Fluid handling system, method and lithographic apparatus

Abstract

A fluid handling system comprising: a liquid confinement structure configured to confine immersion liquid in a space between at least part of the liquid confinement structure and a surface of a substrate, the liquid confinement structure having an opening formed for the passage of a radiation beam to pass through the immersion liquid and thereby illuminate the surface of the substrate; and a diagnostic tool configured to detect abnormalities in the fluid handling system, the diagnostic tool comprising an acoustic system configured to measure acoustic properties of the liquid confinement structure and / or the immersion liquid, the acoustic system comprising a transducer configured to emit acoustic waves to and / or receive acoustic waves from the immersion liquid.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to European Application No. 22211041.3, filed December 2, 2022, which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present invention relates to a fluid handling system and a device manufacturing method.The present invention also relates to a lithographic apparatus comprising a fluid handling system. [Background technology]

[0003] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (often referred to as a "design layout" or "design") from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate (e.g., a wafer). Known 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 through a radiation beam in a predetermined direction (the "scan" direction) while simultaneously scanning the substrate parallel or non-parallel to this direction.

[0004] As semiconductor manufacturing processes continue to improve, the dimensions of circuit elements are continually decreasing while the amount of functional elements, such as transistors, per device has steadily increased over the past few decades, following a trend commonly referred to as "Moore's Law." The semiconductor industry pursues technologies that enable the creation of smaller and smaller features to keep up with Moore's Law. To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm.

[0005] Further improvements in resolution of smaller features may be realized by providing an immersion fluid, such as water, having a relatively high refractive index onto the substrate during exposure. The effect of the immersion fluid is that the exposure radiation in the fluid has a shorter wavelength than in a gas, allowing for imaging of smaller features. The effect of the immersion fluid is also to increase the effective numerical aperture (NA) of the system, which also increases the depth of focus. Summary of the Invention [Problem to be solved by the invention]

[0006] The immersion fluid may be confined to a localized area between the projection system of the lithographic apparatus and the substrate by the fluid handling structure.

[0007] In lithography systems that use immersion liquid (often referred to as immersion lithography systems), imaging errors can occur when gas (e.g., air) bubbles enter the immersion liquid and enter the beam path. Bubbles in the beam path can distort the image projected onto the substrate. Because the substrate typically moves faster than the bubbles relative to the projection lens, the presence of bubbles suspended in the immersion liquid can lead to characteristic streaks on the exposed substrate. Bubbles that adhere to the substrate can lead to recognizable circular imaging defects. However, by the time such defects are observed, many substrates have already been exposed with imaging errors, resulting in reduced yield.

[0008] It is an object of the present invention to provide a fluid handling system and method in which an abnormal event, for example the presence of a bubble or a contaminant in the fluid handling system, can be quickly detected. [Means for solving the problem]

[0009] According to a first aspect of the present invention there is provided a fluid handling system comprising: a liquid confinement structure configured to confine immersion liquid in a space between at least part of the liquid confinement structure and a surface of a substrate, the liquid confinement structure having an opening formed for the passage of a radiation beam to pass through the immersion liquid and thereby illuminate the surface of the substrate; and a diagnostic tool configured to detect a condition in the fluid handling system, the diagnostic tool comprising an acoustic system configured to measure acoustic properties of the liquid confinement structure and / or the immersion liquid, the acoustic system comprising a transducer configured to emit acoustic waves to and / or receive acoustic waves from the immersion liquid.

[0010] According to a second aspect of the present invention, there is provided a lithographic apparatus comprising a substrate holder configured to hold a substrate, a projection system configured to project a radiation beam onto the substrate held by the substrate holder, and a fluid handling system as described above.

[0011] According to a third aspect of the present invention, there is provided a device manufacturing method in a lithographic apparatus having a substrate holder configured to hold a substrate, a projection system configured to project a beam of radiation onto a substrate held by the substrate holder, and a fluid handling system, the method comprising: using the fluid handling system to confine immersion fluid to a space between at least part of the fluid handling system and a surface of the substrate; emitting an acoustic probe signal into the immersion liquid; receiving a return signal in response to the probe signal; detecting a condition in the fluid handling system based on the return signal; and projecting a patterned beam of radiation through the immersion fluid in the space onto the substrate.

[0012] According to a fourth aspect of the present invention, there is provided a droplet removal system comprising: a liquid supply configured to supply liquid to a space between at least a portion of the droplet removal system and a surface of a substrate; a removal unit configured to remove liquid from the space; and a diagnostic tool configured to detect a condition in the droplet removal system, the diagnostic tool comprising an acoustic system configured to measure acoustic properties of the droplet removal system and / or the liquid, the acoustic system comprising a transducer configured to emit sound waves to and / or receive sound waves from the liquid.

[0013] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments, features, and advantages of the present invention, are described in detail below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0014] Embodiments of the 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, and in which:

[0015] FIG. 1 depicts a schematic overview of a lithographic apparatus.

[0016] Figures 2a, 2b, 2c and 2d each show in cross section two different versions of a fluid handling system, which may extend all around, with different features illustrated on the left and right sides of each version.

[0017] Figures 3a and 3b depict schematically part of a known fluid handling system in first and second operational states, respectively.

[0018] Figure 4 depicts schematically part of a known fluid handling system.

[0019] Figure 5 depicts schematically part of a known fluid handling system.

[0020] FIG. 6 shows a schematic diagram of a diagnostic tool in one embodiment.

[0021] FIG. 7 is a graph of the response to an acoustic signal as a function of frequency for the diagnostic tool of FIG.

[0022] Figure 8 depicts schematically in cross section part of a fluid handling system including a diagnostic tool in an embodiment.

[0023] Figure 9 shows a schematic diagram in plan view of part of a fluid handling system including a diagnostic tool in an embodiment.

[0024] Figure 10 depicts a schematic cross-sectional view of a fluid handling system including a diagnostic tool in an embodiment.

[0025] The features shown in the figures are not necessarily to scale and are not limited to the size and / or arrangement shown. The figures are understood to include optional features that are not essential to the invention. Furthermore, not all features of a device are shown in each figure, and a figure may show only some of the components relevant to describing a particular feature. DETAILED DESCRIPTION OF THE INVENTION

[0026] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (eg, having wavelengths of 365, 248, 193, 157 or 126 nm).

[0027] The terms "reticle," "mask," or "patterning device," as used in this text, may be broadly interpreted to refer to a general patterning device that may be used to impart an incident radiation beam with a patterned cross-section that corresponds to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. Besides the classic mask (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0028] Figure 1 schematically illustrates a lithographic apparatus. The lithographic apparatus includes an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV or DUV radiation), a mask support (e.g., mask table) MT configured to support a patterning device (e.g., mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., substrate table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support WT according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern formed in the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. A controller 500 controls the overall operation of the apparatus. The controller 500 may be a central control system or a system of multiple separate sub-controllers within various subsystems of the lithographic apparatus.

[0029] In operation, the illumination system IL receives a radiation beam B from the radiation source SO, for example via the beam delivery system BD. The illumination system IL may include various types of optical components, or any combination thereof, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0030] The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, appropriate for the exposure radiation being used and / or other factors such as the use of an immersion liquid or vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0031] The lithographic apparatus is of a type (also referred to as immersion lithography) in which at least a part of the substrate W may be covered by an immersion liquid, such as water, having a relatively high refractive index, so as to fill an immersion space 11 between the projection system PS and the substrate W. More information about immersion techniques is given in US 6,952,253, which is incorporated herein by reference.

[0032] The lithographic apparatus may be of a type having two or more substrate supports WT (also known as "dual stage") In such a "multi-stage" apparatus, the substrate supports WT may be used in parallel, and / or preparation steps for a subsequent exposure of a substrate W may be performed on a substrate W placed on one substrate support WT while another substrate W on the other substrate support WT is being used to expose a pattern onto another substrate W.

[0033] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not shown). The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean parts of the lithographic apparatus, for example parts of the projection system PS or parts of a system for providing immersion liquid. The measurement stage may move below the projection system PS when the substrate support WT is spaced apart from the projection system PS.

[0034] In operation, a radiation beam B is incident on a patterning device, such as a mask MA, which is held on a mask support MT, and is patterned according to a pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The substrate support WT may be accurately driven by the second positioner PW and position measurement system IF, for example, to position different target portions C at focusing and alignment positions in the path of the radiation beam B. Similarly, the first positioner PM and other appropriate position sensors (not explicitly shown in FIG. 1 ) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, they may also be located in spaces between the target portions. Substrate alignment marks P1, P2 located between target portions C are known as scribe-lane alignment marks.

[0035] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes: x, y, and z. Each of the three axes is orthogonal to the other two. Rotation around the x axis is referred to as Rx rotation. Rotation around the y axis is referred to as Ry rotation. Rotation around the z axis is referred to as Rz rotation. The x and y axes define a horizontal plane, and the z axis defines a vertical direction. The Cartesian coordinate system is not intended to limit the invention and is used for illustration purposes only. Alternatively, other coordinate systems, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, so that the z axis has a component along the horizontal plane.

[0036] Immersion techniques have been introduced into lithography systems to enable improved resolution of smaller features. In an immersion lithography apparatus, a layer of immersion liquid, having a relatively high refractive index, is interposed in an immersion space 11 between the apparatus's projection system PS (through which a patterned beam is projected towards the substrate W) and the substrate W. The immersion liquid covers at least a portion of the substrate W below the final element of the projection system PS. In this way, at least a portion of the substrate W during exposure is immersed in the immersion liquid.

[0037] In commercial immersion lithography, the immersion liquid is water. The water is typically highly pure distilled water, such as ultrapure water (UPW), commonly used in semiconductor manufacturing plants. In immersion systems, the UPW is frequently purified and may have to undergo additional processing steps before being supplied to the immersion space 11 as the immersion liquid. Other liquids besides water that have a high refractive index, such as hydrocarbons such as fluorocarbons and / or aqueous solutions, may also be used as the immersion liquid. Furthermore, other fluids besides liquids are anticipated for use in immersion lithography.

[0038] Reference is made herein to localized immersion, where the immersion liquid in use is confined to an immersion space 11 between the final element 100 and a surface facing the final element 100. The facing surface is the surface of the substrate W or a surface of the support stage (or substrate support WT) that is flush with the surface of the substrate W (note that references in the following text to the surface of the substrate W may also or instead refer to the surface of the substrate support WT, and vice versa, unless otherwise stated). A fluid handling structure 12 present between the projection system PS and the substrate support WT is used to confine the immersion liquid to the immersion space 11. The immersion space 11, filled with immersion liquid, is smaller in plan than the top surface of the substrate W, and remains substantially stationary relative to the projection system PS while the substrate W and substrate support WT move underneath.

[0039] Other immersion systems are also envisaged, such as unconfined immersion systems (so-called "all wet" immersion systems) and bath-based immersion systems. In an unconfined immersion system, the immersion liquid covers more than the surface below the final element 100. The liquid outside the immersion space 11 is present as a thin liquid film. The liquid may cover the entire surface of the substrate W or the substrate W and a substrate support WT flush with the substrate W. In a bath-based system, the substrate W is completely immersed in a bath of immersion liquid.

[0040] The fluid handling structure 12 is a structure that supplies immersion liquid to and removes immersion liquid from the immersion space 11, thereby confining the immersion liquid to the immersion space 11. It includes features that are part of a fluid supply system. The arrangement disclosed in PCT Patent Application Publication No. WO 99 / 49504 is an early fluid handling structure that comprises pipes that supply or withdraw immersion liquid from the immersion space 11 and that operate in response to relative movement of a stage below the projection system PS. In newer designs, the fluid handling structure extends along at least part of the boundary of the immersion space 11 between the final element 100 of the projection system PS and the substrate support WT or substrate W, and partially defines the immersion space 11.

[0041] The fluid handling structure 12 may have a choice of different functions, each of which may result from corresponding features that enable the fluid handling structure 12 to perform that function. The fluid handling structure 12 may be referred to by a number of different terms, each describing a function, such as barrier member, sealing member, fluid supply system, fluid removal system, liquid confinement structure, etc.

[0042] The fluid handling structure 12 as a barrier member is a barrier to the flow of immersion liquid from the immersion space 11. As a liquid confinement structure the structure confines the immersion liquid to the immersion space 11. As a seal member the sealing features of the fluid handling structure 12 form seals to confine the immersion liquid to the immersion space 11. The sealing features may include an additional gas flow from openings in the surface of the seal member, such as a gas knife.

[0043] The fluid handling structure 12 may supply immersion fluid and may therefore form part of a fluid supply system.

[0044] The fluid handling structure 12 may at least partly confine the immersion fluid and therefore may form part of a fluid confinement system.

[0045] The fluid handling structure 12 may provide a barrier to the immersion fluid as a barrier member, such as a fluid confinement structure.

[0046] The fluid handling structure 12 may generate or use gas flows, for example to help control the immersion fluid flow and / or position.

[0047] The gas flow may form a seal to confine the immersion fluid and the fluid handling structure 12 may be referred to as a seal member. Such a seal member may be a fluid confinement structure.

[0048] An immersion liquid may be used as the immersion fluid, and the fluid handling structure 12 in this case may be a liquid handling system. With reference to the above description, references in these paragraphs to features defined in relation to a fluid are understood to include features defined in relation to a liquid.

[0049] The lithographic apparatus has a projection system PS. During exposure of a substrate W, the projection system PS projects a patterned beam of radiation onto the substrate W. To reach the substrate W, the path of the radiation beam B passes from the projection system PS through immersion liquid confined by a fluid handling structure 12 between the projection system PS and the substrate W. The projection system PS has a lens element at the end of the beam's path that comes into contact with the immersion liquid. This lens element that comes into contact with the immersion liquid may be referred to as the "final lens element" or "final element". The final element 100 is at least partly surrounded by the fluid handling structure 12. The fluid handling structure 12 may confine immersion liquid below the final element 100 and above an opposing surface.

[0050] Figures 2a, 2b, 2c and 2d show different features that may be present in various fluid handling systems. Designs may share some features in common with Figures 2a, 2b, 2c and 2d unless otherwise stated. The features described herein may be selected individually or in combination as shown or as required. The figures show different versions of a fluid handling system with different features illustrated on the left and right sides, which may extend around the entire periphery. Thus, for example, a fluid handling system may have the same feature extending around the entire periphery. For example, a fluid handling system may only have the feature on the left side of Figure 2a, or the right side of Figure 2a, or the left side of Figure 2b, or the right side of Figure 2b, or the left side of Figure 2c, or the right side of Figure 2c, or the left side of Figure 2d, or the right side of Figure 2d. Alternatively, a fluid handling system may be provided with any combination of features from these figures, at different circumferential positions. The fluid handling system may comprise various fluid handling structures 12, as described below.

[0051] Figure 2a shows a fluid handling system comprising a fluid handling structure 12 around a bottom surface of a final element 100. The final element 100 has an inverted truncated conical shape. The truncated conical shape has a flat bottom and a conical surface. The truncated conical shape has a flat bottom protruding from the flat surface. The flat bottom is the optically active part of the bottom surface of the final element 100 through which the radiation beam B may pass. The final element 100 may have a coating 30. The fluid handling structure 12 surrounds at least part of the truncated conical shape. The fluid handling structure 12 has an inner surface facing the conical surface of the truncated conical shape. The inner surface and the conical surface may have complementary shapes. The top surface of the fluid handling structure 12 may be substantially flat. The fluid handling structure 12 may fit around the truncated conical shape of the final element 100. The bottom surface of the fluid handling structure 12 may be substantially flat and, in use, the bottom surface may be parallel to a facing surface of the substrate support WT and / or substrate W. The bottom surface of the fluid handling structure 12 may thus be referred to as the surface facing the surface of the substrate W. The distance between the bottom surface and the facing surface may be in the range of 20 to 500 micrometers, desirably in the range of 70 to 200 micrometers.

[0052] The fluid handling structure 12 extends closer to the facing surfaces of the substrate W and substrate support WT than the final element 100. An immersion space 11 is therefore defined between the inner surface of the fluid handling structure 12, the flat surface of the frusto-conical portion and the facing surface. During use, the immersion space 11 is filled with immersion liquid. The immersion liquid fills at least part of the buffer space between the complementary surfaces between the final element 100 and the fluid handling structure 12 (e.g. at least part of the space between the complementary inner surfaces and the conical surface).

[0053] Immersion liquid is supplied to the immersion space 11 through openings formed in a surface of the fluid handling structure 12. Immersion liquid may be supplied through supply openings 20 in an inner surface of the fluid handling structure 12. Alternatively or additionally, immersion liquid is supplied from lower supply openings 23 formed in a bottom surface of the fluid handling structure 12. The lower supply openings 23 may surround the path of the radiation beam B and may be formed as a series of openings in an array or a single slit. Immersion liquid is supplied to fill the immersion space 11 and the flow through the immersion space 11 below the projection system PS is laminar. Supply of immersion liquid from the lower supply openings 23 additionally prevents bubbles from entering the immersion space 11. This supply of immersion liquid may act as a liquid seal.

[0054] Immersion liquid may be recovered from recovery openings 21 formed in the inner surface. Recovery of immersion liquid through the recovery openings 21 may be caused by application of negative pressure. Recovery through the recovery openings 21 may be the result of a flow velocity of immersion liquid through the immersion space 11. Alternatively, recovery may be the result of both. The recovery openings 21 may be arranged opposite the supply openings 20 in plan view. Additionally or alternatively, immersion liquid may be recovered through an overflow recovery part 24 arranged on the top surface of the fluid handling structure 12. The functions of the supply openings 20 and recovery openings 21 may be swapped (i.e. the liquid flow direction is reversed). In this case, the flow direction can be changed depending on the relative movement of the fluid handling structure 12 and the substrate W.

[0055] Additionally or alternatively, immersion liquid may be recovered from below the fluid handling structure 12 through recovery openings 25 formed in its bottom surface. The recovery openings 25 may serve to hold a meniscus 33 of immersion liquid against the fluid handling structure 12. The meniscus 33 is formed between the fluid handling structure 12 and the facing surface and acts as a boundary between the liquid space and the external gas environment. The recovery openings 25 may be a perforated plate which may recover a substantially single-phase flow of immersion liquid. The recovery openings in the bottom surface may be a series of pinning openings 32 through which immersion liquid is recovered. The pinning openings 32 may recover a two-phase flow of immersion liquid.

[0056] Optionally, a gas knife opening 26 is provided radially outwardly relative to the inner surface of the fluid handling structure 12. Gas may be supplied through the gas knife opening 26 at an increased velocity to assist liquid confinement of the immersion liquid in the immersion space 11. The supplied gas may be humidified and may comprise substantially carbon dioxide. Radially outwardly of the gas knife opening 26 is provided a gas recovery opening 28 for recovering gas supplied through the gas knife opening 26.

[0057] Further openings, for example those open to atmosphere, a gas source or vacuum, may be present at the bottom surface of the fluid handling structure 12, i.e. the surface of the fluid handling structure 12 facing the substrate W. An example of such an optional further opening 50 is shown by the dotted line on the right-hand side of Figure 2a. As shown, the further opening 50 may be a supply or an outlet, as indicated by the double arrow. For example, if configured as a supply, the further opening 50 may be connected to a liquid supply or a gas supply or any other supply. Alternatively, if configured as an outlet, the further opening 50 may be used to extract fluid and may be connected to, for example, atmosphere, a gas source or vacuum. For example, at least one further opening 50 may be present between the gas knife opening 26 and the gas recovery opening 28, and / or between the pinning opening 32 and the gas knife opening 26.

[0058] Two different versions of the fluid handling structures 12 on the left and right sides of FIG. 2a hold the meniscus 33. The version of the fluid handling structure 12 on the right side of FIG. 2a may hold the meniscus 33 in a position substantially fixed relative to the final element 100 due to the fixed position of the pinning aperture 32. The version of the fluid handling structure 12 on the left side of FIG. 2a may hold the meniscus 33 below the recovery aperture 25, and the meniscus 33 may move along the length and / or width of the recovery aperture 25. To direct the radiation beam B to both ends of the substrate W during exposure, the substrate support WT supporting the substrate W is driven relative to the projection system PS. To maximize the output of the substrate W exposed by the lithographic apparatus, the substrate support WT (and also the substrate W) is driven as fast as possible. However, there is a critical relative speed (often expressed as the critical scan speed), beyond which the meniscus 33 between the fluid handling structure 12 and the substrate W becomes unstable. An unstable meniscus 33 is associated with a greater risk, for example, of losing the immersion liquid in the form of one or more droplets. Furthermore, an unstable meniscus 33 is associated with a greater risk of introducing air bubbles into the immersion liquid, especially when the limited immersion liquid exceeds the edge of the substrate W.

[0059] Droplets present on the surface of the substrate W can impose a heat load and can cause defects. Droplets can evaporate and leave drying marks, can move and carry contaminants such as particles, can collide with larger immersion liquid masses and introduce gas bubbles into the larger masses, and can evaporate and impose a heat load on the surface on which they are disposed. Such heat loads can be a cause of distortion and / or a source of positioning errors when the surface is associated with the positioning of components of the lithographic apparatus relative to the substrate W during imaging. Thus, the formation of droplets on the surface is undesirable. To avoid the formation of such droplets, the speed of the substrate support WT is limited to the critical scan speed at which the meniscus 33 is stable. This limits the throughput of the lithographic apparatus.

[0060] The left-hand side of the fluid handling system in Figure 2a may comprise a spring 60. The spring 60 may be an adjustable passive spring configured to exert a biasing force on the fluid handling structure 12 in the direction of the substrate W. In this way, the spring 60 may be used to control the height of the fluid handling structure 12 above the substrate W. Such adjustable passive springs are described in US 7,199,874, which is incorporated herein by reference in its entirety. Other biasing devices (e.g., those using electromagnetic forces) are also suitable. The spring 60 is optionally shown with the left-hand side of Figure 2a, but does not need to be included with the other features of the left-hand side of Figure 2a. The spring 60 is not shown in any of the other figures, but may be included with various other fluid handling systems described in relation to Figures 2a, 2b, 2c or 2d.

[0061] Figure 2b shows a fluid handling system showing, on the left and right, two different versions of the fluid handling structure 12 that allow movement of the meniscus 33 relative to the final element 100. The meniscus 33 may move in the direction of the moving substrate W. This reduces the relative velocity between the meniscus 33 and the moving substrate W, which may result in improved stability and a reduced risk of collapse of the meniscus 33. Increasing the velocity of the substrate W at which the meniscus 33 collapses allows for faster movement of the substrate W below the projection system PS, thus increasing throughput.

[0062] Features shown in Figure 2b that are in common with Figure 2a share the same reference numerals. The fluid handling structure 12 has an inner surface that is complementary to the conical surface of the frusto-conical shape. The bottom surface of the fluid handling structure 12 is closer to the opposing surface than the flat bottom surface of the frusto-conical shape.

[0063] Immersion liquid is supplied to the immersion space 11 through supply openings 34 formed in the inner surface of the fluid handling structure 12. The supply openings 34 are located at the bottom side of the inner surface (e.g. below the bottom surface of the frusto-conical shape). The supply openings 34 are arranged around the inner surface away from the path of the radiation beam B.

[0064] Immersion liquid is recovered from the immersion space 11 through recovery openings 25 in the bottom surface of the fluid handling structure 12. As the facing surface moves below the fluid handling structure 12, a meniscus 33 may move on the surface of the recovery opening 25 in the same direction as the movement of the facing surface. The recovery openings 25 may be formed of a porous member. The immersion liquid may be recovered in a single phase. The immersion liquid may be recovered in a two-phase flow. The two-phase flow is received in a chamber 35 in the fluid handling structure 12 and separated into liquid and gas. The liquid and gas are recovered from the chamber 35 through further channels 36, 38.

[0065] An inner periphery 39 of the bottom of the fluid handling structure 12 extends from the inner surface into the immersion space 11 to form a plate 40. The inner periphery 39 defines a small opening of a size that matches the shape and size of the radiation beam B. The plate 40 may serve to isolate the immersion liquid at either end. Immersion liquid supplied flows inward towards the opening, through the inner opening and radially outwards towards the surrounding recovery opening 25 below the plate 40.

[0066] The fluid handling structure 12 may consist of two parts, an inner part 12a and an outer part 12b, as shown on the right hand side of Figure 2b. The inner part 12a and the outer part 12b may move relative to each other mainly in a plane parallel to their opposing faces. The inner part 12a may have a supply opening 34 and may have an overflow collection part 24. The outer part 12b may have a plate 40 and a collection opening 25. The inner part 12a may have an intermediate collection part 42 for collecting immersion liquid flowing between the inner part 12a and the outer part 12b.

[0067] Thus, the two different versions of the fluid handling structure in Figure 2b allow movement of the meniscus 33 in the same direction as the substrate W, enabling faster scanning speeds and increased throughput of the lithographic apparatus. However, the speed of movement of the meniscus 33 on the surface of the recovery opening 25 in the fluid handling structure 12 on the left side of Figure 2b may be slow. The fluid handling structure 12 on the right side of Figure 2b allows faster movement of the meniscus 33 by moving the outer part 12b relative to the inner part 12a and the final element 100. However, it may be difficult to control the intermediate recovery part 42 to ensure that enough immersion liquid is provided between the inner part 12a and the outer part 12b to prevent contact between them.

[0068] Figure 2c shows a fluid handling system showing, on the left and right, two different versions of a fluid handling structure 12 that may be used to pin a meniscus 33 of immersion liquid against the fluid handling structure 12 as described above with respect to Figures 2a and / or 2b. Features shown in Figure 2c that are in common with Figures 2a and / or 2b share the same reference numbers.

[0069] The fluid handling structure 12 has an inner surface complementary to the conical surface of the frusto-conical shape. The bottom surface of the fluid handling structure 12 is closer to the facing surface than the flat bottom surface of the frusto-conical shape. Immersion liquid is supplied to the immersion space 11 through openings formed in the surface of the fluid handling structure 12. The immersion liquid may be supplied through supply openings 34 in the inner surface of the fluid structure 12. Alternatively or additionally, the immersion liquid may be supplied through supply openings 20 in the inner surface of the fluid structure 12. Alternatively or additionally, the immersion liquid may be supplied through lower supply openings 23. The immersion liquid may be collected via an outlet (e.g. a collection opening 21 and / or an overflow collection opening 24 formed in the inner surface and / or one or more openings in the surface of the fluid handling structure 12 as described below).

[0070] The two different versions of the fluid handling structure 12 on the left and right of Figure 2c pin the meniscus 33. The version of the fluid handling structure 12 on the right of Figure 2c may pin the meniscus 33 in a substantially fixed position relative to the final element 100 due to the fixed position of the collection opening 32a. The version of the fluid handling structure 12 on the left of Figure 2c may pin the meniscus 33 below the collection opening 25, and the meniscus 33 may move along the length and / or width of the collection opening 25.

[0071] 2c. As described above with respect to Figure 2b, the inner periphery of the bottom surface of the fluid handling structure 12 may extend from the inner surface into the immersion space 11 to form a plate 40 as shown on the left. As described above, this may form small openings, may isolate the immersion liquid at either end, and / or may allow immersion liquid to flow inward towards the opening, through the inner opening and radially outward towards a surrounding recovery opening 25 below the plate 40. This feature is shown on the left in Figure 2c, but may optionally be combined with the other shown features. Preferably, as shown on the left, immersion liquid is supplied to the immersion space 11 through supply openings 34 formed in the inner surface of the fluid handling structure 12. The supply openings 34 are located at the bottom side of the inner surface (e.g. below the bottom surface of the frusto-conical shape). The supply openings 34 are located around the inner surface, away from the path of the radiation beam B. Alternatively or additionally, immersion liquid may be supplied through supply openings 20 in the inner surface of the fluid structure 12. Alternatively or additionally, immersion liquid is supplied through lower supply openings 23. Supply openings 34 are the preferred liquid supply, although any combination of supply openings 34, supply openings 20 and / or lower supply openings 23 may be provided.

[0072] As shown on the left side of Figure 2c, the fluid handling system may comprise a fluid handling structure 12 as described above and a further device 3000. The fluid handling structure 12 may have an outlet such as a recovery opening 25 and a liquid supply opening such as a lower supply opening 23. It will be appreciated that the fluid handling structure 12, in combination with the further device 3000, may have any configuration as disclosed in relation to the left side of Figure 2a, the right side of Figure 2a, the left side of Figure 2b, the right side of Figure 2b or the right side of Figure 2c (described below).

[0073] The further device 3000 may be referred to as a droplet catcher. The further device 3000 is provided to reduce the amount of liquid remaining on the surface of the substrate W after the fluid handling structure 12 has moved over the surface. The further device 3000 may comprise a liquid supply 3010 and at least one outlet 3020. The at least one outlet 3020 may be shaped to surround the at least one supply 3010 in plan view. The at least one liquid supply 3010 may be configured to provide the further liquid to a space 3110 between at least part of the further device 3000 and the surface of the substrate W. The further device 3000 may be configured to recover at least part of the liquid via the at least one outlet 3020. The further device 3000 may be used to combine the liquid remaining on the surface of the substrate W with the liquid in the space 3110, and the further device 3000 is used to remove the liquid so that the amount of liquid remaining on the surface of the substrate W is reduced.

[0074] In Figure 2c the further device 3000 is shown as a separate device to the fluid handling structure 12. The further device 3000 may be located in the vicinity of the fluid handling structure 12. Alternatively, the further device 3000 may be part of (i.e. configured integrally with) the fluid handling structure 12 (see Figure 3d, although either configuration is an option).

[0075] The further device 3000 may be configured to provide a liquid to the space 3110 that is separate from the liquid provided by the fluid handling structure 12 .

[0076] Additionally or alternatively, the fluid handling structure 12 may have components as shown on the right-hand side of Figure 2c. More specifically, the fluid handling structure 12 may comprise at least one liquid supply, two outlets (e.g. recovery openings 32a and 32b) and two gas supply (e.g. gas supply openings 27a and 27b) formed on a surface of the fluid handling structure 12. Gas supply opening 27a may be omitted, i.e. is optional. The at least one liquid supply may be the same as the lower supply opening 23, supply opening 20 in the bottom surface of the fluid handling structure 12 described above, or the liquid supply opening 34 formed on an internal surface of the fluid handling structure 12 as described with respect to the left-hand side of Figure 2b. The liquid supply, outlets and gas supply may be formed on a surface of the fluid handling structure 12. Specifically, these components may be formed on the surface of the fluid handling structure 12 facing the substrate W, i.e. the bottom surface of the fluid handling structure 12.

[0077] At least one of the two outlets may comprise a porous material 37 therein. The porous material 37 may be provided in an opening, for example recovery opening 32a through which the fluid handling structure 12 may recover single-phase immersion liquid from the fluid handling structure 12 below. The other of the two outlets, such as recovery opening 32b, may recover immersion fluid as a two-phase outlet. The porous material 37 may not be flush with the bottom surface of the fluid handling structure 12.

[0078] In particular, the fluid handling structure 12 may comprise a liquid supply (e.g. lower supply opening 23). Radially outward from the liquid supply is a first outlet (e.g. recovery opening 32a), radially outward from the first outlet is a first gas supply (e.g. gas supply opening 27a), radially outward from the first gas supply is a second outlet (e.g. recovery opening 32b) and radially outward from the second outlet is a second gas supply (e.g. gas supply opening 27b). As with Figure 2a, further openings, for example those open to atmosphere, a gas source or vacuum, may be present in the bottom surface of the fluid handling structure 12, as described above (in relation to the fluid handling structure 12).

[0079] For example, at least one further opening (not shown) may be provided in the bottom surface of the fluid handling structure 12. The further opening is optional. The further opening may be provided between the first outlet (e.g. collection opening 32a) and the first gas supply (e.g. gas supply opening 27a) as described in the arrangements above. Alternatively or in addition, the further opening may be provided between the second outlet (e.g. collection opening 32b) and the second gas supply (e.g. gas supply opening 27b) as described in the arrangements above. The further opening may be the same as the further opening 50 described above.

[0080] Optionally, the fluid handling structure 12 comprises a recess 29. The recess 29 may be provided between the collection openings 32a and 32b, or between the gas supply openings 27a and 32b. The shape of the recess 29 may be uniform around the fluid handling structure 12 or may optionally include a sloped surface. If a recess 29 is provided between the collection openings 32a and 32b, the gas supply opening 27b may be provided in the sloped surface, as shown in Figure 2c. If a recess 29 is provided between the supply openings 27a and 32b, the gas supply opening 27b may be provided in the sloped surface or in a part of the bottom surface of the fluid handling structure 12 that is parallel to the surface of the substrate W. Alternatively, the shape of the recess 29 may vary around the fluid handling structure 12. The shape of the recess 29 may be varied to change the effect of gas supplied from the gas supply on the fluid below the fluid handling structure 12.

[0081] Figure 2d shows a fluid handling system in which the left and right halves show two different versions of the fluid handling structure 12. The fluid handling structure 12 in the left half of Figure 2d has a liquid injection buffer 41a that holds a buffer amount of immersion liquid, and liquid injection holes 41 that supply immersion liquid from the liquid injection buffer to the space 11. Outer sides of the liquid injection holes 41 are provided inner liquid recovery openings 43 for directing liquid to inner recovery buffers 43a in which a porous member is provided. Recesses 29 similar to those described in relation to Figure 2c are provided outer sides of the inner liquid recovery openings 43. Outer sides of the recesses 29 in the underside of the fluid handling structure 12 are provided gas guide grooves 44 into which outer recovery holes 44a open. The outer recovery holes 44a direct a two-phase recovery flow to outer recovery buffers 44b in which a porous member is provided. Outermost, gas sealing holes 45 are provided connecting between the gas sealing buffer volume 45a and the space below the fluid handling structure 12 to provide a gas flow for inclusion in the immersion liquid.

[0082] The fluid handling structure 12 in the right half of Figure 2d has a liquid supply opening 20 in its inner sloping surface. Provided below the fluid handling structure 12 are (from the inside to the outside) an extraction opening 25 provided with a porous member 37, a first gas knife opening 26a, a second gas knife opening 26b and a third gas knife opening 26c. Each of these openings opens into a groove below the fluid handling structure 12 which provides a buffer volume. The outermost part of the fluid handling structure 12 is stepped to provide greater spacing between the fluid handling structure 12 and the substrate W.

[0083] 2a-2d show examples of different configurations that may be used as part of a fluid handling system. While the examples provided above refer to specific extraction and recovery sections, it is understood that the exact same type of extraction and / or recovery section need not be used. In some cases, different terminology is used to indicate the location of the components, but the same functional features may be provided. Examples of the aforementioned extraction sections include recovery opening 21, overflow recovery section 24, recovery opening 25 (preferably comprising a perforated plate and / or chamber 35), gas recovery opening 28, pinning opening 32, recovery opening 32a, recovery opening 32b, and / or intermediate recovery section 42. Examples of the aforementioned supply sections include supply opening 20, lower supply opening 23, gas knife opening 26, gas supply opening 27a, gas supply opening 27b, and / or supply opening 34. In general, extraction sections used to extract / recover fluids, liquids, or gases are interchangeable with other uses for extracting / recovering fluids, liquids, or gases, respectively. Similarly, a supply used to supply a fluid, liquid or gas may be interchangeable with other uses for supplying a fluid, liquid or gas, respectively. An extraction may extract / recover a fluid, liquid or gas from a space by being connected to a negative pressure that draws the fluid, liquid or gas into the extraction. A supply may supply a fluid, liquid or gas to a space by being connected to a corresponding supply.

[0084] As previously mentioned, while the use of immersion fluid / liquid is useful in increasing the resolution of smaller features on a substrate, there are challenges with the use of immersion fluid / liquid in terms of defects introduced onto the substrate.

[0085] Generally, when an immersion liquid is used, droplets of the immersion liquid may be left behind on the surface of the substrate W. The meniscus 33 at the edge of the immersion liquid may collide with the droplets on the surface of the substrate W. When the droplets hit the meniscus 33, gas may become trapped in the immersion liquid. This results in bubbles in the immersion liquid. The formation of bubbles in the immersion liquid may lead to defects on the substrate W. The droplets remaining on the surface of the substrate W may cause dried spots and / or affect the chemical properties of the resist, leading to defects.

[0086] Figures 3a and 3b show part of a fluid handling system 301. The fluid handling system 301 may confine immersion liquid to a liquid confinement space or immersion space 11 between part of the projection system PS and the surface of the substrate W. The immersion liquid may be any of the immersion fluids mentioned above. For example, the immersion liquid may be water. A radiation beam B projected from the projection system PS may irradiate the surface of the substrate W through the immersion liquid.

[0087] Figure 3a shows only a part of a fluid handling system 301 comprising a liquid confinement structure supporting a meniscus 310 of immersion liquid. The meniscus 310 forms a boundary between the immersion liquid and the ambient environment of the fluid handling system 301. Although not shown in Figure 3a, the main part of the fluid handling system 301 is disposed in the direction indicated by arrow 306. The main part of the fluid handling system 301 may comprise immersion liquid and may comprise any part of the various structures disclosed above with reference to Figures 2a to 2d or any other system that localizes immersion liquid below the projection system PS. In particular, the main part of the fluid handling system 301 may comprise an immersion space such as the immersion space 11 as described with reference to Figures 2a to 2d.

[0088] As shown in Figure 3a, a fluid handling system 301 is provided above a substrate W. The substrate W may comprise a wafer 305 and a resist coating 304 on the wafer 305. There is a channel 308 between the fluid handling system 301 and the substrate W. A part of the channel 308 between a main part of the fluid handling system 301 and a meniscus 310, arranged in a direction 306, may comprise immersion liquid. A part of the channel 308 between the meniscus 310 and an environment external to the fluid handling system 301, arranged in a direction 307, may comprise gas.

[0089] The fluid handling system 301 comprises a first outlet portion 302. The first outlet portion 302 comprises a first outlet conduit 302b. The first outlet conduit 302b is a fluid conduit and may provide a flow of immersion liquid out of the fluid handling system 301. The first outlet portion 302 also comprises a first outlet opening 302a provided in an upper surface of the channel 308. The first outlet opening 302a is an end of the first outlet conduit 302b.

[0090] The fluid handling system 301 comprises a second outlet portion 303. The second outlet portion 303 comprises a second outlet conduit 303b. The second outlet conduit 303b is a conduit for a fluid, such as a gas. The second outlet portion 303 also comprises a second outlet opening 303a provided in an upper surface of the channel 308. The second outlet opening 303a is the end of the second outlet conduit 303b.

[0091] Between the first outlet 302 and the second outlet 303 is an upper surface of the channel 308 designated as damper 311. The length of damper 311 defines the spacing of the first outlet 302 and the second outlet 303 along the length of the channel 308.

[0092] The first outlet 302 may be configured to remove immersion liquid by means of a fluid flow 309. The only fluid flow through the first outlet 302 may be substantially the fluid flow 309 of immersion liquid. However, the first outlet 302 may also remove gas from the environment external to the fluid handling system 301. In this way, the fluid flow through the first outlet 302 may be a two-phase flow. When there is a fluid flow through the first outlet 302, there may simultaneously be a gas flow 314 through the second outlet 303.

[0093] The second outlet 303 may be configured to extract gas from the channel 308. Figure 3b shows the gas extraction gas flow 314. The gas flow 314 may create a negative pressure in the channel 308.

[0094] Although not shown in Figures 3a and 3b, a main part of the fluid handling system 301 arranged in direction 306 may comprise a fluid handling structure having an inner surface configured to confine immersion liquid. The first outlet 302 and the second outlet 303 are arranged radially away from the main part of the fluid handling system 301. The second outlet 303 may be arranged further away from the inner surface of the fluid handling structure than the first outlet 302. Alternatively, the first outlet 302 and the second outlet 303 may be part of the main part of the fluid handling system 301. The second outlet 303 may be arranged further away from the centre of the fluid handling system 301 than the first outlet 302.

[0095] A first operational state of the fluid handling system 301 is shown in Figure 3a. In the first operational state, there is no relative movement between the substrate W and the fluid handling system 301. The first outlet 302 may be configured such that, in the first operational state, the amount of immersion liquid removed therethrough does not substantially exceed the amount required to maintain the meniscus 310 at substantially the same position along the channel 308. The fluid flow rate through the first outlet 302 is the minimum flow rate that is capable of keeping the meniscus 310 substantially stationary in the absence of relative movement between the substrate W and the fluid handling system 301.

[0096] A second operational state of the fluid handling system is shown in Figure 3b. In the second operational state, the substrate W may move relative to the fluid handling system 301. The second operational state comprises a scanning movement in a scanning direction. The scanning direction may be substantially perpendicular to the direction of propagation of the radiation beam B. The scanning direction may be direction 312 as shown in Figure 3b. It should be noted that the second operational state may comprise relative movements between the substrate W and the fluid handling system 301 other than the scanning movement. For example, the second operational state may comprise a preparatory movement before the scanning movement.

[0097] The first outlet 302 may be configured such that the amount of immersion liquid extracted therethrough is substantially the same in both the first and second operating states. Movement of the substrate W in direction 312 generates a shear force on the immersion liquid in the channel 308. This causes the meniscus 310 to move along the channel 308 in direction 313. The increased flow of immersion liquid into the channel 308 may be referred to as Couette flow, or alternatively as shear-driven flow or pressure-driven flow. The creation of a negative pressure in the channel 308 by the gas flow 314 also supports the movement of the meniscus 310 along the channel 308.

[0098] In the second operating state, the meniscus 310 is not held stationary by the fluid flow through the first outlet 302. The fluid flow through the first outlet 302 is sufficient to keep the meniscus 310 stationary only if there is no relative movement between the fluid handling system 301 and the substrate W. Thus, in the second operating state, the meniscus 310 moves along the channel 308.

[0099] Advantageously, the maximum allowable speed of relative movement between the fluid handling system 301 and the substrate W is increased. The speed of relative movement between the meniscus 310 and the substrate W is below a critical scan speed so that significant droplet formation does not occur. The speed of relative movement between the fluid handling system 301 and the meniscus 310 increases the speed of relative movement between the fluid handling system 301 and the substrate W. The speed of relative movement between the fluid handling system 301 and the substrate W can be increased by up to twice that of the critical scan speed of known systems in which the meniscus 310 in the channel 308 is substantially stationary.

[0100] The damper 311 may be configured such that its surface properties support proper movement of the edge of the meniscus 310. In particular, the surface of the damper 311 may be coated or configured to be either liquidphobic, liquidphilic, or porous.

[0101] The surface of the damper 311 may be configured so that it is substantially parallel to the surface of the substrate W. Alternatively, the surface of the damper 311 may be curved or angled away from the surface of the substrate W. A first end of the surface of the damper 311 is at the first outlet 302 and a second end of the surface of the damper 311 is at the second outlet 303. The surface of the damper 311 may be configured so that the distance between the surface of the damper 311 and the surface of the substrate W is greater at the second end than at the first end.

[0102] The damper 311 mentioned above may be referred to as the first damper 311. As shown in at least Figures 3a and 3b, the fluid handling system 301 may comprise a second damper 315. The surface of the second damper 315 is a length of the upper surface of the channel 308 on the other side of the first outlet 302 to the first damper 311. The second damper 315 may be configured such that immersion liquid is supported between the surface of the second damper 315 and the surface of the substrate W.

[0103] The surface of the second damper 315 may be parallel to the surface of the substrate W. The distance between the surface of the second damper 315 and the surface of the substrate W may be the same as the distance between all or at least a portion of the surface of the first damper 311 and the surface of the substrate W. Alternatively or additionally, the distance between all or at least a portion of the surface of the first damper 311 and the surface of the substrate W may be larger than the distance between at least a portion of the surface of the second damper 315 and the surface of the substrate W.

[0104] An upper surface 316 of the channel 308, which starts at the second outlet 303 and extends in a direction 307 towards the environment external to the fluid handling system 301, may be parallel to the surface of the substrate W. Alternatively, the upper surface 316 of the channel 308 may be sloped / curved such that the spacing between the upper surface 316 of the channel 308 and the surface of the substrate W varies. The pressure of the gas in the channel 308 may depend on the shape of the upper surface 316. The shape of the surface 316 may be determined to generate an appropriate pressure of gas in the channel 308 to support movement of the meniscus 310 under the intended operating conditions.

[0105] The meniscus control surface may allow for two different operational states: in a first operational state, liquid is removed through the meniscus control surface such that the meniscus is held stationary within the channel 308, i.e., the meniscus 310 is pinned to the meniscus control surface; in a second operational state, there may be substantially no liquid removal through the meniscus control surface such that the meniscus 310 can move along the channel 308, as described above with reference to Figures 3a and 3b.

[0106] The first operating state is used when high speed movement over long distances is required so that long dampers are not required. In the first operating state, the speed of relative movement between the substrate W and the fluid handling system 301 may be limited to be lower than the speed at which substantial droplet formation occurs on the substrate W. The second operating state is used when high speed movement over short distances is required. In the second operating state, the speed of relative movement between the substrate W and the fluid handling system 301 may be higher than in the first operating state due to movement of the meniscus 310.

[0107] Figure 4 shows schematically part of another fluid handling system 301 which comprises a liquid confinement structure which differs from the one described above with reference to Figures 3a and 3b by further comprising a meniscus control surface 401. The meniscus control surface 401 is constituted by the upper surface of the channel 308, i.e. on the opposite side of the channel 308 from the substrate W.

[0108] The meniscus control surface 401 may be located next to the damper 311, between the first outlet 302 and the second outlet 303. The meniscus control surface 401 is preferably located near the first outlet 302.

[0109] It should be noted that Figure 4 shows the meniscus control surface 401 diagrammatically and is not to scale. The meniscus control surface 401 is preferably significantly shorter than the damper 311. For example, the length of the meniscus control surface 401 may be between about 1 mm and 10 mm, and preferably less than 5 mm. The length of the damper 311 may be between about 20 mm and 50 mm, or may be longer.

[0110] The meniscus control surface 401 may be formed from any of a number of materials known in the art. For example, the meniscus control surface 401 may be formed from metal or plastic. Preferably, the meniscus control surface 401 is coated, such that its surface properties depend on the coating. In particular, a coating may be applied that makes the meniscus control surface 401 hydrophilic. Preferably, the damper 311 is configured with a hydrophobic surface. Such surface properties of the meniscus control surface 401 and the damper 311 support different first and second operating states, as described in detail below.

[0111] The meniscus control surface 401 may be the surface of a microsieve. The microsieve has small openings arranged to allow a fluid, such as immersion liquid, to flow through them. On the opposite side of the microsieve to the channel 308 may be a bypass flow path. The bypass flow path may be arranged to provide a liquid flow along the opposite side of the meniscus control surface 401 to the substrate W. The bypass flow path may comprise a liquid inlet 402 configured to supply a liquid flow 403 to the bypass flow path. The bypass flow path may comprise a liquid outlet 405 configured to provide a liquid flow 404 out of the bypass flow path.

[0112] The bypass flow path may be arranged to wet the apertures of the microsieve. That is, liquid flow along the bypass flow path may ensure that substantially all of the apertures of the microsieve are covered by liquid even when there is substantially no liquid flow through the apertures. In this way, the microsieve may have a wetted surface in all operating conditions of the fluid handling system 301. The microsieve is preferably configured so that liquid at its apertures has a high capillary pressure.

[0113] 4, the fluid handling system 301 may comprise a flow control system configured to control the flow rate of liquid through the liquid outlet 405. The flow control system may, for example, comprise a variable displacement pump, a multi-way valve system which may apply different flow restrictions, or any other technique for controlling the flow rate of liquid through the liquid outlet 405.

[0114] The liquid received by the liquid inlet 402 may be branched from the same liquid supply as for the main part of the fluid handling system 301. Alternatively, a separate liquid supply may be provided for the bypass flow path.

[0115] The flow control system may be configured to control at least part of the fluid handling system 301 in one of a first and a second operational state.

[0116] In the first operating state, the flow control system may be configured to apply a negative pressure on the microsieve. The flow control system may be configured so that the flow rate of the liquid stream 404 out of the liquid outlet 405 is greater than the flow rate of the supply liquid stream 403 through the liquid inlet 402. The flow of immersion liquid through the microsieve openings provides additional liquid in the liquid stream 404 exiting the bypass channel. The effect of the flow of liquid through the microsieve is to pin the meniscus 310 to the surface of the microsieve. That is, the immersion liquid meniscus 310 is held substantially stationary between the surface of the microsieve and the surface of the substrate W. The flow control system is preferably configured so that in the first operating state, the negative pressure applied on the microsieve is less than the capillary pressure of the microsieve openings. This ensures that all of the microsieve openings remain wet in the first operating state.

[0117] The microsieve is preferably located near the first outlet 302 to reduce the overall wetted area in the first operating state.

[0118] In the second operating state, the flow control system may be configured to apply a negative fluid pressure to the microsieve opening that is less than, and preferably substantially less than, the capillary pressure of the opening. The pressure differential across the microsieve is preferably minimized and may be substantially zero. The flow rate of liquid through the liquid outlet 405 may be substantially the same as the flow rate of liquid through the liquid inlet 402. There may be substantially no flow of immersion liquid or gas through the microsieve opening. If there is a small amount of liquid flow from the channel 308 through the microsieve opening that covers the liquid in the channel 308, this may be compensated for by reducing the liquid removal through the first removal portion 302.

[0119] In the second operational state, the meniscus 310 is free to move relative to the surface of the microsieve and the surface of the damper 311. In this way, the fluid handling system 301 may be operated with a moveable meniscus substantially as described in RD681087.

[0120] In the second operating state, the flow control system may instead be configured to apply a slight positive pressure on the micro-sieve such that there is a small flow of liquid from the bypass flow path through the micro-sieve and into the channel 308. This may increase the allowable movement speed of the substrate W relative to the fluid handling system 301 in the second operating state.

[0121] In a first operating state, the flow rate of the liquid flow 404 exiting the bypass flow path may be a first fluid flow rate. In a second operating state, the flow rate of the liquid flow 404 exiting the bypass flow path may be a second fluid flow rate. The first fluid flow rate may be greater than the second fluid flow rate.

[0122] The fluid handling system 301 partly shown in Figure 4 may be substantially the same as the part of the fluid handling system 301 shown in Figures 3a and 3b.

[0123] Advantageously, the provision of the meniscus control surface 401 allows the meniscus 310 to be properly controlled when long travels are required. An advantage of the meniscus control surface 401 being wetted in all operating states is that there is substantially only liquid flow through the meniscus control surface 401 in all operating states. Such a single-phase flow does not exert large forces on the substrate W. Different operating states can be switched between quickly.

[0124] If pinning of the meniscus 310 were instead performed in the first outlet 302, it would be impossible to avoid a flow of both liquid and gas through the first outlet 302. This two-phase flow would increase the required extraction force through the first outlet 302 and exert a large force on the substrate W. Furthermore, the time required to switch from the second operating state to the first operating state may exceed 100 ms.

[0125] Figure 5 shows schematically part of another fluid handling system 301' which comprises a liquid confinement structure which differs from the fluid handling system 301 by the absence of the first outlet 302. In the fluid handling system 301' a meniscus control surface 401 additionally provides the fluid extraction which in the fluid handling system 301 was performed by the first outlet 302.

[0126] In fluid handling system 301', fluid flow through the microsieves may be increased by substantially the same amount as fluid flow through first outlet 302 in fluid handling system 301. Fluid withdrawal through liquid outlet 405, i.e. liquid flow 404 out of the bypass flow path, may likewise be increased due to the increased fluid flow through the microsieves.

[0127] In the first and second operational states, the fluid flow rate may be varied appropriately to take into account the absence of first outlet 302. Otherwise, the operation of fluid handling system 301 may be the same as fluid handling system 301'.

[0128] Advantageously, in fluid handling system 301' there is no first outlet 302. This reduces the footprint of the outlet and also reduces costs.

[0129] In the fluid handling systems 301, 301' described above, the meniscus control surface 401 is a microsieve. The meniscus control surface 401 may be any other type of surface through which a liquid can flow. For example, the meniscus control surface 401 may be a porous member or may comprise a microslit or a capillary.

[0130] In the fluid handling systems 301, 301' described above, a first outlet portion 302 and a second outlet portion 303 have been described. There may be a plurality of such first outlet portions 302 and / or a plurality of such second outlet portions 303. The plurality of first outlet portions 302 may be provided around a centre of the fluid handling system 301. The plurality of first outlet portions 302 may be provided in any configuration. For example, they may be circular, square, rectangular or star-shaped. The first outlet opening 302a of each first outlet portion 302 may have any shape. For example, each first outlet opening 302a may be circular, square, rectangular or slot-shaped. The plurality of second outlet portions 303 may be provided around a centre of the fluid handling system 301. For example, they may be circular, square, rectangular or star-shaped. The configuration of the second outlet portions 303 may be the same as or different from the configuration of the first outlet portion 302.

[0131] The decision whether to use the first or second operating state, and the decision about the relative speed of movement between the fluid handling system 301 and the substrate W in each operating state, may depend on many different circumstances. These may include the length of movement required, the type of process being performed, and the surface properties of the substrate W or substrate support. For example, the use of the first operating state, and the speed of movement in the first operating state, may depend on how hydrophobic the surface of the substrate W is.

[0132] In the fluid handling systems 301, 301' described above, the bypass flow path comprises a substantially only liquid flow. The bypass flow path may also provide a fluid flow with fluid that is a gas bubbly flow. That is, the fluid flow in the bypass flow path may comprise both a liquid flow and a gas flow.

[0133] In a first operating state, the fluid handling system 301, 301′ includes a flow control system that is configured such that in addition to the flow of immersion liquid through the openings in the microsieve, there is also a small gas flow through the microsieve, which may allow a greater force to be applied to hold the meniscus 310 stationary against the surface of the microsieve.

[0134] In the fluid handling systems 301, 301′ described above, the meniscus control surface 401 and the surface of the damper 311 have been described as being at the upper surface of the channel 308. In a typical configuration for a horizontally oriented substrate W, the surface is the upper surface of the channel 308. However, the meniscus control surface 401 and the surface of the damper 311 may also be provided on a surface of the fluid handling system 301 that is substantially parallel to the surface of the substrate W. The surface of the substrate W is not limited to being horizontal.

[0135] As mentioned above, it is undesirable for bubbles to enter the immersion liquid and enter the path of the projection beam, as this can lead to imaging errors. The presence of bubbles in the immersion liquid can be determined from the presence of characteristic streaks or circular imaging errors on exposed substrates. However, at this point it is too late to take corrective action, and many substrates have been incorrectly exposed, resulting in reduced yield. Therefore, a diagnostic tool is proposed that can detect abnormalities such as bubbles and other contaminants in fluid handling systems that can lead to imaging errors early in the device manufacturing process. Advantageously, the diagnostic tool allows corrective action to be taken before many substrates have been erroneously exposed.

[0136] The diagnostic tool may be implemented in any suitable fluid handling system, such as the types of fluid handling systems described above. The diagnostic tool may be integrated into the fluid handling system at the design stage, during manufacturing, or may be retrofitted. In some cases, modifications to the fluid handling system as described below provide additional benefits. The diagnostic tool may be used when the substrate is moving (e.g. during or between exposures) or when the substrate is stationary (e.g. during a calibration process or during maintenance of the lithographic apparatus).

[0137] The diagnostic tool may perform contamination diagnosis in the fluid handling structure 12 by listening to the acoustic properties of the fluid handling structure 12 and / or by detecting bubbles in the immersion space 11 by assessing the acoustic properties of the immersion space 11. As shown in Figure 6, a diagnostic tool according to an embodiment of the invention may include a transducer 601 configured to emit an acoustic probe signal into the immersion liquid and to detect an acoustic response or return signal (e.g. an echo) from the immersion liquid. The transducer 601 may, for example, be a piezoelectric device coupled to a membrane (not shown) in contact with the immersion liquid. The acoustic probe signal may, for example, be a swept frequency (e.g. chirp) or a pulsed signal. Return signals from multiple (e.g. around 10) pulses may be combined to obtain an adequate signal-to-noise ratio.

[0138] The diagnostic tool works by viewing the fluid handling structure 12 and / or immersion space 11 as an acoustic system with a characteristic fingerprint based primarily on its geometry (channel configuration and dimensions, materials, etc.) and the presence / absence of bubbles. Changes in this characteristic occur due to the presence of solid or soft matter contaminants (e.g. foreign objects such as particles or fibers) and / or bubbles. Any such changes can be detected, for example by a signal analyzer, to determine that an abnormality exists and / or analyzed to diagnose the nature or cause of the abnormality. Through the use of appropriate acoustic models, in some cases requiring only one dimension, various changes affecting the acoustics in the fluid handling structure 12 can be identified, and in some cases accurately located. Changes affecting the acoustics may include blockages, which alter the effective area or volume of the system and can be considered as changes in boundary conditions. Other changes affecting the acoustics may include changes in the compliance of parts of the system (e.g. flexibility of wall materials), which affect the effective speed of sound in the system.

[0139] If an abnormality is detected or diagnosed, corrective action may be taken (e.g., automatically). The corrective action may take a variety of forms, depending on the nature of the detected abnormality. In the case of bubble detection, the corrective action may involve one or more of: pausing the exposure to allow the bubble to dissipate; increasing the flow of liquid to flush the bubble; reprocessing an already exposed substrate; modifying scanning parameters (e.g., route, speed, acceleration) for the current or subsequent exposure; or performing manual cleaning or maintenance. In the case of detection of contamination that blocks or restricts the fluid flow, the corrective action may involve one or more of: increasing or reversing the flow of fluid to remove the contaminant; modifying scanning parameters (e.g., route, speed, acceleration) for the current or subsequent exposure; activating an integrated cleaning device (e.g., for sticky wafers / substrates, a reverse flow system or integrated cleaning station as disclosed in US2011128516, etc.); or performing manual cleaning or maintenance. Although performing manual cleaning or maintenance is undesirable as it reduces availability of the equipment, it is preferable to perform any necessary manual cleaning or maintenance as soon as a significant issue is detected (before many substrates have been incorrectly exposed). Thus, the present invention can provide advantages in the early detection and / or diagnosis of problems that adversely affect exposure.

[0140] Figure 6 shows an arrangement in which the characteristics of a fluid handling system comprising a fluid handling structure 12 are designed to assist in the localization of a detected abnormality, for example to determine which holes or channels of the fluid handling system are affected. Figure 6 is greatly simplified in order to illustrate and explain the principle. The generation of an acoustic pulse (e.g. a swept frequency (e.g. a chirp) or a simple pulse) by an acoustic transducer 601 causes the fluid handling structure 12 (including the tubing, connecting channels 200, main outflow channel, lower feed opening 23) to respond acoustically. The acoustic response is converted into an electrical signal by the transducer 601. The geometry, dimensions (and materials) of the components of the fluid handling structure 12 determine the dominant resonant frequencies at which there is a strong response in the received signal. By designing specific characteristics (e.g. hole size, tubing length, cross section, cross-sectional profile, etc.), a unique resonant frequency can be given to each part, such as the lower feed opening 23 or other passages. Significant contamination can affect the resonant characteristics of the entire system and / or single components. In the latter case, amplitude changes and / or shifts (or phase changes) of specific resonances indicate distortion or blocking of the part, ie, localization of contamination.

[0141] This is the acoustic response (pressure output P out The applied pressure P divided by in 7 which shows a nominal response with a particular resonant peak associated with a particular part of the fluid handling structure 12 (for example a particular one of the lower feed openings 23). The dotted line shows a shift in the frequency response when contaminants are present and can be located in the part associated with the lowered or shifted resonant peak.

[0142] It should be noted that the fluid handling structure 12 may have a very large number of components and only a limited number of resonant peaks may be identifiable. In such cases, only selected components (e.g. those that are prone to contamination or are critical) may be tuned to have specific, identifiable resonances. It is also possible to tune a small number of components to each resonant frequency. In such cases, identifying an altered resonant peak narrows the location of the contamination to a small number of components rather than one component, but this is still useful compared to having no information about the presence or location of contamination and can save significant time in the inspection and cleaning process.

[0143] The immersion space 11 is relatively difficult to define as an acoustic system, for example due to the free surfaces at the edge (meniscus) of the immersion liquid. However, the pronounced acoustic resonance properties of bubbles can be used to detect bubbles either floating freely in the immersion liquid or attached to a surface (e.g. the surface of the substrate W). The assumption of negligible heat flow has been shown to be a good approximation for a freely oscillating bubble, giving the so-called Minneart resonance frequency: f M =1 / (2πR0)√(3γp0 / ρ) (1) where R0 is the equilibrium radius of the bubble, p0 is the liquid hydrostatic pressure outside the bubble, γ is the polytropic exponent, and ρ is the density of the surrounding liquid. For a bubble in the immersion liquid with a radius of 10-100 μm, the expected resonant frequencies are in the range 300-30 kHz, or more generally F M R o ≈3 mm.kHz. In some cases, more complex models such as the Rayleigh Plesset equations may be usefully employed.

[0144] To detect bubbles, the transducer 601 is controlled to emit a chirp signal and listen for the response. This allows bubbles (and their size) to be detected very efficiently. The response frequency determines the size of the bubble, while the transmit / receive delay determines the transmission distance to the transducer 601, as the speed of sound in the immersion liquid is well known. By using multiple transducers 601 at different positions in the fluid handling structure 12, the location of the bubble in the immersion liquid can also be determined. Knowledge of the bubble location allows determining whether a bubble is on the path of the exposure beam or not, and whether corrective action should be taken. Repeated measurements give information about the change in the bubble over time (i.e. not only the change in position over time but also in size is visible from a shift in resonant frequency). This is useful for diagnostic purposes.

[0145] 8 and 9 are simplified diagrams of a fluid handling system comprising a fluid handling structure 12, showing possible locations of a transducer 601. Although only a single transducer 601 is shown, multiple transducers 601 may be provided, for example to allow locating a bubble 602. Desirably, the location of the transducer is chosen so as not to interfere with other functions of the system, and to maximise sensitivity to contaminants and / or bubbles to be detected. Because the fluid handling structure 12 is generally square (or rectangular) in plan, whilst the immersion space 11 between the final element 100 and the substrate W is generally circular in plan, there are convenient spaces in the corners of the fluid handling structure 12 where transducers may be located.

[0146] Other effective locations for the transducer 601 include a location within the lower feed openings 23 on the underside of the fluid handling structure 12 between the lower feed openings 23. In a fluid handling structure 12 of the type that has a flow plate (not shown), the transducer 601 may be located below the flow plate, for example near a bend in the flow plate.

[0147] In fluid handling structures 12 having micro-sieves (e.g. recovery openings 25, 42 in Figures 2a-2c), diagnostic tools may be able to determine the condition of the micro-sieves (e.g. determine the percentage of blocked pores in the micro-sieves).

[0148] In most cases, diagnostic tools are most effective when the channel to be diagnosed is completely filled with only one fluid. Outlet channels, which usually have a two-phase flow, can be diagnosed in calibration mode (i.e. during non-exposure) by supplying additional immersion liquid while the substrate holder is stationary relative to the fluid handling structure 12. The additional immersion liquid is supplied to flood the outlet channel, which is used to slowly siphon off the additional immersion liquid while it is remaining filled with liquid.

[0149] A diagnostic tool according to an embodiment can provide more information about the origin and behavior of bubbles 602 during exposure conditions. Such information can be obtained during an actual exposure or a test procedure that simulates actual exposure conditions. This information allows exposure sequences and stage routing (e.g., changes in speed, acceleration, direction) to be planned to avoid bubble defects. The information may be used to determine exposure recipe parameters such as the speed of substrate W movement; acceleration of substrate W; direction of substrate W movement; height of fluid handling structure 12; flow rate of immersion fluid; etc. The insights gained may also be applied in immersion lithography apparatuses that do not have a diagnostic tool installed.

[0150] A further embodiment is shown in Figure 10. The fluid handling system 301 of Figure 10 may comprise some of the features of the fluid handling systems 301, 301' of Figures 3a, 3b, 4 and 5 described above.

[0151] This embodiment of FIG. 10 may differ from the embodiment of FIGS. 3 a, 3 b and 4 by comprising a first outlet 302 but not a second outlet 303 .

[0152] 10, movement of the meniscus 310 along the channel 308 may be passively supported by an inherent pressure generated within the channel 308 during operation. For example, surface tension may result in a reduced pressure within the channel 308 that supports movement of the meniscus 310 along the channel 308.

[0153] A valve 701 may be present on the first outlet conduit 302b to control the flow of fluid through the first outlet 302. The valve 701 improves control of the fluid flow and / or pressure within the channel 308, improving control of the movement of the meniscus 310.

[0154] The embodiments described above provide a number of designs of fluid handling system 301 in which the meniscus 310 may move along the channel 308. One end of the meniscus 310 moves along the surface of the damper 311 and the other end of the meniscus 310 moves along the surface of the substrate W.

[0155] In a fluid handling system 301 where the meniscus 310 moves, the flow of fluid through the first outlet 302 is less than in a fluid handling system where the meniscus is fixed. Under all operating conditions, the flow of fluid through the first outlet 302 is substantially no more than is required to keep the meniscus 310 stationary when there is no relative movement between the fluid handling system 301 and the substrate W. Hence, the meniscus 310 moves along the channel 308 when there is relative movement between the fluid handling system 301 and the substrate W. The meniscus 310 may therefore be supported between the damper 311 and the substrate W.

[0156] In a fluid handling system 301 in which the meniscus 310 moves, it is desirable to have information about the position of the meniscus 310 and / or the volume of immersion liquid in the immersion space 11 between the liquid confinement structure and the surface of the substrate W. Such information may be useful during normal operation of the lithographic apparatus, during calibration and set-up, and / or during maintenance. Such information may also be useful for the development of the fluid handling system 301 and may be obtained in a test setup that is not a fully functional lithographic apparatus. Information about the position of the meniscus 310 and / or the volume of immersion liquid in the immersion space 11 may indicate an abnormality, for example if the position or volume fluctuates beyond acceptable limits.

[0157] As shown in Figure 10, transducers 702, 703 (e.g. acoustic transducers) may be provided to emit an acoustic signal into the immersion liquid in the channel 308 and receive a return signal which is converted to an electrical signal. Although two transducers 702, 703 are shown, it is also possible to use a single transducer for both transmitting and receiving acoustic signals. In other arrangements, more than two transducers 702, 703 (e.g. spaced around the periphery of the fluid handling system 301) may be used. If the fluid handling system 301 has a cornered shape, a transducer or pair of transducers may be located at each corner.

[0158] Transducers 702 and 703 may be used to obtain information about the position of the meniscus 310 by time-of-flight measurements. An acoustic pulse is emitted by transducer 702. Because the meniscus 310 represents a change in acoustic impedance between the immersion liquid and the surrounding gas, some of the acoustic energy is reflected as a pulse echo. The pulse echo may be detected by transducer 703. A timer measures the time interval between the emission of the acoustic pulse and the detection of the pulse echo. It will be appreciated that when the meniscus 310 is in the position indicated by 310′, the acoustic pulse and pulse echo have traveled further than if it were in the position indicated by 310, and therefore information about the position of the meniscus 310 may be obtained from the time-of-flight measurements.

[0159] The transducers 702 and 703 may be used to obtain information about the position of the meniscus 310 by using a signal analyzer to determine the resonant frequency of the immersion liquid. It will be understood that larger volumes of immersion liquid will generally have lower resonant frequencies. Of course, a combination of time-of-flight and frequency analysis may also be used. Doppler techniques may be used to obtain information about the speed of movement of the meniscus 310 relative to the transducers 702, 703.

[0160] The transducers 702, 703 used in the present invention may be, for example, capacitive or piezoelectric ultrasonic transducers. An impedance matching layer may be provided between the transducers and the immersion liquid.

[0161] Diagnostic tools such as those described above may be used in further devices 3000 that function as droplet removal systems (or droplet catchers) such as those described above in Figure 2c. Although bubble detection in the droplet catcher may not be necessary, the diagnostic tools are useful for monitoring that the droplet catcher is functioning properly.

[0162] The present invention may provide a lithographic apparatus, which may have some or all of the other features or components of the lithographic apparatus as described above. For example, the lithographic apparatus may optionally include at least one or more of a source SO, an illumination system IL, a projection system PS, a substrate support WT, etc.

[0163] In particular, the lithographic apparatus may comprise a projection system PS configured to project a radiation beam B onto a region of a surface of a substrate W. The lithographic apparatus may further comprise a fluid handling system 301, 301′ as described in any of the embodiments and variants in Figures 3a to 5 above.

[0164] The lithographic apparatus may comprise an actuator (not shown) configured to drive the substrate W relative to the fluid handling system 301, 301′. In this way, the actuator may be used to control the position of the substrate W (or alternatively the position of the fluid handling system 301, 301′). The actuator may be or comprise a substrate support (e.g. substrate table) WT and / or a substrate holder configured to hold the substrate W and / or a second positioner PW configured to accurately position the substrate support WT.

[0165] Although specific reference may be made in this text 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, including 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.

[0166] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may be implemented by instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of transmission signals (e.g., carrier waves, infrared signals, digital signals, etc.), and the like. Furthermore, firmware, software, routines, and instructions may be described as performing particular actions. However, it should be understood that such description is for convenience only, and that such actions may actually be brought about by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., causing actuators or other devices to interact with the physical world.

[0167] Although specific reference may be made in this text to embodiments of the invention in the context of a lithography apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be generally referred to as lithography tools. Such lithography tools may use atmospheric (non-vacuum) conditions.

[0168] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be understood that the invention is not limited to optical lithography, where the context permits.

[0169] The embodiment includes the following numbered items: Item 1: 1. A fluid handling system comprising: a liquid confinement structure configured to confine immersion liquid in a space between at least a portion of the liquid confinement structure and a surface of a substrate, the liquid confinement structure having an opening formed for the passage of a radiation beam to pass through the immersion liquid and thereby illuminate the surface of the substrate; a diagnostic tool configured to detect an abnormal event in the fluid handling system, the diagnostic tool comprising an acoustic system configured to measure acoustic properties of the liquid confinement structure and / or the immersion liquid; Equipped with the acoustic system comprises a transducer configured to emit acoustic waves into and / or receive acoustic waves from the immersion liquid; Fluid handling systems. Item 2: Item 2. The fluid handling system of item 1, wherein the diagnostic tool is configured to detect a foreign object as the abnormal event. Item 3: 3. The fluid handling system of claim 2, wherein the diagnostic tool is configured to detect bubbles as the foreign body. Item 4: 4. The fluid handling system of claim 2 or 3, wherein the diagnostic tool is configured to detect solid contaminants (e.g. particles or fibres) as the foreign objects. Item 5: 5. A fluid handling system according to any of items 1 to 4, wherein the transducer comprises a piezoelectric transducer preferably coupled to a membrane for contacting the immersion liquid. Item 6: 6. The fluid handling system of any of the preceding items, wherein the acoustic system is configured to emit a probe signal into the immersion liquid and to receive a return signal from the immersion liquid. Item 7: 7. The fluid handling system of claim 6, further comprising a signal analyzer configured to determine the frequency content of the return signal. Item 8: Item 8. The fluid handling system of item 7, wherein the signal analyzer is configured to detect a resonant frequency characteristic of a bubble in the immersion liquid. Item 9: 9. The fluid handling system of claim 7 or 8, wherein the signal analyzer is configured to detect changes in the power spectrum of the return signal. Item 10: the liquid confinement structure has a plurality of passages configured to supply immersion liquid to or remove immersion liquid from the space; each of the paths having a different characteristic resonance; 10. A fluid handling system according to any of items 1 to 9. Item 11: Item 11. A fluid handling system according to item 10, wherein the passages have different lengths, different cross sections and / or different cross-sectional profiles. Item 12: Item 12. A fluid handling system according to any of items 1 to 11, comprising a plurality of transducers arranged in or near a passage configured to supply immersion liquid to or remove immersion liquid from the space. Item 13: a substrate holder configured to hold a substrate; a projection system configured to project a beam of radiation onto the substrate held by the substrate holder; A fluid handling system according to any of items 1 to 12, 1. A lithography apparatus comprising: Item 14: 1. A device manufacturing method in a lithographic apparatus having a substrate holder configured to hold a substrate, a projection system configured to project a radiation beam onto the substrate held by the substrate holder, and a fluid handling system, comprising: using the fluid handling system to confine immersion fluid to a space between at least part of the fluid handling system and a surface of the substrate; emitting an acoustic probe signal into the immersion liquid; receiving a return signal responsive to the probe signal; detecting an abnormal event in the fluid handling system based on the return signal; and projecting a patterned beam of radiation through the immersion fluid in the space onto the substrate; A method for providing Item 15: Item 15. The method of item 14, wherein the steps of emitting the acoustic probe signal and receiving the return signal are performed while the substrate is stationary relative to the fluid handling system. Item 16: Item 15. The method of item 14, wherein the steps of emitting the acoustic probe signal and receiving the return signal are performed while the substrate is moving relative to the fluid handling system. Item 17: 17. The method of any of items 14 to 16, further comprising, in response to detecting an abnormal event, changing at least one parameter of an exposure recipe, such as a speed of movement of the substrate, an acceleration of the substrate, a direction of movement of the substrate, a height of the fluid handling system, or a flow rate of immersion fluid. Item 18: 18. The method according to any of items 14 to 17, further comprising, before the steps of emitting an acoustic probe signal and receiving a return signal, supplying excess immersion liquid so as to overflow a passage for removal of immersion liquid from the space. Item 19: 19. The method of any of items 14 to 18, wherein detecting the abnormal situation comprises detecting at least one of a bubble in the immersion liquid, a contamination in a passage configured to supply the immersion liquid to or remove the immersion liquid from the space, or a blockage in a microsieve provided in a fluid removal path. Item 20: 1. A droplet removal system, comprising: a liquid supply configured to supply liquid to a space between at least a portion of the droplet removal system and a surface of a substrate; a removal portion configured to remove the liquid from the space; a diagnostic tool configured to detect an abnormal event in the droplet removal system, the diagnostic tool comprising an acoustic system configured to measure acoustic properties of the droplet removal system and / or the liquid; Equipped with the acoustic system comprises a transducer configured to emit sound waves to and / or receive sound waves from the liquid; Droplet removal system.

[0170] While specific embodiments of the invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The foregoing description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the following claims.

Claims

1. 1. A fluid handling system comprising: a liquid confinement structure configured to confine immersion liquid in a space between at least a portion of the liquid confinement structure and a surface of a substrate, the liquid confinement structure having an opening formed for the passage of a radiation beam to pass through the immersion liquid and thereby illuminate the surface of the substrate; a diagnostic tool configured to detect a condition in the fluid handling system, the diagnostic tool comprising an acoustic system configured to measure acoustic properties of the liquid confinement structure and / or the immersion liquid; Equipped with the acoustic system comprises a transducer configured to emit acoustic waves into and / or receive acoustic waves from the immersion liquid; Fluid handling systems.

2. The condition is an abnormal situation, Preferably, the diagnostic tool is configured to detect a foreign object as the abnormal event; Preferably, the diagnostic tool is configured to detect bubbles as the foreign object; Preferably, the diagnostic tool is configured to detect solid contaminants (e.g., particles or fibers) as the foreign objects.

10. A fluid handling system according to claim 1.

3. the condition in the fluid handling system comprises a volume of immersion liquid and / or a position of a meniscus of the immersion liquid relative to the liquid confinement structure; and / or the transducer preferably comprises a piezoelectric transducer coupled to a membrane for contacting the immersion liquid; and / or the acoustic system is configured to emit a probe signal into the immersion liquid and to receive a return signal from the immersion liquid. A fluid handling system according to claim 1 or 2.

4. the acoustic system comprising a transducer configured to emit and / or receive acoustic pulses and a timer configured to determine the time of transmission of pulse echoes; or the acoustic system comprises a signal analyzer configured to determine a resonant frequency of the immersion liquid; A fluid handling system according to claim 3 .

5. 5. A fluid handling system according to claim 3 or 4, further comprising a signal analyser configured to determine the frequency content of the return signal.

6. the signal analyzer is configured to detect a resonant frequency characteristic of bubbles in the immersion liquid; and / or the signal analyzer is configured to detect changes in the power spectrum of the return signal; A fluid handling system according to claim 5.

7. the liquid confinement structure has a plurality of passages configured to supply immersion liquid to or remove immersion liquid from the space; the passages each having a different characteristic resonance and / or comprising a plurality of transducers located within or near the passages configured to supply immersion liquid to or remove immersion liquid from the space; A fluid handling system according to any preceding claim.

8. The fluid handling system of claim 7 , wherein the passages have different lengths, different cross sections and / or different cross-sectional profiles.

9. a substrate holder configured to hold a substrate; a projection system configured to project a beam of radiation onto the substrate held by the substrate holder; A fluid handling system according to any preceding claim; 1. A lithography apparatus comprising:

10. 1. A device manufacturing method in a lithographic apparatus having a substrate holder configured to hold a substrate, a projection system configured to project a radiation beam onto the substrate held by the substrate holder, and a fluid handling system, comprising: using the fluid handling system to confine immersion fluid to a space between at least part of the fluid handling system and a surface of the substrate; emitting an acoustic probe signal into the immersion liquid; receiving a return signal responsive to the probe signal; Detecting a condition in the fluid handling system based on the return signal; and projecting a patterned beam of radiation through the immersion fluid in the space onto the substrate; A method for providing the above.

11. The condition is an abnormal situation, Desirably, the steps of emitting the acoustic probe signal and receiving the return signal are performed while the substrate is stationary relative to the fluid handling system; Desirably, the steps of emitting the acoustic probe signal and receiving the return signal are performed while the substrate is moving relative to the fluid handling system. The method of claim 10.

12. and in response to detecting an abnormal event, changing at least one parameter of an exposure recipe, such as a speed of movement of the substrate, an acceleration of the substrate, a direction of movement of the substrate, a height of the fluid handling system, or a flow rate of immersion fluid; and / or and providing excess immersion liquid to overflow a passage for removal of immersion liquid from the space prior to the steps of emitting an acoustic probe signal and receiving a return signal.

12. The method according to claim 10 or 11.

13. detecting the abnormal event comprises detecting at least one of a bubble in the immersion liquid, a contamination in a passage configured to supply immersion liquid to or remove immersion liquid from the space, a blockage in a microsieve provided in a fluid removal path; and / or the condition in the fluid handling system comprises a volume of immersion liquid and / or a position of a meniscus of the immersion liquid relative to a liquid confinement structure; 13. The method according to any one of claims 10 to 12.

14. 1. A droplet removal system, comprising: a liquid supply configured to supply liquid to a space between at least a portion of the droplet removal system and a surface of a substrate; a removal portion configured to remove the liquid from the space; a diagnostic tool configured to detect a condition in the droplet removal system, the diagnostic tool comprising an acoustic system configured to measure acoustic properties of the droplet removal system and / or the liquid; Equipped with the acoustic system comprises a transducer configured to emit sound waves to and / or receive sound waves from the liquid; Droplet removal system.

15. The condition is an abnormal situation, and / or the condition in the droplet removal system comprises a volume of immersion liquid and / or a position of a meniscus of the immersion liquid relative to a liquid confinement structure; The droplet removal system of claim 14.

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