Venting of a heat transfer channel

Abstract

The invention relates to a method (V1, V2) for venting a liquid-filled heat transfer channel (101), which is arranged in and / or on an optical element (115; 19, 20, 22, M1-M6), in particular an optical element (115; 19, 20, 22, M1-M6) of a projection exposure apparatus (1), wherein the heat transfer channel (101) has a plurality of channel portions (108-113) having different channel cross-sections, the method involving: a) providing (S12) at least one flow variable which is indicative of a resonant flow state (120) in a respective channel portion (109, 112); and b) generating (S14) a liquid flow (122) through the heat transfer channel (101) such that the liquid flow (122) successively corresponds to each of the provided flow variables.

Description

[0001] Carl Zeiss SMT GmbH

[0002] 1

[0003] VENTING A HEAT TRANSFER CHANNEL

[0004] The present invention relates to a method for venting a liquid-filled heat transfer channel, which is coupled to an optical element, and in particular an optical element of a projection exposure system, for heat transfer, wherein the heat transfer channel has several channel sections of different channel cross-sections. Furthermore, the present invention also relates to a heat transfer device comprising a liquid-fillable or liquid-filled heat transfer channel, which is coupled or can be coupled to an optical element, and in particular an optical element of a projection exposure system, for heat transfer, a pump connected in series with the heat transfer channel, and a control device connected for controlling the pump.

[0005] Finally, the present invention relates to a projection exposure system which has the heat transfer device.

[0006] The content of priority application DE 102025 102249.6 is fully incorporated by reference.

[0007] Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system, which includes an illumination system and a projection system. The image of a mask (reticule) illuminated by the illumination system is projected by the projection system onto a substrate, such as a silicon wafer, coated with a photosensitive layer (photoresist) and positioned in the image plane of the projection system. This transfers the mask structure onto the photosensitive coating of the substrate.

[0008] Driven by the pursuit of ever smaller structures in the production of integrated circuits, EUV lithography systems are currently being developed that use light with a wavelength in the range of 0.1 nm to 30 nm, particularly 13.5 nm. Since most materials absorb light of this wavelength, such EUV lithography systems must use reflective optics, i.e., mirrors, instead of the previously used refracting optics, i.e., lenses.

[0009] The incident radiation transfers high energy into the optics, which heats the respective optical element. This heating is undesirable, and therefore optical elements are coupled with a heat transfer channel. Carl Zeiss SMT GmbH

[0010] 2

[0011] It is unavoidable that gas will collect in gas bubbles within the heat transfer duct during filling (residual air) and / or during operational flow (gas outgassed from the liquid). This can occur, for example, at the top of duct sections with an increased diameter, such as at the joints of two pipes, at a silencer or vibration damper, at a connection point, at a measuring point (e.g., a T-piece for connecting a pressure sensor), at an undercut, or similar locations. Generally speaking, gas can collect in a gas bubble in any duct section whose upper wall, in an installation position, is located higher than both an inlet and an outlet.If a liquid flows through the heat transfer channel during operation, this excites such gas bubbles to oscillations (so-called fluid-induced vibrations or flow-induced vibrations, technically: fluid-induced vibrations or FIV), which can be transmitted to the coupled optical element and can reduce imaging accuracy.

[0012] Against this background, one object of the present invention is to provide means for venting a liquid-filled heat transfer channel, particularly in the area of ​​optical elements of projection exposure technology.

[0013] Accordingly, a method for venting a liquid-filled heat transfer channel is proposed. The heat transfer channel is coupled to an optical element, and in particular an optical element of a projection exposure system, for heat transfer. The heat transfer channel has several channel sections with different channel cross-sections. The proposed method includes the step of providing at least one flow parameter. The flow parameter is indicative of a resonant flow state in a respective channel section. The method includes the step of generating a liquid flow through the heat transfer channel such that the liquid flow corresponds successively to each of the provided flow parameters.

[0014] The process causes a targeted excitation of resonant flow in each channel section for which a flow parameter is provided. A resonant flow can be understood, for example, as a local, unsteady, and non-linear flow. By exciting the flow at its resonant frequency, the resonant flow—a local, unsteady, and non-linear flow—is induced in the respective channel section, which is a Carl Zeiss SMT GmbH

[0015] 3

[0016] Mixing of the liquid or liquid phase with a gas from a gas bubble or gas phase present within it is achieved. The gas is subsequently carried away from the liquid by the flow. The process is independent of the course of the heat transfer channel or the position of the optical element. The heat transfer channel can be effectively vented using the steps of the proposed process.

[0017] Venting refers to the removal or release of any gas that may be present from the otherwise liquid-filled heat transfer channel.

[0018] Heat transfer refers to the suitability for transferring thermal energy and / or the process of transferring thermal energy. For example, this can mean that the optical element is cooled in imaging mode by transferring thermal energy from the optical element to the fluid in the heat transfer channel. Conversely, it can mean that the optical element is heated in preheating mode by transferring thermal energy from the fluid in the heat transfer channel to the optical element.

[0019] The fluid is suitable for absorbing heat energy from the heat transfer channel and for later releasing the heat energy (e.g.

[0020] Heat transfer operation). One can speak of a heat transfer fluid. The fluid can also be suitable, for example, for absorbing heat energy earlier and releasing the heat energy to the heat transfer channel (e.g., preheating operation). The fluid is, for example, water.

[0021] The term "heat transfer channel" can be understood as a conduit of any shape that is thermally coupled to the optical element. The heat transfer channel is suitable for heat transfer. The heat transfer channel can be a separate component or assembly ("formed on" the optical element) that is connected to the optical element. The heat transfer channel can be a recess in the optical element ("formed in" the optical element). The heat transfer channel can be partially formed within the optical element and partially formed separately and coupled to the optical element ("formed in and on" the optical element). Carl Zeiss SMT GmbH

[0022] 4

[0023] One can say that the heat transfer channel is coupled to an optically active surface and / or layer of the optical element, such as a mirror surface, reflective layer, and / or a radiation-refracting layer, for heat transfer. One can also say that the optical element is coupled to the heat transfer channel for the transfer of thermal energy.

[0024] A channel cross-section can be understood as the shape and size of the heat transfer channel at a specific or arbitrarily chosen location. For example, a channel cross-section can be understood as the shape and size of the heat transfer channel in a plane perpendicular to a track of the channel.

[0025] The term "heat transfer channel" can, for example, refer to a continuous or closed, branched or unbranched conduit including at least one section for heat transfer from / to the optical element. The term "channel section" (for which a flow parameter is provided) can therefore be understood as a minimum requirement of the process and not as an exclusion of providing further flow parameters. It is possible that at least one additional flow parameter is provided that is indicative of a resonant flow state in a respective section of an inlet to the heat transfer channel and / or an outlet from the heat transfer channel, whereby a fluid flow is also generated for this flow parameter.

[0026] The optical element is preferably a projection optic of a projection exposure system. However, the optical element can also be an illumination system. The projection exposure system can be an EUV lithography system. EUV stands for "Extreme Ultraviolet" and refers to a wavelength of the working light between 0.1 nm and 30 nm. The projection exposure system can also be a DUV lithography system. DUV stands for "Deep Ultraviolet" and refers to a wavelength of the working light between 30 nm and 250 nm.

[0027] The flow parameter, which is indicative of a resonant flow state in the respective channel section, can be understood as a value that defines the flow state. The flow parameter can be, for example, a value or a number. The flow parameter can, for example, contain a specification of the mass flow rate of the fluid in the heat transfer channel. The flow parameter can, for example, contain multiple values. The flow parameter can, for example, be a data set or part of a data set. Carl Zeiss SMT GmbH

[0028] 5

[0029] The flow parameter can, for example, be provided as an entry in a provided list.

[0030] A resonant flow state can be understood, for example, as a condition in which, with a constant flow rate, the disturbance energy increases over time. If, for instance, a mass flow rate (control parameter) through the heat transfer channel is selected according to the dimensions of a channel section, this results in an unsteady, non-linear flow that acts as a mixer. At the selected mass flow rate, the flow in the remainder of the heat transfer channel is preferably steady, but upon reaching the resonance frequency of this channel section, a turbulent, unsteady, and non-linear flow develops locally. For technical background, please refer to Chapter 2 of the publication "Linear and Non-Linear Stability of Incompressible Flows in a Double-Faned Rectangular Vessel," Stefan Albensoeder, Cuvillier Verlag, 37075 Göttingen, Germany.

[0031] The flow variable can, for example, specify the pump speed of a pump fluidically connected to the heat transfer channel (e.g., a hydrostatic machine). The flow variable can also, for example, specify a valve position. The flow variable can, for example, specify a setpoint that can be compared with a flow measuring device by a control unit. These are examples of flow control-related variables that can be easily implemented by a control unit.

[0032] The flow parameter may be a Reynolds number or indicative of a Reynolds number. For example, at least one value or specification may be provided which specifies or is indicative of a Reynolds number at which a flow in a particular channel section is resonant. These are examples of a flow-state-related parameter that can be predetermined independently of the device and is therefore easily transferable. Preferably, the Reynolds number is up to 2300, more preferably up to 2000, even more preferably up to 1000, and most preferably up to 500.

[0033] The flow rate may be indicative of laminar flow in at least one other section of the heat transfer channel. Laminar flow improves the transport of the gas mixed into the liquid by flow resonance. Thus, the gas is effectively transported out of the heat transfer channel. Carl Zeiss SMT GmbH

[0034] 6

[0035] Generating the fluid flow may involve setting a mass flow rate of the fluid in the heat transfer channel. The mass flow rate indicates the mass of fluid that flows or is pumped through the heat transfer channel per unit of time. It is therefore a temperature-independent parameter that can be maintained for different fluid temperatures. For example, a thermometer measures the fluid temperature, and a hydrostatic pump is operated accordingly. A mass flow rate is particularly suitable as a setpoint when using a Coriohs flow meter.

[0036] The generation of the fluid flow may be triggered by the filling of the heat transfer channel. "Filling" means filling with fluid. For example, the method may include monitoring or detecting whether the heat transfer channel is being filled with fluid, with the generation of the fluid flow triggered by this filling. For example, the generation of the fluid flow may be triggered according to the provided flow parameters after filling and before irradiating / exposing the optical element with useful radiation / light. For example, the generation of the fluid flow may be triggered according to the provided flow parameters during commissioning. The method thus provides for automation, resulting in the automatic venting of the heat transfer channel after it has been filled.This makes bleeding more reliable. Commissioning can also refer to recommissioning.

[0037] The generation of the liquid flow may occur during a pause operation of the optical element. A pause operation can be understood as a period during which the optical element is not irradiated with useful light. For example, a pause operation may occur during a reticle and / or wafer change. The pause operation may be scheduled periodically. It may also be initiated and / or triggered by a need for venting, thus maintaining a vented state for an extended period.

[0038] It is possible that a flow parameter is provided for each of several channel sections, whereby the liquid flow is generated in a flow sequence through the channel sections. It is therefore proposed that Carl Zeiss SMT GmbH

[0039] 7

[0040] Channel sections are vented sequentially, either away from a pushing pump or towards a suction pump. In short, several channel sections are vented one after the other according to their position along a flow path. For example, if the flow required to vent a channel section can be shorter than the flow required to traverse the entire heat transfer channel, this method can save venting time.

[0041] It is possible that a flow parameter is provided for each of several channel sections, and that the fluid flow is generated in a sequence corresponding to the magnitude of the flow parameter and / or the magnitude of a fluid flow state. In other words, the flow state can be continuously changed, remaining constant at certain values. Time can therefore be saved by having a single flow state value cycle through all possible and / or provided flow states only once. For example, if the flow parameter specifies a flow velocity, mass flow rate, and / or Reynolds number, venting can begin with a low flow velocity and increase in speed, or begin with a high flow velocity and decrease in speed.

[0042] It should be noted here that the flow sequence may be coincidental or intentional, corresponding to the order of the flow state magnitude. For example, a channel section with a resonant flow state at a low Reynolds number may be placed upstream of a channel section with a resonant flow state at a higher Reynolds number along the heat transfer channel.

[0043] The procedure may additionally include the following steps: a) measuring a quantity of liquid in the heat transfer channel and / or a quantity of gas exiting the liquid (downstream of the heat transfer channel) before and after generating the liquid flow, and b) outputting at least one value indicative of both quantities and / or their difference. The quantity of liquid can be understood, for example, as the volume of the liquid, the mass of the liquid, and / or the fill level of a liquid reservoir. By measuring the quantity of liquid before and after venting, the quantity of vented gas can be determined. Thus, for example, proof of the degree of venting can be provided. Carl Zeiss SMT GmbH

[0044] 8

[0045] The process may additionally include the step of monitoring a quantity of liquid in the heat transfer channel and / or a quantity of gas exiting the liquid (downstream of the heat transfer channel), whereby the monitoring is carried out during the generation of the liquid flow, and the liquid flow is generated depending on a change in the monitored quantity of liquid and / or gas. Thus, venting can be controlled depending on the quantity of gas vented. In other words, a specific flow state can be generated as long as venting is effectively ongoing. Therefore, one can say that the liquid flow is continuously generated depending on a change in the monitored quantity of liquid and / or gas. For example, it can be stipulated that venting continues as long as a change in the liquid quantity persists. This allows for particularly thorough venting.

[0046] The procedure may additionally include the following steps: a) monitoring the volume of liquid in the heat transfer channel and / or the volume of gas exiting the liquid (downstream of the heat transfer channel), with monitoring performed during normal operation of the optical element, and b) triggering the generation of liquid flow depending on the monitored volume of liquid and / or gas. This option can be described as demand-based venting. Thus, pauses solely for venting can be avoided based on liquid volume in situations where venting is not necessary.

[0047] The process may additionally include the step: a) monitoring a vibration-indicative quantity that is indicative of a level of flow-induced vibration in the heat transfer channel, wherein the monitoring is performed during the generation of the fluid flow, and wherein the fluid flow is generated depending on a change in the monitored vibration-indicative quantity. Thus, it can be said that the fluid flow is further generated depending on a change in the monitored vibration-dependent quantity. It is therefore proposed to adjust the duration of the venting process to the venting effect. This allows for reduced downtime and increased production times.

[0048] The procedure may additionally include the step: a) monitoring a vibration-indicative quantity that is indicative of a level of flow-induced vibrations in the heat transfer channel, whereby Carl Zeiss SMT GmbH

[0049] 9

[0050] Monitoring is performed during the optical element's operation, and b) the generation of liquid flow is triggered depending on the monitored vibration indicator. This option can also be described as demand-based venting. Thus, pauses solely for venting can be avoided based on vibration measurement in situations where venting is not necessary.

[0051] According to a further aspect of the invention, a heat transfer device is proposed. The heat transfer device comprises: a liquid-precipitable or liquid-filled heat transfer channel, which can be coupled to or is coupled to an optical element, and in particular an optical element of a projection exposure system, for heat transfer; a pump connected in series with the heat transfer channel; and a control device connected for controlling the pump, which is configured to perform the proposed venting method. The optional features described for the method apply accordingly to the proposed heat transfer device, and vice versa. The heat transfer device is suitable, by means of the control device, for exciting a resonant flow in each channel section for which a flow parameter is provided.The heat transfer channel of the proposed heat transfer device can be effectively vented by means of the steps of the procedure carried out by the control device.

[0052] The heat transfer device can be described as a heat transfer system, a heat transfer circuit, and / or a heat transfer circuit. The heat transfer device may contain further elements. For example, it may include a gas outlet, a servo motor, a supply line, a discharge line, and / or a fluid control device (e.g., a valve). The optical element may also be part of the heat transfer device.

[0053] The heat transfer device may have a device configured to measure the amount of liquid in the heat transfer channel and / or the amount of gas escaping from the liquid. This can be referred to as a liquid flow meter and / or a gas flow meter. This meter may measure a single physical quantity, but it may also measure multiple physical quantities, and / or multiple meters may be present and / or interconnected, each measuring at least one physical quantity. For example, a liquid level in a Carl Zeiss SMT GmbH

[0054] 10

[0055] The reservoir, a gas pressure in a reservoir, a gas mass flow in / out of a reservoir, a liquid temperature in the reservoir, a liquid temperature in the heat transfer channel, a liquid mass flow into the heat transfer channel and / or a liquid mass flow out of the heat transfer channel are measured or monitored.

[0056] The heat transfer device may have at least two channel sections, each with a partial volume open only downwards in its installed position, and which have the same and / or similar dimensions. Similar dimensions are defined, for example, as dimensions at which resonant oscillations occur at Reynolds numbers that differ by up to 5% (relative to the higher Reynolds number) or by up to 2%. By having multiple channel sections in which resonant flow occurs under the same flow conditions, the channel sections can be vented simultaneously and more quickly overall.

[0057] According to a further aspect of the invention, a projection exposure system is proposed which incorporates the proposed heat transfer device. The optional features described for the method and / or for the heat transfer device apply accordingly to the proposed heat transfer device, and vice versa. As a result, the influence of flow-induced vibrations on the imaging accuracy of the projection exposure system can be significantly reduced. In other words, the proposed projection exposure system is characterized by high imaging accuracy.

[0058] The term "one" here is not necessarily to be understood as restricting the number to exactly one element. Rather, it can also refer to multiple elements, such as two, three, or more. Similarly, every other counter used here should not be interpreted as restricting the number to the exact number stated. Instead, numerical deviations, both higher and lower, are possible unless otherwise specified.

[0059] Other possible implementations of the invention also include combinations of features or embodiments described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention. Carl Zeiss SMT GmbH

[0060] 11

[0061] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the embodiments of the invention described below. The invention will now be explained in more detail with reference to preferred embodiments and the accompanying figures.

[0062] Fig. 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography!

[0063] Fig. 2 shows a schematic system diagram of a heat transfer device including an optical element!

[0064] Fig. 3 shows a flowchart of a venting procedure that can be carried out during recommissioning / commissioning!

[0065] Fig. 4 shows a flowchart of a venting procedure that can be carried out during a break after an exposure operation.

[0066] In the figures, identical or functionally equivalent elements have been labelled with the same reference symbols, unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

[0067] Fig. 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of the illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optic 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0068] A reticule 7 arranged in the object field 5 is exposed. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in a scanning direction, via a reticule displacement drive 9.

[0069] Figure 1 illustrates a Cartesian coordinate system with an x-direction x, a y-direction y, and a z-direction z. The x-direction x runs perpendicular to the plane of the drawing. The y-direction y runs horizontally, and the z-direction z runs vertically. The scan direction runs in Carl Zeiss SMT GmbH

[0070] 12

[0071] Fig. 1 along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

[0072] The projection exposure system 1 comprises a projection optic 10. The projection optic 10 serves to image the object field 5 onto an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0073] A structure on the reticulum 7 is imaged onto a photosensitive layer of a wafer 13 located in the image plane 12 within the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction y, via a wafer transfer drive 15. The movement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0074] Light source 3 is an EUV radiation source. Light source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation 16 has a wavelength in the range between 5 nm and 30 nm. Light source 3 can be a plasma source, for example, an LPP source (Laser Produced Plasma, plasma generated using a laser) or a DPP source (Gas Discharged Produced Plasma, plasma generated by gas discharge). It can also be a synchrotron-based radiation source. Light source 3 can be a free-electron laser (FEL).

[0075] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 17 can be illuminated by the illumination radiation 16 at grazing incidence (Gl), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light. Carl Zeiss SMT GmbH

[0076] 13

[0077] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics 4.

[0078] The illumination optics 4 comprise a deflecting mirror 19 and, downstream in the beam path, a first faceted mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with a beam-shaping effect in addition to its deflecting function. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first faceted mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugate to the object plane 6 as the field plane, it is also referred to as a field faceted mirror. The first faceted mirror 20 comprises a plurality of individual first facets 21, which can also be referred to as field facets. Only a few of these first facets 21 are shown as examples in Fig. 1.

[0079] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or semicircular edge contour. The first facets 21 can be designed as planar facets or alternatively as convexly or concavely curved facets.

[0080] As is known, for example, from DE 102008009600 A1, the first facets 21 themselves can each be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can, in particular, be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 102008009600 A1.

[0081] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

[0082] In the beam path of the illumination optics 4, a second faceted mirror 22 is arranged downstream of the first faceted mirror 20. If the second faceted mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil faceted mirror. The second faceted mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first faceted mirror 20 is Carl Zeiss SMT GmbH

[0083] 14

[0084] and the second faceted mirror 22, also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 Al, EP 1614 008 Bl and US 6,573,978.

[0085] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0086] The second facets 23 can also be macroscopic facets, which can be round, rectangular or hexagonal, for example, or alternatively facets composed of micromirrors.

[0087] Reference is also made to DE 102008009600 Al in this regard.

[0088] The second facets 23 can have planar or alternatively convex or concave curved reflective surfaces.

[0089] The illumination optics 4 thus form a doubly faceted system. This basic principle is also known as a honeycomb condenser (EnglJ Fly's Eye Integrator).

[0090] It can be advantageous not to arrange the second faceted mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second faceted mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 102017220586 A1.

[0091] With the aid of the second faceted mirror 22, the individual first facets 21 are imaged into the object field 5. The second faceted mirror 22 is the last beam-shaping or indeed the last mirror for the illumination radiation 16 in the beam path before the object field 5.

[0092] In another embodiment of the illumination optics 4, not shown, a transmission optic can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optic can have exactly one mirror, or alternatively two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optic can in particular comprise one or two mirrors for normal incidence (Ni mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (GF mirrors, grazing incidence mirrors). Carl Zeiss SMT GmbH

[0093] 15

[0094] In the embodiment shown in Fig. 1, the lighting optics 4 has exactly three mirrors after the collector 17, namely the deflecting mirror 19, the first faceted mirror 20 and the second faceted mirror 22.

[0095] In a further embodiment of the lighting optics 4, the deflecting mirror 19 can also be omitted, so that the lighting optics 4 after the collector 17 can then have exactly two mirrors, namely the first faceted mirror 20 and the second faceted mirror 22.

[0096] The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optic into the object plane 6 is regularly only an approximate imaging.

[0097] The projection optics 10 comprise a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0098] In the example shown in Fig. 1, the projection optics 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The projection optics 10 is a double-obscured optic. The penultimate mirror M5 and the last mirror M6 each have a transmission aperture for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0099] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0100] The projection optics 10 have a large object-image offset in the y-direction y between a y-coordinate of the center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the yCarl Zeiss SMT GmbH

[0101] 16

[0102] The direction y can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

[0103] The projection optics 10 can be anamorphic. In particular, they have different image scales βx, βy in the x and y directions. The two image scales βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive image scale β indicates an image without image inversion. A negative sign for the image scale β indicates an image with image inversion.

[0104] The projection optics 10 thus lead to a reduction in the x-direction x, that is, in the direction perpendicular to the scan direction, in a ratio of 4'1.

[0105] The projection optics 10 lead to a reduction of 8H in the y-direction y, that is, in the scan direction.

[0106] Other magnification ratios are also possible. Magnification ratios with the same sign and absolute value in the x and y directions (x, y), for example with absolute values ​​of 0.125 or 0.25, are also possible.

[0107] The number of intermediate image planes in the x and y directions x, y in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, different. Examples of projection optics with different numbers of such intermediate images in the x and y directions x, y are known from US 2018 / 0074303 A.

[0108] Each of the second facets 23 is assigned to exactly one of the first facets 21 to form an illumination channel for illuminating the object field 5. This can result, in particular, in illumination according to Köhler's principle. The far field is divided into a multitude of object fields 5 with the help of the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to each of them.

[0109] The first facets 21 are each superimposed on an associated second facet 23 to illuminate the object field 5 onto the reticle 7. The illumination of the object field 5 is particularly homogeneous. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels. Carl Zeiss SMT GmbH

[0110] 17

[0111] The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by the arrangement of the second facets 23. By selecting the illumination channels, in particular the subset of the second facets 23 that carry light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil filling.

[0112] Another preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by a redistribution of the illumination channels.

[0113] Further aspects and details of the illumination of the object field 5 and, in particular, the entrance pupil of the projection optics 10 are described below.

[0114] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0115] The entrance pupil of the projection optics 10 cannot regularly be illuminated exactly by the second faceted mirror 22. When the projection optics 10 image the center of the second faceted mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found where the pairwise determined separation of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in real space. In particular, this surface exhibits a finite curvature.

[0116] The projection optics 10 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second faceted mirror 22 and the reticle 7. This optical element can then be used to account for the different positions of the tangential and sagittal entrance pupils.

[0117] In the arrangement of the components of the illumination optics 4 shown in Fig. 1, the second faceted mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The first faceted mirror 20 is arranged at an angle to the object plane 6. The first faceted mirror 20 is Carl Zeiss SMT GmbH

[0118] 18

[0119] The first faceted mirror 20 is tilted relative to an arrangement plane defined by the deflecting mirror 19. The first faceted mirror 20 is tilted relative to an arrangement plane defined by the second faceted mirror 22.

[0120] Fig. 2 shows a heat transfer device 100 according to one embodiment. The heat transfer device 100 has, for example, a heat transfer channel 101, a reservoir 102, a pump 103, a control unit 104, and several sensors, such as a mass flow sensor 105, a level sensor 106, and a gas flow sensor 107. The selection and arrangement of the sensors is exemplary; more or fewer and / or different sensors may be installed.

[0121] The control unit 104 is coupled to the sensors 105, 106, and 107 to receive their respective sensor signals. The control unit 104 is also coupled to the pump 103 to control and drive the pump 103. In essence, the control unit 104 is configured and wired to selectively generate a specific flow state in the heat transfer channel 101 using the pump 103.

[0122] The heat transfer channel 101 has several channel sections, namely, in the example of Fig. 2, a supply line 108, a distribution chamber 109, several transfer sections 110, 111, a merging chamber 112 and a discharge 113. The representation of these channel sections is purely exemplary.

[0123] Chambers 109, 112 and transmission sections 110, 111 are located in a (for example, multi-part) heat coupling block 114, which is coupled to an optical element 115. For this purpose, the heat coupling block 114 is attached to a rear side 116 of the optical element 115. The rear side 116 is the surface opposite or facing away from an optically effective surface 117 (e.g., mirror surface). The optical element 115 is, for example, one of the mirrors 19 to 22 or M1 to M6 of the projection exposure system 1.

[0124] Next, a method VI for venting the liquid-filled heat transfer channel 101 (hereinafter referred to as the venting method) during commissioning of the heat transfer device 100 is presented. The steps of method VI described below are executed by the control unit 104. Carl Zeiss SMT GmbH

[0125] 19

[0126] In step Sil, the heat transfer channel 101 is filled with a heat transfer fluid 118 (hereinafter referred to as "fluid"), for example, water. For this purpose, the control unit 104 drives, for example, the pump 103 to fill the heat transfer channel 101. Typically, gas bubbles 119 remain in the chambers 109 and 112, collecting in the closed sections at the top. Upon completion of the filling process, the following steps are executed.

[0127] In step S12, at least one flow parameter is provided that is indicative of a resonant flow state 120 in the respective channel section. This is, for example, a list of flow parameters, where the list has at least one entry.

[0128] At least one flow parameter is predetermined. For example, the scientific paper "Q. Liu, F. Gomez, V. Theofilis, Linear instability analysis of incompressible flow over a cuboid cavity, IUTAM_ABCM Symposium of Laminar Turbulent Transition, 2014, Elsevier BV" describes how a Reynolds number can be determined using direct numerical simulation at which a resonant flow pattern develops in a cubic cavity. The Reynolds number is one example of a flow parameter.

[0129] It presents no obstacles for a person skilled in the art to identify the upwardly closed channel sections in which the formation of a gas bubble is likely due to gravity. It is not necessary to vent every channel section, because there may be channel sections (typically located away from the optical element) in which flow-induced vibrations have no or only a negligible effect on the imaging accuracy of the optical element 115.

[0130] In the case of the example illustrated in Fig. 2, it can be concluded, for instance, that the gas bubbles 119 in chambers 109, 112 could be excited to vibrations by a flow of the liquid 118, which vibrations could reduce image quality. Thus, flow parameters are provided for these two chambers 109, 112. One could also say that a flow parameter is provided for each of the chambers 109, 112.

[0131] It is worth noting a special case that can occur intentionally or by chance. Specifically, the same flow parameter may be indicative of a resonant flow in several channel sections. In other words, it is possible that the same flow condition in several channel sections... Carl Zeiss SMT GmbH

[0132] 20

[0133] A resonant flow occurs simultaneously and independently of each other. One reason for this can be that several channel sections have the same or at least very similar dimensions. In the case of the example illustrated in Fig. 2, the distribution chamber 109 and the merging chamber 112 have the same dimension 121 (characteristic length). Thus, in the example illustrated in Fig. 2, it may be sufficient to provide a flow parameter that is indicative of a resonant flow in each of the two chambers 109, 112.

[0134] The list provided in S12 can contain further information, so the list can contain data records. For example, a data record can contain a Rey Nolds number of a resonant flow state of a channel section along with a characteristic length of the channel section (here: dimension 121).

[0135] In step S13, the amount of liquid in the heat transfer channel 101 is measured. For this purpose, the fill level or liquid level in the reservoir 102 is determined, for example, using the level sensor 106. Knowing the total amount of liquid, the amount of liquid in the heat transfer channel 101 can be calculated. Additional information, such as the temperature of the liquid 118, can be recorded and taken into account.

[0136] In step S14, a liquid flow 122 is generated through the heat transfer channel 101 such that the liquid flow 122 corresponds to the provided flow quantity. If several flow quantities are provided, step S14 is executed multiple times so that the liquid flow 122 corresponds successively to each of the provided flow quantities.

[0137] The fluid flow 122 is generated, for example, by setting a mass flow rate of the fluid 118 through the heat transfer channel 101. For example, the control unit 104 is configured as a controller (closed control loop), whereby an actual mass flow rate determined by the mass flow sensor 105 (for example, a Coriolis sensor) is compared with a target mass flow rate determined based on the flow parameter or Reynolds number. For example, if the characteristic length (dimension 121) of the respective channel section 109, 112 is known, the cross-sectional area of ​​the mass flow sensor 105 is known, and the dynamic viscosity of the fluid 118 is known, the target mass flow rate can be calculated based on the Reynolds number. Carl Zeiss SMT GmbH

[0138] 21

[0139] The dynamic viscosity is, for example, 1.001 for water at 20°C and 0.797 for water at 30°C. The temperature of liquid 118 can be measured using one or more temperature sensors (not shown).

[0140] Thus, the respective channel section 109, 112 is vented, and the liquid flow 122 is generated to suit its resonant flow state 120.

[0141] During venting or during the generation of liquid flow, progress can be monitored, for example by performing one of the three steps S15 to S17 during step S14.

[0142] In step S15, the amount of liquid in the heat transfer channel 101 is monitored. For this purpose, the fill level of reservoir 102 is continuously or repeatedly recorded using the level sensor 106. A drop in the fill level can correspond to an additional amount of liquid in the heat transfer channel 101 – and thus to a vented amount of gas.

[0143] In step S16, the amount of gas escaping from the liquid 118 at a venting interface of the servoir 102 can be monitored using the gas quantity sensor 107.

[0144] In step S17, a vibration-indicative parameter can be recorded, for example, via a vibration sensor (not shown) attached to the heat transfer block 114. The fluid flow 122 may generate flow-induced oscillations or vibrations, so that a decreasing profile of these vibrations, for example, a decreasing amplitude and / or decreasing frequency, can serve as a measure of venting.

[0145] In step S18, a decision is made whether to continue generating the liquid flow 112. For example, the liquid flow in S14 may continue to be generated until a minimum duration has elapsed. For example, depending on the liquid quantity monitoring in S15, a decision may be made to continue generating the liquid flow 122 in S14. For example, depending on the gas quantity monitoring in S16, a decision may be made to continue generating the liquid flow 122 in S14. For example, depending on the vibration monitoring or the monitoring of the vibration indicative quantity in S17, Carl Zeiss SMT GmbH

[0146] 22

[0147] A decision is made to continue generating the liquid flow 122 in S14. If a decision is made not to continue generating the liquid flow 122 according to the provided flow rate, the process continues with the next process steps. It can therefore be said that S18 regulates whether the liquid flow 122 is generated depending on a change in the liquid quantity monitored in S15 and / or the gas quantity monitored in S16.

[0148] In step S19, the liquid quantity is measured again. This measurement of the liquid quantity after the liquid flow generation in S14 to S518 corresponds to the measurement of the liquid quantity in S13 before the liquid flow generation. Thus, the liquid quantity is measured before and after venting. This allows for an exact comparison of the liquid quantity in the heat transfer channel 101. It is possible that the measurement in S13 and S519 is more precise than the measurement in S15.

[0149] In step S20, at least one value is output that is indicative of the two liquid quantities measured in S13 and S19. For example, the two liquid quantities are output as a pair of values. For example, a difference in the liquid quantities is output. For example, a liquid quantity before or after the generation of the liquid flow is output together with the difference in the liquid quantity. Using steps S13, S19, and S20, for example, documentation of a state of the heat transfer device 100 can be maintained.

[0150] If more than one flow parameter is provided in step S12, a change can be made in step S21 to a flow parameter corresponding to the next channel section in the flow sequence. For example, the flow parameters may be provided in a flow sequence, and steps S13 to S19 may be executed sequentially for each flow parameter in the provided order. Alternatively, the flow parameters may be provided along with a specification of the flow sequences, and the next flow parameter may be selected in S21. The flow sequence refers, for example, to the sequence of channel sections in a flow direction from pump 103 to reservoir 102. Carl Zeiss SMT GmbH

[0151] 23

[0152] If more than one flow parameter is provided in step S12, a change to the next closest flow parameter in terms of magnitude can be made in step S22. For example, a magnitude-based order of the flow parameters is determined, and then steps S13 to S20 are executed sequentially for each of the provided flow parameters in magnitude order. For example, steps S13 to S20 can be repeated in order of an ascending or descending Reynolds number magnitude.

[0153] By carrying out procedure VI, the heat transfer channel 101 can be effectively vented, so that during operation of the projection exposure system 1 or the optical element 115, no or only minor flow-induced vibrations occur in the heat transfer channel 101. The optical element 115 is more stable and the image quality is ultimately higher.

[0154] Next, a method V2 for venting the liquid-filled heat transfer channel 101 (hereinafter referred to as the venting method) during exposure breaks of the projection exposure system 1 is presented with reference to the flow diagram in Fig. 4. This can be described as a method for on-demand venting.

[0155] The operating phase S24, during which the optical element 115 is irradiated, alternates with a pause phase S27. During the operating phase S24, the radiation (useful light), for example EUV radiation, falls on the mirror surface 117. Therefore, the optical element 115 is cooled by the heat transfer device 100.

[0156] During operating phase S24, one of steps S25 or S26 can be executed. In step S25, the amount of liquid in the heat transfer channel 101 is monitored. The details correspond to the described step S15. Alternatively, the quantity of gas escaping from the liquid 118 can be monitored, as in the described step S16. In step S26, a vibration-indicative quantity is monitored. The details correspond to the described step S17.

[0157] After the end of exposure operation S24, the pause operation S27 follows. Here, in step S28, the subsequent steps S12 to S22 can be triggered, depending on the parameters monitored in steps S25 and / or S26. One could also say that the generation of the Carl Zeiss SMT GmbH

[0158] 24

[0159] Liquid flow in S24 can be triggered according to the flow parameters provided in S12, depending on the parameters monitored in S25 and S26 during the exposure operation in S24.

[0160] Steps S12 to S22 follow as already described. Afterwards, the pause operation S27 ends, and a new exposure operation follows, for example, in S24.

[0161] As a result, in the venting procedure V2, the indicators for the presence of a gas bubble 119 are monitored during exposure, i.e., during the productive operation of the projection exposure system 1, and the heat transfer channel 101 is vented if necessary. Thus, high image quality can be achieved with short pause times.

[0162] Finally, it should be noted that the optical element could also be, for example, an optical element of a DUV lithography system or another projection exposure system. In these cases, the heat transfer block may, for instance, be located on a peripheral side of the optical element to allow a beam path through it.

[0163] Although the present invention has been described using exemplary embodiments, it can be modified in many ways. Carl Zeiss SMT GmbH

[0164] 25 REFERENCE SIGN LIST

[0165] 1 Projection exposure system 2 Lighting system

[0166] 3 light source

[0167] 4 B lighting optics

[0168] 5 object field

[0169] 6 Object level

[0170] 7 reticles

[0171] 8 label holders

[0172] 9 Reticle displacement drive

[0173] 10 Projection optics

[0174] 11 Image field

[0175] 12 Image plane

[0176] 13 wafers

[0177] 14 wafer holders

[0178] 15 W wafer transfer drive

[0179] 16 B lighting beam

[0180] 17 Collector

[0181] 18 Intermediate focus plane

[0182] 19 deflecting mirrors

[0183] 20 first faceted mirror

[0184] 21 first facet

[0185] 22 second faceted mirror

[0186] 23 second facet

[0187] 100 W heat transfer device 101 W heat transfer channel

[0188] 102 Reservoir

[0189] 103 Pump

[0190] 104 Control unit

[0191] 105 Mass flow sensor

[0192] 106 Level sensor

[0193] 107 Gas quantity sensor

[0194] 108 Supply line

[0195] 109 Distribution Chamber

[0196] 110 Transfer cut

[0197] 111 Transfer section

[0198] 112 Merger Chamber

[0199] 113 Derivation

[0200] 114 W heat plug elblock Carl Zeiss SMT GmbH

[0201] 26

[0202] 115 optical element

[0203] 116 Back of the optical element

[0204] 117 optically effective surface of the optical element

[0205] 118 Heat transfer fluid

[0206] 119 Gas bubble

[0207] 120 resonant flow state in a channel section

[0208] 121 Dimension / characteristic length

[0209] 122 Liquid flow through the heat transfer channel Ml mirror

[0210] M2 mirrors

[0211] M3 mirror

[0212] M4 mirrors

[0213] M5 mirror

[0214] M6 mirrors

[0215] 511 Filling the heat transfer channel

[0216] 512 Providing at least one flow parameter

[0217] 513 Measuring a quantity of liquid

[0218] 514 Generating a fluid flow

[0219] 515 Monitoring a quantity of liquid

[0220] 516 Monitoring a quantity of gas

[0221] 517 Monitoring a vibration-indicative quantity

[0222] 518 Deciding on continuing the flow of liquid 519 Measuring a quantity of liquid

[0223] 520 Spending an indicative amount for both sets

[0224] 521 Switch to the next flow quantity in a flow sequence

[0225] 522 Switch to a flow quantity that is closest in magnitude 524 Operation to irradiate the optical element

[0226] 525 Monitoring a quantity of liquid

[0227] 526 Monitoring a vibration-indicative quantity

[0228] 527 Break operation

[0229] 528 Triggering the generation of the fluid flow

[0230] V 1 Venting procedure during commissioning

[0231] V2 venting procedure when a need is identified

Claims

Carl Zeiss SMT GmbH 27 PATENT CLAIMS 1. Method (VI, V2) for venting a liquid-filled heat transfer channel (101) coupled for heat transfer to an optical element (115; 19, 20, 22, M1-M6) and in particular to an optical element (115; 19, 20, 22, M1-M6) of a projection exposure system (1), wherein the heat transfer channel (101) has several channel sections (108 - 113) of different channel cross-sections, comprising: a) Providing (S12) at least one flow parameter indicative of a resonant flow state (120) in a respective channel section (109, 112); and b) Generating (S14) a fluid flow (122) through the heat transfer channel (101) such that the fluid flow (122) corresponds successively to each of the provided flow variables.

2. Method according to claim 1, wherein the flow parameter is a Reynolds number or indicative of a Reynolds number and / or wherein the flow parameter is indicative of a laminar flow condition in at least one further channel section (108 ■ 113).

3. Method according to claim 1 or 2, wherein generating (S14) the liquid flow (122) includes adjusting a mass flow of the liquid (118) in the heat transfer channel (101).

4. Method according to one of claims 1 - 3, wherein the generation (S14) of the liquid flow (122) is carried out towards filling (Sil) the heat transfer channel (101).

5. Method according to one of claims 1 - 4, wherein the generation (S14) of the fluid flow (122) is carried out during a pause operation (S28) of the optical element (115; 19, 20, 22, M1-M6).

6. Method according to one of claims 1 - 5, wherein a flow parameter (S 12) is provided for several channel sections, and wherein the liquid flow (122) is generated in a flow sequence through the channel sections (109, 112) (S21, S14).

7. Method according to one of claims 1-6, wherein a flow quantity (S 12) is provided for several channel sections, and wherein the liquid flow (122) is ordered in a sequence of magnitude of the flow quantity. Carl Zeiss SMT GmbH 28 and / or an amount of a state of fluid flow (122) is generated (S22, S14).

8. Method according to any one of claims 1-7, comprising: a) Measuring the quantity of liquid in the heat transfer channel (101) and / or the quantity of gas exiting the liquid (118) before (S13) and after (S19) the generation (S14) of the liquid flow (122), and b) Output (S20) an indicative amount for both sets and / or their difference.

9. Method according to any one of claims 1-8, comprising: Monitoring (S15, S16) of a liquid quantity in the heat transfer channel (101) and / or a gas quantity escaping from the liquid (118), where the monitoring (S15, S16) is carried out during the generation (S14) of the fluid flow (122), and wherein the liquid flow (122) is generated depending on a change in the monitored liquid quantity (S15) and / or the monitored gas quantity (S16) (S18, S14).

10. Method according to any one of claims 1-9, comprising: a) Monitoring (S25) of a quantity of liquid in the heat transfer channel (101) and / or a quantity of gas escaping from the liquid (118), wherein the monitoring (S25) is carried out during a useful operation (S24) of the optical element (115), and b) Triggering (S28) the generation (S14) of the liquid flow (122) depending on the monitored liquid quantity and / or the monitored gas quantity.

11. Method according to any one of claims 1-10, comprising: Monitoring (S17) of a vibration indicative quantity that is indicative of a measure of flow-induced vibrations in the heat transfer channel (101), where the monitoring (S17) is carried out during the generation (S14) of the fluid flow (122), and wherein the fluid flow (122) is generated depending on a change in the monitored vibration indicative quantity (S18, S14).

12. Method according to one of claims 1 - 11, comprising: Carl Zeiss SMT GmbH 29 a) Monitoring (S26) a vibration indicative quantity that is indicative of a measure of flow-induced vibrations in the heat transfer channel (101), where the monitoring (S26) is performed during a useful operation (S24) of the optical element (101), and b) Triggering (S28) the generation (S14) of the fluid flow (122) depending on the monitored vibration indicative quantity.

13. Heat transfer device (100) comprising: a liquid-fillable or liquid-filled heat transfer channel (101) which can be coupled or connected to an optical element (115; 19, 20, 22, M1-M6) and in particular to an optical element (115; 19, 20, 22, M1-M6) of a projection exposure system (1) for heat transfer, a pump (103) connected in series with the heat transfer channel (101) and a control device (104) connected for controlling the pump (103), which is configured to carry out the method (VI, V2) according to one of claims 1 - 12.

14. Heat transfer device according to claim 13, comprising a device (106, 107) for measuring a quantity of liquid in the heat transfer channel (101) and / or a quantity of gas exiting the liquid (118).

15. Projection exposure system (1) comprising a heat transfer device (100) according to one of claims 13 - 14.

Images