Improved alignment for scatterometer-based particle inspection systems

Abstract

An apparatus, system, and method of patterning device inspection are described. According to an aspect, a method of inspection is disclosed that includes receiving, at a multi-element detector within an inspection system, radiation scattered at a surface of an object. The method also includes measuring, with processing circuitry, an output of each element of the multi-element detector, the output corresponding to the received scattered radiation. Further, the method includes calibrating, with the processing circuitry, the multi-element detector by identifying a valid pixel region comprising one or more elements of the multi-element detector having a measured output above a predetermined threshold. The method also includes identifying an invalid pixel region comprising remaining elements of the multi-element detector. Additionally, the method includes setting the valid pixel region as a default alignment setting between the multi-element detector and a light source that caused the scattered radiation.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 969,261, filed February 3, 2020, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to detection of contaminants on a lithographic patterning device in a lithographic apparatus and system. BACKGROUND

[0004] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually at the target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs) or other devices designed to function as functional units, such as memory devices. In such cases, a patterning device, which can alternatively be referred to as a mask or a reticle, can be used to generate a desired circuit pattern to be formed on individual layers of a device. This pattern can be transferred to a target portion of the substrate (e.g., a portion including a part, or all, of one or more dies) using the lithographic apparatus. Typically, the pattern is transferred by imaging onto a layer of radiation- sensitive material (resist) disposed on the substrate. Generally, a single substrate will contain a network of adjacent target portions each to be patterned by a given lithographic apparatus. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern under the radiation beam across the target portion while simultaneously scanning the substrate parallel or antiparallel to the beam. The pattern can also be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0005] Manufacturing devices, such as semiconductor devices, typically involves using a number of fabrication processes to process a substrate (e.g., a semiconductor wafer) to form various features and typically multiple layers of the devices. These layers and / or features are typically manufactured and / or handled using, for example, deposition, lithography, etching, chemical-mechanical polishing, and ion implantation. Multiple devices can be fabricated on a plurality of dies on the substrate, and then separated into individual devices. Such device manufacturing processes can be considered patterning processes. Patterning processes involve a pattern transfer step, such as optical and / or nanoimprint lithography using a lithographic apparatus, to provide a pattern on a substrate, and typically but optionally one or more related pattern processing steps, such as resist development by a developing apparatus, baking the substrate using a baking tool, etching the pattern by an etching apparatus, etc. Additionally, one or more metrology processes are included in the patterning processes.

[0006] Metrology processes are used at various steps during a patterning process to monitor and / or control the process. For example, metrology processes are used to measure one or more characteristics of a substrate, such as a relative position (e.g., registration, overlay, alignment, etc.) or a dimension (e.g., line width, critical dimension (CD), thickness, etc.) of a feature formed on the substrate during the patterning process, so that, for example, a performance of the patterning process can be determined from the one or more characteristics. If the one or more characteristics are unacceptable (e.g., outside of a predetermined range for the one or more characteristics), one or more variables of the patterning process can be designed or altered, for example, based on the measurements of the one or more characteristics, so that substrates manufactured by the patterning process have one or more acceptable characteristics.

[0007] With advances in lithography and other patterning process technologies, the size of functional elements has continued to decrease, while the amount of the functional elements (such as transistors) per device has steadily increased over the past few decades. At the same time, accuracy requirements in terms of overlay, critical dimension (CD), etc. have become increasingly stringent. Errors, such as errors in overlay, errors in CD, etc. will inevitably be produced in the patterning process. For example, imaging errors can be produced by optical aberrations, patterning device heating, patterning device errors, and / or substrate heating, and can be characterized in terms of, for example, overlay, CD, etc. Additionally or alternatively, the errors can be introduced in other portions of the patterning process, such as in etching, developing, baking, etc., and similarly can be characterized in terms of, for example, overlay, CD, etc. The errors can cause problems in terms of functional operation of the device, including functional failure of the device, contamination, or one or more electrical problems of the functional device. Therefore, it is desirable to be able to characterize one or more of these errors, and take steps to design, modify, control, etc. the patterning process to reduce or minimize one or more of these errors.

[0008] One such error that can be produced is contamination on a surface of the lithographic patterning device. Such contamination can include particles on the surface of the lithographic patterning device that can affect the etching of the pattern itself and / or subsequent inaccuracies in the patterning process, which can result in damaged and / or poorly functioning circuitry.

[0009] As such, these errors can also result in increased costs due to inefficient processing, waste, and processing delays. SUMMARY

[0010] Therefore, there is a need to determine the level / extent of contaminants of a patterning device, including the size and location of the contaminants, and determine whether to accept the device due to being within a predetermined tolerance or reject the device due to being contaminated beyond a predetermined tolerance.

[0011] In some embodiments, lithography inspection apparatuses, systems, and methods are described herein. According to some aspects, an inspection method is described that includes receiving, at a multi-element detector within an inspection system, radiation scattered at a surface of an object. The method also includes measuring, with processing circuitry, an output of each element of the multi-element detector, the output corresponding to the received scattered radiation. Also, the method further includes calibrating, with the processing circuitry, the multi-element detector by identifying an active pixel region comprising one or more elements of the multi-element detector having a measured output above a predetermined threshold, and identifying an inactive pixel region comprising remaining elements of the multi-element detector; and setting the active pixel region as a default alignment setting between the multi-element detector and a light source that caused the scattered radiation.

[0012] According to some aspects, the inspection method can also include receiving, at the multi-element detector, second radiation scattered at the surface of the object; and generating a detection signal based on the output of the active pixels, the detection signal indicating a presence of a foreign particle on the surface. The inspection method can also include determining a stray signal based on the output of the inactive pixel region, the stray signal indicating scattered light; and discarding the output of the inactive pixel region.

[0013] According to some aspects, an illumination spot generated by the scattered radiation on a surface area of the multi-element detector can be smaller than a detection surface area of the multi-element detector, and the active pixel region contains the illumination spot.

[0014] According to some embodiments, the method can also include determining a stray signal in response to receiving a detection signal from the inactive pixel region; and classifying the stray signal as a false positive signal. Also, the method can also include determining a location of the foreign particle based on: measuring pixel outputs from pixels within the active pixel region; identifying one or more pixels within the active pixel region having a highest output level; and inferring a location of the foreign particle based on a location of the identified one or more pixels within the active pixel region.

[0015] According to some embodiments, the method can further include performing a compensation operation by identifying a misalignment condition between the multi-element detector and the light source, and also by reinitializing a calibration operation in response to identifying the misalignment. In this regard, the identifying can further include detecting a plurality of new elements within the active pixel area, or within an inactive pixel area bordering the active pixel area, the plurality of new elements being located outside of an illumination spot created by the scattered radiation on a surface area of the multi-element detector, each of the plurality of new elements generating an output above a predetermined threshold during one or more inspection operations.

[0016] According to some aspects, the method can further include setting a new active pixel area as a default alignment setting between the multi-element detector and the light source. Also, according to some aspects, the misalignment condition can be a drift condition in which a drift (or shift) can occur between the optical elements, which can result in a misalignment between the illumination area and the detection area.

[0017] Further features and advantages of the present disclosure, as well as structure and operation of various embodiments of the present disclosure, are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will readily occur to those skilled in the art based on the teachings contained herein. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable a person skilled in the relevant art to make and use the present disclosure.

[0019] Figure 1A A schematic diagram of a reflective lithography apparatus according to some embodiments is shown;

[0020] Figure 1B A schematic diagram of a transmissive lithography apparatus according to some embodiments is shown;

[0021] Figure 2 A detailed schematic diagram of a reflective lithography apparatus according to some embodiments is shown;

[0022] Figure 3 A schematic diagram of a lithography cell according to some embodiments is shown;

[0023] Figure 4 A schematic diagram of a metrology system according to an exemplary embodiment is shown;

[0024] Figure 5A schematic diagram of a lithographic patterning device inspection system using laser scanning is shown in accordance with some embodiments;

[0025] Figures 6A-6C Alignment of an illumination spot on a lithographic patterning device with a photodetector is illustrated in accordance with some embodiments;

[0026] Figure 7 A conventional spot on a photodetector requiring precise alignment is illustrated;

[0027] Figure 8 An oversized two-dimensional image sensor array to improve positioning tolerance of the illumination spot is illustrated in accordance with some embodiments;

[0028] Figure 9 A flowchart illustrating an exemplary method for inspecting a surface of an object in accordance with some embodiments is illustrated;

[0029] Figure 10 A flowchart illustrating an exemplary method for calibrating an inspection detector used to inspect a surface of an object in accordance with some embodiments is illustrated;

[0030] Figure 11 A flowchart illustrating an exemplary method for detecting alignment drift in accordance with some embodiments is illustrated;

[0031] Figure 12 A flowchart illustrating an exemplary method for aligning illumination optics with detection optics in accordance with some embodiments is illustrated;

[0032] Figure 13 A diagram of a detector device comprising a photodiode array in accordance with some embodiments is illustrated;

[0033] Figure 14 A diagram of a combination of detectors to detect particles on a lithographic patterning device in accordance with some embodiments is illustrated;

[0034] Figures 15A-15B A combination of detectors to detect particles on a lithographic patterning device in accordance with some embodiments is illustrated; and

[0035] Figure 16 The internal construction of a combination sensor is illustrated in accordance with some embodiments.

[0036] The features and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digits of a reference number typically identify the figure in which the element first appears. The drawings provided are not to be construed as being to scale with any of the elements thereof. DETAILED DESCRIPTION

[0037] The present specification discloses one or more embodiments incorporating features of the present disclosure. The one or more disclosed embodiments are merely exemplary of the present disclosure. The scope of the present disclosure is not limited to the one or more disclosed embodiments. The present disclosure is defined by the claims appended hereto.

[0038] Reference to“one embodiment,”“an embodiment,”“example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase“in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

[0039] For purposes of the description hereinafter, spatial or directional terms, such as, for example, “below,” “lower,” “upward,” “upper,” “above,” “on,” “over,” and the like, can be used with respect to the illustrated orientation of one element or feature with respect to another element or feature as shown in the figures. The spatial and directional terms are used for purposes of the description hereinafter to facilitate describing the various embodiments. It is not intended that the spatial or directional terms be limiting, unless otherwise specified. The devices can be oriented in other directions and the spatial or directional descriptions used herein can be interpreted accordingly.

[0040] The term“about” as used herein indicates values of a given quantity that can vary based on a particular technology. Based on the particular technology, the term“about” can indicate values of a given quantity that vary within, for example, 10-30% of the value, such as ±10%, ±20%, or ±30% of the value.

[0041] Embodiments of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure can also be implemented as instructions stored on a machine-readable medium, which can be read and executed by one or more processors. A machine-readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing firmware, software, routines, non-transitory computer readable instructions, etc.

[0042] However, before describing such embodiments in further detail, it is instructive to present an example environment in which embodiments of the present disclosure can be implemented.

[0043] Example lithographic system

[0044] Figure 1A and Figure 1B are schematic illustrations of a lithographic apparatus 100 and a lithographic apparatus 100', respectively, according to some embodiments. In some embodiments, each of the lithographic apparatus 100 and the lithographic apparatus 100' includes the following: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep-ultraviolet or extreme-ultraviolet (EUV) 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 configured to accurately position the patterning device MA; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. As will be further described below, other configurations of the illuminator can be implemented to improve illumination, and compactness of design.

[0045] The lithographic apparatuses 100 and 100' also have a projection system PS configured to project a pattern imparted to the radiation beam B by 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.

[0046] The irradiation system IL may include various types of optical components, such as refractive, reflective, reflective-refractive, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling the radiation beam B.

[0047] The support structure MT holds the patterning apparatus MA in a manner dependent on the orientation of the patterning apparatus MA relative to a reference frame, the design of at least one of the lithography apparatuses 100 and 100', and other conditions such as whether the patterning apparatus MA is held in a vacuum environment. The support structure MT can hold the patterning apparatus MA using mechanical, vacuum, electrostatic, or other clamping techniques. The support structure MT can be a frame or a stage, which may be fixed or movable as needed. By using sensors, the support structure MT can ensure that the patterning apparatus MA is positioned, for example, relative to the projection system PS.

[0048] The term "patterning apparatus" MA should be interpreted broadly as any apparatus capable of imparting a pattern to the radiation beam B in the cross-section of the radiation beam B to generate a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer of a device created in the target portion C to form an integrated circuit.

[0049] The pattern forming apparatus MA can be of the transmissive type (e.g., in...). Figure 1B (as in the lithography equipment 100') or reflective (as in Figure 1A (As in the photolithography apparatus 100). Examples of pattern forming apparatus MA include a mask, a mask, a programmable mirror array, and a programmable LCD panel. Masks are well known in photolithography and include mask types such as binary mask types, alternating phase-shift mask types, attenuation phase-shift mask types, and various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in a different direction. The tilted mirrors impart a pattern to the radiation beam B reflected by the matrix of small mirrors.

[0050] The term "projection system" PS can encompass any type of projection system, including refractive, reflective, reflective-refractive, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation used, or for other factors such as the use of an immersion liquid on a substrate W or the use of a vacuum. Because other gases may absorb excessive radiation or electrons, a vacuum environment can be used for EUV or electron beam radiation. A vacuum environment can therefore be provided throughout the beam path by means of vacuum walls and a vacuum pump.

[0051] The lithographic apparatus 100 and / or the lithographic apparatus 100' can be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such "multiple stage" machines the additional substrate tables can be used in parallel, or

[0052] Reference Figure 1A and Figure 1B The illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' can be separate physical entities, for example when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD (in Figure 1B On the other hand, 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 source SO, the illuminator IL, and the beam delivery system BD if required can be referred to as the radiation system.

[0053] The illuminator IL can include an adjuster AD (in Figure 1B Typically at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner," respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can include various other components (in Figure 1B The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0054] Reference Figure 1AThe radiation beam B is incident on the patterning device (e.g., mask) MA and is patterned by the patterning device MA, which is held on the support structure (e.g., mask table) MT. In the lithography apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. After having been reflected from the patterning device (e.g., mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. By means of the second positioner PW and position sensor IF2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately positioned relative to the path of the radiation beam B (e.g., so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. The patterning device (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0055] Reference is made to Figure 1B The radiation beam B is incident on the patterning device (e.g., mask MA) and is patterned by the patterning device, which is held on the support structure (e.g., mask table MT). Having traversed the mask MA, the radiation beam B travels through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil PPU that is conjugate to the illumination system pupil IPU. Portions of the radiation originate from the intensity distribution at the illumination system pupil IPU and traverse the mask pattern without being affected by diffraction at the mask pattern and produce an image of the intensity distribution at the illumination system pupil IPU.

[0056] By means of the second positioner PW and position sensor IF (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately positioned relative to the path of the radiation beam B (e.g., so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in Figure 1B the lithography apparatus 100) can be used to accurately position the mask MA relative to the path of the radiation beam B (e.g., after mechanical retrieval from a mask library or during scanning).

[0057] In some embodiments, the movement of the mask table MT can be achieved by means of long stroke modules (coarse positioning) and short stroke modules (fine positioning) forming part of the first positioner PM. Similarly, the movement of the substrate table WT can be achieved using long stroke modules and short stroke modules forming part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected with only short stroke actuators, or can be stationary. Mask alignment marks Ml, M2 and substrate alignment marks Pl, P2 can be used to align the mask MA and the substrate W. While the substrate alignment marks (as illustrated) occupy dedicated target portions, the substrate alignment marks can be located in spaces between multiple target portions (referred to as cross-line 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 these dies.

[0058] The mask table MT and the patterning device MA can be located in a vacuum chamber, wherein an in-vacuum robot IVR can be used to move patterning devices, such as masks, 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 transport operations, similar to the in-vacuum robot IVR. Both the in-vacuum robot and the out-of-vacuum robot need to be calibrated for smooth transfer of any payload (e.g., a mask) onto the stationary kinematic mount of the transfer station.

[0059] The lithographic apparatus 100' can include a patterning device transfer system. An exemplary patterning device transfer system can be a patterning device exchange device (V) including, for example, an in-vacuum robot IVR, a mask table MT, a first positioner PM, and other similar components for transferring and positioning a patterning device. The patterning device exchange device V can be configured to transfer a patterning device between a container carrying the patterning device and a processing tool (e.g., the lithographic apparatus 100').

[0060] The lithographic apparatuses 100 and 100' can be used in at least one of the following modes:

[0061] 1. In a step mode, an entire pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single static exposure) while a support structure (e.g., the mask table) MT and the substrate table WT are held static. The substrate table WT is then moved along the X and / or Y direction so that a different target portion C can be exposed.

[0062] 2. In scan mode, in which the support structure (e.g., the mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g., the mask table) MT can be determined by the (de-) magnification and the image reversal characteristics of the projection system PS.

[0063] 3. In an alternative mode, in which a support structure (e.g., the mask table) MT holding the programmable patterning device is kept essentially stationary, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulse radiation source SO can be used and the programmable patterning device is updated as desired at least once every time the substrate table WT is moved in a direction transverse to the projection direction.

[0064] Combinations and / or variations on the above described modes of use or entirely different modes of use can also be employed.

[0065] In some embodiments, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the beam of EUV radiation of the EUV source.

[0066] Figure 2 The lithographic apparatus 100 is shown in more detail in Figure 1. The lithographic apparatus 100 includes the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. The EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. EUV radiation can be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor, in which a very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 can be created by a discharge caused by a discharge produced plasma source. For example, the very hot plasma 210 can be created by an electric discharge. In some embodiments, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0067] Radiation emitted by the hot plasma 210 is transmitted from the source chamber 211 into the collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as a contaminant barrier or foil trap) positioned in or behind an opening in the source chamber 211. The contaminant trap 230 can comprise a channeling structure. The contaminant trap 230 can also comprise a gas barrier, or a combination of a gas barrier and a channeling structure. The contaminant trap or contaminant barrier 230 as further indicated herein comprises at least a channeling structure, as is known in the art.

[0068] The collector chamber 211 can comprise a radiation collector CO which can 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 that traverses the collector CO can be reflected from a grating spectral filter 240 off to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus IF is located at or near the opening 219 in the enclosing structure 220. The virtual source point IF is an image of the plasma 210 from which the radiation is emitted. The grating spectral filter 240 is particularly used to suppress infrared (IR) radiation.

[0069] Subsequently, the radiation traverses an illumination system IL which can include a facetted field mirror device 222 and a facetted pupil mirror device 224, arranged to provide a desired angular distribution of the radiation beam 221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 221 at the patterning device MA, which can be held on a support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by a projection system PS via reflective elements 228, 230 onto a substrate W held on a wafer stage or substrate table WT.

[0070] There can be more elements than shown in the figures. The grating spectral filter 240 can be optional, depending on the type of lithography apparatus. In addition, there can be more mirrors present than shown in the figures, for example, 1 to 6 additional reflective elements in the projection system PS than the reflective elements shown in the figure. Figure 2 There can be more elements than shown in the figures. The grating spectral filter 240 can be optional, depending on the type of lithography apparatus. In addition, there can be more mirrors present than shown in the figures, for example, 1 to 6 additional reflective elements in the projection system PS than the reflective elements shown in the figure.

[0071] The collector optics CO (as Figure 2The nested collector is depicted as having grazing incidence reflectors 253, 254 and 255, to serve as an example of a collector (or collector mirror) only. The grazing incidence reflectors 253, 254 and 255 are disposed axially symmetric around the optical axis O, and this type of collector optics CO is preferably used in combination with a discharge produced plasma source (often referred to as a DPP source).

[0072] Exemplary lithographic cell

[0073] Figure 3 A schematic diagram of a lithographic cell 300, sometimes also referred to as a litho cell or litho cluster, is shown. The lithographic apparatus 100 or 100' can form part of the litho cell 300. The litho cell 300 can also include apparatus to perform pre-exposure and post-exposure processes on the substrate. Conventionally, these include a spin coater SC for depositing a coating of resist on a substrate, a developing apparatus DE for developing the exposed resist, a chill plate CH and a bake plate BK. A substrate handler, or robot RO, picks substrates from input / output stations I / O1, I / O2, moves them between the different process apparatus and transports them to a load bench LB of the lithographic apparatus. These devices are often collectively referred to as track or track and develop systems, and are controlled by a track control unit or track and develop system control unit TCU, which itself is controlled by a supervisory control system SCS that also controls the lithographic apparatus via a litho control unit LACU. The different apparatus can thus be operated to maximize throughput and process efficiency.

[0074] Exemplary metrology system

[0075] Figure 4 A schematic diagram of a metrology system 400 that can be implemented as part of the lithographic apparatus 100 or 100' is shown, in accordance with some embodiments. In some embodiments, the metrology system 400 can be configured to measure height and height variations on a surface of a substrate W. In some embodiments, the metrology system 400 can be configured to detect a position of an alignment mark on a substrate, and to align the substrate relative to a patterning device or other component of the lithographic apparatus 100' using the detected position of the alignment mark.

[0076] In some embodiments, the metrology system 400 can include a radiation source 402, a projection grating 404, a detection grating 412, and a detector 414. The radiation source 402 can be configured to provide a beam of electromagnetic narrowband radiation having one or more passbands. In some examples, the one or more passbands can be within a spectrum of wavelengths between about 500 nm and about 900 mm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the radiation source 402 generates light within an ultraviolet (UV) spectrum of wavelengths between about 225 nm and 400 nm. The radiation source 402 can also be configured to provide the one or more passbands with a substantially constant center wavelength (CWL) value over a long period of time (e.g., over the useful life of the radiation source 402). As discussed above, in current metrology systems, such a configuration of the radiation source 402 can help prevent the actual CWL value from shifting from the desired CWL value. Also, as a result, the use of a constant CWL value can improve the long-term stability and accuracy of a metrology system (e.g., the metrology system 400) compared to current metrology systems.

[0077] The projection grating 404 can be configured to receive one or more beams of radiation generated from the radiation source 402 and provide a projected image onto a surface of a substrate 408. Imaging optics 406 can be included between the projection grating 404 and the substrate 408 and can include one or more lenses, mirrors, gratings, etc. In some embodiments, the imaging optics 406 are configured to focus the image projected from the projection grating 404 onto the surface of the substrate 408.

[0078] In some embodiments, the projection grating 404 provides an image on the surface of the substrate 408 at an angle θ relative to the surface normal. The image is reflected by the substrate surface and re-imaged on the detection grating 412. The detection grating 412 can be the same as the projection grating 404. Imaging optics 410 can be included between the substrate 408 and the substrate detection grating 412 and can include one or more lenses, mirrors, gratings, etc. In some embodiments, the imaging optics 410 are configured to focus the image reflected from the surface of the substrate 408 onto the detection grating 412. Due to the oblique incidence, when the image projected by the projection grating 404 is received by the detection grating 412, then a height variation (Zw) in the surface of the substrate 408 will cause the image to be shifted by a distance (s) given by the following equation (1):

[0079] s = 2Z w sin(θ) (1)

[0080] In some embodiments, the displaced image of the projection grating 404 is partially transmitted by the detection grating 412, and the transmitted intensity is a periodic function of the displacement of the image. This displaced image is received and measured by the detector 414. The detector 414 can include a photodiode or a photodiode array. Other examples of the detector 414 include a CCD array. In some embodiments, the detector 414 can be designed to measure wafer height variations as low as 1 nm based on the received image.

[0081] Example embodiments of alignment of scatterometer-based particle inspection systems

[0082] Figure 5 A schematic of a lithographic patterning device inspection system 500 using laser scanning is shown in accordance with some embodiments. In one example, the inspection system 500 includes a laser source scanner that scans the surface of the lithographic patterning device in the X direction 502 (across the entire lithographic patterning device) while the lithographic patterning device 504 is slowly moved past the scanning laser. It will be appreciated that the scanning operation can be performed on the glass side (e.g., 502(a) and / or the pellicle side (e.g., 502(b)). If there is contamination on the lithographic patterning device 504, light can be scattered as will be described further herein and a detector 506 can process the scattered light and provide further analysis of the detected contamination. It will be appreciated that the detector 506 can be positioned at different locations to detect different scanning operations (e.g., positioned at location 506(a) to detect a glass side scanning operation and / or positioned at location 506(b) to detect a pellicle side scanning operation).

[0083] In some embodiments, if no contamination is detected, the detector can not detect any scattering from the surface of the lithographic patterning device 504 and the detected light will not be further processed. As previously described, any contamination found on the surface of the lithographic patterning device 504 can cause a modification to the pattern being processed which will result in an unintended pattern or faulty circuit.

[0084] In one example, the detector 506(a) can detect the intensity of the light to determine the size of the particle 508 by detecting the level of intensity of the reflection. This can be done in a way that associates higher levels of intensity with larger particle sizes. This is because larger particles will scatter more light and thus will appear brighter to the detector 506(a), whereas smaller particles will scatter less light and thus will appear dimmer to the detector 506(a).

[0085] It will be appreciated that the size-intensity correlation is simply a measure to determine the size of the particle 508. In some examples, the particle 508 can be small but highly reflective (e.g. metallic) and thus the intensity correlation can yield a particle size that appears larger than it actually is. Alternatively, the particle 508 can be large but less reflective (e.g. carbon) and thus the intensity correlation can yield a particle size that appears smaller than it actually is.

[0086] Accordingly, further processing can provide improved detection of particles and particle sizes that contaminate the surface of a lithographic patterning device, as will be further described herein.

[0087] In one example, as Figures 6A-6C further described in Figure 6A , Figure 6A A lithographic patterning device 602 (e.g. reticle) is described that is illuminated by an illumination beam 604. Particle detection can be accomplished by scatterometry, in which a raster scan of the illumination spot is performed across the substrate. As previously described, when a particle is present on the substrate (e.g. the surface of the reticle / lithographic patterning device 602), the scattered light can be measured by a static photodetector 606. It will be appreciated that in some embodiments, the photodetector is also movable. The movement of the photodetector can follow a raster scan or other scan sequence that will enable scanning of the entire surface of the lithographic patterning device. In one example, the intensity of the detected light can be related to the size of the detected particle.

[0088] To measure micron-scale particles, the optics can be positioned to sub-micron tolerances. This requires a certain degree of alignment between the illumination area 608 on the reticle and the detected area 610 on the detector 606. As such, mechanical tolerances and optical distortions can introduce dynamic alignment errors that are difficult to correct. For example, the illumination spot must be precisely aligned so that when the illumination spot hits a particle 506, the scattered light is positioned into the photodetector 606. Notably, if the lithographic patterning device 602 is perfectly clean, the reflected light can be dark and the light can go into the beam dump. However, when any type of contamination is present, the illuminated contamination can produce light scattering that can need to be measured by the photodetector 606. Accordingly, a high degree of alignment of the spot (from the scattering) and the photodetector can be required and will need to be on the order of microns, which requires specialized manufacturing tools, as previously described.

[0089] In some embodiments, as Figure 6B and 6CAs shown, when there is a large amount of overlap between the illuminated spot 608 and the detected spot 610, the ability of the photodetector to accurately detect particle contamination can be reduced. For example, in Figure 6B , the detector can still detect contamination in the overlapping region, but can not detect contamination in the edge regions where there is no overlap. Further, when the overlap is not well aligned (e.g., Figure 6C ), an illuminated pixel that can contain a particle can not be aligned with a detection pixel because the illuminated pixel is not within the overlap / alignment region. As such, the detector can not be able to detect the particle because it can not process any information related to the pixel from which scattered light can be received. As will be further described in Figure 10 , the detected particle image 612 within region 610 can be determined as the signal processed by the detector, where any detection or signal generated by pixels not within region 610 (e.g., from pixel 614) can be considered a false positive detection and discarded.

[0090] Figure 7 FIG. 1 illustrates a conventional spot on a photodetector that requires accurate alignment, according to some embodiments. For example, a conventional spot on a photodetector can be required for perfect alignment between the illuminated region and the detected region.

[0091] According to some embodiments, to overcome the strict alignment requirements between the illuminated region and the detector region, the present disclosure can implement a two-dimensional image sensor array as shown in Figure 8 to improve the positioning tolerance of the illuminated spot.

[0092] In Figure 8 , a sensor array larger than the expected reflection spot can be employed. This improves the optical alignment tolerance and improves manufacturability. In one embodiment, a two-dimensional image sensor array in the form of a charge-coupled device (CCD), complementary metal-oxide-semiconductor (CMOS), or discrete photodetectors can be used in place of a single photodiode cell. In another embodiment, the array can be an array of photodiodes.

[0093] Using an array of photodetectors, such as an array of photodiodes, it can be possible to relax the positioning tolerances in all of the illumination spot, the multiaspect mirror, the optics, or the photodetector, as the array of image sensors is oversized and the resulting spot can fall on different areas of the array of image sensors without the need for precise alignment. For example, area 802 can represent the entire area of the array of photodetectors, which can capture the unwanted reflections 804, and the illumination spot 806 within the predefined active pixel area 808. The illumination spot 806 can be detected at any location within area 802 (e.g., side, corner, middle, etc.). In one embodiment, the active pixel area 808 can be identified / defined based on a calibration process as defined in, for example Figure 10 This calibration allows the inspection system to have increased tolerances and flexibility in the alignment or correspondence between the illuminated area on the lithographic patterning device and the illuminated area on the detector, while at the same time maintaining a high detection accuracy, as the detector array is large enough to achieve full overlap.

[0094] In one embodiment, the image processing algorithm can be designed and calibrated to select which pixels to activate and which to ignore, as the pixels to be ignored contain unwanted noise due to light not originating from the particle. Using this algorithm, any alignment drift over time will not create problems as it would when using a single photodiode, as the array is able to accommodate higher tolerances within the oversized detection area. Furthermore, pellicle sag can sometimes cause the illumination spot to change. This can also be calibrated by dynamically activating different pixels as the spot progresses across the lithographic patterning device. According to one aspect, a calibration mask with known particle size can be placed in the particle scanner system.

[0095] Based on the alignment of the optics and the photodetector, the particle can scatter light into specific areas of the array of photodetectors. Thus, the calibration processing algorithm can detect which areas of the array are detecting light and which are not. As such, the areas that are receiving light can be turned on for future particle scans, while the areas that did not receive light during the calibration process will be turned off for future particle scans. Also, the pixel areas that receive particle light can be thresholded to determine whether the signal from that specific pixel area should be used or discarded. Reference is made here to Figures 9-11 Further descriptions of the calibration and readout methods are provided.

[0096] Figure 9A flowchart illustrating an exemplary method 900 for inspecting a surface of an object, such as a reticle or pellicle (e.g., a photolithographic patterning device), is shown in accordance with some embodiments. It should be appreciated that the operations of the method need not be performed in the order shown and that some operations can be optional or additional.

[0097] Method 900 begins at step 902. In step 902, a surface of an object (e.g., a reticle, a pellicle, etc.) is illuminated with an illumination beam. In embodiments, the illumination beam is provided to the object surface at an oblique angle. In step 904, scattered light from the illuminated object surface is intercepted. In step 906, the scattered light is projected onto a sensor (e.g., sensor 504 of FIG. 1, which includes a sensor array). In embodiments, the sensor "views" the object surface at an oblique angle, while the illumination beam can provide normal light. In step 908, the scattered light is processed to detect particles located on the object surface. For example, a processor coupled to the sensor can be used to analyze the real image for particle detection. Figure 5

[0098] In step 910, the particle size and location of the detected particles are determined. This information can be used to make decisions regarding the use of the object being evaluated. For example, a decision 912 can need to be made as to whether the object needs to be rejected based on whether the determined particle size and location are within a predetermined range or other limit.

[0099] Figure 10 A flowchart illustrating an exemplary method 1000 for calibrating an inspection detector for inspecting a surface of an object is shown in accordance with some embodiments. It should be appreciated that the operations of the method need not be performed in the order shown and that some operations can be optional or additional.

[0100] Method 1000 begins at step 1002, which can be a continuation of step 908. This method can be used to perform a calibration to identify the area within the sensor array that will detect the scattered light. In addition, this method can be used to recalibrate for detected drift operations, as will be discussed further in Figure 11 Step 1002. As previously discussed, this eliminates the need for tight alignment tolerances in order to have as close to perfect or accurate an overlap as possible between the illuminated area and the detected area. Instead, a sensor array that is oversized can encompass the entire area formed by the scattered light within a larger tolerance range.

[0101] ​At step 1004, a plurality of array elements are identified as a portion of an active area (e.g., active area 808) encompassing an illuminated device area. At step 1006, a plurality of array elements within the active area are identified as an illuminated area (e.g., illuminated area 806) corresponding to the illuminated area on the device. As described in Figure 8 The active area is larger than the illuminated area and includes additional pixels, as described in

[0102] The setting of both the active area and the smaller illuminated area allows for further relaxation of tolerances. For example, some illuminated spots can encompass portions of a pixel, but not the entire pixel. Thus, including that pixel as an active pixel would allow the detector to read out the output of that pixel to cover the entire illuminated spot. Otherwise, that portion of the pixel would not be read out, resulting in portions of the illuminated spot not being read out. When identifying the illuminated area, particles within the illuminated area can be detected at step 1008. In this regard, the detector can determine signals received from pixels within the illuminated area as signals received from pixels classified as active pixels, and can further determine signals corresponding to the presence of extraneous particles (e.g., particles) in response to detection signals received from those pixels classified as active pixels.

[0103] When a detector element receives scattered light, the detector element generates a signal (e.g., a detection signal based on the received radiation). The detector can then generate an overall detection signal as a sum of the outputs of one or more pixels of the detector. Based on the detection signal, the detector can identify spurious signals, and signals corresponding to the presence of extraneous particles on a surface of a lithographic patterning device (e.g., patterning device 606). In one example, this determination can be based on which pixel is generating a readout. For example, spurious signals can be signals generated at pixels that have been previously identified as inactive (e.g., during calibration), where signals corresponding to the presence of extraneous particles on the surface can be generated at pixels that have been previously identified as active (e.g., within an active area designated to receive the scattered light). When a signal is determined to be a spurious signal, the signal can be classified as a false positive signal and discarded. The identification of false positive signals can help eliminate false detections, and false readouts, that result in process delays in lithographic patterning equipment.

[0104] Figure 11 A flowchart illustrating an example method 1100 for detecting alignment drift, in accordance with some embodiments, is shown. It should be understood that the operations of the methods need not be performed in the order shown and that some operations can be optional or additional operations can be included.

[0105] At step 1102, within the detector array, a plurality of cells are detected that receive illumination. At step 1104, it is determined whether the array cells are within a previously defined active area or outside. If the detected cells are within the active area, the method continues to step 904 as previously discussed. If it is determined that any of the plurality of cells are outside the active area, at step 1106, a drift is determined and recalibration is performed in accordance with Figure 10 the method provided in

[0106] A lithographic apparatus (e.g., lithographic apparatus 100) applies a desired pattern to a substrate, such as to a target portion of the substrate. During the manufacture of integrated circuits (ICs) using a lithographic apparatus, a lithographic patterning device (e.g., a mask or reticle) produces a circuit pattern on a separate layer to be formed on the IC. This pattern can be transferred, for example, onto a target portion (e.g., including a portion of a die, one or several dies) of the substrate (e.g., a silicon substrate). To reduce the manufacturing cost of the IC, then, it can be beneficial to expose multiple substrates for each IC. Also, the lithographic apparatus can be used continuously. That is, in some embodiments, to keep the manufacturing cost of all types of ICs at a minimum possible, the idle time between multiple substrate exposures is also minimized. This can include inspection, particle detection, and calibration. As such, the lithographic apparatus can absorb heat that can cause expansion of components of the apparatus, resulting in drift, movement, and changes in uniformity.

[0107] To ensure good imaging quality on the patterning device and the substrate, then, a controlled uniformity of the illumination beam can be maintained. As such, the entire lithographic process of the illumination beam can be controlled with at least some uniformity. Therefore, it can be necessary to use recalibration to perform compensation for any expansion that results in drift or movement. In some examples, a photodetector array can be oversized relative to an illumination area on the lithographic patterning device, and physical recalibration implemented by any type of movement or physical adjustment to the detector can not be necessary. Instead, the recalibration process can redefine the active area and the illumination area based on the detected scattered light projected onto the sensor array.

[0108] Further, drift detection can be part of a broader diagnostic capability. In this regard, a centroid tracking algorithm can be used to predict when an alignment is approaching a maximum out-of-specification setting not only with respect to drift, but also with respect to movement and any type of uniformity change. According to one embodiment, when a calibration reticle having a known particle size is inserted into the system for calibration, the effective pixel signal strength can be measured and the centroid can be calculated. For example, if the signal is split evenly between two pixels, the centroid is located at the center of the two pixels. As one pixel begins to record stronger intensity values and the other pixel begins to become lower in intensity, the "centroid" can be seen as moving toward the pixel of higher intensity. Two or more pixels can be utilized to detect the centroid. Thus, over a period of time, the centroid can be tracked and drift data can be measured. This can help determine whether the system is moving toward an out-of-tolerance condition (i.e., moving away from a tolerance condition). An out-of-tolerance condition can be a situation in which the effective pixel is no longer tracking the particle with the correct effective pixel.

[0109] While it is possible to set ineffective photodiodes to reject unwanted light, it is beneficial to measure the output of the ineffective photodiodes to measure the strength of false positives due to unwanted scattered light. According to some embodiments, real particles can illuminate the detection area being calibrated. Ghost particles can illuminate the detection area as well as the surrounding area. Thus, by monitoring the signal strength of the surrounding area, detection of ghost particles, i.e., false positive detection, can be flagged.

[0110] The sensor array can be an array of photodiodes, a CCD array, etc. For example, an array of photodiodes can provide additional advantages over the advantages of a CCD array. For example, the processing time of a photodiode can increase the processing speed of image reading and detection.

[0111] Figure 12 A flowchart depicting an exemplary method 1200 for aligning an illumination optic with a detection optic is illustrated in accordance with some embodiments. According to some aspects, the method 1200 can include the operation of receiving 1202, at a multi-element detector within the inspection system, radiation scattered at a surface of a lithographic patterning device. An illumination source can illuminate a portion of the lithographic patterning device (e.g., a reticle). As previously described, alignment between the illumination source and the detection system can be needed to improve detection accuracy. In this regard, and to improve alignment tolerances, a multi-element detector can be used. Such a detector can be an array of photodiodes. While other multi-element detectors (e.g., CCD, CMOS, etc.) can be used, an array of photodiode sensors provides certain advantages, including efficient and convenient processing of the illuminated area and related data.

[0112] The method 1200 can also include a measuring operation 1204 of the output of each element of the multi-element detector, the output corresponding to the received scattered radiation. In this regard, the detector can measure the output of each photodiode of the photodiode array to determine where the scattered light is incident on the photodiode array. This can eliminate the need for constant manual physical alignment between the illumination source and the detector that can be required. Instead, the method 1200 allows for an increased detection area that can be programmatically enabled or disabled for the specified pixels within the active area that receive light. In this regard, when there is system drift, or misalignment, over time, a simple recalibration process can be performed rather than manually realigning the operation. This also allows for larger manufacturing tolerances of the optical system as any misalignment can be compensated or adjusted by controlling which pixels are activated / deactivated. Thus, pixels that receive scattered light will have an output, while pixels that do not receive light can have no output, or can have an output with a value below a threshold of sufficient magnitude.

[0113] The method 1200 can further include a calibration operation 1206. In this regard, the method 1200 can include calibrating the multi-element detector by identifying an active pixel area of the multi-element detector that includes one or more elements having a measured output above a predetermined threshold, and identifying an inactive pixel area of the multi-element detector that includes the remaining elements. As described herein Figure 8 When an illumination spot is incident on the photodiode array, pixels that receive light can be designed as active pixels, while pixels that do not receive light or receive unwanted reflections can be designated as inactive pixels. This designation can depend on the measured value output for each pixel. As described herein, pixels that receive light can provide an output above a predetermined threshold, e.g., an output with a magnitude sufficient to correspond to the received incident light.

[0114] The method 1200 can also include setting 1208 the active pixel area as a default alignment setting between the multi-element detector and a light source that causes the scattered radiation. Setting the active pixel area is important for aligning the light incident on the reticle with its corresponding reflection (scattering) on the detector. Once the active area is determined, the active area can be designated as the location from which all future readings can be taken (unless a drift situation occurs). At this point, the detector can be considered calibrated and ready to perform inspection operations.

[0115] The method 1200 can include, at Figure 12other operations not illustrated. For example, the method 1200 can include receiving second radiation scattered at a surface of the object and generating a detection signal based on the output of the active pixels. In this regard, the second radiation scattering can be radiation scattering that occurs after the detector is calibrated. Further, the detection signal can be a signal that indicates whether a particle is detected. As described herein, a reticle without contamination can not produce scattered light when illuminated. Thus, when light is received at the detector, the detector can measure the output of each pixel within the active area and perform a weighted summation operation (using an operational amplifier, etc.). The multi-element detector can then generate a detection signal that indicates whether a contaminant is present. For example, if a contaminant is present, the weighted sum can equal a value of "1," where the weighted sum can equal "0" or a value close thereto. This indicates whether a contaminant is present.

[0116] According to some embodiments, additional measures can be taken to determine the location of the contaminant. For example, additional processing can be performed by the detector to determine which pixels within the active pixel area have the greatest output (indicating the strongest intensity). Because the illumination spot on the detector corresponds to the illumination spot on the reticle, the detected location of the contaminant as measured by the pixel output will correspond to a location within the illumination spot on the reticle. Thus, this operation can infer the location of the contaminant based on determining the location at which the contaminant is located within the active pixel area.

[0117] The method 1200 can also enable the detector to discard the output of the inactive pixel area. This inactive pixel area is the area outside of the designated active pixel area. Alternatively, the detector can also read the output of the pixels within the inactive pixel area to determine whether a false positive condition occurs. This condition can be defined as a condition in which the system receives stray light.

[0118] The illumination spot produced by the scattered radiation on the surface area of the detector can be smaller than the detection surface area of the detector in which the active pixel area contains the illumination spot. This can be because the illumination spot can be circular, while the active pixel area can not necessarily be circular.

[0119] In some aspects of the disclosure, misalignment conditions can occur due to drift conditions, or pellicle sag, which can cause the illumination spot to change. Thus, in one example, the method 1200 can include calibrating the change in the illumination spot by dynamically activating different pixels as the spot traverses across the entire reticle. Thus, the method 1200 can require a new calibration process whereby a new set of photodiodes are detected and determined to be part of the active area. This can enable the detector to adjust the active pixel area to accommodate for tolerances and / or changes in any of the above conditions.

[0120] Figure 13 A detector device 1300 including a photodiode array is illustrated in accordance with some embodiments. The photodiode array (PDA) 1302 can be a linear array of discrete photodiodes on an integrated circuit (IC) chip. In one example, the PDA can be placed at the image plane of a spectrometer to allow for the simultaneous detection of a range of wavelengths. In this regard, the PDA can be thought of as an electronic version of photographic film. In accordance with some embodiments, a processor 1304 can process signals received from the PDA and determine whether the received signals are signals indicative of detected particles (i.e., detected signals 1306) or signals indicative of ghost particles (i.e., ghost signals 1308 indicative of false positives). In one aspect, signals from pixels identified as active pixels during the calibration process are summed and processed. For example, the calibration process can identify pixels 6, 7, 10, and 11 as active pixels (it will be appreciated that this is merely one example, and that any number of pixels can be identified as active pixels during the calibration process, and can vary from 1 pixel to n pixels), the total output of which can be summed and processed as signals indicative of detected particles on the surface of the lithographic patterning device.

[0121] As previously mentioned, the PDA 1302 can also detect ghost signals 1308. In one aspect, the PDA 1302 can be configured to reject data received from pixels that have not been identified as active. For example, using the above example, the processor can be configured to only process data received from pixels 6, 7, 10, and 11, and discard or delete data received from any other pixels within the PDA 1302. In another aspect, the processor 1304 can be configured to process signals received from inactive pixels (e.g., pixels 1, 2, 3, 4, etc.). In this regard, the processor 1304 can process all signals received from inactive pixels and output detected ghost signals 1308 indicative of ghost particle (false positive) detections.

[0122] As previously mentioned, the calibration procedure can determine which photodetectors are activated. In this regard, the outputs of those active photodetectors are summed together to produce an output signal. Inactive photodiodes can be so classified and can be configured to reject unwanted light that would result in false positive readings.

[0123] In one embodiment, the processor can be an analog summing processor or a digital summing processor. In analog summing, each analog output can be enabled or disabled prior to entering a summing amplifier. In digital summing, each output can be discretely digitized and each output can be digitally enabled / disabled.

[0124] In some embodiments, the manufacture of the particle inspection system can allow for detection of particle contamination and recalibration to compensate for drift and other component variations; provide loose optical alignment tolerances between the illumination system and the photodetectors; provide a loose drift budget over time since compensation can be made through recalibration; and provide sufficient throughput that can meet the necessary throughput since the use of a discrete analog-to-digital converter that can be sampled simultaneously with the photodiode array is used to operate at the same sampling rate as a reticle inspection system.

[0125] To determine the size of the detected particles, the intensity of the scattered light can be measured. As previously mentioned, larger objects can scatter more light and thus provide a higher intensity reading at the detector. However, this is not always the case since certain objects can have higher reflectivity properties and thus can provide a higher intensity than larger objects simply because of the composition of the certain object and not because of the size of the certain object. Therefore, in addition to the photodetector array, the use of an imaging device can be employed to more accurately measure the size of the detected objects.

[0126] In one example, a high resolution 2D pixel array (i.e., camera) can be employed to determine size by magnifying enough to directly measure the number of pixels. The pixels can be made small enough to have enough resolution to see the smallest particle size of interest. Using a 2D sensor for coarse detection in scatterometry mode would require reading all the pixels at a rate of millions of frames per second. This speed is not feasible for any sensor. Also, using another sensor can face space limitations.

[0127] Figure 14A sensor array 1400 including detectors (e.g., detectors 606 with detector pixels) arranged in different configurations is shown in accordance with some embodiments. In some embodiments, the detectors 606 incorporate two sensor technologies in a single physical sensor to read in both scatterometry mode and high resolution imaging mode. According to some aspects, the detectors 606 can be configured to incorporate two or more sensor technologies: CCD / CMOS pixels 1402 in a two-dimensional array and one or more photodiodes 1404. The configuration or placement of the photodiodes can be arranged in any arrangement, two of which are shown in Figure 14 The dedicated photodiodes are electronically added together, giving an instantaneous value equivalent to the total photons on all the photodetector pixels. This approach allows for high speed readout, as the photodiodes can be read out in the millions of times per second, while the CMOS / CCD pixels must be clocked in series and typically have frame rates up to the thousands of frames per second.

[0128] Figures 15A-15B A combination of detectors to detect particles on a lithographic patterning device is illustrated in accordance with some embodiments. In Figures 15A-15B The sensor can be used to coarsely detect particles and provide a reading at each pixel 1502. Thus, once a particle is found at a high resolution more slowly (CCD / CMOS), the pixel data can be read out. To avoid retriggering on the same particle (e.g., in the next line scan), a keep out area of the size of the image sensor will be maintained to avoid repeating the triggering event. In this regard, the photodiode readout signal 1504 can be initially read out. When the value of the readout signal 1504 exceeds a threshold 1508, then it is determined that a particle of some type is detected, and this triggers the CMOS readout operation to occur (e.g., CMOS readout signal 1506). In this way, the two detectors can operate in series, where the photodiode array detects a particle, and the CCD / CMOS array can detect the size of the detected particle. Also, in one example, when the 2D array reader 1512 of the CCD / CMOS array is activated, a block out zone 1510 can be triggered in order to avoid triggering of another particle by the photodiode array. It will be appreciated that during the 2D array readout 1512, another exposure cannot be triggered. However, if two particles are in close proximity to each other, then a rescan operation can be performed. Thus, the block out zone can temporarily pause the photodiode array readout until the CCD / CMOS readout is complete.

[0129] According to some embodiments, the detector array may include one or more types of pixel technologies that enable the detector to process data and identify particles and particle sizes in a more efficient and convenient manner. In some embodiments, such as Figure 16 As shown, detector 1602 may include a combination of CMOS / CCD pixel array 1402 and photodiode pixel array 1404. This combination allows one array (e.g., photodiode array 1404) to detect the particles while other arrays (e.g., CMOS / CCD array 1402) detect particle size simultaneously. This is because photodiode arrays do not require high-resolution capture / processing of information, allowing them to process data more quickly. Therefore, photodiode arrays can quickly identify the presence of particles, and then CMOS / CCD pixel processing can occur after particle size detection. According to one aspect, photodiode array 1404 can determine a series of pixels that have identified particles (based on...). Figure 13 (Example). Therefore, a processor (e.g., processor 1304) can request summing amplifier 1604 to process pixel data from CMOS / CCD pixels within the neighborhood of the photodiode's effective pixels. In one aspect, the processor may include circuitry including row decoder 1606 and column decoder 1608, analog-to-digital converter 1610, and interface 1612. According to some embodiments, analog-to-digital converter 1610 may output a pixel value 1614 indicating a pixel reading for particle detection. In one example, pixel value 1614 may correspond to a single pixel value.

[0130] According to some embodiments, Figure 16 The method described provides a two-step approach: 1) improving the efficiency of particle detection by rapidly detecting particles, and 2) improving the efficiency of particle size detection by collecting image data around the effective pixels where the particles are detected.

[0131] Other aspects of the invention are set forth in the following numbered aspects.

[0132] 1. An inspection method, comprising:

[0133] The radiation scattered at the surface of the object is received at the multi-element detector within the inspection system;

[0134] The output of each element of the multi-element detector is measured using a processing circuit, the output corresponding to the received scattered radiation;

[0135] Calibrating the multi-element detector using processing circuitry by identifying a valid pixel region comprising one or more elements of the multi-element detector having a measured output above a predetermined threshold, and identifying an invalid pixel region comprising remaining elements of the multi-element detector; and

[0136] setting the valid pixel region to a default alignment setting between the multi-element detector and a light source causing the scattered radiation.

[0137] 2. The inspection method of aspect 1, further comprising:

[0138] receiving, at the multi-element detector, second radiation scattered at the surface of the object; and

[0139] generating a detection signal based on the output of the valid pixels, the detection signal indicating the presence of a foreign particle on the surface.

[0140] 3. The inspection method of aspect 2, further comprising:

[0141] determining a stray signal based on the output of the invalid pixel region, the stray signal indicating scattered light; and

[0142] discarding the output of the invalid pixel region.

[0143] 4. The inspection method of aspect 1, wherein,

[0144] an illumination spot produced on a surface area of the multi-element detector by the scattered radiation is smaller than a detection surface area of the multi-element detector, and

[0145] the valid pixel region contains the illumination spot.

[0146] 5. The inspection method of aspect 1, further comprising:

[0147] determining a stray signal in response to receiving a detection signal from the invalid pixel region; and

[0148] classifying the stray signal as a false positive signal.

[0149] 6. The inspection method of aspect 2, further comprising determining a location of the foreign particle based on:

[0150] measuring a pixel output from pixels within the valid pixel region;

[0151] identifying one or more pixels within the valid pixel region having a highest output level; and

[0152] inferred based on a location of the one or more pixels identified as being within the active pixel area.

[0153] 7. The inspection method of aspect 2, further comprising performing a compensation operation, the compensation operation comprising:

[0154] identifying a misalignment condition between the multi-element detector and the light source; and

[0155] reinitializing a calibration operation in response to identifying the misalignment.

[0156] 8. The inspection method of aspect 7, the identifying further comprising:

[0157] detecting a plurality of new elements within the active pixel area, or within an inactive pixel area bordering the active pixel area, the plurality of new elements being located outside of an illumination spot produced by the scattered radiation on a surface area of the multi-element detector, each new element of the plurality of new elements producing an output above a predetermined threshold during one or more inspection operations.

[0158] 9. The inspection method of aspect 7, further comprising:

[0159] setting a new active pixel area to a default alignment setting between the multi-element detector and the light source.

[0160] 10. The inspection method of aspect 7, wherein the misalignment condition is a drift condition.

[0161] 11. A lithography inspection apparatus comprising:

[0162] a multi-element detector configured to:

[0163] measure, with processing circuitry, an output of each element of the multi-element detector, the output corresponding to received scattered radiation;

[0164] calibrate, with the processing circuitry, the multi-element detector by identifying an active pixel area comprising one or more elements of the multi-element detector having a measured output above a predetermined threshold, and identifying an inactive pixel area comprising remaining elements of the multi-element detector; and

[0165] set the active pixel area to a default alignment setting between the multi-element detector and a light source causing the scattered radiation.

[0166] 12. The lithography inspection apparatus of aspect 11, wherein the detector is further configured to:

[0167] receiving second radiation scattered at the surface of the object; and

[0168] generating a detection signal based on the output of the active pixels, the detection signal indicating the presence of a foreign particle on the surface.

[0169] 13. The lithography inspection apparatus of clause 12, wherein the detector is further configured to:

[0170] determining a stray signal based on the output of the inactive pixel region, the stray signal indicating scattered light; and

[0171] discarding the output of the inactive pixel region.

[0172] 14. The lithography inspection apparatus of clause 11, wherein,

[0173] an illumination spot generated by the scattered radiation on a surface area of the multi-element detector is smaller than a detection surface area of the multi-element detector, and

[0174] the active pixel region corresponds to the illumination spot.

[0175] 15. The lithography inspection apparatus of clause 11, wherein the detector is further configured to:

[0176] determining a stray signal in response to receiving a detection signal from a pixel outside the active pixel region; and

[0177] classifying the stray signal as a false positive signal.

[0178] 16. The lithography inspection apparatus of clause 12, wherein the detector is further configured to determine a location of the foreign particle based on:

[0179] measuring pixel output from pixels within the active pixel region;

[0180] identifying one or more pixels within the active pixel region having a highest output level; and

[0181] inferring a location of the foreign particle based on a location of the identified one or more pixels within the active pixel region.

[0182] 17. The lithography inspection apparatus of clause 12, wherein the detector is further configured to perform a compensation operation, the compensation operation comprising:

[0183] identifying a misalignment between the multi-element detector and the light source; and

[0184] reinitializing a calibration operation in response to identifying the misalignment.

[0185] 18. The lithography inspection apparatus of clause 17, the identifying operation by the detector further comprising:

[0186] detecting a plurality of new elements within or bordering the active pixel area, the plurality of new elements being located outside of an illumination spot created by the scattered radiation on the surface area of the multi-element detector, each of the plurality of new elements producing an output above a predetermined threshold.

[0187] 19. The lithography inspection apparatus of clause 16, wherein the detector is further configured to:

[0188] set a new active pixel area to a default alignment setting between the multi-element detector and the light source.

[0189] 20. The lithography inspection apparatus of clause 16, wherein the misalignment condition is a drift condition.

[0190] Although specific reference can be made in this text to the use of the lithography apparatus in the manufacture of ICs, it should be understood that the lithography apparatus described herein can have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms "wafer" or "die" in this text can be considered as being synonymous with the more general terms "substrate" or "target portion", respectively. The substrates referred to herein can be processed, before or after exposure, in one or more treatment units, for example a track or coating and development system unit, a measurement unit, and / or an inspection unit. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrates can be processed more than once, for example in order to create multiple layers of the IC, so that the term "substrate" as used herein can also refer to a substrate that already contains a plurality of processed layers.

[0191] Although specific reference can be made in this text to the use of the lithography apparatus in the manufacture of ICs, it should be understood that the lithography apparatus described herein can have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms "wafer" or "die" in this text can be considered as being synonymous with the more general terms "substrate" or "target portion", respectively. The substrates referred to herein can be processed, before or after exposure, in one or more treatment units, for example a track or coating and development system unit, a measurement unit, and / or an inspection unit. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrates can be processed more than once, for example in order to create multiple layers of the IC, so that the term "substrate" as used herein can also refer to a substrate that already contains a plurality of processed layers.

[0192] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or

[0193] In embodiments described herein, the terms "lens" and "lens element" can refer to any one of a variety of types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components, or combinations thereof, as the context permits.

[0194] Further, as used herein, the terms "radiation" and "beam" and "light" can encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (e.g., having a wavelength λ of 365, 248, 193, 157 or 126 nm), and extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5-20 nm, such as, for example, a wavelength of 13.5 nm), or hard X-rays working at wavelengths smaller than 5 nm, as well as particle beams, such as ion beams or electron beams. In general, radiation having a wavelength between about 400 nm and about 700 nm is considered visible light radiation; radiation having a wavelength between about 780 nm and 3000 nm (or larger) is considered IR radiation. UV refers to radiation having a wavelength of about 100 nm to 400 nm. Within lithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps: G-line 436 nm; H-line 405 nm; and / or I-line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gases) refers to radiation having a wavelength of about 100 nm to 200 nm. Deep UV (DUV) generally refers to radiation having a range of wavelengths from 126 nm to 428 nm, and in some embodiments, excimer lasers can produce DUV radiation used within lithography apparatuses. It is to be understood that radiation having a wavelength in the range of, for example, 5 nm to 20 nm refers to radiation having a certain wavelength band at least partially in the range of 5 nm to 20 nm.

[0195] The term "substrate" as used herein can describe a material on which layers of material are added. In some embodiments, the substrate itself can be patterned, and the material added on top of it can also be patterned, or can remain unpatterned.

[0196] While specific references may be made herein to the use of devices and / or systems according to this disclosure in the manufacture of ICs, it should be clearly understood that such devices and / or systems may have many other possible applications. For example, such devices and / or systems may be used to manufacture integrated optical systems, guide and detect patterns for magnetic domain memories, LCD panels, thin-film magnetic heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any use of the terms "patterning apparatus," "mask," "wafer," or "die" should be considered to be replaced by the more general terms "mask," "substrate," and "target portion," respectively.

[0197] While specific embodiments of this disclosure have been described above, it will be understood that this disclosure can be practiced in ways other than those described. The description is not intended to limit this disclosure.

[0198] It will 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 elucidate one or more exemplary embodiments of this disclosure as conceived by one or more inventors, but not all exemplary embodiments, and are therefore not intended to limit this disclosure and the appended claims in any way.

[0199] The present disclosure has been described above with the aid of functional building blocks that illustrate the implementation of specified functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined herein. Alternative boundaries can be defined as long as the specified functions and their relationships are properly performed.

[0200] The foregoing description of the specific embodiments so fully reveals the general nature of this disclosure that, without departing from the overall concept of this disclosure and without excessive experimentation, others can readily modify and / or adapt various applications of these specific embodiments by applying knowledge within the scope of the art. Therefore, based on the teachings and guidance set forth herein, such adaptations and modifications are intended to fall within the meaning and scope of equivalents of the disclosed embodiments.

[0201] The breadth and scope of this disclosure should not be limited by any of the exemplary embodiments described above, but should be defined only by the appended claims and their equivalents.

Claims

1. An inspection method, comprising: The radiation scattered at the surface of the object is received at the multi-element detector within the inspection system; The output of each element of the multi-element detector is measured using a processing circuit, the output corresponding to the received scattered radiation; The multi-element detector is calibrated by using a processing circuit to identify valid pixel regions of one or more elements of the measured output, including the multi-element detector, that have a value above a predetermined threshold, and invalid pixel regions of the remaining elements of the multi-element detector. as well as The effective pixel area is set as the default alignment between the multi-element detector and the light source that causes the scattered radiation.

2. The inspection method according to claim 1 further includes: The second radiation scattered at the surface of the object is received at the multi-element detector; as well as A detection signal is generated based on the output of the effective pixel region, and the detection signal indicates the presence of foreign particles on the surface.

3. The inspection method according to claim 2 further includes: Based on the output of the invalid pixel region, a stray signal is determined, the stray signal indicating scattered light; as well as Discard the output of the invalid pixel region.

4. The inspection method according to claim 1, wherein, The irradiation spot generated on the surface region of the multi-element detector by the scattered radiation is smaller than the detection surface region of the multi-element detector, and The effective pixel region includes the irradiation spot.

5. The inspection method according to claim 1, further comprising: In response to receiving a detection signal from the invalid pixel region, a stray signal is determined; as well as The spurious signals are classified as false alarms.

6. The inspection method according to claim 2 further includes: The location of the foreign particle is determined based on the following operations: Measure the pixel output from pixels within the effective pixel region; Identify one or more pixels within the effective pixel region that have the highest output level; as well as The location of the foreign particle is inferred based on the position of the identified one or more pixels within the effective pixel area.

7. The inspection method according to claim 2 further includes performing a compensation operation, the compensation operation comprising: Identify misalignment between the multi-element detector and the light source; as well as The calibration operation is reinitialized in response to the identification of the misalignment.

8. The inspection method according to claim 7, wherein identifying the misalignment further comprises: Detect multiple new elements within the effective pixel region or at the boundary of the effective pixel region within the ineffective pixel region, the multiple new elements being located outside the illumination spot generated on the surface region of the multi-element detector by the scattered radiation, each of the multiple new elements producing an output above a predetermined threshold in one or more inspection operations.

9. The inspection method according to claim 7, wherein, The misalignment mentioned refers to the drift situation.

10. A photolithography inspection apparatus, comprising: A multi-element detector, the multi-element detector being configured to: Receive radiation scattered at the surface of an object; The output of each element of the multi-element detector is measured using a processing circuit, the output corresponding to the received scattered radiation; The multi-element detector is calibrated by using a processing circuit to identify valid pixel regions of one or more elements of the measured output, including the multi-element detector, that have a value above a predetermined threshold, and invalid pixel regions of the remaining elements of the multi-element detector. as well as The effective pixel area is set as the default alignment between the multi-element detector and the light source that causes the scattered radiation.

11. The photolithography inspection apparatus according to claim 10, wherein, The detector is also configured to: Receive second radiation scattered at the surface of the object; and A detection signal is generated based on the output of the effective pixel region, and the detection signal indicates the presence of foreign particles on the surface.

12. The photolithography inspection apparatus according to claim 11, wherein, The detector is also configured to: Based on the output of the invalid pixel region, a stray signal is determined, the stray signal indicating scattered light; and Discard the output of the invalid pixel region.

13. The photolithography inspection apparatus according to claim 10, wherein, The irradiation spot generated on the surface region of the multi-element detector by the scattered radiation is smaller than the detection surface region of the multi-element detector, and The effective pixel region includes the irradiation spot.

14. The photolithography inspection apparatus according to claim 10, wherein, The detector is also configured to: In response to receiving a detection signal from a pixel outside the effective pixel region, a spurious signal is determined; and The spurious signals are classified as false alarms.

15. The photolithography inspection apparatus according to claim 11, wherein, The detector is also configured to determine the location of the foreign particles based on the following operations: Measure the pixel output from pixels within the effective pixel region; Identify one or more pixels within the effective pixel region that have the highest output level; as well as The location of the foreign particle is inferred based on the position of the identified one or more pixels within the effective pixel area.

16. The photolithography inspection apparatus according to claim 11, wherein, The detector is also configured to perform a compensation operation, the compensation operation including: Identify misalignment between the multi-element detector and the light source; and The calibration operation is reinitialized in response to the identification of the misalignment.

17. The photolithography inspection apparatus according to claim 16, wherein the identification of the misalignment by the detector further comprises: Detect multiple new elements within the effective pixel region or at the boundary of the effective pixel region within the ineffective pixel region, wherein the multiple new elements are located outside the illumination spot generated on the surface region of the multi-element detector by the scattered radiation, and each of the multiple new elements produces an output higher than a predetermined threshold.

18. The photolithography inspection apparatus according to claim 16 or 17, wherein, The misalignment mentioned refers to the drift situation.

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