System and methods for debris reduction

Abstract

An extreme ultraviolet (EUV) light source includes a vessel, a collector positioned at one end of the vessel, a cap structure positioned at the other end of the vessel, an exhaust module positioned between the collector and the cap structure, a flow inner liner positioned between the exhaust module and the cap structure, and a first plurality of ridge structures positioned on an interior surface of the flow inner liner. Each of the first plurality of ridge structures includes a first surface facing the collector, a second surface facing the cap structure, a third surface close to the interior surface of the flow inner liner, and a forth surface away from the interior surface of the flow inner liner. The first surface is substantially perpendicular to the third surface.

Description

SYSTEMS AND METHODS FOR DEBRIS REDUCTIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 692,544, filed September 9, 2024, titled SYSTEM AND METHODS FOR DEBRIS REDUCTION, which is incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure relates to extreme ultraviolet (“EUV”) light sources, apparatuses, systems, and methods. EUV light sources can be used as, for example, in a semiconductor manufacturing process, such as a lithographic process or a metrology process.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 is alternatively referred to as 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 of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus 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 about 13.5 nm.

[0005] The EUV light can also be used in metrology processes to measure critical dimension and inspect defect during the semiconductor manufacturing processes. For example, the scope of the present disclosure can be implemented in a metrology apparatus to measure and characterize physical properties of materials and components. The metrology apparatus is a precision instrument that ensures productquality and process control. In at least one embodiment, the metrology apparatus employs EUV light to inspect and measure dimensions of targets on the substrate.

[0006] 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.

[0007] In one such method, often termed laser-produced plasma (“LPP”), the desired plasma can be produced by irradiating a source material, for example, in the form of a droplet, stream, or wire, with a laser beam. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosing structure or vessel arranged to provide a vacuum environment to support the plasma. In another method, often termed discharge produced plasma (“DPP”), the plasma can be generated by positioning source material having an appropriate mission line between a pair of electrodes and causing an electrical discharge to occur between the electrodes.

[0008] Infrared radiation used to irradiate the source material may cause heating of surfaces of the vessel that may cause melting of components of the radiation source. Debris from the melted components may result in a degradation in the performance of the radiation source which in turn can lead to degradation of performance of an associated semiconductor manufacturing apparatus.SUMMARY

[0009] Accordingly, it is desirable to provide a structure within a light source (e.g., an EUV light source) to prevent or mitigate the abovementioned effects of heating of surfaces of the chamber.

[0010] In some aspects, a light source includes a vessel, a collector positioned at one end of the vessel, a cap structure positioned at the other end of the vessel, an exhaust module positioned between the collector and the cap structure, a flow inner liner positioned between the exhaust module and the cap structure, and a first plurality of ridge structures positioned on an interior surface of the flow inner liner. Each of the first plurality of ridge structures includes a first surface facing the collector, a second surface facing the cap structure, a third surface close to the interior surface of the flow inner liner, and a forth surface away from the interior surface of the flow inner liner, and the first surface is substantially perpendicular to the third surface.

[0011] In some aspects, a semiconductor manufacturing apparatus includes a light source having a vessel, a collector configured to collect radiation generated from plasma and direct the radiation towards an intermediate focus of the collector, an exhaust module positioned between the collector and the intermediate focus, and a flow inner liner positioned between the exhaust module and the intermediate focus. An interior surface of the flow inner liner includes a first plurality of ridge structures and a second plurality of ridge structures, and an average aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures.

[0012] In some aspects, a method includes collecting, using a collector in a vessel, radiation generated from plasma at an primary focus of the collector, directing the radiation towards an intermediate focus of the collector, and altering a path of undesired radiation to decrease incident radiation from a flow inner liner to an exhaust module positioned between the collector and the intermediate focus.

[0013] Further features and exemplary aspects of the present disclosure, as well as the structure and operation of various aspects, are described in detail below with reference to the accompanying drawings. It is noted that the aspects are not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0014] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the aspects and, together with the description, further serve to explain the principles of the aspects and to enable a person skilled in the relevant art(s) to make and use the aspects.

[0015] FIG. 1 shows a schematic of a reflective lithographic apparatus, according to an exemplary aspect.

[0016] FIG. 2A shows a more detailed schematic of the reflective lithographic apparatus, according to an exemplary aspect.

[0017] FIG. 2B shows a more detailed schematic of the reflective lithographic apparatus, according to an exemplary aspect.

[0018] FIG. 3 shows a schematic of a lithographic cell, according to an exemplary aspect.

[0019] FIG. 4 is a schematic that illustrates an extreme ultraviolet (EUV) light source, according to an exemplary aspect.

[0020] FIG. 5 is a schematic that illustrates an EUV light source, according to an exemplary aspect.

[0021] FIG. 6 is a schematic that depicts a partial view looking from a center of a collector towards an intermediate focus of a vessel, according to an exemplary aspect.

[0022] FIG. 7 is a schematic that illustrates a plane view of an inner surface of a vessel, according to an exemplary aspect.

[0023] FIG. 8A is a schematic that illustrates a cross section of a perspective view of a portion of a flow inner liner, according to an exemplary aspect.

[0024] FIG. 8B is a partial enlargement of FIG. 8B, according to an exemplary aspect.

[0025] FIG. 9A is a schematic that illustrates a cross section of a perspective view of a portion of an inner liner, according to an exemplary aspect.

[0026] FIG. 9B is a schematic that illustrates a cross section of a perspective view of another portion of an inner liner, according to an exemplary aspect.

[0027] FIG. 10 illustrates a flow diagram for an illumination system, according to an exemplary aspect.

[0028] The features and exemplary aspects 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] Provided herein are system, apparatus, device, method, and / or computer program product aspects, and / or combinations and sub -combinations thereof, for decreasing heating of one or more components of a chamber of a light source caused by radiation.

[0030] The aspect(s) described, and references in the specification to “one aspect,” “an aspect,” “an example aspect,” “an exemplary aspect,” etc., indicate that the aspect(s) described may 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 one skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0031] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, may 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 may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0032] The term “about” or “substantially” or “approximately” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term “about” or “substantially” or “approximately” can indicate a value of a given quantity that varies within, for example, 1-15% of the value (e.g., ±1%, ±2%, ±5%, ±10%, or ±15% of the value).

[0033] Numerical values, including endpoints of ranges, can be expressed herein as approximations preceded by the term “about,” “substantially,” “approximately,” or the like. In such cases, other aspects include the particular numerical value. Regardless of whether a numerical value is expressed as an approximation, two aspects are included in this disclosure: one expressed as an approximation, and another not expressed as an approximation. It will be further understood that an endpoint of each range is significant both in relation to another endpoint, and independently of another endpoint.

[0034] Aspects of the disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure may also be implemented as instructions stored on amachine-readable medium, which may be read and executed by one or more processors. A machine- readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine -readable medium may include 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. Further, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0035] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure may be implemented.

[0036] Example Lithographic Systems

[0037] FIG. 1 shows a schematic illustration of a lithographic apparatus 100, in which embodiments of the present disclosure may be implemented. Lithographic apparatus 100 can include 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 the 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 the substrate W. Lithographic apparatus 100 also has a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective.

[0038] The illumination system IL can include 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.

[0039] The support structure MT holds the 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. The support structure MT may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which can be fixed or movable, as desired. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0040] The term “patterning device” MA should be broadly interpreted as referring 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 the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0041] The terms “inspection apparatus,” “metrology system,” or the like may be used herein to refer to, e.g., a device or system used for measuring a property of a structure (e.g., overlay error, critical dimension parameters) or used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment apparatus).

[0042] Patterning device MA can be reflective. Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include 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 may be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0043] The term “projection system” PS can encompass 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. A vacuum environment may be used for EUV or electron beam radiation since other gases may absorb too much radiation or electrons. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0044] 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, the additional substrate tables WT can be used in parallel, or preparatory steps may 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 not be a substrate table WT.

[0045] The lithographic apparatus may also be of a type wherein at least a portion of the substrate may 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 may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing 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, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0046] In some aspects, illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100 can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system including, for example, suitable directing mirrors and / or a beam expander.

[0047] Radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the 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), the 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, the 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 (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0048] The lithographic apparatus 100 can be used in at least one of the following modes:

[0049] 1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0050] 2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de- )magnification and image reversal characteristics of the projection system PS.

[0051] 3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the 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 as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation may be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0052] Combinations and / or variations on the described modes of use or entirely different modes of use may also be employed.

[0053] In a further embodiment, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0054] FIG. 2A shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment may be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor, or Sn vapor in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is created by, for example, an electrical discharge causing at least a partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required for efficient generation of the radiation. In some embodiments, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0055] The radiation emitted by hot plasma 210 is 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 include a channel structure. Contamination trap 230 can also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0056] The collector chamber 212 can include a radiation collector CO, which can be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral fdter 240 to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus IF is located at or near an opening 219 in enclosing structure 220. The virtual source point IF is an image of radiation emitting plasma 210. Grating spectral fdter 240 is used in particular for suppressing infra-red (IR) radiation.

[0057] Subsequently the radiation traverses the illumination system IL, which can include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the radiation beam 221 at the patterning device MA, held by the support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by the wafer stage or substrate table WT.

[0058] More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 can optionally be present, depending upon the typeof lithographic apparatus. Further, there may be more mirrors present than those shown in the FIG. 2A, for example there may be one to six additional reflective elements present in the projection system PS than shown in FIG. 2A.

[0059] Collector optic CO, as illustrated in FIG. 2A, is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0060] FIG. 2B shows a different view of lithographic apparatus 100, including the source collector apparatus SO with alternative collection optics, according to some embodiments. 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 embodiments 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.

[0061] In some embodiments, 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.

[0062] Exemplary Lithographic Cell

[0063] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some embodiments. Lithographic apparatus 100 can form part of lithographic cell 300. Lithographic cell 300 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. In some examples, these 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 apparatusvia lithography control unit LACU. Thus, the different apparatuses may be operated to maximize throughput and processing efficiency.

[0064] Example illumination light sources

[0065] FIG. 4 shows a detailed view of source SO and associated elements that can be used in lithographic apparatus 100, according to some embodiments. Elements in FIG. 4 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 embodiments, source SO can be a LPP EUV source. Source SO can comprise a laser system 402 (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 212. For the lithographic apparatus 100, the light pulses can travel along one or more beam paths from the laser system 402 and into the chamber 212 to illuminate a source material (or target material) at an irradiation region 404 (or target region, or primary focus) to generate a plasma. For example, EUV radiation emitting plasma 210 (FIG. 2B) is generated at irradiation region 404. EUV light is produced by the plasma. The EUV light is used for substrate exposure in the exposure device 256.

[0066] In some embodiments, laser system 402 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 embodiments, 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 irradiation region 404. Continuously pumped CO2 amplifiers can be used for laser system 402. 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.

[0067] In some embodiments, 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.

[0068] In some embodiments, a source material can first be irradiated by a pre-pulse (e.g., 1 pm) and thereafter irradiated by a main pulse (e.g., 10 pm). 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 amplifyboth the pre-pulse seed and main pulse seed. In some embodiments, separate amplifiers can be used to amplify the pre-pulse and main pulse seeds.

[0069] In some aspects, source SO can also comprise a beam conditioning unit 406 having one or more optics for beam conditioning, such as expanding, steering, and / or focusing the beam between laser system 402 and irradiation region 404. 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 different locations in 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).

[0070] Beam conditioning unit 406 can comprise a focusing assembly to focus the beam to irradiation region 404 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.

[0071] In some aspects, source SO can also comprise a source material delivery system 408 for delivering source material, such as tin droplets, to irradiation region 404, where the droplets can interact with light pulses from the laser system 402 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 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.

[0072] 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., 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 404, 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).

[0073] In some aspects, source SO can also comprise a controller 410 and / or a drive laser control system 412 for controlling devices in laser system 402 to generate light pulses for delivery into the chamber 212 and / or for controlling movement of optics in beam conditioning unit 406. Source SO can also comprise a droplet position detection system which can comprise one or more droplet imagers 414 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 404). The droplet imager(s) 414 can provide measurement output to a droplet position detection feedback system 416. Droplet position detection feedback system 416 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 410, which can, for example, provide a position, direction and / or timing correction signal to laser system 402 to control laser trigger timing and / or to control movement of optics in beam conditioning unit 406, e.g., to change the location and / or focal power of the light pulses being delivered to irradiation region 404 in chamber 212. Furthermore, source material delivery system 408 can comprise a control system operable in response to a signal from controller 410 (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 404.

[0074] In some aspects, source SO can also comprise collector 258 and a gas dispenser device 420. Gas dispenser device 420 can dispense gas in the path of the source material from source material delivery system 408 (e.g., irradiation region 404). Gas dispenser device 420 can comprise a nozzle through which dispensed gas can exit. Gas dispenser device 420 can be structured (e.g., having an aperture) such that, when placed near the optical path of laser system 402, light from laser system 402 is not blocked by gas dispenser device 420 and is allowed to reach irradiation region 404. A buffer gas such as hydrogen, helium, argon or combinations thereof, can be introduced into chamber 212. The buffer gas can be present in 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.

[0075] 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 402 to pass through and reach irradiation region 404. The same, or another aperture, can be used to allow gas from the gas dispenser device 420 to flow into chamber 212. As shown, collector 258 can be, e.g., a prolate spheroid mirror that has a first focus within or near the irradiation region 404 and a second focus at an intermediate region 218, 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 thatstructures and functions described in reference to FIG. 4 can be used with collectors other than collector 258 (e.g., collector CO (FIG. 2A)).

[0076] FIG. 5 is a schematic that illustrates an EUV light source 500, according to some aspects. In some aspects, EUV light source 500 can be a portion of source SO described with reference to FIGS. 1, 2A, 2B, and 4. The elements of EUV light source 500 shown in FIG. 5 and the elements of source SO shown in FIGS. 1, 2A, 2B, and 4 may be similar. Accordingly, the above discussion of source SO can apply to EUV light source 500 shown in FIG. 5. In some embodiments, EUV light source 500 can include a vessel 508, a collector 502, an exhaust module 506, and a laser 514.

[0077] In some aspects, EUV light source 500 may be referred to as a laser produced plasma (LPP) source. Laser 514 may be arranged to deposit energy into a fuel (e.g., tin). The laser beam from laser 514 incident upon the tin creates a plasma at a plasma formation region 516. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of ions of the plasma. In some aspects, the laser beam from laser 514 may have a wavelength in the infrared range.

[0078] The EUV radiation is collected and focused by collector 502. Collector 502 may have a multiplayer structure configured to reflect EUV radiation (e.g., a desired wavelength). Collector 502 may have an ellipsoidal shape that has an intermediate focus IF on an optical axis of collector 502 and a primary focus at plasma formation region 516. In some aspects, collector 502 can be an embodiment of radiation collector 258 described with reference to FIG. 2B. Accordingly, the above discussion of radiation collector 258 can apply to collector 502 shown in FIG. 5.

[0079] In some aspects, an EUV light source 500 may include a vessel 508. Radiation beam formed from a collector 502 passes through a flow inner liner 526 and a cap structure 504 before it reaches intermediate focus IF. In some embodiments, vessel 508 includes more liners between flow inner liner 526 and collector 502. In some aspects, vessel 508 may also be referred to as radiation conduit. Vessel 508 may be configured to absorb and / or reflect an infrared radiation 510. In some aspects, infrared radiation 510 includes a first wavelength and a second wavelength.

[0080] In some aspects, vessel 508 comprises an inner surface that tapers inwardly from an entrance aperture 520 distal to the intermediate focus IF to an exit aperture 522 positioned at an end of cap structure 504. The terms “entrance” and “exit” are used in reference to a direction of travel of an EUV radiation beam 512. e.g., the EUV radiation is generated at a plasma formation region 516 and exits vessel 508 at intermediate focus IF. The inner surface may refer to the surface that is inside or faces plasma formation region 516.

[0081] A tapering of inner wall 518 of vessel 508 may be such that EUV radiation, namely the EUV radiation that is focused by collector 502 towards intermediate focus IF passes unimpeded through vessel 508. The tapering of the inner walls may be such that other radiation, particularly radiation which is not focused toward the intermediate focus IF, is incident upon vessel 508 (e.g., the inner surface). For example, infrared radiation 510 which is emitted by laser 514 and which does not hit a targetmaterial or a source material or which is not completely absorbed by the target material but is instead scattered or reflected from the target material may be diffracted towards vessel 508 by collector 502.

[0082] In some aspects, the inner surface can be arranged such as vessel 508 has a conical shape with a substantially circular cross-section. In some aspects, vessel 508 can have other shapes such as cylindrical, spherical, semi-spherical, or cuboidal shape. For example, vessel 508 can include a crosssection that is substantially circular, ellipsoidal, square, or any other polyhedral shape.

[0083] In some aspects, a gas dispenser device can provide a gas flow such hydrogen, helium, argon, into vessel 508. The gas flow can carry any resulting debris out of vessel 508 through an exhaust module 506. Exhaust module 506 is attached to a second inner liner 527 and positioned between collector 502 and flow inner liner 526.

[0084] Flow inner liner 526 has an inner wall 518. In some aspects, one or more portions of inner wall 518 can include a least a ridge structure. In some aspects, structures such as ridges on inner wall 518 can extend circumferential around the inner surface of inner wall 518. The inner surface of inner wall 518 can absorb infrared radiation 510. Alternatively or additionally, inner wall 518 can be configured to reflect infrared radiation 510.

[0085] In some aspects, a wavelength of the radiation from laser 514 (e.g., infrared radiation) may differ between a main pulse and a pre-pulse. In addition, the radiation may be incident at different locations or portions of inner wall 518 of flow inner liner 526. In some aspects, the main pulse and the pre-pulse may be generated by two separate lasers that are directed to different locations of inner wall 518.

[0086] In some aspects, infrared radiation 510 from the main pulse may be incident on or reflected from inner wall 518 of flow inner liner 526 towards a surface of exhaust module 506. In some aspects, the path of the infrared radiation is modified such as to minimize the reflected radiation on the surface of exhaust module 506. By altering the path of the infrared radiation, exhaust module 506 stays below the melting temperature of the target material (e.g., tin) during normal operation and above the melting temperature of the target material when a drip off of debris is desired. Thus, spitting of debris towards the intermediate focus IF caused by the molten target material at exhaust module 506 is decreased and a wide thermal input is satisfied for various laser operation.

[0087] In some aspects, the plurality of ridges or ridge structures formed on inner wall 518 prevents back reflection to laser 514 and / or exhaust module 506 and acts as a radiation trap for reflection towards exhaust module 506. In some aspects, one or more features (e.g., angle, coating, depth) of the ridge surface depend on its location within flow inner liner 526 as further described in relation with FIGS. 6 and 7. In some aspects, an emissivity of an interior surface of the plurality ridges may be modified. For example, the emissivity may be increased by coating ridge structures with a high emissivity material (e.g., tungsten or bronze). In some aspects, the emissivity is creased by roughening a top surface of ridge structures.

[0088] FIG. 6 is a schematic depicting a partial view looking from a center of a collector towards an intermediate focus of a vessel 600, according to an exemplary aspect. In some aspects, the inner surface of vessel 600 refers to a surface of a wall of the radiation conduit that is inside, or faces into, a conduit vessel or chamber defined by the wall of the radiation conduit.

[0089] Vessel 600 includes a cap structure 601, a flow inner liner 603, a second liner 605, and a passthrough 607. Passthrough 607 is a component of an exhaust module for directing debris from an interior of vessel 600 to a contaminant removal device, such as a scrubber. In some aspects, passthrough 607 defines an opening in flow inner liner 603. In some aspects, cap structure 601 is substantially shaped like a cone. In some aspects, cap structure 601 includes multiple sub-components, such as a combination of a conical sub-component and a frustum sub-component. In some aspects, flow inner liner includes a plurality of nozzles to form a curtain flow to prevent debris from travelling through cap structure 601. Flow inner liner 603 is physically in contact with cap structure 601 and second liner 605.

[0090] Flow inner liner 603 includes a plurality of ridges 606. The plurality of ridges 606 extends circumferentially around the inner surface of flow inner liner 603. The plurality of ridges 606 is arranged such that when vessel 600 is viewed along a central axis extending though a center of an entrance aperture and a center of exit aperture, plurality of ridges 606 appear concentrically arranged. In some aspects, the plurality of ridges can be arranged as a periodic, or a substantially periodic structure.

[0091] In some aspects, each ridge of plurality of ridges 606 extends from the inner surface of flow inner liner 603. Plurality of ridges 606 is configured to absorb incident radiation from the interior of vessel 600, e.g., incident infrared radiation. Alternatively, and / or additionally, plurality of ridges 606 is configured to reflect incident radiation, e.g., incident infrared radiation.

[0092] In at least one embodiment, an entirety of plurality of ridges shares a same property or parameter. In some embodiments, one or more features of ridges 606 are different at different locations of flow inner liner 603. In some aspects, a first portion of ridges 606 formed in a first portion 604 of flow inner liner 603 has different features compared to a second portion of ridges 606 formed in a second portion 602 of flow inner liner 603. In some aspects, first portion 604 is arranged on an opposite side of passthrough 607. In some aspects, first portion 604 comprises approximately 15% to 25% of a total inner surface of flow inner liner 603. Such range is selected based on the amount of radiation directed to first portion 604. In some aspects, an average aspect ratio of ridges formed in first portion 604 is different from that of ridges formed in second portion 602. For example, the average aspect ratio of ridges in first portion 604 ranges from about 0.99 to about 1. 15. If the average aspect ratio is smaller than 0.99, a radiation absorption reduces, in some instances. However, the average aspect ratio over 1.15 causes first portion 604 to overheat, increasing debris resulting from molten target material, in some instances. As another example, the average aspect ratio of ridges in second portion 602 ranges from about 0.6 to about 1.25. The selection of such range is broader because second portion 602 is exposed less radiation than first portion 604. In some aspects, a pitch of ridges 606 formed in first portion 604 is substantially identical to that of ridges 606 formed in second portion 602.

[0093] In some aspects, first portion 604 may correspond to the portion of inner wall where the pre- pulse may be incident and second portion 602 may correspond to the location of the inner wall wherein the main pulse may be incident.

[0094] In some aspects, deeper ridges are formed in first portion 604. Deeper ridges lead to greater radiation absorption due to increased reflections (or bounces) within the ridge. By increasing the radiation absorption, the radiation reflected towards passthrough 607 is decreased and thus the exhaust module does not overheat during operation which reduces the molten target material.

[0095] In some aspects, at least one of cap structure 601 and second inner liner 605 includes a plurality of ridge structures on the inner surface. The plurality of ridge structures in cap structure 601 and / or second inner liner 605 share a same characteristic as that in flow inner liner 603. For example, the plurality of ridge structures in second inner liner 605 has a first portion arranged opposite to passthrough 607 and a second portion connecting to the first portion. As another example, an average aspect ratio in the first portion of second inner liner 605 is different from that in the second portion of second inner liner 605.

[0096] FIG. 7 is a schematic that illustrates a plane view of an inner surface of a vessel 700 according to an exemplary aspect. The inner surface may include a first portion 702 and a second portion 704. One or more features of the ridges formed in first portion 702 may be different from the features of the ridges formed in second portion 704. In some aspects, ridges formed in first portion 702 may be deeper compared to ridges formed in second portion 704. First portion 702 may correspond to the one or more regions of the inner surface where infrared radiation that may reflect towards the exhaust module is incident (e.g., infrared radiation from the main pulse). Ridges formed in second portion 704 (e.g., region where the infrared radiation does not reflect towards the exhaust module) are less deep to minimize the heating of the ridge (the deeper the ridge is the hotter a tip of the ridge may get due to the increased radiation absorption in the ridge).

[0097] FIG. 8A is a schematic that illustrates a cross section of a perspective view of a portion of a flow inner liner 800, according to an exemplary aspect.

[0098] Flow inner liner 800 comprises an inner wall 818 that tapers inwardly from an entrance aperture (not shown) distal to an intermediate focus region to an exit aperture (not shown) proximal the intermediate focus region. Inner wall 818 also tapers inwardly from one end of a vessel where a collector (not shown) located to the other end of the vessel where a cap structure (not shown) located; the cap structure is proximal to an intermediate focus (not shown) of a radiation source. A plurality of ridge structures 806 are arranged on inner wall 818. In some aspects, ridge structure 806 is integrated with inner wall 818. In some aspects, ridge structure 806 is a separate component attached to inner wall 818. In some aspects, a layer of tungsten or a layer of bronze is deposited on a top surface of ridge structure 806. In some aspects, the layer of tungsten or the layer of bronze is entirely deposited on the top surface of ridge structure 806. In some aspects, the layer of tungsten or the layer of bronze is partially depositedon the top surface of ridge structure 806. In some aspects, the top surface of ridge structure 806 undergoes a roughing process.

[0099] In some aspects, flow inner liner 800 is disposed between the cap structure and an exhaust module (e.g., a passthrough) of the radiation source. The exhaust module is arranged in another inner liner of the vessel. That is, flow inner liner 800 is in contact with and disposed between the cap structure and the another inner liner. Flow inner liner 800 is also disposed between the intermediate focus of the vessel and the collector.

[0100] FIG. 8B is a partial enlargement of FIG. 8B, according to some exemplary aspects. Each ridge structure 806 includes a first surface 811 substantially facing the collector of the vessel, a second surface 812 substantially facing the cap structure of the vessel, a third surface 813 close to inner wall 818, and a fourth surface 814 away from inner wall 818. In some aspects, first surface 811 and second surface 812 are coplanar to each other. In some aspects, first surface 811 and second surface 812 are not coplanar with each other. In some aspects, third surface 813 is a planer surface. In some aspects, third surface 813 includes multiple sub-surfaces (e.g., 813a and 813b) which are not coplanar with each other, and a range of angles between each sub-surfaces is between about 150 degrees and about 179 degrees. Ridge structure 806 includes a first depth DI, a second depth D2, a first angle Al, a second angle A2, athird angle A3, a width W, athickness T and a pitch P. First depth DI, located on first surface 811, is defined as a distance between third surface 813 and fourth surface 814. Second depth D2, located on second surface 812, is defined as a distance between third surface 813 and fourth surface 814. In some aspects, a ratio between first depth DI and second depth D2 ranges from about 87.5% to about 112.5%. If the ratio is out of the selected range, in some instances, a number of radiation reflection (or bounce) between first surface 811 and second surface 812 is not sufficient. In some aspect, an average of the number of radiation between first surface 811 and second surface 812 ranges from 4 to 7. First angle Al is defined by an angle between first surface 811 and third surface 813 (or sub-surface 813a). Second angle A2 is defined by an angle between second surface 812 and third surface 813 (or sub-surface 813b) . Third angle A3 is defined by an angle between first surface 811 and fourth surface 814. In some aspects, third angle A3 is an acute angle to reflect the radiation away from the exhaust module. Width W is defined by a minimum distance between first surface 811 and second surface 812. Pitch P defined by a distance of a combination of width W and thickness T.

[0101] An average aspect ratio is defined as an average depth of ridge structure 806 between width W of ridge structure 806. For example, the average aspect ratio of ridge structure 806 is defined by the average depth of first depth DI and second depth D2 over width W. The average aspect ratio of ridge structure 806 ranges from about 0.99 to about 1.15. If the average aspect ratio is smaller than 0.99, in some instances, the number of radiation reflection (or bounce) between first surface 811 and second surface 812 is not sufficient, reducing radiation absorption. If the average aspect ratio is greater than 1.15, in some instances, the radiation absorption causes flow inner liner 800 to overheat, resulting in additional debris from molten target materials. Each of first angle Al and second angle A2 is about 90degrees (e.g., ranges from about 88 degrees to about 92 degrees). If the angle is out of the selected range, in some instances, the difficulty of control the number of radiation reflection between first surface 811 and second surface 812 increases.

[0102] In some aspects, flow inner liner 800 includes two portions of ridge structures 806: a first portion of ridge structures 806 positioned opposite to the exhaust module in the second inner liner, and a second portion positioned constituting a remainder of flow inner liner 800. In some aspects, a first pitch of the first portion of ridge structures 806 is substantially identical to a second pitch of the second portion of ridge structures. That is, the first surface of the first portion aligns with the first surface of the second portion, the second surface of the first portion aligns with the second surface of the second portion, and the fourth surface of the first portion aligns with the fourth surface of the second portion. In some aspects, a first average aspect ratio of the first portion is different from a second average aspect ratio of the second portion. That is, the third surface of the first portion is not coplanar with the third surface of the second portion. In some aspects, the first average aspect ratio of the first portion ranges from about 0.99 to about 1.15, and the second average aspect ratio of the second portion ranges from about 0.6 to about 1.6.

[0103] In some aspects, an incident radiation 804i towards each first surface 811 of ridge structure 806 defines a plane 808; and the intermediate focus and a primary focus (now shown), or a center of the collector define a line 810 normal to plane 808. Flow inner liner 800 includes a plurality of parallel planes 808 defined by various incident radiations 804i. Each plane 808 divides flow inner liner 800 into two parts: a first part proximal to the cap structure, and a second part proximal to the exhaust module. That is, each plane 808 divides the vessel of the radiation source into two portions: a first portion including the cap structure and the intermediate focus, and a second portion including the collector and the primary focus. A depth of the ridges of the plurality of ridges is configured such as a path of incident radiation 804i is altered (e.g., absorbed or deflected) to minimize radiation incident on the exhaust module. In some aspects, a reflected radiation 804r directs to the first part of flow inner liner 800. Deeper ridges may absorb more infrared radiation because of the longer path of an incident radiation 804i inside the ridge 806. As shown in FIG. 8A, incident radiation 804i is reflected multiple times in the ridge before reflecting out. In some aspects, most of the energy of the incident radiation 804i is significantly dissipated before reflecting out of ridge structure 806. Thus, the infrared radiation that may be incident on the exhaust module is minimized such as the temperature of exhaust module may not exceed the melting temperature of the target material (e.g., tin) and contamination inside the vessel is minimized.

[0104] FIG. 9A is a schematic that illustrates a cross section of a perspective view of a first portion of an inner liner 908, according to an exemplary aspect. Inner liner 908 comprises an inner wall 918 that tapers inwardly from an entrance aperture (not shown) distal to an intermediate focus region to an exit aperture (not shown) proximal the intermediate focus region. In FIG. 9A, the entrance aperture wouldbe disposed towards the bottom of FIG. 9A and the exit aperture would be disposed towards the top of FIG. 9A.

[0105] FIG. 9B is a schematic that illustrates a cross section of a perspective view of a second portion of inner liner 908, according to an exemplary aspect. The entrance aperture would be disposed towards the bottom of FIG. 9B and the exit aperture would be disposed towards the top of FIG. 9B.

[0106] Inner wall 918 may comprise a first plurality of ridges 906a and a second plurality of ridges 906b. In some aspects, first plurality of ridges 906a may have a different aspect ratio compared to second plurality of ridges 906b. In some aspects, first plurality of ridges 906a may be deeper compared to second plurality of ridges 906b. First plurality of ridges 906a may correspond to an area of inner wall 918 where the infrared radiation from the main pulse is incident (e.g., second portion 602 of FIG. 6). Second plurality of ridges 906b may correspond to the area of inner wall 918 where the infrared radiation from the pre-pulse is incident (e.g., first portion 604 of FIG. 6).

[0107] In some aspects, a backwall angle 910, defined by a first surface 911 of ridge 906a or ridge 906b and a third surface 913 of ridge 906a or ridge 906b, of first plurality of ridges 906a is different than the backwall angle of second plurality of ridges 906b. In some aspects, the backwall angle may be selected such as the infrared radiation that escapes from the ridge is not incident on the exhaust module. In some aspects, backwall angle 910 of first ridges 906a is about 90 degrees.

[0108] In some aspects, the features of surface properties of inner wall 918 may be modified to minimize heating of the inner surface. In some aspects, the emissivity of the surface may be modified. In some aspects, the emissivity of the surface is increased. The higher the emissivity of the surface, the higher energy is lost with each bounce of the infrared beam within the ridge. In some aspects, the surface of the ridges may be coated with high emissivity material (e.g., tungsten or bronze). The high emissivity coating may be deposited using a current plasma spray gun, chemical vapor deposition, or atomic layer deposition process. In some aspects, due to the tool angle and accessibility a portion of the ridges may be covered with the high emissivity coating and some surface (e.g., backwall) may remain uncoated. In some aspects, a lower portion of the first plurality of ridges 906a is treated to have high emissivity.

[0109] In some aspects, the surface may be modified to increase scattering. In some aspects, scattering is increased by smoothing the inner surface and then applying a rough coating. Altering the roughness may be applied to the coated or uncoated surface of the inner surface of the ridges. Increasing the scattering provides the advantage of breaking the directionality of the infrared radiation. Because scattering is diffusive, the direction of the reflected infrared radiation is changed such as the infrared radiation is not incident to the same location. In some aspects, at least one of the surface of first plurality of ridges 906a and second plurality of ridges 906b is modified to increase the scattering. In some aspects, metamaterial absorbers may be used to increase the absorption of the infrared radiation.

[0110] Exemplary Flow Diagram[oni] FIG. 10 illustrates flow diagram 1000 according to an exemplary aspect. For example, flow diagram 1000 can be for a radiation source.

[0112] In some aspects, in operation 1002, radiation generated from plasma may be collected using a collector in a radiation source vessel at a primary focus of the collector.

[0113] In some aspects, in operation 1004, the radiation may be directed towards an intermediate focus IF of the radiation source.

[0114] In some aspects, in operation 1006, the path of undesired radiation (e.g., infrared radiation) may be altered to decrease incident radiation from a flow inner liner to an exhaust module positioned between the collector and the intermediate focus. The flow inner liner may be positioned between the exhaust module and the intermediate focus.

[0115] In some aspects, a first plurality of ridge structures are formed on an inner surface of the flow inner liner. In some aspects, a layer is formed over the first plurality of ridge structures to increase an emissivity of the plurality of ridge structures. In some aspects, a textured or rough surface for the interior surface of the first plurality of ridge structures is used.

[0116] In some aspects, a second plurality of ridge structures is formed on the flow inner liner. In some aspects, an average aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures. The first plurality of ridge structures is configured to absorb radiation having a first wavelength. The second plurality of ridge structures is configured to deflect radiation having a second wavelength different from the first wavelength away from the exhaust module.

[0117] Is some aspects, the primary focus and the intermediate focus define a line normal to a plane in the flow inner liner, the plane divides the vessel into a first portion including the intermediate focus and the second portion including the primary focus, and the path of undesired radiation travels toward the first portion of the vessel.

[0118] The lithographic apparatus, metrology apparatus, and radiation source described herein are used in a method for manufacturing a semiconductor device. A semiconductor device manufacturing method comprises receiving a substrate with a photoresist layer. The method further comprises directing a radiation beam from the radiation source to transfer a pattern from a mask onto the photoresist layer. This could be achieved by a patterning device which is configured to form a patterned radiation beam, imparting the patterned radiation beam onto the photoresist layer. The method for manufacturing a semiconductor device further comprises the step of removing a portion of the photoresist layer to form the pattern over the substrate.

[0119] The substrate W may be made of silicon or other semiconductor materials. Alternatively or additionally, the substrate W may include other semiconductor materials such as germanium (Ge) or carbon (C). In some embodiments, the semiconductor substrate is made of a compound semiconductor such as III-V compound semiconductors, II-V compound semiconductors, and / or any suitable integration of Group IV materials. In some embodiments, the substrate W may be a silicon-on-insulator (SOI) or a germanium -on-insulator (GOI) substrate.

[0120] The semiconductor device made from the substrate W may have various device elements. Examples of semiconductor device elements that are formed over the substrate W include transistors(e.g., planar or non-planar metal oxide semiconductor field effect transistors (MOSFET), bipolar junction transistors (BJT), high-voltage transistors, high-frequency transistors, etc.), diodes, CMOS image sensors, passive devices, and / or other applicable elements. Various processes may be performed to form the semiconductor device elements, such as deposition, etching, implantation, epitaxial growth, polishing, thermal treatment, and / or other suitable processes. In some embodiments, the substrate W is coated with a photoresist layer sensitive to the EUV light.

[0121] Although specific reference may be made in this text to the use of the apparatus, system, and / or lithographic apparatus in the manufacture of ICs, it should be explicitly understood that such an apparatus, system, and / or lithographic apparatus described herein may have other possible applications, for example, it can be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCD panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle,” “wafer,” or “die” herein may be considered as synonymous with the more general terms “mask,” “substrate,” and “target portion,” respectively.

[0122] Although specific reference may have been made above to the use of aspects in the context of optical lithography, it will be appreciated that aspects may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may 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.

[0123] 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.

[0124] The term “substrate” as used herein describes a material onto which material layers are added. In some aspects, the substrate itself may be patterned and materials added on top of it may also be patterned, or may remain without patterning. The substrate referred to herein may be processed, before or after exposure, for example, in a track unit (e.g., a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit, and / or an inspection unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example, to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0125] The above examples are illustrative, but not limiting, of the aspects of this disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the relevant art(s), are within the spirit and scope of the disclosure.

[0126] While specific aspects have been described above, it will be appreciated that the aspects may be practiced otherwise than as described. The description is not intended to limit the scope of the claims.

[0127] It is to be appreciated 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 may set forth one or more but not all exemplary aspects as contemplated by the inventor(s), and thus, are not intended to limit the aspects and the appended claims in any way.

[0128] The aspects have 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.

[0129] The foregoing description of the specific aspects will so fully reveal the general nature of the aspects 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, without departing from the general concept of the aspects. 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.

[0130] The breadth and scope of the aspects should not be limited by any of the above -described exemplary aspects, but should be defined only in accordance with the following claims and their equivalents.

[0131] The embodiments can be further described using the following clauses:1. An extreme ultraviolet (EUV) light source including a vessel; a collector positioned at one end of the vessel; a cap structure positioned at the other end of the vessel; an exhaust module positioned between the collector and the cap structure; a flow inner liner positioned between the exhaust module and the cap structure; and a first plurality of ridge structures positioned on an interior surface of the flow inner liner, wherein each of the first plurality of ridge structures includes a first surface facing the collector, a second surface facing the cap structure, a third surface close to the interior surface of the flow inner liner, and a forth surface away from the interior surface of the flow inner liner, and the first surface is substantially perpendicular to the third surface.2. The EUV light source of clause 1, wherein the second surface is substantially perpendicular to the third surface.3. The EUV light source of clause 1, wherein the third surface includes a first plane and a second plane, and the first plane and the second plane are not coplanar.4. The EUV light source of clause 1, wherein the first plurality of ridge structures is coated with a layer configured to increase an emissivity of the first plurality of ridge structures.5. The EUV light source of clause 1, wherein the first plurality of ridge structures is coated with tungsten or bronze.6. The EUV light source of clause 1, wherein the fourth surface is not perpendicular to the first surface.7. The EUV light source of clause 1, further including a second plurality of ridge structures connecting to the first plurality of ridge structures, wherein an aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures.8. The EUV light source of clause 7, wherein each of the second plurality of ridge structures includes a first surface aligning with the first surface of the first plurality of ridge structures, a second surface aligning with the second surface of second plurality of ridge structures, and a third surface close to the interior surface of the flow inner liner, and the third surface of the second plurality of ridge structures is not coplanar with the third surface of the first plurality of ridge structures.9. The EUV light source of clause 7, wherein the aspect ratio of the first plurality of ridge structures ranges from about 0.99 to about 1.15.10. A method including collecting, using a collector in a vessel, radiation generated from plasma at an primary focus of the collector; directing the radiation towards an intermediate focus of the collector; and altering a path of undesired radiation to decrease incident radiation from a flow inner liner to an exhaust module positioned between the collector and the intermediate focus.11. The method of clause 10, further including forming a first plurality of ridge structures on an inner surface of the flow inner liner; and forming a layer over the first plurality of ridge structures to increase an emissivity of the first plurality of ridge structures.12. The method of clause 10, wherein the primary focus and the intermediate focus define a line normal to a plane in the flow inner liner, the plane divides the vessel into a first portion including the intermediate focus and the second portion including the primary focus, and the path of undesired radiation travels toward the first portion of the vessel.13. The method of clause 10, further including forming a first plurality of ridge structures and a second plurality of ridge structures on the flow inner liner, wherein an aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures, wherein the first plurality of ridge structures is configured to absorb radiation having a first wavelength, and wherein the second plurality of ridge structures is configured to deflect radiation having a second wavelength different from the first wavelength away from the exhaust module.14. A semiconductor manufacturing apparatus including a light source comprising: a vessel; a collector configured to collect radiation generated from plasma and direct the radiation towards an intermediate focus of the collector; an exhaust module positioned between the collector and the intermediate focus; and a flow inner liner positioned between the exhaust module and the intermediate focus, wherein an interior surface of the flow inner liner includes a first plurality of ridge structures and a second plurality of ridge structures, and an aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures.15. The semiconductor manufacturing apparatus of clause 14, wherein a pitch of the first plurality of ridge structures is substantially identical to that of the second plurality of ridge structures.16. The semiconductor manufacturing apparatus of clause 15, wherein an interior surface of the first plurality of ridge structures is coated with a coating layer configured to increase an emissivity of the interior surface of the first plurality of ridge structures.17. The semiconductor manufacturing apparatus of clause 15, wherein the first plurality of ridge structures is coated with tungsten or bronze.18. The semiconductor manufacturing apparatus of clause 15, wherein a backwall angle of the first plurality of ridge structure is different from that of the second plurality of ridge structures. 19. The semiconductor manufacturing apparatus of clause 15, wherein a surface property of the first plurality of ridge structures is modified to increase scattering of incident radiation on the interior surface.20. The semiconductor manufacturing apparatus of clause 15, wherein the first plurality of ridge structures faces the exhaust module.

Claims

CLAIMS1. An extreme ultraviolet (EUV) light source, comprising: a vessel; a collector positioned at one end of the vessel; a cap structure positioned at the other end of the vessel; an exhaust module positioned between the collector and the cap structure; a flow inner liner positioned between the exhaust module and the cap structure; and a first plurality of ridge structures positioned on an interior surface of the flow inner liner, wherein each of the first plurality of ridge structures includes a first surface facing the collector, a second surface facing the cap structure, a third surface close to the interior surface of the flow inner liner, and a forth surface away from the interior surface of the flow inner liner, and the first surface is substantially perpendicular to the third surface.

2. The EUV light source of claim 1, wherein the second surface is substantially perpendicular to the third surface.

3. The EUV light source of claim 1, wherein the third surface includes a first plane and a second plane, and the first plane and the second plane are not coplanar.

4. The EUV light source of claim 1, wherein the first plurality of ridge structures is coated with a layer configured to increase an emissivity of the first plurality of ridge structures.

5. The EUV light source of claim 1 , wherein the first plurality of ridge structures is coated with tungsten or bronze.

6. The EUV light source of claim 1, wherein the fourth surface is not perpendicular to the first surface.

7. The EUV light source of claim 1, further comprising: a second plurality of ridge structures connecting to the first plurality of ridge structures, wherein an average aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures.

8. The EUV light source of claim 7, wherein each of the second plurality of ridge structures includes a first surface aligning with the first surface of the first plurality of ridge structures, a second surface aligning with the second surface of second plurality of ridge structures, and a third surfaceclose to the interior surface of the flow inner liner, and the third surface of the second plurality of ridge structures is not coplanar with the third surface of the first plurality of ridge structures.

9. The EUV light source of claim 7, wherein the average aspect ratio of the first plurality of ridge structures ranges from about 0.99 to about 1.15.

10. A method comprising: collecting, using a collector in a vessel, radiation generated from plasma at a primary focus of the collector; directing the radiation towards an intermediate focus of the collector; and altering a path of undesired radiation to decrease incident radiation from a flow inner liner to an exhaust module positioned between the collector and the intermediate focus.

11. The method of claim 10, further comprising: forming a first plurality of ridge structures on an inner surface of the flow inner liner; and forming a layer over the first plurality of ridge structures to increase an emissivity of the first plurality of ridge structures.

12. The method of claim 10, wherein the primary focus and the intermediate focus define a line normal to a plane in the flow inner liner, the plane divides the vessel into a first portion including the intermediate focus and the second portion including the primary focus, and the path of undesired radiation travels toward the first portion of the vessel.

13. The method of claim 10, further comprising: forming a first plurality of ridge structures and a second plurality of ridge structures on the flow inner liner, wherein an average aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures, wherein the first plurality of ridge structures is configured to absorb radiation having a first wavelength, and wherein the second plurality of ridge structures is configured to deflect radiation having a second wavelength different from the first wavelength away from the exhaust module.

14. A semiconductor manufacturing apparatus comprising: a light source comprising: a vessel;a collector configured to collect radiation generated from plasma and direct the radiation towards an intermediate focus of the collector; an exhaust module positioned between the collector and the intermediate focus; and a flow inner liner positioned between the exhaust module and the intermediate focus, wherein an interior surface of the flow inner liner includes a first plurality of ridge structures and a second plurality of ridge structures, and an average aspect ratio of the second plurality of ridge structures is different from that of the first plurality of ridge structures.

15. The semiconductor manufacturing apparatus of claim 14, wherein a pitch of the first plurality of ridge structures is substantially identical to that of the second plurality of ridge structures.

16. The semiconductor manufacturing apparatus of claim 15, wherein an interior surface of the first plurality of ridge structures is coated with a coating layer configured to increase an emissivity of the interior surface of the first plurality of ridge structures.

17. The semiconductor manufacturing apparatus of claim 15, wherein the first plurality of ridge structures is coated with tungsten or bronze.

18. The semiconductor manufacturing apparatus of claim 15, wherein a backwall angle of the first plurality of ridge structure is different from that of the second plurality of ridge structures.

19. The semiconductor manufacturing apparatus of claim 15, wherein a surface property of the first plurality of ridge structures is modified to increase scattering of incident radiation on the interior surface.

20. The semiconductor manufacturing apparatus of claim 15, wherein the first plurality of ridge structures faces the exhaust module.

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