Method for producing surface microstructures

Abstract

The present invention relates to a method for designing and fabricating surface microstructures, which includes 3D scanning an existing surface microstructure and transferring the processing data of the scanned microstructure into a material by using a suitable writing tool. The surface microstructures fabricated by the method of the present invention have a wide range of applications, such as security features in optical security elements, alignment layers for liquid crystals, anti-reflective surfaces, AR / VR applications, optical filters, optical coupling, micro-optics as well as for light management in many different technical fields.

Description

[Technical field]

[0001] The present invention relates to a method for producing surface microstructures, including adapting the microstructural parameters of available surface microstructures to the requirements of various applications. [Background technology]

[0002] The surface of a material determines how the material interacts with the environment. For example, the surface of a material is the interface with other materials, such as gases, liquids, and solids. Parameters that describe some of the surface properties are, for example, surface tension, friction, or adhesion. Depending on the application, each of these parameters may be desired to be somewhere between high and low. The surface of a material also determines its interaction with light, such as reflection and scattering.

[0003] Material properties such as the refractive index or polarity of the material strongly contribute to some of the above parameters, but surface texture also has a large influence on these parameters. For example, surface roughness has a strong influence on frictional forces and light scattering properties. Techniques that can change the surface topography of solid materials have become very important for many applications in various industrial sectors. For example, techniques can be used to create anisotropic surface microstructures on the surface of isotropic materials, providing an orientation capability for liquid crystals. Anisotropic surface microstructures that scatter light are used, for example, as security features in optical security elements.

[0004] The dimensions of the surface microstructure are important. For example, if the size and spacing of the microstructure elements are on the same order as the wavelength of light to which the microstructure is exposed, scattering of light may occur. On the other hand, if the structure dimensions are sufficiently smaller than the wavelength of light, scattering may not occur, but the effective refractive index of the surface may be reduced compared to the refractive index in the bulk of the material. Thus, surfaces with such microstructures can be used for anti-reflective purposes.

[0005] In some of the above mentioned techniques, the desired structures are designed with the aid of computer programs and then transferred to the surface of the material, for example using ablation or lithography techniques. The dimensions of such deterministic structures can be freely selected. Other techniques, for example based on self-organization mechanisms, provide non-deterministic surface microstructures. In contrast to computer-designed deterministic structures, which can be freely scaled, the structural dimensions of such non-deterministic structures are determined not only by the material properties but also by the process conditions. By modifying the process parameters and material properties, the structural dimensions can be varied, but usually only within limited ranges. Moreover, the area in which such surface microstructures can be manufactured may be limited.

[0006] It would therefore be desirable to have available methods capable of producing surface microstructures that can be inexpensively manufactured over larger areas that are not reachable with currently available technology.

[0007] WO01 / 29148A1 discloses a method for producing polymer films or coatings with surface microstructures based on phase separation of materials. In this method, known as the monomer corrugation (MC) technique, a material composition containing crosslinkable and non-crosslinkable materials is applied as a layer to a substrate. When the layer is irradiated with UV light, the crosslinkable materials start to crosslink and phase separation between the crosslinked and non-crosslinked materials starts to occur. Removal of the non-crosslinked materials results in an MC layer exhibiting a surface microstructure. The dimensions of the surface structure can be controlled by the type and proportion of materials in the composition as well as process parameters such as temperature, UV dose and process duration. The surface microstructures can be isotropic or anisotropic. Anisotropic surface microstructures can be achieved when the crosslinkable material in the composition is a liquid crystal material. The anisotropy direction can be determined by an alignment layer beneath the layer formed from the composition. By using an alignment layer that provides an alignment pattern, patterns with different anisotropy directions can be generated in the MC layer. The MC layer can be applied, for example, as an alignment layer for liquid crystals, an optical retardation layer, an anti-reflective coating and an optical diffuser. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a method for producing surface microstructures, in particular non-deterministic surface microstructures, which can be produced inexpensively over larger areas that are not reachable with currently available technology. [Means for solving the problem]

[0009] The present invention relates to - providing a material having a surface microstructure with a topography, which surface microstructure is considered to be the original surface microstructure; - providing a 3D surface profilometer; - obtaining digital data of the original surface microstructure topography by a 3D surface profilometer; -Providing writing tools; - processing the digital data of the original surface microstructure topography to obtain structure description data to be written by the writing tool; - providing structural description data of the desired surface microstructure to a writing tool; providing a target material; - optionally providing a resin; - creating a desired surface microstructure in or on a target material, including writing a structure in or on the target material or in a resin using the structure description data with a writing tool; The present invention provides a method for producing a desired surface microstructure, comprising:

[0010] In the context of this application, a "surface microstructure" is a relief microstructure of a material surface, and therefore has a three-dimensional topography.

[0011] The term "original surface topography" refers to the surface structure whose digital data is obtained by the 3D surface profilometer.

[0012] In the context of this application, the term "3D surface profilometer" includes any tool capable of providing digital data of the surface microstructure topography. Suitable 3D surface profilometers use techniques such as, for example, atomic force microscopy (AFM), scanning tunneling microscopy (STM), scanning electron microscopy (SEM), white light interferometry, optical microscopy, confocal microscopy, hyperfocal imaging, or laser scanning.

[0013] In the context of this application, a "writing tool" includes any tool capable of creating or defining a microstructure in or with another material provided, as long as it has a suitable resolution to write the desired surface microstructure. A first suitable type of writing tool adds material in the shape of the desired surface microstructure to the surface of the target material by printing, for example jet printing and 3D printing, in particular high resolution printing. Another suitable type of writing tool removes material from the surface of the target material, for example by laser ablation, preferably pulsed laser ablation, electron beam or ion beam writing. A preferred type of writing tool is a tool used in lithography methods, for example light or electron beam lithography, where a light or electron beam selectively illuminates a resin, which causes a change in the solubility of the irradiated areas of the resin. In contrast to the above-mentioned writing tools, which directly create the surface microstructure by adding or removing material, the writing tool used in lithography only creates a latent microstructure with the spatial shape of the desired surface microstructure. The surface microstructure is then created in the resin by developing with a suitable solvent. The surface microstructure created in the resin can also already be the desired surface microstructure. However, preferably, the resin is applied as a layer to the target material, and the microstructure created in the resin is further transferred to the target material by dry or wet etching, thereby forming the desired surface microstructure. Alternatively, the resin is applied as a layer to a photomask material, producing a photomask with the microstructure written in the resin, which is then used in a further photolithography step to create the desired surface microstructure in the target material. A suitable writing tool for lithography is an electron beam lithography (EBL) system or a laser scanning tool. Preferably, the writing tool has the option to scale the lateral dimensions of the written structure. If a writing tool is used to scale the lateral dimensions of the written structure, at least part of the processing of the digital data is performed by the writing tool.

[0014] In principle, any type of material can be used as the target material, such as glass, plastic, metal, ceramics, silicon, fused silica or resin. Preferably, the target material is suitable for anisotropic etching. Preferably, the target material is a silicon wafer or a metal layer on a substrate, such as a glass substrate. Preferred metals are aluminum, silver, chromium and copper. Preferably, the target material has a flat surface.

[0015] Processing the original surface topography digital data may also include converting the digital data into a format that can be read by a writing tool.

[0016] The digital data of the original surface microstructure acquired by the 3D surface profilometer can be further processed, for example, by lateral scaling to change the lateral dimensions of the microstructure. This allows, for example, to adjust the dimensions of the microstructure for a desired interaction with light. For example, if the original surface microstructure provides optimal light scattering properties for visible light, the digital data of the original surface microstructure can be scaled so that the desired surface microstructure created in the target material provides optimal scattering for shorter wavelength light, for example ultraviolet (UV) light, or longer wavelength light, for example infrared (IR) light. It is also possible to apply anisotropic scaling by applying different magnifications in different lateral directions, preferably two different directions that are perpendicular to each other. Anisotropic scaling changes the anisotropy of the surface structure. For example, an anisotropic structure can be generated from an original surface microstructure that is isotropic. On the other hand, the anisotropy of the microstructure can be enhanced by applying a larger magnification along the anisotropic direction than along the direction perpendicular thereto, for example, to provide an increased alignment force for liquid crystals aligned by such surface microstructure. Standard graphic image processing computer programs can be used for processing.

[0017] Preferably, the processing of the digital data includes vectorizing the data.

[0018] Preferably, the processing of the digital data includes binarization of the surface microstructure topography, which removes depth variations. If it is desired to adjust the depth by controlling process parameters during the production of the desired surface microstructure, the value of the structure depth may not even be of interest. Binarization thus reduces the electronic data to a two-dimensional description of the microstructure. The binarized data can for example be normalized so that at any lateral position the data is 0 or 1. In the following, the two levels 0 or 1 are also called bottom or top, respectively. Thus, the lateral region in which each lateral position is assigned a value of 1 is called the top region, and the region in which each lateral position is assigned a value of 0 is called the bottom region. Depending on the original surface microstructure and the applied binarization algorithm, artifacts may occur in the binarized data, which are visible for example as very small top or bottom regions. Such artifacts can be removed by applying filters, such as noise filters, smoothing or other filters, which are also available in some graphic image processing programs. Processing may further include manual manipulation of the binarized microstructure using a suitable computer program.

[0019] There is an original surface microstructure that only has two flat parts, namely a top flat part and a bottom flat part. Such a surface microstructure is already binary, and binarization of the acquired data may not be necessary. According to the above definition, the region belonging to the top flat part is called the top region, and the region belonging to the bottom flat part is called the bottom region.

[0020] The topography of the surface microstructure can be very complex, especially when it appears as a landscape with "hills" and "valleys" of different heights and continuously changing height. Similar to a real landscape, between the larger hills there may be valleys at a higher height level than the tops of some of the smaller hills. Thus, an unambiguous identification of structural elements is not always possible. To describe the lateral dimensions of the surface microstructure topography, a cut plane of the surface microstructure topography at a height of 50% of the structural depth above a lower height level is used. The structural depth and the lower height level may be different in different regions of the surface microstructure. Thus, if only a certain region of a larger area containing the surface microstructure is considered, the structural depth and the lower height level of the considered region are applied to the evaluation of the surface microstructure cut plane. Then, similar to the binarization of digital data, which will be described in more detail below, the area of ​​the microstructure cut by the cut plane is assigned as the top region of the surface microstructure, and the other region is called the bottom region. As mentioned above, the assignment of top and bottom regions to the surface microstructure resulting from the cut surface is performed only to provide an unambiguous identification of the microstructure elements. However, it does not necessarily mean that the digital data of the surface microstructure is binarized. In particular, the binarization may be subject to different algorithms, which will be further explained below, that may lead to different assignments of top and bottom regions. The introduction of the terms top and bottom regions for both the surface microstructure topography with continuous height changes and the binarized microstructure data simplifies the characterization of the microstructure and avoids the introduction of further terms.

[0021] In the context of this application, the "structure depth" of the surface microstructure in a particular region is the height difference between the upper height level and the lower height level of the surface microstructure. The "upper height level" is the average height of the highest hill in each region. To identify the highest hill, take the height maxima of all hills in each region and rank them in order of their height. The highest hill is the 10% of hills with the greatest height. If there are less than 10 hills in each region, the upper height level of the surface microstructure is the height of the highest hill. Similarly, the "lower height level" of the surface microstructure is the average height of the lowest valley in each region. To identify the lowest valley, take the height minima of all valleys in each region and rank them in order of their height. The lowest valley is the 10% of hills with the smallest height. If there are less than 10 valleys in each region, the lower height level of the surface microstructure is the height of the lowest hill.

[0022] In principle, the original surface microstructure can have any value of structure depth. Preferably, the structure depth of the original surface microstructure is in the range of 10 nm to 100 μm, more preferably in the range of 30 nm to 10 μm, most preferably in the range of 50 nm to 2 μm.

[0023] In the context of the present invention, the term "average structure width" is the average width of the apex region. In the case of anisotropic surface microstructures, the average structure width can be different along different lateral directions.

[0024] Preferably, the original surface microstructure includes an area in which the average structure width measured along a direction perpendicular to the anisotropy direction is in the range of 10 nm to 1 mm, more preferably in the range of 50 nm to 100 μm, and most preferably in the range of 100 nm to 10 μm when the surface microstructure is anisotropic. When the original surface microstructure is anisotropic, the original surface microstructure preferably includes an area in which the average structure width along the anisotropy direction is preferably in the range of 50 nm to 5 mm, more preferably in the range of 200 nm to 200 μm, and most preferably in the range of 500 nm to 50 μm.

[0025] In the context of the present invention, the term "average lateral structure distance" is the average distance between adjacent apex regions. In the case of anisotropic surface microstructures, the average lateral structure distance can be different along different lateral directions.

[0026] Preferably, the original surface microstructure comprises an area in which the average lateral structure distance measured along a direction perpendicular to the anisotropy direction is in the range of 10 nm to 1 mm, more preferably in the range of 50 nm to 100 μm, and most preferably in the range of 100 nm to 10 μm, if the surface microstructure is anisotropic. If the original surface microstructure is anisotropic, the original surface microstructure preferably comprises an area in which the average lateral structure distance along the anisotropy direction is preferably in the range of 50 nm to 5 mm, more preferably in the range of 200 nm to 200 μm, and most preferably in the range of 500 nm to 50 μm.

[0027] In the context of the present invention, the term "microstructure fill factor" is defined as the ratio of the total area of ​​the top region to the integrated area of ​​the total top and bottom regions. Preferably, the original surface microstructure has at least one region with a microstructure fill factor in the range of 0.050 to 0.95, more preferably in the range of 0.2 to 0.8, and most preferably in the range of 0.3 to 0.7.

[0028] Preferably, the original surface microstructure is optically effective, meaning that incident light is modulated in a characteristic manner that is dependent on the surface microstructure, and more preferably, the interaction with light is such that the light is diffracted, refracted or scattered.

[0029] The original surface microstructure may be isotropic or anisotropic, and in some regions the microstructure may be isotropic and in other regions the microstructure may be anisotropic. The original surface microstructure may be periodic or aperiodic, and in some regions the microstructure may be periodic and in other regions the microstructure may be aperiodic.

[0030] In the context of the present invention, the term "anisotropy direction" in an anisotropic microstructure is intended to mean the direction along the local axis of symmetry in the plane of the microstructure, for example along the grooves of a surface microstructure.

[0031] The degree of anisotropy can be described by the order parameter.

[0032] In accordance with the above, in the context of the present invention, parameters by which a microstructure can be characterized (hereinafter referred to as microstructure parameters) include, but are not limited to, average structure width, average lateral structure distance, microstructure fill factor, anisotropy direction, degree of anisotropy and structure depth. Depending on the type of microstructure, not all of these microstructure parameters can be reasonably used for its characterization.

[0033] In a preferred embodiment of the invention, the process includes disposing the microstructure multiple times at different locations to form a larger area of ​​the microstructure. In many computer programs, this corresponds to operations such as "copy" and "paste" in the graphic image processing computer program mentioned above. For that purpose, all or part of the area of ​​the microstructure can be selected as a "basic microstructure element". If the microstructure within the basic microstructure element is uniform, a large area with a uniform microstructure can be generated by disposing the basic microstructure element multiple times at different locations. On the other hand, if the basic microstructure element includes areas where one or more of its microstructure parameters are different, the multiple disposed basic microstructure elements form a larger area of ​​the microstructure where the different areas of the basic microstructure element are repeated. For example, if a basic microstructural element has a rectangular shape and is composed of two square areas, both of which have anisotropic microstructures, and the anisotropic directions in the two areas are perpendicular to each other, then the basic microstructural element can be correctly arranged multiple times in the x and y directions to create a larger area with a microstructure that has a checkerboard appearance, with areas of parallel anisotropic directions alternating with areas of perpendicular anisotropic directions in the x and y directions. Preferably, the shape of the basic structural element is such that the entire large area can be filled with the basic structural element without gaps. Similar to computer program languages, a basic microstructural element arranged multiple times in different positions is also called a "copy" of the basic microstructural element.

[0034] In the context of this application, a microstructure resulting from multiple applications of a basic microstructural element is referred to as a "composed microstructure."

[0035] Preferably, one or more of the microstructural parameters of the basic microstructural elements are modified by computer software before or after they are disposed at a particular location as part of the composite microstructure. The modification of the microstructural parameters of the basic microstructural elements as well as the size and shape of the area can be different for each additional location. Modified basic microstructural elements are also considered to be basic microstructural elements.

[0036] The composite microstructure can be designed using different basic microstructural elements and then transferred to the writing tool as structure description data. Preferably, the creation of the composite microstructure comprises arranging two basic microstructural elements, the average lateral structural distance of the microstructures being different, and / or the average structural width of the microstructures being different, and / or the microstructural fill factors of the microstructures being different, and / or the anisotropy directions of the microstructures being different, and / or the degree of anisotropy being different, and / or one basic microstructural element comprises a periodic microstructure and the other basic microstructural element comprises a non-periodic microstructure, and / or one basic microstructural element comprises a deterministic microstructure and the other basic microstructural element comprises a non-deterministic microstructure.

[0037] Thus, the composite microstructure preferably comprises two zones in which the average lateral structural distance of the microstructures is different. Preferably, the composite microstructure comprises two zones in which the average structural width of the microstructures is different. Preferably, the composite microstructure comprises two zones in which the microstructures have different microstructural fill factors. Preferably, the composite microstructure comprises a zone with a periodic microstructure and a zone with a non-periodic microstructure. Preferably, the composite microstructure comprises two zones with anisotropic microstructures, in which the anisotropy direction of the microstructures is different. Preferably, the composite microstructure comprises two zones with anisotropic microstructures, in which the degree of anisotropy is different. Furthermore, it is preferred that within the area of ​​the composite microstructure there are regions without microstructures. Naturally, any combination of the above preferred embodiments is possible.

[0038] Preferably, the desired surface microstructure created in or on the target material using the structure description data includes regions having a surface microstructure that is optically effective and regions that provide an optimal surface microstructure for alignment of liquid crystals.

[0039] The structural depth of the desired surface microstructure, which is created in or on the target material using the structural description data, may be the same as or different from the structural depth of the original surface microstructure. Preferably, the structural depth of the desired surface microstructure is smaller than the structural depth of the original surface microstructure. More preferably, the structural depth of the desired surface microstructure is greater than the structural depth of the original surface microstructure. Preferably, the structural depth of the desired surface microstructure is in the range of 10 nm to 100 μm, more preferably in the range of 30 nm to 10 μm, and most preferably in the range of 50 nm to 1 μm.

[0040] Preferably, the desired surface microstructure has at least one region with a microstructure fill factor in the range of 0.050 to 0.95, more preferably in the range of 0.2 to 0.8, and most preferably in the range of 0.3 to 0.7.

[0041] Preferably, the desired surface microstructure includes an area in which the average structure width measured along the direction perpendicular to the anisotropic direction is in the range of 10 nm to 1 mm, more preferably in the range of 50 nm to 100 μm, and most preferably in the range of 100 nm to 10 μm when the surface microstructure is anisotropic. When the desired surface microstructure is anisotropic, the desired surface microstructure preferably includes an area in which the average structure width along the anisotropic direction is in the range of 50 nm to 5 mm, more preferably in the range of 200 nm to 200 μm, and most preferably in the range of 500 nm to 50 μm.

[0042] Preferably, the desired surface microstructure comprises an area in which the average lateral structure distance measured along a direction perpendicular to the anisotropic direction is in the range of 10 nm to 1 mm, more preferably in the range of 50 nm to 100 μm, and most preferably in the range of 100 nm to 10 μm, when the surface microstructure is anisotropic. When the desired surface microstructure is anisotropic, the desired surface microstructure comprises an area in which the average lateral structure distance along the anisotropic direction is in the range of 50 nm to 5 mm, more preferably in the range of 200 nm to 200 μm, and most preferably in the range of 500 nm to 50 μm.

[0043] The above data processing method allows for the design of highly complex patterns of microstructures, even when the original surface microstructure is uniform and can be described by a single set of microstructure parameters. In particular, the same original surface microstructure can be used to design multiple synthetic microstructures. For example, even new microstructures with high complexity can be easily designed on a computer, even if the microstructure itself is non-deterministic. Thus, methods known in the art for generating anisotropic surface microstructures with patterns of different anisotropic directions, for example as described in WO01 / 29148, can be replaced by the method of the present invention. Such synthetic microstructures can be used, for example, to design and create surface microstructures that are optically effective in certain regions, for example they can provide light scattering properties, while other regions provide surface microstructures that are optimal for the alignment of liquid crystals.

[0044] The surface microstructures produced by the method of the present invention have a wide range of applications: for example, they can be used to provide security functions in optical security elements, alignment layers for liquid crystals, anti-reflective surfaces, AR / VR applications, optical filters, optical coupling, micro-optics, as well as light management in many different technical fields.

[0045] The invention is further illustrated by the accompanying drawings, in which it is emphasized that various features are not necessarily drawn to scale. [Brief description of the drawings]

[0046] [Figure 1] 1 shows a sketch of a material with an anisotropic surface microstructure that is considered to be the original surface microstructure. [Diagram 2] 2 shows a 3D plot of simulated acquired digital data of the original surface microstructure topography of FIG. 1. [Figure 3a] This shows a topography based on the same data as in Figure 2. The top has been truncated at a particular height level, so the upper surface is a cut surface of the topography. [Figure 3b] 3a, but showing cut sections of a topography at different height levels. [Figure 4] A binarized microstructure of the topography of Fig. 2 corresponding to the cut surface of Fig. 3b is shown. [Diagram 5] 5 shows a binary surface microstructure having two height levels created in a target material by using the binarized data of FIG. 4. [Figure 6a] 5 shows an enlarged microstructure obtained by scaling the microstructure of FIG. 4 by the same factor in the x and y directions. [Figure 6b] 5 shows a reduced microstructure obtained by scaling down the microstructure of FIG. 4 by the same factor in both x and y directions. [Figure 7a] 5 shows the microstructure resulting from anisotropic scaling by scaling up the microstructure of FIG. 4 by a factor greater than 1 in the y direction. [Figure 7b] 5 shows the microstructure resulting from anisotropic scaling by scaling up the microstructure of FIG. 4 by a factor greater than 1 in the x direction. [Figure 8a] 5 shows the microstructure 10 of FIG. 4 depicted at different reproduction scales. [Figure 8b]FIG. 8b shows a composite microstructure resulting from arranging the elementary microstructure element of FIG. 8a multiple times in the x and y directions. [Figure 9] 8 shows a composite microstructure that is based on the basic microstructure elements of FIG. 8a but to which a different placement algorithm has been applied than that of FIG. 8b. [Figure 10] A portion of the composite microstructure of FIG. 9 is defined as a basic microstructural element, and shows a composite microstructure arranged twice in the x direction and twice in the y direction, with the basic microstructural element rotated 90° in two positions. [Figure 11] 1 shows a sketch of a material with an isotropic surface microstructure, which is considered to be the original surface microstructure. [Figure 12] 12 shows the binarized microstructure of the topography of FIG. [Figure 13] 13 shows the anisotropic microstructure that results from scaling the isotropic microstructure of FIG. 12 horizontally by a factor greater than 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Detailed Description of the Invention The method of the present invention is further illustrated by using an artificial surface microstructure 1 shown in FIG. 1 as the original surface microstructure. The surface microstructure of FIG. 1 was created as a computer model without the use of computational algorithms for illustrative purposes. Therefore, for illustrative purposes, the surface microstructure 1 can be considered as non-deterministic. Furthermore, the surface microstructure 1 is apparently anisotropic and non-periodic, comprising hills 2 and valleys 3 of different heights, with continuous transitions from hill to valley and from valley to hill.

[0048] FIG. 2 shows digital data 4 that would be acquired by a 3D surface profilometer from the surface topography 1 of FIG.

[0049] Once the digital data of the original surface microstructure is available, it can be processed by a computer program, such as a standard graphic image processing program. If it is desired to generate structure description data for creating an analog surface microstructure in a target material using an appropriate writing tool, the manipulation of the digital data of the original surface microstructure can be three-dimensional. In addition to scaling the microstructure laterally in the plane of the surface, the depth of the surface microstructure can also be increased or decreased by scaling the data in the depth direction, which is the direction perpendicular to the surface plane.

[0050] On the other hand, if the writing tool can only transfer lateral structural information, e.g. if a binary lithography process is used, it is preferred to binarize the data of the surface microstructure. The structural description data therefore only contains two height levels. This has the advantage that the boundaries of the microstructure are clearly defined and the lateral dimensions of the surface microstructure created in the target material are almost independent of the process conditions used in photolithography, such as the exposure energy. The depth of the desired surface microstructure in the target material can be selected by adjusting the process parameters. It is also possible to create surface microstructures with different depths in different areas, e.g. by sequential processing of different areas, e.g. by using different process parameters in the respective areas.

[0051] The binarization can be performed directly on the original surface microstructure digital data or after some data processing such as lateral scaling. There are various methods to binarize the surface microstructure data along the depth direction. A simple method is to define a threshold height within the range of height values, such that all height levels above the threshold height are assigned to belong to the top level of the binarized microstructure, and all height levels below the threshold height are assigned to belong to the bottom level of the binarized microstructure. Thus, top and bottom regions are formed, respectively. Of course, if it is desired to generate a surface microstructure with an inverted topography, the assignment as top and bottom levels can be reversed.

[0052] The binarization by defining a threshold height as described above corresponds to a cut surface of the microstructure at a certain height. The height at which the cut surface is made usually has a strong influence on the shape and the microstructure fill factor of the binarized microstructure. A first cut surface 5 at a first height level of the surface microstructure 4 of FIG. 2 is shown in FIG. 3a. The area 6 of the cut surface defines the top area of ​​the corresponding binarized data. A second cut surface 7 at a lower threshold height is shown in FIG. 3b. The total area of ​​the area 8 of the second cut surface, which is assigned as the top area of ​​the corresponding binarized data, is significantly larger than that in the case of the first cut surface. On the one hand, the width of the individual top areas is wider. On the other hand, there are further separate areas corresponding to smaller hills of the original surface microstructure, which are assigned as the bottom area in the first cut surface, but as the top area in the second cut surface. Thus, the microstructure fill factor of the binarized data obtained from the second cut surface is significantly larger than the microstructure fill factor of the binarized data obtained from the first cut surface. Thus, processing of the digital data of the original microstructure makes it possible to modify the microstructure fill factor.

[0053] Preferably, there is at least one region within the microstructure where the microstructure fill factor of the binarized data is in the range of 0.050 to 0.95, more preferably in the range of 0.2 to 0.8, most preferably in the range of 0.3 to 0.7.

[0054] Figure 4 shows a binary microstructure 10 obtained as a result of binarization according to the cut plane of figure 3b, as described above. The microstructure comprises a top region 11 and a bottom region 12. Apparently, the microstructure is anisotropic, with the anisotropy direction being approximately vertical, as indicated by the arrow 13.

[0055] Figure 5 shows a sketch of a desired surface microstructure 14 produced by a method that includes writing a structure in or on a target material or in a resin with a writing tool using the structure description data of Figure 4. The surface microstructure 14 has only a top region 15 and a bottom region 16 and is therefore a binary surface microstructure. The lateral dimensions of the surface microstructure 14 are unchanged compared to the lateral dimensions of the microstructure of Figure 4. The depth of the surface microstructure 14 can be adjusted by the process conditions used in the manufacture.

[0056] The digital data of the surface microstructure can be scaled up or down laterally to change the lateral dimensions of the surface structures. Different magnifications can be used in different lateral directions to achieve anisotropic scaling.

[0057] The microstructure 20 of FIG. 6a is obtained by scaling the microstructure 10 of FIG. 4 by the same factor greater than 1 in the x and y directions. Although the area of ​​the top and bottom regions of the microstructure 20 is enlarged, the microstructure fill factor is unchanged compared to that of the microstructure 10 of FIG. 4. Assuming that the surface microstructure 14 of FIG. 5 produced using the writing tool and the structure description data of FIG. 4 provides optimal light scattering properties for light in a particular wavelength range, a surface microstructure similarly produced using the structure description data of FIG. 6a will provide optimal light scattering properties for light in a wavelength range that includes wavelengths longer than the particular wavelength range mentioned above. The factor for enlarging the lateral dimensions of the original surface microstructure is typically greater than 1.1. Preferably, the factor for enlarging the lateral dimensions of the original surface microstructure is greater than 1.5, more preferably greater than 2, and most preferably greater than 5.

[0058] The microstructure 21 of FIG. 6b is obtained by scaling the microstructure 10 of FIG. 4 by the same factor less than 1 in the x and y directions. Although the area of ​​the top and bottom regions of the microstructure 21 is reduced, the microstructure fill factor is unchanged compared to the fill factor of the microstructure 10 of FIG. 4. Assuming that the surface microstructure 14 of FIG. 5 produced using the writing tool and the structure description data of FIG. 4 provides optimal light scattering properties for light in a particular wavelength range, a surface microstructure similarly produced using the structure description data of FIG. 6b will provide optimal light scattering properties for light in a wavelength range that includes wavelengths shorter than the particular wavelength range mentioned above. The factor for reducing the lateral dimensions of the original surface microstructure is typically less than 0.95. Preferably, the factor for reducing the lateral dimensions of the original surface microstructure is less than 0.8, more preferably less than 0.5, and most preferably less than 0.2.

[0059] The microstructure 22 of FIG. 7a is obtained by anisotropically scaling the microstructure 10 of FIG. 4 in the anisotropy direction y by a factor of 1.5. This corresponds to stretching the microstructure, which has the effect of increasing the anisotropy of the microstructure. In surface microstructures designed for light scattering, if the anisotropy of the microstructure is increased, the anisotropy of the spatial distribution of the scattered light increases. Furthermore, in surface microstructures designed as alignment layers for liquid crystals, the alignment force and alignment quality increase with increasing anisotropy of the microstructure. Also, instead of the example of the microstructure 22, it is preferred to scale the microstructure in an axis perpendicular to the anisotropy axis (which is the x direction) by a factor smaller or larger than 1. Anisotropic scaling can also be applied to isotropic microstructures. Preferably, the scale in the first direction is larger than 1.1 times the scale in the second direction, more preferably larger than 1.5 times, and most preferably larger than 2 times, with the absence of scaling in a particular direction meaning that the scale in the respective direction is 1. Preferably, the second direction is perpendicular to the first direction. Preferably, the first direction is parallel to the anisotropy direction.

[0060] The microstructure 23 of FIG. 7b is obtained by anisotropically scaling the microstructure 10 of FIG. 4 in the direction perpendicular to the anisotropy direction by a factor of 1.5. This has the effect that the anisotropy of the microstructure is reduced. In the case of a surface microstructure designed for light scattering, if the anisotropy of the microstructure is reduced, the anisotropy of the spatial distribution of the scattered light is reduced. Thus, by anisotropic scaling of the microstructure, it is possible to tailor the spatial distribution of the light scattering. Preferably, the scaling factor in the direction perpendicular to the anisotropy direction is greater than 1.1 times the scaling factor in the anisotropy direction, more preferably greater than 1.5 times, and most preferably greater than 2 times, and no scaling in a particular direction means that the scaling factor in the respective direction is 1.

[0061] Figure 8 shows examples of composite microstructures. Figure 8a shows the microstructure 10 of Figure 4 depicted at different reproduction scales, selected as the basic microstructural element. Figure 8b shows the composite microstructure 24 obtained as a result of arranging the basic microstructural element 10 eight times in a matrix of 2 rows by 4 columns. The area of ​​the microstructure 24 is therefore eight times that of the microstructure 10. Preferably, the composite microstructure comprises two or more basic microstructural elements, more preferably five or more basic microstructural elements, and most preferably ten or more basic microstructural elements.

[0062] The elementary microstructure elements can be easily identified in the composite microstructure 24 of FIG. 8b due to their regular arrangement. The regular arrangement can create a superposition of a non-deterministic microstructure of the elementary microstructure elements and a periodic structure generated by the regular arrangement of the elementary microstructure elements. If the desired microstructure manufactured using the data of the microstructure 24 is used for light scattering applications, the spatial distribution of light scattered at such a surface microstructure is accordingly a superposition of light with a smooth angular intensity variation caused by scattering at the non-deterministic microstructure parts and a characteristic angular light intensity maximum caused by scattering at the regular arrangement of the elementary microstructure elements. This effect may be desirable for some applications, but may not be desirable.

[0063] Using more sophisticated algorithms, the effect of regular arrangement can be avoided by constructing the microstructure by arranging the basic microstructural elements multiple times. FIG. 9 shows a microstructure 25, which is also composed of the basic microstructural elements of FIG. 8a. However, the copies of the basic microstructural elements are arranged to overlap slightly, resulting in a certain morphing of the overlapping microstructural elements. In addition, the copies of the basic microstructural elements are arranged with a vertical shift in the second and fourth rows. The resulting image of the microstructure 25 of FIG. 9 has been cut off at the bottom and top to obtain the shape shown in FIG. 9. The regular pattern that can be seen in FIG. 8b is no longer visible in FIG. 9. By further randomizing the position of the copies of the basic microstructural elements, periodicity that may be induced by multiple arrangement of the basic microstructural elements can be avoided.

[0064] Figure 10 shows an example where a part of the composite microstructure 25 of Figure 9 is used as a basic microstructural element. A new composite microstructure 26 is created by disposing the basic microstructural element twice in the x direction and twice in the y direction, with the basic microstructural element rotated by 90° in the two positions. Preferably, the composite microstructure has zones with different anisotropy directions, preferably comprising two, three, four, five or more different anisotropy directions.

[0065] Figure 11 shows an example of an isotropic surface microstructure 30 created using a digital illustration computer program. The surface microstructure 30 comprises isotropic lands 31 of uniform height randomly distributed at the bottom level 32 of the surface. Because the surface microstructure has only two height levels, the binarized microstructure 35 in Figure 12 resulting from a cut across the lands 31 is independent of the height at which the cut is made.

[0066] FIG. 13 shows an anisotropic microstructure 36 resulting from anisotropic scaling of an isotropic microstructure 35 by using a scale factor greater than 1 in the horizontal direction and no scaling change in the vertical direction.

[0067] The preferred surface microstructures used as the original surface microstructures are produced by a method known as the Monomer Corrugation (MC) technique, which uses phase separation and crosslinking of a mixture of crosslinkable and non-crosslinkable materials, as disclosed in International Patent Application WO 01 / 29148 A1, the contents of which are incorporated herein by reference. According to this method, a material composition comprising a crosslinkable material and a non-crosslinkable material is applied as a layer to a substrate. When the layer is irradiated with UV light, the crosslinkable material starts to crosslink and phase separation of the crosslinked and non-crosslinked materials starts to occur. Removal of the non-crosslinked material, for example by washing in a suitable solvent, results in an MC layer exhibiting the surface microstructure. The dimensions of the surface microstructures can be controlled by the type of material and the proportion of each material in the composition as well as process parameters such as temperature, UV dose and process duration. The surface microstructures can be isotropic or anisotropic. An anisotropic surface microstructure can be achieved if the crosslinkable material in the composition is a liquid crystal material. The anisotropic direction can be determined by an alignment layer underneath the layer formed from the composition. By using an alignment layer to provide an alignment pattern, patterns with different anisotropic directions can be generated in the MC layer. The MC layer can be applied, for example, as an alignment layer for liquid crystals, an optical retardation layer, an anti-reflection coating, and an optical diffuser.

[0068] A preferred surface microstructure with a binarized surface depth profile used as the original surface microstructure is generated by the method disclosed in WO2010 / 094441A1 (the contents of which are incorporated herein by reference). This method is based on the above-mentioned MC technique, but modifies the depth profile of the surface microstructure of WO01 / 29148A1 by an additional etching step, so that a surface microstructure with only two height levels is obtained. Thus, the surface microstructure only has a top region and a bottom region, each at a specific height level.

[0069] In a preferred embodiment of the invention, the surface microstructure of the original comprises at least one area in which the microstructure is non-periodic. Preferably, the surface microstructure of the original comprises at least one area in which the microstructure is non-deterministic.

[0070] A useful parameter for characterizing a non-periodic or non-deterministic surface microstructure profile is the autocorrelation function and the associated autocorrelation length. The one-dimensional or two-dimensional autocorrelation function of a surface microstructure profile can be understood as a measure of the predictability of the surface microstructure profile for two points spatially separated by a distance x in a plane.

[0071] The autocorrelation function AC(x) of a function P(x), such as a surface microstructure profile, is defined as follows:

[0072]

number

[0073] Further details regarding autocorrelation functions and corresponding programming problems can be found, for example, in "Numerical recipes in C: the art of scientific computing / William H. Press; Saul A. Teukolsky; William T. Vetterling; Brian P. Flannery. - Cambridge; New York: Cambridge University Press, 1992".

[0074] For a non-periodic or non-deterministic surface microstructure profile, the autocorrelation function decays rapidly with increasing x. On the other hand, for a deterministic surface microstructure profile, such as that found in gratings, the autocorrelation does not decay. However, for gratings, the autocorrelation function is modulated by a periodic function.

[0075] In the following, AC(x) is taken to represent the averaged one-dimensional autocorrelation function. From the averaged one-dimensional autocorrelation function, it is possible to determine the autocorrelation length L, which is a single eigenvalue. To this end, the envelope of the averaged autocorrelation function is constructed by connecting the associated maxima of AC(x) with straight lines. If there is no associated maximum of AC(x) for x>0, then the envelope is taken to be identical to the averaged autocorrelation function. Furthermore, if there is no associated maximum for AC(x)≦AC(0) / 10, then the value of the envelope for AC(x)≦AC(0) / 10 is taken to be equal to AC(x). The autocorrelation length L is determined as the value of x where the envelope of the averaged autocorrelation function eventually decays to less than 10% of AC(0).

[0076] The term associated maxima is used to exclude from consideration small maxima caused, for example, by noise. m (x m To determine whether AC(x) is the relevant maximum, AC(x) ≥ AC m (x m ) Maximum value x m-1 <x m Determine x m-1 ~x m AC in the range m (x m The difference between the value of AC(x) and the minimum value of AC(x) is AC m Diff1 is used as the calculation. Similarly, AC(x) ≧ AC m (x m ) the minimum value x m+1 <x m Determine x m ~x m+1 AC in the range m (x m The difference between the value of AC(x) and the minimum value of AC(x) is AC m Diff2 is calculated. Then, the difference AC m diff is AC m diff1 and AC m Equal to the smaller of diff2. x m+1 If AC does not exist, m Diff is AC m AC mIf diff is greater than 0.5% of AC(0), the maximum AC m (x m ) shall be considered as the relevant maximum.

[0077] Preferably, the original surface microstructure comprises at least one region having a surface microstructure with an averaged one-dimensional autocorrelation function AC(x) having an autocorrelation length smaller than three times the average lateral structure distance in at least one direction, which in the case of an anisotropic surface modulation is perpendicular to the anisotropy direction.

[0078] More preferred are original surface microstructures having an autocorrelation length less than two times the average lateral structure distance. Even more preferred are original surface microstructures having an autocorrelation length less than one average lateral structure distance.

[0079] In another preferred embodiment, the autocorrelation length L is greater than one hundredth of the average lateral structure distance.

[0080] To describe anisotropic surface microstructures, the term surface microstructure aspect ratio (SMAR) is defined in the context of the present invention as the average length / width ratio of the top and bottom regions of the surface microstructure. SMAR strongly determines the azimuthal optical appearance of light scattered by the surface microstructure, or the alignment strength if the surface microstructure is used as an alignment layer for liquid crystals. In the case of SMAR=1, which corresponds to a surface microstructure that is coextensive on average in at least two lateral directions, the scattering properties of the incident light are almost independent of the azimuthal incidence angle of the light, and if used as an alignment layer, no preferred direction for alignment of liquid crystals is determined. Thus, the intensity of light reflected from a surface microstructure with SMAR=1 changes very little when the element containing the surface microstructure is rotated along an axis perpendicular to the surface of the element.

[0081] For the desired anisotropic surface microstructures intended to be used as light scattering surfaces, the intensity of the scattered light depends on the azimuthal incidence angle of the light. To allow this dependence to be visually recognized, the SMAR of the desired surface microstructure is preferably greater than 1.1, more preferably greater than 2, and most preferably greater than 5. For very large SMAR values, the range of azimuthal angles over which a significant amount of light is scattered and incident becomes smaller, which makes it more difficult to visually observe the reflected light, for example when used in optical security devices. Thus, preferably, there is at least one area in the desired surface microstructure where the SMAR is less than 50, more preferably less than 20, and most preferably less than 10. Preferably, the SMAR is in the range of 1.1 to 50, more preferably the SMAR is in the range of 2 to 20.

[0082] The present invention and various embodiments can be summarized by the following items.

[0083] 1.—Providing a material having a surface microstructure with a topography, the surface microstructure being considered as an original surface microstructure; - providing a 3D surface profilometer; - obtaining digital data of the original surface microstructure topography by a 3D surface profilometer; -Providing writing tools; - processing the digital data of the original surface microstructure topography to obtain structure description data to be written by the writing tool; - providing structural description data of the desired surface microstructure to a writing tool; providing a target material; - optionally providing a resin; - creating a desired surface microstructure in or on the target material, including writing the structure in or on the target material or in the resin with a writing tool using the structure description data; A method for producing a desired surface microstructure, comprising:

[0084] 2. The method according to item 1, wherein the original surface microstructure comprises an area in which the average structure width, measured along a direction perpendicular to the anisotropy direction when the surface microstructure is anisotropic, is in the range of 10 nm to 1 mm, more preferably in the range of 50 nm to 100 μm, and most preferably in the range of 100 nm to 10 μm.

[0085] 3. The method according to any of the preceding items, wherein the original surface microstructure comprises an area in which the average lateral structure distance, measured along a direction perpendicular to the anisotropy direction when the surface microstructure is anisotropic, is in the range of 10 nm to 1 mm, more preferably in the range of 50 nm to 100 μm, and most preferably in the range of 100 nm to 10 μm.

[0086] 4. The method according to any of the preceding items, wherein the original surface microstructure has at least one region in which the microstructure fill factor is in the range of 0.050 to 0.95, more preferably in the range of 0.2 to 0.8, and most preferably in the range of 0.3 to 0.7.

[0087] 5. The method according to any of the preceding items, wherein the structural depth of the original surface microstructure is in the range of 10 nm to 100 μm, more preferably in the range of 30 nm to 10 μm, and most preferably in the range of 50 nm to 2 μm.

[0088] 6. A method according to any of the preceding items, wherein the original surface microstructure has at least one area in which the microstructure is anisotropic.

[0089] 7. A method according to any of the preceding items, wherein the original surface microstructure has at least one area in which the microstructure is non-periodic.

[0090] 8. The original surface microstructure - providing a substrate; - providing a material composition comprising a crosslinkable material and a non-crosslinkable material; - forming a layer of the material composition on a substrate; - initiating crosslinking of the crosslinkable material by irradiation with UV light; - Removal of non-crosslinked material 2. The method of claim 1, wherein the polymer is produced by a process comprising the steps of:

[0091] 9. A method according to any of the preceding items, wherein the step of processing the digital data of the original surface microstructure comprises lateral scaling of the microstructure in the plane of the microstructure.

[0092] 10. The method according to item 9, wherein the different magnifications are applied in different lateral directions, preferably in two different directions that are perpendicular to each other.

[0093] 11. A method according to any of the preceding items, wherein the step of processing the digital data of the original surface topography comprises binarizing the digital data.

[0094] 12. A method according to any of the preceding items, wherein the step of processing the digital data of the original surface microstructure comprises the creation of a composite microstructure by arranging two basic microstructure elements, the microstructures having different average lateral structure distances, and / or the microstructures having different average structure widths, and / or the microstructures having different microstructure fill factors, and / or the microstructures having different anisotropy directions, and / or different degrees of anisotropy, and / or one basic microstructure element comprising a periodic microstructure and the other basic microstructure element comprising a non-periodic microstructure.

[0095] 13. The method of any of the preceding items, wherein the desired surface microstructure comprises regions having a surface microstructure that is optically effective and regions that provide an optimal surface microstructure for alignment of liquid crystals.

[0096] 14. The method according to any of the preceding items, wherein the structural depth of the desired surface microstructure is greater than the structural depth of the original surface microstructure.

[0097] 15. The method according to any of the preceding items, wherein the surface microstructure aspect ratio (SMAR) of the desired surface microstructure is preferably greater than 1.1, more preferably greater than 2, and most preferably greater than 5.

Claims

1. - providing a material having a surface microstructure with a topography, which surface microstructure is considered as the original surface microstructure; - providing a 3D surface profilometer; - acquiring digital data of the original surface microstructure topography by a 3D surface profilometer; - providing writing tools; - processing the digital data of the original surface microstructure topography to obtain structure description data to be written by the writing tool; - providing structural description data of the desired surface microstructure to a writing tool; - providing a target material; - optionally providing a resin; - creating a desired surface microstructure in or on the target material, including writing the structure in or on the target material or in the resin with a writing tool using the structure description data; A method for producing a desired surface microstructure, comprising:

2. 2. The method of claim 1, wherein the original surface microstructure comprises an area in which the average structure width, measured along a direction perpendicular to the anisotropy direction when the surface microstructure is anisotropic, is in the range of 10 nm to 1 mm, more preferably in the range of 50 nm to 100 μm, most preferably in the range of 100 nm to 10 μm.

3. 3. A method according to claim 1 or 2, wherein the original surface microstructure comprises an area in which the average lateral structure distance, measured along a direction perpendicular to the anisotropy direction when the surface microstructure is anisotropic, is in the range of from 10 nm to 1 mm, more preferably in the range of from 50 nm to 100 μm, most preferably in the range of from 100 nm to 10 μm.

4. A method according to claim 1 or 2, wherein the original surface microstructure has at least one region in which the microstructure fill factor is in the range of 0.050 to 0.95, more preferably in the range of 0.2 to 0.8, most preferably in the range of 0.3 to 0.

7.

5. 3. A method according to claim 1 or 2, wherein the structure depth of the original surface microstructure is in the range of 10 nm to 100 μm, more preferably in the range of 30 nm to 10 μm, most preferably in the range of 50 nm to 2 μm.

6. 3. The method of claim 1 or 2, wherein the original surface microstructure has at least one area in which the microstructure is anisotropic.

7. 3. The method of claim 1 or 2, wherein the original surface microstructure has at least one area in which the microstructure is non-periodic.

8. The original surface microstructure - providing a substrate; - providing a material composition comprising a crosslinkable material and a non-crosslinkable material; - forming a layer of the material composition on a substrate; - initiating crosslinking of the crosslinkable material by irradiation with UV light; - Removal of non-crosslinked material The method of claim 1 or 2, wherein the polymer is produced by a method comprising:

9. 3. A method according to claim 1 or 2, wherein the step of processing the digital data of the original surface topography comprises lateral scaling of the topography in the plane of the topography.

10. 10. The method according to claim 9, wherein different magnifications are applied in different lateral directions, preferably in two different directions which are perpendicular to each other.

11. 3. A method according to claim 1 or 2, wherein the step of processing the digital data of the original surface topography comprises binarizing the digital data.

12. 3. The method according to claim 1 or 2, wherein the step of processing the digital data of the original surface microstructure comprises the creation of a composite microstructure by arranging two basic microstructure elements, the average lateral structure distance of the microstructures being different, and / or the average structure width of the microstructures being different, and / or the microstructure fill factors of the microstructures being different, and / or the anisotropy directions of the microstructures being different, and / or the degree of anisotropy being different, and / or one basic microstructure element comprising a periodic microstructure and the other basic microstructure element comprising a non-periodic microstructure.

13. 3. The method of claim 1 or 2, wherein the desired surface microstructure includes regions having a surface microstructure that is optically effective and regions that provide an optimal surface microstructure for alignment of liquid crystals.

14. 3. The method according to claim 1 or 2, wherein the structure depth of the desired surface microstructure is greater than the structure depth of the original surface microstructure.

15. 3. The method of claim 1 or 2, wherein the surface microstructure aspect ratio (SMAR) of the desired surface microstructure is preferably greater than 1.1, more preferably greater than 2, and most preferably greater than 5.

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