Method and apparatus for particle removal

Abstract

A system for removing particles from a surface, comprising: a plurality of ultrasonic transducers, the plurality of ultrasonic transducers being arranged in an array; a control system in communication with the plurality of ultrasonic transducers, the control system configured to control phases and amplitudes of transducers in the array to create acoustic particle traps at selected locations on the surface and move particles captured in the particle traps away from the surface; and an actuator configured and arranged to relatively move the array of ultrasonic transducers in a scanning pattern on the surface such that different portions of the surface pass through the generated acoustic particle traps.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application 63 / 392,671, filed on July 27, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The description herein generally relates to systems and methods for contactless removal of certain contaminants. More specifically, the description herein relates to using ultrasonic fields to achieve such removal. Background Art

[0004] Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device (e.g., a mask) can contain or provide a device pattern ("design layout") corresponding to a single layer of the IC, and this pattern can be transferred to a target portion (e.g., comprising one or more dies) on a substrate (e.g., a silicon wafer) that has been coated with a layer of radiation-sensitive material ("resist"), such as by irradiating the target portion through the patterning device's pattern. Typically, a single substrate includes multiple adjacent target portions, to which the pattern is transferred sequentially, one target portion at a time, by the lithographic apparatus. In one type of lithographic apparatus, the entire patterning device pattern is transferred to a target portion at a time; such apparatuses are often referred to as steppers. In an alternative apparatus, often referred to as a stepper-scan apparatus, a projection beam is scanned over the patterning device in a given reference direction (the "scanning" direction) while the substrate is synchronously moved parallel or antiparallel to the reference direction. Different portions of the patterning device pattern are transferred incrementally to a target portion. Since typically the lithographic apparatus will have a magnification factor M (typically <1), the speed F at which the substrate is moved will be a factor M times the speed at which the projection beam scans the patterning device.

[0005] Before the pattern is transferred from the patterning device to the substrate, the substrate may undergo various processes, such as primer coating, resist application, and soft baking. After exposure, the substrate may undergo other processes, such as post-exposure baking (PEB), development, hard baking, and measurement / inspection of the transferred pattern. This series of processes serves as the basis for producing the individual layers of a device (e.g., an IC). The substrate may then undergo various processes, such as etching, ion implantation (doping), metallization, oxidation, chemical mechanical polishing, etc., all of which are aimed at ultimately completing the individual layers of the device. If multiple layers are required in the device, all of the processes, or variations thereof, are repeated for each layer. Ultimately, a device will be present in each target area on the substrate. These devices are then separated from each other by techniques such as sawing or dicing, whereby the individual devices can be mounted on a carrier and connected to pins, etc.

[0006] Therefore, manufacturing devices (such as semiconductor devices) typically involves processing a substrate (e.g., a semiconductor wafer) using multiple fabrication processes to form the various features and multiple layers of the device. These layers and features are typically manufactured and processed using, for example, deposition, photolithography, etching, chemical mechanical polishing, and ion implantation. Multiple devices can be made on multiple dies on a substrate and then separated into individual devices. This device manufacturing process can be considered a patterning process. The patterning process involves a patterning step using a patterning device in a lithography apparatus, such as optical and / or nanoimprint lithography, to transfer the pattern of the patterning device to the substrate, and the patterning process typically but optionally involves one or more related pattern processing steps, such as developing the resist using a developer, baking the substrate using a bake tool, etching using the pattern using an etching apparatus, etc. Summary of the Invention

[0007] In one embodiment, a system for removing particles from a surface includes: a plurality of ultrasonic transducers arranged in an array; a control system in communication with the plurality of ultrasonic transducers, the control system configured to control the phase and amplitude of the transducers in the array to create acoustic particle traps at selected locations on the surface and to move particles trapped in the acoustic particle traps away from the surface; and an actuator configured to move the array of ultrasonic transducers in a scanning pattern over the surface so that different portions of the surface pass through the acoustic particle traps.

[0008] In an embodiment, a method for removing particles from a surface comprises: passing an array of ultrasonic transducers over the surface; during the passage, controlling the phase and amplitude of ultrasonic signals generated by the ultrasonic transducers in the array so as to generate an acoustic particle trap at a location on the surface; and capturing at least one particle in the acoustic particle trap, and controlling the phase and amplitude of the ultrasonic signals generated by the ultrasonic transducers in the array to move the captured at least one particle away from the surface.

[0009] In an embodiment, a computing system is provided that includes a processor and a memory, and includes a non-transitory machine-readable medium including instructions for executing the aforementioned method.

[0010] In one embodiment, a computer program product is provided that includes a computer non-transitory storable medium having instructions recorded thereon, the instructions implementing the aforementioned method when executed by a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The figure shows a schematic diagram of a lithographic apparatus;

[0012] Figure 2 An embodiment of a lithographic cell or cluster is depicted;

[0013] Figure 3 is a schematic diagram of a non-contact particle cleaning device according to an embodiment; and

[0014] Figure 4 Schematic diagram of a hemispherical array composed of transducer blocks. DETAILED DESCRIPTION

[0015] Figure 1A lithographic apparatus LA that can be used in association with the techniques described herein is schematically depicted. The apparatus comprises an illumination optics system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation), a patterning device support or support structure (e.g., mask table) MT configured to support a patterning device (e.g., mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to specific parameters, one or more substrate tables (e.g., wafer stages) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate according to specific parameters, and a projection optics system (e.g., a refractive, reflective, or catadioptric projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0016] The illumination optical system may include various types of optical components for directing, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof. In this particular case, the illumination system also includes a radiation source SO.

[0017] The patterning device holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions such as whether the patterning device is held in a vacuum environment. The patterning device support may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The patterning device support may be a frame or a table, for example, which may be fixed or movable as required. The patterning device support may ensure that the patterning device is located in a desired position, for example relative to the projection system. Any term "reticle" or "mask" used herein may be considered synonymous with the more general term "patterning device".

[0018] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a pattern in the cross-section of a radiation beam so as to produce a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so-called assist features. Typically, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device (such as an integrated circuit) to be produced in the target portion.

[0019] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in photolithography and include mask types such as binary masks, alternating phase-shift masks, and attenuated phase-shift masks, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of smaller mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam reflected by the mirror matrix.

[0020] As depicted here, the apparatus can be transmissive (e.g., using a transmissive patterning device). However, the apparatus can be reflective (e.g., employing a programmable mirror array of the type mentioned above, or employing a reflective mask). The apparatus can employ patterning devices other than classical masks; examples include programmable mirror arrays or LCD matrices.

[0021] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g., water) to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not imply that a structure, such as a substrate, is necessarily immersed in the liquid; rather, "immersion" simply means that the liquid is located between the projection system and the substrate during exposure.

[0022] refer to Figure 1 An illuminator IL receives a radiation beam from a radiation source SO (e.g., a mercury lamp or an excimer laser, LPP (laser produced plasma), or an EUV source). For example, when the source is an excimer laser, the source and the lithographic apparatus may be separate entities. In such a case, the source is not considered to constitute part of the lithographic apparatus, and the radiation beam is delivered from the source SO to the illuminator IL by means of a beam delivery system BD comprising, for example, suitable directing mirrors and / or a beam expander. In other cases, for example, when the source is a mercury lamp, the source may be an integral part of the lithographic apparatus. The source SO and the illuminator IL, and where appropriate, the beam delivery system BD, may be collectively referred to as a radiation system.

[0023] The illuminator IL may include an adjuster AD for adjusting the spatial and / or angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator can be used to adjust the radiation beam so as to have a desired uniformity and intensity distribution in its cross-section.

[0024] The radiation beam B is incident on a patterning device (e.g. a mask) MA which is held on a patterning device support (e.g. a mask table) MT and is patterned by the patterning device. Having passed through the patterning device (e.g. a mask) MA, the radiation beam B passes through a projection optical system PS which focuses the beam onto a target portion C of the substrate W, thereby projecting an image of the pattern onto the target portion C. With the aid of a second positioner PW and a position sensor IF (e.g. an interferometer device, a linear encoder, a two-dimensional encoder, or a capacitive sensor), the substrate table WT can be accurately moved, for example in order to position a different target portion C in the path of the radiation beam B. Similarly, the first positioner PM and the further position sensor ( Figure 1 A further position sensor (not explicitly depicted) is used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B.

[0025] The patterning device (e.g., mask) MA and substrate W can be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks occupy dedicated target portions, the illustrated substrate alignment marks can be located in the spaces between multiple target portions (these target portions are referred to as scribe lane alignment marks). Similarly, where more than one die is disposed on the patterning device (e.g., mask) MA, the patterning device alignment marks can be located between the dies. Smaller alignment marks can also be included within the die, between device features, in which case it is desirable that the marks be as small as possible and not require any different imaging or process conditions than adjacent features. An alignment system for detecting alignment marks is described further below.

[0026] In the example described, the lithographic apparatus LA is of a so-called dual-stage type, having two substrate tables WTa and WTb and two stations—an exposure station and a measurement station—between which the substrate tables can be interchanged. While one substrate on one substrate table is being exposed at the exposure station, another substrate can be loaded onto the other substrate table at the measurement station and various preparatory steps performed. These preparatory steps can include mapping the substrate's surface control using a level sensor LS, measuring the positions of alignment marks on the substrate using an alignment sensor AS, and performing any other type of metrology or inspection. This enables a significant increase in the throughput of the apparatus. More generally, the lithographic apparatus can be of a type having two or more stages (e.g., two or more substrate tables, a substrate table and a measurement table, two or more patterning device tables, etc.). In such a "multi-stage" apparatus, multiple stages can be used in parallel, or preparatory steps can be performed on one or more stages while one or more other stages are being used for exposure. For example, a dual-stage lithographic apparatus is described in U.S. Patent No. 5,969,441, the entire contents of which are incorporated herein by reference.

[0027] Although the level sensor LS and alignment sensor AS are shown adjacent to the substrate table WTb, it will be appreciated that the level sensor LS and alignment sensor AS may additionally or alternatively be provided adjacent to the projection system PS for taking measurements with respect to the substrate table WTa.

[0028] The depicted apparatus can be used in various modes including, for example, step mode or scan mode.The construction and operation of lithographic apparatus are well known to those skilled in the art and need not be further described for an understanding of embodiments of the present invention.

[0029] like Figure 2 As shown in FIG, the lithography apparatus LA forms part of a lithography system known as a lithocell LC, or litho element, or cluster. The lithocell LC may also include equipment for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these equipment include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a bake plate BK. A substrate transport device or robot RO picks up substrates from input / output ports I / O1 and I / O2, moves them between the various process equipment, and then transfers them to a feed station LB of the lithography apparatus. These devices, often collectively referred to as a track or coating and developing system, are under the control of a track or coating and developing system control unit TCU, which is itself controlled by a supervisory control system SCS, which in turn controls the lithography apparatus via a lithography control unit LACU. Thus, the different equipment can be operated to maximize throughput and processing efficiency.

[0030] The patterning device mentioned above includes or can form one or more design layouts or patterns (hereinafter referred to as design patterns for convenience). Design patterns can be generated using a CAD (Computer-Aided Design) program, a process commonly referred to as EDA (Electronic Design Automation). Most CAD programs adhere to a set of predetermined design rules to produce a functional design pattern / patterning device. These rules are set by process and design constraints. For example, design rules define the spatial tolerances between circuit components (such as gates, capacitors, etc.) or interconnects to ensure that the circuit components or lines do not interact in undesirable ways. One or more of the design rule constraints may be referred to as a "critical dimension" (CD). A circuit's critical dimension can be defined as the minimum width of a line or hole, or the minimum space between two lines or holes. Therefore, the CD determines the overall size and density of the designed circuit. Of course, one of the goals in integrated circuit manufacturing is to faithfully reproduce the original circuit design on the substrate (via the patterning device).

[0031] An illumination system provides illumination (i.e., radiation) in the form of an illumination pattern to a patterning device, and a projection system directs and shapes the illumination via the patterning device onto the substrate through an aerial image (AI). The illumination pattern defines the characteristics of the illumination, such as the angular or spatial intensity distribution (e.g., conventional, dipole, annular, quadrupole, etc.), the illumination sigma (σ) setting, etc. The aerial image (AI) is the radiation intensity distribution at substrate level. A resist layer on the substrate is exposed, and the aerial image is transferred to the resist layer as a potential "resist image" (RI) therein. The resist image (RI) can be defined as the spatial distribution of the solubility of the resist in the resist layer.

[0032] A set of conditions for imaging can be considered, and within the total set of possible conditions, the process window for a pattern is the space within this set of conditions within which the processing parameters used to generate the pattern achieve satisfactory imaging of the pattern. That is, for a given pattern, there can be a set of values ​​for depth of focus, illumination intensity, illumination pattern, numerical aperture, and other controllable variables that produce an image with sufficiently good imaging of lines or features, including line width, spacing, or other aspects of the imaging pattern that are defined to meet the specifications for the desired imaging. The process window provides an indication of the sensitivity of the process to variations in input parameters such as radiation dose.

[0033] Process parameters are parameters of the patterning process. The patterning process can include processes both upstream and downstream of the actual photolithographic transfer of the pattern. Process parameters can fall into multiple categories. The first category can include parameters of the lithographic apparatus or any other equipment used in the patterning process. Examples of this category include parameters of the lithographic apparatus's illumination system, projection system, substrate stage, and so on. The second category can include parameters of any process performed during the patterning process. Examples of this category include focus, dose, bandwidth, exposure duration, development temperature, and the chemical composition used in development. The third category can include parameters of the designed pattern. Examples of this category include resolution enhancement technology (RET) or optical proximity correction adjustments, such as the shape and / or position of assist features. The fourth category can include parameters of the substrate. Examples include properties of structures beneath the resist layer, the chemical composition of the resist layer, and / or the physical dimensions of the resist layer. The fifth category can include parameters that characterize the temporal variation of one or more parameters of the patterning process. Examples of this category include characteristics of high-frequency stage movement (e.g., frequency, amplitude, etc.), characteristics of high-frequency laser bandwidth changes (e.g., frequency, amplitude, etc.), and / or characteristics of high-frequency laser wavelength changes. These high frequency changes or movements are those that are higher than the response time of the mechanisms used to adjust the underlying parameters (e.g., stage position, laser intensity, etc.) A sixth category may be characteristics upstream or downstream of exposure, such as post-exposure bake (PEB), development, etching, deposition, resist application, doping, and / or packaging.

[0034] Given the high accuracy required, even small amounts of contamination can cause imaging problems. In one example, particles on the backside of a reticle used in an EUV system can cause the reticle to flex relative to the electromagnetic chuck that supports it. This flexure can lead to overlay errors due to variations in the reticle's shape.

[0035] Current methods for inspection and particle removal are often slow. A complete inspection of a reticle can take 15 minutes or longer. Once defects are identified, the particle size (e.g., height) is measured using a confocal microscope at a cost of approximately 30 seconds per defect. Larger particles (e.g., 1 μm to 25 μm) can be removed using methods such as grinding, bonded sticks, and the like. These methods are also typically performed offline rather than in a scanner. Such methods are applied to inspect and clean reticles, wafers, fixtures, and essentially any surface in a lithography system that could be susceptible to contamination.

[0036] Optical tweezers have been proposed as a means of removing identified particles. However, lasers represent a problematic heat source in scanners, even offline, and can damage the article being cleaned. Due to limitations such as size and reflectivity, not all types of materials can be removed. Furthermore, optical tweezers tend to involve high power densities, which can damage the object being cleaned.

[0037] Therefore, an acoustic trapping device using low-power acoustic waves has been proposed. By appropriately manipulating the acoustic source, acoustic radiation forces can capture and manipulate particles without damaging the substrate (or reticle). The range of particle sizes that can be manipulated with acoustic tweezers has increased from nanometers to millimeters, making them more versatile than optical tweezers. Similarly, the range of materials that can be manipulated is also much greater.

[0038] Figure 3 Schematic diagram of an acoustic particle trap according to an embodiment. Particles 102 are detected on the surface of a reticle 104 or other substrate. A hemispherical array of ultrasonic transducers 106 generates a targeted 3D acoustic wave field 108 that is used to pick up and lift particles 102 from the surface of the reticle 104. The resulting system is non-contact, has no tendency to introduce further contamination, does not damage the substrate being cleaned, and operates at relatively low power density.

[0039] exist Figure 4 In the embodiment shown in FIG, the hemispherical array of ultrasonic transducers 106 is arranged into eight separate blocks 402a, 402b, 402c, 402d of transducers (four of these blocks are not visible on the side in this view). Each block includes one or more ultrasonic transducers 404, and these blocks together comprise the hemispherical array of ultrasonic transducers 106. Adjacent blocks are controlled to be opposite in phase to each other. The use of blocks allows for simplified control while maintaining sufficient control over the acoustic field. The phase and amplitude of each block are controlled according to the inverse filter W, where

[0040] (1)

[0041] The coefficients of the inverse filter are optimized to produce a target wavefield H, where H = GW and G is a matrix.

[0042] (2)

[0043] (3)

[0044] (4)

[0045] like Figure 3 As shown in FIG, these blocks are driven according to an inverse filter to generate an acoustic particle trap 102 at a distance from the transducer. The entire hemispherical array of ultrasonic transducers 106 can then be scanned in a scanning pattern across the surface of the object being cleaned, so that different portions of the surface pass through the acoustic particle trap formed by the acoustic wave field 108, and as the acoustic particle trap passes over the particles, the acoustic particle trap lifts the particles and removes them from the surface. Thus, no inspection step is required before removing the particles. In principle, the hemispherical array of ultrasonic transducers 106 can be included within a lithography system, such as within a reticle inspection module of the system. This can allow cleaning to be performed without taking the system offline or removing the reticle to be inspected.

[0046] These blocks create a series of trapping nodes, and particles passing by the transducer will levitate to a stable trapping node. In principle, the node can then be moved to different positions relative to the transducer for a specific desired motion of the trapped particle. For example, by increasing the amplitude of the acoustic vibration, the particle can be displaced upward in the z dimension.

[0047] In an embodiment, an optional system for removing particles from the chamber once the particles are lifted can be included. In this method, a vacuum system 110 can be used to pull the particles out of the chamber. Alternatively or additionally, a gas source 112 can be used to provide a gas flow through a gas inlet 113. The gas flows through and carries the particles away along the surface to be cleaned, for example, carrying the particles to a particle reservoir 114. As will be appreciated, for EUV applications, because the optical path is maintained under vacuum conditions, it is not preferred to introduce gas into the system. Once collected, the particles can be measured and statistical data including average size, size standard deviation, and material type can be generated. For this purpose, a reservoir or downstream component can include a particle detector 116 configured to perform the necessary measurements.

[0048] In an embodiment, the hemispherical array of ultrasound transducers 106 includes an outlet 118 in fluid communication with the particle reservoir 114 , such as via the vacuum system 110 or directly (not shown).

[0049] These embodiments may include a computer-readable medium programmed with instructions that, when executed, perform any of the methods described herein. Additionally, aspects of the present application may take the form of a computer program product embodied in any one or more physical computer-readable media having computer-usable program code embodied thereon.

[0050] Any combination of one or more computer-readable media can be utilized.Computer-readable media can be a computer-readable signal medium or a computer-readable storage medium.Computer-readable storage media can be, for example, but not limited to: electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, equipment, devices, or any suitable combination of the foregoing.More specific examples (non-exhaustive list) of computer-readable media will include the following: an electrical connector with one or more wires, a portable computer floppy disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable optical disc read-only memory (CDROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.In the context of this document, a computer-readable storage medium can be any tangible medium that can contain or store a program used for or in conjunction with an instruction execution system, equipment, or device.

[0051] The computer program instructions may also be loaded onto a computer, or other programmable data processing device, or other apparatus, to cause a series of operational steps to be performed on the computer, or other programmable device, or other apparatus to produce a computer-implemented process, such that the instructions executed on the computer or other programmable device provide a process for implementing the functions / actions specified in one or more boxes in the flowchart and / or block diagram.

[0052] A data processing system suitable for storing and / or executing program code will include at least one processor coupled directly or indirectly to a storage element via a system bus. The storage element may include local memory used during the actual execution of the program code, a bulk storage, and a cache memory that provides temporary storage of at least some program code in order to reduce the number of times code must be retrieved from the bulk storage during execution.

[0053] Input / output or I / O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be connected to the system directly or through intervening I / O controllers. Network adapters can also be connected to the system to enable the data processing system to be connected to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the currently available types of network adapters.

[0054] The description of the present application has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments have been chosen and described in order to best explain the principles of the invention, its practical application, and to enable those skilled in the art to understand the invention for various embodiments with various modifications as may be appropriate for the particular application contemplated.

[0055] Aspects of the present disclosure may be further described using the following aspects:

[0056] 1. A system for removing particles from a surface, comprising:

[0057] a plurality of ultrasonic transducers arranged in an array;

[0058] a control system in communication with the plurality of ultrasonic transducers, the control system being configured to control the phase and amplitude of the transducers in the array to create acoustic particle traps at selected locations on the surface and to move particles trapped in the acoustic particle traps away from the surface; and

[0059] An actuator is configured to move the array of ultrasonic transducers in a scanning pattern over the surface such that different portions of the surface pass through the acoustic particle trap.

[0060] 2. The system of aspect 1, wherein the array is a hemispherical array.

[0061] 3. The system of aspect 1 , wherein the plurality of ultrasound transducers are arranged in a plurality of tiles, each tile comprising a plurality of the ultrasound transducers, and wherein the plurality of tiles together comprise the array.

[0062] 4. The system of aspect 3, wherein the phase and amplitude of the ultrasonic transducers in the plurality of ultrasonic transducers comprising each block are controlled as a group, and the control system is configured to control the plurality of blocks to generate the acoustic particle trap and move particles trapped in the acoustic particle trap away from the surface.

[0063] 5. The system of clause 1, wherein the system is located in a reticle inspection module of a lithographic apparatus.

[0064] 6. The system of aspect 1, wherein the array of ultrasonic transducers comprises an outlet in fluid communication with a particle reservoir for collecting particles removed from the surface.

[0065] 7. The system of aspect 6, wherein the particle reservoir comprises a particle detector configured to measure a size of the collected particles.

[0066] 8. The system according to aspect 1, further comprising:

[0067] Gas source; and

[0068] A gas inlet is configured to receive gas from the gas source and generate a gas flow across the surface such that particles removed from the surface are entrained in the gas flow.

[0069] 9. A method for removing particles from a surface, comprising:

[0070] passing an array of ultrasonic transducers over the surface;

[0071] During the pass, controlling the phase and amplitude of ultrasonic signals generated by ultrasonic transducers in the array such that acoustic particle traps are generated at locations on the surface; and

[0072] At least one particle is trapped in the acoustic particle trap, and the phase and amplitude of ultrasonic signals generated by ultrasonic transducers in the array are controlled to move the trapped at least one particle away from the surface.

[0073] 10. The method of clause 9, wherein the array is a hemispherical array.

[0074] 11. The method of aspect 9, wherein the plurality of ultrasound transducers are arranged in a plurality of tiles, each tile comprising a plurality of the ultrasound transducers, and the plurality of tiles together comprising the array.

[0075] 12. The system of aspect 11, wherein controlling the phase and amplitude of the ultrasonic transducers in the plurality of ultrasonic transducers comprises controlling each block as a group, and the plurality of blocks are controlled to generate the acoustic particle trap and move particles trapped in the acoustic particle trap away from the surface.

[0076] 13. The method of clause 9, wherein the system is located in a reticle inspection module of a lithographic apparatus.

[0077] 14. The method of aspect 8, further comprising collecting particles removed from the surface.

[0078] 15. The method of aspect 14, further comprising measuring the size of the collected particles.

[0079] Although specific reference has been made herein to the manufacture of ICs, it should be clearly understood that the description herein has many other possible applications. For example, the description herein can be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. The skilled person will understand that in the context of such alternative applications, any use of the terms "reticle," "wafer," or "die" in this context should be considered interchangeable with the more general terms "mask," "substrate," and "target portion," respectively.

[0080] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV radiation (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 nm to 100 nm).

[0081] As used herein, the terms "optimize" and "optimized" refer to or imply adjusting a patterning device (e.g., a lithographic device), a patterning process, etc., so that the result and / or process has more desirable characteristics, such as higher projection accuracy of the design layout on the substrate, a larger process window, etc. Thus, as used herein, the terms "optimize" and "optimized" refer to or imply a process of identifying one or more values ​​for one or more parameters that provide an improvement (e.g., a local optimum) in at least one relevant metric compared to an initial set of one or more values ​​for those one or more parameters. "Optimal" and other related terms should be interpreted accordingly. In embodiments, the optimization steps may be applied iteratively to provide further improvements in one or more metrics.

[0082] While the concepts disclosed herein may be used for imaging on substrates such as silicon wafers, it should be understood that the disclosed concepts may be used with any type of lithographic imaging system, for example, with lithographic imaging systems for imaging on substrates other than silicon wafers.

[0083] The foregoing description is intended to be illustrative rather than restrictive. Accordingly, those skilled in the art will appreciate that modifications may be made as described without departing from the scope of the claims hereinafter appended.

Claims

1. A system for removing particles from a surface, comprising: a plurality of ultrasonic transducers arranged in an array; a control system in communication with the plurality of ultrasonic transducers, the control system being configured to control the phase and amplitude of the transducers in the array to create acoustic particle traps at selected locations on the surface and to move particles trapped in the acoustic particle traps away from the surface; as well as An actuator is configured to move the array of ultrasonic transducers in a scanning pattern over the surface such that different portions of the surface pass through the acoustic particle trap.

2. The system according to claim 1, wherein: The array is a hemispherical array.

3. The system according to claim 1, wherein: The plurality of ultrasound transducers are arranged in a plurality of tiles, each tile comprising a plurality of the ultrasound transducers, and wherein the plurality of tiles together comprise the array.

4. The system according to claim 3, wherein: The phase and amplitude of the ultrasonic transducers in the plurality of ultrasonic transducers comprising each block are controlled as a group, and the control system is configured to control the plurality of blocks to generate the acoustic particle trap and move particles trapped in the acoustic particle trap away from the surface.

5. The system according to claim 1, wherein: The system is located in a mask inspection module of a lithography apparatus.

6. The system according to claim 1, wherein: The array of ultrasonic transducers includes an outlet in fluid communication with a particle reservoir for collecting particles removed from the surface.

7. The system according to claim 6, wherein: The particle reservoir includes a particle detector configured to measure a size of the collected particles.

8. The system of claim 1, further comprising: Gas source; and A gas inlet is configured to receive gas from the gas source and to generate a gas flow across the surface such that particles removed from the surface are entrained in the gas flow.

9. A method for removing particles from a surface, comprising: passing an array of ultrasonic transducers over the surface; During the pass, controlling the phase and amplitude of ultrasonic signals generated by ultrasonic transducers in the array such that an acoustic particle trap is generated at a location on the surface; as well as At least one particle is trapped in the acoustic particle trap, and the phase and amplitude of an ultrasonic signal generated by an ultrasonic transducer in the array are controlled to move the trapped at least one particle away from the surface.

10. The method according to claim 9, wherein: The array is a hemispherical array.

11. The method according to claim 9, wherein: The plurality of ultrasound transducers are arranged in a plurality of blocks, each block comprising a plurality of the ultrasound transducers, and the plurality of blocks together comprise the array.

12. The method according to claim 11, wherein: Controlling the phase and amplitude of the ultrasonic transducers of the plurality of ultrasonic transducers includes controlling each block as a group, and the plurality of blocks are controlled to generate the acoustic particle trap and move particles trapped in the acoustic particle trap away from the surface.

13. The method according to claim 9, wherein: The system is located in a mask inspection module of a lithography apparatus.

14. The method of claim 8, further comprising collecting particles removed from the surface.

15. The method of claim 14, further comprising measuring the size of the collected particles.

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