Workpiece having a hollow structure, method for forming a hollow structure at least partially, mirror, and lithography system

Abstract

The present invention relates to a workpiece comprising at least one hollow structure (27) extending into the workpiece (25) and configured to allow a fluid (28) to flow through it. The hollow structure (27) has a first portion and an adjacent second portion oriented at an angle (γ) of 60° to 120° with respect to each other. The hollow structure (27) has rounded portions (37a, 37b) where the first portion and the second portion merge with each other. The surface of the walls of the hollow structure (27) of the first portion, the second portion, and / or the rounded portions (37a, 37b) has a roughness R of 25 μm or less, preferably 10 μm or less, particularly preferably 5 μm or less, and particularly 2 μm or less. a The present invention also relates to a method for forming a hollow structure (27) in a workpiece (25) at least partially by selective laser-induced etching. The present invention also relates to a mirror, in particular an EUV mirror (24), comprising a workpiece in the form of a substrate (25) configured as described above, and a reflective coating (26) applied to the surface (25a) of the substrate (25) that reflects radiation, in particular EUV radiation (16). The present invention also relates to a lithography system, in particular an EUV lithography system, comprising at least one of the above workpieces and / or at least one of the above mirrors (M4).

Description

[Technical Field]

[0001] The present invention relates to a workpiece, preferably a substrate for a mirror, more particularly a substrate for an EUV mirror, comprising at least one hollow structure extending within the substrate and configured to allow fluid to flow through it. The present invention also relates to a method for forming at least partially a hollow structure in a workpiece. The present invention also relates to a mirror, more particularly an EUV mirror, comprising a workpiece in the form of a substrate configured as described above. The present invention further relates to a lithography system, more particularly an EUV lithography system, comprising at least one mirror configured as described above and a temperature control device, more particularly a cooling device, configured to flow a temperature control fluid, more particularly a cooling fluid, through at least one hollow structure. [Background technology]

[0002] A lithography system may be a lithography apparatus for exposing a wafer, or any other optical apparatus used in lithography, such as an inspection system for measuring or inspecting masks, wafers, etc., used in lithography. A lithography system may be configured to operate with radiation in the EUV wavelength range, for example. In this application, the EUV wavelength range is understood to be a wavelength range of approximately 5 nm to approximately 30 nm.

[0003] In EUV lithography systems, such as EUV lithography apparatuses, optical elements that reflect radiation, particularly mirrors in projection systems, are exposed to high radiation output. As the output of the EUV radiation source increases, the average output radiated to the mirror can reach 50W, one-third of which is absorbed by the reflective coating layer system, leading to widespread and localized heating of the mirror or substrate. Even when using so-called zero-expansion materials, such as titanium-doped quartz glass or glass-ceramic, this heating alters the shape of the mirror surface coated with the reflective coating. These shape changes are particularly related to the linear thermal expansion (CTE) or zero-crossing temperature (T) within the volume of the substrate. ZCThis is due to the non-uniformity of the temperature and the fact that the coefficient of thermal expansion deviates significantly from zero when the temperature is outside the zero-crossing temperature range.

[0004] To lower the temperature of the mirror in an EUV lithography system, it is known to introduce a hollow structure in the form of a cooling channel into the mirror substrate and to flow a cooling fluid through this hollow structure. Such channels can be fabricated by milling the substrate and then closed with a cover.

[0005] Because of the mirror suspension mount and its generally unfavorable effects on image aberration, turbulence and vibration ("flow-induced vibrations," FIV) caused by the flow of the cooling medium (generally liquid) should be avoided. However, the inside of milled flow channels is generally angular and rough, which is unfavorable with respect to FIV.

[0006] Selective laser-induced etching (SLE) makes it possible to form microchannels, contoured holes, and other features in transparent components made of materials such as quartz glass, borosilicate glass, sapphire, or ruby. In selective laser-induced etching, light in the form of ultrashort pulse laser radiation (ps or fs pulses) is focused onto a volume (focal volume) of the transparent workpiece. In this case, the pulse energy is absorbed only within the focal volume as a result of a multiphoton process. Within the focal volume, the optical and chemical properties of the transparent material change without cracking, or possibly with microcracks, making it selectively chemically etchable. Depending on the laser parameters used, the material modification may be microcracks or other deep damage. For example, by deflecting the focus within the material using a microscanner system, a continuous region (continuous irradiation volume) is modified, which can then be removed by wet chemical etching. In wet chemical etching, it is preferable to immerse the component in an etching solution, usually for several weeks or months, allowing the etching solution to (selectively) remove the modified material. By scanning or moving laser radiation within the volume of the workpiece, a desired hollow structure, such as a flow channel, can be fabricated.

[0007] One limiting factor in selective laser-induced etching of flow channels in fused silica and other materials, such as titanium-doped fused glass, is that the etching selectivity is relatively low, at about 1:500 to about 1:1500, compared to other transparent materials, such as sapphire, which has an etching selectivity of 1:1000. Due to the low etching selectivity, during etching, the region at the edge of the component where the etching solution first acts forms a flow channel in a wider form than the interior of the component's volume. An overly wide region can lead to non-uniform cooling of the component and, in some cases, may mechanically penetrate. In extreme cases, if the etching is too strong, a short circuit may occur between adjacent flow channels. Generally, the conical flow channel cross-section that occurs when the etching selectivity is insufficient is also undesirable.

[0008] Patent Document 1 describes an optical element that reflects EUV radiation and in which at least one flow channel through which a cooling medium can flow is preferably formed. The substrate is formed from fused silica, particularly titanium-doped fused silica, or glass ceramic. The flow channel has a length of 10 cm or more, and the cross-sectional area of the flow channel has a variation of + / - 20% or less over the length of the flow channel. Patent Document 1 states that flow channels with such characteristics are usually fabricated by selective laser-induced etching, and that the etching selectivity should be improved to fabricate such flow channels. The interior of such flow channels may have a small roughness.

[0009] Patent Document 2 describes a method for manufacturing a component of a projection exposure apparatus for semiconductor lithography, in which a hollow structure is fabricated in a component, such as a mirror body, by selective laser-induced etching. The hollow structure can be configured as a temperature control flow channel that extends between two perforations that serve as inlets and outlets for a temperature control fluid within the temperature control plane and in a direction perpendicular to the temperature control plane within the temperature control plane. The temperature control flow channel is connected to the perforations via two 90° bends.

Prior Art Documents

Patent Documents

[0010] [Patent Document 1] International Publication No. 2021 / 115643 [Patent Document 2] German Patent Application Publication No. 102019200750 [Summary of the Invention] [Problems to be Solved by the Invention]

[0011] An object of the present invention is to provide a workpiece, a mirror, and a lithography system that reduce flow-induced vibration that occurs when a fluid flows through a hollow structure. [Means for Solving the Problems]

[0012] This object is achieved by a workpiece of the aforementioned type, wherein the hollow structure has a first part and an adjacent second part that are oriented at an angle of 60° to 120° with respect to each other, preferably an angle of 80° to 100°, particularly an angle of 90°, and the hollow structure has a rounded portion where the first part and the second part merge with each other, and the surface of the wall of the hollow structure of the first part, the second part, and / or the rounded portion has a roughness R of 25 μm or less, preferably 10 μm or less, particularly preferably 5 μm or less, especially 2 μm or less. a The roughness R, also referred to as the average roughness, indicates the average distance of the measurement points on the surface from the average line of the surface. Therefore, the average roughness corresponds to the arithmetic mean of the absolute value deviations from the average line. a

[0013] In the recognition of the present inventors, considering the normal flow velocity of the fluid flowing through the hollow structure, especially when the two parts of the hollow structure of the workpiece are oriented substantially perpendicular to each other (i.e., at an angle of 60° to 120°), at the transition between the two parts in the form of an angle or a sharp edge, flow separation that causes turbulent flow and induces flow-induced vibration occurs on the wall of the hollow structure. For this reason, it is proposed that the two parts of the hollow structure merge with each other at a rounded portion having a streamline profile as much as possible.

[0014] ​The rounded portion is understood to mean a portion without corners. As a result, the first portion continuously merges with the second portion at the rounded portion. The cross-section or diameter of the hollow structure is usually constant within the rounded portion, but may vary arbitrarily. Generally, the cross-section or diameter of the rounded portion corresponds to the cross-sections of the two portions, but this is not mandatory when the rounded portion is located at a branching point (see below).

[0015] Hollow structures with rounded portions can be fabricated completely or partially by selective laser-induced etching. The hollow structure has walls that form the interface between the interior of the hollow structure and the material of the workpiece. In particular, when fabricating hollow structures by selective laser-induced etching, reducing the surface roughness of the walls of the hollow structure can counteract the generation of flow-induced vibrations. This is especially advantageous for the rounded portions mentioned above. Generally, both the rounded portions and the first and second portions satisfy the above-mentioned roughness requirements.

[0016] For the fabrication of the aforementioned workpieces, it is advantageous to improve the etching selectivity ratio, especially during selective laser-induced etching. The etching selectivity ratio can be improved in various ways, for example, by following the etch front with a flexible hose. Rounded sections facilitate such hose following. If the microscopic roughness of the surface of the hollow structure's walls is too large, the hose may get caught, especially on the rounded parts of the walls. Therefore, if the surface roughness of the hollow structure's walls is small, such hose following will also be easier.

[0017] According to one embodiment, the surface of the wall of the hollow structure has a recess. In this case, the surface of the inner wall of the hollow structure has a surface structure having a recess, which will be referred to below as a depression or recess, and is usually concave.

[0018] In one advanced form of this embodiment, the recess is configured in a crater-like shape. In this application, a crater-like recess is understood to mean a depression or recess whose bottom is surrounded by an annularly raised wall, which will also be referred to below as a crater rim. A crater-like recess may have a substantially circular geometric structure in plan view, but it is also possible for a recess to have a geometric structure different from a circular geometric structure in plan view, such as a polygonal geometric structure or an angular geometric structure.

[0019] In yet another development, adjacent recesses on the wall of a hollow structure are interconnected. The number and lateral extent of the surface recesses are usually large enough for adjacent recesses to be interconnected. When the recesses are crater-like, the rim of each crater surrounding a recess either forms part of the crater rim of an adjacent recess on the opposite side of the recess, or merges with the bottom of an adjacent recess. In this development, adjacent recesses are not merely connected to each other, but at least partially overlap each other.

[0020] In yet another developmental form, the recesses on the surface of the walls of a hollow structure form a honeycomb-like surface structure. As mentioned above, adjacent recesses are usually interconnected, rather than simply touching each other as in a honeycomb. Unlike a honeycomb, the recesses are generally not arranged in a regular grid. The shape and size of the recesses forming the honeycomb-like surface structure can also vary. In particular, the edges between two adjacent recesses, which can be formed in the form of crater rims, generally form a mesh-like surface structure that complements the honeycomb structure.

[0021] In one developed form, the recess has a maximum lateral extent of 500 μm or less, preferably 450 μm or less, and particularly 400 μm or less. The maximum lateral extent is understood to mean the maximum lateral distance between two points along the edge of the recess in a plan view of the recess. In the case of a crater-like recess, the maximum lateral extent indicates the maximum lateral distance between two points on the edge of each crater.

[0022] In yet another developmental form, the recess has a maximum depth of 20 μm or less, preferably 15 μm or less, and particularly 10 μm or less. The maximum depth is understood to mean the height distance measured between the bottom of the recess and the highest point on the edge of the recess or crater edge.

[0023] For example, if a hollow structure has a channel with a rectangular or square cross-section, the surface of the hollow structure's walls may be planar. If, for example, a hollow structure has a circular cross-section and the surface of its walls has curvature, then to determine the lateral distance and depth of a recess, it is assumed that the surface of the hollow structure extends in a substantially planar manner in the portion of the measurement area. If necessary, the lateral distance and depth of a recess can be determined, for example, by using the unfolding of the cylindrical surface forming the side surface of the channel.

[0024] In yet another embodiment, the first portion, the second portion, the adjacent portion, and the rounded portion each form a flow channel portion of a fluid-flow channel. The fluid-flow channel forms a circumferentially closed, elongated cavity that extends between the first and second ends of the flow channel without branching. At one or both ends, the flow channel can merge into a further hollow structure located within the volume of the workpiece. It is also possible for one or both ends of the flow channel to open to the outside of the workpiece. In this case, the cross-section or diameter of the rounded portion substantially corresponds to the cross-section of both portions of the flow channel. The walls of the hollow structure in this case form the sides of the flow channel.

[0025] In one advanced form of this embodiment, the flow path has a diameter of 1 mm to 20 mm, preferably 1 mm to 5 mm, and / or a length of 10 cm or more, preferably 15 cm or more, and particularly 20 cm or more. The flow path may have a circular cross-section, but may also have a cross-section that deviates from a circular geometric structure. In this case, the diameter of the flow path is understood to mean the so-called equivalent diameter, i.e., the diameter of the circle whose area corresponds to the cross-section of the non-circular flow path in this case. It has been found that flow paths having diameters within the above value range are advantageous for fluid flow.

[0026] Particularly when the workpiece has a large volume, it is advantageous if the length of the flow path is relatively long. The diameter of the flow path can vary in the longitudinal direction of the flow path in some cases, but it is generally advantageous if the longitudinal variation of the diameter of the flow path is as small as possible.

[0027] In one embodiment, the cross-sectional area of the flow path has a variation of + / - 20% or less, preferably + / - 10% or less, particularly + / - 2% or less over the length of the flow path. In this embodiment, the flow path is usually 10 cm or more in length, preferably 15 cm or more, particularly 20 cm or more. In the present application, a variation of + / - x% in the cross-sectional area of the flow path is understood to mean a deviation of + / - x% from the average cross-sectional area A of the flow path. M The average cross-sectional area A M is defined as the average of the maximum cross-sectional area A MAX and the minimum cross-sectional area A MIN along the length of the flow path, as described in Patent Document 1 cited above (A M = ( MAX + A MIN ) / 2), and the entire above-mentioned document is incorporated herein by reference.

[0028] In one embodiment, the R / D ratio of the radius of curvature R of the rounded portion to the diameter D of the rounded portion is 2 to 6, preferably 2.5 to 5, particularly 2.5 to 3.5. Regarding fluid-excited vibration, for example, a large improvement exceeding 50% can already be achieved when the R / D ratio is greater than 2. Ideally, since the maximum improvement regarding fluid-excited vibration is usually obtained, the R / D ratio is about 2.5 to 3.5, for example 3.0. The R / D ratio should not exceed a value greater than 6. In this embodiment, the rounded portion has a constant radius of curvature.

[0029] The cross-section of the flow path of the rounded portion is usually circular, but in some cases, it can deviate from the circular geometric structure and have, for example, an elliptical geometric structure. In this case, the diameter of the rounded portion is understood to mean the so-called equivalent diameter in the above definition.

[0030] The ratio of the diameter of the rounded portion to the radius of curvature of the rounded portion was found to represent a parameter essential for guiding a streamlined flow free from turbulence, and therefore for avoiding flow-induced oscillations.

[0031] In yet another embodiment, the diameter D of the rounded portion is 2 mm to 20 mm, preferably 2 mm to 12 mm. The diameter of the rounded portion or the flow channel structure of the hollow structure of this specified order can generate a volumetric flow rate sufficient for efficient temperature control of the optical element under given boundary conditions. The fluid velocity in the hollow structure is generally on the order of several meters per second.

[0032] In one embodiment, the hollow structure includes a plurality of temperature-controlled channels extending beneath the surface of the workpiece, and the hollow structure includes a fluid distribution section connected to the temperature-controlled channels via a distribution channel, and a fluid recovery section connected to the temperature-controlled channels via a recovery channel. The temperature-controlled channels typically serve to cool the workpiece and are therefore also referred to below as cooling channels.

[0033] Temperature-controlled channels generally extend to the shallow region below the surface that is the temperature-controlled surface. The shallow region is understood to mean a distance of 10 mm or less from the temperature-controlled surface of the workpiece. The distance from the temperature-controlled surface is measured in the thickness direction of the workpiece, which is perpendicular to the temperature-controlled surface of the workpiece from which the temperature-controlled channels extend downward. As a result of the small distance of the cooling channels from the temperature-controlled surface of the workpiece, effective cooling of the temperature-controlled surface can be achieved. This distance is understood to mean the minimum distance between each temperature-controlled channel and the temperature-controlled surface of the workpiece.

[0034] Generally, the fluid distribution section and the fluid recovery section each have a larger flow path cross-section than the individual cooling channels. This allows for the setting of beneficial flow conditions. It is preferable that the fluid distribution section and / or fluid recovery section be located at a greater distance from the temperature-controlled surface than the cooling channels. This arrangement allows for keeping surface deformation caused by fluid pressure within the fluid distribution section and / or fluid recovery section, which generally have cavities with a larger surface area than the cooling channels, within acceptable limits. The fluid distribution section is usually connected to a fluid inlet, and the fluid recovery section is usually connected to a fluid outlet. Each cooling channel can be connected to exactly one distribution channel and exactly one recovery channel, but in principle, it is also possible to connect a group of two or possibly three or more cooling channels to a common distribution channel and a common recovery channel.

[0035] In yet another embodiment, the first portion forms the end portion of a temperature-controlled channel connected to a distribution channel, the second portion forms the distribution channel portion connected to the end portion, and / or the first portion forms the end portion of a temperature-controlled channel connected to a recovery channel, and the second portion forms the recovery channel portion connected to the end portion.

[0036] The cooling channels extend substantially parallel to the temperature-controlled surface to which the reflective coating is applied when the workpiece is a mirror substrate. Because the installation space within the substrate is limited, the distribution channels or recovery channels connected to each cooling channel generally move away from the surface with the reflective coating at approximately right angles; that is, the recovery channel portion or distribution channel portion and the adjacent end portion of the cooling channel usually extend at approximately right angles to each other, i.e., there is approximately a 90° deflection of the fluid flowing through the hollow structure.

[0037] The aforementioned rounded portion, in particular by selecting an appropriate ratio of the radius of curvature to the diameter, can avoid or at least substantially reduce flow-induced vibrations.

[0038] In principle, the fluid distribution section and the fluid recovery section may have different designs. For example, the flow path cross-sections of the fluid distribution section and the fluid recovery section may taper off, for example, in the form of a funnel, starting from the distribution and recovery channels, respectively, so that the cavities formed by the fluid distribution and recovery sections within the workpiece do not become unnecessarily large.

[0039] In yet another embodiment, the fluid distribution section forms an inlet channel from which the distribution channel branches, and / or the fluid recovery section forms an outlet channel from which the recovery channel branches. In this embodiment, the fluid recovery section and the fluid distribution section generally extend substantially lateral to the longitudinal direction of the distribution channel and lateral to the longitudinal direction of the recovery channel. Generally, the distribution channel and the recovery channel branch substantially perpendicular to the inlet channel and the outlet channel, respectively. For example, the fluid distribution section and the fluid recovery section can be configured in the form of cylindrical channels extending into the workpiece from an inlet opening and an outlet opening on the outside of the workpiece, respectively. In this case, the inlet channel and the outlet channel can be configured, for example, in the form of perforations, but they can also be fabricated by the selective laser-induced etching described above.

[0040] In one advanced form of this embodiment, the first part forms a junction of distribution channels adjacent to the inlet channel, the second part forms a branching section of the inlet channel adjacent to the junction, and / or the first part forms a junction of recovery channels adjacent to the outlet channel, and the second part forms a branching section of the outlet channel adjacent to the junction of recovery channels.

[0041] As described above, the longitudinal directions of the inlet and outlet channels extend substantially perpendicular to the longitudinal directions of the respective recovery and distribution channels. At each branching point of the distribution or recovery channel, a streamlined geometric structure that can be created by providing rounded portions at the branching points of the inlet or outlet channels is also advantageous. In this way, steps can be avoided and edges can be rounded, resulting in a more streamlined geometric structure for the hollow structure, which can avoid or at least significantly reduce fluid separation in the inlet and outlet channels.

[0042] The ratio of the diameter to the radius of the rounded portion is preferably within the range of values ​​described above. However, the rounded portion may not have a constant radius of curvature at the branching point. The flow channel diameter of the rounded portion at the branching point does not necessarily have to be constant. For example, the cross-section of the rounded portion may taper starting from the inlet channel or the outlet channel.

[0043] In yet another embodiment, the angle between the branching portion of the inlet channel and the confluence portion of the distribution channel is greater than 90°, preferably greater than 100°, and / or the angle between the branching portion of the outlet channel and the confluence portion of the recovery channel is greater than 90°, preferably greater than 100°. It has been found that it is beneficial for flow guidance when the branching portions of the inlet and outlet channels and the confluence portions of the distribution and recovery channels are oriented at obtuse angles to each other.

[0044] Yet another aspect of the present invention relates to the aforementioned type of workpiece having recesses on the surface of the walls of a hollow structure. In this case, the hollow structure is usually fabricated by selective laser-induced etching. The walls of the hollow structure have a unique surface structure having recesses configured as described above, as will be described again in detail below.

[0045] In one embodiment, the recess is configured in a crater shape.

[0046] In yet another embodiment, adjacent crater-like recesses communicate with each other.

[0047] In yet another embodiment, the recesses on the surface of the hollow wall form a honeycomb structure.

[0048] In yet another embodiment, each recess has a maximum lateral spread of 500 μm or less, preferably 450 μm or less, and particularly 400 μm or less.

[0049] In one embodiment, the recess has a maximum depth of 20 μm or less, preferably 15 μm, and particularly 10 μm or less.

[0050] In one embodiment, the surface of the wall of the hollow structure has a roughness R of 25 μm or less, preferably 10 μm or less, particularly preferably 5 μm or less, and especially 2 μm or less. a It holds.

[0051] In one embodiment, the hollow structure is configured in the form of a preferably curved channel through which a fluid can flow.

[0052] In one advanced form of this embodiment, the flow path has a diameter of 1 mm to 2 mm, preferably 1 mm to 5 mm, and / or a length of 10 cm or more, preferably 15 cm or more, and particularly 20 cm or more.

[0053] In yet another development of this embodiment, the cross-sectional area of ​​the flow path has a variation of + / -20% or less, preferably + / -10% or less, and particularly + / -2% or less over the length of the flow path.

[0054] In both embodiments described above, the material of the workpiece is preferably selected from the group including quartz glass, particularly titanium-doped quartz glass, and glass ceramics. In this case, the workpiece is usually a substrate for a mirror, more precisely a substrate for an EUV mirror. In this case, to avoid deformation of the surface to which the reflective coating is applied, which may be due to uneven heating of the workpiece material, the substrate for an EUV lithography mirror is usually manufactured from a so-called zero-expansion material with a very low coefficient of thermal expansion. As described above, these materials are hard and brittle, making machining difficult. However, using the selective laser-induced etching method described above, hollow structures of virtually any shape can be fabricated from such materials.

[0055] In yet another embodiment, the workpiece material has a zero-crossing temperature of 0°C to 100°C, preferably 19°C to 40°C, and particularly preferably 19°C to 32°C. The zero-crossing temperature is defined in particular by the average incident radiation output during the operation of the EUV mirror.

[0056] In one embodiment, the workpiece material has a spatial variation of zero-crossing temperature of less than 3K, preferably less than 2K, particularly preferably less than 1K, and especially less than 0.1K. High spatial uniformity of zero-crossing temperature is usually required to enable efficient operation of the EUV mirror.

[0057] In yet another embodiment, the workpiece is monolithic, that is, integrally formed and does not have a joint surface to which two or more parts of the workpiece are interconnected. The rounded portion of a monolithic workpiece cannot be easily created by machining, for example, by drilling or milling, in hard and brittle glass materials. In principle, it is also possible to construct the workpiece from two or more parts. In this case, the joint surface does not pass through the rounded portion, that is, the joint surface does not intersect with the rounded portion.

[0058] A further aspect of the present invention relates to a method for forming at least partially a hollow structure in a workpiece, particularly a workpiece configured as described above, by selective laser-induced etching, the method comprising the steps of: focusing pulsed laser radiation onto a normally continuous irradiation volume of the workpiece; and forming at least partially a hollow structure in the irradiation volume by selective etching of the workpiece.

[0059] As described above, hollow structures can be formed completely or partially, particularly part by part, by selective laser-induced etching. In particular, the first part, second part, and / or rounded part of a hollow structure in the form of a channel can be formed by selective laser-induced etching. For simplicity, the hollow structures formed by this method will be assumed to be channels.

[0060] As described above, the etching process is carried out from the edge or surface of the workpiece into the irradiation volume of the workpiece. Etching creates a channel portion that extends into the irradiation volume, which extends from the entrance to the channel portion on the surface of the workpiece to the end face of the channel portion where the etch front is formed. At the etch front or end face, further material from the workpiece is gradually removed along the irradiation volume until the channel is completely formed, i.e., until the channel extends throughout the entire irradiation volume. Thus, during the etching process, the length of the etched channel portion gradually increases in a manner comparable to tunneling.

[0061] Similarly, as mentioned above, depending on the material of the workpiece in which the flow channels are formed, the etching selectivity ratio of the irradiated volume to the unirradiated volume of the workpiece is relatively low, and can be as low as 1:500. As a result, the period during which the flow channel walls within the volume of the workpiece are exposed to the etching medium is significantly shorter than that of the edges of the workpiece, so that the edges of the workpiece, where the etching solution first acts, have a wider flow channel shape than the interior of the workpiece volume.

[0062] This problem can be solved by a method in which the end faces of the channel portions formed in the irradiated volume during selective laser-induced etching are etched at a higher etching rate than the (circumferentially etched) channel walls of the channel portions.

[0063] Preferably, the ratio of the etching rate at the channel wall to the etching rate at the end face of the channel portion, or etching selectivity ratio, is at least 1:1500, and particularly preferably at least 1:2000. In this application, an improvement in etching selectivity ratio is understood to mean a decrease in the above ratio, i.e., an increase in the etching rate at the end face of the channel portion relative to the etching rate at the channel wall. Except as further described below where the channel wall is sealed against etching, increasing the etching rate at the end face of the channel relative to the etching rate at the channel wall increases the overall etching rate.

[0064] In this way, a channel that can have a considerable length can be formed in the workpiece, and the cross-sectional area of ​​the channel is substantially constant over the length of the channel, or fluctuates only slightly, specifically by + / -20% or less, and in some cases by + / -10% or less or + / -2%. This also applies when the workpiece is a substrate made of quartz glass, particularly titanium-doped quartz glass, or glass ceramic, for a reflective optical element, as described in Patent Document 1. For example, a workpiece that may be a substrate for a reflective optical element can be constructed in a monolithic manner (see above).

[0065] Increasing the etching rate at the end face relative to the etching rate at the channel wall is advantageous or necessary to form a substantially constant cross-section over the length of the channel, and various measures can be implemented individually or in combination for this purpose.

[0066] One such measure is to raise the temperature of the end face of the channel portion to 20K or more, preferably 40K or more, and especially 60K or more, than the temperature of the channel wall portion, in order to increase the etching rate. In this case, the etching selectivity ratio is improved by keeping the workpiece and the etching solution or etching liquid at the lowest possible temperature, just above or possibly just below the freezing point of the etching solution. In contrast, the etch front of the end face of the channel is kept at the highest possible temperature, 20K or more, preferably 40K or more, and ideally 60K or more, than the temperature of the etching solution and the workpiece (the rest of it), and therefore the temperature of the (circumferential) channel wall portion.

[0067] In this case, the end face of the flow channel can be heated by at least one heating device, and it is preferable to guide this heating device along with the end face of the flow channel during the formation of the flow channel. As described above, during the formation of the flow channel, the position of the end face of the flow channel or the etch front changes, that is, it moves along the entire length of the irradiation area. Therefore, it is advantageous to guide the heating device along with the etch front in order to raise the temperature of the etch front / end face compared to the surrounding area of ​​the workpiece.

[0068] The heating device can be located outside the flow path, for example, on or near the surface of the workpiece at the minimum distance from the flow path. In this case, the heating device can be guided along, for example, a surface parallel to the flow path or along the etch front of the flow path. In this case, the heating device can be, for example, a resistance heater that contacts the surface to transfer contact heat to the material of the workpiece. However, the heating device can also be a heating light source, for example an infrared light source, or a laser focused on the etch front along the direction of the flow path or a portion of the flow path, or optionally a laser focused on the end face of the portion of the flow path through the material of the workpiece. It is also possible to guide or pass the heating device (for example, in the form of a resistance heater or light source) through the flow path and to keep the heating device at a constant distance from the etch front, ideally. In this case, the heating device can be attached to a suitable carrier element smaller in dimensions than the diameter of the flow path. Such a carrier element will be referred to below as a probe.

[0069] Another measure involves exposing the end faces of the channel sections to a higher flow rate of etching solution compared to the channel walls in order to increase the etching rate. The flow rate of the etching solution at the end faces of the channel sections can be increased, for example, by swirling the etching solution. For this purpose, a probe can be permanently or (periodically) intermittently inserted into the channel section. The probe may have a swirling device, such as a propeller or turbine, to swirl the etching solution and thus increase the flow rate of the etching solution at the etch front.

[0070] In yet another apparatus, particles that have begun to be etched from the end faces of the flow channel are mechanically removed to increase the etching rate. To increase the etching rate from the end faces of the flow channel, in this case, a nozzle can be permanently or intermittently positioned in front of the inlet of the flow channel, or a nozzle can be permanently advanced or intermittently inserted into the flow channel using a fluid supply device, for example, in the form of a probe or hose. Since the non-irradiated material surrounding the workpiece is etched at the flow channel wall, the flow of etching solution generated by the nozzle removes more particles that have begun to be etched from the end faces of the flow channel than the flow channel wall. As an alternative to or in addition to the nozzle, a probe may also include a mechanical agitator, brush, etc., positioned near the etch front or guided along the etch front to remove etched particles.

[0071] Another measure involves irradiating the end face of the channel portion with ultrasound to reduce the ratio of the etching rate at the channel wall to the etching rate at the end face of the channel portion, i.e., to improve the etching selectivity ratio. The effects of ultrasound may include the detachment of particles that have begun to be etched, the recirculation of the etching solution, and / or the heating effect of the etch front. To irradiate the end face of the channel portion with ultrasound, an ultrasonic generator can be used, which is placed outside the workpiece and radiates ultrasound to the end face of the channel portion through the surface of the workpiece adjacent to the channel portion. Alternatively or additionally, an ultrasonic generator attached to a probe can be inserted into the channel portion to irradiate the end face of the channel portion with ultrasound.

[0072] In another measure, to increase the etching rate, it is preferable that the channel walls of the channel portion be sealed against etching, and that a protective lacquer be applied to the channel walls during sealing. In this variation, the etched channel portion is sealed against etching by the etching solution at the circumferential channel walls rather than the end faces. For sealing purposes, it is possible to use a lacquer that has a protective effect against etching and is unaffected or only slightly affected by the etching solution, such as a polymer lacquer. For sealing purposes, it may be appropriate to periodically remove the workpiece from the etching bath or etching solution, for example daily, and wash and dry it to seal any channel portions that have been newly etched during the day. Alternatively, it is possible to remove the entire previous sealing of the channel portion using, for example, an organic solvent, and apply a new sealant that extends just before the etch front or just before the end face of the channel.

[0073] The sealant can be applied by immersing the workpiece in a protective lacquer. In this case, it is necessary to avoid applying the sealant to the end faces of the channel portions that will later form the etch front. This can be done by inserting a probe and mechanically cleaning or by irradiation with (laser) light to remove the lacquer from the end faces. UV-curing lacquer can also be used. In this case, a probe can be inserted into the channel portion, radiating not in the direction of the channel, i.e., not towards the end faces, but towards the side, i.e., towards the circumferential channel wall. Finally, the uncured lacquer is washed off from the etched channel portion. Alternatively, a lacquer-impregnated sponge or felt attached to a probe can be inserted into the channel portion, and then, for example, a spacer mandrel can be used to prevent the end faces of the channel, i.e., the intended etch front, from getting wet.

[0074] As described above, the workpiece can be formed from quartz glass, particularly titanium-doped quartz glass, or glass ceramic. As previously noted, especially in the case of quartz glass, the etching selectivity ratio for other materials such as sapphire is relatively low, so it is desirable to improve the etching selectivity ratio for this material. However, quartz glass, particularly titanium-doped quartz glass, is often used in the manufacture of substrates for reflective optical elements. In the case of glass ceramic, the above method can also be advantageously used in some cases.

[0075] In selective laser-induced etching, the laser radiation focused within the volume of the workpiece generally has a wavelength on the order of approximately 1 μm, or approximately 500 nm if double-frequency light is used. Neither of these wavelengths can cause coupling to the infrared absorption band of quartz glass or titanium-doped quartz glass, nor can they cause excitation to the conduction band of quartz glass in a two-photon process. Therefore, the use of laser radiation with a wavelength on the order of approximately 1 μm is highly inefficient for these materials in any case, because this light is absorbed only in a multiphoton process rather than linearly.

[0076] Therefore, in the case of selective laser-induced etching for at least partially forming a hollow structure, regardless of whether the above-mentioned improvement in etching selectivity is achieved, it is advantageous if the pulsed laser radiation is focused within the irradiation volume at at least one wavelength absorbed by the absorption band of the workpiece material in the wavelength range of 2500 nm to 3120 nm, 2150 nm to 2230 nm, or 1380 nm to 1400 nm. The workpiece material can be quartz glass or titanium-doped quartz glass in particular.

[0077] For both materials, namely quartz glass and titanium-doped quartz glass, it is appropriate to use laser radiation that can be absorbed in a two-photon process at approximately 2500 nm, 2230 nm, or 1380 nm, i.e., laser radiation having a wavelength that is, for example, twice the wavelength of one of the absorption bands or wavelengths mentioned above. Alternatively, laser radiation with different wavelengths can be used, as long as the total photon energy corresponds to the energy of one of the absorption bands mentioned above.

[0078] The absorption band of hydroxyl groups in quartz glass is evident from the transmittance curve of quartz glass as a function of wavelength, which can be obtained, for example, at "https: / / www.heraeus.com / media / media / hqs / doc_hqs / products_and_solutions_8 / optics / Daten_und_Eigenschaften_Quarzglas_fuer_die_Optik_DE.pdf". The absorption band or transmittance as a function of wavelength of titanium-doped quartz glass can be obtained, for example, at "www.pgo-online.com / de / kurven / ule_tkurve.html". Needless to say, the strength used for glass with a low OH content must be higher than the strength used for glass with a high OH content.

[0079] In the case of a workpiece made of quartz glass, pulsed laser radiation can be focused within the irradiation volume at at least one wavelength of 351 nm or less, preferably 308 nm or less, particularly preferably 275 nm or less, and especially particularly 266 nm or less, for the purpose of forming a hollow structure at least partially. For absorption into the conduction band, in the case of quartz glass, it is appropriate to use light or laser radiation from an excimer laser with wavelengths of 351 nm, 308 nm, 248 nm, or 193 nm, or frequency-multiplied light from a solid-state laser with a wavelength of 266 nm. A laser emitting at a wavelength of approximately 275 nm can also be used for this purpose.

[0080] In the case of workpieces made of titanium-doped quartz glass, pulsed laser radiation can be focused into the irradiation volume at at least one wavelength between 260 nm and 520 nm when forming at least a portion of the hollow structure. For absorption into the conductive band, it has been found that using laser radiation between 260 nm and 520 nm to focus into the irradiation volume is advantageous for titanium-doped quartz glass.

[0081] When forming a hollow structure at least partially by the selective laser-induced etching described above, pulsed (spatially and temporally) coherent laser radiation, particularly pulsed coherent excimer laser radiation, can be focused within the irradiation volume. It has been found that when quartz glass or titanium-doped quartz glass is irradiated with coherent pulsed radiation in the UV wavelength range, light guide structures are formed first, followed by small channels (microchannels), whereas formation after the breakdown of the spatial coherence of the laser light occurs only with a significant delay. The light guide structures already have a high density of broken bonds and can therefore be expected to be easily etchable. The (micro)channels, in any case, increase the surface area of ​​the etching solution during the etching process.

[0082] Therefore, in the cases described herein, it is proposed to use excimer laser radiation or frequency-multiplier solid-state laser radiation in the UV wavelength range of approximately 351 nm or less, for example 275 nm or less, instead of infrared radiation with pulse widths in the ps or fs range for selective laser-induced etching. The pulse width of the pulsed laser radiation is generally in the low ns or high ps range. Preferably, in this case, in order to prevent the laser beam from losing its spatial and temporal coherence, the collimated and unfiltered laser beam generated by the laser source is focused directly into the irradiation volume, more precisely into the focal volume within the irradiation volume.

[0083] When forming a hollow structure at least partially, selective etching can be performed in the irradiated volume using reactive plasma, preferably the reactive plasma is supplied to the end faces of the channel portions formed during the selective etching of the irradiated volume. In this case as well, the end faces of the channel portions formed in the irradiated volume can be etched at a higher etching rate than the channel walls of the channel portions.

[0084] The reactive plasma or reactive plasma species may be, for example, a reactive oxygen species, such as an oxygen radical, but it may also be another reactive species, such as a reactive hydrogen species. In etching using reactive plasma, a relatively small plasma source attached to a probe or the like can be guided along the pre-irradiated channel, or more precisely along the etched channel portion, to the end face of the channel portion in order to locally expose the end face of the channel portion to the reactive plasma. In this case, the plasma source can be periodically inserted into and removed from the channel portion to purge the waste material. Alternatively, continuous or semi-continuous purging can also be used. Purge without introducing the probe into the channel portion is preferably performed using a solution or a liquid jet, while purging with the probe inserted is preferably performed using a gas jet.

[0085] Currently, the smallest plasma source diameter is approximately 10 mm, making it impossible to create significantly smaller diameter channels by inserting probes into each channel. Instead, in this case, a more powerful plasma source that remains near the channel inlet (outside the workpiece) is required. In this case, the etch front of the cooling channel can be followed by guiding the plasma to the vicinity of the end face of the cooling channel or the vicinity of the end face of the etched channel portion via a supply channel. As a supply channel for plasma or plasma species, for example, a small tube or hose with its free end located near the etch front of the channel end face can be used. The hose may have annular or helical reinforcing elements to allow for good flexibility and stabilization of its cross-section. In this case, since there will be a loss of reactive atoms or species, such an external plasma source needs to be designed to be correspondingly more powerful. For example, a supply channel in the form of a small tube may need to be replaced periodically, or may be made of an etching-resistant material, or may be provided with an etching-resistant inner coating or lining.

[0086] As described in Patent Document 1 above, in order to improve the etching selectivity ratio during the etching process, it is possible to irradiate the etch front, i.e., the area on the substrate where the etching solution is acting on the material, with laser radiation used for material modification or laser radiation of other wavelengths. In this case, in particular, the actual damage or modification of the material during selective laser-induced etching can be carried out only within the etching bath. In most of the other means described above, the formation of an irradiation volume by focusing pulsed laser radiation and the selective etching of the workpiece within the irradiation volume can be carried out not only sequentially in time, but in some cases in parallel in time. In the latter case, the etching apparatus needs to be equipped with an exposure system that can focus pulsed laser radiation into the irradiation volume when the workpiece is placed in the etching bath or etching solution. The etching bath or etching solution can be (slightly) acidic, substantially neutral, or basic etching solution. The advantage of a substantially neutral etching solution is that it minimizes surface roughening. Neutral or slightly acidic water, especially demineralized water or distilled water, can also be used as the etching solution. See also the paper "Water-assisted femtosecond laser ablation for fabricating three-dimensional microfluidic chips" by Yan Li and Shiliang Qu (Current Applied Physics, Vol. 13, Issue 7, 2013, pages 1292-1295).

[0087] A further aspect of the present invention relates to a mirror, in particular an EUV mirror, comprising a workpiece in the form of a substrate configured as described above, and a reflective coating applied to the surface of the substrate that reflects radiation, in particular EUV radiation. The reflective coating may include a plurality of layers made of materials having different real refractive indices in order to reflect radiation.

[0088] A further aspect of the present invention relates to a lithography system, particularly an EUV lithography system, comprising at least one workpiece and / or at least one mirror, particularly an EUV mirror, and a temperature control device, particularly a cooling device, configured to flow a temperature-controlled fluid, particularly a cooling fluid, into at least one hollow structure. The workpiece can be an optical component or a non-optical, for example, mechanical component, such as a wafer chuck, wafer table, or, for example, a mount, particularly in the form of a frame for mounting an optical element, a frame for mounting a sensor, or a structural component of the lithography system, such as a support frame used in an EUV lithography system, specifically an EUV lithography apparatus.

[0089] The temperature control device can also function as a cooling device and can be configured to circulate, for example, a cooling medium in the form of a cooling fluid, such as cooling water, through a hollow structure. For this purpose, the temperature control device or cooling device may optionally have a pump and appropriate supply and removal lines. The temperature control device can also function as a heating device to heat the workpiece or substrate. In this case, a temperature control fluid, generally in the form of a heating fluid which is also a liquid, is supplied through a hollow structure in the form of a flow channel. It is also possible for the temperature control device to be configured to both heat and cool the mirror. It is preferable to use water as the temperature control fluid and circulate it through a hollow structure in the form of a flow channel in both the cooling and heating cases.

[0090] The hollow structure of the workpiece or substrate has an inlet opening for fluid inflow and an outlet opening for fluid outflow. To connect the hollow structure to a temperature control device, the inlet and outlet openings can be connected to ports on the fluid supply line and the fluid removal line, respectively. If multiple fluidically separated hollow structures or flow channels extend into the workpiece or substrate, they are connected to the temperature control device by separate inlet and outlet openings.

[0091] Further advantages and aspects of the present invention will become apparent from the following description of embodiments of the present invention with reference to drawings illustrating essential details of the invention, and from the claims. Each of the features can be implemented individually or in any combination in one variant of the present invention.

[0092] An exemplary embodiment is shown in the schematic diagram and described below. [Brief explanation of the drawing]

[0093] [Figure 1] A schematic diagram of the meridian cross-section of a projection exposure apparatus for EUV projection lithography is shown. [Figure 2a] Figure 1 shows a schematic cross-sectional view of a mirror in a projection exposure apparatus, which has a hollow structure with multiple temperature-controlled channels in the form of cooling channels, and the ends of the channels merge into a distribution channel or a recovery channel via rounded portions. [Figure 2b] Figure 1 shows a schematic cross-sectional view of a mirror in a projection exposure apparatus, which has a hollow structure with multiple temperature-controlled channels in the form of cooling channels, and the ends of the channels merge into a distribution channel or a recovery channel via rounded portions. [Figure 3a] A schematic diagram of the rounded portion between the end of the distribution channel and the cooling channel is shown, where the channel diameter is the same but one of four different radii of curvature is selected. [Figure 3b] A schematic diagram of the rounded portion between the end of the distribution channel and the cooling channel is shown, where the channel diameter is the same but one of four different radii of curvature is selected. [Figure 3c] A schematic diagram of the rounded portion between the end of the distribution channel and the cooling channel is shown, where the channel diameter is the same but one of four different radii of curvature is selected. [Figure 3d] A schematic diagram of the rounded portion between the end of the distribution channel and the cooling channel is shown, where the channel diameter is the same but one of four different radii of curvature is selected. [Figure 4a] A schematic diagram of the rounded portion between the end of the recovery channel and the cooling channel is shown, where the channel diameter is the same, but one of four different radii of curvature is selected. [Figure 4b]A schematic diagram of the rounded portion between the end of the recovery channel and the cooling channel is shown, where the channel diameter is the same, but one of four different radii of curvature is selected. [Figure 4c] A schematic diagram of the rounded portion between the end of the recovery channel and the cooling channel is shown, where the channel diameter is the same, but one of four different radii of curvature is selected. [Figure 4d] A schematic diagram of the rounded portion between the end of the recovery channel and the cooling channel is shown, where the channel diameter is the same, but one of four different radii of curvature is selected. [Figure 5a] The diagram shows a perspective view of a substrate for an EUV mirror having a hollow structure similar to those shown in Figures 2a and 2b, in which the end portion of the cooling channel is oriented at an obtuse angle to the distribution channel or recovery channel. [Figure 5b] A schematic diagram of the rounded portion at the transition between the end of the cooling channel and the distribution channel is shown. [Figure 6a] The diagram shows a substrate for an EUV mirror having a hollow structure similar to that shown in Figures 2a and 2b, in which the distribution channel and the recovery channel are directed at obtuse angles to the inlet channel and the outlet channel, respectively, and merge with the inlet channel or the outlet channel at a rounded portion. [Figure 6b] The diagram shows a substrate for an EUV mirror having a hollow structure similar to that shown in Figures 2a and 2b, in which the distribution channel and the recovery channel are directed at obtuse angles to the inlet channel and the outlet channel, respectively, and merge with the inlet channel or the outlet channel at a rounded portion. [Figure 6c] The diagram shows a substrate for an EUV mirror having a hollow structure similar to that shown in Figures 2a and 2b, in which the distribution channel and the recovery channel are directed at obtuse angles to the inlet channel and the outlet channel, respectively, and merge with the inlet channel or the outlet channel at a rounded portion. [Figure 6d] The diagram shows a substrate for an EUV mirror having a hollow structure similar to that shown in Figures 2a and 2b, in which the distribution channel and the recovery channel are directed at obtuse angles to the inlet channel and the outlet channel, respectively, and merge with the inlet channel or the outlet channel at a rounded portion. [Figure 6e] Figures 6a to 6d show a diagram of a multi-part substrate for an EUV mirror with a hollow structure configured similarly. [Figure 6f] Figures 6a to 6d show a diagram of a multi-part substrate for an EUV mirror with a hollow structure configured similarly. [Figure 7a] A schematic diagram of one step in a method for selective laser-induced etching of a channel into a substrate is shown. [Figure 7b] A schematic diagram of one step in a method for selective laser-induced etching of a channel into a substrate is shown. [Figure 8] A schematic diagram is shown of the channel portion formed during selective laser-induced etching, which has a higher temperature edge than the rest of the substrate. [Figure 9] To increase the etching rate, the end faces of the flow channels are exposed to an etching solution at a higher flow rate; a schematic diagram similar to Figure 8 is shown. [Figure 10] To increase the etching rate, etched particles are mechanically removed from the end faces of the flow channels; a schematic diagram similar to Figure 8 is shown. [Figure 11] A schematic diagram similar to Figure 8 shows how ultrasonic waves are irradiated onto the end faces of the flow channel to improve the etching selectivity. [Figure 12] A schematic diagram similar to Figure 8 shows the channel walls of the channel section sealed with protective lacquer. [Figure 13] A schematic diagram similar to Figure 8 shows etching being performed by reactive plasma supplied to the end face of the flow channel. [Figure 14a] A schematic diagram of a flow channel formed during selective laser-induced etching is shown, which has an end face to which a purging fluid is supplied via a flexible hose. [Figure 14b] A schematic diagram of a flow channel formed during selective laser-induced etching is shown, which has an end face to which a purging fluid is supplied via a flexible hose. [Figure 14c] A schematic diagram of a nozzle attached to the outlet end of a hose is shown. [Figure 15a] A schematic diagram of a flexible hose being inserted into a flow path using a rigid guide element and a follower device including a drive roller and guide roller is shown. [Figure 15b] A schematic diagram of a flexible hose being inserted into a flow path using a rigid guide element and a follower device including a drive roller and guide roller is shown. [Figure 15c] A schematic diagram of a flexible hose being inserted into a flow path using a rigid guide element and a follower device including a drive roller and guide roller is shown. [Figure 16a] This diagram shows a schematic representation of the insertion and tracking of a flexible hose using a tracking device with two chucks. [Figure 16b] This diagram shows a schematic representation of the insertion and tracking of a flexible hose using a tracking device with two chucks. [Figure 16c] This diagram shows a schematic representation of the insertion and tracking of a flexible hose using a tracking device with two chucks. [Figure 16d] This diagram shows a schematic representation of the insertion and tracking of a flexible hose using a tracking device with two chucks. [Figure 17a] Figures 7a and 7b show schematic diagrams of the surface of the channel wall fabricated as described above. [Figure 17b] Figures 7a and 7b show schematic diagrams of the surface of the channel wall fabricated as described above. [Figure 18a] A schematic diagram similar to Figure 17a is shown at a different scale. [Figure 18b] A schematic diagram similar to Figure 17b is shown at a different scale. [Figure 19] In relation to Figures 7a and 7b, another schematic diagram of the surface of the channel wall fabricated as described above is shown. [Modes for carrying out the invention]

[0094] In the following drawings, identical or functionally identical components shall be referred to by the same reference numeral.

[0095] The essential components of the EUV lithography optical apparatus in the form of microlithography projection exposure apparatus 1 are described below as an example with reference to Figure 1. The description of the basic configuration of projection exposure apparatus 1 and its components should not be understood as limited in this case.

[0096] One embodiment of the illumination system 2 of the projection exposure apparatus 1 includes, in addition to the light source or radiation source 3, an illumination optical unit 4 that illuminates the object field of view 5 on the object surface 6. In an alternative embodiment, the light source 3 may be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0097] A reticle 7 positioned in the object field of view 5 is illuminated. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable, particularly in the scanning direction, by a reticle displacement drive 9.

[0098] For illustrative purposes, Figure 1 shows an orthogonal xyz coordinate system. The x-direction extends perpendicular to the plane of the figure. The y-direction extends horizontally, and the z-direction extends vertically. In Figure 1, the scanning direction extends in the y-direction. The z-direction extends perpendicular to the object plane 6.

[0099] The projection exposure apparatus 1 includes a projection optical unit 10. Using the projection optical unit 10, the object field of view 5 is imaged onto the image field of view 11 of the image plane 12. The structure on the reticle 7 is imaged onto the photosensitive layer of the wafer 13, which is positioned in the region of the image field of view 11 of the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable by a wafer displacement drive 15, particularly along the y-direction. Firstly, the displacement of the reticle 7 by the reticle displacement drive 9, and secondly, the displacement of the wafer 13 by the wafer displacement drive 15, can be performed in synchronous manner.

[0100] Radiation source 3 is an EUV radiation source. Radiation source 3 emits EUV radiation 16, which is also referred to below as the radiation used, illumination radiation, or illumination light. In particular, the radiation used has a wavelength in the range of 5 nm to 30 nm. Radiation source 3 may be a plasma source, such as an LPP (laser-generated plasma) source or a DPP (gas discharge plasma) source. It may also be a synchrotron-based radiation source. Radiation source 3 may be a free-electron laser.

[0101] Illumination radiation 16 emitted from radiation source 3 is focused by a collector mirror 17. The collector mirror 17 may be a collector mirror having one or more elliptical and / or hyperbolic reflecting surfaces. Illumination radiation 16 may be incident on at least one reflecting surface of the collector mirror 17 at an oblique incidence (GI), i.e., at an incidence angle greater than 45°, or at a perpendicular incidence (NI), i.e., at an incidence angle less than 45°. The collector mirror 17 may be structured and / or coated to first optimize its reflectivity for the radiation used, and second to suppress external light.

[0102] Downstream of the collector mirror 17, the illumination radiation 16 propagates through the intermediate focal point of the intermediate focal plane 18. The intermediate focal plane 18 can form a separation between the radiation source module, which has the radiation source 3 and the collector mirror 17, and the illumination optical unit 4.

[0103] The illumination optical unit 4 comprises a deflection mirror 19 and a first facet mirror 20 located downstream of it in the beam path. The deflection mirror 19 may be a planar deflection mirror or a mirror having a beam influence effect beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 19 may be embodied as a spectral filter that separates the wavelength of light used by the illumination radiation 16 from external light of different wavelengths. The first facet mirror 20 includes a plurality of individual first facets 21, also referred to below as field facets. Figure 1 shows only some of these facets 21 as examples. A second facet mirror 22 is located downstream of the first facet mirror 20 in the beam path of the illumination optical unit 4. The second facet mirror 22 includes a plurality of second facets 23.

[0104] Therefore, the illumination optical unit 4 forms a dual facet system. This basic principle is also called a fly-eye integrator. Using the second facet mirror 22, each individual first facet 21 is imaged into the object field of view 5. The second facet mirror 22 is the last beam shaping mirror or, in fact, the final mirror for the illumination radiation 16 in the beam path upstream of the object field of view 5.

[0105] The projection system 10 includes a plurality of mirrors Mi, which are numbered sequentially according to their arrangement in the beam path of the projection exposure apparatus 1.

[0106] In the example shown in Figure 1, the projection system 10 includes six mirrors M1 to M6. Substitution with four, eight, ten, twelve, or any other number of mirrors Mi is equally possible. The second-to-last mirror M5 and the final mirror M6 each have a through aperture for illumination radiation 16. The projection system 10 is a double-shielded optical unit. The projection optical unit 10 has an image-side numerical aperture greater than 0.4 or 0.5, and may be greater than 0.6, for example, 0.7 or 0.75.

[0107] Similar to the mirrors of the illumination optical unit 4, mirror Mi can have a highly reflective coating for illumination radiation 16.

[0108] Figures 2a and 2b show an example of an embodiment of the mirror M4 of the projection system 10, which in the illustrated example includes a monolithic workpiece in the form of a substrate 25. In the illustrated example, the material of the substrate 25 is titanium-doped quartz glass with a very low coefficient of thermal expansion. The substrate 25 can also be formed from another material with the lowest possible coefficient of thermal expansion, such as glass ceramic. The zero-crossing temperature T of the substrate 25 ZC The zero-crossing temperature range is 0°C to 100°C, usually 19°C to 40°C, and especially 19°C to 32°C. ZC The temperature is substantially constant throughout the entire volume of the substrate 25, with spatial variations of less than 3K, less than 2K, less than 1K, or less than 0.1K, and the spatial variations are due to the zero-crossing temperature T ZC This shows the difference between the maximum and minimum values.

[0109] A reflective coating 26 that reflects EUV radiation 16, as shown in Figure 1, is applied to the surface 25a of the substrate 25. The EUV radiation 16 from the projection system 10 strikes a portion of the surface 25a located within the reflective coating 26, and this portion forms the optically usable portion of the reflective coating 26, which is not shown here. To reflect the EUV radiation 16, the reflective coating 26 may have multiple layers made of materials with different real refractive indices, for example, Si and Mo, when the wavelength of the EUV radiation 16 is 13.5 nm.

[0110] The substrate 25 has a hollow structure 27 through which a fluid 28, which is water in the illustrated example, can flow. The fluid 28, indicated by the arrows in Figure 2a, enters the substrate 25 through a side inlet opening 29 so as to flow through a plurality of temperature-controlled channels in the form of cooling channels 31 that form part of the hollow structure 27, thus specifically cooling the surface 25a of the temperature-controlled substrate 25 to which the reflective coating 26 is applied.

[0111] To supply fluid 28 to an inlet opening 29 and remove the fluid 28 from an outlet opening (not shown in Figures 2a and 2b), the projection exposure apparatus 1 includes a temperature control device 32 configured in the form of a cooling device schematically shown in Figure 1. In the illustrated example, the cooling device 32 serves to supply a coolant in the form of cooling water 28 to the mirror M4 and for this purpose includes a supply line (not shown) that is fluid-tightly connected to the inlet opening 29. The cooling device 32 also includes a removal line (not shown) to remove the cooling water 28 from a coolant outlet (not shown). Other mirrors M1-M3, M5, and M6 of the projection system 10 may also have hollow structures 27, which are connected to the cooling device 32 or optionally to further cooling devices provided for this purpose for cooling purposes. Instead of the cooling device 32, the projection exposure apparatus 1 may also be provided with a temperature control device, i.e., a device used for cooling and / or heating the mirrors M1-M6. A suitable temperature-controlled fluid 28, such as water heated to a desired temperature before being supplied to the hollow structure 27, can be used for heating.

[0112] As is clear from Figure 2a, the fluid 28 enters the inlet channel 33 of the hollow structure 27 through the inlet opening 29. This inlet channel forms a fluid distribution section, from which multiple distribution channels 34 branch off, each connected to one of multiple temperature-controlled channels, hereafter referred to as cooling channels 31. In the illustrated example, the cooling channels are positioned at a distance A of approximately 5 mm from the surface 25a of the planar substrate 25 and extend parallel to the surface 25a, i.e., parallel to the XY plane of the XYZ coordinate system. The cooling channels 31 extend linearly, are oriented parallel, and extend longitudinally in the direction corresponding to the Y direction, covering almost the entire portion of the surface 25a of the substrate 25 that is covered by the coating 26. See Figure 2b. From the cooling channels 31, the fluid 28 flows through multiple recovery channels 36 to a fluid recovery section, configured as an outlet channel 35 in the example shown in Figure 2b. The outlet channel 35 has the aforementioned outlet opening (not shown in Figures 2a and 2b), through which the fluid 28 exits the hollow structure 27 of the substrate 25.

[0113] As is clear from Figure 8b, the hollow structure 27 has a first rounded portion 37a where each distribution channel 34 merges into the cooling channel 31. Therefore, the hollow structure 27 also has a second rounded portion 37b where each cooling channel 31 merges into the recovery channel 36. In the illustrated example, the cooling channel 31 extends linearly in the horizontal direction corresponding to the Y direction, and the distribution channels 34 and recovery channels 36 extend linearly in the vertical direction corresponding to the Z direction. Therefore, the longitudinal axis of the cooling channel 31 is oriented at an angle γ of 90° with respect to the distribution channels 34 and recovery channels 36. The rounded portions 37a and 37b serve to induce a streamlined flow as much as possible in order to avoid or at least significantly reduce the generation of turbulence that would occur in the case of a non-rounded "angular" 90° bend. The reduction of turbulence results in a reduction of flow-induced oscillations of the reflective optical element M4.

[0114] The distribution channel 34, the cooling channel 31 connected to the distribution channel, and the recovery channel 36 connected to the cooling channel 31, as shown in Figures 2a and 2b, form three parts of a continuous curved channel 31, 34, and 36, and in the illustrated example, its length L C The length is approximately 10 cm. However, the length L of channels 31, 34, and 36 CThe length can be increased to approximately 15 cm or more, approximately 20 cm, or even more than approximately 20 cm. The diameter of the channels 31, 34, and 36 can be, for example, approximately 1 mm to approximately 20 mm, and especially approximately 1 mm to approximately 5 mm. In principle, the cross-sectional area A of the channels 31, 34, and 36 q The length L of the channels 31, 34, and 36 is C The variation over the length should be less than + / -20% or less, or less than + / -10%. In the illustrated example, the channels 31, 34, and 36 have a length L C Cross-sectional area A where the variation over the range is less than or equal to + / -2%. q It holds.

[0115] As shown in Figures 3a-3d and 4a-4d, for optimized flow guidance in a 90° bend, it is advantageous for the rounded sections 37a and 37b to have a constant radius of curvature R. The parameter essential for optimal flow guidance is expressed by the ratio of the radius of curvature R of the rounded sections 37a and 37b to the flow channel diameter D.

[0116] Figures 3a to 3d show the first rounded portion 37a connecting the end portion 31a of each cooling channel 31 and the distribution channel portion 34a connected to the end portion 31a, for four different ratios of the radius of curvature R of the rounded portion 37a to the diameter D of the rounded portion 37A. In this case, the radius of curvature R is measured at the center of the rounded portion 37a, as shown in Figures 3a to 3d. The diameter D of the rounded portion 37a is 5 mm in all four illustrated examples. In this case, the diameter D of the rounded portion 37a corresponds to the diameter D of the distribution channel 34 and the diameter D of the cooling channel 31. The length L is approximately 50 mm in the explanatory diagrams of Figures 3a to 3d. As is clear from Figures 3a to 3d, the R / D ratios are R / D=2, R / D=3, R / D=4, and R / D=5 in the four illustrated examples, respectively.

[0117] Similar to Figures 3a to 3d, Figures 4a to 4b show the second rounded portion 37b that merges the end portion 31b of each cooling channel 31 with the recovery channel portion 36a connected to the end portion 31b. The diameter D of the rounded portion 37b is 10 mm in Figures 4a to 4d. In the explanatory diagrams of Figures 4a to 4d, the length L is approximately 60 mm. In the explanatory diagrams of Figures 4a to 4d, the R / D ratios are R / D=2, R / D=3, R / D=4, and R / D=5 in the four illustrated examples, respectively. The diameter D of each rounded portion 37a and 37b is typically 2 mm to 20 mm, and ideally 2 mm to 12 mm.

[0118] As described above, there is an optimal ratio between the radius of curvature R and the diameter D of each rounded portion 37a, 37b such that centrifugal force acts so that the pressure of the fluid 28 outside the rounded portions 37a, 37b rises only slightly compared to the inside of the rounded portions 37a, 37b, thereby achieving a reduction in boundary layer separation upstream and downstream of the rounded portions 37a, 37b. Figures 3a-3d and 4a-4d show the contours of the region where the turbulent kinetic energy of the fluid 28 exceeds a specified value. In this case, it is assumed that the fluid 28 flows from the distribution channel portion 34a or the recovery channel portion 36a into each end portion 31a or 31b of the cooling channel 31.

[0119] For this purpose, it was found that the ratio of the radius of curvature R of the rounded portions 37a and 37b to the diameter D of the rounded portions 37a and 37b is particularly favorable between 2 and 6, more preferably between 2.5 and 5, and ideally between 2.5 and 3.5. When the R / D ratio is less than 2, a significant reduction in boundary layer delamination is usually not possible. The optimal value for the R / D ratio is typically between 2.5 and 3.5, but the optimal value may be outside this range in some cases. When the R / D ratio exceeds 6.0, the flow behavior usually deteriorates.

[0120] In reality, the rounded portions 37a and 37b cannot be fabricated on the monolithic substrate 25 using conventional processing methods, as described above. In the illustrated example, only the inlet channel 33 and outlet channel 35 are fabricated by conventional processing methods, specifically by introducing each perforation into the substrate 25. In contrast, as will be explained in more detail below, the distribution channel 34, cooling channel 31, and recovery channel 36 are fabricated by selective laser-induced etching of the substrate 25 material. In principle, the inlet channel 33 and outlet channel 35 can also be fabricated by selective laser-induced etching.

[0121] In the hollow structure 27 described above, only two parts 37a and 37b are rounded, while the distribution channel 34, recovery channel 36, and cooling channel 31 extend in a straight line. However, more complex hollow structures 27 can also be fabricated using the selective laser-induced etching described above. Figures 5a and 5b show an example of such a hollow structure 27 on a substrate 25, which substantially corresponds to the hollow structure 27 shown in Figures 2a and 2b. The difference between this hollow structure 27 and the hollow structure 27 in Figures 2a and 2b is that the cooling channel 31 has a slight curvature that follows the curvature of the concave curved surface 25a in the illustrated example. In the example shown in Figure 5b, the end portion 31a of each cooling channel 31 adjacent to the distribution channel 34 is oriented at an angle γ of approximately 115°. Although the cooling channel 31 has a curvature that extends in the ZX plane, it is possible to define a longitudinal axis that defines the angle γ for the end portion 31a connected to the rounded portion 31a. The second rounded portion 37b, which is not shown in Figures 5a and 5b, is understood to be realized in a manner corresponding to the first rounded portion 37a. The R / D ratio of the radius of curvature R to the straightness D of each rounded portion 37a and 37b is usually within the range of values ​​described above.

[0122] In the case of the substrate 25 shown in Figures 6a to 6f, the hollow structure 27 is substantially designed as the hollow structure 27 shown in Figures 2a and 2b, but differs from the latter in that the distribution channel 34 and recovery channel 36 do not extend vertically, but are oriented at an angle of approximately 25° with respect to the thickness direction Z of the substrate 25. As with the hollow structure 27 shown in Figures 2a and 2b, the hollow structure 27 shown in Figures 6a to 6d has two rounded portions 37a and 37b (not shown) between each distribution channel 34 or recovery channel 36 and the cooling channel 31. The angle γ between the distribution channel 34 or recovery channel 36 and the cooling channel 31 is 90° in this case as well, but extends in a plane inclined at approximately 25° with respect to the thickness direction Z, as is clear from Figure 6d which shows that the angle γ' between the longitudinal axis of the inlet channel 33 and each distribution channel 34 is approximately 115°.

[0123] The hollow structure 27 shown in Figures 6a to 6d has a rounded portion 38 where the confluence portion 34b of each distribution channel 34 transitions to the inlet channel 33, or more precisely, to the branching portion 33a of the inlet channel 33, or where the confluence portion 36b of each recovery channel 36 transitions to the branching portion 35a of the outlet channel 35. In the illustrated example, the rounded portion 38 does not have a constant diameter or channel cross-section; instead, the channel cross-section decreases starting from the branching portion 33a. The rounded portion 38 does not have a constant radius of curvature R, as in the case of the two curved portions 37a, 37b extending between each distribution channel 34 or recovery channel 36 and each cooling channel 31. Therefore, an optimized ratio of radius of curvature R to diameter D cannot be specified. The rounded portion 38 can also be fabricated using the selective laser-induced etching described above.

[0124] The difference between the hollow structure 27 shown in Figures 6e and 6f and the hollow structure 27 shown in Figures 6a to 6d is that the substrate is not a monolithic configuration, but is composed of three substrate components 39a, 39b, and 39c made of titanium-doped quartz glass. The second substrate component 39b and the third substrate component 39d are attached to the lower surface of the first substrate component 39a, or more precisely, permanently connected to the lower surface of the first substrate component 39a. In the illustrated example, this permanent connection is formed by thermal bonding, in which case the planar lower surface of the first substrate component 39a is connected to the planar upper surface of the second substrate component 39a and the planar upper surface of the third substrate component 39b. In some cases, the two substrate components 39a, 39b; 39a, 39c can be connected to each other by ringing before bonding.

[0125] The cooling channel 31, each rounded section 37a, 37b, and the adjacent distribution channel 34 and recovery channel 36 extend to the first substrate component 39a, except for their respective confluence sections 34b and 36b. The confluence section 34b of the distribution channel 34 extends to the second substrate component 39b, and the confluence section 36b of the recovery channel 36 extends to the third substrate component 39c. Furthermore, the inlet channel 33 of the hollow structure 27 extends to the second substrate component 39b, and the outlet channel 35 of the hollow structure 27 extends to the third substrate component 39c. The inlet channel 33 and outlet channel 35 are introduced to the second and third substrate components 39a and 39b, respectively, by perforation. After the confluence section 34b of the distribution channel 34 is perforated into the upper surface of the second substrate component 39b, the second substrate component is connected to the lower surface of the first substrate component 39a. The confluence portion 36b of the recovery channel 36 is correspondingly perforated from the upper surface of the third substrate component 39c. Therefore, as can be seen in Figure 6f, no rounded portions are formed at each confluence portion 34b, 36b.

[0126] As can also be seen in Figure 6f, each distribution channel 34 formed in the first substrate component 39a is directly adjacent to each confluence portion 34b. Similarly, the distribution channels 34 and recovery channels 36 are mostly formed by drilling from the underside of the first substrate component 39a. Only the rounded portions 37a, 37b and the cooling channel 31 are fabricated in the first substrate component 39a by selective laser-induced etching. For this purpose, as will be explained in more detail below, the first substrate component 39a, with the distribution channels 34 and recovery channels 36 pre-drilled, is immersed in an etching solution. The joining of the second and third substrate components 39b and 39c is usually performed after the selective laser-induced etching of the first substrate component 39a. However, in principle, it is possible to not perform selective laser-induced etching until after the final connection or joining of the three substrate components 39a to 39c.

[0127] The hollow structure 27 having at least one rounded portion 37a, 37b is not limited to the example described above, and in principle, other more complex hollow structures 27 having one or more of this type of portion can also extend into the substrate 25. Furthermore, not only can the cooling channel 31 have the curvature described in relation to Figures 5a and 5b, but the distribution channel 34 and the recovery channel 36 can also extend in a curved manner.

[0128] Figures 7a and 7b show two method steps of a selective laser-induced etching method for forming a channel 31 in a substrate 25 for one of the six mirrors Mi of the projection optical unit 10 in Figure 1. After the formation of the channel 31, more precisely after the formation of multiple channels 31, the high-reflectivity coating 26 described above is applied to the substrate 25. In the illustrated example, the channel 31 is a through channel that can be used as a cooling channel through which a cooling medium, not shown, usually in the form of water, can flow into the substrate 25. In order to form the channel 31 in the substrate 25, the method step shown in Figure 7a involves focusing pulsed laser radiation, more precisely a pulsed laser beam 40, into a continuous irradiation volume 41 of the substrate 25. In this case, the laser beam 40 is generated by a laser source 42 and incident in free space propagation to a focusing optical unit 43, which in the simplest case may be a focusing lens element.

[0129] The substrate 25 is the wavelength λ of the laser beam 40. L The material is transparent to the light, and therefore the laser beam 40 can be focused into a focal volume V around the focal position of the laser beam 40. In this case, the pulse energy of each pulse of the pulsed laser beam 40 is usually absorbed by a multiphoton process only within the focused volume V. At the focal volume V, the optical and chemical properties of the transparent material of the substrate 25 change without cracking, or possibly with microcracks, making it selectively chemically etchable. For example, by deflecting or moving the focal volume V of the substrate 25 using a microscanner system (not shown), it is possible to modify a continuous region within the substrate 25 that forms a continuous irradiation volume 41. In the example shown in Figure 7a, the focal volume V that forms a linear irradiation volume 41 is moved along the Y axis of the XYZ coordinate system.

[0130] Depending on the laser parameters used, the modification of the substrate 25 material may be microcracks or other deep damage. As shown in Figure 7b, the irradiated volume 41 modified by the pulsed laser beam 40 is subsequently removed by wet chemical etching. During wet chemical etching, the substrate 25 is usually immersed in an etching solution 44 for several weeks or months, and the etching solution preferably forms channels 31 in the substrate 25 by (selectively) dissolving the modified material of the irradiated volume 41 from the substrate 25 until this material is completely removed.

[0131] In selective laser-induced etching, a laser beam 40, usually in the form of ultrashort pulse laser radiation (ps or fs pulses), is focused into a focal volume V. The laser wavelength λ L This can be in the infrared wavelength range, for example, about 1 μm. In this example, the substrate 25 is made of titanium-doped quartz glass. In the case of this material, the pulsed laser beam 40 is at least one wavelength λ between 260 nm and 520 nm in order for the laser radiation to be absorbed by the conduction band of the titanium-doped quartz glass. LIt has been found that it is advantageous if the light is focused into the irradiation volume 41. When the substrate material 25 is (undoped) quartz glass, the wavelength λ of the laser beam 40 L If the wavelength is in the UV range, specifically below 266 nm, for example 248 nm or 193 nm, it is advantageous for absorption in the conduction band. In the latter case, the laser source 42 can be configured, for example, as an excimer laser or as a frequency-multiplier solid-state laser.

[0132] In particular, when the substrate 25 is made of quartz glass or titanium-doped quartz glass, it has been found that if the laser beam 40 in the focal volume V satisfies the coherence condition, that is, if a coherent laser beam 40 is radiated into the irradiation volume 41, it is advantageous for the following reasons: When coherent laser radiation is irradiated onto quartz glass, a light guide structure is formed first, followed by microchannels, whereas when non-coherent laser radiation is used, the formation of such structures, and consequently the corresponding material modification, occurs only with a significant delay. Therefore, it has been found that using a coherent laser beam 40 having a wavelength in the UV wavelength range, such as 351 nm or less, 308 nm or less, 275 nm or less, or 266 nm or less, generated by an excimer laser or frequency-multiplier solid-state laser, in combination with a relatively long pulse width, such as on the order of approximately 100 picoseconds to 100 nanoseconds, generated by a Q-switched solid-state laser or gas discharge laser, is advantageous for selective laser-induced etching of quartz glass or titanium-doped quartz glass.

[0133] As an alternative to, or possibly as an addition to, focusing laser radiation in the UV wavelength range, particularly in the case of the two materials mentioned above, namely quartz glass or titanium-doped quartz glass, the irradiation volume 41 of the substrate 25 is irradiated with (at least one) wavelength λ absorbed in the infrared absorption band of the substrate 25, in the wavelength range of 2500nm to 3120nm, 2150nm to 2230nm, or 1380nm to 1400nm. LA laser beam 40 having the following properties can also be irradiated. For this purpose, the laser beam 40 is absorbed in the corresponding absorption band in a two-photon process, with a wavelength λ in the aforementioned wavelength range. L It can have, for example, twice the wavelength λ. Alternatively, the laser source 42 can have a different wavelength λ L It can also generate laser radiation, the sum of which photon energy corresponds to one of the absorption bands mentioned above. For this purpose, the laser source 42 may include two or more lasers.

[0134] For the sake of simplicity, Figures 7a and 7b show a single irradiation volume 41, but it is understood that in principle, two or more irradiation volumes 41 can be formed in the substrate 25 to form two or more channels 31 in the substrate 25. It is also understood that an interconnected (cooling) channel network can be formed in the substrate 25. In principle, curved channels 31 can also be formed by selective laser-induced etching, i.e., each channel 31 does not necessarily have to be configured linearly, as shown in Figures 7a and 7b. In principle, any desired hollow structure 27 can be fabricated by scanning or moving the laser beam 40 within the volume of the substrate 25.

[0135] The flow path 31 can be configured as described in relation to Figures 2a, 2b or 5a, 5b, and can be connected to a distribution flow path 34 or a recovery flow path 36. In particular, each end portion 31a, 31b of the flow path 31 can merge with each distribution flow path portion 34a of the distribution flow path 34 or each recovery flow path portion 36a of the recovery flow path 36 at rounded portions 37a, 37b.

[0136] The selective laser-induced etching method described above is not limited to the substrate 25 for the mirror of the EUV lithography apparatus 1, but can also be used, for example, to form channels in the substrate 25 of a reflective or transmissive optical element of a DUV lithography system. The selective laser-induced etching method can also be used to form channels in other workpieces or components of a lithography system, for example, in workpieces intended to be incorporated into components such as actuators or sensors, which are intended to act as mounts for optical elements, or in workpieces in the form of wafer chucks or wafer tables where temperature control using a hollow structure or channels 31 is intended.

[0137] As can be seen in Figure 8, during the wet chemical etching step shown in Figure 7b, the etching process is carried out from the edge or side surface 25b of the substrate 25 into the irradiation volume 41, and etching forms a channel portion 45 that extends into the irradiation volume 41 from the channel inlet on the side surface 25b of the substrate 25 to the end surface 47 of the channel portion where the etch front is formed. The etch front or end surface 47 of the etched channel portion 45 is adjacent to the unetched volume region 41a of the irradiation volume 41. As the duration of the etching process progresses, further material is gradually ablated along the irradiation volume 41, i.e., the unetched volume region 41a of the irradiation volume 41 decreases until the channel 31 extends throughout the entire irradiation volume 41.

[0138] When etching materials such as quartz glass, titanium-doped quartz glass, and certain glass ceramics, the etching selectivity ratio of the irradiated volume 41 is relatively low compared to the unirradiated volume surrounding the substrate 25, and may be on the order of only 1:500. As a result, the channels 31 formed near each channel inlet on the surface 25a of the substrate 25 during etching may have a significantly larger cross-sectional area than those further inside the volume of the substrate 25. However, a cross-sectional area that is not constant over the length of the channel 31 is usually disadvantageous with respect to vibrations caused by the flow of a cooling medium (generally liquid), for example.

[0139] To form a substantially constant cross-sectional area for each channel 31 over the length of the channel 31, the etching rate A of the channel portion 45 is higher than that of each (circumferential) channel wall 46. S It is advantageous if the end face 47 of the flow channel portion 45 is etched (etching rate A R S In this way, the etching selectivity can be improved, meaning that more material is ablated in the direction of the remaining irradiation volume 41a or in the direction of the later-formed channel 31 than in the direction of the channel wall 46, i.e., the direction of the channel 31 corresponding to the Y direction in the XYZ coordinate system shown in Figures 7a and 7b in the illustrated example.

[0140] Etching rate A at the end face of the flow channel portion 45 S The etching rate A at the end face 47 of the flow channel portion 45 is typically on the order of approximately 100 μm / h to several mm / h. S Alternatively, in order to increase the etching selectivity ratio, that is, the etching rate A in the channel wall 46 of the channel portion 45. R and etching rate A at the end face 47 of the flow channel portion 45 S In order to reduce the ratio with, the etching rate A in the substrate 25 material S Raise or ratio A R / A S To reduce this, there are various methods for the material of the substrate 25, some of which are described in more detail below, to increase the etching rate AS or ratio A R / A S They can be used individually or in combination to reduce etching selectivity ratios or ratios A exceeding 1:1500, or in some cases exceeding 1:2000. R / A S This can be achieved in this way. To reduce the total processing time, the substrate 25 can be irradiated simultaneously using multiple laser sources 42, thereby enabling the simultaneous fabrication of multiple channels 31 or multiple etch fronts.

[0141] In the example shown in Figure 8, etching rate A S ​To raise the temperature T at the end face 47 of the flow channel portion 45, the temperature T at the flow channel wall 46 of the flow channel portion 45 is raised. R Temperature T 20K or more, 40K or more, or ideally 60K or more higher S This causes the temperature T at the channel wall 46. R This usually corresponds to the temperature of the etching solution 44, or the end face 47 of the flow channel portion, or the substrate 25 excluding the etch front. R The temperature should be as low as possible, ideally just above or possibly just below the freezing point of the etching solution 44. In contrast, the etch front of the end face 47 of the channel portion 45 should be at the temperature T of the channel wall 46. R More ideally, a temperature T that is 60K or higher, as high as possible. S It is maintained in that state.

[0142] During the etching process, the temperature T of the end face 47 of the flow channel portion 4 is reached. S To maintain this, the end face 47 of the flow channel portion 45 is heated using a heating device 48 that is guided along with the end face 47 of the flow channel portion 45 during the formation of the flow channel 31. In this way, the heating device 48 is kept at a constant distance from the end face 47 of the flow channel portion 45, and the T of the end face 47 of the flow channel portion 45 is maintained. S This makes it possible to keep it approximately constant.

[0143] In the example shown in Figure 8, the heating device 48 is located outside the flow channel portion 45 and rests on the upper surface 25a of the substrate 25, which is the surface of the substrate 25 at the minimum distance from the flow channel 31. After selective laser-induced etching, a reflective coating is applied to the upper surface 25a to form a mirror Mi. In the example shown in Figure 8, the heating device 48 is guided along the upper surface 25a of the substrate 25 in the Y direction parallel to the etch front of the flow channel 31 or end face 47, and for this purpose, a suitable mechanical moving device can be provided in the etching apparatus shown in Figure 7b.

[0144] In the example shown in Figure 8, the heating device 48 is a resistance heater that directly contacts the surface 25a to transfer contact heat to the material of the substrate 25. However, the heating device 48 can also be a heating light source, such as an infrared light source, or a laser that focuses radiation onto the end face 47 of the channel portion 45 during the formation of the channel 31 and is guided along with it. Alternatively, the heating device 48 (in the form of a resistance heater or light source) can be guided or passed through the channel portion 45, and the heating device 48 can be kept at a certain distance from the etch front or the end face 47 of the channel portion 45, ideally. In this case, the heating device 48 can be mounted on a suitable carrier element that is smaller in dimension than the channel diameter.

[0145] Etching rate A at the end face 47 of the flow channel portion 45 S A carrier element (probe) 49, such as one inserted into the flow channel section 45 to raise the flow rate, is shown in Figure 9. In the illustrated example, the probe 49 is inserted into the flow channel section 45 and guided along the end face 47 of the pre-formed flow channel 45 while the flow channel 31 is being formed. The probe 49 can carry, for example, a heating device 48 in the form of a resistance heater.

[0146] However, in the example shown in Figure 9, by increasing the flow rate of the etching solution 44 at the end face 47 of the flow channel portion 45, the etching rate A at the end face 47 of the flow channel portion 45 is increased. S To raise the probe 49, a propeller-shaped rotating device 50 is carried. Needless to say, a different type of rotating device, such as a turbine, can be attached to the probe 49 instead of a propeller. Furthermore, it is not always necessary for the probe 49 to continuously follow the end face 47 of the flow path section 45; the probe 49 can be introduced into the flow path section 45 intermittently (periodically) and then removed again.

[0147] In Figure 10, etching rate A STo increase the etching rate, the nozzle 51 is positioned permanently or intermittently in front of the channel inlet of the channel section 45, thereby mechanically removing particles 52 that have begun to etch from the end face 47 of the channel section 45. Alternatively, the nozzle 51 may be permanently advanced or intermittently inserted using a probe 49, as described in relation to Figure 9. As an alternative to or addition to the nozzle shown in Figure 10, the probe 49 may also include a mechanical agitator, brush, etc., positioned near the end face 47 of the channel section 45 or guided along the etch front, in order to remove etched particles 52 from the end face 47 of the formed channel section 45.

[0148] In the example shown in Figure 11, ultrasonic waves 53 are irradiated onto the end face 47 of the channel portion 45 to improve the etching selectivity. The ultrasonic waves 53 are generated by an ultrasonic vibrator 54, which is inserted into the channel 45 and positioned near the end face 47 of the channel portion 45 on a probe 49, as shown in Figure 9. The effects of the ultrasonic waves may include the detachment of particles 52 that have begun to be etched, the recirculation of the etching solution 44, and / or the heating effect on the etch front or the end face 47 of the channel portion 45. To generate ultrasonic waves 53 in a manner similar to that in Figure 8, the ultrasonic vibrator 54 can, as an alternative, be placed outside the substrate 25, for example on its upper surface 25a, and guided along with the etch front.

[0149] Figure 12 shows the etching rate A at the end face 47 of the flow path 31. SAnother means of increasing the performance is shown, which involves sealing the channel walls 46 of the channel portion 45 against etching or the action of the etching solution 44. For this purpose, in the example shown in Figure 11, a protective lacquer 55 is applied to the channel walls 46. The protective lacquer 55 may be, for example, a polymer lacquer that can withstand the action of the etching solution. To apply the protective lacquer 55, the substrate 25 must be removed from the etching solution 44, cleaned, and dried. The removal and application of the protective lacquer 55 can be performed periodically at predetermined time intervals, for example, once a day, to seal the entire newly etched channel portion or the etched channel portion 45 along the channel walls 46 during the day. In the latter case, the entire previous seal of the channel portion 45 is removed, for example, with an organic solvent, and a new sealant is applied that extends just before the etch front or just before the end face 47 of the channel portion 45.

[0150] For sealing purposes, the entire substrate 25 is typically immersed in a suitable protective lacquer 55. In this case, the end faces 47 of the channel portions 45, which will later form the etch front, must not be coated. This can be done by inserting a probe 49 and mechanically cleaning with a scraper 56, as very schematically shown in Figure 12. Alternatively, irradiation with (laser) light can be performed to remove the protective lacquer 55 from the end faces 47 of the channel portions 45.

[0151] UV-curing lacquer can also be used for sealing. In this case, a probe 49 radiating towards the side, i.e., towards the circumferential channel wall 46, rather than in the channel direction (Y direction), i.e., towards the end face 47, can be inserted into the channel portion 45. Finally, the uncured protective lacquer 55 is washed off from the etched channel portion 45. Alternatively, a sponge or felt impregnated with protective lacquer 55 attached to the probe 49 can be inserted into the channel portion 45. In this case, for example, by using a spacer mandrel, the protective lacquer 55 can prevent the end face 47 of the channel 31, i.e., the intended etch front, from getting wet.

[0152] In the example shown in Figure 13, instead of the wet chemical etching shown in Figure 7b, the channel 31 is etched to the substrate 25 using reactive plasma 57, meaning that in this case, the etching solution 44 is not required. For etching, in this example, a plasma source 58 is used to generate reactive plasma 57 in the form of reactive plasma species, in the illustrated example, in the form of oxygen radicals.

[0153] In the example shown in Figure 13, the etching rate A at the end face 47 of the flow channel portion 45 is also S Specifically, this is achieved by supplying reactive plasma 57 to the end face 47 of the flow channel portion 45. The flow channel 31 in Figure 13 has a minimum diameter d of approximately 5 mm, but the plasma source 58 has a diameter of 10 mm, and this plasma source cannot be introduced into the flow channel portion 45 by the probe 49. Therefore, the plasma source 58 is positioned near the entrance of the flow channel portion 45 and remains outside the substrate 25.

[0154] To guide the reactive plasma 57 to the end face 47 of the flow channel 45, Figure 13 shows a supply channel 59 in the form of a rigid tube, with its outlet end guided near the end face 47 of the flow channel 45. A hose or the like can also be used as the supply channel for the plasma or plasma species 57, with its free end, the outlet end, located near the end face 47 of the flow channel 31. The hose may have annular or helical reinforcing elements to allow for good flexibility and stabilization of its cross-section. For example, the supply channel 59 in the form of a tube or the like may need to be replaced periodically, may be made of an etching-resistant material, or, in the example shown in Figure 13, may be provided with an etching-resistant inner coating or lining.

[0155] If the channel 31 or channel portion 45 has a larger diameter, the plasma source 58 on the probe 49 can be inserted into the channel portion 45 and guided to the end face 47 of the channel portion 45 in order to locally expose the end face 47 of the channel portion 45 to the reactive plasma 57. As a result of the loss of reactive species during transport by the supply device 59, the external plasma source shown in Figure 13 needs to be designed to have a correspondingly higher output, so generating the reactive plasma 57 very close to the end face 47 of the channel portion 45 is advantageous.

[0156] During the etching process, the supply device 59 or optionally the plasma source 58 can be periodically inserted into and removed from the flow channel section 45 to purge waste material. Alternatively, continuous or semi-continuous purging can be used. Purge without introducing the supply path 59 or probe 49 into the flow channel section 45 is preferably performed using a solution or a liquid jet, while purging with the supply path 59 or probe 49 inserted is preferably performed using a gas jet.

[0157] Figures 14a to 14c show yet another means for purging the end face 47 of the flow channel section 45 and the flow channel wall 46 connected to the end face 47 of the flow channel section 45, and removing particles that have begun to etch in the process. In the example shown in Figure 14a, for this purpose, a fluid supply passage in the form of a flexible hose 60 is inserted into the curved flow channel section 45, as shown in the illustration. A fluid flow 61 directed toward the end face 47 of the flow channel section 45 exits from the outlet end 60a of the flexible hose 60. The purging fluid of the fluid flow 61 may be, for example, water.

[0158] To ensure efficient purging, the outlet end 60a of the hose 60 should be positioned at an average distance A' of at least 5 mm from the end face 47 of the flow path section 45, in order to allow for proper swirling of the fluid flow 61 in the area of ​​the end face 47 of the flow path section 45. Furthermore, this achieves thorough purging of the edge region of the flow path wall 46 in order to remove any particles that have not been completely separated from the flow path wall 46 of the flow path section 45. Such particles are, for example, plate-like in shape and have a considerable length, for example, about 3 mm, and adhere particularly to the upper surface of the flow path wall 46. Since such particles and bubbles can block the return flow of the purging fluid by blocking the narrow gap between the upper surface of the flow path wall 46 and the hose 60, such particles should be removed by the fluid flow 61.

[0159] The outlet end 60a of the flexible hose 60 should be positioned at an average distance A' of approximately 15 mm or less from the end face 47 of the flow path section 45, depending on the outflow rate and outflow pressure of the fluid flow 61, because otherwise the return flow effect of the particle-mixed fluid cannot be maintained. To enhance the swirling and return effects, when the end face 47 of the flow path section 45 is made to follow the hose 60 during the fabrication of the flow path 31, the distance A' of the outlet end 60a of the hose 60 can be changed within an optimal range of 5 mm to 10 mm, thereby periodically moving the hose back and forth.

[0160] As shown in Figure 14b, for optimal ingress flow to the end face 47 of the flow channel portion 45, the outlet end 60a of the hose 60 may have a nozzle 51 or attachment, as described above in relation to Figure 10. The nozzle 51 atomizes the outgoing fluid flow 61 over a much larger solid angle range than in the example shown in Figure 14a, where no nozzle is attached to the outlet end 60a of the hose 60. In this way, fluid movement independent of the orientation of the hose 60 occurs, and there is ingress flow around the entire circumference of the end face 47 of the flow channel portion 45. Thus, the equivalent or average ingress flow angle of the fluid flow 61 to the end face 47 of the flow channel portion 45 does not depend on the precise orientation of the outlet end 60a of the hose 60.

[0161] The nozzle 51 or hose attachment attached to the outlet end 60a can be constructed from a thin-walled, convex, curved membrane with a thickness of approximately 10 μm to 50 μm, made of a flexible, ductile, and crack-resistant material with micropores, such as high-grade steel, brass, or carbon composite material. Figure 14c shows a plan view of such a nozzle 51 having multiple micropores. The area ratio of the surface area of ​​the nozzle 51 shown in Figure 14c, which is composed of pores, should exceed 50% to ensure sufficient flow rate. Alternatively, the nozzle 51 can also be constructed from a tightly woven net, a microporous stopper, or a membrane with a comparable atomizing effect. To enhance the atomizing effect and provide optimized backward movement of the purging fluid, the hose 60 can be further perforated on the circumferential side surface of the area of ​​the outlet end 60a, as shown by the circular holes in Figure 14b.

[0162] To enhance the impact or erosion effect of the purging fluid on the end face 47 of the flow channel section 45 and the flow channel wall 46, the fluid flow 61 can be repeatedly switched on and off, i.e., intermittent purging can be performed. This enables the effective removal of small particles near the end face 47 of the flow channel section 45 and large, thin, plate-like particles, such as those on the upper surface of the flow channel wall 46, which are detached from a critical length of approximately 4 mm.

[0163] For efficient purging of the end face 47 of the flow channel portion 45 and the flow channel wall 46 connected to this end face, the flexible hose 60 shown in Figures 14a to 14c must continuously follow the etch front or the end face 47 of the flow channel portion 45 as it moves within the volume of the substrate 25. In this case, the flexible hose 60 may need to be inserted into hard-to-reach areas of the substrate 25. To achieve the effect of inserting the hose 60 into the formed flow channel portion 45 without kinking, the point of force application for the hose 60 to follow must be set as close as possible to the rigid wall defining the flow channel portion 45, and the direction of the force must be parallel to the initial path of the flow channel portion 45. Figure 15a illustrates this substantive matter based on the transition between the inlet flow channel 33 drilled in the substrate 25 and the confluence portion 34b of the distribution flow channel 34 of the hollow structure 27 shown in Figures 5a and 5b.

[0164] The point of force application, shown by the horizontal line in Figure 15a, should be as close as possible to the wall or material edge of the inlet channel 33 at the transition to the confluence 34b of the distribution channel 34 when the hose 60 is passed through the confluence 34b of the distribution channel 34, and the direction of the force, shown by the arrow in Figure 15a, should be as parallel as possible to the longitudinal direction of the confluence 34b of the distribution channel 34. If the direction of the force and the point of force application deviate significantly from the position and orientation shown in Figure 15a, this will inevitably cause kinking of the flexible hose 60 when it is inserted into the confluence 34b of the distribution channel 34, which may prevent further insertion of the hose 60 and cause damage.

[0165] To insert and follow the hose 60 without kinking into the confluence portion 34b of the distribution channel 34, which is oriented at a 90° angle to the inlet channel 33, it is advantageous to displace the point of force application and the direction of force for hose feeding outward from the substrate 25. For this purpose, it is advantageous to form a stable, rigid connection between the starting point of the confluence portion 34b of the distribution channel 34 and the hose 60.

[0166] Such a connection can be made using a rigid guide element 62, as shown in Figure 15b. The guide element 62 has a rod-shaped portion whose outer diameter is slightly smaller than the diameter of the cylindrical inlet channel 33. The rigid guide element 62 also has an internal channel 63 whose diameter is slightly larger than the diameter of the hose 60 to be guided. The guide element 62 is inserted into the inlet channel 33 by the rod-shaped portion. In this case, the opening of the internal channel 63 formed on the side of the rod-shaped portion is positioned opposite the opening of the confluence portion 34b of the distribution channel 34, thereby effectively forming a shape-connection type engagement. Using the rigid guide element 62, the point of force and direction of force for supplying and following the hose 60 are shifted from the base plate 25 to the end face of the rigid guide element 62, enabling kink-free insertion of the hose 60.

[0167] The precise path of the flow path 63 within the rigid guide element 62, the outlet position and outlet angle of the internal flow path 63 relative to the side surface of the rod-shaped portion, and the shape or geometric structure of the guide element 62 can be adapted or defined according to the desired path of the hollow structure 27. In the illustrated example, the internal flow path 63 extends along the longitudinal axis of the center of the guide element 62 and is guided tangentially in an arc from the free end of the rod-shaped portion of the guide element 62 at the desired outlet angle. The guide element 62 can be configured substantially rotationally symmetric with respect to the longitudinal axis, but this is not necessarily required.

[0168] The rod-shaped portion of the guide element 62 is connected to a portion that protrudes laterally beyond the substrate 25 and has a diameter slightly larger than the rod-shaped portion inserted into the inlet channel 33. This is advantageous because the shoulder formed between the rod-shaped portion and the protruding portion can act as a stopping surface when the rigid guide element 62 is inserted.

[0169] To guide the return flow of the purge fluid between the hose 60 and the wall of the internal flow path 63 as intended, in the example shown in Figure 15b, a return flow adapter 64 is fluid-tight or water-tightly attached to the end face of the portion of the guide element 62 that protrudes laterally beyond the substrate 25. The return flow adapter 64 is used in the slot portion of the internal flow path 63, and the returning purge fluid is guided laterally to the side of the return flow adapter 64 via the radial flow path shown in Figure 15b and supplied to a fluid line (not shown).

[0170] The rigid guide element 62 described above can be fabricated monolithically, for example, by additive manufacturing, such as using 3D printing. An Al-Si alloy can be used as the material for the rigid guide element 62 to meet the requirements of complexity and watertightness. As described above, the design of the guide element 62 fabricated by 3D printing can be adapted to the geometric structure of the hollow structure 27. For example, in this case, it is possible to realize a hose guide having a different outlet angle for the hose 60 than that of the side of the rigid guide element 62, and this outlet angle is adapted to the geometric structure of each flow path. For example, it is possible to realize an outlet angle of 90° with respect to the longitudinal axis of the rigid guide element 62. The return flow adapter 64 can also be fabricated by 3D printing. Unlike the explanatory diagram in Figure 15b, the return flow adapter 64 can be integrated with the guide element 62 rather than forming a separate component.

[0171] To enable multiple hoses to simultaneously follow multiple flow path sections processed in parallel, the guide element 62 can have multiple internal flow paths 63 that are separated from each other. In this case, the outlet positions on the sides of the rod-shaped portion of the guide element 62 can be selected in various ways in the longitudinal and / or circumferential or radial directions.

[0172] For automatic hose tracking, a tracking device 64, as shown in Figures 15b and 15c, can be used. In the illustrated example, the tracking device 65 includes a track roller 66a and a directly driven drive roller 66b. As can be seen in Figure 15c, the track roller 66a and drive roller 66b have grooved cross-sectional shapes, and their side cross-sections are also adapted to the cross-section of the hose 60 to apply effective contact pressure to the hose 60. In this way, sufficient feeding force can be applied to guide the hose 60, and significant dents in the hose 60 can be prevented. To increase adhesion, the sides of the guide roller 66a and drive roller 66b can be further roughened or knurled.

[0173] As can be seen in Figure 15b, in order to follow the hose 60, the guide roller 66a and drive roller 66b are positioned directly adjacent to the guide element 62 or the return flow adapter 64, thereby avoiding kinking and guiding the hose 60 through the internal flow path 63 of the rigid guide element 62 to the confluence portion 34b of the distribution flow path 34. Alternatively, the follower device 65 can be positioned near the inlet of each flow path of the hollow structure 27 without using the guide element 62.

[0174] If the flow channels 31 to be formed and the formed flow channel sections 45 are substantially straight or slightly curved with a radius of curvature greater than 10 mm, the tracking device 65, including the guide rollers 66a and drive rollers 66b shown in Figures 15b and 15c, is generally sufficient for tracking the hose 60, similar to an endoscope tool. The tracking device 65 can also be used to quickly remove the already inserted hose 60 from each flow channel section 45.

[0175] However, in the case of a flow channel wall 46 with a small radius of curvature of less than 10 mm or a flow channel with many changes of direction, the hose 60, which is already bent by the path of the preceding flow channel section 45, is pressed against the outside of the curved portion of the flow channel wall 46, requiring a greater force to be applied to feed it, thus causing difficulties during feeding. Furthermore, the leading edge of the hose may get caught on the microscopically roughened flow channel wall 46 of the flow channel section 45. The limited contact pressure of the follower device 65 shown in Figures 15b and 15c can lead to slippage or kinking of the hose 60, hindering further feeding of the hose 60.

[0176] Figures 16a to 16d show a follower device that can be used to achieve active rotation of the hose 60 in parallel with the feeding operation. The follower device includes a chuck 67 that can be automatically clamped, for example by pneumatic or electrical means, and can be driven directly by a rotary spindle. Furthermore, the chuck 67 is mounted on a linear spindle, which is shown as a rectangle in Figures 16a to 16d. The chuck 67 is released from the hose 60 and moved a corresponding distance, usually several millimeters, from the rigid guide element 62 without moving the hose 60, as shown in Figure 16a, so that the end face 47 of the flow path section 45 is followed by the hose 60. Then, as shown in Figure 16b, the hose 60 is automatically clamped to the chuck 67 and moved to the guide element 62 using the linear spindle. In this way, the hose 60 is inserted into the flow path section 45 with a programmable insertion length. The chuck 67 can then be automatically released again, and this process can be repeated to guide the hose 60 stepwise through the flow path section 45.

[0177] The rotation of the entire chuck 67 allows the hose 60 to rotate in addition to the linear feeding motion, as shown in Figure 16c, when the outlet end of the hose 60 is guided along a greatly curved flow path region. This rotation allows the hose 60 to be introduced into the greatly curved flow path region with minimal friction. During the return of the chuck 67 for reapplication, the follower device includes another fixedly mounted chuck 68 to prevent the hose 60 from rolling back or being accidentally pulled out of the flow path section 45. This other chuck 68 is automatically clamped before the chuck 67 is released for return, as shown in Figure 16d. Thus, the position of the hose 60 does not change during reapplication. As soon as the chuck 67 reaches its starting position and reclamps the hose 60 during return, the other fixed chuck 68 is released again. In this way, automatic continuous follower of the hose 60 can also be achieved.

[0178] In principle, the same tracking device can be combined with the chucks 67 and 68 shown in Figures 16a to 16d, and the guide roller 66a and drive roller 66b shown in Figures 15b and 15b. The above-described tracking device enables the end face 47 of the formed flow path portion 45 to be automatically followed by a non-self-propelled hose 60, even in the case of a complex hollow structure 27 or flow path 31 having a high aspect ratio of length to diameter that may exceed 10:1.

[0179] To simplify the illustrations in Figures 8 to 16d, only one channel portion 45 is shown on the substrate 25. However, it should be noted that in the case of the through channel 31 shown in Figures 7a and 7b, each channel portion 45, which has a channel wall 46 and an etch front on its end face 47, is formed on both sides of the substrate 25. For example, the etching step described above, which particularly increases the etching rate by following the hose 60, is usually performed simultaneously in both channel portions of the through channel 31.

[0180] Figure 17a shows a micrograph of a portion of the surface 46a of the wall 46 of the channel 31, which was fabricated by selective laser-induced etching, as described in relation to Figures 7a and 7b. The channel 31 is not a through channel but a temperature-controlled channel 31 as shown in Figures 2a and 2b, as illustrated in Figures 7a and 7b, and extends beneath the surface 25a of the substrate 25 to which the coating 26 is applied. To fabricate the temperature-controlled channel 31, which merges with the distribution channel 34 and the recovery channel 36 at two rounded sections 37a and 37b, purging with the flexible hose 60 described above in relation to Figures 14a to 16d was performed.

[0181] As can be seen in Figure 17a, the surface 46a has a honeycomb-like surface structure with multiple substantially circular recesses 70, and adjacent recesses 70 are interconnected. As can be seen by referring to Figure 17a and Figure 17b, which shows a cross-section of the surface 46a of the wall 46 of the channel 31 along the horizontal line shown by the dashed line in Figure 17a, the recesses 70 are crater-like, that is, each forms a depression whose bottom is surrounded by an annularly raised wall, also called a crater rim. As can be seen in the cross-section of Figure 17b, the height of the crater rim of each crater-like recess is not generally equal at all points in the circumferential direction, but varies depending on the circumferential position, which is due to the interconnection or overlap between the recesses 70. The crater rims of each recess 70 form a mesh-like surface structure.

[0182] The surface 46a having crater-like recesses 70 as shown in Figures 17a and 17b has a roughness R of less than 25 μm. a The surface roughness R of the wall 46a of the channel 31 has a The roughness R is typically 20 μm or less, 10 μm or less, or 5 μm or less, and can be particularly set to 2 μm or less. Both the temperature control channel 31 and the distribution channel 34 and the recovery channel 36 have a roughness R within the above value range. a It has a surface structure having the aforementioned crater-shaped recess 70.

[0183] Figures 17a and 17b show relatively small details from surface 46a with a lateral extent of approximately 250 μm × 190 μm, while Figure 18a shows a larger area of ​​surface 46a with a lateral extent of approximately 2000 μm × 2000 μm. Figure 18b shows a cross-section of surface 46a from Figure 18a along the horizontal line shown in Figure 18a. Figure 18b shows a particularly large and deep crater-like depression 70, which is circular in plan view, and in the illustrated example, its lateral extent L, corresponding to the diameter of the crater-like depression 70, is approximately 300 μm. The depth T of the crater-like depression 70 is approximately 2 μm. Generally, the crater-like depression 70 typically has a maximum lateral extent L of 500 μm or less, 450 μm or less, or 400 μm or less. The maximum depth T of the crater-like depression 70 is usually 20 μm or less, 15 μm or less, or 10 μm or less.

[0184] Figure 19 shows the surface 46a of the wall 46 of the channel 31 after similar etching treatment, with different laser parameters used during the initial irradiation. As can be seen in Figure 19, the surface 46a similarly has crater-like depressions 70, which have a polygonal basic shape and form a honeycomb surface structure. The depressions 70 of the surface 46a shown in Figure 19 also have the characteristics with respect to the maximum lateral spread E and depth T described above in relation to Figures 17a, 17b and 18a, and 18b. The surface 46a shown in Figure 19 also has a roughness R a The above values ​​apply to this.

Claims

1. The workpiece, preferably a substrate (25) for a mirror, and more particularly a substrate (25) for an EUV mirror (M4), A workpiece (25) comprising at least one hollow structure (27) configured to extend into the workpiece (25) and allow a fluid (28) to flow through it, The hollow structure (27) has first portions (31a, 31b; 34b, 36b) and adjacent second portions (34a, 36a) facing each other at angles of 60° to 120° (γ, γ'), preferably 80° to 100° (γ, γ'), and particularly 90° (γ, γ'), The hollow structure (27) has rounded portions (37a, 37b, 38) where the first portions (31a, 31b; 34b, 36b) and the second portions (34a, 36a; 33a, 35a) meet. The surface (46a) of the wall (46) of the hollow structure (27) of the first portion (31a, 31b; 34b, 36b), the second portion (34a, 36a; 33a, 35a), and / or the rounded portion (37a, 37b, 38) has a roughness R of 25 μm or less, preferably 10 μm or less, particularly preferably 5 μm or less, and particularly 2 μm or less. ａ A workpiece characterized by having the following features.

2. A workpiece according to claim 1, wherein the surface (46a) of the wall (46) of the hollow structure (27) has a recess (70).

3. The workpiece according to claim 2, wherein the recess (70) is configured in a crater shape.

4. A workpiece according to claim 2 or 3, wherein adjacent recesses (70) are in communication with each other.

5. A workpiece according to any one of claims 2 to 4, wherein the recess (70) on the surface (46a) of the wall (46) of the hollow structure (27) forms a honeycomb surface structure.

6. A workpiece according to any one of claims 2 to 5, wherein the recess (70) has a maximum lateral spread (E) of 500 μm or less, preferably 450 μm or less, and particularly 400 μm or less.

7. A workpiece according to any one of claims 2 to 6, wherein the recess (60) has a maximum depth (T) of 20 μm or less, preferably 15 μm or less, and particularly 10 μm or less.

8. A workpiece according to any one of claims 1 to 7, wherein the first portion (31a, 31b), the adjacent second portion (34a; 36a), and the rounded portion (37a, 37b) form flow path portions of flow paths (31, 34, 36) through which a fluid (28) can flow.

9. In the workpiece according to claim 8, the flow channels (31, 34, 36) have a diameter (D) of 1 mm to 20 mm, preferably 1 mm to 5 mm, and / or a length (L) of 10 cm or more, preferably 15 cm or more, particularly 20 cm or more. Ｃ A workpiece having )

10. In the workpiece according to claim 8 or 9, the cross-sectional area (A) of the flow channels (31, 34, 36) ｑ ) is the length (L) of the flow path (31, 34, 36) Ｃ A workpiece in which the variation over the specified range is + / - 20% or less, preferably + / - 10% or less, and particularly + / - 2% or less.

11. A workpiece according to any one of claims 1 to 10, wherein the R / D ratio of the radius of curvature R of the rounded portion (37a, 37b) to the diameter D of the rounded portion (37a, 37b) is 2 to 6, preferably 2.5 to 5, and particularly 2.5 to 3.

5.

12. A workpiece according to any one of claims 1 to 11, wherein the diameter D of the rounded portion (37a, 37b) is 2 mm to 20 mm, preferably 2 mm to 12 mm.

13. A workpiece according to any one of claims 1 to 12, wherein the hollow structure (27) includes a plurality of temperature-controlled channels (31) extending below the surface (25a) of the workpiece (25), and the hollow structure (27) includes a fluid distribution section (33) connected to the temperature-controlled channels (31) via a distribution channel (34), and a fluid recovery section (35) connected to the temperature-controlled channels (31) via a recovery channel (36).

14. A workpiece according to claim 13, wherein the first portion forms an end portion (31a) of the temperature control channel (31) connected to the distribution channel (34), the second portion forms a distribution channel portion (34a) connected to the end portion (31), and / or the first portion forms an end portion (31b) of the temperature control channel (31) connected to the recovery channel (36), and the second portion forms a recovery channel portion (36a) connected to the end portion (31b).

15. A workpiece according to claim 13 or 14, wherein the fluid distribution section (33) forms an inlet passage (33) from which the distribution passage (34) branches, and / or the fluid recovery section (35) forms an outlet passage (35) from which the recovery passage (36) branches.

16. A workpiece according to claim 15, wherein the first portion forms a confluence portion (34b) of the distribution channel (34) adjacent to the inlet channel (33), the second portion forms a branch portion (33a) of the inlet channel (33) adjacent to the confluence portion (34b), and / or the first portion forms a confluence portion (36b) of the recovery channel (36) adjacent to the outlet channel (35), and the second portion forms a branch portion (35a) of the outlet channel (35) adjacent to the confluence portion (36b) of the recovery channel (36).

17. A workpiece according to claim 16, wherein the angle (γ') between the branch portion (33a) of the inlet channel (33) and the confluence portion (34b) of the distribution channel (34) is greater than 90°, preferably greater than 100°, and / or the angle between the branch portion of the outlet channel (35) and the confluence portion (36b) of the recovery channel (35) is greater than 90°, preferably greater than 100°.

18. The workpiece, preferably a substrate (25) for a mirror, and more particularly a substrate (25) for an EUV mirror (M4), A workpiece (25) comprising at least one hollow structure (27) configured to extend into the workpiece (25) and allow a fluid (28) to flow through it, A workpiece characterized in that the surface (46a) of the wall (46) of the hollow structure (27) has a recess (70).

19. The workpiece according to claim 18, wherein the recess (70) is configured in a crater shape.

20. A workpiece according to claim 18 or 19, wherein adjacent recesses (70) are in communication with each other.

21. A workpiece according to any one of claims 18 to 20, wherein the recess (70) on the surface (46a) of the wall (46) of the hollow structure (27) forms a honeycomb surface structure.

22. A workpiece according to any one of claims 18 to 21, wherein each recess (70) has a maximum lateral spread (E) of 500 μm or less, preferably 450 μm or less, and particularly 400 μm or less.

23. A workpiece according to any one of claims 18 to 22, wherein the recess (70) has a maximum depth (T) of 20 μm or less, preferably 15 μm or less, and particularly 10 μm or less.

24. In the workpiece according to claim 18 or 23, the surface (46a) of the wall (46) of the hollow structure (27) has a roughness R of 25 μm or less, preferably 10 μm or less, particularly preferably 5 μm or less, and particularly 2 μm or less. ａ A workpiece having the following characteristics.

25. A workpiece according to any one of claims 17 to 24, wherein the hollow structure (27) is configured in the form of preferably curved flow channels (31, 34, 36) through which a fluid (28) can flow.

26. In the workpiece according to claim 25, the flow channels (31, 34, 36) have a diameter (D) of 1 mm to 20 mm, preferably 1 mm to 5 mm, and / or a length (L) of 10 cm or more, preferably 15 cm or more, particularly 20 cm or more. Ｃ A workpiece having )

27. In the workpiece according to claim 25 or 26, the cross-sectional area (A) of the flow channels (31, 34, 36) ｑ ) is the length (L) of the flow path (31, 34, 36) Ｃ A workpiece in which the variation over the specified range is + / - 20% or less, preferably + / - 10% or less, and particularly + / - 2% or less.

28. A workpiece according to any one of claims 1 to 27, wherein the material of the workpiece is selected from the group including quartz glass, particularly titanium-doped quartz glass, and glass ceramics.

29. In the workpiece according to any one of claims 1 to 28, the material of the workpiece has a zero-crossing temperature (T ＺＣ ) of 0°C to 100°C, preferably 19°C to 40°C, particularly preferably 19°C to 32°C, and the workpiece.

30. In the workpiece according to any one of claims 1 to 29, the material of the workpiece is the spatial variation (ΔT) of the zero-crossing temperature. ＺＣ A workpiece in which the temperature is less than 3K, preferably less than 2K, particularly preferably less than 1K, and especially less than 0.1K.

31. A workpiece according to any one of claims 1 to 30, wherein the workpiece is constructed in a monolithic manner.

32. A method for forming at least partially a hollow structure (27) in a workpiece (25), particularly in the workpiece (25) described in any one of claims 1 to 31, by selective laser-induced etching, The steps include focusing the pulsed laser radiation (40) onto the irradiation volume (41) of the workpiece (25), The steps include: forming the hollow structure (27) in the irradiation volume (41) at least partially by selective laser-induced etching; Methods that include...

33. Mirrors, especially EUV mirrors (24), A workpiece in the form of a substrate (25) according to any one of claims 1 to 32, A reflective coating (26) that reflects radiation, particularly EUV radiation (16), is applied to the surface (25a) of the substrate (25) and A mirror equipped with...

34. A lithography system, particularly an EUV lithography system (1), A lithography system comprising at least one workpiece as described in any one of claims 1 to 31 and / or at least one mirror as described in claim 33, and a temperature control device, particularly a cooling device (32), configured to flow a temperature control fluid, particularly a cooling fluid (28), into at least one hollow structure (27).

Images