Multi-channel phase-locked camera for multi-parameter sensing in lithographic processes

Abstract

A metrology system may include an illumination system, a camera, and an analyzer system. The illumination system sends illumination towards 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 the identification marks of the plurality of modulation frequencies. The analyzer system demodulates the measurement signal based on the plurality of modulation frequencies for each pixel of the camera, and outputs a phase, an amplitude, or the phase and the amplitude of a demodulated component of the measurement signal corresponding to the modulation frequencies.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to U.S. Application No. US63 / 477,929, filed on December 30, 2022, and U.S. Application No. US63 / 509,432, filed on June 21, 2023, both of which are hereby incorporated by reference in their entirety. Technical field

[0003] The present disclosure relates to inspection sensors, such as alignment and scatterometer sensors used in conjunction with a lithography process. Background art

[0004] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, typically onto a target portion of the substrate. For example, a lithographic apparatus can be used to manufacture integrated circuits (ICs). In such an instance, a patterning device (which can be a mask or a reticle) can be used to generate a circuit pattern to be formed on a single layer of the IC. The pattern can be transferred onto a target portion (such as including part of a die, one or more dies) on the substrate (such as a silicon wafer). The transfer of the pattern is typically via imaging onto a layer of radiation - sensitive material (photoresist or simply "resist") provided on the substrate. Generally, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so - called steppers (where each target portion is irradiated by exposing the entire pattern to the target portion at once) and so - called scanners (where each target portion is irradiated by scanning the pattern with a radiation beam in a given direction ("scan direction"), while synchronously scanning the target portion parallel or anti - parallel to this scan direction). The pattern can also be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate.

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

[0006] To monitor a lithography process, parameters of a patterned substrate are measured. The parameters can include, for example, an overlap error between successive layers formed in or on the patterned substrate and a critical linewidth of a developed photosensitive resist. This measurement can be performed on a product substrate and / or a dedicated metrology target. There are various techniques for measuring microstructures formed during a lithography process, including using a scanning electron microscope and various specialized tools. A fast and non-invasive form of specialized inspection tool is a scatterometer, in which a radiation beam is directed onto a target on a substrate surface, and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it is reflected or scattered by the substrate, properties of the substrate can be determined. For example, this can be done by comparing the reflected beam with data stored in a known measurement library associated with known substrate properties. A spectroscopic scatterometer directs a broadband radiation beam onto a substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. In contrast, an angle-resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0007] Such an optical scatterometer can be used to measure parameters such as the critical dimension of a developed photosensitive resist or an overlap error (OV) between two layers formed in or on a patterned substrate. Properties of the substrate can be determined by comparing the properties of the illumination beam before and after it is reflected or scattered by the substrate.

[0008] A lithography system can only output a limited number of finished devices within a given time frame. Faster lithography fabrication is needed, which in turn drives the advancement of faster inspection techniques. Optical inspection can be performed on targets on a wafer using multiple photon wavelengths. A given wavelength can provide information about the target that may not be as apparent at another wavelength. Using multiple parameters (such as multiple wavelengths) during inspection can incur a time cost, thus slowing down the lithography fabrication speed. SUMMARY OF THE INVENTION

[0009] Accordingly, there is a desire to improve multi-parameter inspection techniques to increase fabrication speed and throughput.

[0010] In some aspects, a metrology system can include an illumination system, a camera, and an analyzer system. The illumination system is configured to send illumination towards a target. The illumination has multiple illumination parameters associated with corresponding multiple modulation frequencies. The camera is configured to receive scattered illumination from the target. The camera is further configured to generate a measurement signal encoded with identification flags of the multiple modulation frequencies for each pixel of the camera. The analyzer system is configured to demodulate the measurement signal based on the multiple modulation frequencies for each pixel of the camera. The analyzer system is further configured to output a phase, an amplitude, or both the phase and the amplitude of a demodulated component of the measurement signal corresponding to the modulation frequencies.

[0011] In some aspects, a lithographic apparatus includes 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 may include an illumination system, a camera, and an analyzer system. The illumination system is configured to send illumination towards a target. The illumination has a plurality of illumination parameters associated with corresponding 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 identification flags of the plurality of modulation frequencies. The analyzer system is configured to demodulate the measurement signal for each pixel of the camera based on the plurality of modulation frequencies. The analyzer system is further configured to output a phase, an amplitude, or both a phase and an amplitude of a demodulated component of the measurement signal corresponding to the modulation frequencies.

[0012] 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 aspects described herein. Such aspects are presented herein for illustrative purposes only. Based on the teachings contained herein, additional aspects will be apparent to those skilled in the relevant art(s). BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated herein and form a part of this specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and enable those skilled in the relevant art(s) to make and use the aspects described herein.

[0014] Figure 1A A reflective lithographic apparatus according to some aspects is shown.

[0015] Figure 1B A transmissive lithographic apparatus according to some aspects is shown.

[0016] Figure 2 More details of a reflective lithographic apparatus according to some aspects are shown.

[0017] Figure 3 A lithographic cell according to some aspects is shown.

[0018] Figure 4A and 4B An inspection apparatus according to some aspects is shown.

[0019] Figure 5A , 5B , 5C and 5D show signals that may be received at a phase-locked detector according to some aspects.

[0020] Figure 6 An inspection apparatus according to some aspects is shown.

[0021] Figure 7Shows a flowchart of a detector according to some embodiments.

[0022] Figure 8 and 9 Shows a flowchart of a detection system according to some aspects.

[0023] Figure 10 Shows a detector according to some aspects.

[0024] Figure 11A and 11B Shows the pupil plane of a propagated illumination beam according to some aspects.

[0025] Figure 12 Shows a computer system according to some aspects.

[0026] Figure 13 and 14 Shows a flowchart of operations that can be used to implement with a detection system according to some aspects.

[0027] When combined with the accompanying drawings, the features of the present disclosure will become more apparent through the specific embodiments described below, where like reference characters always identify corresponding elements. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost (s) digit(s) of a reference numeral identify the drawing in which the reference numeral first appears. Unless otherwise indicated, the drawings provided throughout the present disclosure should not be construed as being drawn to scale. Detailed Description

[0028] Each aspect described herein and references in the specification to "one aspect", "aspect", "exemplary aspect", "example aspect", etc. indicate that the described aspect may include a particular feature, structure, or characteristic, but each aspect may not necessarily include that particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that, whether or not explicitly described, it is within the knowledge of those skilled in the art to implement such feature, structure, or characteristic in connection with other aspects.

[0029] Spatial relative terms (such as "beneath", "below", "lower", "above", "on top", "upper", etc.) may be used herein for convenience of description to describe the relationship of one element or feature to (an) other element(s) or (an) other feature(s) illustrated in the drawings. In addition to the orientation depicted in the drawings, spatial relative terms are intended to encompass different orientations of the device during use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptors used herein may be interpreted accordingly.

[0030] The terms "about", "approximate", etc. may be used herein to indicate a value of a given quantity that can vary based on a particular technology. Based on a particular technology, the terms "about", "approximate", etc. may indicate a value of a given quantity that varies within, for example, 10% to 30% of that value (such as ±10%, ±20%, or ±30% of the value).

[0031] 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 machine-readable medium, which can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (such as 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 (such as carrier waves, infrared signals, digital signals, etc.) and others. Additionally, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be understood that such description is for convenience only, and such actions are caused by a computing device, processor, controller, or other device that executes the firmware, software, routines, instructions, etc. The term "machine-readable medium" may be interchangeable with similar terms, such as "computer program product", "computer-readable medium", "non-transitory computer-readable medium", etc. The term "non-transitory" may be used herein to characterize one or more forms of computer-readable media other than transitory propagated signals.

[0032] However, before describing such aspects in more detail, it is beneficial to present an example environment in which aspects of the present disclosure may be implemented.

[0033] Example Lithography System

[0034] Figure 1A and 1BLithographic apparatuses 100 and 100' are shown respectively, which can implement various aspects of the present disclosure. The lithographic apparatus 100 and the lithographic apparatus 100' each include the following: 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, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM, which is 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, which is configured to accurately position the substrate W. The lithographic apparatuses 100 and 100' also have a projection system PS, configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion (e.g., including one or more dies) C of the substrate W. In the lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In the lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0035] The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0036] The support structure MT holds the patterning device MA in a manner depending on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatuses 100 and 100', and other conditions (such as whether the patterning device MA is held in a vacuum environment). The support structure MT may hold the patterning device MA using mechanical, vacuum, electrostatic, or other clamping techniques. The support structure MT may be a frame or a table, for example, which may be fixed or movable. For example, by using sensors, the support structure MT can ensure that the patterning device MA is located at a desired position with respect to the projection system PS.

[0037] The term "patterning device" MA should be interpreted broadly as referring to any device that can be used to impart a pattern in its cross-section to the radiation beam B, such as 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.

[0038] The patterning device MA may be transmissive (as in the Figure 1B lithographic apparatus 100') or reflective (as in the Figure 1Ain the lithographic apparatus 100). Examples of the patterning device MA include a mask, a reticle, a programmable mirror array, and a programmable LCD panel. Masks are well known in lithography and include mask types such as binary mask types, alternating phase-shift mask types, or attenuated phase-shift mask types, 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 in different directions. The tilted mirrors impart a pattern in the radiation beam B reflected by the array of small mirrors.

[0039] The term "projection system" PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as may be appropriate for the exposure radiation being used or for other factors such as the use of immersion or the use of a vacuum on the substrate W. A vacuum environment can be used for EUV or electron beam radiation, since other gases may absorb too much radiation or electrons. Thus, a vacuum environment can be provided to the entire beam path by means of a vacuum wall and a vacuum pump.

[0040] The lithographic apparatus 100 and / or the lithographic apparatus 100' may be of a type having two (dual-platform) or more substrate tables WT (and / or two or more mask tables). In such a "multi-platform" machine, additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some cases, the additional table may not be a substrate table WT.

[0041] The lithographic apparatus may also be of a type in which at least a portion of the substrate can be covered by a liquid having a relatively high refractive index (e.g., water) to fill the space between the projection system and the substrate. Immersion can also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of the projection system. The term "immersion" as used herein does not mean that a structure (such as a substrate) must be submerged in a liquid. For example, during exposure, the liquid can be located between the projection system and the substrate.

[0042] Reference Figure 1A and 1B and, the illuminator IL receives a radiation beam from the radiation source SO. The source SO and the lithographic apparatus 100, 100' can be separate physical entities, such as when the source SO is an excimer laser. In such a case, the source SO is not considered to be part of the lithographic apparatus 100 or 100', and by means of a beam delivery system BD comprising, for example, suitable directing mirrors and / or beam expanders (in Figure 1BIn the former case, the radiation beam B is transmitted from the source SO to the illuminator IL. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100', for example when the source SO is a mercury lamp. The radiation system can include the source SO, the illuminator IL and / or the beam delivery system BD.

[0043] The illuminator IL can include an adjuster AD (in Figure 1B ), for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent of the intensity distribution in the pupil plane of the illuminator (commonly referred to as "σ outer" and "σ inner" respectively) can be adjusted. Additionally, the illuminator IL can include various other components (in Figure 1B ), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B so as to have a desired uniformity and intensity distribution in its cross-section.

[0044] Referring Figure 1A , the radiation beam B is incident on a patterning device, e.g. a mask MA, which is held on a support structure, e.g. a mask table MT, and is patterned by the patterning device MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device, e.g. a mask MA. After reflection from the patterning device, e.g. a mask MA, the radiation beam B passes through a projection system PS which focuses the radiation beam B onto a target portion C of the substrate W. By means of a second positioner PW and a position sensor IF2 (such as an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. so as to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device, e.g. a mask MA, relative to the path of the radiation beam B. The patterning device, e.g. a mask MA, and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0045] Referring Figure 1B , the radiation beam B is incident on a patterning device, e.g. a mask MA, which is held on a support structure, e.g. a mask table MT, and is patterned by the patterning device. After traversing the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU of the pupil IPU of the illumination system. A portion of the radiation emanates from the intensity distribution at the illumination system pupil IPU and traverses the mask pattern without being affected by diffraction at the mask pattern and creates an image of the intensity distribution at the illumination system pupil IPU.

[0046] The projection system PS projects an image of the mask pattern MP onto a photoresist layer coated on a substrate W, where the image is formed by diffracted beams generated from the mask pattern MP by radiation from an intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Radiation diffraction located at the array and different from the zero-order diffraction generates deflected diffracted beams, whose directions change in a direction perpendicular to the lines. The non-diffracted beam (i.e., the so-called zero-order diffracted beam) traverses the pattern without any change in the propagation direction. The zero-order diffracted beam traverses the upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, and reaches the pupil conjugate PPU. The intensity distribution portion associated with the zero-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, the aperture device PD is disposed or substantially disposed in the plane including the pupil conjugate PPU of the projection system PS.

[0047] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zero-order diffracted beam, the first-order diffracted beam, and / or higher-order diffracted beams (not shown). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to the lines can be used to utilize the resolution enhancement effect of dipole illumination. For example, the first-order diffracted beam interferes with the corresponding zero-order diffracted beam at the wafer W level to create an image of the line pattern MP with the highest possible resolution and process window (i.e., the combination of available depth of focus and tolerable exposure dose deviation). In some aspects, astigmatic aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, astigmatic aberration can be reduced by blocking the zero-order beam in the pupil conjugate PPU of the projection system associated with the radiation poles in the opposite quadrants. This is described in more detail in US7,511,799B2 issued on March 31, 2009, which is incorporated herein by reference in its entirety.

[0048] With the aid of a second locator PW and a position sensor IFD (e.g., an interferometric device, a linear encoder, or a capacitive sensor), the substrate stage WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, a first locator PM and another position sensor (not shown in Figure 1B can be used to accurately position the mask MA relative to the path of the radiation beam B (e.g., after mechanically retrieving from a mask library, or during scanning).

[0049] Generally, the movement of the mask table MT can be achieved by means of a long - stroke module (coarse positioning) and a short - stroke module (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate table WT can be achieved using a long - stroke module and a short - stroke module that form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short - stroke actuator or can be fixed. The mask MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in the spaces between the target portions (referred to as scribe alignment marks). Similarly, in the case where more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0050] The mask table MT and the patterning device MA can be in a vacuum chamber V, where an in - vacuum robot IVR can be used to move the patterning device such as the mask into and out of the vacuum chamber. Alternatively, when the mask table MT and the patterning device MA are outside the vacuum chamber, an out - of - vacuum robot can be used for various transportation operations, similar to the in - vacuum robot IVR. Both the in - vacuum and out - of - vacuum robots can be calibrated to smoothly transfer any payload (e.g., the mask) to a fixed motion base at the transfer station.

[0051] The lithographic apparatuses 100 and 100’ can be used in at least one of the following modes:

[0052] 1. In the step mode, when the entire pattern imparted to the radiation beam B is projected onto the target portion C at once (i.e., single - static exposure), the support structure (e.g., the mask table) MT and the substrate table WT remain substantially stationary. Then, the substrate table WT is shifted in the X and / or Y directions so that different target portions C can be exposed.

[0053] 2. In the scan mode, when the pattern imparted to the radiation beam B is projected onto the target portion C (i.e., single - dynamic exposure), the support structure (e.g., the mask table) MT and the substrate table WT are scanned synchronously. The speed and direction of the substrate table WT relative to the support structure (e.g., the mask table) MT can be determined by the magnification (reduction ratio) and image - inversion characteristics of the projection system PS.

[0054] 3. In another mode, the support structure (e.g., the mask table) MT is substantially stationary, thus holding the programmable patterning device, and the substrate table WT is moved or scanned while the pattern imparted to the radiation beam B is projected onto the target portion C. A pulsed radiation source SO may be employed, and the programmable patterning device is updated as needed after each movement of the substrate table WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device such as a programmable mirror array.

[0055] Combinations and / or variations of the described usage modes or entirely different usage modes may also be employed.

[0056] In yet another aspect, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Generally, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0057] Figure 2 The lithographic apparatus 100 is shown in more detail and includes 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 the enclosure structure 220 of the source collector apparatus SO. The EUV radiation-emitting plasma 210 may be formed by a plasma source generated by a discharge. In some aspects, a plasma that excites tin (Sn) (e.g., via laser excitation) is provided to generate EUV radiation.

[0058] Radiation emitted by the EUV radiation-emitting plasma 210 enters the collector chamber 212 from the source chamber 211 via an optional gas barrier or contaminant trap 230 (also referred to in some instances as a contaminant barrier or flap 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 indicated herein includes at least a channel structure.

[0059] 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 from the grating spectral filter 240 to be focused at the virtual source point INTF. The virtual source point INTF is generally referred to as the intermediate focus, and the source collector device is arranged such that the intermediate focus INTF is located at or near the opening 219 in 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 specifically used to suppress infrared (IR) radiation.

[0060] Subsequently, the radiation traverses the illumination system IL, which may include a faceted field mirror device 222 and a faceted pupil mirror device 224, which are arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA and to provide a desired uniformity of the radiation intensity at the patterning device MA. When the radiation beam 221 is reflected at the patterning device MA held by the support structure MT, a patterned beam 226 is formed, and the patterned beam 226 is imaged onto the substrate W by the projection system PS via the reflective elements 228, 229, and the substrate W is held by a wafer stage or a substrate table WT.

[0061] More elements than shown may generally be present in the illumination optical unit IL and the projection system PS. Depending on the type of lithographic apparatus, the grating spectral filter 240 may optionally be present. Further, there may be Figure 2 more mirrors than shown, for example, Figure 2 compared to that shown, there may be 1 to 6 additional reflective elements in the projection system PS.

[0062] As Figure 2 illustrated, the collector optics CO is depicted as a nested collector having grazing-incidence reflectors 253, 254, and 255, only as an example of a collector (or collector mirror). The grazing-incidence reflectors 253, 254, and 255 are axially symmetrically arranged about the optical axis O, and preferably, this type of collector optics CO is used in combination with a discharge-produced plasma source commonly referred to as a DPP source.

[0063] Example lithography cell

[0064] Figure 3FIG. 300 shows a lithography cell 300, sometimes also referred to as a lithography cell or cluster, according to some aspects. A lithography apparatus 100 or 100' may form part of the lithography cell 300. The lithography cell 300 may also include one or more apparatuses for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a baking plate BK. A substrate handler or robot RO picks up substrates from input / output ports I / O1, I / O2, moves them between different process apparatuses, and transfers them to a load rack LB of the lithography apparatus 100 or 100'. These apparatuses, collectively often referred to as a track, are controlled by a track control unit TCU, which in turn is controlled by a monitoring system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0065] Example inspection apparatus

[0066] To control the lithography process to accurately place device features on a substrate, alignment marks are typically provided on the substrate, and the lithography apparatus includes one or more inspection apparatuses for accurately positioning the marks on the substrate. These alignment apparatuses are in effect position measurement apparatuses. Different types of marks and different types of alignment apparatuses and / or systems are known at different times and by different manufacturers. One system widely used in current lithography apparatuses is based on a self-referencing interferometer as described in U.S. Patent No. 6,961,116 (den Boef et al.). Typically, the marks are measured individually to obtain X and Y positions. However, combined X and Y measurements can be performed using the techniques described in U.S. Publication No. 2009 / 195768A (Bijnen et al.). The entire disclosures of these publications are incorporated herein by reference.

[0067] Figure 4A FIG. 400 shows a cross-sectional view of an inspection apparatus 400 that can be implemented as part of a lithography apparatus 100 or 100' according to some aspects. In some aspects, the inspection apparatus 400 may be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). The inspection apparatus 400 may also be configured to detect the position of alignment marks on the substrate and use the detected position of the alignment marks to align the substrate relative to the patterning device or other components of the lithography apparatus 100 or 100'. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0068] The terms "inspection device", "measurement system", etc. may be used herein to refer to, for example, a device for measuring the properties of a structure (such as an overlay sensor, a critical dimension sensor, etc.), a device or system for detecting wafer alignment in a lithographic apparatus (such as an alignment sensor), etc.

[0069] In some aspects, the inspection device 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and 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 an example, the one or more passbands may be within a wavelength spectrum between about 500 nm and about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a wavelength spectrum between about 500 nm and about 900 nm. The illumination system 412 may also be configured to provide one or more passbands having a substantially constant center wavelength (CWL) value over a long period of time (such as during the life cycle of the illumination system 412). In the current measurement system, this configuration of the illumination system 412 may help prevent a shift of the actual CWL value from the desired CWL value, as discussed above. And, as a result, using a constant CWL value may improve the long-term stability and accuracy of the alignment system (such as the inspection device 400) compared to the current alignment device.

[0070] In some aspects, the beam splitter 414 may be configured to receive the radiation beam 413 and split the radiation beam 413 into at least two radiation sub-beams. For example, as Figure 4AAs shown, the radiation beam 413 can be split into radiation sub-beams 415 and 417. The beam splitter 414 can also be configured to direct the radiation sub-beam 415 onto a substrate 420 placed on a platform 422. In one example, the platform 422 is movable along a direction 424. The radiation sub-beam 415 can be configured to irradiate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 can be coated with a radiation-sensitive film. In some aspects, the alignment mark or target 418 can have a one-hundred-eighty degree (i.e., 180°) symmetry. That is, when the alignment mark or target 418 is rotated 180° about a symmetry axis perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 can be substantially the same as the non-rotated alignment mark or target 418. The target 418 on the substrate 420 can be (a) a resist layer grating including bars formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlapping target structure including a resist grating overlapping or interleaved on the product layer grating. Alternatively, the bars can be etched into the substrate. The pattern is sensitive to chromatic aberration in a lithographic projection apparatus, particularly the projection system PL, and the illumination symmetry and the presence of such aberrations will manifest in variations in the printed grating. An on-line method for measuring linewidth, pitch, and critical dimensions in device manufacturing uses a technique called "scatterometry". The method of scatterometry is described in "Multiparameter Grating Metrology Using Optical Scatterometry" by Raymond et al., published in Volume 15, Issue 2, pages 361 - 368 of Journal of Vacuum Science and Technology B in 1997, and "Specular Spectroscopic Scatterometry in DUV Lithography" by Niu et al., published in SPIE Volume 3677 in 1999, both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by the periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. For example, the structure that produces the reflection spectrum is reconstructed using rigorous coupled-wave analysis (RCWA) or by comparison with a library of simulated patterns. Thus, the scatterometry data of the printed grating is used to reconstruct the grating. The parameters of the grating, such as linewidth and shape, can be input into the reconstruction process executed by the processing unit PU through knowledge of the printing step and / or other scatterometry processes.

[0071] In some aspects, according to one aspect, the beam splitter 414 can also be configured to receive a diffracted radiation beam 419 and split the diffracted radiation beam 419 into at least two radiation sub-beams. As Figure 4AAs shown, the diffracted radiation beam 419 can be split into diffracted radiation sub - beams 429 and 439.

[0072] It should be noted that although the beam splitter 414 is shown as directing the radiation sub - beam 415 towards the alignment mark or target 418 and the diffracted radiation sub - beam 429 towards the interferometer 426, the present disclosure is not limited thereto. Other optical arrangements can be used to obtain similar results of irradiating the alignment mark or target 418 on the substrate 420 and detecting an image of the alignment mark or target 418.

[0073] As Figure 4A Illustrated, the interferometer 426 can be configured to receive the radiation sub - beam 417 and the diffracted radiation sub - beam 429 through the beam splitter 414. In an example aspect, the diffracted radiation sub - beam 429 can be at least a portion of the radiation sub - beam 415 that can be reflected from the alignment mark or target 418. In an example of this aspect, the interferometer 426 includes any suitable set of optical elements, such as a combination of prisms, which can be configured to form two images of the alignment mark or target 418 based on the received diffracted radiation sub - beam 429. It should be understood that it is not necessary to form a high - quality image. Resolving the features of the alignment mark 418 may be sufficient. The interferometer 426 can also be configured to rotate one of the two images by 180° relative to the other of the two images and interferometrically recombine the rotated and unrotated images.

[0074] In some aspects, when the alignment axis 421 of the inspection device 400 passes through the center of symmetry (not shown) of the alignment mark or target 418, the detector 428 can be configured to receive the recombined image via the interferometer signal 427 and detect the interference resulting from the recombined image. According to an example aspect, such interference may be due to the alignment mark or target 418 being 180° symmetric and the recombined images interfering constructively or destructively. Based on the detected interference, the detector 428 can also be configured to determine the position of the center of symmetry of the alignment mark or target 418 and thus detect the position of the substrate 420. According to an example, the alignment axis 421 can be aligned with a beam that is perpendicular to the substrate 420 and passes through the center of the image - rotating interferometer 426. The detector 428 can also be configured to estimate the position of the alignment mark or target 418 by implementing sensor characteristics and interacting with wafer - marking process variations.

[0075] In yet another aspect, the detector 428 determines the position of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements:

[0076] 1. Measuring the position change at various wavelengths (position shift between colors);

[0077] 2. Measuring the position change at various orders (position shift between diffraction orders); and

[0078] 3. Measure the position changes of various polarizations (position shifts between polarizations).

[0079] This data can be obtained using any type of alignment sensor, such as a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Patent No. 6,961,116, which employs a self-referencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software; or Athena (Advanced Technology using Higher-Order Alignment Enhancement), as described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated herein by reference in their entirety.

[0080] In some aspects, the beam analyzer 430 can be configured to receive and determine the optical state of the diffracted radiation sub-beam 439. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 can also be configured to determine the position of the stage 422 and correlate the position of the stage 422 with the position of the symmetry center of the alignment mark or target 418. Thus, the position of the alignment mark or target 418 can be accurately known with reference to the stage 422, and thus the position of the substrate 420 can be accurately known. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection device 400 or any other reference element such that the symmetry center of the alignment mark or target 418 can be known with reference to the inspection device 400 or any other reference element. The beam analyzer 430 can be a point or imaging polarimeter with some form of band selectivity. In some aspects, according to other aspects, the beam analyzer 430 can be directly integrated into the inspection device 400 or via several types of fiber optic connections: polarization-maintaining single-mode, multi-mode, or imaging.

[0081] In some aspects, the beam analyzer 430 can also be configured to determine the overlap data between two patterns on the substrate 420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposure pattern on an exposure layer. The reference layer can be an etched layer that already exists on the substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by the lithography apparatus 100 and / or 100'. The exposure layer can be a resist layer exposed adjacent to the reference layer. The exposure layer can be generated by an exposure pattern exposed on the substrate 420 by the lithography apparatus 100 or 100'. The exposure pattern on the substrate 420 can correspond to the movement of the stage 422 relative to the substrate 420. In some aspects, the measured overlap data can also indicate the offset between the reference pattern and the exposure pattern. The measured overlap data can be used as calibration data to calibrate the exposure pattern exposed by the lithography apparatus 100 or 100' such that, after calibration, the offset between the exposure layer and the reference layer can be minimized.

[0082] In some aspects, the beam profiler 430 can also be configured to determine a model of the product stack profile of the substrate 420, and can be configured to measure the overlay, critical dimension, and focus of the target 418 in a single measurement. The product stack profile contains information about the stacked products, such as alignment marks, the target 418, or the substrate 420, and can include optical identification signature metrology caused by process variations, which is a function of illumination variations. The product stack profile can also include product grating profiles, mark stack profiles, and mark asymmetry information. An example of the beam profiler 430 is the Yieldstar manufactured by ASML Corporation of Veldhoven, the Netherlands TM , as described in U.S. Patent No. 8,706,442, which is hereby incorporated by reference in its entirety. The beam profiler 430 can also be configured to process information related to the specific nature of the exposure pattern in the layer. For example, the beam profiler 430 can process the overlay parameters of the image depicted in the layer (an indication of the positioning accuracy of the layer relative to the previous layer on the substrate, or the positioning accuracy of the first layer relative to the marks on the substrate), the focus parameters, and / or the critical dimension parameters (such as line width and its variations). Other parameters are image parameters related to the quality of the depicted image of the exposure pattern

[0083] In some aspects, a detector array (not shown) can be connected to the beam profiler 430 and allows for accurate stack profile detection as discussed below. For example, the detector 428 can be a detector array. For the detector array, multiple options are possible: multimode fiber bundles, discrete pin detectors for each channel, or CCD or CMOS (linear) arrays. For stability reasons, using multimode fiber bundles allows any dissipative elements to be located remotely. Discrete PIN detectors provide a larger dynamic range, but each requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays provide many elements that can be read out at high speed, and are particularly interesting if phase-stepping detection is used

[0084] In some aspects, a second beam profiler 430' can be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, as Figure 4BAs shown. The optical state can be a measure of beam wavelength, polarization, or beam profile. The second beam analyzer 430' can be the same as the beam analyzer 430. Alternatively, the second beam analyzer 430' can be configured to perform one or more functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 422 with the position of the alignment mark or the center of symmetry of the target 418. Thus, the position of the alignment mark or the target 418 can be accurately known with reference to the stage 422, and thus the position of the substrate 420 can be accurately known. The second beam analyzer 430' can also be configured to determine the position of the inspection device 400 or any other reference element such that the center of symmetry of the alignment mark or the target 418 can be known with reference to the inspection device 400 or any other reference element. The second beam analyzer 430' can also be configured to determine the overlap data between two patterns and a model of the product stack profile of the substrate 420. The second beam analyzer 430' can also be configured to measure the overlap, critical dimension, and focus of the target 418 in a single measurement.

[0085] In some aspects, according to other aspects, the second beam analyzer 430' can be directly integrated into the inspection device 400 or via several types of optical fiber connections: polarization-maintaining single-mode, multi-mode, or imaging. Alternatively, the second beam analyzer 430' and the beam analyzer 430 can be combined to form a single analyzer (not shown) that is configured to receive and determine the optical states of the diffracted radiation sub-beams 429 and 439.

[0086] In some aspects, the processor 432 receives information from the detector 428 and the beam analyzer 430. For example, the processor 432 can be an overlap calculation processor. The information can include a model of the product stack profile constructed by the beam analyzer 430. Alternatively, the processor 432 can use the received information about the product mark to construct a model of the product mark profile. In either case, the processor 432 can use or incorporate the product mark profile model to construct a model of the stacked product and the overlapping mark profile. Then, the stacked model is used to determine the overlap offset and to minimize the spectral effect on the overlap offset measurement. The processor 432 can create a baseline correction algorithm based on the information received from the detector 428 and the beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signal, the associated position estimate, and the optical states in the pupil, image, and additional planes. The pupil plane is the plane in which the radial position of the radiation defines the angle of incidence and the angular position defines the azimuthal angle of the radiation. The processor 432 can use the baseline correction algorithm to characterize the inspection device 400 with reference to the wafer mark and / or the alignment mark 418.

[0087] In some aspects, the processor 432 may also be configured to determine a print pattern position offset error estimated by the sensor relative to each marker 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, overlap measurements, critical dimensions, and the focus of each alignment marker or target 418 on the substrate 420. The processor 432 may use a clustering algorithm to group the markers into sets of similar constant offset errors and create an alignment error offset correction table based on this information. The clustering algorithm may be based on overlap measurements, position estimates, and additional optical stack process information associated with each set of offset errors. Overlap is calculated for a number of different markers, for example, the overlap target has a plus or minus bias around the programmed overlap offset. The target with the smallest measured overlap is considered the reference (since it is measured with the best accuracy). From this measured small overlap and the known programmed overlap of its corresponding target, the overlap error can be inferred. Table 1 illustrates how this can be performed. The smallest measured overlap in the example shown is -1 nm. However, this is associated with a target having a programmed overlap of -30 nm. This process may introduce an overlap error of 29 nm.

[0088]

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

[0090] In some aspects, the processor 432 may confirm that all or most members of the group have similar offset errors and apply individual offset corrections from the clustering algorithm to each marker based on its additional optical stack metrology. The processor 432 may determine the correction for each marker and feed the correction back to the lithographic apparatus 100 or 100' to correct the error in overlap, for example, by feeding the correction back into the inspection device 400.

[0091] Example multi-channel phase-locked camera of the inspection device

[0092] Market demand has increased the need for faster photolithographic fabrication of electronic chips (such as integrated circuits). However, to ensure that electronic chip devices are printed accurately, inspection equipment as described above can be used to ensure that device fabrication meets fabrication tolerances.

[0093] The term "production volume" is generally understood to be the quantity of material or items passing through a system or process. In some aspects, the term "production volume" can be used to characterize the rate of photolithographic fabrication. For example, production volume can refer to the rate of completing photolithographic fabrication on a wafer, the rate at which a wafer clears a particular fabrication step and moves to the next step, etc. Production volume can be a performance metric of a lithography apparatus. It is desirable for a lithography system to output as many products as possible in as little time as possible. Photolithographic fabrication can include several complex processes. Each part of the process may involve a trade-off between balancing quality (such as sub-nanometer accuracy, high throughput) and drawbacks (such as slower fabrication, cost). Even a small lithography error in circuit printing can lead to device malfunction (i.e., device failure). To improve pattern transfer accuracy, photolithography can include inspecting printed marks on a substrate. This inspection can be used to determine the consistency of the printed pattern on the substrate, or to align the substrate to correctly receive a new pattern. However, the time added by the inspection process can have an adverse effect on production volume.

[0094] In some aspects, optical inspection of a target on a wafer can be performed using irradiation of multiple colors (or wavelengths). A given wavelength can provide information about the target that may not be as apparent at another wavelength. As used herein, concepts involving "multiple wavelengths", "multiple photon frequencies", "multiple parameter values", etc. can be used to characterize narrowband values in related properties or parameters. In a non-limiting example of a wavelength parameter, a first wavelength can be characterized as including a narrowband wavelength centered at a first central wavelength. A second wavelength can be similarly characterized as including a narrowband wavelength centered at a second central wavelength. The characterization that the first wavelength is different from the second wavelength can be interpreted as the first central wavelength being different from the second central wavelength.

[0095] In some aspects, enumerative adjectives (such as "first", "second", "third", etc.) can be used to distinguish elements that share similarities, but do not determine order, hierarchy, or quantity (unless otherwise stated). For example, the terms "first wavelength" and "second wavelength" can be used in a manner similar to "the i-th wavelength" and "the j-th wavelength" to distinguish two wavelengths without specifying a particular order, hierarchy, or quantity. Additionally, elements in the drawings are not limited to any particular enumerative adjective.

[0096] In some aspects, detector 428, beam analyzer 430, and / or beam analyzer 430' ( Figure 4A and 4Bmay include an image-based detector (e.g., a camera). The camera may include a plurality of pixels to resolve an image (e.g., a charge-coupled device (CCD) camera). Commercial cameras are typically optimized for the human viewing experience (e.g., red-green-blue (RGB) color sensitivity). To achieve RGB sensitivity, commercial cameras may implement color filters at each pixel. Specifically, a given pixel of the camera may be sensitive to a specific color (e.g., one pixel has a red filter, the next pixel has a green filter, the pixel after the next pixel is a blue filter, and the pattern iterates to all pixels - other arrangements are possible).

[0097] In some aspects, a color camera as described above may pose challenges for an inspection sensor used in a lithography process. For example, a commercial camera may be insufficient for lithography inspection because such inspection is performed with more than three wavelengths. Lithography detection may also rely on wavelengths outside the visible RGB range, which is not available in typical cameras. Lithography inspection also involves signal-to-noise ratio (SNR).

[0098] In addition, as inspection times are shortened to increase lithography throughput, the number of photons collected at the detector becomes an increasingly important factor. A disadvantage of a color camera with pixel filters may be that a portion of the total pixels may be restricted to a specific color and will not respond to photons of different colors. In other words, pixels that respond to green wavelengths will reject photons with non-green wavelengths (the rejected photons are wasted). As a workaround, using a monochromatic camera can compensate for the deficiencies of pixel color filters by allowing the camera to receive all photons regardless of their wavelength. However, this means that illumination can be acquired via sequential wavelength steps in order to allow the color signals to be distinguished from one another (e.g., first using far infrared, then near infrared, then red, then green, and so on). But this may have the effect of increasing the inspection time, thereby undesirably reducing throughput.

[0099] Aspects disclosed herein allow for the use of a monochromatic camera to simultaneously detect multiple wavelengths. Moreover, aspects disclosed herein are not limited to detecting multiple wavelengths, but may be applied to simultaneously detect multiple settings of an adjustable parameter, multiple values of a parameter that may have more than one value, or permutations of the settings or values of two or more parameters (e.g., twelve wavelengths, ten wavelengths, two polarizations, five wavelengths of one polarization and five wavelengths of another polarization, four angles of incidence, etc.). For simplicity of discussion, aspects will be described with respect to wavelength and one pixel, but it should be understood that wavelength is merely one possible parameter and the pixel is one of many pixels of the camera.

[0100] Before describing the phase-locked implementation in image-based inspection, it is beneficial to first present some general aspects of phase-locked detection techniques.

[0101] In some aspects, phase-locked detection can use the principle of a lock-in amplifier to provide sensitive detection and selective filtering of weak or noisy signals and can improve the SNR. Lock-in amplifier technology can provide improved accuracy, faster detection times, and reduced noise when performing optical measurements such as alignment position sensing, multi-angle scattering measurements, etc. Phase-locked detection can employ homodyne (single-frequency) detection, heterodyne (multi-frequency) detection, and other well-known variations and optimizations. For simplicity of discussion, each phase-locked channel will be explained with one frequency (e.g., one modulation frequency per channel) for the various aspects disclosed herein, but it should be understood that the various aspects of the present disclosure are envisioned with other well-known phase-locked detection features.

[0102] In some aspects, single-channel phase-locked detection can work by detecting a signal having any number of frequency components. The phase-locked detector can be given a specific frequency to look for. The phase-locked detector can then filter out all frequency components except for the component having the specified modulation frequency (the signal of interest). Figure 5A The curve in shows a composite signal 502 that can be received at a phase-locked detector according to some aspects.

[0103] Note that Figure 5A , 5B , 5C, and the curves in 5D have a vertical axis representing signal amplitude and a horizontal axis representing time.

[0104] In some aspects, the composite signal 502 can have multiple frequency components (in the non-limiting example of, there are three frequency components Figure 5A , , , and as well as noise; noise typically covers a range of frequencies, but for simplicity, the range of frequencies representing noise will be shown). The components are visible as random jagged spikes in the signal in the composite signal 502. Figure 5B shows the signal 504 corresponding to the component. Figure 5C shows the signal 506 corresponding to the component. Figure 5D shows the signal 508 corresponding to the component.

[0105] A desired aspect of phase-locked detection is that the detection technique can lock onto the desired component of the composite signal 502 while suppressing the non- components. For example, if the phase-locked detector is configured to detect a frequency of If the signal (signal 504) is present, the phase-locked detector can effectively ignore the , and components of the composite signal 502 and lock onto the signal 504 buried within it. Thus, the amplitude and phase of the component can be extracted from the composite signal 502. Similarly, the phase-locked detector can be configured to lock onto the amplitude and phase of the component (returning ), the amplitude

[0106] and phase of the component (returning ), or any component.

[0107] Figure 6 FIG. shows an inspection device 600 according to some aspects. In some aspects, the features of inspection device 600 can be implemented in inspection device 400 ( Figure 4A and / or 4B) to allow for multi-channel detection simultaneously when using the structures described with reference to Figure 4A and / or 4B.

[0108] In some aspects, inspection device 600 can include an illumination system 602 (or source branch, illumination source branch, illumination branch, etc.), a detection system 604 (or detection branch, etc.), and an optical system 606.

[0109] In some aspects, illumination system 602 can include an illumination source 608, a modulator 610, and a combiner 612. Illumination source 608 can include source elements 608-1 to 608-n (e.g., first source element, second source element,..., nth source element). Modulator 610 can include modulator elements 610-1 to 610-n (e.g., first modulator element, second modulator element,..., nth modulator element).

[0110] In some aspects, the detection system 604 can include a detector 614 and an analyzer 616 (it is to be understood that a camera can have multiple analyzers 616 (e.g., one analyzer per pixel), but a strict one-to-one correspondence is not required; see Figure 9 ). The analyzer 616 can 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 can operate in the digital domain. It should be understood that portions of the optical system 606 can belong to the illumination system 602, the detection system 604, or both. For example, the optical system 606 can include an objective lens that collects scattered illumination from a target 618 disposed on a substrate 620. The optical system can include a beam splitter 414 ( Figure 4A and 4B ) to direct illumination from the illumination system 602 to the target 618 and to direct scattered illumination from the target 618 to the detector 614.

[0111] In some aspects, the illumination system 602 and the detection system 604 can work together to provide a phase-locked detection capability. 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 sub-harmonic 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).

[0112] In some aspects, the source elements 608-1 through 608-n can respectively generate illumination having photon wavelengths to (e.g., a first wavelength, a second wavelength, …, an nth wavelength). The source elements 608-1 through 608-n can be respectively coupled to the modulator elements 610-1 through 610-n. Based on the master frequency, the modulator elements 610-1 through 610-n can respectively modulate the illumination at frequencies to (e.g., a first frequency, a second frequency, …, an nth frequency) with wavelengths to . This logic applies to all couplings of the source and modulator elements up to the modulator element 610-n, which can modulate the illumination at a frequency with a wavelength . Each of the modulator elements 610-1 through 610-n (and thus each of the frequencies to ) can define a channel (e.g., channels 1 to n, and thus is multi-channel).

[0113] As alluded to above, modulation is not limited to wavelength, but rather other parameters or combinations of parameters of the illumination. For example, a first parameter may be associated with a first polarization (and / or wavelength and / or angle of incidence) of the illumination, a second parameter may be associated with a second polarization (and / or wavelength and / or angle of incidence) of the illumination, and so on.

[0114] In some aspects, the combiner 612 may combine differently parameterized illumination from the source elements 608-1 to 608-n to generate a mixed illumination beam 624 that includes illumination parameters (different wavelengths, polarizations, angles of incidence, etc.). The optical system 606 may direct the illumination beam 624 towards the target 618. The target 618 may scatter photons of the illumination beam 624. The scattered illumination may be collected by the optical system 606 and directed to the detector 614 as scattered illumination 626. Desirably, the parameterization of the illumination beam 624 need not be temporally continuous. All of the different parameters of the illumination beam 624 may overlap in time (e.g., simultaneously), and this feature also applies to the scattered illumination 626. A phase-locking function at the detection branch enables demodulation such that illumination having different illumination parameters can be distinguished. Demodulation may be defined as the process of extracting a modulation signal from its carrier signal.

[0115] In some aspects, the detector 614 may include a camera. The camera may receive timing information (e.g., a master periodic reference signal having a master frequency) from the reference system 622. A camera with a very high sampling rate is desirable such that the true shape of the detected composite signal can be faithfully reconstructed or well approximated.

[0116] As previously mentioned, the discussion will focus on a single pixel of the detector 614, but it should be understood that other pixels may operate in the same manner. The pixels of the detector 614 may have a monochromatic response. That is, regardless of the parameterization, each pixel responds to each received photon (e.g., contrary to the concept of a color camera with color filters, no color-based pixels are rejected). For example, each pixel may be 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 number of received photons. In some aspects, when photons of the scattered illumination 626 are received at a pixel of the detector 614, the resulting measurement signal 628 from the pixel may be a composite signal. With the modulation frequency to The effect of encoding the illumination beam 624 is that the composite measurement signal 628 also carries the modulation frequency to encoding. Thus, the composite measurement signal 628 includes information on the different parameterizations applied by the illumination branch and the effects of the interaction with the target 618 (e.g., the parameters can be multiple wavelengths, multiple wavelengths of one polarization, multiple wavelengths of another polarization, multiple angles of incidence, etc.). In the composite signal 502 ( Figure 5A ), a non-limiting example of a composite signal (with three parameters) is shown.

[0117] In some aspects, analyzer elements 616-1 to 616-n can be used to demodulate the measurement signal 628 into different channels 1 to n. Each channel can be responsible for outputting the corresponding amplitude and phase of each frequency component (i.e., and , and , … and and ). Each pixel of the detector 614 can be considered to have n channels. The multi-channel feature is a desirable feature, especially considering the limitations of commercial lock-in cameras, which are limited to locking to one modulation frequency (i.e., a single channel). The detector 614 and the analyzer 616 together function as a multi-channel lock-in camera. When compiling the information from all the pixels of the multi-channel lock-in camera, the result is a hyperparameterized image (e.g., a hyperspectral image) showing the intensity (amplitude ) and / or phase of all n parameter settings (e.g., wavelength, polarization, angle of incidence, etc.). In a non-limiting example of a four-wavelength measurement, the output of the multi-channel lock-in camera can be used to generate 4 images of intensity , , and (one for each wavelength) from each pixel and / or 4 images of phase , , and from each pixel.

[0118] In some aspects, the detector 614 does not deliberately reject photons, thus allowing for the efficient use of the full intensity provided by the illumination source (as opposed to the color filters of a color camera deliberately rejecting colors). Additionally, since illumination with different parameters can overlap in time, the non-sequential aspect of the measurement technique can allow for faster inspection of the (multiple) lithography targets 618 and have a high SNR due to the feature of not rejecting photons.

[0119] Figure 7 shows a flowchart of a detector 714 according to some aspects. In some aspects, the detector 714 can include a reference Figure 6A structure and function similar to that of the described detector 614. Thus, unless otherwise mentioned, Figure 6 the description of the elements of Figure 7 can also be applied to the corresponding elements of Figure 7 (e.g., reference numerals sharing the two rightmost digits), and will not be reintroduced strictly. Figure 6 Such elements in

[0120] In some aspects, the detector 714 can be a camera (e.g., a QIS camera). The QIS camera can have some desirable properties (e.g., high readout speed and low additive noise). The detector 714 can include pixels 730, a sampling clock 732, a comparator 734, and a counter 736. The pixels 730, the sampling clock 732, and the comparator 734 can operate in the analog domain 751 and the digital domain 753 (which can be used as a transition between analog and digital). The counter 736 can operate in the digital domain.

[0121] In some aspects, the pixels 730 can receive scattered illumination 726 (e.g., from the target 618 ( Figure 6 )). Each pixel of the detector 714 (including the pixels 730) can be sampled at a very high frequency (e.g., in the kHz to MHz range). The sampling rate can be determined by the sampling clock 732. Additionally, the sampling rate can be set to a frequency that is an integer multiple of the modulation frequency to . The relationship between the sampling frequency and the modulation frequency can be such that the Nyquist criterion is satisfied to avoid signal distortion (e.g., the highest available frequency is less than half of the sampling frequency). If the sampling frequency is much higher than the modulation frequency, the criterion can be relaxed. The sampling frequency can be set to be consistent with the master clock 755 (e.g., provided by the reference system 622 ( Figure 6 )).

[0122] In some aspects, the inherent gain of the pixels 730 can be high to reduce the read noise mentioned in the input. The high - gain / low - noise design allows single - photon resolution. The comparator 734 can receive an analog voltage (or current) signal from the pixels 730 and binarize the analog signal (thus, the comparator disclosed herein can also be referred to as an analog - to - digital converter, and the converter bank can be part of an analog - to - digital converter system). The result is a digital pulse train (pulse train 738) during the integration period. The counter 736 can count the pulses. The digital count can be used to estimate the photon arrival rate and thus estimate the intensity at the pixel via digital processing. The counter 736 can output the measurement signal 728. The measurement signal 728 (e.g., pixel output) can be processed and analyzed to extract information related to the modulation frequency to The amplitudes and / or phases of corresponding different channels.

[0123] Figure 8 FIG. 804 shows a flow chart of a detection system 804 according to some aspects. In some aspects, the detection system 804 may include structures and functions similar to those of the detection systems and detectors described with reference Figure 6 and 7 Therefore, unless otherwise mentioned, Figure 6 and 7 the descriptions of the elements of Figure 8 may also apply to the corresponding elements of Figure 8 (e.g., reference numerals sharing the two rightmost digits), and will not be reintroduced strictly. Figure 6 and 7 The such elements in

[0124] In some aspects, the measurement signal 828 may be received at the analyzer 816. During the sampling period, the pulses in the pulse train 838 may be integrated using a counter 736 ( Figure 7 ). (e.g., the measurement signal 828 may include the integrated pulses within the sampling period). In the absence of a dedicated counter (e.g., counter 736 ( Figure 7 ), the measurement signal 828 may include the pulse train 838. Or in an alternative description, the analyzer 816 may be regarded as a counter because the analyzer 816 may receive binary pulses (counts) as inputs.

[0125] In some aspects, by utilizing the analyzer elements of the analyzer 816 (e.g., analyzer elements 616-1 to 616-n ( Figure 6 ), finite-time phase-locked detection of intensity samples (pulses) may be performed at multiple modulation frequencies to . The analyzer may implement pre-generated cosine and sine tables 857 corresponding to the frequencies to . The frequency information may be determined based on the main frequency used to modulate the illumination at the illumination system 602 ( Figure 6 ). The analyzer 816 may combine the pre-computed sine and cosine tables with the data in the measurement signal 828 (e.g., element-by-element multiplication, multiplication after summation, etc.).

[0126] In some aspects, for discrete-time sampling, an and b n The expression of can be given by:

[0127] (Equation 1)

[0128] (Equation 2)

[0129] Here,[[]]END]] is the sampled signal, n is the harmonic of the fundamental frequency, P is the time period for performing the analysis (e.g., ) is the number of sampling points within one period, and is the time interval between samples. In some aspects, the time-sampled signal can be multiplied element-wise with the pre-computed elements of the cosine table and sine table and . Then, the sum of the element-wise multiplied values can also be performed within one measurement period. The time-sampled signal can be interpreted as the total number of detected photons divided by the detection time interval . Dividing by represents an intensity normalization step. The normalization step can be performed at a later stage or even completely omitted to simplify the processing, e.g., if only relative intensities are of interest.

[0130] In some aspects, the analyzer 816 can use the calculations mentioned above to determine the cosine factors to and the sine factors to . Then, the sine factors and cosine factors can be used to determine the intensities (amplitudes to ) and / or phases and for all parameter settings 1 to n. The cosine factors to and the sine factors to can be referred to as the representation of the amplitude and phase in Cartesian form (i.e., in a non-limiting example, the amplitude and phase can be represented in Cartesian form as the coefficients of a Fourier series in cosine-sine form and ). To understand, a cosine-only or sine-only table can be used to simplify the analysis. A cosine-only (or sine-only) table implementation can be used for boundary conditions suitable for discrete cosine transforms (e.g., if the carrier phase is not shifted). After the analyzer 816 can be another analyzer 817. The analyzer 817 can perform operations on the output of the analyzer 816 to further refine the measurement data. For example, the analyzer 817 can perform integration (summation), averaging, filtering, etc. To understand, the analyzers 816 and 817 can be separate, as shown, or can be a single device (e.g., a single computer, processor system, etc.).

[0131] In some aspects, finite time detection can be performed by specifying a measurement sampling time (i.e., the reciprocal of the measurement sampling rate, which can be different from the sampling rate limit of the camera). The measurement sampling rate can be selected via, for example, configuring the detection system 804 to use a frequency divisible by the frequency of the master clock 855 (e.g., an integer multiple of the master clock period). The measurement sampling rate can be configured to satisfy the Nyquist criterion for the highest frequency in to .

[0132] In some aspects, the frequencies to can form at least some of the Fourier components associated with or derived from the measurement integration time . That is, the period of each modulation frequency can fit an exact number of times in . The frequencies to can be evenly spaced in the frequency domain. To prevent channel crosstalk, the frequencies to can be selected such that no one frequency is a harmonic of another frequency. The measurement sampling rate can be an integer multiple of the frequency spacing between at least two of the frequencies to . If a longer integration (longer ) is needed, then the techniques disclosed herein allow the integration time to be increased in multiples of the hardware-allowed basis (lowest) . However, it should be noted that the frequency space will be affected accordingly. In the case where the combination of to satisfies the condition of all having integer multiple periods, then using the time period twice, three times, or more times can still satisfy the condition. In contrast, increasing the measurement time, for example, by a factor of two can allow the frequency spacing to be halved, but there is no requirement to do so.

[0133] In some aspects, additional constraints on the modulation frequency can be further defined to enhance 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 start of the measurement during which the inspection device is in a steady state (e.g., the illumination is on, the modulation is operating, and the target is within the field of view of the inspection device). The second time can be the time to analyze the signal from the target (e.g., ). Then, the channel spacing (in frequency) can be an exact multiple of the reciprocal of the sum of the first time period and the second time period.

[0134] In some aspects, compared with the Figure 7 shown basic QIS process, the number of operations per pixel can be greatly increased. Therefore, it is desirable to digitize the operations to take advantage of the continuous progress of computer capabilities.

[0135] Although Figure 8 shows the single-pixel processing of phase-locked detection, it is also contemplated that multiple pixels can have a combined analysis stream (e.g., multiplexing and demultiplexing).

[0136] Figure 9 shows a flowchart of a detection system 904 according to some aspects. In some aspects, the detection system 904 can include structures and functions similar to those of the detection system and detector described with reference to Figures 6 to 8 . Therefore, unless otherwise mentioned, the description of the elements of Figures 6 to 8 can also be applied to the corresponding elements of Figure 9 (e.g., the reference numerals sharing the two rightmost digits), and will not be strictly reintroduced. Figure 9 Such elements in Figures 6 to 8 can include scattered illumination 926, measurement signal 928, pixels 930-1 to 930-m, sampling clock 932, comparator 934, analog domain 951, digital domain 953, master clock 955, and analyzers 916 and 917 - the structures and functions can be inferred from the description of the similar elements in

[0137] In some aspects, the detection system may further include a pixel read combiner 940 (e.g., a multiplexer) and a demultiplexer 942. The pixel read combiner 940 may combine the analog signals generated by pixels 930-1 to 930-m, which are generated by receiving scattered illumination 926. The illumination incident on each of pixels 930-1 to 930-m may have n parameters (i.e., n modulation frequencies associated with photon wavelength, polarization, angle, etc.). The pixel read combiner 940 and the demultiplexer 942 may interface with a sampling clock 932 such that the measurement signal 928 may include demultiplexed string pulses. They may be distinguished based on the association of the demultiplexed string pulses with the corresponding pixels among pixels 930-1 to 930-m. The analyzer 916 may be used for finite-time phase-locked detection of the data stream originating from multiple pixels (as opposed to the single pixel shown in Figure 8 ). Alternatively, the measurement signal 928 may be separated based on demultiplexing and sent to the corresponding analyzer among multiple analyzers. The multiple analyzers may be grouped together in an analyzer system.

[0138] Figure 10 Detector 1014 is shown in accordance with some aspects. In some aspects, detector 1014 may include a structure and function similar to the detection system and detector described with reference to Figures 6 to 9 . Thus, unless otherwise mentioned, the description of the elements of Figures 6 to 9 may also apply to the corresponding elements of Figure 10 (e.g., the reference numerals sharing the two rightmost digits), and will not be reintroduced strictly.

[0139] In some aspects, detector 1014 may be an integrated QIS camera having stacked layers. Detector 1014 may include a pixel layer 1044, a mixed-signal IC layer 1046, and a logic layer 1048 (e.g., the first layer, the second layer, and the third layer respectively). The pixel layer may receive illumination for subsequent conversion into a digital signal. The mixed-signal IC layer 1046 may provide the conversion of the analog signal generated at the pixel layer into a digital signal (e.g., the comparator mentioned above may be part of the mixed-signal IC layer 1046). Components such as the analyzer mentioned above may be part of the logic layer 1048. The logic layer 1048 may provide digital processing for finite-time phase-locked detection.

[0140] Figure 11A and 11B show the pupil plane 1150 of the propagating illumination beam 1124 in accordance with some aspects. In some aspects, Figure 11A and 11B The elements of may be similar to some of the elements described with reference to Figures 6 to 10 . Thus, unless otherwise mentioned, Figures 6 to 10The description of the elements of Figure 11A and 11B the corresponding elements (e.g., reference numerals sharing two rightmost digits), and will not be strictly reintroduced. Figure 11A and 11B Such elements in Figures 6 to 8 can include the illumination beam 1124, the target 1118, and the substrate 1120—the structure and function can be inferred from the description of the similar elements in

[0141] In some aspects, the illumination beam 1124 can include two or more illumination beams, such as beams 1 to k (in this non-limiting example, k is 12). Figure 11A shows a front view of the pupil plane 1150 centered on the optical axis and the arrangement of beams 1 to k. For clarity, only beams 1, 2, 7, and 8 are shown in Figure 11B . Beam 1 can be radially opposite to beam 7. Beam 2 can be radially opposite to beam 8. Figure 11A and 11B The arrangement shown in is useful for performing angular-resolved scattering measurements. By inspecting at different incident angles, different information about the target 1118 can be obtained. As shown, beams 2 and 8 can have an incident angle on the target 1118, and beams 1 and 7 can have an incident angle

[0142] on the target 1118. Optical elements (e.g., lenses) can be arranged at or near the pupil plane 1150 to converge beams 1 to k at the target 1118.

[0143] Figure 12 shows a computer system 1200 according to some aspects. For example, the computer system 1200 or any other well-known computer system can be used to implement the various aspects and components therein.

[0144] In some aspects, computer system 1200 can include one or more processors (also referred to as central processing units or CPUs), such as processor 1204. Processor 1204 can be connected to a communication infrastructure or bus 1206.

[0145] In some aspects, one or more of the processors 1204 can be, respectively, a graphics processing unit (GPU). In some aspects, a GPU is a type of processor that is a specialized electronic circuit designed to handle math-intensive applications. A GPU can have a parallel architecture that is very efficient for parallel processing of large chunks of data, such as the common math-intensive data found in computer graphics applications, images, videos, etc.

[0146] In some aspects, computer system 1200 can also include (a) plurality of user input / output devices 1203 that communicate with the communication infrastructure 1206 via (a) plurality of user input / output interfaces 1202, such as monitors, keyboards, pointing devices, etc. Computer system 1200 can also include a main memory or primary memory 1208, such as random access memory (RAM). The main memory 1208 can include one or more levels of cache. Control logic (i.e., computer software) and / or data is stored therein in the main memory 1208.

[0147] In some aspects, computer system 1200 can also include one or more secondary storage devices or memories 1210. The secondary memory 1210 can include, for example, a hard disk drive 1212 and / or a removable storage device or drive 1214. The removable storage drive 1214 can be a floppy disk drive, a tape drive, a compact disk drive, an optical storage device, a tape backup device, and / or any other storage device / drive. The removable storage drive 1214 can interact with a removable storage unit 1218. The removable storage unit 1218 can include a computer-usable or readable storage device on which computer software (control logic) and / or data is stored. The removable storage unit 1218 can be a floppy disk, a tape, a compact disk, a DVD, an optical storage disk, and / or any other computer data storage device. The removable storage drive 1214 reads and / or writes to the removable storage unit 1218 in a well-known manner.

[0148] In some aspects, the secondary memory 1210 may include other means, tools, or other methods that allow computer programs and / or other instructions and / or data to be accessed by the computer system 1200. Such means, tools, or other methods may include, for example, removable storage units 1222 and interfaces 1220. Examples of removable storage units 1222 and interfaces 1220 may include program cartridges and cartridge interfaces (such as those found in video game devices), removable memory chips (such as EPROMs or PROMs) and associated sockets, memory sticks and USB ports, memory cards and associated memory card slots, and / or any other removable storage unit and associated interface.

[0149] In some aspects, the computer system 1200 may also include a communication or network interface 1224. The communication interface 1224 enables the computer system 1200 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (collectively and individually referred to by reference numeral 1228). For example, the communication interface 1224 may allow the computer system 1200 to communicate with the remote device 1228 via the communication path 1226, which may be wired and / or wireless and may include any combination of LANs, WANs, the Internet, etc. Control logic and / or data may be sent to and from the computer system 1200 via the communication path 1226.

[0150] In some aspects, it is contemplated that the phase-locking function may be implemented in a variety of ways. For example, may be set to the smallest possible value such that the set of optical signals is just sufficient to discern a useful SNR. In yet another example, may correspond to one or more cycles (e.g., 2π radians) of the modulation signal. For efficiency, the above pre-generated cosine and / or sine tables may cover some limited time range (e.g., the smallest possible value described in the non-limiting example above). However, when measuring longer periods (e.g., the set time exceeds the minimum time to improve SNR), the limited pre-generated cosine and / or sine tables should be extended by the corresponding amount. This may result in the analysis requiring additional hardware space, which may increase cost and complexity.

[0151] In some aspects, the pre-generated tables and their use may be implemented in a way that simplifies digital computations.

[0152] Figure 13 FIG. 1300 shows a flowchart of operations performed in conjunction with the detection system disclosed herein, according to some aspects. In some aspects, the flowchart 1300 may be performed via analyzers 616, 816, 817, 916, and / or 917 ( Figure 6 , 8and any one of 9) or a combination thereof. The pre-generated table 1302 (such as a cosine table, a sine table, etc.) may include discrete elements (the element numbers are traced via an index . The values of the pre-generated table 1302 are represented by , , , …, . Any detection system disclosed herein may generate a measurement signal 1304 based on receiving scattered illumination from a target. The measurement signal 1304 may be discretized (e.g., in digital form), and its elements are considered in the context of the index that is used to describe the pre-generated table 1302 (e.g., , , , etc.). The element may be the first element of the measurement signal 1304. In some aspects, other elements may be located before the element .

[0153] In some aspects, the analysis of the measurement signal 1304 may be performed by combining the measurement signal 1304 and the pre-generated table 1302 (e.g., via a multiplication operation 1306). For example, a multiplication × may be performed. The result is a quantity . Since the pre-generated 1302 may correspond to a periodic table (e.g., a periodic cosine table with j elements), the element for the next multiplication of the pre-generated table may be × to generate a quantity . This operation may be performed multiple times for the corresponding discrete elements (e.g., generating , etc.), which may be represented as a quantity 1308. The quantity 1308 may be aggregated (e.g., via a summation operation 1310) within an integration period (e.g., ). The aggregation operation may be accompanied by a normalization operation based on the number of elements being summed (e.g., extracting the correct value of the modulation amplitude). The aggregated output 1312 may be one of the coefficients and that allow the determination of the phase or amplitude (the output coefficients are also illustrated in Figure 8 and 9 ).

[0154] In some aspects, to improve the analysis efficiency, the pre-generated table 1302 may be implemented together with a cyclic shift register 1314. When When set to a time period longer than one cycle of the cosine / sine table, the loop register 1314 can allow the table 1302 to repeat. To facilitate the use of the shift register 1314, a condition can be imposed such that the summation operation 1310 is performed at exact multiples of the corresponding modulation period. In some aspects, when the summation operation 1310 is performed in each modulation channel, the condition can be to perform the summation operation 1310 at exact multiples of each modulation period. Using the pre-generated table 1302 can be more efficient than extrapolating or preloading additional elements of the extended pre-generated table 1302.

[0155] In some aspects, the process can be reset and restarted during the next integration period. The process can be iterated for multiple different pre-generated tables corresponding to different modulation frequencies, such that information can be extracted from different modulation channels. One or more operations of the flowchart 1300 can be performed using the processor of the camera or an external processor (such as the CPU or GPU of a personal computer).

[0156] Figure 14 A flowchart 1400 showing operations performed in conjunction with the detection system disclosed herein according to some aspects is shown. In some aspects, the flowchart 1400 can have some features in common with the flowchart 1300 ( Figure 13 ) Unless otherwise mentioned, Figure 13 the description of the elements of Figure 14 can also apply to Figure 14 Elements that appear in Figure 13 and correspond to the elements in Figure 6 can have similar reference numerals (e.g., reference numerals sharing the two rightmost digits). Examples of such elements in

[0157] Figure 13 and Output 1412 is output in a continuous manner. This form of continuous output can be regarded as the form of a "finite impulse response" filter. A finite impulse response (FIR) filter can be considered a filter whose impulse response (or response to any finite-length input) has a finite duration because it stabilizes to zero within a finite time. This is in contrast to an infinite impulse response (IIR) filter, which can have internal feedback and can continue to respond indefinitely or for a long time.

[0158] In some aspects, the operations in flowchart 1400 (and 1300 ( Figure 13 )) can be performed at a speed consistent with the sampling rate of the detection system. However, this may result in an excessive amount of data output. By implementing a decimation operation 1420 on output 1412, the problem of large data output can be alleviated. In flowchart 1300 ( Figure 13 )), continuous output can also be achieved by implementing a suitable input from an external timing mechanism.

[0159] In some aspects, a non-transitory tangible device or article (including a non-transitory tangible computer-usable or readable medium on which control logic (software) is stored) is also referred to herein as a computer program product or a program storage device. This includes but is not limited to computer system 1200, main memory 1208, secondary memory 1210, and removable storage units 1218 and 1222, as well as tangible articles implementing any combination of the foregoing. When executed by one or more data processing devices (such as computer system 1200), such control logic causes such data processing devices to operate as described herein.

[0160] Based on the teachings contained in this disclosure, it will be apparent to those skilled in the relevant art(s) how to make and use various aspects of this disclosure using data processing devices, computer systems, and / or computer architectures (different from Figure 12 those shown). In particular, the various aspects described herein can be operated using software, hardware, and / or operating system implementations (different from those described herein).

[0161] Embodiments can be further described using the following items:

[0162] 1. A measurement system, comprising:

[0163] An illumination system configured to send illumination towards a target, the illumination having a plurality of illumination parameters associated with corresponding modulation frequencies;

[0164] A camera configured to receive scattered illumination from the target and generate a measurement signal encoded with identification flags of a plurality of modulation frequencies for each pixel of the camera; and

[0165] An analyzer system configured to demodulate a measurement signal based on a plurality of modulation frequencies for each pixel of a camera and output a phase, an amplitude, or both the phase and the amplitude of a demodulated component of the measurement signal corresponding to the modulation frequencies.

[0166] 2. The measurement system according to item 1, wherein the illumination system mixes different illumination parameters from a set of parameters.

[0167] 3. The measurement system according to item 2, wherein the set of parameters includes one or more wavelengths, one or more polarizations, and one or more angles of incidence at a target.

[0168] 4. The measurement system according to item 1, wherein:

[0169] The illumination system is further configured to apply a plurality of illumination parameters to the transmitted illumination simultaneously; and

[0170] The analyzer system is further configured to perform demodulation on the plurality of illumination parameters simultaneously.

[0171] 5. The measurement system according to item 1, further comprising:

[0172] A multiplexer configured to combine measurement signals from a set of pixels of a camera; and

[0173] A demultiplexer configured to demultiplex the combined measurement signals, wherein demodulation of the measurement signals is performed using the demultiplexed measurement signals.

[0174] 6. The measurement system according to item 1, wherein each pixel of the camera is sensitive to multiple wavelengths in parallel.

[0175] 7. The measurement system according to item 1, wherein the structure of the camera is hierarchical and includes a pixel layer, an analog-to-digital layer, and a logic layer.

[0176] 8. The measurement system according to item 1, further comprising a time reference system configured to provide a timing basis for each modulation frequency among the modulation frequencies.

[0177] 9. The measurement system according to item 1, further comprising a digital-to-analog converter system configured to receive an analog measurement signal from a pixel of the camera and output a digital measurement signal.

[0178] 10. The measurement system according to item 1, wherein:

[0179] Demodulation of the measurement signal is characterized by a measurement sampling time ; and

[0180] is an integer multiple of the period of the modulation frequency.

[0181] 11. The measurement system according to item 1, wherein:

[0182] The demodulation of the measurement signal is characterized by the measurement sampling rate ; and

[0183] is an integer multiple of the frequency interval between at least two of the modulation frequencies.

[0184] 12. The measurement system according to item 1, wherein the analyzer system is further configured to perform demodulation of the measurement signal by combining the data in the measurement signal with at least a cosine table, at least a sine table, one or more sine-only tables, or one or more cosine-only tables.

[0185] 13. The measurement system according to item 12, wherein the combination of the data is performed via a multiplication operation.

[0186] 14. The measurement system according to item 12, wherein the analyzer system is further configured to use a shift register for at least the cosine table, at least the sine table, one or more sine-only tables, or one or more cosine-only tables to perform demodulation of the measurement signal.

[0187] 15. The measurement system according to item 12, wherein:

[0188] The output of the data combination is a plurality of discrete quantities; and

[0189] The analyzer system is further configured to aggregate the discrete quantities.

[0190] 16. The measurement system according to item 15, wherein the aggregation of the discrete quantities is performed within the measurement sampling time .

[0191] 17. The measurement system according to item 15, wherein the aggregation of the discrete quantities is performed within a moving time window.

[0192] 18. The measurement system according to item 17, wherein the output of the phase, amplitude, or phase and amplitude of the demodulated component is continuously performed based on the moving time window.

[0193] 19. The measurement system according to item 18, wherein the analyzer system is further configured to decimate the continuous output based on the moving time window to reduce the data output rate of each pixel of the camera.

[0194] 20. A lithographic apparatus, comprising:

[0195] An illumination source configured to illuminate a pattern of a patterning device;

[0196] A projection system configured to project an image of the pattern onto a substrate; and

[0197] A measurement system, comprising:

[0198] An illumination system, further configured to direct illumination towards a target, the illumination having a plurality of illumination parameters associated with corresponding modulation frequencies;

[0199] A camera, configured to receive scattered illumination from the target and generate a measurement signal encoded with an identification signature of the plurality of modulation frequencies for each pixel of the camera; and

[0200] An analyzer system, configured to demodulate the measurement signal for each pixel of the camera based on the plurality of modulation frequencies and output a phase, an amplitude, or both the phase and the amplitude of the demodulated component of the measurement signal corresponding to the modulation frequencies.

[0201] 21. The lithographic apparatus according to item 20, wherein the illumination system mixes different illumination parameters from a set of parameters.

[0202] 22. The lithographic apparatus according to item 21, wherein the set of parameters includes one or more wavelengths, one or more polarizations, and one or more angles of incidence at the target.

[0203] 23. The lithographic apparatus according to item 20, wherein:

[0204] The illumination system is further configured to apply a plurality of illumination parameters to the directed illumination simultaneously; and

[0205] The analyzer system is further configured to perform demodulation for the plurality of illumination parameters simultaneously.

[0206] 24. The lithographic apparatus according to item 20, further comprising:

[0207] A multiplexer, configured to combine measurement signals from a set of pixels of the camera; and

[0208] A demultiplexer, configured to demultiplex the combined measurement signals, wherein demodulation of the measurement signals is performed using the demultiplexed measurement signals.

[0209] 25. The lithographic apparatus according to item 20, wherein each pixel of the camera is sensitive to multiple wavelengths in parallel.

[0210] 26. The lithographic apparatus according to item 20, wherein the structure of the camera is hierarchical and includes a pixel layer, an analog-to-digital layer, and a logic layer.

[0211] 27. The lithographic apparatus according to item 20, further comprising a time reference system, the time reference system being configured to provide a timing basis for each of the modulation frequencies.

[0212] 28. The lithographic apparatus according to item 20 further comprises a digital-to-analog converter system configured to receive a measurement signal in analog form from the pixels of the camera and output a measurement signal in digital form.

[0213] 29. The lithographic apparatus according to item 20, wherein:

[0214] The demodulation of the measurement signal is characterized by a measurement sampling time ; and

[0215] is an integer multiple of the period of the modulation frequency.

[0216] 30. The lithographic apparatus according to item 20, wherein:

[0217] The demodulation of the measurement signal is characterized by a measurement sampling rate ; and

[0218] is an integer multiple of the frequency interval between at least two of the modulation frequencies.

[0219] 31. The lithographic apparatus according to item 20, wherein the analyzer system is further configured to perform demodulation of the measurement signal by combining the data in the measurement signal with at least a cosine table, at least a sine table, one or more sine-only tables, or one or more cosine-only tables.

[0220] 32. The lithographic apparatus according to item 31, wherein the combination of the data is performed via a multiplication operation.

[0221] 33. The lithographic apparatus according to item 31, wherein the analyzer system is further configured to perform demodulation of the measurement signal using a shift register for at least the cosine table, at least the sine table, one or more sine-only tables, or one or more cosine-only tables.

[0222] 34. The lithographic apparatus according to item 31, wherein:

[0223] The output of the data combination is a plurality of discrete quantities; and

[0224] The analyzer system is further configured to aggregate the discrete quantities.

[0225] 35. The lithographic apparatus according to item 34, wherein the aggregation of the discrete quantities is performed within a measurement sampling time ; and

[0226] 36. The lithographic apparatus according to item 34, wherein the aggregation of the discrete quantities is performed within a moving time window.

[0227] 37. The lithographic apparatus according to item 36, wherein the output of the phase, amplitude, or phase and amplitude of the demodulated component is performed continuously based on the moving time window.

[0228] 38. The metrology system according to clause 37, wherein the analyzer system is further configured to extract a continuous output based on a moving time window to reduce the data output rate for each pixel of the camera.

[0229] As used herein, the terms “radiation,” “beam,” “light,” “irradiation,” etc. may refer to one or more types of electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., having a wavelength λ of 365, 248, 193, 157, 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, for example, 13.5 nm), or hard X-rays operating at less than 5 nm, as well as particle beams (such as ion beams or electron beams). Generally, radiation having a wavelength between about 400 and about 700 nm is considered visible radiation; radiation having a wavelength between about 780 and 3000 nm (or greater) is considered IR radiation. UV refers to radiation having a wavelength approximately between 100 and 400 nm. In lithography, the term “UV” also applies to wavelengths that can be generated by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and / or I-line 365 nm. Vacuum UV or VUV (i.e., UV that is absorbed by gas) refers to radiation having a wavelength approximately between 100 and 200 nm. Deep UV (DUV) generally refers to radiation having a wavelength range from 126 nm to 428 nm, and in some aspects, excimer lasers can generate DUV radiation for use in a lithography apparatus. It should be understood that radiation having a wavelength in the range of, for example, 5 to 20 nm refers to radiation having a certain band, at least a portion of which is in the range of 5 to 20 nm.

[0230] Although some aspects of the present disclosure are described in the context of a lithography apparatus in IC manufacturing, it should be understood that the lithography apparatus described herein can be used for other applications, such as the manufacture of integrated optical systems, the guiding and detecting patterns of magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, etc. Those skilled in the art will appreciate that in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered a specific example of the more general terms “substrate” or “target portion,” respectively. The substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a resist layer to the substrate and develops the exposed resist) and / or a metrology unit. In applicable cases, the various aspects disclosed herein can be applied to such and other substrate processing tools. In addition, the substrate can be processed more than once, such as to create a multi-layer IC, such that the term substrate as used herein can also refer to a substrate that already contains multiple processed layers.

[0231] In addition, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that the various aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, the topography in the patterning device defines the pattern created on the substrate. The topography of the patterning device can be pressed into a resist layer supplied to the substrate, and the resist is then cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein.

[0232] It should be understood that the language or terminology herein is for the purpose of description and not of limitation, such that the terminology or language of this specification is to be interpreted by those skilled in the relevant art(s) in light of the teachings herein.

[0233] The present disclosure has been described above by means of functional building blocks that illustrate implementations of specified functions and their relationships. For convenience of description, the boundaries of these functional building blocks are arbitrarily defined herein. Alternate boundaries can be defined as long as the specified functions and their relationships are appropriately performed. The foregoing description of specific aspects will fully disclose the generality of the present disclosure, and by applying knowledge within the technical field, others can readily modify and / or adapt various applications of such specific aspects without undue experimentation and without departing from the general concept of the present disclosure. Accordingly, such adaptations and modifications are intended to be within the meaning and scope equivalent to the disclosed aspects based on the teachings and guidance presented herein.

[0234] It should be understood that the detailed description section, rather than the summary and abstract sections, is intended to be used to interpret the claims. The summary and abstract sections may state one or more, but not all, aspects of the present disclosure as contemplated by the inventors, and thus are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the claimed subject matter should not be limited by any of the above aspects, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A measurement system, comprising: An illumination system configured to send illumination towards a target, the illumination having a plurality of illumination parameters associated with corresponding multiple modulation frequencies; A camera configured to receive scattered illumination from the target and generate a measurement signal encoded with identification flags of the multiple modulation frequencies for each pixel of the camera; And An analyzer system configured to demodulate the measurement signal based on the multiple modulation frequencies for each pixel of the camera and output the phase, amplitude, or both the phase and amplitude of the demodulated component of the measurement signal corresponding to the modulation frequencies.

2. The measurement system according to claim 1, wherein the illumination system mixes different illumination parameters from a parameter set.

3. The measurement system according to claim 2, wherein the parameter set includes one or more wavelengths, one or more polarizations, and one or more incident angles at the target.

4. The measurement system according to claim 1, wherein: The illumination system is further configured to apply the multiple illumination parameters to the sent illumination simultaneously; and The analyzer system is further configured to perform the demodulation on the multiple illumination parameters simultaneously.

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

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

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

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

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

10. The measurement system according to claim 1, wherein: The demodulation of the measurement signal is characterized by a measurement sampling time ; and is an integer multiple of the period of the modulation frequency.

11. The measurement system according to claim 1, wherein: The demodulation of the measurement signal is characterized by the measurement sampling rate and is an integer multiple of the frequency interval between at least two of the modulation frequencies.

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

13. The measurement system according to claim 12, wherein the combination of the data is performed via a multiplication operation.

14. The measurement system according to claim 12, wherein the analyzer system is further configured to use a shift register for 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 to perform the demodulation of the measurement signal.

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

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