Substrate holder and method of manufacturing substrate holder

Abstract

To provide an object holder for use in a lithographic apparatus, the holder having burls, e.g., of different shapes, sizes and / or compositions, and a method of manufacturing an object holder having such burls.SOLUTION: An object holder (100) for a lithographic apparatus has a main body (400) having a surface (400a). A plurality of burls (406) to support an object are formed on a surface or in apertures of a thin-film stack (410, 440, 450). At least one of the burls is formed by laser-sintering. At least one of the burls formed by the laser-sintering may be a repair of a damaged burl previously formed by laser-sintering or another method.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] <CROSS REFERENCE TO RELATED APPLICATIONS>

[0001] This application claims the benefit of U.S. Provisional Application No. 61 / 594,857, filed February 3, 2012, U.S. Provisional Application No. 61 / 621,648, filed April 9, 2012, and U.S. Provisional Application No. 61 / 621,660, filed April 9, 2012, each of which is incorporated by reference in its entirety into this specification.

[0002] The present invention relates to a substrate holder, a lithographic apparatus, a device manufacturing method, and a method of manufacturing a substrate holder. [Background technology]

[0003]

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

[0004]

[0004] 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, so as to fill the space between the final element of the projection system and the substrate. In an embodiment, the liquid is distilled water, but other liquids can be used. An embodiment of the invention has been described with respect to a liquid. However, other fluids may be suitable, in particular wetting fluids, incompressible fluids and / or fluids with a higher refractive index than air, preferably a higher refractive index than water. Fluids other than gases are particularly desirable. The point is that the exposure radiation has a shorter wavelength in the liquid, allowing smaller features to be imaged (the effect of the liquid can be seen as a larger effective numerical aperture (NA) of the system, and also a larger depth of focus). Other immersion liquids have also been proposed, such as water in which solid particles (e.g. quartz) are suspended, or a liquid in which there is a suspension of nanoparticles (e.g. particles with a maximum dimension of up to 10 nm). The suspended particles may or may not have a similar or the same refractive index as the liquid in which they are suspended. Other liquids that may be suitable are hydrocarbons, such as aromatics, fluorohydrocarbons, and / or aqueous solutions.

[0005]

[0005] In conventional lithographic apparatus, the substrate to be exposed may also be supported by a substrate holder, which is supported by a substrate table. The substrate holder is often a flat, rigid disk whose size and shape correspond to the substrate (but may be of a different size or shape). The substrate holder has an array of protrusions called burls or pimples protruding from at least one side. In an embodiment, the substrate holder has an array of protrusions on two opposite sides. In this case, when the substrate holder is placed on the substrate table, the body of the substrate holder is held a small distance above the substrate table, and the ends of the burls on one side of the substrate holder are on the surface of the substrate table. Similarly, when the substrate is placed on top of the burls on the other side of the substrate holder, the substrate is spaced from the body of the substrate holder. One purpose of this is to help prevent the substrate holder or substrate from being distorted by particles (i.e. contaminant particles such as dust particles) that may be present on the substrate table or substrate holder. Since the total surface of the burls is only a small portion of the total surface of the substrate or substrate holder, if any particles are between the burls their presence is likely to have no effect.

[0006]

[0006] Due to the high accelerations experienced by the substrate when using a high throughput lithographic apparatus, it is not sufficient to simply allow the substrate to rest on the burls of the substrate holder. The substrate is clamped in place. There are two known methods for clamping the substrate in place: vacuum clamping and electrostatic clamping. In vacuum clamping, the space between the substrate holder and the substrate, and optionally between the substrate table and the substrate holder, is partially evacuated, so that the substrate is held in place by the higher pressure of the gas or liquid above it. However, when the beam path and / or the environment near the substrate or substrate holder is kept at low or very low pressure, for example in the case of extreme ultraviolet (EUV) radiation lithography, vacuum clamping may not be feasible. In this case, it may not be possible to generate a pressure difference large enough across the substrate (or substrate holder) to clamp it. Therefore, in these (or other) situations, electrostatic clamping can be used. In electrostatic clamping, electrodes provided on the substrate table and / or substrate holder are raised to a high potential, for example 10-5000 V, and electrostatic forces attract the substrate. Another purpose of the crowbar is therefore to space the substrate, substrate holder and substrate table apart to allow electrostatic clamping.

[0007]

[0007] Burls can be used in different locations in a lithographic apparatus, for example in a support for a patterning device such as a mask, in a substrate gripper or patterning device handling device, and / or in a reticle clamp. Burls in different locations may have different requirements regarding one or more of their dimensions and other physical properties. Different manufacturing methods may be applied. In many cases, damage to one or more burls may require replacement of the entire component. Summary of the Invention [Problem to be solved by the invention]

[0008] It would be desirable to provide object holders for use in a lithographic apparatus having burls, for example of different shapes, sizes and / or compositions, and methods for manufacturing object holders having such burls. [Means for solving the problem]

[0009] According to one aspect of the invention there is provided a method of manufacturing an object holder for use in a lithographic apparatus, the method comprising the steps of providing a body having a surface and forming a plurality of burls on the surface having end faces protruding from the surface and supporting an object, wherein forming at least a portion of at least one of the burls comprises laser sintering.

[0010] According to an aspect of the invention there is provided an object holder for use in a lithographic apparatus comprising a body having a surface and a plurality of burls provided on the surface and having end faces for supporting an object, at least a portion of at least one of the burls being formed by laser sintering.

[0011]

[0011] According to one aspect of the present invention, there is provided a lithographic apparatus comprising a support structure configured to support a patterning device, a projection system arranged to project a beam patterned by the patterning device onto a substrate, and a substrate holder arranged to hold the substrate.

[0012]

[0012] 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 symbols indicate corresponding parts, in which: [Brief description of the drawings]

[0013] [Figure 1] 1 depicts a lithographic apparatus according to an embodiment of the invention; [Diagram 2]

[0014] 1 depicts a liquid supply system for use in a lithographic projection apparatus. [Diagram 3] 1 depicts a liquid supply system for use in a lithographic projection apparatus; [Figure 4]

[0015] 4 depicts another liquid supply system for use in a lithographic projection apparatus; [Diagram 5]

[0016] 1 illustrates, in cross-section, a barrier member that can be used in an embodiment of the invention as an immersion liquid supply system; [Figure 6]

[0017] 1 depicts a lithographic apparatus according to an embodiment of the invention; [Figure 7]

[0018] A more detailed diagram of the device 4100. [Figure 8]

[0019] FIG. 8 is a more detailed diagram of the source collector arrangement SO of the apparatus of FIGS. 6 and 7; [Figure 9]

[0020] 2 depicts a cross-sectional view of a substrate table and substrate holder according to an embodiment of the invention; [Figure 10A]

[0021] 5A-5D illustrate steps of a substrate holder manufacturing method according to an embodiment of the present invention. [Figure 10B] 5A-5C illustrate steps of a substrate holder manufacturing method according to an embodiment of the present invention. [Figure 10C] 5A-5C illustrate steps of a substrate holder manufacturing method according to an embodiment of the present invention. [Figure 10D] 5A-5C illustrate steps of a substrate holder manufacturing method according to an embodiment of the present invention. [Figure 10E] 5A-5C illustrate steps of a substrate holder manufacturing method according to an embodiment of the present invention. [Figure 11]

[0022] 1 illustrates a substrate holder according to an embodiment of the present invention. [Figure 12]

[0023] 1 depicts a support structure for a patterning device according to an embodiment of the present invention. [Figure 13]

[0024] 1 shows a plan view of a portion of a support structure according to an embodiment of the present invention. [Figure 14]

[0025] 14 shows a cross-sectional view of the support structure of FIG. 13. [Figure 15]

[0026] 1 illustrates a substrate holder and gripper according to an embodiment of the present invention. [Figure 16]

[0027] 1 depicts a substrate table according to an embodiment of the present invention; [Figure 17A]

[0028] 5 illustrates steps of a method for repairing a substrate holder according to an embodiment of the present invention. [Figure 17B] 5 illustrates steps of a method for repairing a substrate holder according to an embodiment of the present invention. [Figure 17C] 5 illustrates steps of a method for repairing a substrate holder according to an embodiment of the present invention. [Figure 18A]

[0029] 5 illustrates steps of a method for repairing a substrate holder according to an embodiment of the present invention. [Figure 18B] 5 illustrates steps of a method for repairing a substrate holder according to an embodiment of the present invention. [Figure 18C] 5 illustrates steps of a method for repairing a substrate holder according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014]

[0030] Figure 1 depicts a schematic diagram of a lithographic apparatus according to one embodiment of the invention.

[0031] an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation);

[0032] a support structure (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters; and

[0033] a substrate table (e.g. wafer table) WT constructed to hold a substrate (e.g. resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters; and

[0034] a projection system (eg a refractive projection lens system) PS configured to project a pattern imparted to a radiation beam B by a patterning device MA onto a target portion C of a substrate W (eg comprising one or more dies).

[0015]

[0035] Illumination systems may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, etc. optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0016]

[0036] The support structure MT holds the patterning device MA. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, for example whether or not the patterning device is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure MT may be for example a frame or a table, which may be fixed or movable as required. The support structure MT may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle" or "mask" herein may be considered as synonymous with the more general term "patterning device".

[0017]

[0037] 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 to create a pattern in a target portion of a 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. Generally, the pattern imparted to the radiation beam corresponds to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0018]

[0038] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam which is reflected by the mirror matrix.

[0019]

[0039] The term "projection system" as used herein should be interpreted broadly as encompassing any type of system including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for example depending on the exposure radiation used or other factors such as the use of an immersion liquid or the use of a vacuum. When the term "projection lens" is used herein, it can be considered as synonymous with the more general term "projection system".

[0020]

[0040] As here depicted, the apparatus may be of a transmissive type (e.g. employing a transmissive mask) or it may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).

[0021]

[0041] The lithographic apparatus may be of a type having two or more substrate support structures, such as substrate stages or substrate tables, and / or two or more support structures for a patterning device. In an apparatus having multiple substrate stages, all substrate stages may be identical and interchangeable. In an embodiment, at least one of the multiple substrate stages is specifically adapted for an exposure step and at least one of the multiple substrate stages is specifically adapted for a measurement or preliminary step. In an embodiment of the invention, one or more of the multiple substrate stages are replaced by a measurement stage. The measurement stage includes at least a part of one or more sensor systems, such as a sensor detector and / or a target of the sensor system, but does not support a substrate. The measurement stage is positionable in the projection beam instead of the support structure for the substrate stage or the patterning device. In such an apparatus, additional stages may be used in conjunction, or preliminary steps may be performed on one or more stages while one or more other stages are used for exposure.

[0022]

[0042] With reference to Figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL using a beam delivery system BD, for example comprising suitable directing mirrors and / or beam expanders. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0023]

[0043] The illuminator IL may comprise an adjuster AM for adjusting the angular intensity distribution of the radiation beam. Typically, the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. The illuminator IL may also comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam to have a desired uniformity and intensity distribution over 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 a separate entity from the lithographic apparatus. In the latter case, the lithographic apparatus may be configured such that the illuminator IL is mountable thereon. Optionally, the illuminator IL is detachable and may be provided separately (e.g. by the lithographic apparatus manufacturer or another supplier).

[0024]

[0044] The radiation beam B is incident on a patterning device (e.g. mask) MA, which is held on a support structure (e.g. mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The substrate W is held on a substrate table WT by a substrate holder according to an embodiment of the invention, which is described in more detail below. By means of the second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be precisely moved, for example so that different target portions C can be positioned in the path of the radiation beam B. Similarly, by means of the first positioner PM and another position sensor (not explicitly shown in FIG. 1 ), the patterning device MA can be precisely positioned with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library or during a scan. In general, movement of the support structure MT can be realized by means of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the 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. The substrate alignment marks as illustrated occupy dedicated target portions, but may also be located in spaces between the target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0025]

[0045] The depicted lithographic apparatus can be used in at least one of the following modes:

[0026]

[0046] 1. In step mode, the support structure MT and substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto the target portion C in one go (i.e. a single static exposure). The substrate table WT is then moved in the X and / or 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 that can be imaged in a single static exposure.

[0027]

[0047] 2. In scan mode, the support structure MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion C in a single dynamic exposure, and the length of the scanning movement determines the height (in the scanning direction) of the target portion C.

[0028]

[0048] 3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, a pulsed radiation source is typically used, and the programmable patterning device is updated as required after each movement of the substrate table WT, or between successive radiation pulses during a scan. This mode of operation is readily applicable to maskless lithography using a programmable patterning device such as a programmable mirror array of the type referred to above.

[0029]

[0049] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be used.

[0030]

[0050] In many lithographic apparatus, a liquid supply system IH is used to provide a fluid, in particular liquid, between the final element of the projection system, to allow smaller features to be imaged and / or an increase in the effective NA of the apparatus. Although embodiments of the invention are described further below with respect to such an immersion apparatus, embodiments of the invention can equally be implemented in a non-immersion apparatus. Arrangements for providing liquid between the final element of the projection system and the substrate fall into at least two general categories. These are bath type arrangements and so-called localized immersion systems. In a bath type arrangement, substantially the entire substrate and optionally part of the substrate table are immersed in a bath of liquid. A localized immersion system uses a liquid supply system where liquid is provided only to a localized area of ​​the substrate. In the latter category, the space filled by liquid is smaller than the top surface of the substrate in plan, and the area filled by liquid is substantially stationary relative to the projection system while the substrate moves below it. Another arrangement to which an embodiment of the invention is directed is an all-wet solution, where the liquid is not confined. In this arrangement, substantially the entire top surface of the substrate and all or part of the substrate table are covered in immersion liquid. At least the depth of liquid covering the substrate is small. The liquid may be a film, such as a thin film of liquid on a substrate.

[0031]

[0051] Four different types of localized liquid supply systems are shown in Figures 2-5. Any of the liquid supply devices of Figures 2-5 may be used in a non-confined system, but the sealing features may be absent, not activated, less efficient than normal, or otherwise ineffective in sealing the liquid to only a localized area.

[0032]

[0052] One proposed configuration for a localized immersion system is where a liquid supply system uses a liquid confinement system to provide liquid only to a localized area of ​​the substrate and between the final element of the projection system and the substrate (the substrate typically has a larger surface area than the final element of the projection system). One proposed way to configure this is disclosed in PCT Patent Application Publication WO 99 / 49504. As illustrated in Figures 2 and 3, liquid is supplied by at least one inlet onto the substrate, preferably along the direction of movement of the substrate relative to the final element, and is removed by at least one outlet after passing under the projection system. That is, as the substrate is scanned under the element in the -X direction, liquid is supplied at the +X side of the element and taken up at the -X side.

[0033]

[0053] Figure 2 shows a schematic arrangement in which liquid is supplied via an inlet and taken up on the other side of the element by an outlet connected to a low pressure source. The arrows above the substrate W indicate the direction of liquid flow and the arrows below the substrate W indicate the direction of movement of the substrate table. In the illustration of Figure 2, liquid is supplied along the direction of movement of the substrate relative to the final element, but this does not have to be the case. Various orientations and numbers of inlets and outlets arranged around the final element are possible, an example is shown in Figure 3, where four sets of inlets with an outlet on each side are provided in a regular pattern around the final element. The arrows in the liquid supply and liquid recovery devices indicate the direction of liquid flow.

[0034]

[0054] Another solution for immersion lithography with a localized liquid supply system is shown in FIG. 4. Liquid is supplied by two groove inlets on either side of the projection system PS and removed by a number of separate outlets arranged radially outward of the inlets. The inlets and outlets may be arranged in a plate with a hole in its centre through which the projection beam is projected. Liquid is supplied by one groove inlet on one side of the projection system PS and removed by a number of separate outlets on the other side of the projection system PS, causing a flow of a thin film of liquid between the projection system PS and the substrate W. The choice of which combination of inlets and outlets to use may be determined by the direction of movement of the substrate W (the other combination of inlets and outlets is inoperative). In the cross-sectional view of FIG. 4, the arrows indicate the direction of liquid flow into the inlets and out of the outlets.

[0035]

[0055] Another proposed arrangement is to provide a liquid supply system with a liquid confinement member. The liquid confinement member extends along at least part of the boundary of the space between the final element of the projection system and the substrate table. Such an arrangement is shown in Figure 5. The liquid confinement member is substantially stationary in the XY plane relative to the projection system but is allowed some relative movement in the Z direction (along the optical axis). A seal is formed between the liquid confinement member and the substrate surface. In an embodiment a seal is formed between the liquid confinement member and the substrate surface, which may be a contactless seal such as a gas seal. Such a system is disclosed in US Patent Application Publication US2004-0207824.

[0036]

[0056] The fluid handling structure 12 comprises a liquid confinement member and at least partially confines liquid in a space 11 between the final element of the projection system PS and the substrate W. A contactless seal 16 to the substrate W may be formed around the periphery of the image field of the projection system such that liquid is confined in the space between the surface of the substrate W and the final element of the projection system PS. The space is at least partially formed by the fluid handling structure 12 positioned below and surrounding the final element of the projection system PS. Liquid is brought into the space in the fluid handling structure 12 below the projection system by a liquid inlet 13. Liquid may be removed by a liquid outlet 13. The fluid handling structure 12 may extend a little above the final element of the projection system. The liquid level rises above the final element so that a buffer of liquid is provided. In an embodiment the fluid handling structure 12 has an inner periphery which at its top may exactly conform to the shape of the projection system or its final element, and may for example be circular. At the bottom the inner periphery may exactly conform to the shape of the image field, and may for example be rectangular, but this does not have to be the case.

[0037]

[0057] In an embodiment, the liquid is contained in the space 11 by a gas seal 16 which, in use, is formed between the bottom of the fluid handling structure 12 and the surface of the substrate W. The gas seal is formed by a gas, for example air, synthetic air, N2 or another inert gas. Gas in the gas seal is provided under pressure via an inlet 15 to the gap between the fluid handling structure 12 and the substrate W. The gas is extracted via an outlet 14. The overpressure on the gas inlet 15, the vacuum level at the outlet 14 and the geometry of the gap are arranged such that there is a high velocity inward gas flow 16 which confines the liquid. The force of the gas on the liquid between the fluid handling structure 12 and the substrate W confines the liquid in the space 11. The inlet / outlet may be an annular groove surrounding the space 11. The annular groove may be continuous or discontinuous. The flow of gas 16 is effective to confine the liquid in the space 11. Such a system is disclosed in US Patent Application Publication US2004-0207824.

[0038]

[0058] The example of Figure 5 is a localised area arrangement where liquid is provided to only a localised region of the top surface of the substrate W at any one time. Other arrangements are possible, including fluid handling systems using a single phase extractor or a two phase extractor, for example as disclosed in US Patent Application Publication US2006-0038968.

[0039]

[0059] Another possible configuration is one that operates on the gas drag principle. The so-called gas drag principle is described, for example, in US Patent Application Publications US2008-0212046, US2009-0279060 and US2009-0279062. In that system the extraction holes are preferably configured with a shape having a corner. The corner can be aligned in the step or scan direction. This reduces the force on the meniscus between two openings in the surface of the fluid handling structure for a given velocity in the step or scan direction compared to a fluid handling structure with two outlets aligned perpendicular to the scan direction.

[0040]

[0060] US2008-0212046 also discloses a gas knife positioned radially outward of the primary liquid recovery feature. The gas knife captures any liquid that passes past the primary liquid recovery feature. Such a gas knife may be in a so-called gas drag principle arrangement (as disclosed in US2008-0212046), a single or two phase extractor arrangement (as disclosed in US2009-0262318), or any other arrangement.

[0041]

[0061] Many other types of liquid supply systems are possible. The invention is not limited to any particular type of liquid supply system, nor to immersion lithography. The invention is equally applicable to any lithography. In an EUV lithography apparatus, the beam path is substantially evacuated and does not use the immersion arrangement described above.

[0042]

[0062] The control system 500 shown in FIG. 1 controls the overall operation of the lithographic apparatus and in particular executes the optimization process further described below. The control system 500 may be implemented as a suitably programmed general purpose computer with a central processing unit, volatile and non-volatile storage means. Optionally, the control system may further comprise one or more input / output devices such as a keyboard and a screen, one or more network connections, and / or one or more interfaces to various parts of the lithographic apparatus. It will be appreciated that a one-to-one relationship between the controlling computer and the lithographic apparatus is not required. In an embodiment of the invention, one computer may control multiple lithographic apparatuses. In an embodiment of the invention, multiple computers connected in a network may be used to control one lithographic apparatus. The control system 500 may also be configured to control one or more associated process devices and substrate handling devices in a lithocell or cluster of which the lithographic apparatus is a part. The control system 500 may also be configured to be subordinate to a supervisory control system of the lithocell or cluster and / or to an overall control system of the factory.

[0043]

[0063] 6 shows a schematic diagram of an EUV lithography apparatus 4100 including a source collector apparatus SO. an illumination system (illuminator) EIL configured to condition a radiation beam B (e.g. EUV radiation); a support structure (e.g. mask table) MT constructed to support a patterning device (e.g. mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; and a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (eg a reflection projection system) PS configured to project a pattern imparted to a radiation beam B by a patterning device MA onto a target portion C (eg comprising one or more dies) of a substrate W.

[0044]

[0064] The functions of these basic components of the EUV lithographic apparatus are similar to the functions of the corresponding components of the lithographic apparatus of Figure 1. The following description mainly includes different areas, and redundant descriptions of aspects of the same components are omitted.

[0045]

[0065] In an EUV lithography tool, it is desirable to operate in a vacuum or low pressure environment, as gases can absorb too much radiation, and therefore a vacuum wall and one or more vacuum pumps can be used to provide a vacuum environment throughout the beam path.

[0046]

[0066] Referring to FIG. 6, the EUV illuminator EIL receives a beam of extreme ultraviolet radiation from a source collector apparatus SO. Methods of generating EUV radiation include, but are not necessarily limited to, converting a material having at least one element, such as, for example, xenon, lithium, or tin, into a plasma state having one or more emission lines in the EUV range. In one such method, often referred to as laser-produced plasma ("LPP"), the plasma can be generated by irradiating a fuel, such as droplets, streams, or clusters of a material having the desired emission line-emitting element, with a laser beam. The source collector apparatus SO may be part of an EUV radiation system that includes a laser (not shown in FIG. 6) that provides a laser beam that excites the fuel. The resulting plasma emits output radiation, such as EUV radiation, that is collected using, for example, a radiation collector disposed in the source collector apparatus. The laser and source collector apparatus may be separate elements, for example when a CO2 laser is used to provide the laser beam for exciting the fuel.

[0047]

[0067] In such cases, the laser is not considered to form part of the lithographic apparatus and the radiation beam is delivered from the laser to the source collector apparatus using a beam delivery system, e.g. comprising suitable directing mirrors and / or beam expanders. In other cases, the source may be an integral part of the source collector apparatus, for example when the source is a discharge produced plasma EUV generator, often referred to as a DPP source.

[0048]

[0068] The EUV illuminator EIL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam EB. Typically, at least the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the EUV illuminator EIL may comprise various other components, such as faceted field and pupil mirror devices. The EUV illuminator EIL may be used to condition the radiation beam EB so that it has a desired uniformity and intensity distribution across its cross-section.

[0049]

[0069] The radiation beam EB is incident on a patterning device (e.g. mask) MA, which is held on a support structure (e.g. mask table) MT, and is patterned by the patterning device. After reflecting off the patterning device (e.g. mask) MA, the radiation beam EB passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. By means of a second positioner PW and a position sensor PS2 (e.g. an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be moved accurately, for example so that different target portions C can be positioned in the path of the radiation beam EB. Similarly, a first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam EB. The patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0050]

[0070] The depicted apparatus can be used in the same modes as the apparatus in FIG.

[0051]

[0071] FIG. 7 shows in more detail an EUV apparatus 4100 including a source collector apparatus SO, an EUV illumination system EIL, and a projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained within an enclosed structure 4220 of the source collector apparatus SO. The EUV radiation emitting plasma 4210 may be formed by a discharge-produced plasma radiation source. The EUV radiation may be generated by a gas or vapor, such as, for example, xenon gas, lithium vapor, or tin vapor, whereby a plasma 4210 is generated and emits radiation in the EUV range of the electromagnetic spectrum. The plasma 4210 is generated, for example, by a discharge that produces an at least partially ionized plasma. A partial pressure of, for example, 10 Pa, of xenon, lithium, tin vapor, or any other suitable gas or vapor may be required to efficiently generate radiation. In an embodiment, a plasma of excited tin (Sn) is provided to generate EUV radiation.

[0052]

[0072] Radiation emitted by the plasma 4210 is routed from the source chamber 4211 into the collector chamber 4212 via an optional gas barrier and / or contaminant trap 4230 (sometimes also referred to as a contaminant barrier or foil trap) located in or behind an opening in the source chamber 4211. The contaminant trap 4230 may include a channel structure. The contaminant trap 4230 may also include a gas barrier or a combination of a gas barrier and a channel structure. At least the contaminant trap or contaminant barrier 4230 as illustrated further herein includes a channel structure at least as known in the art.

[0053]

[0073] The collector chamber 4212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 4251 and a downstream radiation collector side 4252. Radiation traversing the collector CO may be reflected off a grating spectral filter 4240 and focused into a virtual source point IF. The virtual source point IF is commonly referred to as an intermediate focus, and the source collector arrangement is positioned such that the intermediate focus IF is at or near an opening 4221 in the enclosure structure 4220. The virtual source point IF is an image of the radiation emitting plasma 4210.

[0054]

[0074] The radiation then traverses the illumination system IL, which may include a faceted field mirror device 422 and a faceted pupil mirror device 424 arranged to give a desired angular distribution of the radiation beam 421 at the patterning device MA, as well as a desired uniformity of the radiation intensity at the patterning device MA. When the radiation beam 421 reflects off the patterning device MA, which is held by the support structure MT, a patterned beam 426 is formed which is imaged by the projection system PS via reflective elements 428, 430 onto the substrate W held by a substrate stage or substrate table WT.

[0055]

[0075] In general, more elements than shown may be present in the illumination optics unit IL and projection system PS. Depending on the type of lithographic apparatus, an optional grating spectral filter 4240 may be present. More mirrors than shown may be present, for example one to six additional reflective elements more than are present in the projection system PS shown in Figure 7.

[0056]

[0076] 7 is shown as a nested collector with grazing incidence reflectors 4253, 4254 and 4255, just as an example of a collector (or collector mirror). Grazing incidence reflectors 4253, 4254 and 4255 are arranged axially symmetrically about optical axis O, and this type of collector optic CO is preferably used in combination with a discharge produced plasma radiation source, often referred to as a DPP radiation source.

[0057]

[0077] Alternatively, the source collector apparatus SO may be part of an LPP radiation system as shown in Figure 8. A laser LA is arranged to impart laser energy to a fuel such as xenon (Xe), tin (Sn) or lithium (Li) to generate a highly ionized plasma 4210 with an electron temperature of tens of electron volts (eV). Energetic radiation produced during de-excitation and recombination of these ions is emitted from the plasma and collected by a near normal incidence collector optic CO and focused into an aperture 4221 in an enclosure structure 4220.

[0058]

[0078] FIG. 9 shows a substrate holder according to an embodiment of the invention. The substrate holder is held in a recess in the substrate table WT and supports a substrate W. The body of the substrate holder 100 has the shape of a flat plate, e.g. a disk, whose shape and size substantially correspond to the substrate W. The substrate holder may be made of, e.g., Si, SiC, SiSiC, aluminum nitride (AIN), Zerodur, cordierite, or other suitable ceramic or glass-ceramic material. The substrate holder has protrusions 106, commonly called burls, at least on the top surface, and in an embodiment on both sides. In an embodiment, the substrate holder is an integral part of the substrate table and does not have burls on the bottom surface. The burls are not to scale in FIG. 9. Some or all of the burls are formed by laser sintering as described below.

[0059]

[0079] In practical embodiments, there may be hundreds or even thousands of burls, e.g., more than 10,000, or more than 40,000, distributed across a substrate holder having a width (e.g., diameter) of, e.g., 200 mm, 300 mm, or 450 mm. The area of ​​the tips of the burls may be, e.g., 1 mm 2 Thus, the total area of ​​all burls on one side of the substrate holder 100 is less than about 10%, for example 1-3% of the substrate holder. Due to such a burl arrangement, particles that may be present on the surface of the substrate, substrate holder or substrate table will likely fall between the burls and therefore will not lead to deformation of the substrate or substrate holder.

[0060]

[0080] The burl arrangement may form a pattern and / or have a periodic arrangement. The burl arrangement may be regular or may vary as desired to provide an appropriate force distribution on the substrate W and substrate table WT. The burl may be of any shape in plan, but are typically circular in plan. The burl may have the same shape and dimensions over their entire height, but are typically tapered. The distance that the burl protrudes from other surface portions of the body 100a of the substrate holder 100 is in the range of about 1 μm to about 5 mm, preferably about 5 μm to about 250 μm. The thickness of the body 100a of the substrate holder 100 is in the range of about 1 mm to about 50 mm, preferably about 5 mm to 20 mm, and is typically 10 mm.

[0061]

[0081] Advantageously, the burls can be formed with very consistent dimensions. Desirably, there is very little variation between the heights of the different burls. Short burls (e.g., less than 20 μm, less than 15 μm, less than 5 μm, or less than 3 μm) can be formed. Shorter burls are advantageous because they enhance heat transfer between the substrate and the substrate holder. The gap between the top surface of the substrate holder away from the burls and the support surface of the substrate on the substrate holder is smaller than for taller supports. Such a small gap enhances heat transfer from the temperature control element (e.g., heater) to the supported substrate. The minimum height of the burls is determined by the total height of the thin film stack and the non-flatness of the substrate and substrate holder. In an embodiment, the height of the burls is 1 μm or 2 μm or more.

[0062]

[0082] The width (eg, diameter) of the burls is 0.5 mm or less. In some embodiments, the width (eg, diameter) of the burls is in the range of about 200 μm to about 500 μm. The spacing between the burls is between about 1.5 mm to about 3 mm.

[0063]

[0083] Additionally, certain embodiments of the present invention allow a wider range of materials to be used for the substrate holder. Materials that are not suitable for conventional methods of forming burls or substrate holders can be used with embodiments of the present invention. In certain embodiments, materials such as cordierite, a low thermal expansion glass ceramic, that are not easily processed to form burls, can be used. Cordierite has excellent properties for use in substrate holders. For example, cordierite has a high Young's modulus of about 140 Gpa and a low thermal conductivity of about 4 W / mK.

[0064]

[0084] Substrate holders manufactured according to embodiments of the invention can have a long service life due to the robustness of the manufacturing method. Embodiments of the invention can exhibit desirable wear characteristics, such as good wear resistance, and are therefore less susceptible to certain contaminants. Advantageously, embodiments of the invention can eliminate the need to coat the substrate holder.

[0065]

[0085] Substrate holders according to certain embodiments of the invention may have thin film components 110 formed on one or both sides. The layer thickness of the thin film component may range from about 2 nm to about 100 μm. Such thin film components may have one or more layers. Each layer may be formed by processes including chemical vapor deposition, physical vapor deposition (e.g., sputtering), dip coating, spin coating, and / or spray coating. In certain embodiments, the components formed on the substrate holder comprise a thin film stack, i.e., include multiple thin film layers. Such components are described further below. Although the thin film stack is described herein as being formed on the top surface of the substrate holder, the thin film stack may be formed on the bottom surface of the substrate holder, or on the substrate table below the substrate holder, or on any other surface of the substrate table or substrate holder, including the surfaces of the substrate holder and substrate table together.

[0066]

[0086] The electronic or electrical components formed on the substrate table may include, for example, electrodes, resistive heaters, and / or sensors such as (but not limited to) strain, magnetic, pressure, capacitive, or temperature sensors. The heaters and sensors can be used to locally control and / or monitor the temperature of the substrate holder and / or substrate. Such local control and / or monitoring can reduce undesired temperature changes in the substrate holder or substrate or induce desired temperature changes in the substrate holder or substrate. Desirably, the heaters and sensors are formed on, around, and above the same area as each other. It is desirable to control the temperature and / or stress of the substrate to reduce or eliminate imaging errors such as overlay errors due to local expansion or contraction of the substrate. For example, in an immersion lithography apparatus, evaporation of liquid (e.g. water) remaining on the substrate can cause local cooling and a thermal load on the surface where the liquid is located, and therefore cause the substrate to shrink. Conversely, the energy delivered to the substrate by the projection beam during exposure can cause significant heating and therefore expansion of the substrate.

[0067]

[0087] In an embodiment, the component formed is an electrode for electrostatic clamping. In electrostatic clamping, an electrode provided on the substrate table and / or substrate holder is raised to a high potential, for example 10-5,000 V. The substrate is grounded or floated. Electrostatic forces in the electric field generated by the electrode attract the substrate to the substrate table and / or substrate holder providing a clamping force, as described further below.

[0068]

[0088] One or more electrical connections are provided to connect an electrical or electronic component on the substrate holder to a voltage source (not shown for convenience). If the component is an electrostatic clamp, an electrode on the substrate has an electrical connection to the voltage source. The component may be on a top surface of the substrate support. At least some of the electrical connections may pass through the body of the substrate support as described in U.S. Patent Application No. US 61 / 555,359, filed November 3, 2011, which is incorporated herein by reference in its entirety.

[0069]

[0089] In an embodiment, one or more local heaters 101 are controlled by a controller 103 such that a desired amount of heat is applied to the substrate holder 100 and the substrate W to control the temperature of the substrate W. One or more temperature sensors 102 that monitor the temperature of the substrate holder 100 and / or the substrate W are connected to the controller 104. An arrangement using one or more heaters and temperature sensors to locally control the temperature of the substrate is described in co-pending U.S. Patent Application Publication No. US2012-0013865, which is incorporated herein by reference in its entirety. The arrangement described therein can be modified to use resistive heaters and temperature sensors as described herein. Details of the thin film stack including components and methods of manufacture thereof are described in U.S. Patent Application No. US13 / 403,706, filed February 23, 2012, and co-pending U.S. Patent Application No. 61 / 621,648, filed April 9, 2012, which are incorporated herein by reference in their entireties.

[0070]

[0090] Substrate holders for use in conventional (e.g. DUV) lithographic apparatus (e.g. immersion lithographic apparatus) desirably include one or more thin film temperature sensors and / or one or more thin film heaters. Other forms of sensors and / or heaters may be provided within, above and / or below the substrate holder.

[0071]

[0091] A substrate holder for use in an EUV lithography apparatus desirably comprises a thin film electrostatic clamp and optionally one or more thin film temperature sensors and / or one or more thin film heaters. Other forms of sensors and / or heaters may be provided in, above and / or below the substrate holder.

[0072]

[0092] As mentioned above, laser sintering can be used to form the burls. This method is illustrated in Figures 10A-10E. The method starts with a flat plate of the desired shape that will form the body 400 of the substrate holder. The flat plate may be preformed by another technique. In one embodiment, the plate is made of SiSiC, although one or more other materials such as Invar™, Zerodur™, ULE™, fused quartz, cordierite, boron nitride, silicon nitride, aluminum nitride (AIN) and / or SiC may also be used. Desirably, the surface 400a of the plate is ground or polished to a desired flatness. In one embodiment, the surface is cleaned, such as with ozone, although this step may be omitted. In one embodiment, the surface 400a may be treated to promote adhesion of one or more subsequent layers, for example by applying a primer layer, although this step may be omitted. An insulating layer 410 is applied onto the plate to insulate one or more metal layers to be formed above from the body of the substrate holder. In one embodiment, the insulating layer 410 improves flatness. Insulating layer 410 can be BCB applied by spin or spray coating as described above, or SiO2 applied by a PECVD process, or other suitable material. Atop the insulating layer is applied a metal layer 440, such as by PVD, resulting in the state shown in FIG. 10A.

[0073]

[0093] The metal layer is then patterned by lithography and selective etching, such as wet etching, to define the desired pattern to form the desired components, such as electrodes, sensors, or heaters. This step also removes the metal layer in the areas where burls will be formed in a subsequent step. At this stage, the substrate holder appears as shown in FIG. 10B.

[0074]

[0094] On the patterned metal layer, an insulating or dielectric layer 450 is applied and openings are made where the burls are desired, down to the body or base layer, i.e. through both insulating layers. The substrate holder is in the position shown in Fig. 10C. Optionally, the exposed areas 400b of the surface of the body 400 are cleaned, e.g. with ozone, and / or treated, e.g. by application of a primer layer, to promote adhesion of the burls that will be formed subsequently.

[0075]

[0095] The burls 406 are formed in the openings through the thin film stack by a laser sintering process. Other structures on the substrate holder, such as vacuum rings, can be formed simultaneously with the burls. It is also possible to form one or more protrusions between the burls that are shorter but have a larger area than the burls. Such protrusions improve thermal conduction between the substrate and the substrate holder. Such protrusions can be, for example, 10 μm or more shorter than the burls 406. There are two types of laser sintering methods that can be used.

[0076]

[0096] In the first method, a thin layer of powder is applied to the area where the burr is to be formed. One or more laser beams are then used to selectively sinter the powder in the area where the burr is to be formed. Once this is completed, another thin layer of powder is applied and selectively heated and sintered. The process is repeated and the burr is built up layer by layer. In one embodiment, each layer has a thickness in the range of 1-1.5 μm. As the sintering pattern can be changed with each layer, the burrs can be stacked in any desired shape and profile. In this method, the powder is applied to a large area and multiple burrs are formed simultaneously or in parallel. Alternatively, the powder may be applied to a small area and each burr formed separately. Further details about this process can be found at A Streek et al.'s "Laser micro sintering - a quality leap through improvement of powder packing" http: / / laz.htwm.de / 43_rapidmicro / 55_Ver%C3%B6ffentlichungen / Laser%20micro%20sintering%20%20a%20quality%20leap%20through%20improvement%20of%20powder%20packing.

[0077]

[0097] In the second method, powder is sprayed with an inert gas onto the area where the burr is to be formed, while one or more laser beams are irradiated onto the exact area where the burr is to be formed. The powder is selectively deposited at the location of the laser beam. By appropriately shifting the irradiation point, a burr of the desired profile is deposited. Further details of this process can be found at the website of S. Kloetar et al. "MICRO-CLADDING USING A PULSED FIBRE LASER AND SCANNER" http: / / laz.htwm.de / 43_rapidmicro / 55_Ver%C3%B6ffentlichungen / Microcladding_LPM2010.pdf.

[0078]

[0098] As with other sintering techniques, laser sintering works by partially melting the powder particles so that they adhere to each other when they cool. The advantage of laser sintering is that it allows control of the space in which sintering occurs by controlled irradiation with the laser beam. In both of the above methods, the powder can be preheated to a temperature close to the relevant melting point, and less energy is applied by the laser to complete the sintering. A variety of materials can be used for the sintering technique. The powder can be made of a single material, for example a metal such as titanium, a semiconductor such as silicon, or a ceramic such as fused quartz, cordierite, and / or aluminum nitride. In some embodiments, the powder is made of two or more components. One component has a relatively low melting point that melts to form a matrix in which the other particle component(s) are embedded. The matrix-forming compound of the powder can be provided as separate particles or as a coating on the particles of another material. The matrix-forming component can be any single material as described above. The particle component may be one or more components selected from the group including cubic silicon nitride, silicon nitride, silicon carbide, titanium nitride, titanium carbide, and / or diamond, such as diamond-like carbon (DLC). The sintering process can be carried out in an inert atmosphere or vacuum, which helps prevent chemical changes in the material being sintered, or in a controlled atmosphere, which promotes chemical changes.

[0079]

[0099] Thus, the material forming the burls can be selected from a wide range of materials to obtain desired properties, such as adhesion strength to the substrate material of the substrate holder. Desirably, the burls are manufactured from the same material as the substrate holder body, or a material compatible therewith. For example, it is generally desirable for the burls to bond well to the base material of the substrate body, to provide a long service life and reliability in use. In some applications, it is desirable for the burls to have a high thermal conductivity to aid in temperature regulation of the substrate. In other applications, a low thermal conductivity may be desired to insulate the substrate. Other relevant properties of the burls that may be affected by the choice of material include electrical conductivity, dielectric strength, and wear resistance properties.

[0080]

[0100] Laser sintering techniques for forming burls typically result in burls with a rough top surface as shown in Figure 10D. In that case, it may be desirable to perform a final polishing step to give the burrs a smooth top surface as shown in Figure 10E. In some cases, for example if the final polishing is done with a coarse slurry, it may be desirable to first protect the thin film stack with an additional coating. However, this is often not necessary if, for example, the thin film stack only contains electrodes for clamping purposes.

[0081]

[0101] A further advantage of the laser sintering process is that the composition of the burl can be varied with height. Thus, as shown in FIG. 11, it is possible to produce a burl with one or more portions or layers with different composition and / or properties. For example, the lower portion 406a of the burl can be formed from a material that bonds well to the substrate material of the substrate holder, while the upper portion 406b of the burl is formed from a material with high wear resistance properties (note that the body may be manufactured by a different technique than the burl). For example, diamond particles such as diamond-like carbon (DLC) may be included in the upper portion 406b of the burl to improve wear resistance. Alternatively, diamond particles (e.g. DLC) may be included in the lower portion 406a to improve thermal conductivity. In some embodiments, the burl is formed with three or more distinct layers. In some embodiments, the burl is formed with a gradation in composition, content or material properties over at least a portion of its height.

[0082]

[0102] It is also possible to vary the composition of the powder to be sintered in a direction substantially parallel to the surface on which the bur is formed. In powder sintering layering methods, this may be achieved by varying the composition of the powder in each powder layer as the powder is applied. In powder jetting methods, this may be achieved by varying the composition of the jetted powder in time synchronization with the movement of the laser hit point. Optionally, in addition to the variation in height, it is possible to fine-tune one or more mechanical and / or other properties of the bur, such as for example the stiffness, by varying the composition of the material of the bur in a direction substantially parallel to the surface on which the bur is formed.

[0083]

[0103] An advantage of certain embodiments of the present invention is that the burls can be formed in almost any three-dimensional shape. In certain embodiments, the burls have a unitary cross section throughout their height. In certain embodiments, the burls taper from the body of the substrate holder. In certain embodiments, the cross section of the burls varies with height. In certain embodiments, the burls have a cross section substantially parallel to the surface of the body of the substrate holder selected from the group consisting of a circle, a square, a rectangle, an oval, a diamond, and / or a "stadium-shaped" or "stadium-shaped" shape. A "stadium-shaped" or "stadium-shaped" shape has two straight parallel sides connected by a curve, e.g., a semicircle.

[0084]

[0104] In some embodiments, a thin film stack is provided on only one side of the substrate holder. In some embodiments, no thin film stack is provided on the substrate holder. In some embodiments, a thin film stack is provided on both sides of the substrate holder. In some embodiments, burls are provided on both sides of the substrate holder. If burls are provided on both sides of the substrate holder, it is not necessary that the same method of forming the burls is used on both sides.

[0085]

[0105] An embodiment of the invention can also be used to form burls on other components within a lithographic apparatus where controlled contact between the component of the apparatus and the object being handled is desired.

[0086]

[0106] FIG. 12 shows an embodiment of the invention which is a support structure for a patterning device such as a mask table MT supporting a mask MA. The body 500 of the mask table, in contrast to the substrate table, comprises through holes 501 for passing the projection beam B. The mask MA is supported by burl areas 502 formed by laser sintering on the mask table 500. The use of burls to support the mask MA has a similar function to the use of burls to support a substrate on a substrate table or holder. For example, the burls can prevent or reduce the chance of the mask being misaligned or distorted due to the presence of particles between the mask and the surface on which it is supported. The burls can clamp the mask to the mask table or other support structure using vacuum and / or electrostatic clamping techniques. In most lithographic apparatus, the projection system PS reduces the projected image by a factor of 4 or 5 in a scanning mode of operation, so the mask moves with a speed and acceleration 4 or 5 times that of the substrate table. A proportional clamping force should therefore be exerted. It is desirable for the mask to be held on the support structure in such a way that no or minimal stress is generated in the mask. The use of burls serves this purpose.

[0087]

[0107] In Figure 12 the burls are provided in discrete regions on either side of the aperture 501. In an embodiment the burls may be provided in a continuous region completely surrounding the aperture or at a number of spaced locations around the aperture. The exact locations of the burls can be determined during construction of the embodiment. For example burls for supporting a mask on a mask table or mask handling device may have a diameter of 100μm to 1μm, desirably 300 to 500μm. The burls may have an elongated planar shape such as an oval or rectangular.

[0088]

[0108] In an embodiment, the burls are formed by laser sintering on a clamp for a mask or reticle. The clamp may be, for example, a layered structure of ULE-Zerodur-ULE or thin film stack-Zerodur-thin film stack. Such a clamp may have a thickness of about 10 mm. The burls may have a pitch of 2-10 mm.

[0089]

[0109] Figure 13 shows a plan view of a support structure of a patterning device for a mask or reticle according to an embodiment of the invention. Figure 14 shows a cross-sectional view of the same support structure along line XX in Figure 13. The support structure includes a support member 512 supported above a body 510 by leaf springs 513. The upper surface of the support member 512 has a central recess 515 surrounded by the area of ​​the burl 106. The central recess 515 is connected to a low pressure (e.g. vacuum) source 517 via a conduit 516.

[0090]

[0110] A patterning device such as a mask MA is placed on the support member 512 and the pressure in the central recess 515 is reduced to clamp the patterning device in place. Leaf springs 513 precisely define the position of the support member 512 substantially perpendicular to the surface of the patterning device MA. However, the support member 512 can move in at least one direction substantially parallel to the surface of the patterning device MA. This means that zero or minimal stresses are thereby generated in the patterning device MA. Such stresses are undesirable as they may distort the pattern defined by the patterning device MA. Providing burls 106 formed by laser sintering on the support member 512 ensures that the patterning device MA is precisely positioned.

[0091]

[0111] FIG. 15 shows a substrate handling arm or gripper 600 according to an embodiment of the invention. The substrate handling arm 600 is driven by one or more actuators (not shown). The substrate handling arm 600 can be used to transport substrates, for example, between a loading dock and a pre-alignment stage, between a pre-alignment stage and a substrate table, and / or between a substrate table and an unloading dock. A similar handling device can be used in a track section of a lithocell or to move a patterning device (e.g. a mask). The substrate handling arm 600 includes a pair of fingers or prongs 601 spaced apart in a substantially horizontal plane. An upper surface or a portion thereof of each of the prongs 601 includes an area 602 having burls formed by laser sintering. The use of burls on the substrate handling arm has one or more of the same advantages as mentioned above, i.e., for example, vacuum and / or electrostatic clamping techniques can be used and / or particles can be prevented from deforming the substrate.

[0092]

[0112] 16 shows an embodiment of the invention in which a substrate holder is integrated with the substrate table WT. The holder WT has a body 700 in which a recess 701 is formed in which a substrate W can be accommodated. The lower surface of the recess 701 is provided with burls 106 formed by laser sintering as described above. The depth of the recess 701 and the height of the burls 106 are determined such that the upper surface of the substrate W is substantially flush with the upper surface of the body 700. In this way, one or more sensors, such as a transmission image sensor TIS provided in the substrate table WT, can perform measurements at substantially the same vertical position as the exposure on the substrate W.

[0093]

[0113] One advantage of embodiments of the present invention is that burls can be reliably and accurately formed on a wider variety of surfaces than previously known methods of forming burls, and thus can be provided on components that were not previously suitable for providing burls by conventional techniques, such as material removal techniques including electrical discharge machining (EDM).

[0094]

[0114] Another advantage is that the methods described herein can be used to repair burls individually or collectively. Two methods of repairing burls according to embodiments of the invention are described below. These methods can be used to repair burls formed by any method, not just laser sintering.

[0095]

[0115] In a repair method according to an embodiment of the invention, steps of which are shown in Figures 17A-17C, individual burls are repaired. As shown in Figure 17A, an object holder 800 has a number of burls 801 and a damaged burl 802. The damaged burl 802 has a rough top surface 802a, e.g., caused by wear or physical damage. The damaged burl is further ground to provide a smooth surface 802b, as shown in Figure 17B. A temporary protective coating may be provided to cover the burl 801 as is during this process. If desired, the ground surface 802b can be cleaned, e.g., with ozone, and / or pre-treated, e.g., by applying a primer. The burl can then be reconstructed to its original shape and / or height (or a different desired shape and / or height) using the laser sintering technique described above. The process may include building a repaired burl 803 to a height greater than the ultimate designed height, as shown in Figure 17C, and grinding it to a level that matches the height of the current burl 801.

[0096]

[0116] In another repair method, the steps of which are shown in Figures 18A-18C, multiple burls 901 on an object holder 900 are repaired simultaneously. This method is particularly applicable to periodic repair of an object holder to reveal wear conditions rather than to address spaced-out damage occurrences. This method can also be used to adjust the height of the burls to accommodate changes in operating parameters, such as changes in the thickness of the substrate being exposed.

[0097]

[0117] In the method of this embodiment, the top surface of the burl 901 shown in FIG. 18A can optionally be cleaned, for example with ozone, or treated, for example by applying a primer. An additional layer 902 is then deposited on the burl 901 by the laser sintering process described above. In an embodiment, the additional layer 902 has a thickness in the range of 1-5 μm, preferably 2-3 μm. In most cases, this process results in a rough top surface 902a shown in FIG. 18B, which is higher than the ultimate desired height of the burl. The burl is then polished to provide the desired flatness and desired roughness of the top surface 902b, which is the desired height, shown in FIG. 18C.

[0098]

[0118] In addition to the immediate benefit of providing a method for repairing burls, i.e., not always having to replace a damaged component, the existence of repair techniques allows for the formation of burls directly on a component when it is economically undesirable to replace the component when one or more burls are damaged.

[0099]

[0119] Advantageously, an embodiment of the invention allows the use of burls on components within a lithographic apparatus such as a substrate table, a support structure for a patterning device, a mask table, a wafer handler, a mask handler, a gripper, a pre-alignment stage, a process device in a track, a substrate handling robot, an adjustment plate, a substrate adjustment unit and / or a sensor mount. Burls manufactured according to an embodiment of the invention can be used whenever an object (e.g. a substrate, a patterning device, an optical element or a sensor) needs to be held or mounted in a precise position. Sensors mounted on burls formed according to an embodiment of the invention may include transmission image sensors and / or interferometric aberration sensors.

[0100]

[0120] One advantage of embodiments of the present invention is that the burls can be formed more accurately than subtractive techniques, such as EDM techniques. Burls can be reliably and accurately formed in accordance with certain embodiments of the present invention. Burls lost or damaged during the manufacturing process can be easily added or repaired. In some embodiments, the body can be formed by a different technique than the burls formed thereon.

[0101]

[0121] It will be understood that any of the features described above may be used in conjunction with any other features, and the present application is not limited to only those combinations expressly described.

[0102]

[0122] Although particular reference is made herein to the use of lithography apparatus in the manufacture of ICs, it should be understood that the lithography apparatus described herein has 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, and the like. In light of these alternative applications, those skilled in the art will recognize that the use of the terms "wafer" or "die" herein may be considered synonymous with the more general terms "substrate" or "target portion", respectively. The substrates described herein may be processed, before or after exposure, for example in a track (a tool that typically applies a layer of resist to the substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, the substrate may be processed multiple times, for example to produce a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0103]

[0123] As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths at or about 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm).

[0104]

[0124] The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive and reflective optical components.

[0105]

[0125] Although particular embodiments of the present invention have been described above, it should be understood that the present invention may be embodied in other ways than as described, at least in the form of a method of operation of the apparatus described herein. For example, at least in the form of a method of operation of the apparatus described herein, embodiments of the present invention may take the form of one or more computer programs including one or more sequences of machine-readable instructions that describe how to operate such an apparatus, or a data storage medium (e.g., a semiconductor memory, magnetic or optical disk) having such computer programs embodied therein. Moreover, the machine-readable instructions may be embodied in two or more computer programs. The two or more computer programs may be stored in one or more different memories and / or data storage media.

[0106]

[0126] Any controllers described herein, each or in combination, are operable when one or more computer programs are read by one or more computer processors in at least one component of the lithographic apparatus. The controllers, each or in combination, have any suitable configuration for receiving, processing, and transmitting signals. The one or more processors are configured to communicate with at least one of the controllers. For example, each controller may include one or more processors that execute computer programs that include machine-readable instructions for the above methods. The controllers may include data storage media that store such computer programs and / or hardware that houses such media. Thus, the controllers may operate according to machine-readable instructions of one or more computer programs.

[0107]

[0127] The present invention may be applied to substrates having a width (eg diameter) of 300 mm, 450 mm or any other size.

[0108]

[0128] One or more embodiments of the invention may be applied to any immersion lithography apparatus, in particular but not limited to the above mentioned types, whether the immersion liquid is provided in the form of a bath, or is provided only to a localized surface area of ​​the substrate, or is unconfined on the substrate and / or substrate table. In an unconfined configuration, the immersion liquid is allowed to flow onto the surface of the substrate and / or substrate table, and thus substantially the entire uncovered surface of the substrate table and / or substrate is wetted. In such an unconfined immersion system, the liquid supply system is unable to confine the immersion liquid, or may provide a percentage of immersion liquid confinement, but does not substantially complete the confinement of the immersion liquid.

[0109]

[0129] A liquid supply system as envisaged herein should be interpreted in a broad sense. In certain embodiments, it may be a mechanism or combination of structures that provides liquid to a space between the projection system and the substrate and / or substrate table. It may comprise a combination of one or more structures, one or more liquid inlets, one or more gas inlets, one or more gas outlets and / or one or more liquid outlets that provide liquid to the space. In an embodiment, the surface of the space may be part of the substrate and / or substrate table, the surface of the space may completely cover the surface of the substrate and / or substrate table or the space may surround the substrate and / or substrate table. The liquid supply system may optionally further comprise one or more elements that control the position, amount, quality, shape, flow rate or any other characteristic of the liquid.

[0110]

[0130] In a first aspect of the invention, there is provided a method of manufacturing an object holder for use in a lithographic apparatus, the method comprising the steps of providing a body having a surface and forming on the surface a plurality of burls having end faces protruding from the surface and supporting an object, wherein forming at least a part of at least one of the burls comprises laser sintering.

[0111]

[0131] The laser sintering process may include applying a layer of powder to a substrate and selectively irradiating the layer of powder with a radiation beam to at least partially melt the powder at the irradiated locations. In one embodiment, the laser sintering process includes irradiating a location on the substrate and spraying powder at the irradiated location.

[0112]

[0132] The body may be formed of a different material than the at least one burl. The at least one burl may comprise at least one material selected from the group consisting of Ti, Si, fused quartz, cordierite, diamond-like carbon, SiC, SiO2, AlN, TiN, and CrN. The at least one burl may be formed of a matrix material and particles embedded within the matrix material. The matrix material may comprise at least one material selected from the group consisting of Ti, Si, fused quartz, cordierite, diamond-like carbon, SiC, SiO2, AlN, TiN, and CrN. The particles may comprise at least one material selected from the group consisting of cubic boron nitride, silicon nitride, silicon carbide, titanium nitride, titanium carbide, and diamond.

[0113]

[0133] At least one of the burls may include a first layer of a first material and a second layer of a second material different from the first material. The first and second materials may have different properties or compositions.

[0114]

[0134] In an embodiment, the object is a substrate or a patterning device. A thin film stack may be provided on the surface, and a number of burls may protrude from the surface beyond the thin film stack.

[0115]

[0135] In a second aspect of the invention, there is provided a method for repairing an object holder having a burl for use in a lithographic apparatus, the method comprising the steps of providing the burl to be repaired, applying a layer of material to the burl to be repaired by laser sintering, and polishing the layer of material.

[0116]

[0136] In a third aspect of the present invention there is provided an object holder for use in a lithographic apparatus comprising a body having a surface and a plurality of burls provided on the surface and having end faces for supporting an object, at least a part of at least one of the burls being formed by laser sintering.

[0117]

[0137] In an embodiment, the body is formed of a material different from the burr portions. At least one burr may comprise at least one material selected from the group consisting of Ti, Si, fused quartz, cordierite, diamond-like carbon, SiC, SiO2, AlN, TiN, and CrN. At least one burr may be formed of a matrix material and particles embedded within the matrix material. The matrix material may comprise at least one material selected from the group consisting of Ti, Si, fused quartz, cordierite, diamond-like carbon, SiC, SiO2, AlN, TiN, and CrN. The particles may comprise at least one material selected from the group consisting of cubic boron nitride, silicon nitride, silicon carbide, titanium nitride, titanium carbide, and diamond.

[0118]

[0138] At least one of the burrs may include a first layer of a first material and a second layer of a second material different from the first material. The first and second materials may differ in properties or composition. At least one of the burrs may have a substantially constant cross section substantially parallel to the surface. At least one of the burrs may taper away from the surface. The cross section substantially parallel to the surface of the at least one burr may be selected from the group consisting of a circle, a square, a rectangle, an oval, a diamond, and a "stadium-shaped" or "stadium-shaped" shape. The body may include at least one material selected from the group consisting of Zerodur, cordierite, SiC, SiCiC, AIN, Invar, ceramic, and glass-ceramic.

[0119]

[0139] The object holder is constructed and adapted to support at least one selected from a substrate, a patterning device, a sensor, and an optical element as an object. In an embodiment, the object is a substrate and the object holder is a substrate holder. The substrate holder may have a diameter substantially equal to 200 mm, 300 mm, or 450 mm. The object may be a patterning device and the object holder is a support structure for the patterning device. The object holder may be a reticle clamp. The object holder may be a substrate gripper. A thin film stack may be provided on the surface and a plurality of burls may protrude from the surface beyond the thin film stack.

[0120]

[0140] In a fourth aspect of the present invention, there is provided a lithographic apparatus comprising a support structure configured to support a patterning device, a projection system configured to project a beam patterned by the patterning device onto a substrate, and a substrate holder according to the third aspect of the present invention configured to hold the substrate.

[0121]

[0141] The lithographic apparatus may include a substrate table, the substrate holder being integral with the substrate table.

[0122]

[0142] In a fifth aspect of the present invention, there is provided an object holder for use in a lithographic apparatus, the object holder comprising a body having a surface and a plurality of burls on the surface and having end faces for supporting an object, such as a substrate, the plurality of burls being formed by laser sintering.

[0123]

[0143] In a sixth aspect of the present invention, there is provided a lithographic apparatus comprising a support structure configured to support a patterning device, a projection system arranged to project a beam patterned by the patterning device onto a substrate, and a table according to the fourth or fifth aspect of the present invention.

[0124]

[0144] In a seventh aspect of the present invention, there is provided a device manufacturing method using a lithographic apparatus, the method comprising projecting a beam patterned by a patterning device onto a substrate while holding the substrate in a substrate holder, the substrate holder comprising a body having a surface and a plurality of burls provided on the surface and having an end surface supporting the substrate, the plurality of burls being formed by laser sintering.

[0125]

[0145] The above description is illustrative and not restrictive. Thus, it will be apparent to one skilled in the art that the invention as described can be modified without departing from the scope of the claims.

Claims

1. 1. A method of manufacturing an object holder for use in a lithographic apparatus, comprising the steps of: Providing a body having a surface; forming a plurality of burls on the surface having end faces protruding from the surface and supporting an object; The method, wherein the step of forming at least a portion of at least one of said burrs comprises laser sintering.

2. The laser sintering applying a layer of powder to the surface; selectively irradiating the layer of powder with a radiation beam to at least partially melt the powder where irradiated; The method of claim 1 , comprising:

3. The laser sintering illuminating a location on the surface; spraying a powder onto the irradiated location; The method of claim 1 , comprising:

4. The method of any one of claims 1 to 3, wherein the body is formed of a different material than the at least one burl.

5. The at least one burr is made of Ti, Si, fused quartz, cordierite, diamond-like carbon, SiC, SiO ２ The method of any one of claims 1 to 4, comprising at least one material selected from the group consisting of AlN, TiN and CrN.

6. The method according to any one of claims 1 to 4, wherein the at least one burl is formed from a matrix material and particles embedded within the matrix material.

7. The method of any one of claims 1 to 6, wherein at least one burl comprises a first layer of a first material and a second layer of a second material different from the first material.

8. The method of claim 7 , wherein the first and second materials have different properties or compositions.

9. The method of any one of claims 1 to 8, wherein the object is a substrate or a patterning device.

10. A method according to any preceding claim, wherein a thin film stack is provided on the surface, and the plurality of burls protrude from the surface further than the thin film stack.

11. 1. An object holder for use in a lithographic apparatus, comprising: a body having a surface; a plurality of burls having end faces provided on the surface to support an object; An object holder, wherein at least a portion of at least one of said burls is formed by laser sintering.

12. The object holder of claim 11 , wherein the object holder supports as the object at least one selected from a substrate, a patterning device, a sensor, and an optical element.

13. 13. The object holder of claim 11 or 12, wherein a thin film stack is provided on the surface, and the plurality of burls protrude from the surface beyond the thin film stack.

14. The object holder of claim 11 , wherein the object holder is at least one of a substrate holder for a substrate, a support structure for a patterning device, a reticle clamp for a reticle, and a substrate gripper for a substrate.

15. a support structure for supporting the patterning device; a projection system that projects the beam patterned by the patterning device onto a substrate; and A substrate holder as claimed in claim 14 for holding the substrate; A lithographic apparatus comprising:

Images