Gas supply module, fluid handling system, lithographic apparatus and device manufacturing method

Abstract

A gas supply module for a fluid handling system of a lithographic apparatus, the gas supply system comprising: a humidifier having a humidifier input and a humidifier output; a first conduit configured to direct gas to the humidifier input; a second conduit configured to supply humidified gas to the fluid handling system; a control valve configured to control gas flow in one of the first conduit and the second conduit; and a measurement system configured to measure pressure downstream of the control valve and generate a control signal, wherein the control valve maintains a constant pressure in one of the first conduit and the second conduit in response to the control signal.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to European Application No. 23156328.9, filed February 13, 2023, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a gas supply module, a fluid handling system, a lithographic apparatus and a device manufacturing method. [Background technology]

[0003] A lithographic apparatus is a machine constructed 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 can, 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 a radiation beam across the substrate in a given direction (the "scan" direction) while synchronously scanning the substrate parallel to or anti-parallel to this direction.

[0004]

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually decreased, while the amount of functional elements, such as transistors, per device has steadily increased for decades, following a trend colloquially known as "Moore's Law." To keep up with Moore's Law, the semiconductor industry pursues technologies that enable the creation of smaller and smaller features. 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]

[0005] Further improvement in resolution of smaller features can be achieved by providing an immersion fluid with a relatively high refractive index, such as water, over the substrate during exposure. The effect of the immersion fluid is to allow imaging of smaller features, since the exposure radiation will have a shorter wavelength in the fluid than in a gas. The effect of the immersion fluid can also be thought of as increasing the effective numerical aperture (NA) of the system and increasing the depth of focus.

[0006]

[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]

[0007] In an immersion lithography apparatus, a gas flow may be used to control the immersion fluid. For example, a gas knife may be used to confine the immersion liquid in a space between the final element of the projection system and the substrate or substrate support. The effectiveness of the gas knife may depend on accurate control of the gas flow. Traditionally, mass flow controllers or mass flow meters have been used to control the gas flow. However, mass flow controllers and mass flow meters are known to be subject to drift and lose accuracy over time. Therefore, mass flow controllers and mass flow meters used in a lithography apparatus must be periodically replaced and / or recalibrated to maintain a desired level of accuracy for the gas flow in the apparatus. Summary of the Invention

[0008]

[0008] It is an object of the present invention to provide a gas flow control system with improved long term stability.

[0009] According to a first aspect of the present invention, there is provided a gas supply module for a fluid handling system of a lithographic apparatus, the gas supply module comprising: a humidifier having a humidifier input and a humidifier output; a first conduit configured to direct gas to the humidifier input; a second conduit configured to supply humidified gas to the fluid handling system; and a control valve configured to control gas flow in one of the first conduit and the second conduit; a measurement system configured to measure pressure downstream of the control valve and generate a control signal; It is equipped with The control valve maintains a constant pressure in one of the first conduit and the second conduit in response to a control signal.

[0010] According to a second aspect of the present invention, there is provided a gas supply module for a fluid handling system of a lithographic apparatus, the gas supply module comprising: a humidifier having a humidifier input and a humidifier output; a first conduit configured to direct gas to the humidifier input; a second conduit configured to supply humidified gas to the fluid handling system; and a control valve configured to control gas flow in one of the first conduit and the second conduit; a feedback system connected to a sensor downstream of the control valve and configured to maintain a constant flow rate in the second conduit.

[0011] According to a third aspect of the present invention, there is provided a lithographic apparatus including a gas supply module.

[0012] According to a fourth aspect of the present invention, - confining liquid to a space between the projection system and the substrate using a gas seal supplied with gas from a gas supply module; projecting a patterned beam of radiation through the liquid onto a substrate using a projection system; measuring pressure at a predetermined location within the gas supply module; controlling gas flow in a gas supply module upstream of the predetermined location to maintain a predetermined gas flow rate at the gas seal; A device manufacturing method is provided, comprising:

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

[0014]

[0014] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0015] [Figure 1]

[0015] A schematic overview of a lithographic apparatus is shown. [Figure 2a]

[0016] Two different versions of the fluid handling system are shown in cross section, with different features of each version shown on the left and right, which may extend all around. [Figure 2b]

[0016] Two different versions of the fluid handling system are shown in cross section, with different features of each version shown on the left and right, which may extend all around. [Figure 2c]

[0016] Two different versions of the fluid handling system are shown in cross section, with different features of each version shown on the left and right, which may extend all around. [Figure 2d]

[0016] Two different versions of the fluid handling system are shown in cross section, with different features of each version shown on the left and right, which may extend all around. [Figure 3]

[0017] 1 depicts, in cross-section, an immersion system for use in a lithographic apparatus; [Figure 4a]

[0018] 1 shows a schematic representation of a humidification device. [Figure 4b]

[0018] A humidification device is illustrated schematically. [Figure 5]

[0019] FIG. 2 is a schematic diagram of a gas supply module according to one embodiment of the present invention. [Figure 6]

[0020] 1 is a graph of pressure versus flow rate in a gas supply module according to one embodiment of the present invention.

[0016]

[0021] Features shown in the drawings are not necessarily to scale, and the illustrated size and / or arrangement is not limiting. It will be understood that the drawings include optional features that may not be essential to the invention. Also, not all features of a device may be shown in each drawing, but only some of the components relevant to the description of a particular feature may be shown. DETAILED DESCRIPTION OF THE INVENTION

[0017]

[0022] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (eg, having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm).

[0018]

[0023] The terms "reticle," "mask," or "patterning device," as used herein, may be broadly interpreted to refer to a general-purpose patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Besides the classic mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0019]

[0024] Figure 1 illustrates a schematic diagram of 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 constructed 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 constructed to hold a substrate (e.g., 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 imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) on the substrate W. A controller 500 controls the overall operation of the apparatus. The controller 500 may be a centralized control system or a system of multiple separate sub-controllers within various subsystems of the lithographic apparatus.

[0020]

[0025] In operation, the illumination system IL receives a radiation beam B from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, 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 in the plane of the patterning device MA.

[0021]

[0026] The term "projection system" PS as used herein should be interpreted broadly as encompassing various types of projection systems, including refractive optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and / or other factors such as the use of an immersion liquid or a vacuum. Where the term "projection lens" is used herein, this may be considered as synonymous with the more general term "projection system" PS.

[0022]

[0027] The lithographic apparatus is of a type in which at least a portion of the substrate W may be covered by an immersion liquid having a relatively high refractive index, e.g. water, so as to fill an immersion space 11 between the projection system PS and the substrate W, which is also referred to as immersion lithography. Further information about immersion techniques is given in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0023]

[0028] The lithographic apparatus may be of a type that includes two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or a substrate W on one substrate support WT may be used to expose a pattern on this substrate W while a preparation step for a subsequent exposure of the substrate W is performed on a substrate W located on another substrate support WT.

[0024]

[0029] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not shown in the drawings). 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 part of the lithographic apparatus, for example part of the projection system PS or part of the system for providing immersion liquid. The measurement stage may be movable below the projection system PS when the substrate support WT is spaced from the projection system PS.

[0025]

[0030] In operation, the radiation beam B is incident on the patterning device MA, e.g., a mask, which is held on the mask support MT, and is patterned according to a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. Using the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM, and possibly further position sensors (not explicitly shown in FIG. 1 ), can 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 substrate alignment marks P1, P2 are shown occupying dedicated target portions, they may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0026]

[0031] To clarify the present 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 about the x-axis is referred to as Rx rotation. Rotation about the y-axis is referred to as Ry rotation. Rotation about the z-axis is referred to as Rz rotation. The x-axis and y-axis define a horizontal plane, while the z-axis is vertical. The Cartesian coordinate system is not a limitation of the present invention and is used for clarity only. Alternatively, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the present invention. The orientation of the Cartesian coordinate system may be different, for example, the z-axis may have a component along the horizontal plane.

[0027]

[0032] 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 that portion of the substrate W below the final element of the projection system PS. Thus, at least that portion of the substrate W that is to be exposed is immersed in the immersion liquid.

[0028]

[0033] In commercial immersion lithography, the immersion liquid is water. Typically, the water is highly pure, distilled water, such as ultrapure water (UPW), which is often used in semiconductor manufacturing plants. In immersion systems, the UPW is often purified and may undergo additional processing steps before being supplied to the immersion space 11 as the immersion liquid. In addition to water, other liquids with high refractive indices, for example hydrocarbons such as fluorocarbons, and / or aqueous solutions, can be used as the immersion liquid. It is also envisioned that other fluids besides liquids may be used in immersion lithography.

[0029]

[0034] In this specification, the description will refer to localized immersion where, in use, immersion liquid is confined to an immersion space 11 between the final element 100 and a surface facing the final element 100. This facing surface is the surface of the substrate W or a surface of the support stage (or substrate support WT) that is coplanar with the surface of the substrate W. (Note that in the following text, references to the surface of the substrate W may additionally or alternatively 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, when filled with immersion liquid, is smaller than the top surface of the substrate W when viewed from above, and the immersion space 11 remains substantially stationary relative to the projection system PS while the substrate W and substrate support WT move underneath.

[0030]

[0035] Other immersion systems are also envisaged, such as unconfined immersion systems (so-called "all wet" immersion systems) and bath 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 even the substrate W and a substrate support WT that is coplanar with the substrate W. In a bath-type system, the substrate W is fully immersed in a bath of immersion liquid.

[0031]

[0036] 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 in 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 remove immersion liquid from the immersion space 11 and that move in response to relative movement of a stage below the projection system PS. In more recent designs, the fluid handling structure extends along at least part of the boundary of the immersion space 11 between a final element 100 of the projection system PS and the substrate support WT or substrate W, so as to partly define the immersion space 11.

[0032]

[0037] The fluid handling structure 12 may have a range of different functions, each of which may result from a corresponding feature that enables the fluid handling structure 12 to achieve that function. The fluid handling structure 12 may be referred to by a number of different terms, each of which refers to a function, such as barrier member, seal member, fluid supply system, fluid removal system, liquid confinement structure, etc.

[0033]

[0038] Immersion liquid may be used as the immersion fluid, in which case the fluid handling structure 12 may be a liquid handling system. In accordance with the above, references in this paragraph to features defined in relation to a fluid may be understood to include features defined in relation to a liquid.

[0034]

[0039] 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 that is confined between the projection system PS and the substrate W by a fluid handling structure 12. The projection system PS has a lens element at the end of the beam path, which lens element comes into contact with the immersion liquid. This lens element that comes into contact with the immersion liquid may be referred to as the "last 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 a facing surface.

[0035]

[0040] Figures 2a, 2b, 2c, and 2d illustrate various features that may be present in variations of fluid handling systems. Designs may share some of the same features as Figures 2a, 2b, 2c, and 2d unless otherwise stated. The features described herein may be selected individually or in combination as shown or as needed. The figures illustrate different versions of fluid handling systems, with different features shown on the left and right sides, which may extend around the entire periphery. Thus, for example, a fluid handling system may have the same features extending around the entire periphery. For example, a fluid handling system may have only the features on the left side of Figure 2a, or only the features on the right side of Figure 2a, or only the features on the left side of Figure 2b, or only the features on the right side of Figure 2b, or only the features on the left side of Figure 2c, or only the features on the right side of Figure 2c, or only the features on the left side of Figure 2d, or only the features on the right side of Figure 2d. Alternatively, a fluid handling system may comprise any combination of the features described in these figures, at various locations around the periphery. The fluid handling system may comprise a fluid handling structure 12 as described in the following variants.

[0036]

[0041] Figure 2a shows the fluid handling structure 12 around the bottom surface of the final element 100. The final element 100 has an inverted truncated conical shape. The truncated conical shape has a flat bottom surface and a conical surface. The truncated conical shape protrudes from the flat surface and has a flat bottom surface. The flat bottom surface is the optically active part of the bottom surface of the final element 100 and 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 towards 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, may be parallel to the facing surface of the substrate support WT and / or substrate W. The bottom surface of the fluid handling structure 12 may therefore 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 20 to 500 micrometers, desirably in the range 70 to 200 micrometers.

[0037]

[0042] 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 an inner surface of the fluid handling structure 12, the flat surface of the frustum 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 complementary surfaces between the final element 100 and the fluid handling structure 12, for example at least part of the space between complementary inner surfaces and the conical surface.

[0038]

[0043] 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 20 on an inner surface of the fluid handling structure 12. Alternatively or additionally, the immersion liquid is supplied from a lower supply opening 23 formed in a bottom surface of the fluid handling structure 12. The lower supply opening 23 may surround the path of the radiation beam B and may be formed by a series of openings in an array or a single slit. The immersion liquid is supplied to fill the immersion space 11 below the projection system PS so that the flow through the immersion space 11 is laminar. The supply of immersion liquid from the lower supply opening 23 additionally prevents the introduction of bubbles into the immersion space 11. This supply of immersion liquid may act as a liquid seal.

[0039]

[0044] 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 due to the application of negative pressure, recovery through the recovery openings 21 as a result of the velocity of immersion liquid flow through the immersion space 11, or recovery may be a result of both. The recovery openings 21 may be located opposite the supply openings 20 in plan view. Additionally or alternatively, immersion liquid may be recovered through an overflow recovery 24 located on the top surface of the fluid handling structure 12. The supply openings 20 and recovery openings 21 may exchange their functions (i.e. the liquid flow direction is reversed). This allows the flow direction to be changed depending on the relative movement of the fluid handling structure 12 and the substrate W.

[0040]

[0045] 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 help to maintain a meniscus 33 of immersion liquid in 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 gaseous external environment. The recovery openings 25 may be a perforated plate that may recover immersion liquid in a substantially single-phase flow. The bottom recovery openings may be a series of pinned openings 32 through which immersion liquid is recovered. The pinned openings 32 may recover immersion liquid in a two-phase flow.

[0041]

[0046] Optionally, radially outwardly to the inner surface of the fluid handling structure 12 is a gas knife opening 26. Gas may be supplied at high speed through the gas knife opening 26 to assist liquid confinement of the immersion liquid in the immersion space 11. The supplied gas may be humidified and may contain substantial carbon dioxide. Radially outwardly from the gas knife opening 26 is a gas recovery opening 28 for recovering gas supplied through the gas knife opening 26.

[0042]

[0047] Further openings, for example open to atmosphere, or to a gas source, or to vacuum, may be present in 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 in dashed lines on the right-hand side of Figure 2a. As shown, the further opening 50 may be a supply member or an extractor, which is indicated by the double-headed arrow. For example, if configured as a supply, the further opening 50 may be connected to a liquid supply or a gas supply, as well as to any of the supply members. Alternatively, if configured as an extractor, the further opening 50 may be used to extract fluid and may be connected to, for example, atmosphere or 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.

[0043]

[0048] The two different versions of the fluid handling structure 12, on the left and right of Figure 2a, pin the meniscus 33. The version of the fluid handling structure 12 on the right of Figure 2a may pin the meniscus 33 in a substantially fixed position relative to the final element 100 because the positions of the pinning openings 32 are fixed. The version of the fluid handling structure 12 on the left of Figure 2a may pin the meniscus 33 below the collection opening 25 so that the meniscus 33 may move along the length and / or width of the collection opening 25. The substrate support WT, which supports the substrate W, is moved relative to the projection system PS so that the radiation beam B is directed onto the entire surface of the substrate W being exposed. To maximise the output of the substrate W exposed by the lithographic apparatus, the substrate support WT (and therefore the substrate W) is moved as fast as possible. However, there is a critical relative speed (often referred to as the critical scan speed), above which the meniscus 33 between the fluid handling structure 12 and the substrate W becomes unstable. An unstable meniscus 33 is at greater risk of losing immersion liquid, for example in the form of one or more droplets, and is also at greater risk of the immersion liquid becoming entrapped with gas bubbles, particularly as the trapped immersion liquid crosses the edge of the substrate W.

[0044]

[0049] Droplets present on the surface of the substrate W can impose a thermal load and can be the source of defects. Droplets can evaporate and leave dry stains, migrate and carry contaminants such as particles, collide with larger bodies of immersion liquid and introduce gas bubbles into the larger bodies, or evaporate and impose a thermal load on the surface on which they are located. Such thermal loads can cause distortions and / or positioning errors when the surface is relevant for positioning components of the lithographic apparatus relative to the substrate W being imaged. Therefore, the formation of droplets on the surface is undesirable. Therefore, to avoid the formation of such droplets, the speed of the substrate support WT is limited to a critical scan speed at which the meniscus 33 remains stable. This limits the throughput of the lithographic apparatus.

[0045]

[0050] 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 apply a biasing force to the fluid handling structure 12 in the direction of the substrate W. The spring 60 can thus be used to control the height of the fluid handling structure 12 above the substrate W. Such adjustable passive springs are described in US Patent No. 7,199,874, which is incorporated herein by reference in its entirety. Other biasing devices, for example electromagnetic forces, may also be suitable. Although the spring 60 is shown on the left-hand side of Figure 2a, this is optional and does not need to be included in 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 also be included in other variations of the fluid handling system described in relation to Figures 2a, 2b, 2c or 2d.

[0046]

[0051] Figure 2b shows two different versions of the fluid handling structure 12, on the left and right, which allow movement of the meniscus 33 relative to the final element 100. The meniscus 33 can move in the direction of movement of the substrate W. This reduces the relative speed between the meniscus 33 and the moving substrate W, which may result in improved stability and a reduced risk of rupture of the meniscus 33. The speed of the substrate W at which the meniscus 33 ruptures is increased, allowing faster movement of the substrate W under the projection system PS, and therefore increased throughput.

[0047]

[0052] Features shown in Figure 2b that are in common with Figure 2a share the same reference numbers. 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 facing surface than the bottom flat surface of the frusto-conical shape.

[0048]

[0053] 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 towards the bottom of the inner surface, possibly below the base of the frusto-conical shape. The supply openings 34 are spaced around the inner surface and around the path of the radiation beam B.

[0049]

[0054] 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 beneath the fluid handling structure 12, a meniscus 33 may migrate over 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 from a porous material. 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 recovered in a chamber 35 within the fluid handling structure 12 where it separates into liquid and gas. The liquid and gas are recovered from the chamber 35 through separate channels 36, 38.

[0050]

[0055] An inner periphery 39 of the bottom surface of the fluid handling structure 12 extends away from the inner surface into the immersion space 11 to form a plate 40. The inner periphery 39 forms a small aperture, which may be sized to match the shape and size of the radiation beam B. The plate 40 may act to isolate the immersion liquid on either side of it. Dispensed immersion liquid flows inward towards the aperture, through the inner aperture and then radially outwards under the plate 40 towards the surrounding collection openings 25.

[0051]

[0056] The fluid handling structure 12 may be in 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 facing surfaces. 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.

[0052]

[0057] The two different versions of the fluid handling structure in Figure 2b thus 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 over the surface of the recovery openings 25 in the fluid handling structure 12 on the left side of Figure 2b will be slower. 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.

[0053]

[0058] Figure 2c shows, on the left and right, two different versions of the fluid handling structure 12 which can be used to pin the meniscus 33 of the immersion liquid to the fluid handling structure 12 as described above in relation 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.

[0054]

[0059] The fluid handling structure 12 has an inner surface that is complementary to the conical surface of the frusto-conical shape. A bottom surface of the fluid handling structure 12 is closer to the facing surface than the bottom flat surface of the frusto-conical shape. Immersion liquid is supplied to the immersion space 11 delivered 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 is supplied through a lower supply opening 23. The immersion liquid may be recovered via an extraction member, for example via recovery openings 21 and / or an overflow recovery 24 formed in the inner surface and / or via one or more openings in the surface of the fluid handling structure 12 as described below.

[0055]

[0060] 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, as the position of the recovery opening 32a is fixed. The version of the fluid handling structure 12 on the left of Figure 2c may pin the meniscus 33 below the recovery opening 25, so that the meniscus 33 may move along the length and / or width of the recovery opening 25.

[0056]

[0061] As described above in relation to Figure 2b, the inner periphery of the bottom surface of the fluid handling structure 12 may extend into the immersion space 11, away from the inner surface, to form a plate 40, as shown on the left side. As described above, this may form small apertures and isolate the immersion liquid on either side and / or allow the immersion liquid to flow inward towards the aperture, through the inner aperture and then radially outwards under the plate 40 towards the surrounding recovery openings 25. This feature is shown on the left side of Figure 2c, although combination with the other features shown is optional. Preferably, as shown on the left side, 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 towards the bottom of the inner surface, possibly below the bottom surface of the frusto-conical shape. The supply openings 34 are spaced around the inner surface and around 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 a preferred liquid supply, although any combination of supply openings 34, supply openings 20 and / or lower supply openings 23 may be provided.

[0057]

[0062] As shown on the left-hand 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 extraction member, 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 may comprise any of the configurations disclosed in relation to the left-hand side of Figure 2a, the right-hand side of Figure 2a, the left-hand side of Figure 2b, the right-hand side of Figure 2b or (as described below) the right-hand side of Figure 2c in combination with the further device 3000.

[0058]

[0063] The further device 3000 may otherwise be referred to as a droplet catcher. The further device 3000 is provided to reduce the buildup of liquid 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 member 3010 and at least one extraction member 3020. The at least one extraction member 3020 may be shaped to surround the at least one supply member 3010 in plan view. The at least one liquid supply member 3010 may be configured to provide 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 some of the liquid via the at least one extraction member 3020. The further device 3000 may be used to mix liquid left on the surface of the substrate W with the liquid in the space 3110 and then extract the liquid using the further device 3000, such that the amount of liquid remaining on the surface of the substrate W is reduced.

[0059]

[0064] The further device 3000 is shown in Figure 2c as a device separate from the fluid handling structure 12. The further device 3000 may be positioned adjacent to the fluid handling structure 12. Alternatively, the further device 3000 may be part of, i.e. integral to, the fluid handling structure 12 (as in Figure 3d) (although either arrangement may be chosen).

[0060]

[0065] The further device 3000 may be configured to provide a liquid to the space 3110 other than the liquid provided by the fluid handling structure 12 .

[0061]

[0066] Additionally or alternatively, the fluid handling structure 12 may have the components shown on the right-hand side of Figure 2c. More specifically, the fluid handling structure 12 may comprise at least one liquid supply member, two extraction members (e.g. recovery openings 32a and 32b) and two gas supply members (e.g. gas supply openings 24a and 24b) formed on a surface of the fluid handling structure 12. Gas supply opening 24a may be omitted, i.e. is optional. The at least one liquid supply member may be the same as the lower supply opening 23 in the bottom surface of the fluid handling structure 12 described above, or the supply opening 20 or liquid supply opening 34 formed on an internal surface of the fluid handling structure 12 described in relation to the left-hand side of Figure 2b. The liquid supply members, extraction members and gas supply members may be formed on a surface of the fluid handling structure 12. In particular, 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.

[0062]

[0067] At least one of the two extraction members may comprise a porous material 37 therein. The porous material 37 may be provided in an opening, for example the recovery opening 32a, through which the fluid handling structure 12 may extract fluid from below the fluid handling structure 12 and recover immersion liquid in a single-phase flow. The other of the two extraction members, for example the recovery opening 32b, may recover immersion fluid as a two-phase extractor. The porous material 37 does not have to be flush with the bottom surface of the fluid handling structure 12.

[0063]

[0068] In particular, the fluid handling structure 12 may comprise a liquid supply member (e.g. lower supply opening 23), together with a first extraction member (e.g. recovery opening 32a) radially outward of the liquid supply member, a first gas supply member (e.g. gas supply opening 24a) radially outward of the first extraction member, a second extraction member (e.g. recovery opening 32b) radially outward of the first gas supply member and a second gas supply member (e.g. gas supply opening 24b) radially outward of the second extraction member. Similar to Figure 2a, further openings, for example open to atmosphere or 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).

[0064]

[0069] 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 located between the first extraction member (e.g., recovery opening 32a) and the first gas supply member (e.g., gas supply opening 24a), as described in the configurations above. Alternatively or additionally, the further opening may be located between the second extraction member (e.g., recovery opening 32b) and the second gas supply member (e.g., gas supply opening 24b), as described in the configurations above. The further opening may be the same as the further opening 50 described above.

[0065]

[0070] 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 24a 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 the recess 29 is provided between the collection openings 32a and 32b, the gas supply opening 24b may be provided in the sloped surface as shown in Figure 2c. If the recess 29 is provided between the supply openings 24a and 32b, the gas supply opening 24b 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 periphery of the fluid handling structure 12. The shape of the recess 29 may vary to change the effect of gas supplied from the gas supply member on the fluid below the fluid handling structure 12.

[0066]

[0071] Figure 2d shows two different versions of the fluid handling structure 12, in its left and right halves. The fluid handling structure 12 in the left half of Figure 2d has a liquid injection buffer 41a that holds a buffer volume of immersion liquid, and liquid injection holes 41 that supply immersion liquid from the liquid injection buffer to the space 11. Outside the liquid injection holes 41 are inner liquid recovery apertures 43 for directing liquid to an inner recovery buffer 43a that comprises a porous member. Recesses 29 similar to those described in relation to Figure 2c are provided outside the inner liquid recovery apertures 43. On the underside of the fluid handling structure 12 outside the recesses 29 are gas guide grooves 44 into which outer recovery holes 44a open. The outer recovery holes 44a direct the two-phase recovery flow to an outer recovery buffer 44b that also comprises a porous member. At the outermost end are gas seal holes 45 that communicate between the gas seal buffer volume 45a and the space below the fluid handling structure 12 to provide a gas flow to contain the immersion liquid.

[0067]

[0072] The fluid handling structure 12 in the right half of Figure 2d has a liquid supply opening 20 in its inner sloping surface. The underside of the fluid handling structure 12 has (from the inside to the outside) an extraction opening 25 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 in the underside of 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.

[0068]

[0073] 2a to 2d show examples of different configurations that can be used as part of a fluid handling system. While the examples provided above refer to particular extraction and recovery members, it will be understood that it is not necessary to use that exact type of extraction and / or recovery member. In some cases, different terminology is used to indicate the location of the member, but the same functional features may be provided. Examples of extraction members referenced above include recovery opening 21, overflow recovery section 24, recovery opening 25 (possibly comprising a perforated plate and / or chamber 35), gas recovery opening 28, pinned opening 32, recovery opening 32a, recovery opening 32b, and / or intermediate recovery section 42. Examples of supply members referenced above include supply opening 20, lower supply opening 23, gas knife opening 26, gas supply opening 24a, gas supply opening 24b, and / or supply opening 34. In general, extraction members used to extract / recover fluids, liquids, or gases are interchangeable with at least one other example used to extract / recover fluids, liquids, or gases, respectively. Similarly, supply members used to supply a fluid, liquid, or gas may be interchangeable with other examples used to supply a fluid, liquid, or gas, respectively. An extraction member may extract / withdraw 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 member. A supply member may supply a fluid, liquid, or gas to a space by being connected to an associated supply.

[0069]

[0074] As explained above, the use of immersion fluid / immersion liquid is beneficial in improving the resolution of smaller features on the substrate W, however the use of immersion fluid / immersion liquid also presents challenges relating to defects introduced onto the substrate W.

[0070]

[0075] 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 any droplets on the surface of the substrate W. When a droplet hits the meniscus 33, gas may become trapped in the immersion liquid, causing bubbles to form in the immersion liquid. The formation of bubbles in the immersion liquid may lead to defects on the substrate W. Droplets remaining on the surface of the substrate W may cause dried spots and / or affect the chemical properties of the resist, which may also lead to defects.

[0071]

[0076] Very small gas bubbles can dissolve in the immersion liquid before reaching the exposure area of ​​the immersion space 11. Carbon dioxide gas bubbles typically dissolve faster than air bubbles. CO2 bubbles have a solubility 55 times greater than that of nitrogen and a diffusion rate 0.86 times that of nitrogen, so they will typically dissolve in 37 times less time than a nitrogen bubble of the same size. Supplying CO2 adjacent to the meniscus 33 means that CO2 gas bubbles dissolve in the immersion liquid much faster than if other gases with lower diffusion rates were used. Therefore, the use of CO2 in the fluid handling structure 12 is known to reduce the number of imaging defects, thereby enabling higher throughput (e.g., faster speeds of the substrate W relative to the fluid handling structure 12) and lower defect rates.

[0072]

[0077] Temperature control in a lithographic apparatus is very important and it is desirable to maintain the temperature of sensitive parts of the apparatus, for example the substrate support WT and its vicinity, at very precise target temperatures. Evaporation of the immersion liquid in a two-phase extraction flow is therefore an undesirable heat load. To minimise this heat load it is desirable to use humidified gas in the fluid handling structure 12.

[0073]

[0078] Figure 3 illustrates a gas supply arrangement within the fluid handling structure 12. The gas supply system comprises a gas source 211 for supplying gas to the at least one gas knife opening 210 and to the at least one gas supply opening 220. In an embodiment, as illustrated in Figure 3, the same gas source 211 is used to provide gas to the at least one gas knife opening 210 and to the at least one gas supply opening 220. The gas supplied to the gas supply opening 220 may be controlled using a valve (not shown) to redirect gas from the gas knife opening 210 to the gas supply opening 220. In an embodiment, the gas supply system may comprise multiple gas sources for providing gas to the at least one gas knife opening 210 and the at least one gas supply opening 220, respectively.

[0074]

[0079] In one embodiment, the gas supply system includes a humidifier 212 for controlling the humidity of the gas provided by at least one of the gas sources. In one embodiment, the gas provided by the gas source 211 is substantially pure CO gas, and the output of the gas supply system is humidified CO gas. In one embodiment, the humidifier 212 increases the humidity of the CO gas provided by at least one of the gas sources. In one embodiment, the humidifier 212 is connected to the gas source 211 as shown in FIG. 3.

[0075]

[0080] In an embodiment, the fluid handling structure 12 may comprise a reservoir 213. The reservoir 213 may be between the at least one gas supply system and the gas knife opening 210 and the gas supply opening 220. In an embodiment, the reservoir 213 may be a section between the gas supply system and at least one of the gas knife opening 210 and the gas supply opening 220, and has an increased cross-sectional area. In an embodiment, the fluid handling structure 12 may comprise a first pathway 214 from the reservoir 213 to the gas knife opening 210 and a second pathway 215 from the reservoir 213 to the gas supply opening 220. In an embodiment, the reservoir 213 may not be provided, i.e. the reservoir 213 is not required.

[0076]

[0081] The provision of reservoir 213 allows for greater control of the gas released from gas knife opening 210 and / or gas supply opening 220. For example, gas may accumulate in reservoir 213 and be more evenly distributed from gas knife opening 210 and gas supply opening 220 along their lengths. The provision of humidifier 212 allows for greater control of the gas released from gas knife opening 210 and / or gas supply opening 220. For example, the humidity of the gas supplied to gas knife opening 210 and / or gas supply opening 220 can be controlled to affect the humidity of the gas atmosphere adjacent meniscus 33.

[0077]

[0082] In an embodiment, the amount of gas supplied to the gas knife opening 220 and / or the gas supply openings 210 is variable. In an embodiment, the gas supplied to the gas knife opening 220 and / or the gas supply openings 210 is dynamically controlled, i.e. the gas supplied can be controlled and varied during use. For example, the gas emitted from either the gas supply openings 220 and / or the gas knife opening 210 may be dynamically controlled in response to particular characteristics of the fluid handling structure 12 including, but not limited to, the direction, speed, velocity and / or location of movement of the fluid handling structure 12.

[0078]

[0083] In one embodiment, gas knife opening 210 comprises a series of individual apertures. For example, gas knife opening 210 may comprise two individual apertures, e.g., each aperture is one of two sides of the quadrilateral shape formed by gas knife opening 210. Alternatively, gas knife opening 210 may have a single individual aperture along each side of the quadrilateral shape formed by gas knife opening 210. Thus, gas knife opening 210 may be provided by four individual apertures. The shape of each aperture is not particularly limited, and gas knife opening 210 may be provided by any number of individual apertures.

[0079]

[0084] Each aperture may be individually controlled to vary the gas flow rate and / or gas velocity of gas exiting the different apertures in the gas knife opening 210. At least one of the apertures may be dynamically controlled in response to particular characteristics of the fluid handling structure 12, including but not limited to the direction, speed, velocity and / or location of movement of the fluid handling structure 12. For example, in use, the apertures of the gas knife opening 210 on an advancing side of the fluid handling structure 12 may be controlled to have gas exiting at a lower gas flow rate and / or gas velocity respectively than the gas flow rate and / or gas velocity exiting the apertures of the gas knife opening 210 on a retreating side of the fluid handling structure 12.

[0080]

[0085] Similarly, gas supply opening 220 may additionally or alternatively comprise a series of individual apertures as described herein, which may be individually controlled as described herein.

[0081]

[0086] 4a and 4b show a humidification device 150 that can be used with the gas supply system of FIG.

[0082]

[0087] The basic configuration of the humidifier 150 is shown in FIG. 4a, and a more complex structure operating on the same principle is shown in FIG. 4b. In FIG. 4a, the humidifier includes a membrane 600 that behaves as if it were impermeable to the liquid (usually (ultrapure) water) that humidifies the gas but permeable to the vapor of that liquid. It should be possible to pressurize the liquid side of the membrane (although this is not necessary for hydrophilic membranes, as explained below), and the liquid should not pass through the membrane. It is also possible to pressurize the gas side (using at least air or its components, such as nitrogen or oxygen), and gas bubbles will not pass through the membrane either. In some cases, the liquid wets the membrane material and then evaporates. In other cases, the membrane 600 allows only the liquid vapor to pass through, and liquid molecules can leave the membrane 600 as they enter the gas. A small amount of gas may dissolve in the liquid from the gas side of the membrane 600, but no bubbles will form in the liquid. Thus, the membrane 600 can be considered permeable to the liquid vapor.

[0083]

[0088] A first conduit 610 directs the gas to be humidified to one side of the membrane 600, and a second conduit 620 directs the liquid for humidifying the gas to the other side of the membrane 600. Because the gas is present on one side of the membrane 600 and the liquid is present on the other side of the membrane 600, vapor from the liquid passes through the membrane 600 to humidify the gas. Preferably, a flow of gas is provided through the membrane 600, such that a third conduit 630 is provided to direct the humidified gas away from the membrane 600, and a fourth conduit 640 is provided to direct the liquid away from the other side of the membrane 600.

[0084]

[0089] A similar humidification device is disclosed in WO 2005 / 010619, and much of what is said there is applicable here, particularly with regard to the shape of membrane 600 and how it is connected. However, in contrast to the disclosure in WO 2005 / 010619, membrane 600 in one embodiment of the invention may be provided with a liquidphilic surface. In other words, liquid on one side of membrane 600 has a contact angle with membrane 600 of less than 90°, preferably less than 70°, more preferably less than 60°, even more preferably less than 50°, and most preferably less than 30°, or even less than 20°.

[0085]

[0090] One class of materials suitable for use as membrane 600 are polymerized fluorinated sulfonic acid copolymers, which are synthetic ionic polymers. The sulfonic acid groups are chemically active but are fixed within the polymer matrix. One such material has the following chemical formula:

[0086] [ka]

[0087]

[0091] The hydrophilic nature of the membrane can be provided, for example, through a coating (on one or both sides of membrane 600) and / or, for example, through the application of an electrical potential to membrane 600. These types of membranes have previously been used in steam purification systems such as those sold under the trade name Intaeger by Rasirc, Inc. of San Diego, California, USA.

[0088]

[0092] The advantage of such membranes is that lower liquid pressures can be used on the liquid side of the membrane, resulting in better efficiency of gas-side evaporation of the liquid, i.e., greater mass transfer across the membrane. Also, with lyophilic membranes, there is no need to pressurize the liquid, and as a result, the actual hardware has a much lower pressure drop (10 times lower) compared to lyophobic membranes.

[0089]

[0093] It is advantageous to maximize the surface area of ​​the membrane 600, and one preferred embodiment is where the membrane 600 is a hollow fiber, with the liquid passing through the inside of the hollow fiber and the gas passing through the outside of the hollow fiber (although the reverse may also be true). One such embodiment is shown in Figure 4b, where the liquid is provided through hollow fibers 660 made up of the membrane 600. Although only one fiber is shown in Figure 4b, it should be understood that the second conduit 620 could be connected to several fibers in parallel.

[0090]

[0094] In the embodiment of FIG. 4b, gas enters a housing 650 that surrounds hollow fibers 660, is directed into the housing by conduit 610, passes through hollow fibers 660, and then, once humidified, the gas is directed out of the housing by a third conduit 630.

[0091]

[0095] To provide the gas and liquid flows, liquid and gas supplies are required, which may take the form of, for example, a pump to supply the liquid and a source of compressed gas.

[0092]

[0096] FIG. 5 shows a schematic diagram of a gas supply module 400 according to one embodiment of the present invention. Gas, e.g., carbon dioxide, is supplied from a gas source (not shown) to an input control valve 401, which regulates the flow of gas into the supply module 400. As will be described in more detail, the flow of gas through the gas supply module 400 is regulated based on pressure measurements at predetermined points within the gas supply module 400. The inventors have determined that a reliable relationship between pressure and gas flow can be determined, and therefore, the flow of gas through the gas supply module 400 can be monitored and controlled using a pressure sensor, which is less subject to long-term drift than a mass flow controller or mass flow meter. Depending on the exact configuration of the gas supply module 400, a variety of different locations may be suitable for the pressure sensor. Preferably, the location of the pressure sensor is selected so that there is a substantially linear relationship between pressure and flow rate, at least over the range of flow rates of interest. Preferably, the pressure sensor is downstream of any variables within the gas supply module 400. Preferably, the pressure sensor is downstream of the humidifier 150. Preferably, the pressure sensor is downstream of the temperature conditioner 408 .

[0093]

[0097] The relationship between pressure and flow rate may be determined through theoretical calculations or by empirical calibration. In many cases, minor manufacturing variations will affect the relationship between pressure and flow rate, so to achieve a desired level of accuracy, it will be desirable to calibrate each gas supply module 400 before installation in the lithographic apparatus. However, such variations are generally stable over time, and therefore subsequent recalibration is likely not required except when making significant changes to the lithographic apparatus or replacing parts in the gas supply module 400.

[0094]

[0098] 5, after the control valve 401, a safety sensor 402 is provided to monitor the gas pressure in the gas supply module 400. There may be two safety sensors 402. The safety sensors 402 monitor whether the pressure in the gas supply module 400 remains within an acceptable range and may warn the user or shut down the apparatus in the event of a dangerous excursion. A manual shut-off valve 403 is provided to manually shut off the gas supply when desired. A filter 404 is provided to ensure that particulates or other contaminants do not enter the lithographic apparatus.

[0095]

[0099] The filtered gas output by the filter 404 passes through a humidifier 150 and a temperature conditioner 408 before being supplied to the fluid handling structure 12 to form, inter alia, the gas knife. It is desirable for the humidifier 150 and the temperature conditioner 408 to be as close as possible to the fluid handling structure 12, whilst the components 401-404 may be located elsewhere, even external to the main part of the lithographic apparatus. A hose 405 may therefore be used to connect the filter 404 to the humidifier 150. The hose 405 may be relatively long, for example several metres, and may therefore form an effective flow resistance, shown in the figures as 406. The humidifier 150 and the temperature conditioner 408 may be included in a point-of-use module 416 which is physically close to the point where the conditioned gas is used.

[0096]

[0100] A pressure sensor 407 (an example of a measurement system) is provided at the outlet of the humidifier 150 and is connected to the control valve 401 in a feedback loop to regulate the flow of gas into the gas supply module 400, so that a constant pressure corresponding to the desired flow rate is maintained at the output of the humidifier 150. An additional sensor 415 may be provided at this location as well, for example for safety or to provide redundancy. A further pressure sensor 410 is shown between the output of the temperature conditioner 408 and the input to the fluid handling structure 12. This is an alternative location for a pressure sensor to provide feedback control to the control valve 401.

[0097]

[0101] Alternatively, the flow of gas through the gas supply module 400 may be regulated by a mass flow controller (another example of a measurement system) within the gas supply module 400. In such a configuration, the mass flow controller replaces the control valve 401 and the feedback loop from the pressure sensor 407 may be omitted. The mass flow controller may have an internal feedback loop. Typically, the mass flow controller is a mass flow meter (i.e., a sensor) combined with a control valve and feedback electronics between the sensor and the control valve.

[0098]

[0102] In one embodiment, temperature conditioner 408 comprises a heat exchanger that is provided with a temperature-controlled fluid via inlet 412. The temperature-controlled fluid may, for example, be from the same source as that used to control the temperature of the projection system PS. Because the temperature of the fluid used to humidify the gas is not as critical as that of other parts of the apparatus, such as the projection system PS, the fluid that has passed through temperature conditioner 408 may conveniently be provided as input to humidifier 150. The temperature of the fluid used to humidify the gas should be high enough to allow a sufficient evaporation rate of the fluid in humidifier 150. Outlet 413 returns the fluid for reconditioning.

[0099]

[0103] The flow restriction 409 leads to a sampling point that can be used for testing purposes, for example, measuring humidity using an external tool. The sampling point is typically capped, and the flow restriction 409 is provided to limit gas leakage if the cap is installed improperly.

[0100]

[0104] As mentioned above, in order to control the gas flow rate based on the measured pressure, it is desirable to know the relationship between pressure and flow rate accurately. Figure 6 shows pressure and flow rate measurements made in an experimental setup corresponding to one embodiment of the present invention. Pressure is given in arbitrary units on the x-axis and flow rate is given in arbitrary units on the y-axis. Pressure measurements were made using pressure sensors 407 (line A, filled circles) and 415 (line B, filled squares) and correlated with flow rate measurements at the output of the gas knife. Pressure sensors 407, 415 are located between the humidifier and the heat exchanger, but may be located elsewhere in the gas supply module. The pressure measured by both sensors has a highly linear relationship to flow rate (R 2 = 0.000 and 0.9974), and by averaging the two pressure readings (line C, open circle), an even more linear measurement (R 2 =0.9992).

[0101]

[0105] The gas supply module 400 described above may also be used in a further device 3000 acting as a droplet removal system (or droplet catcher) as described above in Figure 2c.

[0102]

[0106] The present invention may provide a lithographic apparatus, which may have any / all of the other features or components of the lithographic apparatus described above, for example, the lithographic apparatus may optionally comprise at least one or more of a radiation source SO, an illumination system IL, a projection system PS, a substrate support WT, etc.

[0103]

[0107] In particular, the lithographic apparatus may comprise a projection system PS configured to project a radiation beam B towards a region of a surface of the substrate W. The lithographic apparatus may further comprise a fluid handling system as described in any of the embodiments and variants of Figures 2a to 2d above.

[0104]

[0108] The lithographic apparatus may comprise an actuator (not shown) configured to move the substrate W relative to the fluid handling system. The actuator may thus be used to control the position of the substrate W (or alternatively the position of the fluid handling system). The actuator may be or comprise a substrate support (e.g. substrate table) WT and / or a substrate holder constructed to hold the substrate W, and / or a second positioner PW configured to accurately position the substrate support WT.

[0105]

[0109] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated 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.

[0106]

[0110] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, machine-readable media 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 propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Additionally, firmware, software, routines, and instructions may be described herein as performing particular actions. However, it should be understood that such description is for convenience only, and that such actions actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., which, in execution, may cause actuators or other devices to interact with the physical world.

[0107]

[0111] Although specific reference may be made herein to embodiments of the invention in the context of 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 ambient (non-vacuum) conditions.

[0108]

[0112] Although particular reference may have been made above to the use of embodiments of the present invention in the context of optical lithography, it will be understood that the present invention is not limited to optical lithography, where the context so permits.

[0109]

[0113] Embodiments include the following numbered clauses: 1. A gas supply module for a fluid handling system of a lithographic apparatus, the gas supply system comprising: a humidifier having a humidifier input and a humidifier output; a first conduit configured to direct gas to the humidifier input; a second conduit configured to supply humidified gas to the fluid handling system; and a control valve configured to control gas flow in one of the first conduit and the second conduit; a measurement system configured to measure pressure downstream of the control valve and generate a control signal; It is equipped with The control valve maintains a constant pressure in one of the first conduit and the second conduit in response to a control signal. 2. The gas supply module of clause 1, wherein the control valve is provided in the first conduit. 3. The gas supply module of clause 1, wherein the control valve is provided in the second conduit. 4. A gas supply module as described in clause 1 or 2, wherein the measurement system comprises a pressure sensor configured to measure the pressure in the first conduit. 5. The gas supply module of clause 1, 2, or 3, wherein the measurement system comprises a pressure sensor configured to measure the pressure in the second conduit. 6. A gas supply module as described in any one of clauses 1 to 5, further comprising a heat exchanger downstream of the humidifier configured to regulate the temperature of the humidified gas. 7. The gas supply module of clause 6, further comprising a liquid supply system configured to supply liquid to the humidifier and the heat exchanger. 8. A gas supply module described in any one of clauses 1 to 7, wherein the control valve is configured to maintain pressure in one of the first conduit and the second conduit so that the gas flow rate in the second conduit is a predetermined flow rate, the predetermined flow rate being greater than 50 nlpm, preferably greater than 75 nlpm. 9. A fluid handling system for a lithographic apparatus, comprising a gas supply module according to any one of clauses 1 to 8, the gas supply module being configured to supply gas to a gas seal configured to confine fluid to an area. 10. A lithographic apparatus comprising a fluid handling system according to clause 9. 11. Confining the liquid to the space between the projection system and the substrate using a gas seal supplied with gas from a gas supply module; projecting a patterned beam of radiation through the liquid onto a substrate using a projection system; measuring pressure at a predetermined location within the gas supply module; controlling gas flow in a gas supply module upstream of the predetermined location to maintain a predetermined gas flow rate at the gas seal; A device manufacturing method comprising: 12. A method of calibrating a gas supply module for a fluid handling system of a lithographic apparatus, comprising: measuring pressure at a predetermined location within the gas supply module; Measuring a gas flow rate output by a gas supply module; determining a target pressure at a predetermined location to provide a desired gas flow rate; A method for providing the above. 13. The method of clause 12, wherein the calibration is performed while the gas supply module is fluidly connected to the fluid handling system. 14. A gas supply module for a fluid handling system of a lithographic apparatus, the gas supply system comprising: a humidifier having a humidifier input and a humidifier output; a first conduit configured to direct gas to the humidifier input; a second conduit configured to supply humidified gas to the fluid handling system; and a control valve configured to control gas flow in one of the first conduit and the second conduit; a feedback system connected to a sensor downstream of the control valve and configured to maintain a constant flow rate in the second conduit; A gas supply module comprising:

[0110]

[0114] 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 above description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications to the invention as described may be made without departing from the scope of the claims below.

Claims

1. 1. A gas supply module for a fluid handling system of a lithographic apparatus, the gas supply system comprising: a humidifier having a humidifier input and a humidifier output; a first conduit configured to direct gas to the humidifier input; a second conduit configured to supply humidified gas to the fluid handling system; and a control valve configured to control gas flow in one of the first conduit and the second conduit; a measurement system configured to measure pressure downstream of the control valve and generate a control signal; It is equipped with The control valve is responsive to the control signal to maintain a constant pressure in the one of the first conduit and the second conduit.

2. 2. The gas supply module of claim 1, wherein the control valve is disposed in the first conduit.

3. 2. The gas supply module of claim 1, wherein the control valve is disposed in the second conduit.

4. 3. The gas supply module of claim 1, wherein the measurement system comprises a pressure sensor configured to measure the pressure in the first conduit.

5. 4. The gas supply module of claim 1, 2 or 3, wherein the measurement system comprises a pressure sensor configured to measure the pressure in the second conduit.

6. 6. The gas supply module of claim 1, further comprising a heat exchanger downstream of the humidifier configured to regulate the temperature of the humidified gas.

7. The gas supply module of claim 6 , further comprising a liquid supply system configured to supply liquid to the humidifier and the heat exchanger.

8. 8. The gas supply module of claim 1, wherein the control valve is configured to maintain a pressure in one of the first conduit and the second conduit such that the gas flow rate in the second conduit is a predetermined flow rate, the predetermined flow rate being greater than 50 nlpm, preferably greater than 75 nlpm.

9. 9. A fluid handling system for a lithographic apparatus, comprising: a gas supply module according to any one of claims 1 to 8, the gas supply module being configured to supply gas to a gas seal configured to confine a fluid to an area.

10. A lithographic apparatus comprising a fluid handling system according to claim 9.

11. - confining liquid to a space between the projection system and the substrate using a gas seal supplied with gas from a gas supply module; projecting a patterned beam of radiation through the liquid onto the substrate using the projection system; measuring the pressure at a predetermined location within the gas supply module; controlling gas flow within the gas supply module upstream of the predetermined location to maintain a predetermined gas flow rate at the gas seal; A device manufacturing method comprising:

12. 1. A method for calibrating a gas supply module for a fluid handling system of a lithographic apparatus, comprising the steps of: measuring the pressure at a predetermined location within the gas supply module; measuring the gas flow rate output by the gas supply module; determining a target pressure at the predetermined location to provide a desired gas flow rate; A method for providing the above.

13. The method of claim 12 , wherein the calibration is performed while the gas supply module is fluidly connected to the fluid handling system.

14. 1. A gas supply module for a fluid handling system of a lithographic apparatus, the gas supply system comprising: a humidifier having a humidifier input and a humidifier output; a first conduit configured to direct gas to the humidifier input; a second conduit configured to supply humidified gas to the fluid handling system; and a control valve configured to control gas flow in one of the first conduit and the second conduit; a feedback system connected to a sensor downstream of the control valve and configured to maintain a constant flow rate in the second conduit; A gas supply module comprising:

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