METHOD FOR PRODUCING A BASE BODY OF AN OPTICAL ELEMENT FOR SEMICONDUCTOR LITHOGRAPHY AND BASE BODY FOR AN OPTICAL ELEMENT

Description

[0001] The present application claims the priorities of the following German patent applications: DE 10 2022 208 286.9, filed on August 9, 2022; DE 10 2022 116 694.5, filed on July 5, 2022; DE 10 2022 116 695.3, filed on July 5, 2022

[0002] The invention relates to a method for manufacturing a base body for an optical element for semiconductor lithography, usable for projection exposure systems, and a base body.

[0003] Projection exposure systems for semiconductor lithography exhibit a strong temperature-dependent behavior with regard to their image quality. Both elements not directly involved in the optical imaging, such as mounts and holders or housing parts, and optical elements themselves, such as lenses or, in the case of EUV lithography, mirrors, change their expansion or surface shape when heated or cooled. This directly affects the quality of the system's imaging of a lithography mask, for example, a phase mask or reticulum, onto a semiconductor substrate, a so-called wafer.

[0004] The heating of the individual components of the system during operation results from the absorption of a portion of the radiation used to image the reticulum onto the wafer, also known as useful radiation. This radiation is generated by a light source referred to below as the useful light source. In the case of EUV lithography, the useful light source is a relatively complex plasma source in which a plasma emitting electromagnetic radiation in the desired short-wave frequency ranges is generated by laser irradiation of tin particles.

[0005] Projection exposure systems are typically designed for a steady state during operation, meaning a state in which no significant temperature changes of system components are expected over time. This temperature can vary for different optical elements, depending on their arrangement within the optical system. To minimize the deformation and temporal changes of the optical elements, particularly mirrors, as described above, a material with a low coefficient of thermal expansion is used for the base material, especially mirrors. For example, by adding titanium oxide, the coefficient of thermal expansion of fused silica can be adjusted so that it is zero at a specific temperature, the so-called zero-crossing temperature.The coefficient of thermal expansion itself depends on the temperature, increasing with rising temperature, i.e., it is negative at temperatures below the zero crossing temperature and positive at temperatures above the zero crossing temperature.

[0006] The base bodies for the individual mirrors are generally adjusted so that the zero-crossing temperature corresponds to the constant operating temperature. Furthermore, every effort is made to keep the slope of the coefficient of thermal expansion as shallow as possible in order to minimize the impact of deviations from the zero-crossing temperature on the surface shape of the mirrors.

[0007] Furthermore, the increasing power of useful light sources from generation to generation necessitates the temperature control of at least some mirrors via fluid channels integrated into the base body. Prior art methods for manufacturing base bodies with integrated fluid channels are known, but these have the disadvantage of being unsuitable for materials with a predetermined zero-crossing temperature and a low coefficient of thermal expansion, or they are very complex to implement.

[0008] US2020039868 A1 discloses a method for manufacturing an optical element from a material mixture containing quartz glass powder and an organic binder. The material mixture is cured, reshaped as required by mechanical processing, and then fired and sintered. The element can be shaped by 3D printing.

[0009] US2010234205 A1 teaches a TiO2-containing quartz glass with low thermal expansion. US2012107589 A1, WO2022053632 A1 and WO2022200627 A1 disclose the production of quartz glass by the thermal decomposition of a mixture of SiO2-glass nanoparticles and an organic polymer.

[0010] The object of the present invention is to provide a method which eliminates the disadvantages known from the prior art. A further object of the invention is to provide an improved basic structure.

[0011] This problem is solved by the method in claim 1 and by the base body according to claim 12. The dependent claims relate to advantageous further developments and variants of the invention.

[0012] A method for manufacturing a base body of an optical element for semiconductor lithography, not according to the invention, comprises the following steps First, the production of a material mixture comprising at least two material components. Second, the production of an intermediate body from the material mixture, wherein the material mixture comprises at least one first material component from the material of the subsequent base body and wherein the material mixture comprises a second material component which serves to mechanically stabilize the intermediate body. Third, the production of the base body from the intermediate body by temporary heating and at least partial removal of the second material component.

[0013] In one embodiment of the method, the at least one first material component can comprise a quartz glass powder, in particular a quartz glass powder doped with titanium oxide; the second material component can comprise at least one polymer. The first material component can also comprise several different

[0014] The titanium oxide reduces the coefficient of thermal expansion of the primary material and thus of the material mixture, which ideally can be zero at the operating temperature of the optical element, i.e., the average temperature that develops during operation. The temperature at which the temperature-dependent coefficient of thermal expansion is zero is also known as the zero-crossing temperature. Various measures can be used to influence the zero-crossing temperature and the slope of the coefficient of thermal expansion with changing temperature. The magnitude of the coefficient of thermal expansion depends largely on the percentage of titanium oxide in the predominantly silicon oxide-based material. As the titanium oxide content increases, the coefficient of thermal expansion of the material mixture, i.e., the base material, decreases; that is, the curve of the coefficient of thermal expansion versus temperature shifts downwards along the y-axis.This simultaneously shifts the zero-crossing temperature of the material mixture to a higher temperature. Annealing the base material at a temperature between 900 °C and 1200 °C can, on the one hand, shift the curve of the coefficient of thermal expansion in the positive y-direction, i.e., upwards, thereby lowering the zero-crossing temperature, and on the other hand, can advantageously reduce the slope of the curve, so that the change in the coefficient of thermal expansion around the zero-crossing temperature is reduced with temperature changes.

[0015] The powder can be produced by grinding a starting material with the predetermined physical properties of the base body, or it can be designed in such a way that, according to the manufacturing process according to the invention, it corresponds to the predetermined physical properties of the base body.

[0016] Furthermore, a tool for grinding the starting material can be made from the material of the first material component. This has the advantage that the first material component cannot be contaminated by other substances through tool abrasion, which could affect the physical properties of the base material.

[0017] Alternatively, the starting material can be pulverized without contact, for example using an ultrasound process.

[0018] The powder can be produced using a soot process.

[0019] Furthermore, the titanium oxide content in the ground or non-contact powder can deviate by less than 5%, preferably less than 0.5%, and particularly preferably less than 0.05% from the average titanium oxide content of the base material in a 1g sample. This can be achieved, for example, compared to conventional direct or soot deposition, by thorough mixing of the powder and / or by mixing different powder batches. This has the advantage that smaller fluctuations in the titanium oxide content across the final base material can be achieved than with previous manufacturing processes. This leads to a beneficially smaller variation in the coefficient of thermal expansion across the base material.

[0020] The smaller the deviation, the lower the local inhomogeneities in the coefficient of thermal expansion, which depends, among other things, on the titanium oxide content. This coefficient is further influenced by a tempering process carried out during or after the temporary heating of the base material, and locally by a titanium oxide content that varies with the grain size and the homogeneity of the grain sizes in the material mixture. Therefore, to achieve the predetermined coefficient of thermal expansion, a slight inhomogeneity in the titanium oxide content of the powder can be introduced in a first step, and the coefficient of thermal expansion can then be finalized in a subsequent tempering process.

[0021] The Soot process can be carried out under oxygen-deficient conditions to improve the subsequent tempering process, resulting in an increased number of oxygen defects in the silicon dioxide (Si₂O) produced in the process. The resulting increase in silicon-silicon bonds (Si-Si) introduces an additional potential bond angle, which allows for better stress relief at high temperatures and thus improves temperability.

[0022] In particular, the Soot process allows for the addition of at least one further substance to modify the physical properties of the first material component, which forms a covalent bond. Sodium (Na) is especially suitable for this purpose. Alternatively, to increase the temperability of the base material, it can be doped with fluorine by treatment with a fluorine-containing gas or liquid.

[0023] In addition to the chemical composition, the particle size of the powder can be adjusted; in particular, it can be within a range of 100 nm to 500 µm. The particle size variation can be defined, for example, by ensuring that 90% of the particles are at least half the size of the mean and at most twice the size of the mean within the predetermined range.

[0024] Furthermore, the powder can be dried to reduce the OH content to less than 100 ppm, preferably less than 30 ppm, and particularly preferably less than 10 ppm. A low OH content minimizes the risk of locally varying coefficients of thermal expansion within the base material, which are caused by OH diffusion during a subsequent sintering process. In this case, the temperability deteriorates, which, as explained above, also makes it more difficult to raise the curve of the coefficient of thermal expansion.

[0025] In this case, the deviation in the magnitude of the coefficient of thermal expansion, or the position of the curve of the coefficient of thermal expansion over temperature, can be compensated for in advance by reducing the titanium oxide content by 0.1% to 0.5%.

[0026] This method has the advantage that the zero-crossing temperature can be predicted very well via the titanium oxide content, and therefore time-consuming tempering procedures for adjustment can at least be minimized.

[0027] Alternatively, the powder can be moistened to increase the OH content to a weight-based OH content of 700–1200 ppm. This, in turn, can further improve the temperability of the base material produced by the manufacturing process described above.

[0028] Therefore, when choosing the OH content of the powder for the first material component, an optimum must be found between adjusting the slope of the coefficient of thermal expansion over temperature and the zero-crossing temperature, i.e., the absolute coefficient of thermal expansion, during annealing, and the homogeneity of the coefficient of thermal expansion in the base material.

[0029] In this process, tempering required to adjust the coefficient of thermal expansion, its slope and the zero-crossing temperature can be carried out after or during the temporary heating of the intermediate body in the third process step for the production of the base body.

[0030] In particular, tempering can be carried out with cooling rates from 0.2 K / h to 20 K / h.

[0031] The coefficient of thermal expansion of the base material is adjusted by the manufacturing process according to the invention such that each mirror has a coefficient of thermal expansion of zero at a predetermined temperature, the so-called zero-crossing temperature. Furthermore, the slope of the coefficient of thermal expansion with respect to temperature is made as shallow as possible. In addition to those already described, further measures can be applied to influence the zero-crossing temperature and the slope of the coefficient of thermal expansion.

[0032] In the case of a powder produced with oxygen defects, it is conceivable to sinter the base material in oxygen gas, whereby the oxygen causes the oxygen defects to convert into normal matrix bonds in (Si-O-Si). Since this occurs at the sintering temperature, the matrix has limited flowability, which is why the conversion will preferentially take place at locations with increased local stress, thereby bringing about advantageous stress relief in the base material.

[0033] Furthermore, static pressure can be exerted on the intermediate body during temporary heating. In the so-called sintering process, an intermediate body made of powder, previously pre-shaped by pressure or by the method described above, is heated to a temperature close to the melting point of the material, so that the individual grains of powder can be fused together to form a body that is at least almost pore-free.

[0034] In another process that utilizes static pressure, known as hot isostatic pressing, a powder or solid, as well as pre-formed intermediate bodies, is fused into a pore-free base body under a combination of static pressure, such as in a pressure vessel, and simultaneous heating. To ensure that the static pressure acts only externally on the powder or the future base body, a powder can be placed in a deformable, gas-tight container. If an intermediate body is already present, it can be placed directly into the pressure vessel, provided the intermediate body has a gas-tight outer layer. It is also possible to close residual bubbles in an otherwise completely sintered body.

[0035] Furthermore, at least one functional surface, such as an optical surface of an optical element, can be post-processed from the hardened material mixture of the base body using an abrasive process. The intermediate body can be manufactured at least partially using a 3D printing process.

[0036] In particular, the titanium oxide concentration can vary across the volume of the intermediate body part produced using a 3D printing process. This variation in titanium oxide concentration can be achieved by using material mixtures with different titanium oxide concentrations. Depending on the process, the titanium oxide concentration of the material mixture can be adjusted per layer, within a layer, or, as in the case of the Polyjet process described in more detail below, for each application of a further material mixture, for example, in droplet form. The material mixtures are changed per layer or per partial application within a layer, or continuously mixed, thereby allowing a predetermined titanium oxide concentration to be set.

[0037] Furthermore, the intermediate body can be manufactured using a mold, in particular by 3D printing into a mold. The mold can already contain the approximate surface shape of an optical surface of the optical element to be created. In this case, a gas-impermeable layer can form in the material of the base body at the interface with the mold during sintering, which is advantageous for a subsequent process step, such as hot isostatic pressing.

[0038] A base body of an optical element according to the invention, for example a multilayer mirror, can in particular be produced according to one of the embodiments of the method described above.

[0039] This material can be characterized by having an OH content of less than 100 ppm by weight, preferably less than 30 ppm, and particularly preferably less than 10 ppm. This results, due to the process, in a slope of the coefficient of thermal expansion of the base material in the range of 1.5 ppb / K2 to 2.3 ppb / K2 at 20°C.

[0040] Furthermore, the titanium oxide content of the base material can be at least 5%–15%, and in particular 6.7%–8.5%, by weight. As mentioned above, especially with a dry powder mixture, the zero-crossing temperature can be achieved by reducing the titanium oxide content.

[0041] The base body can be constructed layer by layer, and the geometry of at least the outer layers can be adapted, at least in certain areas, to the geometry of the base body's surface. In a projection exposure system for semiconductor lithography, which includes an optical element according to the invention, the base body of the optical element can be constructed layer by layer. Inhomogeneities in material properties, such as the coefficient of thermal expansion, can be present within the base body. These inhomogeneities can be caused by the distribution of material components in the material mixture and / or the manufacturing process.In cases where inhomogeneities in a plane parallel to the optical surface exhibit a preferred direction, such as effects caused by a 3D printing process, it is advantageous to arrange the optical element in the projection exposure system such that the direction of the greatest inhomogeneities is essentially perpendicular to a scan direction of the projection exposure system. This has the advantage that the imaging errors caused by the inhomogeneities can advantageously be at least partially averaged out during the scanning process.

[0042] The process enables the simple production of complex geometries while simultaneously adjusting the coefficient of thermal expansion and the zero-crossing temperature, although various process parameters exist, some of which have opposing effects. The combination possibilities and areas described above are not exhaustive.

[0043] The method for manufacturing a base body for an optical element by means of an additive process according to claim 1 comprises the following process steps: Providing a first material mixture comprising a first support material and a first structural material; providing a second material mixture comprising a second support material and a second structural material, wherein the support materials comprise at least one monomer and / or at least one oligomer and wherein the structural materials differ in their composition; forming an intermediate body by combining the material mixtures and polymerizing the support materials; completing at least part of the base body by heating the intermediate body to thermally bond the structural materials and remove the support materials.

[0044] In this context, a carrier material is understood to be a material that serves to temporarily hold the structural material and create an initial mechanically stable structure for further processing. In contrast, the structural material is the material that remains within the base body after its completion, or even forms it. The aforementioned initial mechanically stable structure is achieved through the polymerization of the monomers or oligomers of the carrier material. By producing the intermediate body through the combination of material mixtures, it is possible to achieve specific desired properties of the intermediate body, and thus of the subsequent base body, in certain areas. The heating of the intermediate body to create the base body does not necessarily have to occur in a single step.It is quite conceivable to first heat the intermediate body to such an extent that the polymers formed are removed by combustion and, in the same step, a first, still only partial, bond between the individual particles of the structural material is created.

[0045] A solid base body can then be produced in a subsequent sintering step. It goes without saying that, to manufacture a later optical element, the base body thus created can be further supplemented with additional sub-bodies, which were produced using a process different from the one described, in particular a conventional process.

[0046] The formation of an intermediate body can be achieved using a Polyjet printing process.

[0047] The PolyJet process allows material mixtures to be blended at any point within the intermediate structure in any desired ratio. This process is comparable to that used in inkjet printers, where adjusting the mixing ratio of the three primary colors (red, yellow, blue) and black enables the printing of all colors. In this process, a liquid carrier material containing suspended particles in the form of small droplets is applied and immediately cured by ultraviolet irradiation. Furthermore, the polymerization of the carrier material allows for the simple fabrication of even complex intermediate structures.

[0048] To create a basic structure for an optical element, it is advantageous if at least one of the structural materials contains a glass powder. This glass powder can, for example, contain quartz glass and, in particular, glasses known under the trade names ULE or Zerodur.

[0049] Furthermore, at least one of the structural materials may contain an additive.

[0050] For example, a first structural material might contain only one of the aforementioned glasses in powder form, while the second structural material, in an extreme case, might consist solely of a suitable additive. It is also conceivable that the two structural materials differ in the type of additives they contain.

[0051] Similarly, the structural materials can differ in terms of the concentration of additives.

[0052] The additives may include, in particular, the following substances or compounds: titanium, titanium oxide, lithium, aluminum, OH compounds.

[0053] The aforementioned additives are particularly suitable for setting a zero-crossing temperature for the coefficient of thermal expansion of the material of the resulting base body. Titanium, for example, makes it possible to adjust the coefficient of thermal expansion so that it can be zero or close to zero, at least for a predetermined temperature range. Other additives can, for example, protect the material from embrittlement caused by electromagnetic radiation.

[0054] In this way, it becomes possible to adjust the material distribution during the production of the intermediate body in such a way that the concentration of the additives via the base body corresponds to a temperature distribution formed in the base body when the optical element is used.

[0055] In other words, the zero-crossing temperature can be adjusted in certain areas so that, for the temperature distribution expected during operation of the associated projection exposure system, the respective zero-crossing temperature prevails as much as possible throughout the base body. This ensures that, despite temperature changes around the zero-crossing temperature, only minor deformations occur over large portions of the base body's volume. The optical surface can also be designed to correspond to its target surface under the same temperature distribution.

[0056] Besides focusing on a typical temperature distribution when setting the coefficient of thermal expansion across the base body, this can also be varied in such a way that for a number X of possible temperature distributions, a minimal maximum deviation of the optical surface from its target surface is achieved. In this case, the spatial distribution of the additives in the base body would not be optimized for a specific temperature distribution at a single point, but rather a thermal expansion behavior of the base body that, while not perfect, would be tolerable across the aforementioned temperature distributions.

[0057] In an advantageous embodiment of the invention, the concentration of the additives can decrease with increasing distance from a side of the base body intended for an optical effective surface.

[0058] The concentration gradient can, for example, be based on the heat flux determined for the material, thus reducing deformations independently of a specific temperature distribution.

[0059] Furthermore, the concentration of the additives can decrease constantly with increasing distance from a side of the base body intended for an optical effective surface up to a cooled layer in the base body.

[0060] This is the case, for example, with a titanium-containing additive in cooled optical elements, which include fluid lines for temperature control of the base body at a certain distance from the optical surface. The temperature control can be regulated, for instance, such that, regardless of the heat absorbed by the optical surface, the temperature of the base body below the fluid lines—that is, on the side of the fluid lines facing away from the optical surface—can be kept constant. The heat transfer coefficient for this area would then be constant, unlike the area between the optical surface and the fluid lines.

[0061] It is also advantageous if the concentration of the additives in a predetermined sub-area of ​​the base body is adjusted in such a way that the coefficient of thermal expansion in that sub-area is greater than in the remaining volume of the base body.

[0062] This is the case when the lower part of the base body, facing away from the optical surface, is to be deliberately thermally deformed. This predetermined and controlled deformation propagates through the base body to the optical surface, while simultaneous heating of the optical surface by absorption of electromagnetic radiation does not cause any parasitic deformations on the optical surface.

[0063] The method according to the invention can be used in particular for the production of an optical element for a projection exposure system for semiconductor lithography.

[0064] A base body according to the invention for an optical element according to claim 12 is produced at least partially by means of an additive process, wherein the zero-crossing temperature of the coefficient of thermal expansion changes continuously at least in a partial region of the base body.

[0065] In other words, the change in the zero-crossing temperature is chosen such that no abrupt changes occur in the specified sub-region of the base body. This ensures that while the corresponding sub-region of the base body may have locally different coefficients of thermal expansion, no sharp interfaces exist between areas with differing coefficients. Consequently, although the base body reacts differently to temperature changes, no stress peaks occur at interfaces between areas with differing coefficients of thermal expansion.

[0066] In particular, the change in the zero-crossing temperature can be more than 1 K / mm in a range from 20° Celsius to 65° Celsius.

[0067] In an advantageous embodiment of the invention, the zero-crossing temperature, which varies at least partially over the base body, can correspond to a temperature distribution formed in the base body when the optical element is used.

[0068] The described measure ensures that, given the aforementioned temperature distribution, the base body exhibits a temperature throughout its entire surface close to its zero-crossing temperature. This minimizes thermally induced length changes across the base body, as mentioned above. The variation in the zero-crossing temperature across the base body material can be specifically adapted to previously known intensity distributions of electromagnetic radiation affecting the optical element, thus enabling adjustments to previously known settings. Similarly, corresponding adjustments can be made in the areas of the base body adjacent to the optical surface.

[0069] However, adjusting the coefficient of thermal expansion can be used not only to minimize thermally induced changes in length within the base material. It is also conceivable to deliberately create areas within the base material where the coefficient of thermal expansion is higher than in the surrounding area.

[0070] In this case, it is possible to deliberately induce deformations on the effective surface of the optical element by heating or cooling the corresponding area.

[0071] A projection exposure system for semiconductor lithography, comprising optical elements designed as described with regard to the base bodies used, is characterized by increased robustness against thermal influences.

[0072] Another basic body for an optical element, comprising at least one actuator and / or sensor, is characterized by the fact that at least one actuator component and / or one sensor component is integrated into at least one additively manufactured substructure of the basic body. This has the advantage that the actuator component and / or sensor component can be positioned closer to an optical surface or other functional elements, such as fluid channels, of the basic body. This can enable immediate detection of a deformation of the optical surface, thereby advantageously improving the accuracy and, in the case of a thermal sensor, also the response time to a change in temperature on the optical surface.

[0073] In particular, the actuator component and / or the sensor component can be an electrically conductive element. The electrically conductive element can, for example, be a wire, especially a heating wire, or comprise electrically conductive particles. The wire can, for example, be inserted at a predetermined location during the 3D printing process of the base body. In a 3D printing process described below, the particles can be directly integrated into one of the material mixtures used for printing and printed at predetermined positions in the base body. In a further embodiment of the invention, the actuator component and / or the sensor component can comprise electrically conductive components. Electrically conductive components include, in particular, plates or short wires or...These are conductor sections that are integrated into the base material without any further contact. They differ from the particles mentioned above primarily in that they generally cannot be printed directly along with the particles because they are considerably larger. Nevertheless, it is of course possible to integrate these components into the base material between the application of two layers in an additive manufacturing process. For example, a 3D print could be briefly interrupted, the component inserted, and then the print resumed.

[0074] When components are used as actuators, an electric current can be generated in the electrically conductive elements, causing them to heat up due to their ohmic resistance. This also heats the surrounding material of the base body, which then deforms, particularly by expanding, thus achieving the desired deformation at the desired location within the base body. For example, in the case of heating wires, the wires can be directly connected galvanically to a voltage source to generate the required current. If particles or components without galvanic contact with a voltage source are used, the necessary electric current can be generated by induction.Induction coils can also be integrated into the base body, which generate an alternating magnetic field when an alternating voltage is applied and thus cause eddy currents in the particles or components.

[0075] The actuator component and / or the sensor component can include magnetizable elements. These magnetizable elements can be shaped similarly to the particles or components already mentioned; in particular, they can also coincide with them, since magnetizability and electrical conductivity are not mutually exclusive. In the case of magnetizable elements, a desired deformation can be achieved by generating a magnetic field in the region of the magnetizable elements. This can be achieved, for example, by applying a DC voltage to induction coils near the magnetizable elements, so that a time-stable magnetic field forms in the region of the magnetizable elements, causing the elements to experience a magnetic force and resulting in a deformation of the surrounding material. In this case, the induction coils are used in the manner of electromagnets.In principle, it is therefore possible to achieve deformation using the same arrangement of coils and electrically conductive / magnetizable elements, either through thermal expansion or through magnetic force. If the elements are both magnetizable and electrically conductive, and the coils are operated as induction coils, care must be taken to ensure that the frequency of the applied alternating voltage is sufficiently far removed from the mechanical resonant frequencies of the base body to avoid unwanted mechanical vibrations.

[0076] There are various possibilities for operating the aforementioned elements as sensors. For example, the temperature dependence of ohmic resistance when using heating wires can be exploited to determine the current resistance of the heating wires at specific times and derive the ambient temperature from this. It is also conceivable, in principle, to use the integrated particles or components as sensor components, since they too exhibit temperature-dependent behavior, particularly in their electrical properties. For instance, the inductance of an induction coil arranged in the vicinity of the particles or components will depend to a certain extent on the temperature-dependent permeability of the neighboring particles or components and also of the surrounding material.By determining the current inductance of the coils, conclusions can be drawn about the temperature in the area of ​​the coils or also in the area of ​​the particles or components.

[0077] Furthermore, the actuator component and / or the sensor component can be a thermally conductive or heat-generating element. This can be a heat pipe, thermocouple, or even a copper wire. The thermally conductive elements can be connected to a heat source and / or heat sink and used as a thermal actuator. Alternatively, the integrated thermally conductive elements can simply serve as an extension of a temperature sensor.

[0078] A method for producing a base body for an optical element using an additive process not according to the invention comprises the following process steps: Production of at least one subbody configured as a connection geometry of a predetermined structure of the base body using a polyjet process, wherein the material mixture used to produce the base body comprises a carrier material with at least one monomer and / or oligomer and a structural material with a glass powder. Heating of the base body polymerized in the preceding process step to thermally bond the glass powder components and to combust the polymer. Sintering of the base body.

[0079] The process makes it possible to produce almost any geometry, with no transitions between the layers created during the printing of the structure being detectable in the final product.

[0080] Furthermore, two different material mixtures can be used in the production of the base body. This allows the properties in different areas of the base body to be adapted to different requirements, such as a low coefficient of thermal expansion, high elasticity, or high stiffness.

[0081] In particular, a substructure comprising actuator components and / or sensor components, and the base body itself, can be manufactured from two different material mixtures. This allows, for example, the connection geometry, such as the decoupling element with its connecting elements described above, to be manufactured from a first material mixture with high elasticity. The remaining base body can be manufactured from a second material mixture with high stiffness.

[0082] In particular, the base body can comprise a second substructure, which can be manufactured using a conventional manufacturing process. The individual substructures can be joined to each other to form the base body by means of a form-fit or material-fit connection.

[0083] Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing. The drawing shows Figure 1 shows a schematic, meridional section view of a projection exposure system for EUV projection lithography; Figure 2 shows a schematic, meridional section view of a projection exposure system for DUV projection lithography; Figure 3 shows a flowchart for a manufacturing process according to the invention; Figure 4 shows a basic body according to the invention; Figure 5 shows a 3D printing machine (Polyjet) for applying the method according to the invention; Figure 6 shows a schematic detail view of the basic body to explain the method; Figure 7 shows a flowchart for a further manufacturing process according to the invention; Figure 8 shows a further embodiment of the invention; Figure 9 shows a further embodiment of the invention; Figure 10 shows a further embodiment of the invention; and Figure 11 shows a flowchart for an alternative manufacturing process according to the invention.

[0084] The following will first refer to the Figure 1The essential components of a projection exposure system 1 for microlithography are described as an example. The description of the basic structure of the projection exposure system 1 and its components is not intended to be restrictive.

[0085] One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a radiation source 3, a lighting optic 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the lighting system. In this case, the lighting system does not include the light source 3.

[0086] A reticule 7 located in the object field 5 is illuminated. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in one scanning direction, via a reticule displacement drive 9.

[0087] In the Figure 1A Cartesian xyz coordinate system is shown for illustrative purposes. The x-direction runs perpendicular to the plane of the drawing. The y-direction runs horizontally, and the z-direction runs vertically. The scan direction runs in the Fig. 1 along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0088] The projection exposure system 1 comprises a projection optic 10. The projection optic 10 serves to image the object field 5 onto an image field 11 in an image plane 12. The image plane 12 is parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0089] A structure on the reticulum 7 is imaged onto a photosensitive layer of a wafer 13 located in the image plane 12 within the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction, via a wafer transfer drive 15. The movement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0090] Radiation source 3 is an EUV radiation source. Specifically, radiation source 3 emits EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation has a wavelength in the range between 5 nm and 30 nm. Radiation source 3 can be a plasma source, for example, an LPP source (laser-produced plasma) or a DPP source (gas-discharged produced plasma). It can also be a synchrotron-based radiation source. Radiation source 3 can be a free-electron laser (FEL).

[0091] The illumination radiation 16 emanating from the radiation source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 17 can be illuminated with the illumination radiation 16 at grazing incidence (GI), i.e., with angles of incidence greater than 45° relative to the normal direction of the mirror surface, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0092] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the radiation source 3 and the collector 17, and the illumination optics 4.

[0093] The illumination optics 4 comprise a deflecting mirror 19 and, downstream in the beam path, a first faceted mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with an effect that influences the beam shape beyond the mere deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first faceted mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugate to the object plane 6 as the field plane, it is also referred to as a field faceted mirror. The first faceted mirror 20 comprises a plurality of individual first facets 21, which are also referred to as field facets in the following. Of these facets 21, the following are in the Fig. 1 These are just a few examples.

[0094] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or semicircular border contour. The first facets 21 can be designed as planar facets or alternatively as convexly or concavely curved facets.

[0095] As is known, for example, from DE 10 2008 009 600 A1, the first facets 21 can themselves each be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can in particular be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.

[0096] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction.

[0097] In the beam path of the illumination optics 4, a second faceted mirror 22 is arranged downstream of the first faceted mirror 20. If the second faceted mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil faceted mirror. The second faceted mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first faceted mirror 20 and the second faceted mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1, and US 6,573,978.

[0098] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0099] The second facets 23 can also be macroscopic facets, which may, for example, have round, rectangular, or hexagonal edges, or alternatively, facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0100] The second facets 23 can have planar or alternatively convex or concave curved reflective surfaces.

[0101] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (Fly's Eye Integrator).

[0102] It can be advantageous not to arrange the second faceted mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the pupil faceted mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220 586 A1.

[0103] With the aid of the second faceted mirror 22, the individual first facets 21 are imaged into the object field 5. The second faceted mirror 22 is the last beam-shaping, or indeed the last, mirror for the illumination radiation 16 in the beam path before the object field 5.

[0104] In another embodiment of the illumination optics 4, not shown, a transmission optic can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to imaging the first facets 21 into the object field 5. The transmission optic can have exactly one mirror, or alternatively two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optic can in particular comprise one or two mirrors for normal incidence (NI mirrors) and / or one or two mirrors for grazing incidence (GI mirrors).

[0105] The lighting optics 4, in the version shown in the Fig. 1 As shown, after the collector 17 there are exactly three mirrors, namely the deflecting mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

[0106] In a further embodiment of the lighting optics 4, the deflecting mirror 19 can also be omitted, so that the lighting optics 4 after the collector 17 can then have exactly two mirrors, namely the first faceted mirror 20 and the second faceted mirror 22.

[0107] The mapping of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optic into the object plane 6 is regularly only an approximate mapping.

[0108] The projection optics 10 comprise a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0109] In the Figure 1In the illustrated example, the projection optics 10 comprise six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have an aperture for the illumination radiation 16. The projection optics 10 are a double-obscured optic. The projection optics 10 have an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0110] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0111] The projection optics 10 has a large object-image offset in the y-direction between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

[0112] The projection optics 10 can be anamorphic. In particular, they have different magnifications βx, βy in the x and y directions. The two magnifications βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive magnification β indicates a projection without image inversion. A negative magnification β indicates a projection with image inversion.

[0113] The projection optics 10 thus lead to a reduction in the x-direction, that is, in the direction perpendicular to the scan direction, in a ratio of 4:1.

[0114] The projection optics 10 lead to a reduction of 8:1 in the y-direction, that is, in the scan direction.

[0115] Other magnification ratios are also possible. Magnification ratios with the same sign and absolute values ​​in the x and y directions, for example with absolute values ​​of 0.125 or 0.25, are also possible.

[0116] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, different. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303 A1.

[0117] Each pupil facet 23 is assigned to exactly one of the field facets 21 to form an illumination channel for illuminating the object field 5. This can result, in particular, in illumination according to Köhler's principle. The far field is divided into a multitude of object fields 5 by means of the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus on the pupil facets 23 assigned to each of them.

[0118] The field facets 21 are each superimposed on the reticulum 7 by an associated pupil facet 23 to illuminate the object field 5. The illumination of the object field 5 is particularly homogeneous. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0119] The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by the arrangement of the pupil facets. By selecting the illumination channels, in particular the subset of pupil facets that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting.

[0120] Another preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by a redistribution of the illumination channels.

[0121] Further aspects and details of the illumination of the object field 5 and, in particular, the entrance pupil of the projection optics 10 are described below.

[0122] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0123] The entrance pupil of the projection optics 10 cannot always be illuminated exactly by the pupil facet mirror 22. When the projection optics 10 image the center of the pupil facet mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found where the pairwise determined separation of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in real space. In particular, this surface exhibits a finite curvature.

[0124] The projection optics 10 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second faceted mirror 22 and the reticle 7. This optical element can accommodate the different positions of the tangential and sagittal entrance pupils.

[0125] During the Figure 1 In the illustrated arrangement of the components of the illumination optics 4, the pupil facet mirror 22 is arranged in a plane conjugate to the entrance pupil of the projection optics 10. The field facet mirror 20 is arranged tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the deflecting mirror 19.

[0126] The first faceted mirror 20 is arranged at an angle to an arrangement plane defined by the second faceted mirror 22.

[0127] Figure 2 schematically shows in meridional section another projection exposure system 101 for DUV projection lithography, in which the invention can also be used.

[0128] The design of the projection exposure system 101 and the principle of the imaging process are comparable to that in Figure 1 The described structure and procedure apply. Identical components are available with a thickness 100% greater than before. Figure 1 Raised reference numerals denote the reference numerals in Figure 2 So they start with 101.

[0129] Unlike one such as in Figure 1Due to the longer wavelength of the DUV radiation 116 used as useful light in the range of 100 nm to 300 nm, in particular of 193 nm, refractive, diffractive and / or reflective optical elements 117, such as lenses, mirrors, prisms, end plates and the like, can be used in the DUV projection exposure system 101 for imaging or illumination. The projection exposure system 101 essentially comprises a lighting system 102, a reticule holder 108 for receiving and precisely positioning a reticule 107 provided with a structure, by which the subsequent structures on a wafer 113 are determined, a wafer holder 114 for holding, moving and precisely positioning this wafer 113 and a projection lens 110, with several optical elements 117, which are held in a lens housing 119 of the projection lens 110 via mounts 118.

[0130] The illumination system 102 provides DUV radiation 116 required for imaging the reticulum 107 on the wafer 113. A laser, a plasma source, or the like can be used as the source for this radiation 116. In the illumination system 102, the radiation 116 is shaped by optical elements such that, upon striking the reticulum 107, the DUV radiation 116 exhibits the desired properties with respect to diameter, polarization, wavefront shape, and the like.

[0131] The construction of the following projection optics 101 with the lens housing 119 differs in principle from that in, except for the additional use of refractive optical elements 117 such as lenses, prisms, end plates. Figure 1 The structure described above will therefore not be described further.

[0132] Figure 3Figure 1 shows a flowchart of a possible manufacturing process for a base body of an optical element for semiconductor lithography, which can be used, for example, in one of the two systems described in the preceding figures.

[0133] In a first process step 31, a material mixture comprising at least two material components is produced.

[0134] In a second process step 32, an intermediate body is produced from the material mixture, wherein the material mixture comprises at least a first material component from the material of the later base body and wherein the material mixture comprises a second material component which serves to mechanically stabilize the intermediate body.

[0135] In a third process step 33, the base body is produced from the intermediate body by temporary heating and at least partial removal of the second material component.

[0136] The first material component, comprising a quartz glass, in particular a quartz glass doped with titanium oxide, is added to the material mixture as a powder. This powder is produced by grinding a starting material, such that the physical properties of the powder correspond to those of the subsequent base body, or are designed such that the predetermined physical properties of the base body are created according to the manufacturing process according to the invention.

[0137] The tools used for grinding the starting material are advantageously made from the same material as a material of the first material component, or from materials used in the first material component, thus preventing contamination of the first material component by tool abrasion. Furthermore, a non-contact method, such as an ultrasonic process, is also applicable for pulverizing the starting material.

[0138] Alternatively, the first material component can be produced using a so-called SOOT process, in which sand is first reduced with carbon and the resulting silicon is then reacted with chlorine to form silicon tetrachloride. Subsequently, a homogeneous mixture of vaporous silicon tetrachloride, hydrogen, oxygen, and an inert gas is combusted in a high-temperature pyrolysis process using a burner in a cooled combustion chamber. The flame initially produces droplet-like silicon dioxide particles, which then link together in chains, forming three-dimensional secondary particles through branching. These secondary particles, in turn, aggregate to form tertiary particles, which precipitate as a powder in the chamber.

[0139] The burner flame used in the Soot process can be deliberately generated with oxygen deficiency, resulting in an increased number of oxygen defects in the silicon dioxide (Si₂O) produced in the process. The resulting increase in silicon-silicon bonds (Si-Si) introduces an additional possible bond angle, which allows for better stress relief at high temperatures and thus improved temperature control. This simplifies the adjustment of the physical properties of the base body with respect to the coefficient of thermal expansion and the zero-crossing temperature described above. The coefficient of thermal expansion of the base body material is adjusted by the manufacturing process according to the invention such that each mirror has a coefficient of thermal expansion of zero at a predetermined temperature, the so-called zero-crossing temperature.

[0140] Furthermore, the slope of the coefficient of thermal expansion with respect to temperature is designed to be as flat as possible. Various measures can be applied to influence the zero-crossing temperature and the slope of the coefficient of thermal expansion. The magnitude of the coefficient of thermal expansion largely depends on the percentage of titanium oxide in the predominantly silicon oxide-based material. As the titanium oxide content increases, the coefficient of thermal expansion of the material mixture, i.e., the base material, decreases, thus shifting the curve of the coefficient of thermal expansion with respect to temperature in the negative y-direction. This simultaneously shifts the zero-crossing temperature of the material mixture to a higher temperature.Tempering the base body at a temperature between 900 °C and 1200 °C shifts the curve of the coefficient of thermal expansion in a positive y-direction, i.e. upwards, thereby lowering the zero-crossing temperature, and advantageously reduces the slope of the curve.

[0141] Furthermore, it is conceivable to sinter the matrix in oxygen gas, whereby the oxygen causes the oxygen defects to convert into normal matrix bonds in (Si-O-Si). Since this occurs at the sintering temperature, the matrix has limited flowability, so that a conversion will preferentially take place at locations with increased local stress, thereby causing a relaxation in the matrix.

[0142] In addition, it is conceivable to add metals that form a covalent bond during the Soot process. Sodium (Na) is particularly suitable for this purpose. Alternatively, the powder can be doped with a fluorine-containing gas or liquid to increase the temperability of the base material.

[0143] Alternatively, the flame can be operated with excess oxygen, which leads to the formation of peroxide centers, i.e., regions with a Si-O=O-Si bond. These can be reduced by sintering in a reducing atmosphere, such as a hydrogen atmosphere, resulting in the formation of normal matrix bonds and water vapor, which can escape before the sintering process is complete, especially if sintering is carried out under reduced pressure or at least at very low water vapor pressure. Besides a hydrogen atmosphere, sintering can also be performed in a vacuum or in a carbon monoxide (CO) or ammonia (NH3) atmosphere.

[0144] In particular, the powder produced by the Soot process, which has a weight-based OH content of 150 - 300 ppm, can be brought to an OH content of 700 - 1200 ppm by moistening, which in turn improves the temperability of the base material produced by the manufacturing process described above.

[0145] Alternatively, the powder can be dried to an OH content of less than 100 ppm, preferably less than 30 ppm, and particularly preferably less than 10 ppm. A low OH content minimizes the risk of varying coefficients of thermal expansion within the base material, which are caused by OH diffusion during a subsequent sintering process. In this case, the temperability deteriorates, which, as explained above, also makes it more difficult to achieve a favorable thermal expansion curve. The deviation in the coefficient of thermal expansion can be compensated for in advance by reducing the titanium oxide content by 0.1% to 0.5% compared to conventionally manufactured materials.This method has the advantage that the zero-crossing temperature is very predictable via the titanium oxide content, thus minimizing time-consuming tempering processes for setting the zero-crossing temperature. Therefore, when selecting the OH content of the powder for the first material component, an optimum must be found between adjusting the slope of the coefficient of thermal expansion with temperature and the zero-crossing temperature (i.e., the absolute coefficient of thermal expansion) during tempering, and ensuring homogeneity of the coefficient of thermal expansion in the base material.

[0146] In the embodiment described here, the intermediate body can be produced from the material mixture using a so-called Polyjet process, which is comparable to an inkjet printing process. The intermediate body is built up layer by layer, with the minimum resolution depending on the layer thickness produced by the printer. The layer thickness is determined on the one hand by the particle size of the material components and, in the case of the Polyjet process, on the other hand by the dosage of the liquid material mixture.

[0147] The titanium oxide concentration of the material mixture used can be readjusted with each print job by using at least two printheads, thus advantageously allowing the titanium oxide concentration to be precisely controlled across the volume of the optical element. This enables different zero-crossing temperatures to be set in various areas of the substrate, which can be derived from the temperature distributions occurring in the substrate during operation.

[0148] In particular, the almost arbitrary design of the body in the Polyjet process allows the last layers of the intermediate body to be designed in such a way that they are parallel to the later optical effective surface.

[0149] Alternatively, the intermediate body can also be produced layer by layer by laser sintering in a powder bed or a stereolithography process, to name just a few possibilities.

[0150] In each of these processes, and also in other possible manufacturing processes such as injection molding, conventional casting, or stamping, a material mixture is used. The first material component, which later forms the base body, is identical, apart from process-specific requirements such as the moisture content and / or titanium oxide concentration described above. The second material component, which significantly determines the physical properties necessary for the process, such as liquid or solid state, and the melting point of the material mixture (important for injection molding), differs considerably.

[0151] As a further variation, 3D printing can also be performed directly into a mold shaped like a shell. This allows, for example, the shape of the base body's surface, on which the optical surface is subsequently formed, to be predefined. Printing in or onto a shell has the advantage that a gas-tight layer forms at the interface with the shell during sintering, which is necessary for the subsequent hot isostatic pressing.

[0152] In the case that the layering process in a 3D printing process also occurs parallel to the future optical surface, a horizontal layering pattern, rasterized within the vertical layers, can form parallel to the mirror surface. This results in inhomogeneities in the coefficient of thermal expansion both along and perpendicular to the printing direction. The direction with the greater inhomogeneities, which can be determined, for example, by measurements, is perpendicular to the direction in the Figure 1 and the Figure 2 The scan direction of the projection exposure systems is explained, so that the effect on the image quality is averaged out by the scanning.

[0153] The intermediate body is sintered, causing the second material component, which in the described embodiment is a polymer, to burn away and the individual grains of the powder from the first material component to bond together to form the base body. Alternatively, the burning of the second material component and the bonding of the powder grains to form the base body can also be carried out in two separate process steps. In a first step, the second material component is burned (pyrolysis), during which the powder grains already bond at certain points. In a second step, the base body is sintered, producing a pore-free base body from the already bonded grains.Furthermore, the removal of a first part of the polymer, such as polyethylene glycol, from the intermediate can be achieved by immersion in an aqueous solution, and the remaining part, such as polyvinyl butyral, by subsequent combustion (pyrolysis). This two-stage process for removing the different materials of the second component has the advantage that, after the polyethylene glycol is released, an open-pore structure is created. This reduces the amount of material to be removed by pyrolysis, allowing it to be extracted from deeper layers, which in turn allows for a greater wall thickness of the base material.

[0154] Any residual porosity remaining after sintering can be closed by hot isostatic pressing (HIP), provided that the surface of the base body is gas-tight. This can be achieved by flowing a hot gas, preferably an inert gas, over the surfaces.

[0155] Alternatively, the intermediate body can be immersed in a suitable aqueous solution that penetrates only a few micrometers to 1 mm deep and then dries or reacts, forming a gas-tight surface layer that is stable at the temperature used in hot isostatic pressing. Instead of the solution, a melt of a mixed glass, such as sodium silicate glass, can also be used, which can likewise form a gas-tight surface layer. It is also conceivable to apply a gas-tight surface layer to the intermediate body after the second material component has been combusted using the methods described above, thus eliminating the need for sintering the intermediate body. This has the advantage that the bonding of the powder of the first material component into a pore-free glass body is achieved at lower temperatures due to the higher pressure used in hot isostatic pressing.This advantageously minimizes the risk of displacement and / or deformation of fluid channels integrated into the intermediate body, which may have inner diameters of only a few µm, due to the pressure acting in the fluid channels during the bonding of the powder.

[0156] The tempering process for adjusting the slope of the heat transfer coefficient and the zero-crossing temperature, as explained above, can also be carried out during hot isostatic pressing using predetermined cooling rates, which can range from 0.2 K / h to 20 K / h. A further advantage of hot isostatic pressing is that the further the temperature used is from the melting temperature of the base material, the more dimensionally stable the material becomes, thus preserving the geometry and position of structures incorporated into the base, such as fluid channels.

[0157] The shrinkage of the base body relative to the intermediate body that occurs during sintering and / or hot isostatic pressing due to the bonding of the grains and the release of the second material component, and which ranges from 5% to 20%, particularly 5% to 10%, depending on the percentage of the first material component in the material mixture, can be accounted for. It is also possible to compensate for nonlinear shrinkage caused by inhomogeneities in the material mixture or by the process itself through experiments based on the specific geometries of the base body.

[0158] Figure 4Figure 1 shows an optical element according to the invention, designed as a mirror Mx, 117, with a base body 130 having three connections 132.1, 132.2, 132.3 and an optical area 134 comprising the optical surface 131. The base body 130 further comprises material zones 133.1-133.9, which were obtained at least partially according to the manufacturing process described below. These zones differ in the composition of a structural material used in their manufacture. Structural materials with different compositions can be mixed using the manufacturing process described below, thus enabling the production of any desired distribution of titanium oxide in the base body 130. The titanium oxide concentration in the base body determines the zero-crossing temperature, i.e., the temperature at which the coefficient of thermal expansion of the corresponding area of ​​the base body is zero.The inventive method allows the zero-crossing temperature across the base body 130 to be adapted to the prevailing temperature distribution during operation of the associated projection exposure system. This has the advantage that the base body 130 can be operated at a coefficient of thermal expansion of zero even in the presence of temperature gradients across it, so that deviations from the target temperature cause no or virtually no deformation on an optical surface 131 formed on the base body 130. A temperature fluctuation of the base body 130 therefore no longer has any effect on the image quality of the projection system. Figure 1 and the Figure 2 explained projection exposure system 1, 101.

[0159] Figure 5Figure 40 shows a 3D printer 40 used in the inventive method for producing the optical element. This printer comprises a print bed 41 on which the structure of the optical element is printed. The print bed 41 is connected to a guide 46 in the z-direction, so that the distance between the print bed 41 and a print head 42 of the 3D printer 40 can be adjusted. The range of movement of the print bed 41 along the z-axis corresponds to the maximum thickness of the optical element that can be achieved by printing. The print head 42 comprises, in the Figure 4In the illustrated embodiment, two nozzle arrays (not shown) print two different material mixtures. The two nozzle arrays can be controlled such that the two material mixtures can be mixed in any desired ratio at any time, allowing the material transitions in the structure to be either gradual or abrupt. The setup and method are comparable to an inkjet printer. The number of nozzle arrays can be expanded almost indefinitely, enabling the use of even more material mixtures. The material mixtures 43, 44 used for printing comprise a support material and a structural material and are liquid and therefore printable. The structural material is a powder made from glass or other sinterable materials, typically with a particle size of 50 µm to 150 µm. The substances used to create the powder determine the material mixture.The support material comprises a monomer and / or oligomer and a photoinitiator, which typically include onium compounds such as aryldiazonium, diaryliodonium, or triarylsulfonium, although other photoinitiators can also be used. As mentioned previously, the mixture of the support material and the structural material forms a printable liquid. The printhead 42 can be moved in the xy-plane, so that almost the entire print bed 41 can be used to print the optical element. In the printhead 42, a UV light 45, arranged in the form of a curtain, is positioned behind the nozzle arrays in the direction of movement. In the example shown, this UV light has the same width as the nozzle arrays. The material mixtures 43, 44 are polymerized by the UV light 45 immediately after application, thus building up the structure layer by layer.The photoinitiator typically triggers a cationic polymerization by absorbing light, thereby advantageously supporting and accelerating the polymerization process, and is usually destroyed in the process.

[0160] Figure 6 Figure 49 shows a schematic representation of a structure 49 printed from the material mixtures 43, 44 before and after polymerization by UV light 45. The material mixtures 43, 44 each comprise monomers 50, oligomers 51 and the material 45 in the 43. Figure 4The photoinitiator 52, already described, serves as the support material. This support material contains different glass powders 53 and 54 in the two material mixtures 43 and 44, which differ according to the invention in their titanium concentration. As explained above, the titanium concentration in the structure 49 determines the zero-crossing temperature, i.e., the temperature at which the coefficient of thermal expansion is zero. In the printed structure 49, both glass powders 53 and 54 from the two material mixtures 43 and 44 are present, with the glass powder 53 being distributed throughout the entire structure 49 and the glass powder 54 being present only on the left side of the structure 49. This is intended to illustrate the possibility of any combination of the two material mixtures 43 and 44 during 3D printing. The right side of the Figure 5Figure 45 shows the structure after polymerization of monomers 50 and oligomers 51 by UV light. These monomers are connected to each other by lines to illustrate the cross-linking. The photoinitiators 52 are destroyed by the UV light, and the glass powders 53 and 54 remain in their printed positions. This state is called a green compact, which is a dimensionally stable and solid plastic body filled with glass powder 53 and 54. In the subsequent process for manufacturing the optical element Mx, 117, the green compact is heated to over 600° Celsius. At 600° Celsius, the plastic burns, and the glass powder particles dispersed within it are sintered together, bonding so that the structure retains its shape with minimal shrinkage. This so-called brown compact is then sintered into an optical element in a convection or microwave oven at approximately 1300° Celsius.The shrinkage ranges from 5% to 20%, depending on the percentage of glass powder 53, 54 in the material mixture 43, 44, and is particularly between 7% and 15.6%.

[0161] Figure 7 describes a method for manufacturing a base body 30 for an optical element Mx, 117.

[0162] In a first process step 61, a first material mixture, comprising a first carrier material and a first structural material, is provided.

[0163] In a second process step 62, a second material mixture, comprising a second carrier material and a second structural material, is provided.

[0164] In a third process step 63, an intermediate body is formed by combining the material mixtures and polymerizing the carrier materials.

[0165] In a fourth process step 64, at least a part of the base body is produced by heating the intermediate body to thermally join the structural materials and to remove the support materials.

[0166] Figure 8 shows a basic body 230 for an optical element designed as a mirror Mx, 117, as in one of the in the Figure 1 and the Figure 2In a first embodiment of the invention, the mirror Mx, 117 can be used in the projection exposure systems described above. The mirror comprises the base body 230 with an optical surface 231. Cooling channels 233 are formed in the base body 230 below the optical surface 231, which regulate the temperature of the optical element Mx, 117 during operation, for example, during the operation of an associated projection exposure system. Actuator elements designed as heating wires 234 are arranged in the base body 230 below the cooling channels 233. These actuator elements were integrated into the base body 230 using an additive manufacturing process, such as 3D printing or stereolithography. The heating wires 234 are energized by an electric current via a control mechanism not shown in the figure and act collectively as a resistance actuator 241.Due to the ohmic resistance in the heating wire 234, the base body 230 heats up in certain areas, causing thermal expansion of the heated area. This expansion extends to the optical surface 231, where it deforms. By selectively controlling and regulating the temperature distribution in the area of ​​the base body 230 traversed by the heating wires 234, a predetermined deformation 235 on the optical surface 231 can be set using the resistance actuator 241 to correct imaging aberrations. The cooling channels 233 act as heat sinks during temperature control and prevent parasitic heat conduction from the base body 230 towards the optical surface 231.

[0167] Figure 9 shows a further embodiment of a base body 230 of an optical element designed as a mirror Mx, 117, which, like the one in the Figure 8The optical element Mx, 117, comprises cooling channels 233 arranged under the optical surface 231. In contrast to the one described in the Figure 3 In the optical element shown, electrically conductive particles 235 or electrically conductive components 236, such as wires or plates, are integrated into the base body 230 in place of the heating wires 234. If the base body 230 is manufactured using a 3D printer with the PolyJet process, the particles 235 can be selectively printed at predetermined positions within one of the material mixtures printed by the 3D printer. Depending on the mixing ratio of the at least two material mixtures used in the PolyJet process, the concentration of the particles 235 can be precisely controlled. This allows for the creation of areas with high concentration and areas with low concentration or without particles 235 within the base body 230.

[0168] Furthermore, electrically conductive components 236 can also be integrated into the base body 230 using the PolyJet 3D printing process by inserting the components 236 into the base body 230. Alternatively, the components 236 can also be integrated into the base body 230 using other 3D printing processes that can only process a material mixture, such as stereolithography. Induction coils 238 are arranged in a recess 237 in the base body 230 near the particles 235 and the components 236. When an alternating current is applied by a control signal (not shown), these coils induce electrical currents in the particles 235 and / or components 236, causing them to heat up due to their ohmic resistance. This also heats the adjacent areas in the base body 230, resulting in a predetermined deformation of the base body 230 and thus of the optical surface 231.

[0169] Figure 10shows a further embodiment of a base body 230 of an optical element designed as a mirror Mx, 117, which, like the one in the Figure 8 and the Figure 9 The optical element Mx, 117, includes cooling channels 233 arranged under the optical surface 231. Furthermore, the base body 230 also includes the cooling channels already described in the Figure 9 The particles 235 and / or components 236 shown. Instead of the induction coils 238, the base body 230 comprises electromagnets 239, which, like those shown in the Figure 9The induction coils 238, as described above, are arranged in a recess 237 in the base body 230 in close proximity to the particles 235 and components 236. The electromagnets 239 are received in a receptacle 240 formed in the recess 237 and act together with the magnetizable particles 235 and components 236 as an electromagnetic actuator 243. This actuator, like the thermal actuators 241 and 242 described above, can generate a predetermined deformation in the optical working surface 231 to correct imaging errors.

[0170] Figure 11 describes a method for manufacturing a base body 230 for an optical element Mx, 117.

[0171] In a first process step 251, a predetermined structure of the base body 230 is produced with at least two different material mixtures, wherein the material mixtures comprise a support material with at least one monomer and / or oligomer and a structural material with at least one glass powder, and the material mixtures differ by at least two different glass powders in the structural material.

[0172] In a second process step 252, the base body 230 polymerized in the previous process step 251 is heated to thermally bond the glass powder components and to burn the polymer.

[0173] In a third process step 253, the base body 230 is sintered.

[0174] The in the Figures 8 to 10The actuator elements 234, 235, 236, 238, 239 and actuators 241, 242, 243 depicted cause a deformation of the base body 230 by heating certain areas of the base body or by magnetic force. This deformation propagates to the optical surface 231. In the case of thermal actuators 241, 242, this effect is enhanced by a high coefficient of thermal expansion in the region of the integrated actuator elements 234, 235, 236. In combination with a low coefficient of thermal expansion, i.e., a zero-crossing temperature of zero or nearly zero, in the region of the optical surface 231 of the base body 230, the predetermined deformation by the actuators 241, 242, 243 is maximized, and the parasitic deformation caused by absorption of electromagnetic radiation incident on the optical surface is minimized. The coefficient of thermal expansion, or the zero-crossing temperature, can be determined by the value in the Figure 11The described manufacturing processes can be varied in any way via the base body 230. Alternatively, the base body 230 can also be used for a measuring setup or a stage of a coordinate measuring machine and any other application that requires a surface with high temperature stability and / or a high-precision surface. Reference symbol list

[0175] 1 Projection exposure system 2 Lighting system 3 Radiation source 4 Lighting optics 5 Object field 6 Object plane 7 Reticle 8 Reticle holder 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 Wafer 14 Wafer holder 15 Wafer displacement drive 16 EUV radiation 17 Collector 18 Intermediate focus plane 19 Deflection mirror 20 Faceted mirror 21 Facets 22 Faceted mirror 23 Facets 31 First process step 32 Second process step 33 Third process step 30 Base body 131 Optical working surface 132 Connection 133 Material zones 34 Optical area 40 3D printer 41 Object stage 42 Print head 43 Material mixture A 44 Material mixture B 45 UV light 46 X-axis guide 47 Y-axis guide 48 Z-axis guide 49 Structure 50 Monomer 51 Oligomer 52 Photoinitiator 53 Glass powder A 54 Glass powder B 61 Process step 1 62 Process step 2 63 Process step 3 64 Process step 4 101 Projection exposure system 102 Lighting system 107 Reticle 108 Reticle holder 110 Projection optics 113 Wafer 114 Wafer holder116 DUV radiation 117 Optical element 118 Mounts 119 Lens housing M1-M6 Mirror 130 Base body 134 Optical area 230 Base body 231 Optical working surface 232 Deformation 233 Cooling channels 234 Heating wire 235 Particle 236 Component 237 Recess 238 Induction coil 239 Electromagnet 240 Receptacle for electromagnet 241 Resistance actuator 242 Induction actuator 243 Electromagnetic actuator 251 Process step 1 252 Process step 2 253 Process step 3

Claims

1. Method for producing a main body of an optical element (Mx, 117) for semiconductor lithography, wherein it is an additive method which comprises the following method steps: - providing a first material mixture (43) comprising a first carrier material and a first structural material, - providing a second material mixture (44) comprising a second carrier material and a second structural material, - wherein the carrier materials comprise at least one monomer (50) and / or at least one oligomer (51) and wherein the structural materials differ in terms of their composition, - forming an intermediate body by merging the material mixtures (43, 44) and polymerizing the carrier materials, - finishing at least one part of the main body (30) by heating the intermediate body to thermally bond the structural materials and to remove the carrier materials.

2. Method according to Claim 2, characterized in that the formation of an intermediate body is performed using a polyjet printing method.

3. Method according to Claim 1 or 2, characterized in that at least one of the structural materials contains a glass powder (53, 54).

4. Method according to one of Claims 1 to 3, characterized in that at least one of the structural materials contains an additive.

5. Method according to Claim 4, characterized in that the structural materials differ in terms of the type of the additives.

6. Method according to either of Claims 4 and 5, characterized in that the structural materials differ in terms of the concentration of the additives.

7. Method according to one of Claims 4 to 6, characterized in that the additives comprise the following substances or compounds: titanium, titanium oxide, lithium, aluminum, OH compounds.

8. Method according to one of Claims 4 to 7, characterized in that the concentration of the additives over the main body (30) corresponds to a temperature distribution, established during use of the optical element (117), in the main body (30).

9. Method according to one of Claims 4 to 8, characterized in that the concentration of the additives decreases as the distance from a side of the main body (30) that is intended for an optical surface (131) increases.

10. Method according to Claim 9, characterized in that the concentration of the additives constantly decreases as the distance from a side of the main body (30) that is intended for an optical surface (131) to a cooled layer in the main body (30) increases.

11. Method according to one of Claims 1 to 10, characterized in that the method is used to produce an optical element (Mx, 117) for a projection exposure apparatus (1, 101) for semiconductor lithography.

12. Main body (30) for an optical element (Mx, 117), the main body (30) being produced at least partially by an additive method, the zero-crossing temperature of the coefficient of linear thermal expansion changing at least in a partial region of the main body (30), characterized in that the change in the zero-crossing temperature is continuous in the partial region of the main body (30).

13. Main body according to Claim 12, characterized in that the change in the zero-crossing temperature ranges from 20° Celsius to 65° Celsius at more than 1 K / mm.

14. Main body (30) according to either of the preceding Claims 12 and 13, characterized in that the zero-crossing temperature which varies at least partially over the main body (30) corresponds to a temperature distribution, established during use of the optical element (117), in the main body (30).

15. Main body (230) for an optical element (Mx, 117), the main body (230) comprising at least one actuator (241, 242, 243) and / or sensor, characterized in that at least one actuator component (234, 235, 236) of the actuator (241, 242, 243) and / or one sensor component (234, 235, 236) of the sensor is integrated at least in an additively manufactured partial structure of the main body (230).

16. Main body (230) according to Claim 15, characterized in that the actuator component (234, 235, 236) and / or the sensor component (234, 235, 236) is an electrically conductive element (234, 235, 236).

17. Main body (230) according to Claim 16, characterized in that the actuator component (234, 235, 236) and / or the sensor component (234, 235, 236) comprises at least one heating wire (234).

18. Main body (230) according to Claim 16 or 17, characterized in that the actuator component (234, 235, 236) and / or the sensor component (234, 235, 236) comprises electrically conductive particles (235).

19. Main body (230) according to one of Claims 16 to 18, characterized in that the actuator component (234, 235, 236) and / or the sensor component (234, 235, 236) comprises electrically conductive component parts (236).

20. Main body (230) according to one of the preceding Claims 15 to 19, characterized in that the actuator component (234, 235, 236) and / or the sensor component comprises magnetizable elements (235, 236).

21. Main body (230) according to one of the preceding Claims 15 to 20, characterized in that the actuator component (234, 235, 236) and / or the sensor component (234, 235, 236) comprises a thermally conductive element.

22. Projection exposure apparatus (1, 101) for semiconductor lithography, characterized in that it comprises an optical element (Mx, 117) having a main body according to one of Claims 12 to 21.

23. Projection exposure apparatus (1, 101) for semiconductor lithography according to Claim 22, characterized in that the main body of the optical element (Mx, 117) is built up layer by layer and within the main body there are material property inhomogeneities, the optical element being arranged in the projection exposure apparatus (1, 101) in such a way that the direction of the greatest inhomogeneities runs substantially perpendicularly in relation to a scanning direction of the projection exposure apparatus (1, 101).