Improved gas laser
A dual heat exchanger system with separate cooling circuits enhances the efficiency of gas-based lasers by minimizing energy consumption for cooling, enabling the production of more powerful laser beams.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-02-12
- Publication Date
- 2026-03-17
AI Technical Summary
Existing gas-based lasers, such as CO2 lasers, face inefficiencies in thermal management due to the need for active or forced cooling, which consumes significant energy and reduces overall system efficiency.
Implementing a dual heat exchanger system with separate cooling circuits, where the first circuit uses atmospheric cooling to remove most thermal energy and the second circuit uses forced cooling to achieve lower gas temperatures, optimizing the cooling process to enhance laser efficiency.
The dual heat exchanger system significantly reduces energy consumption for cooling, allowing for the generation of more powerful laser beams by maintaining lower gas temperatures, thereby improving the overall efficiency of the laser system.
Smart Images
Figure 2026509215000001_ABST
Abstract
Description
Technical Field
[0001] (Cross - reference to related applications)
[0001] This application claims the priority of European application EP23159917 filed on March 3, 2023, the entire content of which is incorporated herein by reference.
[0002]
[0002] The present invention relates to gas - based lasers, particularly carbon dioxide lasers, lithographic apparatuses including such gas - based lasers, methods for improving the efficiency of gas - based lasers, and the use of such gas - based lasers, methods, or lithographic apparatuses in lithographic methods or apparatuses, particularly in EUV lithography or utilization apparatuses or methods.
Background Art
[0003]
[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can project a pattern from a patterning device (e.g., a mask) onto a layer of radiation - sensitive material (resist) provided on a substrate.
[0004]
[0004] The wavelength of the radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of the features that can be formed on that substrate. Using a lithographic apparatus that uses EUV radiation, which is electromagnetic radiation having a wavelength in the range of 4 - 20 nm, smaller features can be formed on a substrate than with conventional lithographic apparatuses (e.g., those that can use electromagnetic radiation with a wavelength of 193 nm).
[0005]
[0005] In an EUV lithography apparatus, a laser, such as a CO2 laser, is positioned to store energy in a fuel, such as tin (Sn), supplied from a fuel ejector, via the laser beam. Any suitable fuel can be used, although tin is mentioned in the description below. The fuel may be in liquid form, for example, and may be a metal or alloy. The fuel ejector may comprise a nozzle configured to guide tin, for example, in the form of droplets, along a trajectory toward the plasma-forming region. The laser beam is incident on the tin in the plasma-forming region. The storage of laser energy in the tin creates a plasma in the plasma-forming region. Emissions, including EUV radiation, are emitted from the plasma during the de-excitation and recombination of ions in the plasma.
[0006]
[0006] In gas-based lasers such as CO2 lasers, a gas containing carbon dioxide, nitrogen, and helium, as well as potentially other gases such as hydrogen and xenon, is sent to an amplification step, and radio frequency energy is used to energize the gas in the laser and ultimately to release an infrared laser beam with dominant wavebands of 9.6 microns and 10.6 microns. The process of generating the laser beam heats the gas, and the amplification process eventually saturates at a gas temperature of about 220°C. Thus the gas flows through the laser apparatus and is cooled by one or more heat exchange elements. The gas is cooled and recirculated through the laser to generate the laser beam. The large amount of energy supplied to the gas-based laser needs to be converted into heat and removed from the system. Active or forced cooling can be used, but this also requires energy input and reduces the overall efficiency of the system.
[0007]
[0007] The present invention was conceived in an attempt to address at least some of the problems identified above. [Overview of the Initiative]
[0008]
[0008] According to a first aspect of the present disclosure, a gas-based laser is provided comprising a heat exchanger for cooling a compressed gas from a first temperature to a second temperature lower than the first temperature, wherein the heat exchanger comprises at least two heat exchange elements, the first of which is arranged to cool the compressed gas from a first temperature to an intermediate temperature lower than the first temperature, and the second of which is arranged to cool the compressed gas from the intermediate temperature to a second temperature lower than the intermediate temperature, wherein the first and second heat exchange elements are placed in two mutually exclusive heat transfer circuits, the inlet temperature of the coolant in the second heat transfer circuit including the second heat exchange element being lower than the inlet temperature of the coolant in the first heat transfer circuit including the first heat exchange element. The heat transfer circuits may operate on the principle of a reverse heat exchanger.
[0009]
[0009] In this disclosure, there are two separate cooling circuits for removing thermal energy from the gas of a gas-based laser. The first temperature can be about 100°C, and therefore the rate of heat transfer to the coolant in the first heat exchange element is fast, and the gas is cooled logarithmically. This is because the logarithmic mean temperature difference, which is the logarithmic mean of the temperature difference between the two elements exchanging thermal energy, determines the rate of heat transfer, and the larger the logarithmic mean temperature difference, the faster the rate of heat transfer. The gas supplied to the second heat exchange element is at an intermediate temperature, and therefore the coolant in the second heat transfer circuit only needs to remove a smaller proportion of the thermal energy. Previously, the first and second heat exchange elements were in series, and the same coolant was used to cool the gas from a higher first temperature to a lower second temperature. Therefore, all the thermal energy was transferred to the same coolant, and a large amount of energy was required for the active or forced cooling of the coolant. By having separate heat transfer circuits, the first heat transfer circuit can be used to remove most of the thermal energy, and the coolant that absorbs most of the thermal energy can be easily cooled by atmospheric cooling, such as within a cooling tower, while the second heat transfer circuit can be used to cool the gas from an intermediate temperature to a second temperature. Atmospheric cooling is an energetically inefficient method of removing thermal energy from a system. The coolant used in this second heat transfer circuit can then be cooled by forced or active cooling so that a smaller amount of thermal energy needs to be actively removed by freezing, and the coolant can be cooled to a lower temperature than when the same coolant was used to cool the gas from the first temperature to the second temperature. An additional advantage of being able to cool the gas to a lower temperature is that it takes more time to raise the gas temperature up to 220°C, making it possible to generate a more powerful laser beam. Therefore, the efficiency of the laser increases because a more powerful laser beam can be generated.
[0010]
[0010] The first heat exchange element may be configured to cool the compressed gas from about 100°C to about 32°C. Because the high-temperature gas enters the first heat exchange element, the cooling rate is not greatly affected by the temperature of the coolant entering the first heat exchange unit, and therefore, atmospheric cooling can be used to cool the coolant to the operating temperature. Atmospheric cooling, also known as free cooling, is an efficient method of releasing excess thermal energy without requiring active cooling, and can remove a large amount of thermal energy from a system that uses only a small amount of energy to operate auxiliary devices such as pumps and valves. An example of atmospheric cooling or free cooling is a cooling tower without chillers. This is in contrast to active cooling, which requires much more energy input.
[0011]
[0011] The second heat exchange element may be configured to output a cooled compressed gas at a temperature of less than about 20°C, less than about 15°C, less than about 10°C, less than about 5°C, less than about 0°C, less than about -5°C, less than about -10°C, less than about -15°C, less than about -20°C, less than about -25°C, less than about -30°C, less than about -35°C, less than about -40°C, or less than about -45°C.
[0012]
[0012] By dividing the cooling circuit, a second heat exchange element can be configured to cool the gas at a higher cooling rate than previously possible without actually consuming much additional energy. The amount of thermal energy that needs to be removed by active cooling is only a smaller percentage of the total thermal energy. The lower the gas temperature, the better the laser efficiency.
[0013]
[0013] The first heat exchange element may be connected to an atmospheric cooling system, and the second heat exchange element may be connected to a forced cooling system. As described above, atmospheric cooling systems, which remove thermal energy by dissipating energy into the atmosphere, are an efficient method for removing large amounts of thermal energy without using chillers.
[0014]
[0014] The first heat exchange element may be selectively connected to a forced cooling system. In most cases, atmospheric cooling may be used, but since some additional forced cooling may be required, the first heat exchange element may be connected to a forced cooling system. Such a forced cooling system may be the same as the one connected to the second heat exchange element, or it may be a separate system.
[0015]
[0015] The first heat exchange element may include an outlet that is in fluid communication with the inlet of a third heat exchange element located downstream of the amplification section of the gas-based laser, and an optional fourth heat exchange element located downstream of the third heat exchange element.
[0016]
[0016] A third heat exchange element or an optional fourth heat exchange element may be in fluid communication with a compressor configured to compress the gas used in the laser.
[0017]
[0017] A third and / or fourth heat exchange element may be configured to cool the gas leaving the laser amplification section. The gas may be at a temperature of at least 200°C, optionally at least 210°C, and optionally at least 220°C.
[0018]
[0018] The output of a compressor configured to compress the gas used in the laser may be in fluid communication with the inlet of a first heat exchange element. Thus the system may have a complete circuit in which the gas is continuously cooled, used to generate laser light, cooled again, then compressed and circulated through the circuit again.
[0019]
[0019] The second heat exchange element is housed in an adiabatic environment configured to avoid condensation of water vapor in the atmosphere, and / or in a humidity-controlled atmosphere configured to avoid condensation of water vapor in the atmosphere.
[0020]
[0020] Due to the low operating temperature of the second heat exchange element, water vapor in the atmosphere may condense. Therefore, the element may be insulated to prevent this, and / or provided in an atmosphere where the relative humidity is controlled to avoid condensation.
[0021]
[0021] The coolant may include water, glycol, or a mixture thereof. Water is a commonly used coolant due to its high heat capacity, ease of handling, and availability. Glycols have a lower freezing point than water, and therefore it is possible to cool glycol to a temperature lower than that of water without the risk of freezing. Glycols may be selected from ethylene glycol, propylene glycol, and mixtures thereof. A mixture of water and glycol also has a lower freezing point than pure water, so this mixture can be cooled to a temperature lower than that of water. By providing a coolant that can be cooled to a lower temperature, gases can also be cooled to a lower temperature. This means that the laser power can also be increased.
[0022]
[0022] A gas-based laser according to any of the preceding claims, wherein one or both of the first and second heat exchange elements are configured to provide a coolant at temperatures below about 35°C, below about 30°C, below about 25°C, below about 20°C, below about 15°C, below about 10°C, below about 5°C, below about 0°C, below about -5°C, below about -10°C, below about -15°C, below about -20°C, below about -25°C, below about -30°C, below about -35°C, below about -40°C, and below about -45°C.
[0023]
[0023] According to a second aspect of the present disclosure, a lithography apparatus including a gas-based laser according to the first aspect is provided. The lithography apparatus may be an EUV lithography apparatus.
[0024]
[0024] According to a third aspect of the present disclosure, a method for improving the efficiency of a gas-based laser is provided. The method includes: a) cooling compressed gas in a first heat exchange element from a first temperature to an intermediate temperature lower than the first temperature; b) cooling compressed gas in a second heat exchange element from the intermediate temperature to a second temperature lower than the intermediate temperature. The first and second heat exchange elements are placed in two mutually exclusive heat transfer circuits, and the inlet temperature of the coolant in the second heat transfer circuit including the second heat exchange element is lower than the inlet temperature of the coolant in the first heat transfer circuit including the first heat exchange element.
[0025]
[0025] As described with respect to the first aspect, by having two heat transfer circuits, one can be used to remove most of the thermal energy, and the other can be used to cool the gas to a lower temperature. Since the circuits are mutually exclusive, they can accommodate different cooling loads and different cooling temperatures.
[0026]
[0026] The method may include sending the coolant from the first heat exchange element to the third heat exchange element, and optionally, sending the coolant from the third heat exchange element to the fourth heat exchange element. The first, third, and optional fourth heat exchange elements are arranged in the first heat transfer circuit.
[0027]
[0027] The method may include cooling the coolant via an air cooling system within the first heat transfer unit.
[0028]
[0028] The method includes cooling the coolant by a forced cooling system within the second heat transfer circuit. The forced cooling circuit can be any form of active cooling circuit that uses energy to remove thermal energy from the coolant. Thereby, the coolant can be cooled to a temperature lower than the ambient temperature.
[0029]
[0029] According to a fourth aspect of the present disclosure, there is provided the use of a gas-based laser according to the first aspect, a lithographic apparatus according to the second aspect, or a method according to the third aspect of the present disclosure in a lithographic apparatus or method.
[0030]
[0030] Of course, the features described with respect to one embodiment can be combined with any of the features described with respect to another embodiment, and all such combinations are explicitly contemplated and disclosed herein.
Brief Description of the Drawings
[0031]
[0031] Hereinafter, embodiments of the present invention will be described as examples with reference to the attached schematic diagrams. Corresponding reference symbols in the drawings indicate corresponding parts.
[0032] [Figure 1]
[0032] A lithography apparatus according to an embodiment of the present disclosure is shown. [Figure 2]
[0033] A schematic diagram of the flow circuit of an existing heat exchange system is shown. [Figure 3]
[0034] A schematic diagram of the flow circuit of an existing heat exchange system is shown. [Figure 4]
[0035] A schematic diagram of the flow circuit of a gas-based laser according to the present disclosure is shown.
[0033]
[0036] The features and advantages of the present invention will become more apparent by reading the following detailed description in conjunction with the drawings. In the drawings, the same reference symbols indicate corresponding elements throughout. In the drawings, the same reference numbers generally indicate the same elements, functionally similar elements, and / or structurally similar elements.
Modes for Carrying Out the Invention
[0034]
[0037] Figure 1 shows a lithography system including a gas-based laser according to the present invention. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithography apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to adjust the radiation beam B before it is incident on the patterning device MA. The projection system PS is configured to project the radiation beam B (patterned by the mask MA) onto the substrate W. The substrate W may include a pre-formed pattern. In this case, the lithography apparatus aligns the patterned radiation beam B with the pre-formed pattern on the substrate W. In this embodiment, a pellicle 15 is shown in the path of radiation to protect the patterning device MA. It will be understood that the pellicle 15 may be placed in any required position and may be used to protect any mirrors in the lithography apparatus. In embodiments, the pellicle 15 may be omitted.
[0035]
[0038] The radiation source SO, the illumination system IL, and the projection system PS can all be constructed and positioned so that they are isolated from the external environment. A gas (e.g., hydrogen) at a pressure lower than atmospheric pressure may be provided within the radiation source SO. A vacuum may be provided within the illumination system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure much lower than atmospheric pressure may be provided within the illumination system IL and / or the projection system PS.
[0036]
[0039] The radiation source SO shown in Figure 1 is of a type that can be called a laser-generated plasma (LPP) source. Laser 1, such as a CO2 laser, is arranged to store energy in a fuel such as tin (Sn) supplied from a fuel ejector 3 via a laser beam 2. Although tin is mentioned in the following description, any suitable fuel can be used. The fuel may be in liquid form, for example, and may be a metal or alloy. The fuel ejector 3 may comprise a nozzle configured to guide tin, for example, in the form of droplets, along an orbit toward the plasma-forming region 4. The laser beam 2 is incident on the tin in the plasma-forming region 4. The storage of laser energy in the tin creates a plasma 7 in the plasma-forming region 4. Radiation, including EUV radiation, is emitted from the plasma during the de-excitation and recombination of ions in the plasma.
[0037]
[0040] EUV radiation is collected and focused by a per-normal incident radiation collector 5 (sometimes more commonly called a normal incident radiation collector). Collector 5 may have a multilayer structure arranged to reflect EUV radiation (e.g., EUV radiation with a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration with two elliptical foci. As described below, the first focus may be in the plasma-forming region 4, and the second focus may be at an intermediate focus 6.
[0038]
[0041] Laser 1 can be separated from the radiation source SO. In this case, laser beam 2 can be delivered from laser 1 to the radiation source SO with the help of a beam delivery system (not shown) that includes, for example, a suitable guide mirror and / or beam expander and / or other optical systems. Laser 1 and the radiation source SO can together be considered as a radiation system.
[0039]
[0042] The radiation reflected by collector 5 forms radiation beam B. Radiation beam B is focused at point 6 to form an image of the plasma-forming region 4. The plasma-forming region 4 acts as a virtual radiation source for the illumination system IL. Point 6, where radiation beam B is focused, may be called the intermediate focus. The radiation source SO is positioned such that the intermediate focus 6 is located at or near the aperture 8 within the closed structure 9 of the radiation source.
[0040]
[0043] The radiant beam B is incident from the radiation source SO into an illumination system IL configured to adjust the radiant beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Both the faceted field mirror device 10 and the faceted pupil mirror device 11 provide the radiant beam B with a desired cross-sectional shape and a desired angular distribution. The radiant beam B exits the illumination system IL and is incident onto a patterning device MA held by a support structure MT. The patterning device MA reflects the radiant beam B to form a pattern. In addition to the faceted field mirror device 10 and the faceted pupil mirror device 11, or in their place, the illumination system IL may include other mirrors or devices.
[0041]
[0044] Following reflection from the patterning device MA, the patterned radiant beam B is incident on the projection system PS. The projection system comprises several mirrors 13, 14 configured to project the radiant beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a reduction factor to the radiant beam to form an image with features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. In Figure 1, the projection system PS has two mirrors 13, 14, but the projection system may include any number of mirrors (e.g., six mirrors).
[0042]
[0045] The radiation source SO shown in Figure 1 may include components not shown. For example, a spectral filter may be provided within the radiation source. The spectral filter may be substantially transparent to EUV radiation but substantially block wavelengths of other radiation, such as infrared radiation.
[0043]
[0046] Figure 2 is a schematic diagram of the flow circuit of an existing heat exchange system 16. System 16 includes a forced cooling circuit, which includes a forced cooling unit 17. The forced cooling unit 17 can be any active cooling unit that uses energy to remove thermal energy from the coolant. A heat exchanger 18 is provided to exchange thermal energy between the circuit including the forced cooling unit 17 and the circuit including a first heat exchange element 19 and a second heat exchange element 20. Note that the same coolant is supplied to both the first and second heat exchange elements 19 and 20 so that the coolant enters at the same temperature. The coolant that has left the first and second heat exchange elements 19 and 20 is sent via a pump 21 to the heat exchanger 18, which is to be recombined and cooled. The hot gas to be cooled enters point 22 at approximately 100°C and finally exits point 23 at approximately 32°C. Because the cooling circuit is single, the entire coolant is cooled using the forced cooling unit 17. Also, it is not practical to reduce the temperature of the gas exiting the second heat exchange element to below approximately 32°C.
[0044]
[0047] Figure 3 shows another system of the prior art in which the coolant is circulated within a single circuit. The same reference numerals are provided for features corresponding to Figure 2. The illustrated embodiment includes four heat exchange units 19, 20, 24, and 25. A coolant circuit is provided that includes a compressor 26 and a heat exchanger 27. The coolant is returned to the compressor 26 at approximately 28°C and sent to a heat exchanger 27 which is in thermal communication with a forced cooling unit (not shown). The coolant is cooled by the heat exchanger 27 to approximately 18°C and then sent to the first and second heat exchange units 19 and 20. The coolant from the second heat exchange unit 20 is returned to the pump 26. The coolant from the first heat exchange unit 19 is sent to the inlet of the third heat exchange unit 24 and then to the fourth heat exchange unit 25. The coolant from the fourth heat exchange unit 25 is then sent to the pump 26. The gas from the gas-based laser system is sent from the compressor 21 to the first heat exchange unit 19, and then, as soon as it is heated above 220°C, it is sent to the second heat exchange unit 20 before being sent through the gas-based laser amplification unit 25. The high-temperature gas leaves the amplification unit 25 and is then sent to the third and fourth heat exchange units 24 and 25 before being returned to the compressor 26.
[0045]
[0048] Figure 4 is similar to Figure 3, but the cooling circuit is divided into two. In particular, the second heat exchange element 20 is provided with a cooling circuit separated from the cooling circuit connected to the other heat exchange element. By providing a separate cooling circuit, the coolant in the first circuit, which includes the first, third, and optionally fourth heat exchange units, is cooled using atmospheric cooling, while the second cooling circuit can actively cool its associated coolant. This makes it possible to bring the coolant to a lower temperature when it enters the second heat exchange element, and to cool the gas to a lower temperature before it enters the amplification unit 25. The temperature of the coolant exiting the heat exchanger 29 may be about 6°C or lower, and the coolant returning to the compressor 28 may be about 11°C. A separate cooling unit may be provided to provide coolant at a temperature of 0°C or lower.
[0046]
[0049] To quantify the advantages of this disclosure, generating a 30kW laser beam from a gas-based laser requires the use of nearly 500kW of power to generate nearly 400kW of radio frequency (RF) energy, with the remainder lost as heat. This requires approximately 30kW of cooling power to return the cooling water to its original temperature. To generate 30kW of laser energy, 400kW of RF energy and an additional 250kW of pump power are used. Approximately 130kW of energy is also required to cool the coolant. Thus, a large amount of energy is required not only to generate the laser beam but also to cool the coolant necessary for the laser to function.
[0047]
[0050] In a system in which a single pump drives the flow through first and second heat exchange units, a total of 130 kW of energy is required to cool the coolant by driving a chiller. In the heat exchange unit, most of the thermal energy in the initial portion is removed. Therefore, as the coolant flows along the heat exchange unit, the amount of cooling provided along the unit decreases. In contrast, the present disclosure allows most of the thermal energy to be removed by the first heat exchanger, and this thermal energy can be removed by atmospheric cooling, which requires little to no electricity, as atmospheric cooling requires only pump power and does not require forced cooling via a chiller. As a result, only a small portion of the initial thermal energy is removed via the chiller or other active cooling. A considerable amount of electrical energy can be saved by reducing the amount of active cooling required. Furthermore, if the gas in the first heat exchange unit is at a high temperature, the temperature difference between the gas and the coolant will be large, such as 50°C or more. Therefore, the final temperature of the gas exiting the second heat exchange element depends on the temperature of the second heat exchange element, not the first heat exchange unit, and thus the temperature of the coolant in the first heat exchange element is not very important. Consequently, it is possible to control the temperature of the second heat exchange unit in order to control the temperature of the gas after it leaves the heat exchanger. By dividing the cooling circuit into two, a considerable proportion of thermal energy can be removed by the first heat exchange unit without the need for active cooling, thereby reducing the overall cooling requirement of 100kW or more.
[0048]
[0051] While additional energy is required to lower the coolant temperature to approximately 6°C or below, or even below 0°C, this allows the laser beam output to be increased to a maximum of approximately 1 kW. Furthermore, since the second cooling circuit only needs to remove a small portion of the total thermal energy, lowering the coolant temperature to increase the laser beam output is energetically advantageous overall. For example, with a coolant temperature of -15°C, the calculated power gain is approximately 2.5 kW compared to the same carbon dioxide laser with a coolant temperature of 18°C.
[0049]
[0052] It will be understood that various aspects of the present invention may be provided individually or in combination.
[0050]
[0053] While this text specifically refers to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein has other applications. For example, these include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), and thin-film magnetic heads. The substrates described herein can be processed before or after exposure with, for example, track (usually a tool for coating a layer of resist onto the substrate and developing the exposed resist), metrologic tools, and / or inspection tools. Where appropriate, the disclosure herein can be applied to the above and other substrate processing tools. Furthermore, the substrate can be processed multiple times, for example, to produce a multilayer IC, and therefore the term "substrate" as used herein can also refer to a substrate that already contains multiple processed layers.
[0051]
[0054] Although specific embodiments of the present invention have been described above, it goes without saying that the present invention can be implemented in ways other than those described above.
[0052]
[0055] The above description is illustrative and not limiting. Therefore, it will be clear to those skilled in the art that modifications to the described invention can be made without departing from the claims.
Claims
1. A gas-based laser comprising a heat exchanger for cooling a compressed gas from a first temperature to a second temperature lower than the first temperature, The heat exchanger is, The first of at least two heat exchange elements is arranged to cool the compressed gas from the first temperature to an intermediate temperature lower than the first temperature, and The second heat exchange element among the at least two heat exchange elements is arranged to cool the compressed gas from the intermediate temperature to the second temperature which is lower than the intermediate temperature. It comprises at least two heat exchange elements characterized by, A gas-based laser wherein the first and second heat exchange elements are placed in two mutually exclusive heat transfer circuits, and the inlet temperature of the coolant in the second heat transfer circuit is lower than the inlet temperature of the coolant in the first heat transfer circuit.
2. The gas-based laser according to claim 1, wherein the first heat exchange element is configured to cool the compressed gas from about 100°C to about 35°C, preferably to about 20°C.
3. The gas-based laser according to claim 1 or 2, wherein the second heat exchange element is configured to output a compressed gas cooled at a temperature of less than approximately 35°C, less than approximately 20°C, less than approximately 15°C, less than approximately 10°C, less than approximately 5°C, less than approximately 0°C, less than approximately -5°C, less than approximately -10°C, less than approximately -15°C, less than approximately -20°C, less than approximately -25°C, less than approximately -30°C, less than approximately -35°C, less than approximately -40°C, or less than approximately -45°C.
4. The first heat exchange element is connected to an atmospheric cooling system. The gas-based laser according to any one of claims 1 to 3, wherein the second heat exchange element is connected to a forced cooling system.
5. The gas-based laser according to any one of claims 1 to 4, wherein the first heat exchange element is selectively connected to a forced cooling system.
6. The gas-based laser according to any one of claims 1 to 5, wherein the first heat exchange element includes an outlet that is in fluid communication with the inlet of a third heat exchange element located downstream of the amplification section of the gas-based laser, and an optional fourth heat exchange element located downstream of the third heat exchange element.
7. The gas-based laser according to claim 6, wherein the third heat exchange element or the optionally selected fourth heat exchange element is in fluid communication with a compressor configured to compress the gas used in the laser.
8. The gas-based laser according to any one of claims 1 to 7, wherein the output of a compressor configured to compress the gas used in the laser is in fluid communication with the inlet of the first heat exchange element.
9. The gas-based laser according to any one of claims 1 to 8, wherein the second heat exchange element is housed in an adiabatic environment configured to avoid condensation of water vapor in the atmosphere, and / or in a humidity-controlled atmosphere configured to avoid condensation of water vapor in the atmosphere.
10. The gas-based laser according to any one of claims 1 to 9, wherein the coolant comprises water, glycol, alcohol, or a mixture of two or more thereof, and optionally the glycol is selected from ethylene glycol, propylene glycol, and mixtures thereof.
11. A gas-based laser according to any one of claims 1 to 10, wherein one or both of the first and second heat exchange elements are configured to provide a coolant at a temperature of less than about 35°C, less than about 30°C, less than about 25°C, less than about 20°C, less than about 15°C, less than about 10°C, less than about 5°C, less than about -5°C, less than about -10°C, less than about -15°C, less than about -20°C, less than about -25°C, less than about -30°C, less than about -35°C, less than about -40°C, or less than about -45°C.
12. A lithography apparatus comprising a gas-based laser according to any one of claims 1 to 9.
13. The lithography apparatus according to claim 10, wherein the lithography apparatus is an EUV lithography apparatus.
14. A method for improving the efficiency of a gas-based laser, a) Cooling the compressed gas in the first heat exchange element from a first temperature to an intermediate temperature lower than the first temperature, b) Cooling the compressed gas in a second heat exchange element from the intermediate temperature to a second temperature lower than the intermediate temperature, The first and second heat exchange elements are placed within two mutually exclusive heat transfer circuits. A method wherein the inlet temperature of the coolant in a second heat transfer circuit including the second heat exchange element is lower than the inlet temperature of the coolant in a first heat transfer circuit including the first heat exchange element.
15. The system further includes sending the coolant from the first heat exchange element to the third heat exchange element, and optionally sending the coolant from the third heat exchange element to the fourth heat exchange element. The method according to claim 14, wherein the first, third, and optionally selected fourth heat exchange elements are arranged within the first heat transfer circuit.
16. The method according to claim 15, wherein the method includes cooling the coolant within the first heat transfer unit via an atmospheric cooling system.
17. The method according to any one of claims 14 to 16, wherein the method comprises cooling the coolant by a forced cooling system within the second heat transfer circuit.
18. Use of a gas-based laser according to any one of claims 1 to 11, a lithography apparatus according to claim 12 or 13, or a lithography apparatus or method according to any one of claims 14 to 17.