Lithography method for forming three-dimensional microstructures with excessive structural height on a support material

Abstract

To improve a lithographic method for forming three-dimensional microstructures having an excessive structure height in a support material. The present invention relates to a lithographic method for forming three-dimensional microstructures with an excessive structure height in a photostructurable support material by means of an exposure apparatus. The excessive structure height has a height that exceeds the maximum nominal penetration depth. The method comprises the following steps: planar application of a photostructurable support material (1) with a given layer height (H.1) on a substrate support (2); computer-aided modeling of a virtual three-dimensional structural model (10) of the microstructure to be formed with a total height (H.10) that is greater than the maximum nominal penetration depth upon exposure to light on the support material (1); computer-aided division of the total height (H.10) of the structural model (10) into a plurality of substructures (11, 12, 13) that are successively stacked one on top of the other. calculation of virtual photomasks (M.11, M.12, M.13) for each of the substructures (11, 12, 13); structuring with the virtual photomasks (M.11, M.12, M.13) by exposing and developing the support material (1) until the entire virtual photomask (M.11, M.12, M.13) is structured layer by layer; obtaining a completely structured support material (30) including the entire structure model (S.10) and a structured portion corresponding to its entire height (H.10).

Description

Technical Field

[0001] The present invention relates to a lithography method for forming a three-dimensional micro-structure having a large structural height on a photo-structurable support material.

Background Art

[0002] In the trend of miniaturization in many technical fields, recently, micro-structures have found many new application fields, for example, in the fields of optoelectronics, photonics, image processing sensor technology, machine vision, robotics, and motion control systems. In these and further application areas, there is often a need to be able to efficiently form one-dimensional, two-dimensional, and / or three-dimensional micro-structures having a larger structural height or structural depth on a support material at a scale (or order) starting from, for example, 100 micrometers (μm) up to sub-millimeters (mm) (less than millimeters) with the greatest possible accuracy quickly and accessibly. Furthermore, in addition to manufacturing a support material having one-dimensional (abbreviation: 1D), two-dimensional (abbreviation: 2D), and / or three-dimensional (abbreviation: 3D) micro-structures that may have overhangs or cavities in some cases, there is also a requirement to be able to form so-called 2.5D micro-structures on the support material. A person skilled in the art understands the concept of "2.5D" as an object or structure (body) that is three-dimensional (3D) in itself but does not have a defined (clearly bounded) lower edge. In particular, 2.5D micro-structures can have back cuts, undercuts, and / or overhangs. For example, a spherical lens whose lower edge is rounded is called a 2.5D micro-structure. This type of 2.5D micro-structure can be used, for example, in optical applications.

[0003] Within the framework of this invention, the concept of structural height of a microstructure can be understood synonymously with the structural depth of the microstructure. In a three-dimensional Cartesian coordinate system, for example, a flat microstructure having a predetermined length in the X-axis direction and a predetermined width in the Y-axis direction can be defined. The structural height of the microstructure is defined in the Z-axis direction, which serves as an indicator of height. A recess or cavity of a microstructure that can be measured from (relative to) a level (horizontal) plane (Flaechenniveau) can also be defined as the structural depth in the negative Z-axis direction. For simplicity, the term structural height will generally be used below. [Prior art documents] [Patent Documents]

[0004] [Overview of the project] [Problems that the invention aims to solve]

[0005] Two different methods are already known from conventional techniques, and both methods use photons to structure microstructures.

[0006] In maskless single-photon laser beam lithography (1PL), a layer of positive photoresist is exposed using a virtual digital photomask and then developed. By using a virtual photomask, individual points in the photoresist layer are exposed differently due to local (spatial) variations in individual photodose (Lichtdosis), and thus, in combination with the subsequent single development process, can be individually structured.

[0007] However, in this case, light absorption increases exponentially with the thickness of the photoresist layer, which has the disadvantage of severely limiting the penetration depth during exposure of the photoresist. At the same time, the maximum possible structural height or depth that the photoresist can be structured is also subject to the same limitation. On the other hand, an increase in the light dose, i.e., the light intensity per exposure area, can lead to the destruction of the photoresist if it exceeds a predetermined limit. Positive-type photoresists currently available on the market typically have a maximum exposure of 1200 mWs / cm². 2 It can be exposed with a light dose. Therefore, when using only one layer of positive photoresist, the formation of microstructures is limited to a maximum structure height or depth of 100 μm (micrometers).

[0008] Furthermore, so-called direct two-photon laser beam lithography (abbreviated as 2PL) is known from the prior art, and this can be used, for example, to additionally form micro-optical structures on already pre-formed macro-optical systems [structures].

[0009] In this case, the structuring (structure formation) of the support material is based on the sequential scanning of so-called "voxels" using a virtual 3D photomask and a subsequent single development of the photoresist. The concept of "voxel," a combination of the abbreviated syllables "vox" for "volume" and "el" for "elements" in English, is understood in the field of computer graphics as a grid point or image point in a three-dimensional grid. In the case of a spatial dataset that exists discretely in Cartesian coordinates, a voxel represents a discrete value in the XYZ coordinates of that dataset.

[0010] While this method can itself form 2.5D structures and pure 3D structures with structural heights in the millimeter range, its drawback is that, currently, it only produces approximately 3 mm per hour. 2This represents an extremely slow writing (drawing) speed. The layer height (thickness) of each structural layer written (formed) individually corresponds to the size of one voxel, i.e., the size of one image point less than 1 micrometer (μm), in this method. Therefore, with this technique, the total surface area that can be structured is limited to a maximum of a few square millimeters. Furthermore, because the processing time is so slow, such microstructures cannot be formed efficiently or cost-effectively, and the throughput is also low.

[0011] A third known technique is diamond turning technology (Diamantdrehtechnik), but this is limited in principle to the manufacture of rotationally symmetric objects. Even ultra-fine diamond turning technology, which was itself developed for structuring 3D structures on the micrometer scale (or order of magnitude), has its weaknesses. The structure of workpieces manufactured by ultra-fine diamond turning technology usually deviates from the predetermined structural shape on the micrometer scale. In this case, deviations of up to 3 micrometers (μm) are common, and therefore diamond turning technology is not suitable for the fine structuring of microstructures.

[0012] Therefore, the object of the present invention is to provide an improved lithography method for forming (etching or imprinting) three-dimensional microstructures having a large structural height onto a support material. It is desirable that this novel method overcome the known drawbacks (multiple) of the prior art.

[0013] In particular, for one-photon laser beam lithography (1PL method), it is desirable that this novel method enables the rapid and highly accurate fabrication of microstructures with structural heights or depths exceeding 100 micrometers (μm).

[0014] For two-photon laser beam lithography (2PL), it is desirable that this novel method enables the rapid and high-throughput fabrication of relatively large-area microstructures, such as those with a basal surface area of ​​several square centimeters. [Means for solving the problem]

[0015] These problems are solved by the lithography method of the type described at the beginning, having the features of claim 1. [Modes for carrying out the invention]

[0016] Advantageous embodiments and advanced configurations of the present invention are described in the dependent claims and herein.

[0017] A lithography method for forming a three-dimensional microstructure having an excessive structural height on a photostructured support material using an exposure apparatus, wherein the maximum nominal penetration depth of exposure, and therefore the resulting photostructured portion of the support material, is obtained depending on the exposure characteristics of the photostructured support material and the exposure parameters of the exposure apparatus, and the excessive structural height is greater than the value of the maximum nominal penetration depth, comprises the following method steps: -a- Planar (flat) coating of a photostructured support material on a substrate support, wherein the coated support material has a predetermined layer height and a flat surface on the upper side opposite the substrate support, and the properties of the support material can be altered by exposure with an electromagnetic beam; -b- Use of information data as input values, provided that this information data includes data on the maximum nominal penetration depth of the selected photostructured support material and the geometric shape of the three-dimensional microstructure to be formed having excessive structural height; -c- Computer-aided modeling of a virtual three-dimensional structural model of the microstructure to be formed, depending on the information data obtained by step-b-, wherein the structural model includes topographic data of the microstructure to be formed, and the overall height of the structural model for the microstructure to be formed is determined using the topographic data, and the overall height is greater than the maximum nominal penetration depth of the electromagnetic beam during exposure to the support material and less than the height of the coated layer of the support material; -d- Computer-aided division of the total height of a 3D structural model into N (N≧2~n) height layers stacked sequentially vertically, where N is a control variable N≧2~N=n, each of the N (N≧2~n) height layers corresponds to an individual substructure of the structural model, each of the N (N≧2~n) substructures has a sub-height, N is an integer greater than or equal to 2, and N (N≧2~n) is selected such that each of the N (N≧2~n) sub-heights is less than or equal to the possible [maximum] nominal penetration depth of the electromagnetic beam that can be supplied by the exposure apparatus during exposure to the support material, and the sum of the N (N≧2~n) sub-heights of the individual substructures corresponds to the total height of the structural model; -e- Calculation of a virtual photomask for each of the N (N≧2~n) substructures of the structural model, where for each of the N (N≧2~n) photomasks, the respective topographic data of each substructure is converted to a corresponding value of the individual exposure dose, and the exposure dose calculated for a given part of a substructure correlates with the individual height position of the same part within the corresponding substructure; -f- Positioning (positioning) of the first virtual photomask corresponding to the first substructure in the lowest height layer of the structural model, and the alignment markings on the surface of the support material; -g- Alignment exposure of the support material using alignment markings placed on the surface, wherein the structured portion of the first substructure is written (formed) on the support material by spatially resolved exposure starting from the surface of the support material and corresponding to individual exposure doses determined in the first virtual photomask; -h- Wet chemical development of the exposed portion of the support material predetermined by the first virtual photomask, wherein the surface of the structured portion of the first substructure is smoothed until the surface of the structured portion becomes optically smooth after exposure and development, depending on the development rate of the support material and the calculated exposure dose; -i- Acquisition (generation) of a first intermediate product of a partially structured support material, wherein the first intermediate product includes a structured portion of the first substructure; -j- Positioning of a further Nth (N ≥ 2 to n) virtual photomask inside the already structured structured part of the (N - 1) partial structures each preceding the respective (N - 1) intermediate products, provided that the Nth (N ≥ 2 to n) virtual photomask corresponds to the Nth (N ≥ 2 to n) partial structure in the Nth (N ≥ 2 to n) height layer of a structure model that is positioned successively higher next to the (N - 1) height layers each preceding the respective one; -k- Further alignment exposure of the respective (N - 1) intermediate products using the alignment markings arranged on the surface, provided that starting from the already structured structured part of the respective (N - 1) partial structures, the structured part of the Nth (N ≥ 2 to n) partial structure is written (formed) into the respective (N - 1) intermediate products of the support material that is partially structured by spatially resolved exposure according to the individual exposure doses determined in the Nth (N ≥ 2 to n) virtual photomask, and the structured part of the Nth (N ≥ 2 to n) partial structure inside the support material is each positioned deeper than the structured part of the respective (N - 1) partial structure; -l- Wet chemical development of the exposed part of the support material predetermined by the Nth (N ≥ 2 to n) virtual photomask, provided that the surface of the structured part of the Nth (N ≥ 2 to n) partial structure is smoothed until the surface of the structured part becomes optically smooth after exposure and development, depending on the development rate of the support material and the calculated exposure dose; -m- Corresponding repetition of a series of steps -j- (each further positioning of a virtual photomask), -k- (further exposure) and -l- (further development) as required until a total of N (N ≥ 2 to n) virtual photomasks are structured for each layer; -n- Obtaining (generating) a completely structured support material, provided that the completely structured support material includes the structured part corresponding to the entire structure model and its overall height.

[0018] The concept of "excessive structure height" is here understood as a micro-structure (height) whose structure height is greater than the maximum nominal penetration depth of exposure into the optically structurable support material.

[0019] The maximum nominal penetration depth of the exposure results from the following parameters: - The selection of the possible exposure depths, respectively depending on the photo-structurable support material used and the photochemical material properties of the support material selected; - The selection of the appropriate light dose to expose the support material without breaking it; - The selection of the exposure device used; - The selection of the appropriate development time.

[0020] Thus, depending on the exposure parameters of the selected exposure device such as the development time, and in relation to the exposure characteristics or material properties of the photo-structurable support material such as the maximum light dose that can be selected without breaking the support material during exposure, the maximum nominal penetration depth of the exposure is obtained. However, with currently available materials and devices, the nominal penetration depth is generally at most 100 micrometers (μm).

[0021] For example, as an exposure device, it may be suitable for the purpose to use a quadruple microscope objective lens with a numerical aperture of 0.14. Further, for example, in order to achieve an exposure depth in a photo-structurable support material of approximately 50 micrometers (μm) at a light wavelength of 405 nanometers (nm) and a writing (drawing) speed of 100 mm / s using maskless one-photon laser beam lithography (abbreviation: 1PL), a light dose of 750 mWs / cm 2 may be suitable for the purpose. For the selection of the development time, for example, when a product AZ® MIF developer of Microchemicals (www.microchemicals.com) is used as the developer, in particular, it may be advantageous to select a development time of 30 minutes.

[0022] Therefore, the excessive structural height, as defined below, has a height greater than the above reference value of approximately 100 micrometers (μm), and may even be significantly greater than this reference value. Advantageously, the method of the present invention can also form or write (draw) structures on photostructured materials, even structures whose structural height may be on the order of, for example, 500 micrometers (μm) or more. Such excessive structural heights are hereafter referred to as sub-millimeter (mm) scale (order) structural heights.

[0023] In step a, the photostructured support material is first coated (distributed) planarly (flatly) onto the substrate support. Advantageously, the photostructured support material may be a photoresist, which is coated in multiple layers as needed, stacked vertically, until a sufficiently large layer height of the planar support material is obtained, which is sufficiently greater than the excessive structural height of the three-dimensional microstructure to be formed that is to be transferred to the support material.

[0024] The photostructured support material can therefore be applied to the substrate support in one and / or multiple steps according to one of the following current coating methods: dip coating; spin coating; slot die coating; doctor blading; curtain coating; or metering rod or Meyer bar coating.

[0025] In step-b, relevant information for subsequent modeling of the three-dimensional microstructure is collected using the maximum nominal penetration depth when exposing the selected support material, and using the geometric shape, particularly contour data, of the microstructure to be formed that has an excessive structural height.

[0026] Step c can be executed as intended using CAD (Computer-Aided Design) data (set) generated as a virtual or digital 3D structural model from the 3D microstructure to be formed, depending on the information obtained in advance. The virtual structural model in this case includes topographic data of the microstructure to be formed, and the overall height of the structural model for the microstructure to be formed is determined using this topographic data. This overall height of the structural model is greater than the maximum nominal penetration depth of the electromagnetic beam during exposure to the support material and less than the height of the coated layer of the support material. As already described above, microstructures can be formed with an overall structural height or overall structural depth of at least 100 micrometers (μm), and even down to a structural height in the sub-millimeter range. The structural height or structural depth is further related to the Z-axis direction in a 3D Cartesian (orthogonal) coordinate system, where the Z-axis direction defines the height position (Hoehenlage).

[0027] Conceptual topography (Topographie) (derived from the Greek words topos (from the German "Ort" (location)) and grafein (from the German "zeichnen" or "beschreiben" (to describe)); literally "Ortsbeschreibung" (location description)) is further understood as a description of the surface state (properties) or geometric form and physical and chemical properties (characteristics) of a technical surface or microstructure. The description of topography (surface state, surface form, etc.) is generally based on data from measurement methods.

[0028] In the next step-d-, the total height of the 3D structural model is divided into at least two or more N (N≧2~n) height layers, where N≧2~N=n, which are continuously stacked vertically, using computer assistance. Each height layer is less than or equal to the maximum nominal penetration depth of the electromagnetic beam that can be supplied by the exposure apparatus during exposure to the support material, and the sum of the heights of the individual substructures corresponds to the total height of the structural model. The division of the virtual structural model into at least two or more vertically stacked height layers is performed in the Z-axis direction, which corresponds to the height position in the Cartesian coordinate system.

[0029] The next step-e, namely the calculation of a (one) virtual photomask for each substructure of the virtual structural model, is advantageous for controlling the apparatus for maskless graytone lithography. Each virtual photomask thus represents the light intensity for an individual exposure dose or a specific part of the substructure.

[0030] The height position of each part of the structural model, or the maximum structural height of a particular part of a substructure, in this case corresponds to the maximum depth to which this part of the substructure can be formed (imprinted) or written into the support material. The inversion of the structural height of a corresponding substructure of the structural model to the structural depth of the structured part of this substructure in the support material occurs based on photochemical structuring.

[0031] The developable layer thickness in this case is usually determined by the exposure dose or light intensity per unit time [mWs / cm²]. 2 It increases non-linearly along with [ ].

[0032] Next, in step f, a first virtual photomask corresponding to the first substructure in the lowest height layer of the structural model is positioned appropriately on the surface of the support material. Here, the first virtual photomask also records (includes) alignment markings for the formation of the (substructure) on the surface of the support material.

[0033] In the next step-g-, alignment exposure of the support material is performed using alignment markings placed on the surface of the support material. Here, the structuring portion of the first substructure is written (formed) into the support material by spatially resolved exposure, starting from the surface of the support material and corresponding to individual exposure doses determined in the first virtual photomask.

[0034] Following exposure, in step-h-, wet chemical development is performed on the exposed portion of the support material predetermined by the first virtual photomask. Here, the surface of the structured portion of the first substructure is smoothed until the surface of the structured portion is optically smooth after exposure and development, depending on the selected structuring method, i.e., depending on the development rate of the support material used and the calculated exposure dose.

[0035] The concept of an "optically smooth surface" is well known to those skilled in the art, particularly in the field of molding methods for the manufacture of optical elements. For example, as can be seen from Alexander W. Koch et al.'s book "Optische Messtechnik an technischen Oberflaechen", expert-Verlag 1998, ISBN 3-8169-1372-5, a surface is called "optically smooth" if its surface roughness or structure is much smaller than the wavelength λ (lambda) of light in the visible spectrum. For optically valuable (high-precision) elements, a requirement of a maximum non-uniformity (roughness) of λ / 16 for an optically smooth surface is appropriate.

[0036] For the visible spectral region of light with wavelengths λ approximately 380 nm to 780 nm, this means that the surface roughness value for an "optically smooth" surface needs to be at most 23.75 nm (380 nm / 16) to 48.75 nm (780 nm / 16).

[0037] The criteria that must be met for the surface of the structured portion, i.e., the structured recess, on the upper side of the support material to be optically smooth after exposure and development have the effect of preventing unwanted scattered light (stray light) in one or more subsequent further exposure steps. In particular, in the case of further laser structuring, it is important to perform the further structuring without the scattering light effect and the resulting error source.

[0038] The scattering light effect that appears in subsequent structuring of an already structured surface through further exposure and development can be reduced as the roughness of the structured surface, expressed by the average roughness value Ra, decreases. Therefore, further structuring by exposure and development can be performed with greater precision. Advantageously, the structuring of the surface of structured recesses or cavities within the support material is performed so as to adjust the roughness value to preferably 30 nm (nanometers) or less for optically smooth surfaces.

[0039] The concept of "structuring" is understood here as a combination of the method steps "alignment exposure" (step-g-) and "wet chemical development" (step-h-).

[0040] Therefore, the result of structuring is a structure written (formed) on the support material, which has an optically smooth surface suitable for one or more subsequent further structuring steps.

[0041] Step i thus produces a first intermediate product of a partially structured support material, where the first intermediate product includes a structured portion of the first substructure.

[0042] Further steps -j-, -k-, and -l- help to structure the next virtual photomask corresponding to the subsequent next height position of the virtual structural model within the pre-generated structured section.

[0043] Step -m- is followed by a series of steps -j- (further positioning of the virtual photomask), -k- (further exposure), and -l- (further development), which are repeated as needed, until the entire virtual photomask is structured layer by layer.

[0044] By step n, a fully structured support material is obtained as a product according to the present invention. Here, the fully structured support material includes a structured portion that corresponds to the entire virtual three-dimensional structural model along or in conjunction with its overall height. The fully structured support material can further serve, for example, as a master for further shaping of the original structure by a galvanic method or for the manufacture of a master mold by silicon molding.

[0045] This method provides a novel inversion lithography technique for forming three-dimensional (3D) microstructures (patterns) on photochemically structured support materials. Here, the three-dimensional microstructures have excessive structural heights ranging from the micrometer scale to the sub-millimeter scale, which have not been able to be manufactured rapidly and precisely using currently known manufacturing methods.

[0046] In one method of the present invention, it may be advantageous if the photostructured support material is a positive-action (positive-type) photoresist in which the exposed portion is removed from the support material by dissolution during subsequent wet chemical development.

[0047] Photoresist is used in photolithography structuring, particularly in microelectronics and microsystems technologies for the fabrication of structures in the micrometer and submicrometer regions, as well as in circuit board manufacturing. The most important starting materials (raw materials) for photoresist are polymers (e.g., polymethyl methacrylate, polymethylglutarimide) or epoxide resins, solvents such as cyclopentanone or γ-butyrolactone, and photosensitive components.

[0048] In addition to liquid photoresists, there are also solid or dry resists (photofilms: Photofolien).

[0049] During exposure, the solubility of the photolayer is locally altered by the electromagnetic beam in the form of ultraviolet light components, corresponding to the light dose of the virtual photomask (photochemical reaction).

[0050] They can be classified as follows according to the change in solubility: - Negative-tone photoresist: Solubility decreases after exposure. - Positive-tone photoresist: Solubility increases after exposure.

[0051] In the case of positive-action photoresists, the already cured photoresist may be photochemically altered by exposure, making it soluble in the appropriate developer. After development, only the areas that were not protected by the appropriate cover mask before irradiation or that were outside the exposed areas remain.

[0052] The use of positive-action photoresists as photostructured support materials offers the advantage that, depending on the method, layer by layer—according to the calculated virtual photomask(s)—the height layers are successively structured deeper into the positive-type photoresist, ultimately resulting in a recess or cavity in the fully structured positive-type photoresist whose overall height corresponds to the overall height of a predetermined structural model. The unstructured regions of the positive-action photoresist, i.e., regions that have not been exposed and developed, advantageously maintain the layer height initially selected (by step-a).

[0053] Fully structured support materials in the form of positive-acting photoresists can further serve, for example, as masters for further shaping of original structures by galvanic methods or for the production of matrices by silicon molding.

[0054] In one method of the present invention, the alignment exposure of the support material may be particularly advantageous if it is performed by maskless laser lithography based on one-photon absorption and / or two-photon absorption, or by optical maskless lithography using a spatial light modulator and an imaging optical system.

[0055] The concept of "maskless laser lithography" is understood by those skilled in the art as a method for exposing a photostructured support material, preferably a positive-acting photoresist, using a focused laser beam with continuous scanning and simultaneous modulation of light intensity. A laser beam is used as the exposure source. An advantage of this exposure method is that maskless laser lithography allows for exceptionally precise (accurate) defined light doses per pixel, and therefore within a dataset precisely defined using XYZ coordinates. Based on the possibility of using one-photon absorption (abbreviated as 1PL) and / or two-photon absorption (abbreviated as 2PL), this exposure method makes it possible to fabricate true 3D structures. However, a disadvantage of this exposure method is that it is relatively slow due to the continuous scanning.

[0056] The concept of "optical maskless lithography" is understood by those skilled in the art as a method for exposing a photostructured support material, preferably a positive-action photoresist, in which structuring is performed by optical imaging of a (one) surface (pixel matrix) of a spatial light modulator in the support material or, preferably, a photoresist. For this reason, UV light generated by, for example, a UV-LED is used as the exposure source. This exposure method is advantageous in that surface exposure can be performed significantly faster than in the case of maskless laser lithography. However, a disadvantage of the optical maskless lithography method is that true 3D structuring by this exposure method may require tilting the sample or support material during structuring. In a preferred variation of the present invention, if at least one virtual photomask is positioned using alignment markings on the surface of the support material, which is tilted at a predetermined angle, this may be advantageous, particularly for structuring backcuts (Hinterschneidungen).

[0057] As described above, especially when using optical maskless lithography as the exposure method, it may be necessary to tilt the support material during the structuring of true 3D structures such as back cuts, undercuts, and / or overhangs. The appropriate tilt angle required to tilt the support material can be adjusted, for example, by an electric goniometer.

[0058] The method of the present invention also makes it possible to position multiple or all virtual photomasks on the surface of a support material that is tilted at a predetermined angle. Furthermore, within the framework of the method of the present invention, for exposure, the support material can be tilted for multiple or all virtual photomasks, each at the same angle for each height layer to be structured or for each virtual photomask, or at individually different angles.

[0059] In one advanced form of this advantageous method variation, the alignment exposure of the support material and the subsequent wet chemical development of the exposed portion of the support material, predetermined by at least one virtual photomask, can be performed using alignment markings on the surface of the support material, which is positioned at a predetermined inclination angle.

[0060] Alignment markings (or alignment marks) that are structured together with the first virtual photomask on the surface of the support material are useful for precise positioning for subsequent further structuring steps, even during tilt exposure or tilt structuring of the support material.

[0061] In the method of the present invention, it is particularly advantageous if the photostructured support material has a layer height greater than 100 micrometers (μm), preferably greater than 200 micrometers (μm), and especially preferably greater than 500 micrometers (μm), and it is preferable that the support material is coated onto the substrate support in multiple layers (as multiple layers).

[0062] In this case, the layer height of the support material should preferably be selected such that the support material provides sufficient thickness to accommodate the entire structural model, and in particular, the overall height of the structural model.

[0063] In the method of the present invention, advantageously, the overall height of the structural model can be greater than 100 micrometers (μm).

[0064] Advantageously, the method of the present invention makes it possible to fabricate three-dimensional microstructures with excessive structural heights on the micrometer to sub-millimeter scale, which have not been able to be manufactured rapidly and precisely by currently known manufacturing methods. The overall height of the structural model modeled in step-c can also be significantly larger than 100 micrometers (μm), and can reach the sub-millimeter scale.

[0065] In a further advantageous variation of the present invention, in this method, a number N (N≧2~n) can be selected such that each of the N (N≧2~n) substructure heights is less than or equal to the maximum nominal penetration depth, preferably less than 30 micrometers (μm), and particularly preferably less than 20 micrometers (μm).

[0066] As mentioned above, the maximum nominal penetration depth during exposure is essentially determined by a combination of the following factors: - The maximum possible optical dose without damaging the support material; - Maximum development time - Photochemical material properties of the support material used.

[0067] Based on these factors, preliminary tests have shown that, for example, when a structural height of substructures of 50 micrometers (μm) or less is selected, precise structuring of the support material may be possible, depending on the application. The smaller the substructure height selected, the more accurately complex structural models, i.e., structural models with complex geometric shapes including backcuts, can be written (formed) onto the support material, depending on the method.

[0068] In one method of the present invention, it can be particularly suitable for the purpose if a number N (N≧2~n) is selected such that each of the N (N≧2~n) substructure heights of the individual substructures has the same substructure height, which is less than or equal to the maximum nominal penetration depth, preferably less than 30 micrometers (μm), and particularly preferably less than 20 micrometers (μm).

[0069] This variation allows for efficient fabrication of each substructure with the same structural height at all times.

[0070] In one method of the present invention, if the optically smooth surface of the substructure [structured portion] after exposure and development has a roughness with an average roughness value Ra of up to 50 nanometers (nm), preferably up to 40 nanometers (nm), and particularly preferably up to 30 nanometers (nm), exceptionally precise (accurate) structuring can be achieved.

[0071] In particular, in further laser structuring, an optically smooth surface offers the advantage of achieving subsequent further structuring without scattered light (stray light) and therefore without the error source (cause) that it may cause.

[0072] Further details, features, and advantages of the present invention will become apparent from the following description of the embodiments (multiple) schematically shown in the drawings. Each figure shows a side view. [Brief explanation of the drawing]

[0073] [Figure 1] An example of a photostructured support material coated on a substrate support at a certain layer height. [Figure 2] A three-dimensional structural model of an example of a microstructure based on a first implementation variation to be transferred to a support material. [Figure 3] The structural model shown in Figure 2 is divided into multiple substructures corresponding to a series of multiple height layers stacked vertically. [Figure 4] An example of multiple virtual photomasks corresponding to topographic data of individual substructures or height layers of a structural model. [Figure 5] An example of the correlation between each exposure dose of each virtual photomask and the respective topographic data of individual substructures, shown in a simplified chart. [Figure 6] Positioning of an example of a first virtual photomask corresponding to the first substructure of the lowest height layer of a structural model, with an example of alignment markings(s) on the surface of the support material. [Figure 7]Positioning of an example of a further second virtual photomask within the already structured portion of the first substructure after exposure and development of the support material using the first virtual photomask. The second virtual photomask corresponds to the second substructure of the next highest height layer of the structural model, which is continuously positioned following the lowest height layer. [Figure 8] Positioning of an example of a further third virtual photomask within a pre-formed structured portion of a support material after exposure and development using a first virtual photomask and a second virtual photomask. [Figure 9] An example of a fully structured support material having the overall structured portion shown in Figure 2 of the structural model. [Figure 10] Positioning of an example of a first virtual photomask corresponding to the first substructure of the lowest height layer of a structural model of an example of a microstructure according to a second implementation variation, with an example of alignment markings (multiple) on the surface of a support material. [Figure 11] Positioning of an example of a further second virtual photomask in a layer tilted at a certain angle within the already structured part of the first substructure after exposure and development of the support material using the first virtual photomask. The second virtual photomask corresponds to the second substructure of the next highest height layer of the structural model, which is continuously positioned following the lowest height layer. [Figure 12] An example of a fully structured support material having a structured section, which is an example of a structural model with an overhang. [Examples]

[0074] In the following detailed description of the drawings, Figures 1 to 9 relating to a first embodiment variation of the method of the present invention will be referenced.

[0075] Figure 1 schematically shows an example of a photostructured support material 1, such as a positive-action photoresist, arranged on a substrate support 2 as multiple planar layers 1.1, 1.2, 1.3, and 1.4 with an overall layer height H.1. Here, a flat glass plate is used as the substrate support 2. The multiple layers 1.1, 1.2, 1.3, and 1.4 forming the support material 1 are symbolically shown in partial cross-sectional views in Figure 1. In practice, it is important that the multiple layers 1.1, 1.2, 1.3, and 1.4 of the positive-action photoresist are bonded to each other as homogeneously as possible in order to obtain a homogeneously structured support material 1 with a large layer height H.1 and the same photochemical material properties as much as possible in any location. Here, for example, 900 μm (micrometers) is selected for the layer height H.1 or layer depth of the support material 1 or photoresist. In the Cartesian coordinate system, the height direction of the layer height H.1 corresponds to the Z-axis direction. The support material 1 has a flat surface O.1 or outer surface that extends in the direction of the XY plane.

[0076] As a positive-action photoresist, for example, either product AZ® 4562 ("Positive thick resist") or product AZ® 9260 from Microchemicals (www.microchemicals.com) can be selectively used here. The maximum nominal penetration depth of exposure with this photoresist is approximately 75 micrometers (μm).

[0077] Figure 2 shows a side view of an example of a digitally generated virtual three-dimensional structural model 10 of an example of a three-dimensional structure to be transferred to the support material 1. The structural model 10 includes topographic data T.10 of the microstructure to be formed (abzuformend). The structural model 10 has an overall height H.10 corresponding to the maximum elongation (length) of the structural model 10 in the Z-axis direction. The overall height H.10 of the structural model 10 is, for example, 400 μm (micrometers), and is therefore greater than the maximum nominal penetration depth of the electromagnetic beam during exposure of the support material (approximately 75 micrometers), and less than the layer height H.1 of the coated support material 1 on the substrate support 2, which is 900 micrometers.

[0078] Figure 3 shows the virtual three-dimensional structural model 10 shown in Figure 2, which has been divided into multiple substructures 11, 12, and 13 by computer assistance (processing) corresponding to a series of stacked height layers (Hoehenschichten). Substructures 11, 12, and 13 each have partial heights H.11, H.12, and H.13, and each of these partial heights is less than or equal to the possible nominal penetration depth during exposure of the support material 1.

[0079] Here, for example, the same substructure heights H.11, H.12, and H.13 are selected for each substructure 11, 12, and 13, respectively. These substructure heights are, for example, 40 μm, and are therefore less than the nominal penetration depth during exposure of the support material 1. In practice, in the example given here, the total height H.10 of 400 μm needs to be divided into 10 substructures 11, 12, 13, etc., which are stacked vertically (laminated). These substructures each have the same substructure heights H.11, H.12, H.13, etc., of 40 μm. Each substructure 11, 12, and 13 has its own assigned topography data T.11, T.12, and T.13. For simplification, the following schematic diagrams are described in part only for the three illustrated substructures 11, 12, and 13 that are stacked vertically. However, it is well known to those skilled in the art that, depending on the requirements, the appropriate virtual structural model 10 may be divided as needed into multiple substructures having different substructure heights.

[0080] Figure 4 shows examples of multiple virtual photomasks M.11, M.12, and M.13 defined for each of the substructures 11, 12, and 13 of the structural model 10. Furthermore, the topographic data T.11, T.12, and T.13 for each of the individual substructures 11, 12, and 13 or height layers of the structural model 10 are converted to corresponding values ​​for the individual exposure doses. The upper parts indicated by O.11, O.12, and O.13 of the substructures 11, 12, and 13 simply serve to indicate a unique assignment (order) of how each substructure 11, 12, and 13 is stacked vertically to form the entire structural model 10. The photomasks M.11, M.12, and M.13, schematically shown in Figure 4, are correlated with the topographic data T.11, T.12, and T.13 of the individual substructures 11, 12, and 13, insofar as the individual exposure doses obtained for specific parts X, Y, and Z of the substructures 11, 12, and 13 are related to the height position (Hoehenlage) assigned to each substructure 11, 12, and 13, or to the coordinate values ​​in the Z-axis direction of the same part point X, Y, and Z.

[0081] Figure 5 shows the exposure dose I (unit: mWs / cm²) for each virtual photomask M.11, M.12, and M.13. 2 The correlation between the exposure dose I and the topographic data of the individual substructures 11, 12, and 13 is shown in the form of a simplified chart. The larger the selected local (spatial) exposure dose I, the higher the position of parts X, Y, and Z within substructures 11, 12, and 13 will be. The height of these parts is related to their position (Lage) in the structural model 10, and they can be written (formed) deeper into the support material 1 during subsequent structuring using the virtual photomasks M.11, M.12, and M.13. With respect to the support material 1, a higher exposure dose I therefore means that it can be written deeper into the support material 1.

[0082] Figure 6 shows the positioning of the first virtual photomask M.11, which corresponds to the first substructure 11, the lowest height layer of the structural model 10, on the surface O.1 of the support material 1 or positive-action photoresist, with alignment markings 20. The positioning of the photomask M.11 is symbolically indicated here by arrow A. The alignment markings 20, which are also used for positioning in subsequent method steps, are included in the first virtual photomask M.11 and are structured together with the photomask M.11.

[0083] To clearly illustrate the mode of photochemical structuring, which includes alignment exposure of the exposure portion of the support material 1 predetermined by the first virtual photomask M.11 and subsequent wet chemical development, and is symbolically indicated by arrow E, Figure 6 also shows an inverted first virtual photomask M'.11. The inverted first virtual photomask M'.11 corresponds to the first virtual photomask M.11, but its polarity (or orientation) is changed or reversed.

[0084] The inversion of the structural height H.11 (in the "positive" Z-axis direction according to Figure 3) of the corresponding first substructure 11 of structural model 10 to the structural depth (in the "negative" Z-axis direction according to Figure 6) of the structuring portion S.11 of this substructure 11 in the support material 1 is brought about by photochemical structuring. In this case, the structuring parameters are selected such that the surface of the structuring portion S.11 is optically smooth G after the structuring (process) E, i.e., after exposure and development (process). Position 21 indicates the first intermediate product 21 of the structured support material 1, which is structured by the structuring portion S.11 corresponding to the first substructure 11.

[0085] Figure 7 shows the positioning of a further second virtual photomask M.12 within the already structured structural portion S.11 of the first substructure 11 after exposure and development E of the support material 1 using the first virtual photomask M.11. Here, the second virtual photomask M.12 corresponds to the second substructure 12 of the next highest height layer after the structural model 10 which is continuously positioned in the lowest height layer.

[0086] The second virtual photomask M.12 is similarly aligned using the alignment markings 20 on the surface O.1 of the support material 1, which are symbolically indicated by arrow A.

[0087] Further structuring, including alignment exposure of the exposure portion of the support material 1 predetermined by the second virtual photomask M.12 and subsequent wet chemical development, is symbolically indicated by arrow E. Similar to Figure 6, Figure 7 also shows an inverted second virtual photomask M'.12. The inverted second virtual photomask M'.12 similarly corresponds to the second virtual photomask M.12, but its polarity (or orientation) is changed or reversed.

[0088] The inversion of the structural height H.12 (in the "positive" Z-axis direction according to Figure 3) of the corresponding second substructure 12 of structural model 10 to the structural depth (in the "negative" Z-axis direction according to Figure 7) of the structuring portion S.12 of this substructure 12 in the support material 1 is similarly brought about based on photochemical structuring. In this case, the structuring parameters are selected such that the surface of the structuring portion S.12, which is located (positioned) inside or below the pre-structured cavity S.11, is also optically smooth G after structuring (process) E, i.e., after exposure and development (process). Position 22 indicates the second intermediate product 22 of the structured support material 1, which is structured by the structuring portion S.12 corresponding to the second substructure 12.

[0089] Figure 8 shows a repeat of the structuring process already shown in Figures 6 and 7, illustrating the positioning of a further third virtual photomask M.13 within the pre-formed structuring section S.12 of the support material 1 using the first virtual photomask M.11 and the second virtual photomask M.12, i.e., after exposure and development.

[0090] The inverted third virtual photomask M'.13 shown in the same figure corresponds to the third virtual photomask M.13 shown, for example, in Figure 5, but its polarity (or orientation) has been changed or inverted.

[0091] Further structuring, including alignment exposure of the exposed portion of support material 1 predetermined by the third virtual photomask M.13 and subsequent wet chemical development, is also symbolically indicated by arrow E.

[0092] The structuring parameters are selected so that the surface of the structured portion S.13 is also optically smooth G after the structuring (process) E, i.e., after the exposure and development (process). Position 23 indicates a third intermediate product 23 of the structured support material 1, which is already structured by the structured portion S.11 corresponding to the third substructure 13.

[0093] By correspondingly repeating the positioning of further virtual photomasks used to perform further layer-by-layer structuring E, all substructures are structured layer by layer deeper into the support material 1 until the support material 1 ultimately contains the entire structured portion S.10 of the structural model according to the overall height H.10 of the structural model.

[0094] Figure 9 is a side view showing an example of a fully structured support material 30, which has the entire structured portion of the structural model 10 shown in Figure 2, as a product of the manufacturing method.

[0095] Figures 10-12 further describe a further variation of the method of the present invention. This further variation differs from the (first) variation already described only in that it tilts the support material 1 to structure the back cuts (Hinterschneidungen). The same positional symbols are used for comparable (equivalent) methodological features, respectively. Please refer to the detailed description already given for that.

[0096] Figure 10—similar to Figure 6—shows the positioning of the first virtual photomask M.11 corresponding to the first substructure 11 of the lowest height layer of the structural model 10, an example of a microstructure according to a second implementation variation, with alignment markings 20 on the surface of the support material 1.

[0097] Figure 11 shows the positioning of a further second virtual photomask M.12 at a position tilted at an inclination angle α inside the already formed structured portion S.11 of the first substructure 11 after structuring E, i.e., after exposure and development of the support material 1. Here, the second virtual photomask M.12 corresponds to the second substructure 12 of the next highest height layer after the structural model 10 which is continuously positioned following the lowest height layer. The inclination angle α is determined with respect to the horizontal direction, i.e., with respect to the XY plane of the Cartesian coordinate system, at which the support material 1, or in this case the first intermediate product 21 of the structured support material 1, is tilted.

[0098] Figure 12 shows an example of a second intermediate product 22 in which a further second structural portion S.12 forming a three-dimensional back cut or overhang of the structural portion has already been formed. The back cut portion is shown by a dashed line in Figure 12. In some cases, by repeating the further structuring process accordingly, a fully structured support material having a structural portion of a structural model with an overhang can be manufactured. [Explanation of symbols]

[0099] 1. Photostructured support materials, photoresists 1.1 Layer of support material (or further layers 1.2, 1.3, 1.4) 2. Substrate support 10 Structural Models 11. The first substructure of the structural model 12. Second substructure of the structural model 13. The third substructure of the structural model 20 Alignment Marking 21. First intermediate product of structured support material 22 Second intermediate product of structured support material 23 Third intermediate product of structured support material 30 Structured support materials A. Positioning of the virtual photomask (arrow) E Exposure and development (arrow) G Optically smooth surface H.1 Layer height of support material H.10 Overall height of the structural model H.11 Partial height of the first substructure of the structural model H.12 Partial height of the second substructure of the structural model H.13 Partial height of the third structural component of the structural model L.1 Length of the support material First virtual photomask of the first substructure of the M.11 structural model Second virtual photomask of the second substructure of the M.12 structural model Third virtual photomask of the third substructure of the M.13 structural model M'.11 (Polarity changed) Inverted first virtual photomask M'.12 (Polarity changed) Inverted second virtual photomask M'.13 (Polarity changed) Inverted third virtual photomask O.1 Surface or outer surface of the support material O.11 Upper side of the first virtual photomask O.12 Upper part of the second virtual photomask O.13 Upper part of the third virtual photomask S.10 Structural parts of the overall structural model S.11 Structural part of the first substructure of the structural model S.12 Structural part of the second substructure of the structural model S.13 Structural model, third part, structural section T.10 Topographic data for the entire structural model T.11 Topographic data of the first substructure T.12 Topographic data of the second substructure T.13 Topographic data of the third substructure XX axis direction YY axis direction ZZ axis direction α Tilt angle

Claims

1. A lithography method for forming a three-dimensional microstructure having an excessive structural height on a photostructured support material using an exposure apparatus, wherein the maximum nominal penetration depth of exposure, and therefore the resulting photostructured portion of the support material, is obtained depending on the exposure parameters of the exposure apparatus related to the exposure characteristics of the photostructured support material, and the excessive structural height is greater than the value of the maximum nominal penetration depth, the lithography method comprising the following steps: -a- Planar coating of a photostructured support material (1) on a substrate support (2), wherein the coated support material (1) has a predetermined layer height (H.1), a flat surface (O.1) on the upper side opposite to the substrate support (2), and the properties of the support material (1) can be changed by exposure with an electromagnetic beam; -b- Use of information data as input values, wherein the information data includes data on the maximum nominal penetration depth of the selected photostructured support material (1) and on the geometric shape of the three-dimensional microstructure to be formed having an excessive structural height; -c- Computer-aided modeling of a virtual three-dimensional structural model (10) of the microstructure to be formed, depending on the information data obtained by step-b-, wherein the virtual three-dimensional structural model (10) includes topographic data (T.10) of the microstructure to be formed, and the overall height (H.10) of the virtual three-dimensional structural model (10) for the microstructure to be formed is determined using the topographic data (T.10), wherein the overall height (H.10) is greater than the maximum nominal penetration depth of the electromagnetic beam during exposure to the support material (1) and less than the coated layer height (H.1) of the support material (1); -d- Computer-aided division of the total height (H.10) of the virtual 3D structural model (10) into N (N≧2 to n) height layers stacked vertically, wherein each of the N (N≧2 to n) height layers corresponds to an individual substructure (11, 12, 13) of the virtual 3D structural model (10), and each of the N (N≧2 to n) substructures (11, 12, 13) has a sub-height (H.11, H.12, H.13), and the number N is an integer of 2 or more. The number N (N≧2~n) is selected such that each of the N (N≧2~n) sub-heights (H.11, H.12, H.13) is less than or equal to the possible [maximum] nominal penetration depth of the electromagnetic beam that can be supplied by the exposure apparatus during exposure to the support material (1), and the sum of the N (N≧2~n) sub-heights (H.11, H.12, H.13) of the individual substructures (11, 12, 13) corresponds to the overall height (H.10) of the virtual three-dimensional structural model (10); -e- Calculation of virtual photomasks (M.11, M.12, M.13) for each of the N (N≧2 to n) substructures (11, 12, 13) of the virtual three-dimensional structural model (10), wherein for each of the N (N≧2 to n) photomasks (M.11, M.12, M.13), the respective topographic data (T.11, T.12, T.13) of each substructure (11, 12, 13) is converted to a corresponding value of the individual exposure dose, and the exposure dose calculated for a given part (X, Y, Z) of one substructure (11, 12, 13) is correlated with the individual height position (Z) of the same part (X, Y, Z) inside the corresponding substructure (11, 12, 13); -f- Positioning of the first virtual photomask (M.11) and alignment marking (20) on the surface (O.1) of the support material (1) corresponding to the first substructure (11) in the lowest height layer of the virtual three-dimensional structural model (10); -g- Alignment exposure of the support material (1) using the alignment marking (20) placed on the surface (O.1), wherein the structured portion (S.11) of the first substructure (11) is written to the support material (1) by spatially resolved (X, Y, Z) exposure starting from the surface (O.1) of the support material (1) and corresponding to individual exposure doses determined in the first virtual photomask (M.11); -h- Wet chemical development of the exposed portion of the support material (1) predetermined by the first virtual photomask (M.11), wherein the surface of the structuring portion (S.11) of the first substructure (11) is smoothed until the surface of the structuring portion (S.11) becomes optically smooth (G) after the exposure and development (E), depending on the development rate of the support material (1) and the calculated exposure dose; -i- Obtaining a first intermediate product (21) of a partially structured support material, wherein the first intermediate product (21) includes a structured portion (S.11) of the first substructure (11); -j- Positioning of further Nth (N≧2~n) virtual photomasks (M.12, M.13) within the already structured part (S.11) of each preceding (N-1) intermediate product (21), wherein the Nth (N≧2~n) virtual photomasks (M.12, M.13) correspond to the Nth (N≧2~n) height layer of the next higher virtual three-dimensional structural model (10) that is continuously following the preceding (N-1) height layer; -k- Further alignment exposure of each preceding (N-1) intermediate product (21, 22, 23) using alignment markings (20) placed on the surface (O.1), starting from the already structured portion (S.11) of each preceding (N-1) substructure (11), and spatially resolved (X, Y, Z) according to the individual exposure doses determined in the N (N≧2~n) virtual photomasks (M.12, M.13) Upon exposure, the structuring portions (S.12, S.13) of the N (N≧2~n) substructures (12, 13) are written to the preceding (N-1) intermediate product (21) of the partially structured support material, and the structuring portions (S.12, S.13) of the N (N≧2~n) substructures (12, 13) within the support material (1) are each located deeper than the structuring portion (S.11) of the preceding (N-1) substructure (11); -l- Wet chemical development of the exposed portion of the support material (1) predetermined by the N (N≧2 to n) virtual photomask (M.12, M.13), wherein the surface of the structured portion (S.12, S.13) of the N (N≧2 to n) substructure (12, 13) is smoothed until the surface of the structured portion (S.11) becomes optically smooth (G) after exposure and development (E), depending on the development rate of the support material (1) and the calculated exposure dose; -m- A series of steps -j- (positioning of further virtual photomasks), -k- (further exposure), and -l- (further development) are repeated as needed until a total of N (N≧2~n) virtual photomasks (M.11, M.12, M.13) are structured for each layer; -n- Obtaining (generating) a fully structured support material (30), wherein the fully structured support material (30) includes a structured portion (S.10) corresponding to the entire virtual three-dimensional structural model (10) along the overall height (H.10) of the virtual three-dimensional structural model (10). including A method characterized by the following.

2. In the method according to claim 1, The photostructured support material (1) is a positive-action photoresist in which the exposed portion is removed from the support material (1) by dissolution during subsequent wet chemical development. A method characterized by the following.

3. In the method according to claim 1 or 2, The alignment exposure of the support material (1) is performed by maskless laser lithography based on one-photon absorption and / or two-photon absorption, or by optical maskless lithography using a spatial light modulator and imaging optical system. A method characterized by the following.

4. In the method according to claim 1, At least one virtual photomask (M.11, M.12, M.13) is positioned using alignment markings (20) on the surface (O.1) of a support material (1) that is tilted at a predetermined angle (α). A method characterized by the following.

5. In the method according to claim 4, The alignment exposure of the support material (1) and the subsequent wet chemical development (E) of the exposed portion of the support material (1) predetermined by the at least one virtual photomask (M.11, M.12, M.13) are performed using alignment markings (20) on the surface (O.1) of the support material (1) which is positioned at a predetermined inclination angle (α). A method characterized by the following.

6. In the method according to claim 1, The photostructured support material (1) has a layer height (H.1) greater than 100 μm. A method characterized by the following.

7. In the method according to claim 1, The total height (H.10) of the virtual three-dimensional structural model (10) is greater than 100 μm. A method characterized by the following.

8. In the method according to claim 1, The aforementioned number N (N ≥ 2 to n) is selected such that each of the N (N ≥ 2 to n) sub-heights (H.11, H.12, H.13) of the individual substructures (11, 12, 13) is less than or equal to the maximum nominal penetration depth. A method characterized by the following.

9. In the method according to claim 1, The aforementioned number N (N ≥ 2 to n) is selected such that each of the N (N ≥ 2 to n) sub-heights (H.11, H.12, H.13) of the individual substructures (11, 12, 13) has the same sub-height that is less than or equal to the maximum nominal penetration depth. A method characterized by the following.

10. In the method according to claim 1, The optically smooth surface (G) of the substructures (S.11, S.12, S.13) after exposure and development (E) shall have a roughness with an average roughness value of up to 50 nm. A method characterized by the following.

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