Method and apparatus for temperature control of a sensor frame in a microlithographic projection system

Abstract

The invention relates to a method for temperature control of a sensor frame (27) in a microlithographic projection system (20) with optical elements (23, 40 M) attached to a support frame (24). i ), at least one sensor (28) attached to the sensor frame (27) for contactless determination of a relative position of at least one of the optical elements (23, 40, M) i ) and with at least one fluid line (50, 51, 52, 53) guided at least partially along the sensor frame (27) for active temperature control of at least one of the optical elements (23, 40, M) i ), wherein the projection system (20) is located in a vacuum chamber (101). According to the invention, the following steps are carried out: - Using the fluid line (50, 51, 52, 53) as a thermal actuator to introduce heat energy into the sensor frame (27) by passing a thermofluid through the fluid line (50, 51, 52, 53); - Evacuating the vacuum chamber (101) from an initial pressure down to a predetermined minimum pressure; - Control the thermal actuator such that the sensor frame (27) is actively tempered to a predetermined target temperature. The inventive method can significantly reduce the waiting time required after evacuation, during which the sensor frame reaches a target temperature prescribed for continued operation.

Description

[0001] The present invention relates to a method for tempering a sensor frame in a microlithographic projection system.

[0002] Microlithography is used in the production of microstructured components, such as integrated circuits. The microlithography process is carried out in a so-called projection exposure system, which has an illumination system and a projection system. The image of a mask (also called a "reticle") illuminated by the illumination system is projected with the help of the projection system onto a substrate coated with a light-sensitive layer (so-called "photoresist") and arranged in the image plane of the projection system, e.g., a silicon wafer, in order to transfer the mask structure to the light-sensitive coating of the substrate. In subsequent production steps, the transferred structure is implemented in the substrate, e.g., by etching or material deposition.

[0003] Due to the increasing miniaturization of semiconductors and the transition in wavelength during exposure from DUV (e.g., 193 nm) to EUV (e.g., 13.5 nm), projection systems in projection exposure systems must exhibit high image quality. In projection exposure systems in the EUV range (5-20 nm), exclusively reflective optical elements are used to image a mask in the object plane onto a substrate in the image plane, e.g., with a reduction factor of 8:1.

[0004] To achieve high image quality, not only the quality of the individual optical elements of the projection system is important, but also their relative position to one another. To ensure this during ongoing operation of a projection exposure system, it is known to attach the individual optical elements of the projection system to a common support frame. The support frame and the optical elements are regularly and actively temperature-controlled in order to fundamentally reduce changes in the image quality of the projection system, for example due to thermal expansion of the optical elements or the support structure. For example, the support frame and / or optical elements can be traversed by channels for a thermal fluid. By feeding thermal fluid with a predetermined volume flow and / or temperature through these channels, the temperature of the support frame and / or optical elements can be kept fairly constant.

[0005] However, to account for deformations, particularly of the support frame, which cannot be completely eliminated, actuators are usually provided between the support frame and the individual optical elements. These actuators allow the position of the individual optical elements to be readjusted relative to the support frame. This allows for compensation for any relative positional changes of the mirrors that occur during operation.

[0006] In order to precisely control the actuators, the actual position of the individual optical elements must be determined and then compared with the respective target positions. To determine the actual position of the optical elements, it is known to arrange sensors on a sensor frame with which the actual position of the individual optical elements can be precisely determined. The sensors operate without contact. Furthermore, the sensor frame is almost completely mechanically and thermally decoupled from the support frame, so that the sensor frame provides a fundamentally unchanging reference system for determining the position of the optical elements, even if the support frame and / or the optical elements should undergo deformation during operation, for example due to heat input.

[0007] Microlithographic projection systems, especially those designed for wavelengths in the EUV range, are operated in a vacuum environment, as the EUV radiation would otherwise be absorbed by an ambient gas. The vacuum chamber in which the projection system is located must be evacuated during initial commissioning and after maintenance or other service work that requires access to the projection system components.

[0008] It has been found that after creating a vacuum in the vacuum chamber with a projection system inside it, considerable waiting times are sometimes necessary in order to be able to continue operating the projection system.

[0009] The object of the present invention is to provide a method for controlling the temperature of the sensor frame in which the disadvantages explained above are eliminated or only occur to a reduced extent. This object is achieved by the features of independent claim 1. Advantageous embodiments are described in the dependent claims.

[0010] Accordingly, the invention relates to a method for controlling the temperature of a sensor frame in a microlithographic projection system with optical elements attached to a support frame, at least one sensor attached to the sensor frame for contactless determination of a relative position of at least one of the optical elements, and at least one fluid line guided at least partially along the sensor frame for actively controlling the temperature of at least one of the optical elements, wherein the projection system is located in a vacuum chamber. According to the invention, the following steps are carried out, although the steps do not necessarily have to be carried out in the specified order: - Using the fluid line as a thermal actuator to introduce thermal energy into the sensor frame by passing a thermal fluid through the fluid line; - Evacuating the vacuum chamber from an initial pressure to a predetermined minimum pressure; - Controlling the thermal actuator in such a way that the sensor frame is actively tempered to a specified target temperature.

[0011] First, some terms used in the context of the invention will be explained. "Active temperature control" is the introduction of heat that occurs intentionally and in a targeted manner by suitable means, in addition to the heat introduction that may occur unintentionally during the rest of the device's operation. According to the invention, the active temperature control of the sensor frame is achieved with the aid of the fluid line provided for the active temperature control of an optical element. The control of the thermal actuator can be achieved by changing a fluid flow and / or a fluid temperature. For this purpose, the thermal actuator can comprise, in addition to the fluid line, in particular a temperature-controlled fluid reservoir and a pumping device for passing the thermal fluid through the fluid line. Active temperature control can, in principle, enable not only heat introduction but also targeted heat dissipation.

[0012] The "initial pressure" from which the vacuum chamber is evacuated can, in particular, be the ambient pressure of approximately 1 bar. The minimum pressure is usually in the range between 1 Pa and 10 Pa, preferably approximately 5 Pa. When, in the context of the present description, it is stated that a section of a fluid line is guided along a structure, this means that there is only a small distance between the fluid line and the structure in the region of the section, which distance is in particular less than 5 cm, preferably less than 2 cm, more preferably less than 1 cm.

[0013] Within the scope of the invention, it was recognized that a sensor frame, particularly if it is thermally decoupled and not actively temperature-controlled, can have a temperature below a target temperature required for continued operation for an extended period after evacuation. After evacuation, starting from 1 bar down to a minimum pressure of 5 Pa, the temperature deviation can be, for example, 150 mK. This is problematic because, due to the temperature deviation, the actual position of the optical elements cannot be determined with the required precision and, accordingly, precise readjustment of the optical elements is not possible. Temperature deviations of the sensor frame can, in particular, lead to an undesirable shift of the reticle image in the image plane of the projection system (hereinafter also referred to as "line-of-sight" error).While the temperature of the support frame and the optical elements can be quickly raised to the specified target temperature after evacuation using the active temperature control options provided for later operation, the adjustment of the temperature of the sensor frame takes considerably longer due to the thermal decoupling, as the sensor frame can hardly exchange heat with its environment in the vacuum.

[0014] Against this background, the invention provides for the use of an existing fluid line for the active temperature control of an optical element, which is routed at least partially along the sensor frame, to introduce heat energy into the sensor frame. The fluid line is thus diverted from its intended purpose and, instead of being used for the active temperature control of the optical element, is used as a thermal actuator for introducing heat into the sensor frame. The thermal actuator is controlled in such a way that the sensor frame is actively temperature-controlled to a predetermined target temperature. It has been found that the desired target temperature of the sensor frame can be reached and maintained significantly more quickly after evacuation by this measure. Furthermore, it has been recognized that sufficient heat input can occur due to the only small distance between the sensor frame and the sections of the fluid line running along it.The distance between the section extending along the sensor frame and the sensor frame is preferably less than 5 cm, more preferably less than 2 cm, and more preferably less than 1 cm. In particular, the distance can be approximately 0.5 mm.

[0015] Within the scope of the invention, it was further recognized that the heat input into the optical element, which inevitably accompanies the passage of the heated thermal fluid through the fluid line, has only a minor influence on the operational readiness of the projection system after evacuation due to the mass of the optical element, which is usually significantly smaller (for example, by a factor of 100) than the mass of the sensor frame. In particular, the temperature of the optical element can be corrected very quickly with the help of active temperature control of the optical element after the target temperature of the sensor frame has been reached. Due to the large mass of the sensor frame and the fact that the minimum pressure usually already prevails after the target temperature of the sensor frame has been reached, this correction has no or only a minor influence on the temperature of the sensor frame.

[0016] The specified target temperature can correspond to the specified target temperature required for continued operation of the projection system. It is also possible in principle for the thermal actuator to be controlled in such a way that the sensor frame is actively tempered to a specified target temperature that is higher than the target temperature. A target temperature above the target temperature may be necessary, for example, if the optical element has an excessively high temperature after evacuation has ended and must be cooled to a lower temperature. Although, as already explained above, this usually has only a minor impact on the sensor frame due to the difference in mass, this slight heat removal can still be taken into account, so that a reduction from the excessively high target temperature to the target temperature can take place.Alternatively or additionally, when controlling the thermal actuator, it can also be taken into account that heat energy is removed from the sensor frame during evacuation, which can also lead to a reduction from the target temperature that has been set too high to the desired temperature.

[0017] It is advantageous if, after the sensor frame has reached the predetermined target temperature, the optical element is actively tempered to a predetermined target temperature of the optical element. Since the fluid line primarily serves the purpose of actively tempering the optical element, and the mass of the optical element is comparatively low, this is usually possible within a short period of time. To ensure that the heat input into the optical element does not become too great, it can be provided that the thermal actuator is controlled in such a way that a maximum temperature of the at least one optical element tempered by the at least one fluid line is not exceeded.

[0018] In one embodiment, the fluid line is fixed to the sensor frame by means of a fastening element. The fastening element can in particular comprise or be formed from a thermally conductive material. In the context of the present disclosure, a material is referred to as thermally conductive if it has a thermal conductivity of greater than or equal to 1 W / mK. The thermal conductivity of the fastening element can in particular be greater than or equal to 2 W / mK, preferably greater than or equal to 5 W / mK, more preferably greater than or equal to 10 W / mK. Good heat transfer takes place through the fastening element, so that the temperature of the sensor frame can be effectively controlled even when a low pressure already prevails in the vacuum chamber and heat transfer via the existing atmosphere is correspondingly reduced.It is fundamentally irrelevant that heat is only introduced at specific points via the fastening elements, since heat equalization within the sensor frame occurs quickly anyway due to its very high thermal conductivity.

[0019] In one embodiment, the introduction of thermal energy into the sensor frame occurs before the vacuum chamber is evacuated. In this case, thermal energy can be transferred from the fluid line via the atmosphere present in the vacuum chamber, so that the sensor frame can be brought to a desired target temperature particularly efficiently. Alternatively or additionally, the introduction of thermal energy can occur during the evacuation of the vacuum chamber. It is also possible, of course, for the introduction of thermal energy into the sensor frame to occur after the vacuum chamber has been evacuated.

[0020] It can be provided that the projection system has at least one further fluid line for the active temperature control of at least one of the optical elements, wherein the further fluid line is guided contact-free through a through-opening provided in the sensor frame. In the region of the through-opening there is usually a small distance between the fluid line and the sensor frame, so that heat transfer via the gas atmosphere takes place at this point too, at least when there is still sufficient pressure within the vacuum chamber. Even if this is lower than heat transfer that occurs, for example, via a fastening element, it has been shown that such a fluid line can still be used to support the introduction of heat energy into the sensor frame. The further fluid line is therefore preferably used as a further thermal actuator to support the introduction of heat energy into the sensor frame.The two thermal actuators can be controlled together or independently to actively temper the sensor frame to the specified target temperature.

[0021] The thermal actuator can be controlled by adjusting the volume flow of the thermal fluid through the fluid line. Alternatively or additionally, the thermal actuator can also be controlled by adjusting the temperature of the thermal fluid. Furthermore, it can be provided that a temperature of the sensor frame is measured, whereby the measured temperature and / or a temporal change in the measured temperature is used as a control variable for controlling the thermal actuator. By using the current temperature or a temporal change in the temperature as the control variable, the target temperature of the sensor frame can be reached even more reliably, whereby unexpected heat input, for example in the event of malfunctions, can also be taken into account.

[0022] If the support frame has active temperature control, it can be provided that the active temperature control of the support frame is used as an additional thermal actuator for exerting heat on the sensor frame. Through the active temperature control of the support frame, thermal energy can be transferred to the sensor frame or thermal energy can be extracted from the sensor frame. The active temperature control of the support frame represents an additional degree of freedom through which the control objective of temperature-controlling the sensor frame to a specified target temperature can be achieved more reliably and quickly. This applies in particular if the fluid line and the fluid channels provided for the active temperature control of the support frame are fed by independent fluid reservoirs.It is preferably provided that the thermal actuator and the further thermal actuator are controlled independently of each other in order to actively temper the sensor frame to the predetermined target temperature.

[0023] The microlithographic projection system can further comprise an external temperature control unit. The external temperature control unit can, in particular, comprise fluid channels in the region of the walls of the vacuum chamber. The external temperature control unit is preferably used as an additional thermal actuator for exerting heat on the sensor frame. The fluid line and fluid channels provided for the external temperature control unit can preferably be fed by means of mutually independent fluid reservoirs. In particular, it can be provided that the external temperature control unit and the additional thermal actuator are controlled independently of one another in order to actively temperature-control the sensor frame to the predetermined target temperature. The external temperature control unit also creates an additional degree of freedom, through which the control objective of temperature-controlling the sensor frame to a predetermined target temperature can be achieved more reliably and quickly.

[0024] The invention further relates to a device for temperature control of a sensor frame in a microlithographic projection system. The device comprises a vacuum chamber for the microlithographic projection system, a vacuum generator for generating a vacuum in the vacuum chamber, and a control device for controlling a device for actively temperature control of at least one optical element of the microlithographic projection system. The device for active temperature control is connected to at least one fluid line, which runs at least partially along the sensor frame, for actively temperature control of the at least one optical element. According to the invention, the control unit is designed to control the vacuum generator and the device for actively temperature control of the at least one optical element in such a way that the method according to the invention is carried out.The device can be further developed by further features described in connection with the method according to the invention. It can be provided that the fluid line has at least one redundant section, by which the section guided along the sensor frame is extended. A redundant section is a section of the fluid line that would not actually be required for the purpose of conveying the thermal fluid to the desired destination. The redundant section can be formed, in particular, by additional curves or loops of the fluid line guided along the sensor frame. Furthermore, it can be provided that the device has at least one redundant thermally conductive fastening means with which the fluid line is fastened to the sensor frame.A redundant fastening means is a fastening means that would not be required for the purpose of fastening (even taking into account a safety factor) the fluid line to the sensor frame, but serves solely the purpose of providing additional thermal coupling between the fluid line and the sensor frame.

[0025] The invention will now be explained in more detail by way of example using advantageous embodiments with reference to the accompanying drawings. They show: Fig. 1: a schematic representation of a projection exposure system for microlithography; Fig. 2: a schematic sectional view of a first embodiment of a device according to the invention; Fig. 3: a schematic sectional view of a second embodiment of a device according to the invention.

[0026] In Fig. Figure 1 shows a schematic meridional section of a projection exposure system 1 for microlithography. The projection exposure system 1 comprises an illumination system 10 and a projection system 20.

[0027] With the aid of the illumination system 10, an object field 11 is illuminated in an object plane or reticle plane 12. For this purpose, the illumination system 10 comprises an exposure radiation source 13, which, in the illustrated embodiment, emits illumination radiation comprising at least useful light in the EUV range, i.e., in particular, a wavelength between 5 nm and 30 nm, in particular 13.5 nm.

[0028] The illumination radiation emanating from the exposure radiation source 13 is first focused in a collector 14. The collector 14 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.

[0029] After the collector 14, the illumination radiation propagates through an intermediate focus in an intermediate focal plane 15. If the illumination system 10 is constructed in a modular design, the intermediate focal plane 15 can generally be used for the - also structural - separation of the illumination system 10 into a radiation source module, comprising the exposure radiation source 13 and the collector 14, and the illumination optics 16 described below. With such a separation, the radiation source module and illumination optics 16 then together form a modular illumination system 10.

[0030] The illumination optics 16 comprises a deflecting mirror 17. The deflecting mirror 17 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 17 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation from stray light of a different wavelength.

[0031] The deflecting mirror 17 deflects the radiation originating from the exposure radiation source 13 onto a first facet mirror 18. If the first facet mirror 18 is arranged—as in the present case—in a plane of the illumination optics 16 that is optically conjugated to the reticle plane 12 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 18 is a microelectromechanical system (MEMS system) with a plurality of individually pivotable micromirrors 18', as described, for example, in DE 10 2008 009 600 A1.

[0032] In the beam path of the illumination optics 16, a second facet mirror 19 (also called a "pupil facet mirror") is arranged downstream of the first facet mirror 18, resulting in a double-faceted system whose basic principle is also referred to as a honeycomb condenser (fly's eye integrator). The second facet mirror 19 also comprises—as shown—a microelectromechanical system with a plurality of individually pivotable micromirrors 19'.

[0033] The facets of the first facet mirror 18 are each imaged by an associated facet of the second facet mirror 19, superimposing one another, in order to illuminate the object field 11 as homogeneously as possible.

[0034] By selecting the illumination channels ultimately used, which is easily possible by appropriately adjusting the micromirrors 18' of the first facet mirror 18, the intensity distribution in the entrance pupil of the projection system 20 described below can also be adjusted. This intensity distribution is also referred to as the illumination setting.

[0035] With the help of the projection system 20, the object field 11 in the reticle plane 12 is transferred to the image field 21 in the image plane 22.

[0036] The projection system 20 comprises a plurality of mirrors M i , which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0037] In the Fig. 1, the projection system 20 comprises six mirrors M1 to M6 as optical elements 23. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation, which makes the illustrated projection system 20 a double-obscured optical system. The projection system 20 has an image-side numerical aperture that is greater than 0.3, and can also be greater than 0.6, for example, 0.7 or 0.75.

[0038] The reflection surfaces of the mirrors M i can be designed as freeform surfaces without a rotational symmetry axis. The mirrors M i Like the mirrors of the illumination optics 16, they can have highly reflective coatings for the illumination radiation. These reflective coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0039] The projection system 20 can in particular be anamorphic, ie it has in particular different image scales β x , β y in the x- and y-direction. The two magnifications β x , β y of the projection system 20 are preferably at (β x , β y ) - (+ / - 0.25, / +- 0.125). A magnification ratio β of 0.25 corresponds to a reduction in the ratio 4:1, while a magnification ratio β of 0.125 results in a reduction in the ratio 8:1. A positive sign for the magnification ratio β means an image without image inversion, a negative sign an image with image inversion.

[0040] A reticle 30 (also called a mask) arranged in the object field 11 is illuminated by the illumination system 10 and transferred to the image plane 22 by the projection system 20. The reticle 30 is held by a reticle holder 31. The reticle holder 31 can be displaced, in particular in a scanning direction, via a reticle displacement drive 32. In the illustrated embodiment, the scanning direction runs in the y-direction.

[0041] A structure on the reticle 30 is imaged onto a light-sensitive layer of a wafer 35 arranged in the region of the image field 21 in the image plane 22. The wafer 35 is held by a wafer holder 36. The wafer holder 36 can be displaced, in particular along the y-direction, via a wafer displacement drive 37. The displacement of the reticle 30, on the one hand, via the reticle displacement drive 32, and the displacement of the wafer 35, on the other hand, via the wafer displacement drive 37, can be synchronized with each other.

[0042] The Fig. The projection exposure system 1 outlined in Figure 1 and its illumination and projection system 10, 20 essentially correspond to the known state of the art.

[0043] The individual mirrors M i or the optical elements 23 of the projection system 20 are mounted on a common support frame 24 (in Fig. 1 not shown) and can therefore be considered as a unit.

[0044] Fig. Figure 2 shows a schematic sectional view of a device 100 according to the invention, which is suitable for carrying out the method according to the invention. The device 100 comprises a vacuum chamber 101, a vacuum generator 102, a device 104 for actively controlling the temperature of at least one optical element of the projection system 20, and a control unit 103 for controlling the vacuum generator 101 and the device 104. The vacuum generator 102 is configured to pump out an atmosphere present within the vacuum chamber 101, for example, starting from a pressure of 1 bar, until a minimum pressure of, for example, 5 Pa is reached in the vacuum chamber 101. The projection system 20 is located in the vacuum chamber 101. For the sake of simplicity, the Fig. 2 only a single mirror M iof the projection system 20 is shown as an optical element 23. The optical element 23 is connected to a support frame 24 mentioned above via actuators 25. The position of the optical element 23, particularly in relation to the other optical elements 23, can be adjusted within certain limits even during operation via the actuators 25, in order to thereby ensure optimal imaging of the reticle 30 in the image field 21 in the image plane 22 (cf. Fig. 1) to achieve.

[0045] A sensor frame 27 is provided, which is completely thermally and mechanically decoupled from the support frame 24. Sensors 28 are arranged on this sensor frame 27, of which Fig. 2 a single one is shown. The sensors 28 can be used to contactlessly determine the position of the optical elements 23, M i relative to the sensor frame 27 as a reference system and thus the position of the optical elements 23, M ito each other. A sensor 28 regularly detects the relative position of at least one reference point on one of the optical elements 23, M i relative to the sensor 28. From the measurement results of several sensors 28 and taking into account the position of the individual sensors 28, a complete and precise determination of the position of the optical elements 23, M i possible.

[0046] The device 104 is designed here for the active temperature control of the optical element 23. For this purpose, the device 104 has a temperature-controlled fluid reservoir and a pumping device for the thermal fluid. The device 104 also comprises an outlet via which the thermal fluid acted upon by the pumping device is discharged. A fluid line 50 is connected to the outlet and leads to a fluid inlet present on the optical element 23. From this inlet, the thermal fluid is guided in a generally known manner through a channel (not shown here) present within the optical element 23 to a fluid outlet of the optical element 23, which in turn is connected to a fluid inlet of the device 104 via a further fluid line 51. The thermal fluid originating from the fluid reservoir thus exchanges heat with the optical element 23 and then flows back into the fluid reservoir.

[0047] The fluid lines 50, 51 are routed at least partially at a short distance along the sensor frame 27. Furthermore, the fluid lines 50, 51 are connected to the sensor frame 27 by means of fastening elements, which in this case are formed by metal clamps 55. Therefore, a heat exchange takes place between the thermal fluid conveyed through the lines 50, 51 and the sensor frame 27. The invention utilizes this heat exchange, as explained below, by using the fluid lines 50, 51 as a thermal actuator for introducing thermal energy into the sensor frame 27.

[0048] Within the scope of an exemplary embodiment of the method according to the invention, the vacuum chamber 101 is evacuated starting from an ambient pressure of 1 bar until a minimum pressure of 5 Pa is reached. The evacuation process can, for example, extend over a period of one hour. Already during this period, the control unit 103 causes the device 104 to conduct a thermal fluid through the fluid lines 50, 51, wherein the thermal fluid is tempered such that thermal energy is introduced into the sensor frame 27. The introduction of heat occurs, on the one hand, via the atmosphere still present within the vacuum chamber 101 during the evacuation process. In addition, heat is transferred to the sensor frame 27 via the metal clamps 55. In particular, when only a low pressure prevails in the vacuum chamber 101, the heat transfer via the metal clamps 55 can be the dominant heat transfer process.

[0049] The control unit 103 controls the flow through the fluid lines 50, 51 as well as the thermal fluid temperature with the control objective of bringing the sensor frame 27 to a predetermined target temperature. This control takes into account any heat input that is already present, which occurs in particular from other components of the projection system, for example from the support frame 24, or from the walls of the vacuum chamber 101. Furthermore, the control takes into account that the components present in the vacuum chamber 101 cool down during the pumping process. In this case, the predetermined target temperature corresponds to a target temperature of the sensor frame 27 that is predetermined for continued operation of the projection system 20, and the control is carried out in such a way that the sensor frame 27 reaches the target temperature as soon as possible after the end of the pumping process.At the same time, the control unit 103 ensures that a predetermined maximum temperature of the optical element 23 is not exceeded.

[0050] The actual temperature of the sensor frame 27 is monitored using a temperature sensor 105, and a corresponding temperature signal is sent to the control unit 103 at regular intervals. The temperature sensor 105 can be a pyrometer, for example. The control unit 103 uses the actual temperature and a temporal change in the actual temperature as control variables to control the thermal fluid flow through the fluid lines 50, 51 and the thermal fluid temperature. In this way, the control system can react to unforeseen disturbances so that the specified target temperature is reliably reached.

[0051] Fig. 3 shows a schematic sectional view of an alternative device 100 according to the invention, which, as explained below, differs only slightly from the device shown in Fig. 2. In the following, only the differences to the device 100 shown in Fig. 2 shown embodiment will be described.

[0052] The device 100 of the Fig. 3 differs from the device of the Fig. 2 in that it comprises a second device 106 for actively controlling the temperature of an optical element. Device 106 is particularly suitable for actively controlling the temperature of an additional mirror M i trained in Fig. 3 as optical element 40. The device 106 is analogous to that described in connection with Fig. 2, the fluid lines 52, 53 are connected to the optical element 40 via fluid lines 52, 53 in order to actively control the temperature of the optical element 40. However, in contrast to the fluid lines 50, 51, the fluid lines 52, 53 are not connected to the sensor frame 27 via metal clamps. Rather, the fluid lines 52, 53 are guided through through-openings provided in the sensor frame 27. Heat exchange also occurs in the area of ​​the through-openings, albeit to a lesser extent. The fluid lines 52, 53 are used as an additional thermal actuator for supporting the introduction of thermal energy. Since the devices 104 and 106 here have independent fluid reservoirs, it is also possible to control the fluid lines 50, 51 and 52, 53 as independent thermal actuators in order to actively control the temperature of the sensor frame to the specified target temperature.For example, it can be provided that a supply of the thermal fluid through the fluid lines 52, 53 is stopped after a certain pressure has been undershot within the vacuum chamber 101, because in this case, due to the lack of attachment of the lines 52, 53 to the sensor frame 27, only a very small heat input into the sensor frame 27 can be expected.

[0053] In addition, Fig. 3, a device 107 for actively controlling the temperature of the support frame 24 is provided, which is connected via fluid lines 56 in a generally known manner to corresponding connections on the support frame 24. Finally, in contrast to Fig. 2 an external temperature control unit 108 is provided for the active temperature control of the vacuum chamber 101, which is connected in a basically known manner to temperature control channels not shown in the figure within the wall of the vacuum chamber 101.

[0054] In the exemplary method, both the active temperature control of the support frame 24 and the external temperature control unit 108 are used as additional thermal actuators for exerting a heat effect on the sensor frame 27. Since the devices 104, 107 and the external temperature control unit 108 each have separate and independently controllable fluid reservoirs, the active temperature control of the support frame or the external temperature control unit creates additional degrees of freedom, allowing the control objective of controlling the sensor frame 27 to a predetermined target temperature to be achieved more reliably and quickly. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2008 009 600 A1

[0031]

Claims

[1] Method for tempering a sensor frame (27) in a microlithographic projection system (20) with optical elements (23, 40 M) attached to a support frame (24) i ), at least one sensor (28) attached to the sensor frame (27) for contactless determination of a relative position of at least one of the optical elements (23, 40, M i ) and with at least one fluid line (50, 51, 52, 53) guided at least in sections along the sensor frame (27) for the active temperature control of at least one of the optical elements (23, 40, M i ), wherein the projection system (20) is located in a vacuum chamber (101), characterized by the steps: - using the fluid line (50, 51, 52, 53) as a thermal actuator for introducing thermal energy into the sensor frame (27) by passing a thermal fluid through the fluid line (50, 51, 52, 53); - evacuating the vacuum chamber (101) from an initial pressure to a predetermined minimum pressure; - Controlling the thermal actuator such that the sensor frame (27) is actively tempered to a predetermined target temperature. [2] Method according to claim 1, characterized by that at least one of the optical elements (23, 40, M i ), after the sensor frame (27) has reached the predetermined target temperature, actively to a target temperature of the optical element (23, 40, M i ) is tempered. [3] Method according to claim 1 or 2, characterized by that the fluid line (50, 51) is fixed to the sensor frame (27) with at least one thermally conductive fastening element (55). [4] Method according to one of claims 1 to 3, characterized by that the introduction of thermal energy into the sensor frame (27) takes place before evacuation and / or during evacuation of the vacuum chamber (101). [5] Method according to one of claims 1 to 4, characterized by that the projection system (20) has at least one further fluid line (52, 53) for the active temperature control of at least one of the optical elements (40, M i ) which is guided contact-free through a through-opening provided in the sensor frame (27), wherein the further fluid line (52, 53) is used as a further thermoactuator for supporting the introduction of thermal energy into the sensor frame. [6] Method according to one of claims 1 to 5, characterized by that the control of the thermoactuator is carried out by adjusting a volume flow of the thermofluid through the fluid line (50, 51, 52, 53) and / or by adjusting a temperature of the thermofluid. [7] Method according to one of claims 1 to 6, characterized bythat a temperature of the sensor frame (27) is measured, wherein the measured temperature and / or a temporal change in the measured temperature is used as a control variable for controlling the thermal actuator. [8] Method according to one of claims 1 to 7, characterized by that the support frame (24) has an active temperature control (107, 56), wherein the active temperature control (107, 56) of the support frame (24) is used as a further thermal actuator for exerting a heat effect on the sensor frame (27). [9] Method according to claim 8, characterized by that the fluid line (50, 51, 52, 53) and fluid channels (56) provided for the active temperature control of the support frame (24) are fed by fluid reservoirs that are independent of one another, wherein the thermoactuator and the further thermoactuator are controlled independently of one another in order to actively temperature-control the sensor frame (27) to the predetermined target temperature. [10] Method according to one of claims 1 to 9, characterized by in that the microlithographic projection system (20) has an external temperature control unit (108), wherein the external temperature control unit (108) is used as a further thermal actuator for exerting a heat effect on the sensor frame (27). [11] Method according to claim 10, characterized by that the fluid line (50, 51, 52, 53) and the external temperature control unit (108) are fed by independent fluid reservoirs, wherein the thermal actuator and the further thermal actuator are controlled independently of each other in order to actively temperature-control the sensor frame (27) to the predetermined target temperature. [12] Method according to one of claims 1 to 11, characterized by that the thermal actuator is controlled in such a way that a maximum temperature of the at least one optical element (23, 40, M i ) is not exceeded. [13] Device (100) for tempering a sensor frame (27) in a microlithographic projection system (20), comprising a vacuum chamber (101) for the microlithographic projection system (20), a vacuum generator (102) for generating a vacuum in the vacuum chamber (101), and a control device (103) for controlling a device (104) for actively tempering at least one optical element (23, 40, M i ) of the microlithographic projection system (20) and for controlling the vacuum generator (102), wherein the device (104) for active temperature control is provided with at least one fluid line (50, 51, 52, 53) guided at least in sections along the sensor frame (27) for the active temperature control of the at least one optical element (23, 40, M i ) is connected, characterized bythat the control unit (103) is designed to control the vacuum generator (102) and the device (104) for active temperature control such that the method according to one of claims 1 to 12 is carried out.

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