Clamping system and clamping method for patterning devices in lithography apparatus

Abstract

A patterning device (e.g., a reticle) is typically clamped to a chuck of a lithography apparatus by a vacuum clamp, which drives the patterning device in the scanning direction. Acceleration for scanning the patterning device often causes helical and / or torsional deformation of the patterning device. A novel clamping system is described comprising a vacuum clamp configured to apply a clamping force to the patterning device during acceleration, and an actuator configured to apply a biasing force to the patterning device to reduce or eliminate the deformation (e.g., torsional deformation) applied to the patterning device. The actuator is configured to apply a biasing force in response to acceleration.

Description

Technical Field

[0001] (Cross - reference to related applications)

[0001] This application claims the priority of U.S. Patent Application No. 63 / 458,294, filed on April 10, 2023, the entire content of which is incorporated herein by reference.

[0002]

[0002] This specification generally relates to a clamping system and method for a patterning device in a lithographic apparatus.

Background Art

[0003]

[0003] Lithography (e.g., projection) equipment can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device (e.g., a mask) may include or provide patterns ("design layouts") corresponding to individual layers of the IC, and these patterns can be transferred to target portions (e.g., comprising one or more dies) on a substrate (e.g., a silicon wafer) coated with a layer of radiation-sensitive material ("resist") by methods such as irradiating the target portions through the patterns on the patterning device. Generally, a single substrate includes multiple adjacent target portions, and the pattern is transferred to these target portions continuously by the lithography projection equipment, one target portion at a time. In some types of lithography projection equipment, the pattern of the entire patterning device is transferred to one target portion in a single operation. Such equipment is generally referred to as a stepper. In alternative equipment, generally referred to as a step-and-scan device, a projection beam scans the patterning device in a given reference direction ("scan" direction), while simultaneously moving the substrate parallel or counter-parallel to this reference direction. Different parts of the pattern of the patterning device are gradually transferred to a single target area. Since the lithography projection device generally has a reduction ratio M (e.g., 4), the speed F at which the substrate is moved is 1 / M times the speed at which the projection beam scans the patterning device. Further information regarding the lithography devices described herein can be obtained, for example, from U.S. Patent No. 6,046,792, which is incorporated herein by reference. [Overview of the Initiative]

[0004]

[0004] A patterning device (e.g., a reticle) is typically clamped to a chuck of a lithography apparatus by a vacuum clamp to drive the patterning device in the scanning direction. Acceleration for scanning the patterning device often causes helical and / or torsional deformation of the patterning device. A novel clamping system (with corresponding methods) is described, comprising a vacuum clamp configured to apply a clamping force to the patterning device during acceleration, and an actuator configured to apply a biasing force to the patterning device to reduce or eliminate the deformation (e.g., torsional deformation) applied to the patterning device. The actuator is configured to apply a biasing force in response to acceleration.

[0005]

[0005] According to one embodiment, a clamping system is provided. The system comprises a vacuum clamp configured to clamp a patterning device by applying a clamping force to the patterning device during acceleration. The system comprises an actuator configured to reduce or eliminate deformation applied to the patterning device by applying a biasing force to the patterning device during acceleration. The actuator is configured to apply a biasing force in response to acceleration.

[0006]

[0006] In some embodiments, the biasing force is in a direction substantially perpendicular to the direction of acceleration.

[0007]

[0007] In some embodiments, the patterning device includes a reticle.

[0008]

[0008] In some embodiments, the deformation applied to the patterning device during acceleration includes torsional deformation.

[0009]

[0009] In some embodiments, the patterning device has a rectangular shape, and the vacuum clamp further comprises two supports for a first side of the patterning device and one support for a second side of the patterning device, wherein torsional deformation occurs at the second side of the patterning device, and the biasing force is configured to reduce or eliminate the torsional deformation at the second side of the patterning device.

[0010]

[0010] In some embodiments, the biasing force applied by the actuator does not suppress the deformation of the vacuum clamp due to the frictional force caused by acceleration.

[0011]

[0011] In some embodiments, the vacuum clamp includes a reticle vacuum clamp for deep ultraviolet (DUV) lithography equipment.

[0012]

[0012] In some embodiments, the actuator is configured such that the biasing force has a pressing force configured to be applied to a first portion of the patterning device and a tensile force configured to be applied to a second portion of the patterning device.

[0013]

[0013] In some embodiments, the vacuum clamp includes a vacuum pad. The actuator is configured to act on the pad so that the pad applies a biasing force to the patterning device, or the actuator is configured to act directly on the patterning device to apply a biasing force.

[0014]

[0014] In some embodiments, the actuator is a Lorentz force-based actuator. In some embodiments, the actuator is a piezo actuator.

[0015]

[0015] In some embodiments, the actuator is an air pump configured to pressurize the gap between the patterning device and the vacuum pad of the vacuum clamp, or an air pump or air bearing configured to act on the vacuum pad between the vacuum pad and the reticle chuck. In some embodiments, the air pump is configured to create a pressure gradient in the gap such that a pressing force is applied to a first portion of the patterning device and a tensile force is applied to a second portion of the patterning device. Both the pressing force and the tensile force include biasing forces.

[0016]

[0016] In some embodiments, the system comprises one or more processors. The one or more processors, configured with machine-readable instructions, determine that the patterning device is accelerating, and in response to the determination of acceleration, cause the actuator to apply a biasing force to the patterning device to reduce or eliminate the deformation applied to the patterning device.

[0017]

[0017] In some embodiments, the system includes one or more sensors configured to generate output signals that convey information about the acceleration of the patterning device. In some embodiments, one or more processors are configured to determine, based on the output signals, that the patterning device is accelerating.

[0018]

[0018] In some embodiments, the actuator comprises a rotatable coupling. In some embodiments, the rotatable coupling comprises a rotatable yoke. In some embodiments, the rotatable coupling comprises two supports configured to contact a patterning device. The rotatable coupling is configured to rotate in response to the acceleration of the patterning device.

[0019]

[0019] In one embodiment, the center of gravity reaction mass of the rotatable coupling is aligned with the pivot point reaction mass of the rotatable coupling and is separated from the pivot point reaction mass by a target distance along the axis of rotation, such that upon acceleration of the patterning device, the inertia of the rotatable coupling causes the rotatable coupling to rotate about the pivot point reaction mass and the axis of rotation, thereby counteracting deformation of the patterning device.

[0020]

[0020] According to another embodiment, a clamping method is provided. The method is performed by a clamping system and includes one or more of the operations described above.

Brief Description of the Drawings

[0021]

[0021] The accompanying drawings, which are attached to the specification and form a part of the specification, illustrate one or more embodiments and, together with the specification, explain these embodiments. Hereinafter, embodiments of the present invention will be described by way of example only with reference to the accompanying conceptual diagrams in which corresponding reference numerals indicate corresponding parts.

[0022] [Figure 1]

[0022] A lithographic apparatus according to one embodiment is schematically shown. [Figure 2]

[0023] An embodiment of a lithographic cell or cluster according to one embodiment is schematically shown. [Figure 3A]

[0024] A lithographic apparatus comprising a reticle handler turret gripper, a reticle stage reticle clamp, and / or other components according to one embodiment is shown. [Figure 3B]

[0025] An enlarged view of a part of the lithographic apparatus shown in FIG. 3A according to one embodiment is shown. [Figure 4]

[0026] A perspective view of a conventional clamping system according to one embodiment is shown. [Figure 5]

[0027] Shows a side view (in the x - direction from Figure 4) of a conventional clamping system according to an embodiment. [Figure 6]

[0028] Shows the torsion or spiral deformation of a patterning device according to an embodiment. [Figure 7]

[0029] Shows an embodiment of an example of the (present) clamping system according to an embodiment. [Figure 8]

[0030] Shows a side view (in the x - direction from Figure 7) of an embodiment of an example of the present clamping system according to an embodiment. [Figure 9]

[0031] Shows an actuator of an example of the present clamping system with a rotatable coupling according to an embodiment. [Figure 10]

[0032] Shows a clamping method according to an embodiment. [Figure 11]

[0033] Is a block diagram of an example of a computer system according to an embodiment.

Mode for Carrying Out the Invention

[0023]

[0034] Generally, a mask or reticle (e.g., a patterning device) may be a transparent, block-shaped material covered with a pattern defined by different opaque materials. Various masks are fed into a lithography apparatus and used to form layers for semiconductor devices. Clamps in the lithography apparatus (e.g., reticle stage reticle clamps) are used to hold the mask or reticle in place during processing. The clamps accelerate in the x and / or y directions, driving the reticle in the scanning direction of the lithography apparatus during processing. The reticle is typically supported by three supports protruding in the z direction from the clamps, with one support on one clamp on one side of the reticle and two supports on a second clamp on the other side of the reticle. Such a design allows the reticle to flex or bend as needed to maintain its shape. However, this design has other drawbacks, such as hindering processing accuracy because the reticle deforms spirally or twists when accelerated.

[0024]

[0035] Advantageously, the system and method suppress (e.g., reduce and / or eliminate) helical or torsional deformation during acceleration. The system and method suppress helical or torsional deformation by introducing an out-of-plane biasing z-force at a clamp with a single z-support. These biasing z-forces may be actively introduced via actuators that actively press and / or pull against the vacuum pad, or via actuators that protrude from the vacuum pad and act directly on the reticle, or they may be passively introduced by replacing one support with a rotatable yoke having two z-supports. In the passive embodiment, the center of gravity of the yoke is below the pivot of the rotatable yoke, so that during acceleration, the inertia of the yoke causes rotation around the pivot point, thereby counteracting reticle deformation as described later.

[0025]

[0036] While this specification may sometimes refer specifically to the manufacture of integrated circuits (ICs), it should be understood that the descriptions herein have many other applications. For example, they can be used in the manufacture of integrated optical systems, induction and detection patterns for magnetic domain memories, liquid crystal display panels, thin-film magnetic heads, and the like. Those skilled in the art will understand that in the context of such alternative applications, the terms “reticle,” “wafer,” or “die” used herein should be considered interchangeable with the more general terms “mask,” “substrate,” and “target portion,” respectively. Furthermore, the terms “reticle” or “mask” used herein can be considered synonymous with the more general term “patterning device.”

[0026]

[0037] As an introduction, various procedures such as priming, resist coating, and soft baking may be performed on the substrate before transferring the pattern from a patterning device such as a mask to the substrate. After exposure, other procedures such as post-exposure baking (PEB), development, hard baking, and measurement ("post-exposure procedures") and / or other inspections may be performed on the substrate. Based on this series of procedures, individual layers of a device such as an IC are fabricated. Subsequently, various treatments such as etching, ion implantation (doping), metallization, oxidation, and chemical mechanical polishing may be performed on the substrate to finish the individual layers of the device. If multiple layers are required within the device, the above procedures, in whole or in part, are repeated for each layer. Ultimately, devices will be present in each target area on the substrate. These devices are then separated from each other by methods such as dicing or sawing. Individual devices can be mounted on a carrier or connected to pins.

[0027]

[0038] Manufacturing devices such as semiconductor devices typically involves processing a substrate (e.g., a semiconductor wafer) using several fabrication processes to form various features and multiple layers of the device. Such layers and features are typically manufactured and processed using processes such as deposition, lithography, etching, chemical mechanical polishing, and ion implantation, and / or other processes. Multiple devices may be manufactured on multiple dies on a substrate and then separated into individual devices. This device manufacturing process can be considered a patterning process. A patterning process involves a patterning step, such as photolithography and / or nanoimprint lithography, which uses a patterning device in a lithography apparatus to transfer a pattern on the patterning device to the substrate, and typically, optionally, one or more related pattern processing steps, such as resist development using a developer apparatus, baking the substrate using a bake tool, and etching the pattern using an etching apparatus. A patterning process usually includes one or more metronome processes.

[0028]

[0039] Lithography is a manufacturing step in devices such as integrated circuits (ICs), where patterns formed on a substrate define the functional elements of devices such as microprocessors and memory chips. Similar lithography techniques are also used in the formation of flat panel displays, microelectromechanical systems (MEMS), and other devices.

[0029]

[0040] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements have steadily decreased. However, the number of functional elements, such as transistors, per device has steadily increased over the decades, following a trend commonly known as "Moore's Law." At current technological levels, device layers are manufactured using lithography projection equipment that projects the design layout onto a substrate using illumination from a deep ultraviolet light source, producing individual functional elements with dimensions far below 100 nm, i.e., less than half the wavelength of radiation from the light source (e.g., a 193 nm light source).

[0030]

[0041] This process, in which features with dimensions smaller than the classical resolution limit of a lithography projector are printed, is generally known as low-k1 lithography, using the resolution formula CD = k1 × λ / NA, where λ is the wavelength of radiation used (currently, in most cases, 248 nm or 193 nm), NA is the numerical aperture of the projection optical component in the lithography projector, CD is the "critical dimension" (generally the smallest feature size to be printed), and k1 is the empirical resolution coefficient. Generally, the smaller k1, the more difficult it becomes to reproduce a pattern on the substrate that resembles the shape and dimensions planned by the designer to achieve specific electrical functionality and performance. To overcome these difficulties, elaborate fine-tuning steps are applied to the lithography projector, design layout, or patterning device. These steps include, but are not limited to, optimizing NA and optical coherence settings, customized lighting systems, using phase-shift patterning devices, optical proximity effect correction (OPC, sometimes referred to as "optical and process correction") in the design layout, or other methods generally defined as "resolution enhancement techniques" (RET).

[0031]

[0042] As used herein, the term “projection optics” should be interpreted broadly to encompass various types of optical systems, including, for example, refractive optics, reflective optics, apertures, and reflective-refractory optics. The term “projection optics” may also include components that operate collectively or individually, according to any of these design types, to guide, shape, or control a radiated projection beam. The term “projection optics” may include any optical component of a lithography projection apparatus, regardless of where that optical component is located in the optical path of the lithography projection apparatus. Projection optics may include optical components for shaping, adjusting, and / or projecting radiation from a radiation source before the radiation passes through a patterning device, and / or optical components for shaping, adjusting, and / or projecting radiation after the radiation has passed through a patterning device. Projection optics generally do not include the radiation source and the patterning device.

[0032]

[0043] Figure 1 schematically shows an embodiment of a lithography apparatus LA included in and / or associated with the present system and / or method. The apparatus comprises an illumination system (illuminator) IL configured to adjust a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a support structure (e.g., mask table) MT connected to a first positioner PM constructed to support a patterning device (e.g., mask) MA and configured to precisely position the patterning device according to certain parameters; a substrate table (e.g., wafer table) WT (e.g., WTa, WTb, or both) connected to a second positioner PW configured to hold a substrate (e.g., resist-coated wafer) W and configured to precisely position the substrate according to certain parameters; and a projection system (e.g., refractive projection lens system) PS configured to project the pattern applied to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (e.g., comprising one or more dies, often referred to as a field). The projection system is supported on a reference frame RF. As shown, the apparatus is of the transmissive type (e.g., using a transmissive mask). Alternatively, the device may be of the reflective type (for example, using a programmable mirror array as described above, or using a reflective mask).

[0033]

[0044] The illuminator IL receives the radiation beam from the radiation source SO. The radiation source and the lithography apparatus may be separate entities, for example, when the radiation source is an excimer laser. In such cases, the radiation source is not considered to form part of the lithography apparatus, and the radiation beam is transmitted from the radiation source SO to the illuminator IL with the help of a beam delivery system BD, for example, equipped with a suitable guide mirror and / or beam expander. In other cases, for example, when the radiation source is a mercury lamp, the radiation source may be an integral part of the apparatus. The radiation source SO and the illuminator IL, together with the beam delivery system BD as needed, may be referred to as a radiation system.

[0034]

[0045] The illuminator IL may modify the beam intensity distribution. The illuminator may be positioned to limit the radial range of the emitted beam so that the intensity distribution is non-zero within the annular region of the pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the beam distribution in the pupil plane so that the intensity distribution is non-zero within a plurality of equally spaced sectors in the pupil plane. The intensity distribution of the emitted beam in the pupil plane of the illuminator IL may be referred to as the illumination mode.

[0035]

[0046] The illuminator IL may include an adjuster AD configured to adjust the (angle / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial ranges of the intensity distribution at the pupil plane of the illuminator (generally referred to as σ-outer and σ-inner, respectively) can be adjusted. The illuminator IL may be operable to change the angular distribution of the beam. For example, the illuminator may be operable to change the number and angular range of sectors at the pupil plane, where the intensity distribution is non-zero. Different illumination modes can be achieved by adjusting the beam intensity distribution at the pupil plane of the illuminator. For example, by limiting the radial and angular ranges of the intensity distribution at the pupil plane of the illuminator IL, the intensity distribution may have a multipolar distribution, such as a bipolar, quadrupole, or hexapole distribution. The desired illumination mode can be obtained, for example, by inserting an optical element that provides that illumination mode into the illuminator IL or by using a spatial light modulator.

[0036]

[0047] The illuminator IL may be operable to change the polarization of the beam, and may be operable to adjust the polarization using an adjuster AD. The polarization state of the radiated beam across the 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 radiated beam may be unpolarized. Alternatively, the illuminator may be configured to linearly polarize the radiated beam. The polarization direction of the radiated beam may vary across the pupil plane of the illuminator IL. The polarization direction of the radiation may differ in different regions of the pupil plane of the illuminator IL. The polarization state of the radiation may be selected depending on the illumination mode. In a multi-pole illumination mode, the polarization of each pole of the radiated beam may be approximately perpendicular to the position vector of that pole on the pupil plane of the illuminator IL. For example, in a bi-pole illumination mode, the radiation may be linearly polarized in a direction approximately perpendicular to the line that bisects the two opposing sectors of the two poles. The radiated beam may be polarized in one of two different orthogonal directions, which may be referred to as the X-polarized state and the Y-polarized state. In the quadrupole illumination mode, the radiation in each pole's sector may be linearly polarized in a direction approximately perpendicular to the line bisecting that sector. This polarization mode may be referred to as XY polarization. Similarly, in the hexapole illumination mode, the radiation in each pole's sector may be linearly polarized in a direction approximately perpendicular to the line bisecting that sector. This polarization mode may be referred to as TE polarization.

[0037]

[0048] Furthermore, the illuminator IL generally includes various other components such as an integrator IN and a capacitor 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 inducing, shaping, or controlling radiation. Thus, the illuminator provides a regulated radiation beam B having the desired uniformity and intensity distribution in its cross-section.

[0038]

[0049] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithography apparatus, and other conditions such as whether the patterning device is held in a vacuum environment. The support structure may hold the patterning device using mechanical, vacuum, electrostatic, or other clamping techniques. The support structure may be, for example, a frame or a table, which may be fixed or movable as needed. The support structure may ensure that the patterning device is in a desired position relative to, for example, the projection system.

[0039]

[0050] As used herein, the term “patterning device” should be interpreted broadly to refer to any device that can be used to impart a pattern to a target portion of a substrate. In one embodiment, the patterning device is any device that can be used to create a pattern on a target portion of a substrate by imparting a pattern to the cross-section of a radiation beam. It should be noted that the pattern imparted to the radiation beam may not precisely correspond to the desired pattern on the target portion of the substrate, for example, if the pattern includes phase-shift features or so-called assist features. Generally, the pattern imparted to the radiation beam corresponds to a specific functional layer of a device, such as an integrated circuit, that is created on the target portion of the device.

[0040]

[0051] Patterning devices can be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well-known in lithography and include mask types such as binary masks, Levenson (alternating) phase-shift masks, halftone (attenuated) phase-shift masks, and various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in a different direction. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[0041]

[0052] The projection system PS may have an optical transfer function that is non-uniform, and this non-uniformity can affect the pattern projected onto the substrate W. For unpolarized radiation, such effects can be fairly well described by two scalar maps that describe the transmission (apodization) and relative phase (aberration) of radiation emanating from the projection system PS as functions of the position within the pupil plane of the projection system PS. These scalar maps, sometimes called transmission maps and relative phase maps, can be expressed as a linear combination of an exact set of basis functions. A convenient set is the Zernike polynomials, which form a set of orthogonal polynomials defined on the unit circle. Determining each scalar map may involve determining the coefficients in such an expansion. Since the Zernike polynomials are orthogonal on the unit circle, the Zernike coefficients can be obtained by sequentially calculating the inner product of the measured scalar map and the Zernike polynomial and dividing the result by the square of the norm of the Zernike polynomial.

[0042]

[0053] The transmission map and relative phase map are field and system dependent. That is, generally, each projection system PS will have a different Zernike expansion for each field point (i.e., each spatial position in the image plane). The relative phase at the pupil plane of the projection system PS may be determined, for example, by projecting radiation from a point source through the projection system PS at the objective plane of the projection system PS (i.e., the plane of the patterning device MA) and measuring the wavefront (i.e., the trajectory of points of the same phase) using a shear interferometer. Since the shear interferometer is a common-path interferometer, it is advantageous that a secondary reference beam is not required for wavefront measurement. The shear interferometer may include a diffraction grating, such as a two-dimensional grid, at the image plane of the projection system (i.e., the substrate table WTa or WTb), and a detector positioned to detect interference patterns on 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 the shear direction coordinate at the pupil plane. The detector may include, for example, an array of sensing elements such as a charge-coupled device (CCD).

[0043]

[0054] The projection system PS of a lithography apparatus may not produce visible fringes; therefore, the accuracy of wavefront determination can be improved by using phase stepping techniques, such as moving the diffraction grating. Stepping may be performed within the plane of the diffraction grating, perpendicular to the scanning direction of the measurement. The stepping range may be one grating period, and at least three (uniformly distributed) phase steppings may be used. For example, three scan measurements may be performed in the y-direction, and separate scan measurements may be performed at different positions in the x-direction. Such stepping of the diffraction grating effectively converts phase variations into intensity variations, thereby determining the phase information. Furthermore, for detector calibration, stepping may be applied to the grating in a direction perpendicular to the diffraction grating (z-direction).

[0044]

[0055] The diffraction grating may be sequentially scanned in two perpendicular directions, which may coincide with the (x, y) axes of the projection system PS coordinate system, or may form an angle such as 45 degrees with respect to these axes. The scan may be performed over an integer of the grating period, for example, over one grating period. This scan averages the phase variation in one direction and reconstructs the phase variation in the other direction. As a result, the wavefront is determined as a function of both directions.

[0045]

[0056] The transmission (apodization) at the pupil plane of the projection system PS may be determined, for example, by projecting radiation from a point source through the projection system PS at the objective plane of the projection system PS (i.e., the plane of the patterning device MA), and measuring the intensity of the radiation at the plane conjugate to the pupil plane of the projection system PS using a detector. The same detector used for wavefront measurement to determine aberrations may also be used.

[0046]

[0057] The projection system PS may comprise multiple optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of these optical elements to correct aberrations (phase variations across the pupil plane of the entire field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements in the projection system PS in one or more different ways. The projection system may have a coordinate system, the optical axis of which extends in the z direction. The adjustment mechanism may be operable to perform any combination of the following: displacing one or more optical elements, tilting one or more optical elements, and / or deforming one or more optical elements. The displacement of an optical element may be in any direction (x, y, z, or a combination thereof). The tilt of an optical element typically moves it out of the plane perpendicular to the optical axis by rotating it about the x and / or y axes, but in the case of a non-rotationally symmetric aspherical optical element, rotation about the z axis may be used. The deformation of the optical element may include low-frequency shapes (e.g., astigmatism) and / or high-frequency shapes (e.g., free-form aspherical surfaces). The deformation of the optical element may be performed, for example, by applying force to one or more sides of the optical element using one or more actuators, and / or by heating one or more selected areas of the optical element using one or more heating elements. Generally, it would be impossible to adjust the projection system PS to correct apodization (transmission variation across the pupil plane). A transmission map of the projection system PS may be used when designing the patterning device (e.g., mask) MA of the lithography apparatus LA. Using computer lithography techniques, the patterning device MA may be designed to correct apodization at least partially.

[0047]

[0058] Lithography equipment may be of the 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 table WTa and table WTb under a projection system without a substrate, specialized for facilitating measurement and / or cleaning). In such a “multistage” machine, additional tables may be used in parallel, or preparation steps may be performed on one or more tables while one or more other tables are used for exposure at the same time. For example, alignment measurements may be performed using an alignment sensor AS, and / or level measurements (height, tilt, etc.) may be performed using a level sensor LS.

[0048]

[0059] The lithography apparatus may be of a type in which at least a portion of the substrate may be covered with a liquid having a relatively high refractive index, such as water, to fill the space between the projection system and the substrate. The immersion liquid may also be applied to other spaces in the lithography apparatus, such as between the patterning device and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of the projection system. As used herein, the term “immersion” does not mean that the structure, such as the substrate, must be submerged in the liquid, but rather that the liquid is located between the projection system and the substrate during exposure.

[0049]

[0060] During operation of the lithography apparatus, the radiant beam is regulated and supplied by the illumination system IL. The radiant beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT, and is patterned by the patterning device. After crossing the patterning device MA, the radiant beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the help of a second positioner PW and a position sensor IF (e.g., an interferometer device, a linear encoder, a 2D encoder, or a capacitive sensor), the substrate table WT can be precisely moved to position, for example, various target portions C within the path of the radiant beam B. Similarly, using a first positioner PM and another position sensor (not shown in Figure 1), the patterning device MA can be precisely positioned relative to the path of the radiant beam B, for example, after or during a machine search of a mask library. In general, the movement of the support structure MT can be achieved with the help of long-stroke modules (coarse positioning) and short-stroke modules (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate table WT can be achieved using long-stroke modules and short-stroke modules that 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 only to short-stroke actuators or may be fixed. The patterning device MA and the substrate W can be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. The illustrated substrate alignment marks occupy dedicated target portions, but the substrate alignment marks may be located in the space between the target portions (these are known as scribe line alignment marks). Similarly, in situations where two or more dies are provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0050]

[0061] The illustrated apparatus can be used in at least one of the following modes: 1. In step mode, the support structure MT and substrate table WT are kept essentially stationary, and simultaneously, the pattern applied to the projection beam is projected onto the target portion C in one pass (i.e., single static exposure). Next, the substrate table WT is shifted in the X and / or Y directions so that another target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C that is imaged during single static exposure. In scan mode, the support structure MT and substrate table WT are scanned synchronously, and simultaneously, the pattern applied to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure MT can be determined by the scaling (reduction) and image inversion characteristics of the projection system PS. 2. In scan mode, the maximum size of the exposure field limits the width of the target portion (in the non-scanning direction) during single dynamic exposure, while the length of the scan operation determines the height of the target portion (in the scanning direction). 3. In another mode, the support structure MT is kept essentially stationary, holding the programmable patterning device, and the pattern applied to the radiation beam is projected onto the target portion C simultaneously with the movement or scanning of the substrate table WT. In this mode, a pulsed radiation source is generally used, and the programmable patterning device is updated as needed after each movement of the substrate table WT or between consecutive radiation pulses during scanning. This operating mode can be readily applied to maskless lithography utilizing programmable patterning devices such as the type of programmable mirror array mentioned above. Combinations and / or variations of the above-described operating modes, or entirely different operating modes, may also be used.

[0051]

[0062] The substrate may be processed before or after exposure with, for example, a track (typically a tool for coating a layer of resist onto the substrate and developing the exposed resist), a metronome tool, or an inspection tool. Where applicable, the disclosure herein may apply to such and other substrate processing tools. Furthermore, the substrate may be processed multiple times, for example, to produce a multilayer IC, and therefore the term "substrate" as used herein may also refer to a substrate that already contains multiple processed layers.

[0052]

[0063] As used herein, the terms “radiation” and “beam” encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation or deep ultraviolet (DUV) radiation (e.g., having wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having wavelengths in the range of 5 nm to 20 nm), as well as particle beams such as ion beams or electron beams.

[0053]

[0064] The various patterns on or provided by a patterning device may have different process windows, i.e., spaces of processing variables under which patterns are generated within the specification. Examples of pattern specifications related to potential systematic defects include inspections for necking, line pullback, line thinning, critical dimension (CD), edge placement, overlap, resist top loss, resist undercut, and / or bridging. The process window of a pattern on a patterning device or in a particular area thereof may be obtained by merging (e.g., overlapping) the process windows of individual patterns. The boundary of the process window of a group of patterns comprises the boundary of some of the process windows of the individual patterns. In other words, these individual patterns limit the process window of that group of patterns. These patterns are called “hot spots” or “process window limiting patterns (PWLP),” and are used interchangeably herein. When controlling a portion of the patterning process, it is possible and economical to focus on hot spots. If there are no defects in the hot spots, it is more likely that there are no defects in the other patterns as well.

[0054]

[0065] As shown in Figure 2, the lithography apparatus LA may form part of a lithographic cell LC, sometimes referred to as a lithocell or cluster, and the lithographic cell also includes equipment for performing pre-exposure and post-exposure processes on the substrate. Conventionally, this includes one or more spin coaters SC for depositing one or more resist layers, one or more developers for developing the exposed resist, one or more cooling plates CH, and / or one or more bake plates BK. A substrate handler, i.e., a robot RO, takes one or more substrates from input / output ports I / O1 and I / O2, moves them between various process equipment, and delivers them to the loading bay LB of the lithography apparatus. These devices, often collectively referred to as tracks, are under the control of a track control unit TCU, the TCU itself is controlled by a monitoring and control system SCS, which in turn controls the lithography apparatus via a lithography control unit LACU. In this way, the various devices can be operated to maximize throughput and processing efficiency.

[0055]

[0066] To ensure that substrates exposed by a lithography apparatus are exposed accurately and consistently, and / or to monitor a part of a patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., a photolithography step), it is desirable to inspect the substrate or other objects to measure or determine one or more properties such as alignment, overlay (e.g., between structures in an overlying layer, or between structures within the same layer that are separately provided, e.g., by a double patterning process), line thickness, critical dimension (CD), focus offset, and material properties. For example, contamination on a reticle clamp film (e.g., as described herein) can adversely affect the overlay because clamping the reticle over such contamination will distort the reticle. Therefore, a manufacturing facility where a lithocell LC is located typically also includes a metrology system to measure some or all of the substrates W (Figure 1) processed in that lithocell or other objects within that lithocell. The metrology system may be part of the lithocell LC, or for example, part of the lithography apparatus LA (such as the alignment sensor AS (Figure 1)).

[0056]

[0067] One or more measured parameters may include, for example, alignment, overlays between continuous layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical linewidth) of features formed in or on the patterned substrate, focus or focus error of the photolithography step, dose or dose error of the photolithography step, optical aberration of the photolithography step, etc. This measurement is often performed on one or more dedicated metronidatory targets provided on the substrate. The measurement can be performed after resist development but before etching, after etching, after deposition, and / or at other points in time.

[0057]

[0068] There are various methods for measuring structures formed by patterning processes, including scanning electron microscopes, image-based measurement tools, and / or various specialized tools. As mentioned above, specialized metronome tools in a fast, non-invasive form work by irradiating a target on the surface of a substrate with a radiation beam and measuring the properties of the scattered (diffracted / reflected) beam. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. This is sometimes called diffraction-based metronome. One application of such diffraction-based metronome is measuring the asymmetry of features within a target. This can be used, for example, as a measure of overlay, but other applications are also known. For example, asymmetry can be measured by comparing opposing parts of the diffraction spectrum (e.g., comparing the -1st and +1st order in the diffraction spectrum of a periodic grid). Another application of diffraction-based metronome is measuring the feature width (CD) within a target.

[0058]

[0069] Thus, in device manufacturing processes (e.g., patterning or lithography processes), substrates or other objects may undergo various types of measurements during or after the process. Measurements may determine whether a particular substrate is defective, establish adjustments to the process and the equipment used in the process (e.g., aligning two layers on a substrate or aligning a patterning device to a substrate), measure the performance of the process and equipment, or be for other purposes. Examples of measurements include optical imaging (e.g., optical microscopy), non-imaging optical measurements (e.g., diffraction-based measurements such as the ASML YieldStar metrology tool and the ASML SMASH metrology system), mechanical measurements (e.g., stylus profiling, atomic force microscopy (AFM)), and / or non-optical imaging (e.g., scanning electron microscopy (SEM)).

[0059]

[0070] Metrology results may be provided directly or indirectly to the monitoring and control system (SCS). If an error is detected, adjustments may be made to the exposure of subsequent substrates and / or to the subsequent exposure of exposed substrates (especially if the inspection can be performed immediately and quickly enough to allow one or more other substrates in the same batch to still be exposed). Substrates that have already been exposed may be removed and reprocessed to improve yield or discarded, thereby avoiding further processing of substrates known to be defective. If only a portion of a target area of ​​a substrate is defective, further exposure may be performed only on the target area that meets the specifications.

[0060]

[0071] Metrology equipment is used to determine the properties of one or more substrates, in particular how the properties of one or more different substrates differ, or how different layers of the same substrate differ from layer to layer. As already mentioned, metrology equipment may be integrated with lithography equipment LA or lithocell LC, or it may be a separate device.

[0061]

[0072] To enable metrologic, one or more targets can be provided on the substrate. In one embodiment, the target is specially designed and may include a periodic structure. In one embodiment, the target is part of a device pattern, e.g., a periodic structure of the device pattern. In one embodiment, the target on the substrate may comprise one or more 1-D periodic structures (e.g., grids), which are printed such that after development, the features of the periodic structure are formed by solid resist lines. In one embodiment, the target may comprise one or more 2-D periodic structures (e.g., grids), which are printed such that after development, one or more periodic structures are formed by solid resist pillars or vias in the resist. Alternatively, these bars, pillars, or vias may be etched into the substrate (e.g., one or more layers on the substrate).

[0062]

[0073] In one embodiment, one of the parameters of interest in the patterning process is the overlay. The overlay can be measured by dark-field scatometry, which blocks zero-order diffraction (corresponding to specular reflection) and processes only higher-order diffraction. Overlay based on diffraction by dark-field detection of diffraction order enables overlay measurement for smaller targets. These targets may be smaller than the illumination spot and surrounded by device product structures on the substrate. In one embodiment, multiple targets can be measured in a single radiographic scan.

[0063]

[0074] As lithography nodes shrink, more complex wafer designs become possible. To ensure that complex designs are accurately transferred to physical wafers, designers may use a variety of tools and / or techniques. These tools and techniques may include mask optimization, source mask optimization (SMO), OPC, control design, and / or other tools and / or techniques.

[0064]

[0075] This system and / or method may be used as a standalone tool and / or technology, and / or in conjunction with other semiconductor manufacturing processes, to enhance the accurate transfer of complex designs to physical wafers.

[0065]

[0076] As described above, the clamping system comprises a vacuum clamp configured to apply a clamping force to a patterning device during acceleration associated with a lithography scan, and an actuator configured to apply a biasing force to the patterning device to reduce or eliminate deformation (e.g., torsional deformation) applied to the patterning device. The actuator is configured to apply a biasing force in response to acceleration. The patterning device may be a reticle and / or other patterning device. The vacuum clamp may include, for example, a reticle vacuum clamp for deep ultraviolet (DUV) lithography equipment.

[0066]

[0077] As an example that is not limited to a specific purpose, Figures 3A and 3B show a lithography apparatus 300 (for example, similar to and / or identical to the lithography apparatus shown in Figure 1) (or a part thereof). The lithography apparatus 300 may also pattern a substrate such as a semiconductor wafer using a patterning device such as a reticle to form a semiconductor device. Figure 3A shows various components of the lithography apparatus 300, and / or other components, including tool handlers 306, 307, 308, a reticle stage 310, and a reticle clamp 312 (only one side is visible in Figure 3A), which constitute a part of the clamp system 302. In some embodiments, the lithography apparatus 300 is configured for deep ultraviolet (DUV) lithography. In some embodiments, a similar apparatus may be configured for extreme ultraviolet (EUV) lithography. In some embodiments, the clamp system 302 comprises a reticle stage 310, a reticle clamp 312 (e.g., a vacuum clamp), an actuator (see Figures 7 to 9), or one or more processors and / or computing systems as described herein (see Figure 11), one or more (e.g., acceleration) sensors, and / or other components. These components will be described in turn below.

[0067]

[0078] In some embodiments, the tool handlers 306, 307, and 308 comprise a reticle handler turret gripper 306, a reticle handler robot gripper 307 (having associated clamps 308, etc., for gripping the reticle) and / or other components. The reticle handler robot gripper 307 may, for example, move the reticle out of the pod 320 (after, for example, the user has placed the reticle in the pod 320). The reticle handler turret gripper 306 may, for example, move the reticle from the reticle handler robot gripper 307 to the reticle clamp 312. The lithography apparatus 300 may include various other mechanical components 322 (such as transfer mechanisms, lifting mechanisms, rotating mechanisms, motors, power generation and transmission components, structural components, etc.) configured to facilitate the movement and control of the reticle through the lithography apparatus 300.

[0068]

[0079] Figure 3B is a magnified view of a portion of the lithography apparatus 300. Figure 3B shows the clamping system 302, the reticle handler turret gripper 306, the reticle stage 310, the reticle clamp 312 (only one side is visible in Figure 3B), the mechanical components 322, the reticle handler robot gripper 307, and / or other components. As shown in Figure 3B, the reticle handler turret gripper 306 is configured to allow the reticle to be clamped by the clamping system 302 by moving the reticle from the reticle handler robot gripper 307 to the reticle clamp 312. Moving the reticle includes moving the reticle horizontally, vertically, and / or away from the membrane and the clamp 312 in any direction. The reticle handler turret gripper 306 and / or the reticle handler robot gripper 307 may include various motors, translators, rotating components, clamps, clips, power sources, power transmission components, vacuum mechanisms, and / or other components to facilitate the movement of the reticle.

[0069]

[0080] Figure 4 shows a perspective view of a conventional clamping system 402 according to one embodiment. The system 402 is shown clamping a patterning device 400 such as a reticle and / or other patterning devices. The system 402 comprises a reticle clamp 412, which may be a vacuum clamp, and / or other components. The clamp 412 may have a thin zero-dure (or equivalent) membrane with a vacuum clamping pad on one side 421 (the side that clamps the patterning device 400), and the other side 423 may be attached to a chuck 425 (e.g., a short-stroke reticle stage).

[0070]

[0081] In a lithography apparatus, the clamp 412 is used to fix the patterning device 400 during processing. During acceleration 401, the reticle (vacuum) clamp 412 applies a clamping force (e.g., by vacuum) to the patterning device 400, clamping it (in the left-y direction in the example shown in Figure 4). As mentioned above, the reticle (vacuum) clamp 412 may be part of the DUV lithography apparatus. Acceleration 401 may be associated with the movement of the patterning device 400 for lithography operation. For example, Figure 4 shows the movement (scanning) direction 450 of the chuck 425 (reciprocating in the y direction in this example).

[0071]

[0082] In some embodiments, as shown in Figure 4, the patterning device 400 has a rectangular shape. The patterning device 400 is supported by three supports 409, 411, and 413 that protrude in the z direction through and / or from the clamp 412, with one support 409 at one clamp 412 on one side of the patterning device 400 and two supports 411 and 413 at a second clamp 412 on the other side of the patterning device 400.

[0072]

[0083] Figure 5 shows a side view (in the x-direction from Figure 4) of a conventional clamping system 402. The forces acting on the patterning device 400 during acceleration are shown. Figure 5 shows the reaction forces 510, 512, and 514 from supports 409, 411, and 413 acting on the (bottom) side 520 of the patterning device 400, respectively. The patterning device 400 is driven in the scanning direction (401 in Figure 4) using a frictional force 525 from a (vacuum) clamp 312 (Figure 4) that clamps the patterning device 400 on one side 520 (e.g., the reticle's reflective side) by a chuck (e.g., chuck 425 shown in Figure 4). There is an offset e between the center of gravity / point of inertia 530 of the patterning device 400 and the side 520 to which the patterning device 400 is clamped and to which the driving / scanning force is applied (via the frictional force from clamp 312). The offset e is approximately half the thickness of the patterning device 400. This generates an inertial force 535 in the opposite direction to the frictional force 525. The combined effect of these forces causes the patterning device 400 to deform in a torsional or helical direction (in this example, the x-direction) as the scan accelerates.

[0073]

[0084] Figure 6 shows an example of torsional or helical deformation 600 of the patterning device 400. As described above, the (vacuum) clamp 412 (see Figure 4) comprises two supports 411 and 413 for the first edge 602 of the patterning device 400 and one support 409 for the second edge 604 of the patterning device 400. During acceleration, torsional deformation occurs in the second edge 604 of the patterning device 400. The deformation 600 can be approximately 80 nm or more (for example) out of plane (e.g., out of plane formed by the patterning device 400) and approximately 66 nm or more (similarly, for example) in plane.

[0074]

[0085] In conventional scan operation profiles, when exposure (e.g., related to lithography) begins, the acceleration force is reduced to zero, and no scanning force acts on the patterning device 400. Despite the absence of acceleration force, the patterning device 400 often deforms in response to a setpoint in the scan process (due to its natural frequency). Conventional clamps 412 were often configured to have an attenuation function that reduces the deformation to an acceptable level before the start of the scan in order to reduce residual torsion or helical deformation. However, this has drawbacks. For example, it takes time to attenuate the deformation of the patterning device 400 to an acceptable level, which can limit the throughput of the lithography apparatus.

[0075]

[0086] To address these and other issues, more recent scan operation profiles allow the patterning device 400 to continue its acceleration phase even during exposure. However, as described above, the patterning device 400 deforms during exposure. The system and method are configured to compensate for deformation due to acceleration during exposure and / or other deformations. A clamp with a single z-support suppresses (e.g., reduces and / or eliminates) the helical or torsional deformation 600 of the patterning device during the acceleration phase by introducing an out-of-plane force.

[0076]

[0087] Figure 7 shows an example embodiment of the clamping system 302. The system 302 is shown clamping a patterning device 700, such as a reticle, and / or other patterning devices. For simplification and to facilitate the following explanation, Figure 7 shows the patterning device 700 as a single material block in the shape of a right-angle prism. In some embodiments, part or all of the patterning device 700 may be formed from an opaque, transparent or semi-transparent material such as ultra-low thermal expansion quartz (SFS), a transparent material such as glass, an opaque material such as metal, a polymer, ceramics, and / or other material. Any number of materials can be used to fabricate the patterning device 700.

[0077]

[0088] System 302 comprises a reticle clamp 312, an actuator 702, and / or other components. The clamp 312 may be, for example, a vacuum clamp. The clamp 312 may have a thin zero-dure (or equivalent) membrane with a vacuum clamp pad on one side (the side that clamps the patterning device 700), and the other side may be attached to a chuck 725 (e.g., a short-stroke reticle stage). In some embodiments, the clamp system 302 includes and / or is configured to communicate with one or more sensors, one or more processors as described below, and / or a computing system (see Figure 11), and / or other components. The various components of the clamp system 302 may be connected in any arrangement using any coupling components to make the clamp system 302 function as described herein.

[0078]

[0089] The patterning device 700 is fixed by a clamp 312 during processing in a lithography apparatus (see Figures 3A to 3B). During acceleration (in the left or right-y direction in the example shown in Figure 7), a clamping force (e.g., by vacuum) is applied to the patterning device 700 by the reticle (vacuum) clamp 312, thereby clamping the patterning device 700. As mentioned above, the reticle (vacuum) clamp 312 may be part of the DUV lithography apparatus. Acceleration may be associated, for example, with the movement of the patterning device for lithography operation.

[0079]

[0090] The patterning device 700 is supported by three supports 710, 712, and 714 that protrude in the z direction through and / or from the clamp 312, one support 710 at one clamp 312 on one side of the patterning device 700 and two supports 712 and 714 at the second clamp 312 on the other side of the patterning device 700. As described above, in this design as well, the patterning device 700 can bend and flex as needed to maintain its shape.

[0080]

[0091] The clamping system 302 is configured to suppress (e.g., reduce and / or eliminate) helical or torsional deformation (see Figure 6) of the patterning device 700 during acceleration. The actuator 702 is configured to suppress helical or torsional deformation by introducing out-of-plane biasing z forces 750 and 752 to the clamp 312, which has a single z support 710. These biasing z forces 750 and 752 may be actively introduced via the actuator 702 by actively pressing and / or pulling on the vacuum pad of the clamp 312, or by protruding from the vacuum pad and acting directly on the patterning device 700. These biasing z forces 750 and 752 may be passively introduced by replacing one support 710 with a rotatable yoke having two z supports (for example, as shown in Figure 9 below).

[0081]

[0092] The actuator 702 is configured to apply a biasing force (e.g., out-of-plane biasing z forces 750 and 752) in response to acceleration. As shown in Figure 7, the out-of-plane biasing z forces 750 and 752 (e.g., biasing forces) may be in the z direction substantially perpendicular to the y direction of acceleration (left or right in this figure). The actuator 702 may comprise a motor, one or more movable biasing elements, a pump, one or more processors (e.g., which may function as controllers for the actuator), electrical components, and / or other components. For example, in some embodiments, the actuator 702 may be, and / or include, a Lorentz force-based actuator, a piezo actuator, an air pump, an air bearing, a rotatable coupling (e.g., as shown in Figure 9 and below), and / or other actuators.

[0082]

[0093] In some embodiments, as shown in Figure 7, the patterning device 700 has a rectangular shape, and the (vacuum) clamp 312 comprises two supports 712, 714 for the first side 760 of the patterning device 700 and one support 710 for the second side 762 of the patterning device 700, wherein torsional deformation occurs on the second side 762 of the patterning device 700, and biasing forces (e.g., out-of-plane biasing forces z-forces 750 and 752) are configured to reduce or eliminate the torsional deformation occurring on the second side 762 of the patterning device 700. In some embodiments, the (vacuum) clamp 312 comprises a vacuum pad, and the actuator 702 is configured to act on the pad so that the pad applies a biasing force to the patterning device 700. In some embodiments, the actuator 702 is configured to act directly on the patterning device 700 to apply a biasing force.

[0083]

[0094] In some embodiments, as shown in Figure 7, the actuator 702 is configured to have a biasing force of a pressing (biasing z) force 750 configured to be applied to a first portion 780 of the patterning device 700, and a tensile (biasing z) force 752 configured to be applied to a second portion 782 of the patterning device 700. For example, the actuator 702 may be an air pump configured to pressurize the gap between the patterning device 700 and the vacuum pad of the (vacuum) clamp 312. In another example, the actuator 702 may be an air pump or air bearing configured to act on the vacuum pad between the vacuum pad and a reticle chuck (e.g., chuck 725). The air pump may be configured to create a pressure gradient in the gap such that a pressing (biasing z) force 750 is applied to the first portion 780 of the patterning device 700 and a tensile (biasing z) force 752 is applied to the second portion 782 of the patterning device 700. For example, both the compressive force 750 and the tensile force 752 may include biasing forces.

[0084]

[0095] In some embodiments, one or more processors (see Figure 11) are operably coupled to the actuator 702 and configured to determine that the patterning device 700 is accelerating (in this example, in the y-direction). The one or more processors may also, in response to the determination of acceleration, cause the actuator 702 to apply a biasing force (e.g., 750, 752) to the patterning device 700 to reduce or eliminate deformation (e.g., torsional or helical) applied to the patterning device 700. For example, one or more sensors included in the lithography apparatus may generate an output signal that conveys information regarding the acceleration of the patterning device 700. The one or more sensors may include, for example, one or more accelerometers and / or other sensors. The one or more processors may be configured to determine that the patterning device 700 is accelerating based on the output signal and / or other information. In some embodiments, the one or more processors may determine that the patterning device 700 is accelerating based on instructions and / or commands and / or other information provided and / or associated with the lithography apparatus.

[0085]

[0096] In some embodiments, one or more processors and / or one or more sensors may be associated with control software included in and / or running on a lithography apparatus 300 (Figures 3A to 3B), for example. One or more processors are configured with machine-readable instructions. Communication may be wired and / or wireless, for example, as described below (in conjunction with Figure 11). One or more processors can facilitate the reception of control commands from a user via a user interface. These control commands may be received in real time or near real time. In some embodiments, control commands include adjustments to the scan movement profile, e.g., forces applied by actuator 702, and / or other control commands.

[0086]

[0097] Figure 8 shows a side view (in the x-direction from Figure 7) of an example embodiment 801 of the actuator 702 (Figure 7) of the clamp system 302 (Figure 7). Figure 8 shows the pressure gradients of +800 and -800 between the lower surface of the vacuum pad of the (vacuum) clamp 312 and the chuck 725. The pressure gradients of +800 and -800 are configured to apply counterforces / torques 810 and 812 to the patterning device 700 to suppress deformation of the patterning device 700 during acceleration. The acceleration corresponds to the movement (scanning) direction 850 of the chuck 725 (reciprocating in the y-direction in this example). In this example, the actuator 702 may be formed by, for example, an air pump.

[0087]

[0098] The offset f between the center of gravity / point of inertia 860 of the patterning device 700 and the (bottom) side 870 to which the patterning device 700 is clamped and to which the driving / scanning force is applied (via frictional force from the clamp 312) is shown. The offset f is again approximately half the thickness of the patterning device 700. However, the pressure gradients +800 and -800 are configured to counteract forces that may cause torsional or helical (in this example, x-direction) deformation of the patterning device 700 during scanning acceleration.

[0088]

[0099] Figure 9 shows an embodiment 900 of another example of the actuator 702 (Figure 7) of the clamp system 302 (Figure 7). Embodiment 900 comprises a rotatable coupling 902 and / or other components. The rotatable coupling 902 includes a rotatable yoke, as shown, for example, in Figure 9. In some embodiments, the rotatable coupling 902 (e.g., the rotatable yoke) comprises two supports 904 and 906 configured to contact the patterning device 700. The rotatable coupling 902 is configured to rotate in response to the acceleration of the patterning device 700 (e.g., without requiring a processor and / or sensors). For example, the center of gravity reaction mass 910 of the rotatable coupling 902 may be aligned with the pivot point reaction mass 912 of the rotatable coupling 902 and may be located a target distance 914 from the pivot point reaction mass 912 along the axis of rotation 916. When the patterning device 700 is accelerated, the inertia of the rotatable coupling 902 counteracts the deformation of the patterning device by rotating the rotatable coupling 902 around the pivot point reaction mass 912 and the rotation axis 916. For this reason, in this embodiment 900 as well, the actuator 702 is configured to apply a biasing force in response to acceleration.

[0089]

[0100] Figure 10 shows clamping method 1001. For example, as described above, method 1001 may be carried out by a clamping system. In some embodiments, the clamping system includes and / or is configured to communicate with one or more processors and / or computing systems, as described later (see Figure 11). The operation of method 1001 shown below is intended to be illustrative. In some embodiments, method 1001 may be achieved by one or more additional operations not described, and / or without one or more operations not described. Also, the order of operations of method 1001 shown in Figure 10 and described below is not intended to be limiting.

[0090]

[0101] In some embodiments, one or more parts of Method 1001 are implemented 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 that process information electronically, as described with respect to Figure 11 below). One or more processing devices may include one or more devices that perform some or all of the operations of Method 1001 in response to instructions electronically stored in an electronic storage medium. 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 operations of Method 1001 (see, for example, the description with respect to Figure 11 below). For example, one or more processing devices may detect acceleration of a patterning device based on information from a sensor output signal and apply a biasing force to an actuator.

[0091]

[0102] In operation 1002, a clamping force is applied to the patterning device with a vacuum clamp during acceleration to clamp the patterning device. The patterning device may be a reticle and / or other patterning device. The vacuum clamp may be part of the lithography apparatus. In some embodiments, the lithography apparatus is configured for DUV or EUV radiation. For example, the vacuum clamp may include a reticle vacuum clamp for deep ultraviolet (DUV) lithography apparatus. Acceleration may be associated with, for example, the movement of the patterning device for lithography operation. In some embodiments, operation 1002 is performed by a vacuum clamp and / or other components of the lithography apparatus, similar to and / or identical to the vacuum clamps described in Figures 3A to 3B, Figure 7, Figure 8, etc. and herein.

[0092]

[0103] Operation 1004 includes applying a biasing force to the patterning device with an actuator during acceleration to reduce or eliminate deformation (e.g., torsional deformation and / or other deformation) applied to the patterning device. The actuator is configured to apply a biasing force in response to acceleration. The biasing force may be in a direction substantially perpendicular to the direction of acceleration. In some embodiments, the actuator is the same as or similar to the actuators described herein, as shown in Figures 7 to 8 and / or Figure 9. For example, the actuator may be a Lorentz force-based actuator, a piezo actuator, an air pump, an air bearing, a rotatable coupling, and / or other actuators.

[0093]

[0104] In some embodiments, the patterning device has a rectangular shape, and the vacuum clamp comprises two supports for a first side of the patterning device and one support for a second side of the patterning device, wherein torsional deformation occurs at the second side of the patterning device, and the biasing force is configured to reduce or eliminate the torsional deformation at the second side of the patterning device. In some embodiments, the vacuum clamp comprises a vacuum pad, and the actuator is configured to act on the pad so that the pad applies a biasing force to the patterning device, or the actuator is configured to act directly on the patterning device to apply a biasing force.

[0094]

[0105] In some embodiments, the actuator is configured to have a biasing force that includes a pressing force configured to be applied to a first portion of the patterning device and a tensile force configured to be applied to a second portion of the patterning device. For example, the actuator may be an air pump configured to pressurize the gap between the patterning device and the vacuum pad of a vacuum clamp, or an air pump or air bearing configured to act on the vacuum pad between the vacuum pad and the reticle chuck. The air pump may be configured to create a pressure gradient in the gap such that a pressing force is applied to the first portion of the patterning device and a tensile force is applied to the second portion of the patterning device. Note that, for example, both the pressing force and the tensile force may include a biasing force.

[0095]

[0106] In some embodiments, operation 1004 includes one or more processors, configured with machine-readable instructions, determining that the patterning device is accelerating. In response to the determination of acceleration, one or more processors may cause actuators to apply a biasing force to the patterning device to reduce or eliminate the deformation applied to the patterning device. For example, one or more sensors may generate output signals that convey information about the acceleration of the patterning device. One or more processors may be configured to determine that the patterning device is accelerating based on the output signals and / or other information.

[0096]

[0107] In some embodiments, the actuator comprises a rotatable coupling. The rotatable coupling may include, for example, a rotatable yoke. In some embodiments, the rotatable coupling (e.g., a rotatable yoke) comprises two supports configured to contact a patterning device. The rotatable coupling is configured to rotate in response to the acceleration of the patterning device (e.g., without requiring a processor and / or sensors). For example, the center of gravity reaction mass of the rotatable coupling may be aligned with the pivot point reaction mass of the rotatable coupling and a target distance from the pivot point reaction mass along the axis of rotation, so that when the patterning device accelerates, the inertia of the rotatable coupling causes the rotatable coupling to rotate around the pivot point reaction mass and the axis of rotation, thereby counteracting deformation of the patterning device.

[0097]

[0108] Figure 11 is a block diagram showing a computer system 1100 that can assist in the implementation of the methods, flows, and systems disclosed herein. The computer system 1100 includes a bus 1102 or other communication mechanism for communicating information and a processor 1104 (or a plurality of processors 1104 and 1105) connected to the bus 1102 for processing information. The computer system 1100 also includes a main memory 1106, such as random access memory (RAM), or other dynamic storage device connected to the bus 1102 for storing information and instructions executed by the processor 1104. The main memory 1106 is also used to store temporary variables or other intermediate information during the execution of instructions executed by the processor 1104. The computer system 1100 further includes a read-only memory (ROM) 1108 or other static storage device connected to the bus 1102 for storing static information and instructions for the processor 1104. A storage device 1110, such as a magnetic disk or optical disk, is provided on the bus 1102 and is connected to it for storing information and instructions.

[0098]

[0109] The computer system 1100 may be connected via a bus 1102 to a display 1112, such as a cathode ray tube (CRT), flat panel, or touch panel display, for displaying information to the computer user. An input device 1114, including alphabet and other keys, is connected to the bus 1102 to transmit information and command selections to the processor 1104. Another type of user input device is a cursor control unit 1116, such as a mouse, trackball, or cursor directional keys, for transmitting directional information and command selections to the processor 1104 and controlling cursor movement on the display 1112. Such input devices typically have two degrees of freedom along two axes: a first axis (e.g., x) and a second axis (e.g., y), which allow the device to determine its position in a plane. A touch panel (screen) display may also be used as an input device.

[0099]

[0110] In one embodiment, one or more flows and / or portions of methods described herein may be performed by a computer system 1100 in response to a processor 1104 executing one or more sequences of one or more instructions contained in main memory 1106. Such instructions may be read into main memory 1106 from another computer-readable medium, such as a storage device 1110. The processor 1104 performs the flows and / or processing steps described herein by executing the sequence of instructions contained in main memory 1106. One or more processors in a multiprocessing arrangement may be employed to execute the sequence of instructions contained in main memory 1106. In other embodiments, hard-wired circuits may be used instead of or in conjunction with software instructions. Therefore, the contents described herein are not limited to any particular combination of hardware circuits and software.

[0100]

[0111] As used herein, the terms “computer-readable medium” or “machine-readable medium” mean any medium involved in providing instructions for execution to the processor 1104. Such mediums can take many forms, including, but are not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks such as the storage device 1110. Volatile media include dynamic memory such as the main memory 1106. Transmission media include coaxial cables, copper wires, and fiber optic components, including wiring with a bus 1102. Transmission media can also take the form of sound waves or light waves, such as those generated in radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tapes, and other magnetic media, CD-ROMs, DVDs, and other optical media, punch cards, paper tapes, and other media with physical hole patterns, RAM, PROMs, EPROMs, FLASH-EPROMs, and other memory chips or cartridges, carrier waves as described below, or other computer-readable media.

[0101]

[0112] Various forms of computer-readable media may be involved in transmitting one or more sequences of one or more instructions to the processor 1104 for execution. For example, the instructions may initially be transmitted by a magnetic disk of a remote computer. The remote computer can load these instructions into its dynamic memory and send them over a telephone line using a modem. A modem local to computer system 1100 can receive data over the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector connected to bus 1102 can receive the data transmitted by the infrared signal and place the data on bus 1102. Bus 1102 transmits the data to main memory 1106, and the processor 1104 retrieves the instructions from main memory 1106 and executes them. Instructions received by main memory 1106 may optionally be stored in storage device 1110 before or after execution by processor 1104.

[0102]

[0113] The computer system 1100 may also include a communication interface 1118 connected to the bus 1102. The communication interface 1118 provides bidirectional data communication coupling to a network link 1120 connected to a local network 1122. For example, the communication interface 1118 may be an Integrated Services Digital Network (ISDN) card or modem that provides data communication connectivity to a corresponding type of telephone line. Alternatively, the communication interface 1118 may be a local area network (LAN) card that provides data communication connectivity to a compatible LAN. It may also be implemented by a wireless link. In such implementations, the communication interface 1118 transmits and receives electrical, electromagnetic, or optical signals that convey digital data streams representing various types of information.

[0103]

[0114] The network link 1120 typically provides data communication to other data devices through one or more networks. For example, the network link 1120 may provide connectivity to a host computer 1124 or data equipment operated by an Internet service provider (ISP) 1126 via a local network 1122. The ISP 1126 then provides data communication services via a global packet data communication network commonly referred to today as the "Internet" 1128. Both the local network 1122 and the Internet 1128 use electrical, electromagnetic, or optical signals to transmit digital data streams. Signals across various networks, signals on the network link 1120, and signals via the communication interface 1118 are exemplary forms of information-carrying carriers that transmit digital data to and from the computer system 1100.

[0104]

[0115] The computer system 1100 can send messages and receive data, including program code, via a network, network link 1120, and communication interface 1118. In the case of the Internet, server 1130 may also transmit the code of a requested application program via the Internet 1128, ISP 1126, local network 1122, and communication interface 1118. One such download application may, for example, provide all or part of the method described herein. The received code may be executed by processor 1104 as received and / or stored in storage device 1110 or other non-volatile storage for later execution. In this way, the computer system 1100 may obtain the application code in carrier form.

[0105]

[0116] Various embodiments of the system and method are disclosed in the following list of numbered clauses. 1. A clamping system comprising: a vacuum clamp configured to clamp a patterning device by applying a clamping force to the patterning device during acceleration; and an actuator configured to reduce or eliminate deformation applied to the patterning device by applying a biasing force to the patterning device during acceleration, and to apply a biasing force in response to acceleration. 2. The biasing force is in a direction substantially perpendicular to the direction of acceleration, as described in Clause 1. 3. The patterning device is a system described in any of clauses 1 or 2, comprising a reticle. 4. The deformation applied to the patterning device during acceleration includes torsional deformation, as described in any of the systems described in Clauses 1 to 3. 5. The system according to any one of Clauses 1 to 4, wherein the patterning device has a rectangular shape, and the vacuum clamp further comprises two supports for a first side of the patterning device and one support for a second side of the patterning device, wherein torsional deformation occurs at the second side of the patterning device, and the biasing force is configured to reduce or eliminate the torsional deformation at the second side of the patterning device. 6. The system described in any of clauses 1 to 5, wherein the biasing force applied by the actuator does not suppress deformation of the vacuum clamp due to frictional force caused by acceleration. 7. The vacuum clamp is a system as described in any of clauses 1 to 6, including a reticle vacuum clamp for deep ultraviolet (DUV) lithography equipment. 8. The system according to any one of the clauses 1 to 7, wherein the actuator is configured to have a biasing force comprising a pressing force configured to be applied to a first part of the patterning device and a tensile force configured to be applied to a second part of the patterning device. 9. The system according to any one of Clauses 1 to 8, wherein the vacuum clamp comprises a vacuum pad, and the actuator is configured to act on the pad so that the pad applies a biasing force to a patterning device, or the actuator is configured to act directly on the patterning device to apply a biasing force. 10. The actuator is a Lorentz force-based actuator, as described in any of the systems described in clauses 1 through 9. 11. The actuator is a piezo actuator, as described in any of the systems described in clauses 1 through 10. 12. The system according to any one of Clauses 1 to 11, wherein the actuator is an air pump configured to pressurize the gap between the patterning device and the vacuum pad of the vacuum clamp, or an air pump or air bearing configured to act on the vacuum pad between the vacuum pad and the reticle chuck. 13. The system according to any one of Clauses 1 to 12, wherein the air pump is configured to create a pressure gradient in the gap such that a compressive force is applied to a first portion of the patterning device and a tensile force is applied to a second portion of the patterning device, and both the compressive and tensile forces include a biasing force. 14. The system according to any one of the clauses 1 to 13, further comprising one or more processors configured to determine, by machine-readable instructions, that a patterning device is accelerating, and in response to the determination of acceleration, to cause an actuator to apply a biasing force to the patterning device in order to reduce or eliminate the deformation applied to the patterning device. 15. The system according to any one of the clauses 1 to 14, further comprising one or more sensors configured to generate an output signal that transmits information regarding the acceleration of a patterning device. 16. One or more processors are configured to determine, based on an output signal, that the patterning device is accelerating, as described in any of the systems described in clauses 1 to 15. 17. The actuator is a system according to any one of the clauses 1 to 16, comprising a rotatable coupling. 18. A rotatable coupling is a system described in any of clauses 1 to 17, including a rotatable yoke. 19. The system according to any one of the clauses 1 to 18, wherein the rotatable coupling comprises two supports configured to contact a patterning device, and the rotatable coupling is configured to rotate in response to the acceleration of the patterning device. 20. The system according to any one of Clauses 1 to 19, wherein the center of gravity reaction mass of the rotatable coupling is aligned with the pivot point reaction mass of the rotatable coupling and is located at a target distance from the pivot point reaction mass along the axis of rotation, so that when the patterning device is accelerated, the inertia of the rotatable coupling causes the rotatable coupling to rotate around the pivot point reaction mass and the axis of rotation, thereby counteracting deformation of the patterning device. 21. A clamping method comprising: clamping a patterning device by applying a clamping force to the patterning device with a vacuum clamp during acceleration; and reducing or eliminating deformation applied to the patterning device by applying a biasing force to the patterning device with an actuator configured to apply a biasing force to the patterning device in response to acceleration during acceleration. 22. The method according to Clause 21, wherein the biasing force is in a direction substantially perpendicular to the direction of acceleration. 23. A patterning device comprising a reticle, according to any of the methods described in clauses 21 to 22. 24. The deformation applied to the patterning device during acceleration includes torsional deformation, as described in any of the methods in clauses 21 to 23. 25. The method according to any one of the clauses 21 to 24, wherein the patterning device has a rectangular shape, and the vacuum clamp comprises two supports for a first side of the patterning device and one support for a second side of the patterning device, wherein torsional deformation occurs at the second side of the patterning device, and the biasing force is configured to reduce or eliminate the torsional deformation at the second side of the patterning device. 26. The method according to any one of the clauses 21 to 25, wherein the biasing force applied by the actuator does not suppress deformation of the vacuum clamp due to frictional force caused by acceleration. 27. Vacuum clamps, including reticle vacuum clamps for deep ultraviolet (DUV) lithography apparatus, as described in any of clauses 21 to 26. 28. The method according to any one of the clauses 21 to 27, wherein the actuator is configured to have a biasing force having a pressing force configured to be applied to a first part of the patterning device and a tensile force configured to be applied to a second part of the patterning device. 29. The method according to any one of the clauses 21 to 28, wherein the vacuum clamp comprises a vacuum pad, and the actuator is configured to act on the pad so that the pad applies a biasing force to a patterning device, or the actuator is configured to act directly on the patterning device to apply a biasing force. 30. The actuator is a Lorentz force-based actuator, as described in any of clauses 21 to 29. 31. The actuator is a piezo actuator, as described in any of clauses 21 to 30. 32. The method according to any one of the clauses 21 to 31, wherein the actuator is an air pump configured to pressurize the gap between the patterning device and the vacuum pad of the vacuum clamp, or an air pump or air bearing configured to act on the vacuum pad between the vacuum pad and the reticle chuck. 33. The air pump is configured to create a pressure gradient in the gap such that a pressing force is applied to a first portion of the patterning device and a tensile force is applied to a second portion of the patterning device, the method according to any one of the clauses 21 to 32, wherein both the pressing force and the tensile force include a biasing force. 34. The method according to any one of the clauses 21 to 33, further comprising one or more processors comprising machine-readable instructions determining that a patterning device is accelerating, and in response to the determination of acceleration, causing an actuator to apply a biasing force to the patterning device to reduce or eliminate the deformation applied to the patterning device. 35. The method according to any one of the clauses 21 to 34, further comprising one or more sensors generating an output signal that conveys information regarding the acceleration of the patterning device. 36. The method according to any one of the clauses 21 to 35, wherein one or more processors are configured to determine, based on an output signal, that the patterning device is accelerating. 37. The actuator comprising a rotatable coupling, according to any one of the methods in clauses 21 to 36. 38. The method according to any one of the clauses 21 to 37, wherein the rotatable coupling includes a rotatable yoke. 39. The method according to any one of the clauses 21 to 38, wherein the rotatable coupling comprises two supports configured to contact a patterning device, and the rotatable coupling is configured to rotate in response to the acceleration of the patterning device. 40. The method according to any one of the clauses 21 to 39, wherein the center of gravity reaction mass of the rotatable coupling is aligned with the pivot point reaction mass of the rotatable coupling and is located at a target distance from the pivot point reaction mass along the axis of rotation, and as a result, when the patterning device is accelerated, the inertia of the rotatable coupling causes the rotatable coupling to rotate around the pivot point reaction mass and the axis of rotation, thereby counteracting deformation of the patterning device.

[0106]

[0117] The concepts disclosed herein may be associated with general imaging systems for imaging arbitrary subwavelength features, and may be particularly useful in conjunction with emerging imaging technologies that can produce increasingly shorter wavelengths. Emerging technologies already in use include extreme ultraviolet (EUV) lithography and DUV lithography, which can produce wavelengths of 193 nm using ArF lasers and even 157 nm using fluorine lasers. EUV lithography can produce photons in the 20–5 nm range by using a synchrotron or by colliding high-energy electrons with material (solid or plasma).

[0107]

[0118] The concepts disclosed herein can be used in wafer manufacturing on substrates such as silicon wafers, but it is understood that the disclosed concepts can also be used in any type of manufacturing system, including those used for manufacturing on substrates other than silicon wafers. Furthermore, combinations and subcombinations of the disclosed elements can constitute separate embodiments. For example, an inspection system and associated software can constitute separate embodiments, and / or these features may be used together in the same embodiment.

[0108]

[0119] The above description is illustrative and not limiting. Therefore, it will be apparent to those skilled in the art that modifications can be made as described below without departing from the claims.

Claims

1. A clamp configured to apply a clamping force to a patterning device during acceleration to clamp the patterning device, An actuator configured to apply a biasing force to the patterning device during acceleration to reduce deformation applied to the patterning device, and to apply the biasing force in response to the acceleration, A clamping system equipped with the following features.

2. The biasing force is in a direction substantially perpendicular to the direction of acceleration. The patterning device includes a reticle, The deformation applied to the patterning device during acceleration includes torsional deformation. The patterning device has a rectangular shape, The clamp further comprises two supports for the first side of the patterning device and one support for the second side of the patterning device. The aforementioned torsional deformation occurs at the second edge of the patterning device. The system according to claim 1, wherein the biasing force is configured to reduce the torsional deformation at the second edge of the patterning device.

3. The biasing force applied by the actuator does not suppress the deformation of the clamp caused by the frictional force resulting from the acceleration. The clamp includes a reticle vacuum clamp for deep ultraviolet (DUV) lithography equipment. The system according to claim 1, wherein the actuator is configured to have a pressing force configured to be applied to a first portion of the patterning device and a tensile force configured to be applied to a second portion of the patterning device.

4. The clamp is equipped with a vacuum pad, The actuator is configured to act on the pad so that the pad applies the biasing force to the patterning device, or to act directly on the patterning device to apply the biasing force. The system according to claim 1, wherein the actuator is a Lorentz force-based actuator or a piezo actuator.

5. The actuator is an air pump configured to pressurize the gap between the patterning device and the vacuum pad of the clamp, or an air pump or air bearing configured to act on the vacuum pad between the vacuum pad and the reticle chuck. The air pump is configured to create a pressure gradient in the gap such that a pressing force is applied to the first portion of the patterning device and a tensile force is applied to the second portion of the patterning device. The system according to claim 1, wherein both the pressing force and the tensile force include the biasing force.

6. One or more processors configured to determine that the patterning device is accelerating by being composed of machine-readable instructions, and in response to the determination of acceleration, to instruct the actuator to apply the biasing force to the patterning device to reduce the deformation applied to the patterning device, The system further comprises one or more sensors configured to generate an output signal that transmits information regarding the acceleration of the patterning device, The system according to claim 1, wherein one or more processors are configured to determine, based on the output signal, that the patterning device is accelerating.

7. The actuator is equipped with a rotatable coupling, The rotatable coupling includes a rotatable yoke, The rotatable coupling comprises two supports configured to contact the patterning device, The rotatable coupling is configured to rotate in response to the acceleration of the patterning device, The system according to claim 1, wherein the center of gravity reaction mass of the rotatable coupling is aligned with the pivot point reaction mass of the rotatable coupling and is located at a target distance from the pivot point reaction mass along the axis of rotation, and as a result, when the patterning device is accelerated, the rotatable coupling rotates around the pivot point reaction mass and the axis of rotation due to the inertia of the rotatable coupling, thereby counteracting deformation of the patterning device.

8. The process involves applying a clamping force to the patterning device with a clamp during acceleration to clamp the patterning device, The method involves applying a biasing force to the patterning device using an actuator configured to apply a biasing force to the patterning device in response to the acceleration, thereby reducing the deformation applied to the patterning device, A clamping method, including the following.

9. The biasing force is in a direction substantially perpendicular to the direction of acceleration. The patterning device includes a reticle, The deformation applied to the patterning device during acceleration includes torsional deformation. The patterning device has a rectangular shape, The clamp further comprises two supports for the first side of the patterning device and one support for the second side of the patterning device. The aforementioned torsional deformation occurs at the second edge of the patterning device. The method according to claim 8, wherein the biasing force is configured to reduce the torsional deformation at the second edge of the patterning device.

10. The biasing force applied by the actuator does not suppress the deformation of the clamp caused by the frictional force resulting from the acceleration. The clamp includes a reticle vacuum clamp for deep ultraviolet (DUV) lithography equipment. The method according to claim 8, wherein the actuator is configured to have a pressing force configured to be applied to a first portion of the patterning device and a tensile force configured to be applied to a second portion of the patterning device.

11. The clamp is equipped with a vacuum pad, The actuator is configured to act on the pad so that the pad applies the biasing force to the patterning device, or to act directly on the patterning device to apply the biasing force. The method according to claim 8, wherein the actuator is a Lorentz force-based actuator or a piezo actuator.

12. The actuator is an air pump configured to pressurize the gap between the patterning device and the vacuum pad of the clamp, or an air pump or air bearing configured to act on the vacuum pad between the vacuum pad and the reticle chuck. The air pump is configured to create a pressure gradient in the gap such that a pressing force is applied to the first portion of the patterning device and a tensile force is applied to the second portion of the patterning device. The method according to claim 8, wherein the pressing force and the tensile force both include the biasing force.

13. One or more processors composed of machine-readable instructions determine that the patterning device is accelerating, and in response to the determination of acceleration, instruct the actuator to apply the biasing force to the patterning device to reduce the deformation applied to the patterning device. The system includes one or more sensors generating an output signal that transmits information regarding the acceleration of the patterning device, The method according to claim 8, wherein the one or more processors are configured to determine, based on the output signal, that the patterning device is accelerating.

14. The actuator is equipped with a rotatable coupling, The rotatable coupling includes a rotatable yoke, The rotatable coupling comprises two supports configured to contact the patterning device, The rotatable coupling is configured to rotate in response to the acceleration of the patterning device, The method according to claim 8, wherein the center of gravity reaction mass of the rotatable coupling is aligned with the pivot point reaction mass of the rotatable coupling and is located at a target distance from the pivot point reaction mass along the axis of rotation, and as a result, when the patterning device is accelerated, the rotatable coupling rotates around the pivot point reaction mass and the axis of rotation due to the inertia of the rotatable coupling, thereby counteracting deformation of the patterning device.

Images