. The pixels 730, the sample clock 732, and the comparator 734 can operate in the analog domain 751 and the digital domain 753 (and can act as a transition between analog and digital). The counter 736 can operate in the digital domain.

[0108]

[0119] In some embodiments, pixel 730 can receive scattered illumination 726 (e.g., from target 618 (FIG. 6)). All pixels of detector 714, including pixel 730, can be sampled at a very high frequency rate (e.g., in the kHz to MHz range). The sampling rate can be determined by a sample clock 732. Furthermore, the sampling rate can be determined by modulation frequencies f1 to f n The sampling frequency can be set to a frequency that is an integer multiple of . The relationship between the sampling frequency and the modulation frequency can be such that the Nyquist criterion is met to avoid signal distortion (e.g., the highest usable frequency is less than half the sampling frequency). The criterion can be relaxed if the sampling frequency is much higher than the modulation frequency. The sampling frequency can be set to coincide with a master clock 755 (e.g., provided by reference system 622 (FIG. 6)).

[0109]

[0120] In some embodiments, the pixel 730 has a large intrinsic gain, which can reduce input-referred read noise. A high-gain / low-noise design enables single photon-to-electron resolution. A comparator 734 can receive the analog voltage (or current) signal from the pixel 730 and digitize the analog signal (thus, a comparator as disclosed herein can be referred to as an analog-to-digital converter, and a group of converters can be part of an analog-to-digital converter system). This results in a digital pulse train (pulse train 738) during the integration period. These pulses can be counted by a counter 736. The digital counting can be used to digitally estimate the photon arrival rate at the pixel, and therefore the intensity. The counter 736 can output a measurement signal 728. The measurement signal 728 (e.g., pixel output) can be processed and analyzed to determine the modulation frequencies f1-f. n The amplitude and / or phase of the different channels corresponding to the

[0110]

[0121] FIG. 8 shows a flow diagram of a detection system 804 according to some embodiments. In some embodiments, the detection system 804 may include similar structure and functionality to the detection systems and detectors described with reference to FIGS. 6 and 7. Accordingly, unless otherwise indicated, descriptions of elements in FIGS. 6 and 7 are also applicable to corresponding elements in FIG. 8 (e.g., reference numbers share the rightmost two digits) and will not be reintroduced in detail. Such elements in FIG. 8 may include a scattered illumination 826, a measurement signal 828, a pixel 830, a sample clock 832, a comparator 834, a pulse train 838, an analog domain 851, a digital domain 853, a master clock 855, and an analyzer 816. Structure and functionality can be inferred from the descriptions of similar elements in FIGS. 6 and 7.

[0111]

[0122] In some embodiments, the measurement signal 828 can be received by the analyzer 816. During a sampling period, the pulses of the pulse train 838 can be integrated using the counter 736 (FIG. 7) (e.g., the measurement signal 828 can include integrated pulses during the sampling period). In the absence of a dedicated counter (e.g., the counter 736 (FIG. 7)), the measurement signal 828 can include the pulse train 838. Alternatively, the analyzer 816 can receive digitized pulses (counts) as an input, and thus the analyzer 816 can be considered a counter.

[0112]

[0123] In some embodiments, multiple modulation frequencies f1 to f2 are obtained by utilizing analyzer elements of analyzer 816 (e.g., analyzer elements 616-1 to 616-n (FIG. 6)). n The analyzer can perform finite-time lock-in detection of intensity samples (pulses) at frequencies f1 to f n The analyzer 816 can implement pre-generated cosine and sine tables 857 corresponding to the frequency information. The frequency information can be determined based on a master frequency used to modulate lighting in the lighting system 602 (FIG. 6) (e.g., obtaining timing information from the reference system 622). The analyzer 816 can combine the pre-calculated sine and cosine tables with the data in the measurement signal 828 (e.g., element-wise multiplication, multiplication followed by addition, etc.).

[0113]

[0124] In some aspects, for discrete time sampling, a n and b n can be given the formula:

[0114]

number

[0115]

[0125] where s(i) is the sampled signal, n is the harmonic relative to the fundamental frequency, and P is the time period over which the analysis is performed (e.g., t meas ), N Pis the number of sampling points in one period, and Δt is the time interval between samples. In some aspects, the time sampled signal s(i) and the pre-computed elements a of the cosine and sine tables are n (i) and b n Element-wise multiplication with (i) can be performed. The element-wise multiplications can then be summed over one measurement period. The time sampling signal s(i) can be interpreted as the sum of detected photons divided by the detection time interval Δt. The division by Δt represents an intensity normalization step. The normalization step can be performed at a later stage or omitted entirely to simplify the process, for example if only relative intensities are of interest.

[0116]

[0126] In some embodiments, analyzer 816 calculates the cosine coefficients a1 through a2 using the calculations described above. n and sine coefficients b1 to b n can then be determined. Then, using sine and cosine coefficients, the intensities (amplitudes I1 to I n ) and / or phases φ1 to φ n The cosine coefficients a1 to a n and sine coefficients b1 to b n can be referred to as a Cartesian representation of amplitude and phase (i.e., in a non-limiting example, the amplitude and phase are expressed as the coefficients a of a Fourier series in cosine-sine form). n and b n(This can be expressed in Cartesian form as . It will be appreciated that a cosine-only or sine-only table may be used to simplify the analysis. A cosine-only (or sine-only) table implementation can be used for boundary conditions that are valid for the discrete cosine transform (e.g., when the carrier phase is not shifted). Analyzer 816 may be followed by another analyzer 817. Analyzer 817 may perform operations on the output of analyzer 816 to further refine the measurement data. For example, analyzer 817 may perform integration (sum), averaging, filtering, etc. It will be appreciated that analyzers 816 and 817 may be separate as shown, or may be a single device (e.g., a single computer, processor system, etc.).

[0117]

[0127] In some embodiments, the measurement sampling time t meas Finite-time detection can be performed by specifying a measurement sampling rate (i.e., the inverse of the measurement sampling rate, which may differ from the camera's sampling rate limit). The measurement sampling rate can be selected, for example, by configuring the detection system 804 to use a frequency that is divisible by the frequency of the master clock 855 (e.g., an integer multiple of the period of the master clock). The measurement sampling rate is determined by the frequencies f1 through f n can be configured to meet the Nyquist criterion for the highest frequency of

[0118]

[0128] In some embodiments, frequencies f1 to f n is the measurement integration time t meas or measurement integration time t meas That is, the period of each modulation frequency can form at least a portion of the Fourier components derived from t meas It can be fitted to the exact number of times within the frequencies f1 to f n may be evenly spaced in the frequency domain. To prevent channel crosstalk, frequencies f1 to f n can be chosen so that no frequency is a harmonic of another frequency. The measurement sampling rate fmeas is the frequency f1 to f n The integral can be an integer multiple of the frequency separation between at least two of the meas ), the techniques disclosed herein allow for a hardware-enabled base (lowest) t meas It is possible to extend the integration time to a multiple of f1~f. However, it should be noted that this affects the frequency space. n In situations where combinations of all satisfy the condition of having integer multiples of the period, the use of double, triple, or even larger multiples of this time period may still be satisfactory. Conversely, extending the measurement time, for example by a factor of two, may halve the frequency separation, but this is not required.

[0119]

[0129] In some embodiments, additional constraints on the modulation frequency can be further defined to improve the performance of the detection system 804. The total measurement time can include a first time period and a second time period. The first time period can be the time at the beginning of the measurement when the inspection device is in a steady state (e.g., illumination is on, modulation is operating, and the target is in the field of view of the inspection device). The second time period can be the time during which the signal from the target is analyzed (e.g., t meas The channel separation (in frequency) may be an exact multiple of the reciprocal of the sum of the first and second time periods.

[0120]

[0130] In some embodiments, the number of operations per pixel can be significantly greater than the basic QIS flow shown in Figure 7. Therefore, it is desirable to process the operations digitally to take advantage of the ever-increasing advances in computer power.

[0121]

[0131] Although FIG. 8 shows single pixel processing of lock-in detection, it is envisioned that it is also possible to combine analysis streams by multiple pixels (eg, multiplexing and demultiplexing).

[0122]

[0132] FIG. 9 illustrates a flow diagram of a detection system 904 according to some embodiments. In some embodiments, the detection system 904 may include similar structure and functionality to the detection systems and detectors described with reference to FIGS. 6 through 8. Accordingly, unless otherwise indicated, descriptions of elements in FIGS. 6 through 8 are also applicable to corresponding elements in FIG. 9 (e.g., reference numerals share the rightmost two digits) and will not be reintroduced in detail. Such elements in FIG. 9 may include a scattered illumination 926, a measurement signal 928, pixels 930-1 through 930-m, a sample clock 932, a comparator 934, an analog domain 951, a digital domain 953, a master clock 955, and analyzers 916 and 917. Structure and functionality can be inferred from the descriptions of similar elements in FIGS. 6 through 8.

[0123]

[0133] In some embodiments, the detection system may also include a pixel readout combiner 940 (e.g., a multiplexer) and a demultiplexer 942. The pixel readout combiner 940 may combine analog signals generated by the pixels 930-1 through 930-n as a result of receiving the scattered illumination 926. The illumination incident on each of the pixels 930-1 through 930-n may have n parameters (i.e., n modulation frequencies associated with photon wavelength, polarization, angle, etc.). The pixel readout combiner 940 and demultiplexer 942 interact with the sample clock 932 to enable the measurement signal 928 to include a demultiplexed pulse train. The demultiplexed pulse train can be distinguished based on its association with each of the pixels 930-1 through 930-n. The analyzer 916 may be used for finite-time lock-in detection of data streams originating from multiple pixels (as opposed to the single pixel shown in FIG. 8 ). Alternatively, the measurement signal 928 may be demultiplexed and sent to each of multiple analyzers. In an analyzer system, multiple analyzers can be grouped together.

[0124]

[0134] Figure 10 illustrates a detector 1014 according to some embodiments. In some embodiments, the detector 1014 may include similar structure and functionality to the detection systems and detectors described with reference to Figures 6 through 9. Thus, unless otherwise indicated, descriptions of elements in Figures 6 through 9 are also applicable to corresponding elements in Figure 10 (e.g., reference numerals share the rightmost two digits) and will not be reintroduced in detail.

[0125]

[0135] In some embodiments, the detector 1014 can be an integrated QIS camera with stacked layers. The detector 1014 can include a pixel layer 1044, a mixed-signal IC layer 1046, and a logic layer 1048 (e.g., first, second, and third layers, respectively). The pixel layer can receive illumination for subsequent conversion to a digital signal. The mixed-signal IC layer 1046 can convert analog signals generated in the pixel layer to digital signals (e.g., the comparator described above can be part of the mixed-signal IC layer 1046). Components such as the analyzer described above can be part of the logic layer 1048. The logic layer 1048 can provide digital processing for finite-time lock-in detection.

[0126]

[0136] 11A and 11B illustrate a pupil plane 1150 through which an illumination beam 1124 propagates, according to some embodiments. In some embodiments, elements in FIGS. 11A and 11B may be similar to some elements described with reference to FIGS. 6 through 10. Thus, unless otherwise indicated, descriptions of elements in FIGS. 6 through 10 also apply to corresponding elements in FIGS. 11A and 11B (e.g., reference numerals share the rightmost two digits) and will not be reintroduced in detail. Such elements in FIGS. 11A and 11B may include an illumination beam 1124, a target 1118, and a substrate 1120. Structure and function can be inferred from descriptions of similar elements in FIGS. 6 through 8.

[0127]

[0137] In some embodiments, the illumination beam 1124 can include two or more illumination beams, such as beams 1 through k (in this non-limiting example, k is 12). FIG. 11A shows a front view of the pupil plane 1150 with the optical axis at the center, and also shows the arrangement of beams 1 through k. For clarity, FIG. 11B shows only beams 1, 2, 7, and 8. Beam 1 can be diametrically opposed to beam 7. Beam 2 can be diametrically opposed to beam 8. The setup shown in FIGS. 11A and 11B is useful for performing angle-resolved scatterometry. By performing inspections using different angles of incidence, different information about the target 1118 can be obtained. As shown, beams 2 and 8 can have an angle of incidence α on the target 1118, and beams 1 and 7 can have an angle of incidence β on the target 1118. Optical elements (e.g., lenses) can be positioned at or proximate to the pupil plane 1150 so that beams 1 through k converge at the target 1118.

[0128]

[0138] In some embodiments, it may be desirable to overlap the "on" periods of beams 1-k in time (e.g., simultaneously) to reduce measurement time (and thereby increase throughput). Scattered illumination from target 1118 can then be scattered and directed to the detector. The challenge then is to analyze the received radiation to identify which portion of the detected radiation corresponds to which portion of the delivered beams 1-k. This is where the lock-in camera techniques described herein can be utilized. Each of beams 1-k can be assigned to a channel. That is, each beam can be modulated at a given frequency 1-n. In the simplest case, n can be equal to k. In embodiments where each beam has more than one parameter (e.g., wavelength and / or polarization), more modulation frequencies can be introduced (e.g., two wavelengths for each of 12 beams could implement 24 modulation frequencies).

[0129]

[0139] 12 illustrates a computer system 1200 according to some aspects. Various aspects and components thereof may be implemented using, for example, computer system 1200 or any other known computer system.

[0130]

[0140] In some aspects, computer system 1200 may include one or more processors (also referred to as central processing units or CPUs), such as processor 1204. Processor 1204 may be connected to a communication infrastructure or bus 1206.

[0131]

[0141] In some embodiments, each of the one or more processors 1204 may be a graphics processing unit (GPU). In some embodiments, a GPU is a processor that is a specialized electronic circuit designed to process mathematically intensive applications. A GPU may have an efficient parallel structure for parallel processing of large blocks of data, such as mathematically intensive data common in computer graphics applications, images, videos, etc.

[0132]

[0142] In some embodiments, computer system 1200 may further include one or more user input / output devices 1203, such as a monitor, keyboard, pointing device, which communicate with communications infrastructure 1206 via one or more user input / output interfaces 1202. Computer system 1200 may also include main or primary memory 1208, such as random access memory (RAM). Main memory 1208 may include one or more levels of cache. Main memory 1208 stores control logic (i.e., computer software) and / or data.

[0133]

[0143] In some embodiments, computer system 1200 may further include one or more secondary storage devices or memories 1210. Secondary memory 1210 may include, for example, a hard disk drive 1212 and / or a removable storage device or drive 1214. Removable storage drive 1214 may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, a tape backup device, and / or any other storage device / drive. Removable storage drive 1214 may interface with a removable storage unit 1218. Removable storage unit 1218 may include a computer-usable or readable storage device on which computer software (control logic) and / or data is stored. Removable storage unit 1218 may be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and / or any other computer data storage device. The removable storage drive 1214 reads from and / or writes to the removable storage unit 1218 in well-known fashion.

[0134]

[0144] In some embodiments, secondary memory 1210 may include other means, implements, or approaches for enabling computer system 1200 to access computer programs and / or other instructions and / or data. Such means, implements, or approaches may include, for example, a removable storage unit 1222 and interface 1220. Examples of removable storage unit 1222 and interface 1220 may include a program cartridge and cartridge interface (such as those found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface.

[0135]

[0145] In some aspects, computer system 1200 may further include a communications or network interface 1224. Communications interface 1224 enables computer system 1200 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively designated by reference numeral 1228). For example, communications interface 1224 enables computer system 1200 to communicate with remote devices 1228 via communications path 1226. Communications path 1226 may be wired and / or wireless and may include any combination of a LAN, a WAN, the Internet, etc. Control logic and / or data may be transmitted to and from computer system 1200 via communications path 1226.

[0136]

[0146] In some embodiments, it is contemplated that the lock-in function can be implemented in a variety of ways. For example, meas can be set to the smallest possible value so that there is a sufficient set of optical signals to discern a useful SNR. meas may correspond to one or more cycles of the modulated signal (e.g., 2π radians). For efficiency, the pre-generated cosine and / or sine tables described above may cover some finite time range (e.g., t described in the non-limiting examples above). meas However, if measurements are taken over a longer period (e.g., aggregating over a longer period than the minimum to improve SNR), the limited pre-generated cosine and / or sine tables must be expanded by a corresponding amount, which can add to the hardware resources required for analysis, increasing cost and complexity.

[0137]

[0147] In some aspects, the pre-generated tables and their use can be implemented in a manner that simplifies digital computation.

[0138]

[0148] 13 illustrates a flow diagram 1300 of operations performed in connection with the detection system disclosed herein, according to some embodiments. In some embodiments, the flow diagram 1300 can be implemented by any one or combination of the analyzers 616, 816, 817, 916, and / or 917 (FIGS. 6, 8, and 9). The pre-generated table 1302 (e.g., a cosine table, a sine table, etc.) can include discrete elements (element numbers are tracked by index j). The values ​​in the pre-generated table 1302 are p1, p2, p3, ..., p j Any of the detection systems disclosed herein can generate a measurement signal 1304 based on receiving scattered illumination from a target. The measurement signal 1304 can be discretized (e.g., in digital form) and its elements considered in relation to the index j used to describe the pre-generated table 1302 (e.g., m j , m j+1 , m j+2 etc.). element m j may be the first element of the measurement signal 1304. In some aspects, other elements may be j may precede.

[0139]

[0149] In some aspects, analysis of the measured signal 1304 can be performed by combining the measured signal 1304 with the pre-generated table 1302 (e.g., by a multiplication operation 1306). For example, multiplication p j ×m j The result is the quantity v j Since the pre-generation 1302 may correspond to a periodic table (e.g., a cosine table with a periodicity of j elements), the next pre-generated table element in the multiplication is p1×m j+1 and the quantity v j+1 This operation can be performed multiple times for the corresponding discrete elements (e.g., v j+2 etc.), which can be shown as quantity 1308. Quantity 1308 is the integration period (e.g., t meas) (e.g., by an addition operation 1310). The aggregation operation may involve a normalization operation based on the number of elements added (e.g., to extract the correct value of the amplitude of the modulation). The aggregation may be output 1312. This output may be a coefficient a that allows for the determination of the phase or amplitude. n and b n (The power coefficients are also shown in Figures 8 and 9).

[0140]

[0150] In some embodiments, the pre-generated table 1302 can be implemented with a circular shift register 1314 to increase analysis efficiency. meas If is set to a time period longer than one cycle of the cosine / sine table, the table 1302 can be repeated by the circular register 1314. To facilitate the use of the shift register 1314, a condition can be imposed to perform the summing operation 1310 over a length that is an exact multiple of the corresponding modulation period. In some aspects, if the summing operation 1310 is performed for each modulation channel, there may be a condition to perform the summing operation 1310 for an exact multiple of each modulation period. Using a pre-generated table 1302 can be more efficient than extrapolating or pre-loading additional elements that extend the pre-generated table 1302.

[0141]

[0151] In some embodiments, the process can be reset and restarted for the next integration period. The process can be repeated for multiple different pre-generated tables corresponding to different modulation frequencies, allowing information to be extracted from different modulation channels. One or more of the operations in flow diagram 1300 can be performed using the camera's processor or an external processor (e.g., a personal computer's CPU or GPU).

[0142]

[0152] FIG. 14 illustrates a flow diagram 1400 of operations performed in connection with a detection system disclosed herein, according to some embodiments. In some embodiments, flow diagram 1400 may share some features in common with flow diagram 1300 (FIG. 13). Unless otherwise indicated, descriptions of elements in FIG. 13 may also apply to FIG. 14. Elements appearing in FIG. 14 that correspond to elements in FIG. 13 may have similar reference numbers (e.g., reference numbers share the two rightmost digits). Examples of such elements in FIG. 6 may include, for example, a pre-generated table 1402, a measurement signal 1404, a multiplication operation 1406, a quantity 1408, an addition operation 1410, and an output 1412.

[0143]

[0153] In some aspects, a storage register 1416 can be implemented in addition to one or more processes already described with reference to FIG. 13 . The storage register 1416 can be used to store the quantity 1408 in memory (e.g., RAM, cache, non-volatile memory, etc.). The value of the quantity 1408 stored by the storage register 1416 can then be subtracted (e.g., by a subtraction operation 1418) from the sum output by the addition operation 1410. The subtraction can be time-aligned to cover the entire measurement time. The entire measurement time can include a first time period and a second time period as described above. The delay can shift the time window of the aggregation (e.g., a moving time window for the addition operation 1410). This implementation can reduce the coefficient a n and b n (output 1412). This form of continuous output can be considered a form of "finite impulse response" filter. Finite impulse response (FIR) filters settle to zero in a finite time and are therefore considered filters whose impulse response (or response to any finite length input) is of finite duration. This is in contrast to infinite impulse response (IIR) filters, which have internal feedback and can continue to respond indefinitely or for long periods of time.

[0144]

[0154] In some aspects, the operations of flow diagram 1400 (and 1300 (FIG. 13)) can be performed at a speed that matches the sampling rate of the detection system. However, this can result in a very large data output volume. The problem of large data output can be mitigated by implementing a decimation operation 1420 on output 1412. Also, by implementing appropriate input from an external timing mechanism, continuous output can be achieved in flow diagram 1300 (FIG. 13).

[0145]

[0155] In some aspects, a non-transitory, tangible apparatus or article of manufacture comprising a non-transitory, tangible computer-usable or computer-readable medium having control logic (software) stored thereon is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 1200, main memory 1208, secondary memory 1210, removable storage units 1218 and 1222, and tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system 1200), causes such data processing devices to operate as described herein.

[0146]

[0156] Based on the teachings contained herein, it will be apparent to one skilled in the art how to make and use aspects of the present disclosure with data processing devices, computer systems, and / or computer architectures other than those shown in Figure 12. In particular, the aspects described herein may operate with software, hardware, and / or operating system implementations other than those described herein.

[0147]

[0157] The embodiments can be further described using the following clauses.

[0148] 1. An illumination system configured to transmit illumination toward a target, the illumination having a plurality of illumination parameters associated with a corresponding plurality of modulation frequencies; a camera configured to receive scattered illumination from the target, the camera configured to generate, for each pixel of the camera, a measurement signal encoded with a signature of a plurality of modulation frequencies; an analyzer system configured to demodulate, for each pixel of the camera, a measurement signal based on a plurality of modulation frequencies and to output a phase, an amplitude, or a phase and an amplitude of a demodulated component of the measurement signal corresponding to the modulation frequencies; A metrology system comprising: 2. The metrology system of clause 1, wherein the illumination system mixes different illumination parameters from a set of parameters. 3. The metrology system of clause 2, wherein the set of parameters includes one or more wavelengths, one or more polarizations, and one or more angles of incidence at the target. 4. The lighting system is further configured to simultaneously apply multiple lighting parameters to the transmitted lighting; 10. The metrology system of claim 1, wherein the analyzer system is further configured to perform demodulation for multiple illumination parameters simultaneously. 5. A multiplexer configured to combine measurement signals from groups of pixels of the camera; 10. The metrology system of claim 1, further comprising: a demultiplexer configured to demultiplex the combined measurement signal, wherein demodulation of the measurement signal is performed using the demultiplexed measurement signal. 6. The metrology system of clause 1, wherein each pixel of the camera is sensitive to multiple wavelengths in parallel. 7. The metrology system of clause 1, wherein the camera structure is layered and includes a pixel layer, an analog-digital layer, and a logic layer. 8. The metrology system of clause 1, further comprising a time reference system configured to provide a timing base for each of the modulation frequencies. 9. The metrology system of clause 1, further comprising a digital-to-analog converter system configured to receive measurement signals in analog form from pixels of the camera and to output measurement signals in digital form. 10. The demodulation of the measurement signal is performed at the measurement sampling time t meas is characterized by t meas 10. The metrology system of claim 1, wherein: 11. The demodulation of the measurement signal is performed at a measurement sampling rate f meas is characterized by f meas 10. The metrology system of claim 1, wherein t is an integer multiple of a frequency separation between at least two of the modulation frequencies. 12. The metrology system of clause 1, wherein the analyzer system is further configured to perform demodulation of the measurement signal by combining data in the measurement signal with at least a table of cosines, at least a table of sines, one or more sine-only tables, or one or more cosine-only tables. 13. The metrology system of clause 12, wherein the data combination is performed by a multiplication operation. 14. The metrology system of clause 12, wherein the analyzer system is further configured to perform demodulation of the measurement signal using a shift register on at least a table of cosines, at least a table of sines, one or more sine-only tables, or one or more cosine-only tables. 15. The output of a data combination is multiple discrete quantities. 13. The metrology system of clause 12, wherein the analyzer system is further configured to aggregate discrete quantities. 16. The aggregation of discrete quantities is measured at a sampling time t meas 16. The metrology system of claim 15, wherein the metrology system is implemented in 17. The metrology system of clause 15, wherein aggregation of discrete quantities is performed in moving time windows. 18. The metrology system of clause 17, wherein the output of the phase, amplitude, or phase and amplitude of the demodulation components is performed continuously based on a moving time window. 19. The metrology system of clause 18, wherein the analyzer system is further configured to decimate the continuous output based on a moving time window to reduce the camera's per pixel data output rate. 20. An illumination source configured to illuminate a pattern on a patterning device; a projection system configured to project an image of the pattern onto the substrate; 1. A metrology system comprising: an illumination system further configured to transmit illumination toward the target, the illumination having a plurality of illumination parameters associated with a corresponding plurality of modulation frequencies; a camera configured to receive scattered illumination from the target, the camera configured to generate, for each pixel of the camera, a measurement signal encoded with a signature of a plurality of modulation frequencies; an analyzer system configured to demodulate, for each pixel of the camera, a measurement signal based on a plurality of modulation frequencies and to output a phase, an amplitude, or a phase and an amplitude of a demodulated component of the measurement signal corresponding to the modulation frequencies; a metrology system including: 1. A lithographic apparatus comprising: 21. A lithographic apparatus according to clause 20, wherein the illumination system mixes different illumination parameters from a set of parameters. 22. A lithographic apparatus according to clause 21, wherein the set of parameters comprises one or more wavelengths, one or more polarizations, and one or more angles of incidence at the target. 23. The lighting system is further configured to simultaneously apply multiple lighting parameters to the transmitted lighting; 21. The lithographic apparatus of clause 20, wherein the analyzer system is further configured to perform demodulation for multiple illumination parameters simultaneously. 24. A multiplexer configured to combine measurement signals from groups of pixels of the camera; 21. The lithographic apparatus of clause 20, further comprising a demultiplexer configured to demultiplex the combined measurement signal, wherein demodulation of the measurement signal is performed using the demultiplexed measurement signal. 25. A lithographic apparatus according to clause 20, wherein each pixel of the camera is sensitive to multiple wavelengths in parallel. 26. A lithographic apparatus according to clause 20, wherein the camera structure is layered and includes a pixel layer, an analog-digital layer, and a logic layer. 27. A lithographic apparatus according to clause 20, further comprising a time reference system configured to provide a timing base for each of the modulation frequencies. 28. A lithographic apparatus according to clause 20, further comprising a digital-to-analog converter system configured to receive measurement signals in analog form from pixels of the camera and to output measurement signals in digital form. 29. The demodulation of the measurement signal is performed at the measurement sampling time t meas is characterized by t meas 21. The lithographic apparatus of clause 20, wherein is an integer multiple of the period of the modulation frequency. 30. The demodulation of the measurement signal is performed at a measurement sampling rate f meas is characterized by f meas 21. The lithographic apparatus of clause 20, wherein ≡ is an integer multiple of a frequency separation between at least two of the modulation frequencies. 31. A lithographic apparatus according to clause 20, wherein the analyser system is further configured to perform demodulation of the measurement signal by combining data in the measurement signal with a table of at least cosines, a table of at least sines, one or more sine-only tables or one or more cosine-only tables. 32. A lithographic apparatus according to clause 31, wherein the data combination is performed by a multiplication operation. 33. A lithographic apparatus according to clause 31, wherein the analyser system is further configured to perform demodulation of the measurement signal using a shift register on at least a table of cosines, at least a table of sines, one or more sine-only tables or one or more cosine-only tables. 34. The output of a data combination is multiple discrete quantities. 32. The lithographic apparatus of clause 31, wherein the analyzer system is further configured to aggregate the discrete quantities. 35. The aggregation of discrete quantities is measured at sampling time t meas 35. A lithographic apparatus according to clause 34, wherein the lithographic apparatus is implemented in 36. A lithographic apparatus according to clause 34, wherein the aggregation of discrete quantities is performed in a moving time window. 37. A lithographic apparatus according to clause 36, wherein the output of the phase, amplitude or phase and amplitude of the demodulation components is performed continuously based on a moving time window. 38. The metrology system of clause 37, wherein the analyzer system is further configured to decimate the continuous output based on a moving time window to reduce the camera's per pixel data output rate.

[0149]

[0158] As used herein, terms such as "radiation," "beam," "light," "illumination," and the like can refer to one or more types of electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5 to 100 nm, such as 13.5 nm), or hard X-rays operating below 5 nm, and particle beams such as ion beams or electron beams. Generally, radiation having a wavelength of about 400 to about 700 nm is considered visible radiation. Radiation having a wavelength of about 780 to 3000 nm (or longer) is considered IR radiation. UV refers to radiation having a wavelength of about 100 to 400 nm. Within lithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps, i.e., G-line 436 nm, H-line 405 nm, and / or I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gases), refers to radiation having a wavelength of approximately 100-200 nm. Deep ultraviolet (DUV) generally refers to radiation having a wavelength in the range of 126 nm to 428 nm, and in some embodiments, excimer lasers can generate DUV radiation for use in lithography equipment. It will be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm, refers to radiation having a particular wavelength band at least part of which falls within the range of 5-20 nm.

[0150]

[0159] Although some aspects of the present disclosure are described in the context of a lithography apparatus in the manufacture of ICs, it should be understood that the lithography apparatus described herein can be used in other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin-film magnetic heads, and the like. In light of these alternative applications, those skilled in the art will recognize that the terms "wafer" or "die" used herein may be considered specific examples of the more general terms "substrate" or "target portion," respectively. The substrate may be processed, before or after exposure, in, for example, a track unit (a tool that typically applies a layer of resist to the substrate and develops the exposed resist) and / or a metrology unit. Where appropriate, aspects disclosed herein can be applied to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example, to produce a multi-layer IC; thus, the term "substrate," as used herein, can also refer to a substrate that already includes multiple processed layers.

[0151]

[0160] Additionally, while some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device is imprinted into a layer of resist supplied to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is then removed from the resist, leaving a pattern in it after the resist is cured.

[0152]

[0161] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, and thus should be interpreted by one of ordinary skill in the art in light of the teachings herein.

[0153]

[0162] The present disclosure has been described above using functional components illustrating the implementation of specific functions and their relationships. The boundaries of these functional components have been arbitrarily defined herein for the convenience of description. Alternative boundaries may be defined so long as the specific functions and their relationships are appropriately performed. The foregoing description of specific embodiments sufficiently reveals the overall nature of the present disclosure, such that those skilled in the art can readily modify and / or adapt such specific embodiments for various applications without undue experimentation and without departing from the overall concept of the present disclosure. Accordingly, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0154]

[0163] It is understood that the "Detailed Description" section, and not the "Summary" and "Abstract" sections, are intended to be used to interpret the claims. The "Summary" and "Abstract" sections may describe one or more aspects of the disclosure as envisioned by the inventors, but cannot describe all aspects, and thus are not intended to limit the scope of the disclosure and the appended claims in any way. The breadth and scope of protected subject matter should not be limited by any of the above-described aspects, but is instead defined by the following claims and their equivalents.

Claims

1. an illumination system configured to transmit illumination toward a target, the illumination having a plurality of illumination parameters associated with a corresponding plurality of modulation frequencies; a camera configured to receive scattered illumination from the target, the camera configured to generate, for each pixel of the camera, a measurement signal encoded with a signature of the plurality of modulation frequencies; an analyzer system configured, for each pixel of the camera, to demodulate the measurement signal based on the plurality of modulation frequencies and to output the phase, amplitude, or the phase and amplitude of the demodulated components of the measurement signal corresponding to the modulation frequencies; A metrology system comprising:

2. The metrology system of claim 1 , wherein the illumination system blends different illumination parameters from a set of parameters.

3. The metrology system of claim 2 , wherein the set of parameters comprises one or more wavelengths, one or more polarizations, and one or more angles of incidence at the target.

4. the lighting system is further configured to simultaneously apply the plurality of lighting parameters to the transmitted lighting; The metrology system of claim 1 , wherein the analyzer system is further configured to perform the demodulation for the plurality of illumination parameters simultaneously.

5. a multiplexer configured to combine measurement signals from groups of pixels of the camera; 10. The metrology system of claim 1, further comprising: a demultiplexer configured to demultiplex the combined measurement signal, wherein demodulation of the measurement signal is performed using the demultiplexed measurement signal.

6. The metrology system of claim 1 , wherein each pixel of the camera is sensitive to multiple wavelengths in parallel.

7. 10. The metrology system of claim 1, wherein the camera structure is layered and includes a pixel layer, an analog-to-digital layer, and a logic layer.

8. The metrology system of claim 1 , further comprising a time reference system configured to provide a timing base for each of the modulation frequencies.

9. 10. The metrology system of claim 1, further comprising a digital-to-analog converter system configured to receive the measurement signals in analog form from pixels of the camera and to output the measurement signals in digital form.

10. The demodulation of the measurement signal is performed at a measurement sampling time t ｍｅａｓ is characterized by t ｍｅａｓ 2. The metrology system of claim 1, wherein is an integer multiple of the period of the modulation frequency.

11. The demodulation of the measurement signal is performed at a measurement sampling rate f ｍｅａｓ is characterized by f ｍｅａｓ 10. The metrology system of claim 1, wherein .times. ...

12. 10. The metrology system of claim 1, wherein the analyzer system is further configured to perform the demodulation of the measurement signal by combining data in the measurement signal with a table of at least cosines, a table of at least sines, one or more sine-only tables, or one or more cosine-only tables.

13. The metrology system of claim 12 , wherein the combining of the data is performed by a multiplication operation.

14. 13. The metrology system of claim 12, wherein the analyzer system is further configured to perform the demodulation of the measurement signal using a shift register on the at least cosine table, the at least sine table, the one or more sine-only tables, or the one or more cosine-only tables.

15. the output of said combination of said data is a plurality of discrete quantities; The metrology system of claim 12 , wherein the analyzer system is further configured to aggregate the discrete quantities.

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