Cleaning parts of a lithographic apparatus

Abstract

Cleaning contaminant particles from clamps in lithography equipment is described. Used clamps have burl tops that are contaminated with contaminant particles and need to be cleaned before returning to service. Currently, to thoroughly clean the burl tops of such clamps, the hard conductive coating covering the burl top is stripped and a new coating is applied. This requires disconnecting the clamp from the chuck, stripping the various coatings from non-burl areas of the clamp, and removing the high-voltage connections. The high-voltage connections are then re-established, the various coatings are reapplied, and the clamp is verified. Finally, the clamp is reconnected to the chuck, and production can continue. The new cleaning method allows for cleaning of the burl tops without the need to disconnect or remove the caps from the clamp to perform a burl top renewal, saving hours or weeks of downtime.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to US Application No. 63 / 423,927, filed November 9, 2022, which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present description generally relates to methods and systems for cleaning parts of a lithographic apparatus. [Background technology]

[0003] Lithographic (e.g., projection) apparatus are used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device (e.g., mask) may contain or provide a pattern (a "design layout") that corresponds to an individual layer of the IC, which can be transferred onto a target portion (e.g., including one or more dies) on a substrate (e.g., a silicon wafer) that is coated with a layer of radiation-sensitive material ("resist"), such as by illuminating the target portion through the patterning device. Typically, a single substrate will contain several adjacent target portions onto which the pattern is successively transferred by the lithographic projection apparatus, one target portion at a time. In one type of lithographic projection apparatus, the pattern of the entire patterning device is transferred onto one target portion in a single operation. Such an apparatus is commonly referred to as a stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, the projection beam scans across the patterning device in a given reference direction (the "scan" direction) while simultaneously moving the substrate parallel or non-parallel to the reference direction. Different portions of a pattern on a patterning device are progressively transferred onto one target portion. Summary of the Invention [Problem to be solved by the invention]

[0004] Cleaning contaminant particles from clamps in lithography equipment is described. Often, the tops of clamp burrs are coated with a hard, conductive ceramic, such as TiN or CrN. Typically, used clamps have burrs or burr tops contaminated with contaminant particles that need to be cleaned before returning them to service. This contamination can be strongly bonded to the burr-top coating and cannot be removed by simple mechanical action. One method for thoroughly cleaning the burr top is to strip the hard, conductive coating and apply a new such coating. This requires disconnecting the clamp from its chuck, removing various coatings from the non-burr areas of the clamp, and removing the high-voltage connections. The high-voltage connections are then re-established, a cap is added, various coatings are reapplied, and the clamp is verified. Finally, the clamp is reconnected to the chuck, and production can continue. [Means for solving the problem]

[0005] Advantageously, the new cleaning methods and systems described below enable cleaning of the burl top without having to disconnect the clamp from its chuck or remove high voltage connections to perform burl top renewal, saving hours of lithography apparatus downtime and / or providing other benefits. Compared to conventional approaches, the described methods and systems are better able to remove particle contamination from the clamp, require less time for cleaning, do not require chuck disconnection or other disassembly of the lithography apparatus, prevent potential damage to the clamp due to improper handling of other cleaning equipment, and provide other benefits.

[0006] According to an embodiment, there is provided a method for cleaning an object support of a lithographic apparatus, the method comprising applying a chemical cleaning agent to a surface of the object support to release contaminant particles from the surface, the method comprising causing relative movement between a cleaning tool and the surface to clean the contaminant particles from the surface, and the method comprising applying an organic liquid onto the surface to remove the chemical cleaning agent from the surface.

[0007] In some embodiments, the method further comprises generating pre-cleaning image data of the surface identifying the presence of contaminant particles and / or one or more types of contaminant particles, the image data comprising one or more images from a microscopic examination of the surface.

[0008] In some embodiments, the method further comprises determining an initial pre-cleaning flatness of the surface to identify the presence of contaminant particles and the need for cleaning, hi some embodiments, the initial flatness is determined using high voltage phase measurement interferometry.

[0009] In some embodiments, the method further comprises determining a pre-cleaning contaminant particle distribution map for the surface. In some embodiments, the contaminant particle distribution map is determined using microscopy. In some embodiments, the contaminant particle distribution map is determined using white light interferometry.

[0010] In some embodiments, the method further comprises determining, based on the image data of the surface, the flatness of the surface, and / or the distribution of contaminant particles on the surface, whether to apply a chemical cleaning agent and / or where on the surface to apply the chemical cleaning agent, effect relative movement between the cleaning tool and the surface, and / or where on the surface to effect relative movement between the cleaning tool and the surface, and / or whether to apply an organic liquid and / or where on the surface to apply the organic liquid.

[0011] In some embodiments, the method further comprises performing a post-cleaning uniform ion beam machining on the surface, hi some embodiments, the contaminant particles have already been completely removed or reduced to a size small enough that the uniform ion beam machining can remove them.

[0012] In some embodiments, the method further comprises determining a post-cleaning contaminant particle distribution map for the surface and comparing the post-cleaning contaminant particle distribution map to the pre-cleaning contaminant particle distribution map for the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface. In some embodiments, the post-cleaning contaminant particle distribution map is determined using white light interferometry.

[0013] In some embodiments, the method further comprises determining a post-cleaning flatness of the surface and comparing the post-cleaning flatness to a pre-cleaning initial flatness of the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface, hi some embodiments, the post-cleaning flatness is determined using high voltage phase measurement interferometry.

[0014] In some embodiments, in response to the post-cleaning flatness breaching the flatness threshold, the method further comprises performing ion beam processing on the surface to bring the post-cleaning flatness within a flatness specification.

[0015] In some embodiments, the surface comprises a burl top or a portion of a burl top.

[0016] In some embodiments, the chemical cleaning agent comprises potassium hydroxide for tantalum contaminant particles, a chromium etchant for chromium contaminant particles, or a combination thereof.

[0017] In some embodiments, the cleaning tool is a glass pack. In some embodiments, the relative movement comprises a lateral movement, a serpentine movement, a circular movement, or a combination thereof.

[0018] In some embodiments, the object support is a clamp.

[0019] In some embodiments, cleaning comprises planarizing and / or removing contaminant particles.

[0020] In some embodiments, applying the chemical cleaning agent, causing the relative movement, and applying the organic liquid are performed with a clamp coupled to a chuck of the lithographic apparatus. In some embodiments, applying the chemical cleaning agent, causing the relative movement, and applying the organic liquid are performed with a clamp disconnected from a chuck of the lithographic apparatus. In some embodiments, the object support and the lithographic apparatus are associated with semiconductor manufacturing.

[0021] According to another embodiment, there is provided a system for cleaning an object support of a lithographic apparatus, the system comprising: a chemical cleaning agent configured to be applied to a surface of the object support to release contaminant particles from the surface; a cleaning tool configured to be moved relative to the surface to clean the contaminant particles from the surface; and an organic liquid configured to be applied onto the surface to remove the chemical cleaning agent from the surface.

[0022] According to another embodiment, there is provided a system for cleaning a reticle clamp of a lithographic apparatus, the system comprising: a chemical cleaning agent configured to be applied to a surface to release contaminant particles from the surface of the reticle clamp; a cleaning tool configured to be moved relative to the surface to clean the contaminant particles from the surface; and an organic liquid configured to be applied onto the surface to remove the chemical cleaning agent from the surface. [Brief explanation of the drawings]

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments and, together with the description, explain these embodiments. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts and in which:

[0024] FIG. 1 depicts a schematic diagram of a lithographic apparatus according to one embodiment.

[0025] FIG. 2 illustrates a schematic representation of an embodiment of a lithographic cell or cluster, according to one embodiment.

[0026] FIG. 3A illustrates a portion of an extreme ultraviolet (EUV) lithography apparatus according to one embodiment.

[0027] FIG. 3B illustrates a portion of a deep ultraviolet (DUV) lithography apparatus, according to one embodiment.

[0028] FIG. 3C is an enlarged view of a portion of the lithographic apparatus shown in FIG. 3B according to one embodiment.

[0029] FIG. 4 illustrates a contamination particle on a reticle clamp, according to one embodiment.

[0030] FIG. 5 illustrates a method for cleaning a clamp of a lithographic apparatus according to an embodiment.

[0031] FIG. 6 illustrates a high voltage phase measurement interferometric flatness measurement of a clamping surface, according to one embodiment.

[0032] FIG. 7 illustrates a white light interferometry map of contamination particle distribution across a burl surface, according to one embodiment.

[0033] FIG. 8 illustrates a chemical cleaning agent being applied to a surface (e.g., one or more burl tops) of a reticle clamp to release contaminant particles (too small to be seen in this view) from the surface, according to one embodiment.

[0034] FIG. 9 illustrates a second white light interferometry map of post-cleaning contamination particle distribution across the same burl surface and clamp shown in FIG. 7, according to one embodiment.

[0035] FIG. 10 illustrates white light interferometry and scanning electron microscopy data for the cleaned surface (eg, burl top) of the clamp from the previous figure, according to one embodiment.

[0036] FIG. 11 illustrates another white light interferometry map of contamination particle distribution across the burl surface after ion beam processing (and after cleaning), according to one embodiment.

[0037] FIG. 12 shows relatively low and high magnification images of a clamp surface (in this example, the burl top) at various stages of the cleaning method described in FIG. 5, according to one embodiment.

[0038] FIG. 13 is a flow diagram for supplier repair of contaminated clamping surfaces (including the operations of the cleaning method described in FIG. 5) according to one embodiment.

[0039] FIG. 14 is a block diagram of an example computer system according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0040] Generally, a mask or reticle may be a transparent block of material covered with a pattern defined by a different opaque material. Alternatively, the mask or reticle may be an opaque block of material coated with, for example, a patterned mirror. Various masks are loaded into a lithography system and used to form layers of a semiconductor device. The pattern defined on a given mask or reticle corresponds to features to be created in one or more layers of the semiconductor device. Often, multiple masks or reticles are loaded into the lithography system automatically during production and used to form corresponding layers of the semiconductor device. Clamps (e.g., electrostatic reticle clamps) in lithography systems are used to secure the mask or reticle during processing. These clamps can become contaminated with particles (~1-3 μm in lateral dimensions and >25 nm in height) of material transferred from the reticle, resulting in performance degradation over time and requiring periodic cleaning to restore performance. These contaminant particles can cause performance degradation over time, for example, by providing nucleation sites for further contamination growth and / or causing other process problems.

[0041] Cleaning these clamps can require shutting down the lithography equipment and manufacturing process. This cleaning can take hours or weeks to complete, introduce other contaminants into the system, and / or have other drawbacks. Used clamps often have surfaces, such as burl tops, that become contaminated with contaminant particles that need to be cleaned before the clamps can be returned to service. Often, the tops of clamp burls are coated with hard, conductive ceramics, such as TiN or CrN. Contamination can bond strongly to the burl top coating and therefore cannot be removed by simple mechanical action.

[0042] To thoroughly clean the burl top of such a clamp, the hard conductive coating covering the burl top is stripped and a new coating is applied. This requires disconnecting the clamp from the chuck, stripping the various coatings from the non-burl areas of the clamp, stripping the hard conductive coating, and removing the high-voltage connections. The high-voltage connections are then re-established, a cap is added, the various coatings, including those on the burl top, are reapplied, and the clamp is verified to resume use in manufacturing. Finally, the clamp is reconnected to the chuck, and manufacturing can continue.

[0043] Disconnecting the clamp from the chuck carries the risk of damaging the clamp and / or the chuck. Disconnecting also affects clamp flatness, requiring a full cycle of burl-top planarization operations, which increases the time required for clamp cleaning. High-voltage connections are sealed by attaching additional hardware (e.g., glass) using structural epoxy. Because structural epoxy is strong, the underlying barrier is often damaged when removed. Excessive barrier damage around the high-voltage connection can lead to the scrapping of the clamp. Regarding peeling hard conductive coatings, structures created on the burl surface (e.g., glass) to assist clamping can also mismatch with patterns in the hard conductive coating. For example, when the original coating is peeled, an imprint of the initial coating pattern often remains. When a new coating is applied, registration issues can occur, and the new coat may already have a non-optimal structure pre-built. This can affect the clamp roughness and generally requires structure mapping, further increasing cleaning cycle time.

[0044] In contrast, the present systems and methods provide a new cleaning technique that allows for cleaning of burl tops and / or other surfaces without requiring disconnection of clamps or removal of high voltage connections to perform burl top renewal. Additionally, cleaning the clamps of a lithography apparatus with the present cleaning methods and systems can save hours or weeks of downtime associated with traditional inspection and cleaning methods, avoid damage to the clamps due to improper handling of manual cleaning equipment, and / or have other advantages.

[0045] Although specific reference may be made in this text to the manufacture of integrated circuits (ICs), it should be understood that the description herein has many other possible applications. For example, it may be utilized in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display 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 “reticle,” “wafer,” or “die” in this text should be construed as interchangeable with the more general terms “mask,” “substrate,” and “target portion,” respectively. Additionally, any use of the terms “reticle” or “mask” herein may be construed as synonymous with the more general term “patterning device.”

[0046] By way of introduction, before a pattern from a patterning device, such as a mask, can be transferred to the substrate, a substrate may undergo various procedures, such as priming, resist coating, and a soft bake. After exposure, the substrate may undergo other procedures ("post-exposure procedures"), such as a post-exposure bake (PEB), development, a hard bake, and measurement and / or other inspection of the transferred pattern. This array of procedures is used as a basis for creating individual layers of a device, such as an IC. The substrate may then undergo various processes, such as etching, ion implantation (doping), metallization, oxidation, chemical-mechanical polishing, and the like, to complete the individual layers of the device. If multiple layers are required in the device, the entire procedure, or a variation thereof, is repeated for each layer. Eventually, a device is present at each target portion on the substrate. These devices are separated from one another by techniques such as dicing or sawing, and the individual devices may, for example, be mounted on a carrier and connected to pins.

[0047] The fabrication of devices, such as semiconductor devices, typically involves processing a substrate (e.g., a semiconductor wafer) using many fabrication processes to form various features and multiple layers of the device. Such layers and features are typically fabricated and processed using, for example, deposition, lithography, etching, chemical-mechanical polishing, ion implantation, and / or other processes. Multiple devices may be fabricated on multiple dies on the substrate and may be separated into individual devices. This device fabrication process may also be referred to as a patterning process. A patterning process involves a patterning step, such as optical and / or nanoimprint lithography, using a patterning device in a lithography apparatus to transfer a pattern on the patterning device to the substrate, typically (but optionally) involving one or more associated pattern processing steps, such as developing the resist in a developer, baking the substrate using a bake tool, or etching using the pattern in an etcher. One or more metrology processes are typically involved in the patterning process.

[0048] Lithography is a step in the manufacture of devices such as integrated circuits in which patterns formed on a substrate define the functional elements of devices such as microprocessors, memory chips, etc. Similar lithography techniques are also used in the formation of flat panel displays, MEMS (Micro-Electro Mechanical Systems), and other devices.

[0049] As semiconductor manufacturing processes continue to improve, the number of functional elements, such as transistors, per device has steadily increased over the past few decades while the dimensions of the functional elements have continually decreased, following a trend commonly referred to as "Moore's Law." In current technology, device layers are fabricated using lithographic projection apparatus that use illumination from a deep ultraviolet illumination source to project a design layout onto a substrate, producing individual functional elements with dimensions well below 100 nm (i.e., equal to or less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source)).

[0050] Such processes, in which features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus are printed, are commonly known as low-k1 lithography, according to the resolution equation: CD = k1 × λ / NA. Here, λ is the wavelength of the radiation used (most commonly 248 nm or 193 nm today), NA is the numerical aperture of the projection optics in the lithographic projection apparatus, CD is the "critical dimension" (typically the smallest feature size that will be printed), and k1 is an empirical resolution factor. Generally, as k1 decreases, it becomes more difficult to reproduce on a substrate a pattern resembling the shape and dimensions designed by a designer to achieve a particular electrical function and performance. To overcome these difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, design layout, or patterning device. These include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase-shifting patterning devices, optical proximity correction (OPC, sometimes also written as "optical and process correction") in the design layout, overlay metrology, or other methods commonly defined as "resolution enhancement techniques" (RET).

[0051] The term "projection optics" as used herein should be broadly interpreted to encompass various types of optical systems, including, for example, refractive optical elements, reflective optical elements, apertures, and catadioptric optical elements. The term "projection optics," in plural or singular, may include components that operate according to any of these design types for directing, shaping, or controlling a projection beam of radiation. The term "projection optics" may include any optical component in a lithographic projection apparatus (regardless of where the optical component is located in the optical path of the lithographic projection apparatus). Projection optics may include optical components for shaping, conditioning, and / or projecting radiation from a source before the radiation passes through a patterning device and / or optical components for shaping, conditioning, and / or projecting radiation after the radiation has passed through a patterning device. Projection optics generally do not include a source and a patterning device.

[0052] 1 schematically illustrates an embodiment of a lithographic apparatus LA that may be included in and / or associated with the present systems and / or methods. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, EUV radiation), a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters, a substrate table (e.g., a wafer table) WT (e.g., WTa, WTb, or both) configured to hold a substrate (e.g., a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern formed in the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies, often referred to as a field) of the substrate W. The projection system is supported on a reference frame (RF). As depicted, the apparatus may be of a transmissive type (e.g. employing a transmissive mask) or it may be of a reflective type (e.g. employing a programmable mirror array or a reflective mask of a type as described above).

[0053] The illuminator IL receives a beam of radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not to be understood as forming part of the lithographic apparatus; the radiation beam may be passed from the source SO to the illuminator IL by a beam delivery system BD, which may comprise suitable directing mirrors and / or beam expanders. In other cases, the source may be an integral part of the apparatus, for example a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0054] The illuminator IL may adjust the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam so that the intensity distribution is non-zero within an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be able to limit the distribution of the beam in the pupil plane so that the intensity distribution is non-zero in a number of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in the pupil plane of the illuminator IL may be referred to as an illumination mode.

[0055] The illuminator IL may include an adjuster AD configured to adjust the intensity distribution (angular / spatial) of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner," respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. The illuminator IL may be capable of changing the angular distribution of the beam. For example, the illuminator may be capable of changing the number and angular extent of sectors in the pupil plane where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be realized. For example, by limiting the radius and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multipole distribution, such as a dipole, quadrupole, or hexapole distribution. A desired illumination mode may be obtained, for example, by inserting an optical element providing the illumination mode into the illuminator IL or by using a spatial light modulator.

[0056] The illuminator IL may be capable of changing the polarization of the beam, or the polarization may be adjustable using an adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as the polarization mode. The use of different polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across the pupil plane of the illuminator IL. The polarization direction of the radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen depending on the illumination mode. For a multipole illumination mode, the polarization of each pole of the radiation beam may generally be perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, for a dipole illumination mode, the radiation may be linearly polarized in a direction substantially perpendicular to a line bisecting two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions (which may be referred to as X-polarization and Y-polarization states). For a quadrupole illumination mode, the radiation in each pole sector may be linearly polarized in a direction substantially perpendicular to a line bisecting the sector. This polarization mode may be referred to as XY-polarization. Similarly, for a hexapole illumination mode, the radiation in each pole sector may be linearly polarized in a direction substantially perpendicular to a line bisecting the sector. This polarization mode may be referred to as TE-polarization.

[0057] In addition, the illuminator IL will generally comprise various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling radiation. In this way, the illuminator provides the beam of radiation B that is conditioned to have a desired uniformity and intensity distribution in its cross-section.

[0058] The support structure MT supports 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 or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, e.g. with respect to the projection system.

[0059] The term "patterning device", as used herein, should be interpreted broadly to refer to any device that can be used to create a pattern in a target portion of a substrate. In an embodiment, the patterning device is any device that can be used to create a pattern in the cross-section of a radiation beam so as to create a pattern in the target portion of the substrate. It should be noted that the pattern created in the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate if, for example, the pattern includes phase-shifting features or so-called assist features. Generally, the pattern created in the radiation beam will correspond to a particular functional layer in a device being created in the target portion of a device, such as an integrated circuit.

[0060] A patterning device may be transmissive or reflective. Examples of patterning devices include reticles or masks, programmable mirror arrays, and programmable LCD panels. Reticles or masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors that can be individually tilted so as to reflect an incoming beam in different directions. The tilted mirrors form a pattern in a radiation beam that is reflected by the mirror matrix.

[0061] The term "projection system" as used herein should be interpreted broadly to encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation used or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system".

[0062] The projection system PS has an optical transfer function, which may be non-uniform, that can affect the pattern imaged onto the substrate W. For unpolarized radiation, such effects can be best described by two scalar maps that describe the transmission (apodization) and relative phase (aberrations) of radiation exiting the projection system PS as a function of position in the pupil plane. These scalar maps, which may be referred to as transmission maps and relative phase maps, may be expressed as linear combinations of a complete set of basis functions. A convenient set are Zernike polynomials, which constitute a set of orthogonal polynomials defined on the unit circle. Determining each scalar map may involve determining the coefficients in such an expansion. Because the Zernike polynomials are orthogonal on the unit circle, the Zernike coefficients may be determined by computing the dot product of each Zernike polynomial with the measured scalar map in turn and dividing this by the square of the norm of that Zernike polynomial.

[0063] The transmission map and relative phase map are field- and system-dependent. That is, each projection system PS typically has a different Zernike expansion for each field point (i.e., each spatial location in its image plane). The relative phase of the projection system PS at the pupil plane may be determined by projecting radiation from, for example, a point-like source in the object plane (i.e., the plane of the patterning device MA) of the projection system PS through the projection system PS and using a shearing interferometer to measure the wavefront (i.e., the locus of points with the same phase). A shearing interferometer is a general path interferometer and advantageously does not require a second reference beam to measure the wavefront. The shearing interferometer may comprise a diffraction grating (e.g., a two-dimensional grid in the image plane (i.e., the substrate table WTa or WTb) of the projection system) and a detector arranged to detect an interference pattern in a plane conjugate to the pupil plane of the projection system PS. The interference pattern relates to the derivative of the phase of the radiation with respect to coordinates in the pupil plane in the shearing direction. The detector may comprise an array of sensing elements such as a charge coupled device (CCD).

[0064] Because the projection system PS of the lithographic apparatus does not need to generate visible fringes, the accuracy of the wavefront determination can be improved using phase-stepping techniques, such as a movable diffraction grating. Stepping can be performed in the plane of the diffraction grating, in a direction perpendicular to the scan direction of the measurement. The stepping range can be one grating period, and at least three (uniformly distributed) phase steps can be used. Thus, for example, three scan measurements can be performed in the y direction, each scan measurement being performed for a different position in the x direction. This stepping of the diffraction grating effectively converts phase variations into intensity variations, allowing phase information to be determined. The grating can also be stepped in a direction perpendicular to the diffraction grating (z direction) to calibrate the detector.

[0065] The diffraction grating may be scanned continuously in two perpendicular directions, which may be coincident with the axes (x and y) of the coordinate system of the projection system PS, or which may be at an angle, such as 45 degrees, to these axes. The scan may be performed over an integer number of grating periods (e.g., one grating period). The scan averages the phase variations in one direction and allows the phase variations in the other direction to be reconstructed. This allows the wavefront to be determined as a function of both directions.

[0066] The transmission (apodization) of the projection system PS at the pupil plane may be determined by projecting radiation through the projection system PS, for example from a point source in the object plane of the projection system PS (i.e. the plane of the patterning device MA), and using a detector to measure the intensity of the radiation in a plane conjugate to the pupil plane of the projection system PS. The same detector used to measure the wavefront may be used to determine the aberrations.

[0067] The projection system PS may include multiple optical (e.g., lens) elements and may further include an adjustment mechanism configured to adjust one or more of the optical elements to correct aberrations (phase variations across the pupil plane across the field). To achieve this, the adjustment mechanism may be capable of manipulating one or more optical (e.g., lens) elements in one or more different ways within the projection system PS. The projection system may have a coordinate system in which the optical axis extends in the z direction. The adjustment mechanism may be capable of performing any combination of displacing one or more optical elements, tilting one or more optical elements, and / or deforming one or more optical elements. The displacement of the optical elements may be in any direction (x, y, z, or a combination thereof). Tilting an optical element is typically accomplished by rotating it about an axis in the x and / or y directions out of a plane perpendicular to the optical axis, although for non-rotationally symmetric aspherical optical elements, rotation about the z axis may be used. The deformation of the optical element may include low-frequency shapes (e.g., astigmatic shapes) and / or high-frequency shapes (e.g., freeform aspheric surfaces). For example, deformation of the optical element may be performed by using one or more actuators to apply a force to one or more sides of the optical element and / or by using one or more heating elements to heat one or more selected regions of the optical element. Generally, it is not possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). A transmission map of the projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithographic apparatus LA. To at least partially correct for apodization, the patterning device MA may be designed using computational lithography techniques.

[0068] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g. two or more substrate tables WTa, WTb, two or more patterning device tables, e.g. substrate tables WTa and WTb below the projection system without substrates dedicated to facilitating measurement and / or cleaning). In such a "multiple stage" apparatus, the additional tables may be used in parallel, and preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using alignment sensors AS and / or level (height, tilt, etc.) measurements using level sensors LS may be made.

[0069] The lithographic apparatus may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system and the substrate. Immersion liquids may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device and the projection system. Immersion techniques are well known for increasing the numerical aperture of projection systems. The term "immersion", as used herein, does not imply that a structure such as the substrate must be submerged in liquid, but rather only that a liquid is present between the projection system and the substrate during exposure.

[0070] In operation of a lithographic apparatus, a radiation beam is conditioned and provided by an illumination system IL. The radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT. Having passed through the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam on a target portion C of a substrate W. By means 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 may be accurately driven (e.g., to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and other position sensors (not explicitly shown in FIG. 1 ) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B (e.g., after mechanical retrieval from a mask library or during a scan). In general, movement of the support structure MT may be realized by a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. The patterning device MA and the substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks in the illustrated example occupy dedicated target portions, they may be located in spaces between the target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0071] The depicted apparatus may be used in at least one of the following modes: 1. In step mode, the support structure MT and substrate table WT are kept substantially stationary while a pattern formed in the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure), and the substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the support structure MT and substrate table WT are scanned simultaneously while a pattern formed in the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, while the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the support structure MT is kept substantially stationary holding the programmable patterning device, and the substrate table WT is moved or scanned while a pattern formed in the radiation beam is projected onto a target portion C. In this mode, a pulsed radiation source is typically employed and the programmable patterning device is updated, as required, after each movement of the substrate table WT or in between successive pulses of radiation during a scan. This mode of operation can readily be applied to maskless lithography employing a programmable patterning device such as a programmable mirror array of the type described above. Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0072] The substrate may be processed, before or after exposure, in, for example, a track (a tool that typically applies a layer of resist to the substrate and develops the exposed resist), metrology, or inspection tool. Where applicable, the disclosure herein may be applied to such other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example, to form a multi-layer IC, and the term "substrate" as used herein may refer to a substrate that already includes multiple processed layers.

[0073] The terms "radiation" and "beam" as used herein include all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g., having a wavelength of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range 5-20 nm), and particle beams such as ion beams or electron beams.

[0074] Various patterns on or provided by a patterning device may have different process windows (i.e., the space of processing variables within which the patterns are generated). Examples of pattern specifications for potential system defects include checks for necking, line pullback, line thinning, critical dimension (CD), edge placement, overlapping, resist top loss, resist undercut, and / or bridging. The process window of a pattern on a patterning device or area thereof may be obtained by merging the (e.g., overlapping) process windows of each individual pattern. The process window boundary of a group of patterns comprises the process window boundaries of some of the individual patterns. In other words, these individual patterns limit the process window of the group of patterns. These patterns may be referred to as "hot spots" or "process window limiting patterns (PWLPs)," which are used interchangeably herein. When controlling portions of the patterning process, it is possible and economical to focus on hot spots. When hot spots are defect-free, other patterns are likely defect-free as well.

[0075] As shown in FIG. 2, the lithography apparatus LA may form part of a lithography cell LC, sometimes referred to as a lithocell or cluster, which also includes apparatus for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these include one or more spin coaters SC for forming one or more resist layers, one or more developers for developing the exposed resist, one or more chill plates CH, and / or one or more bake plates BK. A substrate handler or robot RO picks up one or more substrates from input / output ports I / O1, I / O2, moves them between different processing equipment, and delivers the substrates to the loading bay LB of the lithography apparatus. These apparatuses, often collectively referred to as tracks, are under the control of a track control unit TCU, which may itself be controlled by a supervisory control system SCS. The supervisory control system SCS also controls the lithography apparatus via a lithography control unit LACU. In this way, different apparatuses can be operated to maximize throughput and processing efficiency.

[0076] To ensure that substrates exposed by a lithographic apparatus are accurately and consistently exposed, and / or to monitor portions of a patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect substrates or other objects to measure or determine one or more characteristics, such as alignment, overlay (e.g., between structures in overlapping layers, or between structures in the same layer that are provided separately relative to the layer, e.g., by a double patterning process), line thickness, critical dimension (CD), focus offset, material properties, etc. For example, contamination on a reticle clamping membrane (e.g., as described herein) can adversely affect overlay because clamping a reticle on such contamination distorts the reticle. For this reason, a manufacturing facility in which a lithocell LC is located typically also includes metrology systems that measure some or all of the substrates W ( FIG. 1 ) processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example part of the lithographic apparatus LA (such as the alignment sensor AS (FIG. 1)).

[0077] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the substrate being patterned, critical dimension (CD) (e.g., critical linewidth) of features formed in or on the substrate being patterned, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. The measurements may be performed on targets on the product substrate itself and / or on dedicated metrology targets provided on the substrate. Measurements may be performed after resist development, but may also be performed before etching, after etching, after deposition, and / or at other times.

[0078] There are various techniques for making measurements of structures formed in patterning processes, including the use of scanning electron microscopes, image-based metrology tools, and / or various specialized tools. As mentioned above, a high-speed and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of a substrate and properties of the scattered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. This may be referred to as diffraction-based metrology. One such application of diffraction-based metrology is in measuring feature asymmetry within a target. This may be used, for example, as a measurement of overlay, although other applications are known. For example, asymmetry may be measured by comparing opposing portions of a diffraction spectrum (e.g., comparing the −1st and +1st orders in the diffraction spectrum of a periodic grating). Another application of diffraction-based metrology is in measuring feature width (CD) within a target.

[0079] Thus, in device manufacturing processes (e.g., patterning processes, lithography processes, etc.), substrates or other objects may be subjected to various types of measurements during or after the process. The measurements may determine whether a particular substrate is defective, may establish adjustments to the process and equipment used in the process (e.g., aligning two layers on a substrate or aligning a patterning device to a substrate), may measure the performance of the process and equipment, or may be used for other purposes. Examples of measurements include optical imaging (e.g., optical microscopes), non-imaging optical measurements (e.g., diffraction-based measurements such as ASML YieldStar metrology tools, ASML SMASH metrology systems), mechanical measurements (e.g., stylus-based profiling, atomic force microscopy (AFM)), and non-optical imaging (e.g., scanning electron microscopes (SEM)).

[0080] The metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, adjustments may be made to the exposure of subsequent substrates (particularly if inspection can be performed quickly enough that one or more other substrates in the batch have not yet been exposed) and / or to subsequent exposures of exposed substrates. Also, already exposed substrates may be removed and reprocessed to improve yield, or may be discarded to avoid performing further processing on substrates found to be defective. If only some target portions of a substrate are defective, further exposures may be performed only on those target portions that meet specification.

[0081] Within a metrology system, a metrology device is used to determine one or more properties of the substrate, and in particular how one or more properties vary between different substrates or between different layers of the same substrate. As mentioned above, the metrology device may be integrated into the lithographic apparatus LA or lithocell LC, or may be a stand-alone device.

[0082] To enable metrology, one or more targets may be provided on the substrate. In one embodiment, the target may be specially designed and comprise a periodic structure. In one embodiment, the target is part of a device pattern (e.g., a periodic structure of a device pattern). In one embodiment, the device pattern is a periodic structure of a memory device (e.g., a structure of a bipolar transistor (BPT), bit line contact (BLC), etc.).

[0083] In one embodiment, a target on a substrate may comprise one or more one-dimensional periodic structures (e.g., gratings) printed such that, after development, the periodic structure features are formed of solid resist lines. In one embodiment, a target may comprise one or more two-dimensional periodic structures (e.g., gratings) printed such that, after development, the periodic structure features are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0084] In one embodiment, one of the parameters of interest in the patterning process is overlay. Overlay can be measured using dark-field scatterometry, in which the zeroth order of diffraction (corresponding to specular reflection) is blocked and only higher orders are processed. Diffraction-based overlay, using dark-field detection of diffraction orders, allows overlay measurements on smaller targets. These targets may be smaller than the illumination spot and may be surrounded by device product structures on the substrate. In one embodiment, multiple targets can be measured in a single radiation capture.

[0085] As lithography nodes continue to shrink, increasingly complex wafer designs may be implemented. Various tools and / or techniques may be used by designers to ensure that complex designs are accurately transferred to the physical wafer. These tools and techniques may include mask optimization, source-mask optimization (SMO), OPC, design for control, and / or other tools and / or techniques. For example, a source-mask optimization process is described in U.S. Patent No. 9,588,438, entitled "Optimization Flows of Source, Mask and Projection Optics," which is incorporated herein by reference in its entirety.

[0086] The present systems and / or methods may be used as stand-alone tools and / or techniques and / or may be used in conjunction with semiconductor manufacturing processes to improve the accuracy of transfer of complex designs onto physical wafers.

[0087] As previously mentioned, the cleaning system is configured to be used to clean clamps of a lithographic apparatus. As non-limiting examples, Figures 3A, 3B, and 3C illustrate portions of a lithographic apparatus 300 (e.g., similar to or the same as the lithographic apparatus shown in Figure 1). Figure 3A illustrates a portion of an extreme ultraviolet (EUV) lithographic apparatus. Figure 3B illustrates a portion of a deep ultraviolet (DUV) lithographic apparatus. Figure 3C is an enlarged view of a portion of the lithographic apparatus shown in Figure 3B, according to one embodiment.

[0088] FIG. 3A illustrates lithographic apparatus components near clamp 312 of lithographic apparatus 300, including tool handlers 306, 307, 308, and / or other components. Lithographic apparatus 300 may also include an EUV inner pod (EIP) 305, a rapid exchange device (RED), and / or other components. In some embodiments, lithographic apparatus 300 may be configured for deep ultraviolet (DUV) lithography with one or more adjustments from that shown in FIG. 3A. FIG. 3B illustrates the DUV apparatus (e.g., with clamp 312 of lithographic apparatus 300 in these figures) and various components of lithographic apparatus 300, including tool handlers 306, 307, 308, reticle chuck 310, reticle clamp 312, and / or other components.

[0089] In some embodiments, tool handlers 306, 307, 308 include reticle handler turret gripper 306, reticle handler robot gripper 307 (with associated components 308, etc. for gripping a reticle during transport), and / or other components. Reticle handler robot gripper 307 may, for example, move a reticle from pod 320 (e.g., after a user has placed the reticle in pod 320). Reticle handler turret gripper 306 may, for example, move a reticle from reticle handler robot gripper 307 to reticle clamp 312. Lithographic apparatus 300 may include various other mechanical components 322 (translation mechanisms, lifting mechanisms, rotation mechanisms, motors, power generation and transmission components, structural components, etc.) configured to facilitate movement and control of reticle 302 through lithographic apparatus 300. For example, lithographic apparatus 300 may include an EUV inner pod (EIP), a rapid exchange device (RED), and / or other components.

[0090] The systems and methods are configured to be used to clean clamps 312 (e.g., reticle clamps) of lithographic apparatus 300. In other embodiments, the systems and methods described herein may be configured to clean any object support in a lithographic apparatus. The object support may include any clamp (e.g., vacuum or electrostatic clamp) or support structure in a lithographic apparatus, including, but not limited to, a reticle (also referred to as a mask) clamp, a wafer (also referred to as a substrate) clamp, and a wafer table. FIG. 3C is an enlarged view of a portion of apparatus 300. FIG. 3C shows reticle 302, reticle handler turret gripper 306, reticle chuck 310, reticle clamp 312, mechanical component 322, reticle handler robot gripper 307, and / or other components. 3C , reticle handler turret gripper 306 is configured to move reticle 302 from reticle handler robot gripper 307 to reticle clamp 312. Moving reticle 302 may comprise moving reticle 302 horizontally, vertically, and / or in other directions toward or away from clamp 312. Reticle handler turret gripper 306 and / or reticle handler robot gripper 307 may include various motors, translators, rotational components, clamps, clips, power sources, power transfer components, vacuum mechanisms, and / or other components that facilitate movement of reticle 302.

[0091] Contamination particles on clamps contact surfaces such as burrs and often collect and grow on the clamp surface over time, necessitating periodic cleaning. Contamination particles typically range in lateral dimensions from about 2-5 μm and up to about 100-200 nm in height (or thickness from the clamp burr surface). As the number and size of the contaminant particles increase, performance degradation and / or other problems, such as overlay drift, can occur. For example, overlay drifts by as much as about 1 nm within a relatively short time period (e.g., 1-3 months), and this drift is unacceptable for semiconductor production, necessitating frequent cleaning. Therefore, devices, systems, and methods for cleaning relevant parts of a lithography apparatus (e.g., clamp-reticle and / or wafer contact areas) are desired.

[0092] FIG. 4 illustrates a contamination particle 400 on a reticle contact area 402 (e.g., clamp surface) of a reticle clamp 404. In this example, the reticle contact area 402 (clamp surface) is a burl surface. The burl surface may be contoured and / or have other shapes so that only certain portions of the burl contact the reticle. View 410 of FIG. 4 illustrates white light interferometry data showing contaminated burl (circular distribution) on the clamp. For example, for an embodiment with a contoured surface, contamination may appear at the peaks of the burl surface. View 412 illustrates a relatively low magnification (e.g., 20X) image of four different burls. View 414 illustrates a higher magnification (e.g., 100X) image showing a clean burl on the left side of view 414 and a contaminated burl on the right side of view 414. Note that each burl has a ridged surface or top that forms the reticle contact area 402.

[0093] FIG. 5 illustrates a method 500 for cleaning a clamp of a lithographic apparatus, which may be a clamp (e.g., an electrostatic clamp as described above) and / or other clamp / object support surface. Cleaning may include planarizing and / or removing contaminant particles from the clamp, and / or other operations. In some embodiments, one or more operations of method 500 may be controlled by one or more processors and / or computing systems, as described below (see FIG. 14 ). The operations of method 500 (e.g., applying a chemical cleaning agent, effecting relative movement, applying an organic liquid, and other operations described below) may be performed with the clamp coupled to or disconnected from the chuck of the lithographic apparatus. The operations of method 500 presented below are for illustrative purposes. In some embodiments, method 500 may be implemented with one or more additional operations not described and / or without one or more of the operations discussed. Additionally, the order in which the operations of method 500 are shown in FIG. 5 and described below is not intended to be limiting.

[0094] In some embodiments, one or more operations of method 500 may be implemented in and / or controlled by one or more processing devices (e.g., digital processors, analog processors, digital circuits designed to process information, analog circuits designed to process information, state machines, and / or other mechanisms for processing information electronically, such as those described with respect to FIG. 14 below). The one or more processing devices may include one or more devices for performing some or all of the operations of method 500 in response to instructions electronically stored on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software specifically designed to perform one or more of the operations of method 500 (see, e.g., the discussion with respect to FIG. 14 below). For example, the one or more processing devices may execute software configured to form a mosaic of images of one or more clamp surfaces, control the performance of an initial flatness measurement, facilitate the determination of an initial particle distribution map, control a uniform hit using ion beam processing, facilitate the determination of a final particle distribution map, compare the final particle distribution map to the initial particle distribution map, control the performance of a final flatness measurement, and / or perform other operations.

[0095] In operation 501, pre-cleaning image data of the surface of the clamp is generated that identifies the presence of contaminant particles, identifies one or more types of contaminant particles, and / or identifies other information. In some embodiments, the types of particles include tantalum contaminant particles, chromium contaminant particles, and / or other types of contaminant particles. In some embodiments, the surface comprises a burl top or a portion of a burl top. In some embodiments, the image data comprises one or more images from a microscopic examination of the surface. Two or more of these images may be combined or stitched together (electronically) to form a mosaic of images indicative of the burl top surface (or a portion thereof). For example, a microscope magnification of 10-100X may be used in this examination. The mosaic of images may be analyzed to identify the presence of contaminant particles, the type of contaminant particles, and / or other information.

[0096] In operation 502, an initial pre-cleaning flatness of the surface is determined. The pre-cleaning flatness is determined, for example, to identify the presence of contaminant particles and the need for cleaning. In some embodiments, a computer system (such as the computer system shown in FIG. 14 and described below) is configured to determine the initial pre-cleaning flatness of the surface to identify the presence of contaminant particles and the need for cleaning. In some embodiments, the initial flatness is determined using high-voltage phase-measuring interferometry and / or other methods. In some embodiments, the computer system forms part of a high-voltage phase-measuring interferometer.

[0097] As a non-limiting example, Figure 6 illustrates high-voltage phase measurement interferometry flatness measurement data 600 for a clamping surface. Figure 6 also illustrates corresponding flatness measurement data 602 for the clamping surface acquired before the clamp was removed from service. The arrows indicate how non-flatness caused by contamination distorts the surface of the clamped reticle such that the image projected from the reticle to the wafer is incorrectly aligned. The flatness of this clamping surface varies irregularly across the clamping surface, as can be seen by the varying shading colors across each data set.

[0098] 5, in operation 503, a pre-cleaning contaminant particle distribution map for the surface is determined. In some embodiments, the pre-cleaning contaminant particle distribution map is determined using microscopy. In some embodiments, the contaminant particle distribution map is determined using white light interferometry.

[0099] As a non-limiting example, Figure 7 illustrates a white light interferometry map 700 of the distribution of contaminant particles 702 across a burl surface 704. Each dot in Figure 7 is a burl surface 704 on a clump, and the shading scale 710 maps the number of particles per burl surface (in this example, the particle distribution matches the overlay signature for the clump).

[0100] Returning to FIG. 5, in operation 504, a chemical cleaning agent is applied to the surfaces (e.g., one or more burl tops) of the reticle clamp to release contaminant particles from the surfaces. In some embodiments, the chemical cleaning agent comprises potassium hydroxide for tantalum contaminant particles, chromium etchant for chromium contaminant particles, or a combination thereof. The chemistries required for removal of other particles, which may be identified by techniques such as scanning electron microscopy / energy dispersive spectroscopy, are known to those skilled in the art. The potassium hydroxide may be, for example, a 50% potassium hydroxide solution, and / or other solutions.

[0101] 8 illustrates a chemical cleaning agent 800 being applied to a surface 802 (e.g., one or more burl tops) of a reticle clamp 804 to release contaminant particles (too small to be seen in this view) from the surface 802. In this example, the chemical cleaning agent is a potassium hydroxide solution. Because the contaminant particles in this example are tantalum contaminant particles, the potassium hydroxide solution is selected for cleaning (e.g., determined based on operations 501, 502, and / or 503, as described above). The chemical cleaning agent 800 may be used in combination with a cleaning tool 850 (e.g., a mechanical cleaning tool such as a glass pack) to clean the contaminant particles from the surface 802 and / or an organic liquid 852 that is applied onto the surface 802 to remove the chemical cleaning agent 800 from the surface 802 (e.g., to rinse the surface 802), as described below.

[0102] Returning to FIG. 5 , in some embodiments, operation 504 includes effecting relative movement between the cleaning tool and the surface to clean contaminant particles from the surface. In some embodiments, the cleaning tool may be configured to move relative to the surface, the surface may be configured to move relative to the cleaning tool, or the cleaning tool and surface may be configured to move relative to each other. In some embodiments, the cleaning tool is a glass puck or other similar cleaning tool. The cleaning tool may be any cleaning tool that is sufficiently flat and chemically inert to the cleaning chemicals. The relative movement may comprise lateral movement, serpentine movement, circular movement, or a combination thereof. In some embodiments, the relative movement may be effected by a human operator, a mechanical actuator (e.g., controlled by a computer system such as the computer system shown and described in FIG. 14 below), and / or other devices. The relative movement is configured to clean contaminant particles from the clamp. For example, the relative movement may range from at least about tens of micrometers (μm) to at least about 4 millimeters (mm). As another example, the relative movements may range from at least about tens of micrometers (μm) to at least about 4 millimeters (mm) in the non-scanning direction of the lithographic apparatus and at least about 2 mm in the scanning direction of the lithographic apparatus (although these movements may be larger if necessary, for example, when a human operator effects the relative movements).

[0103] In some embodiments, operation 504 comprises receiving input and / or selection of a control command from a user via a user interface, the control command comprising instructions to move a cleaning tool based on a region of interest (e.g., a surface such as a burl top) of a chuck of a lithographic apparatus, and / or other control commands.

[0104] In some embodiments, operation 504 includes determining whether to apply a chemical cleaning agent and / or where on the surface to apply the chemical cleaning agent, effect relative movement between the cleaning tool and the surface and / or where on the surface to effect relative movement between the cleaning tool and the surface, apply an organic liquid (operation 505, described below) and / or where on the surface to apply an organic liquid and / or perform other operations and / or where on the surface to perform other operations. One or more of these determinations may be made based on, for example, image data of the surface (see operation 501), the flatness of the surface (see operation 502), the distribution of contaminant particles on the surface (see operation 503), and / or other information. A computer system (such as the computer system shown in FIG. 14 and described below) may be configured to determine whether and / or where on the surface to apply a chemical cleaning agent, where to effect relative movement between the cleaning tool and the surface, and / or where to apply an organic liquid based on image data of the surface, the flatness of the surface, the distribution of contaminant particles on the surface, and / or other information.

[0105] In operation 505, an organic liquid is applied onto a surface. The organic liquid is applied to the surface to remove chemical cleaning agents from the surface. In some embodiments, the organic liquid is an alcohol, such as isopropyl alcohol, and / or other organic liquid. The organic liquid may be dried (e.g., with a drying tool, such as a lint-free wipe, towel, blower, etc.). In some embodiments, to improve operation 505, the organic liquid, such as isopropyl alcohol, may be configured to evaporate or dry relatively quickly.

[0106] A post-cleaning uniform ion beam process is performed on the surface in operation 506. In some embodiments, the contaminant particles have already been completely removed from the surface or have been reduced to a size small enough that the uniform ion beam process can remove them.

[0107] In some embodiments, in operation 506, a post-cleaning contaminant particle distribution map for the surface is determined. The post-cleaning contaminant particle distribution map may be compared to the pre-cleaning contaminant particle distribution map for the surface to confirm that the method 500 for cleaning the surface was able to remove most or all of the contaminant particles from the surface. In some embodiments, the post-cleaning contaminant particle distribution map is determined using white light interferometry and / or other inspection techniques. In some embodiments, a computer system (such as the computer system shown in FIG. 14 and described below) may be configured to determine the post-cleaning contaminant particle distribution map for the surface and compare the post-cleaning contaminant particle distribution map against the pre-cleaning contaminant particle distribution map for the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface.

[0108] In operation 507, the post-cleaning flatness of the surface is determined and compared to the initial pre-cleaning flatness of the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface. The post-cleaning flatness may be determined using, for example, high-voltage phase measurement interferometry. In response to the post-cleaning flatness violating a flatness threshold (e.g., still not sufficiently flat), method 500 and / or operation 507 further comprise performing additional ion beam processing on the surface to bring the post-cleaning flatness within a flatness specification. In some embodiments, a computer system (such as the computer system shown in FIG. 14 and described below) may be configured to determine the post-cleaning flatness of the surface and compare it to the initial pre-cleaning flatness of the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface.

[0109] As further non-limiting examples, Figures 9-13 show various examples of the features described above. Figure 9 illustrates a second white light interferometry map 900 of the post-cleaning contamination particle 902 distribution across the same burl surfaces 704 and clumps shown in Figure 7. Each dot in Figure 9 is a burl surface 704 on a clump, and the shading scale 710 maps the number of particles per burl surface. As shown in Figure 9, after cleaning with potassium hydroxide (see Figure 8), the contamination particle 902 distribution changes relative to the contamination particle 702 distribution. As can be observed, particles from the center of the clump have been removed or moved from the center of the clump toward the edge.

[0110] FIG. 10 illustrates white light interferometry inspection data 1000 and scanning electron microscopy inspection data 1002, 1004, and 1006 for the cleaned surface (e.g., burl top) of the clamp from the previous figure. In some embodiments, other data, such as energy dispersive X-ray spectroscopy data for the cleaned surface, may be used. All of this data indicates that contaminant particles (e.g., tantalum oxide in this example) on the clamp surface have been removed by cleaning. For example, no contaminant particles are visible in the white light interferometry inspection data 1000 (e.g., image of the burl top). Similar and / or low contrast in backscattered electron measurements in the scanning electron microscopy data 1002, 1004, and 1006 indicates a homogeneous burl top surface configuration (free of tantalum oxide contaminant particles). Similarly, energy dispersive X-ray spectroscopy data may be acquired to determine whether a homogeneous burl top surface configuration is present.

[0111] FIG. 11 illustrates another white light interferometry map 1100 of contaminant particle distribution across a burl surface after ion beam processing (and after cleaning), according to one embodiment. Map 1100 shows the distribution of contaminant particles 1102 across the same burl surface 704 and clump shown in FIGS. 7 and 9 after cleaning and ion beam processing. Ion beam processing may be performed, for example, by an ion beam processing system 1150. Each dot in FIG. 11 represents a burl surface 704 on a clump, and the shading scale 1110 maps the number of particles per burl surface. As shown in FIG. 11, after potassium hydroxide cleaning (see FIG. 8) and ion beam processing, the contaminant particle 1102 distribution changes relative to the contaminant particle 702 and / or 902 distribution. As can be seen, the clump is cleaner with relatively fewer particles 1102.

[0112] FIG. 12 shows relatively low 1200 and high 1202 magnification images of a clamp surface (in this example, a burl top) at various stages of the cleaning method shown in FIG. 5 (e.g., method 500 shown in FIG. 5). These images may be acquired with a pre- and / or post-cleaning imager 1250, such as a microscope, a white light interferometer, and / or other imager (e.g., where imager 1250 is both a pre- and post-cleaning imager 1250). FIG. 12 illustrates white light interferometer images of clamp surface 1205 as received (1204), surface 1205 after cleaning with potassium hydroxide and a cleaning tool (1206) (e.g., after operation 504 shown in FIG. 5 and described above), surface 1205 after cleaning with an organic liquid (1208) (e.g., after operation 505 shown in FIG. 5), and surface 1205 after cleaning with ion beam machining (1210). 12 illustrates how these cleaning operations remove contaminant particles 1220 present on the as-received clamp surface 1205 (1204). For example, particles 1220 are not present after cleaning with potassium hydroxide and a cleaning tool (1206).

[0113] FIG. 13 illustrates a flow 1300 diagram 1302 for supplier repair of a contaminated clamp surface (including the operations of cleaning method 500 described above). Note that flow 1300 may additionally or alternatively be performed by the clamp owner and / or some other provider. Flow 1300 begins with the clamp being returned to the supplier (1304). A typical clamp may be returned (1304), for example, after approximately 1000 reticle loads (e.g., as described with respect to FIGS. 3A, 3B, and 3C above). A decision 1306 is made as to whether the contaminated and / or damaged (e.g., burr damage) clamp surface is repairable. If not repairable (“no” at decision block 1307), the clamp is disconnected (1308) from the chuck, and the clamp is stripped and recoated (1310), which may take up to 15 weeks to complete. If repairable ("yes" at decision block 1307), a decision is made as to whether the clamp is contaminated (e.g., with particles as described above) 1312. If not contaminated ("no" at decision block 1313), the clamp remains in contact with the chuck 1314, and low-use repair, cleaning, and / or other operations may be performed 1316 on the clamp and / or clamp surfaces.

[0114] If the clamp is contaminated (“yes” at decision block 1313), a decision 1318 is made as to whether a sufficient amount (e.g., greater than about 150 nm thick) of burl top coating is present on the clamp surface. If so (“yes” at decision block 1319), a decision 1320 is made as to whether repair and / or cleaning 1350 can be performed without disconnecting the clamp from the chuck. If possible (“yes” at decision block 1321), the clamp remains in contact with the chuck (1322), and the operations of method 500 described above (e.g., at least chemical cleaning agent and cleaning tool operation 504 and / or ion beam processing operation 506) are performed on the clamp surface. If repair and / or cleaning 1350 cannot be performed with the clamp in contact with the chuck (“no” at decision block 1321), a decision 1324 is made as to whether repair and / or cleaning 1350 can be performed if the clamp is disconnected from the chuck. If so (“yes” at decision block 1325), the clamp is disconnected from the chuck (1326), the operations of method 500 described above (e.g., at least chemical cleaning agent and cleaning tool operations 504) are performed on the clamp surface, the clamp is re-contacted to the chuck (1328), and the ion beam processing operation 507 is performed on the clamp surface.

[0115] 14 is a block diagram illustrating a computer system 1400 that can assist in implementing a method, flow, or system disclosed herein. The computer system 1400 may be included in and / or electronically coupled to the lithography apparatus LA (e.g., FIGS. 1 and 3A) described above. The computer system 1400 includes a bus 1402 or other communication mechanism for communicating information, and a processor 1404 (or multiple processors 1404, 1405, etc.) coupled to the bus 1402 for processing information. The computer system 1400 also includes a main memory 1406, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 1402 for storing information and instructions to be executed by the processor 1404. The main memory 1406 may be used to store temporary variables or other intermediate information during execution of instructions to be executed by the processor 1404. Computer system 1400 further includes a read-only memory (ROM) 1408 or other static storage device coupled to bus 1402 for storing static information and instructions for processor 1404. A storage device 1410, such as a magnetic disk or optical disk, is provided and coupled to bus 1402 for storing information and instructions.

[0116] The computer system 1400 may be coupled via bus 1402 to a display 1412, such as a cathode ray tube (CRT) or flat-panel or touch-screen display, for displaying information to a computer user. An input device 1414, including alphanumeric and other keys, is coupled to bus 1402 for communicating information and command selections to the processor 1404. Another type of user input device is a cursor control 1416, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor 1404 and for controlling cursor movement on the display 1412. This input device typically has two degrees of freedom in two axes—a first axis (e.g., x) and a second axis (e.g., y)—allowing the device to specify a position in a plane. A touch-screen (screen) display may also be used as an input device.

[0117] According to one embodiment, portions of one or more flows and / or methods described herein may be performed by computer system 1400 in response to processor 1404 executing one or more sequences of one or more instructions stored in main memory 1406. Such instructions may be read into main memory 1406 from another computer-readable medium, such as storage device 1410. Execution of the sequences of instructions stored in main memory 1406 causes processor 1404 to perform the flows and / or process steps described herein. One or more processors in a multi-processor arrangement may be utilized to execute the sequences of instructions stored in main memory 1406. In alternative embodiments, hardware-implemented circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0118] The terms "computer-readable medium" or "machine-readable medium" as used herein refer to any medium that participates in providing instructions to processor 1404 for execution. Such media may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device(s) 1410. Volatile media include dynamic memory, such as main memory 1406. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus 1402. Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tape, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tape, any other physical media with a pattern of holes, RAM, PROMs, and EPROMs, FLASH-EPROMs, any other memory chip or cartridge, a carrier wave as described below, or any other medium from which a computer can read.

[0119] Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to processor 1404 for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer may load the instructions into its dynamic memory and transmit the instructions over a network, such as the Internet. A modem included with computer system 1400 may receive the data and convert the data to an infrared signal using an infrared transmitter. An infrared detector coupled to bus 1402 may receive the data carried in the infrared signal and place the data on bus 1402. Bus 1402 transfers the data to main memory 1406, from which processor 1404 retrieves and executes the instructions. The instructions received by main memory 1406 may optionally be stored on storage device 1410 either before or after execution by processor 1404.

[0120] Computer system 1400 may also include a communication interface 1418 coupled to bus 1402. The communication interface 1418 provides a two-way data communication coupling to a network link 1420 that is connected to a local network 1422. For example, the communication interface 1418 may be an Integrated Services Digital Network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, the communication interface 1418 may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. A wireless link may also be implemented. In any such implementation, the communication interface 1418 sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0121] Network link 1420 typically provides data communication through one or more networks to other data devices. For example, network link 1420 may provide a connection through local network 1422 to a host computer 1424 or to data equipment operated by an Internet Service Provider (ISP) 1426. ISP 1426 provides data communication services through the global packet data communication network commonly referred to as the "Internet" 1428. Local network 1422 and Internet 1428 both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link 1420 and through communication interface 1418, which carry the digital data to and from computer system 1400, are exemplary forms of information carried by carrier waves.

[0122] Computer system 1400 can send messages and receive data, including program code, through the network(s), network link 1420 and communication interface 1418. In the Internet example, a server 1430 might transmit a requested code for an application program through Internet 1428, ISP 1426, local network 1422 and communication interface 1418. One such downloaded application may, for example, provide all or a portion of the methods described herein. Once received, the code may be executed by processor 1404 immediately and / or stored in storage device 1410 or other non-volatile storage for later execution. In this manner, computer system 1400 can obtain application code in the form of a carrier wave.

[0123] Various embodiments of the present systems and methods are disclosed in the following list of numbered items. Item 1: 1. A method for cleaning an object support of a lithographic apparatus, comprising: applying a chemical cleaning agent to the surface of the object support to release contaminant particles from the surface; providing relative movement between a cleaning tool and the surface to clean the contaminant particles from the surface; applying an organic liquid onto the surface to remove the chemical cleaning agent from the surface; A method for providing Item 2: 10. The method of claim 1, further comprising generating pre-cleaning image data of the surface, the pre-cleaning image data identifying the presence of the contaminant particles and / or one or more types of the contaminant particles. Item 3: 10. The method of any of the preceding items, wherein the image data comprises one or more images from a microscopic examination of the surface. Item 4: 10. The method of any of the preceding items, further comprising determining an initial pre-cleaning flatness of the surface to identify the presence of contaminant particles and the need for cleaning. Item 5: 10. The method of any of the preceding items, wherein the initial flatness is determined using high voltage phase measuring interferometry. Item 6: 10. The method of any of the preceding items, further comprising determining a pre-cleaning contamination particle distribution map for the surface. Item 7: 10. The method of any of the preceding items, wherein the contaminant particle distribution map is determined using microscopy. Item 8: 10. The method of any of the preceding items, wherein the contaminant particle distribution map is determined using white light interferometry. Item 9: based on the image data of the surface, the flatness of the surface, and / or the distribution of contaminant particles on the surface; when to apply the chemical cleaning agent and / or where on the surface to apply the chemical cleaning agent; how to effect the relative movement between the cleaning tool and the surface and / or where on the surface the relative movement between the cleaning tool and the surface is effected; and / or when the organic liquid is applied and / or where on the surface the organic liquid is applied; and determining 10. The method according to any of the preceding items. Item 10: 10. The method of any of the preceding items, further comprising performing a post-cleaning uniform ion beam processing on the surface. Item 11: 10. The method of any of the preceding items, wherein the contaminant particles have already been completely removed or have been reduced to a size small enough that the uniform ion beam processing can remove the contaminant particles. Item 12: 10. The method of claim 9, further comprising determining a post-cleaning contaminant particle distribution map for the surface and comparing the post-cleaning contaminant particle distribution map to a pre-cleaning contaminant particle distribution map for the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface. Item 13: 10. The method of any of the preceding items, wherein the post-cleaning contamination particle distribution map is determined using white light interferometry. Item 14: 10. The method of claim 1, further comprising determining a post-cleaning flatness of the surface and comparing the post-cleaning flatness to an initial pre-cleaning flatness of the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface. Item 15: 10. The method of any of the preceding items, wherein the post-cleaning flatness is determined using high voltage phase measuring interferometry. Item 16: 10. The method of claim 1, wherein in response to the post-cleaning flatness breaching a flatness threshold, the method further comprises performing ion beam processing on the surface to bring the post-cleaning flatness within a flatness specification. Item 17: 10. The method of any of the preceding items, wherein the surface comprises a burl top or a portion of a burl top. Item 18: 10. The method of any of the preceding items, wherein the chemical cleaning agent comprises potassium hydroxide for tantalum contaminant particles, a chromium etchant for chromium contaminant particles, or a combination thereof. Item 19: 10. The method of any of the preceding items, wherein the cleaning tool is a glass pack. Item 20: 10. The method of claim 1, wherein the relative movement comprises a lateral movement, a serpentine movement, a circular movement, or a combination thereof. Item 21: 10. The method of any of the preceding items, wherein the object support is a clamp. Item 22: 10. The method of any of the preceding items, wherein the cleaning comprises planarizing and / or removing the contaminant particles. Item 23: 10. The method of claim 1, wherein the applying the chemical cleaning agent, the causing the relative movement, and the applying the organic liquid are performed with the clamp coupled to a chuck of the lithographic apparatus. Item 24: 10. The method of claim 1, wherein applying the chemical cleaning agent, causing the relative movement, and applying the organic liquid are performed with the clamp disconnected from a chuck of the lithographic apparatus. Item 25: 10. The method of any of the preceding items, wherein the object support and the lithographic apparatus are associated with semiconductor manufacturing. Item 26: 1. A system for cleaning an object support of a lithographic apparatus, comprising: a chemical cleaning agent configured to be applied to the surface of the object support to release contaminant particles from the surface; a cleaning tool configured to be moved relative to the surface to clean the contaminant particles from the surface; an organic liquid configured to be applied onto the surface to remove the chemical cleaning agent from the surface; A system comprising: Item 27: 10. The system of claim 1, further comprising a pre-cleaning imager configured to generate image data of the surface confirming the presence of the contaminant particles and / or one or more types of the contaminant particles. Item 28: 10. The system of claim 1, wherein the image data comprises one or more images from a microscopic examination of the surface. Item 29: 10. The system of claim 1, further comprising a computer system configured to determine an initial pre-cleaning flatness of the surface to identify the presence of contaminant particles and the need for cleaning. Item 30: the initial flatness is determined using high voltage phase measuring interferometry; the computer system is part of a high voltage phase measuring interferometer; 10. The system of any of the preceding items. Item 31: 10. The system of claim 1, further comprising a microscope configured to determine a pre-cleaning contamination particle distribution map for the surface. Item 32: 10. The system of claim 1, wherein the contaminant particle distribution map is determined using microscopy. Item 33: 10. The system of claim 1, wherein the contaminant particle distribution map is determined using white light interferometry and a white light interferometer. Item 34: based on the image data of the surface, the flatness of the surface, and / or the distribution of contaminant particles on the surface; when to apply the chemical cleaning agent and / or where on the surface to apply the chemical cleaning agent; where the relative movement between the cleaning tool and the surface is effected; and / or Where the organic liquid is to be applied; and a computer system configured to determine 10. The system of any of the preceding items. Item 35: 10. The system of any of the preceding items, further comprising an ion beam processing system configured to perform post-cleaning uniform ion beam processing on the surface. Item 36: 10. The system of claim 1, wherein the contaminant particles have already been completely removed or reduced to a size small enough that the uniform ion beam processing can remove the contaminant particles. Item 37: 10. The system of claim 9, further comprising a computer system configured to determine a post-cleaning contaminant particle distribution map for the surface and compare the post-cleaning contaminant particle distribution map against a pre-cleaning contaminant particle distribution map for the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface. Item 38: 10. The system of claim 1, wherein the post-cleaning contamination particle distribution map is determined using white light interferometry. Item 39: 10. The system of claim 9, further comprising a computer system configured to determine a post-cleaning flatness of the surface and compare the post-cleaning flatness to an initial pre-cleaning flatness of the surface to confirm that the method for cleaning was able to remove most or all of the contaminant particles from the surface. Item 40: 10. The system of claim 1, wherein the post-cleaning flatness is determined using high voltage phase measurement interferometry. Item 41: 10. The system of claim 1, wherein, in response to the post-cleaning flatness breaching a flatness threshold, ion beam processing is performed on the surface to bring the post-cleaning flatness within a flatness specification. Item 42: 10. The system of any of the preceding items, wherein the surface comprises a burl top or a portion of a burl top. Item 43: 10. The system of any of the preceding items, wherein the chemical cleaning agent comprises potassium hydroxide for tantalum contaminant particles, a chromium etchant for chromium contaminant particles, or a combination thereof. Item 44: 10. The system of any of the preceding items, wherein the cleaning tool is a glass pack. Item 45: 10. The system of claim 1, wherein the relative movement comprises a lateral movement, a serpentine movement, a circular movement, or a combination thereof. Item 46: 10. The system of claim 1, wherein the object support is a clamp. Item 47: 10. The system of claim 1, wherein the cleaning comprises planarizing and / or removing the contaminant particles. Item 48: 10. The system of claim 1, wherein applying the chemical cleaning agent, causing the relative movement, and applying the organic liquid are performed with the clamp coupled to a chuck of the lithographic apparatus. Item 49: 10. The system of claim 1, wherein applying the chemical cleaning agent, causing the relative movement, and applying the organic liquid are performed with the clamp disconnected from a chuck of the lithographic apparatus. Item 50: 10. The system of any of the preceding items, wherein the object support and the lithographic apparatus are associated with semiconductor manufacturing. Item 51: 1. A system for cleaning a reticle clamp of a lithographic apparatus, comprising: a chemical cleaning agent configured to be applied to the surface of the reticle clamp to release contaminant particles from the surface; a cleaning tool configured to move relative to the surface to clean the contaminant particles from the surface; an organic liquid configured to be applied onto the surface to remove the chemical cleaning agent from the surface; A system comprising:

[0124] The concepts disclosed herein may be associated with any general imaging system for imaging subwavelength features and are particularly useful for emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use include EUV (extreme ultraviolet), DUV lithography, which can produce wavelengths of 193 nm using ArF lasers and 157 nm using fluorine lasers. Furthermore, EUV lithography can produce wavelengths in the 20-50 nm range by using synchrotrons or by bombarding materials (solid or plasma) with high-energy electrons to generate photons within this range (20-50 nm).

[0125] While the concepts disclosed herein may be used for wafer fabrication on substrates such as silicon wafers, it is understood that the disclosed concepts may be used with any type of fabrication system, including those used for fabrication on substrates other than silicon wafers. Additionally, combinations and subcombinations of the disclosed elements may constitute separate embodiments. For example, a cleaning system and / or method and an associated lithography apparatus may constitute separate embodiments, and / or these features may be used together in the same embodiment.

[0126] The above description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications may be made to what has been described without departing from the scope of the claims set out below.

Claims

1. 1. A method for cleaning an object support of a lithographic apparatus, comprising: applying a chemical cleaning agent to the surface of the object support to release contaminant particles from the surface; providing relative movement between a cleaning tool and the surface to clean the contaminant particles from the surface; applying an organic liquid onto the surface to remove the chemical cleaning agent from the surface; A method for providing

2. 10. The method of claim 1, wherein applying the chemical cleaning agent, causing relative movement, and applying the organic liquid are performed with a clamp coupled to or disconnected from a chuck of the lithographic apparatus.

3. 1. A system for cleaning an object support of a lithographic apparatus, comprising: a chemical cleaning agent configured to be applied to the surface of the object support to release contaminant particles from the surface; a cleaning tool configured to move relative to the surface to clean the contaminant particles from the surface; an organic liquid configured to be applied onto the surface to remove the chemical cleaning agent from the surface; A system comprising:

4. a pre-cleaning imager configured to generate image data of the surface identifying the presence of the contaminant particles and / or one or more types of the contaminant particles; the image data comprises one or more images from a microscopic examination of the surface; The system of claim 3.

5. and a computer system configured to determine an initial pre-cleaning flatness of the surface to identify the presence of contaminant particles and the need for cleaning; the initial flatness is determined using high voltage phase measuring interferometry; the computer system is part of a high voltage phase measuring interferometer; The system of claim 3.

6. a microscope configured to determine a pre-cleaning contamination particle distribution map for the surface; The contaminant particle distribution map is determined using microscopy. The system of claim 3.

7. The system of claim 6 , wherein the contaminant particle distribution map is further determined using white light interferometry and a white light interferometer.

8. based on the image data of the surface, the flatness of the surface, and / or the distribution of contaminant particles on the surface; when the chemical cleaning agent is applied and / or where on the surface the chemical cleaning agent is applied; where relative movement between the cleaning tool and the surface is effected; and / or Where the organic liquid is to be applied; and a computer system configured to determine The system of claim 3.

9. an ion beam processing system configured to perform post-cleaning uniform ion beam processing on the surface; The contaminant particles have already been completely removed or have been reduced to a size small enough that the uniform ion beam processing can remove them. The system of claim 3.

10. further comprising a computer system configured to determine a post-cleaning contaminant particle distribution map for the surface and compare the post-cleaning contaminant particle distribution map against a pre-cleaning contaminant particle distribution map for the surface to confirm that cleaning was successful in removing most or all of the contaminant particles from the surface; the post-cleaning contamination particle distribution map is determined using white light interferometry; The system of claim 3.

11. further comprising a computer system configured to determine a post-cleaning flatness of the surface and compare the post-cleaning flatness to an initial pre-cleaning flatness of the surface to confirm that cleaning was successful in removing most or all of the contaminant particles from the surface; The post-cleaning flatness is determined using high voltage phase measuring interferometry. The system of claim 3.

12. 12. The system of claim 11, wherein, in response to the post-cleaning flatness breaching a flatness threshold, ion beam processing is performed on the surface to bring the post-cleaning flatness within a flatness specification.

13. the surface comprises a burl top or a portion of a burl top; the chemical cleaning agent comprises potassium hydroxide for tantalum contaminant particles, a chromium etchant for chromium contaminant particles, or a combination thereof; the cleaning tool is a glass pack; the relative movement comprises a lateral movement, a serpentine movement, a circular movement, or a combination thereof; the object support is a clamp; said cleaning comprising planarizing and / or removing said contaminant particles; the object support and the lithographic apparatus are associated with semiconductor manufacturing; The system of claim 3.

14. The system of claim 3 , wherein the object support and the lithographic apparatus are associated with semiconductor manufacturing.

15. 1. A system for cleaning a reticle clamp of a lithographic apparatus, comprising: a chemical cleaning agent configured to be applied to the surface of the reticle clamp to release contaminant particles from the surface; a cleaning tool configured to move relative to the surface to clean the contaminant particles from the surface; an organic liquid configured to be applied onto the surface to remove the chemical cleaning agent from the surface; A system comprising:

Images