Gas flow reallocation in light source

Abstract

An extreme ultraviolet (EUV) system includes a vessel for generating radiation, a mirror, a gas flow assembly, and an exhaust. The system provides a first gas flow path in the vessel when the system is generating EUV radiation. The system provides a second gas flow path in the vessel when the system is not generating EUV radiation. The system can switch between the first gas flow path and the second gas flow path in a few milliseconds.

Description

GAS FLOW REALLOCATION IN LIGHT SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US Application No. 63 / 621,302, filed on January 16, 2024, titled GAS FLOW REALLOCATION IN LIGHT 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. EUV radiation can be used as, for example, exposure radiation in a lithographic process to fabricate semiconductor devices or in an inspection process for quality control.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 circuit 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 silicon wafer). Transfer ofthe pattern is typically via imaging onto a layer of radiationsensitive matenal (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 so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called 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 a 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 photolithography occurs at 13.5 nm.

[0005] 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. In variousimplementations, these methods are suitable for use in the production of microelectronic circuits and / or semiconductor devices.

[0006] In one such method, often termed laser-produced plasma (“LPP”), the desired plasma can be produced by irradiating a source material, for example tin, in the form of a droplet, stream or wire, with a laser beam.

[0007] A laser-produced plasma source does not generate light continuously while a substrate is being exposed. Instead, the source produces bursts of light which typically last up to hundreds of milliseconds and have tens to hundreds of milliseconds in between. Laser pulse timing can be changed so that a laser beam hits targets during the burst (“hit mode”) and misses them between bursts (“miss mode”).

[0008] One or more purge gas flows are used to protect a collector and vessel (e.g., chamber) walls from plasma debris. In some embodiments, purge gas flows includes argon, dry clean air, hydrogen, nitrogen, and a combination thereof. Several milliseconds after the miss mode to hit mode transition, the flows have stabilized to a new hit mode configuration. The flows go through a transient reorganization process between the miss mode and hit mode state.

[0009] Similarly, a hit mode to miss mode transition also happens, and leads to a different transient reorganization process in which the gas flow attempts to settle back into the miss mode configuration. Depending on the amount of time in between bursts, however, the system does not always have enough time to reach this state, which can impact the subsequent miss to hit mode transition.

[0010] Transient reorganization processes during miss to hit mode and hit to miss mode transitions contribute significantly to debris deposition on the collector and chamber walls, drastically decreasing the lifetime of the modules.SUMMARY

[0011] Accordingly, it is desirable to improve gas flows during the hit mode and miss mode transitions to direct debris from plasma generation away from vital components of an EUV light source.

[0012] In some aspects, a system includes a vessel configured for extreme ultraviolet radiation generation, a mirror, a gas flow assembly and an exhaust. In some aspects, the system provides a first gas flow path in the vessel when the system is in a first state and a second flow path in the vessel when the system is in a second state. In some aspects, the system can switch between the first flow path and the second flow path in a few milliseconds. In some aspects, the system can switch states in less than 10 milliseconds.

[0013] In some aspects, a lithography system includes an EUV light source with a vessel for generation of EUV radiation. In some aspects, the light source can provide a first gas flow path in the vessel in a first state and a second gas flow path in the vessel in a second state. In some aspects, the system can switch between the first gas flow path and the second gas flow path in less than 10 milliseconds.

[0014] In some aspects, a method of altering a gas flow path in a light source includes adjusting one or more elements of a first gas flow conduit or a second gas flow conduit to allow gas to flow from thesecond flow conduit to the first gas flow conduit. In some aspects, the method can further include adjusting one or more elements of the first gas flow conduit or the second gas flow conduit to block gas from flowing from the second gas flow conduit to the first gas flow conduit. In some aspects, the adjusting can alter the gas flow path in a light source in less than 10 milliseconds.

[0015] 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

[0016] 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.

[0017] FIG. 1 shows a reflective lithographic apparatus, according to some aspects.

[0018] FIGS . 2A, 2B, and 3 show more details of a reflective lithographic apparatus, according to some aspects.

[0019] FIG. 4 shows a lithographic cell, according to some aspects.

[0020] FIG. 5 shows a source material delivery system, according to some aspects.

[0021] FIG. 6A shows a gas flow configuration in a chamber during a hit mode, according to some aspects.

[0022] FIG. 6B shows a gas flow configuration in a chamber during a miss mode, according to some aspects.

[0023] FIG. 7A and 7B show an embodiment of a gas flow conduit during a hit mode and a miss mode, according to some aspects.

[0024] FIG. 8A and 8B show an additional embodiment of a gas flow conduit during a hit mode and a miss mode, according to some aspects.

[0025] FIG. 8C and 8D show another embodiment of a gas flow conduit during a hit mode and a miss mode, according to some aspects.

[0026] FIG. 9 shows a method of altering a gas flow path in a light source, according to some aspects.

[0027] FIG 10 shows a gas flow in a chamber directly after an on-off droplet transition, according to some aspects.

[0028] 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 left-most 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

[0029] 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.

[0030] 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.

[0031] 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).

[0032] 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,” orthe 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.

[0033] 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.

[0034] Example Lithographic Systems

[0035] 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.

[0036] 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 MS can also be disposed at other locations. For example, measurement sensor MS can be on or near substrate table WT.

[0037] 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).

[0038] 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.

[0039] Paterning device MA can be reflective. Examples of paterning 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 atenuated 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 patern in radiation beam B, which is reflected by a matrix of small mirrors.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 theuniformity of radiation beam B. Measurement sensor MS can be used to monitor the uniformity of radiation beam B.

[0045] 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 IF2 (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 IF1 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.

[0046] In some aspects, lithographic apparatus 100 can be used in at least one of the following modes:

[0047] 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.

[0048] 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 structure MT can be determined by (de-)magnification and image reversal characteristics of projection system PS.

[0049] 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.

[0050] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0051] 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.

[0052] FIG. 2A shows a different view of lithographic apparatus 100, including source SO (e g., source collector apparatus), illumination system IL, and projection system PS, 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- or laser-generated plasma source. In some aspects, a plasma of excited tin (Sn) (e.g ., excited via a laser) is used to produce EUV radiation.

[0053] 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.

[0054] 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.

[0055] 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 a desired 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.

[0056] 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

[0057] 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.

[0058] Collector CO (also called a collector mirror or collector optic), as illustrated in FIG. 2A, is depicted as an example of a nested collector with grazing incidence reflectors 253, 254, and 255.Grazing incidence reflectors 253, 254, and 255 can be disposed axially symmetric around an optical axis O. A collector of this type can be used in combination with a discharge-generated plasma source, often called a DPP source.

[0059] FIG. 2B shows a portion of lithographic apparatus 100 (e.g., FIG. 1), but with alternative collection optics in source SO, 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. 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.

[0060] FIG. 3 shows a detailed view of a portion of lithographic apparatus 100 (e.g., FIGS. 1, 2A, and 2B), according to one or more 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 for generating a train of light pulses and delivering the light pulses into a light source chamber 212. 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 212 to illuminate a source material at an irradiation region 304 to generate a plasma (e.g., plasma region located at EUV radiation emitting plasma 210 in FIG. 2B) that produces EUV light for substrate exposure in the exposure device 256.

[0061] 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 lasersystem 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.

[0062] 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.

[0063] 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.

[0064] 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 ormore mirrors, prisms, lenses, etc., can be provided and arranged to steer the laser focal spot to different locations in the chamber 212. 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).

[0065] 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.

[0066] 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 an EUV emission. The EUV emission is used to expose a substrate such as a resist-coated wafer at exposure device 256. 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.

[0067] In some aspects, the source material for producing an EUV light output for substrate 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., SnB , SnBr2, SnEh, 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., SnEE).

[0068] 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 212 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 measurement output 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 212. 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.

[0069] In some aspects, the lithographic apparatus 100 can also comprise a collector 258 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 intochamber 212. The buffer gas can be present in the chamber 212 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.

[0070] In some aspects, collector 258 can be a near-normal incidence collector mirror having a reflective surface in the form of a prolate spheroid as described above. Collector 258 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 212. As shown, the collector 258 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 256. 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 258 (e.g., collector CO (FIG. 2A)).

[0071] Example Lithographic Cell

[0072] 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 and post-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 mput / 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.

[0073] Example Plasma Material Droplet Source

[0074] FIG. 5 shows a source material delivery system 500, according to some aspects. In some aspects, source material delivery system 500 can be used in a lithographic apparatus or an inspection apparatus. Source material delivery system 500 comprises a nozzle 502, an electromechanical element 504, and a waveform generator 506. Nozzle 502 comprises a capillary 508. Source material delivery system 500 further comprises a shroud 510, a controller 512, a first detector 514, and / or a second detector 516. Controller 512 comprises a processor.

[0075] In some aspects, terms such as “electromechanical,” “electro-actuated,” or the like can be used herein to refer to a material or structure which undergoes a dimensional change (e.g., movement, deflection, contraction, rotation, and the like) when subjected to a voltage, electric field, magnetic field, or combinations thereof. Some examples can include piezoelectric materials, electrostrictive materials, and magnetostrictive materials. Apparatuses and methods for using an electro -actuated element to control a droplet stream are disclosed, for example, in U.S . Patent No. 7,897,947, titled “Laser Produced Plasma EUV Light Source Having a Droplet Stream Produced Using a Modulated Disturbance Wave” and issued March 01, 2011, and U.S. Patent No. 8,513,629, titled “Droplet Generator with Actuator Induced Nozzle Cleaning” and issued August 20, 2013, both of which are incorporated by reference herein in their entireties.

[0076] In some aspects, electromechanical element 504 is disposed on (e.g., surrounding) nozzle 502. It should be appreciated that interactions between nozzle 502 and electromechanical element 504 described herein is directed to interactions between a pressure-sensitive element of nozzle 502 and electromechanical element 504 (e.g., electromechanical element 504 is disposed on capillary 508). Waveform generator 506 is electrically coupled to electromechanical element 504. Controller 512 is electrically coupled to waveform generator 506.

[0077] In some aspects, an EUV -generating-plasma is generated by irradiating target material (e.g., Sn) with a laser, which ionizes some or all of the target material (i.e., excitation). The target material is provided as a stream of coalesced droplets that intersects the laser path. Microscopic interactions between a coalesced target material droplet and the laser can affect efficiency and stability of EUV radiation, which in turn can impact lithographic processes that depend on the EUV radiation. Therefore, it is desirable to control the interaction between coalesced droplet and the laser such that EUV- generation is stable and efficient. One method to improve stability and efficiency is to ensure repeatable coalescence of target material droplets so that each coalesced droplet produces a repeatable interaction with the laser. Structures and functions in aspects of the present disclosure allow for repeatable coalescence of target material droplets.

[0078] In some aspects, nozzle 502 ejects initial droplets of target material, shown in FIG. 5 as a stream of target material 518. Electromechanical element 504 transduces electrical energy from the waveform generator 506 to apply a pressure on nozzle 502 (e.g., on capillary 508). This introduces a velocity perturbation in stream of target material 518 exiting nozzle 502. Stream of target material 518 ultimately coalesces into droplets which are detected by first detector 514 and / or second detector 516 to generate a signal (e.g., a detection signal). As used herein, the term “detect” or the like can be used to refer to capturing an image (e g., using a camera) of the droplet and / or binary indication of the presence or absence of a droplet or when a droplet crosses a given location (e g , using a laser curtain). Detectors 514 and 516 can be trigger detectors, gating detectors, gate detectors, photo diode or other suitable detectors that generate a detection signal in response to a fulfillment of one or more conditions, for example the detected presence of a droplet. One of detectors 514 and 516 can be an image capturedevice and the other can be a gate detector. Controller 512 can determine properties of stream of target material 18 based on the signal from first detector 514. Properties of the stream of target material 518 comprise, for example, velocity profile of the droplet stream at the detection point, gap (time and / or distance) between droplets, presence of uncoalesced droplets (satellite droplets, or simply “satellites”), droplet size, coalescence length, droplet path (or aim), or the like. Controller 512 can use the information from detectors 514 and / or 516 to generate a feedback signal to control operation of the waveform generator 506.

[0079] In some aspects, controller 512 adjusts parameters of electrical signals (e.g., waveform, hybrid waveform) generated by waveform generator 506. Parameters of waveforms comprise, for example, relative phase difference(s) between two or more waveforms in superposition, amplitude, wavelength, and the like. Controller 512 can also determine an adjustment of a waveform parameter based on an external input 520, which originates from another controller or be based on a user input.

[0080] In some aspects, shroud 510 is disposed on nozzle 502. Shroud 510 is disposed so as to cover and protect stream of target material 518 from forces that can disrupt coalescence and droplet generation.

[0081] In some aspects, waveform generator 506 is configured to generate an electrical signal to control the applied pressure on nozzle 502. The electrical signal can comprise a superposition (e.g., hybrid waveform) of a first periodic waveform having a first frequency (e.g., a low frequency sine wave) and a second periodic waveform having a second frequency different from the first frequency (e.g., a high frequency square wave). The term “sine” is used herein to refer to sinusoidal patterns. The second frequency can be an integer multiple of the first frequency. The resulting velocity perturbations in stream of target material 518 allow the initial droplets that are ejected from nozzle 502 to coalesce as they travel away from nozzle 502. A fully coalesced droplet 522 forms at a distance L (“coalescence length”) from the orifice of nozzle 502. In other words, a distance, measured from the nozzle, at which coalesced droplet 522 forms without remnant uncoalesced droplets (e.g., satellites) defines a coalescence length.

[0082] Example Gas Flow Reallocation

[0083] A laser-produced plasma light source does not generate light continuously. Instead, the source produces bursts of light which can last up to hundreds of milliseconds with tens to hundreds of milliseconds in between. The timing of laser pulses change such that the laser pulses hit targets during the bursts (“hit mode”) and miss them between bursts (“miss mode”).

[0084] In some aspects, a laser-produced plasma source produces debris, such as residual tin ions. A gas flow can be configured in a radiation generation chamber to transport generated debris towards a debris collector, which can be inside or outside of the chamber. The gas flow can additionally act to slow plasma-created ions and / or reduce degradation of optics.

[0085] In some aspects, time scales of laser-produced plasma generation are short compared to time scales associated with a gas flow-based debris transport. There can be short periods of time where plasma is no longer generated, but debris from previous plasma events still reside in an EUV source chamber. The sudden appearance or disappearance of the plasma can result in a transient flow reordering process. In some aspects, flow reordering effects can be associated with a rapid upward push of the residual debris, also called an overshoot. Overshoot can result in deposition of contaminants on chamber wall and / or in areas near the intermediate focus INTF where high cleanliness is required.

[0086] In some aspects, a gas flow assembly can dispense gas into a radiation generation chamber. The gas flow assembly can direct gas flow “perpendicular” to a collector in a radiation chamber. A “perpendicular” gas flow may not be exactly perpendicular to a collector surface. Instead a “perpendicular” gas flow can refer to a gas flow that directs gas flow away from a collector and towards a plasma generation region. In some aspects, a “perpendicular” gas flow can additionally flow towards an exhaust.

[0087] In some aspects, a gas flow assembly can direct gas flow “parallel” to a collector in a radiation generation chamber. A “parallel” gas flow may not be exactly parallel to a collector surface. Instead a “parallel” gas flow can refer to a gas flow that generally flows along the surface of a collector. In some aspects, a parallel gas flow can follow the curvature of the collector.In some aspects, gas can be directed “parallel” and “perpendicular” to a collector surface simultaneously. In some aspects, gas can be dispensed in directions other than the “parallel” and “perpendicular” directions described above.

[0088] FIGS. 6A and 6B show gas flow configurations in a radiation generation chamber, according to some aspects. For example, FIGS. 6A and 6B can show gas flow in a chamber of a lithographic apparatus or an inspection apparatus. In some aspects, FIGS. 6A and 6B show a portion of the total gas flow in a radiation generation chamber and are not representative of the total gas flow in the chamber.

[0089] FIG. 6A shows a gas flow 602 during a hit mode, according to some aspects. During the hit mode, droplets are irradiated by one or more laser pulses to generate a radiation emitting plasma. Gas flow 602 is dispensed from a gas flow assembly 620. In some aspects, gas flow 602 is configured to flow towards an irradiation region 603 and carry debris generated during plasma generation towards an exhaust 604.

[0090] FIG. 6B shows a gas flow 606 during a transition between and hit mode and miss mode, according to some aspects. During and hit-miss transition, gas flows in a chamber can undergo a transient reorganization process. Similar to gas flow 602, gas flow 606 can be dispensed from gas flow assembly 620 and carry residual debris generated during plasma generation towards exhaust 604. However, the sudden absence of plasma during the hit-miss transition causes a transient flow reordering process, resulting in overshoot 608. For example, a portion of gas flow 606 misses exhaust 604 and forms overshoot 608. Overshoot 608 can carry debris towards a wall of a chamber 612 and / or towards an intermediate focus (e.g., INTF).

[0091] In some aspects, gas flows 602 and 606 illustrate “perpendicular” gas flows.

[0092] Gas flows in a radiation generation chamber, such as chamber 612 in the lithography apparatus or the inspection apparatus, can be configured to quickly switch between a first gas flow configuration during an hit mode and a second gas flow configuration during an miss mode. Altering gas flow paths during hit-miss and miss-hit transitions reduce the effects of transient reordering of gas flows, such as deposition on chamber walls and / or collection optics.

[0093] In some aspects, both the first gas flow configuration and the second gas flow configuration are configured to prevent debris deposition on a collector and / or chamber walls by directing debris towards a debris collector (e.g., and exhaust or a scmbber).

[0094] In some aspects, a system is configured to switch between a first gas flow configuration and a second gas flow configuration in less than 10 milliseconds. If the switch is greater than 10 milliseconds, a flow reordering effect that associated with a rapid forward push of contaminants over an exhaust increases debris deposition on an internal wall of a chamber, in some instances. In some aspects, the system is configured to switch between a first gas flow configuration and a second gas flow configuration in less than 5 milliseconds.

[0095] In some aspects, one or more components in the system can be configured to alter the gas flow dispensed into a chamber when the system transitions between the first gas flow configuration and the second gas flow configuration.

[0096] FIGS. 7A and 7B show a cross section of gas dispenser device 700, according to some aspects. Gas dispenser device 700 and collector 758 can be cylindrically symmetric. Gas dispenser device 700 comprises a first gas flow conduit 702 and a second gas flow conduit 704. First gas flow conduit 702 can represent multiple conduits arranged around second gas flow conduit 704. In some aspects, first gas flow conduit 702 comprises a surface 706. Surface 706 can comprise adjustable member 708. In some aspects, second gas flow conduit 704 comprises a surface 710. Surface 710 can comprise fixed gap 712. In some embodiments, fixed gap 712 is a continuous opening that separates an upper part of second gas flow conduit 704 from a lower part of second gas flow conduit 704. In some embodiments, fixed gap 712 represents multiple discrete openings surrounding a sidewall of second gas flow conduit 704. In some aspects, first gas flow conduit 702 is configured to direct gas flow “parallel” to a collector surface, as illustrated by flow lines 716. In some aspects, second gas flow conduit 704 is configured to direct gas flow “perpendicular” to a collector surface, as illustrated by flow lines 714. First gas flow conduit 702 and second gas flow conduit 704 can be concentric.

[0097] Adjustable member 708 can be configured to move perpendicular to the collector surface to create an opening 718 in first gas flow conduit 702.

[0098] FIG. 7A shows a configuration of gas dispenser device 700 during a hit mode, according to some aspects. Adjustable member 708 can be positioned to block gas from flowing from second gas flow conduit 704 to first gas flow conduit 702.

[0099] FIG. 7B shows a configuration of gas dispenser device 700 during a miss mode, according to some aspects. In FIG. 7B, adjustable member 708 is positioned to allow gas from second gas flow conduit 704 to flow into first gas flow conduit 702 through opening 718. In some aspects, the amount of gas flowing out of gas flow conduit 704 is decreased, and the amount of gas flowing out of gas flow conduit 702 is increased.

[0100] Comparing to other approaches, a redirection of gas between the hit mode and the miss mode can reduce debris overshoot.

[0101] FIGS. 8 A and 8B show a cross section of gas dispenser device 800, according to some aspects. Gas dispenser device 800 and collector 858 can be cylindrically symmetric. Gas dispenser device 800 further comprises a first gas flow conduit 802 and a second gas flow conduit 804. First gas flow conduit 802 can represent multiple conduits arranged around second gas flow conduit 804. First gas flow conduit 802 comprises an inner surface 806. In some aspects, inner surface 806 comprises a first gap 808. First gap 808 can have a fixed dimension. First gas flow conduit 802 can be configured to provide gas flow “parallel” to a collector surface.

[0102] Second gas flow conduit 804 comprises a sidewall 810. Sidewall 810 comprises one or more second gaps 812. In some embodiments, second gap 812 is a continuous opening that separates an upper part of second gas flow conduit 804 from a lower part of second gas flow conduit 804. In some embodiments, second gap 812 represents multiple discrete openings surrounding sidewall 810. In some aspects, second gap 812 can have a fixed dimension. Second gas flow conduit 804 can be configured to provide gas flow “perpendicular” to a collector surface. First gas flow conduit 802 and second gas flow conduit 804 can be concentric. Inner surface 806 and sidewall 810 can be in contact.

[0103] FIG. 8A shows gas dispenser device 800 during a hit mode, according to some aspects. First gap 808 and second gap 812 are unaligned, and gas does not flow from second gas flow conduit 804 to first gas flow conduit 802.

[0104] FIG. 8B shows gas dispenser device 800 during a miss mode, according to some aspects. In FIG. 8B, second gas flow conduit 804 is retracted with respect to collector 858. When second gas flow conduit 804 is retracted, first gap 808 and second gap 812 can align. In some aspects, gas can flow from second gas flow conduit 804 into first gas flow conduit 802 through second gap 812 and first gap 808. In some aspects, gas flowing out of second gas flow conduit 804 is reduced and gas flowing out of first gas flow conduit 804 is increased. In some embodiments, retracted second gas flow conduit 804 increases a distance from an irradiation region and thereby increases more space for a second flow 814. In some embodiments, second gas flow conduit 804 is fixed, and first gas flow conduit 802 moves vertically to align and misalign first gap 808 and second gap 812.

[0105] FIGS. 8C and 8D show gas dispenser device 800’ during a miss mode and a hit mode, according to some aspects. In some embodiments, first gas flow conduit 802’ is fixed and second gas flow conduit 804’ is tumable. In other words, first gap 808’ and second gap 812’ are vertically arranged at a same level, but the alignment and misalignment of first gap 808’ and second gap 812’ are performed byrotating first gas flow conduit 802’. In this example, second gap 812’ represents multiple discrete openings arranged around sidewall 810’.

[0106] Comparing to other approaches, reducing “perpendicular” gas flow during a hit-miss transition reduces overshoot, increasing the lifetime of vessel (e.g., a chamber) walls.

[0107] FIG. 9 shows a method 900 of altering a gas flow path in a light source, according to some aspects. Method 900 can comprise steps 902 and 904.

[0108] In some aspects, step 902 comprises adjusting one or more elements of a first gas flow conduit or a second gas flow conduit to allow gas to flow from the second gas flow conduit to the first gas flow conduit. In some aspects, an adjustable member of the first gas flow conduit is adjusted to create a gap in the first gas flow conduit that aligns with a gap in the second gas flow conduit, as shown in FIGS. 7A and 7B. Alternatively, a second gas flow conduit can be retracted to align a gap in the second gas flow conduit with a gap in the first gas flow conduit, as shown in FIGS. 8A and 8B. Alternatively, a second gas flow conduit can be rotated to align a gap in the second gas flow conduit with a gap in the first gas flow conduit, as shown in FIGS. 8C and 8D.

[0109] In some aspects, step 904 comprises adjusting one or more elements of the first gas flow conduit or the second gas flow conduit to block gas from flowing from the second gas flow conduit to the first gas flow conduit. In some aspects, an adjustable member of the first gas flow conduit is adjusted to close a gap in the first gas flow conduit, as shown in FIGS. 7A and 7B. In some aspects, a second gas flow conduit is adjusted so that a gap in the second gas flow conduit does not align with a gap in the first gas flow conduit, as shown in FIGS. 8 A and 8B. Alternatively, a second gas flow conduit can be rotated to misalign a gap in the second gas flow conduit with a gap in the first gas flow conduit, as shown in FIGS. 8C and 8D.

[0110] 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, and 10.[oni] In some aspects, pressure gradients between weakly linked components (e.g., tin catch) in a radiation generation chamber can generate high speed gas flows due to pressure changes that occur during hit-miss and miss-hit transitions. Pressure changes can be due to dynamics of gas in the chamber during plasma generation. During a hit mode, gas can increase in temperature and flow from the plasma generation region towards the weakly linked components. As the gas flows towards the weakly linked components, the pressure in the components can increase relative to the pressure in the chamber. During a miss mode, plasma generation ceases, and gas no longer flows towards the components. In some aspects, a high velocity (up to 180 m / s) stream of gas can flow from the weakly linked components towards the chamber during a hit-miss droplet transition due to a pressure difference between the weakly linked components and the inner liner of the chamber.

[0112] For example, an inner liner of a chamber and a source material catch (i.e., reservoir positioned along the same axis as source material delivery system and configured to catch source material droplets not used to generate plasma) can be weakly linked. During plasma generation, gas flows into the source material catch and increases the localized pressure . Directly after an on-off droplet transition, a pressure gradient causes gas to flow into the inner region of chamber from the source material catch, thereby altering the gas flow path of gas in the chamber.

[0113] In some aspects, a weakly linked reservoir is intentionally positioned in a radiation generation chamber to alter gas flow in a chamber during an on-off and / or off-on droplet transition.

[0114] FIG. 10 shows a gas flow in a chamber containing a linked reservoir, according to some aspects. In some aspects, the gas flow configuration shown in FIG. 10 represents a portion of the total gas flow and is not representative of the total gas flow in a chamber 1012.

[0115] In some aspects, FIG. 10 shows a gas flow configuration during a transition from a hit mode state to miss mode state. Gas dispenser device 1020 can dispense gas flow 1002 “perpendicular” to collector 10 8. Reservoir 1004 is linked to chamber 1012. In some aspects, gas flows into reservoir 1004 and increases the pressure in reservoir 1004 during the hit mode state. In some aspects, a pressure gradient is formed between reservoir 1004 and chamber 1012 (e.g. pressure is higher in reservoir 1004 during a hit mode state). When a light source transitions to a miss mode state, gas flow 1006 can flow from reservoir 1004 to chamber 1012 due to the pressure gradient that formed between reservoir 1004 and chamber 1012 during the hit mode state. In some aspects, gas flow 1004 can deform gas flow 1002. Gas flow 1006 directs gas flow 1002 towards exhaust 1008.

[0116] In some aspects, reservoir 1004 can alternatively be configured to provide gas flow 1006 to chamber 1012 during a transition from a miss mode state to a hit mode state.

[0117] In some aspects, gas flow 1006 can exit reservoir 1004 less than 5 milliseconds after a hit-miss mode or miss-hit mode transition. In some aspects, gas flow 1006 can alter the path of gas flow 1002 less than 10 milliseconds after a hit-miss or miss-hit mode transition. In some aspects, gas flow 1006 can alter the path of gas flow 1002 less than 5 milliseconds after a hit-miss or miss-hit transition.

[0118] 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 refersto 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.

[0119] 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, LCDs, 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

Claims

CLAIMS1. A system comprising: a vessel configured for extreme ultraviolet (EUV) radiation generation; a mirror having a reflecting surface; a gas flow assembly; and an exhaust; wherein the system is configured to switch between a first gas flow path in the vessel and a second gas flow path in the vessel in less than 10 milliseconds.

2. The system in claim 1, wherein the gas flow assembly comprises: a first gas flow conduit configured to direct gas substantially parallel to the reflecting surface, wherein the first gas flow conduit comprises an inner surface; and a second gas flow conduit configured to direct gas substantially perpendicular to the reflecting surface, wherein the second gas flow conduit comprises an outer surface; and wherein the inner surface of the first gas flow conduit is adjacent to the outer surface of the second gas flow conduit.

3. The system of claim 2, wherein the outer surface of the second gas flow conduit comprises a fixed gap and the inner surface of the first gas flow conduit comprises an adjustable member, and wherein the adjustable member controls gas to flow from the second gas flow conduit into the first gas flow conduit through the fixed gap in the second gas flow conduit.

4. The system of claim 3, wherein the adjustable member is adjusted to switch gas flow in the vessel from the first gas flow path to the second gas flow path.

5. The system of claim 3, wherein the adjustable member is adjusted to switch gas flow in the vessel from the second gas flow path to the first gas flow path.

6. The system of claim 2, wherein the inner surface of the first gas flow conduit comprises a first fixed gap and the outer surface of the second gas flow conduit comprises a second fixed gap and wherein the second gas flow conduit is adjustable to allow gas to flow from the second gas flow conduit to the first gas flow conduit, via the second gap being aligned with the first gap.

7. The system of claim 6, wherein the second gas flow conduit is adjusted to switch gas flow in the vessel from the first gas flow path to the second gas flow path.

8. The system of claim 6, wherein the second gas flow conduit is adjusted to switch gas flow in the vessel from the second gas flow path to the first gas flow path.

9. The system of claim 1, wherein the vessel comprises a reservoir configured to provide a high velocity stream of gas that switches gas flow in the vessel from the first gas flow path when the system is in a first state to the second gas flow path when the system is in a second state or from the second gas flow path when the system is in the second state to the first gas flow path when the system is in the first state.

10. The system of claim 9, wherein the high velocity stream of gas is provided by pressure changes that occur when the system switches from the first state to the second state.

11. The system of claim 9, wherein the high velocity stream of gas is provided by pressure changes that occur when the system switches from the second state to the first state.

12. The system of claim 1, wherein the system experiences a first state when EUV generation is active and a second state when EUV generation is inactive.

13. The system of claim 12, wherein the first state comprises a duration of 100 to 200 milliseconds and the second state comprises a duration of 20 to 30 milliseconds.

14. The system of claim 12, wherein the first state comprises a duration of about 50 milliseconds and the second state comprises a duration of 20 to 30 milliseconds.

15. The system of claim 12, wherein the first gas flow path is configured to direct gas flow away from the mirror and towards the exhaust when the system is in the first state.

16. The system of claim 12, wherein the second gas flow path is configured to direct gas flow away from the mirror and towards the exhaust when the system is in the second state.

17. A lithography system comprising: a light source comprising a vessel for generation of EUV radiation; wherein the light source is configured to provide a first gas flow path in the vessel in a first state and a second gas flow path in the vessel in a second state; and wherein the lithography system is configured to switch between the first gas flow path and the second gas flow path in less than 10 milliseconds.

18. The lithography system of claim 17, wherein the lithography system experiences the first state when EUV generation is active and the second state when EUV generation is inactive.

19. A method of altering a gas flow path in a light source, the method comprising: adjusting one or more elements of a first gas flow conduit or a second gas flow conduit, wherein the adjusting allows gas to flow from the second gas flow conduit to the first gas flow conduit; and adjusting one or more elements of the first gas flow conduit or the second gas flow conduit, wherein the adjusting blocks the gas from flowing from the second gas flow conduit to the first gas flow conduit; wherein the adjusting alters the gas flow path in the light source in less than 10 milliseconds.

20. The method of claim 19, wherein the adjusting comprises aligning one or more gaps in the first gas flow conduit with one or more gaps in the second gas flow conduit.

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