WO2024022796A1

WO2024022796A1 - Apparatus for and method of supplying gas to a lithography system

Info

Publication number: WO2024022796A1
Application number: PCT/EP2023/069096
Authority: WO
Inventors: Qiushi ZHU; Kevin Weimin Zhang; Yue Ma
Original assignee: Asml Netherlands B.V.
Priority date: 2022-07-26
Filing date: 2023-07-11
Publication date: 2024-02-01

Abstract

Degradation of the reflectivity of one or more reflective optical elements in a system for generating EUV radiation is reduced by the introduction of a small amount of a first gas into a vacuum chamber containing the optical element, with the first gas being separated from a starting gas such as CDA or XCDA. The first gas may be added to the flow of another gas such as hydrogen.

Description

APPARATUS FOR AND METHOD OF SUPPLYING GAS TO A LITHOGRAPHY SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This applications claims priority to US application 63/392,208 which was filed on 26 July 2022 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present disclosure relates to systems for the production of radiation for lithography systems. Such systems typically use reflective optical elements arranged in a vacuum environment. The process of generating and controlling extreme ultraviolet (EUV) radiation in such systems tends to degrade the reflectivity of these optical elements over time. An example of such an environment is the vacuum chamber of an EUV source in which a plasma is created through discharge or laser ablation of a target or source material. In this application, the optical elements are used, for example, to collect and direct the radiation for use outside of the chamber (but still in vacuum), e.g., for semiconductor photolithography. Another example is the vacuum chamber housing the optics for the projection system of such an apparatus.

BACKGROUND

[0003] EUV radiation, e.g., electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays) and including radiation at a wavelength of about 13.5 nm, can be used in photolithography processes to produce extremely small features in substrates such as silicon wafers.

[0004] Some methods for generating EUV radiation include converting a target material (also called a source material) from a liquid state into a plasma state. The target material preferably includes at least one element, e.g., xenon, lithium, or tin, with one or more emission lines in the EUV range. In one such method, a laser produced plasma (“LPP”) method, the required plasma can be produced by using a laser beam to irradiate a target material having the required line-emitting element.

[0005] In more theoretical terms, LPP sources generate EUV radiation by depositing laser energy into a target material having at least one EUV emitting element, such as xenon (Xe), tin (Sn), or lithium (Li), creating a highly ionized plasma with electron temperatures of several 10’s of eV. One LPP technique involves generating a stream of target material droplets and irradiating at least some of the droplets with laser radiation pulses.

[0006] The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma in all directions. In one common arrangement, a near -normal-incidence mirror (often termed a “collector mirror” or simply a “collector”) is positioned to collect, direct, and, in some arrangements, focus the radiation to an intermediate location. The collected radiation may then be relayed from the intermediate location to a set of scanner optics and ultimately to a wafer. [0007] In the EUV portion of the spectrum it is generally regarded as necessary to use reflective optics for the collector and other EUV optics. At the wavelengths involved, the collector is advantageously implemented as a multi-layer mirror (“MLM”). As its name implies, this MLM is generally made up of alternating layers of material over a foundation or substrate.

[0008] The optical element must be placed within the vacuum chamber with the plasma to collect and redirect the EUV radiation. The environment within the chamber is inimical to the optical element and so limits its useful lifetime, for example, by degrading its reflectivity by any one or a combination of several mechanisms. For example, an optical element within the environment may be exposed to high energy ions or particles of target material which can contaminate the optical element’s exposed surface. Particles of target material can also cause physical damage and localized heating of the optical element. The target material may be particularly reactive with a material making up at least one layer of the optical element surface. Temperature stability, ion-implantation, and diffusion problems may need to be addressed even with less reactive target materials, e.g., tin, indium, or xenon. Blistering of the MLM coating must also be avoided. Target material may also deposit on the surface of the optical element.

[0009] There are techniques which may be employed to increase optical element lifetime despite these harsh conditions. For example, a capping layer may be placed on the optical element to protect the surface of the optical element. To make the capping layer more reflective it may also have multiple layers spaced to increase reflectivity at the wavelength of the radiation to be reflected. Such capping layers are, however, themselves prone to damage through mechanisms such as reduction, hydrogen diffusion, and blistering.

[0010] In some systems molecular hydrogen (H2) gas at pressures in the range of about 0.5 to about 3 mbar is used in the vacuum chamber for target material debris mitigation. Hydrogen is relatively transparent to EUV radiation having a wavelength of about 13.5 nm. H2 gas is introduced into the vacuum chamber to slow down by collisions with the gas molecules the energetic debris (ions, atoms, and clusters) of target material created by the plasma. For this purpose a flow of H2 gas is used which may also be counter to the debris trajectory. This flow serves to reduce the damage of deposition, implantation, and sputtering of target material on the optical coating of the optical element.

[0011] In addition to hydrogen, small amounts of other gases may be introduced into the chamber to extend the lifetime of optics within the chamber. Which non-hydrogen gas to use will in generally depend on the chemical composition of the outer layers of the optics, such as, for example, the chemical composition of the capping layer of an MLM. It may be that the facility in which the chamber is deployed, however, may not have access to a ready supply these non-hydrogen gases. It is in this context that the need for the present invention arises.

SUMMARY

[0012] The following presents a concise summary of one or more embodiments in order to provide a basic understanding of those embodiments. This summary is not an extensive overview of all contemplated variations and is not intended to identify key or critical elements of all embodiments nor set limits on the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a streamlined form as a prelude to the more detailed description that is presented later.

[0013] According to one aspect of an embodiment there is disclosed a system for controlling a composition of a gas supplied to a portion of a lithographic apparatus, the system comprising an inlet adapted to be connected to a source of a starting gas, the starting gas comprising a first gas component and a second gas component, a gas fractionator in fluid communication with the inlet and arranged to receive the starting gas and adapted to produce a produce a separated gas having concentrated first gas component, and an outlet in fluid communication with the gas fractionator and arranged to receive separated gas and adapted to be connected to be in fluid communication with the portion of the lithographic apparatus to supply the separated gas to the portion of the lithographic apparatus.

[0014] The first gas may comprise oxygen. The first gas may comprise nitrogen. The portion of the lithographic apparatus may comprise an extreme ultraviolet (EUV) light source. The portion of the lithographic apparatus may comprise a scanner. The starting gas may comprise clean dry air (CD A). The starting gas may comprise extra clean dry air (XCDA).

[0015] The gas fractionator may comprise at least one membrane filter. The gas fractionator may comprise a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters. The gas fractionator may comprise at least one molecular sieve.

[0016] The starting gas may have a second gas concentration greater than 75% by volume and the separated gas may have a second gas concentration less than 5 % by volume.

[0017] The gas fractionator may comprise a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve. The second molecular sieve is not used while the first molecular sieve is being used, with the system further comprising a replacement condition sensing module arranged to sense a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and a controller responsively connected to the replacement condition sensing module and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition.

[0018] The replacement condition may be at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge. The replacement condition sensing module may comprise a first gas concentration sensor arranged to sense a concentration of the first gas in the separated gas and to generate a signal indicative of the concentration of the first gas in the separated gas and the system further may comprise a controller responsively connected to the first gas concentration sensor and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

[0019] The system may further comprise a hydrogen feed line arranged to feed a hydro gen-containing gas into the portion of the lithographic apparatus and wherein the outlet is in fluid communication with the hydrogen feed line to inject the separated gas into the hydrogen feed line.

[0020] According to another aspect of an embodiment there is disclosed a lithographic apparatus including an extreme ultraviolet (EUV) light source system, the lithographic apparatus comprising a chamber including a collector mirror, a hydrogen feed line arranged to feed hydrogen-containing gas into the chamber, an inlet adapted to be connected to a source of a starting gas, the starting gas comprising a first gas component, a gas fractionator in fluid communication with the inlet and arranged to receive the starting gas and adapted to at least partially separate the first gas component from the starting gas to produce a separated gas having a concentrated first gas component, and an outlet in fluid communication with the gas fractionator and arranged to receive the separated gas and connected in fluid communication with the hydrogen feed line to inject the separated gas into the hydrogen feed line to supply the concentrated first gas component to the chamber.

[0021] The first gas may comprise oxygen. The first gas may comprise nitrogen. The gas fractionator may comprise at least one membrane filter. The gas fractionator may comprise a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters. The gas fractionator may comprise at least one molecular sieve. The starting gas may have a second gas concentration greater than 75% by volume and the separated gas may have a second gas concentration less than 5 % by volume.

[0022] The gas fractionator may comprise a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve. The second molecular sieve is not used while the first molecular sieve is being used, and the system further comprises a replacement condition sensing module arranged to sense a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and a controller responsively connected to the replacement condition sensing module and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition. The replacement condition may be at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge.

[0023] The replacement condition sensing module may comprise a first gas concentration sensor arranged to sense a concentration of the first gas in the separated gas and to generate a signal indicative of the concentration of the first gas in the separated gas, and the system further may comprise a controller responsively connected to the first gas concentration sensor and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

[0024] According to another aspect of an embodiment there is disclosed a method of controlling a composition of a gas supplied to a portion of a lithographic apparatus, the method comprising supplying a starting gas, the starting gas comprising a first gas component, at least partially separating the first gas component from the starting gas to produce a separated gas having a concentrated first gas component, and supplying the separated gas to the portion of the lithographic apparatus.

[0025] The first gas component may comprise primarily oxygen. The first gas component may comprise primarily nitrogen. The portion of the lithographic apparatus may comprise an extreme ultraviolet (EUV) light source portion. The portion of the lithographic apparatus may comprise a scanner.

[0026] Supplying the starting gas may comprise supplying clean dry air (CD A). Supplying the starting gas may comprise supplying extra clean dry air (XCDA).

[0027] At least partially separating the first gas component to produce the separated gas is performed using at least one membrane filter. At least partially separating the first gas component to produce the separated gas is performed using a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

[0028] The partially separating the first gas to produce separated gas may be performed using at least one molecular sieve.

[0029] The starting gas may have a second gas concentration greater than 75% by volume and the separated gas may have a second gas concentration less than 5 % by volume.

[0030] At least partially separating the first gas component to produce the separated gas is performed using a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve. The second molecular sieve is not used while the first molecular sieve is being used, and the method further comprises sensing a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and initially directing the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition.

[0031] The replacement condition may be at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge. Sensing the replacement condition may comprise sensing a first gas concentration of the first gas in the separated gas and generating a signal indicative of the concentration of the first gas in the separated gas, and initially directing the starting gas through the first molecular sieve for a first period of time and switching to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas. [0032] Supplying the separated gas to the portion of the lithographic apparatus may comprise injecting the separated gas into a hydrogen feed line arranged to feed a hydrogen-containing gas into the portion of the lithographic apparatus.

[0033] According to another aspect of an embodiment there is disclosed a method of controlling a composition of a gas supplied to an extreme ultraviolet (EUV) light source portion of a lithographic apparatus, the method comprising feeding a hydrogen-containing gas into a hydrogen feed line arranged to feed the hydrogen-containing gas into a chamber of the EUV light source, the chamber including a collector mirror, supplying a starting gas, the starting gas comprising a first gas component, at least partially separating the first gas component to produce a separated gas having a concentrated first gas component, and injecting the concentrated first gas component into the hydrogen feed line to supply the concentrated first gas component to the chamber.

[0034] At least partially separating the first gas component to produce the separated gas is performed using at least one membrane filter. At least partially separating the first gas component to produce the separated gas is performed using a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters. At least partially separating the first gas component to produce the concentrated first gas component is performed using at least one molecular sieve.

[0035] The starting gas may have a second gas concentration greater than 75% by volume and the concentrated first gas component may have a second gas concentration less than 5 % by volume.

[0036] At least partially separating the first gas component to produce the separated gas is performed using a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve. The method may further comprise directing the starting gas through the first molecular sieve, sensing a concentration of the first gas in the separated gas and generating a signal indicative of the concentration of the first gas in the separated gas, and ceasing directing the starting gas through the first molecular sieve and directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

[0037] According to another aspect of an embodiment there is disclosed an apparatus for producing a separated gas, the apparatus comprising a starting gas input, the starting gas having a first oxygen concentration, a gas separator in fluid communication with the starting gas input and having a first sieve filter member and a second sieve filter member, the gas separator being arranged to separate the separated gas from the starting gas, the separated gas having a second oxygen concentration greater than the first oxygen concentration, an oxygen delivery line in fluid communication with the gas separator, an oxygen sensor in fluid communication with the oxygen delivery line and arranged to sense an oxygen concentration in the separated gas, a controller capable of switching the gas separator between a first mode of operation in which the gas separator uses the first sieve filter member but not the second sieve filter member to separate the separated gas from the starting gas and a second mode of operation in which the gas separator uses the second sieve filter member but not the first sieve filter member to separate the separated gas from the starting gas, and a gas control panel capable of adjusting an amount of oxygen from the oxygen delivery line to be delivered to a hydrogen delivery line arranged to deliver gas to a source of extreme ultraviolet radiation. The starting gas may comprise clean dry air (CD A). The starting gas may comprise extra clean dry air (XCDA).

[0038] The first filter element may comprise a first molecular sieve filter and the second filter element may comprise a second molecular sieve filter. The apparatus may further comprise a flashback arrestor (FBA) downstream of the filter on the oxygen delivery line. The apparatus may further comprise an oxygen sensor positioned in the oxygen delivery line downstream of the gas separator.

[0039] The apparatus may further comprise a nitrogen delivery line adapted to deliver nitrogen from the gas separator. The apparatus may further comprise a vent line adapted to controllably vent the nitrogen delivery line and the oxygen delivery line. The controller or a further controller may be adapted to open and close the vent line.

[0040] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated herein and form part of this specification, illustrate the embodiments and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the relevant art(s) to make and use the embodiments. [0042] FIG. 1 is a not-to-scale diagram of an overall broad conception for an EUV lithography system. [0043] FIG. 2A is a partially perspective not-to-scale view of an optical element and gas flow system for an EUV lithography system.

[0044] FIG. 2B is a not-to-scale diagram of an optical element and gas flow system for an EUV lithography system.

[0045] FIG. 3 is a not-to-scale diagram of an overall broad conception for a system for adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0046] FIG. 4 is a not-to-scale diagram of an overall broad conception for another system for adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0047] FIG. 5 is a not-to-scale diagram of an overall broad conception for another system for adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0048] FIG. 6 is a not-to-scale diagram of a gas fractionator for a system for adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0049] FIG. 7 is a not-to-scale diagram of another gas fractionator for a system for adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0050] FIG. 8 is a flowchart of a method of adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0051] FIG. 9 is a flowchart of a method of operating a gas fractionator in a system for adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0052] FIG. 10 is a flowchart of a method of operating a gas fractionator in a system for adding first gas to a chamber in an EUV lithography system according to an aspect of an embodiment.

[0053] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. The embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art based on the teachings contained herein.

DETAILED DESCRIPTION

[0054] Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to promote a thorough understanding of one or more embodiments. It may be evident in some or all instances, however, that any embodiment described below can be practiced without adopting the specific design details described below. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate description of one or more embodiments. In the description that follows and in the claims the terms “up,” “down,” “top,” “bottom,” “vertical,” “horizontal,” and like terms may be employed. These terms are intended to show relative orientation only and not any orientation with respect to gravity unless otherwise indicated or clear from context.

[0055] FIG. 1 is a diagrammatic view of an example of an EUV radiation source, e.g., a laser produced plasma EUV radiation source 100 according to one aspect of an embodiment of the present invention. As shown, the EUV radiation source 100 may include a pulsed or continuous laser source 122, which may for example be a pulsed gas discharge CO2 laser source producing a beam 112 of radiation at 10.6 pm or 1 pm. The pulsed gas discharge CO2 laser source may have DC or RF excitation operating at high power and at a high pulse repetition rate.

[0056] The EUV radiation source 100 also includes a target delivery system 124 for delivering target material in the form of liquid droplets or a continuous liquid stream. In this example, the target material is a liquid, but it could also be a solid or gas. Tin is used as a nonlimiting example of a target material in the description which follows with the understanding that other materials could be used. Also, droplets are used as a nonlimiting example of the form of the tin with the understanding that other forms could be used

[0057] In the system depicted the target material delivery system 124 introduces droplets 114 of the target material into the interior of a vacuum chamber 126 having a chamber wall 127. The vacuum chamber 126 includes an irradiation region 128 where the target material may be irradiated to produce plasma. It should be noted that as used herein an irradiation region is a region where target material irradiation may or is intended to occur and is an irradiation region even at times when no irradiation is actually occurring. The EUV light source may also include a beam steering system 132.

[0058] In the system shown, the components are arranged so that the droplets 114 travel substantially horizontally. The direction from the laser source 122 towards the irradiation region 128, that is, the nominal direction of propagation of the beam 112, may be taken as the Z axis. The path the droplets 114 take from the target material delivery system 124 to the irradiation region 128 may be taken as the X axis. The view of FIG. 1 is thus normal to the XZ plane. While a system in which the droplets 114 travel substantially horizontally is depicted as an example, it will be understood by one having ordinary skill in the art that other arrangements can be used in which the droplets travel vertically or at some angle with respect to gravity between and including 90° (horizontal) and 0° (vertical).

[0059] The EUV radiation source 100 may also include an EUV light source controller system 160 and a laser firing control system 165. The EUV radiation source 100 may also include a detector such as a target position detection system 170 that generates an output indicative of the absolute or relative position of a target droplet, e.g., relative to the irradiation region 128, and provide this output to a target position detection feedback system 162.

[0060] As shown in FIG. 1, the target material delivery system 124 may include a target delivery control system 190. The target delivery control system 190 adjusts the path of the target droplets 114 through or around the irradiation region 128. This adjustment may be accomplished, for example, by repositioning the point at which a droplet generator 192 releases the target droplets 114. The droplet release point may be repositioned, for example, by tilting the droplet generator 192 or by laterally translating the droplet generator 192. The droplet generator 192 extends into the chamber 126 and is preferably externally supplied with target material. A gas source (not shown) places the target material in droplet generator 192 under pressure. Droplets 114 that pass through the irradiation region 128 without being transformed continue to a target material receptacle 134.

[0061 ] Continuing with FIG. 1 , the radiation source 100 may also include one or more optical elements. In the following description, a collector 130 is used as an example of such an optical element, but the description applies to other optical elements as well. The collector 130 may be a normal incidence reflector, for example, implemented as a multilayer mirror. The collector 130 may be in the form of a prolate ellipsoid, with a central aperture 135 to allow the laser radiation 112 to pass through and reach the irradiation region 128. The collector 130 has a first focus at the irradiation region 128 and a second focus at a so-called intermediate point 140 (also called the intermediate focus 140) where the EUV radiation may be output from the EUV radiation source 100 and input to, e.g., an integrated circuit lithography scanner 150.

[0062] The integrated circuit lithography scanner 150 includes a projection system (e.g. a refractive or reflective projection lens system) 156, also referred to as a projection optics box or POB, configured to project a pattern imparted to the radiation beam by patterning device 154 (e.g., a mask) onto a target portion (e.g. comprising one or more dies) of a substrate 152. The substrate 152 is then additionally processed in a known manner to make an integrated circuit device.

[0063] As mentioned above, hydrogen may be introduced into the chamber 126 to mitigate debris contamination. In general, however, the environment in the chamber 126 and the projection system 156 is intended to be as clean as possible, (lowest possible levels of other gases such as oxygen, nitrogen, H2O etc.) to reduce any oxidation risk or unwanted chemical reactions, for example, with either tin or plasma in the chamber 126 as these could cause collector degradation. Also, for example, oxygen can undesirably cause oxidation of other components in the vacuum chamber 126 such as the nozzle of the droplet generator 192.

[0064] It has, however, been determined that the presence of low levels of gases which would otherwise be regarded as impurities in the chamber atmosphere can have a positive effect on preserving or enhancing performance, e.g., reflectivity and longevity, of optical elements in the chamber. It is thus potentially advantageous to deliberately supply a controllable amount of such a gas, gases, or a mixture of such gases into, for example, the vacuum chamber of the source or the projection system. These gases can be supplied, for example, either in an air mixture (air, clean dry air (CD A), or extra clean dry air (XCDA)) or mixed with a noble or inert gas (e.g. argon).

[0065] As mentioned, one of the gases that may be beneficial in low concentrations is oxygen. Oxygen will be used as an example of a nonhydrogen first gas to be introduced into the chamber but it will be understood that depending on the chemical composition of the exposed surfaces of the optical components in the chamber another gas such as nitrogen could be used.

[0066] One method of adding oxygen gas to the vacuum chamber is to bleed the oxygen gas into the flow of hydrogen gas into the chamber. For example, oxygen can be added to the vacuum chamber by adding it to the hydrogen flow passing close to the collector to increase the local concentration of the oxygen to a level that stabilizes the collector capping layer without consuming a significant amount of H* in a water-gas reaction or without oxidizing key components in the chamber.

[0067] There are, however, engineering risks and challenges associated with using oxygen. The use of either pure oxygen facilities such as oxygen facility supply lines or compressed bottled oxygen gas incurs significant costs and raises significant safety concerns. Retrofitting an installed EUV tool to use such pure oxygen facilities can result in extended down times and major alterations in the gas supply infrastructure for these tools, especially for installations that do not already have pure 02 facilities.

[0068] The above discussion is primarily in terms of a reflective optic located in the source vacuum chamber. The beneficial effects of adding a mitigation gas to the gas mixture in a vacuum chamber also extend to reflective EUV optics located in other parts of the system, such as the reflective optical elements in the POB. For example, mitigation gas can be added to the gas mix in the vacuum chamber of the POB to inhibit etching of the surfaces of reflective optical elements that are located there and mitigate SiH4 formation. More specifically, the patterning device 154 is also in a vacuum environment, sometimes referred to as the reticle stage or the reticle micro-environment. Low concentrations of a gas such as oxygen can be added here to mitigate SiH4 formation.

[0069] In the source it is desirable, for at least some applications, that the flow of the hydrogen / oxygen gas mixture be established to flow across (i.e., adjacent to and with a velocity component parallel to) at least part of the surface of the EUV reflective optic. This can be accomplished, for example, by adding outlets to a system for flowing hydrogen in the chamber and then adding the oxygen to the flow of hydrogen. As mentioned, the collector 130 may be in the form of a prolate ellipsoid, with an aperture 135 to allow the laser radiation to pass through and reach the irradiation region 128. This is shown in FIGS. 1, 2A and 2B. The aperture 135 extends through the reflective surface 200 of the collector mirror 130. The aperture 135 is located on an axisymmetric line A of the collector 130. A tubular body 210 extends through the aperture 135. A frustoconical element 220 surrounds the tubular body 210 and is spaced away from the tubular body 210 to define a gap 230 between them.

[0070] The word “tubular” will be understood by the skilled person as a broad term, which may encompass or be synonymous with a variety of different structures. For example, a tubular body may not have parallel walls, but could instead be conical or flared. The tubular body may be any structure that forms a conduit from one side of the collector (e.g. a non-collecting surface) to another, opposite side of the collector (e.g. a collecting surface). The tubular body might have a circular cross-section, or an elliptical cross-section, or any other suitable cross-section.

[0071] In use, a main gas flow is directed through the tubular body 210 which, in this embodiment, is constructed and arranged to guide the gas flow in a direction transverse to the reflective surface 200. This flow is referred to as cone flow, designated by the arrow OF in FIG. 2B. Typically, the cone flow CF is directed toward one or both of the first focal point and the second focal point. The gap 230 between the tubular body 210 and the frustoconical element 220 surrounding the tubular body 210 is arranged together with outlets 250 in a circumferential flow ring 240 to guide gas flow substantially along the reflective surface 200, and away from the tubular body 210 as shown. This flow is referred to as umbrella cone flow or simply umbrella flow, designated by the arrows UF in FfG. 2B. The flow along the surface of the collector 130 towards the center from the circumference can be referred to as the perimeter flow, labelled PF in FIG 2B.

[0072] The rate of the cone flow for hydrogen may be in the range of about 50 SLM to about 165 SLM. The rate of the umbrella cone flow for a hydrogen gas mixture may be in the range of about 40 SLM to about 90 SLM. The rate of the perimeter flow for a hydrogen gas mixture may be in the range of about 60 SLM to about 160 SLM. Under these type of H2 flows, oxygen flow is from about 0.002 to about 0.8 SCCM. Total pressure in the chamber 126 may be in the range of about 1.2 mbar to about 2.2 mbar. Other flow rates and pressures may be used in other embodiments.

[0073] Alternatively there could be a gas manifold system dedicated to flowing oxygen across the surface of the EUV reflective optic in which the apertures / nozzles directed to flow gas along the surface of (with a velocity component substantially locally parallel to) the local surface of the collector 30 are supplied only with oxygen. [0074] Thus, the presence of trace amounts of a first gas such as oxygen or nitrogen in the chamber of the source or the scanner optics in an EUV lithography system can extend the lifetime of optics in the chamber. On the other hand, trace amounts of other gases in such environments can reduce the lifetime of those optics depending on the chemical composition of their exposed surfaces. For example, nitrogen may react with the exposed surfaces of optics having a given chemical composition. For surfaces having other chemical compositions, it may be beneficial to introduce nitrogen but detrimental to introduce oxygen.

[0075] Again using the example of oxygen as the first gas, current lithography tools may be installed at sites that lack oxygen facilities. Therefore, at such sites, the oxygen component of XCDA is used as an alternative pure oxygen as a supply gas to introduce oxygen into the gas in the chamber. This provides inferior optics protection because of the other gases in the XCDA, notably nitrogen at about 78 vol% (volume ratio [molN2/molXCDA]), which participates in surface chemical reactions and plasma interactions. Therefore, it would prove beneficial to reduce the amount of nitrogen in the XCDA gas mixture.

[0076] In accordance with an aspect of an embodiment, these drawbacks are avoided by using XCDA or CDA supply gas as an oxygen source and separating out a majority of nitrogen and injecting the low- nitrogen-content gas into the EUV source or scanner chamber. Using such a system, a reduction of nitrogen from 78 vol% in the gas mixture upstream to the apparatus to less than 5 vol% downstream is possible, a reduction of a factor of sixteen or more.

[0077] The apparatus can flow oxygen-rich/nitrogen-lean gas into the vessel with reduced nitrogen concentration to not greater than 5 vol%, without a gas supply infrastructure upgrade. Similarly, the apparatus can flow nitrogen-rich/oxygen-lean gas into the vessel without a gas supply infrastructure upgrade. As a consequence, systems in the field can be retrofitted without significant down time.

[0078] FIG. 3 is a not-to-scale diagram of an overall broad conception for a system 300 for adding oxygen to a chamber in an EUV lithography system according to an aspect of an embodiment. The system 300 includes a hydrogen source 310. The hydrogen source 310 feeds hydrogen to various flows through inlets to the chamber 126, shown in FIG. 1. For example, the hydrogen source 310 supplies hydrogen to a peripheral flow system 330 through a hydrogen feed line 340. Similarly, the hydrogen source 310 feeds hydrogen to an umbrella cone flow system 350 through hydrogen feed line 355. It will be understood that these feedlines may be consolidated.

[0079] Also shown in FIG. 3 as part of the system 300 is a gas supply 360. This gas supply 360 is a source of, for example, CDA or XCDA. The gas supply 360 supplies oxygen and nitrogen, labeled first gas Gi and second gas G2, as the major components of CDA or XCDA, to a gas fractionator 370 through a line 365. The gas fractionator 370 separates the oxygen component from the nitrogen component in the gas supplied to it. Here and elsewhere herein, the term “component” is used to refer to gases Gi and G2 such as can be separated by conventional gas separation methods with a purity such as can be achieved by conventional gas separation methods. The oxygen component then passes down an oxygen line 380.

[0080] In the example in FIG. 3 the oxygen component then passes through a mixing node 320 to join the hydrogen feed through hydrogen feed line 340 and to a mixing node 325 to join hydrogen feed to the umbrella cone flow system 350 through a line 355. The nitrogen component from the gas fractionator 370 passes along an exhaust line 390 to an exhaust 395. Thus in this system the oxygen is directed to the chamber as Gi and nitrogen is exhausted as G2. It will be apparent that the system can be configmed so that nitrogen is directed to the chamber 126 as Gi and oxygen is exhausted as G2. A controller 327 may be provided to control the amount of oxygen that is mixed into the hydrogen lines 340 and 355.

[0081] The system 300 as described above includes a flashback arrestor (FBA) 385 between the gas fractionator 370 and the mixing nodes 320, 325 designed in a known manner to contain a flashback and prevent it from propagating back into upstream equipment. The system 300 also includes a vent line 397 controllably connected to the oxygen line 380 and the exhaust line 390 by mixing nodes 398 and 399, respectively. Gas can be passed to the vent line 397, for example, depending on an oxygen duty cycle input from the controller 327. One of ordinary skill in the art will understand that a system such as system 300 and the other systems described herein will also typically include other conventional gas handling components such as hoses, orifices, inlets, outlets, connectors, regulators, gauges, sensors, valves, injection controls, bypass lines, vents, and the like as may be dictated by the requirements of a given design. Such components are generally commercially available.

[0082] FIG. 4 is a not-to-scale diagram of an overall broad conception for a system 400 for adding a gas such as oxygen to a chamber in an EUV lithography system according to an aspect of an embodiment. The system 400 of FIG. 4 is similar to the system 300 of FIG. 3 except that the hydrogen source 310 is arranged to provide hydrogen to scanner optics 410 through a mixing node 420.

[0083] FIG. 5 is a not-to-scale diagram of an overall broad conception for a system 500 for adding a gas mixture to a chamber in an EUV lithography system according to an aspect of an embodiment. The system 500 of FIG. 5 is similar to the system 300 of FIG. 3 and the system 400 of FIG. 4 except that the hydrogen source 310 is arranged to provide hydrogen to peripheral flow system 330, umbrella cone flow system 350, and scanner optics 410.

[0084] FIG. 6 is a not-to-scale diagram of a gas fractionator 370 for a system for adding oxygen to a chamber in an EUV lithography system according to an aspect of an embodiment. The gas fractionator 370 shown in FIG. 6 includes a first molecular sieve 610 and a second molecular sieve 620. Each of the first molecular sieve 610 and the second molecular sieve 620 may be implemented as a cartridge in which case the depicted combination of the sieves may be regarded as a dual cartridge configuration. According to an aspect of an embodiment, the sieves are arranged so that only one of them is in use at a time. Control of which of the sieves is in use at a given time is carried out by a controller 640 by controlling valves 650, 655, 660, and 665. The controller 640 performs this control in response to a signal from a sensor 630, which senses the concentration of the added gas component flowing out from the gas fractionator 370. When the sensor 630 detects that the added gas concentration has fallen below a given threshold, indicating that the sieve being used at the time is spent, the controller 640 controls the valves to switch out the spent sieve, i.e., take it offline, and to switch in the other sieve, i.e., put it online. The spent sieve can then be permitted to self-regenerate or may be swapped out without interrupting operation of the gas fractionator 370.

[0085] The above is an example of a system and method in which a replacement condition is detected or sensed, a replacement condition being a condition which indicates that the unit (cartridge or sieve) currently being used is spent and indicating the need to switch over to the use of another unit. The specific example above is the case of when the replacement condition is detected by sensing the gas concentration in the separated component of the gas. This gas concentration will tend to fall off as the gas fractionator is used. When the gas concentration falls below a predetermined threshold, then it is necessary or at least desirable to discontinue use of the unit currently in use by taking it offline, and then bringing the alternative unit online.

[0086] Another possible replacement condition is the total amount of supply gas that has been processed by the unit that is currently in use. Towards this end, a system 300 such as that shown in FIG. 3, system 400 such as that shown in FIG. 4, system 500 such as that shown in FIG. 5, and the systems of FIGS. 6 and 7 may be provided with a flowmeter such as flowmeter 365 of FIG. 6 that measures the volume of supply gas that has passed to the sieve in use and supplies a signal indicative of that volume to the controller 640 which can use the measurement to determine whether to initiate a swap of the active sieve. Another possible replacement condition may be the total operation time of the currently active sieve. The controller 640, for example, may keep track of the total amount of time the active sieve has been in use and can use that measurement to switch to the inactive sieve.

[0087] Thus, the dual cartridge setup described above allows for one sieve to be in operation while the other is self-regenerating or replaced. Dual cartridge molecular sieve filters capable of generating sufficient added gas for intended added gas dose levels in an EUV source or scanner may have a very small footprint - under a few inches in its largest dimension and a kilogram or so in weight - and require only enough electrical power to separate nitrogen and oxygen from a CDA or XCDA or other air source. It is expected that a single unit will be sufficient to supply oxygen gas to multiple source and scanner systems with only minimal changes to existing gas infrastructures.

[0088] FIG. 7 is a not-to-scale diagram of another gas fractionator 370’ for a system for adding gas to the mixture in a chamber in an EUV lithography system according to an aspect of an embodiment. The gas fractionator 370’ shown in FIG. 7 has N membrane separation filters 710, 720, . . . 730 to separate oxygen from nitrogen in a known manner. One of ordinary skill in the art will understand that one membrane gas separation filter may be used or more than one gas membrane filters may be placed in series with each passing at least partially separated gas to the next membrane filter in the series, until the desired concentration of oxygen is achieved.

[0089] The embodiment of FIG. 7 also uses XCDA or CDA or even air as a feed or supply gas, separates out the majority of nitrogen, and injects the outlet low-nitrogen content gas into EUV source or scanner. The reduction of nitrogen is from 80 vol% in the gas mixture upstream to the apparatus to less than 30 vol% downstream, a reduction factor of 2.5 or greater.

[0090] A standard membrane filter module may also have a very small footprint, under a few inches in its largest dimension and a kilogram or so in weight, and requires no external power to separate nitrogen from gas supplied by a supply source.

[0091] FIG. 8 is a flowchart of a method of adding a first gas such as oxygen to a chamber in an EUV lithography system according to an aspect of an embodiment. In a step S100 starting gas having a first gas component and a second gas component (e.g., nitrogen) is supplied to a system for generating concentrated first gas. In a step SI 10, the first gas component is separated from the starting gas. In a step S120, the separated first gas is supplied to a source chamber or scanner chamber. In the particular example shown in FIG. 8, the separated first gas component injected into a hydrogen feed line supplying hydrogen to either of these chambers. The method of FIG. 8 also applies when another component is separated out of the starting gas for use such as nitrogen.

[0092] FIG. 9 is a flowchart of a method of operating a gas fractionator in a system for adding a first gas to a chamber in an EUV lithography system according to an aspect of an embodiment in order to enable continuous operation. In the method shown in FIG. 9, in a step S200, a first cartridge is used to separate a first gas component from a supply gas including a first gas component and a second gas. For example, the supply gas may be air, CDA or XCDA, the first gas component may be essentially oxygen and the second gas component may be essentially nitrogen. While the first cartridge is being used, there is monitoring for a replacement condition the existence of which signals a need to stop using the first cartridge and instead switch over to using the second cartridge. The replacement condition may be the first gas concentration in the first gas component falling below a given threshold. The replacement condition may be exceeding a maximum amount of supply gas that the first cartridge has processed since being put into service. The replacement condition may be exceeding a maximum amount of time that the first cartridge has processed supply gas since being put into service.

[0093] Thus, in a step S220 it is determined whether the replacement condition is present. If the replacement condition is not present, then the system continues to use the first cartridge to separate the first gas as the process reverts to step S200.

[0094] If, on the other hand, it is determined in step S220 that the replacement condition is present, then the system in a step S230 switches flow of gas through the gas fractionator to the second cartridge. Also, at that time, or at any time before the second cartridge is exhausted, the first cartridge can be replaced or allowed to self-regenerate. Then, in a step S240, the second cartridge is used to separate the first gas. In a step S260, it is determined whether a condition for replacing the second cartridge is present. Again, the replacement condition may be, for example, the first gas concentration in the first gas component falling below a given threshold. The replacement condition may be exceeding a maximum amount of supply gas that the second cartridge has processed since being put into service. The replacement condition may be exceeding a maximum amount of time that the second cartridge has processed supply gas since being put into service.

[0095] If in the step S260 it is determined that the replacement condition is not present, then the system continues to use the second cartridge to separate the first gas. If, on the other hand, it is determined in step 260 that the first gas concentration is below the predetermined threshold, then the system in a step S270 switches flow to the first cartridge, which at this point has been replaced or has regenerated and is a functionally fresh cartridge. At that or a later time before the first cartridge has been exhausted, an operator replaces the second cartridge unless the system is one in which the cartridges can selfregenerate.

[0096] It will be appreciated that the steps S220 and S260 may be performed essentially continuously by the control system.

[0097] FIG. 10 is a flowchart of a method of operating a gas fractionator in a system for adding oxygen to a chamber in an EUV lithography system according to an aspect of an embodiment in order to enable continuous operation. The method shown in FIG. 10 is similar to the method shown in FIG. 9 with the concentration of first gas in the first gas component being a specific example of a replacement condition. In the method shown in FIG. 10, in a step S200, a first cartridge is used to separate a first gas component from supply gas including a first gas component and a second gas component. While the first cartridge is being used, the first gas concentration of the gas that has been processed by the first cartridge is sensed in a step S210. In a step S220 it is determined as a replacement condition whether the first gas concentration of the gas being generated by the first cartridge is below a predetermined threshold. If it is determined that the first gas concentration is not below a predetermined threshold, then the system continues to use the first cartridge to separate the first gas.

[0098] If, on the other hand, it is determined in step S220 that the first gas concentration of the gas being generated by the first cartridge is below the determined threshold, then the system in a step S230 switches flow of gas through the gas fractionator to the second cartridge. Also, at that time, or at any time before the second cartridge is exhausted, the first cartridge can be replaced or allowed to selfregenerate. Then, in a step S240, the second cartridge is used to separate the first gas. In a step S250, the first gas concentration in the gas being generated by the second cartridge is sensed. In a step S260, it is determined whether the first gas concentration of the gas being generated by the second cartridge has fallen below a predetermined threshold. If not, then the system continues to use the second cartridge to separate the first gas. If, on the other hand, it is determined in step 260 that the first gas concentration is below the predetermined threshold, then the system in a step S270 switches flow to the first cartridge, which at this point has been replaced or has regenerated and is a fresh cartridge. At that or a later time before the first cartridge has been exhausted, an operator replaces the second cartridge unless the system is one in which the cartridges are allowed to regenerate.

[0099] It will be appreciated that the steps S210 and S250, that is, the first gas concentration sensing steps, may be performed essentially continuously by a first gas concentration sensor while either cartridge is being used and that the determination of the whether the first gas concentration falls below a predetermined threshold in steps S220 and S260 is also performed essentially continuously by the control system.

[0100] The present disclosure is made the aid of functional building blocks illustrating the implementation of specified functions. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Different divisions of functionality are possible so long as the specified functions are appropriately performed.

[0101] The above description includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing these embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is construed when employed as a transitional word in a claim. Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and/or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise.

[0102] The embodiments can be further described using the following clauses.

1. A system for controlling a composition of a gas supplied to a portion of a lithographic apparatus, the system comprising: an inlet adapted to be connected to a source of a starting gas, the starting gas comprising a first gas component and a second gas component; a gas fractionator in fluid communication with the inlet and arranged to receive the starting gas and adapted to produce a produce a separated gas having concentrated first gas component; and an outlet in fluid communication with the gas fractionator and arranged to receive separated gas and adapted to be connected to be in fluid communication with the portion of the lithographic apparatus to supply the separated gas to the portion of the lithographic apparatus.

2. The system of clause 1 wherein the first gas comprises oxygen.

3. The system of clause 1 wherein the first gas comprises nitrogen.

4. The system of clause 1 wherein the portion of the lithographic apparatus comprises an extreme ultraviolet (EUV) light source.

5. The system of clause 1 wherein the portion of the lithographic apparatus comprises a scanner.

6. The system of clause 1 wherein the starting gas comprises clean dry air (CD A).

7. The system of clause 1 wherein the starting gas comprises extra clean dry air (XCDA).

8. The system of clause 1 wherein the gas fractionator comprises at least one membrane filter. 9. The system of clause 1 wherein the gas fractionator comprises a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

10. The system of clause 1 wherein the gas fractionator comprises at least one molecular sieve.

11. The system of clause 1 wherein the starting gas has a second gas concentration greater than 75% by volume and the separated gas has a second gas concentration less than 5 % by volume.

12. The system of clause 11 wherein the gas fractionator comprises a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

13. The system of clause 12 in which the second molecular sieve is not used while the first molecular sieve is being used, the system further comprising a replacement condition sensing module arranged to sense a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and a controller responsively connected to the replacement condition sensing module and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition.

14. The system of clause 13 wherein the replacement condition is at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge.

15. The system of clause 13 wherein the replacement condition sensing module comprises a first gas concentration sensor arranged to sense a concentration of the first gas in the separated gas and to generate a signal indicative of the concentration of the first gas in the separated gas; and the system further comprises a controller responsively connected to the first gas concentration sensor and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

16. The system of clause 1 further comprising a hydrogen feed line arranged to feed a hydrogencontaining gas into the portion of the lithographic apparatus and wherein the outlet is in fluid communication with the hydrogen feed line to inject the separated gas into the hydrogen feed line.

17. A lithographic apparatus including an extreme ultraviolet (EUV) light source system, the lithographic apparatus comprising: a chamber including a collector mirror; a hydrogen feed line arranged to feed hydrogen-containing gas into the chamber; an inlet adapted to be connected to a source of a starting gas, the starting gas comprising a first gas component; a gas fractionator in fluid communication with the inlet and arranged to receive the starting gas and adapted to at least partially separate the first gas component from the starting gas to produce a separated gas having a concentrated first gas component; and an outlet in fluid communication with the gas fractionator and arranged to receive the separated gas and connected in fluid communication with the hydrogen feed line to inject the separated gas into the hydrogen feed line to supply the concentrated first gas component to the chamber.

18. The lithographic apparatus of clause 17 wherein the first gas component comprises oxygen.

19. The lithographic apparatus of clause 17 wherein the first gas component comprises nitrogen.

20. The lithographic apparatus of clause 17 wherein the gas fractionator comprises at least one membrane filter.

21. The lithographic apparatus of clause 17 wherein the gas fractionator comprises a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

22. The lithographic apparatus of clause 17 wherein the gas fractionator comprises at least one molecular sieve.

23. The lithographic apparatus of clause 17 wherein the starting gas has a second gas concentration greater than 75% by volume and the separated gas has a second gas concentration less than 5 % by volume.

24. The lithographic apparatus of clause 22 wherein the gas fractionator comprises a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

25. The lithographic apparatus of clause 24 in which the second molecular sieve is not used while the first molecular sieve is being used, the system further comprising a replacement condition sensing module arranged to sense a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and a controller responsively connected to the replacement condition sensing module and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition.

26. The lithographic apparatus of clause 25 wherein the replacement condition is at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge.

27. The lithographic apparatus of clause 25 wherein the replacement condition sensing module comprises a first gas concentration sensor arranged to sense a concentration of the first gas in the separated gas and to generate a signal indicative of the concentration of the first gas in the separated gas; and the system further comprises a controller responsively connected to the first gas concentration sensor and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

28. A method of controlling a composition of a gas supplied to a portion of a lithographic apparatus, the method comprising: supplying a starting gas, the starting gas comprising a first gas component; at least partially separating the first gas component from the starting gas to produce a separated gas having a concentrated first gas component; and supplying the separated gas to the portion of the lithographic apparatus.

29. The method of clause 28 wherein the first gas component comprises primarily oxygen.

30. The method of clause 28 wherein the first gas component comprises primarily nitrogen.

31. The method of clause 28 wherein the portion of the lithographic apparatus comprises an extreme ultraviolet (EUV) light source portion.

32. The method of clause 28 wherein the portion of the lithographic apparatus comprises a scanner.

33. The method of clause 28 wherein supplying the starting gas comprises supplying clean dry air (CDA).

34. The method of clause 28 wherein supplying the starting gas comprises supplying extra clean dry air (XCDA).

35. The method of clause 28 wherein at least partially separating the first gas component to produce the separated gas is performed using at least one membrane fdter.

36. The method of clause 28 wherein at least partially separating the first gas component to produce the separated gas is performed using a multi-stage membrane filtration system comprising a series arrangement of at least two membrane fdters.

37. The method of clause 28 wherein at least partially separating the first gas to produce separated gas is performed using at least one molecular sieve.

38. The method of clause 28 wherein the starting gas has a second gas concentration greater than 75% by volume and the separated gas has a second gas concentration less than 5 % by volume.

39. The method of clause 28 wherein at least partially separating the first gas component to produce the separated gas is performed using a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

40. The method of clause 39 in which the second molecular sieve is not used while the first molecular sieve is being used, the method further comprising sensing a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and initially directing the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition. 41. The method of clause 40 wherein the replacement condition is at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge.

42. The method of clause 40 wherein sensing the replacement condition comprises sensing a first gas concentration of the first gas in the separated gas and generating a signal indicative of the concentration of the first gas in the separated gas; and initially directing the starting gas through the first molecular sieve for a first period of time and switching to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

43. The method of clause 28 wherein supplying the separated gas to the portion of the lithographic apparatus comprises injecting the separated gas into a hydrogen feed line arranged to feed a hydrogencontaining gas into the portion of the lithographic apparatus.

44. A method of controlling a composition of a gas supplied to an extreme ultraviolet (EUV) light source portion of a lithographic apparatus, the method comprising: feeding a hydrogen-containing gas into a hydrogen feed line arranged to feed the hydrogen-containing gas into a chamber of the EUV light source, the chamber including a collector mirror; supplying a starting gas, the starting gas comprising a first gas component; at least partially separating the first gas component to produce a separated gas having a concentrated first gas component; and injecting the concentrated first gas component into the hydrogen feed line to supply the concentrated first gas component to the chamber.

45. The method of clause 44 wherein at least partially separating the first gas component to produce the separated gas is performed using at least one membrane filter.

46. The method of clause 44 wherein at least partially separating the first gas component to produce the separated gas is performed using a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

47. The method of clause 46 wherein at least partially separating the first gas component to produce the separated gas is performed using at least one molecular sieve.

48. The method of clause 44 wherein the starting gas has a second gas concentration greater than 75% by volume and the concentrated first gas component has a second gas concentration less than 5 % by volume.

49. The method of clause 44 wherein at least partially separating the first gas component to produce the separated gas is performed using a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

50. The method of clause 44 further comprising: directing the starting gas through the first molecular sieve; sensing a concentration of the first gas in the separated gas and generating a signal indicative of the concentration of the first gas in the separated gas; and ceasing directing the starting gas through the first molecular sieve and directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

51. An apparatus for producing a separated gas, the apparatus comprising: a starting gas input arranged to receive a starting gas having a first oxygen concentration; a gas separator in fluid communication with the starting gas input and having a first sieve filter member and a second sieve filter member, the gas separator being arranged to separate the separated gas from the starting gas, the separated gas having a second oxygen concentration greater than the first oxygen concentration; an oxygen delivery line in fluid communication with the gas separator; an oxygen sensor in fluid communication with the oxygen delivery line and arranged to sense the second oxygen concentration; a controller capable of switching the gas separator between a first mode of operation in which the gas separator uses the first sieve filter member but not the second sieve filter member to separate the separated gas from the starting gas and a second mode of operation in which the gas separator uses the second sieve filter member but not the first sieve filter member to separate the separated gas from the starting gas; and a gas control panel capable of adjusting an amount of oxygen from the oxygen delivery line to be delivered to a hydrogen delivery line arranged to deliver gas to a source of extreme ultraviolet radiation, wherein the starting gas comprises clean dry air (CD A) or extra clean dry air (XCDA) .

52. The apparatus of clause 51 wherein the first sieve filter member comprises a first molecular sieve filter and wherein the second sieve filter member comprises a second molecular sieve filter.

53. The apparatus of clause 51 further comprising a flashback arrestor downstream of the gas separator on the oxygen delivery line.

54. The apparatus of clause 51 further comprising an oxygen sensor positioned in the oxygen delivery line downstream of the gas separator.

55. The apparatus of clause 51 further comprising a nitrogen delivery line adapted to deliver nitrogen from the gas separator.

56. The apparatus of clause 55 further comprising a vent line adapted to controllably vent the nitrogen delivery line and the oxygen delivery line.

57. The apparatus of clause 56 wherein the controller or a further controller is adapted to open and close the vent line.

[0103] The above described implementations and other implementations are within the scope of the following claims.

Claims

2. The system of claim 1 wherein the first gas comprises oxygen.

3. The system of claim 1 wherein the first gas comprises nitrogen.

4. The system of claim 1 wherein the portion of the lithographic apparatus comprises an extreme ultraviolet (EUV) light source.

5. The system of claim 1 wherein the portion of the lithographic apparatus comprises a scanner.

6. The system of claim 1 wherein the starting gas comprises clean dry air (CD A).

7. The system of claim 1 wherein the starting gas comprises extra clean dry air (XCDA).

8. The system of claim 1 wherein the gas fractionator comprises at least one membrane filter.

9. The system of claim 1 wherein the gas fractionator comprises a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

10. The system of claim 1 wherein the gas fractionator comprises at least one molecular sieve.

11. The system of claim 1 wherein the starting gas has a second gas concentration greater than 75% by volume and the separated gas has a second gas concentration less than 5 % by volume.

12. The system of claim 11 wherein the gas fractionator comprises a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

13. The system of claim 12 in which the second molecular sieve is not used while the first molecular sieve is being used, the system further comprising a replacement condition sensing module arranged to sense a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and a controller responsively connected to the replacement condition sensing module and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition.

14. The system of claim 13 wherein the replacement condition is at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge.

15. The system of claim 13 wherein the replacement condition sensing module comprises a first gas concentration sensor arranged to sense a concentration of the first gas in the separated gas and to generate a signal indicative of the concentration of the first gas in the separated gas; and the system further comprises a controller responsively connected to the first gas concentration sensor and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

16. The system of claim 1 further comprising a hydrogen feed line arranged to feed a hydrogen-containing gas into the portion of the lithographic apparatus and wherein the outlet is in fluid communication with the hydrogen feed line to inject the separated gas into the hydrogen feed line.

18. The lithographic apparatus of claim 17 wherein the first gas component comprises oxygen.

19. The lithographic apparatus of claim 17 wherein the first gas component comprises nitrogen.

20. The lithographic apparatus of claim 17 wherein the gas fractionator comprises at least one membrane filter.

21. The lithographic apparatus of claim 17 wherein the gas fractionator comprises a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

22. The lithographic apparatus of claim 17 wherein the gas fractionator comprises at least one molecular sieve.

23. The lithographic apparatus of claim 17 wherein the starting gas has a second gas concentration greater than 75% by volume and the separated gas has a second gas concentration less than 5 % by volume.

24. The lithographic apparatus of claim 22 wherein the gas fractionator comprises a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

25. The lithographic apparatus of claim 24 wherein the second molecular sieve is not used while the first molecular sieve is being used, the system further comprising a replacement condition sensing module arranged to sense a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and a controller responsively connected to the replacement condition sensing module and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition.

26. The lithographic apparatus of claim 25 wherein the replacement condition is at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge.

27. The lithographic apparatus of claim 25 wherein the replacement condition sensing module comprises a first gas concentration sensor arranged to sense a concentration of the first gas in the separated gas and to generate a signal indicative of the concentration of the first gas in the separated gas; and the system further comprises a controller responsively connected to the first gas concentration sensor and adapted to initially direct the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

29. The method of claim 28 wherein the first gas component comprises primarily oxygen.

30. The method of claim 28 wherein the first gas component comprises primarily nitrogen.

31. The method of claim 28 wherein the portion of the lithographic apparatus comprises an extreme ultraviolet (EUV) light source portion.

32. The method of claim 28 wherein the portion of the lithographic apparatus comprises a scanner.

33. The method of claim 28 wherein supplying the starting gas comprises supplying clean dry air (CD A).

34. The method of claim 28 wherein supplying the starting gas comprises supplying extra clean dry air (XCDA).

35. The method of claim 28 wherein at least partially separating the first gas component to produce the separated gas is performed using at least one membrane filter.

36. The method of claim 28 wherein at least partially separating the first gas component to produce the separated gas is performed using a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

37. The method of claim 28 wherein at least partially separating the first gas to produce separated gas is performed using at least one molecular sieve.

38. The method of claim 28 wherein the starting gas has a second gas concentration greater than 75% by volume and the separated gas has a second gas concentration less than 5 % by volume.

39. The method of claim 28 wherein at least partially separating the first gas component to produce the separated gas is performed using a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

40. The method of claim 39 in which the second molecular sieve is not used while the first molecular sieve is being used, the method further comprising sensing a replacement condition in which the system swaps from using the first cartridge to using the second cartridge, and initially directing the starting gas through the first molecular sieve for a first period of time and to switch to directing the starting gas through the second molecular sieve based at least in part on sensing the replacement condition.

41. The method of claim 40 wherein the replacement condition is at least one of a concentration of the first gas in the separated gas, a volume of starting gas processed by the first cartridge, and an operating time of the first cartridge.

42. The method of claim 40 wherein sensing the replacement condition comprises sensing a first gas concentration of the first gas in the separated gas and generating a signal indicative of the concentration of the first gas in the separated gas; and initially directing the starting gas through the first molecular sieve for a first period of time and switching to directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

43. The method of claim 28 wherein supplying the separated gas to the portion of the lithographic apparatus comprises injecting the separated gas into a hydrogen feed line arranged to feed a hydrogen-containing gas into the portion of the lithographic apparatus.

45. The method of claim 44 wherein at least partially separating the first gas component to produce the separated gas is performed using at least one membrane filter.

46. The method of claim 44 wherein at least partially separating the first gas component to produce the separated gas is performed using a multi-stage membrane filtration system comprising a series arrangement of at least two membrane filters.

47. The method of claim 46 wherein at least partially separating the first gas component to produce the separated gas is performed using at least one molecular sieve.

48. The method of claim 44 wherein the starting gas has a second gas concentration greater than 75% by volume and the concentrated first gas component has a second gas concentration less than 5 % by volume.

49. The method of claim 44 wherein at least partially separating the first gas component to produce the separated gas is performed using a dual cartridge molecular sieve including a first molecular sieve and a second molecular sieve.

50. The method of claim 44 further comprising: directing the starting gas through the first molecular sieve; sensing a concentration of the first gas in the separated gas and generating a signal indicative of the concentration of the first gas in the separated gas; and ceasing directing the starting gas through the first molecular sieve and directing the starting gas through the second molecular sieve based at least in part on the concentration of the first gas in the separated gas.

51. An apparatus for producing a separated gas, the apparatus comprising: a starting gas input arranged to receive a starting gas having a first oxygen concentration; a gas separator in fluid communication with the starting gas input and having a first sieve filter member and a second sieve filter member, the gas separator being arranged to separate the separated gas from the starting gas, the separated gas having a second oxygen concentration greater than the first oxygen concentration; an oxygen delivery line in fluid communication with the gas separator; an oxygen sensor in fluid communication with the oxygen delivery line and arranged to sense the second oxygen concentration; a controller capable of switching the gas separator between a first mode of operation in which the gas separator uses the first sieve filter member but not the second sieve filter member to separate the separated gas from the starting gas and a second mode of operation in which the gas separator uses the second sieve filter member but not the first sieve filter member to separate the separated gas from the starting gas; and a gas control panel capable of adjusting an amount of oxygen from the oxygen delivery line to be delivered to a hydrogen delivery line arranged to deliver gas to a source of extreme ultraviolet radiation, wherein the starting gas comprises clean dry air (CD A) or extra clean dry air (XCDA).

52. The apparatus of claim 51 wherein the first sieve filter member comprises a first molecular sieve filter and wherein the second sieve filter member comprises a second molecular sieve filter.

53. The apparatus of claim 51 further comprising a flashback arrestor downstream of the gas separator on the oxygen delivery line.

54. The apparatus of claim 51 further comprising an oxygen sensor positioned in the oxygen delivery line downstream of the gas separator.

55. The apparatus of claim 51 further comprising a nitrogen delivery line adapted to deliver nitrogen from the gas separator.

56. The apparatus of claim 55 further comprising a vent line adapted to controllably vent the nitrogen delivery line and the oxygen delivery line.

57. The apparatus of claim 56 wherein the controller or a further controller is adapted to open and close the vent line.