Optical lens and method for ion-etching a curved surface of a substrate

Abstract

The invention relates to an optical lens and a method (100A, 100B) for ion-etching a curved surface of a substrate (200), wherein a method (100A) for ion-etching the curved surface of the substrate includes: forming a mask structure over the curved surface of the substrate (200); arranging a grid electrode (520) between a plasma source (512) for ion etching and the substrate (200) that has the mask structure, with the grid electrode (520) having a curvature profile in the direction of the plasma source (512) that substantially corresponds to a curvature profile of the curved surface of the substrate (200); and ion-etching the curved surface of the substrate (200) by using the mask structure and by applying a voltage to the grid electrode (520) such that a structure is formed in the curved surface of the substrate (200). The optical lens has a variable thickness and a curved surface with an anti-reflection structure in the curved surface for providing anti-reflective properties, wherein the anti-reflection structure covers at least 99% of the curved surface.

Description

[0001] Description

[0002] Optical lens and method for ion etching a curved surface of a substrate

[0003] Various embodiments generally relate to an optical lens and methods for ion etching a curved surface of a substrate.

[0004] Surface structures can provide a wide range of functionalities and are therefore used in numerous fields for a variety of tasks. One example is optical components, such as lenses with spherical, aspherical, or freeform surface contours, where surface structures can modify the optical properties. Even already (e.g., micro-) structured surfaces (e.g., with binary or blaze gratings) on previously mentioned optical components can be structured as described herein.

[0005] Such surface structures can be created in the surface of a component, for example, by ion etching (e.g., inert ion etching or reactive ion etching (RIE). For many manufacturing processes, reactive ion etching can be economically advantageous due to the higher etching rates (e.g., 40 nm / min or more) compared to purely chemical, purely physical (inert), and reactive ion beam etching.

[0006] Surface structures are usually created in planar surfaces of a substrate by means of ( e . g . inert and / or reactive) ion etching . For a wide variety of applications it may be desirable and / or necessary to create corresponding surface structures in substrates with curved surfaces by means of ion etching. In this regard, it has been recognized that when ion etching substrates with curved surfaces, sufficient homogeneity of the surface structures cannot be achieved across the curved surface, since the curved surface leads to locally different etching rates and / or etching directions. The homogeneity of the surface structures is even lower if the substrate has a varying thickness. This is because during ion etching, ions are accelerated towards the surface of the component due to an electric field penetrating the component.The varying thickness of the substrate leads to a varying attenuation of the electric field strength and thus to an additional difference in the local etching rate , which increases the inhomogeneity along the surface structures across the curved surface .

[0007] Various embodiments relate to a method for (inert and / or reactive) ion etching of a substrate with a curved surface, which method is capable of producing homogeneous surface structures for both substrates with curved surfaces and substrates with a thickness variation. This method enables, for example, surface structures in the curved surface of an optical lens (which has a thickness variation) as well as the other optical elements already mentioned to be produced in such a homogeneous manner that at least 90% (e.g., at least 99%) of the optically active surface is covered with the surface structure.

[0008] According to various aspects, a substrate (e.g. an optical element described herein) that already has a structured surface (e.g. provided with optical binary diffraction gratings or blaze gratings) can be provided with an additional surface structure (e.g. with nanostructures (e.g. with moth-eye structures)) by means of the ion etching method described herein with a grid electrode. This additional surface structure can, for example, provide an additional optical function, e.g. anti-reflection coating to avoid intensity losses. Various embodiments relate to a method for inert ion etching of a layer arranged over a curved surface of a dielectric substrate.This process makes it possible, for example, to remove surface coatings from the curved surface of an optical lens (which has a thickness variation) essentially over the entire area with high homogeneity.

[0009] The homogeneous creation of the surface structure and the homogeneous removal of the surface coating are made possible by arranging a grid electrode between the plasma source and the substrate and applying a voltage to the grid electrode during ion etching. The grid electrode has a curvature in the direction of the plasma source that essentially corresponds to the curvature of the curved surface of the substrate. The grid electrode is electrically connected to the substrate holder of the ion etching system and thus the substrate is surrounded (e.g. enclosed) from the plasma by a Faraday cage formed from the grid electrode and the metallic substrate holder. Further embodiments relate to the all-round closed arrangement of the substrate with grid electrodes. This means that all optical surfaces of the substrate can be processed simultaneously by ion etching in a volume plasma.

[0010] Examples of embodiments are shown in the figures and are explained in more detail below.

[0011] It shows

[0012] Figure 1A is a flowchart of a method for ion etching a curved surface of a substrate according to various embodiments;

[0013] Figure 1B shows a flowchart of a method for inert ion etching a curved surface of a substrate according to various embodiments; Figures 2A and 2B show exemplary substrates with a curved surface;

[0014] Figure 3 is a schematic illustration of a moth eye structure;

[0015] Figure 4 illustrates aspects of an exemplary method for forming a mask structure over a curved surface of a substrate according to various embodiments;

[0016] Figure 5A shows a schematic system for ion etching a curved surface of a substrate according to various embodiments;

[0017] Figure 5B shows a schematic grid arrangement; and

[0018] Figures 50 and 5D show an exemplary grid electrode according to various embodiments.

[0019] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "fore", "rear", etc. is used with reference to the orientation of the described figure(s). Since components of embodiments can be positioned in a number of different orientations, the directional terminology is for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention.It is understood that the features of the various exemplary embodiments described herein can be combined with one another, unless specifically stated otherwise. The following detailed description is therefore not to be interpreted in a limiting sense, and the scope of the present invention is defined by the appended claims. If a substrate has a curved surface and / or a thickness variation (or an excessively large material thickness), it is not possible to produce surface structures in the (curved) surface of the substrate with sufficient homogeneity along the (curved) surface using conventional (inert or reactive) ion etching, since the curved surface can lead to locally different etching rates and / or etching directions and this is amplified if the substrate has a varying thickness.The inhomogeneity resulting from the locally dependent etching rate and / or etching direction can increase with increasing substrate thickness. Accordingly, for such a substrate with a curved surface, it is also not possible to remove a layer arranged (e.g. formed) on the curved surface of the substrate with sufficient homogeneity along the (curved) surface essentially over its entire area, since the curved surface, as explained, can lead to locally different etching rates and / or etching directions and this is amplified if the substrate has a varying thickness. Without the grid electrode described herein, locally varying material removal would occur.

[0020] According to various embodiments, methods are provided which make it possible to homogeneously remove substrates having a curved surface and / or having a varying thickness by means of ion etching. For example, one method makes it possible to form (homogeneous) surface structures by means of ion etching even in substrates having a curved surface and / or having a varying thickness. For example, one method makes it possible to homogeneously remove a layer over the entire area by means of ion etching from a substrate having a curved surface and / or having a varying thickness.

[0021] FIG. 1A shows a flowchart of a method 100A for ion etching a curved surface of a substrate according to various embodiments. The method 100A may include forming a mask structure over the curved surface of the substrate (in 102A).

[0022] The method 100A may include arranging a grid electrode between a plasma source for ion etching and the substrate having the mask structure (in 104A). In this case, the grid electrode may have a curvature in the direction of the plasma source that substantially corresponds to a curvature of the curved surface of the substrate. The curvature may also be referred to as the contour or topology of the grid electrode.

[0023] Ion etching can take place in an inert plasma (also called inert ion etching) or a reactive plasma (also called reactive ion etching). In inert ion etching, material is removed from the substrate by physical impact (e.g. using argon ions). Inert gas applications can be used both to create structures on the surface and maskless for the removal of thin layers (e.g. in the case of coating defects or to correct layer thickness). In reactive ion etching, material is removed by a combination of physical impact and chemically reactive removal using a reactive gas (e.g. containing fluorine).

[0024] The method 100A may include (inert or reactive) ion etching of the curved surface of the substrate using the mask pattern and applying a voltage to the grid electrode (in 106A). In this way, a pattern may be formed in the curved surface of the substrate.

[0025] According to various aspects, the ion etching (in 106A) may be multi-step. For example, the method 100A may iteratively (in each step of a plurality of steps): ion etching the curved surface of the substrate using the mask structure and applying a voltage to the grid electrode, and forming a sidewall passivation layer over sidewalls of the structures formed by the ion etching (e.g., by means of polymer layer deposition). The sidewall passivation layer may protect the formed structures from etching in the subsequent ion etching. The ion etching and formation of the sidewall passivation layer may be repeated iteratively until the structure (e.g., a desired depth of the structure) in the curved surface of the substrate is achieved.

[0026] The sidewall passivation layer can advantageously be formed using the grid electrode. A process gas suitable for polymer layer formation (e.g., CHF3) or a mixture (e.g., with argon) is used instead of the etching gas. The process gas pressure and / or the voltage or electrical power at the grid electrode can be adjusted to ensure an optimal layer with the required protective effect for the sidewalls of the structures already created in previous etching steps.

[0027] This process can (except for the use of the grid electrode) correspond to the process commonly known as the "Bosch process" for ion etching of deep structures with numerous application-dependent variations.

[0028] Consequently, the method 100A may iteratively comprise: ion etching the curved surface of the substrate using the mask structure and applying a voltage to the grid electrode, forming a sidewall passivation layer over sidewalls of the structures formed by the ion etching (e.g., by means of polymer layer deposition), while maintaining the grid electrode between the plasma source and the substrate

[0029] As described above, inert or reactive ion etching can also be used to remove layers without a mask structure. In this case, the method may omit the formation of the mask structure (in 102A), and the method (100A) may comprise (in 106A) ion etching of the curved surface of the substrate for (homogeneously) removing a layer on the curved surface of the substrate while applying a voltage to the grid electrode.

[0030] FIG.1B shows a flowchart of a method 100B for (inert or reactive) ion etching of a curved surface of a substrate according to various embodiments.

[0031] Method 100B may include arranging a grid electrode between a plasma source for (e.g., inert) ion etching and the substrate (in 102B). In this case, the grid electrode may have a curvature in the direction of the plasma source that substantially corresponds to a curvature of the curved surface of the substrate.

[0032] Method 100B may include substantially completely removing a layer from the curved surface of the substrate by ion etching while applying a voltage to the grid electrode (in 104B). The layer may, for example, be a layer previously formed (e.g., deposited) over the curved surface of the substrate.

[0033] The method 100B thus makes it possible, for example, to remove defective (e.g., optical layers) from the curved surface of the substrate (e.g., a lens or a (e.g., multifaceted) prism). In this way, a defective layer formed on the substrate can be removed and then re-formed. This can lead to a significant reduction in costs, for example, in the case where the substrate is a (cost-intensive) optical lens and / or a (cost-intensive) optical prism. Clearly, in this way, the affected (expensive) lenses can, for example, be salvaged and then recoated. This method 100B can, for example, replace the cost-intensive ion beam stripping process (and consequently lead to a cost reduction).

[0034] In the following, various aspects and embodiments of the method 100A and the method 100B are described by way of example.

[0035] The substrate 200 with a curved surface can be any type of (electrically non-conductive) substrate on whose curved surface a structure can be formed by ion etching or a layer of whose curved surface can be removed substantially over its entire area. For example, the substrate 200 can consist of a dielectric material (e.g. a glass and / or a crystalline material and / or a polymer). In various embodiments, the substrate can have one or more layers that completely cover the curved surface of the substrate. According to various aspects, the structure can be formed in these one or more layers according to the method 100A. According to various aspects, at least one of these one or more layers can be removed substantially over its entire area according to the method 100B.

[0036] A curved surface is understood to mean a curvature (or a locally varying degree of curvature) that varies locally along the surface. Consequently, a curved surface is understood to mean a non-planar surface. In various embodiments, the curvature of the curved surface of the substrate can have a spherical, aspherical curvature, or a free-form surface.

[0037] For example, FIG. 2A shows a perspective view 202 and a cross-sectional view 204 of an exemplary substrate 200 having a curved surface 203. In this example, the surface 203 is convexly spherically curved. In embodiments, the substrate 200, such as shown in FIG. 2A, may have a locally substantially uniform thickness, d.

[0038] In other embodiments, the curved substrate 200 can have a locally varying thickness. A thickness variation of a substrate is understood to mean a location-dependent thickness of the substrate (with respect to the curved surface). Thus, the curved substrate 200 can have a first thickness at one location on the curved surface 203 and a thickness different from the first thickness at another location on the curved surface 203. An example of this is optical lenses and prisms. FIG. 2B shows various exemplary cross-sections of such a substrate 200 configured with a curved surface (e.g., as an optical lens or prism). As shown, the curved surface 203 can be convex (see cross-sections 206, 208, 210) or concave (see cross-sections 212, 214, 216).Thus, the curved substrate 200, as an optical lens, can be a converging lens (convexly curved at the curved surface 203) or a diverging lens (concavely curved at the curved surface 203). The (second) surface opposite the convexly curved (first) surface 203 of the substrate 200 can also be curved (see cross-sections 206, 210, 212, 216) or can be planar (see cross-sections 208, 214). For example, in the case of the convexly curved (first) surface of the substrate 200 (see cross sections 206, 208, 210), the opposite (second) surface may also be convexly curved (cross section 206), planar (cross section 208), or concavely curved (cross section 210).Accordingly, in the case of the concavely curved (first) surface of the substrate 200 (see cross sections 212, 214, 216), the opposite (second) surface can also be concavely curved (cross section 212), planar (cross section 214), or convexly curved (cross section 216). According to various aspects, the methods 100A, 100B are independent of the configuration of the (second) surface opposite the curved (first) surface 203. In some configurations, the method 100A and / or the method 100B can comprise that during the ion etching of the curved (first) surface 203 of the substrate 200, the (second) surface opposite the curved surface 203 (e.g., curved or planar) is also processed.In one example, in method 100A, a mask structure may also be formed over the opposite (second) surface and a respective grid electrode may be arranged between a plasma source for ion etching facing a respective surface of the substrate 200 and the substrate, and then the curved (first) surface 203 and the opposite (second) surface may be ion etched simultaneously to form a structure in the respective surface. In one example, in method 100B, a grid electrode may also be arranged between the opposite (second) surface of the substrate 200 and a plasma source facing it, and then the curved (first) surface 203 and the opposite (second) surface may be etched substantially over their entire area at the same time.In another example, method 100A and method 100B may take place substantially simultaneously on two opposite sides of the substrate, each with a curved surface. In this case, the grid electrode associated with the opposite surface may have a curvature that substantially corresponds to a curvature of the opposite (second) surface of substrate 200.

[0039] The curved surface may also be referred to as the first surface or first substrate surface and the surface opposite the curved surface may also be referred to as the second surface or second substrate surface.

[0040] As explained above, the curved substrate 200 can have a varying thickness, d. If the (second) surface opposite the curved (first) surface 203 is planar, the curvature of the curved surface essentially corresponds to the thickness. This is shown for illustrative purposes in the cross-section 208, wherein the dashed line represents both the profile of the curved surface and the profile of the thickness, d, along the width, b, of the substrate 200.

[0041] The above-described varying attenuation of the electric field strength due to the varying thickness of the (dielectric) substrate 200 has a significant influence in the case of voluminous substrates. Clearly, the substrate 200 can act as a dielectric barrier to varying degrees locally. The methods 100A, 100 resolve this problem, as explained herein, so that (homogeneous) surface structures can also be formed on and / or in a voluminous substrate, or layers can be removed from the curved surface substantially over the entire area.A voluminous substrate, as used herein, is understood to mean a substrate made of a dielectric material, the material thickness of which, as a whole or in part, in the case of an existing thickness variation, weakens the electric field for accelerating the ions during ion etching completely or locally due to the thickness variation to such an extent that the full-surface etching process is prevented or locally weakened by the thickness variation, so that a homogeneous (inert or reactive) etching removal of the surface of the voluminous substrate is not possible.

[0042] As described, in method 100A (in 102A), a mask structure may be formed over the curved surface 203 of the substrate 200. This mask structure may be associated with the structure to be formed in the curved surface 203. The mask structure may cover portions of the curved surface that are not to be etched by (inert and / or reactive) ion etching, and leave other portions uncovered, so that essentially these other uncovered portions are etched. Thus, the mask structure may enable imaging of the structure to be formed into the curved surface 203.

[0043] Depending on the application, the structure can be, for example, a microstructure or a nanostructure. A microstructure, as used herein, can be understood as a structure which, in one or more dimensions, has a size of or (e.g. regular) a spacing between structural elements in the micrometer range (e.g. less than or equal to 1 mm). Accordingly, a nanostructure, as used herein, can be understood as a structure which, in one or more dimensions, has a size of or (e.g. regular) a spacing between structural elements in the nanometer range (e.g. less than or equal to 1 pm). It is understood that the characterization of a structure as a microstructure or nanostructure can depend on a specific parameter (e.g. a size of the structural elements or a spacing between the structural elements, etc.) which is important, for example, for a specific application.For example, in the case of an optically functional structure, the structural elements can be regularly arranged at a distance from one another that is in the range of the wavelength of the incident electromagnetic radiation or smaller than the wavelength of the incident electromagnetic radiation. Consequently, the wavelength of the incident electromagnetic radiation can define whether the structure is a microstructure or a nanostructure.

[0044] Herein, the term "structure" (e.g., microstructure or nanostructure) is used with reference to the structure to be formed (before reactive ion etching) or formed (after reactive ion etching) in the curved surface 203 of the substrate 200. Therefore, the structure may also be referred to as a surface structure. The method 100A described herein is suitable for any type of such structures and therefore enables the formation of a homogeneous structure (e.g., a microstructure or nanostructure) on the curved surface of a (e.g., voluminous) substrate (with, for example, a locally varying thickness with respect to the curved surface).

[0045] According to various aspects, an anti-reflective structure (e.g., for broadband anti-reflection of the substrate 200, for example, an optical lens) can be formed in the curved surface 203 of the substrate 200 by means of the method 100A. Optical lenses with an anti-reflective structure can be used, for example, in multi-lens systems to reduce reflections of the incident light at a respective optical lens, thereby reducing, for example, aberrations and / or transmission losses of the multi-lens system.

[0046] An example of such an anti-reflective structure is the moth eye structure (also called moth eye nanostructure).

[0047] The moth-eye structure is characterized by a large number of (periodically (or regularly) arranged), preferably conical structures. For illustration, an exemplary moth-eye structure 300 with a large number of conical structures 302 is shown schematically in FIG. 3. These conical structures 302 can be arranged at a distance from one another that is smaller than the wavelength of the incoming electromagnetic wave. In this case, a biomimetic-technical adaptation brings about a broadband increase in the transmittance and thus a reduction in reflection. Physically, this effect is caused by the sub-wavelength period of the structures and the resulting continuous refractive index profile in the resulting effective medium.The method 100A makes it possible to form the plurality of (periodically arranged) conical structures 302 homogeneously on the curved surface 203 of the substrate 200 such that they cover at least 90% (e.g., at least 95%, e.g., at least 97%, e.g., at least 99%) of the curved surface 203 and at the same time can fulfill their function of locally increased transmission.

[0048] Homogeneous structural elements can be understood to mean that the structural elements, such as the conical structures 302, differ in their parameters by a maximum of 20% (e.g., a maximum of 10%, e.g., a maximum of 5%). Such parameters can be structural parameters, such as the extension in the respective dimensions (e.g., height, width, etc.), an increase in the rising or falling flanks of the conical structures, a symmetry of a respective structural element, a distance between the structural elements, etc. Such parameters can also be functional parameters, such as a local transmittance (e.g., reflectance) (defined by several structural elements).For example, the parameter can be a difference between the transmittance in a central region of the curved surface (i.e., in the region of the inflection point of the curved surface) and a transmittance in the edge region (or both edge regions) of the curved surface. Such homogeneously formed structural elements are not possible by (both inert and reactive) ion etching without the use of the grid electrode described herein, since the local properties of the structural elements depend on the curvature of the curved surface and the thickness of the substrate.

[0049] Forming the moth-eye structure 300 by means of (e.g., inert and / or reactive) ion etching has (in the case of reactive ion etching, in addition to the high etching rate of reactive ion etching described above) further advantages (e.g., compared to conventional dielectric interference layers). For example, no constructive interference effects occur, the antireflection effect is largely independent of the angle of incidence, and the risk of layer ablation does not exist because the material itself is structured.

[0050] The mask structure can be formed (in 102A) over the curved surface 203 using a suitable lithography method. Micellar block copolymer nanolithography is described below as an example for forming the mask structure. This can be used, for example, to form the moth-eye structure 300 in the curved surface 203. It is understood that another lithography method can also be used.

[0051] FIG. 4 shows aspects of forming the mask structure using micellar block copolymer nanolithography 400. This mask structure enables, for example, the formation of the moth-eye structure 300 in the curved surface 203 of the substrate 200 by subsequent ion etching using the grid electrode. Micellar block copolymer nanolithography is particularly suitable for the lithography of optical lenses.

[0052] In (self-assembling) micellar block copolymer nanolithography (BCML) 400, micelles made of copolymers (with polymers of different solubility) can be arranged on the curved surface (e.g., by dip coating), in the center of which desired (metal) atoms, such as gold atoms, can be embedded (see 402). In a subsequent process, the (metal) atoms of each micelle can be combined to form a (metallic) (nano-) cluster, and then the polymer layer can be removed (e.g., by reactive plasma etching) (see 404). This can create a (regular) arrangement (e.g., a pattern) of the (metallic) (nano-) clusters (e.g., of gold particles), which forms the mask structure (see 406). This mask structure can then be transferred to the curved surface 203 of the substrate 200 by ion etching.

[0053] FIG. 5A shows a schematic device 500 according to various aspects. This device 500 can be configured for (inert and / or reactive) ion etching of a curved surface 203 of the substrate 200. It is understood that this is an exemplary device and that the ion etching can also be performed with another device that uses the grid electrode described herein (with a corresponding curvature).

[0054] Reactive ion etching is based on chemical and physical etching and enables (as described above) comparatively high etching rates, high material selectivity and anisotropic etching.

[0055] The device 500 may include a process chamber 502. The process chamber 502 may have an opening 504 (e.g., a flange) by means of which the process chamber 502 may be coupled to a pump system for generating a negative pressure (e.g., vacuum) in the process chamber 502. The pump system may include one or more vacuum pumps. A vacuum pump may be any type of vacuum pump, such as a high-vacuum pump (e.g., a turbomolecular pump) or a backing pump (e.g., a scroll pump, a diaphragm pump, or a (e.g., multi-stage) Roots pump, a diffusion pump, or a rotary vane pump). The pump system may be a combination of one or more of the above pumps. For example, the pump system may include a pumping station combining a backing pump and a turbomolecular pump.It is understood that the process chamber 502 may be configured to achieve / maintain the negative pressure when sealed, for example, airtight, dusttight, and / or vacuum-tight. The negative pressure in the process chamber 502 may be a pressure (which is, for example, the external pressure) in a range of approximately 10 mbar to approximately 1 mbar (in other words, rough vacuum) or less, for example, a pressure in a range of approximately 1 mbar to approximately 10. -3 mbar (in other words fine vacuum) or less, for example a pressure in a range of approximately 10 -3 mbar to approximately IO -7 mbar (in other words high vacuum) or less, for example a pressure in a range of less than IO -7 mbar (in other words ultra-high vacuum).

[0056] The process chamber 502 may have at least one lock interface for introducing and / or removing the substrate 200 (e.g., by means of the substrate holder). The process chamber 502 may have a gas inlet 506 for introducing a process gas. The process chamber 502 may have a substrate holder 508 (e.g., formed from an aluminum plate).

[0057] As shown in FIG. 5A, the substrate 200 with a curved surface can be arranged on the substrate holder 508. In this example, the substrate 200 is illustrated as a plano-convex optical lens (i.e., with a curved surface and varying thickness). Optionally, the device 500 can have a cooling line 510 by means of which the substrate holder 508 can be cooled.

[0058] The device 500 may include a plasma source 512. The plasma source 512 may, for example, be an inductively coupled plasma (ICP) source (with, for example, a radio-frequency generator). For example, the plasma source may be located outside the process chamber 502, and the process chamber 502 may include a quartz glass window 514 through which the plasma source 512 can generate the plasma 516 (also referred to as volume plasma) in the process chamber 502.

[0059] The device 500 may include the grid electrode 520 (e.g., arranged between the plasma source 512 and the substrate 200 in FIG. 104) having a curvature substantially corresponding to the curvature (convex in this example) of the curved surface 203 of the substrate 200.

[0060] The device 500 may include a voltage source 518. The voltage source 518 may be configured to apply a (e.g., negative) voltage to the grid electrode 520.

[0061] This voltage can be an alternating voltage (e.g., the voltage source 518 can be a (e.g., 13.56 MHz) high-frequency generator). The voltage can be a pulsed (DC or AC) voltage (e.g., the voltage source 518 can be a (DC or AC) pulse generator).

[0062] The device 500 may include a control device. The control device may be configured to control the ion etching process, such as the high-frequency generator of the plasma source for generating the plasma 516, the generator (e.g., high-frequency generator or pulse generator) of the voltage source 518 for applying the voltage to the grid electrode 520, a gas supply via the gas inlet 506, the substrate cooling, etc.

[0063] The grid electrode 520 may be made of an electrically conductive material (e.g., a metal or a metal alloy) (e.g., to form the Faraday cage with the substrate holder 508). The material of the grid electrode 520 may exhibit chemical resistance in the (inert or reactive) plasma 516 (e.g., against fluorine- and / or oxygen-containing radicals, ions, etc.) and / or a low sputtering rate during (inert and / or reactive) ion etching.

[0064] A grid electrode, as used herein, may be understood to mean any type of electrode that has a plurality of through-openings (thus enabling ion etching of the underlying substrate 200). For example, the grid electrode 520 may have a regular grid arrangement as shown in FIG. 5B. In this case, the grid may be characterized by a mesh size, MW (e.g., a vertical mesh size, MW V, and a horizontal mesh size, MWh) and a mesh width MB (e.g. a vertical mesh width, MB V, and a horizontal mesh width, MB ). In various embodiments, the mesh width can be substantially the same horizontally and vertically, and the mesh web width (thickness of the webs) can be substantially the same horizontally and vertically. According to various aspects, the mesh width can be less than or equal to 1 mm (e.g., less than or equal to 500 pm). For example, the mesh width can be selected such that the transparency of the grid electrode 520 for ion etching at the mesh width (of, for example, less than or equal to 1 mm) is at least 50% (e.g., at least 60%, e.g., at least 70%, e.g., at least 80%). The mesh thickness can also be selected accordingly (e.g., the mesh thickness can be less than or equal to 100 pm). For mesh widths greater than 1 mm, potential differences can occur inside the Faraday cage, which can impair the homogeneity of the structures formed.of the removed layer is reduced. For this purpose, the mesh size of the grid electrode 520 can be smaller than the mean free path in the plasma 516. This shields the plasma 516 from the volume beneath the grid electrode 520 (Faraday cage). Although a grid with rectangular (e.g., square) through-openings was described above, the grid electrode 520 can also have non-rectangular through-openings, such as elliptical (e.g., circular) or polygonal through-openings.

[0065] The grid electrode can also be called an extraction grid electrode.

[0066] In order to achieve the homogeneity described herein, the grid electrode 520 can be arranged at a comparatively small distance from the curved surface 203 of the substrate 200. This distance between the grid electrode 520 and the substrate surface 203 can be, for example, less than or equal to 10 mm (e.g., less than or equal to 6 mm, e.g., less than or equal to 3 mm). It is understood that this distance between the grid electrode 520 and the substrate surface 203 can depend on a mesh size of the grid electrode 520 (e.g., configured as a wire grid). For example, wire webs of the wire grid can cover part of the substrate surface 203 and thus lead to a lower etching rate in these areas. From a threshold distance between the grid electrode 520 and the substrate surface 203, this influence is reduced to such an extent that it is no longer measurable.For example, studies have shown that this threshold distance ranges between approximately 5 mm and approximately 6 mm for a mesh thickness or mesh width of 56 pm. It is understood that the threshold distance may also depend on other factors, such as the parameters used for ion etching.

[0067] The grid electrode 520 can be manufactured, for example, by additive manufacturing using laser sintering in a metal powder bed or by stereolithography using (e.g., UV) laser curing. In additive manufacturing using stereolithography using (e.g., UV) laser curing, the grid can be made of a polymer material, for example, and the dimensional stability of the grid structure can be increased by thermal treatment and / or electrical conductivity can be created by means of a metallic coating.

[0068] The grid electrode can also be formed, for example, by means of galvanic metal deposition on bodies adapted to the shape with a lithographically applied grid structure mask and then removed in a self-supporting manner.

[0069] According to various aspects, the grid electrode 520 can comprise a wire mesh 522. An exemplary grid electrode 520 comprising such a wire mesh 522 is shown in FIG. 5C and FIG. 5D (indicating exemplary dimensions for an associated substrate 200 (e.g., an optical lens) with a convexly curved surface). In this example, the wire mesh 522 has a wire thickness (as mesh web width) of 56 pm and a mesh size of 180 pm. This corresponds approximately to an open area (and thus a transparency) of 58%. This wire mesh 522 enables, for example, a homogeneity of the transparency of greater than or equal to 95% regardless of the curvature of the grid electrode 520.

[0070] The grid electrode 520 can have a first surface 524 in the direction of the plasma source 512. The grid electrode 520 can have a second surface 526 opposite the first surface 524 in the direction of the curved surface 203 of the substrate 200. According to various aspects, the function of the grid electrode 520 described herein can be independent of the shape (e.g. the curvature) of the second surface. The grid electrode 520 can have the curvature in the direction of the plasma source 512 that substantially corresponds to the curvature of the curved surface 203 of the substrate 200. It is understood that there can be local differences in the curvature of the curved surface and the curvature of the grid electrode 520 and the curvature can nevertheless be substantially the same. For example, the example in FIG.5C shows a grid electrode 520 having a plurality of linear sections 528 (arranged at an angle to one another). These plurality of linear sections 528 are arranged such that, as a whole, they have a curvature on the first surface 524 that substantially corresponds to the curvature of the curved surface of the substrate 200 (see, for example, FIG. 5A). Illustratively, the first surface 524 of the grid electrode 520 may run substantially parallel to the curved surface of the substrate 200. According to various aspects, the grid electrode 520 may include a sample holder 527 (e.g., a block made of aluminum).

[0071] FIG. 5D shows an image of a grid electrode 520 fabricated according to the schematic representation of FIG. 5C. Although the grid electrode 520 is illustrated in the example as a section of a semi-ellipsoid, it is understood that depending on the shape of the curved surface of the substrate 200, a different shape of the grid electrode 520 may be used, such as the shape of a semi-ellipsoid.

[0072] According to various aspects, the substrate holder 508 can be electrically conductive. The substrate holder 508 can be electrically conductively connected to the grid electrode 520. In this case, the voltage source 518 can also apply the voltage to the substrate holder 508 and thus indirectly apply it to the grid electrode 520 via the substrate holder 508.

[0073] The substrate holder 508 and the grid electrode 520 can be arranged such that they completely surround the substrate 200. In this way, the substrate holder 508 and the grid electrode 520 can form a Faraday cage surrounding the substrate 200. The substrate 200 is thus surrounded on all sides by conductive material of the same potential, so that the curved surface 203 of the substrate 200 is not charged by bombardment with charge carriers. In this case, essentially no electric fields are present within the space formed by the grid electrode 520 and the substrate holder 508.

[0074] In this way, during ion etching, by applying the voltage to the grid electrode 520, a homogeneous plasma edge zone 525 of the plasma 516 is created on the first surface 524 of the grid electrode 520. Consequently, the plasma edge zone 525 has a profile that essentially corresponds to the curvature of the curved surface 203 of the substrate 200. The respective high-frequency half-wave of the applied voltage then accelerates ions and electrons of the plasma 516 into the (electrically field-free) space formed by the grid electrode 520 and the substrate holder 508, thus causing ion etching (i.e., a transfer of the mask structure into the curved surface of the substrate 200).

[0075] Due to the electrical field-free space (i.e. the Faraday cage) between the grid electrode 520 and the substrate 200, there is no varying weakening of the electric field due to the varying thickness of the substrate 200, so that for substrates with a varying thickness profile and / or voluminous substrates 200, structures with homogeneous properties can be achieved.

[0076] Since the first surface 524 of the grid electrode 520, and thus the plasma edge zone 525 of the plasma 516, has essentially the same curvature as the curved surface of the substrate 200, the electrons and ions of the plasma 516 strike the curved surface at a substantially identical angle of incidence (across the substrate 200) during ion etching. In this way, homogeneous properties can be achieved across the curved surface.

[0077] This enables, for example, in the case of ion etching using the mask structure (i.e., by means of method 100A), the production of the moth-eye structure 300 with homogeneous properties of the conical structures 302 themselves and the arrangement (e.g., the spacing between) the conical structures 302. This makes it possible, for example, to achieve homogeneous transmission and / or reflection properties across the curved surface. In the moth-eye structure 300, the conical shape can play a decisive role, so that purely anisotropic reactive ion etching with ions running (almost) perpendicular to the curved surface of the substrate 200 (i.e., arranged at 90° to the surface) can be undesirable. Optionally, in method 100A, the structures can only be formed in a portion of the curved surface.For example, a first structure may be formed in a first portion of the curved surface using a first mask pattern in a first ion etch, and a second mask pattern may then be used to form a second structure different from the first structure in a second portion of the curved surface different from the first portion in a second ion etch. In one example, the grid electrode 520 may have a non-mesh portion covering a corresponding portion of the curved surface of the substrate 200 such that no structure is formed in the corresponding portion of the curved surface of the substrate 200 by the ion etching. In another example, a mask may be disposed between the grid electrode 520 and the substrate 200.This mask can cover a portion of the curved surface of the substrate 200 so that no structure is formed by the ion etching in the corresponding portion of the curved surface of the substrate 200. In this way, for example in the case of the anti-reflective structure, a local variation (e.g., a contour pattern) of the transparency can be achieved. Consequently, an optical lens produced in this way can have a first portion with a first (homogeneous) transparency and a second portion different from the first portion with a second (homogeneous) transparency different from the first (homogeneous) transparency. For example, a substrate 200 (e.g., the optical lens) with multifunctional optical properties can be produced in this way.

[0078] It is understood that individual aspects of the apparatus 500 described herein may also characterize the method 100A and / or the method 100B without the respective method 100A, 100B necessarily being performed with the apparatus 500. For example, the method 100A may be carried out in an apparatus such that a plurality of substrates are ion etched simultaneously. Thus, a respective mask structure may be formed over each of the plurality of substrates over the curved surface of the respective substrate. Then, a respective grid electrode 520 may be arranged in the apparatus between the plasma source and the respective substrate. The respective grid electrode 520 can have a curvature on the (first) surface 524 facing the plasma source, which curvature essentially corresponds to the curvature of the curved surface of the respective associated substrate of the plurality of substrates.Subsequently, the multiple substrates can be ion-etched simultaneously, so that a respective structure is formed in the respective curved surface of each of the multiple substrates according to the respective mask pattern. This can also be referred to as batch processing (for mass production).

[0079] For example, the method 100A can be carried out in a device such that both the curved surface 203 described herein and the surface opposite this surface (curved or planar) can be ion etched simultaneously. For example, in an optical lens, a structure (e.g., anti-reflective) can be formed on both sides. This can, for example, be done simultaneously, as described herein. In some embodiments, two grid electrodes can be used in this case. In other embodiments, one grid electrode can be used which completely surrounds the optical lens. It is understood that the optical lens is an example of a substrate and that such a grid electrode which completely surrounds the substrate can be used or configured for any type of substrate.

[0080] Accordingly, multiple substrates can also be processed simultaneously using method 100B. According to various aspects, multiple substrates can be processed simultaneously from a respective side using method 100A and method 100B, so that on one side, a structure can be formed in the curved surface of this side using method 100A, and on the other side, a layer can be removed from the curved surface of this side using method 100B.

[0081] The methods 100A, 100B described herein generally enable the processing of voluminous and complex, non-conductive workpieces, such as refractive optics (e.g. lenses, prisms, etc.). In method 100A, a mask structure can be transferred with high homogeneity into a curved (substrate) surface of a substrate by means of ion etching. In this way, for example, an anti-reflective structure for broadband anti-reflection coating (e.g. a moth-eye structure) can be produced in the curved surface of an optical lens such that the anti-reflective structure has homogeneous properties along the curved surface. Partial sections of the curved surface of a substrate can also be processed in order to produce multifunctional (e.g. optical) properties. In method 100B, a layer with high homogeneity can be removed over the entire area of ​​a curved surface of a substrate.

[0082] The grid electrode 520 described herein can be integrated into conventional ion etching systems without additional adaptations.

[0083] The methods described herein can also be used accordingly for essentially planar substrates, for example, to create a surface structure in them. For example, ion etching of dielectric substrates with a thickness greater than a threshold thickness is no longer possible without the use of the grid electrode 520 described herein, since with increasing thickness, the electric field required during ion etching to accelerate the ions from the plasma is weakened by the dielectric of the substrate and thus sufficient acceleration of the ions for material removal is no longer available. Such planar dielectric substrates can, for example, be optical elements such as prisms, thick-walled windows, and / or flat elements, such as neodymium-doped glass plates as amplifier media in solid-state lasers.

[0084] Examples are described below that illustrate various aspects of the methods and the optical lens (obtainable, for example, by method 100A). It is understood that aspects described with respect to one method may also apply to the other method, and that aspects described with respect to one of the methods 100A, 100B may also characterize corresponding aspects of the optical lens processed thereby.

[0085] Example 1 is a method for (inert and / or reactive) ion etching of a curved surface of a substrate, the method comprising: forming a mask structure over the curved surface of the substrate; arranging a grid electrode between a plasma source for ion etching and the substrate having the mask structure, wherein the grid electrode has a curvature in the direction of the plasma source that substantially corresponds to a curvature of the curved surface of the substrate; and ion etching the curved surface of the substrate using the mask structure and applying a voltage to the grid electrode, so that a structure is formed in the curved surface of the substrate.

[0086] Example 2 is the method according to Example 1, wherein the mask structure is formed by micellar block copolymer nanolithography. Example 3 is the method according to Example 1 or 2, wherein the substrate is an optical lens having at least one curved surface.

[0087] Example 4 is the method according to any one of Examples 1 to 3, wherein the substrate consists of a dielectric material, preferably a glass, a crystalline material or a polymer; and / or wherein the substrate has one or more layers in which the structure is formed.

[0088] Example 5 is the method according to any one of Examples 1 to 4, wherein the grid electrode is formed from an electrically conductive material and / or has an electrically conductive coating. For example, the grid electrode may comprise a wire mesh or an electrically conductive grid structure.

[0089] Example 6 is the method according to any one of Examples 1 to 5, wherein the curvature of the curved surface of the substrate has a spherical or aspherical curvature or a freeform surface.

[0090] Example 7 is the method according to any one of Examples 1 to 6, wherein the substrate has a varying thickness.

[0091] Example 8 is the method according to any one of Examples 1 to 7, wherein the grid electrode has a mesh size of less than 1 mm.

[0092] Example 9 is the method according to any one of Examples 1 to 8, wherein the grid electrode has a transparency greater than or equal to 50%.

[0093] Example 10 is the method according to any one of Examples 1 to 9, wherein the grid electrode has a thickness of less than or equal to 100 pm. Example 11 is the method according to any one of Examples 1 to 10, wherein the structure formed in the curved surface is an anti-reflective structure (e.g., for broadband anti-reflection of the substrate), preferably a moth-eye nanostructure.

[0094] Example 12 is the method according to any one of Examples 1 to 11, wherein applying the voltage to the grid electrode comprises applying a pulsed (DC or AC) voltage or an AC voltage to the grid electrode.

[0095] In Example 13, the method according to any one of Examples 1 to 12 may optionally further comprise: processing (e.g., reactive ion etching) one or more (e.g., opposite the curved surface) other (e.g., curved or planar) surfaces of the substrate during the ion etching of the curved surface of the substrate.

[0096] Example 14 is the method according to any one of Examples 1 to 13, wherein the grid electrode has a non-mesh portion covering a corresponding portion of the curved surface of the substrate, so that no pattern is formed by the ion etching in the corresponding portion of the curved surface of the substrate.

[0097] Example 15 is the method according to any one of Examples 1 to 14, further comprising: disposing a mask between the grid electrode and the substrate, the mask covering a portion of the curved surface of the substrate such that no pattern is formed by the ion etching in the corresponding portion of the curved surface of the substrate.

[0098] Example 16 is a method for (inert or reactive) ion etching a plurality of substrates having a curved surface, the method comprising: forming a respective mask structure over the respective curved surface of each substrate of the plurality of substrates; for each substrate of the plurality of substrates, arranging a respective grid electrode between a plasma source for ion etching and the respective substrate having the respective mask structure, wherein the respective grid electrode has a curvature in the direction of the plasma source that substantially corresponds to a curvature of the curved surface of the respective substrate;and simultaneously ion etching the respective curved surface of each substrate of the plurality of substrates using the respective mask structure and applying a respective voltage to the respective grid electrode, so that a respective structure is formed in the respective curved surface of each substrate of the plurality of substrates;

[0099] Example 17 is an optical lens with a curved surface and a varying thickness, wherein the optical lens has an anti-reflective structure in the curved surface for (e.g., broadband) anti-reflective coating of the optical lens, wherein the anti-reflective structure covers at least 90% (e.g., at least 95%, e.g., at least 99%, etc.) of the optically usable area of ​​the lens (e.g., the curved surface). For example, both sides of the optical lens can have the anti-reflective structure.

[0100] Example 18 is the optical lens according to Example 17, wherein the anti-reflective structure is a moth-eye structure.

[0101] Example 19 is the optical lens according to Example 17 or 18, wherein the curvature of the curved surface of the substrate has a spherical or an aspherical curvature or a so-called freeform surface.

[0102] Example 20 is a method for (inert or reactive) ion etching of a curved surface of a substrate, the method comprising: arranging a grid electrode between a plasma source for (inert or reactive) ion etching and the substrate, wherein the grid electrode has a curvature in the direction of the plasma source that substantially corresponds to a curvature of the curved surface of the substrate; and (inert or reactive) ion etching of the curved surface of the substrate while applying a voltage to the grid electrode, such that a surface layer is removed from the curved surface of the substrate substantially over its entire area.

[0103] The method according to Example 20 may, where applicable, optionally be further configured according to one or more of Examples 1 to 16.

[0104] Example 21 is a method for (inert or reactive) ion etching of a layer arranged over a curved surface of a substrate, the method comprising: arranging a grid electrode between a plasma source for (inert or reactive) ion etching and the substrate with the layer arranged over the curved surface, wherein the grid electrode has a curvature in the direction of the plasma source that substantially corresponds to a curvature of the curved surface of the substrate; and (e.g., substantially full-surface) removal of the layer arranged over the curved surface of the substrate by means of (inert or reactive) ion etching while applying a voltage to the grid electrode.

[0105] The method according to Example 21 may, where applicable, optionally be further configured according to one or more of Examples 1 to 16.

[0106] Example 22 is the method according to any one of Examples 1 to 16, 21 or 22, wherein the surface of the substrate (200) already has a surface structuring before ion etching (where applicable, e.g. before forming the mask structure).

[0107] Throughout this description, the terms "connected," "attached," and "coupled" are used to describe both a direct and an indirect connection, a direct or indirect connection, and a direct or indirect coupling. In the figures, identical or similar elements are provided with identical reference numerals where appropriate.

[0108] A "control device" as used herein can be understood as any type of entity (e.g., implementing logic) that allows the processing of data or signals. The control device can, for example, comprise circuitry and / or (at least) one processor, which can execute software stored in a storage device (in some aspects also referred to as a storage medium), in firmware, or in a combination thereof, and can issue instructions based thereon. The control device can, for example, be configured by means of code segments (e.g., software) to control the operation of a system, e.g., a 3D printer. For example, the data or signals can be processed according to at least one (i.e., one or more than one) specific function performed by the processor.A processor may include or be formed from an analog circuit, a digital circuit, a mixed-signal circuit, a logic circuit, a microprocessor, a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), a programmable gate array (FPGA), an integrated circuit, or any combination thereof. Any other manner of implementing the respective functions described in detail herein may also be understood as a processor or logic circuit. It is understood that the control device may control one or more components to perform aspects of the method described herein.

Claims

Patent claims 1. A method (100A) for ion etching a curved surface of a substrate (200), the method (100A) comprising: • forming (102A) a mask structure over the curved surface of the substrate (200); • Arranging (104A) a grid electrode (520) between a plasma source (512) for ion etching and the substrate (200) having the mask structure, wherein the grid electrode (520) has a curvature in the direction of the plasma source (512) that substantially corresponds to a curvature of the curved surface of the substrate (200); and • ion etching (106A) the curved surface of the substrate (200) using the mask pattern and applying a voltage to the grid electrode (520) so that a pattern is formed in the curved surface of the substrate (200); • wherein the substrate (200) is an optical lens having at least one curved surface. Method (100A) according to claim 1, wherein the mask structure is formed by means of micellar block copolymer Nanolithography (400) is formed.

3. The method (100A) according to claim 1 or 2, wherein the substrate (200) consists of a dielectric material, preferably a glass, a crystalline material, or a polymer; and / or wherein the substrate (200) has one or more layers in which the structure is formed.

4. The method (100A) according to any one of claims 1 to 3, wherein the grid electrode (520) consists of an electrically conductive material and / or has an electrically conductive coating.

5. The method (100A) according to any one of claims 1 to 4, wherein the curvature of the curved surface of the substrate (200) has a spherical or an aspherical curvature or a so-called freeform surface.

6. The method (100A) according to any one of claims 1 to 5, wherein the surface of the substrate (200) already has another pattern before the mask structure is formed.

7. The method (100A) according to any one of claims 1 to 6, wherein the substrate (200) has a varying thickness.

8. The method (100A) according to any one of claims 1 to 7, wherein the grid electrode (520) has a mesh size of less than 1 mm.

9. The method (100A) according to any one of claims 1 to 8, wherein the structure formed in the curved surface is an anti-reflective structure, preferably a moth-eye structure (300).

10. The method (100A) according to any one of claims 1 to 9, further comprising: • Processing one or more other surfaces of the substrate (200) during the ion etching of the curved surface of the substrate (200).

11. A method (100B) for ion etching a layer disposed over a curved surface of a substrate, the method (100B) comprising: • Arranging (102B) a grid electrode (520) between a plasma source (512) for ion etching and the substrate with the layer arranged above the curved surface, wherein the grid electrode has a curvature in the direction of the plasma source which substantially corresponds to a curvature corresponds to the curved surface of the substrate; and • removing (104B) the layer arranged over the curved surface of the substrate (200) by means of ion etching while applying a voltage to the grid electrode (520); • wherein the substrate (200) is an optical lens having at least one curved surface.

12. The method (100B) according to claim 11, wherein the substrate (200) consists of a dielectric material, preferably a glass, a crystalline material or a polymer.

13. Method (100B) according to claim 11 or 12, wherein the Substrate (200) has a varying thickness.

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