Method for separating a transparent workpiece

Abstract

The present invention relates to a method for separating a transparent workpiece (1) by means of an ultra-short laser pulse of a laser beam (20) of an ultra-short pulse laser (2), wherein the laser beam (20) is split into a plurality of laser sub-beams (20') by a beam-shaping optical unit (30), wherein each laser sub-beam (20') is focused into and / or onto the workpiece (1) by a focusing optical unit (32), wherein each laser sub-beam (20') forms its own focal zone (200), wherein the laser pulses act on the workpiece (1) in the focal zones (200), whereby material modifications (5) are introduced into or onto the workpiece (1), wherein the material modifications (5) are introduced into the workpiece along a separation line (4), preferably a curved separation line (4), wherein the workpiece (1) is separated along the material modifications (5) with a separation step, through which a shaped edge (10) is produced. According to the invention, the focal zones (200) of the laser sub-beams (20') are located in and / or on a rotationally symmetric envelope (6) to the beam progression direction (Z), wherein the envelope (6) extends at least partially in the thickness direction into the workpiece.

Description

[0001] Method for separating a transparent workpiece

[0002] Technical area

[0003] The present invention relates to a method for separating a transparent workpiece by means of ultrashort laser pulses of a laser beam of an ultrashort pulse laser.

[0004] State of the art

[0005] The processing of transparent workpieces using ultrashort laser pulses is well known. The short pulse length and high peak power can lead to nonlinear absorption of the pulse energy in the material, allowing the processing of materials that are essentially transparent even for the laser light wavelength used.

[0006] To create a bevel on a workpiece, the laser beam is typically applied to the workpiece at a specific angle. However, such angles can lead to aberration of the laser beam, preventing targeted energy deposition into the workpiece.

[0007] Another possibility is to introduce a large number of spatially distributed focus zones into the workpiece in order to create the desired cutting geometry.

[0008] US 2012 / 0223061 A1 discloses a laser processing method for forming a modification region, wherein a plurality of focus zones are simultaneously introduced in a plane perpendicular to the optical axis of a condenser lens, and wherein a plurality of focus zones are simultaneously introduced in a depth direction.

[0009] Description of the invention

[0010] Based on the known prior art, it is an object of the present invention to provide an improved method for separating a transparent workpiece. This object is achieved by a method for separating a transparent workpiece having the features of claim 1. Advantageous further developments emerge from the subclaims, the description, and the figures.

[0011] Accordingly, a method for separating a transparent workpiece by means of ultrashort laser pulses of a laser beam of an ultrashort pulse laser is proposed, wherein the laser beam is split into a plurality of partial laser beams by beam-shaping optics, wherein each partial laser beam is focused into and / or onto the workpiece by focusing optics, wherein each partial laser beam forms its own focus zone, wherein the laser pulses act on the workpiece in the focus zones, whereby material modifications are introduced into and / or onto the workpiece, wherein the material modifications are introduced into the workpiece along a separating line, wherein the workpiece is separated along the material modifications in a separating step, whereby a shaped edge is produced. According to the invention, the focus zones of the partial laser beams are arranged in and / or on an envelope that is rotationally symmetrical to the beam propagation direction.

[0012] The ultrashort pulse laser delivers ultrashort laser pulses. Ultrashort can mean, for example, a pulse length between 500 picoseconds and 10 femtoseconds, and especially between 10 picoseconds and 100 femtoseconds. The ultrashort laser pulses move along the laser beam in the beam propagation direction.

[0013] A transparent material is understood herein to be a material that is essentially transparent to the wavelength of the laser beam of the ultrashort pulse laser. The terms "material" and "transparent material" are used interchangeably here—the material referred to herein is therefore always to be understood as a material that is transparent to the laser beam of the ultrashort pulse laser.

[0014] A beam-shaping optic is an optical element that can form a multitude of sub-laser beams from an input laser beam. Depending on the design of the beam-shaping optic, the sub-laser beams can carry different or identical energies.

[0015] For example, a uniform or non-uniform splitting of the input laser beam can be carried out.

[0016] The beam shaping optics may, for example, comprise a transmissive or reflective diffractive optical element or comprise a liquid crystal or comprise a geometric phase hologram.

[0017] A diffractive optical element is designed to split the input laser beam into two

[0018] To influence spatial dimensions in one or more properties. A diffractive optical element is a fixed component that can be used to produce a precisely defined intensity distribution from the input laser beam. Typically, a diffractive optical element is a specially shaped diffraction grating, whereby the input laser beam is shaped into the desired beam shape through diffraction. The laser beam can pass through a transmissive diffractive optical element or be reflected by a reflective diffractive optical element.

[0019] A liquid crystal can generate a variable phase pattern by switching individual pixels, allowing the distribution of the focal zones to be adjusted in a highly variable manner. Switchable diffractive optical elements are also conceivable, allowing phase manipulation to be discretely switched on or off via a liquid crystal.

[0020] A phase hologram is a device for modulating the phase of an input laser beam, allowing a desired distribution of focal zones to be achieved by diffracting the laser beam by the phase hologram. For example, diffraction of the laser beam by the phase hologram can be achieved by appropriately selecting the polarization of the laser beam. Kim, Jihwan, et al. "Fabrication of ideal geometric-phase holograms with arbitrary wavefronts," Optica, 2015, Vol. 2, No. 11, pp. 958-964.

[0021] A focusing optics can be an optical imaging system that can consist of one or more components. A component can be, for example, a lens, an optically imaging freeform surface, a Fresnel zone plate, or an objective such as a microscope objective or an F-theta objective. The focusing optics can transfer each partial laser beam into its own focus zone. Each of the focus zones is assigned a specific spatial position xO, yO, zO. The positioning of the focus zone in the beam propagation direction can be adjusted using the focusing optics. For example, by adjusting the focusing optics, a focus zone can be placed on the surface of the workpiece, or in the workpiece, or partially on the surface and partially in the workpiece.

[0022] The beam propagation direction is determined in particular by the optical axis of the focusing optics. The optical axis is perpendicular to the entrance surface of the lens.

[0023] When an ultrashort laser pulse is focused into and / or onto the workpiece, the intensity in the focal volume can lead to nonlinear absorption, for example, through multiphoton absorption and / or electron avalanche ionization processes. This nonlinear absorption leads to the generation of an electron-ion plasma, which, upon cooling, can induce permanent structural changes in the workpiece material. Since nonlinear absorption can transport energy into the bulk of the material, these structural changes can be generated inside the sample without affecting the workpiece surface.

[0024] At high laser repetition rates, the workpiece cannot cool completely between pulses, meaning that cumulative effects of the heat introduced from pulse to pulse can influence material modification. For example, the laser repetition frequency can be higher than the inverse of the workpiece's thermal diffusion time, allowing heat to accumulate in the focal zone through the gradual absorption of laser energy until the workpiece's melting temperature is reached. Furthermore, the thermal transport of heat energy to the areas surrounding the focal zone allows a larger area to be processed than the focal zone. After the ultrashort laser pulses are applied, the heated material cools rapidly, effectively freezing the density and other structural properties of the high-temperature state in the material.

[0025] 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 or cavity created by a microexplosion. The material modification produced depends on laser parameters such as the pulse duration, wavelength, pulse energy, and repetition frequency of the laser; on the material properties, including the electronic structure and thermal expansion coefficient; and on the numerical aperture (NA) of the focusing.

[0026] In this case, Type III modifications are predominantly used to perforate the workpiece with the material modifications. However, it is also possible for laser ablation of the workpiece material to take place on the surface of the workpiece, or for only a Type I or Type II modification to be introduced into the workpiece, or for such a modification to be combined with the Type III modification.

[0027] The material modifications are introduced into the material along a dividing line. The dividing line describes the line of impact of the partial laser beams on the surface of the workpiece. A feed moves the partial laser beams and the workpiece relative to each other at a feed rate, while the ultrashort pulse laser emits laser pulses into the workpiece at its repetition frequency. This results in different impact points of the laser pulses on the surface of the workpiece over time. The material modifications can at least partially overlap in both directions, i.e., in the feed direction and perpendicular to it. Even if the focus zones are discrete, the resulting material modifications can be designed by adjusting the laser parameters so that there is partial overlap or that the modifications are connected by cracks.

[0028] "Relatively movable" means that both the laser beam can be moved translationally relative to a stationary workpiece, and the workpiece can be moved relative to the laser beam. It is also possible that both the workpiece and the laser beam can move.

[0029] The separation along the material modifications is ultimately carried out by a separation step, so that the workpiece is divided into the useful part and the so-called non-useful part or section of the workpiece.

[0030] According to the invention, the focus zones of the partial laser beams are arranged in and / or on a rotationally symmetrical envelope relative to the beam propagation direction, with the envelope extending at least partially into the workpiece in the thickness direction. It can also extend through the entire thickness of the material.

[0031] The envelope extends in the thickness direction in sections when it overlaps with a part of the volume of the workpiece along the surface normal of the workpiece.

[0032] The envelope of the focus zones can generally refer to the focus zones of the partial laser beams, where the envelope is the outer boundary of the volume in which the focus zones are located.

[0033] However, the envelope can also be the outer boundary of the volume that is heated by the action of the laser beams above a certain threshold. If the threshold is the material modification threshold, then the envelope refers to the material modifications, where the envelope is the outer boundary of the volume in which the material modifications are located. In particular, all focus zones of the partial laser beams then also lie within the envelope. In any case, the focus zones are preferably evenly distributed within the envelope to ensure uniform energy deposition, in particular to ensure a similar or identical spot density per unit volume.

[0034] The rotational symmetry of the envelope generally describes that the envelope can be mapped onto itself after being rotated by a discrete angle around the ray propagation direction. In other words, the envelope can be mapped onto itself n times when rotated around the symmetry axis. The number n is called the symmetry factor. In particular, the symmetry factor can be higher than 3.

[0035] For example, the envelope in the plane perpendicular to the axis of symmetry has a threefold symmetry, with the cross-section perpendicular to the axis of symmetry essentially corresponding to an isosceles triangle.

[0036] For example, the envelope in the plane perpendicular to the axis of symmetry has a four- or five-fold symmetry, with the cross-section perpendicular to the axis of symmetry essentially corresponding to a square or an isosceles pentagon.

[0037] A special case of rotational symmetry is that the envelope can always be mapped onto itself when rotated around the symmetry axis by any angle.

[0038] For example, the envelope has a circular cross-section in the plane perpendicular to the axis of symmetry.

[0039] For example, the envelope extends through the entire thickness of the material, making it particularly easy to separate the workpiece across its entire thickness during the separation step. The thickness of the workpiece can be, for example, 100 μm or 8 mm, or in between. For example, the thickness can also be 600 μm. For example, the thickness can be 2000 μm or, preferably, 500 μm.

[0040] By successively introducing the material modifications into the envelope, an outer so-called material modification surface is created, which limits all material modifications. After separation, the material modification surface becomes the so-called formed edge of the material. In other words, the geometry of the formed edge results from the cross-section of the envelope perpendicular to the parting line. A formed edge of the workpiece is subdivided into at least so-called chamfers and bevels, whereby the edge of the workpiece is chamfered with a straight section. However, a formed edge can also be round, such as in the case of a so-called C-chamfer. If the parting line is curved, i.e. has sections that are not straight, then a rotationally symmetrical material modification is advantageous, since a rotationally symmetrical material modification does not have a preferred direction.When machining a workpiece along a curved parting line, the optical structure of the machining device or the workpiece itself does not need to be rotated to adjust the orientation to a preferred direction of the parting line. This drastically simplifies the machining device.

[0041] The rotationally symmetric envelope can be composed of at least one cone.

[0042] A cone typically has a height and a base. The conical surface is formed by the surface of the cone, which runs from the base to the apex. Accordingly, the surface of the cone encloses an angle called the conical cone angle. The conical cone angle can range from 130° to 20°, for example, approximately 90°.

[0043] The base of the cone can have a diameter of 50 to 500 pm, preferably between 200 to 300 pm. The height of the cone can be between 100 to 1000 pm, preferably between 50 to 500 pm.

[0044] In particular, the base count can be greater than or equal to 3, so that the cone also includes triangular pyramidal structures, as well as all pyramidal structures with a higher base count. However, the base can also be round.

[0045] In particular, the cone can also be designed as a truncated cone, so that the cone does not extend to a point-like tip, but only to a distance from the cone tip.

[0046] In particular, the cone's mantle can also be curved, in the sense that it does not connect the base and apex with a straight line. The cone's mantle can therefore follow a hyperbolic or spherical function, or correspond to another mathematically unique function.

[0047] If a conical envelope is created by the multitude of focus zones, then the material modification composed of the individual material modifications is also conical. If such composite material modifications are introduced into the workpiece perpendicular to the surface of the workpiece along a parting line and the cone or truncated cone extends across the entire thickness of the workpiece, the entirety of the material modifications forms two inclined surfaces to the surface normal, which are oriented at the opening angle of the cone to the surface normal. The workpiece can then be separated along these surfaces. In other words, the material modification perpendicular to the parting line has a V-shaped cross-section, with the workpiece being separated along both sides of the "V".

[0048] Both the edge of the working part and the non-working part of the workpiece are then chamfered according to the opening angle. In other words, a chamfer with the opening angle is created.

[0049] If the rotationally symmetric envelope consists, for example, of two cones whose tips touch or overlap, and the cone has, for example, a curved surface, i.e. the cone base and the cone tip are not connected by a straight line, then a D-shaped edge can be created in this way, for example on the use side.

[0050] The rotationally symmetric envelope can additionally be composed of a cylinder extending from the tip of the cone.

[0051] This can cause the tip of the cone or truncated cone to be aligned with the surface of the workpiece.

[0052] A cylinder can be created, for example, by arranging individual focus zones one above the other.

[0053] When such composite material modifications are introduced into the workpiece perpendicular to the surface along a parting line, the material modification has a Y-shaped cross-section perpendicular to the parting line. The parting edge accordingly has a portion that runs parallel to the surface normal of the workpiece and a portion that runs at the cone's opening angle. In other words, a bevel with the opening angle is created.

[0054] The rotationally symmetric envelope can be composed of two cones whose tips point towards each other and are connected by a cylinder.

[0055] When such composite material modifications are introduced into the workpiece perpendicular to the surface along a parting line, the material modification perpendicular to the parting line has a substantially X-shaped cross-section. The parting edge accordingly has a central portion that runs parallel to the surface normal of the workpiece, while the upper and lower portions run at the cone opening angles. In other words, a bevel is created with the opening angle on the upper and lower surfaces of the workpiece. The cones can have different opening angles.

[0056] This allows, for example, the workpiece surfaces to be prepared for different applications. For example, the process can be used to create a recess for a display glass. The underside of the workpiece is bonded to a display, while the top side can be touched by an end customer. The underside can be optimized for adhesive distribution, while the top side can be softened accordingly for the user.

[0057] The rotationally symmetric envelope can be composed of at least one ellipsoid.

[0058] An ellipsoid is a solid of revolution of an ellipse and accordingly has a long and a short axis. A special case of an ellipsoid is a sphere.

[0059] When such composite material modifications are introduced into the workpiece perpendicular to the surface along a parting line, the material modification has a substantially O-shaped or O-shaped cross-section perpendicular to the parting line. The parting edge in the useful part or non-use part is accordingly C-shaped.

[0060] The rotationally symmetric envelope must be composed of at least one ellipsoid and at least one cylinder.

[0061] This can cause the tip of the cone or truncated cone to be aligned with the surface of the workpiece.

[0062] If such composite material modifications are introduced into the workpiece perpendicular to the surface of the workpiece along a parting line, the material modification has a substantially U-shaped cross-section perpendicular to the parting line.

[0063] The maximum lateral distance of the focus zones can be between 100pm and 500pm, preferably between 200pm and 300pm.

[0064] The maximum lateral distance is the distance between two focal zones in a plane parallel to the workpiece surface. This allows for a material modification on the useful and non-use parts of the workpiece with a lateral dimension between 100 μm and 500 μm. Such large material modifications are either impossible or very difficult to achieve with a single focal zone.

[0065] Between 10 and 1000 focus zones can be arranged on and / or in the envelope, preferably between 100 and 200 focus zones.

[0066] This makes it possible to distribute the laser beam's energy as evenly as possible within the envelope. At the same time, it makes it possible to create an envelope with the greatest possible rotational symmetry.

[0067] The partial laser beams can be introduced into the workpiece simultaneously in the focus zones.

[0068] In particular, there is no scanning of the various positions of the focus zones, but rather a simultaneous exposure of the workpiece in the focus zones. "Simultaneous" means neglecting the speed of light in the workpiece.

[0069] With a layer thickness of 1 mm and a speed of light of about 300x10 9 mm / s results in a time scale of about 3ps.

[0070] For processing display glass with a thickness of 550 μm, 300 μJ of pulse energy can be used to simultaneously introduce the material modifications. With a spatial pulse spacing of 4 μm and a repetition rate of 100 kHz, this results in an average power of 30 W and a feed rate of 400 mm / s.

[0071] The beam shaping optics can impose a specific polarization on each partial laser beam.

[0072] This ensures that spatially adjacent focal zones have different polarizations and thus do not interfere with each other. For example, the beam-shaping optics can therefore include a polarizing beam splitter.

[0073] The beam shaping optics can also imprint a specific beam shape on each partial laser beam.

[0074] The laser beam may be a non-diffracting laser beam and / or a Gaussian laser beam and / or the partial laser beams may be non-diffracting partial laser beams and / or Gaussian partial laser beams.

[0075] Non-diffracting beams and / or Bessel-type beams are understood to mean, in particular, beams whose transverse intensity distribution is propagation-invariant. In particular, in the case of non-diffracting beams and / or Bessel-type beams, a transverse intensity distribution is essentially constant along a longitudinal direction and / or propagation direction of the beams.

[0076] A transverse intensity distribution is an intensity distribution that lies in a plane oriented perpendicular to the beam propagation direction. Furthermore, the intensity distribution always refers to the portion of the laser beam's intensity distribution that is greater than the modification threshold of the workpiece. Accordingly, the term "focus zone" can also be used for the intensity distribution to emphasize that this portion of the intensity distribution is specifically provided and that focusing achieves an intensity enhancement in the form of the intensity distribution.

[0077] For the definition and properties of non-diffracting beams, please refer to the book "Structured Light Fields: Applications in Optical Trapping, Manipulation and Organization," M. Wördemann, Springer Science & Business Media (2012), ISBN 978-3-642-29322-1. This book is expressly incorporated by reference.

[0078] Non-diffracting laser beams therefore have the advantage of being able to have an intensity distribution that is elongated in the beam propagation direction and significantly larger than the transverse dimensions of the intensity distribution. In particular, this allows the creation of material modifications that are elongated in the beam propagation direction, allowing them to penetrate two sides of the workpiece particularly easily.

[0079] Gaussian laser beams, on the other hand, have a Gaussian-shaped transverse intensity distribution and do not have an elongated focus zone, but rather a beam waist.

[0080] In particular, it is possible that the laser beam entering the beam-forming optics is a Gaussian laser beam and is split by the beam-forming optics into a plurality of non-diffracting partial laser beams.

[0081] In particular, the partial laser beams can have a rotationally symmetric transverse intensity distribution, so that the individual material modifications that make up the entire modification do not have a preferred direction.

[0082] The separation step may comprise a mechanical separation and / or an etching process and / or a thermal treatment.

[0083] Thermal treatment can, for example, involve heating the material or the parting line. For example, the parting line can be locally heated using a continuous-wave CO2 laser, causing the workpiece to expand differently in the material-modified area compared to the untreated or unmodified workpiece. This allows for the formation of continuous and uninterrupted parting surfaces, separating the useful and non-useful parts of the workpiece.

[0084] Mechanical separation can be achieved by applying tensile or bending stress, for example, by applying a mechanical load to the parts of the workpiece separated by the parting line. In particular, a mechanical change can also be achieved by a pulsating action on the part to be separated, for example, by an impact.

[0085] The material can also be separated by etching with a wet chemical solution, whereby the etching process preferentially applies the material to the material modification, i.e., the targeted weakening of the material. For example, the workpiece can be etched in KOH and / or NaOH and / or HF. By preferentially etching the parts of the workpiece weakened by the material modification, this leads to a separation of the workpiece along the separation surface.

[0086] Short description of the characters

[0087] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. In the figures:

[0088] Figure 1 shows a method for separating a workpiece according to the state of the

[0089] Technology;

[0090] Figure 2 is a schematic representation of a workpiece;

[0091] Figure 3A, B, C, D a schematic representation of the rotationally symmetric envelope;

[0092] Figure 4A, B, C, D shows a schematic representation of the method according to the invention;

[0093] Figure 5 is a schematic representation of the method according to the invention;

[0094] Figures 6A to H show a schematic representation of the separating edges that can be produced using the method according to the invention;

[0095] Figure 7 is a schematic representation of a laser system for performing the

[0096] Method; and Figure 8A, B shows a schematic representation of a laser system for carrying out the method;

[0097] Detailed description of preferred embodiments

[0098] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are provided with identical reference numerals, and a repeated description of these elements is partially omitted to avoid redundancies.

[0099] Figure 1 schematically shows a method for separating a transparent workpiece 1 according to the prior art. Figure 1A shows a cross-section of a workpiece 1 onto which the laser beam 20 of an ultrashort pulse laser 2 is incident. The laser beam 20 is applied to the workpiece 1 at an angle of incidence α.

[0100] As it passes into the workpiece 1, the laser beam 20 is refracted at the surface 10 of the workpiece 1 according to Snell's law of refraction, so that the laser beam 20 continues through the material of the workpiece 1 at an angle ß to the surface normal N. By introducing the laser pulses into the workpiece 1 via the laser beam 20, the workpiece 1 is heated in the focus zone 200 of the laser beam 20. The workpiece 1 is vaporized in the focus zone 200, resulting in an explosive expansion of this plasma state into the surrounding material of the workpiece 1. The compression at the impact front of this so-called micro-explosion leads to material stresses there, while a less dense or even empty space (void) remains in the original focus zone 200 of the laser beam.The modification of the material of workpiece 1 in the focus zone 200 is called material modification 5, wherein material modification 5 is, in particular, a type III material modification. In material modifications 5, workpiece 1 is perforated, so to speak.

[0101] While the ultrashort pulse laser 2 emits laser pulses, the laser beam 20 and the workpiece 1 are moved relative to each other at a feed rate V, as shown in Figure 1B. This feed rate V is guided along a separation line 4, which determines where the workpiece 1 is to be separated on the top side. By propagating the laser beam 20 in the material of the workpiece 1 at an angle β, the material modification 5 is also introduced into the material of the workpiece 1 at an angle β.

[0102] Figure 2 shows a workpiece 1 to be manufactured using the method according to the invention. The workpiece is, for example, a display glass. Accordingly, the workpiece 1 can have two recesses, for example, for front cameras or a fingerprint sensor.

[0103] The workpiece 1, in particular, has rounded corners. If such contours are produced using the known method, the angle of attack can lead to beam aberrations, which can significantly influence the quality of the cutting edge. Furthermore, with curved cutting lines 4, the workpiece 1 or the laser beam 20 must be rotated due to the angle of attack.

[0104] In the method according to the invention, the focusing optics do not need to rotate, since the laser beam 20 of the laser 2 is split into a plurality of partial laser beams 20' by a beam-shaping optics 30. Each individual partial laser beam 20' is then focused into and / or onto the workpiece 1 by a focusing optics 32. Each partial laser beam 20' forms its own focus zone 200. The focus zones 200 are delimited by a rotationally symmetrical envelope 6, the cross-section of which specifies the shape of the formed edge 10 of the workpiece 1.

[0105] The focus zones 200 of a laser beam split in this way are shown in spatial arrangement in Figure 3A. Each focus zone 200 has its own position xO, yO, zO. The focus zones 200 of the partial laser beams 20' are arranged around the beam propagation direction Z, here the z-axis. In particular, a rotationally symmetric envelope 6 results from the focus zones 200. Within the envelope, between 10 and 1000 focus zones can be arranged, preferably between 100 and 200 focus zones.

[0106] The symmetry of the envelope 6 is determined here, for example, in the xz-plane, as shown in Fig. 3B. In this example, the envelope 6 is the outer boundary of the focus zones 200, with all focus zones 200 lying within the volume of the envelope. It is clearly visible that the arrangement of the focus zone in the x-z-plane exhibits fourfold symmetry. This means that upon a rotation of the envelope 6 by 90°, the envelope 6 is mapped back onto itself. The maximum lateral distance A of the focus zones 200 can also be determined in the xz-plane, which can be between 100 and 500 pm.

[0107] 3C and 3D show that the envelope 6 has additional structures in the xz and yz planes. For example, the rotationally symmetric envelope along the beam propagation direction is composed of two cones 60 and a cylinder 62. The cones 60 point toward each other and are connected by a cylinder 62. Figure 4 illustrates the various steps of the separation process. Figure 4A shows how a first material modification 5, consisting of a plurality of material modifications, is introduced into a location on the workpiece 1 through the focus zones 200 of the partial laser beams 20'. The rotationally symmetric envelope 6 (for simplicity, only the yz component is shown here) comprises two cones 60 pointing toward each other with different aperture angles, as well as a cylinder 62 that connects the cone tips.

[0108] The material modifications 5 are introduced at various locations on the workpiece 1 by moving the partial laser beams 20' and the workpiece 1 relative to each other at a feed rate V. The material modifications 5 effectively perforate the workpiece 1 along the dividing line 4, as shown in Fig. 4B. The outer surface boundary of successively introduced material modifications 5 is called the material modification surface 50. The shape of the material modification surface 50 results from the cross-section of the envelope 6.

[0109] Fig. 4C further shows that when the workpiece 1 is subjected to a load, material of the workpiece 1 may be ablated from the conical parts of the envelope 6, leaving a groove there in the workpiece 1. In the cylindrical part of the envelope, however, the material of the workpiece may be retained, but provided with Type III modifications. Fig. 4C also shows a possible separation step. By heating the workpiece 1, for example with a CO2 laser beam, a thermal stress can be generated in the workpiece 1 by introducing a temperature gradient, whereby the material along the cylindrical part is separated into a useful part and a non-useful part, as shown in Fig. 4D.

[0110] However, it is also possible for the workpiece 1 to be severed across its entire surface by mechanical action. It is also possible for the workpiece 1 to be severed in a chemical bath. For example, the introduced material modifications 5 may be particularly susceptible to an etching solution, so that the etching process severes the workpiece 1 along the material modification surface 50.

[0111] The advantages of the method are shown schematically in Figure 5. It shows a top view of the workpiece 1 into which material modifications 5 are introduced along a curved parting line 4. In the present case, the envelope 6 has a sixfold symmetry. Accordingly, the envelope 6 has virtually no preferred direction, or the material modification 5 introduced thereby in the workpiece 1 has no preferred direction for crack formation. Rather, the radially symmetrical envelope 6 can also be used to traverse curved parting lines 4 without the workpiece 1 or the laser beam 20 having to rotate. This significantly simplifies material processing.

[0112] Various possible shaped edges 10, or chamfers 10 by rotationally symmetrical envelopes 6 are shown in Fig. 6. The chamfer 10 in Fig. 6A is created by a single cone. The chamfer 10 in Fig. 6B is created by a cone with an adjoining cylinder. The chamfer 10 in Fig. 6C is created by two oppositely oriented cones whose tips are connected by a cylinder. The chamfer 10 in Fig. 6D is created analogously to Fig. 6C, whereby the opening angles of the cones are different. The chamfers 10 in Figs. 6E and 6F are created by envelopes 6 that have a hyperbolic surface. The chamfer 10 in Fig. 6G is created by a sphere to which a cylinder is adjoined. The chamfer 10 in Fig. 6G is created by a sphere.

[0113] An embodiment of a laser system for performing the method is shown in Fig. 7.

[0114] The laser system comprises an optical structure 3 with beam-shaping optics 30 and focusing optics 32. The input laser beam 20 of an ultrashort pulse laser 2 is coupled into the beam-shaping optics 30. By means of the beam-shaping optics 3, the input laser beam 20 is split into a plurality of partial laser beams 20', the wavefronts of which are schematically illustrated.

[0115] To focus the partial laser beams 20', the laser system comprises a focusing optics 32 into which the partial laser beams 20' are coupled. The focusing optics 32 comprises, for example, one or more lens elements. For example, the focusing optics 32 is designed as a microscope objective or telescope.

[0116] In particular, different partial laser beams 20' impinge on the focusing optics 32 with a spatial offset and / or angular offset. By focusing the partial laser beams 20', a focus zone 200 is formed for each partial laser beam 20', each of which is arranged at different spatial positions. It is fundamentally possible for adjacent focus zones 200 to partially overlap.

[0117] The intensity profile in the formed focus zones 200 is essentially defined by the input laser beam 108. For example, the input laser beam 20 can have a Gaussian beam profile. In this case, focusing the input laser beam 20 would create a focus zone 200 having an intensity distribution with a Gaussian intensity profile. Alternatively, the input laser beam 20 can have a Bessel-like beam profile, so that focusing the input laser beam 20 would create a focus zone with a Bessel-like intensity profile.

[0118] For this purpose, the beam-shaping optics 32 are preferably designed as a 3D beam splitter, whereby the focus zones 200 are formed, for example, in such a way that they are identical to one another and / or that they represent copies of one another. In particular, the respective distance between the focus zones 200 can be adjusted using the beam-shaping optics 32.

[0119] Each of the formed focus zones is assigned a specific local position xO, yO, zO, at which a respective focus zone 200 of the workpiece 1 is arranged. In particular, the local position of a focus zone 200 is understood to mean the position of its spatial center and / or center of gravity. Furthermore, each of the formed focus zones 200 is assigned a specific intensity I. For example, several or all focus zones 200 can have the same intensity I. However, it is also possible for several of the formed focus zones 200 to have different intensities I.

[0120] However, it is also possible for the beam-shaping optics 32 to impose a specific beam shape on each partial laser beam 20'. This allows, for example, a quasi-non-diffracting and / or Bessel-shaped laser beam to be generated from a Gaussian input laser beam. For this purpose, the beam-shaping optics can comprise, for example, a diffractive optical element, a liquid crystal, or a geometric phase hologram.

[0121] It is also possible for the beam-shaping optics 32 to assign a specific polarization to each partial laser beam 20'. This allows, in particular, the partial laser beams 20' to be formed with different polarization states. A specific polarization state can thus be assigned to each of the focus zones 200. In particular, by splitting the polarization beams using the beam-shaping optics 30, the focus zones 200 can be arranged and formed such that adjacent focus zones 200 each have different polarization states.

[0122] For laser processing of the workpiece 1, the focus zones 200 are introduced into the workpiece 1 and moved relative to the workpiece 1 with a feed device 7 with a feed along a parting line 4.

[0123] Fig. 8A shows a feed device 6 configured to translate the optical assembly 3 and the workpiece 1 along three spatial axes. The workpiece 1 is arranged on a support surface of the feed device 6, wherein the support surface preferably neither reflects nor absorbs the laser energy that the workpiece 1 does not absorb, nor strongly scatters it back into the workpiece 1.

[0124] In particular, the laser beam 20 can be coupled into the optical structure 3 by a beam guiding device. The beam guiding device can be a free-space path with a lens and mirror system. However, the beam guiding device can also be a hollow-core fiber with coupling and decoupling optics, as shown in Fig. 8B.

[0125] The feed device 7 can move the workpiece 1 under the partial laser beams 20' at a feed rate V, so that the partial laser beams 20' introduce the material modifications 5 along the desired separation line 4. In particular, in the illustrated Fig. 8A, B, the feed device 6 comprises a first axis system 60 with which the workpiece 1 can be moved along the XYZ axes. In particular, the feed device 6 can also comprise a workpiece holder 62 configured to hold the workpiece 1.

[0126] Where applicable, all individual features presented in the embodiments may be combined and / or exchanged without departing from the scope of the invention.

[0127] List of reference symbols

[0128] 1 workpiece

[0129] 10 shaped edge

[0130] 2 ultrashort pulse lasers 20 laser beam

[0131] 20' partial laser beam

[0132] 200 focus zone

[0133] 3 optical structure

[0134] 30 Beam shaping optics 32 Focusing optics

[0135] 4 dividing line

[0136] 5 Material modification

[0137] 6 Envelopes

[0138] 7 Feed device Z Beam propagation direction

[0139] D Thickness of the workpiece

[0140] A maximum lateral distance

Claims

Claims 1 . Method for separating a transparent workpiece (1) by means of ultrashort laser pulses of a laser beam (20) of an ultrashort pulse laser (2), wherein the laser beam (20) is split into a plurality of partial laser beams (20') by beam-shaping optics (30), wherein each partial laser beam (20') is focused into and / or onto the workpiece (1) by focusing optics (32), wherein each partial laser beam (20') forms its own focus zone (200), wherein the laser pulses act on the workpiece (1) in the focus zones (200), whereby material modifications (5) are introduced into and / or onto the workpiece (1), wherein the material modifications (5) are introduced into the workpiece (1) along a separating line (4), preferably a curved separating line (4), wherein the workpiece (1) is separated along the material modifications (5) in a separating step, whereby a shaped edge (10) is characterized bythat the focus zones (200) of the partial laser beams (20') are arranged in and / or on an envelope (6) that is rotationally symmetrical to the beam propagation direction (Z), wherein the envelope (6) extends at least partially in the thickness direction into the workpiece (1).

2. Method according to claim 1, characterized in that the rotationally symmetrical envelope (6) is composed of at least one cone.

3. Method according to one of the preceding claims, characterized in that the rotationally symmetrical envelope (6) is composed of at least one cone and one cylinder which extends from the tip of the cone.

4. Method according to one of the preceding claims, characterized in that the rotationally symmetrical envelope (6) is composed of two cones whose tips are connected to a cylinder.

5. Method according to claim 4, characterized in that the cones have different opening angles.

6. Method according to one of the preceding claims, characterized in that the rotationally symmetrical envelope is composed of at least one ellipsoid.

7. Method according to one of the preceding claims, characterized in that the rotationally symmetrical envelope (6) is composed of at least one ellipsoid and at least one cylinder, wherein the cylinder extends from the ellipsoid along the beam propagation direction (Z).

8. Method according to one of the preceding claims, characterized in that the maximum lateral distance (A) of the focus zones is between 100pm and 500pm, preferably between 200pm and 300pm.

9. Method according to one of the preceding claims, characterized in that between 10 and 1000 focus zones are arranged on and / or within the envelope, preferably between 100 and 200 focus zones are arranged.

10. Method according to one of the preceding claims, characterized in that the partial laser beams (20') are introduced into the workpiece (1) simultaneously in the focus zones (200).

11. Method according to one of the preceding claims, characterized in that a specific beam shape is impressed on each partial laser beam (20') by the beam-shaping optics (30) and / or that a specific polarization is impressed on each partial laser beam (20') by the beam-shaping optics (30).

12. Method according to one of the preceding claims, characterized in that the laser beam (20) is a non-diffracting laser beam and / or a Gaussian laser beam and / or the partial laser beams (20') are non-diffracting partial laser beams and / or Gaussian laser beams.

13. Method according to one of the preceding claims, characterized in that the separating step comprises a mechanical separation and / or an etching process and / or a thermal treatment.

14. Method according to one of the preceding claims, characterized in that the envelope (6) extends through the entire thickness of the workpiece.

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