Laser-generated plasma extreme ultraviolet light source

Abstract

The utility model provides a laser generation plasma extreme ultraviolet light source. The laser generation plasma extreme ultraviolet light source comprises a vacuum chamber; the rotatable crucible is arranged in the vacuum chamber and is provided with an annular inner surface for bearing the liquid metal; and a laser arranged to apply a laser beam to the liquid metal carried on the annular inner surface of the rotatable crucible such that the liquid metal emits extreme ultraviolet light. The laser-generated plasma extreme ultraviolet light source further comprises: a stationary component disposed in the vacuum chamber and located near or around the annular inner surface of the rotatable crucible; a cooling liquid conveying inlet or a nozzle; and a cooling element secured to the stationary assembly and including features to operably couple with the cooling liquid delivered by the cooling liquid delivery inlet or nozzle.

Description

Technical Field

[0001] An embodiment of the present utility model relates to a laser-produced plasma extreme ultraviolet light source. Background Art

[0002] The following content relates to extreme ultraviolet (EUV) light sources and EUV light generation methods, EUV lithography systems and methods, and related technologies. Summary of the Utility Model

[0003] An embodiment of the present disclosure relates to a laser-produced plasma extreme ultraviolet (LPP-EUV) light source, which helps to improve the stability of the output extreme ultraviolet light.

[0004] In one embodiment, a laser-produced plasma extreme ultraviolet light source includes: a vacuum chamber; a rotatable crucible disposed within the vacuum chamber and having an annular inner surface for holding a liquid metal; a laser arranged to apply laser light to the liquid metal held on the annular inner surface of the rotatable crucible to cause the liquid metal to emit extreme ultraviolet light; a stationary assembly disposed within the vacuum chamber and near or surrounding the annular inner surface of the rotatable crucible; a coolant delivery inlet or nozzle; and a cooling element fixed to the stationary assembly and including features for operably coupling with coolant delivered by the coolant delivery inlet or nozzle.

[0005] The cooling element being fixed to the stationary assembly and including features for operably coupling with coolant delivered by the coolant delivery inlet or nozzle helps to improve the stability of the output extreme ultraviolet light. Brief Description of the Drawings

[0006] Aspects of the present disclosure are best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be noted that, in accordance with standard practice in the industry, the various features are not drawn to scale. In fact, for the sake of clarity of discussion, the dimensions of the various features may be arbitrarily increased or reduced.

[0007] Figure 1A 、 Figure 1B and Figure 1C A perspective view schematically illustrating an EUV light source having a rotating liquid metal crucible ( Figure 1A ), an exploded isolated perspective view of a trap assembly of an EUV light source having a cooling plate according to an illustrative embodiment ( Figure 1A ), and an isolated perspective view of the assembled trap assembly ( Figure 1B ); Figure 1C );

[0008] Figure 2 Schematically illustrates Figure 1BIsolated perspective view of a variant embodiment of the cooling plate;

[0009] Figure 3 Schematically illustrates an isolated perspective view of a cooling plate according to another embodiment;

[0010] Figure 4A 、 Figure 4B and Figure 4C Schematically illustrates a perspective view of a rotating liquid metal crucible and a surrounding stationary ring ( Figure 4A ), a perspective view of a gasket of the stationary ring ( Figure 4B ), and an enlarged perspective view of a gasket portion showing the grooves of the gasket ( Figure 4C ).

[0011] Explanation of reference numerals in the drawings

[0012] 10: LPP-EUV light source;

[0013] 12: Vacuum chamber;

[0014] 14: Rotatable crucible / crucible / tower;

[0015] 16: Flat bottom portion;

[0016] 18: Annular outer surface;

[0017] 20: Annular inner surface / inner surface;

[0018] 22: Liquid metal;

[0019] 24: Laser;

[0020] 26: Laser beam / laser ray;

[0021] 28: EUV light / EUV light emission;

[0022] 36: Fixed position / location;

[0023] 40: Trap assembly / liquid metal debris trap assembly;

[0024] 42: Liquid metal debris trap;

[0025] 44, 84: Cooling plate / metal plate;

[0026] 50: Laser opening;

[0027] 52: EUV light opening / EUV opening;

[0028] 56: EUV opening

[0029] 60: Coolant delivery inlet / fluid inlet / coolant inlet / inlet;

[0030] 62: Fluid outlet / Coolant outlet / Outlet;

[0031] 66: Fluid passage / Internal fluid passage;

[0032] 86: Nozzle;

[0033] 88: Surface;

[0034] 90, 110: Groove;

[0035] 92, 112: Ridge;

[0036] 100: Gasket / Cooling element;

[0037] 102: Stationary component / Ring / First annular ring / A annular ring;

[0038] 104: Stationary component / Ring / Second annular ring / A annular ring;

[0039] 106: Coolant delivery nozzle / Nozzle;

[0040] 108: Tube or pipe;

[0041] A: Central axis;

[0042] R: Rotation direction. Detailed implementation

[0043] The following disclosure provides many different embodiments or examples for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these are only examples and are not intended to be limiting. For example, in the following description, forming a first feature above or on a second feature may include embodiments where the first and second features are in direct contact, and may also include embodiments where additional features are formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and / or letters in various examples. Repeating for simplicity and clarity does not itself indicate a relationship between various embodiments and / or arrangements.

[0044] In addition, spatial relative terms may be used herein, such as "below", "beneath", "lower", "above", "upper", etc., to facilitate the description of the relationship between one element or feature shown in the figures and another element or multiple features. Spatial relative terms are intended to cover different orientations of the device during use or operation, as well as the orientations shown in the figures. The device may be oriented in other directions (rotated 90 degrees or other directions), and the spatial relative descriptors used herein may be interpreted accordingly.

[0045] Extreme ultraviolet (EUV) light is used for lithography in semiconductor manufacturing processes, with the aim of producing fine features, i.e., features with small critical dimensions (CDs). A laser-produced plasma (LPP)-EUV light source can be used to generate the required EUV light. In an LPP-EUV light source, a laser beam irradiates a suitable liquid metal, such as liquid tin, and the resulting liquid metal plasma emits EUV light. For example, a tin plasma emits 13.5 nm EUV light, which is a commonly used EUV wavelength in EUV lithography.

[0046] One challenge in EUV lithography processes is that EUV light is generally not suitable for control using refractive optics because most materials have very high absorption of EUV. Therefore, the optical system for shaping and guiding EUV light employs a series of EUV mirrors. However, the EUV light loss for each EUV mirror in the optical system is high. Thus, a high-brightness (i.e., high-power) EUV light source is required.

[0047] One type of LPP-EUV light source employs a droplet injector that sends liquid metal droplets through the vacuum in a vacuum chamber at defined time intervals. A pulsed laser synchronously impacts each liquid metal droplet to generate an EUV-emitting liquid metal plasma.

[0048] Another type of LPP-EUV light source employs a crucible that rotates in a ring, and the crucible holds the liquid metal on its inner surface. The laser is arranged to impact the inner surface at a defined fixed position (i.e., a position fixed relative to the vacuum chamber) to generate an EUV light-emitting liquid metal plasma. Some examples of such LPP-EUV light sources that use liquid tin to produce 13.5 nm EUV light are the TEUS series of LPP-EUV light sources provided by ISTEK B.V. (Eindhoven, Netherlands). This type of LPP-EUV light source can have certain advantages, such as providing high EUV power, good EUV light output stability, advantageously redirecting liquid metal debris away from the fixed position of EUV light emission, and a long LPP-EUV light source lifetime.

[0049] Using a rotating crucible advantageously diffuses the energy input of the laser over the inner annular surface of the rotating crucible to reduce heating and the consequent pressure increase in the vacuum chamber.

[0050] However, this document recognizes that sometimes using only a rotating crucible may not be sufficient to prevent problems in the operation of an LPP-EUV light source. In fact, when the laser power is increased to operate such an LPP-EUV light source at high EUV power (which is desirable for certain EUV lithography tasks), it is observed that the temperature of the inner surface of the crucible rises during use, while the pressure in the vacuum chamber also increases. The surface of the liquid tin exhibits vibrations, and the stability of the output EUV light decreases.

[0051] Embodiments of the present utility model provide a cooling element. The cooling element can be a cooling plate or a gasket, which is fixed to a stationary component disposed in the vacuum chamber and adjacent to or surrounding the annular rotatable crucible. The cooling element includes features for operably coupling with a coolant delivered by a coolant delivery inlet or nozzle.

[0052] Refer to Figure 1A , the LPP-EUV light source 10 includes a schematic vacuum chamber 12 (alternatively, from another perspective, the LPP-EUV light source 10 has certain components in the schematic vacuum chamber 12). The LPP-EUV light source 10 includes a rotatable crucible 14 that is rotated about a central axis A by a motor assembly (not shown) during operation. The rotatable crucible 14 includes a flat bottom portion 16 and a side wall including an annular outer surface 18 and an annular inner surface 20. The rotatable crucible 14 includes an internal heater (not shown) and contains a target metal, such as tin, which is heated to form a liquid metal (e.g., liquid tin), and the liquid metal moves outward under the action of centrifugal force due to the rotation of the crucible to coat the annular inner surface 20. Thus, during the operation of the LPP-EUV light source 10, the liquid tin or other liquid metal 22 is carried by the annular inner surface 20.

[0053] The laser 24 is arranged to apply a laser beam (e.g., a laser ray) 26 to the liquid metal 22 carried by the annular inner surface 20 of the rotatable crucible 14, causing the liquid metal to interact with the laser ray 26 to emit EUV light 28. Although the schematic laser 24 is shown disposed within the vacuum chamber 12, in other embodiments, the laser can be disposed outside the vacuum chamber and the laser ray is guided into the vacuum chamber through an optical window port of the vacuum chamber.

[0054] More specifically, the interaction between the laser ray 26 and the liquid metal 22 occurs at a fixed position 36 where the laser ray 26 impinges on the annular inner surface 20 of the rotatable crucible 14, and a laser-generated plasma is generated at the fixed position 36. As Figure 1AAs shown, the fixed position 36 is partially surrounded by the trap assembly 40. The laser beam 26 can be a pulsed laser beam with an average power of 10 W to 400 W or higher in some non-limiting examples. Thus, the laser beam 26 transfers highly concentrated energy to the fixed position 36, generating sufficient heat to convert the liquid metal 22 at the fixed position 36 into a laser-generated plasma that emits EUV light from the fixed position 36. Figure 1A The emitted EUV light 28 is schematically depicted. "Fixed position" means that the position 36 is fixed relative to the vacuum chamber 12, i.e., it is a fixed position in the reference frame of the vacuum chamber 12. In other words, the fixed position 36 does not rotate with the rotation of the crucible 14. In contrast, as the crucible 14 rotates, the position where the laser beam 26 impinges on the annular inner surface 20 of the rotating crucible 14 changes (in the reference frame of the crucible 14), so over time, the laser beam 26 traces an annular trajectory on the annular inner surface 20 of the rotating crucible 14. Thus, using a rotating crucible 14 is understood to distribute the energy generated by the laser beam 26 over an annular region on the inner surface 20 of the crucible 14, thereby dispersing the energy over the annular region. It should also be noted that EUV light generally emits omnidirectionally from the fixed position 36, and only a part of the EUV light is collected by a suitable EUV optical element and transmitted to an EUV lithography system (not shown) and used for EUV lithography. Figure 1A The EUV light 28 emitted from the trap assembly 40 is shown, and the EUV light 28 is a part of the collected EUV light.

[0055] Although the energy distribution generated by the rotation of the crucible 14 is beneficial for distributing the laser energy over a larger surface of the crucible, however, as disclosed herein, when increasing the output laser power of the laser 24 to provide a high EUV power, it is still observed that the temperature of the inner surface 20 of the rotating crucible 14 rises during use, and at the same time, the pressure in the vacuum chamber also increases. The surface of the liquid tin exhibits vibration, and the stability of the output EUV light decreases.

[0056] Referring to Figure 1A And further referring to Figure 1B And Figure 1C , a method for remedying the above problems is disclosed herein. Figure 1A The LPP-EUV light source 10 of Figure 1A And Figure 1B also includes a trap assembly 40, and the trap assembly 40 includes a liquid metal debris trap 42 and a cooling plate 44 fixed to the liquid metal debris trap 42. Figure 1C shows an exploded view of the trap assembly 40, where the cooling plate 44 is spaced apart from the liquid metal debris trap 42; while Figure 1C shows a perspective view of the assembled trap assembly 40, where the cooling plate 44 is fixed to the liquid metal debris trap 42.Figure 1A also indicates the rotational direction R of the crucible 14.

[0057] As Figure 1A shown, the liquid metal debris trap assembly 40 is a stationary assembly disposed in the vacuum chamber 12 and is located near the annular inner surface 22 of the rotatable crucible 14. The liquid metal debris trap 42 is used to trap liquid metal debris (such as tin particles or the like) generated by the interaction of the laser beam 26 with the liquid metal (such as liquid tin) 22 to generate EUV light-emitting plasma at the fixed position 36. More specifically, the liquid metal debris trap 42 is located near (e.g., partially surrounding) the fixed position 36 and is a stationary assembly in terms of the reference frame of the vacuum chamber 12 because the liquid metal debris trap 42 is in a fixed position. In other words, the position of the liquid metal debris trap 42 does not rotate with the rotation of the crucible 14. The illustrative liquid metal debris trap 42 has a laser opening 50 and an EUV light opening 52, which are respectively arranged to allow the laser beam 26 and the EUV light 28 to pass through. This advantageously enables the liquid metal debris trap 42 to be closely positioned near (e.g., partially surrounding) the fixed position 36 where the EUV light-emitting plasma is generated. Thus, the fixed position 36 is also the position where the liquid metal debris emanates from the plasma. The illustrative liquid metal debris trap 42 has a generally arcuate shape that generally conforms to the curvature of the inner surface 22 of the rotatable crucible 14, again facilitating the close placement of the liquid metal debris trap 42 at the fixed position 36. Since the liquid metal debris trap 42 is located near the fixed position 36 where the EUV light-emitting plasma is generated, it receives a large amount of thermal energy from the laser-generated plasma and should therefore be made of a material capable of withstanding this heating. For example, the liquid metal debris trap 42 may include a metal or metal alloy such as molybdenum, tungsten, or another metal or metal alloy with a suitably high melting point.

[0058] Referring Figures 1A to 1C , the cooling element in this embodiment includes as Figure 1CThe cooling plate 44 shown is fixed to the liquid metal debris trap 42. This advantageously places the cooling plate 44 near the fixed position 36 where the EUV light-emitting plasma is generated, enabling it to well provide the cooling function. The schematic metal plate 44 has an arcuate shape generally consistent with the arcuate shape of the liquid metal debris trap 42, again facilitating the close placement of the liquid metal debris trap assembly 40 at the fixed position 36. Another advantage of integrating the cooling element with the liquid metal debris trap 42 is that since the cooling plate 44 is fixed to the liquid metal debris trap 42 (e.g., fastened with bolts or other means), the cooling plate 44 is in close contact with the liquid metal debris trap 42, providing a large amount of thermal mass near the fixed position 36 to cool and stabilize the temperature at the fixed position 36. Since the cooling plate 44 is located near the fixed position 36 where the EUV light-emitting plasma is generated, it receives (and advantageously dissipates and / or removes) a large amount of thermal energy from the laser-generated plasma, and thus should be made of a material capable of withstanding this heating. For example, the cooling plate 44 may include molybdenum, tungsten, or another metal or metal alloy with a suitably high melting point.

[0059] Referring Figure 1B and Figure 1C , the cooling plate 44 includes an EUV opening 56 that is aligned with the EUV light opening 52 of the liquid metal debris trap 42. During operation, the laser beam 26 passes through the laser opening 50 of the liquid metal debris trap 42, and a portion of the emitted EUV light 28 passes through the EUV openings 52 and 56 of the liquid metal debris trap 42 and the cooling plate 44, respectively. In this way, the trap assembly 40 does not interfere with the transmission of the laser beam 26 or the transmission of the EUV light emission 28. The cooling liquid delivery inlet 60 is fixed to the cooling plate 44 to deliver cooling liquid into one or more fluid channels within the cooling plate 44 ( Figure 1B not shown in Figure 2 ); and, the fluid outlet 62 is fixed to the cooling plate 44 to receive the cooling liquid after it has flowed through one or more fluid channels within the cooling plate 44. During operation of the LPP-EUV light source 10, the cooling liquid flows into the cooling liquid delivery inlet 60, flows through one or more fluid channels passing through the cooling plate 44, in which it absorbs heat emitted from the fixed position 36 where the EUV light-emitting plasma is generated, and then flows out of the fluid outlet 62. The cooling liquid can be a gaseous fluid, such as argon or another inert gas, nitrogen, etc.; or the cooling liquid can be a liquid fluid, such as water or liquid nitrogen. Figure 1BNot shown are fluid ports that extend through the vacuum chamber 12 from outside the vacuum chamber 12 and suitable inlet and outlet coolant lines that connect to deliver coolant liquid to the fluid inlet 60 and remove coolant liquid from the fluid outlet 62, respectively. The connections of the fluid lines to the coolant inlet 60 and the coolant outlet 62 (and to the fluid ports of the vacuum chamber 12) are suitably sealed connections such that coolant liquid does not leak into the vacuum chamber 12. The flow rate of the coolant liquid can be adjusted according to the heat generated at the fixed location 36 where the EUV light-emitting plasma is generated. The heat generated can be, for example, a function of the laser power of the laser 24 that applies the laser beam 26.

[0060] Figure 2 An isolated perspective view of the cooling plate 44 is shown, including the EUV opening 56 and the fluid inlet 60 and the fluid outlet 62. Figure 2 Also schematically shown is at least one fluid passage 66 through the cooling plate 44. The fluid passage 66 is in communication (i.e., fluidly connected) with the coolant inlet 60 and the fluid outlet 62 so that coolant can enter at least one fluid passage 66 through the inlet 60 and exit at least one fluid passage 66 through the outlet 62. The fluid passage 66 can be implemented in various ways, such as a pipe embedded in the cooling plate 44, or a passage drilled or otherwise formed in a bulk molybdenum, tungsten, or other material that constitutes the cooling plate 44. In another contemplated embodiment, the cooling plate 44 can be substantially hollow such that at least one fluid passage includes the hollow interior of the cooling plate.

[0061] As previously referenced Figure 1A As described, the trap assembly 40 is positioned near the fixed location 36 where the EUV light-emitting plasma is generated such that the liquid metal debris trap 42 can be suitably positioned to trap liquid metal debris emitted from the fixed location 36 due to laser interaction; and the cooling plate 44 is also sufficiently close to the fixed location 36 to absorb and transport heat away from the fixed location 36 of the EUV light-emitting plasma. Since the cooling plate 44 is fixed to the liquid metal debris trap 42, there can be efficient heat transfer from the liquid metal debris trap 42 to the cooling plate 44. Optionally, this heat transfer can be enhanced by including a heat-conducting material at the interface between the liquid metal debris trap 42 and the cooling plate 44.

[0062] In some embodiments, the trap assembly 40 is positioned such that the liquid metal debris trap 42 faces the fixed location 36 where the EUV-emitting plasma is generated, such that liquid metal debris emanating from the fixed location 36 strikes and adheres to the liquid metal debris trap 42. In this case, the cooling plate 44 operates at least in part based on heat transfer from the liquid metal debris trap 42 to the cooling plate 44. In other embodiments, the trap assembly 40 is positioned such that the cooling plate 44 faces the fixed location 36 where the EUV-emitting light plasma is generated. In this case, liquid metal debris emanating from the fixed location 36 strikes and adheres to the cooling plate 44, such that the cooling plate 44 effectively serves as part of the liquid metal debris trap 42.

[0063] In other embodiments, it is contemplated that the liquid metal debris trap 42 and the cooling plate 44 are configured as a single piece; that is, the cooling plate is integral with the liquid metal debris trap. For example, the liquid metal debris trap may include at least one fluid passage 66 therethrough.

[0064] Referring Figure 3 , a detached perspective view of a cooling plate 84 according to another embodiment is shown. The cooling plate 84 may replace Figures 1B to 1C and Figure 2 the cooling plate 44 of the trap assembly 40, and the cooling plate 84 is suitably fixed to the liquid metal debris trap 42. An exemplary cooling plate 84 is a metal plate having a generally arcuate shape similar to that of the Figures 1B to 1C and Figure 2 cooling plate 44 of the embodiment, and includes an EUV opening 56 that aligns with the EUV opening 52 of the liquid metal debris trap 42 when the cooling plate 84 is fixed to the liquid metal debris trap 42.

[0065] The cooling plate 84 has a cooling function similar to that of the Figures 1B to 1C and Figure 2 cooling plate 44 in the embodiment, but operates in a different manner. The cooling plate 84 does not include one or more internal fluid passages 66 (see Figure 2 ) connected to the fluid inlet 60 and the fluid outlet 62. Instead, as Figure 3 shown, during operation of the cooling plate 84, the coolant flows out of the nozzle 86 onto the surface 88 of the cooling plate 84. The surface 88 of the cooling plate 84 includes or has formed therein a plurality of alternating grooves 90 and a plurality of raised portions or ridges 92. As Figure 3 schematically indicated, the coolant flowing onto the surface 88 spreads out on the surface 88, and the plurality of alternating grooves 90 and the plurality of raised portions or ridges 92 enhance the heat dissipation efficiency of the coolant. In an exemplary embodiment, as Figure 3As shown, a plurality of grooves 90 and a plurality of ridges 92 are oriented along a portion of the annular inner surface 20 of the crucible 14 adjacent to the cooling plate 84. In this orientation, the coolant tends to flow through the grooves 90, thereby facilitating heat transfer along the cooling plate 84.

[0066] In the embodiment referred to Figure 3 above, the nozzle 86 directs a coolant flow onto the surface 88 of the cooling plate 84 that includes a plurality of grooves 90 and a plurality of ridges 92 that are alternately arranged. Different from the embodiments previously referred to Figures 1B to 1C and Figure 2 above, in the Figure 3 embodiment, the coolant thus flows into the vacuum chamber 12 (see Figure 1A ). This increases the pressure in the vacuum chamber 12. If the pressure in the vacuum chamber rises too high, there will be poor absorption of EUV light. Therefore, the flow rate of the coolant flowing out of the nozzle 86 is appropriately controlled to limit the pressure increase. In some non-limiting illustrative embodiments, the vacuum chamber 12 has a base pressure (in the absence of coolant flow from the nozzle 86) that is in the range of about 1*10 -4 Pa to 1*10 - 3 Pa, and with the flow of the coolant from the nozzle 86, the pressure in the vacuum chamber 12 rises to a pressure below 1 Pa. In some non-limiting illustrative examples, the flow rate of the coolant can be 2000 sccm (i.e., standard cubic centimeters per minute) or less. In the above embodiment, the coolant is preferably argon or another inert gas, although another type of coolant, such as nitrogen, is also contemplated.

[0067] The cooling plate 84 should be made of a material capable of withstanding the heat dissipated by the laser-generated plasma generated at the fixed position 36 and may include, for example, molybdenum, tungsten, or other metals or metal alloys having a suitably high melting point. The plurality of grooves 90 and the plurality of ridges 92 that are alternately arranged can be formed by chemical etching (e.g., lithographically controlled etching of the plurality of grooves 90) or computer numerical control (CNC) machining, etc. Without loss of generality, Figure 3The indicated groove 90 has a width a and a height c, and the ridge 92 has a width b and a height d. In some non-limiting illustrative embodiments, the groove / ridge width ratio a:b of the groove 90 to the ridge 92 is in the range of 10:1 to 1:1. In some non-limiting illustrative embodiments, the groove / ridge height ratio c:d of the groove 90 to the ridge 92 is in the range of 1:10 to 99:100. Values within these ranges are expected to provide sufficient depth and width for the groove 90 and the ridge 92 to provide the desired improvement in heat dissipation efficiency. If the cooling plate 84 is manufactured from an original sheet whose surface 88 was initially planar by cutting or etching the groove 90 in the original planar surface, the height d of the ridge 92 is the thickness of the original sheet, and the height c of the groove 90 is the depth to which the groove 90 was cut or etched into the original planar surface.

[0068] In the embodiments described so far, the cooling element includes the cooling plate 44 or the cooling plate 84, which in the illustrated embodiment is fixed to the liquid metal debris trap 42. More generally, the cooling plate may be fixed to another stationary component located adjacent to the fixed position 36 where the laser-generated plasma is generated. The coolant flows onto the cooling plate 84 or through the cooling plate 44.

[0069] Referring to Figure 4A 、 Figure 4B and Figure 4C in other embodiments, the cooling element includes a gasket 100 fixed to stationary components 102, 104 surrounding the rotatable crucible 14. Figure 4A A perspective view schematically shows Figure 1A a part of the LPP-EUV light source 10 of Figure 4A which shows the rotatable crucible 14 and depicts the incident laser light rays (such as a laser beam) 26 at the fixed position 36 on the liquid metal 22 incident on the inner surface of the crucible 14, and the part where the emitted EUV light 28 is collected. Figure 1A The LPP-EUV light source of Figure 4A may include other components depicted in Figure 4A but not shown in Figures 4A to 4C such as a vacuum chamber 12, a laser 24 (generating the laser beam 26 shown in Figures 4A to 4C ), EUV optical elements, and a liquid metal debris trap 42. In the embodiments of Figure 4ASchematically shown, the first annular ring 102 and the second annular ring 104 are fixed together by a gasket 100 interposed between the first and second annular rings. In some non-limiting exemplary embodiments, the annular rings 102 and 104 may comprise stainless steel, although other materials are also contemplated. Figure 4B A perspective view of the separate gasket 100 is shown. The gasket 100 includes features for operatively coupling with a coolant. These features include a plurality of alternating grooves 110 and a plurality of ridges 112 formed or provided on a surface 102' of the gasket 100. The coolant delivery nozzle 106 is arranged to deliver coolant to approximately the center of the vacuum chamber 12 (not shown in Figure 4A but see Figure 1A ), and then the coolant flows outwardly and across the surface of the gasket 100, the surface 102' of the gasket 100 including a plurality of alternating grooves 110 and a plurality of ridges 112. The coolant delivery nozzle 106 may be arranged, for example, at the distal end of a tube or conduit 108 that passes through a port of the vacuum chamber 12 and extends to approximately the center of the vacuum chamber 12.

[0070] Figure 4C An enlarged view of a portion of the gasket 100 is shown to better illustrate the plurality of alternating grooves 110 and a plurality of ridges 112 provided on the surface 102' of the gasket 100. In operation, the coolant flows outwardly from the Figure 4A nozzle 106 as shown. The plurality of grooves 110 advantageously provide a flow path or conduit that allows the coolant to pass through the interface between the rings 102 and 104. This helps to define a fluid flow that delivers the coolant to and across the rotating crucible 14, thereby providing cooling to the crucible 14. To facilitate a generally radially outward flow, as best seen in Figure 4C , the plurality of alternating grooves 110 and a plurality of ridges 112 are radially oriented such that the plurality of grooves 100 provide a radially oriented coolant flow conduit. Without loss of generality, in Figure 4CIn [the figure], the groove 110 is marked as having a width a and a height c, and the ridge 112 is marked as having a width b and a height d. In some non - limiting exemplary embodiments, the groove / ridge width ratio a:b of the groove 110 to the ridge 112 is in the range of 10:1 to 1:1. In some non - limiting exemplary embodiments, the groove / ridge height ratio c:d of the groove 110 to the ridge 112 is in the range of 1:10 to 99:100. Values within the expected range will provide sufficient width for the groove 110 to provide a desired channel for the outward flow of the coolant to improve the heat dissipation efficiency. The gasket 100 can also promote cooling through the heat conduction of the material of the gasket 100. For this purpose, the gasket 100 can include, for example, copper, carbon nanotubes (CNT), or another highly thermally conductive material. The plurality of alternately arranged grooves 110 and the plurality of ridges 112 can be formed by chemical etching (e.g., photolithographic pattern control to etch the grooves 110) or CNC machining, etc.

[0071] Similar to Figure 3 the embodiment of Figures 4A to 4C In the embodiment of [the figure], the nozzle 106 flows the coolant into the vacuum chamber 12. This can increase the pressure in the vacuum chamber 12. If the pressure in the vacuum chamber rises too high, poor absorption of EUV light may occur. Therefore, the flow rate of the coolant flowing out of the nozzle 106 is appropriately controlled to limit the pressure increase. In some non - limiting illustrative embodiments, the vacuum chamber 12 has a base pressure (in the absence of coolant flow from the nozzle 106) in the range of about 1*10 -4 Pa to 1*10 -3 Pa, and in the case of coolant flow from the nozzle 106, the pressure in the vacuum chamber 12 rises to a pressure below 1 Pa. In some non - limiting illustrative examples, the flow rate of the coolant can be 2000 sccm or lower. In the said embodiment, the coolant is preferably argon or another inert gas, although another type of coolant, such as nitrogen, is also considered.

[0072] In the schematic gasket 100, as Figure 4B shown, the plurality of alternately arranged grooves 110 and the plurality of ridges 112 extend to the entire 360° circumference of the annular gasket 100. This has certain advantages in providing a radially symmetric outward flow of the coolant output from the centrally - arranged nozzle 106 and also provides continuous cooling of the entire circumference of the rotating crucible 14. However, in some other embodiments, it is expected that the plurality of alternately arranged grooves 110 and the plurality of ridges 112 only extend to a part of the gasket circumference, particularly in the circumference part adjacent to the fixed position 36 where EUV light - emitting plasma is generated (therefore, there is the maximum laser - induced heating).

[0073] The embodiments described are representative embodiments. More generally, the method can be implemented as an LPP-EUV light source 10, which includes a vacuum chamber 12, a rotatable crucible 14 disposed in the vacuum chamber 12 and having an annular inner surface 20 for carrying liquid tin or other liquid metal 22; a laser 24 arranged to apply a laser beam 26 to the liquid metal 22 carried on the annular inner surface 20 of the rotatable crucible 14 to cause the liquid metal 22 to emit EUV light 26; and a stationary component (e.g., a liquid metal debris trap 42 or a closed annular ring 102 and annular ring 104 in a non-limiting illustrative embodiment), disposed in the vacuum chamber 12 and near the annular inner surface 20 of the rotatable crucible 14 (e.g., the liquid metal debris trap 42 is one embodiment) or surrounding the rotatable crucible (e.g., the annular ring 102 and annular ring 104 are one embodiment). To provide cooling, such an LPP-EUV light source 10 also includes a coolant delivery inlet or nozzle (e.g., inlet 60 or nozzle 86 or nozzle 106) and a cooling element (e.g., Figure 1B and Figure 2 cooling plate 44 of Figure 3 or Figures 4A to 4C gasket 100 of Figures 4A to 4C which is fixed to the stationary component and includes features for operably coupling with the coolant delivered by the coolant delivery inlet or nozzle (e.g., illustrative embodiments of such features include at least one fluid channel 66 passing through the cooling plate 44, or alternating multiple grooves 90 and multiple ridges 92 of the cooling plate 84, or

[0074] Some further embodiments are described below.

[0075] In a non-limiting illustrative embodiment, a laser-produced plasma (LPP)-extreme ultraviolet (EUV) light source includes: a vacuum chamber; a rotatable crucible disposed within the vacuum chamber and having an annular inner surface for holding a liquid metal; a laser arranged to apply laser light to the liquid metal held on the annular inner surface of the rotatable crucible to cause the liquid metal to emit extreme ultraviolet light; a stationary assembly disposed within the vacuum chamber and near or surrounding the annular inner surface of the rotatable crucible; a coolant delivery inlet or nozzle; and a cooling element fixed to the stationary assembly and including features for operably coupling with coolant delivered by the coolant delivery inlet or nozzle. In some embodiments, the stationary assembly includes a liquid metal debris trap located near the annular inner surface of the rotatable crucible and having at least one opening arranged to allow the laser light and EUV light to pass through the liquid metal debris trap, and the cooling element includes a cooling plate fixed to the liquid metal debris trap. In some embodiments, the cooling plate has at least one opening that is aligned with the at least one opening of the liquid metal debris trap to allow the laser light and EUV light to pass through the cooling plate. In some embodiments, the features for operably coupling with coolant include one or more fluid channels within the cooling plate, the coolant delivery inlet or nozzle includes an inlet fixed to the cooling plate to deliver coolant into the one or more fluid channels within the cooling plate, and the LPP-EUV light source further includes a fluid outlet fixed to the cooling plate to receive the coolant after it has passed through the one or more fluid channels within the cooling plate. In some embodiments, the features for operably coupling with coolant include a plurality of grooves and a plurality of ridges alternately disposed on the surface of the cooling plate, and the coolant delivery inlet or nozzle includes a nozzle arranged to deliver coolant to the surface of the cooling plate including the alternately disposed plurality of grooves and a plurality of ridges. In some embodiments, the grooves and ridges of the alternately disposed plurality of grooves and a plurality of ridges are oriented along a portion of the annular inner surface of the rotatable crucible adjacent to the cooling plate. In some embodiments, the ratio a:b is in the range of 10:1 to 1:1, where a is the width of the grooves in the alternately disposed plurality of grooves and a plurality of ridges and b is the width of the ridges in the alternately disposed plurality of grooves and a plurality of ridges. In some embodiments, the ratio c:d is in the range of 1:10 to 99:100, where c is the height of the grooves in the alternately disposed plurality of grooves and a plurality of ridges and d is the height of the ridges in the alternately disposed plurality of grooves and a plurality of ridges.In some embodiments, the stationary assembly includes a first annular ring and a second annular ring surrounding a rotatable crucible, the cooling element includes a gasket, and the features for operably coupling with a coolant include a plurality of grooves and a plurality of ridges alternately arranged on the surface of the gasket. The first annular ring and the second annular ring are fixed together by the gasket inserted between the first annular ring and the second annular ring, and the coolant delivery inlet or nozzle includes a nozzle arranged to deliver the coolant into the vacuum chamber and through the surface of the gasket, and the surface of the gasket includes a plurality of grooves and a plurality of ridges alternately arranged. In some embodiments, the ratio a:b is in the range of 10:1 to 1:1, where a is the width of the grooves among the plurality of grooves and the plurality of ridges alternately arranged, and b is the width of the ridges among the plurality of grooves and the plurality of ridges alternately arranged.

[0076] A method of generating extreme ultraviolet light, the method comprising: rotating a crucible disposed in a vacuum chamber and having an annular inner surface for carrying a liquid metal; generating a laser-generated plasma at a fixed position relative to the vacuum chamber by applying a laser beam to the liquid metal carried on the annular inner surface of the rotating crucible, wherein the laser-generated plasma emits extreme ultraviolet light; using a liquid metal debris trap disposed at the fixed position to trap liquid metal debris generated by generating the laser-generated plasma; and cooling the fixed position by flowing a coolant onto or through a cooling plate fixed to the liquid metal debris trap. In some embodiments, the cooling plate includes one or more fluid channels inside the cooling plate, and the cooling includes flowing the coolant through the one or more fluid channels inside the cooling plate. In some embodiments, the cooling plate includes a plurality of grooves and a plurality of ridges alternately arranged on the surface of the cooling plate, and the cooling includes flowing the coolant onto the surface of the cooling plate including the plurality of grooves and the plurality of ridges alternately arranged. In some embodiments, the grooves and ridges of the plurality of grooves and the plurality of ridges alternately arranged are oriented along a portion of the annular inner surface of the crucible adjacent to the cooling plate. In some embodiments, the ratio a:b is in the range of 10:1 to 1:1, where a is the width of the grooves among the plurality of grooves and the plurality of ridges alternately arranged, and b is the width of the ridges among the plurality of grooves and the plurality of ridges alternately arranged. In some embodiments, the ratio c:d is in the range of 1:10 to 99:100, where c is the height of the grooves among the plurality of grooves and the plurality of ridges alternately arranged, and d is the height of the ridges among the plurality of grooves and the plurality of ridges alternately arranged. In some embodiments, the liquid metal debris trap and the cooling plate include one or more aligned openings, and generating the laser-generated plasma includes applying the laser beam through the one or more aligned openings of the liquid metal debris trap and the cooling plate, and a portion of the emitted EUV light passes through the one or more aligned openings of the liquid metal debris trap and the cooling plate.

[0077] A method of generating extreme ultraviolet light, the method comprising: rotating a crucible disposed in a vacuum chamber and having an annular inner surface for carrying a liquid metal; generating a laser-produced plasma at a fixed position relative to the vacuum chamber by applying a laser beam to the liquid metal carried on the annular inner surface of the rotating crucible, wherein the laser-produced plasma emits extreme ultraviolet light; and cooling the rotating crucible by flowing a coolant into the vacuum chamber and through grooves of a plurality of grooves and a plurality of ridges alternately arranged, the plurality of grooves and the plurality of ridges alternately arranged being provided on a surface of a gasket interposed between a first annular ring and a second annular ring, the first annular ring and the second annular ring being fixed together and surrounding the rotating crucible. In some embodiments, the ratio a:b is in the range of 10:1 to 1:1, where a is the width of the grooves in the plurality of grooves and the plurality of ridges alternately arranged, and b is the width of the ridges in the plurality of grooves and the plurality of ridges alternately arranged. In some embodiments, the ratio c:d is in the range of 1:10 to 99:100, where c is the height of the grooves in the plurality of grooves and the plurality of ridges alternately arranged, and d is the height of the ridges in the plurality of grooves and the plurality of ridges alternately arranged.

[0078] The foregoing has outlined features of multiple embodiments so that those skilled in the art may better understand aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis to design or modify other processes and structures for achieving the same purposes and / or obtaining the same advantages as the embodiments introduced herein. Those skilled in the art should also realize that such equivalent structures do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and modifications without departing from the spirit and scope of the present disclosure.

Claims

1. A laser generated plasma extreme ultraviolet light source, characterized in that: include: Vacuum chamber; A rotatable crucible, disposed in the vacuum chamber and having an annular inner surface for carrying liquid metal; a laser arranged to apply laser light to the liquid metal carried on the annular inner surface of the rotatable crucible to cause the liquid metal to emit extreme ultraviolet light; a stationary assembly disposed within the vacuum chamber and located adjacent to the annular inner surface of the rotatable crucible or surrounding the rotatable crucible; A coolant delivery inlet or nozzle; as well as A cooling element is secured to the stationary component and includes features for operatively coupling with the coolant delivered by the coolant delivery inlet or nozzle.

2. The laser generated plasma extreme ultraviolet light source according to claim 1, characterized in that: The stationary assembly includes a liquid metal debris catcher located adjacent the annular inner surface of the rotatable crucible and having at least one opening arranged to allow the laser light and the extreme ultraviolet light to pass through the liquid metal debris catcher, and The cooling element includes a cooling plate fixed to the liquid metal chip catcher.

3. The laser generated plasma extreme ultraviolet light source according to claim 2, characterized in that: The cooling plate has at least one opening, and the at least one opening is aligned with the at least one opening of the liquid metal debris trap so that the laser light and the extreme ultraviolet light pass through the cooling plate.

4. The laser generated plasma extreme ultraviolet light source according to claim 2, characterized in that: The features for operably coupling with a cooling fluid include one or more fluid channels within the cooling plate, The coolant delivery inlet or nozzle comprises an inlet fixed to the cooling plate to deliver the coolant to the one or more fluid channels inside the cooling plate, and The laser generated plasma extreme ultraviolet light source further includes a fluid outlet fixed to the cooling plate to receive the cooling liquid after passing through the one or more fluid channels inside the cooling plate.

5. The laser generated plasma extreme ultraviolet light source according to claim 2, characterized in that: The features for operably coupling with a cooling liquid include a plurality of grooves and a plurality of ridges arranged alternately on a surface of the cooling plate, and The cooling liquid delivery inlet or nozzle comprises a nozzle arranged to deliver the cooling liquid onto the surface of the cooling plate comprising the plurality of grooves and the plurality of ridges arranged alternately.

6. The laser generated plasma extreme ultraviolet light source according to claim 5, characterized in that: The grooves and ridges of the alternating plurality of grooves and the plurality of ridges are oriented along a portion of the annular inner surface of the rotatable crucible adjacent the cooling plate.

7. The laser generated plasma extreme ultraviolet light source according to claim 5, characterized in that: The ratio a:b is in the range of 10:1 to 1:1, wherein a is the width of a groove among the plurality of grooves and the plurality of ridges arranged alternately, and b is the width of a ridge among the plurality of grooves and the plurality of ridges arranged alternately.

8. The laser generated plasma extreme ultraviolet light source according to claim 5, characterized in that: The ratio c:d is in the range of 1:10 to 99:100, wherein c is the height of the grooves in the alternating plurality of grooves and the plurality of ridges, and d is the height of the ridges in the alternating plurality of grooves and the plurality of ridges.

9. The laser generated plasma extreme ultraviolet light source according to claim 1, characterized in that: The stationary assembly includes a first annular ring and a second annular ring surrounding the rotatable crucible, The cooling element comprises a gasket, The features for operably coupling with a coolant include a plurality of grooves and a plurality of ridges arranged alternately on a surface of the gasket, The first annular ring and the second annular ring are fixed together by the spacer interposed between the first annular ring and the second annular ring, and The cooling liquid delivery inlet or nozzle comprises a nozzle arranged to deliver cooling liquid into the vacuum chamber and across the surface of the gasket, the surface of the gasket comprising the plurality of grooves and the plurality of ridges arranged alternately.

10. The laser generated plasma extreme ultraviolet light source according to claim 9, characterized in that: The ratio a:b is in the range of 10:1 to 1:1, wherein a is the width of a groove among the plurality of grooves and the plurality of ridges arranged alternately, and b is the width of a ridge among the plurality of grooves and the plurality of ridges arranged alternately.

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