Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
  • B23K26/0624—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses using ultrashort pulses, i.e. pulses of 1 ns or less
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P54/00—Cutting or separating of wafers, substrates or parts of devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/50—Working by transmitting the laser beam through or within the workpiece
  • B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B33/00—Severing cooled glass
  • C03B33/02—Cutting or splitting sheet glass or ribbons; Apparatus or machines therefor
  • C03B33/0222—Scoring using a focussed radiation beam, e.g. laser
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P34/00—Irradiation with electromagnetic or particle radiation of wafers, substrates or parts of devices
  • H10P34/40—Irradiation with electromagnetic or particle radiation of wafers, substrates or parts of devices with high-energy radiation
  • H10P34/42—Irradiation with electromagnetic or particle radiation of wafers, substrates or parts of devices with high-energy radiation with electromagnetic radiation, e.g. laser annealing
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P72/00—Handling or holding of wafers, substrates or devices during manufacture or treatment thereof
  • H10P72/04—Apparatus for manufacture or treatment
  • H10P72/0428—Apparatus for mechanical treatment or grinding or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/36—Electric or electronic devices
  • B23K2101/40—Semiconductor devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic materials other than metals or composite materials
  • B23K2103/52—Ceramics
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic materials other than metals or composite materials
  • B23K2103/54—Glass
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic materials other than metals or composite materials
  • B23K2103/56—Inorganic materials other than metals or composite materials being semiconducting

Definitions

• Method for dividing a transparent workpiece by means of pulsed laser radiation by creating a beam convergence zone in the volume of the workpiece, in which the intensity of the laser radiation exceeds a threshold value for non-linear absorption, the beam convergence zone and the workpiece being moved relative to one another and thus a flat area running along a predetermined dividing line Weakening is produced in the workpiece, and the workpiece is then divided along the parting line.
• dicing of wafers plays an important role in the manufacture of semiconductor devices, which are becoming ever smaller and more complex.
• the classic dicing methods are based on the use of a diamond saw for wafers that are thicker than 100 ⁇ m.
• Laser-based processes are increasingly being used for thinner wafers.
• WO 2016/059449 A1 describes a dicing method in which pulsed laser radiation is used to generate a beam convergence zone in the volume of the workpiece, ie the semiconductor substrate, in which the intensity of the laser radiation locally exceeds a threshold value for non-linear absorption.
• multi-photon processes occur accordingly, for example in the form of multi-photon ionization or avalanche ionization, which lead to the formation of a plasma.
• the rate of plasma formation increases above a threshold determined by the material of the workpiece and the parameters of the laser radiation. This is why one also speaks of an "optical breakthrough".
• the resulting modification and thus processing of the workpiece has a high level of precision, since spatially localized, reproducible small amounts of energy are introduced into the material.
• the good spatial localization is primarily achieved by focusing the laser radiation by means of coupling optics that are as aberration-free as possible and have a high numerical aperture.
• a beam convergence zone is generated in the form of an extended, "spike-shaped" focus volume in the cited publication in the direction of the laser beam axis.
• This beam convergence zone is moved relative to the workpiece in order to result in a along a predetermined separation line
• Possible weakening mechanisms due to the modifications introduced are the formation of voids and/or cracks, structural changes in the material of the workpiece, Ri coupled to the modification area in each case sse, transient or permanent stresses, thermomechanical stresses, stresses due to local increases or decreases in volume, solidification cracks, etc breaks along the dividing line.
• the modifications in the workpiece are produced with laser pulses with a pulse duration in the range of 100-15000 fs at a wavelength of 500 nm to 2000 nm and a repetition rate of 10 kHz to 2 MHz.
• the beam shaping for generating the beam convergence zone is designed on the basis of undisturbed linear propagation of the laser radiation in the volume of the workpiece.
• the propagation of the laser radiation within the workpiece in the stated pulse duration range is subject to non-linear effects.
• the propagation of the laser radiation in the volume of the workpiece is disturbed by non-linear effects (e.g. self-focusing and two-photon absorption even outside the beam convergence zone) to such an extent that effective energy coupling into the desired area of the beam convergence zone is prevented to a considerable extent.
• a defined localization of the energy deposit and the resulting modification of the material of the workpiece cannot be achieved with high peak intensity of the radiation, as is the case with short pulse durations.
• the material can be modified with a long pulse duration (e.g. > 1 ns) and thus a lower peak intensity, but since a higher energy is typically required and diffusion effects become effective, greater damage due to an increased thermally loaded volume is accepted. Accordingly, the result of the separating process is not satisfactory in terms of the quality of the broken edge.
• a long pulse duration e.g. > 1 ns
• the object of the invention is to provide an improved method for dividing a transparent workpiece.
• the aforementioned disadvantages of known methods are to be avoided.
• the invention solves this problem based on a method of the type specified at the outset in that non-linear propagation of the laser radiation in the volume of the workpiece is achieved by selecting the duration of the energy input generated by the non-linear absorption of the pulsed laser radiation in the beam convergence zone and/or by spatial beam shaping is suppressed outside the beam convergence zone.
• the essence of the invention is the consideration of the non-linear propagation characteristic for introducing the weakening into the workpiece.
• process parameters that are as optimal as possible with regard to the duration of the energy input and/or the beam shaping are defined, as a result of which an improved Control of the energy deposition is made possible.
• the local energy density in the volume of the workpiece is ultimately controlled by the duration of the energy input and the energy coupling within the beam convergence zone is improved. Damage in the surrounding volume, ie outside the beam convergence zone, is reduced to a minimum.
• the invention achieves the lowest possible interaction outside, in particular in the propagation direction of the laser radiation in front of the beam convergence zone, in order to minimize disruptive non-linear effects (eg self-focusing, non-linear absorption) or other propagation disturbances.
• modifications or zones of high electron density that occur first do not account for more than 50%, preferably not more than 20%, particularly preferably not more than 10% of the incident energy from the shield parts of the beam convergence zone that are reached later in the beam direction.
• a suitable fluence can be achieved in a targeted and defined manner in the beam convergence zone by means of beam focusing.
• the desired modification only occurs in this area.
• the combination of temporal and spatial beam shaping results in a uniform, tailor-made energy deposition over the entire specified beam convergence zone. As a result, the separation process is facilitated. Spalling or material stresses are minimized.
• the quality of the breaking edge is improved compared to the prior art.
• the targeted selection of the process parameters means that a) the intensity threshold for non-linear absorption in the beam convergence zone is exceeded, b) power or intensity thresholds for undesired non-linear effects outside the beam convergence zone are not reached, c) the energy required for the desired modification is introduced in a controlled and localized manner so that the desired areal weakening results in the desired geometry
• the wavelength of the laser radiation should be selected so that the linear absorption of the laser radiation in the material of the workpiece is below 20%, better still below 10%, particularly preferably below 5% over a length of one centimeter in the direction of the laser beam.
• the wavelength of the laser radiation should be selected with the proviso that the non-linear refractive index in the volume of the workpiece at this wavelength is so low that non-linear effects do not prevent sufficient energy deposition in the beam convergence zone.
• the wavelength should be in a range that ensures good focusability.
• the duration of the energy input can be specified, for example, by the pulse duration of the pulsed laser radiation.
• An upper limit of the duration results from the tolerable size of the thermal damage zone due to thermal diffusion.
• an upper limit to the duration is given by the maximum tolerable energy absorbed in the beam convergence zone. The longer the duration, the greater the energy input when the intensity is above the nonlinear absorption threshold. Too much energy and/or energy introduced over too long a period of time prevents local limitation of the attenuation to the beam convergence zone.
• the lower limit of the energy input duration is important.
• the pulse duration should be greater than a critical value, where the Critical value is, for example, the quotient of pulse energy and material-specific critical power, above which non-linear propagation, in particular self-focusing, occurs in the volume of the workpiece. This ensures that the energy deposition is not excessively disturbed by non-linear effects, thus ensuring a sufficiently high and localized energy deposition in the beam convergence zone.
• the duration of the energy input e.g. the pulse duration
• the amount of the energy input e.g. pulse energy
• a pulse event should be selected according to the proviso that damage, i.e. a desired modification in the volume of the workpiece within the beam convergence zone by a single laser pulse or a Laser pulse burst consisting of a sequence of a predetermined number of laser pulses.
• a suitable individual pulse can be, for example, a laser pulse with a Gaussian time profile and a specific pulse duration.
• a burst comprises a specified number of laser pulses with a short time interval (pulse repetition frequency in the GHz or THz range).
• the energy input in the sense of the invention relates to the energy input during a single pulse event through non-linear induced absorption in the beam convergence zone.
• the duration of the energy input results accordingly from the pulse duration or the burst duration.
• the laser pulses do not necessarily have to have a Gaussian shape, a "flat top” shape or any other common shape. Any pulse shapes are conceivable.
• the effective duration of the energy input is decisive. In the method according to the invention, this is preferably 20-500 ps.
• the two-dimensional weakening is then generated repetitively in that the workpiece is incrementally moved further along the dividing line relative to the beam convergence zone from pulse event to pulse event. If possible, the weakening is produced during a single movement process along the dividing line. In this way, a high process speed can be achieved and the workpiece reliably breaks with high quality of the cutting edge along the parting line.
• the shortest possible duration of the energy input during which the desired modification occurs with a probability of at least 80%, preferably at least 90%, particularly preferably at least 95%, is preferably determined.
• the duration of the energy input when introducing the weakening is then selected so that it is greater than or equal to this determined shortest possible value, which can depend on numerous factors (material, size and geometry of the beam convergence zone, wavelength, pulse shape, etc.).
• the selected duration of the energy input can be a factor of 10, preferably a factor of 5, particularly preferably a factor of 2 above the determined shortest possible value.
• the factor is in the range from 1.1 to 5. This achieves good control of the energy input for the desired generation of the weakening.
• the beam convergence zone should have an elongated shape perpendicular to the workpiece surface. Similar to WO 2016/059449 A1 cited above, the beam convergence zone should be elongated in the direction of the beam and thus extend over most of the full thickness of the workpiece in order to provide suitable attenuation.
• the length of the beam convergence zone in the beam direction can be greater by a factor of at least 10, preferably by a factor of at least 50, particularly preferably by a factor of at least 100 than the extent of the beam convergence zone perpendicular to the desired flat weakening.
• the laser beam can initially have a Gaussian profile or any other feasible input beam shape.
• Gauss-Bessel beams or other beam shapes that can essentially be described as non-diffracting beams are particularly suitable.
• a tailor-made spatial intensity distribution in the beam convergence zone is expediently carried out using suitable optical components, such as focusing optics in combination with beam shaping optics, also with adaptive beam shaping components, such as spatial light modulators (SLM) or piezo mirrors.
• SLM spatial light modulators
• An improvement can be achieved by depth-dependent aberration correction.
• the aim of spatial beam shaping is to ensure that the energy input into the desired beam convergence zone is as undisturbed as possible, namely from the workpiece surface (beam entry surface) down to the depth required for the cutting process in the workpiece.
• the extent of the beam convergence zone should be greater transversely to the beam axis in the direction parallel to the plane of attenuation than perpendicular to it.
• the aim of the invention is to achieve as little interaction as possible outside, in particular in the propagation direction of the laser radiation in front of the beam convergence zone, in order to minimize disruptive non-linear effects.
• the beam can advantageously be shaped in such a way that those beam components (consisting of individual beams or bundles of individual beams) of the laser radiation that converge closer to the workpiece surface in the volume of the workpiece enclose the same or smaller angle with the beam axis than those beam components that are further away from the workpiece surface converge in the volume of the workpiece. In any case, this should apply to the majority of the beam components that converge in the beam convergence zone; the deviation of a small part of the beam components from this geometry can be tolerated in individual cases as long as non-linear effects are sufficiently suppressed.
• the method according to the invention is particularly suitable for dividing semiconductor wafers into chips.
• non-linear propagation of the laser radiation which is disadvantageous for the dicing process, is prevented or at least minimized.
• the propagation of the laser radiation in the material of the substrate is undisturbed and an elongated modification zone can be introduced with each pulse event.
• a planar weakening is produced along a predetermined dividing line. This serves as a predetermined breaking point when breaking through a subsequently applied tensile stress.
• the method according to the invention is also suitable for dividing flat glass products or else ceramic and crystalline workpieces.
• Fig. 1 Schematic of the invention
• Fig. 2 schematic illustration of the spatial
• Fig. 5 Process of optimizing the pulse duration as
• Fig. 7 Diagram to illustrate the
• a laser beam 2 in the form of pulsed laser radiation is radiated onto the workpiece from above.
• the laser beam 2 is shaped (e.g. by focusing optics in combination with a spatial light modulator, not shown) in such a way that a beam convergence zone 3 elongate in the beam direction is created in the volume of the workpiece 1 .
• the intensity of the laser radiation exceeds the threshold value for non-linear absorption, so that a correspondingly spatially limited modification of the material of the workpiece 1 occurs.
• the beam convergence zone 3 is incrementally moved relative to the workpiece (arrow direction).
• a plurality of modification zones 5 lying next to one another along a dividing line 4 are produced in the volume of the workpiece 1, which together form a weakening plane.
• the workpiece 1 is then broken into two parts 1a, 1b along the parting line 4 by the action of a small mechanical force.
• the dividing line does not have to be straight as in FIG. 1 .
• a separation of the workpiece parts 1a, 1b along a curved separating line is also conceivable.
• the core of the invention is the consideration of the non-linear propagation characteristics of the laser radiation 2 for the introduction of the modification zones 5 in the workpiece 1.
• the propagation of the laser radiation 2 in the volume of Workpiece 1 would be disturbed by non-linear effects (e.g. self-focusing and two-photon absorption even outside the beam convergence zone) to such an extent that effective energy coupling, which is limited to the desired area of the beam convergence zone 3 on the one hand, but also fills it out as completely as possible, to a considerable extent extent prevented.
• process parameters that are as optimal as possible with regard to the duration of the energy input and beam shaping are defined according to the invention, which enables extensive control of the energy deposition. Damage in the surrounding volume, ie outside of the beam convergence zone 3, is reduced to a minimum.
• FIG. 2 schematically illustrates the spatial beam shaping according to the invention on the basis of sections through the workpiece 1 .
• two beam components 6, 7 of the laser radiation 2 (FIG. 1) incident from above converge in a beam convergence zone 3 far below the workpiece surface (beam entry surface).
• the beam components 6, 7 enclose an acute angle with the beam axis 8, so that an elongated beam convergence zone 3 results.
• the beam components 6 , 7 propagating through the volume of the workpiece 1 at an angle to the beam axis 8 ensure that the beam components 6 , 7 overlap exclusively in the beam convergence zone 3 .
• the fluence of the laser radiation in the volume of the workpiece remains so low that as few non-linear effects as possible occur.
• the various beam components 6, 7, 9 or 10, 11, 12 merge into two broader beam components 13, 14, so that a single elongated beam convergence zone 3 is formed.
• the beam shaping ensures that during a pulse event (single laser pulse or pulse burst) in the beam convergence zone 3 (i.e. further up in Fig. 2) modifications (or zones of high electron density) arising first (or zones of high electron density) only a small part of the incident energy are separated from the later (further below) reached parts of the beam convergence zone 3 shield. This can generally be achieved by the narrowest possible angular spectrum of the beam components 6 , 7 , 9 , 10 , 11 , 12 , 13 , 14 of the incident laser radiation in relation to the beam axis 8 .
• Fig. 3 illustrates, in turn, using sectional views (upper images) and using top views (lower images) of the workpiece 1, the successive introduction of a large number of modification zones 5 by the converging beam components 13, 14 of the laser radiation 2.
• the Workpiece 1 moves relative to the beam convergence zone 3 (to the right in FIG. 3).
• the modification zones 5 are introduced in close proximity.
• a portion of the laser radiation 2 is thereby shielded by the modification zones 5 that have already been introduced in each case.
• the corresponding shielding angle segment is shown in the lower figures of FIG. It can be seen that the angular segment is larger in the case of closely adjacent modification zones 5 (left image) than in the case of modification zones 5 that are further apart (middle representation).
• the modification zones are again closely adjacent.
• the beam is shaped here in such a way that the extent of the beam convergence zone 3 and corresponding to the modification zone 5 shown in each case is greater transversely to the beam axis 8 in the direction parallel to the attenuation plane (ie along the dividing line 4) than perpendicular thereto.
• that portion of the laser radiation 2 which is shielded by the modification zones 5 already introduced in each case during the repetitive introduction of the modification zones 5 is reduced.
• the shielding angle segment is smaller than in the bottom left figure. The smaller extent of the modification zones 5 transversely to the dividing line 4 thus allows for closely adjacent modification zones, so that overall a larger proportion of the area can be weakened and the quality of the fracture point can thus be improved.
• the wavelength of the laser radiation is determined on the basis of the circumstances of the workpiece 1 (material and thickness). Ideally, the wavelength of the laser radiation should be selected so that the linear absorption of the laser radiation in the material of the workpiece is below 20%, better still below 10%, particularly preferably below 5% over a length of one centimeter in the direction of the laser beam. In addition, the wavelength of the laser radiation should be selected on the basis that the non-linear refractive index in the volume of the workpiece is as low as possible at this wavelength. For example, a longer wavelength reduces two-photon absorption outside the beam convergence zone.
• the wavelength should be in a range that ensures good focusability, and from this point of view, a shorter wavelength is preferable.
• a suitable wavelength is set on the basis of the different optimization criteria.
• the beam shaping is determined according to the criteria explained above, whereby the thickness and the material of the workpiece (refractive index) are also taken into account.
• the pulse duration and pulse energy again with the proviso to avoid non-linear effects in the propagation of the laser radiation 2 through the volume of the workpiece 1 outside the beam convergence zone 3, but in any case to reduce them. More details on this are explained below with reference to FIGS. 5 and 6.
• the shortest possible duration of the energy input generated by the non-linear absorption of the pulsed laser radiation ie here the shortest possible pulse duration for the desired achievement of the modification in the workpiece 1 is determined. This depends on the previously defined parameters, namely material, geometry of the beam convergence zone 3, ie beam shape and wavelength.
• the optimal pulse duration is found with the optimization steps shown in FIG. A possible starting point for the iterative optimization can result from the necessary energy density for modifying the material of the workpiece 1 on the one hand and the respective critical power from which the self-focusing of the laser radiation 2 propagating in the volume of the workpiece 1 takes place on the other hand.
• the pulse duration must be selected at least long enough so that the peak powers achieved by the laser radiation are below the material-specific parameters that are critical for self-focusing.
• the successful modification is checked with a probability of at least 95% in the sequence shown in FIGS. 5 and 6, for example according to ISO 21254 (“lasers and laser-related equipment—test methods for laser-induced damage threshold”).
• the pulse duration and pulse energy of the pulsed laser radiation 2 are determined by the optimization in such a way that a modification by a single laser pulse or a laser pulse burst consisting of a predetermined sequence of laser pulses takes place reliably (at least 95% probability).
• the minimum required pulse duration is selected for which the modification still takes place reliably.
• the pulse duration can optionally be adjusted upwards, depending on the result, if an improved result and/or increased process stability can be achieved as a result.
• the upper limit is still determined by the thermal damage area during the laser irradiation.
• the fluence is then adjusted in the desired modification range (>95% probability) according to an analogous procedure by increasing or reducing the pulse energy.
• the optimization steps in FIGS. 5 and 6 ensure that an optimal pulse duration and pulse energy for the selected beam formation, ie for the desired geometry of the modification zone 5, is used.
• a 525 ⁇ m thick silicon wafer is irradiated with pulsed laser radiation at a wavelength of 1960 nm.
• a significant reduction in non-linear propagation and thus the first occurrence of modifications can be seen from a pulse duration of 20 ps.
• the determination of the modification probability by an individual Laser pulse shows that from a pulse duration of 25 ps, a probability of >95% is reached.
• the pulse energy is 15 pJ. In this way, modification zones with a diameter of 5 pm and a length of 350 pm in the direction of the beam can be generated by means of spatial pulse shaping.
• the modification zones are lined up in a row at a distance of 10 ⁇ m, in that the focus of the laser radiation, ie the beam convergence zone, is moved relative to the wafer.
• the wafer can then be broken at right angles with a small mechanical force. A clean breaking edge is created.
• the heat-affected area along the breaking edge is small.
• the surface roughness is less than 5 pm.
• the speed of the relative movement of the laser beam 2 and the workpiece 1 can be reduced to such an extent that the modification zones 5 in the volume of the workpiece 1 overlap.
• the diagram in FIG. 7 shows how the interaction of the parameters of the feed rate v, the modification probability P and the input pulse energy Ein forms different regimes.
• X1 denotes the area where the modifications are introduced in a continuous (overlapping) manner.
• Ein which has an influence on the extent of the modification zones 5 perpendicular to the beam propagation, an overlap occurs.
• the feed rate is increased, the distances between the introduced modification zones 5 are increased with the same repetition rate of the pulse events, and separate, i.e. non-overlapping, modification zones 5 are formed (regime X2).
• regime X3 the pulse energy is too low, so the probability of a modification is too low. Sufficient weakening of the workpiece 1 to allow fracture is not achieved.

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• 2021
  • 2021-01-14 DE DE102021100675.9A patent/DE102021100675B4/de active Active
• 2022
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