Conditioning system, sub-atmospheric pressure conditioning method, method of conditioning a system, and related lithographic apparatus and method

Abstract

The present invention provides an adjustment system for a lithography apparatus, the adjustment system being configured to adjust one or more optical elements of the lithography apparatus, wherein the adjustment system is configured to have a low pressure at the one or more optical elements. Also provided is a lithography apparatus including such an adjustment system, an application of such an adjustment system, a method for adjusting a system, and a lithography method including a low-pressure cooling system.

Description

Technical Field

[0001] This invention relates to an adjustment device for a lithography apparatus, an assembly for a lithography apparatus including such an adjustment device, the use of a low-pressure adjustment device in a lithography apparatus, and a method for adjusting a system or subsystem of a lithography apparatus. Prior Technology

[0002] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. Lithography apparatuses can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus can project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate.

[0003] The wavelength of radiation used by a lithography apparatus to project a pattern onto a substrate determines the minimum size of a feature that can be formed on that substrate. Compared to conventional lithography apparatuses (which may, for example, use electromagnetic radiation with a wavelength of 193 nm), lithography apparatuses using EUV radiation with electromagnetic radiation having wavelengths in the range of 4 nm to 20 nm can be used to form smaller features on a substrate.

[0004] It is difficult to collect EUV radiation into a beam, guide it onto a patterned device (e.g., a mask), and project the patterned beam onto a substrate because it is impossible to fabricate refractive optical elements for EUV radiation. Therefore, reflectors (i.e., mirrors) must be used to perform these functions. Even constructing reflectors for EUV radiation is difficult. The best available normal-incident reflector for EUV radiation is a multilayer reflector (also known as a distributed Bragg reflector) consisting of numerous layers alternating between relatively high-refractive-index and relatively low-refractive-index layers. Each cycle of high-refractive-index and low-refractive-index layers has a thickness equal to half the wavelength (λ / 2) of the radiation to be reflected, resulting in constructive interference between the reflected radiation at the high-to-low refractive-index boundary. Such multilayer reflectors do not achieve particularly high reflectivity, and a significant proportion of the incident radiation is absorbed by the multilayer reflector.

[0005] Absorbed radiation, including infrared radiation emitted by the radiation source, can cause temperature rise in multilayer reflectors. Multilayer reflectors are known to be formed on substrates made of materials with extremely low coefficients of thermal expansion, such as ULE™. However, in some cases, the cross-section of the beam incident on the reflector can be small enough that localized heating of the reflector causes undesirable deformation of the reflector's surface profile. Such deformation leads to imaging errors, and the continued need for imaging smaller features means that the amount of permissible deformation will only decrease.

[0006] Existing reflectors in lithography devices, particularly EUV projection systems, are passively cooled, i.e., cooled by radiation, conduction, and convection. However, none of these cooling methods allows for high heat transfer rates. Specifically, reflectors are typically operated in high vacuum or low hydrogen pressure, minimizing heat transfer via convection. Active cooling of reflectors has been avoided because the risk of introducing vibrations into the reflector is potentially more problematic than deformation caused by localized heat build-up.

[0007] WO2017 / 153152 describes a reflector for EUV radiation, comprising a reflector substrate and a reflective surface. The reflector substrate has a plurality of coolant channels formed therein, the coolant channels being substantially linear, substantially parallel to each other, and substantially parallel to the reflective surface, and configured such that coolant flows parallel through the coolant channels and contacts the reflector substrate. By providing linear coolant channels that are parallel to each other and parallel to the reflective surface, the coolant can be circulated to control localized temperatures without causing problematic vibrations in the reflector.

[0008] The present invention has been designed to provide an improved or alternative adjustment system for lithography devices. Summary of the Invention

[0009] According to a first aspect of the present invention, an adjustment system for a lithography apparatus is provided, the adjustment system being configured to adjust one or more optical elements of the lithography apparatus, wherein the adjustment system is configured to have low air pressure at one or more optical elements.

[0010] According to a second aspect of the present invention, an adjustment system for a lithography apparatus is provided, the adjustment system being configured to adjust one or more optical elements of the lithography apparatus, wherein the adjustment system is configured to have low pressure at one or more optical elements, wherein the adjustment system includes a liquid conditioning fluid, preferably water, and wherein the system includes a low-pressure conditioning fluid reservoir for storing at least a portion of the liquid conditioning fluid.

[0011] According to a third embodiment of the present invention, an adjustment system for a lithography apparatus is provided, the adjustment system being configured to adjust one or more optical elements of the lithography apparatus, wherein the adjustment system is configured to have low air pressure at one or more optical elements, and wherein the adjustment system includes a liquid adjustment fluid, preferably water, and wherein the system includes a pump downstream of the optical element and a flow limiter upstream of the optical element.

[0012] According to a fourth embodiment of the present invention, an adjustment system for a lithography apparatus is provided, the adjustment system being configured to adjust one or more optical elements of the lithography apparatus, wherein the adjustment system is configured to have low air pressure at one or more optical elements, and wherein an adjustment fluid reservoir is disposed below the optical elements such that the hydrostatic pressure difference between the optical elements and the adjustment fluid reservoir reduces the pressure at the optical elements to below atmospheric pressure.

[0013] According to a fifth aspect of the present invention, an adjustment system for a lithography apparatus is provided, the adjustment system being configured to adjust one or more optical elements of the lithography apparatus, wherein the adjustment system is configured to have low air pressure at one or more optical elements, and wherein the system includes first and second regulating fluid reservoirs, wherein the first and second regulating fluid reservoirs are fluidly connected to each other via valves, the valves being operable to control the level of regulating fluid in the regulating fluid reservoirs in fluid communication with the optical elements.

[0014] Water conditioning systems can be used to condition modules. In this context, conditioning encompasses adding or removing heat from the module. Thus, cooling refers to the removal of heat and not necessarily a decrease in temperature. Similarly, heating refers to the addition of heat and not necessarily a decrease in temperature. It should be understood that the operating temperature of any optical element needs to be kept as constant as possible or at least within a controlled temperature range. Although this application focuses primarily on and refers to cooling, it should also be understood that in some situations, the system can be used to heat modules or sub-modules of a lithography apparatus. Conditioning systems typically include thermal control components such as heat exchangers, heaters, and / or coolers, and optionally include temperature sensors. Such systems also typically include a water bath or reservoir open to or pressurized by the atmosphere, a pump for delivering the water flow, and a distribution system typically including pipes, manifolds, and the like. The system is designed to handle and operate at water pressures of approximately 3 to 8 bar. While higher pressures can be used, additional safety requirements exist for systems operating above approximately 10 bar, making them generally less desirable. However, pressure differences can cause mechanical stress and deformation, but these pressure differences are usually not a problem because the precise shape of the components has a very small (if any) effect on the operation of the device. However, lithography devices, especially EUV lithography devices, are extremely sensitive to any deformation, even the smallest deformation, of their optical elements.

[0015] It has been found that if the relative pressure between the conditioning system and the outside of the optical element is greater than atmospheric pressure, the surface of the optical element will deform, and this deformation affects the performance of the optical element. Since the conditioning system is used in lithography apparatuses, the main parts of the lithography apparatus to be conditioned are under vacuum or only under extremely low pressure in a gas (usually hydrogen), regardless of whether cooling or heating is used. Therefore, it has been found that low pressure is required to avoid associated performance losses due to deformation of critical components. Although this has previously been mitigated by providing deeper conditioning channels within the substrate of the conditioning system, the impact on thermal performance and the conditioning provided are insufficient when it is necessary to extend the conditioning channels deep into the substrate to reduce or eliminate deformation. By providing a conditioning system configured to operate at low pressure at one or more optical elements, i.e., with low operating pressure, the deformation of the surface of the conditioned optical element is eliminated or at least reduced to an acceptable level, and it is possible to provide conditioning fluid in channels that are not deep within the substrate, which means improved thermal efficiency. In the context of this application, low pressure is a pressure of less than 1 bar.

[0016] An adjustment system is configured to adjust one or more optical elements of a lithography apparatus. One or more of these optical elements may be reflectors. Adjustment may also be referred to as thermal adjustment. To adjust the optical elements, the adjustment system needs to be in thermal communication with one or more optical elements of the lithography apparatus. The optical elements therefore have adjustment fluid channels configured to allow adjustment fluid to flow through these channels. In this invention, the pressure within such adjustment fluid channels is low, i.e., less than 1 bar. In use, the optical elements and other units of the lithography apparatus will experience an increase in temperature unless cooled. This is because the optical elements are exposed to radiation used in the lithography process, and some of these optical elements are absorbed, resulting in an increase in temperature. If the optical elements are not cooled, they will become hot and their performance will be adversely affected. As the operating power of the lithography apparatus increases, it is necessary to similarly increase the adjustment capability, particularly the cooling capability, of such apparatus. In other cases, it may be necessary to provide heat energy to the components of the lithography apparatus to bring them to the desired operating temperature.

[0017] The regulating system can be configured to operate between approximately 0.02 bar and approximately 0.9 bar. The system preferably operates at a minimum pressure of not less than 0.02 bar. The system can operate at approximately 0.2 bar to approximately 0.8 bar. The system can operate at approximately 0.1 bar, approximately 0.2 bar, approximately 0.3 bar, approximately 0.4 bar, approximately 0.5 bar, approximately 0.6 bar, approximately 0.7 bar, approximately 0.8 bar, or approximately 0.9 bar. Approximately 0.3 bar has been found to be a particularly suitable operating pressure. As mentioned above, by operating below atmospheric pressure (1 bar), it is possible to avoid problems associated with deformation caused by using pressures above 1 bar, and it also allows for any regulating channel to be provided closer to the surface to be regulated compared to other conditions, thereby improving regulating efficiency. Of course, if the pressure is too low, there is a risk of cavitation, and there will not be a sufficient pressure differential to induce flow of the regulating fluid. Furthermore, if the system pressure is below the vapor pressure of the regulating fluid (which may be water), the regulating fluid may boil at a lower than desired temperature; for example, water boils at 22˚C at 0.02 bar. It has been found that operating pressures between approximately 0.02 bar and 0.9 bar provide the correct balance before deformation, cavitation, allowing the regulating fluid channel to be sufficiently close to the surface to be effectively regulated, and allowing the regulating fluid to flow through the system. The regulating system of this invention also allows, in some situations, the avoidance of the need to manufacture optical elements such as reflectors under pressure. It should be understood that at certain points in the regulating system, the pressure may be approximately atmospheric pressure or even slightly higher than atmospheric pressure. Even so, the system is configured such that the pressure at one or more regulated optical elements is low atmospheric pressure during use. Since the optical elements are in an extremely low pressure environment within a lithography device of approximately several Pascals of hydrogen, the pressure difference between the regulating fluid channel within the optical element and the outside of the optical element is practically equal to the pressure of the regulating fluid within the regulating fluid channel.

[0018] The conditioning system may include a liquid conditioning fluid, preferably water. The conditioning fluid may contain one or more additives to improve performance, such as corrosion inhibitors to prevent corrosion within the system. While conditioning fluids such as carbon dioxide can be used in other systems, this typically requires much higher pressures to achieve the necessary mass flow rate for effective conditioning, and therefore additional safety considerations and the required high pressures, such as 20 to 100 bar, are not compatible with avoiding deformation. Although other water-cooling systems can be described at a wide range of pressures, they do not achieve the suitability for the specific range described herein, nor for operation at low pressures at the conditioned unit, i.e., at the optical components. Pressures above atmospheric pressure have been previously used because such pressures can be more easily achieved by providing a standard pumping device that pressurizes water above atmospheric pressure to pump it through the conditioning system, and the deformation problem has been addressed by modifying the configuration of the conditioning channels. Water is preferred due to its safety, high thermal mass, and availability.

[0019] The system may include a regulating fluid reservoir. The regulating fluid reservoir may be at least partially filled with a regulating fluid, preferably water. By having a regulating fluid reservoir, there exists a thermal mass of regulating fluid that can circulate through the system to remove heat from it or add heat to it.

[0020] The system may include a pump downstream of the optical element and a flow limiter upstream of the optical element. Thus, the pump's suction side can be fluidly connected to the regulating channel of the optical element, such that when the pump is in operation, a pressure below atmospheric pressure is generated at the optical element. The flow limiter upstream of the optical element ensures that the pressure at the optical element is below atmospheric pressure. The invention is not particularly limited by the precise size or nature of the flow limiter, as such size or nature will depend on the size of the pipe carrying the regulating fluid, the required flow rate, and the required pressure of the system; however, such size or nature can be conventionally determined by those skilled in the art, and the pressure at the regulated optical element can be conventionally measured to confirm the pressure therein.

[0021] The system may include a low-pressure regulating fluid reservoir. Therefore, the system may include a regulating fluid reservoir for low-pressure applications. The low-pressure regulating fluid reservoir may be connected to a vacuum pump. The vacuum pump may be configured to allow control of the pressure within the regulating fluid reservoir to provide the desired low pressure by removing gas from the reservoir. Optionally, a gas inlet may be provided, allowing the introduction of a gas such as air or nitrogen into the regulating fluid reservoir to increase its pressure to the point of being too low. The system may include a controller operable to control the vacuum pump and / or the gas inlet to achieve the desired low pressure.

[0022] In some embodiments including a low-pressure regulating fluid reservoir, the pump is located downstream of the optical element and the flow limiter is located upstream of the optical element. In other embodiments including a low-pressure regulating fluid reservoir, the pump may be located upstream of the optical element because the downstream portion of the regulating system is connected to the low-pressure regulating fluid reservoir, and therefore the pressure at the optical element can be maintained at a low pressure. Optionally, a flow limiter is provided upstream of the pump and downstream of the optical element, i.e., between the pump and the optical element, to control the flow rate of the regulating fluid and prevent the pressure at the optical element from exceeding atmospheric pressure.

[0023] A low-pressure regulating fluid reservoir may include a deformable separator between a liquid regulating fluid and a gas. The deformable separator may be in the form of a diaphragm. By placing a deformable separator between the regulating fluid and the gas within the low-pressure regulating fluid reservoir, a low pressure can be maintained without any evaporation of the regulating fluid. The gas above the deformable separator can adjust its pressure to control the pressure within the system. The invention does not particularly limit the gas composition pair and may include, for example, air or nitrogen. The gas pressure can be adjusted to regulate the pressure within the system. Furthermore, the separator can deform to accommodate any pressure changes and also acts as a vibration damper.

[0024] The control system may include one or more vibration dampers, which can be used to attenuate pressure control errors or flow-induced vibrations. The one or more vibration dampers may be in the form of one or more hydraulic accumulators. Since optical elements are also extremely sensitive to vibration, it is necessary to reduce or eliminate vibration where possible. By providing one or more vibration dampers (which may be in the form of one or more hydraulic accumulators), any vibration can be reduced.

[0025] In one embodiment, a regulating fluid reservoir may be positioned below the optical element such that the hydrostatic pressure difference between the optical element and the regulating fluid reservoir reduces the pressure at the optical element to below atmospheric pressure. Therefore, if the regulating fluid reservoir is positioned at a height below the return side of the optical element, the hydrostatic pressure difference is sufficient to reduce the pressure of the regulating fluid at the optical element to below atmospheric pressure. A pump may be provided to supply the regulating fluid to the optical element, and the hydrostatic pressure difference prevents the pressure from exceeding atmospheric pressure. A pressure control device may be present between the optical element and the regulating fluid reservoir. The pressure control device may be configured to control the flow rate of the regulating fluid passing through it in order to control the pressure at the optical element. Optionally, a pressure sensor configured to control the pressure control device may be provided. A pressure controller may be provided that receives input from the pressure sensor and is operable to control the pump and / or a gas inlet flow controller.

[0026] In one embodiment, the system may include first and second regulating fluid reservoirs. The first and second regulating fluid reservoirs may be in fluid communication with each other via valves. The valves are operable to control the level of regulating fluid in the coolant reservoirs, which are in fluid communication with the optical elements to control pressure. In another embodiment, the level of regulating fluid in the regulating fluid reservoirs may be controlled by providing an overflow of regulating fluid, and thus the static pressure on the optical elements may be controlled, wherein the height of the overflow of regulating fluid is related to the height of the optical elements.

[0027] According to a sixth embodiment of the present invention, a lithography apparatus is provided, which includes the adjustment system according to a first embodiment of the present invention. The lithography apparatus may be an EUV lithography apparatus.

[0028] According to a seventh embodiment of the present invention, a low-pressure regulating system is provided for use in a lithography apparatus. Preferably, the regulating system is the regulating system according to a first embodiment of the present invention.

[0029] According to an eighth aspect of the present invention, a method is provided for regulating a system or subsystem of a lithography apparatus, wherein the method includes providing a liquid conditioning fluid at low pressure to the system or subsystem to be regulated. The system or subsystem may include optical elements, such as reflectors or mirrors. One or more optical elements may be present. Suitable distribution members, such as tubes and manifolds, may be provided to allow the conditioning fluid to be provided to the optical elements.

[0030] According to a ninth aspect of the present invention, a lithography method is provided, comprising projecting a patterned radiation beam onto a substrate, wherein the patterned beam is guided or patterned using at least one optical element, the at least one optical element comprising an adjustment system according to any aspect of the present invention.

[0031] It will be understood that a feature described with respect to one variant or embodiment may be combined with any feature described with respect to another variant or embodiment, and all such combinations are expressly considered and disclosed herein. Simple Explanation of the Diagram

[0032] Embodiments of the invention will now be described with reference to the accompanying schematic drawings, which are merely examples, in which corresponding element symbols indicate corresponding portions, and in these drawings:

[0033] Figure 1 depicts a lithography apparatus according to an embodiment of the present invention;

[0034] Figure 2 depicts a first embodiment of the system according to the present invention;

[0035] Figure 3 depicts a second embodiment of the system according to the present invention;

[0036] Figure 4 depicts a third embodiment of the system according to the present invention;

[0037] Figure 5 depicts a fourth embodiment of the system according to the present invention;

[0038] Figure 6 depicts a fifth embodiment of the system according to the present invention;

[0039] Figure 7 depicts a sixth embodiment of the system according to the present invention; and

[0040] Figure 8 depicts a seventh embodiment of the system according to the present invention.

[0041] The features and advantages of the present invention will become more apparent from the detailed description for the foregoing in conjunction with the accompanying drawings, in which similar reference characters consistently identify corresponding elements. In the drawings, identical reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Implementation

[0042] Figure 1 illustrates a lithography system according to an embodiment of the present invention. The lithography system includes 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 includes an illumination system IL, a support structure MT configured to support a patterned device MA (e.g., a mask), a projection system PS, and a substrate stage 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 patterned 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 configuration, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W.

[0043] The radiation source SO, the irradiation system IL, and the projection system PS can all be constructed and configured to isolate them from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure can be provided in the radiation source SO. A vacuum can be provided in the irradiation system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure sufficiently below atmospheric pressure can be provided in the irradiation system IL and / or the projection system PS.

[0044] The radiation source SO shown in Figure 1 belongs to the type that can be called a laser-generated plasma (LPP) source. A laser, such as a CO2 laser, is configured to deposit energy via a laser beam onto a fuel, such as tin (Sn), supplied by a fuel emitter. Although tin is mentioned in the following description, any suitable fuel can be used. The fuel can be, for example, in liquid form and can be, for example, a metal or alloy. The fuel emitter may include a nozzle configured to guide tin, for example, in droplet form, along a trajectory toward the plasma-forming region. The laser beam is incident on the tin at the plasma-forming region. The deposition of laser energy into the tin generates plasma at the plasma-forming region. Radiation, including EUV radiation, is emitted from the plasma during the de-excitation and recombination of ions in the plasma.

[0045] 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 multilayer structure configured to reflect EUV radiation (e.g., EUV radiation with a desired wavelength such as 13.5 nm). The collector may have an elliptical configuration with two elliptical foci. The first focal point may be located at the plasma formation region, and the second focal point may be located at the intermediate focal point, as discussed below.

[0046] The laser can be separated from the radiation source SO. In this case, the laser beam can be delivered from the laser to the radiation source SO by means of a beam delivery system (not shown in the figure) including, for example, suitable guide mirrors and / or beam expanders and / or other optics. The laser and the radiation source SO can be considered together as a radiation system.

[0047] Radiation reflected by the collector forms a radiation beam B. Radiation beam B is focused at a single point to form an image of the plasma formation region, which serves as a virtual radiation source for irradiating the system IL. The point where radiation beam B is focused can be called the intermediate focal point. The radiation source SO is configured such that the intermediate focal point is located at or near an opening in the enclosure structure of the radiation source.

[0048] A radiated beam B is transmitted from a radiation source SO to an illumination system IL, which is configured to adjust the radiated beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the desired cross-sectional shape and desired angular distribution for the radiated beam B. The radiated beam B is transmitted from the illumination system IL and incident on a patterned device MA held by a support structure MT. The patterned device MA reflects and patterns the radiated beam B. In addition to or in place of the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL may also include other mirrors or devices.

[0049] After reflection from the patterning device MA, the patterned radiating beam B enters the projection system PS. The projection system includes a plurality of mirrors 13 and 14 configured to project the radiating beam B onto the substrate W held by the substrate stage WT. The projection system PS can apply a reduction factor to the radiating beam to form an image with features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 can be applied. Although the projection system PS in Figure 1 has two mirrors 13 and 14, the projection system can include any number of mirrors (e.g., six mirrors).

[0050] In use, the optical elements of a lithography apparatus, such as mirrors or reflectors, are heated by radiation, thus necessitating the adjustment of these optical elements. Therefore, the adjustment system according to the present invention is integrated into the lithography apparatus to provide the required adjustment. Adjustment typically requires removing heat energy from the optical elements when they become hot during use.

[0051] The radiation source SO shown in Figure 1 may include components not shown. For example, a spectral filter may be incorporated into the radiation source. The spectral filter may substantially transmit EUV radiation, but substantially block radiation of other wavelengths, such as infrared radiation.

[0052] Figures 2 to 8 are schematic depictions of the adjustment system according to the present invention.

[0053] Figure 2 depicts an embodiment of a regulating system 15 according to a first embodiment of the present invention. The regulating system 15 includes a regulating fluid reservoir 16. In the depicted example, the top of the regulating fluid reservoir 16 is shown open. Although in practice the regulating fluid reservoir may or may not be open, it is depicted open to demonstrate that the regulating fluid 17 (which may be water) therein is not pressurized to above atmospheric pressure and may be at ambient pressure. The regulating fluid reservoir 17 is connected to an optical element 19 via an optional flow limiter 18. An optional pressure sensor 20 may be provided to measure the pressure of the regulating fluid when it enters or is inside the optical element 19. A pump 21 is connected between the optical element 19 and the regulating fluid reservoir 16. In use, the regulating fluid 17 from the regulating fluid reservoir 16 (which may also be referred to as a regulating fluid vessel or container) is transferred to the optical element 19 via a pressure difference between the reservoir outlet and the pump inlet generated by the pump. In other embodiments, the flow rate depends on gravity based on the relative positions of the tank and the optical element. A pump 21 connected to the output side of the optical element 19 pumps the regulating fluid 17 back to the regulating fluid reservoir 16, whereby the regulating fluid can then be recirculated through the regulating system 15. The flow limiter 18 can be any suitable design, and the invention is not particularly limited by the accuracy of the flow limiter. The flow limiter 18 is used to provide the required pressure drop at the optical element 19, such that the regulating fluid at or within the optical element 19 is below atmospheric pressure. In any of the depicted embodiments, the regulated optical element 19 contains at least one channel through which the regulating fluid can absorb heat from or provide heat to and transport to the optical element, thereby regulating the optical element 19. The level of the regulating fluid 17 in the regulating fluid reservoir 16 is merely illustrative and may be higher or lower than the point at which the regulating fluid 17 returns via the pump 21.

[0054] Figure 3 depicts a regulating system similar to that of Figure 2, although the difference is that the regulating fluid reservoir 16 is not at atmospheric pressure. In fact, the system is sealed to lower the pressure to the desired level and then sealed to maintain that low pressure. A gas connection 22 can be provided to reduce the pressure within the system if the pressure increases above the desired level. Similarly, additional gas or regulating fluid can be added to the system if the pressure drops too much or more regulating fluid is needed.

[0055] Figure 4 depicts a regulating system similar to that of Figure 3, although it has a deformable separator 23, which can take the form of a diaphragm, separating the regulating fluid 17 within the regulating fluid reservoir 16 from the gas above the regulating fluid. The separator 23 prevents either component of the regulating fluid from evaporating, thus avoiding regulating fluid loss and eliminating the need for a vacuum pump or controlled gas inlet. The separator 23 also dampens flow-induced vibrations within the system.

[0056] Figure 5 depicts another embodiment of the regulating system 15 according to the present invention. This embodiment is similar to the embodiment of Figure 2, although it has a closed system and a low-pressure regulating fluid reservoir 16. The regulating fluid reservoir 16 is maintained at a pressure below atmospheric pressure by a vacuum pump 24. The vacuum pump 24 is configured to reduce the pressure within the system by removing the gas present therein. A controlled gas inlet may be provided, which can add gas or remove gas from the system as needed.

[0057] Figure 6 depicts an embodiment similar to that of Figure 5, although the pump 21 for moving the regulating fluid through the system is positioned between the regulating fluid reservoir 16 and the inlet of the optical element 19. In this embodiment, the regulating fluid 17 is pumped by the pump 21 and reaches the optical element 19 via the restrictor 18. The outlet fluid of the optical element 19 is connected to the low-pressure regulating fluid reservoir 16. The vacuum pump 24 and gas connector 22 are operable to remove and introduce gas as needed to control the pressure within the system.

[0058] Figure 7 depicts yet another embodiment of the regulating system according to the present invention. In this embodiment, a low pressure is generated by utilizing a hydrostatic pressure difference 25 caused by a regulating fluid reservoir 16, which is located at a height lower than that of the optical element 19. The hydrostatic pressure difference 25 reduces the pressure on the return side of the optical element 19. The pump 21 compensates for this and is able to supply regulating fluid to the supply side of the optical element 19. The dashed boxes surrounding the regulating fluid reservoir 16, the pump 21, and the flow limiter 18 indicate that these components are located below the optical element, and the precise positioning of these components relative to the optical element 19 is merely illustrative. It should be understood that the flow limiter 18 may be provided adjacent to the return side of the optical element 19.

[0059] Figure 8 depicts yet another embodiment of the regulating system according to the present invention. In this embodiment, there are two regulating fluid reservoirs 16a and 16b. The two regulating fluid reservoirs 16a and 16b are connected via a valve 26 operable to control the water level in the regulating fluid reservoir 16a. This further controls the hydrostatic pressure of the regulating fluid supplied to the optical element 19, which is combined with a water pump 21 connected to the return side of the optical element.

[0060] In summary, this invention provides a low-pressure regulation system capable of regulating key components of a lithography apparatus and directly activating such components, thereby increasing thermal efficiency and improving performance under higher thermal loads without causing undesirable deformation of optical elements. This invention has a specific, but not exclusive, application in cooling the optical elements of lithography apparatuses.

[0061] Although specific embodiments of the invention have been described above, it will be understood that the invention may be practiced in other ways different from those described.

[0062] The above description is intended to be illustrative and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the claims set forth below.

[0063] 10: Faceted field mirror devices 11: Faceted pupil mirror device 13: Mirror 14: Mirror 15: Regulation System 16: Regulating fluid reservoir 16a: Regulating fluid reservoir 16b: Regulating fluid reservoir 17: Regulating fluid 18: Flow limiter 19: Optical Components 20: Pressure sensor 21: Pump / Water Pump 22: Gas Connector 23: Deformable Separator 24: Vacuum pump 25: Hydrostatic pressure difference 26: Valve B: Radiation beam IL: Irradiation system LA: Microfilm Installation MA: Patterning device MT: Support structure PS: Projection system SO: Radiation source W: substrate WT: substrate table

Claims

1. A conditioning system comprising: a sub-atmospheric pressure conditioning fluid reservoir configured to operate at low pressure and store at least a portion of a liquid conditioning fluid, wherein the conditioning system is used in a lithography apparatus, wherein the conditioning system is configured to condition one or more optical elements of the lithography apparatus, wherein the one or more optical elements are conditioned under vacuum or a low gas pressure, wherein the conditioning system is configured to have a low gas pressure at the one or more optical elements, wherein the liquid conditioning fluid is water, and wherein the conditioning system is configured to operate between about 0.02 bar and 0.9 bar.

2. The regulating system of claim 1, wherein the low-pressure regulating fluid reservoir is connected to a vacuum pump and / or a gas inlet.

3. The regulating system of claim 1, wherein the regulating system further comprises: a pump upstream of the one or more optical elements, and a flow limiter between the pump and the one or more optical elements.

4. As in the regulating system of request item 1, wherein: The low-pressure regulating fluid reservoir includes a deformable separator, wherein the deformable separator is disposed between the liquid regulating fluid and a gas.

5. A conditioning system comprising: a liquid conditioning fluid comprising water; a low-pressure conditioning fluid reservoir configured to operate at low pressure and store at least a portion of the liquid conditioning fluid; a flow limiter; and a pump, wherein the conditioning system is for a lithography apparatus, wherein the conditioning system is configured to condition one or more optical elements of the lithography apparatus, wherein the one or more optical elements are conditioned under vacuum or a low gas pressure, wherein the conditioning system is configured to have a low gas pressure at the one or more optical elements, wherein the pump is located downstream of the one or more optical elements, and wherein the flow limiter is located upstream of the one or more optical elements, wherein the conditioning system is configured to operate between about 0.02 bar and 0.9 bar.

6. The regulating system of claim 5, wherein the regulating system further includes a regulating fluid reservoir.

7. The regulating system as claimed in claim 5, wherein the low-pressure regulating fluid reservoir is connected to a vacuum pump and / or a gas inlet.

8. A conditioning system comprising: a low-pressure conditioning fluid reservoir configured to operate at low pressure and store at least a portion of a liquid conditioning fluid; wherein the conditioning system is used for a lithography apparatus, wherein the conditioning system is configured to condition one or more optical elements of the lithography apparatus, wherein the one or more optical elements are conditioned under vacuum or a low gas pressure, wherein the conditioning system is configured to have a low gas pressure at the one or more optical elements, and wherein the low-pressure conditioning fluid reservoir is disposed below the one or more optical elements such that a hydrostatic pressure difference between the one or more optical elements and the low-pressure conditioning fluid reservoir reduces the low gas pressure at the one or more optical elements to below atmospheric pressure, wherein the conditioning system is configured to operate between about 0.02 bar and 0.9 bar.

9. A conditioning system comprising: a conditioning fluid reservoir; a low-pressure conditioning fluid reservoir configured to operate at low pressure and store at least a portion of a liquid conditioning fluid; wherein the conditioning system is used in a lithography apparatus, wherein the conditioning system is configured to condition one or more optical elements of the lithography apparatus, wherein the one or more optical elements are conditioned under vacuum or a low gas pressure, wherein the conditioning system is configured to have a low gas pressure at the one or more optical elements, and wherein the conditioning fluid reservoir and the low-pressure conditioning fluid reservoir are fluidly connected to each other via a valve operable to control the level of the conditioning fluid in the conditioning fluid reservoir fluidly connected to the one or more optical elements, such that a hydrostatic pressure difference is achieved between the one or more optical elements and the low-pressure conditioning fluid reservoir, wherein the conditioning system is configured to operate between about 0.02 bar and 0.9 bar.

10. The control system of claim 9, wherein the control system is configured to operate at approximately 0.3 bar.

11. The regulating system of claim 9, wherein the regulating system further includes a liquid regulating fluid comprising water.

12. The adjustment system of claim 9, wherein at least one of the one or more optical elements is a reflector or a mirror.

13. The regulating system as described in request item 9, wherein: The regulating system further includes one or more vibration dampers, and the one or more vibration dampers are in the form of one or more hydraulic accumulators.

14. A lithography apparatus comprising: a conditioning system configured to condition a liquid conditioning fluid, wherein the liquid conditioning fluid comprises water; and a low-pressure conditioning fluid reservoir configured to operate at low pressure and store at least a portion of the liquid conditioning fluid, wherein the conditioning system is configured to condition one or more optical elements of the lithography apparatus, wherein the one or more optical elements are conditioned under vacuum or a low gas pressure, and wherein the conditioning system is configured to have a low gas pressure at the one or more optical elements, wherein the conditioning system is configured to operate between about 0.02 bar and 0.9 bar.

15. A method for low-pressure regulation in a lithography apparatus, comprising: regulating one or more optical elements of the lithography apparatus under vacuum or a low gas pressure; using a low gas pressure of about 0.02 bar and 0.9 bar at the one or more optical elements; using water as a liquid regulating fluid; and storing at least a portion of the liquid regulating fluid in a low-pressure regulating fluid reservoir.

16. A method for regulating one system or subsystem of a lithography apparatus, the method comprising: regulating one or more optical elements of the system or subsystem under vacuum or a low gas pressure; using a low gas pressure of about 0.02 bar and 0.9 bar at the one or more optical elements; using water as a liquid regulating fluid; and storing at least a portion of the liquid regulating fluid in a low-pressure regulating fluid reservoir.

17. The method of claim 16, wherein the system or subsystem includes an optical element, a reflector or a mirror.

18. A lithography method comprising: projecting a patterned radiation beam onto a substrate, guiding or patterning the patterned radiation beam using at least one optical element, the at least one optical element being regulated using a regulation system, the regulation system comprising: a low-pressure regulating fluid reservoir configured to operate at low pressure and store at least a portion of a liquid regulating fluid, wherein the regulation system is for a lithography apparatus, wherein the regulation system is configured to regulate the at least one optical element of the lithography apparatus, wherein the one or more optical elements are regulated under vacuum or a low gas pressure, wherein the regulation system is configured to have a low gas pressure at the at least one optical element, and wherein the liquid regulating fluid is water, wherein the regulation system is configured to operate between about 0.02 bar (bara) and 0.9 bar (bara).

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