Contamination detection metrology system, lithographic apparatus, and methods thereof

Abstract

A system (400) includes an illumination system (402), a detector (404), and a comparator (406). The illumination system includes a radiation source (408) and a spatial light modulator (410). The radiation source generates a beam (442) of radiation. The spatial light modulator directs the beam toward a surface (436) of an object (428) and adjusts a spatial intensity distribution of the beam at the surface. The detector receives radiation scattered at the surface and radiation (444) scattered by a structure (434) near the surface. The detector generates a detection signal based on the received radiation. The comparator receives the detection signal, generates a first image based on the detection signal, and distinguishes between false signals and signals corresponding to a presence of a foreign particle on the surface based on the first image and the adjusted spatial intensity distribution.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 955,883, filed December 31, 2019, and U.S. Provisional Patent Application No. 63 / 115,809, filed November 19, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to lithography systems, such as inspection systems for detecting contaminants on photomasks in lithography equipment. Background Technology

[0004] A photolithography apparatus is a machine that applies a desired pattern onto a substrate, typically a target portion of the substrate. Photolithography apparatuses can be used in the fabrication of integrated circuits (ICs). In this case, a patterning apparatus, alternatively called a mask or photomask, can be used to generate a circuit pattern to be formed on a single layer of the IC. The pattern can be transferred onto a target portion (e.g., comprising a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). Typically, the pattern is transferred by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a grid of adjacent target portions patterned sequentially. Known photolithography apparatuses include so-called steppers and so-called scanners. In a stepper, each target portion is irradiated by exposing the entire pattern onto the target portion at once. In a scanner, each target portion is irradiated by scanning the pattern with a radiation beam in a given direction (“scanning” direction) while simultaneously scanning the target portion parallel or antiparallel to this scanning direction. A pattern can also be transferred from a patterning apparatus to a substrate by imprinting the pattern onto the substrate.

[0005] Another type of lithography system is the interferometric lithography system. In this system, there is no pattern forming device; instead, the light beam is split into two beams, and these two beams interfere at a target portion of the substrate using a reflection system. This interference causes lines to form at the target portion of the substrate.

[0006] During photolithography operations, different processing steps may require different layers to be formed sequentially on the substrate. The layer ordering is typically accomplished by exchanging a different mask for each pattern transfer process, based on the desired pattern for each layer. Typical photolithography systems operate within sub-nanometer tolerances or margins for both the patterns on the masks and the patterns transferred from the masks to the wafer. Contaminant particles on the mask can introduce errors into the transferred pattern. Therefore, it is desirable to maintain a contaminant-free mask capable of accurately transferring patterns onto the wafer with sub-nanometer precision.

[0007] Within the environment of a photolithography apparatus, highly dynamic processes occur, such as mask transfer, wafer transfer, controlled gas flow, degassing of vacuum chamber walls, liquid distribution (e.g., photoresist coating), temperature changes, metal deposition, rapid movement of numerous actuated components, and structural wear. Over time, these dynamic processes introduce and accumulate contaminant particles within the photolithography apparatus. Summary of the Invention

[0008] There is a need to provide improved inspection techniques for detecting contaminants on optically critical components of lithography equipment.

[0009] In some embodiments, a system includes an illumination system, a detector, and a comparator. The illumination system includes a radiation source and a spatial light modulator. The radiation source is configured to generate a beam of radiation. The spatial light modulator is configured to direct the beam toward a surface of an object and adjust the spatial intensity distribution of the beam at the surface. The detector is configured to receive radiation scattered at the surface and radiation scattered by structures near the surface and to generate a detection signal based on the received radiation. The comparator is configured to receive the detection signal, generate a first image based on the detection signal, and distinguish between spurious signals and signals corresponding to the presence of foreign particles on the surface based on the first image and the adjusted spatial intensity distribution.

[0010] In some embodiments, a method includes: generating a beam of radiation; using a spatial light modulator to adjust the spatial intensity distribution of the beam; receiving scattered radiation at a detector, wherein the scattered radiation includes radiation scattered at the surface and radiation scattered by structures near the surface; using the detector to generate a detection signal; receiving the detection signal at a processor; generating a first image based on the detection signal; and using the processor to distinguish between spurious signals and signals corresponding to the presence of foreign particles on the surface based on the first image and the adjusted spatial intensity distribution.

[0011] In some embodiments, the photolithography apparatus includes: an illumination device, a projection system, and a measurement system. The measurement system includes the illumination system, a detector, and a processor. The illumination system includes a radiation source and a spatial light modulator. The illumination device is configured to illuminate a pattern formed by a pattern forming apparatus. The projection system is configured to project an image of the pattern onto a substrate. The radiation source is configured to generate a beam of radiation. The spatial light modulator is configured to guide the beam toward a surface of an object and adjust the spatial intensity distribution of the beam at the surface. The detector is configured to receive radiation scattered at the surface and radiation scattered by structures near the surface and to generate a detection signal based on the received radiation. The processor is configured to receive the detection signal, generate a first image based on the detection signal, and distinguish between spurious signals and signals corresponding to the presence of foreign particles on the surface based on the first image and the adjusted spatial intensity distribution.

[0012] Further features of this disclosure, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It should be noted that this disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the art based on the teachings contained herein. Attached Figure Description

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

[0014] Figure 1A A schematic diagram of a reflective lithography apparatus according to some embodiments is shown.

[0015] Figure 1B A schematic diagram of a transmission lithography apparatus according to some embodiments is shown.

[0016] Figure 2 A more detailed schematic diagram of the reflective lithography apparatus according to some embodiments is shown.

[0017] Figure 3 A schematic diagram of a photolithography unit according to some embodiments is shown.

[0018] Figure 4 , Figure 5A , Figure 5B and Figure 6 A schematic diagram of a measurement system according to some embodiments is shown.

[0019] Figure 7 The graph shows the transmittance of the film relative to the radiation wavelength according to some embodiments.

[0020] Figure 8 The arrangement of polarizers that can be used in a measurement system according to some embodiments is shown.

[0021] Figure 9 A schematic diagram of a measurement system according to some embodiments is shown.

[0022] Figure 10 A portion of a measurement system according to some embodiments is shown.

[0023] The features of this disclosure will become apparent from the specific embodiments described below, when viewed in conjunction with the accompanying drawings, in which the same reference numerals consistently identify corresponding elements. In the drawings, the same reference numerals generally indicate the same, functionally similar, and / or structurally similar elements. Additionally, the leftmost numeral of the reference numerals generally identifies the drawing in which the reference numeral first appears. Unless otherwise stated, the drawings provided throughout this disclosure should not be construed as tolerancing drawings. Detailed Implementation

[0024] This specification discloses one or more embodiments incorporating the features of this disclosure. The disclosed embodiments are provided as examples. The scope of this disclosure is not limited to the disclosed embodiments. The claimed features are defined by the appended claims.

[0025] The described embodiments, as well as the references to "an embodiment," "embodiment," "exemplary embodiment," etc., used in the specification, may include specific features, structures, or characteristics. However, each embodiment may not necessarily include the specific features, structures, or characteristics described. Furthermore, such phrases do not necessarily refer to the same embodiment. Additionally, when a specific feature, structure, or characteristic is described in connection with an embodiment, it should be understood that, whether explicitly described or not, implementing such a feature, structure, or characteristic in combination with other embodiments is within the knowledge of those skilled in the art.

[0026] For ease of description, spatial relative terms such as “below,” “under,” “lower,” “above,” “on,” “higher,” etc., are used herein to describe the relationship between one element or feature and another element or feature as illustrated in the accompanying drawings. These spatial relative terms are intended to cover different orientations of the device other than those depicted in the figures during use or operation. The device may be otherwise oriented (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein may be interpreted accordingly.

[0027] As used herein, the term "approximately" refers to a value associated with a given quantity that may vary based on a specific technique. Based on the specific technique, the term "approximately" may refer to a value associated with a given quantity that varies, for example, within 10% to 30% above or below the value (e.g., ±10%, ±20%, or ±30% of the value).

[0028] Embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of this disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any means for storing or transmitting information in a machine-readable (e.g., computing device) form. For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); disk storage media; optical storage media; flash storage devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Additionally, in this document, firmware, software, routines, and / or instructions may be described as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and these actions are actually generated by a computing device, processor, controller, or other means of executing firmware, software, routines, instructions, etc. The term "non-transitory" may be used herein to characterize computer-readable media used for storing data, information, instructions, etc., with the sole exception of transient propagated signals.

[0029] However, it is helpful to present example environments in which embodiments of this disclosure may be implemented before describing such embodiments in more detail.

[0030] Example lithography system

[0031] Figure 1A and Figure 1BThese are schematic diagrams of lithography apparatus 100 and 100', respectively, in which embodiments of the present disclosure can be implemented. Lithography apparatus 100 and 100' each include: an irradiation system (irradiator) IL configured to modulate a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask stage) MT configured to support a pattern forming apparatus (e.g., a mask, stencil, or dynamic pattern forming apparatus) MA and connected to a first positioner PM configured to accurately position the pattern forming apparatus MA; and a substrate stage (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate W. Lithography apparatuses 100 and 100' also have a projection system PS configured to project a pattern imparted by the radiation beam B by the pattern forming apparatus MA onto a target portion (e.g., comprising one or more dies) C of the substrate W. In lithography apparatus 100, the pattern forming apparatus MA and the projection system PS are reflective. In the photolithography equipment 100', the pattern forming apparatus MA and the projection system PS are transmissive.

[0032] 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.

[0033] 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 maintained in a vacuum environment. The support structure MT can employ mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus MA. The support structure MT can be a frame or a stage, and 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.

[0034] 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, so as 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 formed in the target portion C to form an integrated circuit.

[0035] The pattern forming apparatus MA can be a transmissive type (such as in...). Figure 1B(as in a lithography device 100') or reflective (as in...) Figure 1A (As in the photolithography apparatus 100). Examples of pattern forming apparatus MA include photomasks, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in photolithography and include mask types such as binary mask types, alternating phase-shift mask types, or attenuation phase-shift mask types, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted 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.

[0036] 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. A vacuum environment can be used for EUV or electron beam radiation because other gases may absorb excessive radiation or electrons. A vacuum environment can therefore be provided throughout the beam path by means of vacuum walls and a vacuum pump.

[0037] The lithography apparatus 100 and / or lithography apparatus 100' can be of the type having two (dual-platform) or more substrate stages WT (and / or two or more mask stages). In such a "multi-platform" machine, additional substrate stages WT can be used in parallel, or one or more other substrate stages WT can be used for exposure while preparatory steps are performed on one or more stages. In some cases, the additional stage may not be a substrate stage WT.

[0038] The photolithography apparatus may also be of the type in which at least a portion of the substrate may be covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces within the photolithography apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system. As used herein, the term “immersion” does not mean that a structure such as a substrate must be immersed in a liquid, but rather that “immersion” simply means that the liquid is located between the projection system and the substrate during exposure.

[0039] refer to Figure 1A and Figure 1BThe irradiator IL receives a radiation beam from the radiation source SO. When the source SO is an excimer laser, the source SO and the lithography apparatus 100, 100' can be separate physical entities. In this case, the source SO is not considered part of the lithography apparatus 100 or 100', and the radiation beam is delivered by means of a beam delivery system BD including, for example, suitable directional mirrors and / or beam expanders (in... Figure 1B (In the middle) the beam is transferred from the source SO to the irradiator IL. In other cases, such as when the source SO is a mercury lamp, the source SO may be a component of the lithography apparatus 100, 100'. The source SO, the irradiator IL, and the beam transfer system BD, which may be provided if necessary, can be collectively referred to as the radiation system.

[0040] The irradiator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam (in... Figure 1B (In the middle). Typically, at least the outer radial range and / or inner radial range (typically referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in the pupil plane of the irradiator can be adjusted. Furthermore, the irradiator IL may include various other components (in... Figure 1B (In the middle), such as integrator IN and concentrator. The irradiator IL can be used to adjust the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0041] refer to Figure 1A The radiation beam B is incident on and patterned by the patterning apparatus (e.g., a mask) MA, which is held on the support structure (e.g., a mask stage) MT. In the lithography apparatus 100, the radiation beam B is reflected from the patterning apparatus (e.g., the mask) MA. After being reflected from the patterning apparatus (e.g., the mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto the target portion C of the substrate W. The substrate stage WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B) by means of the second positioner PW and the position sensor IF2 (e.g., an interferometer device, a linear encoder, a 2D encoder, or a capacitive sensor). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning apparatus (e.g., the mask) MA relative to the path of the radiation beam B. The pattern forming apparatus (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0042] refer to Figure 1BThe radiation beam B is incident on and patterned by the patterning apparatus (e.g., mask MA), which is held on the support structure (e.g., mask stage MT). Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto the target portion C of the substrate W. The projection system has a pupil PPU conjugate to the illumination system pupil IPU. A portion of the radiation originates from the intensity distribution at the illumination system pupil IPU and traverses the mask pattern unaffected by diffraction at the mask pattern, producing an image of the intensity distribution at the illumination system pupil IPU.

[0043] The projection system PS projects an image MP' of the mask pattern MP onto a photoresist layer coated on the substrate W, wherein the image MP' is formed by a diffracted beam generated from the marked pattern MP by means of radiation from the intensity distribution. For example, the mask pattern MP may comprise an array of lines and spacings. Diffraction of radiation different from zero-order diffraction at the array produces a diffracted beam that has a directional change in a direction perpendicular to the lines. The undiffracted beam (i.e., the so-called zero-order diffracted beam) traverses the pattern without any change in propagation direction. The zero-order diffracted beam passes through the upper lens or upper lens group of the projection system PS (located upstream of the conjugate pupil PPU of the projection system PS) to reach the conjugate pupil PPU. A portion of the intensity distribution in the plane of the conjugate pupil PPU and associated with the zero-order diffracted beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. An aperture device PD is, for example, positioned at or approximately located on the plane of the conjugate pupil PPU that includes the projection system PS.

[0044] The projection system PS is arranged to capture not only the zeroth-order diffraction beam, but also first-order or higher-order diffraction beams (not shown) by means of a lens or lens group L. In some embodiments, dipole illumination for imaging a line pattern extending in a direction perpendicular to the line can be used to take advantage of the resolution enhancement effect of dipole illumination. For example, a first-order diffraction beam interferes with a corresponding zeroth-order diffraction beam at the level of the wafer W to produce an image of the line pattern MP with the highest possible resolution and process window (i.e., a combination of available depth of focus and permissible exposure dose deviation). In some embodiments, astigmatism can be reduced by providing a radiating pole (not shown) in the phase limit of the pupil IPU of the illumination system N. Furthermore, in some embodiments, astigmatism can be reduced by blocking the zeroth-order beam in the conjugate pupil PPU of the projection system that is associated with a radiating pole in the phase limit. This is described in more detail in US7,511,799B2, published March 31, 2009, the entire contents of which are incorporated herein by reference.

[0045] With the aid of the second positioner PW and the position sensor IF (e.g., an interferometer device, linear encoder, 2D encoder, or capacitive sensor), the substrate stage WT can be moved accurately (e.g., to position different target portions C in the path of the radiation beam B). Similarly, (e.g., after mechanical acquisition from a mask library or during scanning), the first positioner PM and another position sensor (not in use) Figure 1B (As shown in the figure) can be used to accurately position the mask MA relative to the path of the radiation beam B.

[0046] Typically, the movement of the mask stage MT can be achieved using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate stage WT can be achieved using a long-stroke module and a short-stroke module that form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask stage MT may be connected only to the short-stroke actuator, or it may be fixed. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the mask MA and the substrate W. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in the space between multiple target portions (referred to as scribing alignment marks). Similarly, in cases where more than one die is disposed on the mask MA, the mask alignment marks M1, M2 can be located between these dies.

[0047] The mask stage MT and pattern forming apparatus MA can be located within a vacuum chamber V, where an in-vacuum robot IVR can be used to move the pattern forming apparatus (such as a mask or mask plate) into and out of the vacuum chamber. Alternatively, when the mask plate platform or mask stage MT and pattern forming apparatus 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 to smoothly transfer any payload (e.g., a mask) onto a fixed kinematic support at the transfer station.

[0048] The lithography apparatuses 100 and 100' can be used in at least one of the following modes:

[0049] 1. In step mode, while keeping the support structure (e.g., mask stage) MT and the substrate stage WT substantially stationary, the entire pattern imparted to the radiation beam B is projected onto the target portion C in one pass (i.e., single static exposure). The substrate stage WT is then moved along the X and / or Y directions, allowing exposure of different target portions C.

[0050] 2. In scanning mode, while simultaneously scanning the support structure (e.g., mask stage) MT and the substrate stage WT, the entire pattern of the radiation beam B is projected onto the target portion C in a single exposure (i.e., a single dynamic exposure). The velocity and orientation of the substrate stage WT relative to the support structure (e.g., mask stage) MT can be determined by the (reduced) magnification and image inversion characteristics of the projection system PS.

[0051] 3. In another mode, while the support structure (e.g., mask stage) MT of the programmable patterning apparatus is held substantially fixed and the substrate stage WT is moved or scanned, a pattern imparted by the radiation beam B is projected onto the target portion C. A pulsed radiation source SO can be used, and the programmable patterning apparatus can be updated as needed after each movement of the substrate stage WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography utilizing programmable patterning apparatuses such as programmable mirror arrays.

[0052] Alternatively, combinations and / or variations of the usage patterns described above, or entirely different usage patterns, may be used.

[0053] In some embodiments, the lithography apparatus can generate DUV and / or EUV radiation. For example, the lithography apparatus 100' can be configured to operate using a DUV source. In another example, the lithography apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Typically, the EUV source is configured in a radiation system, and a corresponding irradiation system is configured to modulate the EUV radiation beam from the EUV source.

[0054] Figure 2 The lithography apparatus 100 is shown in more detail, including a source collector device SO, an irradiation system IL, and a projection system PS. The source collector device SO is constructed and arranged such that a vacuum environment can be maintained within the enclosure structure 220 of the source collector device SO. A plasma 210 emitting EUV radiation can be formed by a discharge-generated plasma source. EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), in which a very hot plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, the very hot plasma 210 is generated by a discharge that causes at least partial ionization of the plasma. For efficient radiation generation, a partial pressure of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required, for example, 10 Pa. In some embodiments, a plasma of excited tin (Sn) is provided to generate EUV radiation.

[0055] Radiation emitted by the thermal plasma 210 is transferred from the source chamber 211 to the collector chamber 212 via a gas barrier or contaminant trap 230 (also referred to in some cases as a contaminant barrier or vane trap) optionally located in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier, or a combination of a gas barrier and a channel structure. Contaminant traps or contaminant barriers 230, as further indicated herein, at least include a channel structure.

[0056] The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected to be focused at a virtual source point IF. The virtual source point IF is often referred to as the intermediate focus, and the source collector device is arranged such that the intermediate focus IF is located at or near the opening 219 in the enclosure structure 220. The virtual source point IF is an image of the plasma 210 emitting radiation. A grating spectral filter 240 is specifically used to suppress infrared (IR) radiation.

[0057] Subsequently, the radiation traverses the illumination system IL, which may include a faceted field mirror assembly 222 and a faceted pupil mirror assembly 224. The faceted field mirror assembly 222 and the faceted pupil mirror assembly 224 are arranged to provide a desired angular distribution of the radiation beam 221 at the patterning apparatus MA, and to provide desired radiation intensity uniformity at the patterning apparatus MA. When the radiation beam 221 is reflected at the patterning apparatus MA, held by the support structure MT, a patterned beam 226 is formed, and the patterned beam 226 is imaged onto the substrate W, held by the wafer platform or substrate stage WT, via the projection system PS through reflective elements 228 and 229.

[0058] The illumination optics unit IL and projection system PS can typically contain more elements than are shown. The grating spectral filter 240 may be optional, depending on the type of photolithography equipment. Additionally, more elements may be present than those shown. Figure 2 The mirror shown in the figure has more mirrors, for example, in the projection system PS, besides the mirrors that may exist. Figure 2 In addition to the reflective element shown, there are one to six additional reflective elements.

[0059] Collector CO (e.g.) Figure 2 The image shown is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, and is only an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are arranged axially symmetrically about the optical axis O, and this type of collector CO is preferably used in conjunction with a plasma source generated by discharge (often referred to as a DPP source).

[0060] Exemplary photolithography unit

[0061] Figure 3A lithography unit 300, sometimes referred to as a lithography cell or cluster, is shown according to some embodiments. A lithography apparatus 100 or 100' may form part of the lithography unit 300. The lithography unit 300 may also include one or more devices for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these devices include: a spin coater SC for depositing a resist layer, a developing apparatus DE for developing the exposed resist, a chill plate CH, and a baking plate BK. A substrate transport device or robot RO picks up a substrate from input / output ports I / O1, I / O2, moves the substrate between different process devices, and delivers the substrate to the feed stage LB of the lithography apparatus 100 or 100'. These devices are generally collectively referred to as a track or coating and developing system and are under the control of a track or coating and developing system control unit TCU, which is itself controlled by a management and control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Therefore, different devices can be operated to maximize throughput and processing efficiency.

[0062] Exemplary contaminant detection equipment

[0063] In some embodiments, a measurement system may be used to inspect an object to determine its cleanliness. Inspection techniques may be performed to successfully detect unwanted defects on a surface (e.g., the surface of a mask or substrate) while minimizing false detections (or false alarms). Inspection techniques may include optical inspection.

[0064] The terms “imperfection,” “defect,” “flaw,” etc., may be used in this document to refer to deviations or inhomogeneities of the structure from specified tolerances or margins. For example, a flat surface may have defects such as scratches, pinholes or dents, foreign particles, stains, etc.

[0065] In the context of imperfections, the terms "foreign particles," "contaminant particles," "contaminants," etc., may be used herein to refer to undesirable, irregular, or otherwise undesirable (not intended) particulate matter present in areas or on surfaces designed to prevent the presence of such particulate matter, or otherwise adversely affecting the operation of equipment where particulate matter is present. Some examples of foreign particles may include dust, stray photoresist, or other detached material within the lithography apparatus. Examples of detached material may include steel, gold, silver, aluminum, copper, palladium, platinum, titanium, etc. Material detachment may occur, for example, due to processes such as fabricating metal interconnects on a substrate, and friction and impact on actuating structures. Contaminants may enter sensitive components of the lithography apparatus (e.g., photomasks or substrates) and increase the likelihood of errors during the lithography process. Embodiments of this disclosure provide methods for detecting defects in sensitive components of a lithography apparatus or in the process.

[0066] False alarms are detrimental to photolithography. For example, false alarm detection can slow down production by unnecessarily prompting maintenance actions (e.g., mask replacement) or even suggesting the discarding of a preferably conformal mask. Embodiments of this disclosure provide structures and functions for reducing incidents or eliminating false alarms.

[0067] Figure 4 A schematic diagram of a measurement system 400 according to some embodiments is shown. In some embodiments, the measurement system 400 may be implemented in a photolithography apparatus. The measurement system 400 may include an illumination system 402, a detector 404, and a processor 406. The illumination system 402 may include a radiation source 408 and a spatial light modulator 410. The illumination system 402 may include one or more radiation adjustment elements 412 (e.g., any of a polarizer, wavelength filter, focusing element, beam splitter, beam combiner, etc.). The measurement system 400 may include a housing 414. The housing 414 may include one or more compartments. The housing 414 may include observation windows 416 and 418. The measurement system 400 may include one or more additional illumination systems 424. The illumination systems 424 may be substantially similar to the illumination system 402 in structure and function. The housing 414 may include one or more additional observation windows 426.

[0068] In some embodiments, detector 404 may include sensor element 420 and focusing element 422 (e.g., objective lens or lens system). In some embodiments, detector 404 may be a single-cell photodetector (which may not be able to resolve the image without more photodetectors), in which case sensor element 420 may be a photodiode. In some embodiments, detector 404 may be an image capturing device or a multi-cell photodetector (e.g., a two-dimensional array of photodetectors). Sensor element 420 may include a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS).

[0069] However, before describing embodiments of the measurement system 400 in more detail, it is instructive to present examples of objects 428 that can be inspected using the measurement system 400. In some embodiments, object 428 may include a continuous object or a multi-part object. Figure 4(An enlarged view of the multi-component variant is shown). In embodiments where object 428 may have multiple components, object 428 may be a mask 430 having a surface film 432 disposed on one side of mask 430. Mask 430 may include pattern features 434. Pattern features 434 may include, for example, product and alignment mark patterns to be transferred onto a substrate by a photolithography process. If defects 440 are present on mask 430, particularly on pattern features 434, the quality of pattern transfer may be negatively affected. Therefore, surface film 432 may be a transparent protective device configured to prevent defects 440 from falling on the side of mask 430 with pattern features 434.

[0070] In some embodiments, object 428 may include surfaces 436 and 438. Surface 436 is disposed on the side of object 428 opposite to surface 438. Surface 436 may be configured to contact defect 440 and prevent defect 440 from reaching pattern feature 434 (e.g., defect 440 is shown as being located on surface 436). Surface 438 may be a rear surface of mask 430 (e.g., a non-feature side). Object 428 may be arranged such that a gap exists between the film 432 and mask 430. The gap may range from several micrometers to several millimeters. Due to the distance between surface 436 and pattern feature 434, the likelihood that defect 440 present on surface 436 will have an impact on pattern transfer is reduced, as defect 440 may be out of focus relative to the irradiation used in pattern transfer. However, it is still desirable to monitor surface 436 of film 432 to prevent the count of foreign particles from reaching unacceptable levels. Conversely, foreign particles on the surface 438 of the mask 430 may also negatively affect photolithography. This is because when the foreign particles are sandwiched between the mask 430 and the mask stage, they may penetrate the shape of the mask 430 and be printed or otherwise deform the shape of the mask 430. Alternatively, when the foreign particles are sandwiched between the mask 430 and the mask stage, they may cause damage to the surface of the mask or the mask stage. Or, the foreign particles may be transferred to the mask stage and thus contaminate the mask stage, and may contaminate or damage other masks mounted on the same platform.

[0071] In some embodiments, radiation source 408 may generate a radiation beam 442 for illuminating object 428. Radiation beam 442 may include incoherent radiation. It should be understood that radiation beam 442 may originate from a coherent source. Radiation beam 442 may include a single wavelength (a narrow bandwidth centered on a center wavelength). Radiation beam 442 may include two or more wavelengths (e.g., multiple discrete narrowbands or a continuous spectrum). One or more radiation adjustment elements 412 (e.g., wavelength filters) may be used to select the wavelength used to illuminate object 428. Alternatively or additionally, radiation source 408 may include two or more discrete radiation sources to generate different portions of two or more wavelengths.

[0072] In some embodiments, the spatial light modulator 410 may guide a radiation beam 442 toward a surface 436 of an object 428. The spatial light modulator 410 may adjust the spatial intensity distribution of the radiation beam 442 at the surface 436. That is, illumination guided onto the object 428 may be optional at the pixel level, as opposed to, for example, flood illumination. The spatial light modulator 410 may include a liquid crystal modulator. The spatial light modulator 410 may also include illumination guiding elements or illumination orientation elements (e.g., mirrors) and / or polarizers. The liquid crystal may operate based on the polarization of light. For example, the pixel elements of a liquid crystal device may allow radiation to be fully transmitted, partially transmitted, or not transmitted based on the polarization state of the liquid crystal pixel elements.

[0073] In some embodiments, the spatial light modulator 410 may include a digital micromirror device (DMD). The DMD can operate based on mechanically movable micromirrors that reflect light toward a desired location. Therefore, it appears that the DMD is limited to a "fully open" (reflecting toward the target) or "fully closed" (not reflecting toward the target) state. However, the DMD pixel elements are capable of switching at frequencies on the order of 103 Hz to 104 Hz (i.e., refresh rate). In contrast, the detector 404 may only have a sampling rate on the order of 10 Hz to 10 Hz. By utilizing the speed of the DMD, a "partially open" state of the DMD can be defined, for example, by illuminating the target only for a small fraction of a sampling cycle of the detector 404.

[0074] In some embodiments, the spatial light modulator 410 may employ optical elements (e.g., pixel elements) with spatially variable transmission profiles, which are capable of generating the desired intensity profile via a projection / illumination system at the object plane. For example, it may be chromium on a glass pattern having the desired transmission profile, a photosensitive film, etc.

[0075] In some embodiments, detector 404 may receive radiation represented by detected radiation 444, scattered at surface 436 and scattered by structures (e.g., pattern features 434) near said surface. The detected radiation 444 scattered at surface 436 may include radiation scattered by defects 440 located on surface 436. Detector 404 may generate a detection signal based on the received radiation. Processor 406 may receive and analyze the detection signal. Processor 406 may determine the location of defects on said surface based on the analysis. Processor 406 may generate a first image based on the detection signal. Processor 406 may distinguish between false signals and signals corresponding to the presence of defects 440 on surface 436 based on the analysis and an adjusted spatial intensity distribution. In other words, the measurement system 400 can distinguish between two types of detected radiation: (1) radiation associated with defect 440 (e.g., true detection of foreign particles) and (2) radiation associated with structures other than defect 440 (e.g., false alarms caused by false signals of radiation scattered from pattern feature 434).

[0076] In the context of radiation detection, terms such as "false," "spurious," "pseudo," and "parasitic" can be used to describe signals associated with radiation that does not interact with foreign particles. For example, a false signal can be associated with a detected radiation that makes it appear as if a defect was actually detected at a location when no defect is present.

[0077] In some embodiments, the differentiation performed by processor 406 may include determining the binary presence (e.g., presence or absence) of defect 440. In some embodiments, the differentiation performed by processor 406 may include determining a confidence level (e.g., percentage probability) that defect 440 may be present. Processor 406 may determine the location and / or size of defect 440 based on the detection signal. Processor 406 may present the detection results to a user of measurement system 400 (e.g., on a computer display). The detection results may include, for example, any of the following: the presence, location and / or size of defect 440, captured images, spectral analysis, etc.

[0078] In the context of a surface (e.g., surface 436), the term "lateral" may be used herein to refer to a direction along a plane of said surface. For example, X-naming and Y-naming can be used as positional coordinates to represent a lateral position on surface 436. In another example, the lateral direction may be perpendicular to the optical axis 446 of the measurement system 400.

[0079] In some embodiments, the lateral resolution of the measurement system 400 may be limited by the physical properties of its optical elements (e.g., numerical aperture (NA), aberrations, correction limitations, assembly limitations, etc.). In some embodiments, the NA of the focusing element 422 may be 0.055 (averaged over the observation plane). This can make it difficult to resolve the location of the defect 440, especially when the size of the defect 440 is smaller than half the diameter of the Airy disk of the detection-side optics. When the defect 440 has a diameter smaller than the diffraction limit of the measurement system 400, it is not convenient to determine the presence and size of the defect 440 rather than its location. The lateral resolution of the measurement system 400 can be approximated by the Rayleigh equation:

[0080]

[0081] In equation 1, r o This represents the resolution limit, where λ is the wavelength of the radiation beam 442, and NA is the numerical aperture of the measurement system 400. Regarding the lateral resolution r of the detector 404... d It can be generated by r d =2w is used as an approximation, where w is the width of the detector element (e.g., a pixel) of detector 404. In some embodiments, the lateral resolution of the measurement system 400 can be affected by r. o or r d The smaller of the two is limited. Alternatively, in extreme cases, detector 404 may not have lateral resolution (e.g., a single-cell photodetector).

[0082] In some embodiments, the term "detector element" may be used herein to refer to a single radiation-sensitive element of a detector. For example, a detector element in a multi-cell detector may be associated with pixels in an image generated based on detections performed by the multi-cell detector.

[0083] In some embodiments, the minimum size of detectable particles may be limited by the noise floor of the measurement system 400. The measurement system 400 can correctly identify and determine the size of foreign particles approximately 5 μm or larger. By comparison, the determination of the lateral location of defect 440 may have an uncertainty approximately an order of magnitude larger and may be difficult to improve due to the lateral resolution limitations described above. However, some embodiments of this disclosure can utilize the properties (e.g., spatial modulation) of radiation from a high-resolution illumination system (e.g., illumination system 402) to modulate the radiation received at detector 404, thereby improving the optical resolution of the detection.

[0084] Figure 5A A schematic diagram of a measurement system 500 according to some embodiments is shown. It should be understood that, regarding... Figure 4Either the described structure or function can also be included in the reference. Figure 5A In some embodiments, for example, the irradiation system 424 ( Figure 4 ) can be included in the reference Figure 5A In the embodiments described above. Unless otherwise stated, Figure 5A In and Figure 4 Elements that share similar reference numerals (e.g., reference numerals that share the two rightmost numbers) can have similar structures and functions.

[0085] In some embodiments, the measurement system 500 can be used to inspect the mask 530 for the presence of foreign particles (e.g., defects 540). The measurement system 500 may include an illumination system having a spatial light modulator 510 and a focusing element 512. The measurement system may include a detector 504 and a processor 506. The measurement system may include a sensor element 520 and a focusing element 522.

[0086] In some embodiments, the spatial light modulator 510 can be configured to temporally adjust the spatial intensity distribution of the radiation beam 542 generated by the illumination system. For example, the spatial light modulator 510 can operate at, for example, a frequency f among a plurality of frequencies. A f B and f C To modulate a given region of the radiation beam 542. The frequencies can be different from each other. For example, a frequency f... A (For example, by means of a sinusoidal pattern, a periodic pattern, etc.) modulate the position A of the radiation beam 542 on the surface 538 of the mask 530 (by coordinates (X... A ,Y A The intensity of radiation at point () is represented by a frequency f. B To modulate the position B of the radiation beam 542 on surface 538 (by coordinates (X) B ,Y B The intensity of radiation at point () is represented by a frequency f. C To modulate the position C of the radiation beam 542 on the surface 538 (by coordinates (X) C ,Y C The intensity of radiation at point () is used to represent the intensity at point (). Locations A, B, and C can be different from each other. The intensity modulation of the radiation beam 542 can be represented, for example, by the following equation:

[0087]

[0088] In Equation 2, the subscript i is associated with a position on surface 538 (e.g., i = A, B, or C), DC i A is a constant intensity shift at position i. i It is the amplitude of the intensity modulation at position i, fi It is the intensity modulation frequency at position i (e.g., f). A ), and φ i It is the initial phase at position i. The constant intensity offset DC i and the amplitude A i It can vary depending on the location, for example, to take into account the difference in reflectivity of mask 530.

[0089] In this paper, the terms “spatial coding” and “spatial information coding” can be used to refer to using the properties of the modulated illumination to associate a location in space with different properties of the modulated illumination.

[0090] In some embodiments, detector 504 may receive radiation scattered at surface 538 (represented by detected radiation 544). Detected radiation 544 scattered at surface 538 may include radiation scattered by a defect 540 located on surface 538. Detector 504 may generate a detection signal based on the received radiation.

[0091] In some embodiments, the NA of the focusing element 522 may limit the lateral resolution of the measurement system 500 (e.g., an NA of approximately 0.055). In some embodiments, the detector 504 may be a single-cell photodetector, which severely limits the lateral resolution of the measurement system 500. However, in instances where size, ease of assembly, and / or cost efficiency are significant factors, a single-cell photodetector may be desirable.

[0092] To overcome poor lateral resolution, in some embodiments, different modulation frequencies (e.g., f) are used. A f B and f C Spatial modulation of the illumination can be used to reconstruct the image, even when using a low-resolution detection setup (e.g., mapping the detected modulation frequencies to coordinates on surface 538). For example, radiation scattered from positions A, B, and C can be modulated with modulation frequencies f used to spatially modulate the radiation beam 542. A f B and f C Correlated. Subsequently, the detected radiation 544 can have a corresponding modulation frequency f. A f B and / or f C Furthermore, the time pattern of the detected radiation 544 can be a superposition of different sinusoidal modulation patterns as illustrated in Illustration 548.

[0093] In some embodiments, processor 506 can analyze the detected signal. The analysis may include modulation-based analysis (e.g., frequency analysis). Processor 506 can determine the properties of the detected radiation 544, such as, for example, the modulation frequencies present in the detected radiation 544, and the amplitude and / or phase corresponding to each of the modulation frequencies. Since positions A, B, and C are modulated by different parameters (e.g., corresponding modulation frequencies f), A f B and f C The image is illuminated using (and / or phase) so that the processor 506 can reconstruct the image representing positions A, B, and C by assigning an intensity determined by frequency analysis to each position. In this way, with the modulation frequency f... A f B and f C The intensity corresponding to each modulation frequency in the image can be mapped to the corresponding positions A, B, and C on the reconstructed image.

[0094] In some embodiments, the frequency analysis performed by the processor 506 may include Fourier or cosine transform analysis. The time intensity profile 550 represents the intensity I(t) = I of the detected radiation 544. A (t)+I B (t)+I C The graph 552 represents the intensity I(t). The vertical axis of the time-intensity profile 550 can represent the detected intensity I(t), and the horizontal axis can represent time. The time scale can be envisioned based on the refresh rate of the available spatial light modulator (e.g., typically tens of kHz). The graph 552 represents the result of applying a Fourier transform (e.g., Discrete Fourier Transform (DFT)) to the detected intensity I(t). Simple transforms can also be used to reduce the load on the processor 506, such as Fast Fourier Transform (FFT), Discrete Cosine Transform (DCT), Modified DCT (MDCT), etc. The vertical axis of the graph 552 can represent the amplitude or intensity of the modulation. The horizontal axis of the graph 552 can represent the frequency of the intensity modulation (e.g., in kHz). The location of the light scattering structure can be determined because the frequency information is mapped onto the surface 538. The processor 506 can then generate an image associated with the surface 538 based on mapping the intensity from the graph 552 onto the corresponding locations A, B, and C on the surface 538.

[0095] In some embodiments, using the features described above, the measurement system 500 can achieve lateral resolution exceeding the diffraction limit of its imaging optics. That is, the measurement system 500 can improve the optical resolution of the detection based on frequency analysis of the detected signal. Lateral resolution can also be adaptable and / or non-uniform based on custom grouping using adjustable elements or components (e.g., variable pixel sizes) in the spatial light modulator 510. The use of spatially coded illumination to improve detector resolution can also be applied to camera detectors (i.e., not limited to single-cell detectors). In this way, the reliability of the measurement system 500 can be increased by improving the accuracy of particle position reporting and / or improving the system's ability to resolve the lateral size and shape of defects 540.

[0096] It should be understood that typical detectors operate using discrete exposures (e.g., multiple frames). These exposures depend on parameters such as the exposure length per frame and the number of frames per unit time. Therefore, in some embodiments, a detector receiving a sinusoidal illumination pattern can detect the pattern as a series of discrete illumination intensities following a sinusoidal pattern. This relates to the previously mentioned—that it can be at a frequency f. A (For example, by means of a sine pattern) modulate the position A of the radiation beam 542 on the surface 538 of the mask 530 (by coordinates (X)). A ,Y A The intensity at point () is used to represent the irradiation intensity. It should be understood that this is not limited to continuous modulation patterns, and thus the situation of discrete exposure should be considered.

[0097] In some embodiments, a spatial light modulator 510 can be used to discretize the illumination pattern. The discrete nature of the detection was previously considered in the example given for the DMD by adjusting the ratio of the on / off states of the mirror elements during a sampling period (e.g., one frame).

[0098] In the context of discrete exposures (e.g., multi-frames), the arrangement of patterns can include different sequences of the discrete exposures. Therefore, with, for example, having a frequency f... AA pattern of illumination intensity corresponding to a sinusoidal pattern may no longer appear to have frequency and / or phase (the same logic can be applied to other patterns—B, C, etc.). However, it should be understood that the arrangement of the patterns can still be within the meaning of a periodic pattern having frequency and / or phase. For example, if a series of exposures on the detector side is produced by an arrangement of patterns, an inverse arrangement can be applied to the series to recover the original pattern and its frequency and / or phase. Therefore, it should be understood that the term "periodic pattern" can be used herein to refer to a pattern capable of conveying information about periodicity, such as frequency and / or phase. That is, the term "periodic pattern" can also refer to an arrangement of patterns that may appear non-periodic or non-repeating. The arrangement can still convey periodic information. The arrangement of patterns can also be referred to as a sequence of intensity states that have varied relative to an ordered original sequence of the periodic pattern (wherein the ordered original sequence follows a sine shape, cosine shape, etc.). Furthermore, it should be understood that a periodic pattern does not necessarily have to complete a full cycle or be repeated. For example, a pattern that corresponds only to half a cycle of a cosine (or other) can be referred to as a periodic pattern capable of conveying frequency.

[0099] Figure 5B A schematic diagram of a measurement system 500 in the presence of spurious signals, according to some embodiments, is shown. In some embodiments, regarding Figure 5A The described spatial coding function or feature can be used to distinguish between the detection of foreign particle signals and spurious signals. It should be understood that, regarding... Figure 4 and Figure 5A Either the described structure or function can also be included in the reference. Figure 5B In some embodiments, for example, the irradiation system 424 ( Figure 4 ) can be included in the reference Figure 5A In the embodiments described above. Unless otherwise stated, Figure 5B In and Figure 4 and Figure 5A Elements that share similar reference numerals (e.g., reference numerals that share the two rightmost numbers) can have similar structures and functions.

[0100] In some embodiments, the measurement system 500 can be used to inspect the surface 536 of the film 532. The object 528 may include a mask 530 and the film 532. The mask 530 and the film 532 may be separated by a gap 531. The gap 531 may be in the range of several micrometers to several millimeters. The mask 530 may include patterned features 534. The patterned features 534 may be disposed in the gap 531.

[0101] In some embodiments, detector 504 may be an image capture device or a multi-element photodetector (e.g., a two-dimensional array of photodetectors). Sensor element 520 may include a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS). Detector 504 may receive radiation scattered at surface 536—that is, detected radiation 544. Detected radiation 544 may include radiation scattered by defects 540 located on surface 536 and other undesirable sources that may cause spurious signals. Detector 504 may generate a detection signal based on the received radiation.

[0102] In some embodiments, the film 532 may be transparent and allow a portion of the radiation beam 542 to be transmitted. The radiation transmitted at position A can then be directed to position A' on the mask 530. Pattern features 534 on the mask 530 may be located at or near position A'. Position A' may be located directly below or near position B on the film 532. The radiation scattered at position A' toward detector 504 can then have a similar optical path to the radiation scattered from position B toward detector 504. From a signal detection perspective, if the radiation scattered at position A' is received at detector 504, it appears that a foreign particle may be present at position B. However, since the radiation from position A' does not originate from a foreign particle, the detection of the radiation from position A' may correspond to a false signal. A similar relationship applies to positions C and B'.

[0103] In some embodiments, processor 506 may generate a first image associated with surface 536 based on the detection signal. The first image may correspond to radiation received at one or more detector elements of detector 504 at a given time. Processor 506 may generate one or more additional images associated with surface 536 based on the detection signal. These additional images correspond to times different from the times of the first image. By generating multiple consecutive images, the detector elements of detector 504 may contribute to the detection signal (as shown in illustration 549). Illustration 549 shows time intensity profiles 550a, 550b, and 550c generated by detector elements of detector 504 corresponding to positions A, B, and C on surface 536. The horizontal axis of time intensity profiles 550a, 550b, and 550c may represent the detected intensity, and the vertical axis may represent time.

[0104] It should be understood that in some embodiments, image generation may also include an environment using only a subset of the detector elements. For example, if the detected light energy is below a threshold, processor 506 may ignore contributions from the detector elements, such that only the “lit” area of ​​detector 504 is considered (to reduce processing load). In some embodiments, the concept of analyzing an image may alternatively refer to analyzing the detection signal—which carries information for generating the image—before the image is generated.

[0105] In some embodiments, at different modulation frequencies (e.g., f A f B and f C The spatial modulation of the irradiation can be used (e.g., by mapping the detected modulation frequency to coordinates on surface 536) to distinguish between signals caused by defect 540 and spurious signals. For example, radiation scattered from positions A, B, and C can be modulated with modulation frequencies f used to spatially modulate the radiation beam 542. A f B and f C Correlated. Subsequently, the detected radiation 544 can have a corresponding modulation frequency f. A f B and / or f C Furthermore, the time pattern of the detected radiation 544 can be a superposition of different sinusoidal modulation patterns as illustrated in Illustration 549.

[0106] In some embodiments, the time intensity profile 550a may represent the intensity signal corresponding to position A (e.g., I). A (t)). The time intensity profile 550b can represent the superposition of intensity signals corresponding to positions B and A' (e.g., I B (t) +I A The time intensity profile 550c can represent the superposition of intensity signals corresponding to positions C and B' (e.g., I). C (t) +I B '(t)). In some embodiments, processor 506 may perform frequency analysis based on the detection signals that present time intensity profiles 550a, 550b, and / or 550c. This can typically be done as per [reference to...]. Figure 5A Perform the frequency analysis as described.

[0107] In some embodiments, the frequency analysis performed by processor 506 may include Fourier analysis or cosine transform analysis of the detected signal. For example, graphs 552a, 552b, and 552c represent the results of applying a Fourier transform to the detected intensity corresponding to positions A, B, and C, and any current spurious signals. The vertical axis of graphs 552a, 552b, and 552c may represent the amplitude or intensity of the modulation. The horizontal axis of graphs 552a, 552b, and 552c may represent the frequency of the intensity modulation. In graph 552a, the frequency f may exist alone. A Because of the lack of false signals. In graph 552b, a frequency f can exist. B and f A , where f A This is associated with the spurious signal generated from position A'. In curve 552c, f can exist. C and f B , where f B This is associated with the spurious signal generated from position B'. For clarity, Figure 5A and Figure 5B Only three frequencies are shown, and it should be understood that more or fewer frequencies may be used. More than two frequencies may be superimposed at a given location.

[0108] In some embodiments, processor 506 can determine the association of a given frequency with a spurious signal by relating the detector element of detector 504 to the position on the surface being inspected. For example, based on the optical arrangement of the illumination and the detection branch of measurement system 500, the detector element can be expected to operate at a frequency f A Receive radiation from location A. Similarly, another detector element can be expected to receive radiation at frequency f. B Receive radiation from location B, and another detector element can be expected to receive radiation at frequency f. C Radiation is received from location C. Processor 506 can determine whether any non-characteristic modulation frequencies detected at a given detector element are associated with spurious signals. Alternatively or additionally, locations A, B, and C are illuminated with different phases. Performing this distinction by processor 506 may include associating spurious signals with frequencies and / or phases that are unrelated to or not characterized by location. Processor 506 may be a comparator (e.g., a means of analyzing one or more pieces of information, quantities, or values ​​for performing comparisons). It should be understood that in the case of a single quantity, a comparison can still be made assuming the second value is null or noise (e.g., zero).

[0109] In some embodiments, the frequency analysis performed by the processor 506 may include performing an inverse transform (e.g., an inverse Fourier transform F) based on information in graphs 552a, 552b and / or 552c. -1）The inverse transform can ignore spurious signals to extract the signal of interest in the time domain, as shown in, for example, graphs 554a, 554b, 554c, 556a, 556b, and 556c. In graphs 554a, 554b, and 554c, the vertical axis can represent the corresponding intensity I. A (t), I B (t) and I C (t) (e.g., removing superimposed spurious signals through frequency analysis), and the horizontal axis can represent time. In graphs 556a, 556b, and 556c, the vertical axis can represent the filtered intensity I. A (t), I B (t) and I C The corresponding phase of (t) is given, and the horizontal axis can represent time. In this way, frequency analysis can be used to determine the frequency, amplitude, and / or phase of the modulation used to illuminate a given location on the substrate. The inverse transform can be used to reconstruct the waveform of illumination at a given location on the modulation surface 536 based on ignoring at least one modulation parameter (e.g., frequency, phase, etc.) that is irrelevant to or not characterized by the given location—only the signal of interest is inversely transformed. The reliability of the measurement system 500 can be increased by reducing false detection events.

[0110] In some embodiments, processor 506 may generate a Fourier reconstructed image of surface 536 based on the signal of interest (e.g., removed spurious signals) in graphs 552a, 552b, and 552c. In other words, Fourier reconstruction may include reconstruction of the frequency and / or phase of illumination modulation at a given location, while omitting frequencies and / or phases that are irrelevant to or not characterized by the given location.

[0111] Figure 6 A schematic diagram of a measurement system 600 according to some embodiments is shown. It should be understood that, regarding... Figure 4 , Figure 5A and Figure 5B Either the described structure or function can also be included in the reference. Figure 6 In some embodiments, for example, the housing 414 ( Figure 4 ) can be included in the reference Figure 6 In the embodiments described above. Unless otherwise stated, Figure 6 In and Figure 4 , Figure 5A and Figure 5B Elements that share similar reference numerals (e.g., reference numerals that share the two rightmost numbers) can have similar structures and functions.

[0112] In some embodiments, the measurement system 600 can be used to check for the presence of foreign particles (e.g., foreign particle 640) in the mask 630. The measurement system 600 may include an illumination system having a spatial light modulator 610 and a focusing element 612. The measurement system may include a detector 604 and a processor 606. The detector 604 may include a sensor element 620 and a focusing element 622.

[0113] In some embodiments, the spatial light modulator 610 may be configured to adjust the spatial intensity distribution of the radiation beam 642 generated by the illumination system. The spatial intensity distribution of the radiation beam 642 may include a periodic spatial intensity distribution 611. The periodic spatial intensity distribution 611 may be projected onto a surface 638 of an object including a mask 630. The mask 630 may include a pattern feature 634. The pattern feature 634 may be located on a surface of the mask 630 opposite to the surface 638. The periodic spatial intensity distribution 611 may be temporally adjusted. For example, the periodic spatial intensity distribution 611 may be scanned across the surface 638 or a portion thereof. In some embodiments, the phase of the periodic spatial intensity distribution 611 may be adjusted such that the peaks and valleys of the periodic spatial intensity distribution 611 are translated across the surface 638 or a portion thereof. The periodic spatial intensity distribution 611 may include, for example, a sinusoidal pattern, a step function pattern, a sawtooth pattern, a triangular pattern, and so on, and any combination thereof.

[0114] In some embodiments, the mask 630 may be transparent, translucent, or otherwise have a surface 638 that allows a portion of the radiation beam 642 (represented by the radiation beam 642') to be transmitted through it. The radiation beam 642' may include an evolved periodic spatial intensity distribution 611' that is initially the same as the periodic spatial intensity distribution 611. The initial form of the evolved periodic spatial intensity distribution 611' is shown as intensity profile 551a. As the radiation beam 642' propagates through the mask 630, the evolved periodic spatial intensity distribution 611' may evolve such that the contrast of the evolved periodic spatial intensity distribution 611' is reduced, for example, becoming blurred (shown as intensity profile 551b) and / or approaching a DC-like intensity (shown as intensity profile 551c).

[0115] In some embodiments, the radiation beam 642' may illuminate a structure near the surface (e.g., pattern feature 634). The structure near the surface may scatter radiation toward the detector 604 (represented by the detected radiation 644').

[0116] In some embodiments, detector 604 may receive radiation scattered at surface 638 (represented by detected radiation 644) and detected radiation 644'. Detected radiation 644 scattered at surface 636 may include radiation scattered by foreign particles 640 located on surface 638. Detector 604 may generate a detection signal based on the received radiation. Because the periodic spatial intensity distribution varies over time, detected radiation 644 may experience corresponding modulation in intensity (e.g., scintillation), while detected radiation 644' may experience reduced intensity modulation or no modulation due to its reduced contrast resulting from propagation through mask 630. In other words, radiation scattered by structures near the surface and received at the detector (detected radiation 644') is generated from a portion of the beam that has already been transmitted through the surface (radiation beam 642'), and the transmitted portion includes a periodic spatial intensity distribution with reduced contrast (evolved periodic spatial intensity distribution 611').

[0117] In some embodiments, processor 606 may receive the detection signal. Processor 606 may generate a first image based on the detection signal. The first image may correspond to a first state of periodic spatial intensity distribution 611, meaning that the state of periodic spatial intensity distribution 611 can be adjusted using spatial light modulator 610. Processor 606 may generate a second image based on the detection signal. The second image may correspond to a second state of periodic spatial intensity distribution 611 that is different from the first state. Processor 606 may generate a third image based on the detection signal. The third image may correspond to a third state of periodic spatial intensity distribution 611 that is at least different from the second state (e.g., a 2π phase shift may cause the third phase to be the same as the first phase). Processor 606 may generate additional images for analysis (e.g., as animation). Processor 606 may analyze the first, second, and third images to determine locations on the surface where the adjustment of the state of the periodic spatial intensity distribution exhibits a reduced or decreased optical response. The reduced or decreased optical response may be associated with a flicker-free signal because the spatial variation in intensity has been blurred to the DC level. Furthermore, the DC offset can be separated from the flickering portion of the signal at any image location, and thus effectively removes spurious signals caused by foreign particles 640 from the actual signal. In other words, spurious portions can contribute to the DC offset, while time-varying portions can originate from foreign particles 640. The processor 606 can then determine that the location on the surface exhibiting the reduced optical response is due to spurious signals and not from foreign particles 640. In this way, the reliability of the measurement system 600 can be increased by reducing false detection events.

[0118] The wavelength of illumination can also be used to enhance the detection of foreign particles using the multi-wavelength capability of the embodiments disclosed herein. (The preceding text is about...) Figure 4 The measurement system 400 and the transparency of the object 428 (see information on the surface film 532 (Figure 5) and / or the mask 630) Figure 6 The description describes the structure and function used to generate multiple wavelengths.

[0119] Figure 7 A graph 700 shows the transmittance (vertical axis) of a surface film relative to the radiation wavelength (horizontal axis) according to some embodiments. Graph 700 shows that the transmittance of radiation through the surface film (e.g., surface film 532 of FIG. 5) is wavelength-dependent. For example, at a wavelength of 360 nm, graph 700 shows that the transmittance is approximately 0.003%. In other words, radiation with a wavelength of 360 nm can transmit through the surface film and is attenuated by a factor of 333, i.e., attenuated to 1 / 333. The transmittance at 440 nm is 0.135%, and the corresponding transmission attenuation factor is 7.4. When radiation is transmitted through the surface film once and then backscattered towards the surface film for a second transmission, the difference in transmission intensity between 360 nm and 440 nm is approximately a factor of 2000. Conversely, silver fragments (common foreign particles in lithography equipment) can be directed towards the detector 404 ( Figure 4 The radiation is scattered with a wavelength-dependent reflectivity, which varies by a factor of approximately 10 when switching from 360 nm to 440 nm. In other words, the difference in optical response at the surface of an object can be the difference between a first amount of attenuation of the detected radiation at a first wavelength and a second amount of attenuation of the detected radiation at a second wavelength. A large contrast between the attenuation factor of the surface coating (e.g., 2000) and the attenuation factor of the foreign particles (e.g., 10) can be used to distinguish spurious signals from foreign particles. Other types of foreign particle materials can include copper, aluminum, gold, palladium, and / or platinum. It should be understood that each material can be distinguished from spurious signals based on its unique reflectivity characteristics.

[0120] In some embodiments, since transmittance is wavelength-dependent, optical measurements can utilize the multi-wavelength capability of the measurement system to identify and distinguish foreign particle signals from spurious signals, which will relate to... Figure 4This is a description. However, this should not be construed as limiting, and any structures and functions described herein with respect to other figures may also be used. In some embodiments, the illumination system 402 is configured to adjust the wavelength of the radiation beam 442. The first image generated by the processor 406 may correspond to a first wavelength of the radiation beam 442. The second image generated by the processor 406 may correspond to a second wavelength of the radiation beam 442 that is different from the first wavelength. The processor 406 may perform analysis of the first and second images to determine locations on the surface that exhibit differences in the optical response of the object 428 to the adjustment of the wavelength of the radiation beam 442. The differentiation performed by the processor 406 (differentiating foreign particles from spurious signals) may be based on the analysis. The differentiation may include associating the spurious signals with locations on the surface that exhibit differences in the optical response that are unrelated to or not characterized by foreign particles.

[0121] In some embodiments, optical measurements can utilize the polarization capability of the measurement system to identify and distinguish foreign particle signals from spurious signals. Figure 8 Non-limiting arrangements of polarizers, according to some embodiments, that can be used in measurement systems disclosed herein. It should be understood that, regarding... Figure 4 , Figure 5A , Figure 5B , Figure 6 and Figure 7 Either the described structure or function can also be included in the reference. Figure 8 In some embodiments, for example, spatial light modulator 410 ( Figure 4 ) can be included in the reference Figure 8 In the embodiments described above. Unless otherwise stated, Figure 8 In and Figure 4 , Figure 5A , Figure 5B , Figure 6 and Figure 7 Elements that share similar reference numerals (e.g., reference numerals that share the two rightmost numbers) can have similar structures and functions.

[0122] In some embodiments, the illumination system 802 may include radiation sources 808a and 808b, polarizer 812a (e.g., a P-polarizer), polarizer 812b (e.g., an S-polarizer), and beam combiner 813. Polarizer 812a may be disposed downstream of radiation source 808a. Polarizer 812b may be disposed downstream of radiation source 808b. Beam combiner 813 may be disposed downstream of both polarizers 812a and 812b. In some embodiments, spatial light modulator 410 ( Figure 4 It can be set downstream of the bundle combiner 813.

[0123] In some embodiments, the illumination system 802 may use one or both of radiation sources 808a and 808b to generate a radiation beam 842. Radiation from radiation source 808a may be polarized by polarizer 812a. Radiation from radiation source 808b may be polarized by polarizer 812b. Polarizers 812a and 812b may be orthogonal, such that the radiation beam 842 may have selective polarization. For example, radiation source 808a may be activated alone, such that the polarized radiation beam 842 has a first polarization. Conversely, radiation source 808b may be activated alone, such that the polarized radiation beam 842 has a second polarization (e.g., orthogonal polarization) different from the first polarization. Beam combiner 813 may combine the optical paths of radiation sources 808a and 808b, such that the illumination system 802 is allowed to provide selective polarization along a common optical path. The radiation beam 842 may be directed to spatial light modulator 410 ( Figure 4 ), so that the radiation beam 842 illuminates the object 428 ( Figure 4 It was previously modulated spatially. One can imagine... Figure 8 Spatial light modulator 410 (among other components) Figure 4 Other configurations of the spatial light modulator 410. Figure 4 For example, when implemented as a liquid crystal device, it can also provide polarization functionality.

[0124] In some embodiments, radiation sources 808a and 808b can be configured to generate multiple selectable wavelengths. In some embodiments, radiation sources 808a and 808b can be configured to generate the same wavelength. Even if either radiation source 808a or 808b is fixed at a single wavelength, it can still be used to generate multiple wavelengths. Figure 8 The iterative arrangement shown achieves multi-wavelength capability. That is, more than one beam combiner can be used in conjunction with additional radiation sources and polarizers. The additional radiation sources can then generate additional wavelengths. Furthermore, one or more polarizers can be omitted, allowing the illumination system 802 to selectively generate polarized and unpolarized radiation.

[0125] Refer again Figure 4As a non-limiting example, in some embodiments, processor 406 may generate a first image and a second image based on a detection signal. The first image may correspond to a first polarization. The second image may correspond to a second polarization different from the first polarization. Processor 406 may perform analysis of the first and second images to determine locations on the surface exhibiting differences in optical response to the adjustment of the polarization of the radiation beam 442. Processor 406 may then determine that the location on the surface exhibiting the difference in optical response is due to a spurious signal and not originating from defect 440. This is possible because defect 440 may not have a polarization-dependent response, while pattern feature 434—a structure near surface 436—may have a polarization-dependent diffraction efficiency (e.g., the amount of reflected light changes due to polarization). Irradiation scattered by pattern feature 434 and detected at detector 404 can be distinguished from defect 440. The distinction may include associating the spurious signal with the location on the surface exhibiting the difference in optical response. In other words, the difference in optical response at the surface of an object may be the difference between the intensity of radiation received under the first polarization and the intensity of radiation received under the second polarization. In this way, the reliability of the measurement system 400 can be increased by reducing false detection events.

[0126] Figure 9 A schematic diagram of a measurement system 900 according to some embodiments is shown. It should be understood that, regarding... Figure 4 , Figure 5A , Figure 5B , Figure 6 , Figure 7 and Figure 8 Either the described structure or function can also be included in the reference. Figure 9 In some embodiments, for example, spatial light modulator 410 ( Figure 4 ) can be included in the reference Figure 9 In the embodiments described above. Unless otherwise stated, Figure 9 In and Figure 4 , Figure 5A , Figure 5B , Figure 6 , Figure 7 and Figure 8 Elements that share similar reference numerals (e.g., reference numerals that share the two rightmost numbers) can have similar structures and functions.

[0127] In some embodiments, the measurement system 900 includes an illumination system 902, a detector 904, and a processor 906. The illumination system 902 may include a spatial light modulator 910. The illumination system 902 may generate a radiation beam 942 for illuminating an object 928. The object 928 may be a mask 930 having a surface film 932 located on one side of a mask 930. The mask 930 may include pattern features 934.

[0128] In some embodiments, the spatial light modulator 910 can direct a radiation beam 942 toward the surface of the object 928 (e.g., the surface of the film 932). The spatial light modulator 910 can adjust the spatial intensity distribution of the radiation beam 942 to illuminate a portion of the surface at a non-zero incident angle. The non-zero incident angle can be approximately 30 to 85 degrees, 45 to 85 degrees, 60 to 85 degrees, or greater than 80 degrees.

[0129] In some embodiments, detector 904 may receive radiation (represented by detected radiation 944) along optical path 947 corresponding to radiation already scattered at the irradiated portion of the surface. However, radiation already scattered by structures near the surface (represented by detected radiation 944') may travel along an optical path 947' different from optical path 947. Detector 904 may generate a detection signal based on the received radiation.

[0130] In some embodiments, processor 906 may receive the detection signal. Processor 906 may distinguish between false signals and signals corresponding to the presence of foreign particles 940 on the surface based on the detection signal. The distinction may have an associated error probability, which may be based on the probability of detecting a false signal but failing to distinguish it from the presence of foreign particles 940. Therefore, the distinction may include reducing the probability of detecting false signals based on the difference between optical paths 947 and 947'. A larger difference between optical paths 947 and 947' may result in a greater reduction in the probability of detecting the false signal.

[0131] Referring again to the concepts of modulation and spatial coding of illumination at the pixel level, the sinusoidal modulation pattern is currently seen as an example of how two locations on the surface can be "encoded" with different illumination patterns that change over time. However, the sinusoidal pattern is merely an example and other patterns can be used. For example, discrete and stepped patterns have been discussed with respect to some embodiments.

[0132] Figure 10 A portion of a measurement system 1000 according to some embodiments is shown. It should be understood that, regarding... Figure 4 , Figure 5A , Figure 5B , Figure 6 , Figure 7 , Figure 8 and Figure 9 Either the described structure or function can also be included in the reference. Figure 10 In some embodiments, for example, spatial light modulator 410 ( Figure 4 ) can be included in the reference Figure 10 In the embodiments described above. Unless otherwise stated, Figure 10 In and Figure 4 , Figure 5A , Figure 5B , Figure 6 , Figure 7 and Figure 8 Elements that share similar reference numerals (e.g., reference numerals that share the two rightmost numbers) can have similar structures and functions.

[0133] The measurement system 1000 can be used to identify and / or characterize defects on object 1028. Object 1028 can be, for example, a mask 1030 having a protective coating 1032. Surface 1036 of the coating 1032 may be at risk of developing defects (e.g., scratches or contaminant particles on the surface) upon repeated use. Surface 1038 (e.g., the rear side) of the mask 1030 may also be at risk of developing similar defects. Therefore, it should be understood that the measurement system 1000 can be used to inspect surfaces 1036 and / or 1038 (or any surface of object 1028 normally) by simply changing the orientation of object 1028.

[0134] For simplicity, some components of the measurement system 1000, such as those related to... Figure 4 , Figure 5A , Figure 5B , Figure 6 , Figure 7 , Figure 8 and Figure 9 The components shown are redundant (e.g., radiation sources, detectors, etc.). However, it should be understood that in some embodiments, such components may be as they are in Figure 4 , Figure 5A , Figure 5B , Figure 6 , Figure 7 , Figure 8 and Figure 9 It exists as described above. Using a spatial light modulator, the radiation beam 1042 can be modulated according to a pattern (e.g., a first pattern, a second pattern, additional patterns, etc.). This has already been mentioned above (e.g., regarding...). Figure 5A and Figure 5B The periodic patterns are discussed, along with some examples of patterns.

[0135] In some embodiments, the pattern may be a binary pattern (e.g., a series of irradiated open and closed states). Each location A, B, C, D, etc., on the surface 1036 of the film 1032 can be assigned a different binary pattern, similar to a reference pattern. Figure 5A and Figure 5B How to use f A f B and f C Different periodic patterns. For example, spatial light modulators (e.g., Figure 5A (510) The spatial intensity distribution of the radiation beam 1042 can be adjusted to modulate the irradiation intensity of the radiation beam 1042 at position A on surface 1036 according to the first pattern 1042-A. Similarly, position B on surface 1036 can receive irradiation modulated according to the second pattern 1042-B. Additional positions can receive irradiation modulated according to corresponding additional patterns (e.g., up to the nth position on surface 1036 receiving irradiation modulated according to the nth pattern 1042-n). The modulation pattern can be, for example, a binary pattern. Other patterns will be apparent to those skilled in the art based on this disclosure.

[0136] In some embodiments, the detected radiation 1044 is radiation received at a downstream detector. As an example, the detected radiation 1044 is shown as originating from location D of surface 1036. The detected radiation 1044 may include mixed radiation, including radiation from a defect at location D (e.g., associated with the fourth pattern 1042-D) and other radiation that may be associated with spurious signals. For example, radiation encoded with the first pattern 1042-A may be incident at location A. If the surface film 1032 is at least semi-transparent, the radiation with the first pattern 1042-A may be partially transmitted through the surface film 1032 and undergo multiple reflections between the surface film 1032 and the mask 1030 (as indicated by the arrows from location A' to C and then to C'). The mask 1030 may include pattern features 1034 that scatter radiation upwards toward location D. Such radiation may cause spurious signals to be detected when the detected radiation 1044 is received at the detector. Furthermore, radiation with the third pattern 1042-C can be transmitted through position C of surface 1036 and scattered from position C' in the direction of the detected radiation 1044 due to interaction with pattern feature 1034. As a result, the detected radiation may include a fourth pattern 1042-D (i.e., associated with the "real" signal due to the defect) and a first pattern 1042-A and a third pattern 1042-C associated with the false signal.

[0137] In some embodiments, the detection signal generated from the detected radiation 1044 can be analyzed by a processor (e.g., processor 506 of FIG. 5). Processor 506 can distinguish between spurious signals and signals corresponding to the presence of defects on surface 1036 based on the detection signal. The analysis of the detection signal can be based on the modulation of the radiation beam 1042. If, for example, a binary pattern is used for modulation, the analysis can include determining the binary pattern used at a given location on surface 1036. Since the detection signal can correspond to a superposition of illuminations with more than one binary pattern, the determination can include deconstructing different modulation patterns at a given pixel. With prior knowledge of the spatial distribution of the modulation patterns on surface 1036, the processor can associate or map the pixels of the detector with corresponding locations on surface 1036. The processor can distinguish between spurious signals and “real” signals. The distinction can include associating the spurious signal with a binary pattern that is irrelevant to or not characterized by the given location.

[0138] In some embodiments, there may be more different locations to be irradiated than the available different modulation patterns. In this case, the modulation pattern may be repeated and distributed throughout surface 1036 such that no two identical binary patterns are used at adjacent locations on the surface. For example, Figure 10 The diagram shows a sequence of different binary patterns 1042-A to 1042-n (from left to right). The sequence can restart at 1042-A corresponding to position A2 once all the different modulation patterns have been used at least once. Positions beyond the nth position can be referred to as additional positions. More or fewer different modulation patterns can be used. In this way, the distinction between each position and spurious signals can be enhanced.

[0139] The pattern used to modulate the different “pixels” of the radiation beam 1042 can be further optimized to increase the speed of measurement and information processing. In some embodiments, a set of linearly independent patterns as shown in Table 1 can be used as the first pattern to the nth pattern. Table 1 is a set of linearly independent patterns for n=7. Zero (0) indicates the off state of the irradiation, and a (1) indicates the on state of the irradiation.

[0140]

[0141] and Figure 10The comparison (using eight different patterns) merely illustrates the selectivity and non-limiting properties of formulating distinguishable modulation patterns. In some embodiments, each of the seven linearly independent binary patterns in Table 1 can be constructed using a sequence of eight on or off states. In any pattern, the number of on states can be equal to the number of off states. In the example in Table 1, this would mean that each pattern has four on states and four off states, for a total of eight on or off states. If a larger group of linearly independent patterns is desired (e.g., n>7), more on or off states (e.g., 10 on or off states) can be used. For example, in cases where the physical distance between the locations of patterns to be reused is further separated, the number of linearly independent patterns can be increased. For example, in Figure 10 In the codewords, positions A and A2 can be separated by seven patterns. If positions A and A2 are not so separated, it is possible that a stray illumination from position A' might be detected as if it came from position A2. In such a case, the processor might incorrectly interpret the spurious signal as a "real" signal because the first pattern 1042-A is also expected to come from position A2. It should be understood that linearly independent patterns are not limited to binary patterns (e.g., a sinusoidal pattern associated with a Fourier transform can be linearly independent). It should be understood that the prefixes "first," "second," "third," etc., are arbitrary designations and should not be construed as limiting any pattern to the specific sequence disclosed herein. Using Table 1 as a non-limiting reference, any item in the codewords in Table 1 can be a "first pattern." In the remaining codewords, any item can be a "second pattern."

[0142] In some embodiments, the set of binary patterns can be orthogonal. Similar to Fourier analysis described above (which involves orthogonal relations of sine terms), having orthogonal binary patterns simplifies the amount of processing required to deconstruct the superimposed patterns. Therefore, the speed of measurement can be increased.

[0143] In some embodiments, Table 1 may be referred to as a "code matrix", wherein Represent the entire matrix and Is it related to row index or subscript? The corresponding "code words". For example, 10101001 is from the matrix The codewords. These codewords can be described using orthogonality relations. An example of orthogonality can be described by Equation 1, which is similar to an inner product:

[0144]

[0145] here, and It can be from a matrix Any two codewords, and their indices This represents the j-th on or off state. The code matrix... It can be constructed such that each codeword has the same average value. In the examples provided in Table 1, the average value is... 0.5. For any unequal codeword pair, the result of Equation 1 is zero. Processors can use this property to greatly speed up the calculation of whether the detected signal includes "real" signals and / or spurious signals.

[0146] In some embodiments, orthogonal features can be further constructed to create vectors. The processor can use the vector to distinguish between "real" signals and fake signals, where the vector As given by Equation 2.

[0147]

[0148] here, It is a codeword matrix, and It is a vector representing the sequence of intensities detected at a given pixel by the detector. Each element in the vector can be a numerical value representing the intensity (e.g., zero (0) indicates no intensity was detected). Regarding the average vector... Each of its elements is filled in the vector The average of the intensity values ​​found. The result of the matrix product is a vector with seven elements. (matrix Each linearly independent codeword in the detector has one. A vector can be generated for each pixel of the detector. .vector Each value is actually the result of a scalar product between a codeword (e.g., a modulation pattern in vector form) and a vector (e.g., a vector based on the detection signal).

[0149] In some embodiments, if only scattering from the defect at location B (illuminated by the second pattern 1042-B) exists, then the corresponding vector It can have In the form of, It is a positive value proportional to the detected intensity. If only scattering from position A' (illuminated by the first pattern 1042-A) exists, then It can have In the form of, It is a positive value proportional to the intensity of radiation from location A'. If there is no scattering anywhere, then... All are zero. If there is scattering from both positions B and A', then In this way, by utilizing vectors As a result, the processor can quickly determine which signals come from which locations on surface 1036 and distinguish between "real" signals and false signals.

[0150] In some embodiments, the processor performing the analysis may isolate detector pixels, codewords to be considered, and / or exposure frames (e.g., specific elements of the codewords) to reduce computation and thus increase measurement speed. For example, if the pixel associated with position B on surface 1036 is of interest, the processor does not need to perform the entire matrix multiplication of Equation 2. Instead, the processor can only compute the pixel to be obtained. vector product without having to calculate vectors Other elements.

[0151] In some embodiments, codewords may also involve values ​​other than fully open and fully closed states, such as those selected from 0, 0.5, and 1. In this case, each codeword has an average value of 0.5, which may be desirable to maintain the applicability of equations 1 and 2. Further considering this concept, code sequences can be generalized to include a value spectrum. For example, a raised cosine function, as given by equation 2, can be used:

[0152]

[0153] here, Let M represent the single element corresponding to the nth row and mth column of the code matrix, where M is the codeword length. This is another non-limiting example of how codewords and matrices can be constructed. It should be understood that the concept of binary patterns (0 and 1) has been generalized so that periodic patterns (e.g., cosine functions) can be used in conjunction with analyses similar to or analogous to those described above regarding binary patterns. Therefore, in some embodiments, the term "codeword" is not restricted to binary patterns only. The term "codeword" can be used generally to refer to modulation patterns (e.g., first pattern, second pattern, etc.).

[0154] In some embodiments, Equation 3 produces a value between 0 and 2 (inclusive). The value 2 may correspond to a specific illumination intensity (e.g., maximum). The corresponding average value for each codeword produced by Equation 3 will then be... 1. In some embodiments, the average irradiation intensity associated with the first pattern may be equal to the average irradiation intensity associated with the second pattern. In some embodiments, the average irradiation intensity corresponding to an additional pattern may be equal to the average irradiation intensity of the first pattern and / or the second pattern.

[0155] As another example of constructing linearly independent patterns, in some embodiments such a set can be constructed based on Table 2, which is based on a concept similar to Equation 3, but selected from a set of raised sine, raised cosine, and DC patterns.

[0156]

[0157] Subscript The range is from 1 to M, where M is the length of the column number in the codeword or codeword matrix. Then, Table 2 generates an M×M matrix. Codeword It is a DC signal. Other codewords are raised sine or cosine signals with an integer number of periods. It should be understood that permutations of rows and / or columns can also be used. Furthermore, fewer codewords (e.g., a subset of rows) can also be suitable, resulting in a code matrix of size N×M, where N... <M。

[0158] In some embodiments, comparing the raised sine / cosine values ​​in Table 2 with Equation 3 shows that the values ​​in Table 2 have been normalized by a factor of 1 / 2 compared to Equation 3. This factor can be selected based on constraints of the measurement system 1000. For example, the factor can be chosen to be different for each codeword, thus making the average value different between codewords. For example, when using Equation 2, this difference can lead to crosstalk between pixels (e.g., modulation at the first pixel might affect the detection result at the second pixel based solely on a suboptimal construction of the codeword, regardless of whether radiation is detected at the second pixel). Similarly, using an integer number of periods for the raised sine / cosine allows for a constant average value at all times. The construction of the codeword matrix. However, it should be understood that the constant average value of the codeword matrix... It is not strictly required to achieve the desired results (e.g., spurious signal differentiation and defect detection).

[0159] In some embodiments, an orthogonal relation similar to that in Equation 1 can be applied to the codewords generated by Equation 3 and / or Table 2, as shown in Equation 4:

[0160]

[0161] here, This represents the element associated with the i-th row of the codeword matrix, and This represents the element associated with the k-th row of the codeword matrix. The summation index j indicates the column of the codeword matrix. Much like Equation 1, if unequal codewords are chosen for the calculation, the result is zero.

[0162] In some embodiments, non-orthogonal, linearly independent codewords can be used, provided that there are no negative values ​​in the codeword (e.g., the minimum possible intensity of the illumination is 0). In this case, Equation 2 can be generalized to take the form of Equation 5:

[0163]

[0164] Here, superscript This indicates the transpose, and the superscript + indicates the pseudo-inverse. Vector and As mentioned earlier, in order to use a processor to perform analysis, in some embodiments, this can be achieved by using vectors... and The vector is calculated by the corresponding row multiplication. Specific elements. Using the generalized form of Equation 5, the crosstalk problem discussed above can be mitigated.

[0165] In some embodiments, different code matrices can be applied simultaneously at different wavelengths using the same number of exposures. For example, typical DMD devices are already capable of performing complex exposures using red, green, and blue wavelengths. This can be further modified to include other wavelengths and wavelength combinations. For example, the intensity state of a pattern can be associated with a first wavelength, and a second intensity state of the pattern can be associated with a second wavelength different from the first wavelength. In another example, the intensity state of a first pattern can be associated with a first wavelength, and the intensity state of a second pattern can be associated with a second wavelength different from the first wavelength. In yet another example, using three 7×8 matrices, 7... 3 = 343 unique codewords. In addition, the modulation pattern can usually use multiple wavelengths.

[0166] It should be understood that in some embodiments, a perfect monochromatic wavelength may be infeasible or impractical for production (e.g., hardware limitations). Therefore, it should be understood that the term "first wavelength" can refer to a narrow band centered approximately on one wavelength. The second wavelength can be described similarly. In this case, two distinct wavelengths can refer to two corresponding different center wavelengths.

[0167] In some embodiments, the wavelength defined as “different” can be a function of the measurement system 1000. For example, if the measurement system 1000 can distinguish such a difference, then the first wavelength (having a frequency band or band and a center wavelength) and the second wavelength (having a frequency band or band and a different center wavelength) can be considered different. Conversely, the two wavelength bands may not be different in the sense that they overlap to the extent that the measurement system 1000 cannot distinguish the difference.

[0168] Although foreign particles have already been detected (e.g., defect 440), Figure 4Specific embodiments are described in the context of [the specific embodiments described herein], but the embodiments described herein are not limited to particulate contaminant detection. In some embodiments, the measurement systems described herein can typically detect defects such as scratches, pinholes or dents, foreign particles, stains, etc. It is desirable to detect all types of defects that pose a risk of disrupting the photolithography process.

[0169] In some embodiments, the measurement system described herein may be implemented as a larger system, for example, within a lithography apparatus.

[0170] The embodiments can also be described in the following ways:

[0171] 1. A system comprising:

[0172] An irradiation system, the irradiation system comprising:

[0173] A radiation source, the radiation source being configured to produce a beam of radiation;

[0174] A spatial light modulator, the spatial light modulator being configured to guide the beam toward a surface of an object and adjust the spatial intensity distribution of the beam at the surface;

[0175] A detector configured to receive radiation scattered at the surface and radiation scattered by structures near the surface, and to generate a detection signal based on the received radiation; and

[0176] The comparator is configured to:

[0177] Analyze the detection signal;

[0178] The location of the defect on the surface is determined based on the analysis; and

[0179] The analysis and adjustments are used to distinguish between false signals and signals corresponding to the defects.

[0180] 2. The system according to aspect 1, wherein:

[0181] The spatial light modulator is further configured to adjust the spatial intensity distribution to modulate the illumination intensity of the beam at a first position on the surface according to a first pattern, and to modulate the illumination intensity of the beam at a second position on the surface according to a second pattern different from the first pattern.

[0182] The second position is different from the first position; and

[0183] The analysis includes analysis of the detected signal based on the modulation.

[0184] 3. The system according to aspect 2, wherein:

[0185] The first pattern and the second pattern correspond to the first binary pattern and the second binary pattern; and

[0186] The analysis includes determining the binary pattern used at a given location on the surface.

[0187] 4. The system according to aspect 3, wherein the distinction includes associating the spurious signal with a binary pattern not characterized by the given position.

[0188] 5. The system according to aspect 3, wherein each of the first binary pattern and the second binary pattern includes a plurality of closed states equal to the number of open states.

[0189] 6. The system according to aspect 2, wherein a first intensity state of the first pattern is associated with a first wavelength, and a second intensity state of the first pattern is associated with a second wavelength different from the first wavelength.

[0190] 7. The system according to aspect 2, wherein the intensity state of the first pattern is associated with a first wavelength, and the intensity state of the second pattern is associated with a second wavelength different from the first wavelength.

[0191] 8. The system according to aspect 2, wherein:

[0192] The spatial light modulator is also configured to adjust the spatial intensity distribution in order to modulate the irradiation intensity of the beam at additional locations on the surface according to a corresponding additional pattern.

[0193] The first pattern, the second pattern, and each of the additional patterns are different from one another;

[0194] The distinction includes associating the spurious signal with a pattern that is not characterized by the given location.

[0195] 9. The system according to aspect 8, wherein the first pattern, the second pattern, and the additional pattern are repeated at further additional locations on the surface; and

[0196] Repeated first patterns, second patterns, and additional patterns are distributed on the surface such that no two identical patterns are used at adjacent positions on the surface.

[0197] 10. The system according to aspect 2, wherein the first pattern is linearly independent of the second pattern.

[0198] 11. The system according to aspect 2, wherein the first pattern is orthogonal to the second pattern.

[0199] 12. The system according to aspect 2, wherein:

[0200] The first pattern and the second pattern correspond to a first periodic pattern and a second periodic pattern;

[0201] The frequency and / or phase of the first periodic pattern are different from the frequency and / or phase of the second periodic pattern; and

[0202] The analysis includes frequency analysis.

[0203] 13. The system according to aspect 12, wherein:

[0204] The frequency analysis includes determining the frequency and / or phase of the illumination modulation used at a given location on the surface; and

[0205] The distinction includes associating the spurious signal with frequencies and / or phases that are not characterized by the given position.

[0206] 14. The system according to aspect 12, wherein:

[0207] The sequence of intensity states of the first periodic pattern includes variations relative to the ordered original sequence of the first periodic pattern; and / or

[0208] The sequence of intensity states of the second periodic pattern includes variations relative to the ordered original sequence of the second periodic pattern.

[0209] 15. The system according to aspect 12, wherein the first pattern and / or the second pattern are based on raised sine and / or cosine functions.

[0210] 16. The system according to aspect 2, wherein the analysis includes the product of the first pattern and a vector based on the detection signal.

[0211] 17. The system according to aspect 12, wherein the frequency analysis includes Fourier analysis.

[0212] 18. The system according to aspect 17, wherein the Fourier analysis comprises:

[0213] The Fourier transform of the detected signal; and

[0214] Fourier reconstruction of the waveform of illumination at a given position, based on modulation parameters that are at least ignored and not characterized by the given position.

[0215] 19. The system according to aspect 1, wherein:

[0216] The spatial intensity distribution includes a sequence of a first state, a second state, and a third state based on the adjusted periodic spatial intensity distribution;

[0217] The second state is different from the first and third states; and

[0218] The detection signal includes modulation based on the first state, the second state, and the third state;

[0219] The analysis includes analyzing the modulation to at least determine the locations on the surface that exhibit a reduced optical response to the modulation.

[0220] 20. The system according to aspect 19, wherein the differentiation includes associating the spurious signal with the location on the surface that exhibits the reduced optical response to the adjustment.

[0221] 21. The system according to aspect 19, wherein:

[0222] The radiation scattered by the structure near the surface is generated from the transmission portion of the beam that passes through the surface; and

[0223] The transmissive portion includes the periodic spatial intensity distribution with reduced contrast.

[0224] 22. The system according to aspect 1, wherein:

[0225] The radiation source is also configured to adjust the wavelength of the beam;

[0226] The beam includes different first and second wavelengths;

[0227] The detection signal includes wavelength information of the received radiation based on different first and second wavelengths; and

[0228] The analysis includes analyzing the wavelength information to at least determine the locations on the surface that exhibit differences in optical response to adjustments of the wavelength.

[0229] 23. The system according to aspect 22, wherein the distinction includes associating the spurious signal with the location on the surface that exhibits a difference in optical response to adjustment of the wavelength.

[0230] 24. The system according to aspect 22, wherein the difference in optical response to adjusting the wavelength includes the difference between attenuation of the received radiation based on the first wavelength and attenuation of the received radiation based on the second wavelength.

[0231] 25. The system according to aspect 1, wherein:

[0232] The irradiation system is configured to adjust the polarization of the beam, and the irradiation system further includes a polarizer configured to modify the polarization of the beam;

[0233] The beam includes different first polarizations and second polarizations;

[0234] The detection signal includes polarization information of the received radiation based on the different first and second polarizations; and

[0235] The analysis includes analyzing the polarization information to at least determine the locations on the surface that exhibit differences in optical response to adjustments in polarization.

[0236] 26. The system according to aspect 25, wherein the distinction includes associating the spurious signal with the location on the surface that exhibits a difference in optical response to adjustment of the polarization.

[0237] 27. The system according to aspect 25, wherein the difference in the optical response to the adjustment of the polarization includes the difference between the intensity of the received radiation based on the first polarization and the intensity of the received radiation based on the second polarization.

[0238] 28. The system according to aspect 1, wherein:

[0239] The spatial light modulator is also configured to adjust the spatial intensity distribution so as to illuminate a portion of the surface at a non-zero incident angle;

[0240] The detector is also configured to receive radiation along an optical path of the radiation scattered at the said portion of the surface; and

[0241] The system is configured to reduce the probability of false signal events based on the difference between the optical path and the optical path corresponding to the radiation scattered by the structure near the surface.

[0242] 29. The system according to aspect 1, wherein the spatial light modulator includes a digital micromirror device.

[0243] 30. The system according to aspect 1, wherein the spatial light modulator includes a liquid crystal modulator.

[0244] 31. The system according to aspect 1, wherein the detector comprises a charge-coupled device or a complementary metal-oxide-semiconductor.

[0245] 32. The system according to aspect 1, wherein:

[0246] The spatial light modulator is further configured to adjust the spatial intensity distribution in time to modulate the illumination intensity of the beam at a first position on the surface at a first frequency, and to modulate the illumination intensity of the beam at a second position on the surface at a second frequency.

[0247] The second position is different from the first position;

[0248] The second frequency is different from the first frequency; and

[0249] The system is configured to improve the optical resolution of the detection based on frequency analysis of the detection signal.

[0250] 33. A method comprising:

[0251] Generates a radiation beam;

[0252] The beam is guided toward the surface of the object;

[0253] A spatial light modulator is used to adjust the spatial intensity distribution of the beam;

[0254] The scattered radiation is received at the detector, wherein the scattered radiation includes radiation scattered at the surface and radiation scattered by structures near the surface;

[0255] The detector is used to generate a detection signal;

[0256] The processor is used to analyze the detection signal;

[0257] The location of the defect on the surface is determined based on the analysis; and

[0258] Based on the analysis, false signals and signals corresponding to the defects are distinguished, and the processor is used to make the adjustments.

[0259] 34. The method according to aspect 33, wherein:

[0260] The adjustment includes using the spatial light modulator to adjust the spatial intensity distribution so as to modulate the illumination intensity of the beam at a first position on the surface according to a first pattern, and to modulate the illumination intensity of the beam at a second position on the surface according to a second pattern;

[0261] The second position is different from the first position; and

[0262] The analysis includes analyzing the detection signal based on the modulation.

[0263] 35. The method according to aspect 33, wherein:

[0264] The spatial intensity distribution includes a sequence of a first state, a second state, and a third state based on the adjusted periodic spatial intensity distribution;

[0265] The second state is different from the first and third states;

[0266] The detection signal includes modulation based on the first state, the second state, and the third state; and

[0267] The analysis includes analyzing the modulation to at least determine the locations on the surface that exhibit a reduced optical response to the modulation.

[0268] 36. The method according to aspect 33 further includes:

[0269] The method further includes adjusting the wavelength of the beam;

[0270] The beam includes different first and second wavelengths;

[0271] The detection signal includes wavelength information of the received radiation based on different first and second wavelengths; and

[0272] The analysis includes analyzing the wavelength information to at least determine the locations on the surface that exhibit differences in optical response to adjustments of the wavelength.

[0273] 37. The method according to aspect 33, wherein:

[0274] The method further includes adjusting the polarization of the beam;

[0275] The beam includes different first polarizations and second polarizations;

[0276] The detection signal includes polarization information of the received radiation based on the different first and second polarizations; and

[0277] The analysis includes analyzing the polarization information to at least determine the locations on the surface that exhibit differences in optical response to adjustments in polarization.

[0278] 38. The method according to aspect 33, wherein:

[0279] The adjustment includes adjusting the spatial intensity distribution to illuminate a portion of the surface at a non-zero incident angle, wherein:

[0280] The receiving includes receiving radiation along an optical path of radiation scattered at said portion of said surface; and

[0281] The method also includes reducing the probability of false signal events based on the difference between the optical path and the optical path of radiation scattered by a structure near the surface.

[0282] 39. The method according to aspect 33, wherein:

[0283] The adjustment includes using the spatial light modulator to adjust the spatial intensity distribution in time so as to modulate the illumination intensity of the beam at a first position on the surface at a first frequency, and to modulate the illumination intensity of the beam at a second position on the surface at a second frequency.

[0284] The second position is different from the first position;

[0285] The second frequency is different from the first frequency; and

[0286] The method includes improving the optical resolution of the detection based on frequency analysis of the detection signal.

[0287] 40. A photolithography apparatus, comprising:

[0288] An irradiation device, the irradiation device being configured to irradiate the pattern of a pattern forming apparatus;

[0289] A projection system configured to project an image of the pattern onto a substrate; and

[0290] Measurement system, the measurement system comprising:

[0291] An irradiation system, the irradiation system comprising:

[0292] A radiation source, the radiation source being configured to produce a beam of radiation;

[0293] A spatial light modulator, the spatial light modulator being configured to guide the beam toward a surface of an object and adjust the spatial intensity distribution of the beam at the surface;

[0294] A detector configured to receive radiation scattered at the surface and radiation scattered by structures near the surface, and to generate a detection signal based on the received radiation; and

[0295] Processor, the processor being configured to:

[0296] Analyze the detection signal;

[0297] The location of the defect on the surface is determined based on the analysis; and

[0298] The analysis and adjustments are used to distinguish between false signals and signals corresponding to the defects.

[0299] While specific references may be made herein to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein may have other applications, such as the fabrication of integrated optical systems, patterning for magnetic domain memory, flat panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will understand that, in the context of such alternative applications, any terms “wafer” or “die” used herein may be considered synonymous with the more general terms “substrate” or “target portion,” respectively. Substrates mentioned herein may be processed before or after exposure, for example, in a track unit or coating and developing system unit (a tool typically used to apply a resist layer to a substrate and develop the exposed resist), a measurement unit, and / or an inspection unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Furthermore, the substrate may be processed more than once, for example, to produce multilayer ICs, such that the term “substrate” used herein may also refer to a substrate that already contains multiple processed layers.

[0300] While specific reference has been made above to embodiments of this disclosure in the context of optical lithography, it will be understood that this disclosure can be used in other applications, such as imprint lithography, and is not limited to optical lithography where circumstances permit. In imprint lithography, the morphology in the patterning apparatus defines a pattern formed on a substrate. The morphology of the patterning apparatus can be imprinted into a resist layer supplied to the substrate, whereby the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning apparatus is removed from the resist, thereby leaving a pattern therein.

[0301] It should be understood that the wording or terminology used herein is for descriptive rather than restrictive purposes, and that the terminology or terminology used herein shall be interpreted by those skilled in the art in accordance with the teachings herein.

[0302] As used herein, the term "substrate" describes the material on which the various material layers are added. In some embodiments, the substrate itself may be patterned, and the material added on top of it may also be patterned, or may remain unpatterned.

[0303] While specific reference 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 in the manufacture of integrated optical systems, the guiding and detection of 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 "mask," "wafer," or "die" should be considered to be replaced by the more general terms "mask," "substrate," and "target portion," respectively.

[0304] While specific embodiments of this disclosure have been described above, it will be understood that this disclosure may be practiced in ways different from those described. This specification is not intended to limit this disclosure.

[0305] 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. As the inventors have considered, the Summary and Abstract sections may illustrate one or more embodiments of this disclosure, but not all exemplary embodiments, and are therefore not intended to limit this disclosure and the appended claims in any way.

[0306] The present disclosure has been described above with the aid of functional building blocks that illustrate the implementation of the specified functions and their interrelationships. 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.

[0307] 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 these specific embodiments to various applications 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.

[0308] The breadth and scope of the protected subject matter 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. A system comprising: Irradiation system, detector, and comparator, The irradiation system includes: A radiation source, the radiation source being configured to produce a beam of radiation; A spatial light modulator, the spatial light modulator being configured to guide the beam toward a surface of an object and adjust the spatial intensity distribution of the beam at the surface; The detector is configured to receive radiation scattered at the surface and radiation scattered by structures near the surface, and to generate a detection signal based on the received radiation. The comparator is configured to: Analyze the detection signal; The location of the defect on the surface is determined based on the analysis; and The analysis and adjustments are used to distinguish between false signals and signals corresponding to the defects.

2. The system according to claim 1, wherein: The spatial light modulator is further configured to adjust the spatial intensity distribution to modulate the illumination intensity of the beam at a first position on the surface according to a first pattern, and to modulate the illumination intensity of the beam at a second position on the surface according to a second pattern different from the first pattern. The second position is different from the first position; and The analysis includes analysis of the detected signal based on the modulation.

3. The system according to claim 2, wherein, The first intensity state of the first pattern is associated with a first wavelength, and the second intensity state of the first pattern is associated with a second wavelength different from the first wavelength.

4. The system according to claim 2, wherein, The intensity state of the first pattern is associated with a first wavelength, and the intensity state of the second pattern is associated with a second wavelength different from the first wavelength.

5. The system according to claim 2, wherein: The spatial light modulator is also configured to adjust the spatial intensity distribution such that the illumination intensity of the beam at other locations on the surface is modulated according to a corresponding additional pattern. The first pattern, the second pattern, and each of the other patterns are different from each other; The distinction includes associating the spurious signal with a pattern that is not characterized by a given location.

6. The system according to claim 2, wherein: The first pattern and the second pattern correspond to a first periodic pattern and a second periodic pattern; The frequency and / or phase of the first periodic pattern are different from the frequency and / or phase of the second periodic pattern; and The analysis includes frequency analysis.

7. The system according to claim 6, wherein: The frequency analysis includes determining the frequency and / or phase of the illumination modulation used at a given location on the surface; and The distinction includes associating the spurious signal with frequencies and / or phases that are not characterized by the given position.

8. The system according to claim 6, wherein: The sequence of intensity states of the first periodic pattern includes variations relative to the ordered original sequence of the first periodic pattern; and / or The sequence of intensity states of the second periodic pattern includes variations relative to the ordered original sequence of the second periodic pattern.

9. The system according to claim 1, wherein: The spatial intensity distribution includes a sequence of the adjusted first, second, and third states of the periodic spatial intensity distribution; The second state is different from the first and third states; and The detection signal includes modulation based on the first state, the second state, and the third state; The analysis includes analyzing the modulation to at least determine the locations on the surface that exhibit a reduced optical response to the modulation.

10. The system according to claim 9, wherein, The distinction includes associating the spurious signal with the location on the surface that exhibits the reduced optical response to the adjustment.

11. The system according to claim 9, wherein: Radiation scattered by the structure near the surface is generated from the transmission portion of the beam passing through the surface; and The transmissive portion includes the periodic spatial intensity distribution with reduced contrast.

12. The system according to claim 1, wherein: The radiation source is also configured to adjust the wavelength of the beam; The beam includes different first and second wavelengths; The detection signal includes wavelength information of the received radiation based on different first and second wavelengths; and The analysis includes analyzing the wavelength information to at least determine the locations on the surface that exhibit differences in optical response to adjustments of the wavelength.

13. The system according to claim 12, wherein, The distinction includes associating the spurious signal with the location on the surface that exhibits a difference in optical response to adjusting the wavelength.

14. The system according to claim 12, wherein, The difference in optical response to the adjusted wavelength includes the difference between the attenuation of the received radiation based on the first wavelength and the attenuation of the received radiation based on the second wavelength.

15. The system according to claim 1, wherein: The irradiation system is configured to adjust the polarization of the beam, and the irradiation system further includes a polarizer configured to modify the polarization of the beam; The beam includes different first polarizations and second polarizations; The detection signal includes polarization information of the received radiation based on the different first and second polarizations; and The analysis includes analyzing the polarization information to at least determine the locations on the surface that exhibit differences in optical response to adjustments in polarization.

16. The system according to claim 15, wherein, The distinction includes associating the spurious signal with the location on the surface that exhibits a difference in optical response to the adjustment of the polarization.

17. The system according to claim 15, wherein, The difference in the optical response to the adjustment of the polarization includes the difference between the intensity of the received radiation based on the first polarization and the intensity of the received radiation based on the second polarization.

18. The system according to claim 1, wherein: The spatial light modulator is also configured to adjust the spatial intensity distribution so as to illuminate a portion of the surface at a non-zero incident angle; The detector is also configured to receive radiation along an optical path of radiation scattered at said portion of the surface; and The system is configured to reduce the probability of false signal events based on the difference between the optical path and the optical path corresponding to the radiation scattered by the structure near the surface.

19. The system according to claim 1, wherein: The spatial light modulator is further configured to adjust the spatial intensity distribution in time to modulate the illumination intensity of the beam at a first position on the surface at a first frequency, and to modulate the illumination intensity of the beam at a second position on the surface at a second frequency. The second position is different from the first position; The second frequency is different from the first frequency; and The system is configured to improve the optical resolution of the detection based on frequency analysis of the detection signal.

20. A photolithography apparatus, comprising: An irradiation device, the irradiation device being configured to irradiate the pattern of a pattern forming apparatus; A projection system configured to project an image of the pattern onto a substrate; as well as The measurement system includes an illumination system, a detector, and a processor. The irradiation system includes: A radiation source, the radiation source being configured to produce a beam of radiation; A spatial light modulator, the spatial light modulator being configured to guide the beam toward a surface of an object and adjust the spatial intensity distribution of the beam at the surface; The detector is configured to receive radiation scattered at the surface and radiation scattered by structures near the surface and to generate a detection signal based on the received radiation. The processor is configured to: Analyze the detection signal; The location of the defect on the surface is determined based on the analysis; and The analysis and adjustments are used to distinguish between false signals and signals corresponding to the defects.

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