Lithographic apparatus, substrate table, and method

Abstract

To provide structures and methods for substrate tables that allow increased wear resistance and frictional properties that are conducive to engaging and disengaging a substrate when required.SOLUTION: A substrate table for supporting a substrate includes a surface and coarse burls. Each of the coarse burls includes a burl-top surface and fine burls. The coarse burls are disposed on the surface of the substrate table. The fine burls are disposed on the burl-top surface. The fine burls contact the substrate when the substrate table supports the substrate.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62 / 852,578, filed May 24, 2019, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a substrate table, a textured table surface, and a method for employing burls and nanostructures on a substrate table surface. [Background technology]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device, alternatively referred to as a mask or reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of one or several dies) on the substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning a radiation beam across the pattern in a given direction (the "scan" direction) while the substrate is scanned synchronously parallel or anti-parallel to the direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004]

[0004] Another lithography system is an interference lithography system in which there is no patterning device, and the light beam is split into two beams that are made to interfere at a target portion of the substrate through the use of a reflection system. The interference causes a line to be formed in the target portion of the substrate.

[0005] During lithography operations, various processing steps may require different layers to be formed sequentially on a substrate. Therefore, it may be necessary to position the substrate with high precision relative to previous patterns formed. Generally, alignment marks are placed on the substrate and positioned with respect to a second object to be aligned. Lithography apparatuses can use alignment devices to detect the positions of the alignment marks and to align the substrate using the alignment marks to ensure accurate exposure from the mask. Misalignment between alignment marks of two different layers is measured as an overlay error.

[0006] To monitor the lithography process, parameters of the patterned substrate are measured. These parameters can include, for example, the overlay error between successive layers formed within or on the patterned substrate and the critical linewidth of the developed photosensitive resist. This measurement can be performed on the product substrate and / or on a dedicated metrology target. Various techniques exist for making measurements of the microstructures formed in the lithography process, including the use of scanning electron microscopes and various specialized tools. A fast and non-invasive form of specialized inspection tool is a scatterometer, in which a beam of radiation is directed onto a target on the surface of the substrate and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it is reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. A spectroscopic scatterometer directs a broadband beam of radiation onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered within a specific, narrow angular range. In contrast, angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0007] Such optical scatterometers can be used to measure parameters such as the critical dimensions of a developed photosensitive resist or the overlay error (OV) between two layers formed in or on a patterned substrate. The properties of the substrate can be determined by comparing the properties of the illumination beam before and after the beam has been reflected or scattered by the substrate.

[0008]

[0008] It is desirable to define and maintain tribological properties (e.g., friction, hardness, wear) on the surface of a substrate table. Substrate tables have surface level tolerances that can be difficult to meet due to the precise requirements of lithography and metrology processes. Wafers (e.g., semiconductor substrates) that are relatively thin (e.g., less than 1 mm thick) compared to the width of their surface area (e.g., greater than 100 mm) are particularly sensitive to non-uniformities in the substrate table. In addition, extremely smooth surfaces that come into contact can "stick" to each other, which can be problematic when the substrate has to be released from the substrate table. It is desirable to develop structures and methods for substrate tables that can increase wear resistance and friction properties to aid in engagement and release of substrates when required. Summary of the Invention

[0009] In some embodiments, a substrate table for supporting a substrate comprises a surface and coarse burls. Each coarse burl comprises a burl top surface and a fine burl. The coarse burls are disposed on the surface of the substrate table. The fine burls are disposed on the burl top surface and are configured to contact the substrate when the substrate table supports the substrate.

[0010] In some embodiments, a lithographic apparatus comprises an illumination system, a support, a projection system, and a substrate table. The substrate table comprises a surface and coarse burrs. Each of the coarse burrs comprises a burr top surface and a fine burr. The coarse burrs are arranged on the surface of the substrate table. The fine burrs are arranged on the burr top surface and configured to contact the substrate when the substrate table supports the substrate. The illumination system is configured to generate a beam of radiation. The support is configured to support a patterning device to impart a pattern on the beam. The projection system is configured to project the patterned beam onto the substrate.

[0011] In some embodiments, a method for fabricating a substrate table includes supporting the substrate table to receive a fabrication process, and fabricating a coarse burr and a fine burr on the substrate table, wherein fabricating the coarse burr and the fine burr includes disposing the fine burr on a burr top surface of the coarse burr.

[0012]

[0012] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are described herein for illustrative purposes only. Further embodiments will be readily apparent to those skilled in the art based on the teachings contained herein. [Brief explanation of the drawings]

[0013]

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

[0014] [Figure 1A]

[0014] FIG. 1 shows a schematic diagram of a reflective lithographic apparatus according to some embodiments. [Figure 1B]

[0015] 1 shows a schematic diagram of a transmissive lithographic apparatus according to some embodiments; [Figure 2]

[0016] 1 shows a more detailed schematic diagram of a reflective lithographic apparatus according to some embodiments; [Figure 3]

[0017] 1 shows a schematic diagram of a lithographic cell according to some embodiments. [Figure 4]

[0018] 1 shows a schematic diagram of a substrate stage according to some embodiments. [Figure 5]

[0019] 1 depicts a schematic cross-sectional view of a region of a substrate table according to some embodiments; [Figure 6]

[0020] 10 shows a graph of burl top surface contact area versus clamp pressure according to some embodiments. [Figure 7]

[0021] 1 depicts a schematic cross-sectional view of a region of a substrate table according to some embodiments; [Figure 8]

[0022] 5 illustrates method steps for fabricating a substrate table according to some embodiments; DETAILED DESCRIPTION OF THE INVENTION

[0015]

[0023] The features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the drawings, in which like reference numerals identify corresponding elements throughout. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Furthermore, the leftmost digit(s) of a reference number generally identify the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as drawings to scale.

[0016]

[0024] This specification discloses one or more embodiments incorporating features of the present invention. The disclosed embodiment or embodiments are merely exemplary of the invention. The scope of the invention is not limited to the disclosed embodiment or embodiments. The invention is defined by the claims appended hereto.

[0017]

[0025] References to described embodiments, and to "one embodiment," "an embodiment," "an exemplary embodiment," etc., herein indicate that the described embodiments may include a particular feature, structure, or characteristic, but that each embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is understood that it is within the knowledge of one of ordinary skill in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0018]

[0026] Spatially relative terms such as "beneath," "below," "lower," "above," "on," "upper," and the like may be used herein to facilitate describing the relationship of one element or feature to another element or features, as shown in the figures. Spatially relative terms are intended to encompass various orientations of the device in use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0019]

[0027] As used herein, the term "about" refers to a given quantity that can vary based on a particular technique. Based on a particular technique, the term "about" can refer to a given quantity that can vary within a range of, for example, 10 to 30% of that value (e.g., ±10%, ±20%, or ±30% of that value).

[0020]

[0028] Before describing such embodiments in detail, it will be useful to present an example environment in which embodiments of the present disclosure can be implemented.

[0021]

[0029] Exemplary Lithography System

[0030] 1A and 1B are schematic diagrams of lithographic apparatus 100 and lithographic apparatus 100', respectively, in which embodiments of the present disclosure may be implemented. Lithographic apparatus 100 and lithographic apparatus 100' each comprise: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet radiation or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100' also comprise a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. In lithographic apparatus 100, patterning device MA and projection system PS are reflective. In lithographic apparatus 100', patterning device MA and projection system PS are transmissive.

[0022]

[0031] The illumination system IL may 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.

[0023]

[0032] The support structure MT holds the patterning device MA in a manner that depends on conditions such as the orientation of the patterning device MA relative to a reference frame, the design of at least one of lithographic apparatuses 100 and 100′, and whether or not the patterning device is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be, for example, a frame or a table, and may be fixed or movable as required. 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.

[0024]

[0033] The term "patterning device" MA should be interpreted broadly to refer to any device that can be used to impart a radiation beam B with a pattern in its cross-section to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0025]

[0034] Patterning device MA can be transmissive (as in lithographic apparatus 100′ of FIG. 1B) 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 B in different directions. The tilted mirrors impart a pattern to a radiation beam B that is reflected by the matrix of small mirrors.

[0026]

[0035] As used herein, the term "projection system" PS can include any type of projection system, including refractive, reflective, magnetic, electromagnetic, electrostatic, or any combination thereof, appropriate to the exposure radiation used or other factors such as the use of an immersion liquid or the use of a vacuum. A vacuum environment may be used for EUV or electron beam radiation, as other gases may be too absorbing of the radiation or electrons. A vacuum environment may therefore be provided throughout the beam path using a vacuum wall and vacuum pumps.

[0027]

[0036] Lithographic apparatus 100 and / or lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, the additional substrate tables WT may be used in parallel, or one or more substrate tables WT may be used for exposure while preparatory steps are performed on one or more other tables. In some circumstances, the additional tables may not be substrate tables WT.

[0028]

[0037] The lithographic apparatus may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system and the substrate. Immersion liquids may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. As used herein, the term "immersion" does not mean that a structure such as the substrate must be submerged in liquid, but rather that a liquid is present between the projection system and the substrate during exposure.

[0029]

[0038] 1A and 1B, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example if the source SO is an excimer laser. In this case, 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 via a beam delivery system BD (FIG. 1B), which may comprise, for example, appropriate directing mirrors and / or beam expanders. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example if the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, may be referred to as a radiation system.

[0030]

[0039] The illuminator IL may comprise an adjuster AD (FIG. 1B) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may comprise various other components (FIG. 1B), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to obtain a desired uniformity and intensity distribution in its cross-section.

[0031]

[0040] Referring to Figure 1A, a radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT, and is patterned by the patterning device. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometric device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. Patterning device (eg mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0032]

[0041] Referring to Figure 1B, a radiation beam B is incident on a patterning device (e.g., mask MA), which is held on a support structure (e.g., mask table MT), and is patterned by the patterning device. After traversing the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The projection system has a pupil PPU that is conjugate with the illumination system pupil IPU. A portion of the radiation arises from the intensity distribution in the illumination system pupil IPU and traverses the mask pattern without being affected by diffraction at the mask pattern, producing an image of the intensity distribution in the illumination system pupil IPU.

[0033]

[0042] The projection system PS projects an image MP' of the mask pattern MP. The image MP' is formed on a photoresist layer coated on the substrate W by diffracted beams generated from the mark pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Non-zero-order diffraction of radiation at the array produces stimulated diffraction beams whose direction is changed perpendicular to the lines. Non-diffracted beams (i.e., so-called zero-order diffraction beams) traverse the pattern without changing their direction of propagation. The zero-order diffraction beams traverse the upper lens or upper lens group of the projection system PS, which is upstream of the conjugate pupil PPU of the projection system PS, and reach the conjugate pupil PPU. The portion of the intensity distribution in the plane of the conjugate pupil PPU associated with the zero-order diffraction beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD is, for example, arranged in or approximately in a plane containing the conjugate pupil PPU of the projection system PS.

[0034]

[0043] The projection system PS is positioned to capture not only the zeroth-order diffracted beam but also first-order or higher-order diffracted beams (not shown) via a lens or lens group L. In some embodiments, the resolution-enhancing effect of dipole illumination can be exploited by using dipole illumination to image a line pattern extending in a direction perpendicular to the line. For example, a first-order diffracted beam interferes with a corresponding zeroth-order diffracted beam at the level of the wafer W to produce an image of the line pattern MP at the highest possible resolution and process window (i.e., usable depth of focus combined with an acceptable exposure dose deviation). In some embodiments, astigmatism can be reduced by providing a radial pole (not shown) in an opposing quadrant of the illumination system pupil IPU. Furthermore, in some embodiments, astigmatism can be reduced by blocking the zeroth-order beam in a conjugate pupil PPU of the projection system associated with the radial pole in the opposing quadrant. This is described in more detail in U.S. Pat. No. 7,511,799 B2, issued March 31, 2009, which is incorporated herein by reference in its entirety.

[0035]

[0044] With the aid of a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. to position different target portions C in the path of the radiation beam B). Similarly, the mask MA can be accurately positioned with respect to the path of the radiation beam B (e.g. after mechanical removal of the mask library or during a scan) using the first positioner PM and a further position sensor (not shown in FIG. 1B ).

[0036]

[0045] In general, movement of the mask table MT may 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 may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks as illustrated occupy dedicated target portions, but may also be located in spaces between the target portions (these are 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 may be located between the dies.

[0037]

[0046] The mask table MT and patterning device MA may be within a vacuum chamber V. An in-vacuum robot IVR may be used to move the patterning device, such as a mask, in and out of the vacuum chamber. Alternatively, if the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot may be used for various transport tasks, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for smooth movement of any payload (e.g., a mask) to a fixed kinematic mount in the transfer station.

[0038]

[0047] The depicted lithographic apparatus 100 and 100' can be used in at least one of the following modes:

[0039]

[0048] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C in one go (i.e. a single static exposure), and the substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0040]

[0049] 2. In scan mode, the support structure (e.g. 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 (e.g. mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0041]

[0050] 3. In another mode, the support structure (e.g. mask table) MT holds a programmable patterning device and is kept essentially stationary, while the substrate table WT is moved or scanned while projecting a pattern imparted to the radiation beam B onto a target portion C. A pulsed radiation source SO can be used, with the programmable patterning device being updated as required with each movement of the substrate table WT, or between successive pulses of radiation during a scan. This mode of operation is readily adaptable to maskless lithography using a programmable patterning device such as a programmable mirror array.

[0042]

[0051] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0043]

[0052] In a further embodiment, the lithographic apparatus 100 comprises an extreme ultraviolet (EUV) radiation source. The extreme ultraviolet radiation source is configured to generate a beam of EUV radiation for EUV lithography. Typically, the EUV radiation source is arranged in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV radiation source.

[0044]

[0053] FIG. 2 shows lithographic apparatus 100 in more detail, including a source collector apparatus SO, an illumination system IL, and a projection system PS. The source collector apparatus SO is constructed and arranged to maintain a vacuum environment within an enclosure 220 of the source collector apparatus SO. The EUV radiation-emitting plasma 210 can be formed by a discharge-produced plasma source. To generate EUV radiation, a very hot plasma 210 can be generated from a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 can be generated, for example, by creating an at least partially ionized plasma using a discharge. For efficient radiation generation, a partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required. In some embodiments, a plasma of excited tin (Sn) is provided to generate EUV radiation.

[0045]

[0054] Radiation emitted by the high temperature plasma 210 is delivered from the source chamber 211 into the collector chamber 212 via an optional gas barrier or contaminant trap 230 (sometimes also referred to as a contaminant barrier or foil trap) positioned in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further illustrated herein includes at least a channel structure.

[0046]

[0055] Collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected by a grating spectral filter 240 and focused to a virtual source point IF. The virtual source point IF is commonly called the intermediate focus, and the source collector arrangement is positioned such that the intermediate focus IF is located at or near the opening 219 of the enclosure structure 220. The virtual source point IF is an image of the radiation-emitting plasma 210. The grating spectral filter 240 is used to suppress, in particular, infrared (IR) radiation.

[0047]

[0056] The radiation then traverses an illumination system IL, which may comprise a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA and to provide a desired radiation intensity uniformity at the patterning device MA. When the radiation beam 221 is reflected from the patterning device MA, which is held by a support structure MT, a patterned beam 226 is formed which is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by a wafer stage or substrate table WT.

[0048]

[0057] In general, more elements than shown may be present in illumination optics unit IL and projection system PS. Grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Furthermore, more mirrors may be present than shown in Figure 2, for example, there may be one to six additional reflective elements in projection system PS compared to what is shown in Figure 2.

[0049]

[0058] 2 is shown as a nested collector with grazing incidence reflectors 253, 254, and 255, as just one example of a collector (or collector mirror). Grazing incidence reflectors 253, 254, and 255 are arranged axially symmetrically about optical axis O, and this type of collector system CO is suitable for use in combination with a discharge produced plasma source, often referred to as a DPP source.

[0050]

[0059] Exemplary Lithography Cell

[0060] FIG. 3 illustrates a lithography cell 300, sometimes referred to as a lithocell or cluster, according to some embodiments. Lithography apparatus 100 or 100′ can form part of lithography cell 300. Lithography cell 300 can also include one or more devices that perform pre-exposure and post-exposure processes on a substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing exposed resist, a chill plate CH, and a bake plate BK. A substrate handler, or robot RO, retrieves substrates from input / output ports I / O1 and I / O2, moves them between various process tools, and delivers them to a loading bay LB of lithography apparatus 100 or 100′. These devices, often collectively referred to as a track, are under the control of a track control unit TCU. The TCU is itself controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, these various tools can be operated to maximize throughput and processing efficiency.

[0051]

[0061] The disclosed embodiments may be implemented in hardware, firmware, software, or any combination thereof. The disclosed embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and / or instructions may be described herein as performing certain operations. However, it should be understood that such description is for convenience only and that such operations actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc.

[0052]

[0062] Exemplary Substrate Table

[0063] FIG. 4 shows a schematic diagram of a substrate stage 400 according to some embodiments. In some embodiments, the substrate stage comprises a substrate table 402, a support block 404, and one or more sensor structures 406. In some embodiments, the substrate table 402 comprises a clamp (e.g., an electrostatic clamp) for holding a substrate 408. In some embodiments, each of the one or more sensor structures 406 comprises a transmission image sensor (TIS) plate. A TIS plate is a sensor unit comprising one or more sensors and / or markers for use in a TIS sensing system used to accurately position a wafer relative to the position of a projection system (e.g., projection system PS, FIG. 1) and a mask (e.g., mask MA, FIG. 1) of a lithographic apparatus (e.g., lithographic apparatus 100, FIG. 1). The TIS plate is shown here for illustrative purposes, and embodiments herein are not limited to any particular sensor. The substrate table 402 is disposed on the support block 404. The one or more sensor structures 406 are disposed on the support block 404.

[0053]

[0064] In some embodiments, when the substrate stage 400 supports the substrate 408 , the substrate 408 is disposed on the substrate table 402 .

[0054]

[0065] Terms such as "flat," "flatness," and the like may be used herein to describe a structure with respect to the general plane of the surface. For example, a curved or uneven surface may be a surface that does not conform to a flat surface. Protrusions and depressions on a surface may also be characterized as deviations from a "flat" surface.

[0055]

[0066] Terms such as "smoothness" and "roughness" can be used herein to describe local variations, minute deviations, graininess, or texture of a surface. For example, surface roughness can refer to the minute deviation of a surface profile from a mean line or plane. The deviation is generally measured (in length units) as an amplitude parameter, such as the root mean square (RMS) or arithmetic mean deviation (Ra) (e.g., 1 nm RMS).

[0056]

[0067] In some embodiments, the surface of the aforementioned substrate table (e.g., wafer table WT in FIGS. 1A and 1B, substrate table 402 in FIG. 4) can be flat or burled. When the surface of the substrate table is flat, any particles or contaminants that get stuck between the substrate table and the wafer will print the contaminants through the wafer and cause lithography errors in its vicinity. Thus, the contaminants reduce device yield rates and increase production costs.

[0057]

[0068] Arranging burls on a substrate table helps reduce the undesirable effects of a flat substrate table. When a wafer is clamped to a substrate table with burls, free space in the area where the wafer is not in contact with the substrate table is available. The free space acts as a pocket for contaminants to prevent print errors. Another advantage is that contaminants placed on the burls are more likely to be fractured due to the increased load caused by the burls. Breaking up contaminants also helps mitigate print-through errors. In some embodiments, the combined surface area of the burls can be approximately 1-5% of the surface area of the substrate table. Here, the surface area of the burls refers to the surface that will come into contact with the wafer (e.g., not including the sidewalls). Furthermore, the surface area of the substrate table refers to the span of the surface of the substrate table on which the burls reside (e.g., not including the sides or back of the substrate table). When a wafer is clamped to a substrate table with burls, the load is increased by 100 times compared to a flat substrate table, sufficient to fracture most contaminants. Although the examples herein use a substrate table, this example is not intended to be limiting. For example, embodiments of the present disclosure can be implemented on a reticle table, for a variety of clamping structures (e.g., electrostatic clamps, clamping membranes), and in a variety of lithography systems (e.g., EUV, DUV).

[0058]

[0069] The burl-to-wafer interface, in turn, determines the functional performance of the substrate table. When the surface of the substrate table is smooth, adhesive forces can develop between the smooth surface of the substrate table and the smooth surface of the wafer. The phenomenon of two smooth surfaces coming into contact and sticking to each other is known as ringing. Ringing can cause problems during device fabrication, such as overlay issues due to high friction and in-plane stresses within the wafer (optimally, the wafer should be slippery during alignment). One way to reduce friction at the burl-to-wafer interface is to coat the burls with a low-friction coating (e.g., diamond-like carbon). However, in the presence of water (e.g., immersion lithography), the coating can smooth quite quickly. Another way to reduce friction at the burl-to-wafer interface is to roughen the burl top surface to reduce the contact surface area. However, rough burl tops do not retain their roughness for long. The higher the initial roughness of the burl top, the faster it can smooth and wear.

[0059]

[0070] Furthermore, it has been observed that the burled surface of the substrate table is prone to wear very quickly (i.e., uneven wear), especially at the edges far from the center of the substrate table. Uneven wear can cause the wafer to curve when clamped to the substrate table, which in turn reduces the accuracy of lithographic placement of device features, overlay drift over time, etc. Overall wear can also reintroduce ringing problems and lead to reduced imaging performance due to changes in the spherical shape of the clamping surface.

[0060]

[0071] To prevent frictional wear of the surface, the surface properties of the substrate table can be manipulated, for example by designing nanostructures (e.g. nanopillars or micro-burls) on the burl top surface, i.e. going from a random surface design (coarseness) to a deterministic surface design. The term "micro-burls" may be used herein to refer to a deterministic nano-pillar design on the surface of said burls (e.g. coarse burls). Embodiments of the present disclosure provide structures and methods for manipulating the tribological properties of the surface of a substrate table.

[0061]

[0072] Figure 5 shows a cross-sectional schematic view of a region of a substrate table 500 according to some embodiments. The substrate table 500 comprises a surface 502 and coarse burls 504. Each of the coarse burls 504 comprises a burl top surface 506 and fine burls 508, which are shown in inset 510. The inset 510 is a top-down view of the coarse burls 504.

[0062]

[0073] In some embodiments, coarse burls 504 are disposed on surface 502. Fine burls 508 are disposed on burl top surface 506. While FIG. 5 depicts the coarse burls 504 and fine burls 508 as having circular areas, it should be understood that the coarse burls 504 and fine burls 508 can have other area shapes (e.g., square, oval, etc.). Also, while FIG. 5 depicts the fine burls 508 as having a circular and / or octagonal arrangement, any number of fine burls 508 (including one) and any arrangement (e.g., a grid or random distribution) across the burl top surface 506 can be used.

[0063]

[0074] In some embodiments, each of the coarse burrs 504 has a width or diameter of approximately 100-1000 microns (parallel to the plane of the surface 502). Each of the coarse burrs 504 has a height of approximately 10-200, 10-150, or 10-100 microns (perpendicular to the plane of the surface 502). Each of the fine burrs 508 has a width or diameter of approximately 1-15 microns. Each of the fine burrs 508 has a height of approximately 10-50, 20-40, or 20-30 nm. The distance between two fine burrs is approximately 50-200, 50-150, or 50-100 microns. Each of the fine burrs 508 has a contact area (for contacting the substrate 518) with a surface roughness of less than approximately 1 nm RMS.

[0064]

[0075] Other dimensions may be selected for the coarse burrs 504 and / or the fine burrs 508. For example, the dimensions for the coarse burrs 504 may be based on the size of typical or expected contaminant particles in a lithographic apparatus.

[0065]

[0076] Contact surface area is a parameter that affects friction, and therefore dimensions for the coarse burrs 504 and / or fine burrs 508 can be based on the contact area to achieve a specified friction.

[0066]

[0077] In some embodiments, the substrate table 500 is configured to support a substrate 518. The substrate table 500 can be switched between two states: an engaged state (clamped substrate) and a released state (unclamped substrate). In the released state, the load between the burl top surface 506 and the substrate 518 is primarily due to gravity acting on the substrate 518 (low load). In the low load state, the substrate 518 is in contact with the fine burls 508 and not with the burl top surface 506. The aforementioned dimensions of the fine burls 508 improve the performance of the substrate table 500, for example, by having a relatively small contact area to reduce friction and a height designed to mitigate wear. That is, in some embodiments, the combined surface area of the fine burls 508 can be approximately 1-5% of the surface area of the burl top surface 506. The effect of wear is reduced because the load is spread over a larger burl area at medium loads, when most wear is expected to occur. The relationship between load / pressure and burl contact area is discussed below with reference to FIG. 6. In a different comparison, the combined surface area of the micro-burls 508 may be approximately 0.01-0.025% of the surface area of the substrate table 500 (not including the span of the surface of the substrate table on which the burls reside, e.g., the side or back surface of the substrate table). Reducing friction also reduces in-plane stresses on the substrate 518, allowing the substrate 518 to translate more easily during alignment. Additionally, the micro-burls 508 disrupt the surface of the burl top surfaces 506 sufficiently to prevent ringing. That is, in some embodiments, the micro-burls 508 are configured to reduce ringing (or traction / adhesion) between the substrate table 500 and the substrate 518. As a result, the performance (e.g., overlay performance) of the substrate table 500 can be enhanced. The reduction in ringing is due to the fact that the micro-burls 508 act as springs that peel the substrate from the surface between the micro-burls (the burl top surfaces 506) when the clamping force is released.

[0067]

[0078] Conversely, the engagement of the substrate table 500 creates an increased load between the burl top surface 506 and the substrate 518. On a sufficiently small scale, any surface of a material can be considered elastic, compressible, or otherwise deformable ( FIG. 7 illustrates this behavior). The load can cause the substrate 518 to deform and “sink” into the fine burls 508. If the height of the fine burls 508 is appropriately selected, the substrate 518 can come into contact with the burl top surface 506. The greatly increased contact area increases the friction between the substrate table 500 and the substrate 518. As a result, the substrate 518 can be securely held to undergo a lithography process.

[0068]

[0079] In some embodiments, the height of the fine burls 508 is selected based on selected frictional characteristics. The fine burls 508 can enhance the release of the substrate 518. The height difference between the burl top surfaces 506 and the fine burls 508 causes the fine burls 508 to act like a spring and press against the substrate 518. Therefore, the substrate 518 can be prevented from sticking to the substrate table 500.

[0069]

[0080] FIG. 6 shows a graph 600 of burl top surface contact area versus clamping pressure, according to some embodiments. The vertical axis represents the percentage of the burl top surface area actually in contact with the substrate (e.g., burl top surface 706 in contact with substrate 718 in FIG. 7). The horizontal axis represents the clamping pressure or force applied to the substrate in arbitrary units (AU). Plot line 602 represents a simulation of measuring the actual contact area as the clamping force is varied (ringing effects are ignored). Adjusting the height of the fine burrs allows for adjustment of (a) the low-pressure contact area (0-1.6 AU: region 604), (b) the onset pressure of the high contact area regime (1.6 AU: region 606), and (c) the contact area at full clamping pressure (greater than 3 AU: region 608).

[0070]

[0081] The discussion so far has focused on nanopillars or micro-burrs which, among other benefits, help to reduce ringing. However, there may be situations where the presence of the micro-burrs may not provide enough force to promote consistent detachment of the substrate from the top surface of the burrs. Embodiments of the present disclosure provide structures and methods for further manipulating the tribological properties of the surface of the substrate table.

[0071]

[0082] 7 shows a cross-sectional schematic view of a region of a substrate table 700 in accordance with some embodiments. The substrate table 700 comprises a surface 702 and coarse burls 704. Each of the coarse burls 704 comprises a burl top surface 706 and fine burls 708, which are shown in inset 710. Inset 710 shows a cross-sectional view of a region of the coarse burls 704. Each of the fine burls 708 comprises a contact surface 712. In some embodiments, the burl top surface 706 comprises a roughened region 714. In some embodiments, each of the coarse burls 704 further comprises intermediate burls 716.

[0072]

[0083] In some embodiments, coarse burls 704 are disposed on surface 702. Fine burls 708 and intermediate burls 716 are disposed on burl top surface 706. The arrangement, shape, and number of fine burls 708 and / or intermediate burls 716 can be described with respect to fine burls 508 ( FIG. 5 ) for similar reasons. Additionally, intermediate burls 716 can have a height that is different from (i.e., unequal in height) that of fine burls 708. The different heights or hierarchical structure serve a similar function as roughened zones. Roughened zones 714 are disposed between fine burls 708. The term “between” can be used herein to refer to a location between, adjacent to, in the immediate vicinity, and / or in the general surrounding area. Thus, roughened zones 714 can be disposed between two of the fine burls 708 or fill the entire burl top surface 706. In some embodiments, the roughened regions 714 can be divided into patches (e.g., multiple roughened regions 714) distributed between, near, in close proximity to, and / or in the general vicinity of the fine burrs 708.

[0073]

[0084] In some embodiments, substrate table 700 is configured to support a substrate 718. A substrate surface 720 of substrate 718 is identified in Figure 7 as the surface in contact with substrate table 700. The function of substrate table 700 and its interaction with substrate 718 may be as described above for substrate table 500 and substrate 518 (Figure 5) for similar reasons. Each of the micro-burrs 708 comprises a contact area (for contacting substrate 718) having a surface roughness of less than approximately 1 nm RMS. Roughened area 714 may have a surface roughness of approximately 2-10, 2-8, or 3-5 nm RMS.

[0074]

[0085] When the substrate table 700 engages the substrate 718, the increased load can cause the substrate 718 to deform and “sink” into the micro-burls 708. This is illustrated by the substrate surface 720 in the inset 710. It is important that the substrate table 700 successfully releases the substrate 718 upon release. Ringing can cause premature wear of the micro-burls 708, especially toward the edges of the substrate table 700 where substrate movement is greatest during clamping / unclamping. Thus, in some embodiments, the roughened regions 714 can contact the substrate 718 when the substrate table 700 engages the substrate 718. In this scenario, the deformed substrate benefits from increased contact area with the burl top surfaces 706. The benefits are as described with respect to FIGS. 5 and 6. In contrast to the burl top surfaces 506 in FIG. 5, the roughened regions 714 enhance the separation of the substrate 718 from the burl top surfaces 706 upon release.

[0075]

[0086] In some embodiments, intermediate burls 716 can be used instead of or in addition to the roughened regions 714 to enhance separation of the substrates 718. The intermediate burls 716 are disposed between the fine burls 708. The layered structure (height difference) created by the intermediate burls 716 can enhance separation by further disrupting the plane of the burr top surfaces 706 in the regions between the fine burls 708.

[0076]

[0087] In some embodiments, each of the coarse burrs 704 further comprises a modified surface 722. The modified surface 722 can be disposed between two of the fine burrs 708 or can fill the entire burr top surface 706. In some embodiments, the modified surface 722 can be divided into patches (e.g., multiple modified surfaces 722) distributed between, near between, in close proximity to, and / or in the general vicinity of the fine burrs 708.

[0077]

[0088] In some embodiments, the modified surface 722 has a low surface energy that is chemically modified. Chemical modification can be achieved using, for example, a chemical bath or rinse. The low surface energy reduces the adhesion between the substrate table 700 and the substrate 718. The reduced adhesion enhances separation of the substrate 718 from the substrate table 700 when released. The modified surface 722 can be implemented instead of or in addition to the roughened areas 714 and / or intermediate burrs 716.

[0078]

[0089] 8 illustrates method steps for fabricating a substrate table according to some embodiments. In step 802, the substrate table is supported to undergo a fabrication process. In step 804, coarse burls and fine burls are fabricated on the substrate table. Fabricating the coarse burls and fine burls includes disposing the fine burls on burl top surfaces of the coarse burls. In step 806, roughened regions and / or intermediate burls are fabricated on the substrate table. Fabricating the roughened regions and / or intermediate burls further includes disposing the roughened regions and / or intermediate burls between the fine burls. Fabricating the roughened regions further includes generating the roughened regions using laser ablation, etching (e.g., reactive ion etching), and / or mechanical procedures (e.g., rough polishing). Fabricating the coarse, fine, and / or intermediate burls further includes fabricating via a lithography process as described herein. In step 808, the top burl surfaces are chemically treated (e.g. dangling bonds are suppressed) to achieve a low surface energy on the top burl surfaces. Chemical treatment or modification can be achieved, for example, by submerging or rinsing the substrate table using chemicals (e.g. acids, solvents, bases). The low surface energy reduces adhesion forces between the substrate table and the substrate.

[0079]

[0090] 8 may be performed in any conceivable order, and not all steps need to be performed. For example, step 808 may be performed instead of or in addition to step 806. The coarse, fine, and / or medium burls and roughened regions may be fabricated simultaneously, non-simultaneously, and / or in any order. In another example, step 806 may be optional (e.g., the burl top surfaces may have the same roughness as the surfaces of the fine burls). The arrangement, shape, and dimensions of the structures on the substrate table (e.g., coarse and fine burls, roughened regions, etc.) may be as described above with respect to FIGS. 5 and 7.

[0080]

[0091] In general, a deterministic burl top surface (e.g., fine burls) can break the traditional compromise between good wear performance and good friction performance. Low friction is desirable when loading a wafer to ensure that the wafer is not stressed when fully clamped. High friction is desirable when the wafer is fully clamped to prevent the wafer from moving during wafer table acceleration (or due to wafer heating). It is desirable to have a stable surface that performs over many (e.g., thousands or tens of thousands) wafer loads, where stability is related to maintaining friction characteristics and the overall flatness of the wafer table. Low friction can be achieved by limiting the surface area of contact. Limiting the surface area of contact can be achieved by roughening the surface or by using burls with a small diameter. Both can lead to higher peak loads and, therefore, faster material removal, changes in overall shape, and / or reduced roughness (changes in friction). Embodiments of the present disclosure have described how the area and height of fine burls can be adjusted to achieve desired friction and wear resistance without compromise. By adjusting the area and height of the microburls, it is possible to achieve low surface area and low friction at low loads, low to medium friction and low wear at medium loads (where most of the wear occurs), and high friction and stability at high loads by contacting the entire top surface of the burls.

[0081]

[0092] The embodiments can be further described using the following clauses. 1. A substrate table for supporting a substrate, comprising: The surface and Coarse burrs disposed on the surface, each of the coarse burrs comprising: Burl top surface, and a fine burr disposed on the burr top surface and configured to contact the substrate when the substrate table supports the substrate; a coarse burr comprising: a substrate table comprising: 2. Each of the coarse burrs comprises a contact surface configured to contact the substrate; and The contact surface has a surface roughness of less than approximately 1 nm RMS. 2. A substrate table according to clause 1. 3. A substrate table according to clause 1, wherein each of the coarse burls has a width of approximately 100 to 1000 microns and a height of approximately 10 to 200 microns. 4. A substrate table according to clause 1, wherein each of the micro-burrs has a width of approximately 1 to 10 microns. 5. The substrate table according to clause 1, wherein the micro-burrs have a height of approximately 10 to 50 nm. 6. The substrate table of clause 1, wherein the distance between two of the micro-burrs is approximately 50 to 200 microns. 7. A substrate table according to clause 1, wherein the total surface area of the contact areas of the micro-burls is less than 0.1% of the total surface area of the substrate table. 8. Each of the coarse burrs further comprises an intermediate fine burr disposed between the fine burrs on the burr top surface; and The height of the fine burrs and the height of the medium fine burrs are not the same; 2. A substrate table according to clause 1. 9. A substrate table according to clause 1, wherein the burl top surface comprises roughened regions disposed between the fine burls. 10. A substrate table according to clause 9, wherein the roughened area is configured to contact the substrate when the substrate table is engaged with the substrate. 11. A substrate table according to clause 9, wherein the roughened region has a surface roughness of approximately 2-8nm RMS. 12. The top surface of the burl has a modified surface having a chemically modified low surface energy; and the modified surface is configured to reduce adhesion forces between the substrate table and the substrate; 2. A substrate table according to clause 1. 13. A lithographic apparatus comprising: an illumination system configured to generate a beam of radiation; a support configured to support a patterning device configured to impart a pattern onto the beam; and a projection system configured to project the patterned beam onto a substrate; and a substrate table configured to support a substrate, the substrate table comprising: Surface, and a coarse burr disposed on the surface; each of the coarse burrs comprises: Burl top surface, and a fine burr disposed on the burr top surface and configured to contact the substrate when the substrate table supports the substrate; a substrate table comprising: 1. A lithographic apparatus comprising: 14. The lithographic apparatus of clause 13, wherein the micro-burrs have a height of approximately 10 to 50 nm. 15. A lithographic apparatus according to clause 13, wherein the burl top surface comprises a roughened surface disposed between the fine burls. 16. A lithographic apparatus according to clause 13, wherein the roughened surface is configured to contact the substrate when the substrate table is engaged with the substrate. 17. The lithographic apparatus of clause 16, wherein the roughened surface has a surface roughness of approximately 2-8 nm RMS. 18. A method of making a substrate table, comprising: supporting a substrate table to receive the fabrication process; and fabricating coarse burrs and fine burrs on the substrate table, wherein fabricating the coarse burrs and fine burrs comprises disposing the fine burrs on bur top surfaces of the coarse burrs; A method comprising: 19. The method of clause 18, further comprising creating a roughened region on the substrate table, wherein creating the roughened region comprises disposing the roughened region between the fine burls on the burl top surface. 20. The method of clause 19, wherein creating a roughened surface further comprises using laser ablation to create a roughened region.

[0082]

[0093] Although specific reference is made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, etc. In light of these alternative applications, those skilled in the art will recognize that when the terms "wafer" or "die" are used herein, they may be considered synonymous with the more general terms "substrate" or "target portion," respectively. The substrates described herein may be processed, before or after exposure, in, for example, a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce multi-layer ICs, and thus the term substrate, as used herein, may also refer to a substrate that already includes multiple processed layers.

[0083]

[0094] Although particular reference has been made to the use of embodiments of the present invention in the field of optical lithography, it should be understood that the present invention may also be used in other fields, for example imprint lithography, depending on the context, and is not limited to optical lithography. In imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device is imprinted into a layer of resist supplied to the substrate and the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is then removed from the resist leaving a pattern in it when the resist is cured.

[0084]

[0095] It is to be understood that the phraseology or terminology used herein is for the purpose of description and not of limitation, and accordingly, the terminology or terminology used herein should be interpreted by one of skill in the art in light of the disclosure herein.

[0085]

[0096] As used herein, the term "substrate" describes a material onto which a layer of material is added. In some embodiments, the substrate itself may be patterned, and the material added onto it may also be patterned or may remain unpatterned.

[0086]

[0097] Although specific reference may be made in this text to the use of the apparatus and / or system according to the present invention in the manufacture of ICs, it should be explicitly understood that such an apparatus and / or system has many other possible applications, such as in integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD panels, thin film magnetic heads, etc. In light of these alternative applications, those skilled in the art will recognize that any use of the terms "reticle," "wafer," or "die" herein may be considered synonymous with the more general terms "mask," "substrate," or "target portion," respectively.

[0087]

[0098] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described, and this description is not intended to limit the invention.

[0088]

[0099] It is understood that the "Description of the Invention" section, and not the "Summary" and "Abstract" sections, are intended to be used to interpret the claims. The "Summary" and "Abstract" sections may describe one or more exemplary embodiments of the invention as envisioned by the inventors, but cannot describe all exemplary embodiments, and therefore are not intended to limit the scope of the invention and the appended claims in any way.

[0089]

[0100] The present invention has been described above using functional components and their relationships that illustrate specific functional embodiments. The boundaries of these functional components have been arbitrarily defined herein for the convenience of description. Alternative boundaries may be defined as long as the specific functions and their relationships are appropriately performed.

[0090]

[0101] The foregoing description of specific embodiments fully reveals the general nature of the present invention, such that those skilled in the art can readily modify and / or adapt such specific embodiments to various uses without undue experimentation and without departing from the general concept of the present invention. Accordingly, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0091]

[0102] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. a substrate table for supporting a substrate, The surface and Coarse burrs disposed on the surface, each of the coarse burrs comprising: Burl top surface, and a fine burr disposed on the burr top surface and configured to contact the substrate when the substrate table supports the substrate; a coarse burr comprising: a substrate table comprising:

2. each of the coarse burrs comprising a contact surface configured to contact the substrate; and the contact surface has a surface roughness of less than approximately 1 nm RMS; A substrate table according to claim 1 .

3. 2. The substrate table of claim 1, wherein each of the coarse burrs has a width of approximately 100 to 1000 microns and a height of approximately 10 to 200 microns.

4. The substrate table of claim 1 , wherein each of the micro-burrs has a width of approximately 1 to 10 microns.

5. The substrate table of claim 1, wherein the micro-burrs have a height of approximately 10 to 50 nm.

6. The substrate table of claim 1, wherein the distance between two of the micro-burrs is approximately 50 to 200 microns.

7. 2. A substrate table according to claim 1, wherein the total surface area of the contact areas of the micro-burls is less than 0.1% of the total surface area of the substrate table.

8. each of the coarse burrs further comprising intermediate fine burrs disposed between the fine burrs on the burr top surface; and The height of the fine burrs and the height of the intermediate fine burrs are not similar. A substrate table according to claim 1 .

9. The substrate table of claim 1 , wherein the burl top surface comprises roughened areas disposed between the fine burls.

10. The substrate table of claim 9, wherein the roughened area is configured to contact the substrate when the substrate table is engaged with the substrate.

11. The substrate table of claim 9, wherein the roughened area has a surface roughness of approximately 2 to 8 nm RMS.

12. the top surface of the burr is provided with a modified surface having a chemically modified low surface energy; and the modified surface is configured to reduce adhesion forces between the substrate table and the substrate. A substrate table according to claim 1 .

13. 1. A lithographic apparatus comprising: an illumination system configured to generate a beam of radiation; a support configured to support a patterning device configured to impart a pattern onto the beam; and a projection system configured to project the patterned beam onto a substrate; and a substrate table configured to support the substrate, the substrate table comprising: Surface, and a coarse burr disposed on the surface; Each of the coarse burrs comprises: Burl top surface, and a fine burr disposed on the burr top surface and configured to contact the substrate when the substrate table supports the substrate; a substrate table comprising:

1. A lithographic apparatus comprising:

14. The lithographic apparatus of claim 13, wherein the micro-burrs have a height of approximately 10-50 nm.

15. The lithographic apparatus of claim 13 , wherein the burl top surface comprises a roughened surface disposed between the fine burls.

16. The lithographic apparatus of claim 13 , wherein the roughened surface is configured to contact the substrate when the substrate table is engaged with the substrate.

17. The lithographic apparatus of claim 16, wherein the roughened surface has a surface roughness of approximately 2-8 nm RMS.

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