Catalytic conversion of gaseous media in optical amplifiers

Abstract

Embodiments of this disclosure relate to the catalytic conversion of a gas medium in an optical amplifier. An extreme ultraviolet (EUV) light system includes an optical amplifier system and an optical conversion system. Each optical amplifier in the optical amplifier system includes a gain medium in the form of a gas mixture that generates an amplified light beam. The optical amplifier system includes a fluid inlet and a fluid outlet through which the gas mixture can flow. The catalytic conversion system is fluidly connected to the fluid outlet of the optical amplifier system and to the fluid inlet of the optical amplifier system. The catalytic conversion system includes a catalytic converter comprising: a housing; a substrate having openings within the housing through which the gas mixture can flow; and a catalyst, applied as a coating to the inner surface of the openings of the substrate, the catalyst comprising particles of a metal. The metal particles may be nanoparticles of a noble metal.

Description

[0001] This application is a divisional application of Chinese invention patent application filed on January 19, 2015, with application number 201580006382.1 and invention title "Catalytic Conversion of Gas Medium for Optical Amplifier".

[0002] Cross-references to related applications

[0003] This application claims the rights of U.S. Provisional Application No. 61 / 934,143, filed January 31, 2014, and U.S. Application No. 14 / 593,278, filed January 9, 2015, which are incorporated herein by reference in their entirety. Technical Field

[0004] The disclosed subject matter relates to a system and method for the catalytic conversion of a gas mixture of gain medium in a driving laser system for generating an amplified beam of an extreme ultraviolet (EUV) laser system. Background Technology

[0005] Extreme ultraviolet (EUV) light, such as electromagnetic radiation with wavelengths of about 50 nm or smaller (sometimes also called soft X-rays) and including wavelengths of about 13 nm, can be used in photolithography processes to create extremely fine features in substrates such as silicon wafers.

[0006] Methods for generating EUV light include, but are not limited to, converting materials containing elements such as xenon, lithium, or tin into a plasma state having an emission line in the EUV range. In one such method, a desired plasma, commonly referred to as laser-induced plasma (“LPP”), can be generated by irradiating a target material, such as droplets, streams, or bundles of material, with an amplified beam, which may be called a driving laser. For this process, the plasma is typically generated in a sealed container (e.g., a vacuum chamber) and monitored using various types of measuring devices.

[0007] CO2 amplifiers and lasers that output a magnified beam at a wavelength of approximately 10600 nm can exhibit certain advantages when driving the laser to irradiate target materials in LPP processes. This is particularly true for certain target materials, such as those containing tin. One advantage, for example, is the ability to achieve a relatively high conversion efficiency between the driving laser input power and the output EUV power. Another advantage of CO2-driven amplifiers and lasers is the ability to reflect relatively long wavelengths of light (e.g., compared to deep UV at 198 nm) from relatively rough surfaces such as reflective optics already coated with tin fragments. This property of 10600 nm radiation can allow the use of reflective mirrors near the plasma, for example, to guide, focus, and / or adjust the optical power of the magnified beam. Summary of the Invention

[0008] In some general aspects, the extreme ultraviolet (EUV) light system includes an optical amplifier system and a catalytic conversion system. The optical amplifier system includes one or more optical amplifiers. Each optical amplifier includes a gain medium that, when energized from an energy source to pump the gain medium, produces an amplified light beam in the form of a gas mixture. The optical amplifier system includes a fluid input through which the gas mixture flows and a fluid output therethrough. The catalytic conversion system is fluidly connected to the fluid output and fluid input of the optical amplifier system. The catalytic conversion system includes a catalytic converter comprising a housing; a substrate within the housing including openings through which the gas mixture can flow; and a catalyst, as a coating applied to the inner surface of the openings of the substrate, the catalyst comprising metallic nanoparticles.

[0009] The implementation may include one or more of the following features. For example, the openings in the substrate may have a honeycomb geometry. The metal may be a precious metal.

[0010] The system may include a heat exchanger separate from the catalyst converter, the heat exchanger comprising pipes through which a gas mixture flows, the pipes being cooled by an external heat sink. The pipes of the heat exchanger may be coated on their inner surfaces with a catalyst that promotes the oxidation of dissociated molecules within the gas mixture.

[0011] The system may include a target material delivery system configured to generate target material at a target location, wherein an amplified beam is guided toward the target location to achieve an interaction between the amplified beam and the target material, thereby generating plasma that emits extreme ultraviolet (EUV) light.

[0012] The catalyst may include gold nanoparticles. The substrate may be made of ceramic material.

[0013] The catalytic conversion system can be connected in parallel with the fluid lines formed by the fluid input and fluid output of the optical amplifier system.

[0014] The catalytic conversion system can be connected in series with a fluid line formed by the fluid input and fluid output of the optical amplifier system.

[0015] In some other general aspects, a method for generating extreme ultraviolet light includes providing pump energy to a gain medium of at least one optical amplifier in an optical amplifier system to generate an amplified beam, the gain medium being in the form of a gas mixture comprising molecules, at least some of which dissociate during the generation of the amplified beam within a conduit; guiding the gas mixture from the conduit through a substrate fixed within a housing and coated with a catalyst using metal nanoparticles to thereby oxidize the dissociated molecules of the gas mixture; guiding the oxidized gas mixture back to the conduit; generating target material at a target location; and focusing the amplified beam to a focal location realizing an optical interaction between the amplified beam and the target material, such that the target material is converted into plasma emitting extreme ultraviolet light.

[0016] Implementations may include the following features. For example, a method may include guiding a gas mixture from a pipe through a temperature-controlled pipe to remove heat from the gas mixture before guiding the oxidized gas mixture back to the pipe.

[0017] The method may include using a catalyst coated on the inner surface of the pipe to at least partially oxidize the dissociated molecules of the gas mixture.

[0018] The method may include adjusting the temperature of the gas mixture exiting from the pipeline. The temperature of the gas mixture can be adjusted by maintaining the temperature of the gas mixture above the temperature of the gas mixture exiting from the pipeline.

[0019] In several other general aspects, the catalytic conversion system is part of the optical amplifier system of the extreme ultraviolet (EUV) light system. The catalytic conversion system includes an input, fluidly connected to the optical amplifier system to receive a gas mixture comprising dissociated molecules of a gain medium; and an output, fluidly connected to the optical amplifier system; a housing between the input and the output; a substrate within the housing, including openings through which the gas mixture can flow; and a catalyst, applied as a coating to the inner surface of the openings on the substrate, the catalyst comprising metallic nanoparticles.

[0020] The implementation may include one or more of the following features. For example, the openings in the substrate may be hexagonal. The housing may be fluidly connected to the inputs and outputs. The metal may be a precious metal.

[0021] In several other general aspects, the catalytic conversion system is part of the gas discharge optical amplifier system of the extreme ultraviolet (EUV) light system. The catalytic conversion system may include a thermal conditioning system that increases the temperature of a gas mixture output from the optical amplifier system, the gas mixture comprising dissociated molecules of a gain medium excited to generate an amplified light beam from the optical amplifier system, and a catalytic converter receiving the gas mixture at the increased temperature output from the thermal conditioning system. The catalytic converter includes a substrate within a housing and includes openings through which the gas mixture can flow; and a catalyst applied as a coating to the inner surface of the openings in the substrate. The catalyst comprises metal particles that accelerate the oxidation of dissociated molecules within the gas mixture.

[0022] The implementation may include one or more of the following features. For example, the openings in the substrate may be hexagonal. The metal particles may be nanoparticles of noble metals.

[0023] In other general aspects, the catalytic conversion system is part of a gas discharge optical amplifier system for extreme ultraviolet (EUV) light systems. The catalytic conversion system includes a catalytic converter that receives a gas mixture output from the optical amplifier system, the gas mixture comprising dissociated molecules of a gain medium excited to generate an amplified light beam from the optical amplifier system, and a heat exchanger separate from the catalytic converter. The catalytic converter includes a substrate within a housing and comprising an opening through which the gas mixture can flow; and a catalyst, comprising metal particles that accelerate the oxidation of dissociated molecules within the gas mixture, applied as a coating to the inner surface of the substrate opening. The heat exchanger includes a conduit through which the gas mixture flows, the conduit being cooled by an external heat sink.

[0024] Implementations may include one or more of the following features. For example, the pipes of the heat exchanger may be coated with a catalyst that accelerates the oxidation of dissociated molecules within the gas mixture on their inner surfaces. The metal particles may be nanoparticles of noble metals. Attached Figure Description

[0025] Figure 1 This is a block diagram of an extreme ultraviolet (EUV) light system, which includes a catalytic conversion system that is part of the light source and coupled to an optical amplifier system.

[0026] Figure 2A This is a graph showing the relationship between the power output from the optical amplifier of the optical amplifier system and the duty cycle of the optical amplifier, without using a catalytic conversion system.

[0027] Figure 2B It was used Figure 1 A graph showing the relationship between the power output of the optical amplifier from the optical amplifier system and the duty cycle of the optical amplifier in the catalytic conversion system, and from... Figure 2A The illustrations are overlaid on top for comparison purposes;

[0028] Figure 3A It is a block diagram of the light source, including the optical amplifier system and the catalytic conversion system;

[0029] Figure 3B It is along Figure 1 and Figure 3A A cross-sectional view of the gas mixture flow direction (line 3B-3B) within the catalytic converter of the catalytic conversion system, including a close-up view of a section of the catalytic converter;

[0030] Figure 4 It can be used Figure 1 and Figure 3A A block diagram of an exemplary optical amplifier system in an EUV optical system;

[0031] Figure 5 It includes Figure 1 and Figure 3A A block diagram of an exemplary lithography system for an EUV light system;

[0032] Figure 6 It includes Figure 1 and Figure 3A A block diagram of an exemplary EUV light system; and

[0033] Figure 7A and Figure 7B This is a block diagram of an exemplary optical amplifier and an exemplary catalytic conversion system. Detailed Implementation

[0034] Reference Figure 1 The extreme ultraviolet (EUV) light system 100 includes a light source (or driving laser system) 105 that generates an amplified beam 110, a target material delivery system 115 configured to generate target material 120, and a beam delivery system 125 configured to receive the amplified beam 110 emitted from the driving laser system 105 and guide the amplified beam 110 toward a target position 130 for receiving the target material 120. The beam delivery system 125 includes a beam transport system 135 and a final focusing assembly 140 that focuses the amplified beam 110 at a focal position 145. The interaction between the amplified beam 110 and the target material 120 generates plasma 121 that emits EUV light or radiation 150. A light collector 155 collects and guides the collected EUV light 160 toward an optical device 165, such as a photolithography tool.

[0035] The driving laser system 105 includes an optical amplifier system 106 and other optical components such as a preamplifier. The optical amplifier system 106 includes at least one optical amplifier 108 having a gain medium 128 and an excitation source including a power source, as well as internal optical elements. The gain medium 128 is a gas mixture capable of optically amplifying molecules at a desired wavelength with high gain. The gain medium 128 within the optical amplifier 108 is contained within an enclosed space 118, such as a conduit. During the electrical pumping of the gain medium 128 of the optical amplifier 108, at least some molecules of the gain medium 128 dissociate into one or more molecules or elements not involved in the optical amplification, and for this purpose, the optical amplifier 108 generates less power. This means that the amplified beam 110 and the target material 120 ultimately produce less plasma 121, which reduces the amount of emitted EUV light 150, thus reducing the amount of collected EUV light 160 that can be used by the optical device 165. This effect is even more pronounced in pulsed systems, where the power supply is turned on in time intervals alternating with the off-time.

[0036] Reference Figure 2A As the duty cycle of optical amplifier 108 increases (by increasing the duty cycle of the power supply), dissociation of molecules in gain medium 128 occurs and the power output from optical amplifier 108 decreases. Duty cycle is the ratio of the time during which input power is applied to the electrodes [T(on)] to the total time during the period [T(on+off)]: T(on) / T(on+off). For example, optical amplifier 108 may comprise a gas mixture serving as gain medium 128, including carbon dioxide (CO2) mixed with other molecules or elements such as helium (He), nitrogen (N2), hydrogen (H2), or water (H2O). When optical amplifier 108 is electrically pumped using gas discharge, energy is transferred to the CO2 molecules, and as the duty cycle increases, more and more of these CO2 molecules dissociate into carbon monoxide (CO) and oxygen (O2).

[0037] Unless the dissociated molecules are converted back into the original molecules of the gas mixture used for optical amplification, the output power of the driving laser system 105 will remain unacceptably low, especially as the duty cycle increases. The process of converting the dissociated molecules back into the original molecules is accomplished via catalytic conversion. The extreme ultraviolet light system 100 or the driving laser system 105 includes a catalytic conversion system 107 that receives a gas mixture comprising dissociated molecules from the optical amplifier 108, performs the steps or multiple steps involved in the catalytic conversion (e.g., oxidation) of molecules into original molecules conducive to optical amplification, and redirects the gas mixture back to the optical amplifier 108. The catalytic conversion system 107 is fluidly connected to an enclosed space 118, which at a first end contains a gain medium 128 such that a gas mixture (containing excess dissociated molecules) in the gain medium 128 flows from the optical amplifier 108 to the catalytic conversion system 107, and at a second end allows a gas mixture (already oxidized) to flow from the catalytic conversion system 107 to the optical amplifier 107. (See reference...) Figure 2B In this way, the gas mixture effectively maintains the original molecules that contribute to optical amplification, and the power output 205 from the driving laser system 105 can be maintained at an appropriate level, even when the duty cycle increases. Furthermore, the power output can be maintained without increasing the amount of energy applied to the excitation source of the optical amplifier 108 and without adding additional gas mixtures containing oxidized molecules to the fluid lines (e.g., the conduit housing the gain medium of the optical amplifier 108). Figure 2B The dashed lines shown indicate that the image is overlaid on the diagram for comparison. Figure 2A Its power output is 200.

[0038] The laser driving system 105 may also include a controller 109 that performs various tasks, such as monitoring components within the optical amplifier 108 and the catalytic conversion system 107, performing analysis or calculations based on the monitored information, and providing instructions to components within the laser driving system 105 based on the results of the analysis or calculations.

[0039] Reference Figure 3AAn exemplary catalytic conversion system 107 may be designed as part of or in combination with an external cooler or heat exchanger that removes excess heat from the gas mixture generated during operation of the optical amplifier 108. In this example, system 107 optionally includes a gas preheater 300, a catalytic converter 305, and a heat exchanger 310. The gas mixture from the optical amplifier 108 flows toward system 107 through a closed conduit or pipe 315 out of the enclosed space 118 of the optical amplifier 108, and the gas mixture from system 107 flows through a closed conduit or pipe 320 and into the enclosed space 118 of the optical amplifier 108 for reuse during operation and generation of the amplified beam 110. The conduits 315, 320 may be made of materials that do not react with the gas mixture flowing through the conduits 315, 320 (such as, for example, stainless steel, aluminum, or metal alloys).

[0040] The gas preheater 300 can be used to increase and regulate the temperature of the gas mixture before and during its entry into the catalytic converter 305, thereby improving the conversion efficiency within the catalytic converter 305. Specifically, by heating the dissociated gas mixture before it enters the catalytic converter 305, the temperature of the dissociated gas mixture can be maintained at a temperature at which the catalyst 330 within the catalytic converter 305 most effectively induces or accelerates the oxidation of the dissociated molecules within the gas mixture. Therefore, for example, the controller 109 can monitor the temperature of the gas mixture within line 315, determine whether the temperature is at an optimal value where the catalyst 330 is most effective, and, if the temperature is below the optimal value, the controller 109 can send a signal to the preheater 300 to increase the temperature of the gas mixture to a specific value.

[0041] Generally, the higher the temperature of the gas mixture, the higher the catalytic efficiency. For example, the catalytic reaction rate within the gas mixture can double for every 10°C increase in temperature applied to the gas mixture. If the catalytic element is installed within a CO2 laser or amplifier, the temperature of the gas mixture can be raised to 60°C, depending on the laser configuration. In another application, a portion of the laser gas mixture (e.g., less than about 10%) can leak out through an external catalytic converter in a closed-loop system, in which case the temperature of the gas mixture can be raised to any desired level (e.g., 100°C). Some catalytic converters (such as those in the automotive industry or early CO2 laser systems) operate at temperatures far exceeding this level, such as about 240°C. High-efficiency materials are used for the catalyst to reduce the need for high gas temperatures to achieve high catalytic conversion efficiency. In the system 100 and method described herein, the temperature setpoint for the gas mixture is determined by balancing the efficiency of the heat exchanger 310 within the catalytic conversion system 107 with the need to increase the rate of catalytic conversion of CO and O2 to CO2. This can be accomplished by systematically studying the power output from the optical amplifier 108, which depends on the temperature of the gas mixture output from the heat exchanger 310 and the temperature of the gas mixture input to the catalytic converter 305 relative to the concentration of CO and / or O2.

[0042] Also refer to Figure 3B The catalytic converter 305 includes a support structure 325 and a catalyst 330 applied to the surface of the support structure 325, the support structure 325 having a surface area for contacting the gas mixture. The catalyst 330 is a substance that initiates or accelerates a chemical reaction (in this case, catalytic conversion or oxidation) without being affected itself. Therefore, the catalyst 330 participates in the reaction but is neither a reactant nor a product of its catalytic reaction. The catalyst 330 can be a metallic substance, such as platinum, rhodium, palladium, and gold, or any one or more of these. For example, the catalyst 330 may include platinum mixed with gold.

[0043] The support structure 325 can be a ceramic structure, such as, for example, Al2O3, SiO2, or TiO2. The catalyst 330 can be coated onto the support structure 325 to create a structure 325 that exposes the maximum surface area of ​​the catalyst to the gas mixture, while also reducing the amount of catalyst required. The support structure 325 can be a honeycomb structure, having a geometry of an array of hollow units through which the gas mixture flows. The units can be cylindrical or hexagonal in shape.

[0044] In one embodiment, catalyst 330 is made of particles (e.g., nanoparticles) of a metal (such as a noble metal, such as gold, silver, palladium, or platinum) applied to the honeycomb support structure 325. If gold is used as the catalyst, it can be used in nanoparticle form. The metal used can be malleable and have a high luster. The metal particles can be applied to structure 325 using any suitable technique (e.g., electroplating). The metal that can be used for catalyst 330 can have a relatively high work function to promote the catalytic reaction. In addition to the actual element used for catalyst 330, the work function depends on the arrangement of atoms at the surface of catalyst 330. A relatively high work function means that the work function is high enough that the metal accelerates the potential chemical reaction (oxidation), but the metal is not oxidized and consumed; therefore, chemical recovery can be performed unchanged at the end of the oxidation that has been used to accelerate or catalyze. Noble metals can be suitable metals for use as catalyst 330. As mentioned above, the metal particles can be nanoparticles, which means that the particles have a size of 100 nanometers (nm) or smaller.

[0045] The heat exchanger 310 can be any suitable device for removing heat from the gas mixture. In some embodiments, the heat exchanger 310 is a hollow tube through which the gas mixture flows, the outer surface of which is cooled by a fluid such as water. In some embodiments, the heat exchanger 310 may be further coated internally with a catalyst such as gold to provide some amount of catalytic conversion of the gas mixture flowing through the heat exchanger 310 tube. Thus, the catalyst coated inside the hollow tube accelerates or causes oxidation of dissociated molecules within the gas mixture. Typically, catalytic conversion occurring within the heat exchanger 310 is insufficient because the surface area of ​​the catalyst reacting with the gas mixture and the amount of time the dissociated molecules are in contact with the catalyst may be less than the amount required to completely convert the dissociated molecules of the gas mixture. However, the heat exchanger 310 can provide oxidation of the dissociated molecules of the gas mixture.

[0046] Therefore, in summary, the catalytic conversion system 107 includes a gas preheater 300 to heat the gas mixture to a stable temperature (and maintain it at that stable temperature), such that the catalytic efficiency within the catalytic converter 305 is close to or at its peak; the catalytic converter 305 includes an active catalyst 330 downstream of the gas preheater 300 on a honeycomb substrate (such as substrate 325). Both the gas preheater 300 and the catalytic converter 305 can be positioned upstream of a gold-plated heat exchanger 310, which can therefore serve as a second stage of catalytic conversion within the system 107. Due to its coating method and relatively small catalytic surface area (compared to the catalytic surface area of ​​the catalytic converter 305), the gold-plated heat exchanger 310 is less efficient than the first stage in the system 107 (including the catalytic converter 305 and optionally the gas preheater 300). The catalytic surface area of ​​the gold-plated heat exchanger 310 is the inner surface of the conduit and is smaller than the catalytic surface area of ​​the catalytic converter 305. The catalytic converter 305 has a high catalytic surface area because it features a honeycomb design with numerous micropores in its structure, allowing reactants (e.g., CO and O2) to contact the catalyst 330 more easily compared to the smooth surface of the gold-plated heat exchanger 310. As an exemplary comparison, the total catalytic surface area of ​​the gold-plated heat exchanger 310 could be approximately 10 m². 2 The order of magnitude, while substrate 325 (which is a honeycomb structure) can provide more than about 100m² for the same footprint or mechanical volume. 2 Surface area.

[0047] The catalytic converter 305 can be a system such as that manufactured by STC Catalysts, Inc. of Hampton, VA (STC). STC manufactures ambient temperature catalysts that can be used without the need for a gas preheater 300. What makes STC catalysts potentially suitable is the fact that they can operate at lower temperatures than other catalysts, thus making them suitable for use within a container housing an optical amplifier 108, which can use CO2 as a gain medium 128 and is preferably located before an internal heat exchanger. However, catalyst materials can perform better at higher temperatures (including those manufactured by STC) and are often used in external gas circulation laser systems (external catalysts). For some applications in the EUV light system 100, it may be possible that a cryogenically operating STC catalyst would be sufficient for converting small amounts of CO and O2 to CO2. However, for EUV light source applications, the power output requirements from the CO2 laser are high enough that a catalytic converter operating at a higher temperature, even using an STC catalyst, would be beneficial.

[0048] Catalytic converter 305 can be pre-manufactured and obtained from companies such as Corning Incorporated of Corning, NY, Engelhard (now BASF Corporation of Iselin, NJ), and Allied Signal.

[0049] Further details regarding the other components of the EUV light system 100 are provided below.

[0050] Optical amplifier 108 may or may not have laser mirrors or other feedback devices forming a laser cavity. Therefore, driving laser system 105 generates an amplified beam 110 due to population inversion in the gain medium of optical amplifier 108, even without a laser cavity. Furthermore, if a laser cavity is present to provide sufficient feedback to driving laser system 105, driving laser system 105 can generate an amplified beam 110 that is a coherent laser beam. The term "amplified beam" includes one or more of the following: light from driving laser system 105 that is merely amplified but not necessarily coherent laser oscillation; and light from driving laser system 105 that is amplified and is also a coherent laser oscillation.

[0051] The optical amplifier 108 in the laser driving system 105 may include a filling gas, comprising CO2, as a gain medium 128, and may amplify light at wavelengths between about 9100 nm and about 11000 nm, particularly at about 10600 nm. Suitable amplifiers and lasers for use in the laser driving system 105 may include pulsed laser devices, such as pulsed gas discharge CO2 laser devices, which generate radiation at about 9300 nm or about 10600 nm, for example, using DC or RF excitation operating at relatively high power (e.g., 10 kW or higher) and high pulse repetition rates (e.g., 50 kHz or more). The optical amplifier 108 in the laser driving system 105 may also include a cooling system, such as a liquid cooling system, that can be used when operating the laser driving system 105 at higher power. The liquid cooling system may use water, which can maintain a lower temperature than the optical amplifier.

[0052] In some implementations, such as Figure 4As shown, the exemplary optical amplifier system 106 includes a first amplifier serving as a preamplifier 400, and a plurality of optical amplifiers 405 serving as optical amplifiers 408. The preamplifier 400 may be a diffusion-cooled CO2 laser, such as the TruCoax CO2 laser manufactured by TRUMPF Inc. of Farmington, CT. The optical amplifiers 408 within the plurality of optical amplifiers 405 may be fast axial-current high-power CO2 lasers (such as the TruCoax CO2 laser manufactured by TRUMPF Inc. of Farmington, CT) with lossless gas circulation and capacitive RF excitation.

[0053] The final focusing assembly 140 focuses the amplified beam 110 so that the diameter of the beam 110 is minimized within the focusing region 145. In other words, the final focusing assembly 140 induces radiation in the amplified beam 110 to converge as it propagates along the propagation direction 112 toward the focusing region 145. In the absence of target material 120, the radiation in the amplified beam 110 diverges as the beam 110 propagates away from the focusing region 145 along the direction 112.

[0054] The final focusing assembly 140, part of the beam delivery system 125, modifies the wavefront of the amplified beam 110 to alter its beam divergence and focus it at a focal position 145. Therefore, if the wavefront of the amplified beam 110 entering the final focusing assembly 140 has zero curvature (and is thus collimated), the output of the final focusing assembly 140 is an amplified beam with positive curvature, meaning the center of the wavefront points in the opposite direction to the propagation direction of the amplified beam; that is, the wavefront is retarded when compared to the edge of the wavefront. Thus, the final focusing assembly 140 positively alters the curvature of the wavefront of the amplified beam 110 relative to the wavefront entering the final focusing assembly 140, thereby focusing the amplified beam 110 at the focal position 145. The final focusing assembly 140 may include one or more transmissive optical elements, each having a curved surface, or one or more reflective elements, all having curved surfaces.

[0055] The light collector 155 captures at least some of the EUV light 150 emitted from the plasma 121 and directs the captured light 160 to an optical device 165 for use in a particular application of the captured extreme ultraviolet light 160. The light collector 155 has a first focal point at or near a target position 130 or a focal position 145, and a second focal point (also referred to as an intermediate focal point) at an intermediate position 161, wherein the EUV light 160 can be output from the extreme ultraviolet light system 100 and can be input to the optical device 165.

[0056] The amplified beam 110 is a pulsed beam and includes at least a first set of pulses focused at a focal point 145 to achieve an interaction between the amplified beam 110 and the target material 120, causing the target material 120 to be converted into plasma 121 emitting extreme ultraviolet light 150. The focal point 145 needs to be sufficiently close to the target material 120 to achieve the interaction between the amplified beam 110 and the target material 120, causing the target material 120 to be converted into plasma emitting extreme ultraviolet light 150. Therefore, the focal point 145 may cover the target location 130, but is not actually superimposed on the target material 120. In other embodiments, the focal point 145 is superimposed on the target material 120.

[0057] The amplified beam 110 may optionally include a second set of pulses that modulate the target material 120 in some way, but do not interact with it to convert the target material 120 into plasma emitting extreme ultraviolet light 150. This second set of pulses may be spatially and temporally alternated with the first set of pulses along the same beam path. For example, the second set of pulses may be configured to interact with the target material 120 before reaching the target position 130 in order to modify the geometry of the target material 120 before reaching the target position 130. The second set of pulses may be referred to as a “pre-pulse” or pre-pulse beam.

[0058] Furthermore, despite Figure 1 Only one amplified beam 110 is shown being directed toward target position 130. In other embodiments, the driving laser system 105 may generate two or more amplified beams 110 along spatially different beam paths or overlay beam paths that are temporally shifted relative to each other. For example, a pre-pulse beam may be directed toward a first target position and the main beam may be directed toward a second target position (target position 130) at the output of the final focusing assembly 140.

[0059] Reference Figure 5 In some embodiments, the extreme ultraviolet (EUV) light system 100 is used in the lithography system 500 to provide extreme ultraviolet (EUV) light 160 to optical equipment such as a lithography exposure apparatus 565. The lithography system 500 includes one or more master controllers 580 connected to one or more control or excitation systems 581, which are connected to components within the EUV light system 100, as shown in reference 100. Figure 6 More details to follow.

[0060] EUV light 160 is directed to a photolithography exposure apparatus 565, which uses the light 160 to create a pattern on a wafer 566. The EUV light 160 can be directed through an illuminator 567, which may include optical elements such as reflective optics that modify aspects of the EUV light 160, such as wavefront curvature. For example, the illuminator 567 may include one or more reflectors coated with a special coating (such as a multilayer coating) that reflects as much EUV light 160 as possible. Because these reflectors tend to absorb some EUV light 160, they can advantageously be used as little as possible.

[0061] EUV light 160 exiting illuminator 567 is directed to reflective mask 570. EUV light 160 exiting reflective mask 570 is then directed through a set of projection optics 568, which includes one or more reflectors coated with a special coating for reflecting EUV light 160, and the projection optics 568 are also configured to focus EUV light 160 onto wafer 566. The projection optics set 568 adjusts the range of angles at which EUV light 160 impacts wafer 566 and enables image transfer from reflective mask 570 to resist on wafer 566. For example, the projection optics set 568 may include a series of four to six curved mirrors, thereby reducing the size of the image and focusing the image onto wafer 566. Each of these mirrors slightly bends EUV light 160 to form the image to be transferred onto wafer 566.

[0062] In addition, the photolithography exposure apparatus 567 may include, among other features, a photolithography controller 572, an air conditioning unit, and a power supply for various electrical components. In some embodiments, the wafer 566 is mounted on a wafer stage 573 and an immersion medium 574 may be provided to cover the wafer 566 for immersion lithography. In other embodiments, the wafer 566 is not covered by the immersion medium 574.

[0063] The wafer 566 can be processed using any number of process steps, which can be one or more combinations of process steps, such as etching, deposition, and photolithography processes using different masks to create opening patterns (such as trenches, channels, or holes) in the wafer material or in the material deposited on the wafer. These openings can be filled with insulating, conductive, or semiconductor materials to build layers of microelectronic features on the wafer. The wafer is then monolithically assembled to form individual chips, which can be integrated into various electronic products, such as computers and other consumer or industrial electronic devices.

[0064] Reference Figure 6In some embodiments, the extreme ultraviolet light system 100 is part of a system that includes other components such as a vacuum chamber 600, one or more controllers 580, one or more excitation systems 581, and a guide laser 582.

[0065] The vacuum chamber 600 can be a single, monolithic structure, or it can be equipped with discrete sub-chambers housing specific components. The vacuum chamber 600 is at least partially rigid, from which air and other gases are removed by a vacuum pump, creating a low-pressure environment within the chamber 600. The walls of the chamber 600 can be made of any suitable metal or alloy suitable for vacuum use (able to withstand even lower pressures).

[0066] Additionally, the final focusing assembly 140 may be located entirely outside the vacuum chamber 600, partially within the vacuum chamber 600 (so that some components of assembly 140 are inside the low-pressure environment while others are outside), or entirely within the vacuum chamber 600. Alternatively, the final focusing assembly 140 may be partially within a sub-chamber 601 of the vacuum chamber 600. For example, as Figure 6 As shown, the final focusing assembly 140 is partially located within the sub-chamber 601 of the vacuum chamber 600.

[0067] The target material delivery system 115 delivers target material 120 to the target location 130. The target material 120 at the target location can be in the form of liquid droplets, a liquid stream, solid particles or clusters, solid particles contained within liquid droplets, or solid particles contained within a liquid stream. Target material 120 can include, for example, water, tin, lithium, xenon, or any material that has an emission line in the EUV range when converted to a plasma state. For example, elemental tin can be used as pure tin (Sn), as tin compounds (e.g., SnBr4, SnBr2, SnH4), or as any combination of tin alloys (e.g., tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or these alloys). Target material 120 can include filaments coated with one of the above elements (such as tin). If the target material 120 is in a solid state, it can have any suitable shape, such as toroidal, spherical, or square. The target material 120 can be delivered by the target material delivery system 115 into the chamber 800 and to the target position 130. The target position 130, also known as the irradiation position, is the location where the target material 120 interacts optically with the magnified beam 110 to generate plasma.

[0068] The light collector 155 may be a collector mirror 655 having an aperture 640 to allow the magnified beam 110 to pass through and reach the focal position 145. The collector mirror 655 may be, for example, an ellipsoidal mirror having a first focal point at the target position 130 or the focal position 145, and a second focal point at an intermediate position 661 (also referred to as the intermediate focal point), wherein EUV light 160 can be output from the extreme ultraviolet light system and can be input to the optical device 165.

[0069] One or more controllers 580 are connected to one or more excitation or diagnostic systems, such as, for example, a droplet position detection feedback system, a laser control system, and a beam control system, as well as one or more target or droplet imagers. The target imager provides an output indicating, for example, the droplet position relative to a target position 130, and provides this output to the droplet position detection feedback system, which can, for example, calculate the droplet position and trajectory, thereby calculating the droplet position error based on individual droplets or on average. The droplet position detection feedback system thus provides the droplet position error as input to the controller 580. The controller 580 can therefore, for example, provide laser position, orientation, and timing correction signals to a laser control system that can be used, for example, to control laser timing circuitry and / or to a beam control system to control the amplified beam position and the shaping of the beam delivery system, thereby changing the position and / or power of the beam focal spot within the chamber 600.

[0070] The target material delivery system 115 includes a target material delivery control system that is responsive to signals from the controller 580, for example operable to modify the release point of the droplets released by the internal delivery mechanism, thereby correcting for errors in the arrival of the droplets at the desired target location 130.

[0071] Additionally, the extreme ultraviolet (EUV) light system 100 may include a source detector for measuring one or more EUV light parameters. EUV light parameters include, but are not limited to, pulse energy, wavelength-dependent energy distribution, energy within a specific wavelength band, energy outside a specific wavelength band, and the angular distribution and / or average power of EUV intensity. The source detector generates a feedback signal used by the controller 580. The feedback signal may, for example, indicate errors in parameters such as the timing and focus of a laser pulse to properly intercept droplets at the correct position and time for effective and efficient EUV light generation.

[0072] In some embodiments, the laser driving system 105 has a master oscillator / power amplifier (MOPA) configuration with multiple amplification stages and a seed pulse initiated by a Q-switched master oscillator (MO) operating at low energy and a high repetition rate (e.g., capable of 100 kHz). From the MO, the laser pulse can be amplified, for example, using an RF-pumped, fast axial-current CO2 amplifier, to generate an amplified beam 110 traveling along the beam path.

[0073] Although three optical amplifiers can be used, this embodiment may use as few as one amplifier as well as more than three amplifiers. In some embodiments, each CO2 amplifier may be an RF-pumped axial CO2 laser cube with a length of 10 meters folded by internal mirrors.

[0074] Alternatively, the driving laser system 105 can be configured as a so-called "self-targeting" laser system, wherein the target material 120 serves as a mirror of the optical cavity. In some "self-targeting" arrangements, a master oscillator may not be required. The driving laser system 105 includes a chain of amplifier chambers arranged in series along the beam path, each chamber having its own gain medium and excitation source, such as a pump electrode. Each amplifier chamber may be RF-pumped, fast axial-flow CO2, and the amplifier chambers may have a combined single-pass gain of, for example, 1,000–10,000 for amplifying light at a wavelength λ of, for example, 10600 nm. Each amplifier chamber may be designed without a laser cavity (resonator) mirror, so that when individually arranged, they do not include the optical components required to pass the amplified beam through the gain medium more than once. However, as described above, the laser cavity can be formed as follows.

[0075] In this embodiment, the laser cavity can be formed by adding a back-side partially reflective optical element to the laser cavity and placing the target material 120 at the target position 130. The optical element can be, for example, a flat mirror, a curved mirror, a phase-conjugate mirror, or a corner reflector with approximately 95% reflectivity for a wavelength of approximately 10600 nm (the wavelength of the amplified beam 110 if a CO2 amplifier chamber is used). The target material 120 and the back-side partially reflective optical element are used to reflect some of the amplified beam 110 back into the driving laser system 105 to form the laser cavity. Therefore, the presence of the target material 120 at the target position 130 provides sufficient feedback for the driving laser system 105 to generate coherent laser oscillations; and in this case, the amplified beam 110 can be considered as a laser beam. When the target material 120 is not present at the target position 130, the driving laser system 105 can still be pumped to generate the amplified beam 110, but it will not generate coherent laser oscillations unless some other component provides sufficient feedback. This arrangement could be a so-called "self-aiming" laser system, in which the target material 120 is used as a mirror of the optical cavity (a so-called plasma mirror or mechanical Q-switch).

[0076] Depending on the application, other types of amplifiers or lasers may also be suitable, such as stimulated excimer or fluorine molecular lasers operating at high power and high pulse repetition rates. Examples include stimulated excimer laser systems with MOPA configurations, as shown, for example, in U.S. Patent Nos. 6,625,191; 6,549,551; and 6,567,450; a stimulated excimer laser having one or more chambers, such as oscillator chambers and one or more amplification chambers (amplification chambers in parallel or series); a master oscillator / power amplifier (MOPO) configuration; a power oscillator / power amplifier (POPA) configuration; or a solid-state laser seeded with one or more stimulated excimer lasers or fluorine molecular amplifiers or oscillator chambers may be suitable. Other designs are possible.

[0077] At the irradiation location, a magnified beam 110, suitably focused by a final focusing assembly 140, is used to generate a plasma with certain characteristics depending on the composition of the target material 120. These characteristics may include the wavelength of the EUV light 160 generated by the plasma and the type and amount of debris released from the plasma. The magnified beam 110 evaporates the target material 120 and heats the evaporated target material to a critical temperature (plasma state) at which electrons are emitted, leaving behind ions. The ions are further heated until they begin to emit photons with wavelengths in the extreme ultraviolet range.

[0078] Reference Figure 7A In one embodiment, the optical amplifier 108 is designed as an axial flow system 700, wherein a gas mixture is pumped into and out of a gas discharge tube 705 at one end 701 via a gas pump and a supply line 710. In other embodiments, the optical amplifier 108 may be designed as a transverse flow system, wherein a molecular gas laser is used instead of a gas discharge tube (e.g., along a conduit) to discharge the gas. Figure 7A and Figure 7B The gas flows downwards and across the gas discharge tube (such as pipes 705, 755). In this way, higher rated power can be obtained for continuous laser operation of molecular gases.

[0079] In axial or transverse flow implementations, fresh gas is supplied to replace gas molecules depleted due to dissociation. In one example where the optical amplifier 108 is a carbon dioxide molecular gas laser, the gas mixture comprises CO2, and He and N2 are added to the gas mixture to increase efficiency. This design can also be applied to transverse flow systems when discussing the axial flow system 700. The axial (or transverse) flow system 700 includes a recirculation pump (or blower), a gas supply source system 715, and a gas source. The gas supply source system 715 includes a recirculation pump (or blower) for pushing the gas mixture from conduit 705 and through line 710, where the gas source replaces depleted gas molecules due to dissociation. The catalytic conversion system 107 can be placed inside (or in series with) the gas line 710 of the axial (or transverse) flow system 700. This arrangement of the catalytic conversion system 107 (i.e., within and therefore in series with the gas line 710) is suitable in cases where the optical amplifier system 106 can tolerate higher levels of oxygen.

[0080] Reference Figure 7B In other embodiments of the axial (or lateral) flow system 750, the catalytic conversion system 107 is positioned outside (i.e., parallel to) the gas line 760 of the axial (or lateral) flow system 750. The system 750 includes a gas discharge tube 755 that contains the gas mixture. This arrangement of the catalytic conversion system 107 (i.e., outside and parallel to the gas line 760) is suitable in situations where the optical amplifier system 106 cannot tolerate high levels of oxygen in the gas mixture (e.g., if oxygen must be less than 0.2% of the total gas mixture).

[0081] Typically, a small fraction of the gas mixture (e.g., about 1-20%, or about 5%) can be drawn downstream from the discharge region of pipe 755 (where the O2 concentration is high), guided through gas line 760, and sent through the catalytic elements 300, 305, 310 of catalytic conversion system 107 (to remove O2 by oxidation) before the gas mixture is reintroduced into gas line 760 (upstream of the discharge region of pipe 755). In this embodiment, catalytic conversion system 107 may also include control valve 770 and recirculation pump or blower 775.

[0082] Again Figure 7B In an external catalyst configuration, the temperature of the gas mixture can be regulated by a gas heat exchanger (such as heat exchanger 310) or a counter-current gas heat exchanger. This external configuration provides greater control over the temperature of the gas mixture because the temperature can be regulated outside the gas line 760. An alternative is to heat the catalyst itself. For example, Figure 1The EUV light source application shown may be intended to heat the gas mixture because heating the gas mixture can result in a finer flow of the gas mixture and a more uniform temperature distribution on the catalyst surface. Other embodiments are within the scope of the following claims.

Claims

1. An extreme ultraviolet light system, comprising: An optical amplifier system includes one or more optical amplifiers, each optical amplifier including a gain medium in the form of a gas mixture that generates a pulsed amplified beam when energy is supplied from an energy source to pump the gain medium, the optical amplifier system including a fluid input through which the gas mixture flows and a fluid output; as well as A catalytic conversion system, fluidly connected to the fluid output of the optical amplifier system and fluidly connected to the fluid input of the optical amplifier system, the catalytic conversion system comprising: A catalytic converter, the catalytic converter comprising: case; A substrate, within the housing, including openings through which the gas mixture can flow; and A catalyst, as a coating applied to the inner surface of the opening of the substrate, the catalyst comprising metal nanoparticles; and A heat exchanger, separated from and located downstream of the catalytic converter, includes a conduit through which the gas mixture flows. The conduit's inner surface is coated with a catalyst that promotes the oxidation of dissociated molecules within the gas mixture. The conduit includes multiple bends. The pulsed amplified beam is guided toward the target location to achieve an interaction between the pulsed amplified beam and the target material, thereby generating plasma that emits extreme ultraviolet (EUV) light.

2. The system of claim 1, wherein, The opening in the substrate has a honeycomb geometry.

3. The system of claim 1, wherein, The pipe is cooled by an external heat sink.

4. The system of claim 1, further comprising a target material delivery system configured to generate the target material at the target location.

5. The system of claim 1, wherein, The catalyst comprises gold nanoparticles.

6. The system according to claim 1, wherein, The substrate is made of ceramic material.

7. The system according to claim 1, wherein, The catalytic conversion system is fluidly connected in parallel with the fluid line formed by the fluid input and fluid output of the optical amplifier system.

8. The system according to claim 1, wherein, The catalytic conversion system is fluidly connected in series with the fluid line formed by the fluid input and the fluid output of the optical amplifier system.

9. The system according to claim 1, wherein, The metal in question is a precious metal.

10. A method for generating extreme ultraviolet light, the method comprising: Pump energy is supplied to the gain medium of at least one optical amplifier in an optical amplifier system to generate a pulsed amplified beam, said gain medium being in the form of a gas mixture comprising molecules, at least some of said gas mixture dissociating within the channel during the generation of said pulsed amplified beam; Regulate the temperature of the gas mixture output from the pipeline; A temperature-controlled gas mixture is guided through a substrate coated with a catalyst made of metal nanoparticles fixed inside a housing, thereby oxidizing the dissociated molecules of the gas mixture. The oxidized gas mixture is guided through a temperature-controlled pipe to remove heat from the oxidized gas mixture, wherein the pipe includes multiple bends; The dissociated molecules of the oxidized gas mixture are at least partially oxidized using a catalyst coated on the inner surface of the temperature-controlled pipe. The oxidized gas mixture is guided back into the pipeline; Generate target material at the target location; and By focusing the pulsed amplified beam to a focal point, the optical interaction between the pulsed amplified beam and the target material is achieved, causing the target material to transform into plasma that emits extreme ultraviolet light. The pulse amplified beam described herein includes a pulse repetition rate of 50 kHz or higher.

11. The method according to claim 10, wherein, Regulating the temperature of the gas mixture includes maintaining the temperature of the gas mixture above the temperature of the gas mixture exiting from the pipe.

12. The method according to claim 10, wherein, The metal in question is a precious metal.

13. The method according to claim 10, wherein, Providing pump energy to the gain medium includes using DC excitation to generate the pulsed amplified beam.

14. The method according to claim 10, wherein, Providing pump energy to the gain medium includes using RF excitation to generate the pulsed amplified beam.

15. A catalytic conversion system for an optical amplifier system in an extreme ultraviolet (EUV) light system, the catalytic conversion system comprising: Catalytic converter, including The input is fluidly connected to the gas preheater of the optical amplifier system to receive a preheated gas mixture comprising dissociated molecules of the gain medium in the optical amplifier system. The output is fluidly connected to the optical amplifier system; A housing located between the input and the output; The substrate, within the housing, includes openings through which the gas mixture can flow; A catalyst, as a coating applied to the inner surface of an opening in the substrate, comprises metal nanoparticles; as well as A heat exchanger, separate from and downstream of the catalytic converter, includes multiple bends and a catalyst configured to accelerate the oxidation of dissociated molecules within the gas mixture.

16. The catalytic conversion system according to claim 15, wherein, The opening in the substrate is hexagonal.

17. The catalytic conversion system according to claim 15, wherein, The housing is fluidly connected to the input and the output.

18. A catalytic conversion system for a gas discharge optical amplifier system in an extreme ultraviolet light system, the system comprising: A gas preheater that increases the temperature of a gas mixture output from the optical amplifier system, the gas mixture comprising dissociated molecules of a gain medium excited to generate an amplified beam from the optical amplifier system; as well as A catalytic converter receives a gas mixture from the gas preheater at an increased temperature, the catalytic converter comprising: A substrate, within a housing and including openings through which the gas mixture can flow; and A catalyst, as a coating applied to the inner surface of the opening of the substrate, the catalyst comprising metal particles that accelerate the oxidation of dissociated molecules within the gas mixture; A heat exchanger, separate from and downstream of the catalytic converter, includes multiple bends and a catalyst configured to accelerate the oxidation of dissociated molecules within the gas mixture.

19. The catalytic conversion system according to claim 18, wherein, The opening in the substrate is hexagonal.

20. The catalytic conversion system according to claim 18, wherein, The particles described are nanoparticles of noble metals.

21. A catalytic conversion system for a gas discharge optical amplifier system in an extreme ultraviolet light system, the catalytic conversion system comprising: A catalytic converter that receives a preheated gas mixture from a gas preheater of the optical amplifier system, the gas mixture comprising dissociated molecules of a gain medium excited to generate an amplified light beam from the optical amplifier system, the catalytic converter comprising: A substrate, within a housing and including openings through which the gas mixture can flow; and A catalyst, as a coating applied to the inner surface of the opening of the substrate, the catalyst comprising metal particles that accelerate the oxidation of dissociated molecules within the gas mixture; and A heat exchanger, separate from and downstream of the catalytic converter, includes a conduit through which the gas mixture flows. The conduit has multiple bends and is cooled by an external heat sink and has its inner surface coated with a catalyst that accelerates the oxidation of dissociated molecules within the gas mixture.

22. The catalytic conversion system according to claim 21, wherein, The metal particles are nanoparticles of precious metals.

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