Target material tank for extreme ultraviolet light source

Abstract

An apparatus for an extreme ultraviolet (EUV) light source includes a body. The body includes a first structure (246) including a first wall and a second structure (248) including a second wall permanently joined to the first wall. An interior (203) of the body is at least partially defined by the first wall and the second wall. The first wall includes a first metallic material, and the second wall includes a second metallic material having a different thermal conductivity than the first metallic material. The interior of the body is configured to be fluidly connected to a target supply system of the EUV light source.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS]

[0001] This application claims priority to U.S. application Ser. No. 62 / 949,144, filed December 17, 2019, and entitled TARGET MATERIAL TANK FOR EXTREME ULTRAVIOLET LIGHT SOURCE, and U.S. application Ser. No. 62 / 986,266, filed March 6, 2020, and entitled TARGET MATERIAL TANK FOR EXTREME ULTRAVIOLET LIGHT SOURCE, both of which are incorporated by reference in their entireties herein.

[0002] This disclosure relates to target material tanks for extreme ultraviolet (EUV) light sources. [Background technology]

[0003]

[0003] EUV light, for example, is electromagnetic radiation having a wavelength of 100 nanometers (nm) or less (sometimes called soft x-ray), and can be electromagnetic radiation including light with wavelengths of, for example, 20 nm or less, 5-20 nm, or 13-14 nm, and can be used in photolithography processes to create extremely small features in a substrate, for example a silicon wafer, by initiating polymerization in a resist layer.

[0004]

[0004] Methods for generating EUV light include, but are not limited to, the conversion of materials containing elements that have emission lines in the EUV range in the plasma state, such as xenon, lithium, or tin. In one such method, often called laser-produced plasma (LPP), the required plasma can be generated by irradiating a target material, which may take the form of, for example, a droplet, plate, tape, stream, or cluster of material, and which is an element that has emission lines in the EUV range in the plasma state, with an amplified light beam, which may be called a drive laser. For this process, the plasma is usually generated in a sealed container, such as a vacuum chamber, and monitored using various types of metrology instruments. Summary of the Invention

[0005] In one aspect, an apparatus for an extreme ultraviolet (EUV) light source includes a body. The body includes a first structure including a first wall and a second structure including a second wall permanently bonded to the first wall. An interior of the body is at least partially defined by the first wall and the second wall. The first wall includes a first metallic material and the second wall includes a second metallic material having a different thermal conductivity than the first metallic material. The interior of the body is configured to be fluidly connected to a target supply system of the EUV light source.

[0006]

[0006] Implementations may include one or more of the following features.

[0007]

[0007] The first end of the first wall and the second end of the second wall may be permanently joined at a braze interface.

[0008]

[0008] The first metallic material may include molybdenum (Mo) and the second metallic material may include stainless steel.

[0009]

[0009] The apparatus may further include a temperature control system configured to control a temperature of at least one of the first wall and the second wall. The temperature control system may include a heating system configured to be thermally coupled to the first wall and a cooling system configured to be thermally coupled to the second wall. The thermal conductivity of the second metallic material may be lower than the thermal conductivity of the first metallic material.

[0010]

[0010] The thermal conductivity of the second metallic material may be lower than the thermal conductivity of the first metallic material. The first wall may extend from a first end to a second end, and the second wall may extend from the first end to the second end. The first end of the first wall may be brazed to the second end of the second wall. The device may further include an O-ring at the first end of the second wall and a removable lid configured to be retained by the O-ring.

[0011]

[0011] The thermal conductivity of the second metallic material may be lower than the thermal conductivity of the first metallic material. The first wall may extend from a first end to a second end, and the second wall may extend from the first end to the second end. The first end of the first wall may be brazed to the second end of the second wall. The device may further include at least one port extending from the second wall. The at least one port may include the second metallic material. The second metallic material may include stainless steel.

[0012]

[0012] The first metallic material may have a first coefficient of thermal expansion and the second metallic material may have a second coefficient of thermal expansion.

[0013]

[0013] The outer side of the first wall may be permanently joined to the inner side of the second wall.

[0014]

[0014] The body may further include a third structure including a third wall. The third wall may include an interior surface and an exterior surface. The interior surface of the third wall may be permanently bonded to the exterior surface of the second wall. The third wall may include a second metallic material. The device may further include a temperature control system configured to control a temperature of at least one of the first wall, the second wall, and the third wall. The thermal conductivity of the second metallic material may be lower than the thermal conductivity of the first metallic material. The temperature control system may include a heating system configured to thermally couple to the first wall and a cooling system configured to thermally couple to the second wall and the third wall. The third wall may be between the second wall and the cooling system.

[0015]

[0015] The apparatus may be a target material tank configured to hold a target material within a body, the target material being capable of emitting EUV light when in a plasma state.

[0016]

[0016] The device may be a connection assembly. The first structure may include at least a first port, and the second structure may include at least a second port. The first port and the second port may be in fluid communication with each other. The device may be configured to provide a flow path between an external device coupled to the second port and a reservoir coupled to the first port.

[0017] In another aspect, an EUV light source includes a target supply system. The target supply system includes a droplet generator configured to generate a stream of targets, at least one apparatus with an interior region configured to fluidly couple to the droplet generator, and a container configured to receive the targets from the droplet generator. The targets include a target material that emits EUV light when in a plasma state. The apparatus includes a first structure including a first wall and a second structure including a second wall permanently bonded to the first wall. The interior region is at least partially defined by the first wall and the second wall. The first wall includes a first metallic material, and the second wall includes a second metallic material having a thermal conductivity different from the first metallic material.

[0018]

[0018] Implementations may include one or more of the following features.

[0019]

[0019] The EUV light source may further include a light source configured to generate a pulse of light, the pulse of light having sufficient energy to convert at least a portion of the target material within the target into a plasma state from which the target material emits EUV light.

[0020]

[0020] The at least one apparatus may be a target material tank configured to hold a target material within an interior region. The target supply system may further include at least one valve. The at least one valve may be configured to fluidly connect or fluidly isolate the interior region of the target material tank from the droplet generator.

[0021]

[0021] At least one of the devices may be a connection assembly. The first structure may include at least a first port, and the second structure may include at least a second port. The first port and the second port may be in fluid communication with each other. The target supply system may further include an external device coupled to the second port and a reservoir coupled to the first port. The reservoir may be configured to hold the target material in the internal cavity and may be fluidly coupled to the droplet generator. The connection assembly may be configured to provide a flow path between the external device and the reservoir. The external device may be a vacuum system or a gas supply system.

[0022] In another aspect, a target delivery system for an EUV light source includes a droplet generator configured to generate a stream of targets and at least one apparatus with an interior region configured to fluidly couple to the droplet generator. The target includes a target material that emits EUV light when in a plasma state. The apparatus includes a first structure including a first wall and a second structure including a second wall permanently bonded to the first wall. The interior region is at least partially defined by the first wall and the second wall. The first wall includes a first metallic material and the second wall includes a second metallic material having a different thermal conductivity than the first metallic material.

[0023]

[0023] Implementations may include one or more of the following features.

[0024]

[0024] The at least one apparatus may be a target material tank configured to hold target material within an interior region.

[0025]

[0025] The target delivery system may further include at least one valve configured to fluidly connect or fluidly isolate at least one interior region of the apparatus from the droplet generator.

[0026]

[0026] At least one of the devices may be a connection assembly. The first structure may include at least a first port and the second structure may include at least a second port. The first port and the second port may be in fluid communication with each other.

[0027]

[0027] Implementations of any of the above-described techniques may include an EUV light source, a system, a method, a process, a device, or an apparatus. Details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a block diagram of an extreme ultraviolet (EUV) light source. [Diagram 2]

[0029] FIG. 2 is a block diagram of a target material tank. [Diagram 3]

[0030] FIG. 2 is a block diagram of a metal connection assembly. [Figure 4]

[0031] FIG. 2 is a block diagram of a target delivery system. [Diagram 5]

[0032] FIG. 2 is a block diagram of another target delivery system. [Figure 6A]

[0033] FIG. 11 is a cross-sectional view of another target material tank in the XY plane. [Figure 6B]

[0034] FIG. 6B is a cross-sectional view of the target material tank of FIG. 6A in the XZ plane. [Figure 6C]

[0035] FIG. 6B is a perspective view of the target material tank of FIG. 6A. [Figure 7]

[0036] FIG. 2 is a block diagram of another EUV light source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029]

[0037] 1, a block diagram of an extreme ultraviolet (EUV) light source 100 is shown. The light source 100 includes a vessel 109 (e.g., a vacuum chamber or evacuated vessel), a light source 105 that generates a light beam 106, and a target supply system 140. The target supply system 140 includes a target material tank 144 having an interior region 103 configured to hold a target material. The target supply system 140 also includes a droplet generator 142 that receives target material from the interior 103 of the target material tank 144. The target supply system 140 also includes a pressure management system 130.

[0030]

[0038] The target material tank 144 is made of two or more metallic materials. In the example shown in FIG. 1, the target material tank 144 includes a first structure 146 and a second structure 148 permanently joined at an interface 150. The interface 150 can be, for example, a brazed interface. The first structure 146 and the second structure 148 are three-dimensional solid structures and are each made of a different metallic material. As described below, using two or more metallic materials to form the target material tank 144 can improve the safety and usability of the target material tank 144 and increase component options.

[0031]

[0039] In actual use, a droplet generator 142 delivers a stream 121 of targets to the interior 101 of the vessel 109. The droplet generator 142 includes a droplet delivery system, such as a nozzle, and may include one or more pressurized vessels containing liquid target material delivered from its target material tank 144. Interaction between the light beam 106 at the plasma generation site 123 and the target material in the target 121p (one of the targets in the stream 121) generates a plasma 196 that emits EUV light 197. The light beam 106 is generated by the light source 105 and delivered to the interior 101 through the light path 107. The plasma 196 generated by the interaction between the light beam 106 and the target material in the target 121p is provided to a lithography tool 199. The target 121p includes a target material, which is any material that has an emission line in the EUV range when in a plasma state. The target material may be, for example, tin, lithium, or xenon. Other materials may also be used as target materials. For example, elemental tin may be used as pure tin (Sn), tin compounds such as SnBr4, SnBr2, SnH4, tin alloys such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys.

[0032]

[0040] The interior 103 of the tank 144 is fluidly coupled to the droplet generator 142 by a fluid communication connection 155. The fluid communication connection 155 is any type of device, structure, or system that allows the target material to flow from the interior 103 of the tank 144 to the droplet generator 142. For example, the fluid communication connection 155 may be a tube or a pipe, or a combination of such elements. The fluid communication connection 155 may be made of any material capable of transporting the target material. The fluid communication connection 155 may include a regulating device, such as the regulating device 452a shown in FIG. 4. The regulating device may be configured to control the flow of the target material through the fluid communication connection 155, for example, by opening, closing, or partially blocking the fluid communication connection 155. In some embodiments, the regulating device may include a freeze valve. In other implementations, the target material tank 144 is directly adjacent to the droplet generator 142 to supply the target material to the droplet generator 142 without using the fluid communication connection 155.

[0033]

[0041] 2, there is shown a cross-sectional side view of a target material tank 244. The target material tank 244 is one implementation of the target material tank 144 (FIG. 1).

[0034]

[0042] The target material tank 244 includes a first structure 246 and a second structure 248. The first structure 246 and the second structure 248 are solid three-dimensional bodies that partially define an interior region 203 within the target material tank 244. The interior region 203 holds a target material mixture 220. The target material mixture 220 includes a target material that emits EUV light when in a plasma state and may also include various impurities.

[0035]

[0043] The first structure 246 is made of a first metallic material. The second structure 248 is made of a second metallic material. The first and second metallic materials are different metallic materials. The first and second metallic materials have different thermal conductivities. The thermal conductivity of the second metallic material may be lower than the thermal conductivity of the first metallic material. For example, the first metallic material may be molybdenum (Mo) having a thermal conductivity of 138 watts per meter per Kelvin at 20 degrees Celsius, and the second metallic material may be stainless steel having a thermal conductivity of 14.4 watts per meter per Kelvin at 20 degrees Celsius. As will be described below, this configuration allows the tank 244 to be operated safely and efficiently, and allows for greater flexibility in the configuration of the various components of the tank 244.

[0036]

[0044] Additionally, the first metallic material and the second metallic material may have different coefficients of thermal expansion. The coefficient of thermal expansion is a material property that defines the degree to which a material expands when heated or contracts when cooled. For example, the first metallic material has a coefficient of thermal expansion of 4.8×10 at 25 degrees Celsius. -6 The second metallic material may be molybdenum (Mo) having a thermal expansion coefficient of approximately 14.4×10 -6 The first wall 216 and the second wall 218 may be stainless steel having a second coefficient of thermal expansion of 100 Kelvin. Some sealing techniques are not robust enough to prevent or minimize relative movement between two joined metals having different coefficients of thermal expansion in the presence of temperature changes. On the other hand, the first wall 216 and the second wall 218 may be joined by brazing at the interface 250. The brazing creates a seal that is robust enough to minimize or prevent relative movement between two joined metals having different coefficients of thermal expansion in the presence of temperature changes. In particular, the brazing creates a seal that minimizes or prevents relative movement between the first wall 216 and the second wall 218 during temperature changes. This reduces wear at the interface 250 and improves the sealing properties of the interface 250.

[0037]

[0045] The first structure 246 includes a first wall 216 and a base portion 217. The first wall 216 extends in the Y direction from a second end 216b to a first end 216a joined to the base portion 217. The base portion 217 defines a port 233 made of a first metallic material. The port 233 fluidly couples the interior region 203 to a fluid communication connection, such as, for example, the target material tank connection 455 (FIG. 4) or the fluid communication connection 555 (FIG. 5). The port 233 allows fluid (e.g., target material) in the interior region 203 to flow from the target material tank 244 into the fluid communication connection.

[0038]

[0046] The first wall 216 and the base portion 217 are made of a first metal material. The second structure 248 includes a second wall 218. The second wall 218 is made of a second metal material. The second wall 218 extends in the Y direction from the second end 218b to the first end 218a. Each of the first wall 216 and the second wall 218 is a three-dimensional solid. The first wall 216 and the second wall 218 have approximately the same cross-sectional size shape in XZ (in the example of FIG. 2, the plane into and out of the page). For example, the first wall 216 and the second wall 218 may have a circular, square, or rectangular cross section in the XZ plane. The tank 244 may be, for example, a rectangular parallelepiped or a cylinder. In the example of FIG. 2, the first wall 216 and the second wall 218 have approximately the same diameter in the XZ plane, and the diameters of the walls 216 and 218 are substantially constant in the Y direction. Other implementations are possible. For example, the diameter of the wall 216 and / or the wall 218 in the XY plane may vary along the Y direction. Furthermore, in some implementations, the base portion 217 is not part of the first structure 246. In these implementations, the first structure 246 is open at the second end 216b. For example, the first structure 246 may have an approximately hemispherical shape.

[0039]

[0047] The second wall 218 is permanently joined to the first wall 216 at the interface 250. For example, the first wall 216 and the second wall 218 may be permanently joined by melting a filler metal material (wherein the filler metal material has a lower melting point than the first metal material and the second metal material) between the first wall 216 and the second wall 218 such that when the filler metal material cools and solidifies, the first wall 216 and the second wall 218 are permanently joined. This method of permanently joining the first metal material to the second metal material is called brazing. Brazing forms a robust seal that prevents moisture and oxygen from entering the interior region 203. In the example shown in FIG. 2, the first end 216a of the first wall 216 is brazed to the second end 218b of the second wall 218 at the interface 250. The interface 250 is a continuous bond such that the tank 244 is a single sealed body.

[0040]

[0048] In the example shown in FIG. 2, an O-ring 212 is positioned at the first end 218a of the second wall 218. The O-ring 212 is a continuous piece or ring of rubber or elastomer that runs around the inside circumference of the first end 218a of the second wall 218. The O-ring 212 is used to seal the top 215 against the second wall 218. The top 215 can be a removable lid (referred to as a removable lid 215) that is configured to be held by the O-ring 212. The O-ring is thermally compatible with a second metallic material that may not rise to the same high temperature as the first metallic material when there is molten target material in the interior 203 of the target material tank 244. The O-ring reduces leakage of the target material 220 when the removable lid is closed on the target material tank 244. The removable lid 215 allows for the placement of the target material within the interior region 203 of the target material tank 244. For example, target material may be placed in interior region 203 by opening removable lid 215, placing target material in target material tank 244, and then resealing removable lid 215 against O-ring 212. Removable lid 215 is made of a second metallic material.

[0041]

[0049] The target material tank 244 includes a temperature control system 231. The temperature control system 231 controls the temperature of the first wall 216 and / or the second wall 218. By controlling the temperature of the first wall 216 and / or the second wall 218, the temperature control system 231 also controls the temperature of the interior region 203.

[0042]

[0050] The temperature control system 231 includes a heating system 232 configured to be thermally coupled to the first wall 216. The heating system 232 may be multiple discrete heating elements positioned at various locations relative to the first wall 216 or may be a single heating element. The heating system 232 may be, but is not necessarily, thermally coupled to the first wall 216 by direct physical contact. By heating the first wall 216, the heating system 232 also heats the interior region 203 containing the target material 220. This allows the target material 220 to transition to or be maintained in a molten, fluid, or molten state in which the target material 220 can flow.

[0043]

[0051] The temperature control system 231 also includes a cooling system 234 configured to be thermally coupled to the second wall 218. The cooling system 234 may be a plurality of discrete cooling elements positioned at various locations relative to the second wall 218 or may be a single cooling element. For example, the cooling system 234 may include channels of fluid, such as water or air, within a tube. The cooling system 234 cools the second wall 218 and the removable lid 215. For example, the cooling system 234 may be cooled to a temperature that is safe to touch, such as approximately 40° C. to 50° C.

[0044]

[0052] The relatively low thermal conductivity of the second metallic material allows the wall 218 to be cooled to a temperature that is safe to touch. This allows an operator to safely manipulate the removable lid 215 to access the tank 214. For example, the target material 220 may be replenished or introduced by opening the lid 215 and placing a solid block of the target material in the interior 203. By cooling the removable lid 215 to a temperature that is safe to touch, an exchange procedure may be safely and efficiently performed without lowering the temperature of the first wall 216. Furthermore, the ability to lower the temperature of the second wall 218 (due to its relatively low thermal conductivity) allows more material to be used for the O-ring 212. Notably, because the second wall 218 and the removable lid 215 can be cooled to a temperature that is safe to touch, the O-ring 212 does not necessarily have to withstand high temperatures and may be made of a material that is relatively less thermally robust. Additionally, because the first structure 246 and the port 233 are made from a first metallic material, a connector, fastener, or other mating device that couples to the port 233 may also be made from the first metallic material.

[0045]

[0053] The target material tank 244 also includes a vacuum port 236 that is configured to connect to a vacuum system (not shown) so that the interior region 203 can be maintained at sub-atmospheric pressure or a particular pressure desired by the user.

[0046]

[0054] 3, there is shown a cross-sectional side view of metallic connection assembly 344. Metallic connection assembly 344 includes a first structure 346 permanently attached to a second structure 348 at interface 350. First structure 346 and second structure 348 are solid three-dimensional bodies that at least partially define interior region 303.

[0047]

[0055] The first structure 346 is made of a first metallic material. The second structure 348 is made of a second metallic material. The first metallic material and the second metallic material are different metallic materials. The first metallic material and the second metallic material have different thermal conductivities. The thermal conductivity of the second metallic material may be lower than the thermal conductivity of the first metallic material. Furthermore, the first metallic material and the second metallic material may have different thermal expansion coefficients. The first metallic material may be, for example, molybdenum, and the second metallic material may be, for example, stainless steel. As will be described below, this allows for greater flexibility in the configuration of the various components of the metallic connection assembly 344.

[0048]

[0056] The first structure 346 includes a first wall 316 that extends in the Y direction from a second end 316b to a first end 316a. The first structure 346 is open at the second end 316b. The open second end 316b is labeled 335 in FIG. 3 and is referred to as an opening 335. The opening 335 provides a fluid connection point for the metal connection assembly 344. In the example shown in FIG. 3, the first structure 346 is open at the second end 316b, although other implementations are possible. For example, the first structure 346 may include a base portion that defines a port, similar to the base portion 217 and port 233 of FIG. 2.

[0049]

[0057] The first wall 316 includes an outer side 316c that does not face the interior region 303. The second structure 348 includes a second wall 318. The second wall 318 extends from a second end 318b to a first end 318a. The second wall 318 includes an inner side 318c that faces the interior region 303. The first wall 316 and the second wall 318 are three-dimensional solids having approximately equal cross-sectional sizes and shapes in the XZ plane. For example, the first wall 316 and the second wall 318 may have a circular, square, or rectangular cross-section in a plane that enters or leaves the page. The first end 316a of the first wall 316 and the second end 318b of the second wall 318 are permanently joined at an interface 350. The interface 350 may be formed by brazing. In the example of FIG. 3, the outer side 316c of the first wall 316 at the first end 316a is brazed directly to the inner side 318c of the second wall 318 at the second end 318b to form an interface 350.

[0050]

[0058] The second structure 348 also includes a top 315. The top 315 and the second wall 318 define one or more ports 338. The top 315 also defines a gas or vacuum port 336. A fluid (such as a gas, liquid, or a flowable substance including gas and / or liquid) can flow through the interior region 303 of the metal connection assembly 344. For example, the fluid can flow from the port 336 to the opening 335 and / or from one or more of the ports 338 into the interior region 303 and through the opening 335. The port 336 can be connected to a vacuum system (not shown) configured to control the pressure of the interior region. The port 336 can also be connected to a gas supply system (not shown) that supplies gas to the interior region 303. In the illustrated example, the port 336 includes a gasket 339 that helps connect the portion 336 to an external device. The port 338 can be connected to an external device, such as, for example, a gas supply system or a vacuum system. A second end 316b of the first wall 316 may connect to a tank or reservoir, such as reservoir 547 (FIG. 5).

[0051]

[0059] This configuration of the metallic connection assembly 344 allows the port 388 and the port 336 to be made of the same or thermally similar material as that used on many external devices. Because the second structure 348, the port 336, and the port 338 are made of a second metallic material, the port 338 and / or the connector used to connect to the port 336 can also be made of the second metallic material. For example, the second metallic material can be stainless steel and the first metallic material can be molybdenum (Mo). Many external devices use stainless steel connectors. In this example, the port 338 and the port 336 are connected to an external device with a stainless steel connector at a stainless steel-stainless steel interface. In this example, a connection interface is created between two identical metals. This allows the entire assembly to be heated to a relatively high temperature (e.g., 300° C. or higher) without degrading the connector. Moreover, this is in contrast to some conventional systems in which the entire structure (including the port for connecting to an external device) is made of a metallic material (such as Mo) that has a relatively high thermal conductivity that exceeds that of the material of the connector (e.g., stainless steel) typically used to connect the external device to the port, which may lead to degradation of the connection because the connector of the external device and the port of the structure are made of different metals.

[0052]

[0060] Referring to FIG. 4, a target supply system 440 is shown. The target supply system 440 is an example of a system in which a multi-metallic or bi-metallic tank or device may be used. The target supply system 440 includes a priming tank 416, a target material tank 444, a reservoir 447, and a droplet generator 142 (FIG. 1). In some embodiments, there may be multiple reservoirs 447, and one or more reservoirs may be pressurized. The target material tank 444 is made of two or more different metal materials and may be, for example, tank 144 or 244. A fluid communication connection 455 fluidly connects the priming tank 416, the target material tank 444, the reservoir 447, and the droplet generator 142. The fluid communication connection 455 is one implementation of the fluid communication connection 155 (FIG. 1). In the example of FIG. 4, the tank 444 is a refill tank.

[0053]

[0061] The fluid communication connection 455 includes an adjusting device 452a between the tank 444 and the reservoir 447. The adjusting device 452a is configured to adjust, direct, or control the flow of the target material from the target material tank 444 to the reservoir 447. In some implementations, the fluid communication connection 455 also includes an adjusting device 452b between the priming tank 416 and the target material tank 444. In implementations including an adjusting device 452b, the adjusting device 452b is configured to adjust, direct, or control the flow of the target material from the priming tank 416 to the target material tank 444. Each adjusting device 452a, 452b can be, for example, a valve. When each adjusting device 452a, 452b is a valve, the valve can be a fluid valve, which can be, for example, a hydraulic valve, a pneumatic valve, a manually operated valve, a solenoid driven valve, or a motor driven valve. In some implementations, one or both of the adjusting devices 452a, 452b is or includes a freeze valve.

[0054]

[0062] The priming tank 416 supplies target material to the target material tank 444, which in turn supplies the reservoir 447. The reservoir 447 supplies the target material to the droplet generator 142. The target supply system 440 is configured to allow the droplet generator 142 to operate while the tank 444 is being refilled. For example, the tank 444 may be refilled while the regulating device 452 is in a state that prevents target material from flowing between the target material tank 444 and the reservoir 447. During this time, the priming tank 416 refills the target material tank 444 with target material or produces a fluid target material from a solid target material. However, the reservoir 447 continues to supply target material to the droplet generator 142. When the supply of target material in the reservoir 447 is low, the regulating device 452 changes state to allow target material to flow from the target material tank 444 to the reservoir 447. Target material flows into reservoir 447, thereby replenishing reservoir 447 while droplet generator 142 continues to produce stream 121 (FIG. 1).

[0055]

[0063] The target supply system 440 is an example of a system in which a tank (such as tank 144 or 244) made of two or more metal materials may be used. Other implementations are possible. For example, the target supply system 440 may include two or more separate reservoirs between the target material tank 444 and the droplet generator 142. The two or more reservoirs are fluidly connected to each other and to the droplet generator 142 and the target material tank 444 via fluid communication connections 455 and may include a conditioning device between each of these elements. Furthermore, a tank made of two or more metals may be used in an EUV light source in a manner other than the configuration shown in FIG. 4. For example, the tank may be directly connected to the droplet generator 142 such that a bimetallic or multimetallic tank serves as a reservoir.

[0056]

[0064] Referring to FIG. 5, a target supply system 540 is shown. The target supply system 540 is another example of a system that may use a multi-metallic or bi-metallic tank or device. The target supply system 540 includes a target material tank 244, a metal connection assembly 344, a reservoir 547, a fluid communication connection 555, and a droplet generator 142. The fluid communication connection 555 fluidly connects the target material tank 244, the reservoir 547, and the droplet generator 142. For example, the fluid communication connection 555 may be a tube or a pipe, or a combination of such elements. In the example of FIG. 5, the target material tank 244 functions as a refill tank. Specifically, the target material tank 244 is configured to refill the reservoir 547 with target material via the fluid communication connection 555 when the supply of target material in the reservoir 547 is low. The metal connection assembly 344 provides a gas connection to the reservoir 547.

[0057]

[0065] Regulating device 552a is coupled to a fluid communication connection 555 between tank 244 and reservoir 547. Regulating device 552b is coupled to a fluid communication connection 555 between reservoir 547 and droplet generator 142. Regulating devices 552a and 552b are configured to regulate, direct, or control the flow of target material from target material tank 244 to reservoir 547 and from reservoir 547 to droplet generator 142, respectively.

[0058]

[0066] Each of the regulating devices 552a, 552b can be, for example, a valve. When each of the regulating devices 552a, 552b is a valve, the valve can be a fluid valve, which can be, for example, a hydraulic valve, a pneumatic valve, a manually operated valve, a solenoid-driven valve, or a motor-driven valve. In some implementations, each of the regulating devices 552a, 552b is or includes a freeze valve.

[0059]

[0067] The fluid communication connection 555 and each of the regulating devices 552a and 552b may be made of a first metallic material such that the first structure 246 of the tank 244, the fluid communication connection 555, and each of the regulating devices 552a and 552b are made of a material that does not adversely affect the target material.

[0060]

[0068] The target material tank 244 holds the target material. The target material flows out of the target material tank 244 through the port 233 into the fluid communication connection 555 and into the reservoir 547. The reservoir 547 supplies the droplet generator 142 with the target material. The target supply system 540 allows the droplet generator 142 to operate while the tank 244 is being refilled. For example, the tank 244 may be refilled when the regulating device 552a is in a state that prevents target material from flowing between the target material tank 244 and the reservoir 547. During this time, the target material tank 244 is refilled with solid target material to generate a fluid target material from the solid target material. For example, the top 215 of the tank 244 may be a removable lid 215, as described above. In these implementations, the tank 244 is replenished with solid target material by opening the top 215, placing solid target material in the tank 244, and resealing the lid 215 to the tank 244. However, the reservoir 547 may still contain a sufficient supply of target material and continue to supply target material to the droplet generator 142. When the supply of target material in the reservoir 547 is low, the regulating device 552a changes state to allow target material to flow from the target material tank 244 to the reservoir 547. Target material flows into the reservoir 547, thereby replenishing the reservoir 547 while the droplet generator 142 continues to generate stream 121 (FIG. 1).

[0061]

[0069] The metallic connection assembly 344 supplies a fluid (e.g., a gas, a liquid, or a liquid containing a gas) to or removes a fluid from the reservoir 547. The first structure 346 of the metallic connection assembly 344 is attached to the reservoir 547 with the opening 335 in fluid communication with the interior of the reservoir 547. The port 338 is connected to an external device 551 using a connector 553 made of a second metallic material. Thus, the port 338 and the connector 553 are made of the same metallic material. The external device can be, for example, a vacuum system or a gas supply. The reservoir 547 can be made of a first metallic material such that the first structure 346 of the metallic connection assembly 344 and the reservoir 547 are made of the same material.

[0062]

[0070] The target supply system 540 is an example of a system in which a tank made of two or more metal materials may be used, including the tank 244 and the metal connection assembly 344. Other implementations are possible. For example, the target supply system 540 may include two or more separate reservoirs between the target material tank 244 and the droplet generator 142. The two or more reservoirs are fluidly connected to each other and to the droplet generator 142 and the target material tank 244 via fluid communication connections 555 and may include a conditioning device between each of these elements. Each of the two or more reservoirs may be connected to one or more of the metal connection assemblies 344 to provide one or more gas connections or vacuums to each of the two or more reservoirs. Additionally, a tank made of two or more metals may be used in an EUV light source in a manner other than the configuration shown in FIG. 5. For example, the tank may be directly connected to the droplet generator 142 such that a bimetallic or multimetallic tank serves as a reservoir.

[0063]

[0071] 6A-6C, another target material tank 644 is shown. FIG. 6A is a side cross-sectional view of the target material tank 644 in the XY plane. FIG. 6B is a cross-sectional view of the target material tank 644 in the XZ plane along line B-B' in FIG. 6A. FIG. 6C is a perspective view of the target material tank 644. The target material tank 644 is identical to the target material tank 244 (FIG. 2) except that it also includes a third wall 619. The third wall 619 provides an additional barrier between the interior region 203 and the cooling system 234, as described below. The presence of the third wall 619 reduces the temperature gradient across the second wall 218.

[0064]

[0072] The third wall 619 is a three-dimensional solid. Like the second wall 218, the third wall 619 is made of a second metal material. The third wall 619 extends in the Y direction from the second end 219b to the first end 219a. The third wall 619 includes an inner surface 619c and an outer surface 619d. In the example of FIGS. 6A-6C, the third wall 619 and the second wall 218 each have a circular cross-sectional shape in the XZ plane. Other implementations are possible. For example, the second wall 218 and the third wall 219 may have a square or rectangular cross-section in the XZ plane.

[0065]

[0073] The interior surface 619c of the third wall 619 may be permanently joined to the exterior surface 218c of the second wall 218. For example, portions of the interior surface 619c and the exterior surface 218c may be permanently joined by melting a filler metal material (wherein the filler metal material has a lower melting point than the second metal material) between the third wall 619 and the second wall 218 such that when the filler metal material cools and solidifies, the third wall 619 and the second wall 218 are permanently joined.

[0066]

[0074] The cooling system 234 is thermally coupled to the exterior surface 619d. Under some conditions, a relatively large temperature difference exists between the interior region 203 and the cooling system 234. This temperature gradient can cause compressive and tensile stresses on objects (such as the second wall 218) between the interior region 203 and the cooling system 234. This compressive and / or tensile stress can cause deformation of the objects. By placing the third wall 619 between the second wall 218 and the cooling system 234, the distance between the interior region 203 and the cooling system 234 is increased, reducing the temperature gradient. By reducing the temperature gradient, the compressive and tensile stresses on the second wall 218 are reduced, thus reducing the likelihood of material deformation in the second wall 218.

[0067]

[0075] 7, there is shown an implementation of an LPP EUV light source 700. The LPP EUV light source 700 is an implementation of the EUV light source 100 (FIG. 1). The EUV light source 700 includes a target supply system 727. The target supply system 727 may include a two-metal or multi-metal target material tank, such as the target material tanks 144 or 244.

[0068]

[0076] The LPP EUV light source 700 is formed in a plasma formation region 705 by irradiating a target mixture 714 with an amplified light beam 710 traveling along a beam path toward the target mixture 714. The target material in the target of the stream 121 discussed with respect to FIG. 1 may be or may include the target mixture 714. The plasma formation region 705 resides in an interior 707 of a vacuum chamber 730. When the amplified light beam 710 strikes the target mixture 714, the target material in the target mixture 714 is converted to a plasma state having elements with emission lines in the EUV range. The resulting plasma has certain characteristics depending on the composition of the target material in the target mixture 714. These characteristics may include the wavelength of the EUV light produced by the plasma, as well as the type and amount of debris emanating from the plasma.

[0069]

[0077] The light source 700 includes a drive laser system 715 that generates an amplified light beam 710 by population inversion in one or more gain media of the laser system 715. The light source 700 includes a beam delivery system between the laser system 715 and a plasma formation region 705, the beam delivery system including a beam delivery system 720 and a focusing assembly 722. The beam delivery system 720 receives the amplified light beam 710 from the laser system 715, steers and modifies the amplified light beam 710 as needed, and outputs the amplified light beam 710 to the focusing assembly 722. The focusing assembly 722 receives the amplified light beam 710 and focuses the beam 710 onto the plasma formation region 705.

[0070]

[0078] In some implementations, the laser system 715 may include one or more optical amplifiers, lasers, and / or lamps to provide one or more main pulses and possibly one or more pre-pulses. Each optical amplifier includes a gain medium, a pump source, and internal optics capable of optically amplifying a desired wavelength with high gain. The optical amplifiers may or may not have laser mirrors or other feedback devices that form a laser cavity. Thus, the laser system 715 generates the amplified light beam 710 by population inversion in the gain medium of the laser amplifier even in the absence of a laser cavity. Furthermore, the laser system 715 may generate the amplified light beam 710 that is a coherent laser beam if there is a laser cavity that provides sufficient feedback to the laser system 715. The term "amplified light beam" encompasses one or more of light from the laser system 715 that is merely amplified but not necessarily coherent lasing and light from the laser system 715 that is both amplified and coherent lasing.

[0071]

[0079] The optical amplifiers in the laser system 715 may include a gas fill including CO2 as a gain medium and may amplify light at wavelengths from about 9100 nm to about 11000 nm, particularly about 10600 nm, with a gain of 900 times or more. Amplifiers and lasers suitable for use in the laser system 715 may include pulsed laser devices, such as pulsed gas discharge CO2 laser devices operating at relatively high powers, e.g., 10 kW or more, and at high pulse repetition rates, e.g., 40 kHz or more, producing radiation at about 9300 nm or about 10600 nm, e.g., by DC or RF excitation. The pulse repetition rate may be, for example, 50 kHz. The optical amplifiers in the laser system 715 may also include a cooling system, such as water, that may be used when operating the laser system 715 at higher powers.

[0072]

[0080] The light source 700 includes a collector mirror 735 having an aperture 740 that passes the amplified light beam 710 to reach the plasma formation region 705. The collector mirror 735 may be, for example, an elliptical mirror having a first focal point at the plasma formation region 705 and a second focal point at an intermediate location 745 (also referred to as an intermediate focal point) where the EUV light may be output from the light source 700 and input, for example, to an integrated circuit lithography tool (not shown). The light source 700 may also include an open-ended hollow conical shroud 750 (e.g., a gas cone) that tapers from the collector mirror 735 toward the plasma formation region 705, allowing the amplified light beam 710 to reach the plasma formation region 705 while reducing the amount of plasma-generated debris that enters the focus assembly 722 and / or the beam delivery system 720. To this end, a gas flow may be provided within the shroud that is directed toward the plasma formation region 705.

[0073]

[0081] The light source 700 may also include a master controller 755 connected to a droplet position detection feedback system 756, a laser control system 757, and a beam control system 758. The light source 700 may include one or more targets or droplet imagers 760 that provide an output indicative of the position of the droplet, e.g., relative to the plasma formation region 705, and provide this output to the droplet position detection feedback system 756, which may, e.g., calculate the position and trajectory of the droplet and therefrom calculate a droplet-by-droplet or average droplet position error. Thus, the droplet position detection feedback system 756 provides the droplet position error as an input to the master controller 755. The master controller 755 may thus provide laser position, direction, and timing correction signals to the laser control system 757, which may be used, e.g., to control the laser timing circuitry, and / or the beam control system 758, which controls the position and shape of the amplified light beam of the beam delivery system 720 to alter the position and / or focusing power of the beam focal spot within the chamber 730.

[0074]

[0082] The supply system 725 includes a target material delivery control system 726 that is operable in response to signals from the master controller 755 to, for example, modify the release point of droplets emitted by the target supply system 727 to correct for errors in the droplets reaching the desired plasma formation region 705.

[0075]

[0083] Additionally, light source 700 may include source detectors 765 and 770 that measure one or more EUV light parameters, including, but not limited to, pulse energy, energy distribution as a function of wavelength, energy within a particular wavelength band, energy outside a particular wavelength band, and angular distribution of EUV intensity and / or average power. Source detector 765 generates a feedback signal that is used by master controller 755. The feedback signal may indicate errors in parameters such as, for example, the timing and focus of the laser pulse to properly intersect the droplet at the correct place and time for effective and efficient EUV light generation.

[0076]

[0084] The light source 700 may also include a guide laser 775 that may be used to align various sections of the light source 700 or to help steer the amplified light beam 710 to the plasma formation region 705. In association with the guide laser 775, the light source 700 includes a metrology system 724 disposed within the focusing assembly 722 to sample a portion of light from the guide laser 775 and the amplified light beam 710. In other implementations, the metrology system 724 is disposed within the beam delivery system 720. The metrology system 724 may include optical elements that sample or redirect a subset of the light, the optical elements being made from any material that can withstand the power of the guide laser beam and the amplified light beam 710. The master controller 755 analyzes the light from the sampled guide laser 775 and uses this information to adjust components within the focusing assembly 722 through the beam control system 758, thus forming a beam analysis system from the metrology system 724 and the master controller 755.

[0077]

[0085] Thus, in summary, the light source 700 generates an amplified light beam 710 that is directed along a beam path and irradiates a target mixture 714 at a plasma formation region 705, converting the target material in the mixture 714 into a plasma that emits light in the EUV range. The amplified light beam 710 operates at a specific wavelength (also referred to as a drive laser wavelength) that is determined based on the design and characteristics of the laser system 715. Furthermore, the amplified light beam 710 can be a laser beam when the target material provides sufficient feedback back into the laser system 715 to generate coherent laser light or if the drive laser system 715 includes suitable optical feedback to form a laser cavity.

[0078]

[0086] Implementations of the present disclosure may be further described using the following clauses. 1. An apparatus for an extreme ultraviolet (EUV) light source, comprising: The apparatus includes a main body, the main body including: a first structure having a first wall; a second structure comprising a second wall permanently joined to the first wall; an interior of the body is at least partially defined by a first wall and a second wall, the first wall including a first metallic material and the second wall including a second metallic material having a different thermal conductivity than the first metallic material; The apparatus, wherein the interior of the body is configured to be fluidly connected to a target delivery system of an EUV light source. 2. The apparatus of claim 1, wherein the first end of the first wall and the second end of the second wall are permanently joined at a brazed interface. 3. The apparatus of claim 1, wherein the first metallic material comprises molybdenum (Mo) and the second metallic material comprises stainless steel. 4. The apparatus described in clause 1, further comprising a temperature control system configured to control a temperature of at least one of the first wall and the second wall. 5.Temperature control system a heating system configured to be thermally coupled to the first wall; a cooling system configured to be thermally coupled to the second wall; 5. The apparatus of claim 4, wherein the thermal conductivity of the second metallic material is lower than the thermal conductivity of the first metallic material. 6. A thermal conductivity of the second metallic material is lower than the thermal conductivity of the first metallic material, a first wall extends from a first end to a second end, a second wall extends from the first end to a second end, the first end of the first wall is brazed to the second end of the second wall, and the device comprises: an O-ring at the first end of the second wall; a removable lid configured to be retained by an O-ring; 2. The apparatus of claim 1, further comprising: 7. A thermal conductivity of the second metallic material is lower than the thermal conductivity of the first metallic material, a first wall extends from a first end to a second end, a second wall extends from the first end to a second end, the first end of the first wall is brazed to the second end of the second wall, and the device comprises: at least one port extending from the second wall, the at least one port comprising a second metallic material; 2. The apparatus of claim 1, further comprising: 8. The apparatus of claim 7, wherein the second metallic material comprises stainless steel. 9. The apparatus of claim 1, wherein the first metallic material has a first coefficient of thermal expansion and the second metallic material has a second coefficient of thermal expansion. 10. The apparatus of claim 1, wherein the exterior of the first wall is permanently joined to the interior of the second wall. 11. The main body is A third structure comprising a third wall, the third wall comprising an interior surface and an exterior surface. 2. The apparatus of claim 1, further comprising: an inner surface of the third wall permanently joined to an outer surface of the second wall, the third wall comprising a second metallic material. 12. The apparatus of claim 11, further comprising a temperature control system configured to control a temperature of at least one of the first wall, the second wall, and the third wall, wherein the thermal conductivity of the second metal material is lower than the thermal conductivity of the first metal material. 13.Temperature control system: a heating system configured to be thermally coupled to the first wall; a cooling system configured to be thermally coupled to the second wall and the third wall; 13. The apparatus of claim 12, wherein a third wall is between the second wall and the cooling system. 14. The apparatus of clause 1, wherein the apparatus is a target material tank configured to hold a target material within the body, the target material emitting EUV light when in a plasma state. 15. The device described in clause 1, wherein the device is a connection assembly, the first structure having at least a first port and the second structure having at least a second port, the first port and the second port being fluidly connected to each other. 16. The apparatus of clause 15, wherein the apparatus is configured to provide a fluid path between an external device coupled to the second port and a reservoir coupled to the first port. 17. An extreme ultraviolet (EUV) light source, comprising: A target supply system, a droplet generator configured to generate a stream of targets, the targets including a target material that emits EUV light when in a plasma state; at least one device comprising an interior region configured to fluidly couple to a droplet generator; The apparatus comprises: a first structure having a first wall; a second structure comprising a second wall permanently joined to the first wall; the interior region is at least partially defined by a first wall and a second wall, the first wall including a first metallic material and the second wall including a second metallic material having a different thermal conductivity than the first metallic material; The EUV light source includes a container configured to receive the target from the droplet generator. 18. The EUV light source of clause 17, further comprising a light source configured to generate pulses of light, the pulses of light having sufficient energy to convert at least a portion of a target material in the target to a plasma state from which the target material emits EUV light. 19. The EUV light source of clause 17, wherein the at least one apparatus is a target material tank configured to hold a target material within an interior region. 20. The EUV light source of claim 19, wherein the target supply system further comprises at least one valve, the at least one valve configured to fluidly connect or fluidly isolate an interior region of the target material tank from the droplet generator. 21. The EUV light source described in clause 17, wherein at least one apparatus is a connection assembly, the first structure having at least a first port, the second structure having at least a second port, and the first port and the second port are in fluid communication with each other. 22. The target supply system is an external device coupled to the second port; a reservoir coupled to the first port; the reservoir is configured to hold a target material within the internal cavity and to be fluidly coupled to the droplet generator; 22. The EUV light source of claim 21, wherein the connection assembly is configured to provide a fluid path between the external device and the reservoir. 23. The EUV light source according to clause 22, wherein the external device is a vacuum system or a gas supply system. 24. A target delivery system for an EUV light source, comprising: a droplet generator configured to generate a stream of targets, the targets including a target material that emits EUV light when in a plasma state; at least one device comprising an interior region configured to fluidly couple to a droplet generator; The apparatus comprises: a first structure having a first wall; a second structure comprising a second wall permanently joined to the first wall; 11. A target delivery system comprising: an interior region at least partially defined by a first wall and a second wall, the first wall including a first metallic material and the second wall including a second metallic material having a different thermal conductivity than the first metallic material. 25. The target supply system of claim 24, wherein at least one apparatus is a target material tank configured to hold target material within an interior region. 26. The target delivery system of clause 24, further comprising at least one valve, the at least one valve configured to fluidly connect or fluidly isolate at least one interior region of the apparatus from the droplet generator. 27. A target delivery system as described in clause 24, wherein at least one device is a connection assembly, the first structure having at least a first port, and the second structure having at least a second port, the first port and the second port being in fluid communication with each other.

[0079]

[0087] Other implementations are within the scope of the claims.

Claims

1. 1. An apparatus for an extreme ultraviolet (EUV) light source, comprising: a body, the body comprising: a first structure comprising a first wall; a second structure comprising a second wall permanently joined to the first wall; an interior of the body is at least partially defined by the first wall and the second wall, the first wall comprising a first metallic material and the second wall comprising a second metallic material having a different thermal conductivity than the first metallic material; the interior of the body is configured to hold a target material and to be fluidly connected to a target supply system of the EUV light source; the first wall of the first structure and the second wall of the second structure constitute side walls surrounding an interior of the body. Device.

2. The apparatus of claim 1 , wherein the first end of the first wall and the second end of the second wall are permanently joined at a braze interface.

3. The apparatus of claim 1 , further comprising a temperature control system configured to control a temperature of at least one of the first wall and the second wall.

4. The temperature control system includes: a heating system configured to be thermally coupled to the first wall; a cooling system configured to be thermally coupled to the second wall; 4. The apparatus of claim 3, wherein the thermal conductivity of the second metallic material is lower than the thermal conductivity of the first metallic material.

5. a thermal conductivity of the second metallic material is lower than a thermal conductivity of the first metallic material, the first wall extends from a first end to a second end, the second wall extends from a first end to a second end, the first end of the first wall is brazed to the second end of the second wall, and the apparatus comprises: an O-ring at the first end of the second wall; a removable lid configured to be retained by the O-ring; The apparatus of claim 1 further comprising:

6. The apparatus of claim 1 , wherein an exterior of the first wall is permanently joined to an interior of the second wall.

7. The body includes: A third structure comprising a third wall, the third wall comprising an interior surface and an exterior surface.

2. The apparatus of claim 1, further comprising: the interior surface of the third wall permanently joined to an exterior surface of the second wall, the third wall comprising the second metallic material.

8. 8. The apparatus of claim 7, further comprising a temperature control system configured to control a temperature of at least one of the first wall, the second wall, and the third wall, wherein a thermal conductivity of the second metallic material is lower than a thermal conductivity of the first metallic material.

9. 10. The apparatus of claim 1, wherein the apparatus is a target material tank configured to hold a target material within the interior of the body, the target material emitting EUV light when in a plasma state.

10. 10. The device of claim 1, wherein the device is a connection assembly, the first structure comprising at least a first port, the second structure comprising at least a second port, and the first port and the second port are in fluid communication with each other.

11. An apparatus for an extreme ultraviolet (EUV) light source, comprising: a body, the body comprising: a first structure comprising a first wall; a second structure comprising a second wall permanently joined to the first wall; an interior of the body is at least partially defined by the first wall and the second wall, the first wall comprising a first metallic material and the second wall comprising a second metallic material having a different thermal conductivity than the first metallic material; the interior of the body is configured to hold a target material and to be fluidly connected to a target supply system of the EUV light source; the first wall of the first structure and the second wall of the second structure form side walls enclosing an interior of the body, a first end of the first wall and a second end of the second wall being permanently joined at a braze interface, and further comprising a temperature control system configured to control a temperature of at least one of the first wall and the second wall. Device.

12. 1. An extreme ultraviolet (EUV) light source, comprising: a target supply system, the target supply system comprising: a droplet generator configured to generate a stream of targets, the targets including a target material that emits EUV light when in a plasma state; at least one device comprising an interior region configured to hold the target material and to be fluidly coupled to the droplet generator; The apparatus comprises: a first structure comprising a first wall; a second structure comprising a second wall permanently joined to the first wall; the interior region is at least partially defined by the first wall and the second wall, the first wall comprising a first metallic material and the second wall comprising a second metallic material having a different thermal conductivity than the first metallic material, and the first wall of the first structure and the second wall of the second structure constitute side walls enclosing the interior region. The EUV light source comprises a container configured to receive the target from the droplet generator.

13. 13. The EUV light source of claim 12, wherein the at least one apparatus is a connection assembly, the first structure comprising at least a first port, the second structure comprising at least a second port, and the first port and the second port being in fluid communication with each other.

14. The target supply system includes: an external device coupled to the second port; a reservoir coupled to the first port; the reservoir is configured to hold the target material within an internal cavity and to be fluidly coupled to the droplet generator; The EUV light source of claim 13 , wherein the connection assembly is configured to provide a flow path between the external device and the reservoir.

15. 1. A target delivery system for an EUV light source, comprising: a droplet generator configured to generate a stream of targets, the targets including a target material that emits EUV light when in a plasma state; at least one device comprising an interior region configured to hold the target material and to be fluidly coupled to the droplet generator; The apparatus comprises: a first structure comprising a first wall; a second structure comprising a second wall permanently joined to the first wall; the interior region is at least partially defined by the first wall and the second wall, the first wall comprising a first metallic material and the second wall comprising a second metallic material having a different thermal conductivity than the first metallic material, and the first wall of the first structure and the second wall of the second structure constitute sidewalls enclosing the interior region.

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