Method for creating a tempered hollow structure in a substrate using a processing light beam

Abstract

In a method for generating a thermal hollow structure in a substrate, particularly in a mirror substrate of an EUV projection exposure system or other semiconductor technology equipment, a substrate (12) consisting of a substrate material is first provided. The substrate (12) is measured to determine the location of gas bubbles or other inclusions (52) within the substrate (12). Then, a thermal hollow structure, which may be, for example, a cooling channel (22), is incorporated into the substrate (12) by successively focusing a processing light beam (34) with a beam axis (48) aligned along a standard direction onto processing locations (44) where the thermal hollow structure (22) is to be formed. This modifies or ablates the substrate material at the processing locations (44).If an inclusion (52) were located on the beam axis (48) oriented along the standard direction, the direction of the beam axis (48) relative to the mirror substrate (12) is changed so that the beam axis (48) does not intersect the inclusion (50). Any residue (74) can be removed by inserting a lance (76) into the cooling channel to break off the residue.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a method for producing a tempering cavity structure in a substrate using a processing light beam. The substrate can, in particular, be a mirror substrate for a mirror of an EUV projection exposure system or another semiconductor technology system. 2. Description of the state of the art

[0002] Microlithographic projection exposure systems are used in chip manufacturing to transfer patterns on a mask onto a photoresist previously applied to a wafer. To do this, the mask is illuminated with light and imaged onto the light-sensitive layer in a reduced size. In EUV projection exposure systems, the light has a wavelength between approximately 5 nm and approximately 30 nm; commercially available systems use light with a wavelength of 13.5 nm.

[0003] However, there are no optical materials with sufficiently high transmittance for such short wavelengths. Therefore, in EUV projection exposure systems, the lenses typically used for longer wavelengths are replaced by mirrors, and the mask also contains a pattern of reflective structures.

[0004] Providing mirrors for EUV projection exposure systems is technologically challenging. The mirror substrate consists of a substrate material, typically glass, e.g., titanium-doped quartz glass such as ULE®, or a glass-ceramic. A coating is vapor-deposited onto the mirror substrate that reflects the EUV light and consists of a multitude of thin double layers with varying refractive indices.

[0005] Even with such complex coatings, the mirrors' reflectivity for EUV light rarely exceeds 70%, and even then only for light that hits the reflective coating perpendicularly or at angles of incidence of a few degrees. The portion of the EUV light not reflected by the coating is absorbed in the mirror substrate, where it leads to significant heating, due to the high power of the EUV light sources used. Even when glass-ceramics with low thermal expansion coefficients are used, the heating can lead to intolerable deformation of the mirrors.

[0006] The developers of other semiconductor technology systems, such as mask or wafer inspection systems, are also confronted with the same problems, since they also use mirrors that heat up under the influence of radiation.

[0007] It was therefore proposed to provide the mirror substrates with cooling channels through which water or another fluid flows during operation, thus dissipating heat. The cooling channels have a cross-section of approximately 1 mm 2 and ideally run at a defined distance below the reflective coating.

[0008] An overview of the methods known to date for creating cooling channels is contained in the applicant's application DE 10 2021 214 310.5. Particularly promising are methods in which a processing light beam is successively focused on processing locations where cooling channels are to be created. This modifies the substrate material at the processing locations so that it can be removed by chemical processing in a subsequent step. Alternatively, the substrate material can also be removed directly by the processing light beam; any resulting residues are then rinsed away with a rinsing fluid.

[0009] However, it has been shown that the machining results are occasionally unsatisfactory because the walls of the cooling channels are not smooth but irregularly shaped.

[0010] Similar problems arise in other contexts. In order to keep a substrate at a precisely defined temperature, a channel created in the substrate can also be used for heating. The substrate does not have to be part of a mirror, but can, for example, carry a sensitive sensor that must be located in a precisely defined position. If the substrate is exposed to high and time-varying thermal stress, e.g. due to fluctuating electrical power losses from neighboring components or radiation that is only incident intermittently, this can lead to changes in the shape of the substrate and thus to undesirable changes in the position of the sensor. Hollow structures through which a cooling or heating fluid flows can also be used with such substrates to keep the substrate at a constant target temperature.

[0011] In the following, we will therefore generally refer to hollow tempering structures, even though these will often be cooling channels.

[0012] The substrate does not need to be transparent to visible light. For example, hollow structures can be created in silicon, which is opaque to visible light, if the processing light beam has a wavelength of around 2 µm. SUMMARY OF THE INVENTION

[0013] The object of the invention is to provide a method for producing a tempering hollow structure in a substrate, in which the tempering hollow structure has a more uniform cross-section than in known methods. 1. Changes in the beam axis

[0014] This object is achieved by a method for producing a tempering hollow structure in a preferably monolithic substrate, in particular in a mirror substrate for a semiconductor technology system, comprising the following steps: a) providing the substrate consisting of a substrate material; b) Measuring where inclusions are located in the substrate; c) machining the tempering cavity structure into the substrate by successively focusing a processing light beam with a beam axis aligned along a standard direction onto processing locations where the tempering cavity structure is to be created, whereby the substrate is modified or removed at the processing locations;wherein in step c), at least if an inclusion measured in step b) would be located on the beam axis aligned along the standard direction, the direction of the beam axis relative to the substrate is changed such that the beam axis does not intersect the inclusion.

[0015] The invention is based on the discovery that irregularly formed tempering cavity structures can be caused by gas bubbles and other inclusions in the mirror substrate. If the processing light beam encounters a gas bubble on its way to the processing location, for example, this acts like a small lens that deflects the incoming processing light beam. The deflected light generally no longer reaches the processing location, which is why the radiation intensity required for the desired modification or ablation of the substrate material may no longer be available there. If this results in less material being modified or ablated at the processing location, this leads to undesirable cross-sectional changes in the tempering cavity structure. In the worst case, the process is aborted because no more material is modified or ablated at all.

[0016] The situation is similar for inclusions, which absorb the processing light and thus weaken the intensity at the processing location.

[0017] According to the invention, this problem caused by the inclusions is solved by first measuring where the inclusions are located in the substrate. If the locations of the inclusions are known, it is possible to predict at which positions in the process the beam axis of the processing light beam would intersect an inclusion. At the predicted positions, the direction of the beam axis of the processing light beam is changed so that the beam axis cannot intersect the respective inclusion. This ensures that at most a small part of the processing light beam is impeded in its propagation by the inclusion. By changing the direction, the processing light beam can propagate obliquely beneath the inclusion and thus reach areas in the substrate that would be shadowed by the inclusion if the processing light beam propagated in the standard direction.

[0018] When calculating in advance the positions at which the direction of the machining light beam's axis is to be changed, a more stringent criterion can be applied than the presence of an intersection point between the beam axis and the inclusion. A change in the direction of the beam axis can, for example, already be carried out if at least p% of the intensity of the machining light beam is exposed to the inclusion. In this case, the calculation is more complex because not only must the beam axis in the substrate be calculated, but the usually Gaussian beam profile of the machining light beam at the level of the inclusion must also be taken into account. The percentage p can be variable and depend, for example, on the position of the inclusion relative to the machining location.

[0019] The cooling hollow structures are typically cooling channels whose cross-section does not need to be constant and can be, for example, circular, rectangular, or annular. However, the cooling hollow structures can also be extended chambers in which the cooling fluid is exchanged only slowly and in which no defined longitudinal axis is present, as is typical for a channel.

[0020] The standard direction along which the machining light beam normally propagates during machining, i.e., in the absence of inclusions, is generally defined to be at least substantially perpendicular to a longitudinal axis of the tempering cavity structure. Especially if the tempering cavity structure is curved or angled, or if the tempering cavity structure is not a channel, the standard direction can also be defined differently. For example, if a channel-shaped tempering cavity structure contains a section angled at 90°, the standard direction within this section can also run parallel to the longitudinal axis of the channel-shaped tempering cavity structure.

[0021] If the machining light beam first propagates along the standard direction, then changes the direction of the beam axis at an inclusion, and then returns to the standard direction after the inclusion, this is equivalent to changing the direction of the beam axis twice at each inclusion.

[0022] However, it is often not possible to process all areas of the substrate shadowed by the inclusion with just one direction deviating from the standard direction. Especially when the inclusion is located very close to the processing location, it is necessary to change the direction of the beam axis more often, for example, three times.

[0023] Typically, the tempering cavity structure is created along a predefined process direction, which in the case of channels extends parallel to the longitudinal axis of the channel. The processing locations can be better reached by the processing light beam if, the first time, the direction of the beam axis changes by a first angle α1 with respect to the standard direction so that the processing light beam is directed below the inclusion, as seen in the process direction. The second time, the direction of the beam axis changes by a second angle α2 with respect to the standard direction so that the processing light beam is directed below the inclusion, as seen against the process direction. In other words, with this process, the processing light beam is directed obliquely from both sides below the inclusion in order to be able to modify or remove substrate material there as well.A third time, the beam axis is either reset to the standard direction or the beam direction is changed by a third angle α3, which runs in a plane perpendicular to the process direction.

[0024] Ideally, the angles α1 and α2 are equal in magnitude, which corresponds to a symmetrical machining situation. If the machining situation is or should be asymmetrical, different angles α1 and α2 can be selected.

[0025] An even better accessibility of areas which would be shaded by the inclusion in the case of a processing light beam propagating in the standard direction can be achieved if the processing light beam passes at least once, when its beam axis is not aligned parallel to the standard direction, through a liquid or solid medium which is immediately adjacent to a section of the surface of the substrate which is passed through by the processing light beam.

[0026] Without such a medium, the processing light beam is subject to refraction at the interface between the substrate and the surrounding atmosphere, which is generally air. If the processing light beam is incident at an angle, it is refracted toward the normal, making access to these areas more difficult. If water or a similar liquid is adjacent to the substrate, this refraction is reduced. If the solid medium has a higher refractive index than the substrate material, refraction away from the normal can even be achieved, further improving accessibility to these areas.

[0027] If the medium is liquid, said section of the substrate surface can be arranged at an incline such that a horizontal surface of the liquid medium facing the surrounding atmosphere is perpendicular to the processing beam. The beam axis of the processing light beam is then not refracted at all upon entering the liquid medium and only slightly refracted upon subsequent entry into the substrate if the liquid medium and the substrate have similar refractive indices. Generally, such an arrangement requires the entire substrate to be tilted so that the surface facing the processing light beam is inclined. The liquid medium can be held in place by barriers that are temporarily attached to the surface and form a trough for the liquid medium.

[0028] Even if the medium is solid and has a higher refractive index than the substrate, a surface facing away from the substrate should be perpendicular to the processing beam to prevent a change in the direction of the beam axis. The medium is then preferably shaped like a wedge or truncated wedge.

[0029] In one embodiment, the processing light beam has a rotationally asymmetric beam profile upon entering the substrate. The longest diameter of the beam profile is at least twice the shortest diameter of the beam profile. The beam axis, before and after the change in direction, lies in a plane in which the beam profile has its shortest diameter.

[0030] Such a beam profile is advantageous because the machining light beam is particularly narrow in the processing direction and, after the change of direction during the machining process, hits the inclusion later than a conventional machining light beam with a rotationally symmetric beam profile. This allows such a beam to process areas that cannot be reached by a conventional machining light beam due to the shadowing caused by the inclusion.

[0031] To generate such a beam profile, the processing light beam can pass through a beam profile modification device before entering the substrate, which changes the beam profile accordingly. In the simplest case, such a beam profile modification device contains at least one cylindrical lens or another anamorphic optical element with a similar effect. Alternatively, diffractive optical elements (DOEs) or spatial light modulators can be used to modify the beam profile. 2. Removing residues

[0032] The method according to the invention makes it possible to produce hollow tempering structures that have significantly more uniform cross-sections and smoother interior surfaces than previously producible tempering structures. In many cases, however, despite the measures according to the invention, residues of substrate material remain in the hollow tempering structures, protruding from the interior surface into the hollow tempering structure, similar to stalactites on a cave wall. If such residues exceed a certain size, functional impairments cannot be ruled out. In extreme cases, the residues are so large that the hollow tempering structure is completely sealed by a structure that, although thin, is impermeable to the cooling or heating fluid flowing through it.

[0033] According to the invention, the remaining residues in the tempering cavity structure are mechanically broken up. This either directly destroys the residues to a large extent or damages them to such an extent that they can be removed in the same or a subsequent processing step. The removal process can also be performed mechanically, e.g., with the aid of a rinsing fluid or with the aid of an element conveying the rinsing fluid. Alternatively, a fluid can be used that chemically dissolves the broken-up residues and carries them away.

[0034] The mechanical breaking can be achieved, for example, with the help of a pressurized fluid that is introduced into an existing tempering cavity structure that is just being formed.

[0035] To break the structure, a lance is preferably inserted into an already created tempering cavity or into the substrate during the creation of a tempering cavity. If a free end of the lance encounters an interfering residue during insertion, the momentum of the moving lance breaks it off and possibly crushes it. This allows even complete closures in the tempering cavity to be broken open. The tilting of the beam direction according to the invention ensures that such closures are thin enough to be broken open by the lance. Simulations have shown that the force typically required to break off a residue is on the order of 0.1 N.

[0036] The remaining residues form protrusions with a maximum height h of 15 µm < h < 50 µm relative to the surrounding and otherwise smooth inner surface. Compared to typical temperature control channel widths of approximately 2 mm, this is a very small value, so that the fluid flow through the protrusions is only slightly disrupted. In this context, a smooth inner surface is defined as one with a maximum roughness depth Rt of less than 5.0 µm and preferably less than 3.0 µm.

[0037] In a subsequent (possibly second) treatment step using a chemically active and preferably liquid medium, the remaining crushed residues can be further removed and rounded. This allows the maximum height h of the protrusions to be reduced to values ​​of 15 < h < 25 µm. Such shallow protrusions generally do not impair the functionality of the substrate during subsequent use.

[0038] The lance can be a separate tool, e.g., a thin but sufficiently stiff wire, designed solely to break up the residues. If the tempering cavity is a channel with a uniform diameter and slight bends, a lance can be used whose diameter matches the diameter of the channel—i.e., one with the same shape but slightly smaller dimensions. This allows the residues to be broken off so that only very short stumps remain.

[0039] Alternatively, a (possibly steerable) hose can be used as a lance. This hose is inserted manually or with the aid of a tracking unit into the already created tempering cavity structure or into the substrate during the creation of a tempering cavity structure in order to dispense a chemical rinsing or processing fluid. A rinsing fluid is preferably used once the processing light beam has removed the substrate material. If the substrate material is only modified by the processing beam, a subsequent chemical processing step using a chemical processing fluid, such as an etching fluid or another chemically active medium, is required. The stiffness of the hose can be adjusted by, among other things, the choice of material, the hose diameter, the wall thickness of the hose and the pressure of the chemical processing fluid in the hose.

[0040] If the lance is a hose, the momentum can also be transferred to the residue indirectly via a flushing fluid. In this case, the flushing fluid exits the hose at sufficiently high pressure and tears the residue from the inner surface of the cavity. Direct contact of the hose with the residue is not necessary in this case. Since the hose does not have to directly touch the residue, it can be comparatively soft, which facilitates navigation in the cavity.

[0041] Due to their greater mass, water or another liquid is particularly suitable as a flushing fluid. However, air or another gas (or mixture) could also be used.

[0042] Preferably, the fluid exits the hose in pulsed form. The pressure surges generated in this way increase the momentum transfer to the residues, causing them to break off faster and more reliably.

[0043] Regardless of the type of lance, it is advisable to move it alternately back and forth while removing the residue. This allows the lance or a fluid escaping from it to repeatedly impact a residue, gradually removing it.

[0044] Mechanical disruption can be performed after the cooling hollow structure has been created. Some processing methods allow for the residues to be mechanically disrupted during the creation of the cooling hollow structure. Such processing methods are described in the patent application filed by the applicant with the German Patent and Trademark Office on the same day, entitled "Method for incorporating cooling hollow structures into a mirror substrate of a mirror for an EUV projection exposure apparatus, and processing system therefor." In these processing methods, a tube is inserted into the substrate, while the processing light beam ablates or modifies the substrate material. This tube can be used as a lance in the manner described above, mechanically disrupting the newly formed residues either through its movement or through the ejection of a fluid.

[0045] A lance for breaking up residues can also be used if residues remain in the tempering cavity structure that are not caused by inclusions. The invention therefore also relates to a method for producing a tempering cavity structure in a substrate, in particular in a mirror substrate for a mirror in a semiconductor technology system, comprising the following steps: a) providing the substrate (12) consisting of a substrate material; b) machining the tempering hollow structure (22) into the substrate (12) by successively focusing a processing light beam (34) with a beam axis (48) aligned along a standard direction onto processing locations (44) at which the tempering hollow structure (22) is to be created, whereby the substrate material is modified or removed at the processing locations (44); c) Inserting a lance into an already created tempering cavity structure or into the substrate during the creation of a tempering cavity structure, thereby breaking up residues in the tempering cavity structure.

[0046] The combination of the above-described (possibly multiple) tilting of the beam axis of the processing light beam with the use of a lance to break up remaining residues results in the inner surfaces of the tempering cavity structures in substrates with bubbles or other inclusions being so smooth that disruptive elevations, which do not contribute to the function of the tempering cavity structure but were caused by inclusions during the creation of the tempering cavity structures, have a height between 15 µm and 50 µm. The maximum height can be reduced to 25 µm if, after the lance has been inserted, the tempering cavity structure is rinsed and / or chemically processed with an etching liquid or another chemically active medium, e.g., an oxidizing or reducing agent.

[0047] When creating very small tempering cavity structures in high-purity glass, it may happen that by chance no inclusion obstructs the processing light beam. However, the larger the tempering cavity structures, the more likely it is that they will obstruct the processing light beam. However, only those inclusions located between the substrate surface, into which the processing light beam penetrates, and the tempering cavity structure are potentially disruptive. The distance between the tempering cavity structure and this surface is often between 20 mm and 30 mm.

[0048] Glasses of the highest purity class 0, for example, have the property that for a volume of 100 cm 3 a total bladder cross-sectional area of ​​0.03 mm 2is permissible, with the maximum permitted bubble diameter being 100 µm. For typical channel widths of 2 mm and a total channel length of 50 cm, statistically there is exactly one bubble with a maximum diameter of 100 µm that obstructs the processing light beam. The creation of a 10 mm wide and 10 cm long channel hollow structure is also statistically disrupted by exactly one bubble.

[0049] If the substrate is a mirror substrate for a mirror of an EUV projection exposure apparatus or other semiconductor technology apparatus, the method may comprise the step of applying a multilayer coating to the substrate which is designed to reflect at least 50% of incident EUV light.

[0050] The invention therefore also relates to a mirror comprising a substrate according to the invention and a coating supported by a support surface of the substrate. If the mirror is a mirror of an EUV projection exposure system or another semiconductor technology system, the coating should have the property of reflecting at least 50% of EUV light, particularly light with a wavelength of 13.5 nm.

[0051] While, as mentioned above, the tempering cavity is often located at a distance of 20 mm to 30 mm from the surface onto which the processing light beam was directed, after the shaping of the mirror substrate by material removal, the distance of the tempering cavity from the substrate surface is often only a few millimeters. In particular, the tempering cavity can extend at a distance of 1.0 mm to 50.0 mm, 1.0 mm to 20.0 mm, 1.0 mm to 10.0 mm, or 1.0 mm to 5.0 mm from the substrate surface. The inclusion can be located in this gap.

[0052] However, due to the material removal for the purpose of shaping, it is possible that an inclusion which has impeded the propagation of the processing light beam is no longer present in the later mirror. As a result, elevations can remain in the tempering cavity structures without the cause being recognizable in the finished mirror. The invention therefore further relates to a mirror with a tempering cavity structure which has a smooth inner surface. The substrate consists of glass or a glass ceramic. The inner surface has a locally limited elevation which does not contribute to the function of the tempering cavity structure and has a height h of between 15 µm and 50 µm. The tempering cavity structure runs from the carrier surface at a distance of 1.0 mm to 50.0 mm, from 1.0 mm to 20.0 mm, from 1.0 mm to 10.0 mm or from 1.0 mm to 5.0 mm.

[0053] The invention further relates to a semiconductor technology system which contains a mirror according to the invention, a substrate according to the invention and / or a substrate produced by the method according to the invention. The system can be, for example, a projection exposure system, a mask inspection system or a wafer inspection system. Semiconductor technology systems contain substrates or mirrors for which temperature control with the aid of temperature control hollow structures is advantageous in many cases. In addition to the substrates and mirrors, such systems typically contain a light source which can be designed, for example, to generate EUV radiation, as well as mechanical components with which masks (also called reticles), wafers or sensors can be aligned and / or moved. 2. Changes in the beam profile

[0054] In addition to or as an alternative to the change in the beam axis described above, the beam profile of the processing light beam can be changed. A corresponding method for creating a tempering cavity structure in a substrate comprises the following steps: a) providing a substrate consisting of a substrate material; b) Machining of tempering hollow structures into the substrate by successively focusing a processing light beam on processing locations where tempering hollow structures are to be created, whereby the substrate material is modified or removed at the processing locations, wherein the processing light beam passes through a beam profile changing device on its way to the substrate, which redistributes radiant energy in the processing light beam in the radial direction.

[0055] The inventors have recognized that tempering hollow structures with more uniform cross-sections can be created if the beam profile of the processing light beam is modified on its path to the substrate. Typically, the processing light beam is generated by a laser, so that the processing light beam initially, i.e., before entering the beam profile modification device, has a Gaussian beam profile. With such a beam profile, the majority of the radiation energy is concentrated in a relatively small area around the beam axis; the intensity then slowly decreases outwards. However, such a Gaussian beam profile is disadvantageous for the desired modifications in the substrate material because local and temporal fluctuations in the processing threshold—i.e., the intensity above which the desired material modifications occur—have a strong impact on the width of the material area modified by the processing light beam.A tempering cavity structure created with such a processing light beam therefore often has an irregular cross-section, which is disadvantageous for the subsequent passage of a tempering fluid.

[0056] More uniform cross-sections of the tempering hollow structures can be created if the beam profile modification device converts the initially Gaussian beam profile into a top-hat beam profile. With a top-hat beam profile, the radiation energy is evenly concentrated in a wider area around the beam axis, but then drops more steeply outwards. Due to the steeper drop, local and temporal fluctuations in the processing threshold have a less pronounced impact on the size of the material area modified by the processing light beam.

[0057] Alternatively, the beam profile modification device can convert the Gaussian beam profile into a donut beam profile. With such a beam profile, the intensity maximum is located outside the beam axis, resulting in an approximately ring-shaped intensity distribution in the beam cross-section. Since the intensity drops rapidly at the outer beam edge even with a donut beam profile, the advantage of more uniform cross-sections of the tempering cavity is retained. However, the low intensity on the beam axis has the advantage that inclusions of gas bubbles or other contaminants located on the beam axis lead to less shadowing and thus less of an impact on the processing result. The processing light beam essentially passes outside the inclusion and converges behind the inclusion so that the substrate material is evenly modified there.

[0058] If the processing light beam is not generated by a laser or if the beam profile of the processing light beam is not Gaussian for other reasons, e.g. because the laser in a luminophore excites the emission of non-Gaussian distributed secondary radiation, the beam profile changing device can also convert such other beam profiles into a top-hat or a donut beam profile.

[0059] Beam profile modification devices such as diffractive optical elements (DOEs) can be used to specifically modify the angular distribution of the incident processing light. In the far field or behind a Fourier optic, a top-hat, donut, or other desired spatial intensity distribution is then created.

[0060] Preferably, the beam profile modification device adjusts the type and extent of radial redistribution of the radiation energy variably depending on the processing situation. This allows the optimal beam profile to be generated for every processing situation.

[0061] For example, if the substrate contains numerous large gas bubbles or other inclusions, the location of the inclusions in the substrate material can be measured before step b). If an inclusion is located on a beam axis of the processing light beam directed at a processing location, the beam profile is converted into a donut beam profile beforehand. If there is no inclusion on the beam axis of the processing light beam directed at the processing location, the beam profile can be converted into a top-hat beam profile or another beam profile that leads to particularly good processing results.

[0062] The beam profile modification device must then be capable of generating different beam profiles as needed. For this purpose, it can, for example, have an interchangeable holder for several diffractive optical elements that can be used to generate different beam profiles.

[0063] A continuous variation of the generated beam profile is possible if the beam profile changing device has a pair of complementary axicon elements whose spacing can be adjusted. Such a pair of complementary axicon elements produces a donut beam profile in which the diameter of the light-free region continuously increases with increasing spacing between the axicon elements.

[0064] In many cases, it is most effective for the beam profile changer to convert a Gaussian beam profile either into a top-hat beam profile or a donut beam profile. The processing light beams generated by common laser light sources have a Gaussian beam profile; a top-hat beam profile is often preferred, provided no gas bubbles or other inclusions obstruct the processing light beam. If this is the case, the beam profile briefly changes from a top-hat to a donut beam profile to allow the processing light beam to bypass the inclusion.

[0065] Such flexible and rapid switching between different types of beam profiles is not possible with either interchangeable DOEs or axicon elements. However, beam profile changing devices that incorporate a spatial light modulator are suitable, as described in Kuang, Zheng et al., "Ultrafast laser beam shaping for material processing at imaging plane by geometry masks using a spatial light modulator," Optics and Lasers in Engineering 70 (2015): 1-5.

[0066] An array of tiltable micromirrors can be used as a spatial light modulator. The type and extent of the radial redistribution of the radiant energy can then be adjusted by changing the tilt angles of the micromirrors. Such a micromirror array changes the angular distribution similarly to a DOE, but offers the possibility of changing the angular distribution flexibly and very quickly (typically within a few microseconds) within wide limits. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In the following, exemplary embodiments of the invention are explained in more detail with reference to the drawings. In these drawings: Fig. 1 a mirror for an EUV projection exposure system in a schematic cross-section; Fig. 2 a mirror substrate into which cooling channels are inscribed using a processing light beam; Fig. 3 an enlarged section of the Fig. 2, in which a gas bubble is located; Fig. 4 one of the Fig. 3 corresponding section, whereby the processing light beam is blocked to a greater extent by the gas bubble; Fig. 5a to 5d show several phases of a machining process in which the direction of the beam axis of the machining light beam is changed several times; Fig. 6a to 6d the Fig. 5a to 5d show corresponding representations, wherein the processing light beam passes through a water bath created on the surface of the mirror substrate in some processing steps; Fig. 7a to 7e the Fig. 5a to 5d show corresponding representations for explaining a variant in which the processing light beam passes through a diamond wedge resting on the surface of the mirror substrate during some processing steps; Fig. 8 one of the Fig. 2 corresponding schematic representation according to another embodiment in which a rotationally asymmetric beam profile of the processing light beam is generated; Fig. 9a and Fig. 9b the rotationally asymmetric beam profile of the processing light beam in two vertical section planes; and Fig. 10 one of the Fig. 5a corresponding representation with a processing light beam having a rotationally asymmetric beam profile; Fig. 11a to 11d show several phases of a machining process in which residues in a previously created cooling channel are broken off with a lance inserted into the cooling channel; Fig. 12 a variant in which the residue is not broken off directly by the lance but indirectly via an outflowing fluid; Fig. 13 a cooling channel with a protrusion remaining after breaking off the residue; Fig. 14 the cooling channel according to the Fig. 13 after an additional chemical processing step; Fig. 15 shows a machining process with a machining light beam in which the mirror substrate is covered by a liquid layer; Fig. 16 the processing process according to the Fig. 15, in which the liquid has a lower refractive index than the mirror substrate; Fig. 17 the processing process according to the Fig. 15, in which the liquid has a higher refractive index than the mirror substrate; Fig. 18 the processing process according to the Fig. 15, in which the liquid is tempered and circulated; Fig. 19 a processing process in which several processing light beams are directed simultaneously from different directions onto the mirror substrate; Fig. 20 a machining process in which the machining light beam is guided over the mirror substrate with the aid of a polygon scanner and a z-shifter; Fig. 21 a Gaussian beam profile as generated by a laser light source; Fig. 22 a top-hat beam profile as can be generated by a beam profile changing unit; Fig. 23 a donut beam profile, as can also be generated by the beam profile changing unit; Fig. 24 a section of the mirror substrate and a processing light beam penetrating therein with a Gaussian beam profile; Fig. 25 the section of the Fig. 24, but wherein the processing light beam has a donut beam profile; Fig. 26a to 26c show the effect of a pair of axicon elements on the machining light beam at different axial distances between the axicon elements; Fig. 27 a beam profile changing unit with a micromirror array with which almost any beam profile can be set; Fig. 28 a measurement setup for locating gas bubbles in mirror substrates, in which ultrashort light pulses pass through the mirror substrate; Fig. 29 a measurement setup for locating gas bubbles in mirror substrates, in which scattered light emanating from gas bubbles is detected by incoherent lensless imaging; and Fig. 30 a variant of the Fig. 29, in which the mirror substrate is illuminated incoherently from different directions; Fig. 31 an arrangement of measuring cameras relative to a mirror substrate for the purpose of process monitoring; and Fig. 32 a schematic representation of a microlithographic EUV projection exposure system. DESCRIPTION OF PREFERRED EMBODIMENTS 1. Structure of an EUV mirror

[0068] The Fig. Figure 1 shows a schematic cross-section of a mirror, designated overall by 10, for an EUV projection exposure system or other semiconductor technology system. Mirror 10 can be arranged in the illumination system or in the projection lens.

[0069] The mirror 10 comprises a mirror substrate 12, which in the illustrated embodiment is made of a glass ceramic. Suitable glass ceramics are offered under the trade names Clearceram® or Zerodur® and have the property of having a very low coefficient of thermal expansion at the operating temperature of the mirror 10. The mirror substrate 12 is monolithic, i.e., it consists of a single, continuous piece of material that was not obtained by joining individual pieces.

[0070] The mirror substrate 12 has a precisely machined support surface 14, the curvature of which determines the optical properties of the mirror 10. The support surface 14 of the mirror substrate 12 bears a coating 16 that predominantly reflects incident EUV light 18. As can be seen in the enlarged section C, the coating 16 consists of several double layers 20 applied to the support surface 14. The coating 16 can have a reflection coefficient of more than 70% for perpendicularly incident EUV light 18.

[0071] The non-reflected portion of the UV light 18 penetrates the mirror substrate 12 and is absorbed there, predominantly near the carrier surface 14. As a result of this absorption, the mirror substrate 12 heats up, particularly near the areas of the carrier surface 14 exposed to the EUV light 18. Since the thermal expansion coefficient of the substrate material is not identical to zero and is also temperature-dependent, the heating can lead to changes in the shape of the mirror substrate 12, which affect the optical properties of the mirror 10. However, due to the extremely tight specifications in semiconductor technology systems, changes in the optical properties of the mirrors are not tolerable or, at best, only negligible.

[0072] In order to minimize temperature fluctuations and the resulting changes in shape of the mirror substrate 12, several cooling channels 22 are incorporated into the mirror substrate 12. Typically, the cooling channels 22 run close to and parallel to the carrier surface 14. The cooling channels 22 in the Fig. However, the arrangement of the cooling channels 22 shown in Figure 1 is only an example and may vary in real systems. For example, only a single cooling channel 22 may be provided, which meanders through the mirror substrate 12 or part of it.

[0073] During operation of the semiconductor technology system, water or another cooling fluid flows through the cooling channels 22. The water absorbs the heat introduced by the EUV light 18 and dissipates it from the mirror substrate 12. For this purpose, the cooling channels 22 are connected to a pump unit 24 and a cooling unit 26. The pump unit 24 draws the water from the cooling channels 22 and directs it via a return line 28 to the cooling unit 26. There, the water is cooled to its target temperature before flowing through the cooling channels 22 again. 2. Creating the cooling channels

[0074] The Fig. 2 shows the mirror substrate 12 in a modified orientation prior to the material-removing creation of the carrier surface 14 shown in dashed lines. Above, in a modified orientation of the mirror substrate 12, a processing device 30 is schematically shown, with which the cooling channels 22 are inscribed into the mirror substrate. The processing device 30 has a light source 32 that generates a processing light beam 34. The light source 32 is preferably a high-power laser that generates ultrashort pulses. The processing light beam 34 passes through a focusing lens 36 and can then be directed onto the mirror substrate 12 at different angles with the aid of an adjustment device 38. For this purpose, the adjustment device 38 in the illustrated embodiment comprises a tiltable mirror 40, which is additionally arranged so as to be linearly movable parallel to the process direction indicated by 42.The process direction 42 runs in the longitudinal direction of the cooling channel 22 and thus corresponds to the direction along which the modification or removal process proceeds.

[0075] If the mirror 40 is tilted as well as moved linearly, the direction of the beam axis of the processing light beam 34 can be changed without significantly changing the location of the focus 44. In the Fig. In Figure 2, various tilt and movement positions of the mirror 40 are indicated by dashed lines. In these positions, only the direction of the beam axis changes, while the focus 44 remains virtually unchanged. To ensure that the focus 44 remains exactly at the same location, the focusing lens 36 must also be moved along the optical axis.

[0076] In order to be able to process material at all desired locations in the mirror substrate 12, the relative arrangement between the mirror substrate 12 and the processing device 30 must be variable. For this purpose, for example, the mirror substrate 12 can be moved linearly in all three spatial directions using a traversing table (not shown), as indicated by a multiple arrow 45. It is often expedient for the mirror substrate 12 to be movable not only linearly but also tiltable about at least one axis.

[0077] The traversing table and the adjustment device 38 are then controlled by a control device 46 such that the processing light beam 34 is successively focused on all processing locations at which cooling channels 22 are to be created.

[0078] Alternatively, the relative arrangement between the mirror substrate 12 and the processing device 30 can of course also be changed by moving the processing device 30.

[0079] At the focus 44 created by the focusing lens 36, the intensity of the processing light beam 34 is so high that irreversible modifications of the substrate material occur. Depending on the process, substrate material can be removed in such a way that it can be washed away in a subsequent process step. However, modifications to the substrate material that merely result in it being able to be selectively removed from the mirror substrate 12 in a subsequent chemical processing step are also possible. In both cases, the location of the focus 44 determines where a cooling channel 22 is created in the mirror substrate 12.

[0080] To create a cooling channel 22 with a sufficiently large cross-section, the machining light beam 34 traverses the entire cross-section at a specific axial position according to a predetermined pattern. This process is then repeated at adjacent axial positions until the cooling channel 22 has the desired axial dimension. 3. Avoiding gas bubbles and other inclusions - first embodiment

[0081] The Fig. 3 shows an enlarged section of the Fig. 2, while the processing light beam 34 creates the cooling channel 22. The processing light beam 34 has a beam axis 48, which in this case is understood to be the energetic center axis of the processing light beam 34. For processing light beams 34 with a rotationally symmetric beam profile, as typically generated by the lasers used as light source 32, the beam axis 48 generally coincides with the axis of symmetry.

[0082] In the Fig. In the configuration shown in Figure 3, the surface 50 of the mirror substrate 12 facing the processing device 30 runs parallel to the process direction 42. To reduce scattering losses on the surface 50, it can be polished before processing. The beam axis 48 of the processing light beam 34 is aligned perpendicular to the surface 50 and thus also perpendicular to the process direction 42. The processing light beam 34 therefore penetrates the mirror substrate 12 perpendicularly, so that the beam axis 48 does not experience any deflection due to refraction at the surface 50, which forms the interface between the mirror substrate 12 and the surrounding atmosphere (generally air).

[0083] The direction perpendicular to the surface 50 is referred to below as the standard direction because it is preferred to produce the cooling channels 22 with a machining light beam 34 aligned in this way, apart from the exceptions discussed below.

[0084] In the Fig. 3 shows a spherical gas bubble 52, which was created during the production of the mirror substrate 12. When processing light hits the gas bubble 52, it is refracted at the interface of the gas bubble 52 and is generally deflected so that it no longer reaches the focus 44. The processing light falling on the gas bubble 52 is thus lost for processing.

[0085] In the Fig. 3, only a relatively small part of the processing light beam 34 hits the gas bubble 52. If the processing light beam 34 has a Gaussian beam profile, the intensity decreases significantly with increasing distance from the beam axis 48, so that even with the configuration shown in the Fig. 3, material processing is still possible. However, the greater the proportion of processing light that falls on the gas bubble 52, the less light is available at focus 44 for material processing.

[0086] In the Fig. 4, the beam axis 48 intersects the gas bubble 52, so that a significant portion of the processing light, in particular the generally more energetic center of the processing light beam 34, does not reach the focus 44 and thus cannot contribute to the material processing. As shown in the Fig. 4 by a darkly shaded area, the gas bubble 52 leads to a shadowing 54 when a processing light beam 34 impinges on the mirror substrate 12 parallel to the standard direction. The processing light beam 34 cannot process the substrate material in the area of ​​the shadowing 54, so that a cooling channel 22 cannot be created there. Such a process interruption must be avoided.

[0087] According to the invention, the location of gas bubbles 52 and similar inclusions in the mirror substrate 12 is therefore measured before the cooling channels 22 are incorporated. To measure the locations of the gas bubbles 52, a small area of ​​the mirror substrate 12 can be illuminated with white light, for example, from one side. On the opposite side, a camera records an image of the area. The position and size of the gas bubbles can then be calculated based on the light scattering shown in the image. In this way, the entire mirror substrate can be successively measured. Alternative methods for locating the gas bubbles 52 are explained further below in Section 11.

[0088] To avoid the Fig. 4, if a gas bubble 52 were to be located on the beam axis 48 aligned along the standard direction, the direction of the beam axis 48 relative to the mirror substrate 12 is changed so that the beam axis 48 does not intersect the gas bubble 52, as shown in the Fig. 5a. This is achieved by directing the processing light beam 34 at a different angle onto the surface 50 of the mirror substrate 12 with the aid of the adjustment device 38. The processing light beam 34 is then refracted at the surface 50 of the mirror substrate 12, so that the beam axis 48 in the mirror substrate no longer runs parallel to the standard direction, but at an angle α1 thereto. References to the "direction of the beam axis 48" below always refer to the beam axis 48 within the mirror substrate 12, i.e., after refraction at the surface 50.

[0089] Since the air surrounding the mirror substrate 12 has a smaller refractive index than the substrate material, the processing light beam 34 is refracted towards the normal, as shown in the Fig. 5a. Due to the oblique beam axis 48, the processing light beam 34 reaches areas of the mirror substrate 12 that are located at the lower end of the shadow 54 indicated by dashed lines. The processing light beam 34, which is not shadowed by the gas bubble 52, can thus process the substrate material in these areas in the desired manner. Fig. 5a clearly shows that the greater the distance between the gas bubble 52 and the cooling channel 22, the larger the machinable area. If the gas bubble 52 is located directly above the cooling channel 22, the machinable area within the shadow 54 is very small.

[0090] If the Fig. 5a is reached, the processing is interrupted by switching off or dimming the light source 32. Now the direction of the processing light beam 34 is changed a second time in order to Fig. 5b. The beam axis 48 now runs at an angle α2 = - α1 to the standard direction. While in the Fig. 5a the processing light beam 34 is directed under the gas bubble 52 as seen in the process direction 42, the processing light beam 34 extends in the Fig. 5b, viewed opposite to the process direction 42, beneath the gas bubble 52. In this way, additional areas located within the shadowing area 54 can be processed. The angles α1 and α2, which the beam axis 48 forms with respect to the vertical standard direction in front of and behind the gas bubble 52, are approximately 13° in the illustrated embodiment. The larger this angle, the larger the area that can be reached by the processing light beam 34 within the shadowing area. However, there are limits to the size of the angles α1, α2 because the processing light beam 34 becomes increasingly polarized the more the angles of incidence α1, α2 approach the Brewster angle. In addition, large angles of incidence α1, α2 lead to an unwanted extension of the pulse duration and to a distortion of the beam profile, since the path to the processing location for the flank of the processing light beam 34 inclined towards the surface is significantly shorter than for the other flank.

[0091] The processing with the Fig. The inclination of the beam axis 48 shown in Figure 5b can be continued for a certain time until the gas bubble 52 is sufficiently far away, cf. Fig. 5c. Then, the direction of the beam axis 48 is changed a third time by returning it to the standard direction. For this purpose, the processing light beam 34 is again directed perpendicularly to the surface 50 using the adjustment device 38. This state is shown in the Fig. 5d shown.

[0092] In the Fig. 5c and Fig. 5d shows that a small area 56 within the shadow 54 could not be reached by the processing light beam 34. However, the area 56 is so small that the cooling channel experiences a cross-sectional constriction there, but still remains permeable to the subsequent cooling fluid. If the gas bubble 52 is further away from the cooling channel 22 and / or the angles α1, α2 are increased in magnitude, the size of the unprocessed area 56 can be reduced. 4. Further examples

[0093] The following describes variants with which the remaining unprocessed areas 56 can be further reduced.

[0094] The Fig. 6a illustrates again (similar to the Fig. 3) the situation when the processing light beam 34 aligned along the standard direction hits the gas bubble 52 and therefore the direction of the beam axis 48 has to be changed.

[0095] As the Fig. As shown in Figure 6b, in this variant, the direction of the beam axis 48 in the mirror substrate is not effected by tilting the processing light beam 34, but by tilting the mirror substrate 12. This measure is necessary so that the processing light beam 48 can enter perpendicularly into a water bath 60 that was created on the surface 50 of the mirror substrate 12. For this purpose, barriers 62 are temporarily attached to the surface 50, of which Fig. 6b to 6d, only the barrier 62 running perpendicular to the paper plane is visible. Two barriers running parallel to the paper plane are not shown for reasons of clarity.

[0096] The barriers 62 together form a trough 64 from which the filled water 60 cannot flow out. The water 60 has a refractive index that is slightly lower than that of the mirror substrate 12. As a result, the processing light beam 34 is only slightly refracted at the surface 50 of the mirror substrate. As a comparison with the Fig. As shown in Figure 5b, a larger area within the shadow 54 can be reached by the processing light beam 34.

[0097] The Fig. 6c shows the processing at a later time, after the mirror substrate 12 has been moved against the process direction 42.

[0098] The processing is then continued on the opposite side of the gas bubble 52, as Fig. 6d. For this purpose, the mirror substrate 12 is tilted in the opposite direction and the trough 64 is mirror-symmetrically relocated. This allows the processing light beam 34 to process an area 56' which, during the Fig. 6a and Fig. 6b was not accessible to the processing light beam 34. As shown in the Fig. 6d, a small area 56 remains unprocessed in this variant as well, since it cannot be reached by the processing light beam 34 from any side.

[0099] The advantage of using a liquid is that it eliminates the need for polishing the surface 50. Without polishing, the surface 50 would be so rough that a large portion of the incident processing light beam 34 would be lost for processing due to scattering. Further explanations can be found below in Section 7.

[0100] In an alternative embodiment, the processing light beam does not pass through a liquid medium, but rather a solid medium that is directly adjacent to the surface 50 of the mirror substrate in the section through which the processing light beam 34 passes.

[0101] The Fig. 7a shows again the starting position as in the Fig. 6a. Here, too, processing is interrupted and the direction of the beam axis 48 is changed for the first time. For this purpose, a wedge 66 is placed on the surface 50, which has a wedge surface 68 running obliquely to the surface 50. In the illustrated embodiment, the wedge 66 consists of diamond, which has a refractive index of approximately 2.39. Since this is significantly higher than the refractive index of the substrate material (approximately 1.48), the processing light beam 34 is refracted at the interface between the wedge 66 and the surface 50 not towards the normal, but away from the normal. As a result, the processing light beam 34 can be directed even further below the gas bubble 52 into the shadow 54, see. Fig. 7b.

[0102] As the Fig. As shown in Figure 7c, the processing is continued in this configuration until the processing light beam 34 is far enough away from the gas bubble 52. The direction of the beam axis 48 is now changed a second time in order to process the area 56', which could not previously be reached by the processing light beam 34. In this processing step, the wedge 66 is not required, since the area 56' is far enough away from the shadow 54. An oblique beam axis 48 as in the Fig. 5a is sufficient to completely process the area 56', cf. Fig. 7d.

[0103] Then the direction of the beam axis 48 is changed a third time and returned to the standard direction, as shown in the Fig. 7e illustrated. 5. Rotationally asymmetric beam profile

[0104] The Fig. Figure 8 shows a processing device 30 according to another embodiment. Changes in the beam direction 48 are not effected by tilting the processing light beam 34, but by tilting the mirror substrate 12, as shown in the Fig. 8 is indicated by a dashed line. The traversing table on which the mirror substrate 12 is mounted during processing must therefore be tiltable about at least one rotational axis. Fig. The adjustment device 38 shown in Figure 2 can therefore be omitted.

[0105] For this purpose, the processing device 30 has a beam profile changing device 70 with which the beam profile of the processing light beam 34 can be changed. Generally, the light source 32 generates a processing light beam 34 that has a Gaussian and thus rotationally symmetrical beam profile. However, such a beam profile is relatively wide in the process direction 42, so that the processing light beam 34 reaches the gas bubble 52 early during processing, even though the focus 44 is still far from the shadow 54 (see FIG. Fig. 3).

[0106] The beam profile changing device 70 generates a beam profile that is narrower in the process direction 42, which runs parallel to the y-direction. Fig. 9a and Fig. Figure 9b shows the beam profile 71 in the xz-plane and the yz-plane, respectively. It can be seen that the beam profile 71 is significantly narrower in the y-direction than in the x-direction. The longest diameter of the beam profile (usually assumed to be the half-width of the Gaussian distribution) is at least twice as large as its shortest diameter.

[0107] If the processing light beam 34 is directed obliquely onto the mirror substrate 12 with a beam profile that is so narrow in the process direction 42 (ie the y-direction), as is the case with Fig. As illustrated in Figure 10, even areas just below the gas bubble 52 can be reached by the processing light beam 34. Perpendicular to the paper plane (i.e., in the x-direction), however, the processing light beam 34 is considerably wider. The beam axis 48 before and after the change in direction thus lies in the yz-plane, where the beam profile has its shortest diameter.

[0108] To convert the initially rotationally symmetric beam profile into the rotationally asymmetric beam profile according to the Fig. 9a and Fig. 9b, the beam profile changing device 70 can contain a plurality of cylindrical lenses or other anamorphic optical elements. The use of a diffractive optical element or a spatial light modulator is also possible, allowing different beam profiles to be quickly and flexibly adjusted. 6. Removing residues

[0109] The Fig. 11a shows in a Fig. 10 shows a cooling channel 22 already created in the mirror substrate 12. However, the inner surface 72 of the cooling channel 22 is not completely smooth, but rather has a residue 74. In the illustrated embodiment, this has the shape of a thorn-like elevation that extends from one side of the otherwise smooth inner surface 72 of the cooling channel 22 almost to the opposite side of the inner surface 72. The residue 74 thus significantly impedes the flow of a cooling liquid.

[0110] The residue 74 was caused by a gas bubble 52 located near the surface 50 of the mirror substrate 12. Here, it was assumed that the beam axis 48 of the processing light beam 34 was not tilted in the manner according to the invention. The resulting shadow 54 behind the gas bubble 52 therefore leads to the processing light beam 48 not being able to reach the substrate material in the area of ​​the residue 74, as is the case in the Fig. 4 is illustrated.

[0111] Even when using the method according to the invention, it can happen in individual cases that residues 74 remain in the cooling channel 22. If a gas bubble 52 is located differently than in the Fig. 11a shown not near the surface 50, but directly above the cooling channel 22, it is difficult to reach the area 54 shaded by the gas bubble 52 by a tilted processing light beam 34.

[0112] To remove the residue 74, a lance 76 is pushed into the cooling channel 22, as shown in Fig. 11b. In the illustrated embodiment, the lance 76 is a thin but comparatively stiff wire. The wire is just soft enough to follow curves in the cooling channel 22 and thus allow the lance to advance to the residue 74. If the free end 78 of the lance 76 hits the residue 74, as shown in the Fig. 11b, the force exerted by the lance 76 causes the residue 74 to break off, cf. Fig. 11c. If the residue 74 does not break off immediately or only a small piece of it, it may be useful to move the lance 76 back and forth several times, as shown in the Fig. 11c is indicated by a double arrow 79. Due to the mechanical action of the lance 76, the broken-off part of the residue 74 is usually broken up into smaller pieces, as shown in the Fig. 11d shows.

[0113] The Fig. Figure 12 shows a variant in which the lance 76 is not designed as a wire, but as a hose. The hose is connected to a pressure source (not shown), which ensures that water 82 or another liquid emerges from the open end 78 of the hose under pressure surges, as shown in the Fig. 12. In this variant, the residue 74 is not torn off by direct contact with the lance 76, but by the water 82 escaping from the hose under pressure.

[0114] The Fig. 13 shows a section of the Fig. 11c after breaking off the residue 74. As a rule, the fracture edge will not lie exactly on the inner surface 72 of the cooling channel 22. This leads to a protrusion 80 remaining even after removing the residue 74 with the aid of the lance 76, which protrudes from the otherwise smooth inner surface 72 of the cooling channel 22. The maximum height h of the protrusion 80 is, however, small and lies between 15 µm and 50 µm, as shown in the Fig. 13 is indicated.

[0115] If the mechanical removal with the aid of the lance 76 is followed by a chemical processing step, the maximum height h of the elevations 80 can be reduced to values ​​between 15 µm and 25 µm, cf. Fig. 14.

[0116] The inner surface 72 of the cooling channel 22 is therefore not completely smooth when using the lance 76, but has an elevation 80 with a maximum height h in the specified value ranges at locations where a gas bubble 52 or another inclusion has hindered the creation of the cooling channel 22 using the processing light beam 34. The gas bubble 52 is located between the surface 50 of the mirror substrate 12 and the cooling channel 22. The Fig. 13 and Fig. 14 The distance between the surface 50 and the cooling channel 22, designated by a, is typically between 20 mm and 30 mm. 7. Immersion

[0117] As already mentioned above in connection with the Fig. As explained in the exemplary embodiment shown in Figures 6a to 6d, the surface 50 of the mirror substrate 12 through which the processing light beam 34 passes must be very smooth so that a significant portion of the processing light beam 34 is not lost due to scattering at the surface 50. It can be shown that the surface roughness (arithmetic or root mean square) should be significantly smaller than the wavelength of the processing light beam 34. For typical wavelengths between 350 nm and 2200 nm, the surface 50 must therefore normally be smoothed in a separate upstream smoothing step (e.g., polishing or lapping) before processing with the processing light beam 34.

[0118] Such a smoothing step can be omitted if the surface 50 is covered with a film of a liquid 83 during processing with the processing light beam 34, as is the case with Fig. 15. As a result, the interface between the liquid 83 and the surrounding air 84 becomes the new surface 50'. Since liquids form a homogeneous and very smooth surface, the laser processing light beam 34 is not scattered by it.

[0119] Suitable liquids must be transparent to the processing light beam 34. Ideally, the liquid 83 has a similar refractive index to the mirror substrate 12 (so-called index-matching liquids). However, other liquids, such as water, can also be used, provided they are transparent to the processing light beam 34. If a liquid 83 with a refractive index different from that of the mirror substrate 12 is used, the offset resulting from the refraction must be taken into account when positioning the processing light beam 34.

[0120] The liquid 83 is held on the mirror substrate 12 by a border (not shown), which prevents it from flowing away. The border can consist entirely or partially of a sealing compound that is applied to the surface 50 of the mirror substrate 12. After processing with the processing light beam 34, the sealing compound must be removed again in a cleaning process.

[0121] Alternatively, the border can be formed by a specially manufactured component, which can be made of POM or Teflon, for example, and has a shape adapted to the surface 50 so that it can be easily attached. For differently shaped surfaces 50, components with different geometries must be kept in stock. Unlike a sealing compound, such a component can be reused.

[0122] The thickness d of the liquid film should be selected such that the surface 50 of the mirror substrate 12 is completely wetted, i.e., no parts of the substrate 12 should protrude. A value of approximately 1 µm can be considered the lower limit for the thickness. The upper limit of the thickness d of the liquid film is limited by the focal length of the focusing lens 36 and the possible dimensions of the border. Depending on the design of the processing device 30, the focusing lens 36 or the last optical element of the processing device 30 can also come into direct contact with the liquid 83, resulting in a classic immersion beam path. However, the processing device can also be separated from the liquid 83 by an air gap.

[0123] The choice of liquid 83 can also be used to change the distance of the focus 44 and / or its size without having to replace or adjust the optics of the processing device 30. If the refractive index of the liquid 83 is smaller than that of the mirror substrate 12 (cf. Fig. 16), the focus shifts 44 compared to identical refractive indices (cf. Fig. 15) deeper into the mirror substrate 12. If, however, the refractive index of the liquid 83 is greater than that of the mirror substrate 12, the focus 44 shifts towards the surface 50, cf. Fig. 17. In addition, the size of the focus 44 can be influenced by the refractive index of the liquid 83.

[0124] The liquid 83 can also be used to dissipate heat generated during processing from the mirror substrate 12. Due to the long-lasting processing with the high-energy processing light beam 34, heat is generated both in the vicinity of the cooling channel 22 and directly on the surface 50 of the mirror substrate by partial absorption of the processing light beam 34. In order to counteract a temperature increase of the mirror substrate 12, the liquid 83 can be continuously exchanged and tempered (e.g. with a thermostat), as is the case with the Fig. 18 shows. The liquid 83 is circulated by a pump 90 during short processing breaks via a return line 91, cooled in a cooling unit 92, and released from there back to the surface 50. If the pump 90 operates very evenly, the circulation of the liquid 83 can also be carried out during processing with the processing light beam 34. 8. Multiple processing light beams

[0125] It has been observed that, in certain configurations, the modifications in the substrate material generated by the processing light beam 34 are not limited to the area in which the cooling channels 22 are to be created. Since high energy densities are also generated in the space between the surface of the mirror substrate 12 and the cooling channel 22, undesired modifications to the substrate material can also occur there. Especially when the cooling channels 22 run at a very short distance, e.g., 1 mm to 5 mm, from the surface 50, even the smallest material modifications can have a noticeable impact on the optical function of the mirror.

[0126] The energy density in this area of ​​the mirror substrate 12 can be significantly reduced if, instead of a single processing light beam 34, several processing light beams 34 are used to create the cooling channels 22. These beams are directed onto the mirror substrate 12 from different directions. The incident light energy is then distributed over a significantly larger volume, reducing the energy density. At the focus 44, the processing light beams 34 constructively interfere spatially and temporally, ensuring the required high energy density is available there.

[0127] The Fig. Figure 19 schematically illustrates this approach. It shows three processing light beams 34a, 34b, and 34c with differently oriented beam axes 48a, 48b, and 48c, respectively.

[0128] It can be seen that the light is distributed over a larger volume in the area above the cooling channel 22, which is why undesired material modifications can no longer occur there. The beam axes 48a, 48b, 48c meet at the focus 44, so that the maximum energy is available there. Each processing light beam 34a, 34b, 34c can thus have a power that is reduced by approximately one third compared to the power that would be required with just a single processing light beam 34. Instead of three processing light beams, two or four processing light beams can also be used. The beam profile of the multiple processing light beams can, for example, correspond to a top-hat profile, as explained above. If gas bubbles 52 or other inclusions are located in the path of the processing light beams, the measures described in detail above can be taken. 9. Parallel processing

[0129] The task often arises to create multiple temperature control hollow structures in one substrate, or one (or a small number of) temperature control hollow structures in each of several substrates. To increase the cost-effectiveness of production, the invention produces multiple temperature control hollow structures simultaneously.

[0130] The simplest solution is to generate multiple processing light beams that are directed simultaneously onto the substrate. The processing light beams can then be directed independently onto the substrate using an array of small microscanners. However, currently available devices of this type do not allow the processing light beams to be controlled so that their foci are only a few millimeters apart. However, this is useful if, for example, several cooling channels are to be created that are closely spaced. While such closely spaced foci can be created in larger numbers using so-called photonic drill engines (PDEs), the focus positions cannot be controlled independently.

[0131] It is therefore proposed to use only one processing light beam, but to move it very quickly across the substrate using a polygon scanner. Commercially available polygon scanners achieve feed rates of up to several hundred m / s.

[0132] The Fig. 20 illustrates this in a Fig. 2. When the processing light beam 34 hits a rapidly rotating polygon mirror 94, it is deflected in different directions, as shown in the Fig. 20 is indicated by a dashed beam path. An F-theta lens, indicated here with only one focusing lens 36, focuses the processing beam 34, whereby the beam axis 48 always remains parallel, which corresponds to a telecentric beam path.

[0133] If a so-called z-shifter 96 is additionally used, the focus 44 can be freely positioned in a three-dimensional volume without changing the diameter of the focus 44, as is the case with zoom lenses

[0134] In order to prevent the processing light beam 34 from hitting locations that are not to be processed during the scanning movement, the processing light beam 34 can pass through a modulator 98, which allows only those of the high-frequency ultrashort light pulses generated by the light source 32 to pass through that are intended to reach the substrate 12 (so-called pulse picking), as is known per se in the prior art.

[0135] During operation, the processing light beam 34 travels at high speed along a line across the mirror substrate 12 and successively encounters the cooling channels 22. When the focus 44 sweeps over a gap between two adjacent cooling channels 22, the modulator 98, which is tuned to the scanning movement, prevents the emission of light pulses. Once the line has been completely processed, processing can be continued at a different height (i.e., z-coordinate), which is effected by appropriately controlling the z-shifter 96. If the depth range of the z-shifter 96 is large enough, cooling channels 22 can also be created in more than one plane, as is the case for the processing light beam 48 indicated by dashed lines in the Fig. 20 is shown.

[0136] In this way, directly adjacent cooling channels 22 can be processed quasi-simultaneously with only one processing light beam 34, without special manufacturing-related specifications regarding the distances between the cooling channels 22 or the like having to be observed. 10. Changes in the beam profile

[0137] It has already been mentioned above in section 8 with reference to the Fig. 8 to 10 explain that with the aid of a beam profile changing device 70, the beam profile of the processing light beam 34 can be changed in order to better guide the processing light beam past gas bubbles and other inclusions.

[0138] In the following, further aspects are described how material processing can be improved in different situations, especially with and without disturbing inclusions, by targeted modification of the beam profile. a) Top-Hat beam profile

[0139] The Fig. Figure 21 shows the beam profile of the processing light beam 34, ie the intensity distribution I(r) as a function of the radius r measured from the beam axis. If the light source 32 is a laser, the processing light beam 34 has a Gaussian beam profile 100, as shown in Fig. 21. The processing threshold for the process is indicated by a dashed line 102. The processing threshold 102 indicates the intensity above which the desired modifications in the substrate material occur. The intersection points of the processing threshold 102 with the beam profile 100 thus determine the width d soll of the material area modified by the processing light beam 34.

[0140] However, it has been shown that the processing threshold 102 is not exactly constant in time and space. This can be caused, for example, by material inhomogeneities in the mirror substrate 12. The oblique flanks of the Gaussian beam profile 100 result in fluctuations in the processing threshold 102 being directly translated into width fluctuations of the material area modified by the processing light beam 34, as shown in the Fig. 21. When the processing light beam 34 coincides with the Fig. 21 is focused in the mirror substrate 12, this can lead to uneven cross sections of the cooling channel 22.

[0141] The Fig. 8, therefore, converts the Gaussian beam profile 100, as generated by the light source 32, into a top-hat beam profile 104, as shown in the Fig. 22 is indicated by a solid line. In the top-hat beam profile 104, the flanks of the profile are considerably steeper than in the Gaussian beam profile 100, which is shown in the Fig. 22 is indicated by a dotted line. Therefore, local and temporal changes in the processing threshold 102 have less of an impact on the width of the material area modified by the processing light beam 34. A cooling channel 22 created with the top-hat beam profile 104 therefore has a more uniform cross-section. Furthermore, less energy is lost unused with a top-hat beam profile 102. The higher efficiency enables higher process speeds and reduces the heat input into the substrate material.

[0142] To convert the Gaussian beam profile 100 into the top-hat beam profile 104, the radiant energy guided in the processing light beam 34 must be redistributed radially. For this purpose, the beam profile changing device 70 can contain a diffractive optical element (DOE) that changes the angular distribution of the incident processing light beam 34. The desired top-hat beam profile 104 is then obtained behind the focusing lens 36, which acts as a Fourier optic.

[0143] Preferably, the diffractive optical element is interchangeably received in an exchange holder so that it can be exchanged for a diffractive optical element with different properties. b) Donut beam profile

[0144] The Fig. Figure 23 shows a donut beam profile 106 generated by a different diffractive optical element. As the comparison with the Gaussian beam profile 100 shows, with the donut beam profile 106, even more radiation energy is shifted outward from the center of the processing light beam 34, resulting in a drop in intensity along the beam axis. The greatest radiation energy is thus not achieved along the beam axis, but rather at a distance from it. With the donut beam profile 106, the flanks of the profile are also steeper than with the Gaussian beam profile 100, creating cooling channels 22 with a more uniform cross-section.

[0145] The donut beam profile 106 has additional advantages when gas bubbles or other inclusions are present in the light path of the processing light beam 34. The Fig. Figure 24 schematically shows an enlarged section of the mirror substrate 12 and the processing light beam 34 penetrating therein, which is to be focused into the focus 44. It is assumed that a gas bubble 52 is located in the mirror substrate 12, specifically on the beam axis of the processing light beam 34. As explained in connection with the Fig. As already explained in Figure 3, the gas bubble 52 acts like a spherical lens, which is why processing light incident on the gas bubble 52 does not reach the focus 44. The gas bubble 52 thus effectively leads to the shadowing indicated at 54.

[0146] If the processing light beam 34 has a Gaussian beam profile 100, as shown in the Fig. 24 is indicated by a dashed line, the gas bubble 52 causes a larger portion of the energy guided in the processing light beam 34 to not reach the focus 44. As a result, the processing threshold 44 may not be exceeded there, or may only be exceeded in a very small area. As a result, material is not modified in certain locations, so that potentially disruptive residues 74 remain in the cooling channels 22.

[0147] However, if the processing light beam 34 reaches the Fig. 23, the shading effect of the gas bubble 52 is lower, as shown by the Fig. 25. Since the processing light beam 34 carries comparatively little energy along the beam axis, the shadowing by the gas bubble 52 has a less severe effect on the intensity in the focus 44, which leads to more uniform processing results. c) Axicon elements

[0148] If the gas bubble 52 is particularly large, the Fig. The donut beam cross-section 106 shown in Figure 23 does not provide a significant improvement. Such an improvement is only possible if even more light energy is shifted from the beam center to the outside.

[0149] A variably adjustable radial redistribution of the radiation energy to the outside is possible if the beam profile changing device 70 contains a pair of axicon elements 108, 110, as shown in the Fig. 26a to 26c. The axicon elements 108, 110 have a variable spacing b. For this purpose, for example, the second axicon element 110 can be arranged to be movable along the optical axis OA with the aid of an actuator (not shown).

[0150] In the Fig. In the configuration shown in Figure 26a, the two axicon elements 108, 110 touch each other, i.e. the distance b is 0. In this configuration, the pair of axicon elements 108, 110 has no effect on a collimated processing light beam 34.

[0151] If the second axicon element 110 is displaced to the right by an amount b, the refraction of light at the conical axicon surfaces results in a redistribution of radiation energy from the inside to the outside, as shown by the Fig. 26b. This results in a ring-shaped beam profile in which a central cylindrical region 112 with a radius r i remains free of light. If the radius r i are increased, the distance b between the axicon elements 108, 110 is increased accordingly, as shown in the Fig. 26c illustrated.

[0152] By varying the distance b between the axicon elements 108, 110, an annular beam profile can be created in which no light is located in a central region 114. The radius r i the central region 114 can be adapted to the size of the gas bubbles 52. d) Beam profile modification device with micromirror array

[0153] Preferred is a processing of the mirror substrate 12 in which, in the absence of gas bubbles 52 and other inclusions, the processing light beam 34 has the exemplary Fig. 22. If the mirror substrate 12 is measured before processing in order to determine the locations of the gas bubbles 52, it is possible to predict when in the processing process the beam profile of the processing light beam 34 will differ from that shown in the Fig. 22 shown top-hat beam profile 104 to that shown in the Fig. 23 shown donut beam profile 106 must be changed. Thus, while the processing light beam 34 inscribes the cooling channel 12 into the mirror substrate 12, the beam profile of the processing light beam 34 repeatedly changes between the Fig. 22 shown as an example top-hat beam profile 104 and the one in the Fig. 23 example of the donut beam profile 106.

[0154] Replacing diffractive optical elements in an exchangeable holder is too slow to perform the above-mentioned change between different beam profiles 104, 106. In this case, the beam profile changing device 70 can contain a micromirror array 116, with which the angular distribution of the processing light beam 34 can be changed quickly and flexibly.

[0155] In the Fig. In the embodiment shown in a schematic cross-section in Figure 27, the beam profile changing device 70 comprises an M-prism 118, whose inclined boundary surfaces 120, 122 direct the incident processing light beam 34 onto the micromirror array 116 and the light beams reflected therefrom onto the Fourier lens 124, which collimates the incident light beams. For this purpose, the micromirror array 116 comprises a plurality of individually tiltable micromirrors 126, which can be continuously tilted by individually adjustable angles within a predetermined angular range.

[0156] In the Fig. 27, only 5 such tiltable micromirrors 126 are visible; in real systems, several hundred or even several thousand micromirrors 126 can be arranged two-dimensionally, whereby largely arbitrary intensity distributions and thus beam profiles can be generated behind the Fourier lens 124.

[0157] In the Fig. In the constellation of mirror positions shown by way of example in Figure 27, for example, two light beams 128a, 128b located inside in front of the micromirror array 116 and two light beams 130a, 130b located outside exchange their roles, ie the light beams 128a, 128b are located outside behind the Fourier lens 124 and the light beams 130a, 130b are located inside.

[0158] Since the switching of the micromirrors 126 only takes a few milliseconds, the Fig. 27, a very rapid change of the beam profile during processing can be achieved. 11. Measurement of inclusions

[0159] A known method that can be used to locate gas bubbles 52 and other inclusions has already been described above. In this known method, a camera is used to capture scattered light caused by the inclusions when the mirror substrate 12 is illuminated.

[0160] Further methods are explained below that enable even better localization of the inclusions. a) Ultrashort laser pulses

[0161] The Fig. Figure 28 shows a measurement setup that can be used to locate gas bubbles 52 and other inclusions using ultrashort light pulses.

[0162] The measurement setup comprises a trough 140 for holding the mirror substrate, which is filled with a liquid 141 whose refractive index matches the refractive index of the mirror substrate 12 to be measured as closely as possible. As a result, light is not refracted at the surface of the mirror substrate 12, or at most, to a negligible extent. This significantly simplifies the measurement, especially with irregularly shaped mirror substrates 12. If no liquid 141 is used, the geometry of the mirror substrate 12 must be precisely measured so that the refraction occurring at the surface and any total internal reflection can be mathematically accounted for. Such an immersion measurement is also useful for other optical measurement methods.

[0163] The measurement setup also includes a first measurement unit with a first light source 142a and a first detector 144a. The first light source 142a can be configured, for example, as an LED and generates ultrashort, broadband light pulses. The center wavelength of the generated light is matched to the mirror substrate and the liquid 141 with the aim of achieving the highest possible transparency and can be, for example, 2 µm for mirror substrates made of glass-ceramic; the pulse duration is preferably between 10 fs and 50 fs.

[0164] Passage of such a short and in the Fig. When the light pulse indicated at 146 in FIG. 28 strikes the mirror substrate 12 and the surrounding liquid 141, a broadening of the light pulse occurs due to chromatic dispersion. The broadened light pulse 148 is received by the first detector 144a and subsequently analyzed. The first detector 144a can directly measure the pulse duration. Alternatively, the phase front and / or the spectrum of the light pulse 148 can be measured, from which the pulse duration can be derived.

[0165] In order to measure the entire mirror substrate 12, the first measuring unit is moved relative to the mirror substrate 12 (or vice versa), as shown in the Fig. 28 is indicated by a horizontal arrow. This creates a 2D grid of measuring points in a plane perpendicular to the paper plane of the Fig. 28. If a gas bubble 52 is located in the light path at a measurement position, no dispersion occurs in the region of the gas bubble, with the result that the light pulse 148' received by the first detector 144a is somewhat less broadened. Thus, at measurement positions where the broadening is less than usual, a gas bubble 52 is present. The diameter of the gas bubble 52 can be determined from the extent to which the broadening deviates at a given measurement position.

[0166] Since the longitudinal position of the light path at which the gas bubble 52 is located is unknown, additional measurements along a different direction are required. For this purpose, the measurement setup includes a second measuring unit, which is configured identically to the first measuring unit and thus has a second light source 142b and a second detector 144b. The second measuring unit is aligned orthogonally to the first measuring unit in order to be able to measure the mirror substrate in the transverse direction. By correlating the measurements, the location of the gas bubble 52 in the mirror substrate 12 can be determined.

[0167] If the liquid 141 and the mirror substrate 12 absorb only a small amount of the light generated by the light sources 142a, 142b, gas bubbles 52 can be measured at all locations on the mirror substrate 12 without requiring high light outputs, which could lead to damage to the substrate material. The larger the bandwidth of the light pulses 146, the greater the broadening of the light pulses 146 due to dispersion, which in turn increases measurement accuracy. In contrast to the image-based measurement methods mentioned above, gas bubbles 52 with a diameter of only 50 µm or less can be localized in this way. b) Incoherent lensless imaging

[0168] The Fig. Figure 29 shows a measurement setup with which gas bubbles 52 and other inclusions can be detected using incoherent lensless imaging. Systems for incoherent lensless imaging are very inexpensive and require only a detector 150 comprising a standard 2D image sensor 151 and an amplitude mask 152, as well as a light source 154 and an evaluation unit 156. The light source 154, which can be an LED, for example, generates incoherent light 158 ​​with a wavelength for which the mirror substrate 12 is transparent. The incoherent light 158 ​​is scattered by the gas bubbles 52 and detected by the detector 150.

[0169] As the Fig. 29 shows, the amplitude mask 152 is located immediately in front of the image sensor 151, so that the detector 150 can have a thickness of less than 1 mm with side dimensions of, for example, 8 mm x 8 mm.

[0170] The incoherent lensless imaging method, also known as "FlatScope," is described in detail, for example, in a paper by Adams JK et al. entitled "Single-frame 3D fluorescence microscopy with ultraminiature lensless FlatScope," Sci Adv. 2017 Dec 8;3(12):e1701548. Doi: 10.1126 / sciadv.1701548. PMID: 29226243; PMCID: PMC5722650. Compared to previously known lensless imaging methods, the FlatScope method is characterized by an optimized arrangement of the apertures in the amplitude mask 152, which modulates the incoherent point spread function, enabling the recovery of high-frequency spatial information.

[0171] Furthermore, the amplitude mask 152 of the FlatScope method allows the complexity of the image reconstruction algorithm to be reduced so that the image can be reconstructed from the measurement data of the image sensor 151 almost in real time. This real-time capability makes it possible to measure the mirror substrate 12 while the processing light beam 34 is already modifying the substrate material at other locations. The measurement results are then incorporated in real time into the planning of the subsequent processing sequence.

[0172] A further advantage of the FlatScope method is that sharp images can be calculated over a wide distance range without requiring the distance between the detector 150 and the mirror substrate 12 to be known. Mirror substrates 12 with conventional dimensions can be measured in this way with just a single image.

[0173] In the Fig. In the variant shown in Figure 30, the direction of the illumination is varied. Two or more detectors 150a, 150b and two or more light sources 154a, 154b can be used for this purpose. Alternatively, measurements can be performed successively to allow time to move a single detector 150 and / or a single light source 154. Varying the direction of illumination is advantageous because it allows the angle dependence of the light scattering at the gas bubbles 52 to be utilized. 12. Process monitoring

[0174] To avoid rejects and / or costly reworking of the mirror substrates 12, the creation of the cooling channels 12 should be continuously monitored using the processing light beam 34. Such monitoring can, for example, involve measuring the position of the processing light beam 34 relative to the mirror substrate 12. This can utilize the effect that the processing light beam 34 generates a colored plasma in glass. A measuring camera that captures the plasma then provides information on the location of the processing light beam 34 in the mirror substrate 12.

[0175] More complex measuring instruments such as spectrographs, which allow conclusions about the process flow from the spectrum of the process light generated during processing, can also be considered. Within the scope of process monitoring, for example, the process can be aborted if measured values ​​​​exceed specified measuring ranges.

[0176] The simplest approach is to arrange measuring cameras and other measuring instruments in the half-space adjacent to the surface 50 of the mirror substrate 12 and in which the processing device 30 is also located. The latter should be aligned with the mirror substrate 12 such that the processing light beam 34 strikes the polished surface 50 of the mirror substrate 12 perpendicularly.

[0177] Although the Fig. 2 is not to scale, it is clear from this illustration that the available space in this half-space is predominantly occupied by the processing device 30. Therefore, it is difficult to arrange measuring instruments near the processing device 30. This applies even more so to processing devices 30 that simultaneously generate several processing light beams 34 for parallel processing (see item 9 above) and therefore have correspondingly larger dimensions.

[0178] The Fig. 31 shows in a Fig. 2, the schematic representation shows the mirror substrate 12 and the processing device 30 arranged in the half-space above it, with the light source 32. Also shown are three measuring cameras 160, which capture the surfaces on two opposite transverse sides and on the back of the mirror substrate 12 and are therefore arranged outside the said half-space. These surfaces are generally not polished, but matte, so that the process light emerging from them is scattered and can thus be easily captured by the measuring cameras 160. With the help of the measuring cameras 160, the position of the processing light beam 34 within the mirror substrate 12 can be continuously measured during laser processing.

[0179] Instead of the measuring cameras 160 or in addition to them, photodiodes for measuring light intensity, spectroscopes for wavelength-resolved detection of plasma, vibrometers for measuring mechanical vibrations and polarization measuring instruments for measuring material stresses can be used as measuring instruments.

[0180] The advantage of the Fig. The advantage of the arrangement of the measuring instruments shown in Figure 31 on the surface not penetrated by the processing light beam is primarily that more or larger measuring instruments can be used than is possible in the limited installation space near the processing device. Conversely, more space remains for the processing device, for example, to be able to direct even more processing light beams 34 simultaneously onto the mirror substrate 12. 13. Projection exposure system

[0181] The Fig. Figure 32 shows a semiconductor technology system using the example of a projection exposure system 200 for EUV semiconductor lithography. Other semiconductor technology systems, such as a mask inspection system or a wafer inspection system, sometimes contain the same or similar components, as explained here using the example of the EUV projection exposure system 200.

[0182] The projection exposure system 200 comprises an illumination system 202 with a radiation source 204 and illumination optics 206 for illuminating an object field 208 in an object plane 210, in which a reflective reticle 212 is arranged. In the illustrated embodiment, the radiation source 204 is an EUV radiation source that emits EUV radiation as working radiation 214, in particular in a wavelength range between 5 nm and 30 nm. The radiation source 204 can be a plasma source, for example, an LPP (Laser Produced Plasma) source or a GDPP (Gas Discharged Produced Plasma) source. Alternatively, a synchrotron-based radiation source or a free-electron laser (FEL) can be used as the radiation source 204.

[0183] In addition, the projection exposure system 200 comprises a projection optics 216 for imaging the object field 208 into an image field 218 located in an image plane 220 of the projection optics 216. A wafer 222 carrying a light-sensitive layer (resist) is arranged in the image plane 220. Components for the synchronous movement of the reticle 212 and the wafer 222 are included in the Fig. 32 only indicated and not provided with reference symbols.

[0184] The projection exposure system 200 comprises a plurality of mirrors Mn, which are numbered according to their arrangement in the beam path of the projection exposure system 200. In the present case, a total of 10 mirrors M1 to M10 are present in the beam path.

[0185] The mirrors M3 and M4 are designed as facet mirrors containing a plurality of individual mirrors. The remaining mirrors Mn are each a mirror 10 with a monolithic mirror substrate 12 and a coating 16 carried thereon, as shown in the Fig. 1. For the sake of simplicity, these mirrors are shown in the Fig. 32 is indicated as a cuboid. However, the surfaces of the mirrors 10 exposed to the EUV radiation 214 and provided with the coating 16 are not planar in reality, but curved.

[0186] Mirrors M1 to M4 in illumination system 206 serve to illuminate a section of reticle 212 with the desired illumination angle distribution. Mirrors M5 to M10 of projection optics 216 project this section onto wafer 222 in a reduced size. As a result, the structures contained in reticle 212 are imaged onto the light-sensitive layer supported by wafer 222. 14. Concluding remarks

[0187] All of the exemplary embodiments explained above, as well as individual process steps, concepts, or design principles, can be combined with one another. For example, gas bubbles 52 can first be localized using the methods and devices described above under item 11, while processing with multiple processing light beams 34 is carried out in immersion according to the methods and devices described above under item 9, as explained above under item 7. Process monitoring can be carried out as explained above under item 12. Gas bubbles 52 can be avoided during processing using the methods described above under items 3 to 5; remaining residues can be removed using the methods and devices explained above under item 6. 15. List of reference symbols 10 mirrors 12 Mirror substrate 14 Carrier surface 16 Coating 18 EUV light 20 double shifts 22 Cooling channel 24 pump unit 26 Cooling unit 28 Return line 30 processing equipment 32 light source 34 processing light beam 36 Focusing lens 38 Adjustment device 40 tilting mirrors 42 Process direction 44 Focus 45 Travel table 46 Control device 48 beam axis 50 surface 52 Gas bubble 54 Shading 56 unprocessed area 60 water bath 62 Barrier 64 tub 66 Wedge 68 wedge surface 70 Beam profile changing device 72 interior surface 74 behind 76 Lance 78 free end of the lance 79 Double arrow 80 Survey 82 Water 83 Liquid 90 pump 91 Return line 92 Cooling unit 94 polygon mirrors 96 z-shifter 98 Modulator 100 Gaussian beam profile 102 Processing threshold 104 Top-Hat beam profile 106 Donut beam profile 108 first axicon element 110 second axicon element 112 cylindrical area 114 central area 116 micromirror array 118 M-Prism 120 interface 122 Interface 124 Fourier lens 126 micromirrors 128a Light beam 128b light beam 130a light beam 130b light beam 140 tub 141 Liquid 142a first light source 142b second light source 144a first detector 144b second detector 146 light pulses 148 received light pulses 148' received light pulse after passing through gas bubble 150 detector 150a first detector 150b second detector 151 image sensor 152 Amplitude mask 154 Light source 156 Evaluation unit 158 incoherent light 200 projection exposure system 202 Lighting system 204 Radiation source 206 Lighting optics 208 Object field 210 Object level 212 reticles 214 Working radiation 216 Projection optics 218 image field 220 image plane 222 wafers 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 2021 214 310.5

[0008] Cited non-patent literature

[0000] Kuang, Zheng et al. “Ultrafast laser beam shaping for material processing at imaging plane by geometry masks using a spatial light modulator”, Optics and Lasers in Engineering 70 (2015): 1-5

[0065] Adams JK et al. entitled “Single-frame 3D fluorescence microscopy with ultraminiature lensless FlatScope”, Sci Adv. 2017 Dec 8;3(12):e1701548. Doi: 10.1126 / sciadv.1701548. PMID: 29226243; PMCID: PMC5722650

[0170]

Claims

[1] Method for producing a tempering hollow structure in a substrate, in particular in a mirror substrate for a semiconductor technology system, comprising the following steps: a) providing the substrate (12) consisting of a substrate material; b) measuring where inclusions (52) are located in the substrate; c) machining the tempering hollow structure (22) into the substrate (12) by successively focusing a processing light beam (34) with a beam axis (48) aligned along a standard direction onto processing locations (44) at which the tempering hollow structure (22) is to be created, whereby the substrate material is modified or removed at the processing locations (44); characterized bythat in step c), at least if an inclusion (52) measured in step b) would be located on the beam axis (48) aligned along the standard direction, the direction of the beam axis (48) relative to the substrate (12) is changed such that the beam axis (48) does not intersect the inclusion (50). [2] Method according to claim 1, characterized by that the tempering hollow structure is a channel (22) and the standard direction is at least substantially perpendicular to a longitudinal axis of the channel (22). [3] Method according to claim 1 or 2, characterized by that at each inclusion (52) the direction of the beam axis (48) is changed at least twice. [4] Method according to claim 3, characterized bythat the tempering hollow structure (22) is produced along a process direction (42), and that the first time the direction of the beam axis (48) changes by a first angle α1 with respect to the standard direction such that the processing light beam (34) is directed under the inclusion (52) as seen in the process direction (42), and that the second time the direction of the beam axis (48) changes by a second angle α2 with respect to the standard direction such that the processing light beam (34) is directed under the inclusion (52) as seen against the process direction (42). [5] Method according to one of the preceding claims, characterized bythat the processing light beam (34) passes at least once, when its beam axis (48) is not aligned parallel to the standard direction, through a liquid or solid medium (60; 66) which is directly adjacent to a section of the surface (50) of the substrate (12) through which the processing light beam (34) passes. [6] Method according to claim 5, characterized by that the medium (60) is liquid and the section of the surface (50) of the substrate (12) is arranged inclined such that a horizontal surface of the liquid medium (60) facing the surrounding atmosphere is perpendicular to the incident processing light beam (34). [7] Method according to claim 5, characterized by that the medium (66) is solid, has a greater refractive index than the substrate (12) and has a surface facing away from the substrate (12) which is perpendicular to the incident processing light beam (34). [8] Method according to claim 7, characterized bythat the medium (66) has the shape of a wedge (66) or truncated wedge. [9] Method according to one of the preceding claims, characterized by that the processing light beam (34) has a rotationally asymmetric beam profile (71) upon entering the substrate (12), wherein the longest diameter of the beam profile (71) is at least twice as large as the shortest diameter, and that the beam axis (48) lies before and after the change in its direction in a plane in which the beam profile (71) has its shortest diameter. [10] Method according to claim 9, characterized by that the processing light beam (34) passes through an anamorphic optical element before entering the substrate (12). [11] Method according to one of the preceding claims, characterized by that residues in the tempering cavity structure (22) are mechanically broken up. [12] Method according to claim 11, characterized bythat the residues in the tempering cavity structure (22) are broken up by inserting a lance (76) into an already produced tempering cavity structure (22) or into the substrate during the production of a tempering cavity structure (22). [13] Method according to claim 11, characterized by that after or during insertion of the lance (76) the tempering hollow structure (22) is rinsed with a chemically active medium, whereby the residues (74) are further removed. [14] Substrate (12) with a tempering cavity structure (22) having a smooth inner surface (71), wherein the substrate (12) consists of glass or a glass ceramic and has at least one inclusion (52), characterized by that the inner surface (71) has a locally limited elevation (80) with a height h between 15 µm and 50 µm, which elevation does not contribute to the function of the tempering hollow structure (22). [15] Substrate according to claim 14 characterized bythat the maximum height of the elevation (80) is less than 25 µm. [16] Substrate according to one of claims 14 or 15, characterized by that the tempering hollow structure (22) has an area of ​​at least 2 mm x 50 cm. [17] Substrate according to one of claims 14 to 16, characterized by that a distance of the tempering hollow structure (22) from a surface (50) of the substrate is between 20 mm and 50 mm, and that the inclusion (52) is located between the surface (50) and the tempering hollow structure (22). [18] A mirror (10) comprising a substrate (12) according to any one of claims 14 to 17 and a coating (16) carried by a support surface (14) of the substrate (12). [19] Mirror according to claim 18, characterized by that the tempering hollow structure extends from the carrier surface (14) at a distance of 1.0 mm to 50.0 mm, from 1.0 mm to 20.0 mm, from 1.0 mm to 10.0 mm or from 1.0 mm to 5.0 mm. [20] Mirror according to claim 18 or 19, characterized by that the inclusion (52) is located between the carrier surface (14) and the tempering hollow structure (22). [21] Mirror with a tempering hollow structure (22) having a smooth inner surface (71), wherein the substrate (12) consists of glass or a glass ceramic, characterized by that the inner surface (71) has a locally limited elevation (80) which does not contribute to the function of the tempering hollow structure (22) and has a height h of between 15 µm and 50 µm, and that the tempering hollow structure (22) extends from the carrier surface (14) at a distance of 1.0 mm to 50.0 mm, from 1.0 mm to 20.0 mm, from 1.0 mm to 10.0 mm or from 1.0 mm to 5.0 mm. [22] Semiconductor technology plant with a mirror according to one of claims 18 to 21 and / or with a substrate according to one of claims 14 to 17 and / or with a substrate produced by a method according to one of claims 1 to 13.

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