Apparatus and method for removing debris

Abstract

A radiation source includes a vessel defining a radiation generation region and a contamination removing module coupled to the vessel. The contamination removing module includes a stack of plates having an opening to form a first flow channel through the stack, a housing enclosing the stack of plates to form a second flow channel, and a closure member inside the housing. A diameter of the closure member is equal to or smaller than an inner diameter of the housing.

Description

APPARATUS AND METHOD FOR REMOVING DEBRISCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US Application No. 63 / 777,583, filed on March 25, 2025, titled APPARATUS AND METHOD FOR REMOVING DEBRIS, and US Application No.64 / 001 / 976, filed on March 10, 2026, titled APPARATUS AND METHOD FOR REMOVING DEBRIS, which are incorporated herein by reference in their entireties.TECHNICAL FIELD

[0002] The embodiments provided herein relate to a carrier gas scrubber used with a radiation source, and more particularly to a radial flow scrubber configured to separate and remove contaminants from the carrier gas.BACKGROUND

[0003] Illumination generated by a radiation source can be used by tools used for semiconductor manufacturing processes. Examples of such radiant processing apparatuses include a lithographic apparatus, a metrology or inspection apparatus (e.g., a mask inspection apparatus, an actinic mask inspection apparatus, a defect inspection apparatus, a dimension measurement apparatus, or the like), among others.

[0004] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (e.g., a photoresist or resist) provided on a substrate. To project a pattern on a substrate, a lithographic apparatus can use electromagnetic radiation. The wavelength of radiation can determine the minimum size of features that are to be formed on the substrate, with smaller wavelengths allowing for smaller features. For example, a lithographic apparatus that uses extreme ultraviolet (EUV) radiation (having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.4 nm) can print smaller features on a substrate as compared to a lithographic apparatus that uses radiation with a wavelength of 193 nm. A drawback of operating at EUV wavelengths is that many optical materials can absorb EUV illumination, thereby attenuating EUV illumination intensity. Reflective optics can help mitigate attenuation. EUV lithography can implement one or more reflective surfaces to guide EUV radiation along an optical path.

[0005] A mask inspection apparatus (e.g., actinic mask inspection apparatus) is an apparatus that can be used to measure dimensions or detecting defects in masks or mask blanks. Mask blanks used in EUV lithography generally have a multilayer structure that functions as a Bragg reflector. Layers of the multilayer structure can be altematingly molybdenum and silicon. The projected pattern in a lithographic process can become deformed if a defect is present in the multilayer structure. Therefore,a mask inspection is an important, and often necessary, step of mass-production lithographic processes to check whether a defect is present in a mask. EUV mask inspection can be used for several purposes and in several different stages of lithographic fabrication.

[0006] Mask inspection can be used to detect phase defects that occur in mask blanks. Such phase defects can occur during the manufacturing of the multilayer stack of the mask blank. If undetected, phase defects are reproduced on all chips that correspond to the part of the mask containing the phase defects. Such phase defects can be correctly detected by using the same or similar actinic EUV wavelength as the lithography tool (e.g., 13.4 nm). At a stage associated with quality control of EUV patterned masks, patterned mask inspection masks can be inspected. Mask inspection can be used to measure critical dimensions on the mask blank. In addition to phase defects, absorber pattern defects on the surface can be detected. Mask inspection can also be used for simulating exposure and determining the deterioration of optical contrast of a defect detected in the actinic inspection. Mask inspection can also be used for optical proximity correction (OPC) evaluation or during a mask repair process to improve pattern transfer fidelity. Further, it can be used for inspecting optical contrast after fixing the defect. In addition to the above, mask inspection can also be used to measure small particle / amplitude effects.

[0007] A metrology apparatus is an apparatus that measures critical dimensions of a feature on the wafer and inspects various aspects of the wafer during the semiconductor manufacturing process. A metrology apparatus can also measure and characterize physical properties of materials and components. The metrology apparatus is a precision instrument that ensures product quality and process control. In at least some embodiments, the metrology apparatus employs EUV radiation to inspect and measure dimensions of targets on the substrate.

[0008] Plasma-based EUV sources can use target materials that, when in a plasma state, emit electromagnetic radiation with wavelengths in the EUV range. The target material, such as tin, can be collected in a tin catch system that is cleaned periodically.SUMMARY

[0009] Some embodiments provide a radiation source including a vessel defining a radiation generation region and a contamination removing module coupled to the vessel. The contamination removing module includes a stack of plates having an opening to form an inner flow channel through the stack, a housing enclosing the stack of plates to form an outer flow channel, and a closure member inside the housing. A diameter of the closure member is equal to or smaller than an inner diameter of the housing.

[0010] Some embodiments provide a method for removing debris including guiding a flow, through a duct, to an inner flow channel of a stack of plates along a first direction. The flow is directed through intervals between the stack of plates along a second direction, wherein the second direction issubstantially orthogonal to the first direction. The flow is guided through a space between the stack of plates and a housing to an outlet, along a third direction.

[0011] Some embodiments provide a radiation source, including a vessel defining a radiation generation region and a contamination removing module coupled to the vessel. The contamination removing module includes a stack of fin elements including an opening in a center of the stack to form an inner flow channel through the stack; a housing enclosing the stack of fin elements to form an outer flow channel; and a closure member inside the housing, wherein a diameter of the closure member is equal to or smaller than an inner diameter of the housing.

[0012] Some embodiments provide a method for removing debris, including guiding a flow, through a duct, to an inner flow channel of a stack of fin elements along a first direction. The flow is directed through intervals between the stack of fin elements along a second direction, wherein the second direction is substantially orthogonal to the first direction. The flow is guided through a space between the stack of fin elements and a housing to an outlet, along a third direction.

[0013] Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention.BRIEF DESCRIPTION OF FIGURES

[0014] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, taken in conjunction with the accompanying drawings.

[0015] Fig. 1 is a diagram showing an example semiconductor manufacturing system including a radiant processing apparatus and a radiation source, consistent with embodiments of the present disclosure.

[0016] Fig. 2 is a cross-sectional side view of a radial flow -through scrubber, consistent with some embodiments of the present disclosure.

[0017] Fig. 3A is a cross-sectional side view of the flow resistance in the radial flow-through scrubber shown in Fig. 2, consistent with some embodiments of the present disclosure.

[0018] Fig. 3B is a cross-sectional side view of gas flow in the radial flow-through scrubber shown in Fig. 2, consistent with some embodiments of the present disclosure.

[0019] Fig. 4 is a cross-sectional side view of a system including a radial flow-reversing scrubber connected to a radiation source, consistent with some embodiments of the present disclosure.

[0020] Fig. 5 is a cross-sectional perspective view of the scrubber shown in Fig. 4.

[0021] Fig. 6A is a cross-sectional side view of the flow resistance in the radial flow -reversing scrubber shown in Fig. 4, consistent with some embodiments of the present disclosure.

[0022] Fig. 6B is a cross-sectional side view of gas flow in the radial flow -reversing scrubber shown in Fig. 4, consistent with some embodiments of the present disclosure.

[0023] Fig. 7 A is a top view of a scrubber plate, consistent with embodiments of the present disclosure.

[0024] Fig. 7B is a cross-sectional view of the scrubber plate shown in Fig. 7A, consistent with embodiments of the present disclosure.

[0025] Fig. 8 is a flowchart of an example method for removing debris, consistent with embodiments of the present disclosure.

[0026] Fig. 9 is a perspective view of a portion of an alternate construction for the scrubber, consistent with embodiments of the present disclosure.

[0027] Fig. 10A is a side view of a portion of a plurality of fin element stacks, consistent with embodiments of the present disclosure.

[0028] Fig. 10B is a side view of a portion of a plurality of fin element stacks, consistent with embodiments of the present disclosure.

[0029] Fig. 10C is a side view of a portion of a plurality of fin element stacks, consistent with embodiments of the present disclosure.

[0030] Fig. 11 is a perspective view of a single fin element, consistent with embodiments of the present disclosure.

[0031] Fig. 12 is a cross-sectional view of a portion of a stack of fin elements, consistent with embodiments of the present disclosure.DETAILED DESCRIPTION

[0032] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the disclosed embodiments as recited in the appended claims. For example, although some embodiments are described in the context of EUV-based radiant processing apparatuses, the present disclosure is not so limited. Unless infeasible, embodiments described herein can be implemented in any type of radiant processing apparatus.

[0033] Electronic devices are constructed of circuits formed on a piece of semiconductor material called a substrate. The semiconductor material may include, for example, silicon, gallium arsenide, indium phosphide, or silicon germanium, or the like. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. The size of these circuits has decreased dramatically so that many more of them can be fit on the substrate. For example, an IC chip in a smartphone can be as small as a thumbnail and yet may include over 2 billion transistors, the size of each transistor being less than 1 / 1000th the size of a human hair.

[0034] Making these ICs with extremely small structures or components is a complex, timeconsuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in defects in the finished IC, rendering it useless. Thus, one goal of the manufacturing process is to avoid such defects to maximize the number of functional ICs made in the process; that is, to improve the overall yield of the process.

[0035] Speed, or throughput, has been a traditionally important metric alongside yield. Throughput is a measurable quantity that characterizes the manufacture speed of a fab (e.g., number of IC units produced per unit time). Throughput has become even more important in view of recent global chip shortages. As there are multiple steps in the fabrication of a chip device (e.g., multiple steps for multiple layers), each step can have a characteristic throughput. For example, a throughput value can be assigned to how quickly a radiant processing system can conduct an illumination optimization process. Innovations in the design or functions of source optimizers can increase throughput or resolve problems in another aspect while mitigating adverse impact to throughput.

[0036] Yield is a metric that characterizes failure rate in device fabrication, which relates to cost and efficiency. Yield can be defined as a ratio of all the wafers that are produced by a fab to the number of wafers that were introduced to the fab. Or yield can be the number of working chips that survive the device fabrication process performed on a wafer to the number of potential chips that can be fabricated from that wafer in the ideal case of zero failure. As some wafers or chips fail during fabrication, the overall yield is less than 100%. For example, to obtain a 75% yield for a 50-step process (where a step can be indicative of the number of layers formed on a wafer), each individual step should have a yield greater than 99.4%. In contrast, if individual steps have a yield of 95%, the compounding errors at each step result in an overall process yield as low as 7-8%. Every wafer or chip lost during fabrication is a sunk cost and lost time for the fab.

[0037] To achieve lithographic prints of device structures with a high yield, small wavelength illumination (e.g., EUV wavelength) can be used to print structures that are smaller compared to limitations of using larger wavelengths. Similarly, the small wavelength illumination allows for higher resolution imaging. This is crucial for accurately measuring and inspecting the extremely fine features in a metrology or an inspection system. In a plasma-based EUV source, a plasma can be created by delivering a high power laser to a target material (e.g., a droplet of tin). To prevent contamination of the environment in the radiation source, the tin can be removed by introducing a carrier gas (e.g., hydrogen gas, FE) into the radiation source to carry the tin contaminants (e.g., tin-containing debris and tin-containing vapor) out of the radiation source to a gas scrubbing device.

[0038] Objects and advantages of the disclosure can be realized by the elements and combinations as set forth in embodiments described herein. However, embodiments of the present disclosure are not necessarily required to achieve such exemplary objects or advantages. Some embodiments can achieve a different feature or enhancement without necessarily achieving any expressly stated object or advantage.

[0039] The term “patterning device” may be considered synonymous with similar terms of art, such as “reticle” or “mask.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a pattern on a cross section of a radiation beam. The radiation beam then can recreate the pattern in a target portion of a substrate.

[0040] The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, or 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 or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system.”

[0041] Illumination can be understood to be a form of radiation. Hence, the terms “radiation” and “illumination” can be used herein interchangeably.

[0042] Relative dimensions of components in drawings may be exaggerated for clarity. Within the following description of drawings, the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described. As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a component may include A or B, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0043] Fig. 1 is a diagram showing an example semiconductor manufacturing system including a radiant processing apparatus and a radiation source, consistent with embodiments of the present disclosure. For example, the radiation source may include a laser produced plasma EUV radiation source 100. The EUV radiation source 100 may include at least one pulsed or continuous laser source 102, which may for example be a pulsed gas discharge CCE laser source or a solid-state laser producing a beam 104 of radiation with a wavelength from about 1 micrometer (pm) to about 10 pm. The laser source 102 may have DC or RF excitation operating at high power and at a high pulse repetition rate.

[0044] The EUV radiation source 100 also includes a target material delivery system 106 for delivering target material in the form of liquid droplets or a continuous liquid stream. In this example, the target material is a liquid, but it could also be a solid or a gas. The target material may be made up of tin or a tin compound, although other materials may be used. The target material delivery system 106 introduces droplets 108 of the target material into an interior of a source vessel 109 to an irradiation region 112 where the target material may be irradiated to produce plasma. The source vessel 109 includes liners and is enclosed in a vacuum chamber 110. In some cases, an electrical charge is placed on the target material to permit the target material to be steered toward or away fromthe irradiation region 112. As used herein, an “irradiation region” is a region where target material irradiation may occur or is intended to occur, and is an irradiation region even at times when no irradiation is actually occurring. The EUV radiation source 100 may also include abeam steering system 114.

[0045] The components of the EUV radiation source 100 are arranged so that the droplets 108 travel substantially linearly. The direction from the laser source 102 towards the irradiation region 112, that is, the nominal direction of propagation of the beam 104, may be taken as the z-axis. The path the droplets 108 take from the target material delivery system 106 to the irradiation region 112 may be taken as the x-axis. The view of Fig. 1 is thus normal to the x-z plane. While a system in which the droplets 108 travel substantially vertically is depicted, it will be understood by one of ordinary skill in the art that other arrangements may be used in which the droplets travel linearly or at some angle with respect to a gravity between and including 90 degrees (horizontal) and 0 degrees (vertical).

[0046] The EUV radiation source 100 may also include an EUV light source controller system 116 and a laser firing control system 118. The EUV radiation source 100 may also include a detector such as a target position detection system which may include one or more droplet imagers 120 that generate an output indicative of the absolute or relative position of a target droplet, e.g., relative to the irradiation region 112, and provide this output to a target position detection feedback system 122.

[0047] The target material delivery system 106 may include a target delivery control system 124. The target delivery control system 124 is operable in response to a signal provided by the controller system 116 to adjust paths of the target droplets 108 through the irradiation region 112. This may be accomplished, for example, by repositioning the point at which a target delivery mechanism 126 releases the target droplets 108. The droplet release point may be repositioned, for example, by tilting the target delivery mechanism 126 or by laterally translating the target delivery mechanism 126. The target delivery mechanism 126 extends into the source vessel 109 and is externally supplied with target material and a gas source to place the target material in the target delivery mechanism 126 under pressure.

[0048] The EUV radiation source 100 may also include one or more optical elements, such as a collector 128. Other optical elements may be used, consistent with embodiments of the present disclosure. The collector 128 may be a normal incidence reflector, for example, implemented as a multi-layer mask (MLM) with additional thin barrier layers, for example B4C, ZrC, S13N4, or C, deposited at each interface to effectively block thermally-induced interlayer diffusion. Other substrate materials, such as aluminum (Al) or silicon (Si), can also be used. The collector 128 may be formed as a prolate ellipsoid, with a central aperture to allow the beam 104 to pass through and reach the irradiation region 112. The collector 128 may be, e.g., in the shape of a ellipsoid that has a first focus at the irradiation region 112 and a second focus at a so-called intermediate point 130 (also called the intermediate focus 130) where the EUV radiation may be output from the EUV radiation source 100 and input to a radiant processing apparatus 132, e.g., an integrated circuit lithography scanner whichuses the radiation, for example, to process a wafer workpiece 134 in a known manner using a reticle or mask 136. The wafer workpiece 134 is then additionally processed in a known manner to obtain an integrated circuit device. In some embodiments, the radiant processing apparatus 132 includes a metrology or an inspection tool which uses the radiation to measure and inspect features over the wafer workpiece 134, or any suitable patterning devices.

[0049] The EUV radiation source 100 also includes a temperature sensor 138, e.g., a thermocouple positioned within the source vessel 109 to measure the local temperature, e.g., temperature at the sensor of gas within the source vessel 109. Although one temperature sensor 138 is shown in Fig. 1, it will be understood that additional temperature sensors may be used. The temperature sensor 138 generates a signal indicative of the measured temperature and supplies it as an additional input to the controller system 116. The controller system 116 bases the control signal it supplies to the beam steering system 114 at least in part on this temperature signal.

[0050] Contamination removing devices, such as scrubbers, are devices designed to separate and remove contaminants from a carrier gas. An ideal contamination removing device has the following characteristics: high scrubbing efficiency (i.e., a vast majority of contaminants in the carrier gas are captured), low pressure drop, compact size, and scalable. One type of contamination removing device relies on condensation of tin vapor on plate-fin elements. In some existing systems, the contamination removing device directly borders the EUV cone, with vertical fins extending radially from the vessel axis. For example, the contamination removing device may be configured with a conical or a frustum shape having a large frontal surface area (e.g., a cross-sectional area that receives the carrier gas flow). The gas to be scrubbed is forced into the center of the cone and has to exit the cone through fins or blades positioned on the sides of the cone. A goal with the contamination removing device is to have a low pressure drop from the inlet gas pressure to the outlet gas pressure to enable a good vacuum pressure. If the pressure drop is too high, it may not be possible to maintain a good vacuum and the lithography system will suffer a throughput loss. In another embodiments, the contamination removing device is externally coupled to the source vessel 109 through a duct.

[0051] Plate-fin scrubbers involve tradeoffs between the size of the scrubber, the pressure drop in the carrier gas flow that the scrubber induces, and the scrubbing efficiency (e.g., the amount of contaminant removed from the carrier gas). Scrubbing efficiency improves with higher pressure drop, but increasing the size of the scrubber generally improves the scrubbing efficiency while reducing the pressure drop. In some embodiments, the EUV source may be tightly constrained on all three of these aspects (pressure drop, scrubber size, and scrubbing efficiency). One way to obtain favorable scrubbing efficiency and pressure drop is to increase the flow cross-sectional area, which becomes bulky and unscalable in an EUV source. Additionally, the tin concentration in the carrier gas is non-uniform, which makes simply expanding the frontal area of an axial scrubber an ineffective method to address performance requirements.

[0052] A drop in scrubbing efficiency is particularly problematic, as the tin concentration may rise above the tin wool formation threshold, which can clog the source exhaust within a few days of operation. The clog may also lead to a large pressure drop in the system such that it cannot be used. The EUV source would then need to be shut down to clear the clogs, causing delays to wafer processing times. Further increasing the cross-sectional area (e.g., making the overall scrubber larger) requires making modifications to the adjacent scanner, which is an impractical approach.

[0053] Two key design parameters for a scrubber are efficiency of tin extraction and low resistance to flow. With prior scrubber designs, one way to increase the tin extraction efficiency and keep a low resistance to flow was to make frontal area larger (e.g., a larger opening in the cone). Per unit area of flow, the incoming gas has a lower velocity, so there is a lower pressure drop within the scrubber and the flow passing through the blades has a longer time to interact with the blades (i.e., higher tin extraction). But the frontal area can only be expanded by a limited amount before the scrubber exceeds the space allocated to it, because space within the overall system is needed for other purposes.

[0054] Scaling the prior scrubber designs is done at the expense of the other modules in the system because of the above-mentioned size constraints of the system. To increase the tin extraction efficiency under the size constraint, the scrubber can include more blades to provide more scrubbing surface area. But the spacing between any two blades is a sensitive parameter for flow resistance. If two blades are very close (i.e., there is little space between any two adjacent blades), then the flow resistance is high. The pressure drop and the scrubbing efficiency are inversely proportional in this sort of architecture (with the size constraint).

[0055] Fig. 2 is a cross-sectional side view of a radial flow -through scrubber 200, consistent with some embodiments of the present disclosure. The scrubber 200 includes a housing 202 having an inlet 204 located proximate and coupled to a radiant processing system, e.g., EUV radiation source 100 shown in Fig. 1, and an outlet 206 located at an opposite end of the scrubber 200 from the inlet 204. A stack of scrubber plates 208 is positioned inside the housing 202. Each of scrubber plate 208 has a disc-shaped body having a planar or substantially planar surface and a circumferential or substantially circumferential edge; the disc-shaped body of scrubber plate 208 defines a central opening extending through scrubber plate 208 and bounded by an inner diameter, and an outer perimeter defined by an outer diameter. In some embodiments, scrubber plate 208 is a unitary structure. In some embodiments, scrubber 208 includes a plurality of discrete segments arranged about a central axis to form a disc shape. The stack of scrubber plates 208 includes an opening to form an inner flow channel 210 (e.g., the central opening of scrubber plate 208) through the stack. A deflector 212 is positioned at an end of the stack of scrubber plates 208 proximate to the outlet 206 and is configured to prevent a flow of gas directly from the inlet 204 to the outlet 206, such that the gas flows in between the scrubber plates of the stack 208 from the inner flow channel 210 to an outer flow channel 214, created between an outer edge of the scrubber plates of the stack 208 and an inner surface of the housing 202.In some embodiments, one or more heating elements 216 are in contact with the stack of scrubber plates 208 to heat the scrubber plates to prevent solid contaminant accumulation from forming in between the scrubber plates and blocking the spaces between the scrubber plates.

[0056] An inlet gas flow 220 enters the scrubber 200 via the inlet 204 (shown by the outlined arrows in Fig. 2). The inlet gas flow 220 enters the housing 202 through the inner flow channel 210 and continues until reaching the deflector plate 212. Upon interception, the inlet gas flow 220 is redirected to form gas flow 222. The gas flow 222 travels through lateral channels defined by interstitial spacing between adjacent scrubber plates of the stack of scrubber plates 208, which is orthogonally or substantially orthogonally to the inlet gas flow 210 entering the scrubber 200, passing through the scrubber plates of the stack 208. In comparison with other approaches, the lateral channels defined by gaps between adjacent scrubber plates reduces the diffusion distance for the contaminants to reach the inner surface of the housing 202 by depositing and / or condensing contaminants from the gas flow 222. The orthogonal gas flow 222 encounters the inner surface of the housing 202 and is redirected into the outer flow channel 214 as outer channel gas flow 224. In some embodiments, the outer channel gas flow 224 is in generally a same direction as the inlet gas flow 220. The outer channel gas flow 224 is directed by the inner surface of the housing 202 to an outlet gas flow 226 and exits the housing 202 via the outlet 206 as an exit gas flow 228. Although not shown in Fig. 2, a conduit is connected to the outlet 206 to further process the exit gas flow 228.

[0057] In some embodiments, a portion of the housing 202 proximate to the inlet 204 includes a plurality of perforations 240. One or more secondary gas inlets 242 may be coupled to the housing 202 proximate to the inlet 204 to introduce a secondary gas 244 into the housing 202 to help reduce condensation of contaminated gas inside the housing 202 before the inlet gas flow 220 reaches the stack of scrubber plates 208.

[0058] Fig. 3A is a cross-sectional side view of the flow resistance in the radial flow-through scrubber 200 shown in Fig. 2, consistent with some embodiments of the present disclosure. The inlet gas flow 220 enters the scrubber 200 and flows into the inner flow channel 210 in the center of the stack of scrubber plates 208. The gas flows through openings in between the scrubber plates of the stack 208 and out of the scrubber 200 as the exit gas flow 228. While the gas is flowing through the scrubber 200, it encounters resistance at different locations. The total resistance 300 encountered by the gas flow through the scrubber 200 is a sum of an inner flow resistance 302 in the inner flow channel 210, a core resistance 304 as the gas flow passes in between the scrubber plates of the stack 208, and an outer flow resistance 306 in the outer flow channel 214.

[0059] The radial flow scrubber has three distinct components to the flow resistance. First is the inner flow resistance 302; the flow must travel different distances to the different channels. The inlet resistance is small since there is little surface area contacting the gas to cause viscous losses. Next is the resistance 304 for the scrubber core channels (e.g., a flow path between any two adjacent scrubber plates). In some embodiments, like with an axial scrubber, with identical scrubber plate spacing, theresistance 304 in each scrubber core channel is identical. Finally, there is the outer flow resistance 306, caused by friction with the outer vessel wall. The outer flow resistance 306 increases for flows coming from channels farther from the outlet. Combining the three effects of negligible inner flow resistance 302, constant core channel resistance 304, and outer flow resistance 306 that increases with distance from the outlet, the overall flow resistance 300 for a path through a given channel increases with the channel’s distance from the outlet.

[0060] Fig. 3B is a cross-sectional side view of gas flow in the radial flow -through scrubber 200 shown in Fig. 2, consistent with some embodiments of the present disclosure. The inlet gas flow 220 enters the scrubber 200 and flows into the inner flow channel 210 in the center of the stack of scrubber plates 208. The orthogonal gas flow 222 is through openings in between the scrubber plates of the stack 208. The orthogonal gas flow 222 is redirected by the inner surface of the housing 202 to outer channel gas flow 224 and out of the scrubber 200 as the exit gas flow 228. While the gas is flowing through the scrubber 200, it encounters resistance at different locations. As shown in Fig. 3B by the different arrow widths (with wider arrows indicating a greater flow volume), most of the inlet gas flow 220 flows directly through the inner flow channel 210 until it encounters the deflector 212. The gas flow resistance is higher close to the inlet 204 while the gas pressure near the inlet 204 is lower. As the gas flows through the scrubber 200, the pressure increases as the inlet gas flow 220 approaches the deflector 212 while the resistance decreases.

[0061] Previous scrubber designs are size-constrained by other modules in the system located around the scrubber, making it difficult to scale the scrubber (e.g., make the scrubber larger). The flow through scrubber described herein is located external to the EUV source and is not mechanically constrained by other modules around it. For example, it is relatively easy to include more plates in the stack (to make the stack taller) or to reduce the number of plates in the stack (to make stack shorter) depending on the flow amount through the scrubber.

[0062] Embodiments of the present disclosure can provide a radiation source including a vessel defining a radiation generation region and a contamination removing module coupled to the vessel. The contamination removing module includes a stack of scrubber plates having an opening in the middle of the stack to form an inner flow channel through the stack. A housing encloses the stack of scrubber plates to form an outer flow channel around the stack of scrubber plates. A closure member is positioned inside the housing at the bottom of the stack of scrubber and has a diameter equal to or smaller than an inner diameter of the housing so that the closure member covers one end (e.g. the bottom of the stack) of scrubber plates and redirects the flow in an opposite direction from the inner flow channel.

[0063] The flow-reversing architecture described herein yields benefits via a pressure balance between the inner core of the scrubber and outer housing of the scrubber, leading to a higher scrubbing efficiency and a lower pressure drop over prior scrubber architectures. Both the radial andflow-reversing elements contribute to the high performance function of the scrubber in comparison with other approaches.

[0064] Fig. 4 is a cross-sectional side view of a contamination removing system 400 including a radial flow -reversing scrubber connected to a radiation source, consistent with some embodiments of the present disclosure. The contamination removing system 400 includes a radiation source, such as the EUV radiation source 100, which is described in greater detail in connection with Fig. 1. The EUV radiation source 100 includes the source vessel 109. For ease of illustration and explanation, only the relevant elements of the lithographic system are described in connection with Fig. 4. In some embodiments, a different radiation source may be used without changing the operation of the contamination removing system 400. The source vessel 109 includes one or more outlets 402. The outlets 402 connect to a source outlet pipe 404. As shown in Fig. 4, in some embodiments, the source outlet pipe 404 encircles the source vessel 109 and functions as a peripheral channel to facilitate gas flow. Gas may exit the “right side” of the source vessel 109 via the outlet 402 and direct to the outlet 402 through the source outlet pipe 404. In some embodiments, the gas may also exit the “left side” of the source vessel 109 via the outlet 402 and flow directly into the source outlet pipe 404. The source outlet pipe 404 carries the gas out of the EUV radiation source 100 and connects to a scrubber inlet pipe 410. In some embodiments, the source outlet pipe 404 and the scrubber inlet pipe 410 are integrated into one continuous duct.

[0065] The scrubber inlet pipe 410 provides an input path for the gas into a scrubber 412. The scrubber inlet pipe 410 transports the contaminant-laden (e.g., tin-laden) fluid flow into the inside volume of the scrubbing core. In some embodiments, the scrubber inlet pipe 410 includes a heating element (not shown in Fig. 4). In some embodiments, the scrubber inlet pipe 410 includes stainless steel with a contaminant-resistant (e.g., tin-resistant) coating. One purpose of the coating is to protect a metal material of the scrubber inlet pipe 410 from corrosion and attack by liquid tin and hydrogen radicals. In some embodiments, a drainage component may be coupled to the scrubber inlet pipe 410 for directing the liquid tin toward a designated storage point.

[0066] To maintain separated inlet and outlet flows, the scrubber inlet pipe 410 feeds into an inlet elbow pipe 414 that carries the gas into a stack of scrubber plates 416. In some embodiments, the inlet elbow pipe 414 includes a heating element (not shown in Fig. 4). In some embodiments, the inlet elbow pipe 414 includes stainless steel with a contaminant-resistant coating such that the contaminant in the inlet gas flow does not condense onto interior surfaces of the inlet elbow pipe 414.

[0067] The stack of scrubber plates 416 includes a plurality of disc-like plates stacked at a desired spacing. Each of scrubber plate 416 has a disc-shaped body having a planar or substantially planar surface and a circumferential or substantially circumferential edge; the disc-shaped body of scrubber plate 416 defines a central opening extending through scrubber plate 416 and bounded by an inner diameter, and an outer perimeter defined by an outer diameter. In some embodiments, scrubber plate 416 is a unitary structure. In some embodiments, scrubber 416 includes a plurality of discretesegments arranged about a central axis to form a disc shape. These plates form radial flow channels where debris is separated and removed from the hydrogen carrier gas. In some embodiments, the stack of scrubber plates 416 may be held together by structural support rods, which maintain the desired plate spacing. The plates may have some draft angle such that liquid condensate drips off of them due to gravity.

[0068] The stack of scrubber plates 416 includes an opening to form an inner flow channel 418 (e.g., the central opening) through the center of the stack of scrubber plates 416. The stack of scrubber plates 416 is located inside an outer vessel 420 and is positioned within the outer vessel 420 to create an outer flow channel 422 between an outer edge of the stack of scrubber plates 416 and an interior surface of the outer vessel 420. An inner surface of the outer vessel 420 (e.g., a surface facing the stack of scrubber plates 416) is configured to shield other components of the EUV radiation source 100 from contaminant spraying (e.g., tin spitting) from the scrubber 412. In some embodiments, the inner surface of the outer vessel 420 provides an additional surface for contaminant (e.g., tin) condensation (e.g., other than the stack of scrubber plates 416) and / or provides indirect heating to the stack of scrubber plates 416. In some embodiments, the inner surface of the outer vessel 420 includes stainless steel with a contaminant-resistant coating such that the contaminant debris in the gas flow does not condense onto the inner surface of the outer vessel 420.

[0069] While the stack of scrubber plates 416 is shown in Fig. 4 as cylindrical (e.g., circular or discshaped plates), it is noted that other shapes for the plates are contemplated and may be used such that the stack of scrubber plates 416 includes an opening in the plates to form the inner flow channel 418. The outer vessel 420 also provides the main structural support for the scrubber 412, and may support other machine components.

[0070] In some embodiments, the draft angle of the plates varies (e.g., the plates do not have to be completely flat). The plate configuration is not determined by the pressure drop or the scrubbing efficiency, but relates to how to collect the contaminant (e.g., tin) to be scrubbed. If the plates are shaped such that they slope outward (e.g., toward the outer vessel 420), the contaminant drips out and flows to the outside of the stack of scrubber plates 416. In other embodiments, the plates can be shaped such that they slope inward (e.g., toward the inner flow channel 418) to collect contaminants in the center of the stack of scrubber plates 416. The slope of the scrubber plates may have some impact on the pressure drop, but it is a small factor. A design feature of the scrubber plates is to avoid a capillary effect between the plates, such that the plates are not spaced too close together that the collected contaminant will create a clog and block the gas flow between two plates, which would affect the pressure drop. In some embodiments, the plates include a tapered outer edge to form a fin-shaped component configured to capture the contaminant.

[0071] In comparison with other approaches, a cross-sectional dimension of the exhaust flow path is increased to lower gas velocity and increase the residence time. In addition, the inner flow channel 418 is increased to increase the residence time. Moreover, the plate spacing between adjacentscrubber plates 416 is reduced to shorten the diffusion distance, resulting in an increased contaminantcapture probability.

[0072] A flow blocker 424 is positioned at a lower end of the stack of scrubber plates 416 to prevent gas from flowing below the stack of scrubber plates 416. The flow blocker 424 is configured to block gas flow from traveling out the bottom of the stack of scrubber plates 416 and forces the gas flow through the radial channels in between the scrubber plates and into the outer flow channel 422. In some embodiments, the flow blocker 424 is configured to include a drain path for the contaminant (e.g., liquid tin). In some embodiments, the flow blocker 424 includes a titanium nitride (TiN)-coated stainless steel or a contaminant-resistant coated stainless steel with a resistive heating element brazed onto a surface of the flow blocker 424.

[0073] In some embodiments, there is empty space between the flow blocker 424 and a bottom of the outer vessel 420. The empty space may be present to accommodate changing the height of the stack of scrubber plates 416 without requiring replacing the outer vessel 420. In some embodiments, a contaminant collection component (not shown in Fig. 4) is located in the empty space to collect condensed tin dripping from the scrubber plates.

[0074] The flow blocker 424 redirects the gas flow through the outer flow channel 422 upward into an exit housing 426 and out of the scrubber 412 via a scrubber exit 428. The exit housing 426 is configured with geometric features to direct the exiting gas flow to the scrubber exit 428.

[0075] In some embodiments, one or more heating elements 430 are connected to the stack of scrubber plates 416, to heat the stack of scrubber plates 416 to help prevent the contaminant accumulation in between the individual plates and blocking the flow of gas. The heating elements 430 may be configured to constantly, or periodically, bring the contaminant scrubbing surfaces (e.g., the scrubbing plates) above the melting temperature. In some embodiments, the heating elements 430 reside within the support rods of the stack of scrubber plates 416. In some embodiments, a heating element 430 is cylindrical in shape. In some embodiments, a heating element 430 includes an external structural shell and an internal resistive heating element with electrical isolation between the heating element and the external shell. In some embodiments, the external shell includes a material resistant to contaminant (e.g., tin) formation. In some embodiments, the internal heating element includes a high temperature electrically resistant material.

[0076] In some embodiments, the heating elements 430 includes a cartridge heater in the stack of scrubbing plates 416. In some embodiments, there is a heating element connected to an interior wall of the outer vessel 420 to prevent clogs along the outer flow channel 422. In some embodiments, there is a heating element on the gas inlet path (e.g., in the inlet elbow pipe 414) because if the inlet surface is too cold, there may be a contaminant (e.g., tin) buildup before the gas enters the scrubber 412.

[0077] Gas exits the EUV radiation source 100 via the outlet 402 and the source outlet pipe 404. The gas flows into the scrubber inlet pipe 410, the inlet elbow pipe 414, and the inner flow channel 418. Because the flow blocker 424 prevents the gas flow’s further progress along the inner flow channel418, the gas is forced to turn and flow in between the plates of the stack of scrubber plates 416 and into the outer flow channel 422. The gas flow is reversed in an opposite direction in the outer flow channel 422 toward the scrubber exit 428.

[0078] Fig. 5 is a cross-sectional perspective view of the scrubber 412 shown in Fig. 4. The components of the scrubber 412 are described in connection with Fig. 4. Inlet gas flow 500 enters the scrubber 412 via the scrubber inlet pipe 410. The inlet gas flow 500 enters the inlet elbow pipe 414 (gas flow 502) and the inner flow channel 418 (gas flow 504). After the gas flow 504 has entered the inner flow channel 418 along a first direction (e.g., downward in Fig. 5), the gas turns and flows in between the scrubber plates of the stack 416 (gas flow 506) in a second direction orthogonally or substantially orthogonally to the first direction, and then flow into the outer flow channel 422 (gas flow 508) in a third direction opposite to the first direction (e.g. upward in Fig 5). Because the flow blocker 424 is positioned at one side (e.g., the bottom in Fig. 5) of the stack of scrubber plates 416, the gas flow (e.g., gas flow 504 or gas flow 506) is forced to deviate from its original path and undergo a substantial change in direction (e.g., as gas flow 508). The gas flow 508 moves from the outer vessel 420 into the exit housing 426 (gas flow 510) and exits the scrubber 412 through the scrubber exit 428 (gas flow 512). The gas flow 512 enters further piping (not shown in Figs. 4 and 5) for further processing outside of the scrubber 412. In some embodiments, the gas flow 512 is passed through a gas cooler to reduce its temperature.

[0079] In a radial flow device such as the scrubber 412, the gas flow responsible for the mass transfer must turn perpendicular or substantially perpendicular to the inlet axis and flow outward. The physics of a scrubber requires that the carrier gas flowing through a scrubbing channel has sufficiently low velocity such that the contaminant (e.g., tin atoms) has enough time to diffuse to the channel surfaces. This low velocity in turn requires that the total cross-sectional area for the flow through the fin channels, referred to as the frontal area, must also be large. The radial scrubber design allows this frontal area to be scaled within compact spaces by utilizing the perimeter of the flow volume and leveraging the length of the conduit.

[0080] In addition to the resistance variation across flow channel paths, the pressure over the inner region also varies in a radial scrubber due to the presence of the bottom flow blocker. As the carrier gas flows through the inner region and collides with the flow blocker, its kinetic energy (dynamic pressure) is converted to static pressure. Therefore, channels farthest from the inlet to the radial scrubber have the most pressure to drive flow.

[0081] These two insights into the radial scrubber design - that driving pressure to the core channels increases with distance from the inlet and resistance for a given path through a channel increases with distance from outlet - inform why the flow reversing scrubber described herein is an effective configuration. For flow-through devices, the channels with the most driving pressure also have the least flow resistance. This leads to the vast majority of the flow traveling through the few channels closest to the outlet. For flows with any significant inlet velocity, this both increases the requiredpressure drop, as the majority of the flow is being squeezed through a small area, and severely decreases scrubbing efficiency as contaminant (e.g., tin) concentration is overloaded to a few scrubbing channels. As a result, radial flow through scrubbers will generally underperform an axial flow counterpart.

[0082] In contrast, the flow reversing radial scrubber described in the present disclosure aligns the highest pressure channels with the highest resistance flow paths. This leads to a more uniform flow distribution, and allows for the design to properly utilize the entire volume for its intended scrubbing function while maintaining a modest pressure drop. In doing so, it enables an advantage of the radial scrubber design, using the higher flow cross-section to drive performance improvements.

[0083] The scrubbing efficiency (and also the pressure drop) is a function of several distributions: the velocity distribution of the gas coming into the scrubber, the contaminant (e.g., tin) concentration distribution, and the temperature distribution. With the flow reversing scrubber, the pressure drop is more uniform and the pressure drop between plates is small. If there is a high flow velocity, then the scrubbing efficiency in that area is low because the time of contact of the flow to the scrubber plate surface is short. If the spacing between the scrubber plates is adjusted to fix the pressure drop, then the scrubbing efficiency also drops because there is less surface area contacting the flow.

[0084] The flow reversing scrubber design permits using a uniform stack of scrubber plates without having to adjust the fin spacing or the fin length. The desired benefits (e.g., scrubbing efficiency and pressure drop) can be achieved through the architecture of the scrubber itself. The pressure balancing in the scrubber happens in a natural way because of the flow reversal.

[0085] Fig. 6A is a cross-sectional side view of the flow resistance in the radial flow -reversing scrubber 412 shown in Fig. 4, consistent with some embodiments of the present disclosure. The inlet gas flow 500 enters the scrubber 412 and flows into the inner flow channel 418 in the center of the stack of scrubber plates 416. The gas is then redirected through openings in between the scrubber plates of the stack 416 and out of the scrubber 412 as the exit gas flow 512. While the gas is flowing through the scrubber 412, it encounters resistance at different locations. The total resistance 600 encountered by the gas flow through the scrubber 412 is a sum of an inner flow resistance 602 in the inner flow channel 418 (e.g., there is some flow resistance starting at the inlet elbow pipe 414 and into the inner flow channel 418), a core resistance 604 as the gas flow passes in between the scrubber plates of the stack 416 (e.g., between every two plates in the stack of scrubber plates 416), and an outer flow resistance 606 in the outer flow channel 422. It is noted that, similar to a parallel electrical circuit, the more plates in the stack of scrubber plates 416, the lowerthe core resistance 604 will be. To achieve maximum efficiency for the scrubber 412, the total resistance 600 should be minimized.

[0086] Based on the flow design of the scrubber 412, the end plates in the stack (e.g., the plates farther from the inlet elbow pipe 414) have the most flow going through them (as compared to the higher plates in the stack; e.g., the plates closer to the inlet elbow pipe 414). The front plates (e.g., the plates close to the inlet elbow pipe 414) correspondingly receive less flow going through them.

[0087] Fig. 6B is a cross-sectional side view of gas flow in the radial flow-reversing scrubber 412 shown in Fig. 4, consistent with some embodiments of the present disclosure. The gas flow 504 enters the inner flow channel 418, along a first direction, in the center of the stack of scrubber plates 416. The gas flow 506 is constrained to move through openings in between the scrubber plates of the stack 416, following a second direction orthogonal or substantially orthogonal to the first direction. The gas flow 506 is redirected by an inner surface of the outer vessel 420 and the flow blocker 424, resulting in gas flow 608 traveling through the outer channel along a third direction, and out of the scrubber 412 as the gas flow 510. The third direction is opposite to or substantially opposite to the first direction. While the gas is flowing through the scrubber 412, it encounters resistance at different locations. As shown in Fig. 6B, the different gas flow arrows have approximately the same widths, indicating a similar flow volume throughout the scrubber 412. The gas flow pressure and the gas flow resistance are the lowest at an upper portion of the outer vessel 420 (e.g., near the inlet elbow pipe 414 and the scrubber exit 428). The gas flow pressure and the gas flow resistance are higher at a lower portion of the outer vessel 420 (e.g., near the flow blocker 424).

[0088] Previous scrubber designs are size-constrained by other modules in the system located around the scrubber, making it difficult to scale the scrubber (e.g., make the scrubber larger). The flow reversing scrubber described herein is located external to the EUV source and is not mechanically constrained by other modules around it. For example, it is relatively easy to include more plates in the stack (to make the stack taller) or to reduce the number of plates in the stack (to make stack shorter) depending on the flow amount through the scrubber.

[0089] Fig. 7A is a top view of a scrubber plate 700, consistent with embodiments of the present disclosure. Scrubber plate 700 has a disc-shaped body having a planar or substantially planar surface and a circumferential or substantially circumferential edge; the disc-shaped body of scrubber plate 700 defines a central opening extending through scrubber plate 700 and bounded by an inner diameter, and an outer perimeter defined by an outer diameter. In some embodiments, scrubber plate 700 is a unitary structure. In some embodiments, scrubber 700 includes a plurality of discrete segments arranged about a central axis to form a disc shape. While the scrubber plate 700 is shown in Fig. 7A as being circular, other shapes for the scrubber plate 700 are contemplated and considered to be within the scope of the present disclosure. The scrubber plate 700 has an outer diameter Do702 (e.g., the outer perimeter) and an inner diameter D! 704. The inner diameter 704 of the scrubber plate 700 defines the inner flow channel 418 through the stack of scrubber plates 416. In some embodiments, the inner diameter 704 is the same as the diameter of the inlet elbow pipe 414. In some embodiments, the scrubber plate 700 also includes one or more holes 706 configured such that a heating element 430 may pass through the hole 706 and provide support to the stack of scrubber plates 416.

[0090] Fig. 7B is a cross-sectional view of the scrubber plate 700, consistent with embodiments of the present disclosure. The scrubber plate 700 is shaped such that an outer edge of the scrubber platetapers to form a fin-shaped component or a fin 708. The hole 706 passes through the fin 708. The fin 708 is angled relative to the horizontal plane such that the fin 708 may capture a contaminant (e.g., tin) as the gas flow 506 passes through the stack of scrubber plates 416 toward the outer flow channel 422. In some embodiments, the scrubber plate 700 may be configured as a hollow disk with a conical angle. The angle is configured to drip condensed contaminant (e.g., tin) towards a desired direction. In some embodiments, the angle is configured to drip the contaminant (e.g., tin) towards the outer flow channel 422. In other embodiments, the angle is configured to drip the contaminant (e.g., tin) towards the inner flow channel 418.

[0091] In some embodiments, the scrubber plate 700 is constructed of a material resistant to contaminant (e.g., tin) formation at an elevated temperature. In some embodiments, the material has a high thermal conductivity, to reduce temperature gradients required to heat the fin surface above the contaminant (e.g., tin) melting point. In some embodiments, the scrubber plate 700 may be constructed from molybdenum.

[0092] Fig. 8 is a flowchart of an example method 800 for separating and removing debris from a gas flow, consistent with embodiments of the present disclosure. In some embodiments, the method 800 is performed by a contamination removing module, such as the scrubber 412 of Fig. 4 or the scrubber 200 of Fig. 2.

[0093] At step 802, a flow is guided through a duct (e.g., scrubber inlet pipe 410 and inlet elbow pipe 414) to an inner flow channel (e.g., inner flow channel 418) along a first direction. For example and referring to Fig. 4, the first direction may be downward through the inner flow channel 418.

[0094] At step 804, the flow is directed through intervals in a stack of scrubber plates (e.g., stack of scrubber plates 416) along a second direction. In some embodiments, the second direction is substantially orthogonal to the first direction. For example and referring to Fig. 4, if the first direction is downward through the inner flow channel 418, the second direction may be radially through spaces in between the plates of the stack of scrubber plates 416 and orthogonal to the inner flow channel 418.

[0095] At step 806, the flow is guided through a space between the stack of scrubber plates (e.g., stack of scrubber plates 416) and a housing (e.g., outer vessel 420) to an outlet (e.g., scrubber exit 428) along a third direction. In some embodiments, the third direction may be substantially opposite to the first direction. For example and referring to Fig. 4, if the first direction is downward through the inner flow channel 418, the third direction may be upward through the outer flow channel 422 to the scrubber exit 428.

[0096] In some embodiments, guiding the flow through the space between the stack of scrubber plates 416 and the outer vessel 420 (e.g., the outer flow channel 422) includes reversing the flow from the first direction to the third direction off a closure member (e.g., flow blocker 424) positioned at a bottom of the housing. For example and referring to Fig. 4, the closure member may include the flow blocker 424 positioned at a bottom end of the stack of scrubber plates 416 (e.g., an end of the stack of scrubber plates 416 remote from an inlet to the inner flow channel 418). As shown in Fig. 4, the flowblocker 424 may not be positioned adj cent to a bottom of the outer vessel 420, and there may be empty space between the flow blocker 424 and the bottom of the outer vessel 420. The empty space may be present to accommodate changing the height of the stack of scrubber plates 416 without requiring replacing the outer vessel 420.

[0097] In some embodiments, a complex fin geometry may be used to attempt to rebalance the flow. For example, a conical fin stack may be used, where the plate disc inner diameters contract as they get farther from the inlet. As another example, varying the channel height (e.g., the plate spacing) and length throughout the scrubbing core could also potentially redistribute flow. However, both of these options require unique parts and greater complexity in manufacturing the core.

[0098] Fig. 9 is a perspective view of a portion of an alternate construction for a scrubber 900, consistent with embodiments of the present disclosure. The scrubber 900 includes an outer vessel 902 (e.g., the outer vessel 420 shown in Figs. 4 and 5). Only two layers of fin elements 904 are shown in Fig. 9 for clarity of illustration. However, each stack may include a plurality of fin elements 904, such as between 15 and 30 fin elements. In some instances, a stack of fewer than 15 fin elements reduces the residence time of gas within the scrubber 900. In another instances, a stack of more than 30 fin elements increase the total volume of the outer vessel 902 without a proportional increase in performance. Each layer of fin elements 904 is arranged in a discontinuous annular manner when viewed along a longitudinal axis of a flow path entering the scrubber 900. In each layer, the fin elements 904 are circumferentially spaced to define a segmented circular profile in the scrubber 900. In one embodiment, each layer of fin elements 904 includes three fin elements as shown in Fig. 9 for clarity of illustration. However, each layer may include a plurality of fin elements, such as between 8 and 16. In some instances, a layer of fewer than 8 fin elements results in insufficient thermal resolution, leading to increased power consumption for each stack of fin elements. In another instances, a layer of more than 16 fin elements provides redundant segmentation without a proportional improvement in temperature control. In some embodiments, a plurality of stacks of fin elements is arranged in a discontinuous cylinder and each stack of fin elements is physically separated from a neighboring stack of fin elements on either side by a gap.

[0099] The scrubber 900 further includes a plurality of heating elements 906a, 906b, and 906c, and each heating element is dedicated to an individual stack of fin elements. For example, heating element 906a is coupled to fin element 914a and fin element 916a, heating element 906b is coupled to fin element 914b and fin element 916b, and heating element 906c is coupled to fin element 914c and fin element 916c. Each heating element extends vertically through the stack of fin elements such that the heating element is in physical contact with each fin element in the stack. Each stack of fin elements includes a respective heating element, and each heating element is independently controllable. For example, only heating element 906a is activated and receives energy via a switch 910 and a power supply 912. When the active heating element 906a is energized, it is configured to provide thermal energy to its corresponding fin elements 914a and 916a. Conversely, the non-powered (e.g., inactiveor unheated) heating elements 906b and 906c are maintained at a baseline temperature lower than a temperature of heating element 906a.

[0100] Each stack of fin elements 904 is individually and selectively heated based on various activation sequences. In one embodiment, the heating elements 906a-c are energized sequentially in an order corresponding to their physical positioning (e.g., clockwise or counter-clockwise). In another embodiment, the heating elements 906a-c are energized in a non-sequential or interleaved pattern, such as energizing every other heating element in a first segment followed by the other heating elements in a second segment. In yet another embodiment, the activation order is dynamically determined based on the deposition rate or accumulated thickness of target material. In yet another embodiment, the heating elements are energized in a segmented manner, wherein a subset of heating elements is energized simultaneously to provide localized thermal regulation to a specific region of a stack. In some embodiments, the heating elements 906a-c have a rod-shaped configuration. Such rodshaped configuration is oriented transversely relative to each stack of fin elements and is configured to provide localized thermal energy to the coupled fin elements.

[0101] The scrubber 900 achieves a low pressure drop by individually activating one heating element at a time and cycling the heating of the fin element stacks. In some embodiments, only one heated fin element stack is maintained at a temperature above 232°C such that it melts and drains tin, while the rest of the fin element stacks with inactive heater elements cool the gas, acting as a partial gas cooler. It is noted that for target materials other than tin, the heating elements would be maintained at a temperature above the melting point of the target material. By operating only some of the heating elements, the overall tin-containing gas temperature is lower, resulting in higher gas density, lower gas velocity, lower viscosity, and thus a lower pressure drop. The lower outlet temperature may also reduce engineering requirements on subsequent vacuum elements, lower engineering costs.

[0102] In some embodiments, because only one heating element is activated at any given time, it allows using a single power supply (e.g., power supply 912), one cable in a service loop, and a relay circuit (e.g., switches 910) in place of multiple power supplies and cablings, thereby reducing component costs and service complexity. In some embodiments, each heating element is coupled to multiple wires; for example, from two to four wires, including one positive line, one neutral line, one optional ground protection line, and one optional thermocouple line. In some embodiments, each heating element is implemented as a cartridge rod heater with welded vacuum flanges, enabling the electrical connections to the heating element to be located in the atmosphere (e.g., outside the vacuum maintained inside the outer vessel 902), eliminating in-vacuum electrical connections.

[0103] Fig. 10A is a side view of a portion of a plurality of fin element stacks 1002 and 1004a-n (e.g., stacks of fin elements shown in Fig. 9), illustrating a structural arrangement of fin elements in a scrubber (e.g., scrubber 900 in Fig. 9). Fin element stack 1004a includes a heating element 1008a coupled to a plurality of fin elements 1012a. Fin element stack 1002 includes a heating element 1006 coupled to a plurality of fin elements 1010. Fin element stack 1004b includes a heating element 1008bcoupled to a plurality of fin elements 1012b. Fin element stack 1004n includes a heating element 1008n coupled to a plurality of fin elements 1012n. The plurality of stacks 1002 and 1004a-n are laterally spaced from one another by a first distance dl, ranging from about 3 millimeters (mm) to about 45 mm. A distance smaller than 3 mm increases a risk of mechanical interference and thermal shunting, in some instances. A distance greater than 45 mm reduces an effective residence time, lowering the scrubbing efficiency, in some instances. Within each stack, each layer of the fin elements 1010 and 1012a-n is arranged in parallel and are coaxially aligned. As shown in Fig. 10A, only one fin element stack 1002 is heated through a heating element 1006, the remaining heating elements 1008a-n of fin element stacks 1004a-n are maintained at a baseline temperature lower than a temperature of the heating element 1006.

[0104] Fig. 10B is a side view of a portion of a plurality of fin element stacks 1002 and 1004a-n (e.g., stacks of fin elements shown in Fig. 9), illustrating a structural arrangement of fin elements in a scrubber (e.g., scrubber 900 in Fig. 9). Fig. 10B illustrates an alternative embodiment to the arrangement shown in Fig. 10A, wherein like reference numerals denote like elements. In this embodiment, adjacent fin elements are vertically offset (shifted) by a second distance d2 defined by a plane of each fin element, and arranged in an alternating (staggered) pattern. The second distance d2 ranges from about 5 mm to about 15 mm. A distance smaller than 5 mm or greater than 15 mm results in non-uniformity of cross-sectional dimensions and unbalanced pressure drop across the fin elements, in some instances. The adjacent fin element stacks are laterally contiguous such that a horizontal separation is eliminated. In some embodiments, as the adjacent fin elements are vertically offset, each fin element from a first stack can overlap or sit between two fin elements from a second stack without physical interference.

[0105] Fig. 10C is a side view of a portion of a plurality of fin element stacks 1002 and 1004a-n (e.g., stacks of fin elements shown in Fig. 9), illustrating a structural arrangement of fin elements in a scrubber (e.g., scrubber 900 in Fig. 9). Fig. 10C illustrates an alternative embodiment to the arrangement shown in Fig. 10B, wherein like reference numerals denote like elements. In this embodiment, the fin elements in a same layer are horizontally separated by the first distance dl and the adjacent fin elements in adjacent stacks are vertically offset by the second distance d2.

[0106] While Figs. 10A-10C depict four fin element stacks for clarity of illustration, the scrubber may include a plurality of stacks, such as from 8 to 16 stacks as described above. Similarly, while Figs.lOA-lOC depict three fin elements for clarity of illustration, each stack may include a plurality of fin elements, such as from 15 to 30 fin elements as described above. In some embodiments, each fin element stack includes an identical number of fin elements. In some embodiments, the plurality of fin element stacks has different numbers of fin elements; for example, the stack is arranged in an alternating configuration such that a first set of stacks has a first number of fin elements and a second set of stacks has a second number of fin elements, and the second number is at least one greater than the first number. In some embodiments, a center portion of each fin element protrudes from at leastone side in a direction parallel to a longitudinal axis of the heating element. In some embodiments, the center portion of each fin element from the same stack are in physical contact with each other. In some embodiments, the center portion of each fin element from the same stack are separate from each other.

[0107] Fig. 11 is a perspective view of a single fin element 1100 usable in the scrubber shown in Fig.9, consistent with embodiments of the present disclosure. The fin element 1100 has a fin width 1102, a fin length 1104, and a fin height 1106. In some embodiments, the fin width 1102 is in a range of 50 mm to 300 mm. A fin width smaller than 50 mm reduces the heated surface, resulting in less residence time, in some instances. A fin width greater than 300 mm increases the difficulty in maintaining lateral temperature uniformity and / or increases power consumption, in some instances. In some embodiments, the fin length 1104 is in a range of 20 mm to 150 mm. A fin length smaller than 20 mm reduces the heated surface, resulting in less residence time, in some instances. A fin length greater than 150 mm increases the flow drag, requiring significantly higher pump power, in some instances. In some embodiments, the fin height 1106 is in a range of 10 mm to 30 mm. A fin height smaller than 10 mm increases manufacturing costs without significant improvement, in some instances. A fin height greater than 30 mm enlarges a flow path dimension, resulting in less residence time, in some instances. The fin element 1100 has an inner portion 1110 that faces an interior of the outer vessel 902 as shown in Fig. 9 and an outer portion 1112 that is opposite the inner portion 1110 as faces a wall of the outer vessel 902. The inner portion 1110 may be constructed with a sharp leading edge (e.g., facing an inner radius of the scrubber 900) facing the incoming exhaust flow to reduce the head-on pressure drop, angling out to the outer portion 1112 (e.g., an outer radius of the scrubber 900). The fin element 1100 also includes an opening 1114 sized and shaped such that a heating element may be inserted through the opening 1114.

[0108] In some embodiments, a fin element constructed from a Plasma Electrolytic Oxidation (PEO) coated aluminum (for example, aluminum alloy A16061) may be suitable for use in the high temperature conditions of the scrubber. The aluminum alloy for the fin element may be used instead of refractory metals, to help reduce the cost of scrubber components.

[0109] Fig. 12 is a cross-sectional view of a portion of a stack of fin elements 1100 usable in the scrubber shown in Fig. 9, consistent with embodiments of the present disclosure. To enable an electrical connection to the heating elements to be placed outside the vacuum the exists inside the outer vessel 902 (not shown in Fig. 12), a top 1200 of the outer vessel includes a vacuum sealing element 1202, such as a welded flange. The vacuum sealing element 1202 includes an opening sized and shaped such that a wire of heating element 1204 may pass through the vacuum sealing element 1202 and into the fin elements 1100. In some embodiments, the vacuum sealing element includes a pair of flange plates and a sealing member, such as an O-ring, disposed interfacially therebetween.

[0110] In some embodiments, multiple heating elements 1204 are used per stack of fin elements 1100. For example, in situations where the stack of fin elements is long in the vertical direction, a firstheating element 1204 is inserted into the stack of fin elements from the top of the stack and a second heating element 1204 (not shown in Fig. 12) is inserted into the stack of fin elements from the bottom of the stack. In such a construction, a separate vacuum sealing element may be provided at the bottom of the outer vessel 902 such that the electrical connection for the second heating element may be placed outside the vacuum.

[0111] The embodiments may further be described using the following clauses:1. A radiation source, including:a vessel defining a radiation generation region; anda contamination removing module coupled to the vessel, wherein the contamination removing module includes:a stack of plates having an opening to form an inner flow channel through the stack; a housing enclosing the stack of plates to form an outer flow channel; and a closure member inside the housing, wherein a diameter of the closure member is equal to or smaller than an inner diameter of the housing.2. The radiation source of clause 1, wherein the contamination removing module is coupled to the vessel through a duct, wherein the duct is configured to direct a flow path to the inner flow channel.3. The radiation source of clause 2, wherein the contamination removing module further includes one or more heating components in contact with the duct.4. The radiation source of any one of clauses 1-3, wherein the contamination removing module further includes one or more heating components in contact with the stack of plates.5. The radiation source of any one of clauses 1-4, wherein the contamination removing module further includes one or more heating components in contact with an inner surface of the housing. 6. The radiation source of any one of clauses 1-5, wherein the closure member is in contact with one or more heating components and is separated from the stack of plates.7. The radiation source of any one of clauses 1-6, wherein each plate is disc-shaped and includes an opening to form the inner flow channel.8. The radiation source of any one of clauses 1-7, wherein each plate includes a tapered outer edge to form a fin-shaped component configured to capture a contaminant.9. The radiation source of any one of clauses 1-8, wherein the housing is cylindrical.10. A method for removing debris, including:guiding a flow, through a duct, to an inner flow channel of a stack of plates along a first direction;directing the flow through intervals between the stack of plates along a second direction, wherein the second direction is substantially orthogonal to the first direction; andguiding the flow through a space between the stack of plates and a housing to an outlet, along a third direction.11. The method of clause 10, wherein the third direction is substantially opposite to the first direction.12. The method of clauses 10 or 11, wherein guiding the flow through the space between the stack of plates and the housing includes reversing the flow from the first direction to the third direction off a closure member positioned at an end of the housing.13. The method of clause 12, further including:heating the closure member.14. The method of any one of clauses 1-13, further including:heating the stack of plates.15. The method of any one of clauses 1-14, further including:heating the duct.16. The method of any one of clauses 1-15, further including:heating an inner surface of the housing.17. A radiation source, including:a vessel defining a radiation generation region; anda contamination removing module coupled to the vessel, wherein the contamination removing module includes:a stack of fin elements including an opening in a center of the stack to form an inner flow channel through the stack;a housing enclosing the stack of fin elements to form an outer flow channel; anda closure member inside the housing, wherein a diameter of the closure member is equal to or smaller than an inner diameter of the housing.18. The radiation source of clause 17, wherein the stack of fin elements includes a plurality of segments of fin elements, each segment including a plurality of fin elements.19. The radiation source of clause 18, further including:a heating element extending through the plurality of fin elements in a single segment.20. The radiation source of clauses 18 or 19, further including:a plurality of heating elements, each heating element extending through the plurality of fin elements in a single segment.21. The radiation source of clause 20, wherein each of the plurality of heating elements is configured to separately heat a corresponding segment of fin elements.22. The radiation source of any one of clauses 17-21, wherein the contamination removing module is coupled to the vessel through a duct, wherein the duct is configured to direct a flow path to the inner flow channel.23. The radiation source of clause 22, wherein the contamination removing module further includes one or more heating components in contact with the duct.24. The radiation source of any one of clauses 17-23, wherein the contamination removing module further includes one or more heating components in contact with an inner surface of the housing.25. The radiation source of any one of clauses 17-24, wherein each fin element includes a sharp leading edge facing the inner flow channel.26. The radiation source of clause 25, wherein each fin element angles outward from the leading edge toward an outer portion of the fin element.27. A method for removing debris, including:guiding a flow, through a duct, to an inner flow channel of a stack of fin elements along a first direction;directing the flow through intervals between the stack of fin elements along a second direction, wherein the second direction is substantially orthogonal to the first direction; and guiding the flow through a space between the stack of fin elements and a housing to an outlet, along a third direction.28. The method of clause 27, wherein the third direction is substantially opposite to the first direction.29. The method of clauses 27 or 28, wherein guiding the flow through the space between the stack of fin elements and the housing comprises reversing the flow from the first direction to the third direction off a closure member positioned at a bottom of the housing.30. The method of clause 29, further including:heating the closure member.31. The method of any one of clauses 27-30, further including:heating the stack of fin elements.32. The method of any one of clauses 27-31, further including:heating the duct.33. The method of any one of clauses 27-32, further including:heating an inner surface of the housing.

[0112] Block diagrams in the figures may illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. It should be understood that in some alternative implementations, functions indicated in a block may occur out of the order noted in the figures. For example, two blocks shown in succession may be executed or implemented substantially concurrently, or two blocks may sometimes be executed in reverse order, depending upon the functionality involved. Some blocks may also be omitted.

[0113] It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in connection with various embodiments, and other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the technology disclosed herein. It is intended that the specification and examples beconsidered as exemplary only, with a true scope of the invention being indicated by the following claims.

Claims

CLAIMS1. A radiation source, comprising:a vessel defining a radiation generation region; anda contamination removing module coupled to the vessel, wherein the contamination removing module includes:a stack of plates defining an opening to form a first flow channel through the stack;a housing enclosing the stack of plates to define a second flow channel; and a closure member coupled to the housing, wherein a diameter of the closure member is equal to or smaller than an inner diameter of the housing.

2. The radiation source of claim 1, wherein the contamination removing module is coupled to the vessel through a duct, wherein the duct is configured to direct a flow path to the first flow channel.

3. The radiation source of claim 2, wherein the contamination removing module further includes one or more heating components in contact with the duct.

4. The radiation source of claim 1, wherein the contamination removing module further includes one or more heating components in contact with the stack of plates.

5. The radiation source of claim 1, wherein the closure member is in contact with one or more heating components and is separated from the stack of plates.

6. The radiation source of claim 1, wherein each plate is disc-shaped and includes an opening to form the first flow channel.

7. The radiation source of claim 6, wherein each plate includes a tapered outer edge to form a fin-shaped component configured to capture a contaminant.

8. A method for removing debris, comprising:guiding a flow, through a duct, to an inner flow channel of a stack of plates along a first direction;directing the flow through intervals between the stack of plates along a second direction, wherein the second direction is substantially orthogonal to the first direction; andguiding the flow through a space between the stack of plates and a housing to an outlet, along a third direction.

9. The method of claim 8, wherein the third direction is substantially opposite to the first direction.

10. The method of claim 8, wherein guiding the flow through the space between the stack of plates and the housing comprises reversing the flow from the first direction to the third direction off a closure member positioned at an end of the housing.

11. The method of claim 8, further comprising:heating the stack of plates to melt contaminants deposited on the stack of plates.

12. A radiation source, comprising:a vessel defining a radiation generation region; anda contamination removing module coupled to the vessel, wherein the contamination removing module includes:a stack of fin elements including an opening in a center of the stack to form an inner flow channel through the stack;a housing enclosing the stack of fin elements to form an outer flow channel; anda closure member inside the housing, wherein a diameter of the closure member is equal to or smaller than an inner diameter of the housing.

13. The radiation source of claim 12, wherein the stack of fin elements includes a plurality of segments of fin elements, each segment including a plurality of fin elements.

14. The radiation source of claim 13, further comprising:a heating element extending through the plurality of fin elements in a single segment.

15. The radiation source of claim 13, further comprising:a plurality of heating elements, each heating element extending through the plurality of fin elements in a single segment.

16. The radiation source of claim 15, wherein each of the plurality of heating elements is configured to separately heat a corresponding segment of fin elements.

17. The radiation source of claim 12, wherein the contamination removing module is coupled to the vessel through a duct, wherein the duct is configured to direct a flow path to the inner flow channel.

18. The radiation source of claim 12, wherein the contamination removing module further includes one or more heating components in contact with an inner surface of the housing.

19. The radiation source of claim 12, wherein each fin element includes a sharp leading edge facing the inner flow channel.

20. The radiation source of claim 17, wherein each fin element is laterally spaced from one another by a first distance ranging from about 3 millimeters (mm) to about 45 mm.

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