Method for segmenting a workpiece

Abstract

The invention relates to a method for separating a workpiece (1), wherein material of the workpiece (1) is removed along a separation line (3) by means of a laser beam (20) comprising ultrashort laser pulses of an ultrashort pulse laser (50), wherein the material of the workpiece (1) is transparent to the wavelength of the laser beam (20) and has a refractive index of between 2.0 and 3.5, more preferably between 2.5 and 3.5, and the workpiece (1) is separated along a kerf (4) resulting from the removal of material in a separation step.

Description

Technical Field

[0001] The present invention relates to a method for dividing a workpiece by means of a laser beam, said laser beam comprising ultrashort laser pulses from an ultrashort pulse laser. Background Technology

[0002] In recent years, the development of lasers with very short pulse lengths, especially sub-nanosecond pulse lengths, and high average power, especially in the kilowatt range, has given rise to a new type of materials processing. Short pulse lengths and high pulse peak power or high pulse energy of several hundred µJ enable nonlinear absorption of pulse energy in the workpiece material, making it possible to process essentially transparent or substantially transparent materials, regardless of the laser wavelength used.

[0003] A particular application of this type of laser irradiation is the segmentation and processing of workpieces. Here, the laser beam is preferably introduced into the material perpendicularly, as this minimizes reflection losses on the material surface in principle. However, segmenting high-refractive-index materials remains an unsolved problem, especially due to the significant distortion of the laser beam caused by the large difference in refractive index between the surrounding medium and the workpiece material, making it impossible to target energy deposition into the material effectively. Summary of the Invention

[0004] Based on known prior art, the objective of this invention is to provide an improved method for dividing workpieces.

[0005] This task is accomplished through a method for dividing the workpiece. The specifications and accompanying drawings present advantageous improvements.

[0006] Correspondingly, a method for dividing a workpiece is proposed, wherein material of the workpiece is removed along a dividing line by means of a laser beam (which includes ultrashort laser pulses from an ultrashort pulse laser), wherein the material of the workpiece is transparent to the wavelength of the laser beam and has a refractive index between 2.0 and 3.5, preferably between 2.5 and 3.5, and the workpiece is divided along a groove created by the removal of material in the dividing step.

[0007] An ultrashort pulse laser provides an ultrashort laser pulse. Here, "ultrashort" means, for example, that the pulse length is between 500 picoseconds and 10 femtoseconds, and more particularly between 10 picoseconds and 100 femtoseconds. Here, the ultrashort laser pulse moves along the beam propagation direction of the laser beam formed therefrom.

[0008] Here, transparent material is understood to be a material that is substantially transparent to the wavelength of the laser beam of an ultrashort pulse laser. The terms "material" and "transparent material" are used interchangeably, and therefore, the material referred to herein is always understood to be a material that is transparent to the laser beam of an ultrashort pulse laser.

[0009] When a laser beam falls at a certain angle from the surrounding medium (such as air) onto the surface of a transparent material, the laser beam is refracted by the angle of refraction. Here, the angle of incidence and the angle of refraction are related to each other by Snell's law of refraction through the refractive indices of the workpiece material and the surrounding medium.

[0010] Further properties of laser beams reflected and refracted on a surface are given by Fresnel's equations. Fresnel's equations describe the polarization-dependent transmission and reflection behavior of a laser beam on a surface. In particular, the law of reflection is considered, which states that when a laser beam is incident perpendicularly on the surface of a material, the following applies to reflectivity: .

[0011] For example, when the refractive index of the material is n = 2.5 and the refractive index of air is n = 1, 18% of the incident laser intensity is reflected at the surface of the material. Correspondingly, the material of the workpiece can be transparent to the wavelength of the laser, yet the laser beam can still be weakly coupled into the material due to so-called Fresnel reflection and correspondingly weakly transmitted through the material.

[0012] When an ultrashort laser pulse is focused onto the material of a workpiece, the intensity in the focused volume can induce nonlinear absorption through processes such as multiphoton absorption and / or electron avalanche ionization. This nonlinear absorption leads to the generation of electron-ion plasma, which, upon cooling, can cause permanent structural changes in the workpiece material.

[0013] Material modification resulting from the introduction of ultrashort laser pulses into transparent materials can be categorized into three distinct levels, as described in K. Itoh et al., “Ultrafast Processes for Bulk Modification of Transparent Materials,” MRS Bulletin, Vol. 31, p. 620 (2006): Type I involves isotropic refractive index changes; Type II involves birefringence; and Type III involves so-called voids or cavities generated by micro-explosions. The resulting material modification depends on laser parameters (such as pulse duration, wavelength, pulse energy, and repetition rate), material properties (especially electronic structure and coefficient of thermal expansion), and the numerical aperture (NA) of the focused area.

[0014] For example, high laser pulse energies can be used to generate type III modified cavities. Here, the formation of the cavity is attributed to the explosive expansion of highly excited vaporized material from the focused volume to the surrounding material. This process is also known as a micro-explosion. Because this expansion occurs within the mass of the material, the micro-explosion leaves a lower-density or hollow core (cavity) surrounded by a dense material shell. Due to the compression at the micro-explosion impact front, stresses are generated in the transparent material, which can lead to spontaneous or accelerated crack formation.

[0015] In particular, in the case of micro-explosions near the surface, the material will deflagrate, effectively removing material near the surface. Therefore, the formation of cavities inside the material and the deflagration on the material surface have the same cause. In particular, "near the surface" can refer to the upper surface (here, "top side") and lower surface (here, "bottom side") of the workpiece relative to the beam propagation direction.

[0016] At high laser repetition rates, materials cannot be completely cooled between pulses, thus the heat within the material increases from one pulse to another. For example, the laser repetition frequency can exceed the reciprocal of the material's thermal diffusion time, allowing heat to accumulate in the focal region through continuous absorption of laser energy until the material's melting temperature is reached. As the heat is transferred to the area surrounding the focal region, it can also melt and evaporate an area larger than the focal region, thereby achieving material removal.

[0017] Due to the material's high refractive index, its surface is subjected to exceptionally high stress, leading to material removal.

[0018] The aforementioned effect is used to remove material along the dividing line. The dividing line describes the impact line of the laser beam on the workpiece surface. For example, through feeding, the laser beam and the workpiece are displaced relative to each other at the feed rate, thus resulting in different impact points of the laser pulses on the workpiece surface over time. The ability to displace relative to each other here means that the laser beam can translate relative to the fixed workpiece, and the workpiece can also displace relative to the laser beam. It is also possible for movement to occur between the workpiece and the laser beam. During this movement between the workpiece and the laser beam, the ultrashort pulse laser emits laser pulses at its repetition frequency into the material of the workpiece.

[0019] Therefore, the ultrashort laser pulse generates material removal along the dividing line, making the grooves on the material surface the sum of the material removal.

[0020] As a result, the material on the surface is specifically damaged or weakened, creating the target fracture point of the workpiece along the groove. With the help of the subsequent cutting step, the workpiece can be cut along the cutting line with particular ease.

[0021] The partitioning step can include mechanical partitioning and / or etching processes and / or thermal shock and / or self-partitioning steps.

[0022] Thermal shock can be achieved, for example, by heating the material or the dividing line. The dividing line can be locally heated, for example, by means of a continuous-wave CO2 laser, causing the material in the introduced weakened region to expand to a different degree compared to untreated or unmodified material. However, thermal shock can also be achieved through a hot air stream, or by baking on a hot plate or heating the material in a furnace. In particular, a temperature gradient can be applied during the dividing process. As a result, cracks promoted by material weakening undergo crack growth, thus forming a continuous and unobstructed dividing surface through which parts of the workpiece are separated from each other.

[0023] Mechanical separation can be achieved by applying tensile or bending stress, for example, by applying a mechanical load to the portion of a workpiece separated by a dividing line. Tensile stress can be applied, for example, when opposing forces (forces pointing away from the dividing line) act at the respective force joints on the portion of the workpiece separated by the dividing line in the plane of the material. Bending stress can be generated if these forces are not parallel or are antiparallel to each other. Once the tensile or bending stress exceeds the bonding force of the material, the workpiece is separated. Mechanical changes can also be achieved, in particular, by pulsed action on the portion to be separated. For example, lattice vibrations can be generated in the material by impact. Tensile and compressive stresses can also be generated due to the deflection of lattice atoms, which can trigger crack formation. This method can also be generally referred to as the "scribe and break" method, in which the material is typically first scratched and then selectively broken along a defined dividing line.

[0024] Materials can also be divided by etching with a wet chemical solution, wherein the etching process preferably begins at targeted areas of material weakness. By preferably etching the weakened portions of the workpiece, the workpiece is divided along a dividing line.

[0025] In particular, so-called self-splitting can be performed by selectively guiding cracks, which is achieved through the orientation of material removal within the material. Here, the formation of cracks from material removal to adjacent material removal enables the complete separation of the two parts of the workpiece without having to perform another splitting step.

[0026] The advantage of this is that it allows for the selection of an ideal segmentation method for the corresponding material of the workpiece, resulting in high-quality segmentation edges.

[0027] When passing along the dividing line once, a groove can be formed on the top and / or bottom side of the workpiece by removing material.

[0028] This makes it possible to divide the workpiece particularly easily using the segmentation step.

[0029] A laser beam can be introduced into the material such that the top side is located within the focal region of the laser beam. Therefore, it is preferable to introduce the slot into the top side of the material. Alternatively, the laser beam can also be introduced into the material such that the bottom side is located within the focal region of the laser beam. Therefore, it is preferable to introduce the slot into the bottom side of the material.

[0030] However, it is also possible to introduce slots on both the top and bottom sides simultaneously, so that the laser beam only needs to pass over the workpiece once.

[0031] The refractive index difference between the environmental medium and the workpiece material can be greater than 1.5.

[0032] As mentioned above, according to Fresnel's formula, the refraction and reflection of the laser beam depend on the refractive indices of the surrounding medium and the workpiece material. However, the surrounding medium here does not have to be air, but can also be other materials, such as glass. The large difference in refractive index ensures that the refractive properties of the laser beam achieve near-surface material removal as it transitions from the surrounding medium to the workpiece material.

[0033] The material may contain silicon or silicon, or the material may be silicon carbide (SiC) or contain silicon carbide.

[0034] Silicon carbide is transparent in the visible and infrared spectral ranges, yet it has a refractive index of n > 2.5. This results in large reflection losses, despite the material being transparent to the wavelength of laser light.

[0035] The workpiece may be, for example, a silicon wafer that should be separated into chips.

[0036] The workpiece can have a thickness between 100 µm and 2000 µm, preferably 700 µm. For example, the workpiece can have a material thickness of 500 µm. Furthermore, the workpiece can comprise different material layers, i.e., have a layer system. Each material layer can be transparent to the wavelength of the laser. Thus, this method can also be used to cleave processed and treated wafer systems.

[0037] Material removal can consist of surface material removal and localized material depth removal, wherein the localized material depth removal can have a width greater than 10 µm perpendicular to the dividing line and a depth greater than 1 µm.

[0038] This allows the material stress to gradually shift towards the depth direction of the material, and thus the segmentation process can produce a smoother segmented surface.

[0039] Localized material depth removal, for example, has a diameter of a few micrometers, approximately between 1 µm and 20 µm, and a removal depth between 0.1 µm and 5 µm. Surface material removal, on the other hand, has a diameter of, for example, 5 mm to 10 mm and a removal depth of 0 µm to 10 µm. Thus, localized material depth removal is limited to small diameters with larger material depths, while surface material removal is limited to large diameters and small material depths.

[0040] If the material modification is introduced overlapping along the dividing line, the diameter can be measured perpendicular to the dividing line. In the case of separate material modifications, the diameter can also be the maximum diameter of material removed.

[0041] The laser beam can be a non-diffractive laser beam and has a focused region that is elongated along the beam propagation direction, preferably having an elongated focused region with a variable length along the beam propagation direction.

[0042] Non-diffractive beams and / or Bessel beams are particularly understood as beams in which there is no propagation difference in the transverse intensity distribution. In the case of non-diffractive beams and / or Bessel beams, the transverse intensity distribution is substantially constant, particularly along the longitudinal direction and / or propagation direction of the beam.

[0043] The transverse intensity distribution is understood as the intensity distribution located in a plane oriented perpendicular to the longitudinal direction and / or propagation direction of the beam. Furthermore, the focal region is always understood as the portion of the laser beam's intensity distribution that exceeds the material's modification threshold. The term "focal region" here indicates the targeted provision of this portion of the intensity distribution, and the achievement of an intensity increase in the form of an intensity distribution through focusing.

[0044] For the definition and properties of non-diffractive beams, please refer to the book *Structured Light Fields: Applications in Optical Trapping, Manipulation and Organisation*, by M. Wördemann, Springer Science & Business Media (2012), ISBN 978-3-642-29322-1. It is explicitly and fully cited here.

[0045] Accordingly, non-diffractive laser beams have the advantage of having a focused region that is elongated along the beam propagation direction, and the lateral dimension of the focused region is significantly larger than that of the beam. This, in particular, enables the removal of material elongated along the beam propagation direction, ensuring ease of workpiece segmentation.

[0046] In particular, elliptical non-diffractive beams with radially asymmetric lateral focusing regions can be generated using non-diffractive beams. An elliptical quasi-non-diffractive beam, for example, has a principal maximum value coinciding with the center of the beam. The center of the beam is given here at the point where it intersects the principal axis of the ellipse. Elliptical quasi-non-diffractive beams can also be generated, in particular, by the superposition of multiple intensity maximum values, where in this case only the envelope of the maximum intensities involved is elliptical. Each maximum intensity need not necessarily have an elliptical intensity profile.

[0047] The diameter of the lateral focusing area can be less than 5 µm, and / or the length of the longitudinal focusing area can be greater than 50 µm, and / or the length of the longitudinal focusing area can be less than 1.2 times the material thickness.

[0048] Due to the small diameter, it is possible to produce exceptionally clean slit surfaces using the slitting process, as material removal and therefore targeted material weakening can be precisely oriented along the slitting line. The large longitudinal focus area allows for particularly deep material removal, enabling material weakening along the slitting line and precise pre-determining of the subsequent slitting surface. If the longitudinal focus area is greater than 1.2 times the material thickness, it is also particularly easy to introduce grooves into the top and bottom sides of the workpiece.

[0049] The focused area, elongated along the beam propagation direction, can penetrate the top side and / or the bottom side and / or both sides of the workpiece.

[0050] This allows for targeted weakening of the material along the dividing line, enabling simple segmentation through the segmentation process.

[0051] By extending the focal zone to penetrate only the top side of the workpiece, a groove can preferably be formed on the top side. By extending the focal zone to penetrate only the bottom side of the workpiece, a groove can preferably be formed on the bottom side. When the length of the extended focal zone is longer than the material thickness, grooves can be formed on both the top and bottom sides, especially by extending the focal zone.

[0052] Non-diffractive beams can be generated using axial conical mirrors, diffractive optical elements, or freeform optical surfaces that reflect or refract light.

[0053] Beamforming optics can be designed, for example, as diffractive optical elements (DOEs), freeform surfaces, axial cones, or microaxial cones, or combinations of these components or functions. When a beamforming optics forms a non-diffractive laser beam in front of a processing optics using a laser beam, the depth of the focal region introduced into the material can be determined by focusing the processing optics. However, beamforming optics can also be designed to generate a non-diffractive laser beam only when imaged using the processing optics.

[0054] A diffractive optical element is configured to influence an incident laser beam in one or more properties across two spatial dimensions. A diffractive optical element is a fixed component capable of producing a specific non-diffractive laser beam from an incident laser beam. Typically, a diffractive optical element is a specially shaped diffraction grating in which the incident laser beam is diffracted into a desired beam shape.

[0055] An axial cone is a conically ground optical element that transforms an incident Gaussian laser beam into a non-diffractive laser beam as it passes through it. The axial cone particularly possesses a cone angle α', calculated from the beam incident surface and the outer surface of the cone. Consequently, the edge of the Gaussian laser beam is refracted to a focal point different from that closer to the axis. This results in a particularly elongated focusing region along the beam propagation direction.

[0056] Non-diffraction beams can be transmitted to the workpiece through a telescope.

[0057] Here, a telescope is an optical structure or fabricated optics device capable of imaging a laser beam, or, together with beamforming optics, providing a non-diffractive beam in or on a material. Such a telescope is particularly capable of magnifying and / or reducing effects.

[0058] Some of the optical functions of a telescope can be integrated into beamforming optics. For example, an axial cone can have a spherically ground rear side, allowing the axial cone to integrate beamforming functionality with lensing effects.

[0059] Enlarging and / or reducing the intensity distribution of a laser beam or its transverse intensity allows the laser beam intensity to be distributed over large or small focal areas. By adapting the intensity to large or small areas, it is possible to select between type I, type II, and type III modifications, especially through enlargement and / or reduction.

[0060] In particular, it can also achieve magnified or reduced material removal by magnifying or reducing the radially asymmetrical transverse intensity distribution. Furthermore, the optical system can be magnified or reduced to adapt to given processing conditions, allowing for more flexible use of the device.

[0061] The pulse duration of the ultrashort laser pulse can be between 100 fs and 100 ns, preferably between 100 fs and 10 ps, ​​and / or the average laser power can be between 1 W and 1 kW, preferably 50 W, and / or the wavelength can be between 300 nm and 1500 nm, preferably 1030 nm, and / or the laser pulse can be a single laser pulse or part of a laser pulse train, wherein the laser pulse train includes between 1 and 20 laser pulses, preferably between 1 and 4, and / or the repetition rate of the single laser pulse and / or the laser pulse train can be 100 kHz, and / or the pulse energy or pulse train energy can be between 10 µJ and 50 mJ.

[0062] This allows for the adjustment of optimal processing parameters for each type of material.

[0063] The workpiece and the laser beam can move relative to each other at a feed rate, wherein the feed rate is preferably between 0.05 m / s and 5 m / s.

[0064] Material is removed along the dividing line by moving the laser beam and the workpiece relative to each other.

[0065] This type of feed can be achieved, in particular, using axis devices. An axis device is, for example, an XYZ table that can translate along all spatial axes. However, it is also possible for the axis device to rotate around a specific axis, thereby producing exceptionally high-quality circular or arc-shaped dividing lines.

[0066] Laser pulses or laser pulse trains can be introduced into materials at a constant spatial spacing.

[0067] In cases of curved or angular feed trajectories, locally reducing the feed rate can be beneficial. However, with a constant repetition frequency of the laser, this can lead to overlapping of adjacent material modifications or undesirable heating or melting of the material. For this reason, the control electronics can adjust the pulse emission based on the relative position of the laser beam and the workpiece.

[0068] For example, the feed device can have a position-resolved encoder that measures the position of the feed device and the laser beam. Based on the position information, the pulse emission of the laser pulse in the ultrashort pulse laser can be triggered by a corresponding triggering system of the regulating electronics.

[0069] In particular, computer systems can be used to implement pulse triggering. For example, the position of laser pulse emission can be determined before processing the material for the corresponding dividing line, thereby ensuring the optimal distribution of the laser pulse along the dividing line.

[0070] This ensures that the spacing of the material modification remains constant even when the feed rate changes. Furthermore, it enables the production of uniformly segmented surfaces with high surface quality. Attached Figure Description

[0071] Other preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings. As shown herein: Figure 1A , Figure 1B A schematic diagram of the method; Figure 2A , Figure 2B , Figure 2C A diagram illustrating the segmentation steps; Figure 3A , Figure 3B , Figure 3C Another schematic diagram of the method; Figure 4A , Figure 4B Micrographs of the grooved material; Figure 5 Another photomicrograph of the grooved material; Figure 6 Micrographs of layered systems segmented using this method; Figure 7A , Figure 7B Schematic diagram of a non-diffractive beam; Figure 8 A schematic diagram of the apparatus for performing the method; and Figure 9A , Figure 9B Another schematic diagram of the device. Detailed Implementation

[0072] Preferred embodiments are described below with the aid of the accompanying drawings. Here, identical, similar, or functionally equivalent elements in different drawings are given the same reference numerals, and repeated descriptions of these elements are omitted in part to avoid redundancy.

[0073] exist Figure 1A The diagram schematically shows a workpiece 1 made of a material with a high refractive index NM. A laser beam 2 is directed onto the workpiece 1, and this laser beam is focused such that a sub-beam 20 of the laser beam 2 falls onto the top side 10 of the workpiece 1 at an incident angle α. Here, the laser beam 2 falls onto the surface 10 of the workpiece 1, for example, from air having a refractive index NL = 1.

[0074] Workpiece 1 is transparent, especially to the wavelength of laser beam 2. Therefore, according to Fresnel's formula, laser beam 2 or its sub-laser beam 20 is refracted according to the refractive indices NM, NL and the incident angle α.

[0075] For example, the material of workpiece 1 is silicon carbide with a refractive index NM = 2.5. Here, the refractive index difference between the material of workpiece 1 and the surrounding medium is particularly greater than 1.5, so the refractive effect is particularly large. The material of workpiece 1 can have a material thickness D of approximately D = 700 µm, which is between D = 100 µm and D = 2000 µm.

[0076] For example, due to the tapered sub-laser beam 20, a non-diffractive laser beam 2 is formed in the material of the workpiece 1. This non-diffractive laser beam has a focused region 22 that is elongated along the beam propagation direction. The elongated focused region 22 penetrates the top side 10 and bottom side 12 of the material of the workpiece 1. In the elongated focused region 22, the material of the workpiece 1 is evaporated by a nonlinear absorption effect, thus resulting in material removal at the top side 10 and bottom side 12.

[0077] Furthermore, it is possible to achieve surface modification, such as deformation or material removal, on the top side 10 due to nonlinear absorption effects, so that the ideal non-diffractive beam 2 is absent, at least in the region near the surface. However, after penetrating the region near the surface, a non-diffractive laser beam 2 is formed, for example, due to a self-healing effect. In the specification, the laser beam 2 is still described as a non-diffractive beam 2, taking into account such surface effects.

[0078] exist Figure 1B As shown, material is removed along the dividing line 3. For this purpose, the workpiece 1 and the laser beam 20 move relative to each other with a feed V between V = 0.05 m / s and V = 5 m / s. By selectively weakening the material of the workpiece 1 along the dividing line 3, a target fracture point is formed along the dividing line 3, allowing the workpiece 1 to be divided along this target fracture point in a subsequent dividing step.

[0079] The pulse duration of the ultrashort laser pulse is particularly between 100 fs and 100 ns, preferably between 100 fs and 10 ps, ​​and / or the average laser power is between 1 W and 1 kW, preferably 50 W, and / or the wavelength is between 300 nm and 1500 nm, preferably 1030 nm, and / or the laser pulse can be a single laser pulse or part of a laser pulse train, wherein the laser pulse train includes between 1 and 20 laser pulses, preferably between 1 and 4, and / or the repetition rate of the single laser pulse and / or the laser pulse train can be 100 kHz, and / or the pulse energy or pulse train energy can be between 10 µJ and 5 mJ.

[0080] Since the repetition rate R is, for example, R = 100 kHz, the spacing between the impact positions of the laser pulses can be estimated from 0.5 µm to 50 µm together with the feed rate V.

[0081] Here, the laser beam 20 can have a focusing region 22, the diameter of which is less than 5µm perpendicular to the beam propagation direction. Thus, material removal by the laser beam 20 can be precisely oriented on the dividing line 3. On one hand, different laser pulses can be superimposed or spatially overlapped, thereby accumulating heat in the material of the workpiece 1, thus weakening the material of the workpiece 1. However, on the other hand, it is also possible to separate the laser pulses so that perforation of the material of the workpiece 1 is only performed on the surface along the dividing line 3.

[0082] exist Figure 1A As also shown, the length of the elongated focal region 22 of the laser beam 20 in the beam propagation direction is greater than the material thickness D. In particular, the length of the focal region 22 of the laser beam is specified as 800 µm, making the focal region greater than 50 µm, but less than 1.2 times the material thickness D. This enables the laser beam 20 to create grooves on the top and bottom sides of the material of the workpiece 1 in conjunction with the feed V. This, in particular, ensures that the elongated focal region 22 penetrates the top side 10 and the bottom side 12.

[0083] Figure 2 illustrates a feasible segmentation step, which involves applying a mechanical load to the material of workpiece 1. Figure 2A As specifically shown, slot 4 passes through Figure 1A A non-diffractive laser beam 20 is introduced on the top side 10 and the bottom side 12.

[0084] For example, bending stress can be applied as a mechanical force to the parts 100 and 102 of workpiece 1 that are to be separated. Bending stress can cause the material of workpiece 1 on the top side 10 to be compressed towards the notch 4, while the material of workpiece 1 on the bottom side 12 is stretched away from the notch. This creates a stress gradient from the bottom side 12 towards the top side 10. Once the stress along the stress gradient exceeds the bonding force of the material of workpiece 1, the material of workpiece 1 relaxes to form a crack, which extends, for example, from the notch 4 in the top side 12 of the material of workpiece 1 to the notch 4 in the bottom side 12. Here, in Figure 2B The image shows this state of the material of workpiece 1. Figure 2C The subsequent state is shown, in which parts 100 and 102 of the workpiece exist separately and independently. Therefore, workpiece 1 is divided along dividing line 3.

[0085] Such a segmentation step can also be achieved, in particular, by applying a thermal gradient, for example, by irradiating the groove 4 with a CO2 continuous-wave laser. Alternatively, it is also possible to etch the material of workpiece 1 along the groove 4 in a chemical bath, wherein targeted material weakening allows for selective etching of the material of workpiece 1. Another possibility lies in achieving a self-segmentation process of workpiece 1 by targeted material weakening with type III modification, causing the material stress to exceed the bonding force. However, in any case, the material weakening along the segmentation line 3 predetermines the direction of the segmentation process.

[0086] exist Figure 3A The following method is illustrated, wherein the focal region 22 of the laser beam 20 is shorter than the material thickness D, and a notch 4 is generated only in the top side 10 of the material of the workpiece 1. However, the notch 4 in the top side 10 of the workpiece is sufficient to cause targeted material weakening, making it possible to divide the workpiece 1 along the dividing line 3 using a dividing step. This is exemplarily illustrated in... Figure 3B , Figure 3C As shown, parts 100 and 102 of workpiece 1 are separated here by a splitting step.

[0087] exist Figure 4A A micrograph of the top side 10 of workpiece 1 is shown, to which a non-diffractive laser beam 20 was applied. Figure 4B The diagram shows the relevant height profile along the y-direction. It is clearly visible that the slot 4 consists of localized material depth removal 40 and surface material removal 42. Here, the surface material removal 42 can be part of the aforementioned surface modification. The corresponding removal depth is calculated from the initial surface 10 of the workpiece 1. Therefore, in the current case, a material depth removal 40 of 2.5 µm is obtained, while the surface material removal 42 has a removal depth of 1.5 µm. Furthermore, the surface material removal 42 has a diameter or cross-section of 80 µm, while the material depth removal, measured in cross-section, is only 20 µm.

[0088] When the laser beam 20 irradiates the top side 10 of the material of the workpiece 1, material depth removal 40 and material surface removal 42 are achieved. Here, material surface removal 42 is first achieved over the entire width of the laser beam 20. However, the material surface removal 42 and the edges generated at the removal edges also act as shielding due to the high refractive index of the material. As a result, the formation of the non-diffractive laser beam shifts to a deeper material layer, where an elongated focusing region 22 is formed and thus material depth removal 40 is achieved.

[0089] Furthermore, the shape of the slot 4 can also reflect the intensity distribution of the laser beam 20 or the shape of the focusing area 22. By forming the slot 4 based on a nonlinear absorption effect (as described above), the central laser beam portion can form the slot 4 particularly effectively, while the sub-laser beams near the edges cannot achieve this.

[0090] In addition, Figure 4A , Figure 4B As shown, the groove is continuous on the top side 10 of the material. Correspondingly, in the current case, the feed rate or repetition rate of the laser is high enough that adjacent laser pulses overlap and thus create continuous target fracture points on the top side 10 of the workpiece 1. In particular, the groove 4 can also be generated in a single method step.

[0091] exist Figure 5 The diagram illustrates perforation of the material of workpiece 1 along dividing line 3. Here, laser pulses are introduced into the workpiece material at 50 µm intervals. The laser pulse intervals can be determined specifically from the laser repetition frequency R and feed rate V. The surface material removal has a concentric diffraction ring shape, where the thickness of the material removal increases towards the center. In this region, surface material removal 42 transitions to localized depth material removal 40.

[0092] Figure 6 As shown, workpiece 1 can also comprise a layer system composed of different materials 1A-1D. In particular, a removal threshold can be achieved in the transition region between layers 1A-1D using a non-diffractive laser beam 20, the focal region 22 of which is longer than the total material thickness D, i.e., the sum of all material thicknesses of workpiece 1. Here, the removal threshold is an intensity threshold and can be increased or at least changed due to chemical interface conditions, above which material of workpiece 1 is removed. Each material layer can, in particular, have a refractive index between 2.0 and 3.5.

[0093] exist Figure 7A The image shows the transverse intensity distribution or focusing region 22 of the non-diffractive laser beam 20. The non-diffractive laser beam 20 is a so-called Bessel-Gaussian beam, where the transverse intensity distribution is radially symmetrical in the xy-plane; therefore, the intensity of the non-diffractive laser beam 20 depends only on the radial spacing relative to the optical axis. In particular, the diameter of the transverse intensity distribution is less than 5 µm. Figure 7B The image shows the longitudinal beam cross-section, i.e., the longitudinal intensity distribution. The longitudinal intensity distribution has a high-intensity, elongated region of approximately 3 mm in size. Consequently, the longitudinal extension of the focusing region 22 is significantly greater than its lateral extension.

[0094] exist Figure 8An embodiment of the apparatus 5 for performing the method is shown. Here, the laser pulse is provided by an ultrashort pulse laser 50 and deflected by a beamforming optics 52. The laser beam 20 is deflected to the material 1 by the beamforming optics 52 via, for example, a telescope system 54 or other types of processing optics.

[0095] In the illustrated example, the beamforming optics 52 is an axial conical lens to shape the incident laser beam 20 into a non-diffractive laser beam 20. However, the axial conical lens can also be replaced by other elements to produce a non-diffractive laser beam. The axial conical lens produces a tapered, convergent laser beam 20 from the preferably collimated input beam 20. Here, the beamforming optics 52 can also cause the incident laser beam 20 to form a radially asymmetric intensity distribution or focal region 22. Finally, the laser beam 20 can be imaged into material 1 by a telescope optics 54, which consists of two lenses 540, 542, wherein the imaging can be magnified or reduced. However, it is also possible to integrate a portion of the telescope optics 54, particularly the first lens 540, into the beamforming optics 52.

[0096] exist Figure 9A The image shows a feed device 6 configured to translate the processing optics 54 and the material 1 along three spatial axes XYZ. The laser beam 20 of the ultrashort pulse laser 50 is deflected onto the material 1 by the processing optics 54. Here, the material 1 is arranged on the placement surface of the feed device 6, wherein the placement surface preferably does not reflect, absorb, or strongly scatter laser energy that is not absorbed by the material back to the material 1.

[0097] The laser beam 20 can be coupled into the processing optics 54 via a beam guide 56. Here, the beam guide 56 can be a free-space path with a lens and mirror system, such as... Figure 9A As shown. However, the beam guiding device 56 can also be a hollow fiber with coupling-in and coupling-out optics, such as... Figure 9B As shown.

[0098] exist Figure 9A In the current embodiment, the laser beam 20 is deflected toward the material 1 by a mirror structure and introduced into the material 1 by processing optics 54. In the material 1, the laser beam 20 causes material removal. The processing optics 54 can be moved and adjusted relative to the material by means of the feed device 6, such that, for example, a preferred direction or axis of symmetry of the lateral intensity distribution of the laser beam 20 can be adapted to the feed trajectory and therefore the dividing line 4.

[0099] Here, the feeding device 6 enables the material 1 to move with a feed V under the laser beam 20, so that the laser beam 20 grooves the workpiece 1 along the desired dividing line 3. In the illustrated... Figure 9A In particular, the feeding device 6 includes a first axis system 60 by means of which the material 1 can be moved along the XYZ axes and rotated when necessary. The feeding device 6 may also have a workpiece support 62 configured to hold the material 1.

[0100] The feed device 6 can also be connected to a regulating electronics 64, which translates user commands from the device's user into control commands for the feed device 6. Predefined cutting patterns can be stored in the memory of the regulating electronics 64, and the process can be automatically controlled by the regulating electronics 64.

[0101] The regulating electronics 64 can also be connected to the ultrashort pulse laser 50. Here, the regulating electronics 64 can request or trigger the output of laser pulses or laser pulse sequences. The regulating electronics 64 can also be connected to other mentioned components, and thus coordinate material processing.

[0102] Therefore, position-controlled pulse triggering can be achieved, for example, by reading the shaft encoder 600 of the feed device 6, and the shaft encoder signal can be interpreted as position information by the regulating electronics 64. Thus, it is possible, for example, for the regulating electronics 64 to automatically trigger the emission of a laser pulse or laser pulse sequence when the internal adder for accumulating the stroke reaches a certain value and then resets to 0. Therefore, for example, laser pulses or laser pulse sequences can be automatically emitted into material 1 at regular intervals.

[0103] By also being able to process the feed speed V and feed direction, as well as the dividing line 3, in the regulating electronics 64, automated emission of laser pulses or laser pulse sequences is possible.

[0104] Based on the measured velocity and the fundamental frequency provided by laser 2, the adjustment electronics 64 can also calculate the sequence of laser pulses to be emitted or the spacing or position of the laser pulses. This, in particular, enables the material modification 5 in material 1 to emit laser energy non-overlappingly or uniformly along the dividing line 3.

[0105] By emitting laser pulses or pulse sequences at a controlled location, the complex programming of the segmentation process is eliminated. Furthermore, the process speed can be easily and freely selected.

[0106] Where applicable, all individual features shown in the embodiments can be combined and / or interchanged with each other without departing from the scope of the invention.

[0107] List of reference numerals 1. Workpiece 10 Top side 12 Bottom side 2. Laser beam 20 sub-laser beams 3 dividing line 4 slots 40 Material Depth Removal 42 Material Surface Removal 5 devices 50 μs ultrashort pulse laser 52 Beamforming Optical Devices 54 Telescope System 56 Beam-guiding optics 6. Feeding device 60-axis system 62 Workpiece support 64. Adjusting electronic devices

Claims

1. A method for dividing a workpiece (1), wherein, Material of the workpiece (1) is removed along the dividing line (3) by means of a laser beam (20), the laser beam comprising an ultrashort laser pulse from an ultrashort pulse laser (50), wherein the material of the workpiece (1) is transparent to the wavelength of the laser beam (20) and has a refractive index between 2.0 and 3.

5. Furthermore, in the segmentation step, the workpiece (1) is segmented along the groove (4) created by the removal of the material. The laser beam (20) is a non-diffractive laser beam and has a focusing area (22) elongated in the beam propagation direction, wherein the focusing area (22) penetrates the top side (10) and bottom side (12) of the workpiece (1), such that when passing along the segmentation line (3) once, the material of the workpiece (1) removed is used to form a groove (4) on the top side (10) and bottom side (12) of the workpiece (1).

2. The method according to claim 1, characterized in that, The partitioning step includes mechanical partitioning and / or etching processes and / or thermal shock and / or self-partitioning steps.

3. The method according to claim 1 or 2, characterized in that, The length of the focusing region (22) is greater than 50 µm.

4. The method according to claim 1 or 2, characterized in that, The removal of the material from the workpiece (1) consists of surface material removal (42) and localized material depth removal (40), wherein the localized material depth removal (40) has a width greater than 10 µm perpendicular to the dividing line (3) and a depth greater than 1 µm.

5. The method according to claim 1 or 2, characterized in that, The refractive index difference between the environmental medium and the material of the workpiece (1) is greater than 1.

5.

6. The method according to claim 1 or 2, characterized in that, The material of the workpiece (1) comprises silicon, or the material of the workpiece comprises silicon carbide.

7. The method according to claim 1 or 2, characterized in that, The workpiece (1) has a thickness (D) between 100 µm and 2000 µm.

8. The method according to claim 1 or 2, characterized in that, The laser beam (20) has an elongated focusing region (22) with a variable length in the beam propagation direction.

9. The method according to claim 1 or 2, characterized in that, - The diameter of the focal region (22) is less than 5 µm, and / or - The length of the focal region (22) is less than 1.2 times the material thickness (D).

10. The method according to claim 1 or 2, characterized in that, The non-diffractive laser beam is generated by an axial conical mirror, a diffractive optical element, or a reflective or refracting freeform optical surface.

11. The method according to claim 1 or 2, characterized in that, The non-diffractive laser beam is transmitted to the workpiece (1) through a telescope (54).

12. The method according to claim 1 or 2, characterized in that, - The pulse duration of the ultrashort laser pulse is between 100 fs and 100 ns, and / or - Average laser power is between 1 W and 1 kW. - Wavelengths between 300 nm and 1500 nm, and / or - A laser pulse is a single laser pulse or part of a laser pulse train, wherein a laser pulse train comprises between 1 and 20 laser pulses, and / or - The repetition rate of the single laser pulse and / or laser pulse train is 100 kHz, and / or - The pulse energy or pulse train energy is between 10 µJ and 50 mJ.

13. The method according to claim 1 or 2, characterized in that, The workpiece (1) and the laser beam (20) move relative to each other at a feed rate (V).

14. The method according to claim 12, characterized in that, The laser pulse or the laser pulse train is introduced into the material of the workpiece (1) at a constant spatial spacing.

15. The method according to claim 1 or 2, characterized in that, The material of the workpiece (1) has a refractive index between 2.5 and 3.

5.

16. The method according to claim 1 or 2, characterized in that, The material of the workpiece (1) is silicon, or the material of the workpiece is silicon carbide (SiC).

17. The method according to claim 1 or 2, characterized in that, The workpiece (1) has a thickness (D) of 700 µm.

18. The method according to claim 12, characterized in that, The pulse duration of the ultrashort laser pulse is between 100 fs and 10 ps.

19. The method according to claim 12, characterized in that, The average laser power is 50 W.

20. The method according to claim 12, characterized in that, The wavelength is 1030 nm.

21. The method according to claim 12, characterized in that, A laser pulse train consists of between one and four laser pulses.

22. The method according to claim 13, characterized in that, The feed rate (V) is between 0.05 m / s and 5 m / s.

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