System and method for debris removal in radiation source

Abstract

A light source includes a vessel having a vessel wall defining an interior of the vessel comprising an irradiation region; and a first plurality of gas outlets arranged on the vessel wall. The first plurality of gas outlets being coupled to a first gas source configured to deliver a first gas to the interior of the vessel. The vessel wall is exposed to a suppressive material configured to suppress the deposition of tin or a tin alloy on the vessel wall.

Description

SYSTEM AND METHOD FOR DEBRIS REMOVAL IN RADIATION SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 701,216, filed September 30, 2024, titled SYSTEM AND METHOD FOR DEBRIS REMOVAL IN RADIATION SOURCE, which is incorporated herein by reference in its entirety.FIELD

[0002] The present application relates to extreme ultraviolet (“EUV”) radiation sources and methods thereof. In particular, this disclosure relates to, for example, improving the lifetime of a radiation source that is designed for integration into semiconductor manufacturing process tools, such as a lithographic apparatus and a metrology apparatus.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a semiconductor wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (photoresist or simply “resist”) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include an exposure tool, such as steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] A lithographic apparatus typically includes an illumination system that conditions radiation generated by a radiation source before the radiation is incident upon the patterning device. A patterned beam of EUV light can be used to produce extremely small features on a substrate. EUV light (also sometimes referred to as soft x-rays) is generally defined as electromagnetic radiation having wavelengths in the range of about 5-100 nm. One particular wavelength of interest for lithography occurs at 13.5 nm.

[0005] A metrology apparatus plays a critical role during a semiconductor manufacturing process by providing inspection and measurement functions on wafers and / or reticles. The metrology apparatus is designed to detect and quantify defects, as well as to measure critical dimensions and analyze chemicalcompositions, ensuring that the manufacturing process meets a rigorous quality and accuracy standards required at advanced technology nodes.

[0006] During the manufacturing process, specifically during various stages such as lithography, etching, deposition, and chemical mechanical polishing (CMP), the metrology apparatus can leverage EUV light to scan a surface of the wafer, pattern defects, or any anomalies that may impact yield. For reticle inspection, the metrology apparatus examines the reticles for defects such as missing features, extra features, or contamination, which could be transferred to the substrate during the lithography process. The metrology can even provide overlay measurement, ensuring that different layers of the devices are aligned with each other during the manufacturing process. Moreover, the metrology offers in-line process control by providing real-time feedback, allowing users to adjust process parameters on the fly.

[0007] Methods to produce EUV light include, but are not necessarily limited to, converting a source material into a plasma state that has a chemical element with an emission line in the EUV range. These elements can include, but are not necessarily limited to, xenon, lithium, and tin.

[0008] In one such method, often termed laser-produced plasma (“LPP”), the desired plasma can be produced by irradiating a source material target, for example, in the form of a droplet, stream, or wire, with a laser beam. In another method, often termed discharge produced plasma (“DPP”), the plasma can be generated by positioning a target of source material having an appropriate emission line between a pair of electrodes and causing an electrical discharge to occur between the electrodes. In some applications, particularly for generating EUV light, the source material may be tin or a tin alloy.

[0009] Due to a substantial concentration of tin vapor and the existence of various gaseous tin compounds, such as stannane (SnH ). the radiation source may include a liner provided on an EUV vessel wall to protect the vessel wall from deposition of tin during operation of the radiation source. In some cases, such a liner can be, for example, an aluminum liner having a native oxide layer that protects the liner from residue. In addition, one or more gases can be flowed from the chamber wall - often called a “shower” flow, to direct debris away from the liner and towards an exhaust.

[0010] Conventional systems have been inadequate to fully alleviate the problem of tin or tin alloy deposition, which persists as small amounts of debris, such as tin or a tin alloy stick to the liner during operation of the radiation source. It has been found that, in some cases, hydrogen and other gases used in the vessel can gradually remove the native oxide layer of the aluminum liner, leaving the bare aluminum vulnerable to agglomerating residue.SUMMARY

[0011] It has been found that the deposition rate of debris, such as a tin-containing material on a liner or an EUV vessel wall of a radiation source can be understood as the sum of three contributing factors: (1) a deposition rate of debris on the liner from the vaporization of the target material during an EUV- generating process; (2) an effective etching rate of the debris through the presence of a reactive gasspecies (e.g., hydrogen radicals and / or ionized hydrogen gas), and (3) an effective redeposition rate of a reactive species (e.g., SnH ) formed by debris and the reactive gas that occurs when the reactive species decomposes. High efficiency operation of the radiation source, and thus a prolonged lifetime of the radiation source, can be achieved by minimizing the deposition and redeposition rates while simultaneously maximizing the etching rate.

[0012] Accordingly, it is desirable to provide methods and systems that reduce the deposition and redeposition rate of the debris within the vessel while simultaneously increasing the etching rate of the debris.

[0013] In some aspects, a light source can comprise a vessel having a vessel wall, the vessel wall defining an interior of the vessel comprising an irradiation region. The light source can also comprise a first plurality of gas outlets arranged on the vessel wall. The first plurality of gas outlets can be coupled to a first gas source configured to deliver a first gas to the interior of the vessel. The vessel wall can be exposed to a material configured to suppress the deposition of tin or a tin alloy on the vessel wall.

[0014] In some aspects, a lithographic apparatus can comprise an illumination system configured to receive light from a light source and illuminate a pattern of a patterning device, a projection system configured to project an image of the pattern onto a substrate, and a substrate table configured to position the substrate with respect to the image of the pattern. The light source can comprise can comprise a vessel having a vessel wall, the vessel wall defining an interior of the vessel comprising an irradiation region. The light source can also comprise a first plurality of gas outlets arranged on the vessel wall. The first plurality of gas outlets can be coupled to a first gas source configured to deliver a first gas to the interior of the vessel. The vessel wall can be exposed to a material configured to suppress the deposition of tin or a tin alloy on the vessel wall.

[0015] In some aspects, a method can comprise generating plasma in an irradiation region of a vessel, wherein the vessel includes a liner, delivering a first gas to the irradiation region, and exposing the liner to a material configured to suppress the deposition of tin or a tin alloy on the liner.

[0016] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0017] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0018] FIG. 1 shows a reflective lithographic apparatus, according to some aspects.

[0019] FIGS. 2A, 2B, and 3 show more details of a reflective lithographic apparatus, according to some aspects.

[0020] FIG. 4 shows a lithographic cell, according to some aspects.

[0021] FIG. 5 shows a radiation source, according to some aspects.

[0022] FIGS. 6A and 6B show an enlarged area of a vessel wall of a radiation source, according to some aspects.

[0023] FIG. 7 shows an enlarged area of a vessel wall of a radiation source, according to some aspects.

[0024] FIG. 8 shows an enlarged area of a vessel wall of a radiation source, according to some aspects.

[0025] FIG. 9 shows a flowchart of a process for operating a radiation source, according to some aspects.

[0026] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0027] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0028] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0029] The terms “about,” “approximately,” or the like can be used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0030] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can comprise read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine-readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0031] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.Example Lithographic Systems

[0032] FIG. 1 shows a lithographic apparatus 100 in which aspects of the present disclosure can be implemented. In some aspects, lithographic apparatus 100 can comprise the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position substrate W. Lithographic apparatus 100 also comprises a projection system PS configured to project a pattern imparted to radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of substrate W. In lithographic apparatus 100, patterning device MA and the projection system PS are reflective.

[0033] Illumination system IL can comprise various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B. Illumination system IL can also comprise a sensor ES that provides a measurement of, for example, one or more of energy per pulse, photon energy, intensity, average power, and the like. Illumination system IL can comprise a measurement sensor MS for measuring a movement of radiation beam B and a uniformity compensator UC that allow an illumination slit uniformity to be controlled. Measurement sensor MScan also be disposed at other locations. For example, measurement sensor MS can be on or near substrate table WT.

[0034] In some aspects, support structure MT can support patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of lithographic apparatus 100, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. Support structure MT can implement mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. Support structure MT can be a frame or a table. Support structure MT can be fixed or movable. By using sensors, support structure MT can ensure that patterning device MA is at a desired position (e.g., a given position with respect to the projection system PS).

[0035] The term “patterning device” can be used herein to refer to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in target portion C of substrate W. The pattern imparted to radiation beam B can correspond to a particular functional layer in a device being created in target portion C to form an integrated circuit.

[0036] Patterning device MA can be reflective. Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks can include different mask types, such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors can impart a pattern in radiation beam B, which is reflected by a matrix of small mirrors.

[0037] In some aspects, the term “projection system” can be used herein to refer to any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. Atmospheric gas can absorb EUV or electrons used for exposing a substrate. Therefore, a vacuum environment can be used for EUV or electron beam radiation. A vacuum environment can be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0038] Lithographic apparatus 100 can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may be different from substrate table WT.

[0039] In some aspects, lithographic apparatus 100 can be of a type in which at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system.Immersion techniques can increase the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be located between the projection system and the substrate during exposure.

[0040] Illuminator IL can receive a radiation beam from a radiation source SO. Source SO and lithographic apparatus 100 can be separate physical entities. In such cases, source SO is not considered to be part of lithographic apparatus 100 and radiation beam B can pass from source SO to illuminator IL with the aid of a beam delivery system (not shown), which can include, for example, suitable directing mirrors and / or a beam expander. In other cases, source SO can be an integral part of the lithographic apparatus 100. A radiation system can comprise source SO, illuminator IL, and / or beam delivery system BD.

[0041] In some aspects, illuminator IL can be used to condition radiation beam B to have a desired uniformity and intensity distribution in its cross section. The desired uniformity of radiation beam B can be maintained by using uniformity compensator UC. Uniformity compensator UC can comprise a plurality of protrusions (e.g., fingers) that can be adjusted in the path of radiation beam B to control the uniformity of radiation beam B. Measurement sensor MS can be used to monitor the uniformity of radiation beam B.

[0042] Radiation beam B can be incident on patterning device MA, which is held on the support structure MT, and In this manner, radiation beam B can be patterned by the patterning device MA. In lithographic apparatus 100, radiation beam B can be reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device MA, radiation beam B can pass through projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IFD2 (for example, an interferometric device, linear encoder, or capacitive sensor), substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, first positioner PM and another position sensor IFD 1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0043] In some aspects, lithographic apparatus 100 can be used in at least one of the following modes:

[0044] 1. In step mode, support structure MT and substrate table WT can be kept essentially stationary, while an entire pattern imparted to radiation beam B is projected onto a target portion C at one time (e.g., a single static exposure). Substrate table WT can then be shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0045] 2. In scan mode, support structure MT and substrate table WT can be scanned synchronously while a pattern imparted to radiation beam B is projected onto a target portion C (e.g., a single dynamic exposure). The velocity and direction of substrate table WT relative to support structureMT can be determined by (de-)magnification and image reversal characteristics of projection system PS.

[0046] 3. In another mode, support structure MT can be kept substantially stationary holding a programmable patterning device, and substrate table WT can be moved or scanned while a pattern imparted to radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated after each movement of substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0047] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0048] In some aspects, lithographic apparatus 100 can comprise an EUV radiation source configured to generate a beam of EUV radiation for EUV lithography. The EUV radiation source can be configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.Example Illumination Sources and Illumination Optics

[0049] FIG. 2A shows a different view of source SO, illumination system IL, and projection system PS that can be used in lithographic apparatus 100, according to some aspects. Source SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of source SO. An EUV radiation emitting plasma 210 can be formed by a discharge-generated plasma source. In some aspects, a plasma of excited tin (Sn) (e.g., excited via a laser) is used to produce EUV radiation.

[0050] The radiation emitted by the EUV radiation emitting plasma 210 can be passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 211. Contaminant trap 230 can comprise a channel structure. Contamination trap 230 can also comprise a gas barrier and / or a channel structure.

[0051] In some aspects, collector chamber 212 can comprise a radiation collector CO. Radiation collector CO can be a so-called grazing incidence collector. Radiation collector CO can comprise an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses radiation collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point INTF. Virtual source point INTF can be referred to as the intermediate focus. Source collector apparatus can be arranged such that the intermediate focus INTF is located at or near an opening 219 of enclosing structure 220. The virtual source point INTF can be an image of the EUV radiation emitting plasma 210. Grating spectral filter 240 can be used for suppressing infrared (IR) radiation.

[0052] Subsequently, the radiation traverses the illumination system IL. Illumination system IL can include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide adesired angular distribution of radiation beam 221, at patterning device MA, as well as a desired uniformity of radiation intensity at patterning device MA. Upon reflection of beam of radiation 221 at patterning device MA, held by support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by projection system PS via reflective elements 228, 229 onto substrate W held by the wafer stage or substrate table WT. In some aspects, other configurations of mirrors and / or optical devices can be used to direct radiation beam 221 to patterning device MA.

[0053] More elements than shown can generally be present in illumination system IL and projection system PS. Grating spectral filter 240 can optionally be present, depending upon the type of lithographic apparatus. Further, there can be more mirrors present than those shown in the FIG. 2A, for example there can be one to six additional reflective elements present in the projection system PS than shown in FIG. 2A.

[0054] In some aspects, uniformity compensator UC, sensor ES, and / or measurement sensor MS shown in FIGS. 2A and 2B can be as described above in reference to FIG. 1.

[0055] Collector CO, as illustrated in FIG. 2A, is depicted as an example of a nested collector with grazing incidence reflectors 253, 254, and 255 (or collector mirror). Grazing incidence reflectors 253, 254, and 255 can be disposed axially symmetric around an optical axis O. A collector optic of this type can be used in combination with a discharge-generated plasma source, often called a DPP source.

[0056] FIG. 2B shows a different view of source SO with alternative collection optics that can be used in lithographic apparatus 100, according to some aspects. It should be appreciated that structures shown in FIG. 2A that do not appear in FIG. 2B (for drawing clarity) can still be included in aspects referring to FIG. 2B. Elements in FIG. 2B having the same reference numbers as those in FIG. 2A have the same or substantially similar structures and functions as described in reference to FIG. 2A.

[0057] In some aspects, the lithographic apparatus 100 can be used, for example, to expose a substrate W such as a resist-coated wafer with a patterned beam of EUV illumination. In FIG. 2B, illumination system IL and projection system PS are represented combined as an exposure device 256 (e.g., an integrated circuit lithography tool such as a stepper, scanner, step and scan system, direct write system, device using a contact and / or proximity mask, etc.) that uses EUV light from source SO. Lithographic apparatus 100 can also comprise collector 258 that reflects EUV light from the EUV radiation emitting plasma 210 along a path into the exposure device 256 to irradiate substrate W. Collector 258 can comprise a near-normal incidence collector mirror having a reflective surface in the form of a prolate spheroid (e.g., an ellipse rotated about its major axis). The prolate spheroid structure can have a graded multi-layer coating with alternating layers of molybdenum and silicon, and in some cases, one or more high temperature diffusion barrier layers, smoothing layers, capping layers and / or etch stop layers.

[0058] FIG. 3 shows a detailed view of source SO and associated elements that can be used in lithographic apparatus 100, according to some aspects. Elements in FIG. 3 having the same reference numbers as those in FIGS. 1, 2A, and 2B have the same or substantially similar structures and functions as described in reference to FIGS. 1, 2A, and 2B. In some aspects, source SO can be a LPP EUV source.Source SO can comprise a laser system 302 (or a suitable illumination system) for generating illumination to be used in the production of EUV -producing plasma. Source SO can generate a train of light pulses and deliver the light pulses into a light source chamber 312. For the lithographic apparatus 100, the light pulses can travel along one or more beam paths from the laser system 302 and into the chamber 312 to illuminate a source material (or target material) at an irradiation region 304 (or target region, or primary focus) to generate a plasma. For example, EUV radiation emitting plasma 210 (FIGS. 3B) is generated at irradiation region 304. EUV light is produced by the plasma. The EUV light is used for substrate exposure in the exposure device 356. In some aspects, exposure device 356 is used for inspection and measurement in a metrology apparatus.

[0059] In some aspects, laser system 302 can comprise a pulsed laser device, e.g., a pulsed gas discharge CO2 laser device producing radiation at 9.3 pm or 10.6 pm, e.g., with DC or RF excitation, operating at relatively high power, e.g., 10 kW or higher and high pulse repetition rate, e.g., 50 kHz or more. In some aspects, the laser can be an axial-flow RF-pumped CO2 laser having an oscillator amplifier configuration (e.g., master oscillator / power amplifier (MOPA) or power oscillator / power amplifier (POPA)) with multiple stages of amplification and having a seed pulse that is initiated by a Q-switched oscillator with relatively low energy and high repetition rate, e.g., capable of 100 kHz operation. From the oscillator, the laser pulse can then be amplified, shaped and / or focused before reaching the irradiation region 304. Continuously pumped CO2 amplifiers can be used for the laser system 302. Alternatively, the laser can be configured as a so-called “self-targeting” laser system in which the droplet serves as one mirror of the optical cavity of the laser.

[0060] In some aspects, depending on the application, other types of lasers can also be suitable, e.g., an excimer or molecular fluorine laser operating at high power and high pulse repetition rate. Some examples include, a solid state laser, e.g., having a fiber, rod, slab, or disk-shaped active media, other laser architectures having one or more chambers, e.g., an oscillator chamber and one or more amplifying chambers (with the amplifying chambers in parallel or in series), a master oscillator / power oscillator (MOPO) arrangement, a master oscillator / power ring amplifier (MOPRA) arrangement, or a solid state laser that seeds one or more excimer, molecular fluorine or CO2 amplifier or oscillator chambers, can be suitable. Other suitable designs are envisaged.

[0061] In some aspects, a source material can first be irradiated by a pre -pulse and thereafter irradiated by a main pulse. Pre-pulse and main pulse seeds can be generated by a single oscillator or two separate oscillators. One or more common amplifiers can be used to amplify both the pre -pulse seed and main pulse seed. In some aspects, separate amplifiers can be used to amplify the pre-pulse and main pulse seeds.

[0062] In some aspects, source SO can also comprise a beam conditioning unit 306 having one or more optics for beam conditioning, such as expanding, steering, and / or focusing the beam between the laser system 302 and irradiation region 304. For example, a steering system, which can comprise one or more mirrors, prisms, lenses, etc., can be provided and arranged to steer the laser focal spot to differentlocations in the chamber 312. For example, the steering system can comprise a first flat mirror mounted on a tip-tilt actuator, which can move the first mirror independently in two dimensions, and a second flat mirror mounted on a tip-tilt actuator which can move the second mirror independently in two dimensions. With the described arrangement(s), the steering system can controllably move the focal spot in directions substantially orthogonal to the direction of beam propagation (beam axis or optical axis).

[0063] Beam conditioning unit 306 can comprise a focusing assembly to focus the beam to irradiation region 304 and adjust the position of the focal spot along the beam axis. For the focusing assembly, an optic, such as a focusing lens or mirror, can be used that is coupled to an actuator for movement in a direction along the beam axis to move the focal spot along the beam axis.

[0064] In some aspects, the source SO can also comprise a source material delivery system 308 for delivering source material, such as tin droplets, to irradiation region 304, where the droplets can interact with light pulses from the laser system 302 to produce plasma and generate EUV emission. The EUV emission is used to expose a substrate such as a resist-coated wafer at exposure device 356. More details regarding various droplet dispenser configurations can be found in, e.g., U.S. Pat. No. 7,872,245, issued on January 18, 2011, titled “Systems and Methods for Target Material Delivery in a Laser Produced Plasma EUV Light Source”, U.S. Pat. No. 7,405,416, issued on July 29, 2008, titled “Method and Apparatus for EUV Plasma Source Target Delivery”, U.S. Pat. No. 7,372,056, issued on May 13, 2008, titled “LPP EUV Plasma Source Material Target Delivery System”, and International Appl. No. WO 2019 / 137846, titled “Apparatus for and Method of Controlling Coalescence of Droplets in a Droplet Stream”, published on July 18, 2019, the contents of each of which are incorporated by reference herein in their entirety.

[0065] In some aspects, the source material for producing an EUV light output for exposure can include, but is not necessarily limited to, a material that includes tin, lithium, xenon or combinations thereof. The source material can be in the form of liquid droplets and / or solid particles contained within liquid droplets. For example, the element tin can be used as pure tin, as a tin compound, e.g., SnBr4, SnBr2, SnFL, as a tin alloy, e.g., tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or a combination thereof. Depending on the material used, the source material, when sent to irradiation region 304, can be at various temperatures, for example, room temperature or near room temperature (e.g., tin alloys, SnBr4), at an elevated temperature (e.g., pure tin), or at temperatures below room temperature (e.g., SnH4).

[0066] In some aspects, the source SO can also comprise a controller 310 and / or a drive laser control system 312 for controlling devices in laser system 302 to generate light pulses for delivery into the chamber 312 and / or for controlling movement of optics in beam conditioning unit 306. Source SO can also comprise a droplet position detection system which can comprise one or more droplet imagers 314 that provide an output signal indicative of the position of one or more droplets (e.g., to ensure that droplets arrive on target at irradiation region 304). The droplet imager(s) 314 can provide measurementoutput to a droplet position detection feedback system 316. Droplet position detection feedback system 316 can compute a droplet position and trajectory, from which a droplet error can be computed (e.g., on a droplet-by-droplet basis, or on average). The droplet error can then be provided as an input to controller 310, which can, for example, provide a position, direction and / or timing correction signal to laser system 302 to control laser trigger timing and / or to control movement of optics in beam conditioning unit 306, e.g., to change the location and / or focal power of the light pulses being delivered to irradiation region 304 in chamber 312. Furthermore, source material delivery system 308 can comprise a control system operable in response to a signal from controller 310 (which in some implementations can include the droplet error described above, or some quantity derived therefrom) to modify the release point, initial droplet stream direction, droplet release timing and / or droplet modulation to correct for errors in the droplets arriving at irradiation region 304.

[0067] In some aspects, source SO can also comprise collector 358 and a gas dispenser device 320. Gas dispenser device 320 can dispense gas in the path of the source material from source material delivery system 308 (e.g., irradiation region 304). Gas dispenser device 320 can comprise a nozzle through which dispensed gas can exit. Gas dispenser device 320 can be structured (e.g., having an aperture) such that, when placed near the optical path of laser system 302, light from laser system 302 is not blocked by gas dispenser device 320 and is allowed to reach irradiation region 304. A buffer gas such as hydrogen, helium, argon or combinations thereof, can be introduced into chamber 312. The buffer gas can be present in the chamber 312 during plasma discharge and can act to slow plasma- created ions, reduce degradation of optics, and / or increase plasma efficiency. Alternatively, a magnetic field and / or electric field (not shown) can be used alone, or in combination with a buffer gas, to reduce damage caused by fast-moving ions.

[0068] In some aspects, collector 358 can be a near-normal incidence collector mirror having a reflective surface in the form of a prolate spheroid as described above. Collector 358 can be formed with an aperture to allow the light pulses generated by laser system 302 to pass through and reach irradiation region 304. The same, or another aperture, can be used to allow gas from the gas dispenser device 320 to flow into chamber 312. As shown, the collector 358 can be, e.g., a prolate spheroid mirror that has a first focus within or near the irradiation region 304 and a second focus at an intermediate region 318, where the EUV light can be transmitted to exposure device 356. It is to be appreciated that other optics can be used in place of the prolate spheroid mirror for collecting and directing light to an intermediate location for subsequent delivery to a device utilizing EUV light. It is also envisaged that structures and functions described in reference to FIG. 3 can be used with collectors other than collector 358 (e.g., collector CO (FIG. 2A)).Example Lithographic Cell

[0069] FIG. 4 shows a lithographic cell 400, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatus 100 (FIGS. 1, 2A, 2B, and 3) can form part of lithographic cell 400. Lithographic cell 400 can also comprise one or more apparatuses to perform pre -exposure andpost-exposure processes on a substrate. These can include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input / output ports I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.Example Radiation Source

[0070] FIG. 5 shows a radiation source 500 in more detail, according to some aspects. In some aspects, radiation source 500 can be used in a lithographic apparatus or a metrology apparatus. Radiation source 500 includes a vessel 501 enclosing an irradiation region that includes a plasma forming region 502. Radiation source 500 further includes an exhaust 503, a shroud 504, and a collector 505, according to some aspects. Vessel 501 is defined by a chamber that encloses vessel 501. In some aspects, an interior vessel wall 550 is disposed in the region enclosed by vessel 501. According to some aspects, vessel 501 is formed of a plurality of components 501a-c. Component 501a is a cap structure proximal to an intermediate focus of radiation source 500. Components 501b-c are frustum-shaped structures of vessel 501. Component 501b is arranged between component 501a and component 501c. Component 501b is coupled to exhaust 503. Component 501c is coupled to shroud 504. In some aspects, any of components 501a-c includes multiple sub -components. For example, component 501b includes a first subcomponent coupled to exhaust 503 and a second sub-component positioned between the first subcomponent and component 501c. In some aspects, components 501a-c are also referred as to a liner or a modular structure of vessel 501.

[0071] According to aspects, a droplet of source material is injected into radiation source 500 through shroud 504. Shroud 504 protects a trajectory of source material droplets between a droplet generator (not shown) and plasma forming region 502. In some aspects, as the droplet of source material enters plasma forming region 502, the droplet can be irradiated by a laser beam (e.g., a CO2 laser or other excitation laser), thereby causing the droplet of source material to evaporate and form an excited plasma 508. As plasma 508 relaxes to a lower excited state or to a ground state, plasma 508 can emit photons of EUV radiation. According to aspects, this EUV radiation is collected and concentrated by collector 505 into a radiation beam and directed towards the intermediate focus adjacent to a beam exit 510.

[0072] In some aspects, vessel 501 is substantially parallelepiped in a region surrounding collector 505 and plasma forming region 502. In some aspects, to direct the EUV radiation towards beam exit 510, vessel 501 has a substantially conical shape.

[0073] According to aspects, interior vessel wall 550 is provided along a length of vessel 501 defined by components 501a-c. In some aspects, interior vessel wall 550 is provided along one or more of components 501a-c. Interior vessel wall 550 can distribute heat and can protect vessel 501 from residueand debris formed during the operation of radiation source 500. The length and placement of interior vessel wall 550 can be determined by, for example, the amount of residue of the source material that is present in various sections of vessel 501, the heat generated in various sections of vessel 501, and other similar concerns.

[0074] According to aspects, at least one of components 501a-c has a plurality of gas flow outlets on its interior surface to prevent debris, such as particulate and / or gaseous source material, from sticking to interior vessel wall 550. In some aspects, the plurality of gas flow outlets generate a primary gas flow that directs the debris toward exhaust 503 for a subsequent scrubbing process. However, as explained above, the debris can, in some aspects, agglomerate onto interior vessel wall 550. To suppress the deposition and / or the redeposition of the debris, such as a tin-containing material, at least one suppressive material is applied to the interior surface of at least one of components 501a-c.

[0075] The suppressive material can be a solid deposition, a flowing gas, or a combination of both. In some aspects, the suppressive material is deposited on the interior surface of at least one of components 501a-c. In some aspects, the suppressive material is a gaseous substance flowing along the interior surface of at least one components 501a-c. In some aspects, both forms of suppressive material - deposited and gaseous - are utilized in conjunction on at least one of components 501a-c. For example, the interior surface of component 501b is coated with a layer of a first suppressive material, and then a second suppressive material is delivered through the gas outlets onto a top surface of the layer of the first suppressive material. Each of the gas outlets of component 501b aligns with an opening on the layer of the first suppressive material. In another example, component 501c is coated solely with a layer of a third suppressive material, whereas component 50 lb is treated exclusively with a fourth suppressive material delivered through the gas outlets. The suppressive materials described here can be identical or different, depending on various applications.

[0076] FIGS. 6A and 6B show an enlarged portion of a vessel wall 600 of a radiation source, according to some aspects. According to aspects, vessel wall 600 comprises a first layer 621 and a second layer 622 in contact with first layer 621. First layer 621 is referred to as an interior layer of vessel wall 600 and has an interior surface 621s opposite to an interface between first layer 621 and second layer 622. Referring to FIG. 6A, interior surface 621s faces an interior of the vessel. Referring to FIG. 6B, a suppressive layer 640 is deposited on interior surface 621s of first layer 621 and faces the interior of the vessel. Second layer 622 is referred to as a middle layer of vessel wall 600 or an exterior layer of vessel wall 600. In some aspects, vessel wall 600 represents a liner or a modular structure of the radiation source. For example, vessel wall 600 represents a component coupling to an exhaust of the radiation source.

[0077] In some aspects, first layer 621 and second layer 622 are made of the same material, such as aluminum, stainless steel, titanium or any suitable combination. In some aspects, first layer 621 comprises material that is different from second layer 622. For example, first layer 621 includes aluminum and second layer 622 includes stainless steel.

[0078] Second layer 622 and first layer 621 can be provided with a plurality of gas outlets or gas outlets 625 connected to a gas source 650. In some aspects, the plurality of gas outlets 625 are circumferentially distributed along vessel wall 600. By way of the gas outlets 625, gas source 650 can be configured, in some aspects, to provide a flow of gas into the interior of the vessel. This flow of gas from gas source 650 can, in some aspects, be a low pressure gas flow that directs particulate and / or gaseous debris away from first layer 621 and towards the exhaust of the vessel. According to some aspects, the flow of gas from gas source 650 is referred to as a shower flow. In another aspects, gas source 650 is configured to deliver a suppressive gaseous substance along interior surface 621s to prevent decomposition of the debris. For example, when the debris includes stannate the suppressive gaseous substance includes at least one of oxygen, hydrogen sulfide, an inert gas, cyanide, an arsenic compound, an antimony compound, a selenium compound, methane, or a combination thereof.

[0079] As shown in FIG. 6B, suppressive material 640 is formed on interior surface 621s of first layer 621 and is configured to suppress the deposition of debris thereon. Each opening in suppressive material 640 aligns with a respective opening in first layer 621. In some aspects, an inner diameter of each opening of suppressive material 640 is identical to an inner diameter of a respective opening in first layer 621. In some aspects, the inner diameter of each opening of suppressive material 640 is different from an inner diameter of a respective opening in first layer 621. In aspects in which first layer 621 is not present, suppressive material 640 can be provided directly on an interior surface of second layer 622.

[0080] According to some aspects, suppressive material 640 is a metal oxide layer, such as aluminum oxide, zirconium dioxide, titanium dioxide, magnesium oxide, tantalum oxide, hafnium oxide, yttrium oxide or a combination thereof, disposed on interior surface 621s. In some aspects, suppressive material 640 includes silicon dioxide. In some aspects, suppressive material 640 is a metal oxide layer that replaces a native oxide layer of first layer 621 or second layer 622. In some aspects, suppressive material 640 is a metal oxide layer that supplements a native oxide layer of first layer 621 or second layer 622.

[0081] In some aspects, suppressive material 640 is disposed before or during installation of the radiation source before operation of the radiation source. For example, in some aspects, suppressive material 640 is a coating formed on interior surface 621s before installation of first layer 621, so that first layer 621 is continuously exposed to suppressive material 640 during operation of the radiation source.

[0082] According to aspects, a metal oxide used as suppressive material 640 can have one or more favorable characteristics. In some aspects, it can be desirable to use a metal oxide having a sufficient hardness to prevent delamination from first layer 621. In some aspects, it can be desirable to use a metal oxide that is highly stable, particularly due to the high temperatures created from the operation of the radiation source. In some aspects, a suitably stable metal oxide may be a metal oxide having a sufficiently large Gibbs free energy of formation at standard conditions (i.e., 1 atmosphere and 0 °C). According to some aspects, a suitably stable metal oxide may be one having a Gibbs free energy of lessthan -800 kJ mol1at standard conditions. Particular examples of metal oxides that are both hard and stable include oxides of Y, Zr, Hf, Ti, Al, Ta, or a combination thereof. In some aspects, when suppressive material 640 is made of a tough and stable metal oxide, suppressive material 640 may be more stable against degradation than, for example, the native oxide of a liner or vessel wall. In some aspects, vessel wall 600 is coupled to a cooling mechanism to decrease a temperature at least one of first layer 621, second layer 622 and suppressive material 640.

[0083] In at least one embodiment, FIG. 6B shows two suppressive materials for preventing both the deposition and redeposition of the debris. For example, gas source 650 supplies a gaseous suppressive material along a top surface of solid suppression material 640.

[0084] FIG. 7 shows an enlarged portion of a vessel wall 700, according to some aspects. Vessel wall 700 can comprise a second layer 722 and a first layer 721 including a plurality of gas outlets 725 connected to a gas source 750 that can supply a first flow of, for example, hydrogen gas, to the interior of the vessel to guide debris toward the exhaust. Second layer 722 can be a middle layer of vessel wall 700 or an exterior layer of vessel wall 700. In some aspects, vessel wall 700 represents a liner or a modular structure of a radiation source. In addition, second layer 722 and first layer 721 each include one or more second gas outlets 735 that are connected to a second gas source 760. Second gas source 760 is configured to supply various gases to the interior of the vessel to expose an interior surface 721s of first layer 721 to a suppressive material configured to suppress the deposition of the debris inside the vessel.

[0085] In some aspects, second gas source 760 can be configured to supply a second gas to the interior of the vessel and along interior surface 721s. The second gas can, in some aspects, be the material configured to suppress the deposition or the decomposition of the debris inside the vessel.

[0086] According to some aspects, the second gas includes oxygen. The oxygen can be delivered to the interior of the vessel as pure oxygen gas. In some aspects, the oxygen can be delivered as one component of extremely clean dry air (XCDA). In some aspects, the oxygen can be delivered as a molecule that is dissociated by exposure to the irradiation region. For example, water (H2O) and carbon monoxide (CO) each decompose, under irradiation from one or more specific wavelengths of light, into respective oxygen, hydrogen, and carbon gases.

[0087] According to aspects, oxygen can interact to replenish a native oxide that is normally present on first layer 721. For example, in some aspects, first layer 721 can be aluminum, and a native oxide layer on first layer 721 can be thinned or removed due to the introduction of hydrogen gas from gas source 750. According to aspects, introducing oxygen from second gas source 760 can replenish such a native oxide layer on first layer 721. In some aspects, the concentration of oxygen at first layer 721 or vessel wall can be controlled to promote regrowth of the native oxide layer on first layer 721.

[0088] According to some aspects, the second gas acts as a catalytic poison. As discussed above, the decomposition of a reactive species (e.g., SnFfi) can increase a redeposition rate of on first layer 721. In some cases, a suppressive material of first layer 721 can act as a catalyst for the decomposition of areactive species. For example, aluminum can act as a catalyst for decomposition of SnFU. Thus, in some aspects, the second gas can be a gas that poisons such a catalysis. In some aspects, the second gas can by a cyanide, an arsenic compound, an antimony compound, a selenium compound, methane, or hydrogen sulfite, or a combination thereof, which can act as a poisoning agent. In some aspects, providing such a catalytic poisoning agent can reduce the decomposition of one or more reactive species. In turn, according to aspects, the redeposition rate on first layer 721 can be reduced.

[0089] According to some aspects, second gas source 760 can supply an additional hydrogen gas to the interior of the vessel. Such additional hydrogen gas can, according to aspects, suppress the deposition of the source material on first layer 721 by increasing an effective etch rate of the debris. As one example, when the source material is tin or a tin alloy, a higher concentration of hydrogen gas near first layer 721 can increase the etching of the tin or a tin alloy from first layer 721 by increasing the formation of SnH from the tin or tin alloy. However, aspects are not limited to hydrogen gas, and other gases that are reactive with the source material can be used.

[0090] Moreover, aspects are not limited to only a single second gas source 760 and a corresponding set of second gas outlets 735. In some aspects, vessel wall 700 can comprise a plurality of gas sources, each with a corresponding plurality of gas outlets, combining one or more of the above second gases. As one non-limiting example, vessel wall 700 can comprise a second gas source that supplies oxygen gas through a plurality of second gas outlets, a third gas source that supplies an arsenic or other catalytic poisoning agent through a plurality of third gas outlets, and a fourth gas source that supplies hydrogen gas through a plurality of fourth gas outlets. Further, vessel wall 700 can, in some aspects, comprise a plurality of gas sources each connected to a same set of gas outlets. As a non-limiting example, vessel wall 700 can comprise a second gas source that supplies oxygen gas, a third gas source that supplies an arsenic or other catalytic poisoning agent, and a fourth gas source that supplies hydrogen gas, where each gas is supplied through the plurality of gas outlets 725. That is, there is no requirement that each gas be supplied through a separate set of gas outlets. In some aspects, all gases can be supplied to vessel wall 700 through the same set of gas outlets. In at least one embodiment, a solid suppressive material is deposited on first layer 721 to further prevent the deposition of the debris. In some aspects, vessel wall 700 is coupled to a cooling mechanism to decrease a temperature at least one of first layer 721, second layer 722 and the suppressive material coated on first layer 721.

[0091] FIG. 8 shows an enlarged portion of a vessel wall 800, according to some aspects. Vessel wall 800 comprises a second layer 822 and a first layer 821 (if present) including one or more pluralities of gas outlets connected to one or more gas sources (not shown). Second layer 822 is referred to as a middle layer of vessel wall 800 or an exterior layer of vessel wall 800. In some aspects, vessel wall 800 represents a liner or a modular structure of a radiation source. In some aspects, vessel wall 800 can include a coolant source 830 and a temperature controller 850 connected to first layer 821. However, aspects are not limited to this example, and temperature controller 850 and coolant source 830 can be connected to second layer 822.

[0092] According to some aspects, temperature controller 850 can monitor the temperature of first layer 821 and adjust a supply of coolant from coolant source 830 to thereby control a temperature of first layer 821. In some aspects, temperature controller 850 can be implemented as a computing device, one or more processors or processing modules of a computing device, or a software module implemented on a processor or processing module of a computing device.

[0093] According to aspects, the formation of an oxide on first layer 821 can be sensitive to the temperature of first layer 821. For example, as the temperature of first layer 821 increases, the rate of formation of an oxide layer on first layer 821 can also increase.

[0094] In addition, the rate of decomposition of a reactive species in the chamber can also be sensitive to temperature, according to some aspects. For example, as a temperature of first layer 821 decreases, the rate constant of decomposition of the reactive species (e.g., SnFfi decomposing to Sn and hydrogen gas) also correspondingly decreases. Thus, in some aspects, increasing the temperature of first layer 821 increases the rate of formation of an oxide layer. On the other hand, as the temperature of first layer 821 decreases, the formation of the reactive species (e.g., SnFU) increases relative to the rate of SnFU decomposition and the rate of SnFU redeposition. Thus, in some aspects, the temperature of first layer 821 is adjusted to by balancing the rate of formation of an oxide layer with the rate of decomposition of the reactive species. In at least one embodiment, the temperature of first layer 821 ranges from about 15 degrees Celsius to about 30 degrees Celsius.Example Method of Suppressing Source Material Deposition

[0095] FIG. 9 shows a flowchart of a process 900 of exposing a vessel wall to a suppressive material configured to suppress the deposition of tin and / or the decomposition of stannane, according to some aspects.

[0096] In operation 910, plasma is generated within a vessel of a radiation source. Operation 910 can be performed by the generation of a EUV radiation for a lithographic apparatus or a metrology apparatus. In some aspects, the plasma can be generated at operation 910 by exposing a source material (e.g., tin or a tin alloy, as described above) to irradiation or electric discharge, causing the source material to form the plasma.

[0097] Process 900 can proceed, according to aspects, to operation 920 by delivering a shower flow to the interior of the vessel wall. As discussed above, a shower flow may, in some aspects, be a flow of hydrogen gas and / or a flow of suppressive gas through a plurality of gas outlets toward an interior of the vessel. In some aspects, the flow of suppressive gas is delivered along an interior wall of a liner or a modular structure of the vessel.

[0098] According to aspects, process 900 can then proceed to operation 930 by exposing the liner or a vessel wall to a suppressive material configured to suppress the deposition of the source material on the liner or the vessel wall. Operation 930 can, in some aspects, further comprise forming a solid suppressive layer, such as a metal oxide, on the liner, supplying oxygen or another gas into the vessel through the liner, or controlling the supply of a coolant to the liner, or any combination thereof.

[0099] The method steps of FIG. 9 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 9 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-8.

[0100] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength X of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-100 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G- line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0101] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, UCDs, thin-film magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0102] Furthermore, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation,heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0103] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0104] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. The foregoing description of specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0105] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above -described aspects, but should be defined in accordance with the following claims and their equivalents.

[0106] Some embodiments may further be described using the following clauses:1. A light source comprising: a vessel having a vessel wall, the vessel wall defining an interior of the vessel; and a first plurality of gas outlets arranged on the vessel wall, the first plurality of gas outlets being coupled to a first gas source configured to deliver a first gas to the interior of the vessel, wherein the vessel wall is exposed to a suppressive material configured to suppress the deposition of tin or a tin alloy on the vessel wall.2. The light source of clause 1, wherein the suppressive material is a metal oxide layer disposed on an interior surface of the vessel wall that faces the interior of the vessel.3. The light source of clause 2, wherein the metal oxide layer comprises a metal oxide having a Gibbs free energy of formation, at standard conditions, of less than -800 kJ mol1.4. The light source of clause 3, wherein the metal oxide comprises an oxide of Y, Zr, Hf, Ti, Al, or Ta, or a combination thereof.5. The light source of clause 4, wherein the metal oxide comprises more than one ofY, Zr, Hf, Ti, Al, and Ta.6. The light source of clause 1, wherein the suppressive material is oxygen gas delivered to the interior of the vessel.7. The light source of clause 6, wherein the oxygen gas is delivered as pure oxygen, as a component of extremely clean dry air, or as a molecule that is dissociated by exposure to an irradiation region, or a combination thereof.8. The light source of clause 7, wherein: the oxygen gas is delivered at least as a molecule that is dissociated by exposure to the irradiation region; and the molecule is water (H2O) or carbon monoxide (CO).9. The light source of clause 6, wherein the first plurality of gas outlets is configured to deliver both the oxygen gas and the first gas to the interior of the vessel.10. The light source of clause 6, further comprising: a second plurality of gas outlets arranged on the vessel wall, wherein the second plurality of gas outlets is coupled to a second gas source configured to deliver the oxygen gas to the interior of the vessel.11. The light source of clause 6, wherein: the first gas is hydrogen gas, and the hydrogen gas and the oxygen gas are configured to be delivered simultaneously.12. The light source of clause 1, further comprising: a second gas source coupled to the first plurality of gas outlets, wherein the second gas source is configured to perform chemical catalyst poisoning.13. The light source of clause 12, where the second gas source is configured to deliver a cyanide, an arsenic compound, an antimony compound, a selenium compound, methane, or hydrogen sulfite, or a combination thereof, to the interior of the vessel.14. The light source of clause 10, further comprising: a third plurality of gas outlets, wherein the third plurality of gas outlets is coupled to a third gas source configured to perform chemical catalyst poisoning.15. The light source of clause 14, wherein the third gas source is configured to deliver a cyanide, an arsenic compound, an antimony compound, a selenium compound, methane, or hydrogen sulfite, or a combination thereof, to the interior of the vessel.16. The light source of clause 1, wherein the first gas supplied to the interior of the vessel by the first plurality of gas outlets comprises a mixture of more than one of hydrogen gas, oxygen gas, and a gas configured to perform chemical catalyst poisoning.17. The light source of clause 1, wherein the suppressive material is a coolant that is configured to be circulated through the vessel wall.18. The light source of clause 17, further comprising:a temperature controller coupled to the vessel wall, wherein the temperature controller is configured to monitor and adjust a temperature of the vessel wall.19. The light source of clause 18, wherein the temperature controller is configured to circulate the coolant through the vessel wall to maintain the temperature of the vessel wall at a temperature that promotes a formation of an oxide on the vessel wall.20. The light source of clause 18, wherein the temperature controller is configured to circulate the coolant through the vessel wall to maintain the temperature of the vessel wall at a temperature that reduces a decomposition and redeposition rate of a tin compound on the vessel wall.21. The light source of clause 6, wherein the oxygen gas is configured to dispose an oxygen gas layer on the vessel wall facing the interior of the vessel to replenish a metal oxide layer depleted by hydrogen radicals.22. A lithographic apparatus comprising: an illumination system configured to receive light from the light source according to clause 1 and illuminate a pattern of a patterning device; a projection system configured to project an image of the pattern onto a substrate; and a substrate table configured to position the substrate with respect to the image of the pattern.23. A method comprising: generating plasma in an irradiation region of a vessel, wherein the vessel includes a liner; delivering a first gas to the irradiation region; and exposing the liner to a material configured to suppress the deposition of tin or a tin alloy on the liner.24. The method of clause 23, wherein the exposing the liner to the material comprises forming a metal oxide layer on an interior surface of the liner that faces the irradiation region.25. The method clause 24, wherein forming the metal oxide layer comprises forming an oxide of Y, Zr, Hf, Ti, Al, or Ta, or a combination thereof.26. The method of clause 23, wherein exposing the liner to the material comprises delivering oxygen gas to the irradiation region.27. The method of clause 26, wherein the delivering oxygen gas comprises delivering oxygen as pure oxygen, one component of extremely clean dry air, or as a molecule that is dissociated by exposure to the irradiation region, or a combination thereof.28. The method of clause 27, wherein: delivering oxygen gas comprises delivering molecules of water (H2O) or carbon monoxide (CO), or a combination thereof.29. The method of clause 25, further comprising: injecting the first gas from a first gas source through a first plurality of gas outlets into the irradiation region; and injecting oxygen gas from a second gas source through the first plurality of gas outlets.30. The method of clause 26, whereindelivering the first gas to the irradiation region comprises delivering hydrogen gas to the irradiation region, and delivering oxygen gas to the irradiation region comprises delivering the hydrogen gas and the oxygen gas to the irradiation region simultaneously. 31. The method of clause 23, wherein exposing the liner to the material further comprises delivering, to an interior of the vessel, a mixture of more than one of hydrogen gas, oxygen gas, and a gas configured to perform chemical catalyst poisoning through same gas outlets.

Claims

CLAIMS1. A light source comprising: a vessel having a vessel wall, the vessel wall defining an interior of the vessel; and a first plurality of gas outlets arranged on the vessel wall, the first plurality of gas outlets being coupled to a first gas source configured to deliver a first gas to the interior of the vessel, wherein the vessel wall is exposed to a suppressive material configured to suppress the deposition of tin or a tin alloy on the vessel wall.

2. The light source of claim 1, wherein the suppressive material is a metal oxide layer disposed on an interior surface of the vessel wall that faces the interior of the vessel.

3. The light source of claim 2, wherein the metal oxide layer comprises a metal oxide having a Gibbs free energy of formation, at standard conditions, of less than -800 kJ mol1.

4. The light source of claim 3, wherein the metal oxide comprises an oxide of Y, Zr, Hf, Ti, Al, or Ta, or a combination thereof.

5. The light source of claim 1, wherein the suppressive material is oxygen gas delivered to the interior of the vessel.

6. The light source of claim 5, wherein the oxygen gas is delivered as pure oxygen, as a component of extremely clean dry air, or as a molecule that is dissociated by exposure to an irradiation region, or a combination thereof.

7. The light source of claim 6, wherein: the oxygen gas is delivered at least as a molecule that is dissociated by exposure to the irradiation region; and the molecule is water (H2O) or carbon monoxide (CO).

8. The light source of claim 5, wherein the first plurality of gas outlets is configured to deliver both the oxygen gas and the first gas to the interior of the vessel.

9. The light source of claim 5, further comprising: a second plurality of gas outlets arranged on the vessel wall, wherein the second plurality of gas outlets is coupled to a second gas source configured to deliver the oxygen gas to the interior of the vessel.

10. The light source of claim 5, wherein: the first gas is hydrogen gas, and the hydrogen gas and the oxygen gas are configured to be delivered simultaneously.

11. The light source of claim 1, further comprising: a second gas source coupled to the first plurality of gas outlets, wherein the second gas source is configured to perform chemical catalyst poisoning.

12. The light source of claim 11, where the second gas source is configured to deliver a cyanide, an arsenic compound, an antimony compound, a selenium compound, methane, or hydrogen sulfite, or a combination thereof, to the interior of the vessel.

13. The light source of claim 9, further comprising: a third plurality of gas outlets, wherein the third plurality of gas outlets is coupled to a third gas source configured to perform chemical catalyst poisoning.

14. The light source of claim 13, wherein the third gas source is configured to deliver a cyanide, an arsenic compound, an antimony compound, a selenium compound, methane, or hydrogen sulfite, or a combination thereof, to the interior of the vessel.

15. The light source of claim 1, wherein the first gas supplied to the interior of the vessel by the first plurality of gas outlets comprises a mixture of more than one of hydrogen gas, oxygen gas, and a gas configured to perform chemical catalyst poisoning.

16. The light source of claim 1, wherein the suppressive material is a coolant that is configured to be circulated through the vessel wall.

17. The light source of claim 16, further comprising: a temperature controller coupled to the vessel wall, wherein the temperature controller is configured to monitor a temperature of the vessel wall and circulate the coolant through the vessel wall to maintain the temperature of the vessel wall at a temperature that promotes a formation of an oxide on the vessel wall.

18. A method comprising : generating plasma in an irradiation region of a vessel, wherein the vessel includes a liner; delivering a first gas to the irradiation region; andexposing the liner to a material configured to suppress the deposition of tin or a tin alloy on the liner.

19. The method of claim 18, wherein exposing the liner to the material comprises forming a metal oxide layer on an interior surface of the liner that faces the irradiation region.

20. The method claim 19, wherein forming the metal oxide layer comprises forming an oxide of Y, Zr, Hf, Ti, Al, or Ta, or a combination thereof.

21. The method of claim 20, further comprising: injecting the first gas from a first gas source through a first plurality of gas outlets into the irradiation region; and injecting oxygen gas from a second gas source through the first plurality of gas outlets.

22. The method of claim 21, wherein delivering the first gas to the irradiation region comprises delivering hydrogen gas to the irradiation region, and delivering oxygen gas to the irradiation region comprises delivering the hydrogen gas and the oxygen gas to the irradiation region simultaneously.

23. The method of claim 18, wherein exposing the liner to the material further comprises delivering, to an interior of the vessel, a mixture of more than one of hydrogen gas, oxygen gas, and a gas configured to perform chemical catalyst poisoning through same gas outlets.

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