Method for separating a workpiece

Abstract

The invention relates to a method for separating a workpiece (104) which has a transparent material (102). Multiple focal elements (120) are provided by means of an inlet laser beam (108), and the focal elements (120) are applied to the material (102). By applying the focal elements (120) to the material (102), material modifications (138) are produced in the material (102) along a specified machining line (128), and the material (102) is separated along the machining line (128) using an etching method with a wet-chemical solution, wherein the temperature of the wet-chemical solution during the etching method equals at least 100 °C and / or maximally 150 °C.

Description

[0001] Process for separating a workpiece

[0002] The invention relates to a method for separating a workpiece comprising a transparent material.

[0003] From DE 10 2019 218 995 A1 a method for laser beam modification of a material which is at least largely transparent to the laser beam is known, wherein a focus zone of a single pulse of the laser beam which is elongated in the beam propagation direction is brought into interaction with the material and wherein by interaction of the single pulse with the material a channel penetrating the material from a first end face to a second end face with a channel width of at most 1 pm is produced.

[0004] EP 3 597 353 A1 discloses a method for separating a transparent material by means of an elongated focus zone of a laser beam.

[0005] WO 2016 / 089799 A1 discloses a method for separating a transparent material using several parallel non-diffracting laser beams.

[0006] From JP 2020 004 889 A a method for separating and in particular beveling a transparent material is known, wherein a plurality of focus points for laser processing of the material are generated by means of a spatial light modulator.

[0007] US 2020 / 0147729 A1 and US 2020 / 0361037 A1 each disclose methods for forming a bevelled edge region on a transparent material by means of a laser beam.

[0008] DE 10 2018 110 211 A1 discloses a method for creating a cavity in a substrate made of brittle material, preferably glass or glass-ceramic, wherein a laser beam is used to create filamentary damage in the volume of the substrate, and wherein the substrate is exposed to an etching medium that removes material from the substrate at a removal rate of between 2 pm and 20 pm per hour. WO 2017 / 062798 A1 discloses a method for forming vias in a glass-based substrate, wherein a plurality of etching paths are created and etching is carried out along the etching paths using a hydroxide-based etching material, wherein an etching rate along the etching paths is at least 12 times greater than an etching rate outside the etching paths.

[0009] From WO 2018 / 162385 A1 a method for introducing at least one recess into a transparent or transmissive material is known, wherein the material is selectively modified along a beam axis by means of electromagnetic radiation and the recesses are subsequently produced by one or more etching steps, wherein different etching rates occur in a modified and in the unmodified regions.

[0010] The invention is based on the object of providing a method as mentioned above which enables the workpiece to be separated at the highest possible speed and / or in the shortest possible time.

[0011] This object is achieved according to the invention in the method mentioned at the outset in that a plurality of focus elements are provided by means of an input laser beam, the material is exposed to the focus elements, material modifications are formed in the material along a predetermined processing line by exposing the material to the focus elements, and the material is separated along the processing line by means of an etching process with a wet-chemical solution, wherein a temperature of the wet-chemical solution during the etching process is at least 100°C and / or at most 150°C.

[0012] Because the temperature of the wet-chemical solution during the etching process is within the specified range, the material can be etched at a particularly high etching rate at the material modifications arranged along the processing line, with the etching rate outside the material modifications being lower than the etching rate at the material modifications along the processing line. This allows for selective etching at a particularly high etching rate at the material modifications along the processing line. This results in the shortest possible etching time to separate the material along the processing line. This allows the process to be carried out at an increased speed.

[0013] In particular, the etching process for separating the material takes place after the material has been exposed to the focus elements and / or after the material modifications have been formed along the processing line.

[0014] By applying the focus elements to the workpiece material, material modifications are formed, which are arranged in the material at positions and / or distances corresponding to the focus elements. In particular, a distance between adjacent focus elements corresponds to a distance between adjacent material modifications formed in the workpiece material by these focus elements. However, it is also fundamentally possible for multiple material modifications and / or elongated material modifications to be formed using one focus element, for example, if the focus element has a Bessel-like shape.

[0015] In particular, the focus elements arranged along the processing line are spaced apart and / or have an intensity such that the material modifications formed by the focus elements along the processing line enable separation of the material by etching using the wet-chemical solution.

[0016] In particular, the provided focus elements are each arranged at different spatial positions in the material. The spatial position of a specific focus element is understood to mean, in particular, a center position of the corresponding focus element.

[0017] The provision of multiple focus elements by means of the at least one input laser beam can be understood in particular to mean that the focus elements are provided simultaneously. However, this can also be understood to mean that one or more focus elements are provided at different times, i.e., that, for example, at a specific time, at least one focus element is available for laser processing of the workpiece at a specific position, and at a different time, at least one further focus element is available for laser processing of the workpiece at a different position.

[0018] It may be advantageous if the wet chemical solution is an aqueous KOH solution with a concentration of at least 15 wt.% and / or at most 50 wt.%. This enables selective etching of the material at the material modifications positioned along the processing line.

[0019] For the same reason, it may be advantageous if the wet chemical solution is an aqueous NaOH solution with a concentration of at least 15 wt% and / or at most 50 wt%.

[0020] In particular, it can be provided that the temperature of the wet-chemical solution is kept constant over time during the etching process. This allows for selective etching with an at least approximately constant etching rate. This also allows the etching process to be carried out as controlled as possible.

[0021] The temperature is chosen in particular to maximize the etching rate of the material at the material modifications and to minimize or minimize the evaporation of the wet chemical solution. The boiling point of the wet chemical solution, for example, in the case of a KOH or NaOH solution, depends on the corresponding KOH or NaOH concentration.

[0022] The fact that the temperature of the wet-chemical solution is kept constant over time means, in particular, that the actual temperature of the wet-chemical solution during the etching process deviates from the specified (time-constant) temperature or target temperature by less than the difference values ​​mentioned in the following paragraph.

[0023] In particular, the temperature is controlled to a temporally constant target temperature of at least 100°C and / or at most 150°C, wherein an actual temperature of the wet chemical solution during the etching process deviates from the target temperature by less than 7 K and in particular less than 5 K and in particular less than 3 K and in particular less than 1 K.

[0024] In particular, it can be provided that the wet-chemical solution is an aqueous KOH solution or an aqueous NaOH solution, wherein a concentration of the solution is selected such that a boiling temperature of the solution is at least 5% and in particular at least 10% and in particular at least 15% higher than a temporally constant target temperature of the wet-chemical solution during the etching process.

[0025] For example, the etching process has a duration of at least 5 minutes and / or at most 180 minutes and preferably of at least 10 minutes and / or at most 90 minutes.

[0026] In particular, it can be provided that the material is exposed to the wet-chemical solution to carry out the etching process. In particular, the material is partially or completely exposed to the wet-chemical solution. In particular, the material is partially or completely immersed in the wet-chemical solution. In particular, the material is then partially or completely surrounded by the wet-chemical solution.

[0027] The etching process can be carried out with ultrasound assistance. For example, the etching process takes place in an ultrasonic-assisted etching bath. This facilitates material separation, in particular. Furthermore, the speed of the etching process can be further increased.

[0028] It may be provided that the material is additionally subjected to mechanical stress and / or force for separation, and / or that the material is additionally subjected to heat for separation. This, in particular, allows for optimized separation of the material.

[0029] It may be advantageous if the distance between adjacent focus elements is at least 3 pm and / or at most 70 pm, and preferably at least 5 pm and / or at most 10 pm. This allows the etching process on the material modifications formed by the focus elements to be carried out selectively at a particularly high etching rate.

[0030] For the same reason, it may be advantageous if the distance between adjacent material modifications is at least 3 μm and / or at most 70 μm, and preferably at least 5 μm and / or at most 10 μm. The distance between adjacent material modifications in the specified value ranges refers to a distance direction oriented parallel to a feed direction in which the focus elements are moved relative to the material during laser processing of the material, and / or to a distance direction lying in a plane oriented perpendicular to the feed direction. In particular, the distance refers to a distance direction lying in a processing surface on which material modifications are arranged.

[0031] It may be advantageous if the input laser beam and / or a laser beam from which the focus elements are formed is a pulsed laser beam, in particular an ultrashort pulse laser beam. By applying the focus elements to the material, laser pulses, in particular ultrashort laser pulses, are introduced into the material. This allows, for example, type III material modifications to be formed in the material, which enable the material to be separated.

[0032] For the same reason, it may be advantageous if a particular focus element is assigned a pulse energy of at least 0.5 pJ and / or at most 10 pJ, and preferably of at least 1 pJ and / or at most 5 pJ.

[0033] For example, a wavelength of the input laser beam and / or the laser beam from which the focus elements are formed is at least 300 nm and / or at most 1500 nm. For example, the wavelength is 515 nm or 1030 nm.

[0034] In particular, the input laser beam and / or the laser beam from which the focus elements are formed has an average power of at least 1 kW to 1 kW. For example, the laser beam comprises pulses with a pulse energy of at least 10 pJ and / or at most 50 mJ. It can be provided that the laser beam comprises individual pulses or bursts, wherein the bursts have 2 to 20 subpulses and, in particular, a time interval of approximately 20 ns.

[0035] In particular, the input laser beam and / or a laser beam from which the focus elements are formed has a diffractive beam profile and / or a Gaussian beam profile.

[0036] In particular, the focus elements have a diffractive beam profile and / or are designed to be diffraction-limited. For example, one or more focus elements have a Gaussian shape and / or a Gaussian intensity profile.

[0037] It is also possible, in principle, for one or more focus elements to have a Bessel-like shape and / or a quasi-non-diffracting intensity profile and / or a Bessel-like intensity profile. For example, a Bessel-like beam profile is then assigned to the input laser beam.

[0038] The focus elements provided for forming the material modifications along the processing line may, but do not necessarily have to, have the same shape and / or intensity profile.

[0039] It can be advantageous if the input laser beam is split into a plurality of partial beams using a beam splitting element, and the focus elements are formed by focusing the partial beams coupled out of the beam splitting element. This allows the focus elements to be formed as copies of each other. In particular, this allows the focus elements to be introduced into the workpiece material in a technically simple manner at different positions and / or at different distances.

[0040] For the same reason, it may be advantageous if the input laser beam is split by means of the beam splitting element by phase imprinting on a beam cross-section of the input laser beam or if it comprises phase imprinting on a beam cross-section of the input laser beam.

[0041] For example, the beam splitting element is designed as a 3D beam splitting element or comprises a 3D beam splitting element.

[0042] For example, the beam splitting element comprises multiple components and / or functionalities. It can be provided that the beam splitting element comprises both a 3D beam splitting element and a polarization beam splitting element.

[0043] It can be provided that the division of the input laser beam is carried out exclusively by phase imposition on the beam cross-section of the input laser beam.

[0044] In particular, the phase imprint occurs in the transverse direction of the input laser beam. The transverse direction lies in a plane oriented perpendicular to the beam propagation direction of the input laser beam.

[0045] Alternatively or additionally, it can be provided that the input laser beam is split by means of the beam splitting element through polarization beam splitting or includes polarization beam splitting. For example, adjacent focus elements can then be formed with different polarization states. This can, in particular, prevent interference between adjacent focus elements. This allows adjacent focus elements to be arranged, for example, at a particularly close distance from one another.

[0046] It is fundamentally possible for the input laser beam to be split using both phase imprinting and polarization beam splitting.

[0047] It can be advantageous if the processing line is spatially continuous across the thickness of the workpiece material and / or across the thickness of a workpiece segment to be separated from the workpiece. This makes it possible, for example, to divide the workpiece into two parts or to separate a workpiece segment from the workpiece.

[0048] In particular, the machining line extends from an outside of the workpiece to an inside area of ​​the material.

[0049] The outer side of the workpiece refers specifically to the outer side of the workpiece material. The focus elements are inserted into this material.

[0050] For example, the processing line extends in particular spatially continuously from a first outer side of the workpiece, through which the focus elements and / or a laser beam are coupled into the material to form the focus elements, to a second outer side of the workpiece spaced apart in the thickness direction of the workpiece.

[0051] In particular, the processing line is assigned material modifications and / or cracks that extend from an inner area of ​​the material to an outer area of ​​the workpiece. This allows wet chemical solutions to be coupled into these material modifications or cracks on the outer side of the processing line.

[0052] In particular, a shape of the processing line corresponds to a shape and / or cross-sectional shape, and in particular to a desired shape and / or desired cross-sectional shape of a separation surface to be formed or already formed by separating the material. Thus, the processing line can be used to define an edge geometry and / or a cross-sectional geometry, and in particular, a desired edge geometry and / or desired cross-sectional geometry of a separation surface created by separating the material.

[0053] For example, the at least one processing line has a total length between 50 pm and 5000 pm, and preferably between 100 pm and 1000 pm. This allows workpieces with a thickness within the specified range to be processed and, in particular, separated. The material of the workpiece has, for example, a thickness between 50 pm and 5000 pm, and preferably between 100 pm and 1000 pm, for example, approximately 500 pm.

[0054] The processing line is not necessarily spatially continuous, but may comprise various spatially separated sections. In particular, the processing line may have gaps and / or interruptions where no focus elements are arranged.

[0055] In particular, the processing line corresponds to a connecting line between adjacent focus elements within the material.

[0056] In particular, it can be provided that the processing line is at least partially a straight line, and / or that the processing line is at least partially curved and / or is a curve.

[0057] By executing the machining line as a curve, rounded segments can be cut off from the workpiece, for example, creating rounded edges.

[0058] When the machining line is designed as a curve, for example, a specific angle of attack range is assigned to the machining line, which the machining line has with respect to an outer side of the workpiece.

[0059] In particular, it can be provided that a distance between adjacent focus elements has a distance component that is non-zero and oriented parallel to a thickness direction of the workpiece. In particular, the respective distance between all adjacent focus elements provided for laser processing of the workpiece has a distance component that is non-zero and oriented parallel to the thickness direction of the workpiece.

[0060] The thickness direction of the workpiece is to be understood in particular as a direction which is oriented transversely and in particular perpendicular to an outer side of the workpiece, through which the focus elements and / or a laser beam are coupled into the material to form the focus elements.

[0061] In particular, the distance component parallel to the thickness direction has a value which is greater than zero.

[0062] A neighboring focus element is understood to mean, in particular, a nearest neighbor of a specific focus element.

[0063] In particular, it can be provided that the distance between the adjacent focus elements has a distance component that is non-zero and oriented parallel to a beam propagation direction of a laser beam from which the focus elements are formed. In particular, the respective distance between all adjacent focus elements provided for laser processing of the workpiece has this non-zero distance component.

[0064] It can be advantageous if the angle of attack between the machining line and an outer side of the workpiece, through which the focus elements are coupled into the workpiece material, is at least 1° and / or at most 90°, at least in some sections. Depending on the selected angle of attack, this allows, for example, a vertical separation of the workpiece or the workpiece to be chamfered at a specific angle.

[0065] The fact that the processing line has a certain angle of attack or angle of attack range at least in sections is to be understood in particular that the processing line has at least one section with this angle of attack or angle of attack range.

[0066] In particular, the angle of attack can be at least 10° and / or at most 80°, preferably at least 30° and / or at most 60°, particularly preferably at least 40° and / or at most 50°. In particular, it can be provided that the angle of attack of the processing line is constant at least in sections, and / or that the processing line has several sections with different angles of attack.

[0067] The material modifications introduced into transparent materials by ultrashort laser pulses are divided into three different classes, see K. Itoh et al., "Ultrafast Processes for Bulk Modification of Transparent Materials," MRS Bulletin, vol. 31, p. 620 (2006): Type I is an isotropic refractive index change; Type II is a birefringent refractive index change; and Type III is a so-called void. The material modification produced depends on the laser parameters of the laser beam from which the respective focus element is formed, such as the pulse duration, wavelength, pulse energy, and repetition frequency of the laser beam, as well as on the material properties, such as the electronic structure and thermal expansion coefficient, as well as the numerical aperture (NA) of the focus.

[0068] Type I isotropic refractive index changes are attributed to localized melting by the laser pulses and rapid resolidification of the transparent material. For example, in fused silica, the density and refractive index of the material are higher when the fused silica is rapidly cooled from a higher temperature. Thus, when the material melts in the focal volume and then cools rapidly, the fused silica exhibits a higher refractive index in the modified areas than in the unmodified areas.

[0069] The birefringent refractive index changes of type II can arise, for example, from interference between the ultrashort laser pulse and the electric field of the plasma generated by the laser pulse. This interference leads to periodic modulations in the electron plasma density, which, upon solidification, results in a birefringent property—i.e., direction-dependent refractive indices—of the transparent material. A type II modification, for example, is also associated with the formation of so-called nanogratings. The voids (cavities) of type III modifications can be created, for example, with high laser pulse energy. In this case, the formation of the voids is attributed to an explosive expansion of highly excited, vaporized material from the focal volume into the surrounding material. This process is also referred to as a microexplosion.Because this expansion occurs within the bulk of the material, the microexplosion leaves behind a less dense or hollow core (the void), or a microscopic defect at the submicrometer or atomic level, surrounded by a dense material shell. The densification at the shock front of the microexplosion creates stresses in the transparent material, which can lead to or promote spontaneous crack formation.

[0070] In particular, the formation of voids can also be associated with Type I and Type II modifications. For example, Type I and Type II modifications can occur in the less stressed areas around the applied laser pulses. Therefore, when a Type III modification is introduced, a less dense or hollow core, or a defect, is always present. For example, in sapphire, a Type III modification does not create a cavity through microexplosion, but rather an area of ​​lower density. Due to the material stresses that occur during a Type III modification, such a modification is often accompanied by or at least promotes crack formation. The formation of Type I and Type II modifications cannot be completely prevented or avoided when introducing Type III modifications. Therefore, the discovery of "pure" Type III modifications is unlikely.

[0071] At high repetition rates of the laser beam, the material cannot cool completely between pulses, so that cumulative effects of the heat introduced from pulse to pulse can influence the material modification. For example, the repetition frequency of the laser beam can be higher than the inverse of the material's thermal diffusion time, so that heat accumulation can occur at the focal elements through successive absorption of laser energy until the material's melting temperature is reached. Furthermore, through the thermal transport of heat energy to the areas surrounding the focal elements, a larger area than the focal elements can be melted. After the introduction of ultrashort laser pulses, the heated material cools rapidly, so that the density and other structural properties of the high-temperature state are, to a certain extent, frozen in the material.

[0072] It may be advantageous if, by applying the focus elements to the material, material modifications are formed in the material, wherein the material modifications are Type III material modifications and / or wherein the material modifications are accompanied by crack formation in the material. In particular, these material modifications can be used to separate the material by etching, particularly selective etching.

[0073] In particular, it can be provided that the focus elements are moved relative to the material of the workpiece in a feed direction. Preferably, the focus elements lie at least approximately in a plane that is oriented, in particular, perpendicular to the feed direction.

[0074] Due to the relative movement of the focus elements to the material of the workpiece, a processing surface corresponding to the processing line is formed, along which material modifications are arranged and / or along which the material of the workpiece can be separated.

[0075] In particular, the workpiece is divided into two or more workpiece segments during its separation or at least one workpiece segment is separated from the workpiece during its separation.

[0076] A workpiece segment formed by separating the workpiece can be a useful segment and / or a work piece segment, which in particular has a separating surface that has a shape corresponding to the shape of the processing line and / or processing surface. Furthermore, a workpiece segment formed by separating the workpiece can be a cutting segment and / or waste segment. In particular, separating the workpiece along the processing surface creates a workpiece segment with a separating surface whose geometry corresponds to the processing surface.

[0077] A transparent material is understood, in particular, to be a material that is transparent to the input laser beam and / or a laser beam from which the focus elements are formed. In particular, it is understood to be a material through which at least 70%, and in particular at least 80%, and in particular at least 90% of the laser energy of the input laser beam and / or the laser beam from which the focus elements are formed is transmitted.

[0078] In particular, a focus element is understood to be a focused radiation region of the input laser beam, which in particular has a specific spatial extent and / or which in particular is spatially coherent. To determine the spatial dimensions of a specific focus element, such as a diameter of the focus element, only intensity values ​​that lie above a certain intensity threshold are considered. The intensity threshold is chosen, for example, such that values ​​lying below this intensity threshold have such low intensity that they are no longer relevant for an interaction with the material to form material modifications. For example, the intensity threshold is 50% of a global intensity maximum of the focus element.

[0079] In particular, a specific focus element is assigned a spatial interaction area in which the focus element interacts with the material of the workpiece when it is introduced into it.

[0080] In particular, the focus elements incorporated into the material interact with the material through nonlinear absorption, i.e., the laser radiation associated with the focus elements interacts with the material through nonlinear absorption. In particular, it is due to this interaction between the focus elements and the material that the material modifications are formed.

[0081] In particular, it can be provided that the respective focus elements according to the above definition have a maximum spatial extent of at least 0.5 μm and / or at most 60 μm, preferably at least 2 μm and / or at most 10 μm. In particular, a maximum spatial extent of an interaction region associated with a specific focus element with the material of the workpiece is at least 0.5 μm and / or at most 60 μm, and preferably at least 2 μm and / or at most 10 μm.

[0082] The maximum spatial extent of a particular focus element is understood to mean, in particular, the largest spatial extent of the focus element in any spatial direction.

[0083] In particular, the terms "at least approximately" or "approximately" generally mean a deviation of no more than 10%. Unless otherwise stated, the terms "at least approximately" or "approximately" specifically mean that an actual value and / or distance and / or angle deviates from an ideal value and / or distance and / or angle by no more than 10%.

[0084] The following description of preferred embodiments, taken in conjunction with the drawings, serves to further explain the invention. They show:

[0085] Fig. 1 is a schematic representation of an embodiment of a device for laser processing a workpiece;

[0086] Fig. 2 is a schematic cross-sectional view of a portion of a workpiece material in which a separation of the material along a processing line is provided; Fig. 3 is a schematic cross-sectional view of the portion according to Fig. 2, wherein the material is subjected to multiple focus elements to form material modifications;

[0087] Fig. 4 is a schematic cross-sectional view of a section of the material in which material modifications were produced by applying focus elements to the material, which modifications are accompanied by crack formation in the material;

[0088] Fig. 5 is a cross-sectional view of a simulated intensity distribution of focus elements for laser processing of the workpiece;

[0089] Fig. 6a is a schematic perspective view of a workpiece with material modifications formed thereon, wherein the workpiece is arranged in an etching bath for carrying out an etching process; and

[0090] Fig. 6b is a schematic perspective view of two workpiece segments formed by separating the workpiece according to Fig. 6a.

[0091] Identical or functionally equivalent elements are provided with the same reference numerals in all figures.

[0092] An embodiment of a device for laser processing a workpiece is shown in Fig. 1 and designated 100 there. Using the device 100, localized material modifications, such as defects in the submicrometer range or atomic range, can be created in a material 102 of the workpiece 104, which result in material weakening. The workpiece 104 can be separated at these material modifications. For example, a workpiece segment can be separated from the workpiece 104 using the material modifications created. In particular, using the device 100, material modifications can be introduced into the material 102 at an angle of incidence, so that by separating a corresponding workpiece segment from the workpiece 104, an edge region of the workpiece 104 can be chamfered or beveled.

[0093] The device comprises a beam splitting element 106 into which an input laser beam 108 is coupled. This input laser beam 108 is provided, for example, by a laser source 110. For example, the input laser beam 108 is a pulsed laser beam and / or an ultrashort pulse laser beam.

[0094] The input laser beam 108 is understood, in particular, to be a beam bundle comprising a plurality of parallel beams. The input laser beam 108 has, in particular, a transverse beam cross-section 112 and / or a transverse beam extension with which the input laser beam 108 impinges on the beam splitting element 106.

[0095] The input laser beam 108 impinging on the beam splitting element 106 has, in particular, at least approximately planar wavefronts 114.

[0096] By means of the beam splitting element 106, the input laser beam 108 is split into a plurality of partial beams 116 and / or partial beam bundles. In the example shown in Fig. 1, two mutually different partial beams 116a and 116b are indicated.

[0097] The partial beams 116 or partial beam bundles coupled out of the beam splitting element 106 have, in particular, a divergent beam profile. In particular, the beam splitting element 106 is designed as a far-field beam shaping element.

[0098] To focus the partial beams 116 coupled out of the beam splitting element 106, the device 100 comprises a focusing optics 118 into which the partial beams 116 are coupled. In particular, different partial beams 116 impinge on the focusing optics 118 with a spatial offset and / or angular offset.

[0099] The focusing optics 118, for example, has one or more lens elements. For example, the focusing optics 118 is designed as a microscope objective. The focusing optics 118 has, for example, a focal length between 5 mm and 50 mm.

[0100] For example, the beam splitting element 106 is arranged at least approximately in a rear focal plane of the focusing optics 118.

[0101] The partial beams 116 are focused by means of the focusing optics 118, forming a plurality of focus elements 120, each arranged at different spatial positions. It is generally possible for different and / or adjacent focus elements to spatially overlap in sections.

[0102] For example, one or more partial beams 116 and / or partial beam bundles are assigned to a specific focus element 120. For example, a respective focus element 120 is formed by focusing one or more partial beams 116 and / or partial beam bundles.

[0103] A focus element 120 is understood, in particular, to be a focused radiation region, such as a focus spot, a focal point, or a focal line. In particular, the focus elements 120 each have a specific geometric shape and / or a specific intensity profile, wherein the geometric shape is understood, for example, to be a spatial shape and / or spatial extent of the respective focus element 120.

[0104] The geometric shape and / or intensity profile of a specific focus element 120 is referred to below as the focus distribution 121 of the focus element 120. The focus distribution 121 is a property of the respective focus elements 120 and describes their shape and / or intensity profile. In particular, multiple focus elements 120 or all formed focus elements 120 have the same focus distribution.

[0105] The focus distribution of the formed focus elements 120 is defined by the input laser beam 108, the focus elements 120 being formed by splitting the input laser beam 108 using the beam splitting element 106. If the input laser beam 108 were focused before being coupled into the beam splitting element 106, for example, a single focus element would be formed with the focus distribution associated with the input laser beam 108.

[0106] For example, the input laser beam 108, when provided, for example, by the laser source 110, has a Gaussian beam profile. By focusing the input laser beam 108, a focus element would be formed in this case, which has a focus distribution with a Gaussian shape and / or a Gaussian intensity profile.

[0107] Alternatively, it may be provided, for example, that a quasi-non-diffracting and / or Bessel-like beam profile is assigned to the input laser beam 108, so that by focusing the input laser beam 108, a focus element would be formed which has a focus distribution with a quasi-non-diffracting or Bessel-like shape and / or a quasi-non-diffracting or Bessel-like intensity profile.

[0108] The focus distribution of the input laser beam 108 is assigned to the partial beams 116 and / or partial beam bundles formed by splitting the input laser beam 108 by means of the beam splitting element 106 in such a way that by focusing the partial beams 116, the focus elements 120 are formed with this focus distribution and / or with a focus distribution based on this focus distribution.

[0109] In the example shown in Fig. 1, the input laser beam 108 has a Gaussian beam profile, i.e., a focus distribution with a Gaussian shape and / or Gaussian intensity profile is assigned to the input laser beam 108. The focus elements 120 then each have, for example, the focus distribution 121 with this Gaussian shape and / or this Gaussian intensity profile, or with a shape or intensity profile based on this Gaussian shape and / or this Gaussian intensity profile (see Fig. 5).

[0110] If, for example, a Bessel-type beam profile is assigned to the input laser beam 108, the focus elements 120 configured for laser processing the workpiece 104 each have a focus distribution 121 with this Bessel-type beam profile or with a beam profile based on this Bessel-type beam profile. The focus elements 120 can thus be configured, for example, with a focus distribution having an elongated shape and / or an elongated intensity profile.

[0111] It may be provided that the device 100 has a beam-shaping device 122 for beam-shaping the input laser beam 108 (indicated in Fig. 1). For example, this beam-shaping device 122 is arranged upstream of the beam-splitting element 106 with respect to a beam propagation direction 124 of the input laser beam 108 and / or arranged between the laser source 110 and the beam-splitting element 106.

[0112] A beam propagation direction is understood to mean in particular a main beam propagation direction and / or a mean propagation direction of laser beams.

[0113] By means of the beam-shaping device 122, a specific focus distribution and / or a specific beam profile can be assigned to the input laser beam 108. In particular, the focus distribution 121 of the focus elements 120 can be defined by means of the beam-shaping device 122.

[0114] The beam-shaping device 122 can, for example, be configured to form a laser beam with a quasi-non-diffractive and / or Bessel-like beam profile from a laser beam with a Gaussian beam profile. The quasi-non-diffractive and / or Bessel-like beam profile is then assigned to the input laser beam 108 coupled into the beam splitting element 106. Accordingly, the focus elements 120 are then configured with this quasi-non-diffractive and / or Bessel-like beam profile or with a beam profile based on this beam profile.

[0115] For example, the beam-shaping device 122 can comprise an axicon element to form laser beams with a quasi-non-diffracting and / or Bessel-like beam profile. For coupling beams coupled out of the beam-shaping device 122 into the beam splitting element 106, one or more lens elements (not shown) can then be provided.

[0116] Regarding the definition and realization of quasi-non-diffracting and / or Bessel-like beams, reference is made to the book "Structured Light Fields: Applications in Optical Trapping, Manipulation and Organisation", M. Wördemann, Springer Science & Business Media (2012), ISBN 978-3-642-29322-1 as well as to the scientific publications "Bessel-like optical beams with arbitrary trajectories" by I. Chremmos et al., Optics Letters, Vol. 37, No. 23 , December 1, 2012, and "Generalized axicon-based generation of nondiffracting beams" by K. Chen et al., arXiv: 1911.03103vl [physics. optics], November 8, 2019.

[0117] By beam splitting by means of the beam splitting element 106, the focus elements 120 are in particular each formed identically to one another and / or each formed as copies of one another.

[0118] A schematic cross-section of the workpiece 104 and the material 102 is shown in Figs. 2 to 4, wherein a cross-sectional plane is oriented parallel to a thickness direction 126 and / or depth direction of the workpiece (in the example shown, the thickness direction 126 is oriented parallel to the z-direction).

[0119] It is intended that the workpiece 104 is separated along a predefined processing line 128 after laser processing by means of the device 100. The processing line 128 corresponds to a cross-sectional geometry with which the workpiece 104 is to be separated.

[0120] To perform laser processing, the focus elements 120 are introduced into the material 102 of the workpiece 104 (Fig. 3). It is intended that the focus elements 120 introduced into the material 102 of the workpiece 104 are moved relative to the material 102 in a feed direction 130. A relative movement of the focus elements 120 to the material 102 occurs in the feed direction 130, in particular at a defined feed rate.

[0121] Each of the formed focus elements 120 is assigned a specific local position xo, zo, at which a respective focus element 120 is arranged relative to the material 102 of the workpiece 104. For example, the local position of a focus element 120 is understood to be the position of its spatial center and / or center of gravity.

[0122] In particular, the local positions xo, zo of the respective focus elements 120 lie in a plane oriented perpendicular to the feed direction 130, wherein in particular all focus elements 120 designed for laser processing of the workpiece 104 lie in this plane.

[0123] In particular, each of the formed focus elements 120 is assigned a specific intensity I.

[0124] By means of the beam splitting element 106, the local position xo, zo and in particular also the intensity I of the respective focus elements 120 can be adjusted.

[0125] In particular, a respective distance d and / or a respective spatial offset between adjacent focus elements 120 can be adjusted by means of the beam splitting element 106. A distance direction of the distance d adjustable by means of the beam splitting element 106 preferably lies in a plane oriented transversely and in particular perpendicularly to the feed direction 130. For example, the distance d can be adjusted component-wise by means of the beam splitting element 106 in two spatial directions that span the mentioned plane or lie in the mentioned plane (in the example shown in Fig. 3, the x-direction and z-direction).

[0126] The feed direction 130 is oriented transversely and in particular perpendicularly to the thickness direction 126 of the workpiece 104.

[0127] Preferably, the beam splitting element 106 is designed as a 3D beam splitting element or comprises a 3D beam splitting element. The focus elements 120 can thus be designed, for example, such that they are identical to one another and / or that they represent copies of one another.

[0128] Regarding the technical implementation and properties of the beam splitting element 106, which is designed as a 3D beam splitting element, reference is made to the scientific publication "Structured light for ultrafast laser micro- and nanoprocessing" by D. Flamm et al., arXiv:2012.10119vl [physics. optics], December 18, 2020.

[0129] To perform the beam splitting, in one embodiment of the beam splitting element 106, in which the beam splitting element 106 is designed, for example, as a 3D beam splitting element, a defined transverse phase distribution is impressed on the transverse beam cross-section 112 of the input laser beam 108. A transverse beam cross-section or a transverse phase distribution is understood to mean, in particular, a beam cross-section or a phase distribution in a plane oriented transversely and, in particular, perpendicularly to the beam propagation direction 124 of the input laser beam 108.

[0130] The spaced-apart focus elements 120 are formed by interference of the focused partial beams 116, wherein, for example, constructive interference, destructive interference or intermediate cases thereof may occur, such as partially constructive or partially destructive interference.

[0131] To form the focus elements 120 at the respective position xo, zo and / or with the respective distance d, the phase distribution impressed by means of the beam splitting element 106 has a specific optical grating component and / or optical lens component for each focus element 120.

[0132] Due to the optical grating component, after focusing the partial beams 116, a corresponding spatial offset of the formed focus elements 120 results in a first spatial direction, e.g., in the x-direction. Due to the optical lens component, partial beams 116 or partial beam bundles impinge on the focusing optics 118 at different angles or with different convergence or divergence, which, after focusing, results in a spatial offset in a second spatial direction, e.g., in the z-direction.

[0133] The local positions xo, zo can therefore be defined by appropriate design of the beam splitting element 106 or the phase distribution imposed by the beam splitting element.

[0134] The intensity I of the respective focus elements 120 is determined by the phase positions of the focused partial beams 116 relative to one another. These phase positions can be defined by the aforementioned optical grating and optical lens components. The phase positions of the focused partial beams 116 relative to one another can be selected during the design of the beam splitting element 106 such that the focus elements 120 each exhibit a desired intensity.

[0135] Alternatively or in addition to the variants of the beam splitting element 106 described above, the beam splitting element 106 can be designed as a polarization beam splitting element or comprise a polarization beam splitting element. In this case, the beam splitting element 106 performs a polarization beam splitting of the input laser beam 108 into beams, each of which has one of at least two different polarization states.

[0136] In particular, the polarization states mentioned are understood to be linear polarization states, wherein, for example, two different polarization states are provided and / or polarization states oriented perpendicular to each other are provided. In particular, the polarization states are such that an electric field is oriented in a plane perpendicular to the beam propagation direction of the polarized beams (transverse electric).

[0137] For polarization beam splitting, the beam splitting element 106 comprises, for example, a birefringent lens element and / or a birefringent wedge element. The birefringent lens element and / or the birefringent wedge element are, for example, made of a quartz crystal or comprise a quartz crystal.

[0138] Regarding the functionality and design of the beam splitting element 106 as or with a polarization beam splitting element, reference is made to

[0139] DE 10 2020 207 715 Al referred to DE 10 2019 217 577 Al.

[0140] In particular, the beam splitting element 106 can be used to form the partial beams 116 with different polarization states. By focusing these partial beams 116 using the focusing optics 118, the focus elements 120 can be formed, for example, from beams with a specific polarization state. A specific polarization state can thus be assigned to each of the focus elements 120.

[0141] In particular, it can be provided that the focus elements 120 are arranged and formed by polarization beam splitting by means of the beam splitting element 106 such that mutually adjacent focus elements 120 each have different polarization states.

[0142] The coupling of the focus elements 120 into the material 102 occurs, for example, through a first outer side 132 of the material 102 of the workpiece 104. A second outer side 134 of the material 102 of the workpiece 104 is arranged, for example, at a distance from the first outer side 132 in the thickness direction 126 of the workpiece 104. The first outer side 132 and the second outer side 134 are oriented, for example, at least approximately parallel to one another. For example, the workpiece 104 is plate-shaped and / or panel-shaped.

[0143] The material 102 of the workpiece 104 has, for example, an at least approximately constant thickness D in the thickness direction 126.

[0144] The formed focus elements 120 are arranged along the processing line 128. The respective distances d and intensities I of the focus elements 120 arranged along the processing line 128 are selected such that by applying these focus elements 120 to the material 102, material modifications 138 are formed (Fig. 4), which enable a separation of the material 102 along the processing line 128 and / or a processing surface corresponding to this processing line 128 by etching using a wet-chemical solution.

[0145] The respective distance d of the focus elements 120 provided for laser processing of the workpiece 104 can be selected differently for different focus elements 120 and / or different pairs of focus elements 120. However, it is also fundamentally possible for the respective distance d to be identical for all focus elements 120 provided for laser processing of the workpiece 104.

[0146] In particular, a distance component dz of the distance d oriented parallel to the thickness direction 126 of the material 102 is non-zero for all focus elements 120 and / or for all pairs of adjacent focus elements 120. In particular, all adjacent focus elements 120 are spaced apart by a distance component dz non-zero in the thickness direction 126.

[0147] In the illustrations according to Figs. 3 and 4, the focus elements or the material modifications are shown only schematically with regard to number, geometry, extent, and arrangement. In particular, it can be provided that the processing line 128 extends between the first outer side 132 and the second outer side 134 of the workpiece 104 and, in particular, extends continuously and / or uninterruptedly between the first outer side 132 and the second outer side 134.

[0148] It can be provided that the processing line 128 has a plurality of different sections 140. For example, in the example shown in Fig. 3, the processing line 128 has a first section 140a, a second section 140b, and a third section 140c, wherein, with respect to the thickness direction 126, the second section 140b adjoins the first section 140a and the third section 140c adjoins the second section 140b.

[0149] The processing line 128 is not necessarily continuous and / or differentiable. For example, the processing line 128 may have discontinuities. It may be provided that the processing line 128 has interruptions and / or gaps, at which, in particular, no focus elements 120 are arranged.

[0150] The processing line 128 and / or the respective sections 140 of the processing line 128 are not necessarily linear. The processing line 128 and / or the sections 140 can, for example, be configured as a straight line or as a curve.

[0151] Furthermore, the machining line 128 and / or the respective sections 140 of the machining line 128 are assigned a specific angle of attack o and / or angle of attack range, which the machining line 128 or the respective section 140 encloses with the first outer side 132 of the workpiece 104.

[0152] In the illustrated embodiment, the angle of incidence α of the first section 140a and the third section 140c is 45°, and that of the second section 140b is 90°. The material modifications 138 formed by applying and / or introducing the focus elements 120 into the material 102 are arranged at localized positions in the material 102. These local positions of the material modifications 138 correspond at least approximately to the local positions xo, zo of the focus elements 120 in the material 102, by means of which the material modifications 138 were respectively formed.By appropriately selecting processing parameters, such as the respective distances d between the focus elements 120, their respective intensities I, the feed rate oriented in the feed direction 130, and the laser parameters of the input laser beam 108, the material modifications 138 can be formed as Type III modifications, which are particularly associated with the spontaneous formation of cracks 142 in the material 102 of the workpiece 104. In particular, cracks 142 are formed between adjacent material modifications 138.

[0153] It is provided that the material 102 of the workpiece 104 is separated along the processing line 128 or along a processing surface corresponding to this processing line 128 by etching using a wet chemical solution.

[0154] For example, after the material modifications 138 have been formed, the workpiece 104 is introduced into the wet-chemical solution for etching, wherein the wet-chemical solution penetrates through the first outer side 132 and / or the second outer side 134 into the material modifications 138 formed on the processing line 128 or processing surface and, if applicable, cracks 142 into the material 102.

[0155] Fig. 5 shows a simulated intensity distribution of a plurality of focus elements 120, with the spacing d between these focus elements 120 being approximately 8.0 pm. In the grayscale representation shown, brighter areas represent higher intensities.

[0156] The laser processing of the workpiece 104 functions as follows: By means of the device 100, focus elements 120 are formed for laser processing of the workpiece 104, for example by beam splitting the input laser beam 108 with the beam splitting element 106 and subsequent focusing of the partial beams 116.

[0157] The material 102 of the workpiece 104 is subjected to the formed focus elements 120, i.e., the focus elements 120 are introduced into the material 102, wherein the focus elements 120 are positioned along the predetermined processing line 128 in the material 102. The focus elements 120 are then moved through the material 102 in the feed direction 130 relative to the material.

[0158] The material 102 is a material that is transparent to a wavelength of laser beams from which the focus elements 120 are each formed, such as a glass material.

[0159] By applying the focus elements 120 to the material 102, material modifications 138 are formed in the material 102 at the respective positions of the focus elements 120.

[0160] The material modifications 138 formed by the focus elements 120 are arranged along the processing line 128 (see Figs. 3 and 6a), which extends, for example, continuously over the entire thickness D of the material 102. The focus elements 120 or material modifications 138 assigned to the processing line 128 define a cross-sectional geometry of the separation surface resulting from the subsequent separation of the material (Fig. 6b).

[0161] The focus elements 120 are moved along a predetermined trajectory 144 relative to the material 102, whereby planar material modifications 138 are formed in the material 102. In the example shown in Fig. 6a, the trajectory 144 is oriented parallel to the feed direction 130.

[0162] By moving the focus elements 120 relative to the material 102 along the trajectory 144, a processing surface 146 corresponding to the processing line 128 is formed, on which the material modifications 138 are arranged. In particular, the processing line 128 lies in the corresponding processing surface 146.

[0163] The trajectory 144 can generally have rectilinear and / or curved sections. In the case of curved sections, the processing line 128 is rotated during the execution of the relative movement between the material 102 and the focus elements 120, in particular, such that the processing line 128 always lies in a plane oriented perpendicular to the feed direction 130. This can be achieved, for example, by correspondingly rotating the beam splitting element 106 or by rotating the entire device 100 relative to the workpiece 104.

[0164] A distance between adjacent material modifications 138 in the feed direction 130 can be defined, for example, by setting a pulse spacing of laser pulses of the input laser beam 108 and / or by setting the feed rate.

[0165] The material modifications 138 formed along the processing line 128 or processing surface 146 result in a reduction in the strength of the material 102, wherein the strength is reduced in particular due to the cracks 142 formed.

[0166] After the material modifications 138 have been formed in the material 102, an etching process with a wet-chemical solution 148 is performed to separate the material 102 along the processing line 128 and / or processing surface 146. For this purpose, the material 102 is, for example, partially or completely introduced into an etching bath 150 (indicated by the rectangle in Fig. 6a) containing the wet-chemical solution 148. In particular, the material 102 is partially or completely introduced into the wet-chemical solution 148 so that the wet-chemical solution 148 partially or completely surrounds the material 102. The subsequent etching process takes place at a specific temperature of the wet-chemical solution 148 and for a specific duration.The wet-chemical solution penetrates the material modifications 138 and / or cracks 142 associated with the processing line 128 on the outer sides 132, 134 and then penetrates along the processing line 128 into an inner region 152 of the material 102. The inner region 152 is, in particular, a region of the material 102 spaced apart from the respective outer side 132, 134 parallel to the thickness direction 126.

[0167] In particular, etching can be carried out using the etching bath 150 with ultrasound support.

[0168] The temperature of the wet-chemical solution 148 is between 100°C and 150°C. In particular, the temperature of the wet-chemical solution 148 is kept at least approximately constant for the duration of the etching process, with a target value for the temporally constant temperature being within the aforementioned value range. For example, the etching process is carried out at a constant temperature of 130°C.

[0169] With regard to the temperature of the wet-chemical solution 148, "at least approximately constant" is preferably understood to mean that an actual temperature of the wet-chemical solution 148 deviates from the predetermined (time-constant) target value during the etching process by less than 7 K.

[0170] The wet chemical solution is preferably an aqueous KOH solution or an aqueous NaOH solution, each with a concentration between 15 wt% and 50 wt%.

[0171] The duration of the etching process for separating the material 102 depends on the type of material 102 as well as on the positioning and shape of the processing line 128 in the material 102. Typically, the duration is between 5 minutes and 180 minutes.

[0172] By etching using the supplied wet-chemical solution, the material 102 is separated at the processing surface 152 into two distinct workpiece segments 154a, 154b (Fig. 6b). The workpiece segment 154b is a good piece segment and / or a work segment. It has a separation surface 156, which has a shape corresponding to the shape of the processing line 128 or processing surface 146.

[0173] In the example shown in Fig. 6b, the workpiece segment 154a is a reject segment and / or waste segment.

[0174] The optimal parameters of the etching process, such as the duration, the KOH or NaOH concentration of the wet chemical solution and its (time-constant) temperature, are particularly specific to the respective material 102 of the workpiece 104 used.

[0175] Preferably, the parameters are selected such that during the etching process, etching of the material 102 occurs along the processing line 128 or

[0176] The etching of the material modifications 138 arranged on the processing surface 152 is carried out at the highest possible speed and / or etching rate, while at the same time attacking the unmodified areas of the workpiece 104 as little as possible. Consequently, the etching is preferably carried out selectively on the material modifications 138 and / or cracks 142 formed in the material 102 at the highest possible etching rate. This makes it possible to carry out the etching process for separating the material 102 in the shortest possible time.

[0177] The material 102 of the workpiece 104 is, for example, aluminum silicate glass. For example, to form the material modifications 138 as Type III modifications, a laser beam from which the focus elements 120 are formed has a wavelength of 1030 nm and a pulse duration of 3 ps. Furthermore, a numerical aperture assigned to the focusing optics 118 is 0.4, and a pulse energy assigned to a single focus element 120 is 500 to 5000 nJ. Reference symbols: d Angle of attack d Distance dz Distance component

[0178] D Thickness

[0179] XO Position in x-direction

[0180] ZO Position in y-direction

[0181] 100 device

[0182] 102 Materials

[0183] 104 Workpiece

[0184] 106 beam splitting element

[0185] 108 input laser beam

[0186] 110 Laser source

[0187] 112 beam cross-section

[0188] 114 Wavefront

[0189] 116 partial beams

[0190] 116a Partial beam

[0191] 116b partial beam

[0192] 118 Focusing optics

[0193] 120 focus element

[0194] 121 Focus distribution

[0195] 122 Beam shaping device

[0196] 124 Beam propagation direction

[0197] 126 Thickness direction

[0198] 128 processing line

[0199] 130 Feed direction

[0200] 132 first outside

[0201] 134 second outside

[0202] 138 Material modification

[0203] Section 140

[0204] 140a first section

[0205] 140b second section

[0206] 140c third section crack trajectory machining surface wet chemical solution etching bath interior a workpiece segment / waste segmentb workpiece segment separation surface

Claims

Claims: A method for separating a workpiece (104) comprising a transparent material (102), wherein several focus elements (120) are provided by means of an input laser beam (108), the material (102) is exposed to the focus elements (120), material modifications (138) are formed in the material (102) along a predetermined processing line (128) by exposure of the material (102) to the focus elements (120), and the material (102) is separated by means of an etching process with a wet chemical solution along the processing line (128), wherein the temperature of the wet chemical solution during the etching process is at least 100°C and / or at most 150°C. The method according to claim 1, characterized in that the wet chemical solution is an aqueous KOH solution with a concentration of at least 15 wt.% and / or at most 50 wt.%.A method according to claim 1, characterized in that the wet chemical solution is an aqueous NaOH solution with a concentration of at least 15 wt.% and / or at most 50 wt.%. A method according to any of the preceding claims, characterized in that the temperature of the wet chemical solution is kept constant during the etching process, wherein in particular the temperature is regulated to a constant target temperature of at least 100°C and / or at most 150°C, and wherein the actual temperature of the wet chemical solution during the etching process deviates from the target temperature by less than 7 K and in particular by less than 1 K. A method according to claim 4, characterized in that the wet chemical solution is an aqueous KOH solution or an aqueous NaOH solution, wherein the concentration of the solution is selected such that the boiling point of the solution is at least 5% and in particular The temperature of the wet chemical solution is at least 10% greater than a constant target temperature over time. A method according to any of the preceding claims, characterized in that the etching process has a duration of at least 5 minutes and / or at most 180 minutes, and preferably at least 10 minutes and / or at most 90 minutes. A method according to any of the preceding claims, characterized in that the material is exposed to the wet chemical solution for carrying out the etching process, wherein the material is particularly partially or completely immersed in the wet chemical solution.A method according to any one of the preceding claims, characterized in that the distance (d) between adjacent focus elements (120) is at least 3 pm and / or at most 70 pm, and preferably at least 5 pm and / or at most 10 pm, and / or that the distance between adjacent material modifications (138) is at least 3 pm and / or at most 70 pm, and preferably at least 5 pm and / or at most 10 pm. A method according to any one of the preceding claims, characterized in that the input laser beam and / or a laser beam from which the focus elements are formed is a pulsed laser beam, and in particular an ultrashort pulse laser beam, and in particular characterized in that a pulse energy of at least 0.5 pJ and / or at most 10 pJ is assigned to a specific focus element.Method according to one of the preceding claims, characterized in that the input laser beam (108) is split into a plurality of partial beams (116) by means of a beam splitting element (106) and the focusing elements (120) are focused by focusing partial beams (116) coupled out of the beam splitting element (106). A method according to any of the preceding claims, characterized in that the machining line (128) is spatially continuous over a thickness (D) of the material (102) of the workpiece (104) and / or over a thickness of a workpiece segment to be separated from the workpiece (104). A method according to any of the preceding claims, characterized in that a distance (d) between adjacent focus elements (120) has a non-zero distance component (dz) which is oriented parallel to a thickness direction (126) of the workpiece (104). A method according to any of the preceding claims, characterized in that an angle of attack (o) between the machining line (128) and an outer surface (132, 134) of the workpiece (104) through which the focus elements (120) are coupled into the material (102) of the workpiece (104) is at least 1° and / or at most 90°, at least sectionally.A method according to any one of the preceding claims, characterized in that material modifications (138) are formed in the material (102) by applying the focus elements (120), wherein the material modifications (138) are type III material modifications, and / or wherein the material modifications (138) are accompanied by cracking of the material (102). A method according to any one of the preceding claims, characterized in that the focus elements (120) are moved relative to the material (102) of the workpiece (104) in a feed direction (130), and in particular characterized in that the focus elements (120) lie at least approximately in a plane oriented perpendicular to the feed direction (130).

Images