System and method for thermal contact modulation between object and clamp

Abstract

An object clamping system includes an object support structure, a clamp, a gas supply system, and a controller. The clamp is coupled to the object support structure and supports an object on the object support structure. The clamp defines a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact. The gas supply system supplies a backfill gas to the gap. The controller controls the gas supply system and adjusts a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap such that the object remains in a saturated state. The controller dynamically adjusts the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from a radiation source or a radiation detector.

Description

SYSTEM AND METHOD FOR THERMAL CONTACT MODULATION BETWEEN OBJECT AND CLAMPCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 668,587 which was filed on 08 July 2024 and US application 63 / 722,339 which was filed on 19 November 2024 and which are incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to thermal coupling features, for example, control of thermal contact between an object and a stage in lithographic apparatuses and systems.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern of a patterning device (e.g., a mask, a reticle) onto a layer of radiation-sensitive material (photoresist or simply “resist”) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] During lithographic manufacturing processes, an overlay error can occur when there is a misalignment between patterns printed on different layers of a substrate. Such overlay errors may produce defective ICs and, therefore, time-consuming corrections may be taken to fix the errors. As manufacturing throughput goals increase, it becomes increasingly important to reduce overlay errors to save time. One contributor to overlay error is fast chuck heating, also referred to as pre-expose chuck heating (PECH). Fast chuck heating can occur when a reticle, having a higher relative temperature than a reticle stage, is loaded onto the reticle stage, thus quickly transferring heat from the reticle to the reticle stage. Fast chuck heating can cause deformations that cause encoder scales on the chuck to make a positioning error, thereby leading to an undesirable overlay impact. There are no existing alignment systems or methods capable of correcting such overlay impact due to the fast nature of its occurrence.

[0006] Another contributor to overlay error is reticle deformation that results from heating of the reticle caused by exposure to radiation. Such reticle deformation is called intrawafer reticle heating and can create alignment issues that cause overlay errors at the wafer level. There are no existing alignmentsystems or methods capable of correcting intrawafer reticle heating due to its occurrence during exposure.SUMMARY

[0007] Accordingly, it is desirable to prevent or reduce deformations of objects and object support structures in a reliable, uniform, and efficient manner. For example, the object support structure used in a reticle stage can mitigate the impact of fast chuck heating, thereby decreasing reticle stage overlay errors. In another example, the object support structure used in a reticle stage can mitigate the impact of reticle deformation, thereby decreasing overlay errors caused by intrawafer reticle heating. While the embodiments described below are explained in the context of reticle support structures, the disclosed object support structures and functions can also apply to other object support structures such as, for example, wafer support structures.

[0008] In some aspects, an object clamping system can include an object support structure, a clamp, a gas supply system, and a controller. In some aspects, the clamp can be coupled to the object support structure. In some aspects, the clamp can be configured to support an object on the object support structure. In some aspects, the clamp can define a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact. In some aspects, the gas supply system can be configured to supply a backfill gas to the gap. In some aspects, the controller can be configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap. In some aspects, the controller can be configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap such that the object remains in a saturated state. In some aspects, the controller can dynamically adjust the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from a radiation source or a radiation detector. In some aspects, each exposure signal can indicate an exposure period when the object is exposed to radiation. In some aspects, each non-exposure signal can indicate a non-exposure period when the object is not exposed to radiation.

[0009] In some aspects, a lithographic apparatus can include an illumination system, a patterning system, a projection system, and an object clamping system. In some aspects, the illumination system can be configured to condition a radiation beam. In some aspects, the patterning system can be configured to impart a pattern onto the radiation beam to form a patterned beam. In some aspects, the projection system can be configured to project the patterned beam onto a target section of a substrate. In some aspects, the object clamping system can include an object support structure, a clamp, a gas supply system, and a controller. In some aspects, the clamp can be coupled to the object support structure. In some aspects, the clamp can be configured to support an object on the object support structure. In some aspects, the clamp can define a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact. In some aspects, the gas supply system can beconfigured to supply a backfill gas to the gap. In some aspects, the controller can be configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap such that the object remains in a saturated state. In some aspects, the controller can dynamically adjust the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from a radiation source or a radiation detector. In some aspects, each exposure signal can indicate an exposure period when the object is exposed to radiation. In some aspects, each non-exposure signal can indicate a non-exposure period when the object is not exposed to radiation.

[0010] In some aspects, a method can include supporting an object on a clamp configured to support the object on an object support structure. In some aspects, the method can further include receiving a signal from a radiation source or a radiation detector indicating whether the object is exposed to radiation. In some aspects, the method can further include adjusting a thermal contact between the object and the clamp by dynamically adjusting a characteristic of a backfill gas at a gap between a backside of the object and the clamp such that the object remains in a saturated state. In some aspects, the backfill gas can be supplied by a gas supply system to the gap.

[0011] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0012] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0013] FIG. 1A shows a reflective lithographic apparatus, according to some aspects.

[0014] FIG. IB shows a transmissive lithographic apparatus, according to some aspects.

[0015] FIG. 1C shows a lithographic cell, according to some aspects.

[0016] FIGS. 2 and 3 show a reticle stage, according to some aspects.

[0017] FIGS. 4 and 5 show a reticle exchange apparatus, according to some aspects.

[0018] FIGS. 6A, 6B, and 6C show a reticle exchange apparatus in different configurations, according to some aspects.

[0019] FIG. 7 shows a schematic plot illustrating heat transfers over time between a reticle and a reticle stage, according to some aspects.

[0020] FIGS. 8 A and 8B show side views of a reticle clamping system forming thermal contact between a reticle and a reticle stage, according to some aspects.

[0021] FIG. 9 shows a method for modulating a thermal contact between a reticle and a reticle stage, according to some aspects.

[0022] FIG. 10 shows a schematic plot illustrating intrawafer reticle heating, according to some aspects.

[0023] FIGS. 11A and 11B show side views of a reticle clamping system forming thermal contact between a reticle and a reticle stage based on exposure signals and non-exposure signals, according to some aspects.

[0024] FIGS. 12A and 12B show schematic plots illustrating reduced intrawafer reticle heating, according to some aspects.

[0025] FIG. 13 shows a method for adjusting a thermal contact between an object and a clamp such that the object remains in a saturated state, according to some aspects.

[0026] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0027] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0028] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0029] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0030] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine -readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0031] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0032] Example Lithographic Systems

[0033] FIGS. 1A and IB show a lithographic apparatus 100 and a lithographic apparatus 100’, respectively, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100’ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0034] The illumination system IL can include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0035] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one ofthe lithographic apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0036] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0037] The patterning device MA can be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0038] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0039] Lithographic apparatus 100 and / or lithographic apparatus 100’ can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

[0040] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged inliquid. For example, a liquid can be located between the projection system and the substrate during exposure.

[0041] Referring to FIGS. 1A and IB, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100’ can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100’, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. IB) including, for example, suitable directing mirrors and / or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100’ , for example, when the source SO is a mercury lamp. A radiation system can comprise the source SO, the illuminator IL, and / or the beam delivery system BD.

[0042] The illuminator IL can include an adjuster AD (in FIG. IB) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “□ -outer” and “□ -inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in FIG. IB), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0043] Referring to FIG. 1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0044] Referring to FIG. IB, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0045] The projection system PS projects an image of the mask pattern MP, where the image is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP can include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

[0046] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zeroth order diffracted beams, first order diffracted beams, and / or higher order diffracted beams (not shown). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first- order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0047] With the aid of the second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in FIG. IB) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0048] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marksPl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0049] Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0050] The lithographic apparatus 100 and 100’ can be used in at least one of the following modes:

[0051] 1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0052] 2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de- jmagnification and image reversal characteristics of the projection system PS.

[0053] 3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0054] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0055] In some aspects, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0056] In some aspects, lithographic apparatus 100’ includes a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.

[0057] Example Lithographic Cell

[0058] FIG. 1C shows a lithographic cell 102, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatuses 100 or 100’ can form part of lithographic cell 100. Lithographic cell 102 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input / output ports I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 100’. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0059] Example Reticle Stage

[0060] FIGS. 2 and 3 show a reticle stage 200, according to some aspects. Reticle stage 200 can include top stage surface 202, bottom stage surface 204, side stage surfaces 206, and clamp 300. In some aspects, reticle stage 200 with clamp 300 can be implemented in lithographic apparatus 100 or 100’. For example, reticle stage 200 can be support structure MT in lithographic apparatus 100 or 100’. In some aspects, clamp 300 can be disposed on top stage surface 202. For example, as shown in FIG. 2, clamp 300 can be disposed at a center of top stage surface 202 with clamp frontside 302 facing perpendicularly away from top stage surface 202.

[0061] In some lithographic apparatuses, for example, lithographic apparatus 100 or 100’, a reticle stage 200 with a clamp 300 can be used to hold and position a reticle 408 for scanning or patterning operations. In one example, the reticle stage 200 can rely on powerful drives, large balance masses, and heavy frames to support it. In one example, the reticle stage 200 can have a large inertia and can weigh over 500 kg to propel and position a reticle 408 weighing about 0.5 kg. To accomplish reciprocating motions of the reticle 408, which are typically found in lithographic scanning or patterning operations, accelerating and decelerating forces can be provided by linear motors that drive the reticle stage 200.

[0062] In some aspects, as shown in FIGS. 2 and 3, reticle stage 200 can include first encoder 212 and second encoder 214 for positioning operations. For example, first and second encoders 212 and 214 can be interferometers. First encoder 212 can be attached along a first direction, for example, a transverse direction (i.e., X-direction) of reticle stage 200. And second encoder 214 can be attached along a second direction, for example, a longitudinal direction (i.e., Y-direction) of reticle stage 200. In some aspects, as shown in FIGS. 2 and 3, first encoder 212 can be orthogonal to second encoder 214.

[0063] As shown in FIGS. 2 and 3, reticle stage 200 can include clamp 300. Clamp 300 is configured to hold reticle 408 in a fixed plane on reticle stage 200. Clamp 300 includes clamp frontside 302 and can be disposed on top stage surface 202. In some aspects, clamp 300 can use mechanical, vacuum, electrostatic, or other suitable clamping techniques to hold and secure an object. In some aspects, clamp300 can be an electrostatic clamp, which can be configured to electrostatically clamp (i.e., hold) an object, for example, reticle 408 in a vacuum environment. For EUV generation performed in a vacuum environment, it can be difficult to use vacuum clamps to clamp a mask or reticle. Instead, electrostatic clamp(s) can be used. For example, clamp 300 can include an electrode, a resistive layer on the electrode, a dielectric layer on the resistive layer, and burls projecting from the dielectric layer. In use, a voltage can be applied to clamp 300, for example, several kV. And current can flow through the resistive layer, such that the voltage at an upper surface of the resistive layer will substantially be the same as the voltage of the electrode and generate an electric field. Also, a Coulomb force, attractive force between electrically opposite charged particles, will attract an object to clamp 300 and hold the object in place. In some aspects, clamp 300 can be a rigid material, for example, a metal, a dielectric, a ceramic, or a combination thereof.

[0064] Example Reticle Exchange Apparatus

[0065] FIGS. 4, 5, 6A, 6B, and 6C show a reticle exchange apparatus 401, according to some aspects. Reticle exchange apparatus 401 can be configured to minimize reticle exchange time, particle generation, and contact forces or stresses from clamp 300 and / or reticle 408 to reduce damage to clamp 300 and reticle 408 and increase overall throughput in a reticle exchange process, for example, in a lithographic apparatus 100 or 100’.

[0066] As shown in FIGS. 4 and 5, reticle exchange apparatus 401 can include reticle stage 200, clamp 300, and in-vacuum robot 400. In-vacuum robot 400 can include reticle handler 402.

[0067] In some aspects, reticle handler 402 can be a rapid exchange device (RED), which is configured to efficiently rotate and minimize reticle exchange time. For example, reticle handler 402 can save time by moving multiple reticles from one position to another substantially simultaneously, instead of serially.

[0068] In some aspects, as shown in FIG. 4, reticle handler 402 can include one or more reticle handler arms 404. Reticle handler arm 404 can include reticle baseplate 406. Reticle baseplate 406 can be configured to hold an object, for example, reticle 408.

[0069] In some aspects, reticle baseplate 406 can be an extreme ultraviolet inner pod (EIP) for a reticle. In some aspect, reticle baseplate 406 includes reticle baseplate frontside 407, and reticle 408 includes reticle backside 409.

[0070] In some aspects, as shown in FIGS. 4 and 5, reticle baseplate 406 can hold reticle 408 such that reticle baseplate frontside 407 and reticle backside 409 each face top stage surface 202 and clamp frontside 302. For example, reticle baseplate frontside 407 and reticle backside 409 can be facing perpendicularly away from top stage surface 202 and clamp frontside 302.

[0071] As shown in FIG. 5, reticle exchange apparatus 401 can include reticle exchange area 410, which is the cross-sectional area between clamp 300, reticle 408, reticle baseplate 406, and reticle handler arm 404 during a reticle exchange process.

[0072] In some aspects, as shown in FIG. 4, reticle handler arms 404 can be arranged symmetrically about reticle handler 402. For example, reticle handler arms 404 can be spaced from each other by about 90 degrees, 120 degrees, or 180 degrees. In some aspects, reticle handler arms 404 can be arranged asymmetrically about reticle handler 402. For example, two reticle handler arms 404 can be spaced from each other by about 135 degrees, while another two reticle handler arms 404 can be spaced from each other by about 90 degrees.

[0073] In one example, during a reticle exchange process, reticle handler arm 404 of reticle handler 402 positions reticle 408 on reticle baseplate 406 towards clamp 300 in reticle exchange area 410. As described above, a reticle handoff from reticle handler 402 to clamp 300 includes an unknown reticle position offset, which includes a reticle vertical distance offset (i.e., Z-direction offset) and a reticle tilt offset (i.e., Rx offset and RY offset). Tilt or excessive non-alignment between clamp 300 and reticle 408 can be a source of particle generation and can damage reticle 408 or clamp 300 over time. Reticle backside 409 and clamp frontside 302 can be in coplanar alignment for a final handoff. Despite calibration, variations still exist due to reticle mechanical and positioning tolerances, which can lead to high corner impacts and unpredictable first contact points between clamp 300 and reticle 408.

[0074] In one example, the reticle exchange process can involve lowering reticle stage 200 with clamp 300, which starts far away from reticle handler 402, as close to reticle 408 as possible until clamp 300 contacts reticle 408 to account for all possible offsets and / or tilts. During a reticle exchange process, reticle stage 200 with clamp 300 can be adjusted in a multi-stage movement (e.g., long stroke stage (coarse motion), short stroke stage (fine motion)).

[0075] As shown in FIGS. 6A through 6C, reticle exchange apparatus 401 can include clamp 300, reticle 408, and reticle baseplate 406. The multi-stage movement can occur in four stages: (1) approach; (2) first contact; (3) full contact; and (4) voltage applied to clamp.

[0076] First, as shown in FIG. 6A, reticle exchange apparatus 401 can be in an approach configuration 20 and clamp 300 can be adjusted in a substantially vertical direction (i.e., Z-direction) toward reticle backside 409. In approach configuration 20, clamp 300 is turned off (i.e., no applied voltage) and reticle handler 402 deactivates the vertical direction (i.e., Z-direction) and tilt (i.e., Rx and RY, rotation about X-direction and rotation about Y-direction, respectively) servo motors of reticle handler arm 404 in reticle exchange area 410. The motors (i.e., Z, Rx, and RY) brake and rotation about Z-direction (i.e., Rz) activates.

[0077] Second, as shown in FIG. 6B, reticle exchange apparatus 401 can be in a first contact configuration 30 and clamp 300 can be adjusted in a substantially vertical direction (i.e., Z-direction) toward reticle backside 409 until clamp 300 makes contact with reticle backside 409. In first contact configuration 30, clamp 300 is turned off and clamp 300 makes contact with reticle backside 409, for example, a corner of reticle 408, and then rotates or tilts about the contact (i.e., Rx and RY).

[0078] Third, as shown in FIG. 6C, reticle exchange apparatus 401 can be in a full contact configuration 40 and clamp 300 can be rotationally adjusted about the contact (i.e., Rx and RY) towardreticle backside 409 until clamp 300 makes full contact with reticle backside 409. In full contact configuration 40, clamp 300 is turned off and clamp 300 makes full contact with reticle backside 409, for example, all four corners of reticle 408, and is coplanar with reticle backside 409.

[0079] In some aspects, in full contact configuration 40, clamp 300 makes contact with all four corners of reticle 408 and continues to move in a substantially vertical direction (i.e., Z-direction) until a mechanical force of at least 5 N is achieved.

[0080] Fourth, with clamp frontside 302 and reticle backside 409 aligned and coplanar, clamp 300 is turned on (i.e., a voltage is applied to clamp 300) and reticle 408 is held in a fixed plane on clamp 300.

[0081] In some aspects, as shown in FIG. 5, reticle exchange apparatus 401 can include clamp controller 360. Clamp controller 360 can be coupled to clamp 300 and be configured to control a position of clamp 300. For example, clamp controller 360 can be configured to control reticle stage 200 to allow compliant movement of clamp 300. In some aspects, clamp controller 360 can be coupled to servo motors or servo actuators (i.e., X-direction, Y-direction, Z-direction, Rx, RY, RZ) of reticle stage 200 and / or clamp 300. For example, clamp controller 360 can control translations of reticle stage 200 with clamp 300 along an x-axis, y-axis, and z-axis (i.e., X-direction, Y-direction, Z-direction) and rotations about the x-axis, y-axis, and z-axis (i.e., Rx, RY, RZ), where the x-axis, y-axis, and z-axis are orthogonal coordinates.

[0082] Example Cumulative Heat Transferred to Chuck

[0083] FIG. 7 shows a schematic plot 700 illustrating a cumulative heat transfer from a reticle (e.g. reticle 408) to a reticle stage, also referred to as a chuck, (e.g., reticle stage 200), according to some aspects. In some aspects, plot 700 can indicate a cumulative heat transferred to chuck 702 (in arbitrary units) from the reticle to the chuck over a period of time 704 (in arbitrary units). In some aspects, cumulative heat transferred to chuck 702 can range from about 0 arbitrary units to about 100 arbitrary units. In some aspects, time 704 can range from about 0 arbitrary units to about 100 arbitrary units. In the example aspect shown in FIG. 7, the reticle can be loaded on the chuck at a value of 0 for time 704.

[0084] In some aspects, time 704 can include a fast chuck heating period 708 and a chuck thermal recovery period 710. In some aspects, fast chuck heating period 708 can begin at a value of about 0 for time 704 and can end when chuck thermal recovery period 710 begins. In some aspects, chuck thermal recovery period 710 can begin when fast chuck heating period 708 ends and can end at a value of about 100 arbitrary units for time 704. In the example aspect shown in FIG. 7, fast chuck heating period 708 can last about 25% of the duration of time 704 and chuck thermal recovery period 710 can last about 75% the duration of time 704. A person skilled in the art would understand that fast chuck heating period 708 and chuck thermal recovery period 710 can be various proportions of the duration of time 704.

[0085] In some aspects, fast chuck heating period 708 can occur when a reticle with an ambient temperature is loaded onto a cooled reticle stage, thus quickly transferring heat from the reticle to the reticle stage. For example, the reticle can have a temperature of about 22 degrees Celsius (or higher orlower values within a predetermined fabrication temperature range), while the reticle stage can be about 16 degrees Celsius or lower. In some aspects, fast chuck heating period 708 also can be referred to as a pre-expose chuck heating (PECH) period because the heat transfer occurs before the reticle is exposed to radiation. Fast chuck heating period 708 can be disadvantageous for overlay processes because excessive heat transfer to the chuck can cause deformations in its material structure. Chuck deformations can cause the encoder scales (e.g., first encoder 212 and second encoder 214) on the chuck to make a positioning error, thereby leading to an overlay impact. Existing alignment systems or methods are unable to correct such overlay impact due to the fast nature of its occurrence. The magnitude of cumulative heat transferred to chuck 702 can scale with the temperature difference between the reticle and the reticle stage. Therefore, a reticle stage with a stronger cooling source may create a larger temperature difference between the reticle and the reticle stage, thereby increasing the impact of PECH even further.

[0086] In some aspects, heat transfer 706 can illustrate a cumulative heat transferred from the reticle to the chuck during time 704 for a first material forming the clamp (e.g. clamp 300) on the chuck. In some aspects, heat transfer 707 can illustrate a cumulative heat transferred from the reticle to the chuck during time 704 for a second material alternatively forming the clamp (e.g., clamp 300) on the chuck. In some aspects, a comparison between heat transfer 706 and heat transfer 707 can illustrate that different materials can have different thermomechanical properties which may be more or less resistant to heat transfer, thereby mitigating PECH by varying magnitudes. In the example aspect shown in FIG. 7, heat transfer 707 can reduce the impact of PECH by a factor of about two times more than heat transfer 706. However, despite the choice of materials, heat transfer 706 and heat transfer 707 both illustrate that undesirable residual heat can remain in the reticle stage by the end of time 704. Therefore, to enable future lithographic apparatuses to decrease the reticle stage cooling temperature for better reticle heating performance, the PECH overlay impact should be further mitigated by aspects described below.

[0087] Example Reticle Clamping System

[0088] FIGS. 8 A and 8B show side views of a reticle clamping system 800 forming thermal contact between a reticle and a reticle stage, according to some aspects. In some aspects, reticle clamping system 800 can be incorporated in an aspect of reticle exchange apparatus 401 described with reference to FIGS. 4, 5, and 6A-6C. The elements of reticle clamping system 800 shown in FIGS. 8 A and 8B and the elements of reticle exchange apparatus 401 shown in FIGS. 4, 5, and 6A-6C may be similar. Accordingly, the above discussion of reticle exchange apparatus 401 can apply to reticle clamping system 800 shown in FIGS. 8 A and 8B. In some aspects, reticle clamping system 800 can include a reticle support structure 820, a clamp 830, a gas supply system 840, and a controller 850. While the embodiments described below are explained in the context of reticle support structures, the disclosed object support structures and functions can also apply to other object support structures such as, for example, wafer support structures.

[0089] In some aspects, reticle clamping system 800 can be configured to mitigate the impact of fast chuck heating on reticle support structure 820. Accordingly, reticle clamping system 800 can include various components to limit or slow down a heat transfer rate from a reticle 832 toward clamp 830 and reticle support structure 820, as described below. Therefore, in some aspects, reticle clamping system 800 can stabilize a heat interaction between reticle 832 and clamp 830 and reticle support structure 820 by dynamically modulating a thermal contact between reticle 832 and clamp 830 and reticle support structure 820. When the thermal contact is decreased in a certain timeframe after reticle 832 is loaded on clamp 830, the fast effect of encoder bending can be diminished.

[0090] In some aspects, reticle clamping system 800 can dynamically provide or remove backfill gas between reticle 832 and clamp 830 to regulate the thermal contact. In some aspects, reticle clamping system 800 can dynamically modulate the thermal contact by changing a backfill gas pressure between reticle 832 and clamp 830 because decreased gas pressure can decrease the heat transfer coefficient between reticle 832 and clamp 830. Therefore, the pressure of the backfill gas can dictate a heat transfer rate between reticle 832 and clamp 830. Accordingly, reticle clamping system 800 can mitigate the impact of fast chuck heating impact by dynamically switching on and off a backfill gas supply to increase or decrease the heat transfer between reticle 832 and clamp 830. For example, before loading reticle 832 onto clamp 830, the backfill gas supply can be switched off. Once reticle 832 is affixed to clamp 830 and after a period of overhead waiting time, the backfill gas supply can be switched on at the onset of exposing the reticle to radiation.

[0091] FIG. 8A shows a side view of reticle clamping system 800 before reticle 832 is loaded on clamp 830 disposed on reticle support structure 820. In the example aspect shown in FIG. 8A, reticle 832 is not being exposed to radiation from illuminator IL. When reticle 832 is being loaded onto clamp 830 and is not being exposed, reticle clamping system 800 can be configured to minimize thermal contact between reticle 832 and clamp 830 and reticle support structure 820, as described below.

[0092] In some aspects, reticle support structure 820 can be an aspect of reticle stage 200 as described with reference to FIGS. 2 and 3. In some aspects, reticle support structure 820 can be implemented in lithographic apparatus 100 or 100’ as described with reference to FIGS. 1 A and IB. For example, reticle support structure 820 can be an aspect of support structure MT in lithographic apparatus 100 or 100’. In some aspects, reticle support structure 820 can include encoder scales (e.g., first encoder 212 and second encoder 214 as shown in and described with reference to FIGS. 2 and 3) for positioning operations. For example, the encoder scales can be interferometers. For illustration purposes, the encoder scales are not shown in FIGS. 8A and 8B.

[0093] In some aspects, a cooling structure 860 can be coupled to or disposed in reticle support structure 820. In some aspects, cooling structure 860 can be configured to cool reticle support structure 820, clamp 830, or both. In some aspects, cooling structure 860 can include one or more fluid ducts and / or fluid channels that are connected to a coolant supply system. The one or more fluid ducts and / or fluid channels of cooling structure 860 can be configured for directing a temperature conditioning fluidsuch as, for example, water, alcohol, glycol, phase change coolant, etc., through reticle support structure 820, clamp 830, or both. In some aspects, cooling structure 860 can maintain reticle support structure 820, clamp 830, or both at a target temperature lower than a temperature of reticle 832 by passing a fluid conditioned to a target temperature through at least one or more fluid ducts and / or fluid channels.

[0094] In some aspects, clamp 830 can be disposed on a surface of reticle support structure 820. In some aspects, clamp 830 can be configured to support reticle 832 on reticle support structure 820. In some aspects, clamp 830 can be an aspect of clamp 300 as described with reference to FIGS. 2 and 3.

[0095] In some aspects, clamp 830 can use mechanical, vacuum, electrostatic, or other suitable clamping techniques to hold and secure reticle 832. In some aspects, clamp 830 can be an electrostatic clamp configured to hold reticle 832 in a vacuum environment. For example, clamp 830 can include an electrode, a resistive layer on the electrode, a dielectric layer on the resistive layer, and burls projecting from the dielectric layer. In use, a voltage can be applied to clamp 830, for example, several kV. Current can flow through the resistive layer, such that the voltage at an upper surface of the resistive layer will substantially be the same as the voltage of the electrode and generate an electric field. In some aspects, clamp 830 can use a Coulomb force to attract reticle 832 and hold reticle 832 in place. In some aspects, clamp 830 can be a rigid material, for example, a metal, a dielectric, a ceramic, or a combination thereof.

[0096] In some aspects, reticle 832 can be an aspect of reticle 408 as described with reference to FIGS. 4, 5, and 6A-6C. In some aspects, reticle 832 can be configured to receive radiation from illuminator IL. In some aspects, reticle 408 can include a reticle backside 836. In some aspects, reticle backside 836 can be an aspect of reticle backside 409 as described with reference to FIGS. 4, 5, and 6A-6C. During the loading process shown in FIG. 8A, reticle 832 can be brought toward clamp 830 by reticle handler 402 of in-vacuum robot 400 as described with reference to FIGS. 4, 5, and 6A-6C.

[0097] In some aspects, a gap 834 can exist between reticle backside 836 and clamp 830 when reticle 832 is being loaded onto clamp 830. In some aspects, gap 834 can be made from an interface material such as, for example, empty vacuum space, air, or burls of clamp 830. Therefore, gap 834 can limit reticle 832 and clamp 830 from being in full contact.

[0098] In some aspects, gas supply system 840 can be configured to supply a backfill gas (e.g., backfill gas 842 as shown in and described with reference to FIG. 8B below) to gap 834. In some aspects, gas supply system 840 can include a supply device 841 and an extraction device 843. As shown in FIG. 8 A, gas supply system 840 can be configured to supply no backfill gas when reticle 832 is being loaded onto clamp 830 and reticle 832 is not being exposed to radiation. Accordingly, the absence of backfill gas at gap 834 during this process can prevent or limit fast heat transfer from reticle 832 to clamp 830 and reticle support structure 820.

[0099] In some aspects, controller 850 can be coupled to gas supply system 840. In some aspects, controller 850 can be configured to control the gas supply system 840 and to adjust a thermal contact between reticle 832 and clamp 830 by dynamically adjusting a characteristic of the backfill gas in gap 834 in response to a radiation exposure of reticle 832. Accordingly, in some aspects, controller 850 canbe coupled to illuminator IL to receive an exposure signal indicating whether or not radiation is being emitted from illuminator IL. Alternatively, in some aspects, the controller 850 can be coupled to receive the exposure signal from the source vessel or a radiation detector situated at the reticle level, a wafer stage controller, an exposure controller or an overall scanner controller or any other means conventionally known within a lithographic apparatus and configured to provide exposure and nonexposure signal. In response to the exposure signal, for example, controller 850 can switch off gas supply system 840 when reticle 832 is not being exposed and can switch on gas supply system 840 when reticle 832 is being exposed. In this manner, controller 850 can prevent, decrease, or minimize thermal contact between reticle 832 and clamp 830 and reticle support structure 820 when reticle 832 is not being exposed. As a result, in some aspects, controller 850 can limit a heat transfer rate from reticle 832 to clamp 830 and reticle support structure 820 by dynamically adjusting the characteristic of the backfill gas.

[0100] In some aspects, the characteristic of the backfill gas can be a thermodynamic characteristic such as, for example, pressure that is provided in gap 834. Therefore, in some aspects, controller 850 can be configured to reduce the thermal contact between reticle 832 and clamp 830 by adjusting the backfill gas pressure. In some aspects, controller 850 can adjust the characteristic of the backfill gas (e.g., the backfill gas pressure) in response to the reticle being loaded on the clamp. In some aspects, controller 850 can adjust the backfill gas pressure by reducing an amount of backfill gas or turning off gas supply system 840. Accordingly, in some aspects, controller 850 can be coupled to in-vacuum robot 400 to receive a loading signal indicating whether or not reticle 432 is being loaded onto clamp 830. In response to the loading signal, for example, controller 850 can switch off gas supply system 840 when reticle 832 is being loaded onto clamp 830 and can switch on gas supply system 840 after reticle 832 has been loaded onto clamp 830. In this manner, controller 850 can prevent, limit, or minimize thermal contact between reticle 832 and clamp 830 and reticle support structure 820 when reticle 832 is being loaded onto clamp 830. As a result, in some aspects, controller 850 can limit a heat transfer rate from reticle 832 to clamp 830 and reticle support structure 820 by dynamically adjusting the characteristic of the backfill gas.

[0101] FIG. 8B shows a side view of reticle clamping system 800 when reticle 832 is affixed to clamp 830 and being exposed to radiation from illuminator IL. When reticle 832 is affixed to clamp 830 and is being exposed, reticle clamping system 800 can be configured to produce thermal contact between reticle 832 and clamp 830 and reticle support structure 820, as described below.

[0102] In some aspects, after reticle 832 has been affixed to clamp 830, reticle clamping system 800 can be inactive for a period of overhead waiting time. The overhead waiting time can be any duration, depending on the lot size of wafer to be processed. Once the overhead waiting time is over, reticle 832 can be exposed to radiation from illuminator IL.

[0103] In some aspects, during exposure of reticle 832, a backfill gas 842 can be supplied to gap 834 to enhance thermal contact between reticle 832 and clamp 830. Providing backfill gas 842 duringexposure of reticle 832 can be beneficial to illumination performance because the thermal contact can prevent overheating of reticle 832, thereby avoiding deformation or loss.

[0104] Accordingly, in some aspects, controller 850 can be configured to control the gas supply system840 and to adjust a thermal contact between reticle 832 and clamp 830 by dynamically adjusting a characteristic of the backfill gas in gap 834 in response to a radiation exposure of reticle 832. Accordingly, in some aspects, controller 850 can be coupled to illuminator IL to receive an exposure signal indicating whether or not radiation is being emitted from illuminator IL. In response to the exposure signal, for example, controller 850 can switch on gas supply system 840 when reticle 832 is being exposed. In this manner, controller 850 can increase or maximize thermal contact between reticle 832 and clamp 830 and reticle support structure 820 when reticle 832 is being exposed. As a result, in some aspects, controller 850 can increase a heat transfer rate from reticle 832 to clamp 830 and reticle support structure 820 at a desirable time of exposure by dynamically adjusting the characteristic of the backfill gas.

[0105] In some aspects, the characteristic of the backfill gas can be a thermodynamic characteristic such as, for example, pressure that is provided in gap 834. Therefore, in some aspects, controller 850 can be configured to increase the thermal contact between reticle 832 and clamp 830 by adjusting the backfill gas pressure at an onset of the radiation exposure of reticle 832. In some aspects, controller 850 can adjust the backfill gas pressure by increasing an amount of backfill gas or turning on gas supply system 840.

[0106] In some aspects, backfill gas 842 can be provided at an interface between reticle 832 and clamp 830. In some aspects, backfill gas 842 can include hydrogen gas. In some aspects, backfill gas 842 can include other gases or a mixture of gases. Backfill gas 842 can be one example medium for dynamically modulating the thermal contact between reticle 832 and clamp 830. A person skilled in the art would understand that another medium could be supplied between reticle 832 and clamp 830 to dynamically modulate the thermal contact.

[0107] In some aspects, gas supply system 840 can be configured to supply and / or remove backfill gas 842 to and / or from gap 834. In some aspects, gas supply system 840 can be a distribution system having at least one of valves, ducts, hoses, or channels to supply and / or remove backfill gas 842 to and / or from gap 834. In some aspects, gas supply system 840 can be configured to tune a downstream set point pressure of backfill gas 842 at gap 834. For example, gas supply system 840 can include a supply device841 and an extraction device 843 to manage the pressure of backfill gas 842.

[0108] In some aspects, supply device 841 can be constructed and arranged to supply backfill gas 842 to gap 834. In some aspects, supply device 841 can include at least one of valves, ducts, hoses, or channels to supply backfill gas 842 (e.g., hydrogen gas) to gap 834. In some aspects, supply device 841 can inject backfill gas 842 (e.g., hydrogen gas) into gap 834 with a high gas pressure. In some aspects, supply device 841 can inject backfill gas 842 (e.g., hydrogen gas) into gap 834 with a high flow rate to rapidly increase the gas pressure or a low flow rate to gradually increase the gas pressure.

[0109] In some aspects, extraction device 843 can be constructed and arranged to extract backfill gas 842 from gap 834. In some aspects, extraction device 843 can include at least one of valves, ducts, hoses, or channels to extract backfill gas 842 (e.g., hydrogen gas) from gap 834. In some aspects, extraction device 843 can pump out backfill gas 842 (e.g., hydrogen gas) from gap 834 with high suction. In some aspects, extraction device 843 can extract backfill gas 842 (e.g., hydrogen gas) from gap 834 with a high flow rate to rapidly decrease the gas pressure or a low flow rate to gradually decrease the gas pressure.

[0110] In the example aspect of FIG. 8B, supply device 841 supplies backfill gas 842 and extraction device 843 extracts backfill gas 842 in the same two-dimensional direction. A person skilled in the art would understand that supply device 841 and extraction device 843 can transmit backfill gas 842 in any direction within a three-dimensional space of reticle clamping system 800.

[0111] In some aspects, reticle clamping system 800 can reduce the impact of fast chuck heating overlay impact by controlling the heat transfer between reticle 832 and clamp 830 to limit bending of the encoder scales. For example, by decreasing a backfill gas pressure after reticle 832 is affixed on clamp 830 and gradually increasing the backfill gas pressure at the onset of the first exposure of reticle 832, reticle clamping system 800 can provide a performance improve of about 50%, as compared to a lithographic apparatus that does not dynamically modulate backfill gas.

[0112] Example Method for Modulating Thermal Contact

[0113] In some aspects, an object (e.g., reticle 832) can be loaded and supported on a clamp (e.g., clamp 830) configured to support the object on an object support structure (e.g., reticle support structure 820). In some aspects, a reticle can be supported on a reticle support structure.

[0114] In some aspects, adjusting a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap. In some aspects, adjusting a heat transfer rate between the reticle and the clamp by regulating a characteristics of the backfill gas such as the pressure of the backfill gas, wherein the backfill gas supply is switched off before loading the reticle onto the clamp and switched on at the onset of exposing the reticle to radiation to mitigate the impact of fast chuck heating.

[0115] In some aspects, a signal can be received from a radiation source (e.g., radiation source 1180) or a radiation detector (e.g., radiation detector 1182) or any one of the alternatives mentioned above, indicating whether the object is exposed to radiation or the onset of exposing the reticle to radiation.

[0116] In some aspects, a thermal contact can be adjusted between the object and the clamp by dynamically adjusting a characteristic of a backfill gas (e.g., backfill gas 842) at a gap (e.g., gap 834) between a backside of the object (e.g., reticle backside 836) and the clamp. In some aspects, the backfill gas can be supplied by a gas supply system (e.g., gas supply system 840) to the gap.

[0117] FIG. 9 shows a method 900 for modulating a thermal contact between a reticle and a reticle stage, according to some aspects. While the method steps described below are explained in the contextof reticle support structures, the disclosed object support structures and functions can also apply to other object support structures such as, for example, wafer support structures.

[0118] In some aspects, at step 902, a reticle (e.g., reticle 832) can be loaded on a clamp (e.g. clamp 830). In some aspects, the clamp can be configured to support the reticle on a reticle support structure (e.g., reticle support structure 820).

[0119] In some aspects, at step 904, a backfill gas (e.g., backfill gas 842) can be supplied by a gas supply system (e.g., gas supply system 840) to a gap (e.g., gap 834) between a backside of the reticle (e.g., reticle backside 836) and the clamp.

[0120] In some aspects, at step 906, a thermal contact can be adjusted between the reticle and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap. In some aspects, the thermal contact can be adjusted by limiting a heat transfer rate from the reticle to the clamp and the reticle support structure by dynamically adjusting the characteristic of the backfill gas. In some aspects, the thermal contact can be adjusted by adjusting a backfill gas pressure at an onset of the exposing the reticle to radiation.

[0121] In some aspects, at step 908, the reticle can be exposed to radiation.

[0122] In some aspects, method 900 can further include turning off the gas supply system when a second reticle is loaded on the clamp.

[0123] The method steps of FIG. 9 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 9 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-8B.

[0124] Example Intrawafer Reticle Heating Plot

[0125] When a reticle is held by a clamp on a reticle stage, the reticle can be exposed to EUV radiation for printing a pattern on a wafer. As the reticle is exposed to the EUV radiation, a temperature of the reticle can increase, which can result in thermal deformation of the reticle. When the exposure ends, the temperature of the reticle can decrease, but the reticle may not exactly revert to its original size and shape before the exposure. Before exposing the reticle to EUV radiation again for a subsequent wafer, reticle alignment can be performed to correct for part of the thermal deformation. Reticle alignment can be performed by measuring the deformation of alignment marks on the reticle outside the exposure field and then aligning the reticle with the wafer according to a position of the measured alignment marks. However, current alignment systems are unable to detect the reticle deformation in the exposure field during exposure. As a result, current alignment systems are unable to correct for all of the reticle deformation, thereby leading to a residual overlay error. This residual error causes intrawafer overlay error at the wafer level. The residual error can be referred to as intrawafer reticle heating and can drift over a wafer lot as the reticle continues to deform with each subsequent exposure.

[0126] FIG. 10 shows a schematic plot 1070 illustrating exposure of a wafer lot and the effect of intrawafer reticle heating on overlay content 1072 (in arbitrary units) over time 1074 (in arbitrary units)as a reticle repeatedly heats up and cools down with each exposure, according to some aspects. In some aspects, overlay content 1072 can range from about 0 arbitrary units to about 100 arbitrary units. In some aspects, overlay content 1072 can be a quantity of overlay at a wafer level, but overlay content 1072 can represent a deformation of the reticle as it heats up over time 1074 due to repeated exposures. In some aspects, time 1074 can range from about 0 arbitrary units to about 100 arbitrary units.

[0127] In some aspects, plot 1070 can include one or more exposures 1076 such that each exposure 1076 depicts an exposure of the reticle for one wafer in the wafer lot. In the example shown by FIG. 10, plot 1070 can include 24 exposures 1076. In some aspects, successive exposures 1076 can occur at repeating intervals in time 1074. During each interval between successive exposures 1076, a wafer can be exchanged for a subsequent wafer, the reticle can cool down, and / or reticle alignment can be performed. When reticle alignment is performed during each interval between successive exposures 1076, part of the deformation can be corrected to decrease the value of overlay content 1072 for a subsequent wafer. However, with each successive exposure 1076, the reticle heats up again and the value of overlay content 1072 increases for that exposure 1076.

[0128] In some aspects, the length of the line of each exposure 1076 can represent an amount of deformation that occurs within one wafer due to the intrawafer reticle heating during the time 1074 of the exposure 1076. In earlier exposures 1076 of the wafer lot (depending on the starting conditions of the reticle), the length of the line of each exposure 1076 can be longer relative to later exposures 1076 because there is a greater thermal drift in the reticle as it heats up and cools down at the beginning of the wafer lot. Therefore, intrawafer overlay error can be most prominent at the beginning of the wafer lot. In later exposures 1076 of the wafer lot, the length of the line of each exposure 1076 can be shorter relative to earlier exposures 1076 because the reticle is in a steady state of temperature. However, the minimum value of overlay content 1072 for each of the later exposures 1076 (e.g. the lowest point of each line of exposures 1076) in the wafer lot can be higher relative to those of earlier exposures 1076 because the reticle is at a hotter temperature than at the beginning of the lot.

[0129] In some aspects, plot 1070 illustrates an oscillating pattern 1078 of exposures 1076 and a steady state pattern 1079 of exposures 1076. In some aspects, in oscillating pattern 1078, each minimum value of overlay content 1072 for each exposure 1076 can increase relative to the previous one. In some aspects, in steady state pattern 1079, each minimum value of overlay content 1072 for each exposure 1076 can be about equal relative to the previous one. Steady state pattern 1079 can represent a saturated state of the reticle such that the temperature is saturated and the effect of intrawafer reticle heating is lesser but still present at the end of the wafer lot.

[0130] Intrawafer reticle heating can be difficult to correct because the effect is unique for each wafer in the lot. For example, as shown in FIG. 10, the length of the line of earlier exposure 1076 can be longer relative to later exposures 1076. Existing correction methods may measure overlay for an average wafer and correct for deformations via a feedback loop, but such methods have been insufficient for reducing the effect of intrawafer reticle heating.

[0131] Example Reticle Clamping System for Reducing Intrawafer Reticle Heating

[0132] FIGS. 11 A and 1 IB show side views of a reticle clamping system 800’ forming thermal contact between a reticle and a reticle stage, according to some aspects. In some aspects, reticle clamping system 800’ can be an alternative embodiment of reticle clamping system 800 as shown in and described with regard to FIGS. 8A and 8B. The elements of reticle clamping system 800’ shown in FIGS. 11A and 11B and the elements of reticle clamping system 800 shown in FIGS. 8 A and 8B may be similar. Accordingly, the above discussion of reticle clamping system 800 can apply to reticle clamping system 800’ shown in FIGS. 11 A and 1 IB. In some aspects, reticle clamping system 800’ can include a reticle support structure 820, a clamp 830, a gas supply system 840, a controller 850, and a radiation source 1180 and / or a radiation detector 1182. The numbered elements previously discussed with regard to reticle clamping system 800 can have the same structure and functions in reticle clamping system 800’ and the detailed description related to those elements is incorporated in this section. While the embodiments described below are explained in the context of reticle support structures, the disclosed object support structures and functions can also apply to other object support structures such as, for example, wafer support structures.

[0133] In some aspects, reticle clamping system 800’ can be configured to mitigate the impact of intrawafer reticle heating. Accordingly, reticle clamping system 800’ can include various components to limit or slow down a heat transfer rate from a reticle 832 toward clamp 830 and reticle support structure 820, as described below. Therefore, in some aspects, reticle clamping system 800 can limit cool down of reticle 832 and keep reticle 832 in a saturated state by dynamically modulating a thermal contact between reticle 832 and clamp 830 and reticle support structure 820.

[0134] In some aspects, reticle clamping system 800’ can dynamically provide or remove backfill gas between reticle 832 and clamp 830 to regulate the thermal contact. In some aspects, reticle clamping system 800’ can dynamically modulate the thermal contact by changing a backfill gas pressure between reticle 832 and clamp 830 because decreased gas pressure can decrease the heat transfer coefficient between reticle 832 and clamp 830. Therefore, the pressure of the backfill gas can dictate a heat transfer rate between reticle 832 and clamp 830. Accordingly, reticle clamping system 800’ can mitigate the impact of thermal deformation by dynamically switching on and off a backfill gas supply to increase or decrease the heat transfer between reticle 832 and clamp 830. For example, when reticle 832 is not being exposed to EUV radiation, the backfill gas supply can be switched off.

[0135] FIG. 11A shows a side view of reticle clamping system 800’ during a period when the reticle is not being exposed to EUV radiation from illuminator IE, referred to as a non-exposure period, according to some aspects. Because reticle 832 is not being exposed, reticle clamping system 800’ can be configured to minimize thermal contact between reticle 832 and clamp 830 and reticle support structure 820, as described below.

[0136] In some aspects, clamp 830 can be coupled to reticle support structure 820. In some aspects, clamp 830 can be configured to support reticle 832 on reticle support structure 820. In some aspects,clamp 830 can define a gap 834 between a reticle backside 836 of reticle 832 and clamp 830 such that reticle 832 and clamp 830 are not in full contact.

[0137] In some aspects, gas supply system 840 can be configured to supply a backfill gas (e.g., backfill gas 842 as shown in and described with reference to FIG. 11B below) to gap 834. As shown in FIG. 11 A, gas supply system 840 can be configured to supply no backfill gas when reticle 832 is not being exposed to radiation. Accordingly, the absence of backfill gas at gap 834 during this process can prevent or limit a cool down of reticle 832 to maintain a saturated state.

[0138] In some aspects, controller 850 can be coupled to gas supply system 840. In some aspects, controller 850 can be configured to control the gas supply system 840 and to adjust a thermal contact between reticle 832 and clamp 830 by dynamically adjusting a characteristic of the backfill gas in gap 834 such that reticle 832 remains in a saturated state.

[0139] In some aspects, controller 850 can be coupled to a radiation source 1180 and / or a radiation detector 1182. In some aspects, radiation source 1180 can be an embodiment of illuminator IL. Radiation source 1180 can be configured to send an exposure signal to controller 850 indicating that radiation is being emitted from radiation source 1180. Radiation source 1180 can be configured to send a non-exposure signal to controller 850 indicating that radiation is not being emitted from radiation source 1180. In some aspects, radiation detector 1182 can be disposed near reticle 832 and can be configured to detect the presence of radiation at reticle 832. Radiation detector 1182 can be configured to send an exposure signal to controller 850 indicating that radiation is present at reticle 832. Radiation detector 1182 can be configured to send a non-exposure signal to controller 850 indicating that radiation is not present at reticle 832.

[0140] In some aspects, controller 850 can dynamically adjust the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from radiation source 1180 and / or radiation detector 1182. In some aspects, each exposure signal can indicate an exposure period when reticle 832 is exposed to radiation. In response to an exposure signal, controller 850 can switch on gas supply system 840 when reticle 832 is being exposed. In some aspects, each non- exposure signal can indicate a non-exposure period when reticle 832 is not exposed to radiation. In response to a non-exposure signal, for example, controller 850 can switch off gas supply system 840 when reticle 832 is not being exposed. In this manner, controller 850 can prevent, decrease, or minimize thermal contact between reticle 832 and clamp 830 and reticle support structure 820 when reticle 832 is not being exposed. As a result, in some aspects, controller 850 can limit a heat transfer rate from reticle 832 to clamp 830 and reticle support structure 820 to prevent or limit reticle 832 from cooling down between exposure periods.

[0141] In some aspects, the characteristic of the backfill gas can be a thermodynamic characteristic such as, for example, pressure that is provided in gap 834. Therefore, in some aspects, controller 850 can be configured to reduce the thermal contact between reticle 832 and clamp 830 by reducing an amount of backfill gas or turning off the gas supply system in response to each non-exposure signal.Reducing the thermal contact between reticle 832 and clamp 830 can include decreasing a heat transfer coefficient between reticle 832 and clamp 830. In some aspects, controller 850 can reduce the thermal contact between reticle 832 and clamp 830 during a preceding non-exposure period (e.g., as shown in FIG. 11 A) such that heating of reticle 832 is minimized during a subsequent exposure period (e.g., as shown in FIG. 1 IB). Therefore, deformation of reticle 832 can be limited due to the lower temperature differential of reticle 832 between non-exposure periods and exposure periods. With a limited deformation of reticle 832, the effect of intrawafer reticle heating can be lessened.

[0142] In some aspects, controller 850 can be configured to initiate an object support exchange process or a wafer exchange process during a non-exposure period. For example, controller 850 can initiate an exchange of a wafer support structure such as, for example, substrate table WT, for another wafer support structure. In another example, controller 850 can initiate an exchange of a wafer such as, for example, substrate W, for a subsequent wafer.

[0143] In some aspects, a non-exposure period may last longer than expected. For example, a system error may occur, measurements may be taken multiple times, or other interruptions may happen during such non-exposure periods. As a result, reticle 832 may begin to cool down as it sits on clamp 830 during such non-exposure periods. However, reticle clamping system 800’ can limit such cool down by maintaining the reticle in a saturated state. Therefore, reticle clamping system 800’ can be less sensitive to timing variations and can provide a robustness improvement for overlay corrections.

[0144] FIG. 1 IB shows a side view of reticle clamping system 800’ when reticle 832 is being exposed to radiation from radiation source 1180 and / or illuminator IL, according to some aspects. When reticle 832 is affixed to clamp 830 and is being exposed, reticle clamping system 800’ can be configured to produce thermal contact between reticle 832 and clamp 830 and reticle support structure 820, as described below.

[0145] In some aspects, during exposure of reticle 832, a backfill gas 842 can be supplied to gap 834 to enhance thermal contact between reticle 832 and clamp 830. Providing backfill gas 842 during exposure of reticle 832 can be beneficial to illumination performance because the thermal contact can prevent overheating of reticle 832, thereby avoiding deformation or loss.

[0146] In some aspects, as described above, controller 850 can dynamically adjust the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from radiation source 1180 and / or radiation detector 1182. In this manner, controller 850 can increase or maximize thermal contact between reticle 832 and clamp 830 and reticle support structure 820 when reticle 832 is being exposed. In some aspects, controller 850 can increase the thermal contact by increasing an amount of backfill gas or turning on gas supply system 840 in response to each exposure signal. As a result, in some aspects, controller 850 can increase a heat transfer rate from reticle 832 to clamp 830 and reticle support structure 820 at a desirable time of exposure by dynamically adjusting the characteristic of the backfill gas.

[0147] In some aspects, the sequence of alternating exposure signals and non-exposure signals mean the intra-wafer exposure and non-exposure periods i.e. between dies and / or also such periods between wafers. However, the time duration of non-exposure periods between dies is too less so it is envisaged to mostly dynamically adjust the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals between wafers such that the object or the reticle 832 is maintained in a saturated state.

[0148] Example Reduced Intrawafer Reticle Heating Plot

[0149] FIGS. 12A and 12B show schematic plots illustrating reduced intrawafer reticle heating as compared to the intrawafer reticle heating of plot 1070, according to some aspects.

[0150] FIG. 12A shows a schematic plot 1290 illustrating the reduced intrawafer reticle heating on overlay content 1072 (in arbitrary units) over time 1074 (in arbitrary units) as compared to the intrawafer reticle heating of plot 1070, according to some aspects. The similarly numbered elements of plot 1290 shown in FIG. 12A and the elements of plot 1070 shown in FIG. 10 may be similar. Accordingly, the above discussion of plot 1070 can apply to plot 1290 shown in FIG. 12A. The detailed description of numbered elements previously discussed with regard to plot 1070 is incorporated in this section.

[0151] In some aspects, plot 1290 can include one or more improved exposures 1292 depicted as solid lines that are overlaid on corresponding exposures 1076 from plot 1070, which are depicted as hollow outlines. Each improved exposure 1292 can represent an exposure of the reticle for one wafer in which the thermal contact between the reticle and clamp is adjusted accordingly. Meanwhile, each exposure 1076 can represent an exposure of the reticle for one wafer in which the thermal contact is not adjusted. In the example shown by FIG. 12A, plot 1290 can include 24 improved exposures 1292. In some aspects, successive improved exposures 1292 can occur at repeating intervals in time 1074. During each interval between successive improved exposures 1292, a wafer can be exchanged for a subsequent wafer, the reticle can cool down, and / or reticle alignment can be performed. During each interval between successive improved exposures 1292, backfill gas can be decreased or turned off to minimize cooling of the reticle and therefore limit the deformation of the reticle when it heats up again during a subsequent exposure.

[0152] In some aspects, the length of the line of each improved exposure 1292 can represent an amount of deformation that occurs within one wafer due to the intrawafer reticle heating during the time 1074 of the improved exposure 1292. The length of the line of each improved exposure 1292 can be shorter than the respective length of the line of each corresponding exposure 1076 at the same time 1074. Accordingly, decreasing backfill gas during each interval between improved exposures 1292 can cause a higher value in overlay content 1072 at the start of exposing each wafer, but also cause a lower value in overlay content 1072 at the end of exposing each wafer, as compared to exposures 1076. A shorter line for improved exposures 1292 can represent less overlay content 1072 and therefore less deformation, which means better overlay performance than exposures 1076. Therefore, improvedexposures 1292 can better limit intrawafer reticle heating because the reticle is more stable with saturated reticle heating.

[0153] FIG. 12B shows a schematic plot 1290’ illustrating the reduced intrawafer reticle heating as an isolated effect on overlay content 1072 (in arbitrary units) over time 1074 (in arbitrary units) as compared to the intrawafer reticle heating of plot 1070, according to some aspects. In some aspects, plot 1290’ can be a modified depiction of plot 1290 as shown in and described with regard to FIG. 12A. The similarly numbered elements of plot 1290’ shown in FIG. 12B and the elements of plot 1290 shown in FIG. 12A and plot 1070 shown in FIG. 10 may be similar. Accordingly, the above discussion of plot 1290 and plot 1070 can apply to plot 1290’ shown in FIG. 12B. The detailed description of numbered elements previously discussed with regard to plot 1290 and plot 1070 is incorporated in this section.

[0154] In some aspects, plot 1290’ differs from plot 1290 by starting each of exposure 1076 and improved exposures 1292 at a value of zero overlay content 1072. This graphical depiction can represent “perfect reticle alignment,” which excludes any overlay effects resulting from imperfect reticle alignment that merely estimates the deformation in the exposure field. Accordingly, plot 1290’ can show overlay content 1072 solely resulting from the reticle deformation caused by heating during exposures. Therefore, plot 1290’ can provide a clearer illustration of how much improved exposures 1292 reduce intrawafer reticle heating by using backfill gas modulation, as compared to exposures 1076 that do not adjust thermal contact. For example, performance improvement 1294 is depicted as the difference between the last exposure 1076 and the last improved exposure 1292.

[0155] Example Method

[0156] FIG. 13 shows a method 1300 for adjusting a thermal contact between an object and a clamp such that the object remains in a saturated state, according to some aspects. While the method steps described below are explained in the context of reticle support structures, the disclosed object support structures and functions can also apply to other object support structures such as, for example, wafer support structures.

[0157] In some aspects, at step 1302, an object (e.g., reticle 832) can be supported on a clamp (e.g., clamp 830) configured to support the object on an object support structure (e.g., reticle support structure 820). In some aspects, a reticle can be supported on a reticle support structure.

[0158] In some aspects, at step 1304, a signal can be received from a radiation source (e.g., radiation source 1180) or a radiation detector (e.g., radiation detector 1182) indicating whether the object is exposed to radiation. In some aspects, a non-exposure signal can be received that indicates a nonexposure period when the object is not exposed to radiation. In some aspects, an exposure signal can be received that indicates an exposure period when the object is exposed to radiation.

[0159] In some aspects, a thermal contact can be adjusted between the object and the clamp by dynamically adjusting a characteristic of a backfill gas (e.g., backfill gas 842) at a gap (e.g., gap 834) between a backside of the object (e.g., reticle backside 836) and the clamp such that the object remains in a saturated state. In some aspects, the backfill gas can be supplied by a gas supply system (e.g., gassupply system 840) to the gap. In some aspects, when a non-exposure signal has been received, the thermal contact can be reduced by reducing an amount of backfill gas or turning off the gas supply system in response to the non-exposure signal. In some aspects, the thermal contact can be reduced during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period. In some aspects, when an exposure signal has been received, the thermal contact can be increased by increasing an amount of backfill gas or turning on the gas supply system in response to the exposure signal.

[0160] In some aspects, method 1300 can further include initiating an object support exchange process or a wafer exchange process during a non-exposure period.

[0161] The method steps of FIG. 13 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 13 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-12B.

[0162] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength I of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-100 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G- line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0163] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, aspects disclosed hereincan be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0164] Furthermore, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0165] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0166] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. The foregoing description of specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0167] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above-described aspects, but should be defined in accordance with the following claims and their equivalents.

[0168] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. Other aspects of the invention are set-out as in the following first and second set of numbered clauses.

[0169] First Set of Clauses1. An object clamping system comprising:an object support structure; a clamp configured to support an object on the object support structure, wherein the clamp defines a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact; a gas supply system configured to supply a backfill gas to the gap; and a controller configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap in response to a radiation exposure of the object.2. The object clamping system of clause 1 , wherein the controller is further configured to limit a heat transfer rate from the object to the clamp and the object support structure by dynamically adjusting the characteristic of the backfill gas.3. The object clamping system of clause 1, wherein the characteristic of the backfill gas comprises a backfill gas pressure.4. The object clamping system of clause 3, wherein the controller is further configured to reduce the thermal contact by adjusting the backfill gas pressure in response to the object being loaded on the clamp.5. The object clamping system of clause 3, wherein the controller is further configured to increase the thermal contact by adjusting the backfill gas pressure at an onset of the radiation exposure of the object.6. The object clamping system of clause 1 , wherein the controller is further configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap such that the object remains in a saturated state; wherein the controller dynamically adjusts the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from a radiation source or a radiation detector; and wherein each exposure signal indicates an exposure period when the object is exposed to radiation and each non-exposure signal indicates a non-exposure period when the object is not exposed to radiation.7. The object clamping system of clause 6, wherein the controller is further configured to reduce the thermal contact by reducing an amount of backfill gas or turning off the gas supply system in response to each non-exposure signal.8. The object clamping system of clause 7, wherein the controller is further configured to reduce the thermal contact during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period.9. The object clamping system of clause 6, wherein the controller is further configured to increase the thermal contact by increasing an amount of backfill gas or turning on the gas supply system in response to each exposure signal.10. The object clamping system of clause 1, wherein the object comprises a reticle and the object support structure comprises a reticle support structure.11. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning system configured to impart a pattern onto the radiation beam to form a patterned beam; a projection system configured to project the patterned beam onto a target section of a substrate; and an object clamping system according to any one of clauses 1-10.12. A method comprising: loading an object on a clamp configured to support the object on an object support structure; receiving a signal from a radiation source or a radiation detector indicating whether the object is exposed to radiation; and adjusting a thermal contact between the object and the clamp by dynamically adjusting a characteristic of a backfill gas at a gap between a backside of the object and the clamp, wherein the backfill gas is supplied by a gas supply system to the gap.13. The method of clause 12, wherein the adjusting the thermal contact comprises limiting a heat transfer rate from the object to the clamp and the object support structure by dynamically adjusting the characteristic of the backfill gas.14. The method of clause 12, wherein the adjusting the thermal contact comprises adjusting a backfill gas pressure at an onset of the exposing the object to radiation.15. The method of clause 12, further comprising turning off the gas supply system when a second object is loaded on the clamp.16. The method of clause 12, wherein: the receiving the signal comprises receiving a non-exposure signal indicating a non-exposure period when the object is not exposed to radiation; and the adjusting the thermal contact comprises reducing the thermal contact by reducing an amount of backfill gas or turning off the gas supply system in response to the non-exposure signal.17. The method of clause 12, wherein: the receiving the signal comprises receiving an exposure signal indicating an exposure period when the object is exposed to radiation; and the adjusting the thermal contact comprises increasing the thermal contact by increasing an amount of backfill gas or turning on the gas supply system in response to the exposure signal.18. The method of clause 12, wherein the adjusting the thermal contact comprises reducing the thermal contact during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period.19. The method of clause 12, further comprising initiating an object support exchange process or a wafer exchange process during a non-exposure period.20. The method of clause 12, wherein the supporting the object on the clamp comprises supporting a reticle on a reticle support structure.

[0170] Second Set of Clauses1. An object clamping system comprising: an object support structure; a clamp configured to support an object on the object support structure, wherein the clamp defines a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact; a gas supply system configured to supply a backfill gas to the gap; and a controller configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap in response to a radiation exposure of the object.2. The object clamping system of clause 1 , wherein the controller is further configured to limit a heat transfer rate from the object to the clamp and the object support structure by dynamically adjusting the characteristic of the backfill gas.3. The object clamping system of clause 1, wherein the characteristic of the backfill gas comprises a backfill gas pressure.4. The object clamping system of clause 3, wherein the controller is further configured to reduce the thermal contact by adjusting the backfill gas pressure in response to the object being loaded on the clamp.5. The object clamping system of clause 4, wherein the controller adjusts the backfill gas pressure by reducing an amount of backfill gas or turning off the gas supply system.6. The object clamping system of clause 3, wherein the controller is further configured to increase the thermal contact by adjusting the backfill gas pressure at an onset of the radiation exposure of the object.7. The object clamping system of clause 1, wherein the backfill gas comprises hydrogen gas.8. The object clamping system of clause 1, further comprising a cooling structure configured to cool the object support structure, or the clamp, or both the object support structure and the clamp.9. The object clamping system of clause 1, wherein the object comprises a reticle and the object support structure comprises a reticle support structure.10. The object clamping system of clause 1, wherein the object comprises a wafer and the object support structure comprises a wafer support structure.11. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning system configured to impart a pattern onto the radiation beam to form a patterned beam; a projection system configured to project the patterned beam onto a target section of a substrate; and an object clamping system, comprising: an object support structure;a clamp configured to support an object on the object support structure, wherein the clamp defines a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact; a gas supply system configured to supply a backfill gas to the gap; and a controller configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap in response to a radiation exposure of the object.12. The lithographic apparatus of clause 11, wherein the controller is further configured to limit a heat transfer rate from the object to the clamp and the object support structure by dynamically adjusting the characteristic of the backfill gas.13. The lithographic apparatus of clause 11, wherein the characteristic of the backfill gas comprises a backfill gas pressure.14. The lithographic apparatus of clause 13, wherein the controller is further configured to reduce the thermal contact by adjusting the backfill gas pressure in response to the object being loaded on the clamp.15. The lithographic apparatus of clause 14, wherein the controller adjusts the backfill gas pressure by reducing an amount of backfill gas or turning off the gas supply system.16. The lithographic apparatus of clause 13, wherein the controller is further configured to increase the thermal contact by adjusting the backfill gas pressure at an onset of the radiation exposure of the object.17. The lithographic apparatus of clause 11, wherein the backfill gas comprises hydrogen gas.18. The lithographic apparatus of clause 11, further comprising a cooling structure configured to cool the object support structure, or the clamp, or both the object support structure and the clamp.19. The lithographic apparatus of clause 11, wherein the object comprises a reticle and the object support structure comprises a reticle support structure.20. The lithographic apparatus of clause 11 , wherein the object comprises a wafer and the object support structure comprises a wafer support structure.21. A method comprising: loading an object on a clamp configured to support the object on an object support structure; supplying backfill gas, with a gas supply system, to a gap between a backside of the object and the clamp; adjusting a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap; and exposing the object to radiation.22. The method of clause 21, wherein the adjusting the thermal contact comprises limiting a heat transfer rate from the object to the clamp and the object support structure by dynamically adjusting the characteristic of the backfill gas.23. The method of clause 21, wherein the adjusting the thermal contact comprises adjusting a backfill gas pressure at an onset of the exposing the object to radiation.24. The method of clause 21 , further comprising turning off the gas supply system when a second object is loaded on the clamp.25. The method of clause 21, wherein the loading the object on the clamp comprises loading a reticle on a clamp configured to support the reticle on a reticle support structure.26. An object clamping system comprising: an object support structure; a clamp coupled to the object support structure and configured to support an object on the object support structure, wherein the clamp defines a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact; a gas supply system configured to supply a backfill gas to the gap; and a controller configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap such that the object remains in a saturated state; wherein the controller dynamically adjusts the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from a radiation source or a radiation detector; and wherein each exposure signal indicates an exposure period when the object is exposed to radiation and each non-exposure signal indicates a non-exposure period when the object is not exposed to radiation.27. The object clamping system of clause 26, wherein the characteristic of the backfill gas comprises a backfill gas pressure.28. The object clamping system of clause 26, wherein the controller is further configured to reduce the thermal contact by reducing an amount of backfill gas or turning off the gas supply system in response to each non-exposure signal.29. The object clamping system of clause 28, wherein the reducing the thermal contact comprises decreasing a heat transfer coefficient between the object and the clamp.30. The object clamping system of clause 28, wherein the controller is further configured to reduce the thermal contact during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period.31. The object clamping system of clause 26, wherein the controller is further configured to increase the thermal contact by increasing an amount of backfill gas or turning on the gas supply system in response to each exposure signal.32. The object clamping system of clause 26, wherein the controller is further configured to initiate an object support exchange process or a wafer exchange process during a non-exposure period.33. The object clamping system of clause 26, wherein the object comprises a reticle and the object support structure comprises a reticle support structure.34. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning system configured to impart a pattern onto the radiation beam to form a patterned beam; a projection system configured to project the patterned beam onto a target section of a substrate; and an object clamping system, comprising: an object support structure; a clamp coupled to the object support structure and configured to support an object on the object support structure, wherein the clamp defines a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact; a gas supply system configured to supply a backfill gas to the gap; and a controller configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap such that the object remains in a saturated state; wherein the controller dynamically adjusts the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from a radiation source or a radiation detector; and wherein each exposure signal indicates an exposure period when the object is exposed to radiation and each non-exposure signal indicates a non-exposure period when the object is not exposed to radiation.35. The lithographic apparatus of clause 34, wherein the characteristic of the backfill gas comprises a backfill gas pressure.36. The lithographic apparatus of clause 34, wherein the controller is further configured to reduce the thermal contact by reducing an amount of backfill gas or turning off the gas supply system in response to each non-exposure signal.37. The lithographic apparatus of clause 36, wherein the reducing the thermal contact comprises decreasing a heat transfer coefficient between the object and the clamp.38. The lithographic apparatus of clause 36, wherein the controller is further configured to reduce the thermal contact during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period.39. The lithographic apparatus of clause 34, wherein the controller is further configured to increase the thermal contact by increasing an amount of backfill gas or turning on the gas supply system in response to each exposure signal.40. The lithographic apparatus of clause 34, wherein the controller is further configured to initiate an object support exchange process or a wafer exchange process during a non-exposure period.41. The lithographic apparatus of clause 34, wherein the object comprises a reticle and the object support structure comprises a reticle support structure.42. A method comprising: supporting an object on a clamp configured to support the object on an object support structure;receiving a signal from a radiation source or a radiation detector indicating whether the object is exposed to radiation; and adjusting a thermal contact between the object and the clamp by dynamically adjusting a characteristic of a backfill gas at a gap between a backside of the object and the clamp such that the object remains in a saturated state, wherein the backfill gas is supplied by a gas supply system to the gap.43. The method of clause 42, wherein: the receiving the signal comprises receiving a non-exposure signal indicating a non-exposure period when the object is not exposed to radiation; and the adjusting the thermal contact comprises reducing the thermal contact by reducing an amount of backfill gas or turning off the gas supply system in response to the non-exposure signal.44. The method of clause 42, wherein: the receiving the signal comprises receiving an exposure signal indicating an exposure period when the object is exposed to radiation; and the adjusting the thermal contact comprises increasing the thermal contact by increasing an amount of backfill gas or turning on the gas supply system in response to the exposure signal.45. The method of clause 42, wherein the adjusting the thermal contact comprises reducing the thermal contact during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period.46. The method of clause 42, further comprising initiating an object support exchange process or a wafer exchange process during a non-exposure period.47. The method of clause 42, wherein the supporting the object on the clamp comprises supporting a reticle on a reticle support structure.

Claims

CLAIMS1. An object clamping system comprising: an object support structure; a clamp configured to support an object on the object support structure, wherein the clamp defines a gap between a backside of the object and the clamp such that the object and the clamp are not in full contact; a gas supply system configured to supply a backfill gas to the gap; and a controller configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap in response to a radiation exposure of the object.

2. The object clamping system of claim 1, wherein the controller is further configured to limit a heat transfer rate from the object to the clamp and the object support structure by dynamically adjusting the characteristic of the backfill gas.

3. The object clamping system of claim 1, wherein the characteristic of the backfill gas comprises a backfill gas pressure.

4. The object clamping system of claim 3, wherein the controller is further configured to reduce the thermal contact by adjusting the backfill gas pressure in response to the object being loaded on the clamp.

5. The object clamping system of claim 3, wherein the controller is further configured to increase the thermal contact by adjusting the backfill gas pressure at an onset of the radiation exposure of the object.

6. The object clamping system of claim 1 , wherein the controller is further configured to control the gas supply system and to adjust a thermal contact between the object and the clamp by dynamically adjusting a characteristic of the backfill gas in the gap such that the object remains in a saturated state; wherein the controller dynamically adjusts the characteristic of the backfill gas in response to a sequence of alternating exposure signals and non-exposure signals received from a radiation source or a radiation detector; and wherein each exposure signal indicates an exposure period when the object is exposed to radiation and each non-exposure signal indicates a non-exposure period when the object is not exposed to radiation.

7. The object clamping system of claim 6, wherein the controller is further configured to reduce the thermal contact by reducing an amount of backfill gas or turning off the gas supply system in response to each non-exposure signal.

8. The object clamping system of claim 7, wherein the controller is further configured to reduce the thermal contact during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period.

9. The object clamping system of claim 6, wherein the controller is further configured to increase the thermal contact by increasing an amount of backfill gas or turning on the gas supply system in response to each exposure signal.

10. The object clamping system of claim 1, wherein the object comprises a reticle and the object support structure comprises a reticle support structure.

11. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning system configured to impart a pattern onto the radiation beam to form a patterned beam; a projection system configured to project the patterned beam onto a target section of a substrate; and an object clamping system according to any one of claims 1-10.

12. A method comprising: loading an object on a clamp configured to support the object on an object support structure; receiving a signal from a radiation source or a radiation detector indicating whether the object is exposed to radiation; and adjusting a thermal contact between the object and the clamp by dynamically adjusting a characteristic of a backfill gas at a gap between a backside of the object and the clamp, wherein the backfill gas is supplied by a gas supply system to the gap.

13. The method of claim 12, wherein the adjusting the thermal contact comprises limiting a heat transfer rate from the object to the clamp and the object support structure by dynamically adjusting the characteristic of the backfill gas.

14. The method of claim 12, wherein the adjusting the thermal contact comprises adjusting a backfill gas pressure at an onset of the exposing the object to radiation.

15. The method of claim 12, further comprising turning off the gas supply system when a second object is loaded on the clamp.

16. The method of claim 12, wherein: the receiving the signal comprises receiving a non-exposure signal indicating a non-exposure period when the object is not exposed to radiation; and the adjusting the thermal contact comprises reducing the thermal contact by reducing an amount of backfill gas or turning off the gas supply system in response to the non-exposure signal.

17. The method of claim 12, wherein: the receiving the signal comprises receiving an exposure signal indicating an exposure period when the object is exposed to radiation; and the adjusting the thermal contact comprises increasing the thermal contact by increasing an amount of backfill gas or turning on the gas supply system in response to the exposure signal.

18. The method of claim 12, wherein the adjusting the thermal contact comprises reducing the thermal contact during a preceding non-exposure period such that heating of the object is minimized during a subsequent exposure period.

19. The method of claim 12, further comprising initiating an object support exchange process or a wafer exchange process during a non-exposure period.

20. The method of claim 12, wherein the supporting the object on the clamp comprises supporting a reticle on a reticle support structure.

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