Compensation of thermally induced deformations during operation in the manufacturing process of an optical element with thermal control during operation

Abstract

The invention relates to a method for manufacturing an optical element (1) for an optical system with a desired surface shape (1a) and / or a desired optical effect during the operation of the optical system, wherein the optical element (1) maintains a mean operating temperature T during the operation of the optical system. X̅ The invention comprises a system controlled by at least one thermal manipulator (2). The invention also relates to an optical element for an optical system and an optical system for a semiconductor technology system.

Description

Technical area

[0001] The invention relates to methods for producing an optical element for an optical system with a desired surface shape and / or a desired optical effect during operation of the optical system. Furthermore, the invention relates to an optical element for an optical system and an optical system for a semiconductor technology system. background

[0002] Semiconductor technology systems include, for example, projection exposure systems, which are used to manufacture microstructured or nanostructured components in microelectronics or microsystems technology. To precisely manufacture components with structures in the nanometer and micrometer range, a corresponding projection exposure system must be able to precisely image structures contained on a reticle onto a substrate, such as a wafer. However, the radiation exposure from the working light of the projection exposure system used for imaging causes the optical elements of the projection exposure system to heat up, which can cause imaging errors.Driven by current demands for increased throughput, especially in EUV projection exposure systems, the power of the radiation source and, consequently, the performance within the optical systems of the projection exposure system are constantly increasing. Since even the best coatings on EUV optics do not achieve reflectivities close to 100%, the absorbed power in the optical elements also increases. This, in turn, leads to thermally induced deformations, which can significantly degrade the imaging quality of the optical systems.

[0003] Although DE 10 2010 030 913 A1 attempted to anticipate and compensate for deformations caused by the increased temperature during operation of an EUV projection exposure system during the manufacturing process, the optical elements of an optical system of a projection exposure system are typically not illuminated at a constant temperature over time. Rather, significant fluctuations in operating temperature occur depending on the operation of the scanner. For example, the temperature stress on the optical elements and the resulting aberrations can vary, particularly due to changes in the illumination settings and / or imaging of different reticles.

[0004] The object of the present invention is therefore to further develop a method for producing an optical element for an optical system with a desired surface shape and / or a desired optical effect during operation of the optical system such that the optical element reliably exhibits the desired surface shape and / or desired optical effect in different usage scenarios of the optical system, in particular with different lighting settings. Furthermore, the object of the present invention is to provide an advantageous optical element and an advantageous optical system.

[0005] According to a first teaching of the present invention, the above-mentioned object for a method for producing an optical element for an optical system with a desired surface shape and / or a desired optical effect during operation of the optical system is achieved in that the optical element has a mean operating temperature T X̅ which is controlled by at least one thermal manipulator, and the method comprises: - Determining the actual surface shape and / or the actual optical power of the optical element at the average operating temperature T X̅ , wherein the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ of a desired surface shape and / or the desired optical effect at the average operating temperature T X̅ deviates, and - Machining the optical element to adapt the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ depending on the specific actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ .

[0006] The optical element can be an optical element for an optical system of a semiconductor technology system. The optical element is, for example, a reflective optical element, e.g., a mirror or a mask. The optical element can comprise a substrate with a substrate surface. The substrate can comprise, for example, SiSic, Zerodur® from Schott AG, ULE® from Corning Inc., quartz glass, and / or any other type of glass. Furthermore, the optical element can comprise a coating. In particular, the optical element comprises a coating suitable for reflecting light from the EUV wavelength range (1-20 nm), in particular 13.5 nm.

[0007] The optical system can be a projection system of a semiconductor technology system, for example, a lithography lens. The optical system comprises at least one optical element. Preferably, the optical system comprises a plurality of optical elements. The optical system can comprise an arrangement of optical elements that serve to manipulate and / or shape light to generate, magnify, and / or correct images. For example, the optical system can comprise various optical elements such as lenses, mirrors, prisms, and / or filters that are positioned in a specific arrangement to focus, deflect, scatter, and / or filter light rays.

[0008] During operation of the optical system, the optical element at least substantially has a desired surface shape and / or a desired optical effect. In particular, the optical element at least substantially has a desired surface shape and / or a desired optical effect at the average operating temperature T X̅ during operation of the optical system. The desired surface shape and / or the desired optical effect of the optical element during operation of the optical system can be predetermined, for example, by an optical design. It is conceivable, for example, that the desired surface shape and / or the desired optical effect of the optical element during operation of the optical system at least substantially corresponds to the surface shape or the desired optical effect according to the underlying optical design.

[0009] The optical element has an average operating temperature T X̅ The average operating temperature T X̅ is controlled during operation of the optical system by at least one thermal manipulator. The at least one thermal manipulator can control the distribution of the operating temperature T X̅ in time t and optionally in place r→ With the aid of the at least one thermal manipulator, the operating temperature during operation of the optical system can be brought to and / or maintained at a desired target temperature. The average operating temperature T X̅ For example, it corresponds at least substantially to a target temperature. In particular, the average operating temperature T X̅ controlled in such a way that the average operating temperature T X̅the target temperature at least substantially, in particular the target temperature ± 0.5 K, in particular ± < 0.5 K. It is conceivable, for example, that the average operating temperature T X̅ the target temperature ± 0.5 K, in particular ± < 0.5 K. The target temperature and / or the average operating temperature T X̅ are, for example, between 25 °C and 30 °C. In particular, the average operating temperature T X̅During operation of the optical system, the temperature is kept constant by the at least one thermal manipulator. The at least one thermal manipulator can be, for example, a heater, in particular an IR heater or a sector heater, or a water cooling system. In particular, the thermal manipulator is suitable for locally controlling the temperature of the optical element in such a way that a temperature profile is generated across the optical element, which is selected such that the temperature profile is the same for all different illumination settings.The temperature profile can preferably be selected such that the temperature profile across the optical element has a temperature at every location on the optical element equal to or higher than the maximum temperature generated in the optical element by the radiation from a radiation source, for example, a semiconductor technology system, at one of the illumination settings of a lighting unit and / or an imaging setting of the optical system. The temperature profile can be kept constant over time during operation of the optical system, in particular of the semiconductor technology system comprising the optical system. The optical element can be temperature-controlled, for example, using electromagnetic radiation.The radiation intensity can be selected such that the profile of the absorbed radiation intensity above the optical element at any location on the optical element has a radiation intensity equal to or higher than the maximum absorbed radiation intensity generated by the radiation of a radiation source in one of the illumination settings of the illumination unit and / or an imaging setting of the optical system in the optical element, wherein in particular the profile of the absorbed radiation intensity is kept constant over time during operation of the optical system, in particular of the semiconductor technology system.

[0010] The method may include determining the actual surface shape of the optical element at the average operating temperature T X̅ Alternatively or additionally, the method may comprise determining the actual optical effect of the optical element at the average operating temperature T X̅The actual surface shape and / or the actual optical power of the optical element at the average operating temperature T X̅ can depend in particular on the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ Determining can be understood, for example, as determining, measuring, and / or calculating or simulating.

[0011] The method further comprises machining the optical element to adapt the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ depending on the specific actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ . Based on the determined actual surface shape at the average operating temperature T X̅the optical element can be machined in such a way that the actual surface shape corresponds to the desired surface shape at the average operating temperature T X̅ at least substantially corresponds. Based on the determined actual optical power, the optical element can be processed such that the actual optical power at the average operating temperature T X̅ the optical target effect at the average operating temperature T X̅ at least substantially corresponds. Processing the optical element may, for example, comprise polishing the optical element.

[0012] It has been shown that the process can be used to produce an optical element that reliably exhibits the desired surface shape and / or optical effect in various usage scenarios of the optical system. Because the average operating temperature T X̅of the optical element is controlled, in particular kept constant, with the aid of the at least one thermal manipulator, the desired surface shape and / or desired optical effect of the optical element at the average operating temperature T X̅ be provided. In an optical system, in the event that no thermal manipulator is present, the operating temperature of an optical element increases predominantly due to the radiation from the radiation source, and the operating temperature can vary with different illumination settings, which, for example, the user of the optical system adjusts depending on the required structure. Thermally induced deformations during operation of the optical element, in particular of the optical system, are therefore generally time-dependent. However, with the aid of at least one thermal manipulator, the average operating temperature T X̅of the optical element can be advantageously controlled, in particular kept constant. With the at least one thermal manipulator, the operating temperature can be modified such that a required correction of a thermal deformation becomes less sensitive to fluctuations in parameters such as pressure, cooling water temperatures, material properties, in particular the zero crossing temperature (ZCT) of the thermal expansion, and / or power. The at least one manipulator can in particular be designed such that the corrected temperature distribution functions as universally as possible for users during operation. With the method, for example, optical elements can be specifically reworked during production. The method for processing the optical element can be used to correct the optical element, in particular to correct the surface shape and / or optical effect of the optical element.

[0013] According to an advantageous embodiment of the method according to the first teaching, the actual surface shape and / or the actual optical effect of the optical element is determined at the average operating temperature T X̅ by means of a simulation. In particular, the simulation can be used to determine the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ be determined without adjusting the average operating temperature T X̅ is actually required. In other words, the simulation can be used to determine the final surface shape and / or the final optical effect that the optical element will have at the average operating temperature T X̅The actual surface shape and / or the actual optical effect of the optical element can be determined, for example, using a finite element simulation.

[0014] As a basis for the simulation, for example, spatially resolved material data of the optical element at a measuring temperature T M , which depends on the average operating temperature T X̅ deviates, in particular a manufacturing temperature T F For example, spatially resolved material data of the optical element can be obtained by optical interferometry and / or ultrasonic measurements of the optical element at the measuring temperature T MIn particular, realistic material models, such as thermal hysteresis, nonlinear expansion behavior, and / or specifically measured homogeneity and / or inhomogeneity data, can be considered. The optical element can, for example, comprise a material that has a non-zero homogeneous and / or inhomogeneous thermal expansion coefficient, in particular glass ceramics such as Zerodur® or titanium-doped quartz glass such as ULE, and / or other local variations, for example with regard to the refractive index. These properties of the optical element, in particular of the material, can be taken into account, for example, in the simulation.

[0015] According to a further advantageous embodiment of the method according to the first teaching, the determination of the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅measuring the actual surface shape and / or the actual optical effect of the optical element at at least one measuring temperature T M and interpolating or extrapolating to the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ The interpolation or extrapolation to the actual surface shape and / or the actual optical power of the optical element at the average operating temperature T X̅ is carried out in particular based on the measured actual surface shape and / or the actual optical effect of the optical element at the at least one measuring temperature T MWith extrapolation, function values ​​outside an interval can be determined, at least approximately, based on the function values ​​known within that interval. With interpolation, a continuous interpolant can be determined based on at least two measured values, which represents the measured values.

[0016] The actual surface shape and / or the actual optical effect of the optical element can, for example, be measured at a first measuring temperature T M1 and at least one second measuring temperature T M2 measured and based on the measured actual surface shape and / or the actual optical power of the optical element at the first measuring temperature T M1 and the second measuring temperature T M the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ interpolated or extrapolated. The at least one measurement temperature T Mdeviates in particular from the average operating temperature T X̅ It is conceivable, for example, that the actual surface shape and / or the actual optical effect of the optical element at a first measuring temperature T M1 is measured, whereby the first measuring temperature T M1 22 °C + 5 K, and at a second measuring temperature T M2 is measured, whereby the second measuring temperature T M2 22 °C + 10 K. From this, it is possible to interpolate to 22 °C + 7 K or extrapolate to 22 °C + 12 K. The minimum of one measurement temperature T M can be adjusted, for example, with the aid of a measuring device comprising at least one thermal manipulator, wherein the optical element is preferably only temporarily adjusted to the at least one measuring temperature T M It is also conceivable that at least one of the measuring temperatures T Mto the manufacturing temperature T F is.

[0017] According to a further advantageous embodiment of the method according to the first teaching, the determination of the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ measuring the actual surface shape and / or the actual optical power of the optical element at the average operating temperature T X̅ It is conceivable, for example, that the measurement of the actual surface shape and / or the actual optical effect of the optical element takes place at an ambient temperature which corresponds to the average operating temperature T X̅ For this purpose, the environment in which the measurement is carried out, such as a clean room, can be adjusted to the average operating temperature T X̅ be heated.

[0018] Alternatively, it is conceivable that the measurement of the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ by means of a suitable measuring device. The measuring device can, for example, comprise at least one thermal manipulator, wherein the optical element is preferably only temporarily heated to the average operating temperature T X̅ It is conceivable, for example, that the measuring device comprises an optical heat source, for example a heater, in particular an IR heater, an oven, or a bath with an adjustable water temperature. With the aid of the measuring device, the optical element can be heated such that the average operating temperature T X̅is achieved. In particular, the thermal manipulator of the optical system is reproduced as best as possible in the measuring device. Furthermore, the measuring device can comprise a measuring device, in particular a measuring sensor, for measuring the surface shape and / or for measuring the optical effect of the optical element.

[0019] The measurement of the surface shape and / or the optical power of the optical element can be carried out while heating the optical element at medium operating temperature T X̅, for example by means of an IR heater. It is also conceivable that measurements are carried out with the thermal manipulator activated and / or deactivated, so that the difference between the measurements can be incorporated into the optical element, in particular into the surface of the optical element. The measurement of the surface shape of the optical element can be carried out absolutely or relative to a reference surface. In particular, the measuring device can comprise a measuring device for measuring the surface shape of the optical element absolutely or relative to a reference surface. The measurement can, for example, be carried out relative to a reference surface and the processing of the optical element can comprise incorporating the difference to the reference surface into the surface of the optical element. The procedure is repeated, for example, until convergence, i.e. until the measured surface corresponds to the reference surface.

[0020] According to a further advantageous embodiment of the method according to the first teaching, the processing of the optical element can be carried out at a manufacturing temperature T F The manufacturing temperature T F can, for example, be more than 0.5 K, preferably more than 1 K, more preferably more than 2 K, particularly preferably more than 5 K from the average operating temperature T X̅ It is also conceivable that the manufacturing temperature T F by 10 to 20 K from the average operating temperature T X̅ For example, the manufacturing temperature T F around room temperature. The manufacturing temperature T F is, for example, 22 °C. During the manufacture of the optical element, the average operating temperature T X̅For example, it can only be adjusted during the determination, in particular the measurement, of the surface and / or the optical effect of the optical element. The determination of the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ , and the processing of the optical element, especially at the manufacturing temperature T F , for adapting the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ can be done iteratively.

[0021] According to a further advantageous embodiment of the method according to the first teaching, the processing of the optical element can be carried out at the average operating temperature T X̅It is conceivable, for example, that the processing of the optical element takes place at an ambient temperature which corresponds to the average operating temperature T X̅ For this purpose, the environment in which the processing takes place, such as a clean room, can be adjusted to the average operating temperature T X̅ The average operating temperature T X̅ can be adjusted during the manufacturing of the optical element. This allows the optical element to be manufactured directly with compensation. By machining the optical element at the expected average operating temperature T X̅ Furthermore, there are no waiting times for temperature adjustment for measurement purposes, nor are there any inaccuracies due to insufficient waiting time and incomplete heating of the optical element. However, it should be noted that any measurements for process validation must also be performed at the average operating temperature T X̅must be made.

[0022] According to a further advantageous embodiment of the method according to the first teaching, the method can determine a difference between the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ and the desired surface shape and / or the desired optical effect of the optical element at the average operating temperature T X̅ The method may, for example, include determining a deviation of the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ on the desired surface shape and / or the desired optical effect of the optical element at the average operating temperature T X̅In particular, the method may include determining a required surface correction for adapting the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ to the desired surface shape and / or the desired optical effect of the optical element at the average operating temperature T X̅ The processing of the optical element can, in particular, depend on the determined difference between the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ and the desired surface shape and / or the desired optical effect of the optical element at the average operating temperature T X̅It is conceivable, for example, that the method comprises determining a compensation which improves a target function for optimizing an optical effect, in particular an aberration state, of the optical element, in particular of the optical system, compared to a state without compensation, for example by determining an expected surface shape change due to the temperature difference with the opposite sign.

[0023] According to a further advantageous embodiment of the method according to the first teaching of the present invention, the method can comprise a partial compensation of the difference between the actual surface shape and the desired surface shape and / or the actual optical effect and the desired optical effect by means of a correction means and / or at least one further manipulator. The at least one further manipulator can in particular be a rigid-body manipulator. It is conceivable, for example, that a partial correction of the difference is carried out by correction means, for example a reticle or semiconductor substrate table available in the optical system, and / or at least one further manipulator, which, for example, causes rigid-body movements and / or deformations of optical elements.

[0024] The processing of the optical element to adapt the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ can be carried out by means of a correction means and / or at least one further manipulator, taking into account the partial compensation of the difference between the actual surface shape and the desired surface shape and / or the actual optical effect and the desired optical effect.

[0025] It is conceivable, for example, that a predefined target function is calculated from one or more residual error images and the necessary compensation, in particular surface change, in the optical element is determined in such a way that at least an improvement of the target function is achieved.

[0026] According to a second teaching of the present invention, the above-mentioned object for a method for producing an optical element for an optical system with a desired surface shape and / or a desired optical effect during operation of the optical system is achieved in that the optical element has a mean operating temperature T X̅ which is controlled by at least one thermal manipulator, and the method comprises: - Determining the actual surface shape and / or the actual optical effect of the optical element at a manufacturing temperature T F , - Determining a change in the actual surface shape and / or the actual optical effect of the optical element due to a temperature difference T X̅ - T F between the manufacturing temperature T F and the average operating temperature T X̅ , and - Machining the optical element to adapt the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ depending on the specific actual surface shape and / or the actual optical effect at the production temperature T F and depending on the specific change in the actual surface shape and / or the actual optical effect due to the temperature difference T X̅ - T F between the average operating temperature T X̅ and the manufacturing temperature T F .

[0027] The method may include determining the actual surface shape of the optical element at a manufacturing temperature T F Alternatively or additionally, the method may comprise determining the actual optical effect of the optical element at a manufacturing temperature T F The manufacturing temperature TF deviates in particular from the average operating temperature T X̅ The method may also include determining a change in the actual surface shape of the optical element due to a temperature difference T X̅ - T F between the manufacturing temperature T F and the average operating temperature T X̅ Alternatively or additionally, the method may include determining a change in the actual optical power of the optical element due to a temperature difference T X̅ - T F between the manufacturing temperature T F and the average operating temperature T X̅ include.

[0028] The method further comprises processing the optical element to adapt the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅. The machining of the optical element can be carried out depending on the specific actual surface shape and / or the specific actual optical effect at the manufacturing temperature T F and depending on the specific change in the actual surface shape and / or the actual optical effect due to the temperature difference T X̅ - T F between the average operating temperature T X̅ and the manufacturing temperature T F take place.

[0029] According to an advantageous embodiment of the method according to the second aspect, determining the change in the actual surface shape and / or the actual optical effect of the optical element due to the temperature difference T X̅ - T F between the manufacturing temperature T F and the average operating temperature T X̅ determining a difference between the actual surface shape and / or the actual optical power of the optical element at the manufacturing temperature TF and the desired surface shape and / or the desired optical effect of the optical element at the average operating temperature T X̅ . In particular, the method may include determining a required surface correction for adapting the actual surface shape and / or the actual optical effect of the optical element at the average operating temperature T X̅ to the desired surface shape and / or the desired optical effect of the optical element at the average operating temperature T X̅ include.

[0030] According to a further advantageous embodiment of the method according to the second aspect, the change in the actual surface shape and / or the actual optical effect of the optical element is determined based on a mathematical model for determining the local deformation during a temperature change. The method can, for example, determine the surface shape and / or the optical effect of the optical element at the average operating temperature T X̅ deviating from the actual surface shape and / or the actual optical effect of the optical element at the manufacturing temperature T F based on a simulation calculation. To determine the change in the actual surface shape and / or the actual optical effect of the optical element, the surface shape and / or the optical effect of the optical element at the average operating temperature T X̅be simulated, in particular with the help of a finite element simulation. In other words, the simulation can be used to determine the final surface shape and / or the final optical effect of the optical element at the average operating temperature T X̅ be determined without adjusting the average operating temperature T X̅ is required. Here, too, spatially resolved material data, for example by optical interferometry and / or ultrasonic measurements of the optical element at the manufacturing temperature T F The simulation can be based on a usage scenario that results in a static temperature distribution in the optical element. With the help of the mathematical model, in particular the finite element simulation, the surface shape of the optical element at the average operating temperature T X̅This can then be used to draw conclusions about the optical effect of the optical element at the average operating temperature T X̅ It is conceivable that with the help of a simulation the optical effect, for example an optical aberration effect, of the optical element at the average operating temperature T X̅ determined, in particular calculated.

[0031] It is conceivable, for example, that the method according to the first teaching and / or second teaching comprises determining a compensation which improves a target function for optimizing an optical effect, in particular an aberration state, of the optical element, in particular of the optical system, compared to a state without compensation, for example by determining an expected surface shape change as a result of the temperature change with the opposite sign.

[0032] The method according to the first teaching and / or second teaching can comprise a calculation of the temperature distribution in the optical element. For example, based on the predicted operation of the optical element, simulations can be used to calculate which average temperature distribution will prevail in the optical element. From this, a surface deformation can be calculated, which must be taken into account during manufacture of the optical element. The method can comprise a calculation of the deformation of the surface of the optical element and / or an extraction of the required surface correction. In this case, the local variation of material parameters within the optical element, e.g., the refractive index variation and / or the thermal expansion coefficient variation, can be taken into account.In particular, if the material of the optical element, for example Zerodur®, exhibits thermal hysteresis, the temporal progression of temperature and deformation during operation of the optical element can also be taken into account, at least in part, when selecting the optimal compensation for operation.

[0033] According to a further advantageous embodiment of the method according to the second teaching of the present invention, the method can comprise a partial compensation of the determined change in the actual surface shape and / or the actual optical effect of the optical element by means of a correction means and / or at least one further manipulator. The at least one further manipulator can in particular be a rigid-body manipulator. It is conceivable, for example, that a partial correction of the change is carried out by correction means, for example a reticle or semiconductor substrate stage available in the optical system, and / or at least one further manipulator, which, for example, causes rigid-body movements and / or deformations of optical elements.

[0034] The processing of the optical element to adapt the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ can be carried out taking into account the partial compensation of the specific change in the surface shape and / or the optical effect of the optical element by means of the correction means and / or the at least one additional manipulator. For example, it is conceivable that a predefined target function is calculated from one or more residual error images and the necessary compensation, in particular the surface change, in the optical element is determined in such a way that at least an improvement in the target function is achieved.

[0035] According to an advantageous embodiment of the method according to the second teaching of the present invention, the processing of the optical element can be carried out at the manufacturing temperature T F The manufacturing temperature T F can, for example, be more than 0.5 K, preferably more than 1 K, more preferably more than 2 K, particularly preferably more than 5 K from the average operating temperature T X̅ It is also conceivable that the manufacturing temperature T F by 10 to 20 K from the average operating temperature T X̅ For example, the manufacturing temperature T F around room temperature. The manufacturing temperature T F is, for example, 22 °C. Determining the actual surface shape and / or the actual optical effect of the optical element at the manufacturing temperature T F , and processing the optical element at the manufacturing temperature T Ffor adapting the actual surface shape and / or the actual optical effect of the optical element to the desired surface shape and / or the desired optical effect at the average operating temperature T X̅ can be done iteratively.

[0036] According to an advantageous embodiment of the method according to the first or second teaching of the present invention, the method may comprise determining the optical power of the optical system. In particular, the method may comprise determining an aberration and / or the wavefront of the optical system. The method may comprise determining the desired surface shape and / or the desired optical power of the optical element at the average operating temperature T X̅depending on the specific optical power of the optical system. It is conceivable, for example, that certain or all optical elements, degrees of freedom and / or manipulators are taken into account for determining the desired surface shape and / or the desired optical power of the optical element, in particular for determining a required surface correction of the optical element. The method can be used, for example, to reduce thermally induced aberrations during operation of the optical system. For example, selected or all manipulators of the optical system can be taken into account in the optimization. This includes, in particular, thermal manipulators, with the help of which the temperature of optical elements can be adjusted during operation.A direct consequence of the concept is, for example, that all manipulators are relieved of the travel distance to compensate for the mean contribution during operation, so that travel distance is freed up for an improved correction effect.

[0037] The method can be used, in particular, to take into account the average deformation in the surface design of the optical element and thus to compensate for thermal aberrations. Compensation need not be limited to a specific optical element; rather, the thermally induced aberrations can also be corrected on one or more other optical elements. In other words, an error does not necessarily have to be corrected on the same optical element on which it originates. Machining the optical element to adapt the surface shape and / or the optical power of the optical element to the desired surface shape and / or the desired optical power at the average operating temperature T X̅For example, this can be done by taking into account an already partially compensated aberration in the optical system, for example, by at least one correction means and / or at least one manipulator. It is conceivable, for example, that the method includes determining a compensation that improves a target function for optimizing the aberration state of the optical system with the optical element compared to a state without compensation. In principle, specifics of an individual optical system and / or optical element, for example, material parameters such as ZCT and / or reflectivities, can be taken into account, which allows a reduction of performance fluctuations.

[0038] According to a third teaching of the present invention, the above-mentioned object for an optical element for an optical system with a desired surface shape and / or a desired optical effect during operation of the optical system is achieved in that the optical element is heated to a measuring temperature T M , in particular a manufacturing temperature T F , has a first surface shape and at an average operating temperature T X̅ has the desired surface shape and / or the desired optical effect, wherein the optical element has the average operating temperature T X̅ during operation of the optical system, which is controlled by at least one thermal manipulator. The optical element is in particular manufactured by a method according to the first or second teaching of the present invention.

[0039] According to a fourth teaching of the present invention, the above-mentioned object is achieved by an optical system for a semiconductor technology plant comprising: at least one optical element according to the third teaching, and at least one thermal manipulator which determines the average operating temperature T X̅ of the optical element. A semiconductor technology system can, for example, be a projection exposure system, a wafer inspection system, or a mask inspection system.

[0040] According to an advantageous embodiment of the optical system according to the fourth teaching, by providing a predetermined state in which the average operating temperature T X̅ of the optical element and the average operating temperature T X̅at least one further optical element differ from one another by at least 1 K, compared to a state in which the optical element and the at least one further optical element have at least substantially the same temperatures, at least one imaging error is reduced by at least 20%, preferably at least 25%, particularly preferably at least 30%.

[0041] The at least one aberration can be, for example, a distortion, a focus error, an astigmatism, a coma (tail error), a specific contribution to the wavefront development according to Zernike polynomials, and / or an RMS value ("root means square") of the wavefront deviation, for example in its field dependence. The aberration can be, in particular, a Zernike RMS5 and / or, depending on the application of the semiconductor technology system for a predetermined combination of illumination and structure, the distortion ("overlay") and / or the target / actual deviation of the focus. Furthermore, it can be a stray light contribution ("flare").The at least two optical elements can in particular be the first and last optical element of the optical system and / or the first optical element in at least almost perpendicular incidence and the largest optical element, preferably in grazing incidence.

[0042] The exemplary embodiments of the present invention described above in this description should also be understood as disclosed in all combinations with one another. The individual features of each teaching can be combined with any or all features of the other teachings. In particular, features, in particular steps, of the method according to the first teaching can be combined with features, in particular steps, of the method according to the second teaching. For example, in the measurement-based method, it is possible to start with an actual surface that is already very close to the optimal design state due to a simulation-based correction or due to production in a heated state. Such a combination allows the reduction of potential errors in the process chain.Another possible combination would be to support the simulation-based correction with measurements, using the measurements as reference points for interpolation, extrapolation, or calibration of the simulation. This is particularly interesting in cases where the desired operating state is not available in the measurements.

[0043] Further embodiments and advantages of the invention are explained in the following detailed description of some exemplary embodiments of the present invention in conjunction with the drawing. Short description of the drawing

[0044] In the following, exemplary embodiments and variants of the invention are explained in more detail with reference to the drawings. The aspects of the disclosure can best be understood from the following detailed description in conjunction with the accompanying figures. The figures are schematic and simplified, showing only details to improve the understanding of the claims, while other details are omitted. The same reference numerals are used throughout for identical or corresponding parts. The individual features of each aspect can each be combined with any or all features of the other aspects. These and other aspects, features and / or technical effects are apparent from and are clarified by the figures described below. It shows Fig. 1a, Fig. 1b an optical element at a manufacturing temperature T F and at an operating temperature T B, which was produced using a process according to the state of the art, Fig. 2a, Fig. 2b an optical element at a manufacturing temperature T F and at an average operating temperature T X̅ which was produced by a process according to the first or second teaching of the present invention, and Fig. 3 a measuring device for determining a surface shape and / or an optical effect of an optical element at an average operating temperature T X̅ in the context of a procedure according to the first doctrine.

[0045] In Fig. Figure 1a shows an optical element 1' from the prior art, which is designed as an EUV mirror. The optical element 1' was manufactured at a manufacturing temperature T F of about 22°C. At the manufacturing temperature T FThe optical element 1' has a desired surface shape 1a'. While the surface shape of the optical element 1' was optimally polished to the design surface during the manufacturing process, the surface shape changes during the operation of an optical system in which the optical element 1' is used, in areas of increased temperature (brighter areas) due to thermal deformations, as in Fig. 1b. The optical element 1' has an operating temperature T B of > 22 °C, for example 30 °C, a surface shape 1b' that deviates from the desired surface shape 1a'.

[0046] In Fig. 2a is an optical element 1 at a manufacturing temperature T F and in Fig. 2b at an average operating temperature T Bwhich was produced by a method according to the first or second teaching of the present invention. While the optical element 1 is kept at the manufacturing temperature T F has a deviation from the desired surface shape according to the optical design of the optical element, the optical element 1 at the average operating temperature T B the target surface shape 1a. The thermal deformation due to the difference in the average operating temperature T F to the manufacturing temperature T F was already taken into account during production.

[0047] For example, the optical element 1 was produced according to a method for producing an optical element for an optical system with a desired surface shape and / or a desired optical effect at an average operating temperature T X̅during operation of the optical system, which is controlled by at least one thermal manipulator 2, according to the second teaching, which involves determining the actual surface shape 1b and / or the actual optical effect of the optical element 1 at the manufacturing temperature T F , determining the change in the actual surface shape 1b and / or the actual optical effect of the optical element 1 due to the temperature difference T X̅ - T F between the manufacturing temperature T F and the average operating temperature T X̅ , and processing the optical element 1 to adapt the actual surface shape 1b and / or the actual optical effect of the optical element 1 to the desired surface shape 1a and / or the desired optical effect at the average operating temperature T X̅ depending on the specific actual surface shape 1b and / or the actual optical effect at the manufacturing temperature T Fand depending on the specific change in the actual surface shape 1b and / or the actual optical effect due to the temperature difference T X̅ - T F between the average operating temperature T X̅ and the manufacturing temperature T F includes.

[0048] The determination of the change in the actual surface shape 1b and / or the actual optical effect of the optical element 1 was carried out based on a mathematical model for determining the local deformation during a temperature change. For example, it is conceivable that the method includes a calculation of the temperature distribution, a calculation of the deformations, and / or an extraction of the required surface correction.

[0049] To determine the temperature distribution using the heat conduction equation (1), the energy source, the thermal coupling to the environment of the optical element 1, and / or thermal material properties are determined. Based on the power occurring at the optical element 1, the absorbed power at any location on the surface of the optical element 1 can be calculated using the material properties. This yields the source fS(r→,t) for the heat conduction equation, where in this case fV(r→,t) is zero. With knowledge of the environment around the optical element 1, e.g., air or other gases, pressure, distances to any neighboring components and / or components in direct contact with the optical element, especially contact surfaces, materials, the thermal boundary conditions of the heat conduction equation (1) can be determined according to equation (2). Furthermore, the thermal material parameters of the optical element, such as heat capacity c, thermal conductivity λ, and density ρ, are required.

[0050] To solve the equation, the finite element method (FEM) can be used to discretize the 3D space. The heat conduction equation for the temperature distribution T(r→,t) depending on the location r→ and time t is given by ∂T(r→,t)∂t−αΔT(r→,t)=fV(r→,t) with the thermal conductivity α=λρc and the volume source fV(r→,t) Due to the surface load fS(r→,t) the boundary condition also applies to all surface points r→O of the optical element: −λ∇nT(r→O,t)=μ(T(r→O,t)−T0)+fs(r→O,t) with the temperature of the adjacent material T0, the heat transfer coefficient µ and the derivative in the surface normal direction ∇ n Not explicitly listed here is the heat change due to thermal radiation, which can generally also be taken into account.

[0051] Based on the temperature and / or temperature distribution and with the aid of the thermal expansion coefficient, the relative volume change per volume element can be determined. The equilibrium point of the mechanical forces, which arise from both mechanical boundary conditions and the temperature gradient, is then determined using the material parameters, such as density, Young's modulus, and / or Poisson's ratio. This determines the deformation at each point in the optical element 1. For the optical effect of a mirror, the points on the optical surface are particularly important. r→OF relevant.

[0052] With the calculated deformation of the optical surface dO(r→OF) anywhere r→OF in the normal direction, you can determine how much the design surface needs to be changed. One option here would be the inverse deformation - dO(r→OF) However, it is often more advantageous to consider the existing manipulators beforehand: If the rigid body degrees of freedom of the optical part are equipped with manipulators, it may be advisable to first calculate the calculated surface deformation K[dO(r→OF)] to correct and then simply remove the remaining portion from the surface.

[0053] Alternatively, it is conceivable that the optical element 1 is produced according to a method for producing an optical element for an optical system with a desired surface shape and / or a desired optical effect at an average operating temperature T X̅ during operation of the optical system, which is controlled by at least one thermal manipulator 2, according to the first teaching. The method comprises, for example, determining the actual surface shape 1b and / or the actual optical effect of the optical element 1 at the average operating temperature TX̅ , wherein the actual surface shape 1b and / or the actual optical effect of the optical element 1 at the average operating temperature T X̅ from the desired surface shape 1a and / or the desired optical effect at the average operating temperature T X̅ deviates, and processing the optical element 1 to adapt the actual surface shape 1b and / or the actual optical effect of the optical element 1 to the desired surface shape 1a and / or the desired optical effect at the average operating temperature T X̅ depending on the specific actual surface shape 1b and / or the actual optical effect of the optical element 1 at the average operating temperature T X̅ . The actual surface shape 1b and / or the actual optical effect of the optical element 1 at the average operating temperature T X̅ For example, this was done with the help of a Fig. 3 shown measuring device 3 measured.

[0054] In Fig.3 is a measuring device 3 for determining an actual surface shape 1b and / or the actual optical effect of the optical element 1 at the average operating temperature T X̅ The measuring device 3 comprises a thermal manipulator 2, wherein the optical element 1 is temporarily heated to the average operating temperature T X̅ is heated. The thermal manipulator 2 is, for example, an IR heater. Furthermore, the measuring device 3 comprises a measuring device, 4 in particular a measuring sensor, for measuring the surface shape 1a of the optical element 1. The measurement of the surface shape 1a of the optical element 1 can be carried out with simultaneous heating of the optical element 1 at a medium operating temperature T X̅It is also conceivable that measurements are taken with the thermal manipulator 2 activated and deactivated, so that the difference between the measurements can be incorporated into the optical element 1, in particular into the surface 1a of the optical element 1. 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 2010 030 913 A1

[0003]

Claims

[1] Method for producing an optical element (1) for an optical system with a desired surface shape (1a) and / or a desired optical effect during operation of the optical system, characterized by that the optical element (1) has an average operating temperature T X̅ which is controlled by at least one thermal manipulator (2), and the method comprises: - Determining the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ , wherein the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ of the desired surface shape (1a) and / or the desired optical effect at the average operating temperature T X̅ deviates, and - processing the optical element (1) to adapt the actual surface shape (1b) and / or the actual optical effect of the optical element (1) to the desired surface shape (1a) and / or the desired optical effect at the average operating temperature T X̅ depending on the specific actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ . [2] Method according to claim 1, characterized by that the determination of the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ by means of a simulation. [3] Method according to claim 1 or 2, characterized by that the determination of the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅measuring the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at at least one measuring temperature T M and interpolating or extrapolating to the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ includes. [4] Method according to one of claims 1 to 3, characterized by that the determination of the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ measuring the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ includes. [5] Method according to one of claims 1 to 4, characterized by that the processing of the optical element (1) is carried out at a manufacturing temperature T F occurs. [6] Method according to one of claims 1 to 5, characterized bythat the processing of the optical element (1) at the average operating temperature T X̅ occurs. [7] Method according to one of claims 1 to 6, characterized by that the method comprises determining a difference between the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the average operating temperature T X̅ and the desired surface shape (1a) and / or the desired optical effect of the optical element (1) at the average operating temperature T X̅ includes. [8] Method according to one of claims 1 to 7, characterized by that the procedure further includes: - partially compensating the difference between the actual surface shape (1b) and the desired surface shape (1a) and / or the actual optical effect and the desired optical effect by means of a correction means and / or at least one further manipulator, in particular a rigid body manipulator, and - processing the optical element (1) to adapt the actual surface shape (1b) and / or the actual optical effect of the optical element (1) to the desired surface shape (1a) and / or the desired optical effect at the average operating temperature (T X̅ ) taking into account the partial compensation of the difference between the actual surface shape (1b) and the desired surface shape (1a) and / or the actual optical effect and the desired optical effect by means of the correction means and / or the at least one further manipulator. [9] Method for producing an optical element (1) for an optical system with a desired surface shape (1a) and / or a desired optical effect during operation of the optical system, characterized by that the optical element (1) has an average operating temperature T X̅which is controlled by at least one thermal manipulator (2), and the method comprises: - Determining the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at a manufacturing temperature T F , - Determining a change in the actual surface shape (1b) and / or the actual optical effect of the optical element (1) due to a temperature difference T X̅ - T F between the manufacturing temperature T F and the average operating temperature T X̅ , and - processing the optical element (1) to adapt the actual surface shape (1b) and / or the actual optical effect of the optical element (1) to the desired surface shape (1a) and / or the desired optical effect at the average operating temperature T X̅ depending on the specific actual surface shape (1b) and / or the actual optical effect at the manufacturing temperature T Fand depending on the specific change in the actual surface shape (1b) and / or the actual optical effect due to the temperature difference T X̅ - T F between the average operating temperature T X̅ and the manufacturing temperature T F . [10] Method according to claim 9, characterized by that the determination of the change in the actual surface shape (1b) and / or the actual optical effect of the optical element (1) due to the temperature difference T X̅ - T F between the manufacturing temperature T F and the average operating temperature T X̅ determining a difference between the actual surface shape (1b) and / or the actual optical effect of the optical element (1) at the manufacturing temperature T F and the desired surface shape (1a) and / or the desired optical effect of the optical element (1) at the average operating temperature T X̅ includes. [11] Method according to claim 9 or 10, characterized by that the determination of the change in the actual surface shape (1b) and / or the actual optical effect of the optical element (1) is carried out on the basis of a mathematical model for determining the local deformation in the event of a temperature change. [12] Method according to one of claims 9 to 11, characterized by that the procedure further includes: - partial compensation of the determined change in the actual surface shape (1b) and / or the actual optical effect of the optical element (1) by means of a correction means and / or at least one further manipulator, in particular a rigid body manipulator, and - processing the optical element (1) to adapt the actual surface shape (1b) and / or the actual optical effect of the optical element (1) to the desired surface shape (1a) and / or the desired optical effect at the average operating temperature T X̅taking into account the partial compensation of the determined change in the actual surface shape (1b) and / or the actual optical effect of the optical element (1) by means of the correction means and / or the at least one further manipulator. [13] Method according to one of claims 9 to 12, characterized by that the processing of the optical element (1) at the manufacturing temperature T F occurs. [14] Method according to one of the preceding claims, characterized by that the procedure further includes: - Determining the optical effect, in particular the wavefront, of the optical system, and - Determining the desired surface shape (1a) and / or the desired optical effect of the optical element (1) at the average operating temperature T X̅ depending on the specific optical power of the optical system. [15] Optical element (1) for an optical system with a desired surface shape (1a) and / or a desired optical effect during operation of the optical system, in particular produced by a method according to claims 1 to 14, characterized by that the optical element (1) at a measuring temperature T M , in particular a manufacturing temperature T F , has a first surface shape and at an average operating temperature T X̅ the desired surface shape (1a) and / or the desired optical effect, wherein the optical element (1) has the average operating temperature T X̅ during operation of the optical system, which is controlled by at least one thermal manipulator (2). [16] Optical system for a semiconductor technology plant comprising: - at least one optical element (1) according to claim 15, and - at least one thermal manipulator (2) which determines the average operating temperature T X̅ of the optical element (1). [17] Optical system according to claim 16, characterized by that by providing a predetermined state in which the average operating temperature T X̅ of the optical element (1) and the average operating temperature T X̅ at least one further optical element differ from one another by at least 1 K, compared to a state in which the optical element (1) and the at least one further optical element have at least substantially the same temperatures, at least one imaging error is reduced by at least 20%, preferably at least 25%, particularly preferably at least 30%.

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