Optical element, optical arrangement and insert component

Abstract

The present invention relates to an optical element (M4) for reflecting radiation, particularly for reflecting EUV radiation, comprising: a substrate (25), a reflective coating (28) applied to a surface (27) of the substrate (25), a plurality of cooling channels (29) operating in the substrate (25) below the surface (27) to which the reflective coating (28) is applied, a distributor (33) for connecting at least one cooling fluid inlet (32) to the plurality of cooling channels (29), and a collector (35) for connecting the plurality of cooling channels (29) to at least one cooling fluid outlet (34a, b). The distributor (33) and / or the collector (35) are integrated into at least one, preferably rod-shaped, insertion member (31), which is inserted into at least one cavity (30) formed in the substrate (25). The present invention also relates to an optical configuration, particularly an EUV lithography system, comprising: at least one optical element (M4) formed in the manner described above, and a cooling device designed to allow cooling fluid to flow through the plurality of cooling channels. The present invention also relates to an insertion member (31) for insertion into a cavity (30) of a substrate (25), particularly a substrate (25) of an optical element (M4) formed in the manner described above.

Description

[Technical Field]

[0001] This invention relates to an optical element for reflecting radiation, particularly for reflecting EUV radiation, comprising: a substrate, a reflective coating applied to the surface of the substrate, a plurality of cooling channels operating in the substrate below the surface to which the reflective coating is applied, a distributor for connecting at least one cooling fluid inlet to the plurality of cooling channels, and a collector for connecting the plurality of cooling channels to at least one cooling fluid outlet. This invention also relates to an optical configuration, particularly an EUV lithography system, comprising at least one such optical element and a cooling device designed to allow cooling fluid to flow through the plurality of cooling channels. This invention further relates to an insertion member, particularly for an optical element formed in the manner described above. [Previous Technology]

[0002] As the power of the radiation sources used in their operation continues to increase, the heat load on reflective optics used in lithography, particularly EUV lithography, is also increasing. This is especially true for mirrors in the projection system of EUV lithography apparatuses. Generally, it is attempted to use materials with a coefficient of thermal expansion as close as possible to "zero" as the substrate for such reflective optics, which are also referred to as mirrors below, to simplify the problem. In practice, it is best to meet this requirement at a certain temperature (also known as the zero cross temperature).

[0003] In this projection system, each mirror is heated differently depending on various settings or lighting conditions, thus the mirror can only operate near zero cross temperature. This causes the mirror (more precisely, the surface with the reflective coating) to deform under the thermal load during radiation. As the thermal load increases, this "mirror heating" problem limits the performance of the optical configuration in which the mirror is located.

[0004] There are some electromechanical integration methods to solve this problem. Another relatively simple concept involves directly cooling the corresponding reflector, that is, allowing cooling fluid to flow through the substrate of the reflector, or more precisely, through cooling channels formed on the substrate. The advantage of this concept is that the temperature of the reflector can be set relatively precisely by the temperature of the cooling fluid, that is, the reflector has a thermal reference.

[0005] A distributor is needed to connect at least one cooling fluid inlet of a substrate to a plurality of cooling channels, and a collector is needed to connect the plurality of cooling channels of the substrate to at least one cooling fluid outlet, so as to achieve as few direct connections as possible on the substrate of the reflector.

[0006] DE 10 2019 217 530 A1 discloses an optical element in the form of a mirror, having a first layer made of a first material and a second layer made of a second material, which are placed together along an interface. The optical element has a cooling device that extends and is configured to cool the optical element in a region of the interface. The cooling device may have a plurality of cooling channels through which a cooling fluid (e.g., cooling water) can flow. The cooling channels may extend parallel to each other and laterally toward side channels, wherein the side channels are connected to a cooling fluid inlet or a cooling fluid outlet. In this case, the corresponding side channels function as distributors or current collectors formed in the substrate.

[0007] When cooling fluid (especially coolant) flows through cooling channels, internal pressure is generated in the cooling channels, especially in distributors or collectors, which may cause undesirable deformation of the surface to which the reflective coating is applied. [Summary of the Invention]

[0008] The object of the present invention is to provide optical elements, optical configurations, and insertion members that allow for reduced deformation on the surface of optical elements with reflective coatings due to direct cooling using a cooling fluid. Preferably, the temperature distribution in the substrate can be influenced in a targeted manner during cooling with the cooling fluid. [Objective of the Invention]

[0009] According to the first state, this objective is achieved by an optical element of the type described at the beginning, wherein the distributor and / or current collector is integrated into at least one preferably rod-shaped insert member, which is introduced into at least one cavity formed in the substrate.

[0010] In optical elements, the distributor or current collector is not directly formed in the substrate of the reflective optical element; instead, the distributor and / or current collector is integrated into an insert member that is introduced or inserted into the substrate, more precisely, into a cavity formed in the substrate. The insert member may be integrally formed, but it may also have a body in which other components are integrated (see below). Generally, the insert member or body is formed of a material that does not expand or expands only minimally when a cooling fluid flows through it. Furthermore, the material of the insert member or body should be as free as possible from deformation under temperature changes.

[0011] A cooling channel for the flow of cooling fluid has at least one opening or channel leading to at least one cavity, wherein at least one insert member is received in the cavity. It has been found advantageous for the insert member to have a rod-like, elongated, or substantially cylindrical geometry to facilitate the distribution of cooling fluid between cooling channels in the form of a distributor comb (or a wave-like distributor) and / or the collection of cooling fluid from the cooling channels in the form of a collector comb. It should be understood that the rod-like or substantially cylindrical geometry of the insert member is not necessarily a circular cylindrical geometry.

[0012] Two (or selectively more) insert members that satisfy the functions of a distributor or a collector can be introduced into the substrate. The two or more insert members can be introduced into a common cavity or into two or more independent cavities. One or more cavities can be through holes or channels. However, it has been found that using cavities in the form of blind vias or blind holes is advantageous for the current purpose.

[0013] In one embodiment, the distributor and the collector are both integrated into a common insert member, with at least one cooling fluid inlet and at least one cooling fluid outlet preferably formed on the same side of the insert member to connect to at least one conduit, preferably a dual conduit. In this case, cooling fluid can be supplied and discharged within the same insert member. Ideally, the cooling fluid inlet and cooling fluid outlet are formed on the same side of the insert member, such as the end side, to reduce the number of connectors used to supply and guide the cooling fluid. This is beneficial for reducing the dynamic and thermoplastic interactions between the typically metallic material of the connector and the substrate material (e.g., in the form of a zero-crossing material). If the insert member has a generally rod-shaped form, the cooling fluid inlet and cooling fluid outlet are typically located on the same end side of the rod-shaped insert member. The other end side is located in the substrate, for example, at or near the bottom of the cavity if the cavity is formed in the form of a blind hole.

[0014] By integrating the supply and extraction devices into a common insertion member, the design freedom of optical elements can be increased. If the cooling fluid flows in opposite directions in the distributor and collector within the insertion member, the dynamic performance of cooling may also be improved, taking into account the vibration caused by the flow, thereby selectively compensating for the forces exerted by the flowing cooling fluid.

[0015] In this improved embodiment, at least one coolant inlet is radially mounted inside the rod-shaped insert member for connection to the interior of the inner tube of the dual-pipe system, and at least one coolant outlet is radially mounted outside the rod-shaped insert member for connecting the gap between the inner and outer tubes of the dual-pipe system, or vice versa. In this way, with the aid of the dual-pipe system, cooling fluid can be supplied to and withdrawn from the insert member through the same connector of the dual-pipe system. For example, cooling fluid can be supplied to an optical element inside the inner tube and can be guided away from the optical element in the gap between the inner and outer tubes. However, cooling fluid can also be supplied to the optical element through the gap in the dual-pipe system and guided away from the optical element through the interior of the inner tube of the dual-pipe system.

[0016] In another specific embodiment, the optical element includes at least one seal for sealing a gap relative to the surrounding environment, the gap being formed between the wall of the cavity and an insert member introduced into the cavity. The insert member is typically introduced into the cavity with a very small gap. This results in a gap being formed between the wall of the cavity and the insert member, through which cooling fluid could escape from the cavity to the surrounding environment of the substrate or optical element without a seal. At least one seal is disposed between the wall of the cavity and the insert member to prevent this. In the case of a rod-shaped insert member, the seal typically extends circumferentially on the side of the insert member. In this case, the seal may be, for example, an O-ring. The seal is disposed between an inlet and an outlet formed in the insert member (see below) for supplying cooling fluid from the periphery of the optical element to the cooling channel and for guiding cooling fluid from the cooling channel to the periphery of the optical element, respectively.

[0017] In this case, a contactless seal is achieved at the passage of cooling fluid from the insert member to the corresponding cooling channel in the substrate of the optical element by means of the narrow gap between the cavity wall and the insert member. The dimensions of the insert member and the cavity wall are ideally selected such that the gap or the width of the gap is minimized at the operating temperature of the optical element, and for example, less than 0.5 mm or less than 0.1 mm. With the gap having the minimum possible width, the cooling fluid passage between adjacent cooling channels can be minimized. Furthermore, with a small gap width, flow separation of the cooling fluid can be reduced or selectively avoided entirely, which reduces or ideally completely prevents flow-induced vibration (FIV).

[0018] Advantageously, the smaller the deformation of the insert member under temperature changes, the better; that is, the smaller the expansion and contraction, the better. For this purpose, the insert member or its body can be formed of a material with a very low coefficient of thermal expansion. This is, for example, if the insert member or its body is formed of constant steel. If the insert member or its body is produced by additive manufacturing, glass or glass-ceramic with a low coefficient of thermal expansion can be selectively used as the material. For example, the material can be titanium-doped fused silica, such as that offered by Corning Incorporated under the ULE® brand.

[0019] Due to the gap, the cooling fluid passes between two areas: the area where the cooling fluid is supplied to the insertion member of the cooling channel via a distributor or via a corresponding inlet of the distributor, and the area where the cooling fluid is drawn out of the corresponding cooling channel via a corresponding outlet of the collector. Therefore, due to this gap, there is a slight pressure loss in the supplied cooling medium. However, this pressure loss is generally not a problem, as flow rate often plays a decisive role in cooling performance. Furthermore, sealing by means of a gap (so-called gap sealing), despite the pressure loss at the gap seal, still allows the transmission of pressures of several hundred bar, as is known in hydraulic cylinders on machinery.

[0020] If the distributor and collector are configured on different sides of the outer circumference of the reflective coating, the cooling channels in the substrate generally extend substantially in a straight line below the surface on which the reflective coating is applied, or the curvature of the cooling channels matches the curvature of the surface on which the reflective coating is applied.

[0021] In another specific embodiment, at least one cooling channel has at least one deflection portion for deflecting the cooling fluid, particularly for reversing the flow direction of the cooling fluid. By accommodating the distributor and / or collector within (optionally shared) insert members, the design freedom of the cooling channels is increased; that is, they can have different geometries, such as spiral or meandering extensions. In order for the cooling fluid supplied to the cooling channel via the distributor of the insert member to be discharged again via the collector of the same insert member, the cooling channel typically needs to have (at least) a deflection portion that deflects the cooling fluid. It may be advantageous if the deflection portion reverses the flow direction of the cooling fluid, such that the deflected cooling fluid flows in parallel and opposite directions, but this is not mandatory.

[0022] The geometry or region beneath the surface covered by the corresponding cooling channel can be defined according to which regions or segments of the optical element should have a uniform cooling effect: as described in more detail below, the cooling effect of the cooling medium in the corresponding cooling channel can be set in a targeted manner. However, it is generally not possible to influence the temperature of the cooling fluid in a targeted, spatially varied manner within the same cooling channel. Due to the measures further described below, targeted control of cooling in the corresponding region can be achieved to set a desired (e.g., uniform) temperature distribution on the surface to which the reflective coating is applied.

[0023] A single cooling channel may have two or more channel sections that extend from the distributor, via corresponding deflection sections, back to the collector. In this case, the flow of cooling fluid is divided into two or more channel sections starting from the distributor or the distributor's inlet, and then converges again at the collector's outlet. However, the same cooling channel may also start from the distributor and return to the collector via deflection sections. If multiple inlets or outlets are provided there, cooling fluid can also be supplied to two or more cooling channels that are horizontal in the longitudinal direction of the insert member. For example, two cooling channels may be adjacent to each other in this case on a web or the like formed in the substrate, and may extend horizontally in the longitudinal direction of the insert member on opposite sides. In this case, the cooling channels return to the outlet via corresponding deflection sections. In this way, cooling channels located on one side (e.g., the right side) of the insert member and cooling channels located on the other side (e.g., the left side) of the insert member can produce different cooling effects.

[0024] In another specific embodiment, the distributor has a plurality of inlets for connecting at least one cooling fluid inlet to at least one cooling channel in each case, and / or the collector has a plurality of outlets for connecting a cooling fluid outlet to at least one cooling channel in each case. The inlets and outlets open on the outer side of the insert member, typically along its (e.g.) cylindrical side surface. A corresponding inlet or outlet is connected to another inlet or outlet only through a gap. A corresponding inlet or outlet may lead directly into a corresponding cooling channel that extends below a surface to which a reflective coating is applied. In this case, the cooling channel has an opening leading to a cavity, or the wall of the cavity cuts into the cooling channel. Alternatively, the inlet or outlet may not lead directly to a corresponding cooling channel. In this case, one or more connecting channels are formed in a substrate between the corresponding cooling channel and the cavity where the insert member is located, for connecting the corresponding inlet or outlet of the insert member to the cooling channel.

[0025] In another specific embodiment, the inlet leads to at least one common inlet channel connected to at least one cooling fluid inlet, and / or the outlet leads to at least one common outlet channel connected to at least one cooling fluid outlet. The at least one common inlet channel preferably extends radially inward within the insert member, and the at least one common outlet channel preferably extends radially outward within the insert member, and vice versa. In the case of a rod-shaped insert member, (at least one) common inlet channel and (at least one) common outlet channel may, for example, extend substantially in the axial direction. The (at least one) radially inward inlet channel and (at least one) radially outward outlet channel facilitate the supply of cooling fluid to the insert member and the guidance of the cooling fluid away from the insert member via a single coolant connector, for example, by a common dual conduit.

[0026] In this specific embodiment, the feed port is connected to a common inlet channel via a feed channel that preferably extends radially, and / or the discharge port is connected to a common outlet channel via a discharge channel that preferably extends radially. From the inlet or outlet channel, the feed or discharge channel extends outward to the side surface of the insert member or to the gap region between the insert member and the substrate. The respective feed or discharge channel may specifically extend to the side surface or to the gap to supply cooling fluid to or guide cooling fluid away from the respective cooling channel.

[0027] In one development, the inlet is formed as a feed groove at least partially circumferentially formed on the side surface of the insert member, or the inlet has such a feed groove, and / or the outlet is formed as a discharge groove at least partially circumferentially formed on the side surface of the insert member, or the outlet has such a discharge groove. Supplying cooling fluid to and withdrawing cooling fluid from the cooling channel can be achieved in a particularly simple manner by means of the feed groove and discharge groove, which are typically introduced into the insert member by milling. The feed groove or discharge groove can be milled deep into the insert member or its body so that it directly meets or intersects with the inlet or outlet channel. In this case, each inlet is formed by a feed groove, and each outlet is formed by a discharge groove. However, the feed groove and / or discharge groove may also not extend to the inlet and outlet channels, respectively. In this case, the inlet and outlet each have at least one corresponding feed channel and discharge channel, which lead to the corresponding feed groove or discharge groove, respectively.

[0028] In the case where the inlet channel, as further described above, is formed radially inward, the corresponding feed port may have a feed channel, for example, a feed groove leading to a side surface of the insert member. Conversely, if (at least one) outlet channel is further configured radially outward, the corresponding discharge port may be in the form of a discharge groove. It should be understood that the arrangement of the feed groove and / or discharge groove may be selectively omitted entirely. In particular, this is possible when the insert member is not conventionally manufactured but by additive manufacturing methods, as in this case even relatively complex structures can be introduced into the insert member, or more precisely, into the body of the insert member. In particular, components that realize multiple different functions can be integrated into the insert member in this way, as will be described in more detail below.

[0029] In another specific embodiment, the distributor has at least one switchable valve for supplying cooling fluid to at least one cooling channel, preferably configured between a common inlet channel and a feed port. In its simplest case, the switchable valve may have only two switching states, enabling or blocking the supply of cooling fluid to the feed port. However, the valve may also switch between multiple switching states to enable the setting of the flow rate of the cooling fluid through the valve. Switching between the valve's switching states is achieved automatically using a suitable control device. Generally, this requires connecting the switchable valve to the control device via a suitable electrical connection (e.g., via wires). If the flow rate of the cooling fluid through the valve can be set incrementally or selectively continuously, it is also possible to set the cooling effect of the fluid supplied through the feed port incrementally or continuously. In this way, the substrate temperature in the region of the corresponding cooling channel extending beneath the surface with the reflective coating can be affected. For example, the valve may be a miniature valve based on the principle of shape memory alloys. It is also possible to use valves based on other operating principles to achieve this purpose, provided that their size is small enough.

[0030] In one development, the distributor has at least two switchable valves connected in parallel for supplying cooling fluid from the inlet channel to the feeder. The parallel connection of two or more valves is particularly advantageous if a single valve has only a few on / off states, such as only two. In this case, it may be advantageous to use two or more valves connected in parallel to set the flow rate and thus the cooling effect. For example, this allows three different flow rates to be set using two valves, each with two on / off states: no flow rate (both valves: closed), maximum flow rate (both valves: open), and half of the maximum flow rate (one valve: open, one valve: closed). By utilizing the flow rate of the cooling fluid to set the cooling effect, the flow rate can be reduced, and therefore, vibrations caused by the flow can be reduced.

[0031] In another specific embodiment, the insertion member has at least one temperature control element for controlling the temperature of the cooling fluid, particularly at least one heating element for heating the cooling fluid before supplying it to at least one cooling channel. The temperature control element is preferably disposed between the inlet channel and the feed port. The temperature control element controls the temperature of the cooling fluid, i.e., heats and / or cools the cooling fluid supplied to at least one cooling channel. Specifically, the temperature control element may be at least one heating element for heating the cooling fluid supplied to at least one cooling channel. By using a heating element, it is possible to reduce the cooling effect of the cooling fluid in the corresponding cooling channel. Therefore, an effect similar to that of a switchable valve can be obtained by means of a heating element.

[0032] In order to establish temperature gradients in or between the various cooling channels, the inlet channel may be operated with a significantly colder cooling fluid than in conventional methods (e.g., at a temperature of 18°C), and the cooling fluid supplied to cooling channels that should be cooled less or not at all may be heated (e.g., to room temperature, i.e., to 22°C) before entering the respective cooling channel. For example, the heating element may be a small heater based on silicon nitride operation, but may also be a different type of heating element whose size can be adjusted to be small enough.

[0033] The insert member may have only a switchable valve or only a temperature control or heating element, but it is also possible to combine both types of structural elements in the insert member. For example, both the switchable valve and the temperature control or heating element may be configured between the inlet channel and the same feed port. It is also possible to integrate the switchable valve and the temperature control or heating element into the same component.

[0034] In another embodiment, the insertion member has at least one temperature sensor for monitoring the temperature of the cooling fluid in at least one cooling channel, at least one inlet channel, and / or at least one outlet channel. Knowledge of the temperature in the respective cooling channel or inlet channel and / or outlet channel allows for conclusions regarding the temperature distribution of the optical element in the surface region coated with the reflective coating. Based on the temperature distribution, parameters of the optical configuration of the integrated optical element can be adjusted.

[0035] In cases where the temperature in a corresponding cooling channel should be measured using a temperature sensor, the temperature sensor may, for example, be positioned between the outlet and the outlet channel. Where a temperature control or heating element is present, the temperature sensor may also be positioned between the inlet channel and the feed port, specifically downstream of the temperature control or heating element in the direction of the cooling fluid flow, or within the temperature control or heating element itself. Generally, positioning the temperature sensor between the inlet channel and the temperature control or heating element is disadvantageous because the temperature of the cooling fluid at this location is not significantly different from the temperature in the inlet channel, and can be selectively measured using a separate temperature sensor. The temperature of the cooling fluid in the inlet channel is preferably measured using a temperature sensor positioned directly near the cooling fluid inlet. Correspondingly, the temperature of the cooling fluid in the outlet channel can also be determined using a suitably positioned temperature sensor. The temperature sensor positioned in the outlet channel is preferably positioned directly near (at least one) the cooling fluid outlet.

[0036] In one development of this specific embodiment, the insert member has a closed-loop control device (controller) for regulating the temperature of the cooling fluid to a target temperature by acting on at least one switchable valve and / or on at least one temperature control element. One or more temperature sensors can be used for closed-loop control of the temperature in each cooling channel, and thus for closed-loop control of the temperature on the surface of the optical element to which the reflective coating is applied. In this case, the temperature sensor is combined with the valve and / or with the temperature control or heating element to form a control loop, that is, the closed-loop control device acts as an actuator on the valve or the temperature control or heating element. However, it is also possible to integrate one or more temperature sensors into the insert member without configuring the valve, temperature control or heating element, or other actuators for the control loop in the insert member.

[0037] In another embodiment, the insert member has at least one cable channel for guiding wires for electrical contact with at least one valve, at least one temperature control element, and / or at least one temperature sensor. The respective wires are guided or received in the cable channel. Similar to the inlet and outlet channels, the cable channel may extend in the longitudinal direction of the (rod-shaped) insert member. To prevent the wires in contact with the valve, temperature control element, and / or temperature sensor from contacting the cooling fluid, it may be advantageous to mold the respective components into the body of the insert member.

[0038] In a further specific embodiment, the substrate has a first part body and a second part body placed together at an interface, a reflective coating applied to the surface of the first part body, and a plurality of cooling channels extending in the substrate in the interface region between the two part bodies.

[0039] To allow for sufficient geometric design flexibility, the channel geometry of the cooling channel can advantageously be formed in two or more partial bodies of the substrate, which are connected to each other by a suitable joining method or selectively by optical contact joining at one or more interfaces. The cross-section of the respective cooling channel can be separated between the two partial bodies. In this case, a corresponding groove or recess can be formed in the first partial body, and another groove or recess can be formed in the second partial body. When the two partial bodies are joined along the interface, the two grooves or recesses are placed together to form a single cooling channel, for example as described in DE 10 2019 217 530 A1. In this case, the corresponding recess is milled in both the first and second partial bodies. However, the recess may also be milled only in the first partial body or only in the second partial body, and the corresponding other partial body covers the recess in the form of a cap to form the cross-section of the cooling channel. In both cases, the interface extends within or on the edge of the cross-section of the respective cooling channel. The cap covering the cooling channel is typically the first partial body, on which a surface with a reflective coating is formed.

[0040] Another aspect of the present invention relates to an optical configuration, particularly an EUV lithography system, comprising: at least one optical element configured as described above, and a cooling device designed to allow coolant to flow through a plurality of cooling channels. The EUV lithography system may be an EUV lithography apparatus for exposing wafers, or may be some other optical configuration using EUV radiation, such as an EUV inspection system, for example, for inspecting photomasks, wafers, etc., used in EUV lithography. The reflective optical element may be, in particular, a mirror of a projection system of an EUV lithography unit. The optical configuration may also be a lithography system for another wavelength range (e.g., for the DUV wavelength range), such as a DUV lithography apparatus or inspection system for inspecting photomasks, wafers, etc.

[0041] For example, the cooling device may be configured to allow a coolant in the form of a cooling fluid (e.g., coolant, such as cooling water) to flow through the cooling passage. For this purpose, the cooling device may optionally have a pump and suitable supply and outlet lines. In particular, the supply of cooling fluid to at least one insertion member and the guidance of the cooling fluid from the at least one insertion member may be achieved by means of dual piping. Optionally, the cooling device may also have a closed-loop control device, which has been further described above in the context of the insertion member, wherein a sensor signal from a temperature sensor is transmitted to the closed-loop control device and is designed to act on the switchable valve and / or temperature control element in the manner described above.

[0042] Another aspect of the present invention relates to an insertion member for introduction into a cavity of a substrate, particularly a substrate of an optical element configured as described above, comprising: a body having at least one cooling fluid inlet and at least one cooling fluid outlet; a distributor integrated in the body for connecting the at least one cooling fluid inlet to a plurality of feed ports; and a collector integrated in the body for connecting the at least one cooling fluid outlet to a plurality of discharge ports, wherein the at least one cooling fluid inlet and the at least one cooling fluid outlet are preferably formed on the same side of the rod-shaped insertion member for connection to at least one conduit, preferably to two conduits.

[0043] The insert member described herein has the advantages further described above in the context of optical elements. The insert member can be manufactured in a conventional manner by appropriately machining the body of the insert member. In this case, the insert member can be integrally formed or can be composed of the body.

[0044] In one specific embodiment, the body is produced by an additive manufacturing method. In this case, the body or insert member typically has a rod-like form. If the insert member has a rod-like form, the body can be manufactured by an additive manufacturing method (3-D printing), for example by powder bed manufacturing, typically without a support structure. During additive manufacturing, the longitudinal direction of the body of the insert member corresponds to the structural direction. Typically, the individual layers produced during additive manufacturing have a generally circular cross-section. To achieve the desired surface quality on the side surfaces of the rod-like insert member, it is typically necessary to print the external geometry of the body within a range of about 1 mm. Therefore, it is recommended not to print the dispenser grooves in this process, but rather to introduce these dispenser grooves retroactively in a conventional manner, that is, typically by machining, for example by milling.

[0045] Additive manufacturing of the main body allows for the creation of structures in the distributors and collectors that promote the flow of cooling fluid and, in particular, reduce vibrations caused by the flow. Such structures are typically impossible to achieve using conventional manufacturing methods. Furthermore, additive manufacturing can integrate the functional components further described above (e.g., in the form of valves, temperature controls, or heating elements and temperature sensors) into the main body, thereby achieving maximum functional integration with minimal volume.

[0046] Other features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, from the accompanying drawings which show important details of the invention, and from the scope of the claims. In a variant of the invention, each feature may be implemented individually or as a plurality of features in any desired combination.

Implementation Method

[0058] Referring to FIG1, the basic components of an optical configuration for EUV lithography, in the form of a lithography projection exposure apparatus 1 (EUV lithography apparatus), will be described below by way of example. In this context, the description of the basic structure and components of the projection exposure apparatus 1 should not be interpreted restrictively.

[0059] In a specific embodiment of the illumination system 2 of the projection exposure apparatus 1, in addition to including a light source or radiation source 3, an illumination optical unit 4 is included for illuminating the object field 5 in the object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0060] The mask 7, which is positioned in the object field 5, is illuminated. The mask 7 is held by a mask holder 8. The mask holder 8 can be displaced by a mask displacement driver 9, particularly in the scanning direction.

[0061] In a specific embodiment of the illumination system 2 of the projection exposure apparatus 1, in addition to including a light source or radiation source 3, an illumination optical unit 4 is included for illuminating the object field 5 in the object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0062] For illustrative purposes, Figure 1 illustrates the Cartesian xyz coordinate system. The x-direction is perpendicular to the drawing plane and enters the drawing plane. The y-direction moves horizontally, and the z-direction moves vertically. In Figure 1, the scan direction moves along the y-direction. The z-direction is perpendicular to the object plane 6.

[0063] The projection exposure apparatus 1 includes a projection system 10. The projection system 10 is used to image the object field 5 onto an image field 11 in an image plane 12. The structure on the mask 7 is imaged onto the photosensitive layer of the wafer 13, wherein the wafer 13 is disposed in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced by a wafer displacement driver 15, particularly along the y-direction. The mask 7 is displaced by a mask displacement driver 9 on one hand, and the wafer 13 is displaced by the wafer displacement driver 15 on the other hand, which can be performed synchronously.

[0064] Radiation source 3 is an EUV radiation source. Specifically, radiation source 3 emits EUV radiation 16, which is also referred to below as operational radiation, illumination radiation, or illumination light. Specifically, the operational radiation has a wavelength in the range of 5 nm to 30 nm. Radiation source 3 can be a plasma source, such as an LPP source ("laser-generated plasma") or a GDPP source ("gas discharge-generated plasma"). It can also be a synchrotron-based radiation source. Radiation source 3 can be a free electron laser (FEL).

[0065] Illumination radiation 16 emitted from radiation source 3 is focused by a concentrator mirror 17. The concentrator mirror 17 may be a concentrator mirror having one or more elliptical and / or hyperboloidal reflective surfaces. At least one reflective surface of the concentrator mirror 17 may be impacted by the illumination radiation 16 with grazing incidence (GI) (i.e., an incident angle greater than 45°) or with normal incidence (NI) (i.e., an incident angle less than 45°). The concentrator mirror 17 may be structured and / or coated, primarily to optimize its reflectivity to the radiation in use, and secondarily to suppress incoming light.

[0066] Downstream of the light collector mirror 17, the illumination radiation 16 propagates through the intermediate focal point in the intermediate focal plane 18. The intermediate focal plane 18 can represent the separation between the radiation source module (which has the radiation source 3 and the light collector mirror 17) and the illumination optical unit 4.

[0067] The illumination optics unit 4 includes a deflecting mirror 19 and a first faceted mirror 20 disposed downstream of it in the beam path. The deflecting mirror 19 may be a planar deflecting mirror or a mirror having a beam-affecting effect beyond mere deflection. Alternatively or additionally, the deflecting mirror 19 may be in the form of a spectral filter that separates the wavelength of the illumination radiation 16 used from the wavelength of incoming light that deviates from it. The first faceted mirror 20 includes a plurality of individual first facets 21, which are also referred to hereinafter as field facets. Only a few of these facets 21 are shown in FIG. 1 by way of example. In the beam path of the illumination optics unit 4, a second faceted mirror 22 is disposed downstream of the first faceted mirror 20. The second faceted mirror 22 includes a plurality of second facets 23.

[0068] The illumination optics unit 4 thus forms a double-faceted system. This basic principle is also called a fly-eye concentrator (fly-eye integrator). With the help of the second faceted mirror 22, each of the first facets 21 is imaged into the object field 5. The second faceted mirror 22 is the last beam-forming mirror, or actually the last mirror in the beam path upstream of the object field 5 for illumination radiation 16.

[0069] The projection unit 10 includes a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure device 1.

[0070] In the example shown in Figure 1, the projection optics unit 10 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors M1 are also possible. The penultimate mirror M5 and the last mirror M6 each have a through-hole for illumination radiation 16. The projection optics unit 10 is a double-shielded optics unit. The image-side numerical aperture of the projection optics unit 10 is greater than 0.4 or 0.5, and may be greater than 0.6, and may be, for example, 0.7 or 0.75.

[0071] Just like the reflector of the illumination optics unit 4, the reflector Mi may have a highly reflective coating for illumination radiation 16 (EUV radiation).

[0072] Figures 2a-d show in detail the fourth reflector M4 of the projection system 10. The reflector M4 has a substrate 25 formed of a so-called zero-expansion material. In this example, the zero-expansion material is titanium-doped quartz glass (ULE®), but the substrate 25 may also be formed of other zero-crossing materials. The substrate 25 has a first partial body 26a and a second partial body 26b, which are placed (joined) together at an interface 25a, which is flat in the example shown. A coating 28, whose lateral edges are shown in dashed lines in Figure 2a, is applied to a surface 27 of the first partial body 26a, which is flat in Figures 2a-d. The reflective coating 28 is designed to reflect EUV radiation 16. For this purpose, the reflective coating 28 is designed as an interference layer system and has a plurality of layers alternating between high and low refractive indices. In the example shown in Figure 2a, the reflective coating 28 is applied only to a portion of the surface 27 of the first partial body 26a, but it is understood that the reflective coating 28 may also cover the entire surface 27 of the first partial body 26a.

[0073] As is clearly seen from FIG. 2a, a plurality of cooling channels 29 extend in the substrate 25 below the surface 27 having the reflective coating 28. In the example shown in FIG. 2a, the cooling channels are formed by grooves introduced into a second part body 26b adjacent to the interface 25a. The first part body 26a is plate-shaped and covers the grooves or cooling channels 29 in the second part body 26b over the entire area. It is understood that a portion of the cross-section of the cooling channel 29 may also be formed in the first part body 26a. Furthermore, the substrate 25 is not necessarily composed of two or more part bodies 26a, b; rather, the substrate 25 may optionally have a monolithic form. In any case, the relatively small distance between the cooling channels 29 and the surface 27 to which the reflective coating 28 is applied is advantageous for effectively cooling the optical element M4 in the area where EUV radiation 16 is incident on the reflective coating 28.

[0074] To allow a cooling fluid in the form of cooling water (not depicted in Figures 2a-d) to flow through the cooling channel 29, a rod-shaped, substantially cylindrical insert member 31 has been introduced into the cylindrical cavity 30 of the substrate 25. In the example shown, the cavity 30 is formed as a blind hole. In the example shown, the rod-shaped insert member 31 has an integral form and matches the geometry and dimensions of the cavity 30 in terms of its geometry and dimensions. The insert member 31 may protrude beyond the substrate 25 or beyond the cavity 30 to the outside, as shown in Figure 2a; however, this is not mandatory.

[0075] As can be clearly seen from Figure 2b, the insertion member 32 has a cooling fluid inlet 32 ​​and a distributor 33 for connecting the cooling fluid inlet 32 ​​to a plurality of cooling channels 29. The insertion member 31 also has two cooling fluid outlets 34a, b, which are connected to the plurality of cooling channels 29 by means of a collector 35. The cooling fluid inlet 32 ​​and the two cooling fluid outlets 34a, b form an opening on the common end side 36 of the rod-shaped insertion member 31.

[0076] For the connection between the cooling fluid inlet 32 ​​and the plurality of cooling channels 29, the distributor 33 has a common inlet channel 37, which abuts the cooling fluid inlet 32 ​​at the end side 36 of the insert member 31. The inlet channel 37 extends along the longitudinal axis of the rod-shaped insert member 31 at its center, which extends parallel to the Y direction of the XYZ coordinate system shown in FIG. 2a. A plurality of feed ports 38 formed in the insert member 31 lead to the common inlet channel 37, each feed port serving to establish a connection between the distributor 33 and one of the cooling channels 29. The number of feed ports 38 corresponds to the number of cooling channels 29 in the example shown.

[0077] The collector 35 has two outlet channels 39a and b, which are adjacent to corresponding cooling fluid outlets 34a and b, for establishing a connection between the two cooling fluid outlets 34a and b and a plurality of cooling channels 29. The two outlet channels 39a and b extend longitudinally along the rod-shaped insert member 31 and are radially offset outward from the center of the insert member 31. A plurality of outlets 40 formed in the insert member 31 lead to the common outlet channels 39a and b, each outlet for establishing a connection between the collector 35 and one of the cooling channels 29. The number of outlets 40 corresponds to the number of cooling channels 29 in the example shown.

[0078] As can be clearly seen from FIG. 2c, the cavity 30 formed in the substrate 25 cuts into the cooling channel 29: in this way, the first opening 41a of the corresponding feed port 38 connected to the distributor 33 is formed in the corresponding cooling channel 29. Therefore, the corresponding cooling channel 29 is connected to the discharge port 40 of the collector 35 of the insertion member 31 through the second opening 41b in the substrate 25.

[0079] As can be clearly seen from Figures 2a and 2c, the corresponding cooling channels 29 in the substrate 25 extend substantially perpendicular to the longitudinal direction of the insertion member 31. The corresponding cooling channels 29 have a self-contained elongated profile with two channel portions 42a and 42b extending on opposite sides of the insertion member 31: starting from the first opening 41a, the first channel portion 42a initially extends linearly in the positive X direction until it reaches a first semi-circular deflection portion 43a for reversing the flow direction of the cooling fluid. From the first deflection portion 43a, the first channel portion 42a continues linearly to the second opening 41b. Starting from the first opening 41a, the second channel portion 42a correspondingly initially extends linearly in the negative X direction until it reaches a second semi-circular deflection portion 43b for reversing the flow direction of the cooling fluid. From the second deflection portion 43b, the first channel portion 42b continues linearly back to the second opening 41b.

[0080] In the example shown in FIG2a, the cooling fluid flow from the inlet 38 is divided into two channel portions 42a, b as it passes through the first opening 41a. The cooling fluid flowing through the two channel portions 42a, b then converges at the second opening 41b and exits the cooling channel 29 through the second opening 41b and the associated outlet 40.

[0081] The distributor 33 and the collector 35 are separated from each other in the insert member 31, meaning there is no fluid connection between the distributor 33 and the collector 35 in the insert member 31. However, a (not actually necessary) fluid connection exists between the respective inlets 38 and the respective outlets 40 via a gap 44, which is shown in FIG. 2d and formed between the cylindrical side surface 47 of the insert member 31 and the cylindrical wall 30a of the cavity 30 (see the arrow in FIG. 2d). The gap 44 illustrated in FIG. 2d has a gap width b slightly less than about 0.5 mm or 0.1 mm. The dimensions of the insert member 31 and the cavity 30 are matched to each other as precisely as possible so that the width b of the gap 44 is as small as possible. To avoid a significant change in the width b of the gap 44 when the reflector M4 is heated, the insert member 31 is formed of a material with a low coefficient of thermal expansion, specifically invariant steel (Invar) in the example shown.

[0082] An O-ring seal 45 is used to seal the circumferential gap 44 relative to the optical element M4. This seal is introduced into a circumferential annular groove formed on the side surface of the insert member 31, as can be clearly seen from FIG. 3a, which shows the insert member 31 in a partial cross-sectional view. Although it is theoretically possible to provide other seals for separating the inlet 38 from the outlet 40 in a fluid-tight manner, such seals are generally not required because the pressure loss on the gap 44 is relatively low.

[0083] Several options exist for the design of the feed inlet 38 starting from the common inlet channel 37 in the example shown, and the design of the discharge outlet 40 starting from the two outlet channels 39a, 39b. In the case of the insert member 31 shown in Figures 2a-d and 3a, the corresponding feed inlet 38 has a feed groove 46 that is introduced into the side surface 47 of the insert member 31 and extends completely around the side surface 47 in the circumferential direction. As can be easily seen from Figure 3a, the corresponding feed inlet 38 also has a plurality of feed channels 48 that extend radially and are radially adjacent to the feed groove 46, which connects the feed groove 46 and the inlet channel 37. The corresponding feed channels 48, in the form of radial holes, lead to the feed groove 46.

[0084] In the insert member 31 shown in FIG. 3a, the corresponding outlet 40 is formed as a discharge groove 49, which is also formed on the side surface 47 of the insert member 31 and extends completely around the latter in the circumferential direction. Since the two outlet channels 34a, 34b are further outward in the radial direction than the inlet channel 37, the discharge groove 49 in the illustrated example has such a deep shape that the latter cuts into the outlet channels 34a, 34b, so it is possible not to provide radial holes for connecting the corresponding discharge groove 49 to the outlet channels 34a, b. Unlike that shown in FIG. 2a-d and FIG. 3a, it is also possible to selectively omit the provision of the feed groove 46 and / or discharge groove 49 entirely.

[0085] The insert member 31 shown in Figures 2a-d and 3a (with a cooling fluid inlet 31 radially mounted on its end face 36 and two cooling fluid outlets 34a-b radially mounted on its outer side) allows the insert member 31 to be connected to a dual conduit 50, which is shown exemplarily in Figure 3b. The dual conduit 50 has an inner tube 51a and an outer tube 51b. In the example shown in Figure 3b, cooling fluid 53 is supplied to the coolant inlet 32 ​​of the insert member 31 inside the interior 52 of the inner tube 51a. Thus, the cooling fluid 53 is guided out of the insert member 31 from the two cooling fluid outlets 34a, b in the gap 54 between the inner tube 51a and the outer tube 51b. The dual conduit 50 can be connected to the insert member 31 in a fluid-tight manner in the region of its end face 36.

[0086] The insert member 31 shown in Figures 2a-d and 3a is a conventionally manufactured member, in which the distributor 33 and the collector 35 are introduced into a rod-shaped cylindrical blank made of constant steel by machining (usually by drilling and / or milling). Typically, it is not easy to integrate functional components in such conventionally manufactured insert members 31.

[0087] Figures 4a-c show an insert member 31 having a substantially cylindrical body 55, produced by an additive manufacturing method. In the additive manufacturing method, the body 55 is manufactured layer by layer by a powder bed, specifically along the construction direction, indicated by the arrow in Figure 4a, which corresponds to the longitudinal direction of the body 55. At the end, the body 55 has a tapered portion on which a central cooling fluid inlet 32 ​​and a single annular cooling fluid outlet 34 are formed. Similar to the insert member 31 shown in Figures 2a-d, the insert member 31 shown in Figures 4a-c is inserted into the cylindrical cavity 30 of the substrate 25 shown in Figure 2a. In this case, the tapered portion of the body 55 in Figure 4a protrudes beyond the substrate 25 to the outside and serves to contact the insert member 31 with the dual conduits 50 shown in Figure 3b.

[0088] The main body 55 of the rod-shaped insert member 31 is formed as a hollow structure and has a plurality of cavities inside, which make it possible to integrate different functional components into the insert member 31. However, basically, the structure of the insert member 31 of FIG4a-c is no different from that of the insert member 31 shown in FIG2a-d and FIG3a, as can be clearly seen from FIG5a, b and FIG6a, b, in which the distributor 33 and the collector 40 are highlighted in each case, which will be described in more detail below.

[0089] As can be clearly seen from Figures 5a and 5b, two switchable valves 56a and 56b are configured in the distributor 33 between an inlet channel 37 (which extends along the longitudinal direction of the insertion member 31) and a corresponding feed port 38. The two valves 56a and 56b are connected in parallel, that is, the cooling fluid 53 can flow in parallel from the inlet channel 37 through the two valves 56a and 56b and reach the same feed port 38, provided that the valves 56a and 56b are in a switching state that facilitates the supply of cooling fluid 53 to the feed port 38. As can be clearly seen from Figure 5b, each feed port 38 has a feed groove 46 that extends in the circumferential direction incompletely around the side surface 47 of the insertion member 31 to provide space for the valves 56a and 56b, which are inserted into the body 55 from the outside via the side surface 47 and are flush with the supply groove 46. The supply tank 46 is connected to two valves 56a and 56b via two parallel supply channels 48a and 48b. Furthermore, the two supply channels 48a and 48b are interconnected via a connection portion 48c, which connects the outputs of the two valves 56a and 56b to each other.

[0090] If the cooling fluid 53 is supplied to two separate cooling channels 29 via the same feed trough 46, the two cooling channel portions 42a, 42b shown in FIG. 2a can be separated from each other by means of a web formed in the substrate 25. If the connecting portion 48c is omitted in this case, the flow rates of the two separate cooling channels connected to the feed trough 46 can be set independently of each other by means of the first valve 56a or the second valve 56b.

[0091] Figures 6a and 6b show a collector 40 having a discharge groove 49 that surrounds the insertion member 31 in an annular manner, similar to the insertion member 31 shown in Figures 2a-d. In the example shown, the collector 40 has three outlet channels 39a-c that extend in the longitudinal direction of the insertion member 31 and connect to a common annular cooling fluid outlet 34. The respective outlet channels 39a-c are connected to the associated discharge groove 49 via corresponding discharge channels 57a-c that extend radially.

[0092] As shown in Figures 7a and 7b, two cable channels 58a and 58b are integrated into the body 55 for electrical contact with valves 56a and 56b, and these cable channels extend along the longitudinal direction of the insertion member 31. Wires 59 for electrical contact with the respective first and second valves 56a and 56b extend within the cable channels 58a and 58b. As can be seen from Figure 7a, the wires 59 are guided out of the cable channels 58a and 58b in the region of the end side 36 or in the tapered portion of the body 55 and connected to a control device (not shown) for actuating valves 56a and 56b. To seal the cable channels 58a and 58b in a fluid-tight manner, valves 56a and 56b may be selectively molded into the body 55. However, valves 56a and 56b may also be sealed relative to the cable channels 58a and 58b in any other manner. Needless to say, the cable channels 58a and 58b may also be used for electrical contact with other functional components integrated into the body 55, as described in more detail below.

[0093] By means of switchable valves 56a, b (which in each case are connected to a feed trough 46 for one of the cooling channels 29 shown in FIG. 2a), it is possible (which will be described below based on FIG. 8a) to set or influence the zone-by-zone temperature distribution below the surface 27 on which the reflective coating 28 is applied.

[0094] In FIG. 8a, the cooling channel 29 of FIG. 2a is depicted based on the flow direction of the cooling fluid 53. As described above, the cooling fluid 58 supplied to the cooling channel 29 via the feed trough 46 is divided into two channel portions 42a, b, and guided back to the associated discharge trough 49 through deflection regions 43a, b. By means of two switchable valves 56a, b (each of which can switch between a fully closed first switching state and a fully open second switching state), three different flow rates through the respective cooling channels 29 can be set, which are distinguished by different types of dashed lines in FIG. 8a.

[0095] In the first set of cooling channels 29, illustrated by dashed lines in Figure 8a, both valves 56a and b are in a first switching state, meaning no cooling fluid 53 flows through the first set of cooling channels 29. Therefore, no cooling is achieved through the first set of cooling channels, and the substrate 25 has a first temperature T1 around the first set of cooling channels 29. In the second set of cooling channels 29, illustrated by dashed lines with long dashes in Figure 8a, the first valve 56a is in a first switching state, and the second valve 56b is in a second switching state, or vice versa. Therefore, the cooling fluid 53 flows through the corresponding cooling channel 29 at half its maximum flow rate, and the substrate 25 has a second temperature T2 around the corresponding cooling channel 29. In the third set of cooling channels 29, illustrated by dashed lines with short dashes in Figure 8a, both valves 56a and b are in a second switching state, meaning the cooling fluid 53 flows through the second set of cooling channels 29 at its maximum flow rate. Therefore, the substrate 25 has a third temperature T3 around the cooling channels 29 of the third group, and the following applies: T1 > T2 > T3.

[0096] By appropriately activating the two valves 56a and b, the corresponding cooling channels 29 can be assigned to one of the three groups, thus allowing for zonal temperature control of the substrate 25. In this way, a spatially relevant temperature distribution of the substrate 25 below the surface 27 where the reflective coating 28 is applied can be set (within limitations). The resolution and geometry of the resulting temperature distribution are defined by the size and geometry of the area covered by the corresponding cooling channel 29 below the surface 27. In the example shown in FIG8a, the temperature distribution in the substrate 25 can be set as a plurality of elongated temperature zones that extend in the X direction, have only a small range in the Y direction, and substantially correspond to the range of the corresponding cooling channel 29.

[0097] In the example shown in FIG. 8b, the configuration of the cooling channels 29 differs from that in FIG. 8a or FIG. 2a. Specifically, they are concentrically arranged around the center of the surface 27 of the substrate 25 to which the reflective coating 28 is applied. This center roughly corresponds to the middle (in the longitudinal direction) of the insert member 31 shown in FIG. 8b, from which the innermost and shortest concentric cooling channels 29 begin. In the example shown in FIG. 8b, the cooling channels 29 are also divided into three groups according to their flow rate, and these groups are concentrically arranged around the middle of the insert member 31.

[0098] It is understood that, instead of the diagrams shown in Figures 8a and 8b, it is possible to define different configurations of the cooling channel 29, and thus different configurations and geometries of the temperature zones, wherein the corresponding temperatures T1, T2, and T3 of the substrate 25 can be set.

[0099] Unlike the figures 8a and 8b, if the two channel portions 42a and 42b do not form a common cooling channel 29, but instead form two separate cooling channels, as further described above in the context of Figure 5b, then the temperatures in the substrate 25 on the left and right sides of the insertion member 31 can be set independently.

[0100] Figure 9a schematically shows the supply of two adjacent cooling channels 29a, b, each of which is supplied with cooling fluid 53 via dedicated valves 56a, 56b. The cooling fluid 53 is supplied to valves 56a, b via a common inlet channel 37, flows through the inlet and the corresponding cooling channel 29a, b, and exits the corresponding cooling channel 29a, b via an outlet connected to an outlet channel 39. The cooling fluid 53 is supplied to the insertion member 31 (shown in dashed lines in Figure 9a) via a cooling device 60, which is part of the EUV lithography apparatus 1 and includes a pump and other components not shown here. In the example shown in Figure 9a, valves 56a, b can be switched between more than two switching states to set the flow rate of the cooling fluid 53 through the corresponding cooling channel 29a, b. For example, valves 56a, b shown in Figures 9a and 5a, b can be in the form of miniature valves, which facilitate switching between switching states using shape memory alloys.

[0101] In the example shown in FIG. 9b, the insertion member 31, in addition to the two valves 56a and b, also has two temperature control elements in the form of heating elements 61a and b, which are used to heat the cooling fluid 53 before supplying it to the corresponding cooling channels 29a and b. The heating elements 61a and b are disposed between the inlet channel 37 and the feed port (not shown here) of the insertion member 31 to the corresponding cooling channels 29a and b, downstream of the corresponding switchable valves 56a and b in the flow path. By heating the cooling fluid 53 with the help of the corresponding heating elements 61a and b, the temperature in the relevant cooling channels 29a and b can be set. If heating elements 61a and b are used, the temperature in the inlet channel 37 can be selected to be lower than other conventional temperatures, for example, it can be about 18°C. By means of the corresponding heating elements 61a and b, the temperature in the relevant cooling channels 29a and b can be raised to, for example, room temperature (22°C), provided that cooling is not required in the area of ​​the substrate 25 associated with the cooling channels 29a and b. It should be understood that, in the example shown in Figure 9b, the valves 56a and 56b inserted in component 31 can be optionally omitted entirely. For example, heating elements 61a and 61b can be in the form of small silicon nitride-based heaters. Other types of temperature control elements 61a and 61b are also possible, such as Peltier elements, which facilitate cooling of the cooling fluid 53 or a combination of heating and cooling of the cooling fluid 53.

[0102] The insertion member 31 shown in FIG. 9b also has temperature sensors 62a, b, which are associated with the corresponding cooling channels 29a, b. The temperature sensors 62a, 62b are disposed in the region of the corresponding outlet (not shown here) of the insertion member 31 and are used to measure the temperature of the cooling fluid 53 as it exits the corresponding cooling channel 29a, b. This configuration is advantageous because the temperature of the cooling fluid 53 at the inlet of the cooling channel 29a, b substantially corresponds to the temperature of the cooling fluid 53 in the inlet channel 37. It should be understood that, supplementarily or alternatively, the temperature of the cooling fluid 53 can also be measured at the inlet of the corresponding cooling channel 29a, b using the corresponding temperature sensor disposed inside or downstream of the corresponding heating element 61a, b. In this way, the temperature of the cooling fluid 53 can be measured at both the inlet and outlet of the corresponding cooling channel 29a, b.

[0103] In the example shown in FIG9c, the temperature of the cooling fluid 53 in the inlet channel 37 and the outlet channel 39 is also measured by corresponding dedicated temperature sensors 62c and 62d. As can be clearly seen from FIG9c, the temperature sensor 62c in the inlet channel 37 is configured directly adjacent to the cooling fluid inlet 32 ​​to record and selectively correct for crosstalk or effects of heat sources in the feed port or cooling device 60 (see below). Therefore, the temperature sensor 62d is configured adjacent to the cooling fluid outlet 34 in the outlet channel 39 to determine and selectively correct for exposure load or temperature rise during exposure (see below).

[0104] In the control loop, information provided by temperature sensors 62a-d can be used to set a desired temperature distribution in substrate 25, such as a substantially uniform temperature distribution. A controller 63 is shown exemplarily in FIG. 9b, wherein a second temperature sensor 62b configured in the second cooling channel 29b provides the controller with the actual temperature TIST of the cooling fluid 53 monitored or measured at the output of the second cooling channel 29b. The controller 63 adjusts the actual temperature TIST in the second cooling channel 29b to a target temperature TSOLL, which is typically specified for the controller 63 by an external device (e.g., cooling device 60). In the example shown, the controller 63 appropriately operates on the second heating element 61b to minimize the difference between the actual temperature TIST and the target temperature TSOLL.

[0105] It is understood that, for this purpose, the controller 63 can act not only on the second heating element 61b, but also on all heating elements 61a, b and / or the switchable valves 56a, b of FIG. 9a. Furthermore, for closed-loop temperature control, the controller 63 can use not only the actual temperature TIST measured by the second temperature sensor 62b, but also the actual temperature measured by other temperature sensors 62a, 62c, 62d. Generally, as more temperature sensors are provided, the local resolution during closed-loop control of the temperature distribution will also improve.

[0106] However, the insertion member 31 may not include functional components that facilitate the adjustment of temperature distribution. In this case, the temperature sensors 62a, 62b are only used to monitor the temperature in the cooling channels 29a, b or the substrate 25, to determine, for example, a malfunction in the supply of cooling fluid 53 to the reflector M4 or, if necessary, to selectively adjust the parameters of the EUV lithography apparatus 1, such as the power of the radiation source 3.

[0107] The electrical contact between the heating elements 61a, b and the temperature sensors 62a-d can be achieved in the manner further described above in the context of Figures 7a, b, that is, by means of two cable channels 58a, b integrated in the body 55 of the insertion member 31, or by means of corresponding wires 59.

[0108] The insert member 31 illustrated in Figures 4a-c and the body 55 produced by additive manufacturing method are conducive to achieving maximum functional integration with minimal volume: although functional components in the form of valves 56a, b, heating elements 61a, b, and / or temperature sensors 62a-d are integrated, the insert member 31 shown in Figures 4a-d can have a small outer diameter of no more than about 35 mm. This size design of the insert member 31 is advantageous or necessary due to the relatively small thickness of the substrate 25, since it would otherwise be impossible to integrate it into the cavity 30 of the substrate 25. [Simplified Explanation of the Diagram]

[0047] Exemplary specific embodiments are illustrated in the schematic diagram and explained in the following description. In detail:

[0048] Figure 1 schematically shows a meridional section of a projection exposure apparatus used for EUV lithography;

[0049] Figures 2a-d show schematic diagrams of the reflector of the projection exposure apparatus of Figure 1, which has a plurality of cooling channels and an insertion member inserted into a cavity in the substrate;

[0050] Figures 3a and 3b show schematic diagrams of the insert member of Figures 2a-d and the dual pipes for connecting the cooling circuit to the insert member, shown in partial cross-section in each case;

[0051] Figures 4a-c show schematic diagrams of an insert member having a valve for controlling the flow rate of cooling fluid through the cooling channel;

[0052] Figures 5a and 5b show schematic diagrams of the distributors of the insertion components in Figures 4a-c, each having two valves for controlling the flow rate of cooling fluid through the cooling channel;

[0053] Figures 6a and 6b show schematic diagrams of the current collector of the insertion component in Figures 4a-c;

[0054] Figures 7a and 7b show schematic diagrams of the cable channels of the insertion components in Figures 4a-c;

[0055] Figures 8a and 8b show schematic diagrams of the flow through two different configurations of the cooling channels of the insert member of Figures 4a-c, wherein the cooling fluid flows through the cooling channel group at different flow rates; and

[0056] Figures 9a and 9b show schematic diagrams of the flow through two cooling channels, using corresponding valves or valves, heating elements and temperature sensors.

[0057] In the following description of the drawings, the same element symbols are used for the same or functionally identical components.

Claims

1. An optical element for reflecting radiation, comprising: a substrate; a reflective coating applied to a surface of the substrate; a plurality of cooling channels operating in the substrate below the surface to which the reflective coating is applied; a distributor for connecting at least one cooling fluid inlet to the plurality of cooling channels; and a collector for connecting the plurality of cooling channels to at least one cooling fluid outlet, characterized in that: the distributor and / or the collector is integrated into at least one insert member, the insert member being introduced into at least one cavity formed in the substrate.

2. The optical element as claimed in claim 1, wherein the distributor and the collector are both integrated into the same insert member.

3. The optical element as claimed in claim 2, wherein the at least one cooling fluid inlet and the at least one cooling fluid outlet are formed on the same side of the insertion member to connect to at least one conduit.

4. The optical element as claimed in claim 3, wherein the at least one coolant inlet is radially mounted inside the rod-shaped insert member for connecting to the interior of an inner tube of the dual-channel system, and the at least one coolant outlet is radially mounted outside the rod-shaped insert member for connecting to a gap between the inner tube and an outer tube of the dual-channel system, or vice versa.

5. The optical element as claimed in any one of claims 1 to 4 further comprises: at least one seal for sealing a gap relative to the surrounding environment, the gap being formed between a wall of the cavity and the insert member introduced into the cavity.

6. An optical element as claimed in any one of claims 1 to 4, wherein at least one cooling channel has at least one deflection portion for deflecting the cooling fluid.

7. The optical element as claimed in any one of claims 1 to 4, wherein the distributor has a plurality of inlets for connecting the at least one cooling fluid inlet to at least one cooling channel in each case, and / or wherein the collector has a plurality of outlets for connecting the cooling fluid outlet to at least one cooling channel in each case.

8. The optical element as claimed in claim 7, wherein the feed ports lead to at least one common inlet channel connected to at least one cooling fluid inlet and / or wherein the discharge ports lead to at least one common outlet channel connected to at least one cooling fluid outlet.

9. The optical element as claimed in claim 8, wherein the feed ports are connected to the common inlet channel via a plurality of feed channels, and / or wherein the discharge ports are connected to the common outlet channel via a plurality of discharge channels.

10. The optical element as claimed in claim 7, wherein the feed ports form or have a feed groove formed on at least a portion of the side surface of the insert member, and / or wherein the discharge ports form or have a discharge groove formed on at least a portion of the side surface of the insert member.

11. The optical element as claimed in any one of claims 1 to 4, wherein the distributor has at least one switchable valve for supplying a cooling fluid to at least one of the cooling channels.

12. The optical element as claimed in claim 11, wherein the distributor has at least two switchable valves connected in parallel to supply the cooling fluid from the inlet channel to the feed port.

13. The optical element as claimed in any one of claims 1 to 4, wherein the insertion member has at least one temperature control element for controlling the temperature of the cooling fluid.

14. The optical element as claimed in any one of claims 1 to 4, wherein the insertion member has at least one temperature sensor for monitoring a temperature of the cooling fluid in at least one cooling channel, at least one inlet channel, and / or at least one outlet channel.

15. The optical element as claimed in claim 14, wherein the insertion member has a closed-loop control device for adjusting the temperature of the cooling fluid to a target temperature by acting on the at least one switchable valve and / or the at least one temperature control element.

16. The optical element as claimed in any one of claims 1 to 4, wherein the insertion member has at least one cable channel for guiding a plurality of wires to electrically contact the at least one valve, the at least one temperature control element, and / or at least one temperature sensor.

17. An optical element as claimed in any one of claims 1 to 4, wherein the substrate has a first partial body and a second partial body joined together at an interface, the reflective coating is applied to a surface of the first partial body, and the plurality of cooling channels extend in the substrate in the region of the interface between the two partial bodies.

18. An optical configuration comprising: at least one optical element as claimed in any one of claims 1 to 17, and a cooling device designed to allow a cooling fluid to flow through the plurality of cooling channels.

19. An insert member for insertion into a cavity of a substrate, comprising: a body having at least one cooling fluid inlet and at least one cooling fluid outlet; a distributor integrated into the body for connecting the at least one cooling fluid inlet to a plurality of feed ports; and a collector integrated into the body for connecting the at least one cooling fluid outlet to a plurality of discharge ports, the at least one cooling fluid inlet and the at least one cooling fluid outlet being formed on the same side of the insert member for connection to at least one conduit.

20. The insert member as described in claim 19, wherein the body is produced by an additive manufacturing method.

Images