Method and device for controlling the temperature of a sensor frame in a microlithographic projection system

Abstract

The invention relates to a method for controlling the temperature of a sensor frame (27) in a microlithographic projection system (20) with optical elements (23, 40, Mi) fastened to a support frame (24), at least one sensor (28) fastened to the sensor frame (27) for determining, in a non-contact manner, a relative position of at least one of the optical elements (23, 40, Mi) and with at least one fluid line (50, 51, 52, 53) guided at least in some portions along the sensor frame (27) for actively controlling the temperature of at least one of the optical elements (23, 40, Mi), 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 for introducing thermal energy into the sensor frame (27) by conducting a thermal fluid through the fluid line (50, 51, 52, 53); – evacuating the vacuum chamber (101) starting from an initial pressure down to a predefined minimal pressure; – controlling the thermal actuator such that the temperature of the sensor frame (27) is actively controlled to a predefined target temperature. As a result of the method according to the invention, a wait time needed after the evacuation, within which the sensor frame reaches a target temperature specified for further operation, can be significantly reduced.

Description

Method and device for tempering a sensor frame in a microlithographic projection system

[0001] This patent application claims priority from German patent application DE 10 2023 210 937.9, filed on November 3, 2023, to which reference is made and the contents of which are incorporated herein in their entirety ("incorporation by reference").

[0002] The present invention relates to a method for tempering a sensor frame in a microlithographic projection system.

[0003] 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 onto a substrate, e.g., a silicon wafer, coated with a light-sensitive layer (so-called "photoresist") and arranged in the image plane of the projection system. This transfers 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.

[0004] Due to the progressive miniaturization in the semiconductor sector and the transition of the wavelength during exposure from DUV (e.g. 193 nm) to EUV (e.g. 13.5 nm), projection systems of projection exposure systems must have a high imaging 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.

[0005] To achieve high image quality, it is not only the quality of the individual optical elements of the projection system that is important, but also their relative position to one another. In order to ensure the latter 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, support frames and / or optical elements can have channels for a thermal fluid running through them. By conducting 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.

[0006] 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 changes in the position of the mirrors relative to each other that occur during operation.

[0007] In order to control the actuators precisely, 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. The sensor frame is also almost completely mechanically and thermally decoupled from the support frame, so that the sensor frame offers a fundamentally unchangeable 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.

[0008] 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 a gas present in the environment. The vacuum chamber in which the projection system is located must be evacuated, for example, during initial commissioning, when replacing the gas in the vacuum chamber, or after maintenance or other service work that requires access to the components of the projection system.

[0009] It has been found that after a vacuum has been created 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.

[0010] 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 do not occur or occur only to a reduced extent. This object is achieved by the features of independent claim 1. Advantageous embodiments are described in the dependent claims.

[0011] Accordingly, the invention relates to a method for temperature control 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 with at least one fluid line guided at least partially along the sensor frame for the active temperature control 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, whereby 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 thermoactuator in such a way that the sensor frame is actively tempered to a predetermined target temperature.

[0012] First, some terms used within the scope of the invention will be explained. "Active temperature control" is a heat input that is intentionally and specifically applied by suitable means in addition to the heat input that may occur unintentionally during the rest of the operation of a device. According to the invention, the active temperature control of the sensor frame is carried out with the aid of the fluid line that is provided for the active temperature control of an optical element. The control of the thermoactuator can be achieved by changing a fluid flow and / or a fluid temperature. In addition to the fluid line, the thermal actuator can, in particular, comprise a temperature-controlled fluid reservoir and a pumping device for conveying the thermal fluid through the fluid line. Active temperature control can, in principle, enable not only heat input but also targeted heat dissipation.

[0013] 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 regularly in the range between 1 Pa and 10 Pa, preferably approximately 5 Pa. When, in the context of the present description, it is mentioned 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.

[0014] 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 after evacuation for a longer period of time. 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 also not possible. Temperature deviations of the sensor frame can, in particular, lead to an undesired 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 While 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 temperature adjustment of the sensor frame takes considerably longer due to the thermal decoupling, as the sensor frame can hardly exchange heat with its surroundings in a vacuum.

[0015] Against this background, the invention provides for using a fluid line which is already present for the active temperature control of an optical element and which is guided at least partially along the sensor frame, in order 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 heated to a predetermined target temperature. It has been found that the desired target temperature of the sensor frame can be reached and kept stable much more quickly after evacuation by this measure. It has also been recognized that sufficient heat can be introduced due to the only small distance between the sensor frame and the sections of the fluid line which run along it.A 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, more preferably less than 1 cm. In particular, the distance can be approximately 0.5 mm.

[0016] 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, is due to the mass of the optical element, which regularly significantly (for example by a factor of 100) is smaller than the mass of the sensor frame, has only a minor influence on the operational readiness of the projection system after evacuation. 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 little or no influence on the temperature of the sensor frame.

[0017] The specified target temperature can correspond to the specified setpoint temperature required for continued operation of the pro ection 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 setpoint temperature . A target temperature above the setpoint temperature may be necessary, for example, if the optical element has an excessively high temperature after evacuation has ended and needs to be cooled to a lower temperature . As already explained above, this generally has only a minor effect on the sensor frame due to the difference in mass . Nevertheless, this slight removal of heat can also be taken into account so that the temperature can be reduced from the excessively high target temperature to the setpoint temperature .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.

[0018] It is advantageous if the optical element , after the sensor frame has reached the specified target temperature , 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 small, 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.

[0019] 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 there is already a low pressure 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 takes place quickly within the sensor frame due to its very high thermal conductivity.

[0020] In one embodiment, the introduction of thermal energy into the sensor frame takes place before the vacuum chamber is evacuated. In this case, thermal energy from the fluid line through the atmosphere in the vacuum chamber, allowing the sensor frame to be brought to a desired target temperature particularly efficiently. Alternatively or additionally, heat energy can be introduced during the evacuation of the vacuum chamber. It is also possible, of course, for heat energy to be introduced into the sensor frame after the evacuation of the vacuum chamber.

[0021] 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 at this point too, at least when there is still sufficient pressure within the vacuum chamber, heat transfer via the gas atmosphere takes place. Even if this is lower than heat transfer which takes place, 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.

[0022] The control of the thermoactuator can be achieved by adjusting the volume flow of the thermofluid through the fluid line. Alternatively or additionally, the control of the thermoactuator can also be achieved by adjusting the temperature of the thermofluid. In addition, it can be provided that a The 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.

[0023] 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 a heat effect on the sensor frame. The active temperature control of the support frame can transfer thermal energy to the sensor frame or also remove thermal energy from the sensor frame. The active temperature control of the support frame represents an additional degree of freedom by means of which the control objective of temperature controlling the sensor frame to a predetermined 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 means of 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.

[0024] The microlithographic projection system may further comprise an external temperature control unit. The external temperature control unit may, 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 a heat effect on the sensor frame. The fluid con- The fluid channels provided for the control unit and the external temperature control unit can preferably be fed by means of 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 control the temperature of the sensor frame to the specified target temperature. The external temperature control unit also creates an additional degree of freedom, through which the control objective of controlling the sensor frame to a specified target temperature can be achieved more reliably and quickly.

[0025] 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 is not actually required for the purpose of conveying the thermal fluid to the desired destination. would be required. The redundant subsection 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 the fluid line to the sensor frame (even taking a safety factor into account), but serves solely the purpose of establishing additional thermal coupling between the fluid line and the sensor frame.

[0026] The invention will now be explained in more detail by way of example using advantageous embodiments with reference to the accompanying drawings. They show: Figure 1: a schematic representation of a projection exposure system for microlithography; Figure 2: a schematic sectional view of a first Embodiment of a device according to the invention; Figure 3: a schematic sectional view of a second embodiment of a device according to the invention.

[0027] 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.

[0028] Using the lighting system 10, an object field 11 in an object plane or reticle plane 12. The For this purpose, the illumination system 10 comprises an exposure radiation source 13 which, in the illustrated embodiment, emits illumination radiation at least comprising useful light in the EUV range, that is to say in particular with a wavelength between 5 nm and 30 nm, in particular of 13.5 nm.

[0029] The illumination radiation emanating from the exposure radiation source 13 is first concentrated 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.

[0030] 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 in principle 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.

[0031] 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.

[0032] 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 is also described, for example, in DE 10 2008 009 600 A1.

[0033] 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'.

[0034] The facets of the first facet mirror 18 are each imaged by an associated facet of the second facet mirror 19, superimposed on one another, in order to illuminate the object field 11 as homogeneously as possible.

[0035] 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.

[0036] 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.

[0037] For this purpose, the projection system 20 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0038] In the example shown in Figure 1, the projection system 20 comprises six mirrors Mx to M6 as optical elements 23. Alternatives with four, eight, ten, twelve, or a different number of mirrors M1 are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation, thus making the projection system 20 shown a doubly 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, and can be, for example, 0.7 or 0.75.

[0039] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without a rotational symmetry axis. The mirrors Mi, like the mirrors of the illumination optics 16, 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.

[0040] The projection system 20 can in particular be anamorphic, ie it has in particular different image scales ß x , ß y in the x- and y-direction. The two magnifications ß x , ß y of the projection system 20 are preferably (ß x , ß y ) = (+ / - 0.25, / + - 0. 125) . A magnification ß of 0.25 corresponds to a reduction in the ratio 4:1, while a magnification ß of 0.125 results in a reduction ratio of 8:1. A positive sign for the magnification ß means an image without image inversion, a negative sign means an image with image inversion.

[0041] 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.

[0042] 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 wafer 35, on the other hand, via the wafer displacement drive 37, can be synchronized with each other.

[0043] The projection exposure system 1 sketched in Figure 1 and its illumination and projection system 10, 20 essentially correspond to the known state of the art.

[0044] The individual mirrors Mi or the optical elements 23 of the projection system 20 are mounted on a common support frame 24 (not shown in Figure 1) and can thus be considered as a unit.

[0045] 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 designed 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, only a single mirror Mi of the projection system 20 is shown as the optical element 23 in the illustration in Figure 2.The optical element 23 is connected to a support frame 24 mentioned above via actuators 25. The position of the optical element can be adjusted via the actuators 25. 23, particularly in relation to the other optical elements 23, can be adjusted within certain limits even during operation in order to achieve optimal imaging of the reticle 30 in the image field 21 in the image plane 22 (cf. Figure 1).

[0046] Thermally and mechanically completely from the supporting frame 24 is decoupled from the sensor frame 27. Sensors 28 are arranged on this sensor frame 27, a single one of which is shown in Figure 2. With the sensors 28, the position of the optical elements 23, Mi relative to the sensor frame 27 as a reference system and thus the position of the optical elements 23, Mi relative to one another can be determined without contact. In this case, a sensor 28 regularly detects the relative position of at least one reference point on one of the optical elements 23, Mi relative to the sensor 28. From the measurement results of several sensors 28 and taking into account the position of the individual Sensors 28 enable a complete and precise determination of the position of the optical elements 23, Mi.

[0047] The device 104 is designed in the present case 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. Starting from this inlet, the thermal fluid is guided in a basically 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.

[0048] The fluid lines 50, 51 are guided at least in sections 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 the present case are formed by metal clamps 55. Therefore, a heat exchange takes place between the thermal fluid conducted through the lines 50, 51 and the sensor frame 27. The invention makes use of 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.

[0049] In an exemplary embodiment of the method according to the invention, the vacuum chamber 101 is evacuated from an ambient pressure of 1 bar until a minimum pressure of 5 Pa is reached. The pumping process can, for example, extend over a period of one hour. During this period the control unit 103 causes the device 104 to conduct a thermal fluid through the fluid lines 50, 51, the thermal fluid being heated to such a temperature that thermal energy is introduced into the sensor frame 27. The heat is introduced on the one hand via the atmosphere still present within the vacuum chamber 101 during the pumping process. In addition, heat is transferred to the sensor frame 27 via the metal clamps 55. In particular when there is only a low pressure left in the vacuum chamber 101, the heat transfer via the metal clamps 55 can be the dominant heat transfer process.

[0050] The control unit 103 controls the flow through the fluid lines 50, 51 and the thermal fluid temperature with the control objective of bringing the sensor frame 27 to a predetermined target temperature. In this control, an already existing heat input, 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, is taken into account. In addition, the control takes into account that the components present in the vacuum chamber 101 cool down during pumping. In this case, the predetermined target temperature corresponds to a desired temperature of the sensor frame 27 predetermined for the continued operation of the projection system 20 and the control is carried out in such a way that the sensor frame 27 reaches the desired 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.

[0051] 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, for example, a pyrometer. 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.

[0052] Figure 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 100 shown in Figure 2. Only the differences from the embodiment shown in Figure 2 will be described below.

[0053] The device 100 of Figure 3 differs from the device of Figure 2 in that it has a second device 106 for actively controlling the temperature of an optical element. The device 106 is designed in particular for actively controlling the temperature of an additional mirror Mi, which is shown in Figure 3 as an optical element 40. The device 106 is connected to the optical element 40 via fluid lines 52, 53 in a manner analogous to that described in connection with Figure 2 in order to actively control the temperature of the optical element 40. However, the fluid lines 52, 53, in contrast to the fluid lines 50, 51, 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. A heat exchange, albeit a smaller one, also takes place in the region of the through-openings. instead. The fluid lines 52, 53 are used in this respect as an additional thermal actuator for supporting the introduction of thermal energy. Since the devices 104 and 106 in the present case 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 predetermined target temperature. For example, it can be provided that a supply of the thermal fluid through the fluid lines 52, 53 is switched off after a certain pressure has been undershot within the vacuum chamber 101, because in this case only a very small heat input into the sensor frame 27 can be expected due to the lack of attachment of the lines 52, 53 to the sensor frame 27.

[0054] Additionally, Figure 3 shows a device 107 for actively controlling the temperature of the support frame 24, which is connected to corresponding connections on the support frame 24 via fluid lines 56 in a generally known manner. Finally, in contrast to Figure 2, an external temperature control unit 108 is provided for actively controlling the temperature of the vacuum chamber 101, which is connected in a generally known manner to temperature control channels within the wall of the vacuum chamber 101 (not shown in the figure).

[0055] Both the active temperature control of the support frame 24 and the external temperature control unit 108 are used in the exemplary method 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, additional free space is provided by the active temperature control of the support frame or the external temperature control unit. degrees of safety are created, by means of which the control objective of tempering the sensor frame 27 to a predetermined target temperature can be achieved more reliably and quickly.

Claims

Patent claims 1. Method for temperature control of a sensor frame (27) in a microlithographic projection system (20) with optical elements (23, 40 Mi) fastened to a support frame (24), at least one sensor (28) fastened to the sensor frame (27) for contactless determination of a relative position of at least one of the optical elements (23, 40, Mi) 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 ± ), 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 in that the at least one of the optical elements (23, 40, M ± ) after the sensor frame (27) has reached the predetermined target temperature, is actively tempered to a target temperature of the optical element (23, 40, Mi).

3. Method according to claim 1 or 2, characterized in 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 in that the introduction of thermal energy into the sensor frame (27) takes place before the evacuation and / or during the evacuation of the vacuum chamber (101).

5. Method according to one of claims 1 to 4, characterized in that the projection system (20) has at least one further fluid line (52, 53) for actively controlling the temperature of at least one of the optical elements (40, Mi), which is guided contact-free through a through-opening present in the sensor frame (27), wherein the further fluid line (52, 53) is used as a further thermal actuator for supporting the introduction of thermal energy into the sensor frame.

6. Method according to one of claims 1 to 5, characterized in that the control of the thermal actuator is carried out by adjusting a volume flow of the thermal fluid through the fluid line (50, 51, 52, 53) and / or by adjusting a temperature of the thermal fluid.

7. Method according to one of claims 1 to 6, characterized in that 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 in 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 in that the fluid line (50, 51, 52, 53) and the fluid channels (56) provided for the active temperature control of the support frame (24) are fed by fluid reservoirs independent of one another, wherein the thermal actuator and the further thermal actuator 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 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. The method according to claim 10, characterized in 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 in that the thermal actuator is controlled such that a maximum temperature of the at least one of the at least one fluid line (50, 51, 52, 53) tempered optical element (23, 40, Mi) 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 controlling the temperature of at least one optical element (23, 40, Mi) of the microlithographic projection system (20) and for controlling the vacuum generator (102), wherein the device (104) for actively controlling the temperature is connected to at least one fluid line (50, 51, 52, 53) guided at least in sections along the sensor frame (27) for actively controlling the temperature of the at least one optical element (23, 40, Mi), characterized in that the control unit (103) is designed to control the vacuum generator (102) and the device (104) for actively To control tempering in such a way that the method according to one of claims 1 to 12 is carried out.

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