Enhanced thermal conductivity in vacuum

Abstract

A bonded component for a lithographic apparatus comprising a joint (16) between two or more mating surfaces (17a, 19a), at least one of the mating surfaces comprising tin (18). The bonded component for the lithographic apparatus comprises a joint between two or more components (17, 19) formed of a material other than tin, the two components being joined at their respective mating surfaces, at least one of the mating surfaces comprising tin. A lithographic apparatus comprising a bonded component comprising a tin layer, the use of tin as a thermally conductive interface material in a lithographic apparatus, and a method for increasing the thermal conductivity of a bonded connection in a lithographic apparatus are also described.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 62 / 950,869, filed December 19, 2019, entitled ENHANCED THERMAL CONDUCTIVITY IN VACUUM, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to bonded components for lithographic apparatus, the use of tin as a thermally conductive interface material in lithographic apparatus, and methods for increasing the thermal conductivity of bonded connections in lithographic apparatus. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004]

[0004] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on the substrate. Lithographic apparatus that use extreme ultraviolet (EUV) radiation, which is electromagnetic radiation having a wavelength in the range of 4 to 20 nm, can be used to form smaller features on a substrate than lithographic apparatus that use electromagnetic radiation having a higher wavelength, for example 193 nm.

[0005]

[0005] During operation, EUV lithography apparatus generate a lot of heat, which must be managed. This can be achieved by providing heat sinks, cooling channels, or other cooling means. To aid in thermal control, it is desirable to have good thermal transfer between components of the lithography apparatus. While direct cooling of aluminum components is possible, there is a risk of leakage, which is clearly undesirable. To increase the thermal conductivity of the joints, thin foils or thermal pastes may be applied to the joints between components, but thin foils are difficult to handle and require manual labor to apply. Therefore, there is a high risk of contamination caused by parts of the thin foil or thermal paste peeling off, as well as a high risk of incorrect application of the thin foil or thermal paste.

[0006]

[0006] The techniques and structures described herein are intended to address or overcome one or more of the problems set forth above. Summary of the Invention

[0007]

[0007] According to a first aspect of the devices and techniques described in this specification, a bonded component for a lithographic apparatus is provided having a bond between two or more mating surfaces, at least one of the mating surfaces comprising tin.

[0008]

[0008] According to one aspect of the devices and techniques described herein, there is provided a joined component for a lithographic apparatus comprising a joint between two or more components formed of a material other than tin, the two components being joined at their respective mating surfaces, one or more of the mating surfaces comprising a tin surface. The one or more mating surfaces comprising tin may comprise a thin layer of tin. The thin layer of tin may be a tin coating formed by electroplating or other methods. The thin tin coating added between two like metals helps prevent the parts from cold welding in a vacuum and allows for part refurbishment. The two components may be formed of the same material, for example, both may be formed of aluminum or both may be formed of stainless steel. The two components may be formed of different materials, for example, one component may be formed of aluminum and the other may be formed of stainless steel.

[0009] EUV radiation is generally produced by applying energy to a target material (sometimes referred to as "fuel") such as tin via a laser beam, creating a plasma that emits EUV radiation upon de-excitation and recombination of the plasma's ions with electrons. Due to the method of generating EUV radiation, i.e., illuminating tin droplets with a laser to form a tin plasma, a high tin vapor pressure exists in the area of ​​the collector mirror, and tin atoms can deposit on the collector's surface. Thus, because tin is already present in the lithography apparatus, adding tin as a thermally conductive layer between components to be bonded in the lithography apparatus does not present a potential source of contaminants that was not previously present. In contrast, thermal paste or metal foil, most commonly indium foil, would present a new source of contaminants. While it will be appreciated that in bonded components, the mating surfaces of the components that form the bond will abut and therefore tend to retain material between the mating surfaces, meaning that the choice of material for the bond is seemingly irrelevant, even small amounts of contamination present in the lithography apparatus can have deleterious effects. The presence of tin at one or more mating surfaces comprising the bond enhances heat transfer through the bond by up to an order of magnitude, allowing the component to be cooled (or heated, if necessary) more effectively than one that does not have tin at the bond interface. Even if some tin does enter the lithography apparatus through the bond, it is not a new type of contaminant, and because there is already a tin mitigation in place, the tin contamination from the bond can be addressed without the need for any additional mitigation.

[0010]

[0010] Tin can be in a metallic form. Because metallic tin is used to generate EUV radiation, lithographic apparatus are configured to accommodate the presence of metallic tin. The use of tin alloys or compounds would introduce additional potential contaminants that may require specific mitigation features to be provided within the apparatus. Metallic tin also has advantageous thermal properties that provide favorable heat transfer characteristics.

[0011]

[0011] Tin can be provided on one or more of the mating surfaces comprising the joint. It will be understood that there can be more mating surfaces comprising the joint, but most joints comprise two mating surfaces. If tin is provided on only one of the mating surfaces, the tin will be disposed between the mating surfaces of the components when the components forming the joint are brought together. Similarly, if both mating surfaces comprise tin, the result will also include the presence of tin between the two components forming the joint.

[0012]

[0012] The tin may be provided as a layer. Because the components forming the joint are generally formed from stainless steel or aluminum, it is not necessary for the majority of the components forming the joint to be made from tin; a layer of tin between the components forming the joint is sufficient. In one embodiment, one component is a stainless steel component and the other component is an aluminum component. In some embodiments, the components may each be formed from stainless steel. In some embodiments, the components may each be formed from aluminum. In some embodiments, the components may each be formed from the same material, which is a material other than tin. In other embodiments, the components may be formed from other suitable materials.

[0013] The tin layer may have a thickness of about 0.1 microns to about 20 microns. The tin layer may have a thickness of about 1 micron to about 15 microns. The tin layer may have a thickness of about 5 microns to about 10 microns. The presence of even a very thin tin layer increases the contact conductance of the aluminum component compared to an uncoated aluminum component. The contact conductance of a 0.1 micron thick tin layer on aluminum is about 38 kW / m for uncoated aluminum. 2 K, compared to approximately 80 kW / m 2 K(p=2000kN / m 2, at RMS roughness σ=4 μmm m=2. And at a thickness of 5 to 10 microns, tin has a coefficient of about 105 kW / m 2 Tin has a thermal contact conductance of 0.1K. Also, the thermal contact conductance of tin is somewhat insensitive to surface roughness and clamping force, so it remains effective even as roughness increases or clamping force decreases. In any case, the thermal contact conductance of a joint with tin is much greater than that without tin (e.g., aluminum to aluminum). Thus, the presence of tin increases the thermal contact conductance compared to an uncoated joint under any surface roughness or clamping pressure.

[0014]

[0014] The tin can be an electroplated tin layer. Applying the tin by electroplating provides a tin layer with a uniform plating thickness and eliminates the need for manual steps (such as applying metal foil or thermal paste). This reduces the risk of errors during assembly and also reduces the possibility of contamination. In various circumstances, other techniques for applying the tin are also possible, such as vapor deposition or flow application.

[0015]

[0015] The joint can be a bolted joint. A bolted joint is a joint in which one or more bolts provide a clamping force to secure two or more components together. The bolts provide the clamping force against a tin layer captured within the joint. Because the mating surfaces of the components forming the joint are held together, there is heat transfer through the joint, which is assisted by the presence of the tin layer.

[0016]

[0016] Tin is provided on a mating surface, which may be part of a component comprising one of aluminum or stainless steel. As previously mentioned, in a lithographic apparatus, the component may be made from stainless steel or aluminum. Other materials may be used, but aluminum and stainless steel are the most prevalent. Tin may be provided at the joint between an aluminum and a stainless steel joint. Tin may also be provided at the joint between two of the same material. Tin is advantageous because it is inert to both aluminum and stainless steel, and therefore its presence is not likely to damage the component.

[0017]

[0017] The bonded component may be any component that includes a bond. The bonded component may be a thermal management element. As mentioned above, during operation, a lithographic apparatus generates a lot of heat and it is necessary to ensure that the components do not overheat. It is therefore necessary to provide cooling to the components. The thermal management element may be a cooling device configured to transfer heat away from a given area of ​​the lithographic apparatus.

[0018]

[0018] The components to be joined may include at least one coolant channel. The coolant channel may be configured to receive water as a coolant, although any other suitable coolant may be used. The coolant may be a liquid or a gas and may change phase upon passing along the coolant channel. The coolant channel may have any suitable shape and profile, and the present invention is not limited by the particular shape or dimensions of the coolant channel.

[0019]

[0019] The coolant channel may include a stainless steel passage configured to receive the coolant flow. Stainless steel is more leak resistant than aluminum and is therefore highly suitable for use in the cooling channel.

[0020]

[0020] The tin can be substantially pure. For example, the tin can be greater than 95%, greater than 99%, or greater than 99.9% pure. Having high purity tin reduces the risk of contamination with other substances that may be more difficult to deal with in a lithographic apparatus.

[0021] According to a second aspect of the devices and techniques described herein, there is provided a lithographic apparatus including a bonded component according to the first aspect.

[0022]

[0022] The presence of a bonded connection comprising tin results in a significant increase in thermal conductivity across the bond, resulting in improved heat transfer between the components being joined.

[0023]

[0023] In this way, components made of different materials, such as aluminum and stainless steel, can be connected, and the thermal conductance between the different materials is improved by the presence of tin between them. Suitable materials for different components, such as stainless steel for the coolant channels, can be combined without resulting in a decrease in thermal conductance. If the thermal conductance is too low, the transfer of heat from one component to another will be reduced, and therefore the cooling of the components may be reduced. This can lead to overheating of the components, which is undesirable.

[0024] According to a third aspect of the devices and techniques described herein, there is provided the use of tin as a thermally conductive interface material in a lithographic apparatus.

[0025]

[0025] Metal foils and thermal pastes have been used to increase thermal conductance, but this has been limited to the electronics packaging industry. For example, thermal pastes are commonly used in computers to avoid the presence of an insulating air layer between the processor (which heats up during use) and the associated heat sink. Thermal pastes comprise a matrix material, usually a polymer, and an electrically insulating but thermally conductive filler. The use of thermal paste in lithography equipment would result in contamination. Also, temperatures reached in computers are typically lower than approximately 60°C, while temperatures reached in lithography equipment are typically much higher. Furthermore, tin results in lower contact conductance compared to corresponding lead layers, all else being equal. Even so, tin is preferred in EUV lithography equipment due to its properties of generating EUV radiation because tin does not introduce new types of potential contaminants into the equipment.

[0026]

[0026] According to a fourth aspect of the devices and techniques described in this specification, there is provided a method for increasing the thermal conductivity of a bonded connection in a lithographic apparatus, the method comprising providing a tin layer to the bonded connection.

[0027] As explained, the presence of a tin layer at the bonded connection greatly enhances the thermal conductivity of the bond, while also mitigating the risk of introducing additional contamination into the device.

[0028]

[0028] It will be understood that any feature described with respect to one embodiment may be combined with any feature described with respect to another embodiment, and all such combinations are expressly contemplated and disclosed in this specification. [Brief explanation of the drawings]

[0029]

[0029] Various system and technique embodiments are now described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts and in which:

[0030] [Figure 1]

[0030] A lithographic apparatus is depicted. [Figure 2]

[0031] 1 illustrates a schematic diagram of components of a lithographic apparatus;

[0031]

[0032] The features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the drawings, in which like reference numerals identify corresponding elements throughout and in which like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION OF THE INVENTION

[0032]

[0033] Figure 1 shows a lithography system. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate a beam of extreme ultraviolet (EUV) radiation 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 condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In this embodiment, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W. In this embodiment, a contamination blocking pellicle 15 is shown in the path of the radiation to protect the patterning device MA. It will be understood that the pellicle 15 may be in any required position and may also be used to protect any of the mirrors in the lithography apparatus.

[0033]

[0034] The source SO, illumination system IL, and projection system PS may all be constructed and arranged so as to be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the source SO. A vacuum may be provided in the illumination system IL and / or projection system PS. A small amount of gas (e.g., hydrogen) at a pressure significantly below atmospheric pressure may be provided in the illumination system IL and / or projection system PS.

[0034]

[0035] The radiation source SO shown in FIG. 1 is of a type that may be referred to as a laser-produced plasma (LPP) source. A laser, which may be, for example, a CO laser, is arranged to deposit energy via a laser beam onto a target material, such as tin (Sn), provided from a target material emitter. While the following description refers to tin, any suitable target material may be used. The target material may be, for example, in liquid form, and may be, for example, a metal or alloy. The target material emitter may include a nozzle configured to direct tin, for example, in the form of droplets, along a trajectory toward the plasma formation region. The laser beam is incident on the tin in the plasma formation region. Deposition of laser energy on the tin creates a plasma in the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma upon de-excitation and recombination of the ions of the plasma.

[0035]

[0036] The EUV radiation is collected and focused by a near-normal incidence radiation collector (sometimes more commonly referred to as a normal incidence radiation collector). The collector may have a multi-layer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength, such as 13.5 nm). The collector may have an elliptical shape and have two elliptical foci. The first focus may be at the plasma formation region, and the second focus may be at an intermediate focus, as described below.

[0036]

[0037] The laser may be separate from the radiation source SO, in which case the laser beam may be passed from the laser to the radiation source SO with the aid of a beam delivery system (not shown), e.g., comprising appropriate directing mirrors and / or beam expanders and / or other optical components. The laser and radiation source SO may together be considered a radiation system.

[0037]

[0038] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is positioned such that the intermediate focus is located at or near an aperture in an containing structure of the radiation source.

[0038]

[0039] The radiation beam B enters from the radiation source SO into an illumination system IL configured to condition the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Together the facetted field mirror device 10 and facetted pupil mirror device 11 provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes through the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA reflects and pattern the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and facetted pupil mirror device 11.

[0039]

[0040] Following reflection from the patterning device MA, the patterned radiation beam B enters a projection system PS. The projection system comprises a number of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a demagnification factor to the radiation beam to form an image with smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of four may be applied. Although in Figure 1 the projection system PS has two mirrors 13, 14, the projection system may include any number of mirrors (for example six mirrors).

[0040]

[0041] The radiation source SO shown in Figure 1 may include components that are not shown, for example the radiation source may be provided with a droplet generator, a tin catcher, a hydrogen flow nozzle, and an exhaust outlet.

[0041]

[0042] FIG. 2 is a schematic depiction of a bonded connection 16. A thin layer of tin 18 is disposed between mating surfaces 17a, 19a of a first component 17 and a second component 19. In an exemplary embodiment, the first component 17 can be aluminum, and the second component 19 can be stainless steel. In the illustrated embodiment, the tin layer 18 is approximately 5 microns to approximately 10 microns thick, although it will be understood that thinner or thicker layers can be used. The tin layer 18 can be natively formed on the mating surface 17a, or natively formed on the mating surface 19a, or can be formed on each of the mating surfaces 17a and 19a. The tin layer 18 can be formed on either or both surfaces by electroplating or other suitable methods.

[0042]

[0043] The first component 17 may be part of a cooling device for a collector mirror of an EUV lithography apparatus, such as a collector flow ring, and the second component 19 may be a stainless steel channel with coolant channels 20 configured to receive a coolant, such as water.

[0043]

[0044] In use, the first component 17 is exposed to a heat source, such as a plasma generated in a lithography apparatus. Thermal energy is absorbed by the first component 17, causing it to heat up. While previously, thermal energy was transferred directly from the first component 17 to the second component 19, the rate of heat transfer can be increased by the presence of the tin layer 18, thereby more efficiently cooling the components exposed to the thermal energy. Thermal energy can be transferred from the first component 17 to the tin layer 18 and then to the second component 19 more efficiently than without the tin layer 18. If the second component 19 includes coolant channels 20, the thermal energy is transferred to the coolant, which carries the thermal energy away.

[0044]

[0045] It will be understood that the tin layer may be continuous or discontinuous, and it will also be understood that the tin layer may extend over substantially the entire area of ​​the joint or may only partially extend over the area of ​​the joint.

[0045]

[0046] It will be understood that various aspects of the concepts described herein may be provided or combined. While particular reference is made herein to the use of lithography apparatus in the manufacture of ICs, it should be understood that the lithography apparatus described herein have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. The substrates described herein may be processed, before or after exposure, in, for example, a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce a multi-layer IC, and thus the term substrate, as used herein, may also refer to a substrate that already includes multiple processed layers.

[0046]

[0047] While specific embodiments of the present invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, various layers may be replaced by other layers which perform the same functions.

[0047]

[0048] The above description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications to the invention as described may be made without departing from the scope of the claims below. Other aspects of the invention are described in the following numbered examples.

[0048] Example A1. A bonded component for a lithographic apparatus comprising a bond between two or more mating surfaces, at least one of the mating surfaces comprising tin. Example A2. The joined components of Example A1, wherein the tin is in a metallic state. Example A3. The joined components of Example A1, wherein tin is provided on one or more of the mating surfaces comprising the joint. Example A4. The joined components of Example A1, wherein the tin is provided as a layer. Example A5. The joined component of Example A4, wherein the tin layer has a thickness of from about 0.1 microns to about 20 microns. Example A6. The joined component of Example A1, wherein the tin is an electroplated tin layer. Example A7. The joined components of Example A1, where the joint is a bolted joint. Example A8. The joined components of Example A1, wherein the tin is provided as a layer on the mating surface of the first component, the first component comprising one of aluminum and stainless steel. Example A9. The joined components of Example A8, further comprising a second component joined to the first component at a joint, the second component being formed from the other of aluminum and stainless steel. Example A10. The bonded component of Example A1, wherein the bonded component is a thermal management element. Example A11. The joined component of Example A1, wherein the component comprises at least one coolant channel comprising a stainless steel passage configured to receive a flow of coolant. Example A12. The joined components of Example A2, wherein the tin metal is substantially pure tin. Example A13. A lithographic apparatus comprising a bonded component according to Example A9. Example A14. A method of increasing the thermal conductivity of a bonded connection of a component of a lithographic apparatus, the method comprising providing a tin layer on the bonded connection. Example A15. Bonded components for a lithographic apparatus comprising a bond between two or more components formed of a material other than tin, the two components being bonded at their respective mating surfaces, at least one of the mating surfaces comprising tin. Example A16. The joined components of Example A15, wherein the two or more components are each formed from the same material. Example A17. The joined components of Example A16, wherein the two or more components each comprise stainless steel. Example A18. The joined components of Example A16, wherein the two or more components each comprise aluminum. Example A19. The joined components of Example A15, wherein one of the components is formed from aluminum and the other of the components is formed from stainless steel. Example A20. The joined components of Example A15, wherein one of the mating surfaces has a tin coating. Example B1. Use of tin as a thermally conductive interface material in a lithography apparatus. Example C1. A method of increasing the thermal conductivity of a bonded connection in a lithographic apparatus, the method comprising providing a tin layer on the bonded connection.

Claims

1. 1. A bonded component for an EUV lithography apparatus comprising a bond between two or more mating surfaces, at least one of the mating surfaces comprising a tin layer, the tin layer being substantially pure tin, the tin layer being provided on a mating surface of a first component, the first component comprising one of aluminum and stainless steel, and the joint being a bolted joint.

2. A bonded component for an EUV lithography apparatus having a joint between two or more mating surfaces, at least one of the mating surfaces having a tin layer, the tin layer being substantially pure tin, the tin layer being provided on a mating surface of a first component, the first component comprising one of aluminum and stainless steel, and further comprising a second component bonded to the first component at the joint, the second component being formed from the other of the aluminum and stainless steel.

3. The bonded component of claim 1 or 2, wherein the tin layer has a thickness of from about 0.1 microns to about 20 microns.

4. 3. The joined component of claim 1, wherein the tin layer is an electroplated tin layer.

5. The joined component of claim 1 or 2, wherein the component comprises at least one coolant channel comprising a stainless steel passage configured to receive a flow of coolant.

6. 3. An EUV lithography apparatus comprising a bonded component according to claim 1 or 2.

7. 1. A bonded component for an EUV lithography apparatus comprising a bond between two or more components formed of a material other than tin, the two components being bonded at their respective mating surfaces, at least one of the mating surfaces comprising a tin layer, the tin layer being substantially pure tin, any of the two or more components comprising stainless steel or aluminum, and the two or more components each being formed of the same material.

8. A bonded component for an EUV lithography apparatus having a joint between two or more components formed of a material other than tin, the two components being bonded at their respective mating surfaces, at least one of the mating surfaces having a tin layer, the tin layer being substantially pure tin, one of the components being formed of aluminum and the other of the components being formed of stainless steel.

9. The joined components of claim 7 , wherein the two or more components each comprise stainless steel.

10. The joined components of claim 7 , wherein the two or more components each comprise aluminum.

11. 1. A bonded component for an EUV lithography apparatus comprising a bond between two or more components formed of a material other than tin, the two components being bonded at respective mating surfaces, at least one of the mating surfaces comprising a tin layer, the tin layer being substantially pure tin, and the two or more components each comprising stainless steel or aluminum.

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