Substrate holder, lithography apparatus and method for manufacturing device

Abstract

A substrate holder (WT) used in a lithography device and configured to support a substrate, the substrate holder comprising: a body (20) having a body surface; a plurality of burls (21) protruding from the body surface, wherein each burl has a distal end configured to engage with the substrate, the shape of the distal end of the burl being roughly consistent with the support plane, thereby enabling the substrate to be supported on the burl in a roughly flat state; and flow control features (22, 22c, 22d) configured to form an air cushion near the periphery of the substrate holder when the substrate is being lowered onto the substrate holder.

Description

[0001] This application is a divisional application of a patent application with an application date of August 24, 2016, application number 201680056571.4, and invention name “Substrate holder, lithography equipment and method for manufacturing device”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the priority of European patent application EP15187184.5 filed on September 28, 2015, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present invention relates to a substrate holder, a lithography apparatus using the substrate holder, and a method for manufacturing a device using the substrate holder. Background Art

[0005] A lithographic apparatus is a machine that applies a desired pattern to a substrate, typically a target portion of a substrate. For example, a lithographic apparatus may be used to manufacture an integrated circuit (IC). In this case, a pattern forming device, alternatively referred to as a mask or reticle, may be used to generate a circuit pattern to be formed on a single layer of an integrated circuit. The pattern may be transferred to a target portion (e.g., including a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). Typically, the transfer of the pattern is performed by imaging the pattern onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned in succession. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern along a given direction (the "scanning" direction) while scanning the substrate in a direction parallel or antiparallel to the direction by a radiation beam. In addition, the pattern can be transferred from the pattern forming device to the substrate by imprinting the pattern onto the substrate.

[0006] It has been proposed to immerse the substrate in a lithographic projection apparatus in a liquid having a relatively high refractive index, such as water, in order to fill the space between the final optical element of the projection system and the substrate. In an embodiment, the liquid is distilled water, although other liquids may be used. This means that imaging of smaller features is achieved because the exposure radiation has a shorter wavelength in the liquid. The effect of the liquid can also be considered to increase the effective numerical aperture (NA) of the system and also increase the depth of focus.

[0007] The substrate is typically clamped to a substrate holder during exposure. Two clamping techniques are commonly used. In vacuum clamping, a pressure difference across the substrate is established, for example by connecting the space between the substrates to a negative pressure so that the higher pressure above the substrate applies a force that holds the substrate to the substrate holder. In electrostatic clamping, electrostatic forces are used to apply a force between the substrate and the substrate holder. Several different arrangements are known to achieve this. In one arrangement, a first electrode is provided on the lower surface of the substrate and a second electrode is provided on the upper surface of the substrate holder. A potential difference is established between the first electrode and the second electrode. In another arrangement, two semicircular electrodes are provided on the substrate holder and a conductive layer is provided on the substrate. A potential (voltage) difference is applied between the two semicircular electrodes so that the two semicircular electrodes and the conductive layer on the substrate behave like two capacitors connected in series.

[0008] The substrate holder usually has a plurality of burls for supporting the substrate. The total area of ​​the burls contacting the substrate is small compared to the total area of ​​the substrate. Therefore, there is little chance that contaminant particles randomly located on the surface of the substrate or substrate holder will be trapped between the burls and the substrate. In addition, in the manufacture of the substrate holder, it is easier to make the tops of the burls precisely coplanar than to make large surfaces accurately flat.

[0009] In order to load the substrate onto the substrate holder in preparation for exposure, it is placed by the substrate handling robot onto so-called lifting pins (e-pins) protruding through the substrate holder. The e-pins are then retracted to lower the substrate onto the substrate holder. A clamping force is then applied so that the substrate is held very firmly during exposure. The clamping force is large enough to hold the substrate in place even when subjected to very large accelerations and to resist thermal expansion, for example due to absorption of energy from the projection beam during exposure. If the substrate is deformed (so that it is, for example, convex), the clamping force tends to flatten the substrate against the substrate holder. Summary of the invention

[0010] For example, it would be desirable to provide an improved substrate holder that is better able to handle deformed substrates.

[0011] According to one aspect of the present invention, there is provided a substrate holder for a lithographic apparatus and configured to support a substrate, the substrate holder comprising:

[0012] a body having a body surface;

[0013] A plurality of protrusions protrude from a surface of the body, wherein:

[0014] Each burl has a distal end configured to engage the substrate,

[0015] The shape of the distal end of the burl remains substantially consistent with the support plane, thereby enabling the substrate to be supported on the burl in a substantially flat state; and

[0016] Flow control features are configured to form an air cushion about a perimeter of the substrate holder as a substrate is being lowered onto the substrate holder. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, wherein:

[0018] Figure 1 schematically illustrates a lithographic apparatus;

[0019] Figure 2 shows a plan view of a substrate holder according to an embodiment;

[0020] Figure 3 is a graph showing the height of the surface of a substrate holder along the radius of the substrate holder according to an embodiment;

[0021] Figure 4 yes Figure 3 an enlarged view of a portion of a graph of;

[0022] Figure 5 is a graph showing deformation occurring in two different types of substrates when the two different types of substrates are held on a conventional substrate holder;

[0023] Figure 6 is a graph showing substrate-to-substrate deformation occurring in two different types of substrates when the two different types of substrates are held on a conventional substrate holder;

[0024] Figure 7 is a graph showing deformation occurring in two different types of substrates when the two different types of substrates are held on a substrate holder according to an embodiment; and

[0025] Figure 8 is a graph showing substrate-to-substrate deformation occurring in two different types of substrates when the two different types of substrates are held on a substrate holder according to an embodiment. DETAILED DESCRIPTION

[0026] Figure 1 The lithography apparatus according to an embodiment of the present invention is schematically shown. The lithography apparatus comprises:

[0027] - an illumination system (illuminator) IL configured for conditioning a radiation beam B (e.g. UV radiation or DUV radiation);

[0028] a support structure (eg mask table) MT configured to support a patterning device (eg mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters;

[0029] a support table, e.g. a sensor table, for supporting one or more sensors, or a substrate support device 60 configured to hold a substrate (e.g. a resist-coated substrate) W, said support table being connected to a second positioning device PW configured to accurately position a surface of said table (e.g. of the substrate W) according to certain parameters; and

[0030] - a projection system (eg a refractive projection lens system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg comprising a portion of a die, one die or more dies).

[0031] The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape or control the radiation.

[0032] The support structure MT holds the pattern forming device MA. The support structure MT holds the pattern forming device MA in a manner that depends on the orientation of the pattern forming device MA, the design of the lithographic equipment, and other conditions such as whether the pattern forming device MA is maintained in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the pattern forming device MA. The support structure MT can be a frame or a table, for example, it can be fixed or movable as required. The support structure MT can ensure that the pattern forming device MA is located in a desired position, for example relative to the projection system PS. It can be considered that any term "reticle" or "mask" used in this document can be considered to be synonymous with the more general term "pattern forming device".

[0033] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to form a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate (for example if the pattern includes phase-shifting features or so called assist features). Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device being formed in the target portion (e.g. an integrated circuit).

[0034] The pattern forming device MA can be transmissive or reflective. Examples of pattern forming devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary masks, alternating phase shift masks, attenuated phase shift masks, and various hybrid mask types. An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be independently tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[0035] The term "projection system" as used herein should be broadly interpreted as including any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems or any combination thereof, as appropriate to the exposure radiation used or other factors such as the use of immersion liquid or the use of a vacuum. It is intended that any use of the term "projection lens" as used herein be considered synonymous with the more general term "projection system".

[0036] As shown here, the lithographic apparatus is of the transmissive type (eg employing a transmissive mask). Alternatively, the lithographic apparatus may be of the reflective type (eg employing a programmable mirror array of the type described above, or employing a reflective mask).

[0037] The lithographic apparatus may be of a type having two or more stages (or platforms, or supports), for example two or more substrate stages, or a combination of one or more substrate stages and one or more sensors or measuring stages. In such a "multi-stage" machine, multiple stages may be used in parallel, or preparatory steps may be performed on one or more stages while one or more other stages are being used for exposure. The lithographic apparatus may have two or more patterning device stages (or platforms, or supports). These patterning device stages may be used in parallel in a manner similar to substrate, sensor and measuring stages. The lithographic apparatus may be of a type having a measuring station and an exposure station, with multiple sensors at the measuring station for characterizing the product substrate before exposure; exposure is performed at the exposure station.

[0038] The lithographic apparatus is of a type in which at least a portion of the substrate W may be covered by an immersion liquid 10 having a relatively high refractive index, such as water such as ultrapure water (UPW), so as to fill an immersion space 11 between the projection system PS and the substrate W. The immersion liquid 10 may also be applied to other spaces in the lithographic apparatus, such as the space between the pattern forming device MA and the projection system PS. Immersion techniques may be used to increase the numerical aperture of the projection system. The term "immersion" as used herein does not mean that structures such as the substrate W must be immersed in the immersion liquid 10, but rather "immersion" only means that the immersion liquid 10 is located between the projection system PS and the substrate W during exposure. The path of the patterned radiation beam B from the projection system PS to the substrate W passes entirely through the immersion liquid 10.

[0039] Reference Figure 1 , the illuminator IL receives a radiation beam from a radiation source SO. The radiation source SO and the lithographic apparatus may be separate entities (for example when the radiation source SO is an excimer laser). In this case, the radiation source SO is not considered to form a part of the lithographic apparatus, and the radiation beam is transferred from the radiation source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directional mirrors and / or a beam expander. In other cases, the radiation source SO may be an integral part of the lithographic apparatus (for example when the radiation source SO is a mercury lamp). The radiation source SO and the illuminator IL, and the beam delivery system BD provided if necessary, may be referred to together as a radiation system.

[0040] The illuminator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam B. Typically, at least the outer and / or inner radial extent (generally referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the pupil plane of the illuminator IL may be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator IL may be used to adjust the radiation beam B so as to have a desired uniformity and intensity distribution in its cross section. Similar to the radiation source SO, the illuminator IL may or may not be considered to form part of the lithographic apparatus. For example, the illuminator IL may be an integral part of the lithographic apparatus or may be an entity separate from the lithographic apparatus. In the latter case, the lithographic apparatus may be configured to allow the illuminator IL to be mounted thereon. Optionally, the illuminator IL is detachable and may be provided separately (for example, by the lithographic apparatus manufacturer or other supplier).

[0041] The radiation beam B is incident on a patterning device (e.g. a mask) MA held on a support structure (e.g. a mask table) MT and is patterned by the patterning device MA. After passing through the patterning device MA, the radiation beam B passes through a projection system PS which focuses the radiation beam onto a target portion C of the substrate W. With the aid of a second positioning device PW and a position sensor IF (e.g. an interferometer device, a linear encoder or a capacitive sensor), the substrate support apparatus 60 can be precisely moved, for example in order to position different target portions C in the path of the radiation beam B.

[0042] Similarly, for example after mechanical acquisition from a mask library or during scanning, the first positioning device PM and the further position sensor ( Figure 1 The first positioner PM (not explicitly shown in the figure) is used to accurately position the patterning device MA relative to the path of the radiation beam B. In general, movement of the support structure MT may be realized with the help 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 support apparatus 60 may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW.

[0043] In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a short-stroke actuator only, or may be fixed. The patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, they may be located in the spaces between target portions C (these are known as scribe alignment marks). Similarly, where more than one die is provided on the patterning device MA, the patterning device alignment marks M1, M2 may be located between the dies.

[0044] The device shown in the figure can be used in at least one of the following modes:

[0045] 1. In step mode, the entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure) while the support structure MT and the substrate support device 60 are held substantially stationary. The substrate support device 60 is then moved in the X-direction and / or the Y-direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

[0046] 2. In scanning mode, a pattern imparted to the radiation beam B is projected onto a target portion C while the support structure MT and the substrate support device 60 are scanned synchronously (i.e. a single dynamic exposure). The speed and direction of the substrate support device 60 relative to the support structure MT may be determined by the (or less) magnification and image reversal characteristics of the projection system PS. In scanning mode, the maximum size of the exposure field limits the width of the target portion C (in the non-scanning direction) in a single dynamic exposure, while the length of the scanning motion (and the size of the exposure field) determines the height of the target portion C (in the scanning direction).

[0047] 3. In another mode, the support structure MT holding the programmable patterning device is held substantially stationary and the substrate support apparatus 60 is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. In this mode, a pulsed radiation source is typically employed and the programmable patterning device is updated as required after each movement of the substrate support apparatus 60 or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography using a programmable patterning device, such as a programmable mirror array of the type described above.

[0048] Additionally, combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0049] The controller 500 controls the overall operation of the lithographic apparatus, in particular, performs the operation process further described below. The controller 500 can be implemented as a properly programmed general-purpose computer, including a central processing unit, volatile and non-volatile storage devices, one or more input and output devices such as keyboards and screens, one or more network connections, and one or more interfaces of various parts of the lithographic apparatus. It should be understood that a one-to-one relationship between the control computer and the lithographic apparatus is not necessary. One computer can control multiple lithographic apparatuses. Multiple networked computers can be used to control one lithographic apparatus. The controller 500 can also be configured to control one or more associated processing devices and substrate processing devices in a lithographic cell or cluster, and the lithographic apparatus forms a part of the lithographic cell or cluster. The controller 500 can also be configured to be subordinate to a supervisory control system of a lithographic cell or cluster and / or an overall control system of a wafer factory.

[0050] Arrangements for providing immersion liquid between the final optical element of the projection system PS and the substrate W can be divided into three main categories. These types are: bath type arrangements, so called partial immersion systems and full wet immersion systems. Embodiments of the invention relate in particular to partial immersion systems.

[0051] In order to load the substrate onto the substrate support device 60 for exposure, the substrate is picked up by a substrate handling robot and lowered onto a set of e-pins protruding through the substrate holder. The e-pins are actuated so that they can be retracted and they can be provided with suction ports at their tips to clamp the substrate. There can be three e-pins around the center of the substrate holder. Once the substrate has been placed on the e-pins, the e-pins are retracted so that the substrate is lowered onto the protuberances of the substrate holder and supported by the protuberances. The clamping system is started so that the substrate is clamped on the substrate holder. The clamping system can be started before the substrate has contacted the substrate holder. These steps are usually performed at the loading / unloading station.

[0052] Although the substrate is ideally completely flat, some deformation inevitably occurs, and it is expected that the lithographic apparatus will achieve acceptable performance with deformed substrates. In some cases, less stringent performance metrics are used when deformed substrates are exposed. For example, larger overlay errors may be allowed when the substrate curvature is greater than a specified amount. However, it is expected that the performance of the lithographic apparatus will be improved even for deformed substrates.

[0053] Deformed substrates are generally divided into two types, which are sometimes referred to as "bowl-shaped substrates" and "umbrella-shaped substrates". Bowl-shaped substrates are curved upward at the edges, i.e., the surface to be exposed is concave, like a bowl. Umbrella-shaped substrates are curved downward at the edges, i.e., the surface to be exposed is convex, like an umbrella. If the substrate is to be exposed at both sides, the orientation of the substrate when it is loaded onto the lithographic apparatus determines whether it is a bowl-shaped substrate or an umbrella-shaped substrate. Although a flat substrate may initially be deformed under its own weight while being held by the e-pins, such as becoming an umbrella-shaped substrate, it may deform differently when the substrate is lowered.

[0054] Studies and simulations conducted by the present inventors have determined that differently deformed substrates and flat substrates behave differently when loaded onto a substrate holder and clamped, resulting in undesirable differences during exposure. For example, the overlay error between substrates may vary significantly. Such substrate-to-substrate deformation is particularly undesirable because it is difficult to predict and compensate for. Overlay errors that are consistent between substrates can often be compensated, for example, by adjusting the position of the substrate during exposure.

[0055] The inventors' studies have shown that when the umbrella-shaped substrate is lowered onto the burls of the substrate, the umbrella-shaped substrate contacts the burls near the edge before contacting the burls near the center. The friction between the burls and the lower surface of the substrate can then prevent the substrate from completely relaxing to a flat, unstressed state. If a delay is introduced before starting the substrate clamping system to allow the substrate to completely relax, throughput will be reduced. As a result, the umbrella-shaped substrate is compressed into a plane. Although the absolute value of the compression in the plane may be small, it is significant for the very stringent overlay error budget for high-resolution lithography.

[0056] The inventors' studies have also shown that when a flat or bowl-shaped substrate is lowered onto the burls of the substrate, the substrate contacts the burls at the center before contacting the burls near the edges. As the clamping force is applied, the substrate tends to expand in-plane. Although the absolute amount of expansion may be small, it is significant because the overlay error budget for high-resolution lithography is very tight. Initially flat substrates also tend to undergo in-plane expansion. Therefore, the deformation that occurs on the compressed umbrella-shaped substrate and the expanded flat substrate further provides greater substrate-to-substrate deformation.

[0057] According to the present invention, a substrate holder for use in a lithographic apparatus and configured to support a substrate is provided, the substrate holder comprising:

[0058] a body having a body surface;

[0059] A plurality of protrusions protrude from a surface of the main body; wherein,

[0060] Each burl has a distal end configured to engage a substrate;

[0061] The shape of the distal end of the burl remains substantially consistent with the support plane, thereby enabling the substrate to be supported on the burl in a substantially flat state; and

[0062] Flow control features are configured to form an air cushion about a perimeter of the substrate holder as the substrate is being lowered onto the substrate holder.

[0063] As the substrate is being lowered onto the substrate holder, the flow control feature causes an accumulation of gas near the periphery of the substrate. In other words, the pressure under the periphery of the substrate increases. This pressure increase slows down the descent of the periphery of the substrate, especially if the substrate is an umbrella-shaped substrate, so that it contacts the burls more nearly simultaneously over the entire area of ​​the substrate. This can reduce or eliminate the compression effect that occurs when the umbrella-shaped substrate is clamped on the substrate holder. With the substrate holder according to the present invention, the umbrella-shaped substrate behaves more like a flat substrate, at least reducing the overlap difference from substrate to substrate.

[0064] Another advantage of the present invention is that the flow control features improve the thermal coupling between the substrate and the substrate holder in the peripheral region. This improves temperature control of the substrate.

[0065] In an embodiment, the flow control feature comprises a raised area proximate the periphery of the substrate holder.

[0066] The raised area may be easily provided in the manufacture of the substrate holder and may be shaped to have a desired effect.

[0067] In an embodiment, the raised area is annular around substantially the entire circumference of the substrate holder.

[0068] By providing the raised area to be annular, a substantially uniform and rotationally symmetrical effect can be achieved.

[0069] In an embodiment, the width of the raised area in the radial direction of the substrate holder is in the range of 2 mm to 80 mm, desirably in the range of 10 mm to 50 mm.

[0070] With a width within this range, a suitable air cushion effect can be achieved for the degree of deformation of the umbrella-shaped substrate that usually occurs. If the raised area does not have a clearly defined boundary, the width of the raised area should be considered to be the radial innermost part of the raised area (no more than 50 μm below the support plane) and the radial outermost part of the raised area (no more than 50 μm below the support plane).

[0071] In an embodiment, the raised region has a distal surface, and a distance between the distal surface and the supporting plane is at least 3 μm.

[0072] A spacing of 3 μm or more between the top of the raised area and the support plane ensures that if a contaminant particle lands on the raised area, it does not cause deformation of the substrate.

[0073] In an embodiment, the raised region has a distal surface, and the distance between the distal surface and the supporting plane is at most 50 μm.

[0074] A spacing of 50 μm or less between the top of the raised area and the supporting plane helps ensure that the air cushion effect is effective.

[0075] In an embodiment, the raised region has a distal surface, and the distal surface is substantially parallel to the support plane.

[0076] If the distal surface is parallel to the support plane, the air cushion is effective.

[0077] In an embodiment, the raised area has a distal surface, and the distal surface is inclined relative to the support plane so that a distance between the distal surface and the support plane at a radial inner portion thereof is smaller than a distance between the distal surface and the support surface at a radial outer portion thereof.

[0078] If the distal surface is inclined outwards, the inward airflow caused by the extraction of gas through the vacuum clamping system will easily create an air cushion. It is also possible that the distal surface is inclined inwards.

[0079] In an embodiment, the raised region has a distal surface, and the distal surface is concave.

[0080] The concavity on the distal surface helps retain gas to form an air cushion.

[0081] In an embodiment, there is also a sealing structure radially outside the flow control structure.

[0082] The sealing structure external to the flow control structure forms a narrow gap relative to the substrate when the substrate is loaded to reduce the gas flow required to maintain the low pressure under the substrate for clamping.

[0083] In an embodiment, a distance between a distal sealing surface of the sealing structure and the support plane is smaller than a distance between a distal surface of the flow control structure and the support plane.

[0084] The sealing structure may be much narrower than the flow control structure so that the gap between the distal sealing surface and the support plane may be small without an unacceptable risk of contaminant particles being trapped.

[0085] According to an embodiment of the present invention, there is also provided a lithography apparatus for projecting an image onto a substrate, the lithography apparatus comprising:

[0086] A substrate holder as described above; and

[0087] A clamping system for clamping a substrate on a substrate holder.

[0088] According to an embodiment of the present invention, there is also provided a method for manufacturing a device using a lithographic apparatus, the lithographic apparatus having a substrate holder as described above and a clamping system for clamping a substrate to the substrate holder, the method comprising:

[0089] loading a substrate onto a substrate holder;

[0090] engaging the clamping system; and

[0091] The pattern is exposed onto the substrate.

[0092] Figure 2A substrate holder WT according to an embodiment of the present invention is shown. The substrate holder WT comprises a body 20 which is generally circular in plan view. The diameter of the body 20 is ideally equal to the diameter of the substrate to be supported. The diameter of the body 20 may be, for example, 300 mm or 450 mm. The body 20 has a substantially flat body upper surface 20 a, as described below. The body upper surface 20 a is provided with a plurality of burls 21 protruding therefrom. The shape of the distal end surfaces of the burls 21 is accurately maintained in accordance with the support plane SP to support the substrate. In other words, the distal end surfaces of the burls 21 are coplanar.

[0093] Around the periphery of the substrate holder WT there is a flow control structure 22, described further below. Outside the flow control structure 22 there is a sealing structure 23. The flow control structure and the sealing structure may be as follows: Figure 3 spaced or adjacent as shown, Figure 3 The height of the surface of the substrate holder along the radius of the substrate holder is shown. The sealing structure 23 comprises a pair of concentric walls 23a, 23b which protrude upwardly from the upper surface 20a of the substrate holder WT (see Figure 4 , Figure 4 yes Figure 3 ). A small gap, for example about 3 μm to 10 μm, is retained between the upper sealing surfaces of the walls 23a, 23b. The purpose of the sealing structure 23 is twofold. Firstly, if a vacuum clamp is used to fix the substrate W on the substrate holder WT, the sealing structure reduces the airflow into the space below the substrate W, thereby reducing the energy required to maintain a negative pressure. Secondly, in an immersion lithography apparatus, the sealing structure 23 may also play a role in reducing the entry of immersion liquid into the space below the substrate W. The sealing structure does not need to have two walls, and in some cases a single wall is sufficient. In an embodiment of the present invention, the sealing structure is omitted.

[0094] In the central region of the substrate holder WT a plurality of through holes 24 are provided. The through holes 24 may fulfil two functions. Firstly, they allow e-pins (not shown) to protrude through the substrate holder WT in order to receive the substrate W. Secondly, they allow the space between the substrate W and the substrate holder WT to be connected to an underpressure in order to achieve the effect of vacuum clamping as described above. The number and arrangement of the through holes 24 may be varied as required to achieve the above functions, in particular depending on whether separate holes are used for e-pins and for connection to an underpressure.

[0095] In an embodiment, the height of the burl 21 is in the range of 100 μm to 500 μm, for example about 150 μm. The diameter of the distal surface of the burl 21 may be in the range of 100 μm to 300 μm, for example about 200 μm. The pitch of the burls (i.e. the distance between the centers of two adjacent burls) may be in the range of about 0.5 mm to 3 mm, for example about 1.5 mm. In an embodiment, the total area of ​​the distal surfaces of all burls 21 is in the range of 1% to 3% of the total area of ​​the substrate W or substrate holder WT. The burl 21 may be truncated cone-shaped, with slightly inclined side walls. In an embodiment, the side walls may be vertical or even protruding if this is more convenient for manufacturing. In an embodiment, the burl 21 is circular in a plan view. If desired, the burl 21 may also be formed in other shapes. The burl 21 may be treated, for example provided with a coating or structure, to reduce friction and / or increase wear resistance.

[0096] The knobs 21 are distributed substantially over the entire area of ​​the body upper surface 20a, up to the sealing structure 23. The knobs 21 are disposed on top of the flow control structure upper surface 20a. In an embodiment, the pattern of the knobs 21 is substantially uniform over the entire area of ​​the upper surface 20a, i.e., the knobs have a consistent pitch. In an embodiment, the pattern of the knobs 21 varies in at least some portions of the upper surface 20a, such as near the edge of the through-hole 24 or the wafer. The pattern of the knobs may be varied in order to control parameters of the support of the substrate, such as the local stiffness of the substrate holder to which the substrate is subjected and / or the friction between the substrate and the substrate holder.

[0097] The flow control structure 22 comprises a raised area located on the main body upper surface 20a of the substrate holder WT in the peripheral region of the substrate holder WT. The profile of the flow control structure 22 is as follows Figure 3 As shown, Figure 3 is a graph of the height relative to the support plane SP as a function of the radial position. Figure 4 yes Figure 3 An enlarged view of a portion of the graph of FIG. 1 to better illustrate the shape of the flow control structure and the sealing structure. Figure 4 The horizontal axis is magnified more than the vertical axis. It is important to note that Figure 3 and Figure 4 There are two things to note about the diagram. First, the horizontal axis (r) and the vertical axis (z), although shown in arbitrary units, are of very different scales. The arbitrary units used for z are about 1000 times smaller than the arbitrary units used for r. Second, to avoid confusion about the form of the flow control structure, the burls have been omitted from this figure, the shape of the distal ends of these burls all remaining consistent with the support plane SP.

[0098] From a functional point of view, the most important part of the flow control structure 22 is the upper flow control surface 22a. The upper flow control surface 22a is generally planar and arranged parallel to the support plane SP. The distance between the upper flow control surface 22a and the support plane SP is in the range of about 3 μm or 10 μm to about 50 μm, for example 20 microns. In an embodiment, the upper flow control surface is lower than the top of the sealing structure 23. In an embodiment, the upper flow control surface 22a is concave, for example, the shape remains consistent with a portion of the annulus. In an embodiment, the upper flow control surface 22a is not parallel to the support plane SP. In an embodiment, the upper flow control surface 22a is inclined so that the gap between the upper flow control surface 22a and the support plane SP increases with the increase of the radius. In an embodiment, the upper flow control surface 22a is inclined so that the gap between the upper flow control surface 22a and the support plane SP decreases with the increase of the radius. The function of the upper flow control surface 22a is to create an air cushion, ie a pressure build-up, when a substrate being lowered onto the substrate holder WT approaches the supporting plane.

[0099] When the substrate is lowered onto the substrate holder WT, the gas present between the substrate W and the substrate holder WT is compressed and if the gas cannot escape quickly enough, pressure build-up will occur. Gas can escape from the space between the descending substrate W and the substrate holder WT via two paths: through the through hole 24 in the substrate holder WT, or through the gap between the substrate W and the sealing structure 23 around the periphery of the substrate holder. As the substrate W descends, this gap decreases, thereby reducing the rate of gas flowing out by this route. By starting a vacuum pump or other negative pressure source and connecting it to the through hole 24, gas can be extracted from the space between the descending substrate W and the substrate holder WT quickly enough to prevent pressure build-up, which would otherwise limit the speed at which the substrate can be lowered onto the substrate holder, thereby preventing a negative impact on production output.

[0100] In an embodiment of the present invention, when the substrate W is being lowered onto the substrate holder, the presence or provision of the flow control structure causes a local pressure accumulation in the peripheral region of the substrate holder. This pressure accumulation generates an upward force on the peripheral region of the substrate W, thus tending to deflect the edge of the substrate W upward. The parameters of the flow control structure 22 (particularly its width in the radial direction, its spacing from the support plane SP, and its shape) can be selected to provide a desired effect on the periphery of the descending substrate. The parameters of the flow control structure can be selected so as to provide a desired compromise between the deflection of the substrate edge and the delay of loading the substrate.

[0101] The flow control structure 22 also includes an inclined segment 22b, which connects the upper flow control surface 22a to the main body upper surface 21a of the substrate holder WT. The shape of the inclined segment 22b and the corners 22c and 22d (which connect the inclined segment 22b to the upper flow control surface 22a) is not critical to the function of the flow control structure and can therefore be selected as required for ease of manufacturing. The inclined segment can be concave or convex. A stepped reduction in the height of the raised area is also possible. Similarly, for manufacturing reasons, the exact form of the corner 22e, which connects the upper flow control surface 22a to the wall 23a, can be selected as required.

[0102] The substrate holder WT can be made of SiSiC or other ceramic materials. The protrusions, flow control structures and sealing structures can be formed on the body 20 by conventional techniques. For example, the substrate holder is made by removing material from a blank, for example using electrical discharge machining. A final lapping process can be used to ensure that the protrusions have the correct height. The conventional electrical discharge machining process can be modified so as to leave additional material where needed to form the flow control structure. However, the flow control structure does not need to have any specific structural properties, and its dimensional tolerances are not particularly strict. Therefore, the flow control structure can be formed by adding material to an existing substrate holder, for example by additive manufacturing techniques such as 3D printing. Existing substrate holders can be modified to have a flow control structure.

[0103] Studies by the present inventors have shown that substrate holders according to embodiments of the present invention provide improved performance of loaded substrates, in particular more consistent performance between different types of deformed substrates. Figures 5 to 8 This situation is shown.

[0104] Figure 5 The in-plane deformation in arbitrary units (vertical axis) is shown as a function of radius in arbitrary units (horizontal axis) for an initially flat substrate (continuous line) and an initially umbrella-shaped deformed substrate. It can be seen that the flat substrate undergoes a positive in-plane deformation (i.e., expansion), while the umbrella-shaped substrate undergoes a negative in-plane deformation (i.e., compression). Figure 6 The substrate-to-substrate variation is shown, i.e., the difference between the deformation of a flat substrate and the deformation of an umbrella-shaped substrate. Because the flat substrate and the umbrella-shaped substrate deform in different ways, the substrate-to-substrate variation is greater than the deformation experienced by any single substrate.

[0105] Figure 7 and Figure 8 Corresponds to Figure 5 and Figure 6, but using a substrate holder according to an embodiment of the present invention. The same arbitrary units as for the in-plane deformation are used. Figure 7 As can be seen in FIG. 1 , both the flat substrate (continuous line) and the umbrella-shaped substrate (dashed line) experience positive in-plane deformation, i.e., expansion. Although the in-plane deformation experienced by the flat substrate when using the substrate holder according to an embodiment of the present invention is greater than when using a conventional substrate holder, Figure 8 It can be seen that the variation from substrate to substrate is significantly reduced. Therefore, it should be understood that the substrate holder according to an embodiment of the present invention produces a more consistent performance between different types of deformed substrates. Consistent deformations elsewhere can be compensated during the exposure process, for example, by adjusting the positioning set point of the substrate during exposure. Although it can be considered that different substrate holders can be used for different types of deformed substrates to minimize deformation, substrate holders are not so easy to replace.

[0106] Although the present invention has been described with respect to an exemplary embodiment employing a vacuum clamping system, an electrostatic clamp may also be used. The present invention may be applied in lithographic apparatuses where the beam path is under high vacuum conditions (e.g. EUV lithographic apparatuses) as long as the substrate is loaded onto a substrate holder in an environment having sufficient gas pressure to form an air cushion.

[0107] 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 may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. Those skilled in the art will recognize that in these alternative application scenarios, any term "wafer" or "die" used herein may be considered synonymous with the more general term "substrate" or "target portion", respectively. The substrate referred to herein may be processed before or after exposure, such as in a track (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the disclosed content may be applied to such and other substrate processing tools. In addition, the substrate may be processed more than once, such as to produce a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already includes one or more processed layers.

[0108] As used herein, the terms "radiation" and "beam" include all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength equal to or about 436 nm, 405 nm, 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm). Where the context permits, the term "lens" may refer to any one or combination of various types of optical components, including refractive and reflective optical components.

[0109] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0110] One or more embodiments of the present invention may be applied to any immersion lithography apparatus, particularly but not exclusively to those types described above, and whether the immersion liquid is provided in the form of a bath, over only a localized surface area of ​​the substrate, or is unconfined. In a non-confined arrangement, the immersion liquid may flow over the surface of the substrate and / or substrate table such that substantially the entire uncovered surface of the substrate table and / or substrate is wetted. In such an unconfined immersion system, the liquid supply system may not confine the immersion liquid, or it may provide a proportion of the immersion liquid confinement, but not substantially completely confine the immersion liquid.

[0111] The liquid supply system considered here should be interpreted broadly. In some embodiments, it may be a combination of a mechanism or structure that provides immersion liquid to the space between the projection system and the substrate and / or the substrate table. It may include a combination of one or more structures, including one or more fluid openings for one or more liquid openings, one or more gas openings or one or more openings for two-phase flow. Each opening may be an inlet to the immersion space (or an outlet of a fluid handling structure) or an outlet out of the immersion space (or an inlet into the fluid handling structure). In an embodiment, the surface of the space may be a part of the substrate and / or the substrate table, or the surface of the space may completely cover the surface of the substrate and / or the substrate table, or the space may surround the substrate and / or the substrate table. The liquid supply system may optionally further include one or more elements to control the position, quantity, quality, shape, flow rate or any other characteristics of the immersion liquid.

[0112] The above description is intended to be illustrative rather than limiting. It will therefore be apparent to those skilled in the art that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A substrate holder for use in a lithographic apparatus and configured to support a substrate, the substrate holder comprising: a body having a body surface; A plurality of protrusions protrude from a surface of the body, wherein: Each burl has a distal end configured to engage the substrate, The shape of the distal end of the burl is substantially consistent with the support plane, so that the substrate can be supported on the burl in a substantially flat state; wherein the plurality of burls comprises a plurality of first burls and a plurality of second burls, whereby the substrate holder further comprises a raised area surrounding the plurality of first burls, and the plurality of second burls are arranged on a surface of the raised area, The substrate holder further includes a radially outward wall of the raised region such that at least a portion of an upper surface of the raised region has a reduced clearance with the support plane as it extends toward the wall.

2. The substrate holder according to claim 1, wherein The raised area is ring-shaped.

3. The substrate holder according to claim 1 further includes a sealing structure, which is arranged radially outside the raised area, wherein the sealing structure is configured to reduce the airflow entering the space below the substrate, thereby reducing the energy required to maintain the negative pressure. The substrate holder of claim 3 , wherein the sealing structure surrounds the plurality of first burls and the plurality of second burls.

5. The substrate holder according to any one of claims 1 to 4, wherein the raised area is at a height closer to the body surface than the support surface.

6. The substrate holder according to any one of claims 1 to 4, wherein the width of the raised area in the radial direction of the substrate holder is in the range of 3 mm to 80 mm.

7. The substrate holder of claim 6, wherein the width is in the range of 10 mm to 50 mm.

8. A substrate holder for use in a lithographic apparatus, the substrate holder being configured to support a substrate, the substrate holder comprising: a body having a body surface; A plurality of first protrusions protrude from a surface of the main body, wherein: Each first burl has a distal end configured to engage the substrate, The shapes of the distal ends of the plurality of first protrusions are substantially consistent with the support plane, so that the substrate can be supported on the protrusions in a substantially flat state; wherein the pattern of the plurality of first burls is non-uniform across the surface of the body, and the pattern of the plurality of first burls varies over at least a portion of the body surface proximate a through hole in the body surface; The substrate holder further comprises: a raised area at a lower elevation than the support surface and surrounding the plurality of first burls; a sealing structure located radially outward of the raised area; and A plurality of second protrusions protrude from the main body surface between the protruding area and the sealing structure.

9. The substrate holder of claim 8, wherein the pattern changes in the vicinity of the through hole of the substrate holder.

10. The substrate holder of claim 8, wherein the pattern changes near an edge of the substrate holder.

11. The substrate holder according to any one of claims 8-10 further includes a flow control feature, which is configured to form an air cushion near the periphery of the substrate holder when the substrate is being lowered onto the substrate holder, wherein the flow control feature includes a raised area, which is at a height closer to the main body surface than the support surface.

12. The substrate holder of claim 11, wherein the raised area is annular, the ring surrounding the periphery of the substrate holder. 13 . The substrate holder according to claim 12 , wherein a width of the raised area in a radial direction of the substrate holder is in the range of 3 mm to 80 mm.

14. The substrate holder of claim 13, wherein the width is in the range of 10 mm to 50 mm.

15. A lithographic apparatus for projecting an image onto a substrate, the lithographic apparatus comprising: The substrate holder according to any one of claims 1 to 14; as well as A clamping system for clamping a substrate on the substrate holder.

16. A method of manufacturing a device using the lithographic apparatus according to claim 15, the method comprising: loading a substrate onto the substrate holder; engaging the clamping system; as well as A pattern is exposed onto the substrate.

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