Lithographic apparatus and design of electrostatic chuck

Abstract

Embodiments herein describe methods, apparatus, and systems for reducing the electric field at the clamp-reticle interface using an improved electrostatic clamp. Specifically, the electrostatic clamp includes a clamp body, an electrode layer disposed on a top surface of the clamp body, and a plurality of burls protruding from a bottom surface of the clamp body, the electrode layer including a plurality of notches at predetermined locations that vertically correspond to the locations of the plurality of burls on the bottom surface of the clamp body.

Description

Technical Field

[0001] Cross - reference to related applications This application claims the benefit of U.S. Provisional Application No. 62 / 927,214, filed Oct. 29, 2019, the entire disclosure of which is incorporated herein by reference.

[0002] This disclosure relates to systems and methods for electrostatic chuck design and electric field reduction in a lithographic apparatus.

Background Art

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually a target portion of the substrate. Lithographic apparatuses are used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device, also referred to as a mask or a reticle, can be used to generate a circuit pattern for an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., part of a die, one die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is typically done by imaging onto a layer of radiation - sensitive material (resist) provided on the substrate. Generally, a single substrate contains a network of adjacent target portions that are exposed successively. Known lithographic apparatuses include so - called steppers and scanners. In a stepper, each target portion is irradiated such that the entire pattern is exposed onto the target portion at once. In a scanner, each target portion is irradiated by scanning a radiation beam over the pattern in a given direction (the “scanning” direction) while synchronously scanning the substrate in the same or opposite direction parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] Lithography is widely recognized as one of the major processes in the manufacture of ICs, other devices and / or structures. However, as the dimensions of the features created using lithography become smaller, lithography has become an increasingly critical factor in enabling the manufacture of smaller ICs, other devices and / or structures.

[0005] To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that can be formed on the substrate. A lithography apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 - 20 nm (e.g., 6.7 nm or 13.5 nm) may be used to form smaller features on the substrate than, for example, a lithography apparatus using radiation having a wavelength of 193 nm.

[0006] In a lithography apparatus using EUV radiation, it may be necessary to keep the EUV radiation beam path, or at least a substantial part thereof, under vacuum during the lithography operation. In such a vacuum region of the lithography apparatus, electrostatic chucks may be used to clamp objects such as the patterning device and / or the substrate to structures of the lithography apparatus such as the patterning device table and / or the substrate table, respectively.

[0007] In some cases, an electrostatic chuck may be utilized to hold a reticle in a predetermined position in a lithography apparatus. The electrostatic chuck can include an electrode on the upper surface of the chuck and a plurality of bars disposed on the bottom surface of the chuck. When the chuck is energized (e.g., using a chuck voltage) and the reticle in contact with the bars is attracted, the upper surface of the conductive bars may have a different potential from the back surface of the reticle. This potential difference gives rise to a discharge mechanism at the moment of contact, and the two potentials become equal. This discharge mechanism can cause material movement and particle generation, and ultimately damage to the reticle and / or the chuck.

[0008] In addition, to facilitate the cooling and heat conduction of the reticle, a backfill gas may be provided at the bar-reticle interface in the electrostatic chuck. In some cases, the backfill gas can exert an additional force on the reticle that causes the reticle to lose contact with the bar of the electrostatic chuck and creates a gap between the reticle and the clamp. To counteract this force, the voltage of the electrostatic chuck may be increased. However, the increase in voltage can cause a charge difference between the bar and the back surface of the reticle, generate a discharge, and potentially damage the reticle and / or the clamp.

SUMMARY OF THE INVENTION

[0009] Accordingly, the present disclosure provides a method, apparatus, and system for minimizing the electric field and discharge at the contact point between the bar of the electrostatic chuck and the reticle.

[0010] In some embodiments, the electrostatic chuck includes a chuck body, an electrode layer disposed on the upper surface of the chuck body, and a plurality of bars protruding from the bottom surface of the chuck body. The electrode layer includes a plurality of notches at predetermined positions that vertically correspond to the positions of the plurality of bars at the bottom surface of the chuck body.

[0011] In some embodiments, a method of improving an electrostatic chuck includes fabricating an electrostatic chuck that includes a chuck body, an electrode layer disposed on the upper surface of the chuck body, and a plurality of bars protruding from the bottom surface of the chuck body, wherein the plurality of bars are configured to contact the back surface of the reticle. The method also includes applying a modification to the electrostatic chuck to reduce the electric field between the plurality of bars and the reticle.

[0012] In one embodiment, applying the modification includes reducing the thickness of the conductive coating on the reticle contact surface of the plurality of bars to allow for a reduced voltage difference between the plurality of bars and the reticle. In another embodiment, applying the modification includes removing a predetermined portion of the electrode layer at a position corresponding to the position of each bar to allow for a plurality of notches in the electrode layer.

[0013] In some other embodiments, applying the modification includes connecting each of the plurality of bars together so as to provide a virtual ground to the electrostatic clamp. In some other embodiments, applying the modification includes grounding the plurality of bars. In some other embodiments, applying the modification includes applying a conductive coating to the reticle contact surface or the back surface of the reticle of the plurality of bars, the conductive coating comprising an oxide, diamond, or diamond-like carbon (DLC) material.

[0014] In some embodiments, a lithographic apparatus includes an illumination system, a support structure, and a projection system. The illumination system is configured to condition a radiation beam. The support structure is constructed to support a patterning device that can impart a pattern to a cross-section of the radiation beam to form a patterned radiation beam. The projection system is configured to project the patterned radiation beam onto a target portion of a substrate. The support structure includes an electrostatic clamp. The electrostatic clamp includes a clamp body, an electrode layer disposed on an upper surface of the clamp body, and a plurality of bars protruding from a bottom surface of the clamp body. The electrode layer includes a plurality of notches at predetermined positions that vertically correspond to positions of the plurality of bars at the bottom surface of the clamp body.

[0015] Further features and advantages of the present invention will be described in detail below with reference to the accompanying drawings in conjunction with the structure and operation of various embodiments of the present invention. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein.

Brief Description of the Drawings

[0016] The accompanying drawings are incorporated herein and form a part thereof, illustrate the present invention, and together with the detailed description of the invention, serve to explain the principles of the invention and enable those skilled in the relevant art to manufacture and use the invention.

[0017]

Figure 1

[0018]

Figure 2

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Figure 3

[0020]

Figure 4A

Figure 4B

[0021]

Figure 5

[0022]

Figure 6A

Figure 6B

Figure 6C

[0023]

Figure 7

[0024]

Figure 8

[0025]

Figure 9

[0026] The features and advantages of the present invention will become more apparent from the detailed description of the invention described hereinafter in connection with the drawings that identify corresponding elements with like reference characters. In the drawings, like reference numerals generally refer to the same element, functionally similar elements, and / or structurally similar elements. Also, in general, the leftmost digit of a reference number represents the drawing in which that reference number first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as being to scale.

Mode for Carrying Out the Invention

[0027] This specification discloses one or more embodiments incorporating the features of this invention. The disclosed embodiments are merely illustrative of the present invention. The scope of the present invention is not limited to the disclosed embodiments. The present invention is defined by the appended claims.

[0028] The reference to an embodiment described and "one embodiment", "an embodiment", "exemplary embodiment", etc. in this specification indicates that the embodiment described may have a particular feature, structure, or characteristic, but not necessarily every embodiment has that particular feature, structure, or characteristic. Also, such expressions do not necessarily refer to the same embodiment. Further, when a particular feature, structure, or characteristic related to an embodiment is described, it should be understood that it is within the knowledge of those skilled in the art to combine and operate such feature, structure, or characteristic with other embodiments, whether or not explicitly stated.

[0029] For ease of explanation in this book, spatially relative terms such as "downward", "lower", "upward", "upper" may be used to describe the relationship between one element or feature shown in the drawings and another element or feature. Such spatially relative terms are intended to encompass different orientations of the device in use and operation in addition to the orientation shown in the illustration. The device may be in other orientations (such as a 90-degree rotation or other orientations), and the spatially relative descriptions used in this book may be interpreted accordingly in the same way.

[0030] The term "about" used in this book indicates a value of a given quantity that may vary based on a particular technology. Based on a particular technology, the term "about" can indicate, for example, a value of a given quantity that varies within a range of 10 - 30% of the value (such as ±10%, ±20%, or ±30% of the value).

[0031] Embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Also, embodiments of the present disclosure may be implemented as instructions stored in a machine-readable medium that can be loaded and executed by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (such as a computer device). For example, the machine-readable medium may be a read-only memory (ROM), a random access memory (RAM), a magnetic disk storage medium, an optical storage medium, a flash memory device, electrical, optical, acoustic, or other forms of propagated signals (such as carrier waves, infrared signals, digital signals), etc. Further, firmware, software, routines, and / or instructions may be described in this book as performing certain operations. However, such descriptions are for convenience only, and it should be understood that such operations actually occur when a computer device, processor, controller, or other device executes the firmware, software, routines, instructions, etc.

[0032] However, before describing such embodiments in more detail, it is beneficial to present an exemplary environment in which embodiments of the present disclosure can be implemented.

[0033] Example of a lithography system

[0034] FIG. 1 shows a lithography system including a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and supply the EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA includes an illumination system IL, a support structure (e.g., a mask table) MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0035] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident on the patterning device MA. To that end, the illumination system IL may include a facet field mirror device 10 and a facet pupil mirror device 11. The facet field mirror device 10 and the facet pupil mirror device 11 together provide an EUV radiation beam B having a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the facet field mirror device 10 and the facet pupil mirror device 11.

[0036] After being adjusted in this way, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. To that end, the projection system PS may comprise a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction ratio to the patterned EUV radiation beam B’ to form an image having features smaller than the corresponding features on the patterning device MA. For example, a reduction ratio of 4× or 8× may be applied. In FIG. 1 the projection system PS is illustrated as having only two mirrors 13, 14, but the projection system PS may include a different number of mirrors (for example, six or eight mirrors).

[0037] The substrate W may include a previously formed pattern. In such a case, the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B’ with the pattern previously formed on the substrate W.

[0038] A relative vacuum, i.e., a small amount of gas (for example, hydrogen) at a pressure sufficiently lower than atmospheric pressure, may be provided to the radiation source SO, the illumination system IL, and / or the projection system PS.

[0039] The radiation source SO may be a laser-produced plasma (LPP) source, a discharge-produced plasma (DPP) source, a free electron laser (FEL), or another radiation source capable of generating EUV radiation.

[0040] Example of a reticle stage

[0041] Figures 2 and 3 relate to some embodiments and are schematic views of an exemplary reticle stage 200. The reticle stage 200 can include a top stage surface 202, a bottom stage surface 204, side stage surfaces 206, and a clamp 300. In some embodiments, the reticle stage 200 having the clamp 300 can be implemented in a lithography apparatus LA. For example, the reticle stage 200 can be a support structure MT in the lithography apparatus LA. In some embodiments, the clamp 300 can be disposed on the top stage surface 202. For example, as shown in FIG. 2, the clamp 300 can be disposed at the center of the top stage surface 202 with the clamp front surface 302 facing in a direction perpendicular to and away from the top stage surface 202.

[0042] In some lithography apparatuses, such as the lithography apparatus LA, a reticle stage having the clamp 300 can be used to hold and position a reticle for a scanning or patterning operation. As an example, the reticle stage 200 can require a powerful drive device, a large balance mass, and a heavy frame to support it. As an example, the reticle stage 200 has a large inertia and can weigh more than 500 kg to propel and position a reticle of about 0.5 kg. To achieve the reciprocating movement of the reticle typically seen in a lithography scanning or patterning operation, acceleration and deceleration forces can be provided by a linear motor that drives the reticle stage 200.

[0043] In some embodiments, as shown in FIGS. 2 and 3, the reticle stage 200 can include a first encoder 212 and a second encoder 214 for positioning operations. For example, the first and second encoders 212, 214 can be interferometers. The first encoder 212 may be mounted along a first direction of the reticle stage 200, for example, the lateral direction (i.e., the X direction), and the second encoder 214 may be mounted along a second direction of the reticle stage 200, for example, the longitudinal direction (i.e., the Y direction). In some embodiments, as shown in FIGS. 2 and 3, the first encoder 212 can be orthogonal to the second encoder 214.

[0044] As shown in FIGS. 2 and 3, the reticle stage 200 can include a clamp 300. The clamp 300 is configured to hold a reticle on a fixed plane on the reticle stage 200. The clamp 300 includes a clamp front surface 302 and can be disposed on the top stage surface 202. In some embodiments, the clamp 300 can use electrostatic clamping technology to hold and fix an object. For example, the clamp 300 can be an electrostatic clamp configured to electrostatically clamp (i.e., hold) an object such as a reticle in a vacuum environment. Since EUV radiation is required to be performed in a vacuum environment, a vacuum clamp cannot be used for clamping a mask or a reticle, and instead, an electrostatic clamp can be used. For example, the clamp 300 can include an electrode, a resistive layer on the electrode, a dielectric layer on the resistive layer, and a barb protruding from the dielectric layer. During use, a voltage of, for example, several kV can be applied to the clamp 300. Then, a current flows through the resistive layer, thereby making the voltage on the upper surface of the resistive layer substantially equal to the voltage of the electrode and generating an electric field. Also, the Coulomb force, i.e., the attractive force between electrically opposite charged particles, attracts the object to the clamp 300 and fixes this object in place. In some embodiments, the clamp 300 can be made of a rigid material such as, for example, metal, dielectric, ceramic, or a combination thereof.

[0045] Exemplary Electrostatic Clamp Design

[0046] FIGS. 4A and 4B are schematic side views of electrostatic clamps 400 and 410 according to embodiments of the present disclosure, respectively. In some embodiments, electrostatic clamps 400 and 410 represent exemplary embodiments of clamp 300 shown in FIGS. 2 and 3. FIG. 4A shows an electrostatic clamp 400 comprising a clamp body 404, an electrode layer 406, and a plurality of bars 408. The electrode layer 406 is disposed on the upper surface of the electrostatic clamp 400, the plurality of bars 408 protrude from the bottom surface of the electrostatic clamp 400, and the clamp body 404 physically separates the electrode layer 40 6 from the bars 408.

[0047] In some embodiments, the clamp body 404 may have a height of about 100 micrometers and may comprise a glass, ceramic, and / or polymer material such as ultra-low expansion glass (ULE), lithium aluminosilicate glass ceramic, silicon infiltrated silicon carbide (SiSiC), benzocyclobutene-based polymer (BCB), etc. The plurality of bars 408 are provided with a conductive coating and are configured to contact the reticle 409. In some embodiments, the plurality of bars may have a height of about 10 micrometers. The plurality of bars 408 are shown for illustrative purposes as having a rectangular surface that contacts the reticle 409, but it should be understood that the plurality of bars 408 may be cylindrical in shape with rounded edges, or circular surfaces, or other surface shapes (e.g., square, oval, ellipse, etc.) that contact the reticle 409. Also, although only three bars 408 are depicted in FIG. 4A, any number of bars 408 and any arrangement of the bars across the bottom surface of the clamp body 404 (e.g., a grid-like distribution or a random distribution) may be used. In some embodiments, the surface of the bar 408 that contacts the reticle may be referred to herein as the bar top. As shown in FIG. 4A, the reticle 409 is shown as having a gravitational sag due to the gravity that pulls the reticle 409 down, by way of example.

[0048] In some embodiments, the electrode layer 406 comprises a continuous layer and may be made of any suitable conductive material, such as a metal or metal alloy, for example, aluminum, chromium, platinum, gold, or any combination thereof. In some embodiments, the electrostatic chuck 400 may be energized, and a voltage may be applied to the electrode layer 406 to generate an electric field (as indicated by the arrows in FIG. 4A). This electric field may induce charges opposite to the charges of the bar 408 on the surface of the reticle 409. The attractive force between the bar 408 and the reticle 409 may hold the reticle 409 in close contact with the electrostatic chuck 400. In some embodiments, the back surface of the reticle 409 may be coated with a conductive thin film, whereby the electrostatic chuck 400 can further hold the reticle 409 in place through the attractive force between the bar 408 and the conductive surface of the reticle 409.

[0049] In some embodiments, a voltage in the range of 100 - 5000 V may be applied to the electrode layer 406 to generate an electrostatic force that overcomes gravity and attracts the back surface of the reticle 409 to the electrostatic chuck 400. However, the bar 408, which is a component of the electrostatic chuck 400 that interfaces with the back surface of the reticle 409, may be at a different potential than the reticle 409. The potential difference at the bar - reticle interface can cause potential material movement, particle generation, and / or discharge that can result in damage to the electrostatic chuck and / or the reticle.

[0050] In some embodiments, FIG. 4B shows an electrostatic chuck 410 that minimizes the electric field and discharge at the contact points between the electrostatic chuck and the reticle.

[0051] In some embodiments, the electrostatic chuck 410 includes a chuck body 414, an electrode layer 416, and a plurality of bars 418.

[0052] In some embodiments, the electrode layer 416 comprises a plurality of notches 417 or voids, in which the electrode material is removed at a plurality of positions on the upper surface of the clamp body 414. In some embodiments, the positions of the plurality of notches 417 in the electrode layer 416 may vertically correspond to the positions of the beads 418 on the bottom surface of the clamp body 414. For example, the notch 417 may be arranged directly above the position of each bead 418 in the electrostatic clamp 41 0 . Each notch 417 may comprise a circular notch (or other surface shape such as a square, oval, ellipse, etc.) that is concentric with respect to the position of each bead 418 on the upper surface of the clamp body 414 rather than on the bottom surface of the clamp body 414. Although only three beads 418 and three notches 417 are depicted in FIG. 4B, any number of beads 418 and notches 417, as well as any arrangement across the bottom and upper surfaces of the clamp body 414, may be used. In some embodiments, by interrupting the electrode layer 416 with the notch 417 in the vicinity of the bead 418, the electric field at the bead 418 can be significantly reduced in order to improve the contact point between the electrostatic clamp 410 and the reticle 419 and minimize discharge.

[0053] FIG. 5 is a three-dimensional perspective view of the upper part of the electrostatic clamp 410 according to an embodiment of the present disclosure. For example, FIG. 5 shows the electrode layer 414 on the upper surface of the electrostatic clamp 410. The electrode layer 414 may include a notch 417 or a missing portion where the electrode material is removed at a position on the upper surface of the clamp corresponding to the position of the bead 418 on the bottom surface of the clamp. In some embodiments, a predetermined portion of the electrode layer 414 may be removed by a machining process, etching, laser ablation, etc., thereby forming the notch 417. For example, etching may be used to strip a predetermined portion of the electrode layer 414, such as by using a chemical substance in a wet etching technique or a dry etching technique. Although only two notches 417 having a circular area are shown in FIG. 5, it should be understood that any number of notches 417 having other surface shapes (e.g., square, oval, ellipse, etc.) may be used in the electrode layer 414. In some embodiments, each notch 417 may have a height (e.g., thickness) of about 50 to 2000 nanometers (nm) and a diameter of about 800 to 1400 micrometers. In some embodiments, removing a predetermined electrode region of 300 μm around the bead may reduce the electrode area by about 7%. Therefore, in order to consider this area reduction, higher clamping force and clamping voltage may be required.

[0054] Figures 6A, 6B, and 6C relate to embodiments of the present disclosure and are schematic views of the bottom view of the bar in an electrostatic chuck. In particular, FIG. 6A shows a configuration 600 of an electrostatic chuck having an electrode layer 606 and a bar 608, and the electrode layer 606 is a continuous layer without any notches. In some embodiments, the electrode layer 606 and the bar 608 can represent exemplary embodiments of the electrode layer 406 and the bar 408 shown in FIG. 4A, respectively. The bar 608 and the electrode layer 606 may be separated by an electrostatic chuck body (as shown by the chuck body 404 in FIG. 4A). In some embodiments, the bar 608 may have a diameter D of about 460 micrometers and may be configured to contact the back surface of the reticle. In some examples, the potential difference between the bar 608 and the reticle can cause a discharge that may result in damage to the reticle and / or the electrostatic chuck.

[0055] FIG. 6B shows a configuration 610 of an electrostatic clamp having an electrode layer 616, a notch 617, and a bar 618. In some embodiments, the electrode layer 616, the notch 617, and the bar 618 may each represent an exemplary embodiment of the electrode layer 416, the notch 417, and the bar 418 shown in FIG. 4B. In some embodiments, the notch 617 constitutes a portion of a predetermined region removed from the electrode layer 616 to reduce the electric field at the bar 618. In some embodiments, by providing the notch 617 in the electrode layer 616, the area of the electrode layer 616 may be reduced. In some embodiments, the reduction in area may require a higher clamping force to maintain contact between the electrostatic clamp and the reticle. Thus, a higher clamping voltage may be required to compensate for the loss of electrode area and to provide an appropriate clamping force to maintain contact at the clamp-reticle interface. In some embodiments, the uniformity of the clamping force may be maintained by spatial filtering enabled by the rigidity of the reticle. For example, the spatial filtering may be due to the thickness of the reticle. In other words, increasing the thickness of the reticle may "blur" small local variations on the back side of the reticle and may be effectively removed by filtering from the printed matter through the front side.

[0056] In some embodiments, one or more portions of the electrode layer 616 may be removed to enable one or more notches 617 having a diameter D of about 800 micrometers. For example, by removing one or more portions of the electrode layer 616 (e.g., the notch 617 having a diameter D of 800 μm), the electric field at the bar 618 may be reduced to about one-eighth, and the clamping voltage may be increased by about 1.07 times to maintain the clamping force, resulting in about one-eighth being obtained.

[0057] FIG. 6C shows another configuration 620 of an electrostatic clamp according to an embodiment, having an electrode layer 626, a notch 627, and a bar 628. In some embodiments, the electrode layer 626, the notch 627, and the bar 628 can each represent an exemplary embodiment of the electrode layer 416, the notch 417, and the bar 418 shown in FIG. 4B. In configuration 620, one or more portions of the electrode layer 626 may be removed, allowing for one or more notches 627 having a diameter D of about 1,400 micrometers. In some embodiments, the notch diameter D of about 1,400 micrometers may be able to reduce the electric field at the bar 628 by about one one-hundred-and-twenty-fifth. Also, the clamp voltage may be increased by about 1.26 times to maintain the clamp force, resulting in about one ninety-ninth being obtained.

[0058] Exemplary embodiments for electric field reduction

[0059] In some embodiments, the method further improves the electrostatic clamp design to minimize the electric field and improve the bar-reticle interface. In some embodiments, the reticle may sag due to gravity and / or backfill gas, and thus, even when the clamp voltage is at a significant level (e.g., on the order of several hundred volts), there is a possibility of losing contact during unloading and reclamping at the reticle stage. This loss of contact can lead to microgap discharge (e.g., an electric arc or arc discharge) in the gap between the clamp and the reticle. Also, in some embodiments, the contact between the bar top (e.g., the surface of the bar that contacts the reticle) and the back surface of the reticle can occur only when the clamp voltage is several hundred volts during loading (and the recontact portion of reclamping). Further, the bar top is often left charged with the opposite polarity from when it was last clamped (when charged with the opposite polarity). For example, this charge may have a value of about 10 to 100 picocoulombs (pC).

[0060] In some embodiments, this charge difference can not only cause microgap discharges, but also result in current flowing across the bar top irregularities and / or destruction of the outermost layer of the insulating reticle coating due to these irregularities. For example, this can lead to local temperatures exceeding 10,000K, along with local melting or vaporization of the material (both metal and oxide), inevitable material movement, and / or micro-welding. Also, the charge difference can cause reticle adhesion and overlay problems for the end user.

[0061] FIG. 7 is a schematic diagram of a bar-reticle interface 700 in an electrostatic chuck, according to an embodiment of the present disclosure. The bar-reticle interface 700 includes an electrostatic chuck 710, a bar 715, a bar top 720, and a reticle 730. Only one bar 715 is shown in FIG. 7, but any number of bars 715 may be present in the electrostatic chuck 710.

[0062] In some embodiments, the bar-reticle interface 700 can be essentially at risk of dielectric breakdown due to a nominal value exceeding 90 V / μm on the bar top for a 2 kV clamp voltage (and potentially higher values at locations where the electric field is amplified, such as at ridgelike protrusions). For example, dielectric breakdown, which may also be called flitting, can occur for internal electric fields on the order of 100 V / μm. In some embodiments, the electric field is essentially higher on the bar top 720 than at locations between adjacent bars 715. This is because the bar 715 is a dielectric (e.g., 110 microns with a relative permittivity εr of about 5) without a 10 μm vacuum gap. The electric field between bars (within the vacuum gap) is on the order of 70 V / μm for a 2 kV clamp voltage, but as shown in FIG. 7, the electric field on the bar exceeds 80 V / μm. In some embodiments, this dielectric breakdown threshold can shift to lower electric field values when mechanical shear compromises the integrity of the dielectric layer (which is expected in an actual clamp).

[0063] Accordingly, some embodiments of the present disclosure provide methods and devices for improving the bar - reticle interface to reduce the electric field by optimizing an electrostatic clamp. In some embodiments, the electrostatic clamp can be optimized to reduce the electric field at the bar - reticle interface by applying various modifications to the clamp. An example of a modification that can be applied may be to reduce the thickness of a conductive coating on the reticle contact surfaces (e.g., bar tops) of a plurality of bars of the electrostatic clamp. For example, the conductive layer or coating on the bar top may comprise titanium nitride (TiN), and the voltage difference between the bar and the reticle can be estimated to be on the order of greater than 10 V for a bar top of about 100 nm. In some embodiments, it may be desirable to minimize this voltage difference to less than 1 V, which can be achieved by reducing the thickness of the conductive layer on the bar top to less than 10 nm. Thus, the local electric field between the bar top and the reticle is reduced by applying a thinner conductive layer to the bar top, whereby the reduced voltage difference between the plurality of bars and the reticle can bring the voltage of the bar top closer to the voltage of the back surface of the reticle before contact.

[0064] In some embodiments, the modification includes minimizing the local electric field by connecting each of the plurality of bars together to provide a virtual ground to the electrostatic clamp. For example, the bars may be electrically connected together such that they effectively form one electrical surface. This modification can maintain the bar top at virtual ground, so that the bar can be at approximately the same voltage as the back surface of the reticle (e.g., within a small electrode tolerance range of about 1% or less than about 20 V for 2 kV in this context).

[0065] In some embodiments, the virtual ground may be easier to implement than a full ground because no external interface is required and there is no risk of a ground loop in the virtual ground.

[0066] In some embodiments, the plurality of bar tops in the electrostatic clamp may be physically grounded to minimize the local electric field at the bar - reticle interface. This modification can maintain the bar tops at a grounded state of approximately 0V, so that the bar can reach the same voltage as the back surface of the reticle, similar to virtual grounding.

[0067] FIG. 8 is a schematic diagram of bars electrically connected in an electrostatic clamp according to an embodiment of the present disclosure. In particular, FIG. 8 shows a plurality of bars 805, bar tops 810, a coating 815, and electrodes E, 820. In some embodiments, the electrostatic clamp may include four electrodes 820. In this case, two of the electrodes 820 operate at a positive voltage, while the other two electrodes 820 operate at a negative voltage. The plurality of bars 805 may include chromium (Cr) or chromium nitride (CrN), the bar tops 810 may include titanium nitride (TiN), and the clamp body of the electrostatic clamp may include glass, ceramic, and / or polymer materials such as ultra - low expansion glass (ULE), lithium aluminosilicate glass ceramic, silicon - infiltrated silicon carbide (SiSiC), benzocyclobutene - based polymer (BCB), etc.

[0068] In some embodiments, the bar tops 810 may be electrically connected to establish virtual grounding. For example, the electrical connection of the bar tops 810 may be under the coating 815. In this case, the coating 815 may be an abrasion - resistant coating that can be conductive or non - conductive. In another example, the electrical connection of the bar tops 810 may be on the side of the coating 815. In this case, the coating 815 may be conductive.

[0069] In some embodiments, virtual ground may be achieved by interconnecting the bar tops 810 on the positive electrode 820 with the bar tops on the negative electrode 820. In some embodiments, all bar tops 810 may be at 0V (e.g., depending on the exact balance of the electrodes). Thus, the bar tops may be at the same potential as the back side of the reticle, thereby preventing the risk of fritting and discharging due to contact between the reticle and the bar. In some embodiments, the configuration shown in FIG. 8 may include a ground connection to establish an appropriate zero voltage for the bar tops 810.

[0070] Some embodiments for modifying the electrostatic chuck to improve the bar-reticle interface may include optimizing the reticle coating, the bar, and the operating conditions. In some embodiments, optimizing the reticle coating may include applying a conductive coating to the reticle contact surface of the plurality of bars or the back side of the reticle, where the conductive coating comprises an oxide, diamond, or diamond-like carbon (DLC) material. For example, the reticle backside coating or top layer may be optimized by using a material that forms a conductive oxide to prevent the formation of a dielectric barrier in the case of oxidation during manufacturing, storage, and / or cleaning. In some embodiments, semiconductive oxides such as titanium dioxide (TiOx), vanadium oxide (VOx), etc. may be considered for the coating.

[0071] In some embodiments, a thick and robust top layer on the reticle backside coating may also be utilized to push the limit of the fritting effect to a higher voltage and make the reticle less susceptible to clamping or mechanical deformation during use. In some embodiments, the reticle coating may require a compatible cleaning process to maintain the quality and thickness of the layer.

[0072] In some embodiments, the frit includes an insulating barrier such as formed by most metal oxides. Certain metal oxides such as molybdenum dioxide (MoO2), ruthenium(IV) oxide (RuO2), etc. may not cause frit as they can maintain conductivity while providing a wear-resistant top layer. Similarly, wear-resistant non-metallic layers such as DLC or (nano)diamond may be protected by designing some conductivity (e.g., doping with boron (B)).

[0073] In some embodiments, the bar of the electrostatic chuck may be optimized to minimize the electric field at the bar-reticle interface. In some embodiments, the conductive bar top material may be replaced with a fully dielectric bar top material to prevent charge accumulation at the bar top and electric field amplification at the bar-reticle interface. In some embodiments, the non-conductive or dielectric bar top may be susceptible to the triboelectric effect (or contact electrification), which is not considered a problem from the perspective of the conductive reticle back coating (in contrast to the wafer chuck).

[0074] In some embodiments, the conductive bar top material may be replaced with a low-conductivity bar top material such as a material having a very high sheet resistance. Using a low-conductivity material for the bar top can reduce the frit current as well as the charge equalization current after polarity switching to maintain an instantaneous temperature low enough to prevent local melting and electrochemical migration. In some embodiments, the electric field amplification can also be prevented by avoiding sharp shapes, edges, and triple points close to the bar-reticle interface, including sharp geometric steps such as ridged protrusions. In some embodiments, the bar top material may be selected such that the bar material is transferred to the reticle (e.g., an Au / Pt / Ag-containing alloy).

[0075] In some embodiments, the operating conditions of the electrostatic chuck may be optimized to reduce the electric field at the bar - reticle interface. For example, during re - clamping and un - loading of the reticle (e.g., when the reticle is in contact with the bar top), the back - fill gas pressure may be removed. This can lead to the disruption and re - establishment of bar - reticle contact at fairly low extrusion forces and fairly low clamp voltages. The removal of the back - fill gas pressure may also indicate that there is less residual charge on the bar top, so that the equalization current may be less when contact is re - established after polarity switching (e.g., during re - clamping or during the un - load - load sequence). In some embodiments, the back - fill gas may be actively evacuated through the supply line to avoid or minimize the impact on throughput. For example, waiting for the back - fill gas to leak out through the leak seal may take a long time. Therefore, the supply line may also serve as an evacuation line for actively removing the back - fill gas.

[0076] In some embodiments, the residual charge from the bar top having an opposite polarity may be removed between unloading and loading by exposure to an ionized gas (e.g., ionization by EUV - induced plasma or by a dedicated ionizer). In some embodiments, the dedicated ionizer may be proximate to or integrated with the electrostatic chuck (e.g., a hydrogen supply). In some embodiments, a conductive medium or an ionized gas (e.g., plasma) may be applied to the bar - reticle interface while the reticle is present in the electrostatic chuck to discharge the bar top and the reticle and maintain a uniform potential.

[0077] In some embodiments, the operating conditions may be modified and the back surface of the reticle may be dehumidified prior to loading / clamping to prevent residual adsorbed water in order to reduce fluttering. In some embodiments, a dry interface between the bar and the reticle may allow current to flow only through such weak points where the unevenness on the bar coincides with the weak points of the oxide barrier layer (although this possibility may be limited). A wet surface may cause surface conductivity on the reticle. That is, the above alignment between the unevenness and the weak points may only need to be close enough to generate a fluttering current through the oxide barrier weak points, which increases the probability of fluttering. Therefore, dehumidifying the back surface of the reticle will help reduce fluttering.

[0078] In some embodiments, the back surface coating of the reticle may be adjusted prior to loading / clamping to strengthen or re-strengthen the top layer (e.g., oxide) so as to minimize the fluttering risk and / or shear damage. This reticle adjustment may be carried out as steps during the cleaning of the reticle and / or as storage requirements.

[0079] In some embodiments, by applying these various modifications to the electrostatic chuck as described herein, the electrostatic chuck is improved to reduce the electric field between the bar and the reticle, thereby preventing the reticle from sticking or adhering and removing higher-order drifts caused by particle formation from the reticle material due to re-clamping. Other advantages include improvement of the reticle loading grid and increased design freedom to cope with reticle heating (e.g., due to more frequent re-clamping).

[0080] Example of an operating method

[0081] FIG. 9 is a flowchart of an exemplary method 900 for improving an electrostatic chuck according to an embodiment of the present disclosure. In some embodiments, method 900 describes the fabrication and modification of the electrostatic chucks (such as electrostatic chucks 400, 410, and / or 710 etc.) described above with reference to FIGS. 2-8. The operations shown in method 900 are not exhaustive, and it should be understood that other operations can be similarly performed before, after, or between any of the illustrated operations. In various embodiments of the present disclosure, the operations of method 900 can be executed in a different order and / or can be varied.

[0082] In operation 902, an electrostatic chuck is fabricated. The electrostatic chuck is fabricated to include a chuck body, an electrode layer disposed on the upper surface of the chuck body, and a plurality of bars protruding from the bottom surface of the chuck body, and the plurality of bars are configured to contact the back surface of the reticle. In some embodiments, the electrostatic chuck may be fabricated by depositing an electrode layer on an insulating substrate. The insulating substrate may comprise glass, ceramic, etc. Then, an insulating layer is disposed and adhered to (or deposited on) the electrode layer. In some embodiments, the plurality of bars may be formed to protrude from the bottom surface of the insulating substrate (such as the chuck body). For example, the plurality of bars may be formed by a lithography process, in which case a mask is applied to the chuck surface and the unmasked material (such as the portion of the chuck surface not covered by the mask) is removed by etching to result in the plurality of bars. In other embodiments, the plurality of bars may be formed by a film forming process. In some embodiments, the plurality of bars may be coated with a predetermined material, and the coating may function to ground the reticle and / or may function to provide a wear-resistant interface between the bar and the reticle.

[0083] In operation 904, a modification to the electrostatic clamp for reducing the electric field between the plurality of bars and the reticle is applied. Applying the modification may include reducing the thickness of the conductive coating on the reticle contact surface of the plurality of bars and / or removing a predetermined portion of the electrode layer at a position corresponding to the position of each bar to allow for a plurality of notches in the electrode layer to reduce the voltage difference between the plurality of bars and the reticle.

[0084] In some embodiments, applying the modification may include connecting each of the plurality of bars together in the plurality of bars to provide a virtual ground to the electrostatic clamp, grounding the plurality of bars, and / or applying a conductive coating to the reticle contact surface or the back surface of the reticle of the plurality of bars. The conductive coating comprises an oxide, diamond or diamond-like carbon (DLC) material.

[0085] Other aspects of the present invention are presented in the following numbered clauses. 1. A clamp body, an electrode layer disposed on the upper surface of the clamp body, and a plurality of bars protruding from the bottom surface of the clamp body, wherein the electrode layer comprises a plurality of notches at predetermined positions vertically corresponding to the positions of the plurality of bars at the bottom surface of the clamp body, an electrostatic clamp. 2. The electrostatic clamp according to clause 1, wherein the plurality of bars comprise contact points between the electrostatic clamp and the reticle. 3. The electrostatic clamp according to clause 1, wherein the plurality of notches comprise voids in the electrode layer that reduce the electric field generated around the plurality of bars. 4. The electrostatic clamp according to clause 1, wherein the plurality of bars are configured to contact the back surface of the reticle. 5. The electrostatic clamp according to clause 4, wherein the reticle comprises a conductive coating. 6. The electrostatic clamp according to clause 1, wherein each of the plurality of bars in the plurality of bars comprises a conductive coating. 7. The electrostatic chuck according to claim 1, wherein each of the plurality of notches has a diameter of approximately 300 to 1400 μm. 8. A method for improving an electrostatic chuck, comprising: fabricating the electrostatic chuck, comprising a chuck body, an electrode layer disposed on an upper surface of the chuck body, and a plurality of bars protruding from a bottom surface of the chuck body, the plurality of bars being configured to contact a back surface of a reticle; and applying a modification to the electrostatic chuck to reduce an electric field between the plurality of bars and the reticle. 9. The method according to claim 8, wherein applying comprises reducing a thickness of a conductive coating on a reticle contact surface of the plurality of bars to allow a reduced voltage difference between the plurality of bars and the reticle. 10. The method according to claim 8, wherein applying comprises removing a predetermined portion of the electrode layer at a position corresponding to a position of each bar to allow a plurality of notches in the electrode layer. 11. The method according to claim 8, wherein applying comprises connecting each of the plurality of bars together to provide a virtual ground to the electrostatic chuck. 12. The method according to claim 8, wherein applying the modification to the electrostatic chuck comprises grounding the plurality of bars. 13. The method according to claim 8, wherein applying the modification to the electrostatic chuck comprises applying a conductive coating to a reticle contact surface of the plurality of bars or the back surface of the reticle, the conductive coating comprising an oxide, diamond, or diamond-like carbon (DLC) material. 14. An illumination system configured to adjust a radiation beam, a support structure constructed to support a patterning device capable of forming a patterned radiation beam by imparting a pattern to a cross-section of the radiation beam, and a projection system configured to project the patterned radiation beam onto a target portion of a substrate, wherein the support structure a clamp body, an electrode layer disposed on the upper surface of the clamp body, and a plurality of bars protruding from the bottom surface of the clamp body, The electrode layer includes a plurality of notches at predetermined positions vertically corresponding to positions of the plurality of bars on the bottom surface of the clamp body, and an electrostatic clamp. A lithography apparatus. 15. The plurality of bars include contact points between the electrostatic clamp and the patterning device. The lithography apparatus according to claim 14. 16. The plurality of notches include omissions in the electrode layer that reduce an electric field generated around the plurality of bars. The lithography apparatus according to claim 14. 17. The patterning device includes a reticle, The plurality of bars are configured to contact the back surface of the reticle. The lithography apparatus according to claim 14. 18. The reticle includes a conductive coating. The lithography apparatus according to claim 17. 19. Each bar of the plurality of bars includes a conductive coating. The lithography apparatus according to claim 14. 20. Each notch of the plurality of notches has a diameter of approximately 300 to 1400 μm. The lithography apparatus according to claim 14.

[0086] Conclusion

[0087] Although this document may specifically refer to a "reticle", this is only an example of a patterning device, and it should be understood that the embodiments described herein may be applicable to any type of patterning device. Further, the embodiments described herein may be used to provide safe support for any object so that the object does not fall due to clamp failure and damage either itself or another device.

[0088] Although this book may specifically refer to the use of a lithographic apparatus in the manufacture of ICs, the lithographic apparatus described herein is to be understood as capable of having other applications such as the manufacture of integrated optical systems, guiding and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, etc. Those skilled in the art will be able to understand that in these other applications, the terms "wafer" or "die" in this specification are to be regarded as synonymous with the more general terms "substrate" or "target portion", respectively. The substrates referred to in this book may be processed, before or after exposure, by, for example, a track unit (a device typically for applying a resist layer to a substrate and developing the resist after exposure), a metrology unit, and / or an inspection unit. Where applicable, the disclosure of this specification may also apply to these or other substrate processing apparatuses. Also, the substrate may be processed multiple times, for example, to manufacture a multilayer IC, in which case the term "substrate" in this specification may also mean a substrate already containing a number of processed layers.

[0089] Although the above may specifically refer to the use of embodiments of the present invention in optical lithography, it is understood that, as far as the context permits, the present invention is not limited to optical lithography and may be used in other applications such as imprint lithography, for example. In imprint lithography, the pattern generated on a substrate is defined by the topography of a patterning device. The topography of the patterning device is pressed against a layer of resist supplied to the substrate, and then the resist is cured by electromagnetic radiation, heat, pressure, or a combination thereof. When the patterning device is removed from the resist, a pattern remains in the cured resist.

[0090] The language or terminology used in this specification is for illustrative purposes only and not for limitation, and is to be interpreted by those skilled in the relevant art in light of the teachings of this book.

[0091] As used herein, the term "substrate" describes a material to which a plurality of material layers are added. In some embodiments, the substrate itself may be patterned and the materials added thereto may also be patterned, or may remain unpatterned.

[0092] Although this book may specifically refer to the use of the apparatus and / or system according to the present invention in the manufacture of ICs, it should be understood that such apparatus and / or system may have many other uses, such as in the manufacture of integrated optical systems, guiding and detecting patterns for magnetic domain memories, LCD panels, thin film magnetic heads, etc. Those skilled in the art should be able to understand that in the context of such alternative uses, the terms "reticle", "wafer", or "die" in this book are considered to be replaced by the more general terms "mask", "substrate", "target portion", respectively.

[0093] The examples described below illustrate, but do not limit, the embodiments of the present disclosure. Other suitable modifications and adaptations for various conditions and parameters commonly encountered in the art, which will be apparent to those skilled in the relevant art, are within the spirit and scope of the present disclosure.

[0094] It should be recognized that the "Detailed Description" section, rather than the "Summary of the Invention" and "Abstract" sections, is intended to be used in the interpretation of the claims. The "Summary of the Invention" and "Abstract" sections describe one or more of the embodiments devised by the inventor, but do not describe all of the exemplary embodiments, and thus are not intended to limit the present invention and the appended claims in any way.

[0095] Above, the present invention has been described using functional blocks that represent specific functions and their relationships. The boundaries of these functional blocks are arbitrarily defined in this book for convenience of explanation. Alternative boundaries may be defined as long as the specific functions and their relationships are properly executed.

[0096] The foregoing description of specific embodiments fully discloses the general nature of the present invention, so that by applying the knowledge of those skilled in the art, without undue experimentation and without departing from the general concept of the present invention, such specific embodiments can be immediately modified and / or adapted for various applications. Accordingly, such modifications and adaptations are intended to be within the meaning and scope of the equivalents of the disclosed embodiments, based on the teachings and advice presented herein.

[0097] 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 claims and their equivalents.

Claims

1. A clamp body, An electrode layer disposed on the upper surface of the clamp body, the electrode layer being applied with a voltage so as to generate a Coulomb force for attracting an object to the clamp body, A plurality of bars protruding from the bottom surface of the clamp body, and The electrode layer includes a plurality of notches at predetermined positions corresponding vertically to the positions of the plurality of bars on the bottom surface of the clamp body. An electrostatic clamp.

2. The plurality of bars include contact points between the electrostatic clamp and the reticle. The electrostatic clamp according to claim 1.

3. The plurality of notches include defects in the electrode layer that reduce an electric field generated around the plurality of bars. The electrostatic clamp according to claim 1 or 2.

4. The plurality of bars are configured to contact the back surface of the reticle, and the reticle includes a conductive coating. The electrostatic clamp according to any one of claims 1 to 3.

5. Each bar among the plurality of bars includes a conductive coating. The electrostatic clamp according to any one of claims 1 to 4.

6. A clamp body, An electrode layer disposed on the upper surface of the clamp body, and A plurality of bars protruding from the bottom surface of the clamp body, and The electrode layer includes a plurality of notches at predetermined positions corresponding vertically to the positions of the plurality of bars on the bottom surface of the clamp body, and Each notch among the plurality of notches has a diameter of approximately 300 to 1400 μm. An electrostatic clamp.

7. A method for improving an electrostatic clamp, comprising: Manufacturing the electrostatic clamp, the electrostatic clamp including a clamp body, an electrode layer disposed on the upper surface of the clamp body, and a plurality of bars protruding from the bottom surface of the clamp body, the plurality of bars being configured to contact the back surface of the reticle; and Applying a modification to the electrostatic clamp to reduce an electric field between the plurality of bars and the reticle, The applying includes removing a predetermined portion of the electrode layer at a position corresponding to the position of each bar so as to enable a plurality of notches in the electrode layer. A method.

8. The applying includes connecting each bar among the plurality of bars together so as to provide a virtual ground to the electrostatic clamp. The method according to claim 7.

9. Applying the modification to the electrostatic clamp comprises grounding the plurality of bars, the method according to claim 7.

10. Applying the modification to the electrostatic clamp comprises applying a conductive coating to the reticle contact surface of the plurality of bars or the back surface of the reticle, the conductive coating comprising an oxide, diamond, or diamond-like carbon (DLC) material, the method according to claim 7.

11. An illumination system configured to adjust a radiation beam, A support structure constructed to support a patterning device capable of forming a patterned radiation beam by imparting a pattern to a cross-section of the radiation beam, A projection system configured to project the patterned radiation beam onto a target portion of a substrate, comprising: The support structure is A clamp body, An electrode layer disposed on an upper surface of the clamp body, the electrode layer to which a voltage is applied to generate a Coulomb force that attracts an object to the clamp body, A plurality of bars protruding from a bottom surface of the clamp body, comprising: The electrode layer comprises a plurality of notches at predetermined positions corresponding vertically to positions of the plurality of bars at the bottom surface of the clamp body, a lithographic apparatus comprising an electrostatic clamp.

12. The plurality of bars comprise a contact point between the electrostatic clamp and the patterning device, and / or the plurality of notches comprise a deficiency in the electrode layer that reduces an electric field generated around the plurality of bars, the lithographic apparatus according to claim 11.

13. The patterning device comprises a reticle, The plurality of bars are configured to contact the back surface of the reticle, The reticle comprises a conductive coating, Each bar of the plurality of bars comprises a conductive coating, the lithographic apparatus according to claim 11 or 12.

14. An illumination system configured to adjust a radiation beam, A support structure constructed to support a patterning device capable of forming a patterned radiation beam by imparting a pattern to a cross-section of the radiation beam, A projection system configured to project the patterned radiation beam onto a target portion of a substrate, comprising: The support structure is A clamp body, An electrode layer disposed on an upper surface of the clamp body, a plurality of bars protruding from the bottom surface of the clamp body; The electrostatic clamp includes an electrode layer having a plurality of notches at predetermined positions corresponding vertically to the positions of the plurality of bars on the bottom surface of the clamp body. A lithographic apparatus, wherein each of the plurality of notches has a diameter of approximately 300 to 1400 μm.

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