Method for producing a diffractive optical element
Patent Information
- Application Number
- EP2024702933
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-01-31
- Filing Date
- 2024-01-30
- Publication Date
- 2025-12-10
AI Technical Summary
Existing methods for producing diffractive optical elements (DOEs) face challenges in achieving high manufacturing precision, leading to inefficient beam shaping and significant stray light due to limitations in the resolution and accuracy of surface profiling, particularly for shorter wavelengths like EUV light.
A method involving a laser mirror with a layer-like structure, where bulges are generated in an electrically conductive reflection layer using heating laser radiation, allowing for precise creation of complex shapes and high spatial resolution, enabling the production of continuous DOEs with improved diffraction efficiency and reduced stray light.
This approach enables the production of DOEs with high diffraction efficiency in the desired diffraction order and minimizes stray light, achieving resolutions suitable for EUV light and beyond, with approximately 99% of reflected light directed into the desired order and less than 1% into other orders.
Smart Images
Figure EP2024052200_08082024_PF_FP
Abstract
Description
[0001] Method for producing a diffractive optical element
[0002] The invention relates to a method for producing a continuous diffractive optical element for beam shaping a light beam having a first wavelength.
[0003] Diffractive optical elements, abbreviated DOEs, allow the beam shaping of a light beam, i.e. the targeted modification of the intensity distribution of the light beam profile perpendicular to the direction of propagation. For beam shaping, the DOE is inserted into the light beam, whereby different optical path lengths at the DOE lead to phase modulations of the light beam, creating interference patterns. The intensity of the light beam is spatially modulated through constructive and destructive superposition. In this way, the usually Gaussian intensity profile of the light beam can be specifically modified and converted, for example, into a doughnut-shaped intensity profile. In general, with DOEs, the light beam is not only deflected in one direction, but, unless absorbed, is distributed over a multitude of deflection angles, each representing a different order of diffraction.In most cases, this effect is undesirable, and the goal is to deflect as much of the light beam as possible into exactly one useful diffraction order, where the desired intensity profile is formed. The remaining light beam is largely distributed among other diffraction orders and is considered stray light or scattered light that must be minimized. The shape of the surface profile of the DOE, which must correspond as closely as possible to a desired, previously calculated profile, has a significant influence on the suppression of unwanted orders. To achieve high diffraction efficiency into the desired diffraction order and, accordingly, good suppression of stray light, a high degree of precision in the DOE manufacturing process is crucial.
[0004] DOEs known in the prior art are glass or plastic substrates onto which microstructures are applied using laser lithography and / or photolithography as well as various wet and dry chemical etching processes. For example, a blazed grating can be applied as a microstructure, i.e. an optical grating in which the individual grating lines have a triangular, sawtooth-shaped cross-section, thus maximizing the diffraction efficiency for a specific diffraction order. Due to the manufacturing process, the desired height profile is usually approximated by a stair-step profile with a specific number of steps. To achieve a high number of steps, which is necessary for the most precise generation of the desired DOE profile and thus a high diffraction efficiency in the desired useful diffraction order, a number of repeated etching processes are required. This entails considerable effort.
[0005] Furthermore, continuous DOEs are known from the prior art, which feature a structuring of the height profile of dielectric laser mirrors by creating bulges in these multi-layer structures. The dielectric arrangement responsible for the reflection of these mirrors comprises several layers of alternating low- and high-refractive-index material, each with an optical thickness of one-quarter of the wavelength to be reflected. The bulges in the dielectric layer structure required for producing a DOE in this process are generated using heating laser radiation, which can be absorbed in a metallic silicon layer located beneath the dielectric layers. The bulges created after irradiation with a focused heating laser beam have the shape of a Gaussian distribution in their cross-section, the width of which corresponds approximately to twice the thickness of the reflective dielectric multi-layer arrangement.The width of the bulge limits the minimum distance between two adjacent bulges. This parameter determines the achievable resolution of the structuring process in the horizontal direction. The smaller the dimensions of the structures that can be replicated, the more precisely the desired surface profile of the DOE can be produced for microscopic structures.
[0006] Based on this, the object of the invention is to provide a method and a device for producing a DOE that enables high manufacturing precision.
[0007] This problem is solved by the subject matter of patent claim 1. Preferred developments can be found in the subclaims.
[0008] According to the invention, a method is thus provided for producing a diffractive optical element for beam shaping a light beam with a first wavelength of at least 10 nm, comprising the following method steps: Providing a laser mirror, wherein the laser mirror has a layered structure comprising a substrate, a dielectric layer and an electrically conductive reflection layer, wherein the dielectric layer is in contact with the substrate, or wherein the laser mirror has a layered structure comprising a substrate, a dielectric layer, an electrically conductive reflection layer and an absorption layer, wherein the absorption layer is located between the substrate and the dielectric layer,
[0009] Creating a plurality of bulges of the electrically conductive reflection layer by treating the laser mirror by means of heating laser radiation with a second wavelength.
[0010] A key aspect of the invention is that a continuous DOE is produced by generating bulges in an electrically conductive reflective layer of a laser mirror by means of targeted heating. In contrast to the prior art methods, in which the bulges are generated in the dielectric layer, the present method provides for generating the bulges in an electrically conductive reflective layer. This has the advantage that the bulges can be arranged closer together and can be written with high spatial resolution. This is due to the fact that the electrically conductive reflective layer can have a very thin layer thickness, so that the temperature change caused by the heating laser radiation is better limited locally due to the resulting reduced thickness of the structure.Due to the smaller possible structure sizes, even complex shapes, such as microscopic sawtooth-shaped surface profiles, can be realized very precisely according to the desired shape. Accordingly, the diffractive optical element according to the invention can direct a high proportion of the light into the desired diffraction order, thus reducing unwanted stray light.
[0011] The provided laser mirror and the DOE produced by the method comprise the substrate, the optional absorption layer, the dielectric layer, and the electrically conductive reflection layer, all of which are preferably parallel to one another, wherein the dielectric layer rests against the substrate and, on the opposite side, against the electrically conductive reflection layer, or, if the absorption layer is present, the absorption layer is arranged between the substrate and the dielectric layer. In particular, it is provided that a bottom side of the dielectric layer or a bottom side of the absorption layer borders an upper side of the substrate. It is further preferably provided that, if the absorption layer is present, a top side of the absorption layer borders an underside of the dielectric layer. In other words, the top side of the electrically conductive reflection layer corresponds to the top side of the DOE or the top side of the laser mirror.
[0012] When we speak of an “electrically conductive reflection layer” in this case, we mean a mirror layer made of a metal or semi-metal and suitable for reflecting light, in particular laser light, of the first wavelength.
[0013] In particular, the DOE is a reflective DOE. This means that the beam shaping of the first wavelength light beam occurs by reflection of the light beam from the diffractive optical element. In contrast to DOEs, where beam shaping occurs by transmission of the laser beam through the DOE (transmittive DOEs), this is a DOE in which the light beam is reflected.
[0014] During the process, bulges are created in the electrically conductive reflective layer, which lead to a microstructuring of the surface of the electrically conductive reflective layer. This means in particular that the surface of the electrically conductive reflective layer is not flat after the process, but has local regions that have a different height than before the process. Preferably, the majority of the bulges have a height of half the first wavelength perpendicular to the electrically conductive reflective layer. The height of the bulges refers to an extension of the bulge perpendicular to the electrically conductive reflective layer relative to an area around the local region. Preferably, the bulges are rotationally symmetrical, with the axis of rotation of the bulges lying perpendicular to the absorption layer. As a result, the bulges are circular when projected onto a plane parallel to the absorption layer.Further preferably, each of the bulges has a sawtooth-shaped height profile. The height of the bulges influences the use of the DOE for beam shaping the light beam with the first wavelength, since efficient beam shaping with the DOE is only possible when the bulges typically have a height of at least half the first wavelength. The method allows DOEs to be produced that are suitable for beam shaping a light beam with a first wavelength of at least 10 nm, in particular EUV light. In other words, this means that the bulges typically have a height greater than 5 nm.
[0015] The method has the advantage that, through treatment with the heating laser beam, the bulges of the thin, electrically conductive, reflective surface can be created with good spatial resolution, as well as with a precise control of the height and location of the bulge. Bulges of varying heights can be created, with a height resolution of at least 0.5 nm, preferably at least 0.1 nm, which, when converted to the manufacturing accuracy of quasi-continuous DOEs, corresponds to a number of steps of more than 2500. In particular, the method can simultaneously achieve a high spatial resolution in the transverse direction of the structured reflective surface profile, which lies at 1 pm. The resolution determines the minimum achievable distance between the highest points of two adjacent bulges. At the same time, the resolution also determines the accuracy with which a given surface profile of the DOE can be achieved.The process thus enables the production of continuous DOEs with small feature sizes and high diffraction efficiency. Accordingly, the electrically conductive reflection layer allows the realization of continuous DOEs by creating bulges, particularly for EUV light with (initial) wavelengths down to 10 nm. In the prior art, 100 nm represents a lower optical wavelength due to the absorption of shorter-wavelength light in dielectric reflection layers. The expansion of the possible wavelength range represents a key aspect of the invention.
[0016] According to a preferred development of the invention, the heating laser radiation comprises a series of focused heating laser beams or a heating laser beam diffracted by a spatial light modulator. A series of focused heating laser beams is understood to mean a single focused heating laser beam that scans the electrically conductive reflection layer or the absorption layer. In this case, either the heating laser beam can be deflected in at least one spatial direction and / or the laser mirror can be moved. To increase the production speed of this writing process, heating laser radiation diffracted by a spatial light modulator can be used instead of a single focused heating laser beam. In this way, parallelization is achieved, so that multiple bulges can be created simultaneously—or in quick succession.Depending on the light modulator, such as a galvo scanner, the diffraction of the heating laser radiation can occur in at least one spatial direction. The light modulator enables rapid redirection or switching of the heating laser beam.
[0017] With regard to the precise shape of the surface profile of the DOE generated by the method, it is preferably provided that, for the purpose of determining this, a topographic image of the reflective metal layer is created using a Mirau interferometer. This creates a topographic map of the height profile of the reflective layer of the DOE. According to a preferred development, this image is electronically compared with the desired, previously calculated height profile, after which a further irradiation with a sequence of heating laser beams can be carried out in order to correct any remaining deviations and better adapt the height profile to the desired one. Particularly preferably, this iterative process is repeated several times in an automated manner in order to achieve further increased manufacturing accuracy.
[0018] In connection with the height of the bulges, the method preferably provides that the height of the bulges can be influenced by a heat input of the heating laser beam per volume into the absorption layer and / or into the dielectric layer and / or into the electrically conductive reflection layer. It is preferably provided that when treating the laser mirror with a series of focused heating laser beams, the second wavelength, a power of the heating laser beam, a focusing of the heating laser beam, a heating duration, the absorption layer of the laser mirror, the dielectric layer of the laser mirror and / or a layer thickness of the electrically conductive reflection layer are selected such that the height of the bulges reaches, in particular, half the first wavelength. The heat input of the heating laser beam can be controlled by various parameters.Preferably, the wavelength of the heating laser beam, i.e., the second wavelength, and an absorption spectrum of the absorption layer and / or the dielectric layer and / or the electrically conductive reflection layer are matched to one another. This ensures that a portion of the heating laser beam is absorbed by the absorption layer and / or the dielectric layer and / or the electrically conductive reflection layer.
[0019] In particular, it is provided that the provided laser mirror is suitable for reflecting a light beam of the first wavelength. Preferably, the laser mirror, which is provided in the first step of the method and essentially represents the blank of the DOE, is a highly reflective laser mirror for reflecting the light beam with the first wavelength. Highly reflective in this context means that the laser mirror has a reflectance for the first wavelength of more than 90% if this lies in the visible or infrared spectral range, and of more than 50% if this lies in the ultraviolet spectral range. It is further preferably provided that the laser mirror is suitable for reflecting light with a first wavelength greater than 10 nm.Due to the precise heights and transverse resolution achievable with this method, approximately 99% of the reflected light can be directed into the desired desired diffraction order. In particular, the proportion of light deflected into other, interfering diffraction orders can be reduced to less than 1%.
[0020] According to a preferred embodiment of the invention, the electrically conductive reflective layer consists at least partially of aluminum and / or silver and / or silicon and / or gold. Silver has the advantage that this material exhibits a high degree of reflection over a broad wavelength range. This means that the electrically conductive reflective layer is designed such that the light beam with the first wavelength is reflected by the electrically conductive reflective layer. When metals are used, the electrically conductive reflective layer enables reflection over a broad wavelength range. With silver and aluminum as the material for the electrically conductive reflective layer, the possible reflection range extends across the entire visible optical wavelength range (400-800 nm) and beyond into the ultraviolet (up to 120 nm for aluminum).For light in the even shorter EUV wavelength range (down to 10 nm), the reflective layer can be realized with conductive metal-semimetal layer structures. A preferred embodiment, particularly for light at 13.5 nm wavelength, as used in EUV lithography, involves the use of a molybdenum-silicon multilayer as the reflective layer. However, by using conductive materials, the reflective layer in the inventive structure can also be realized for long-wavelength light; for example, using gold as the material, high reflection for this layer is achieved in a wavelength range above 700 nm, extending far into the infrared (up to 20 nm wavelength).
[0021] It is further preferred that the absorption layer consists of silicon or gold and / or the substrate consists of silicon, glass, CaF2, MgF2 or sapphire and / or the dielectric layer consists of SiCl, Ta2Os, TiCl, HfCh, Al2O3, MgF2, LaFs, and / or ZrCl. The silicon in the absorption layer is particularly preferably amorphous silicon. It is further preferred that the substrate consists of quartz glass in order to enable the beam shaping of a laser beam even at high power. It is further preferred that the dielectric layer comprises a layer of a material that exhibits a permanently high expansion after heating caused by the heating laser beam. Preferably, ion beam sputtering using argon ions is used to vapor-deposit Ta2Os, which emits argon gas upon heating, leading to a permanent bulging of the overlying electrically conductive reflection layer in the structure according to the invention.Since the reflection of the DOE is achieved by this electrically conductive layer, the arrangement according to the invention does not require a sequence of multiple dielectric layers with different refractive indices. This allows the realization of a very thin structure, which is extremely advantageous for the described high possible resolution of this continuous DOE due to the thin, associated close positioning of the heat source and the reflective layer. At the same time, with the arrangement according to the invention, the dielectric layer can be realized with a material that exhibits a very high relative expansion after heat input, which, for a given desired maximum height of the bulges, in particular half the first wavelength, allows the small overall thickness of the layer structure desired for high spatial resolution.According to a preferred development, the thickness of the first dielectric layer is less than 700 nm, particularly preferably less than 400 nm. The thickness of the electrically conductive reflection layer is preferably less than 300 nm, particularly preferably less than 180 nm, and particularly preferably less than 120 nm. The layer thickness of the electrically conductive reflection layer refers to the extent of the electrically conductive reflection layer perpendicular to its extension. When using thin dielectric layers, a small overall thickness can thus be ensured, so that the temperature change caused by the heating laser beam is better limited locally.
[0022] The heat input of the heating laser beam can be controlled by various parameters. Preferably, the wavelength of the heating laser beam, i.e., the second wavelength, and an absorption spectrum of the absorption layer and / or the electrically conductive reflection layer are matched. This ensures that a portion of the heating laser beam is absorbed by the absorption layer and / or the electrically conductive reflection layer.
[0023] In this context, it is preferably provided that when treating the laser mirror with heating laser radiation, the second wavelength is between 200 and 700 nm and the absorption layer of the laser mirror is made of silicon, or that the second wavelength is between 200 and 2000 nm and the absorption layer of the laser mirror is made of gold, and / or the second wavelength is between 100 and 2000 nm. Using these combinations of wavelength of the heating laser beam and absorption layer, the bulges with a height of more than 50 nm can be produced very reliably. If the absorption layer is omitted, a UV laser with a second wavelength in the range of 200 to 400 nm is preferably used to treat the laser mirror with heating laser radiation.
[0024] According to a preferred development of the invention, the distance between two adjacent bulges is less than 2 pm, preferably less than 1 pm. The additional electrically conductive reflection layer can have a small layer thickness due to the layer structure according to the invention. This small layer thickness enables focusing of the temperature change when generating the bulges by means of heating laser radiation. This means that the bulges can be arranged close to one another. While distances of approximately 8-10 pm are common in the prior art, the distances of the present invention can be limited to less than 1 pm. It is preferably provided that when treating the laser mirror with heating laser radiation on an area of at least 0.25 cm 2The plurality of bulges arranged in a grid-like manner relative to one another are created. The grid-like arrangement of the bulges preferably relates to the plane parallel to the substrate, whereby the grid-like arrangement of the bulges can be oblique, rectangular, centered-rectangular, hexagonal, or square. Deviations from the translational symmetry of the grid-like arrangement are also possible.
[0025] According to a preferred development of the invention, the bulges have a sawtooth-shaped profile. Sawtooth refers to the shape of the teeth of a saw. The resolution of the heating determines the sawtooth shape. A non-ideal resolution leads to rounding of the sawtooth-shaped profile, whereby the radius of the rounding is determined by the resolution. The height resolution of at least 0.1 nm achievable with the method and the transverse resolution of 1 pm allow for very high diffraction efficiency in the useful diffraction order, even with different shapes of the DOE's height profile, such as sawtooth-shaped profiles. Of particular relevance is that this simultaneously minimizes diffraction into other diffraction orders, i.e., the stray light of the DOE.
[0026] According to a preferred embodiment of the invention, the laser mirror has a second dielectric layer. In this case, the electrically conductive reflection layer is arranged between the first dielectric layer and the second dielectric layer. In other words, the second dielectric layer is the uppermost layer and serves, in particular, to protect the metal layer from oxidation by the surrounding atmospheric oxygen.
[0027] As already mentioned, the heat input of the heating laser beam per volume into the absorption layer and / or electrically conductive reflection layer can be influenced by the power of the heating laser beam. In this regard, it is preferably provided that when treating the laser mirror with heating laser radiation, the power of the heating laser beam is at least 10 mW. Particularly preferably, the power is between 10 mW and 1000 mW. According to a preferred development of the invention, when generating a plurality of bulges in the electrically conductive reflection layer using heating laser radiation, the temperature increase of the electrically conductive reflection layer is limited by cooling with a coolant, in particular with water.
[0028] In principle, it is possible that when treating the laser mirror with a series of focused heating laser beams, the heating laser beam is deflected in two dimensions during the treatment and the laser mirror is not displaced during this time. In this way, the grid-like arrangement of bulges is reliably achieved. According to a preferred development of the method, however, it is provided that when treating the laser mirror with a series of focused heating laser beams, the laser mirror is displaced during the treatment along a displacement direction perpendicular to the heating laser beam and the heating laser beam is deflected perpendicular to the displacement direction during the treatment, or that when treating the laser mirror with a diffracted heating laser beam, the heating laser beam is diffracted in at least one spatial direction by a spatial light modulator and directed onto the laser mirror.The heating laser beam can be diffracted in one dimension and deflected in a second dimension, or diffracted in two dimensions, allowing a two-dimensional surface to be processed with a single diffracted heating laser beam. This enables a particularly time-saving and precise production of a DOE with an electrically conductive reflective layer covering an area of at least 0.25 cm. 2 has a plurality of bulges arranged in a grid-like manner. In particular, deviations from a grid-like translational symmetry are also possible. Furthermore, the laser mirror can also be moved along both dimensions of the mirror plane using the displacement device.
[0029] According to the invention, a device for carrying out the method is further provided, wherein the device comprises a heating laser for generating a heating laser beam with the second wavelength, a focusing device for focusing the heating laser beam onto the laser mirror, a laser mirror positioning device, and a controller, wherein the controller is designed to control the heating laser and the laser mirror positioning device. According to a preferred development of the invention, the device comprises a spatial light modulator for diffracting the heating laser beam or a deflection device for deflecting the heating laser beam, and the controller is designed to control the heating laser, the light modulator or the deflection device, and the laser mirror positioning device.The control of the heating laser, the light modulator or the deflection device, and the laser mirror positioning device is carried out in particular dependent on one another, so that the heating laser beam and the impact of the heating laser beam on the laser mirror can be optimally controlled.
[0030] According to a preferred embodiment of the invention, the laser mirror positioning device comprises a chamber designed to accommodate a coolant such that contact is established between the coolant and the laser mirror. Cooling can be achieved, in particular, by enclosing the reflective mirror surface (on the opposite side of the substrate) with a rubber ring for sealing during this process, and by filling the space at the rear with water after sealing. Limiting the temperature increase of the reflective metal mirror layer allows temperature-induced changes in the structure of this film to be avoided, thus achieving a spatially uniformly high level of reflection.
[0031] The invention is explained in more detail below using a preferred embodiment with reference to the drawings.
[0032] The drawings show
[0033] Fig. la is a schematic sectional view of the diffractive optical element without bulges,
[0034] Fig. 1b is a schematic sectional view of the diffractive optical element according to a preferred embodiment of the invention, Fig. 1c is a schematic sectional view of the diffractive optical element according to a second preferred embodiment of the invention,
[0035] Fig. 2 is a schematic representation of a device for carrying out the
[0036] Method according to a preferred embodiment of the invention.
[0037] Figures 1a, 1b and 1c show a schematic sectional view of the DOE 1. The method provides two steps, wherein in a first step, shown in Fig. 1a, a laser mirror 2 is provided as a blank for the DOE 1. The laser mirror 2 is suitable for reflecting a light beam with a first wavelength. In this exemplary embodiment, the laser mirror 2 has a layered structure comprising a substrate 3, an absorption layer 6, a first dielectric layer 4, an electrically conductive reflection layer 5 and a second dielectric layer 9. All four layers 6, 4, 5, 9 are parallel to one another in the present case, wherein the absorption layer 6 is arranged between the substrate 3 and the first dielectric layer 4. The electrically conductive reflection layer 5 is arranged between the first dielectric layer 4 and the second dielectric layer 9.
[0038] In a second step, shown in Figs. 1b and 1c, bulges 7 are created in the electrically conductive reflection layer 5. In the preferred embodiment shown in Fig. 1b, these are rotationally symmetric bulges that are created at an interface between the electrically conductive reflection layer 5 and the first dielectric layer 4. A rotation axis 10 of the rotationally symmetric bulges 7 lies perpendicular to the first dielectric layer 4. When sectioning through the bulge 7 along a plane perpendicular to the absorption layer 6, the bulge 7 is Gaussian with respect to this plane.
[0039] In Fig. 1c, the bulges 7 have a sawtooth-shaped profile. The ideal edge of a perfect sawtooth 7' is shown in a dashed line. The degree of rounding of the ideal shape 7' is determined by the heating resolution. A non-ideal resolution leads to rounding of the sawtooth-shaped profile, with the radius of the rounding being determined by the resolution. By locally limiting the heat development in the electrically conductive reflection layer 5, the resolution can be increased and the sawtooth shape can be achieved and improved. The height resolution of at least 0.1 nm and the transverse resolution of 1 pm achievable with the method allow for a very high diffraction efficiency in the useful diffraction order with the sawtooth-shaped profile.
[0040] The bulges 7 of the electrically conductive reflection layer 5 are produced by treating the laser mirror 2 with a series of focused heating laser beams and / or with a diffracted heating laser beam 13, each with a second wavelength.
[0041] Fig. 2 shows a device 11 for carrying out the method with a diffracted heating laser beam 13. The heating laser beam 13 is emitted by a heating laser 12 and modulated in an acousto-optical modulator 14. The modulation comprises a power modulation of the heating laser pulses. The heating laser beam 13 is then modulated and diffracted in a light modulator 15. The diffraction can also occur in multiple directions. The diffracted heating laser beam 13 is aligned by means of a lens 16 so that a directional deflection of the light modulator 15 is converted into a spatial deflection. By means of a focusing device 17, for example a microscope objective, the heating laser beam 13 is directed onto the laser mirror 2 or onto the substrate layer. The laser mirror 2 is mounted in a laser mirror positioning device 18. The laser mirror positioning device 18 comprises a chamber in which coolant 20 is supplied via the inlet and outlet.Outlet 21 can be introduced. The chamber is directly adjacent to the laser mirror 2 and is sealed with sealing rings 19. In this way, the laser mirror 2 can be cooled from the side facing away from the substrate. List of reference numerals diffractive optical element, DOE laser mirror substrate first dielectric layer electrically conductive reflection layer absorption layer bulge ' ideal shape of the bulge height of the bulge second dielectric layer 0 rotation axis 1 device 2 heating laser 3 laser beam 4 acousto-optical modulator 5 light modulator 6 lens 7 focusing device 8 laser mirror positioning device 9 sealing ring 0 coolant 1 inlet or outlet.
Claims
Patent claims 1. A method for producing a diffractive optical element (1) for beam shaping a light beam having a first wavelength of at least 10 nm, comprising the following method steps: Providing a laser mirror (2), wherein the laser mirror (2) has a layer-like structure comprising a substrate (3), a dielectric layer (4) and an electrically conductive reflection layer (5), wherein the dielectric layer (4) is in contact with the substrate (3), or wherein the laser mirror (2) has a layer-like structure comprising a substrate (3), a dielectric layer (4), an electrically conductive reflection layer (5) and an absorption layer (6), wherein the absorption layer (6) is located between the substrate (3) and the dielectric layer (4), Creating a plurality of bulges (7) of the electrically conductive reflection layer (5) by treating the laser mirror (2) by means of heating laser radiation with a second wavelength.
2. The method of claim 1, wherein the heating laser radiation comprises a series of focused heating laser beams or a heating laser beam diffracted by a spatial light modulator.
3. Method according to one of the preceding claims, wherein the electrically conductive reflection layer (5) consists at least partially of aluminum and / or silver and / or silicon and / or gold.
4. Method according to one of the preceding claims, wherein the distance between two adjacent bulges (7) is less than 2 pm, preferably less than 1 pm.
5. Method according to one of the preceding claims, wherein the bulges (7) have a sawtooth-shaped profile.
6. Method according to one of the preceding claims, wherein the electrically conductive reflection layer (5) has a layer thickness (d) of less than 300 nm, preferably less than 180 nm, particularly preferably less than 120 nm.
7. Method according to one of the preceding claims, wherein the dielectric layer (4) has a layer thickness of less than 700 nm, preferably less than 400 nm.
8. Method according to one of the preceding claims, wherein the laser mirror (2) has a second dielectric layer (9) and the electrically conductive reflection layer (5) is arranged between the first dielectric layer (4) and the second dielectric layer (9).
9. Method according to one of the preceding claims, wherein when treating the laser mirror (2) with the heating laser radiation (13), a power of the heating laser beam is at least 10 mW.
10. Method according to one of the preceding claims, wherein, when producing a plurality of bulges (7) of the electrically conductive reflection layer (5) by means of heating laser radiation (13), the electrically conductive reflection layer (5) is limited in its temperature increase by cooling with a coolant (20).
11. Method according to one of the preceding claims, wherein, when treating the laser mirror (2) with a series of focused heating laser beams, the laser mirror (2) is displaced during the treatment along a displacement direction perpendicular to the heating laser beam (13) and the heating laser beam (13) is deflected during the treatment perpendicular to the displacement direction, or the laser mirror (2) is displaced during the treatment along two mutually orthogonal displacement directions, both perpendicular to the heating laser beam (13), or wherein, when treating the laser mirror (2) with a diffracted heating laser beam (13), the heating laser beam is diffracted in at least one spatial direction by a spatial light modulator and directed onto the laser mirror (2).
12. Device (11) for carrying out the method according to one of the preceding claims, wherein the device comprises a heating laser (12) for generating a heating laser beam (13) with the second wavelength, a focusing device (17) for focusing the heating laser beam (13) onto the laser mirror (2), a laser mirror positioning device (18) and a controller, wherein the controller is designed to control the heating laser (12) and the laser mirror positioning device (18).
13. The device according to claim 12, wherein the device comprises a spatial light modulator (15) for diffracting the heating laser beam (13) or a deflection device for deflecting the heating laser beam (13), and the controller is configured to control the heating laser (12), the light modulator (15) or the deflection device, and the laser mirror positioning device (18).
14. Device according to claim 12 or 13, wherein the laser mirror positioning device (18) has a chamber and the chamber is designed to receive a coolant (20) in such a way that contact is created between the coolant (20) and the laser mirror (2).