WO2024208536A1 - Nozzle for providing a gas flow and method of making the nozzle - Google Patents

Abstract

The present disclosure provides a nozzle for providing a gas outflow, the nozzle comprising: a main channel; the main channel opening into at least one flow restriction section at a downstream end of the main channel, each flow restriction section having a plurality of parallel vanes for creating a uniform gas flow; the at least one flow restriction section opening into a respective outflow section having an increasing cross-sectional area towards an open end thereof adapted to provide the gas outflow.

Description

NOZZLE FOR PROVIDING A GAS FLOW AND METHOD OF MAKING THE NOZZLE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23167139.7 which was filed on 6 April 2023, and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to a nozzle for providing a gas flow and to a method of making the nozzle. The nozzle can be used in, for instance, a lithographic apparatus.

BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] Gas flows may be applied at various locations in the lithographic apparatus, for a variety of functions.

[0006] US2017363975 discloses a lithographic apparatus that injects gas between a patterning device and a patterning device masking blade to help protect the patterning device from contamination. The gas may be injected into the space defined between the patterning device and the patterning device blade by one or more gas supply nozzles that are arranged on at least one side of the patterning device. The one or more gas supply nozzles are coupled to a frame which a patterning device support structure moves relative to. Each nozzle may be constructed and arranged to supply gas over at least the patterning region of the reflective patterning device.

[0007] US2005157278 discloses an exposure apparatus able to maintain reflectances of mirrors and transmittances of lenses and to maintain initial performance over a long period by using exposure light of a wavelength of the vacuum ultraviolet region to illuminate a mask and transfer images of patterns on the mask to a substrate, provided with a gas feed unit for supplying a light path space through which the exposure light passes with a gas mainly comprised of an inert gas or rare gas and introducing a predetermined concentration of hydrogen into the gas fed to at least part of the light path space. In a lithographic process, required gas flow rates, gas composition and pressure conditions may vary per step of the process. Typical gas compositions may vary from hydrogen gas for one application, to extreme clean dry air (XCDA) or nitrogen for another, for example. During operating conditions, the nozzle may have to operate in near vacuum, for instance in the order of 3 to 5 Pa. Herein, the gas composition may comprise mainly hydrogen. For performing an intermittent flushing operation, another gas may be used, such as the mentioned extreme clean dry air. For this purpose, the gas may flow through the nozzle at an increased flow rate. The environment may be set at an intermediate pressure, between low vacuum and atmospheric. The intermediate pressure may be in the range of near vacuum, for instance 0.5 to 1 kPa. Further, the nozzle may also have to be able to operate during maintenance of the lithographic apparatus, wherein the optical section may be partly opened and is at atmospheric pressure (about 1 bar). Other conditions may apply as well, having other gas compositions and/or other pressure environments.

[0008] Detailed laboratory tests and practical application of conventional nozzles have indicated that conventional gas flow devices often have a relatively non-uniform gas flow. Or, alternatively, the conventional nozzles may be optimized for a particular gas flow rate and a particular gas, while the flow may be suboptimal and non-uniform for other flow rates, other gas compositions and/or other pressure environments. A consequence of non-uniform flow is the presence of dead circulation zones, i.e. zones where the flow is minimal to none. In said zones, particles may deposit and contaminate the device. For instance near vulnerable parts in the optical path of high-end lithographic machines, such as the wafer stage, the mask and related components like a protective pellicle, particle contamination and deposition is preferably obviated as much as possible.

[0009] Hence, there is a need for an improved gas flow device providing a more uniform flow. It is an object to provide a nozzle which can provide a substantially uniform gas flow, for multiple gas compositions, varying gas flow rates, and/or for a multitude of pressures.

SUMMARY

[00010] The present disclosure provides a nozzle for providing a gas outflow, the nozzle comprising: a main channel; the main channel opening into at least one flow restriction section at a downstream end of the main channel, each flow restriction section having a plurality of parallel vanes for creating a uniform gas flow; the at least one flow restriction section opening into a respective outflow section having an increasing cross-sectional area towards an open end thereof adapted to provide the gas outflow. [00011] In an embodiment, the main channel branches into at least two branch channels, preferably two branch channels, each branch channel opening into a respective flow restriction section at a downstream end of the respective branch channel of the main channel. [00012] In an embodiment, the main channel comprises at least one flow distribution section at a downstream end, a side of the at least one flow distribution section opening into a respective flow restriction section.

[00013] In an embodiment, a cross-sectional area of the at least one flow distribution section decreases towards the downstream end.

[00014] In an embodiment, the at least two branch channels branch outward from the main channel, the respective flow distribution section being directed inward, the downstream end of one flow distribution section facing towards the downstream end of the other flow distribution section.

[00015] In an embodiment, the nozzle comprises a first plate in which the main channel and the flow restriction section and the outflow section, and optionally the branched channels are recessed, and a second plate covering at least the main channel and the branched channels in the first plate. In an embodiment of the nozzle comprising the branch channels, the branch channels may be recessed in the first plate as well.

[00016] In an embodiment, a gap is present between a top end of at least a part of the vanes, preferably all the vanes, and the second plate.

[00017] According to another aspect, the disclosure provides a lithographic apparatus comprising at least one nozzle as described above.

[00018] The lithographic apparatus may comprise: an illumination section (IL); a reticle stage (RS); a projection system (PS); and a first above described nozzle arranged at an interface between the illumination section (IL) and the reticle stage (RS) and/or a second above described nozzle arranged at an interface between the reticle stage (RS) and the projection system (PS).

[00019] In an embodiment, the at least one nozzle provides a uniform gas flow along an opening to block a range of particles from passing through said opening while allowing passage of radiation through the opening.

[00020] According to yet another aspect, the disclosure provides a method of fabricating a nozzle as described above.

[00021] According to an aspect, the disclosure provides a method comprising the steps of: providing a main channel; providing at least one flow restriction section at a downstream end of the main channel, each flow restriction section having a plurality of parallel vanes for creating a uniform gas flow; the at least one flow restriction section opening into a respective outflow section having an increasing cross-sectional area towards an open end thereof adapted to provide the gas flow out. [00022] In an embodiment, the method comprises the steps of: recessing the main channel, two branched channels, the flow restriction section and the outflow section in a first plate, and covering the first plate with a second plate thereby covering at least the main channel, the two branched channels, and the flow distribution section.

[00023] In an embodiment, the method comprises the step of arranging a brazing foil between the first plate and the second plate, and connecting the first plate to the second plate by brazing.

[00024] In an embodiment, the brazing foil is provided with a cut-out pattern corresponding to at least one of, preferably all of said main channel, said branch channels, said flow restriction section and said outflow section, so that one or more of said channels and/or sections are free from brazing foil.

[00025] The nozzle and method of the disclosure are adapted to provide a relatively uniform gas flow. Herein, the outflow section or diffusor mixes multiple parallel flows from parallel flow channels, providing a uniform outflow. The nozzle may be adapted to provide the gas flow into a vacuum space. [00026] The nozzle and method of the disclosure enable to relatively uniform gas flow. A result of the uniformity of the gas flow is improved cleanability. Cleanability herein relates to absence of dead zones and resulting limited deposition of contaminants and particles. The nozzle and method of the disclosure are suitable to provide a gas curtain to shield one section of the lithographic apparatus from another section.

BRIEF DESCRIPTION OF THE DRAWINGS

[00027] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;

Figure 2 depicts a perspective view of an embodiment of a nozzle according to the disclosure;

Figures 3A and 3B depict a bottom view of respective embodiments of a plate section of a nozzle according to the disclosure;

Figure 4 depicts a cross-sectional view of an embodiment of an outflow section of a nozzle according to the disclosure;

Figure 5 depicts a schematic top view of an embodiment of a detail of an outflow section of a nozzle of the disclosure;

Figure 6 depicts a cross-section in length direction of Figure 5;

Figure 7 depicts a front view of a nozzle of the disclosure;

Figure 8 depicts a cross-sectional view along line III-III in Figure 3A; and

Figure 9 depicts a schematic diagram indicating gas outflow in the outflow section of a nozzle of the disclosure. DETAILED DESCRIPTION

[00028] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W. The support structure MT asnd the patterning device may be arranged in a device section referred to as the reticle stage RS. Walls at the interface between the reticle stage and the illumination section IL and the projection system PS respectively may be provided with openings 15, 16 to allow radiation to pass from one section to the other.

[00029] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[00030] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13, 14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13, 14 in Figure 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[00031] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[00032] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.

[00033] The radiation source SO shown in Figure 1 is, for example, of a type which may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from, e.g., a fuel emitter 3. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form, and may, for example, be a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a tin plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during deexcitation and recombination of electrons with ions of the plasma.

[00034] The EUV radiation from the plasma is collected and focused by a collector 5. Collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes referred to more generally as a normal-incidence radiation collector). The collector 5 may have a multilayer mirror structure which is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two focal points. A first one of the focal points may be at the plasma formation region 4, and a second one of the focal points may be at an intermediate focus 6, as discussed below.

[00035] The laser system 1 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser system 1, the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[00036] Radiation that is reflected by the collector 5 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present at the plasma formation region 4. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9 of the radiation source SO.

[00037] Although Figure 1 depicts the radiation source SO as a laser produced plasma (LPP) source, any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation.

[00038] Generally referring to Figure 2, 3A and 3B, a nozzle 18 of the disclosure comprises a main channel 20. The main channel 20 branches into two branch channels 30, 32. Each branch channel may have a respective flow distribution section 34, 36 at a downstream end thereof. The flow distribution sections 34, 36 are fluidly connected to a respective flow restriction section 22c, b.

[00039] Each flow restriction section has a plurality of parallel vanes 24 for creating a uniform gas flow. Each flow restriction section opens into an outflow section 26 having an increasing cross-sectional area towards an open end 28 thereof adapted to provide the gas outflow. In a practical embodiment, the flow restriction sections 22b, 22c of two adjacent branch channels may jointly constitute one flow restriction section 22 with vanes 24, opening into an outflow section 26. Flow restriction sections 22d, 22e of second branch channels 30a, 32a may jointly constitute the second flow restriction section 22a. [00040] The main channel may comprise at least one flow distribution section 34, 36 at a downstream end, a side of the at least one flow distribution section opening into a respective flow restriction section 22c, 22d. The at least one flow distribution section 34, 36 may have a tapering shape, having a cross section which becomes narrower towards the downstream end 38. Thus, the gas flow in the channels is uniformly divided across the flow restriction section 22, limiting dead flow at any given flow gas rate. The distribution section 34, 36 may be referred to as a dividing manifold chamber. The flow restriction section 22 may be referred to as vane restriction area. The outflow section 26 may be referred to as a diffusor area.

[00041] The two branch channels 30, 32 may branch outward from the main channel, and the respective flow distribution section 34, 36 being directed inward, the downstream end of the respective flow distribution section 34 facing towards the downstream end of the other flow distribution section 36.

[00042] In an embodiment (Fig. 3B), the nozzle 18 may comprise a first part 19 and a second part 21, enclosing a slit or opening 25. The opening 25 may, for instance, function as an opening between respective parts or sections of the lithographic apparatus LA. For instance, the opening 25 may be arranged at the interface between the illumination section IL and the reticle section comprising the mask table MT and/or between the projection system PS and the section comprising the mask table MT.

[00043] The second section 21 may comprise a second main channel 20a. The second main channel can branch into two second branch channels 30a, 32a. Each second branch channel may have a respective flow distribution section 34a, 36a at a downstream end thereof. The flow distribution sections are fluidly connected to a respective flow restriction section 22d, 22e. In a practical embodiment, the flow restriction section 22d, 22e of two adjacent second branch channels 30a, 32a may jointly constitute one second flow restriction section 22a with vanes 24, opening into a single second outflow section 26a. Each flow restriction section has a plurality of parallel vanes 24 for creating a uniform gas flow. The second flow restriction section 22a opens into the second outflow section 26a having an increasing cross-sectional area towards an open end 28a thereof adapted to provide the gas outflow.

[00044] The branch channels 30, 30a, 32, and 32a may have a curved and fluent flow path. The flow path is as fluent and organic as possible, avoiding or entirely obviating sharp or right angles, to enable smooth and virtually laminar flow throughout the entire channel. Herein, the branch channels may have a kind of onion shaped flow path, see Figures 3A and 3B.

[00045] In an embodiment, the first outflow section 26 and the second outflow section 26a are arranged facing each other and along a side of the opening 25. Herein, the gas flow out of said first and second outflow section can be directed along the plane of the opening 25, to create a gas curtain covering the opening 25.

[00046] In a practical embodiment, the nozzle 18 may comprise a first plate 40 and a second plate 42. The gas flow channels, such as the main channel 20, and the branched channels 30, 32, can be recessed in the first plate 40. The channels may, for instance, be arranged by milling, etching or pressing. In a practical embodiment, the channels are arranged by removing material from the first plate 40, creating a cut-out to allow gas flow. The same may apply to the embodiment of Figure 3B.

[00047] The second plate 42 may cover the first plate 40. The second plate may be connected to the first plate by any suitable means, including for instance one or more of adhesive, soldering, brazing, welding, bolting, screwing, melting, and/or riveting. Adhesive may include cyanoacrylate or epoxy based adhesive. Edges of the two plates 40, 42 may for instance be bolted together, in combination with a strengthening structure such as a block or ridge (not shown).

[00048] When the second plate 42 is connected to the first plate 40, the channels are enclosed by plate material, providing gas tight channels to guide the gas flow. The second plate 42 thereby forms a part of walls of the gas flow channels. The second plate 42 may cover only part of the first plate 40. At least, the second plate 42 covers the gas flow channels in the first plate, such as the main channel 20, the branch channels 30, 32, and the flow restriction section22.

[00049] A brazing foil 44 may, for instance, be arranged between the first plate and the second plate. Herein, the first plate can be connected to the second plate by brazing. The brazing foil 44 is preferably provided with a cut-out pattern corresponding to at least the respective main channels 20, 20a and the corresponding branch channels. Upon brazing, the cut-out pattern ensures that the channels are free from brazing material, obviating contamination with brazing material in the gas flow channels. Also, the cut-out pattern in the brazing foil facilitates cleaning of the gas flow channels of the nozzle 18 without inducing brazing material to deposit in the channels upon cleaning. Cleaning herein may involve flushing with pressurized gas or fluid.

[00050] Alternative embodiments may include, but are not limited to: a variant wherein multiple vanes are combined to form larger ‘islands’ wherein such ‘islands’ may be connected to the second plate; a variant having one channel (so no branch channels) opening into one flow restriction section; an embodiment wherein instead of branch channels, the nozzle comprises two separate channels connected to a respective gas source inlet and directly connecting the inlet to a respective flow restriction section.. Other options include for instance connecting, such as by point welding or gluing or brazing one or more of the vanes, which may have an increased height compared to other vanes, to the second plate for stability.

[00051] Figure 4 shows a cross section of the flow restriction section22, having a plurality of parallel vanes 24 creating fluid flow openings 48 between the vanes. The vanes 24 may extend upward from the first plate 40 towards the second plate 42. A gap 50 may be provided between a top end of one or more of the vanes and the second plate 42. In a practical embodiment, almost all to all vanes thus leave at least some space between the top end of the vanes 24 and the second plate 42. In a practical embodiment, the vanes may extend over about 50% to 90% of the height 52 of the flow restriction section 22. Some of the vanes, for instance one or two, may have a mentioned increased height and extend from the first plate up to the second plate, to provide additional support. The vanes extending from the first plate to the second plate may be connected to the second plate 42. [00052] Generally referring to Figure 5, the flow restriction section 22 may be connected to a side of a respective flow distribution section 34, 36 etc. As shown in Figures 2 and 3, the respective flow distribution section may have a cross sectional area which reduces from its upstream end towards its downstream end. Herein, see for instance Fig. 6, the height of the respective flow distribution section 34 may remain substantially constant while the width decreases. This contributes to the gas flow being distributed substantially evenly over the fluid flow openings 48 between the vanes 24.

[00053] Referring to Figures 6, 7 and 8, the channels 20, 30, the flow distribution section, the flow restriction section 22 and the outflow section 26 may be arranged in the first plate 40 as recesses. Herein, the respective gas flow sections may be arranged by removing material, for instance by milling or etching. The outflow section 26 may be provided with a sloping wall, wherein a downstream end 28 has a height exceeding the height at the upstream end of the outflow section 26, i.e. the end connected to the flow restriction section 22. As shown in Figs. 6 and 7, the height of the flow distribution section 34 may significantly exceed the height of the flow restriction section 22.

[00054] In an embodiment, one or more of the channels, i.e. including the main channel 20 and its branch channels 30, 32, may be in part arranged in the first plate 40, and for another part be arranged in the second plate 42. Herein, the flow restriction section may typically be provided in one of the plates. [00055] In a practical embodiment, the first plate 40 may have a thickness in the order of 1 to 5 mm, for instance about 1.5 to 2.5 mm. The second plate may have a thickness in the order of 0.3 to 5 mm, for instance about 0.5 to 1 mm. The vanes may have a height in the order of 0.1 to 0.5 mm. The vanes may have a width in the order of one to five times their height. The fluid flow openings 48 may have a width in the order of one to four times the width of the vanes. The outflow section 26 may have a sloping wall set at an angle of about 5 to 10%. The flow channels 20, 30, 32 and/or the flow distribution sections 34, 36 may have a height in the order of at least two to 10 times height of the flow restriction section 22.

[00056] The nozzle 18 of the disclosure includes a specific inner channel geometry inside the nozzle. The nozzle provides a combination of a ‘dividing manifold’ design, using flow distribution sections 34, 36 etc., plus a defined ‘restriction area’ comprising the flow restriction section 22 with small vanes 24, and a defined ‘diffusor area’ 26. Tests have indicated that the nozzle of the disclosure overcomes the challenge to design these respective areas to satisfy and exceed thresholds for flow uniformity and cleanability, for all flow states, while satisfying the other nozzle requirements (such as, but not limited to, volume claim, manufacturability, pressure drop, mechanical stresses, eigenfrequencies).

[00057] The flow uniformity (applicable for all flow states) of the gas outflow enables the nozzle to function as gas curtain between sections of the lithographic apparatus. Thus, the nozzle can functionally protect the reticle stage RS, protecting the patterning device (reticle) and pellicle from any particle(s) moving upwards, to limit local contamination built-up. The nozzle design allows to clean the nozzle on all internal surfaces and local outer nozzle-areas during service, venting and qualification. [00058] As indicated, the flow uniformity can be obtained for all flow states, including relatively low flow rates (exposure H2) and relatively high flow rates (for service, venting, qualifications, using N2 and/or XCDA). As a consequence, the nozzle design of the disclosure has some fundamental advantages compared to conventional nozzle designs, such as proven flow uniformity (practical TNO- testing versus CFD-simulations in-line). The nozzle 18 provides positive near-term expectations regarding cleanliness (CFD-simulations RME area and particle tracing, elimination of ‘death circulation zones’). The nozzle allows ‘flow switching’ during exposure (due to the design comprising two opposing gas flows, see Figure 3B). The nozzle allows flushing from two directions (due to the two- nozzle design).

[00059] Flow uniformity is achieved by employing a “dividing manifold” design. The flow restriction creates a high penalty if the flow would not distribute uniformly. The challenge is to design the restriction of section 22 for all flow states (i.e. machine states), without spending too much pressure drop budget.

[00060] Referring to Figure 5, for uniform flow, the pressure difference over the restriction section AP = Pup - Pdown is preferably sufficiently large. A threshold for said pressure difference may differ per flow state, for instance low Reynolds number versus high Reynolds number, and low Mach number versus high Mach number.

[00061] The ideal gas law is p = — p # T . For an ideal isothermal gas in a restriction section with high- aspect ratio, wherein h « W,

— P_down ^{= 24/iLQ}‘^^^Pdown. Rewriting this formula provides a means to express the pressure drop over the restriction section. The pressure drop for gasses over the restriction section scales with:

Herein, m is the mass flow rate, in [kg / s]. The mass flow rate herein may equal the volumetric flow rate Q [m³/s] times the density of the gas r, in [kg/m³]. L is the length of the flow channels 48 of the restriction section, W is the Width of the flow channels, and h is the height of the flow channels 48, all in [m]. T is the temperature [K]. The viscosity of the gas is indicated by p, in [Pa.s]. R_s is the specific gas constant, in [J/kg.K]. P is the pressure, in [Pa]-

[00062] For low pressure states (such as during exposure), Pdown « Pup- As P_up = jC X m , it follows that P_up — Pdown — C X m.

[00063] For high pressure states and/or higher gas flow rates (such as servicing, venting, and qualification), the pressure drop across the flow restriction section 22 is relatively small. Thus, Pdown more or less equals P_up, leading to P_up - P_down = Jc X m + P_down - P_down .

[00064] For high pressure flow states, the effectiveness of the pressure drop thus decreases. As a solution, the flow restriction section of the nozzle of the disclosure includes a relatively large number of relatively slender vanes distributed over a relatively wide low restriction section, to help distribute the flow for these states. The decreasing cross section, for instance decreasing width, of the flow distribution sections can be tuned to provide a relatively even distribution of flow across all parallel flow channels 48. For instance, a flow restriction section may comprise more than 20, for instance more than 30, for instance more than 50 vanes.

[00065] The flow uniformity enabled by the nozzle of the present disclosure has been confirmed in practical testing, both in simulations and in prototyping in a lab environment. Figure 9, which is not to scale and is exemplary only, shows a gas outflow uniformity of a restriction section, as a function of a dimension along a width of the restriction section. As the vanes are relatively thin and slender, for instance relative to the width of the restriction section, the gas outflow will mix in the downstream outflow section, providing a uniform gas outflow out of the nozzle.

[00066] The nozzle design of the disclosure is optimized to have a relatively high flow uniformity and cleanability. The nozzle provides a uniform flow both for small and large gas flow rates and during multiple different flow states. Flow states herein may include: 1) hydrogen flow (H2) during exposure (in a low pressure, near vacuum environment at, for instance, 1 to 10 Pa); 2) Flushing at an intermediate pressure; and 3) maintenance at substantially atmospheric pressure.

[00067] Also, the absence of brazing foil above the channels (so only between contacting plate surfaces) improves cleanliness. The features of the nozzle provide combined effects. The restriction area creates a uniform flow for vacuum state. Combined with the vanes, a uniform flow can also be created for atmospheric state. Also, the nozzle has improved cleanliness, because dead zones are substantially obviated.

[00068] The nozzle 18 of the disclosure can be applied as a gas curtain to cover openings in the lithographic apparatus LA. For instance, the opening 25 of the nozzle 18 may be arranged covering one or both of the openings 15, 16 at the interface between the reticle stage and the illumination section IL and/or reticle stage RS and the projection system PS. In use, the nozzle of the disclosure can provide a uniform gas flow covering the respective opening 15, 16 with a gas curtain, allowing radiation to pass from one section to the other while blocking passage of a range of particles.

[00069] 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. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[00070] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic 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 an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions. [00071] 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 appreciated that the invention, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography. [00072] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Features of respective embodiments may, for instance, be combined. 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 claims set out below.

Claims

1. A nozzle for providing a gas outflow, the nozzle (18) comprising: a main channel (20); the main channel opening into at least one flow restriction section (22) at a downstream end of the main channel, each flow restriction section having a plurality of parallel vanes (24) for creating a uniform gas flow; the at least one flow restriction section opening into a respective outflow section (26) having an increasing cross-sectional area towards an open end (28) thereof adapted to provide the gas outflow.

2. The nozzle of claim 1, the main channel (20) branching into two branch channels (30, 32), each branch channel opening into a respective flow restriction section (22) at a downstream end of the respective branch channel.

3. The nozzle of claim 1 or 2, the main channel comprising at least one flow distribution section (34, 36) at a downstream end, a side of the at least one flow distribution section opening into a respective flow restriction section (22b, 22c).

4. The nozzle of claim 3, wherein a cross-sectional area of the at least one flow distribution section (34, 36) decreases towards the downstream end (38).

5. The nozzle of claim 3 or 4, the two branch channels (30, 32) branching outward from the main channel (20), and the respective flow distribution section (34, 36) being directed inward, the downstream end of one flow distribution section (34) facing towards the downstream end of the other flow distribution section (36).

6. The nozzle of one of the previous claims, comprising: a first plate (40) in which the main channel and the flow restriction section and the outflow section are recessed, and a second plate (42) covering at least said recessed main channel and the flow restriction section and the outflow section in the first plate.

7. The nozzle of one of the previous claims, wherein a gap is present between a top end of the vanes (24) and the second plate (42).

8. A lithographic apparatus comprising at least one nozzle according to one of claims 1 to 7.

9. The lithographic apparatus of claim 8, comprising: an illumination section (IL); a reticle stage (RS); a projection system (PS); and a first nozzle arranged at an interface between the illumination section (IL) and the reticle stage (RS) and/or a second nozzle arranged at an interface between the reticle stage (RS) and the projection system (PS).

10. The lithographic apparatus of claim 8 or 9, the at least one nozzle providing a uniform gas flow along an opening to block a range of particles from passing through said opening while allowing passage of radiation through the opening.

11. A method of fabricating a nozzle, the method comprising the steps of: providing a main channel (20); providing at least one flow restriction section (22) at a downstream end of the main channel, each flow restriction section having a plurality of parallel vanes (24) for creating a uniform gas flow; the at least one flow restriction section opening into a respective outflow section (26) having an increasing cross-sectional area towards an open end (28) thereof adapted to provide the gas flow out.

12. The method of claim 10 , comprising the steps of: recessing the main channel, the flow restriction section and the outflow section in a first plate (40), and covering the first plate (40) with a second plate (42) thereby covering at least the main channel, the two branched channels, and the flow restriction section.

13. The method of claim 12, comprising the step of arranging a brazing foil (44) between the first plate and the second plate, and connecting the first plate to the second plate by brazing.