WO2023237610A1

WO2023237610A1 - Method and device for processing at least one sub-region of a layer system

Info

Publication number: WO2023237610A1
Application number: PCT/EP2023/065248
Authority: WO
Inventors: Daniel Grossmann; Marc Sailer
Original assignee: Trumpf Laser Gmbh
Priority date: 2022-06-10
Filing date: 2023-06-07
Publication date: 2023-12-14
Also published as: DE102022114646A1

Abstract

The invention relates to a method for processing a sub-region (1) of a layer system, in particular a micro-LED, by means of ultra-short laser pulses of a laser beam (20) of an ultra-short-pulse laser (2), wherein the at least one sub-region (1) is arranged in a boundary layer (130) on a substrate (30), wherein the substrate (30) is substantially transparent for the wavelength of the ultra-short laser pulses of the laser beam (20), wherein the boundary layer (130) is applied with the ultra-short laser pulses (200) of the laser beam (20) through the substrate (30), whereby the at least one sub-region (1) is processed, wherein the position of the ultra-short laser pulses (202) of the laser beam (20) in the boundary layer (130) is adjusted precisely.

Description

Method and device for processing at least a portion of a layer system

Technical area

The present invention relates to a device and a method for processing at least a portion of a layer system using ultrashort laser pulses of a laser beam from an ultrashort pulse laser.

State of the art

In modern display systems, micro-LEDs are used as light sources to make conventional, global backlighting of the display panel unnecessary. For this purpose, the micro-LEDs are applied to a so-called active matrix so that each micro-LED can be controlled individually. The displays with micro-LEDs therefore have the advantage that the micro-LEDs on the matrix can be controlled locally. This means that individual micro-LEDs can be switched on and off, which means, for example, a high contrast ratio and a very good black level can be achieved. In addition, so-called bleeding of the background lighting through the display panels can be avoided due to their design.

However, the production of such displays with micro-LEDs is challenging because the micro-LEDs are first produced on a substrate and then have to be transferred to a corresponding active matrix. In addition, only functioning micro-LEDs may be transferred to the active matrix in order to avoid pixel errors, for example. The use of lasers has proven successful for transferring the micro-LEDs to a corresponding active matrix. In particular, the Laser Lift-Off (LLO) process, with which a micro-LED can be detached from the substrate, and the so-called Laser Induced Forward Transfer (LIFT) process, with which the micro-LED is transferred from the substrate to the active matrix can become relevant. In both cases, a laser pulse is applied to the boundary layer between the substrate and the micro-LED in order to achieve appropriate processing of the micro-LED. “Laser Processing of Micro-LED - a Coherent Whitepaper” from January 23, 2018 describes that excimer lasers are typically used for the aforementioned processes.

However, excimer lasers have poor temporal pulse quality. In particular, the difficult to control transient response and decay behavior of the laser pulses influences the processing quality. In addition, the pulse length of excimer lasers is in the range of a few 10ns, so that the laser pulses interact with the boundary layer between the substrate and the micro-LED over a long period of time and accordingly have a thermal influence on the exposed materials. This can damage the semiconductor junctions, in particular the pn junctions, of the microLEDs. In addition, the laser beam of an excimer laser does not have a defined polarization, so that they are particularly not suitable for high-performance applications, since the optical components necessary for high laser powers often require a defined polarization of the laser beam.

In order to process a large number of micro-LEDs on the substrate, the laser beam must be moved over the substrate, or the focus position must be adjusted between the laser pulses. However, inertial systems such as X-Y-Z translation tables or galvanic scanners typically do not enable the flexibility and speed that are necessary for highly dynamic process strategies.

Presentation of the invention

Based on the known prior art, it is an object of the present invention to provide an improved method for processing at least a partial area of a layer system, as well as a corresponding device.

The object is achieved by a method for processing at least a portion of a layer system with the features of claim 1. Advantageous further developments result from the subclaims, the description and the figures.

Accordingly, a method for processing at least a partial region of a layer system, in particular a micro-LED, by means of ultrashort laser pulses of a laser beam of an ultrashort pulse laser is proposed, wherein the at least one partial region is arranged at a boundary layer on a substrate, the substrate being essentially transparent for the wavelength the ultra-short laser pulses of the laser beam, wherein the boundary layer is acted upon by the ultra-short laser pulses of the laser beam through the substrate, whereby the at least one partial area is processed. According to the invention, the focus position of the ultra-short laser pulses of the laser beam in the boundary layer is adjusted with pulse precision. The ultra-short pulse laser provides the laser pulses of the laser beam, with the individual laser pulses forming the laser beam in the direction of beam propagation. The pulse duration of the ultra-short laser pulses can be between 50fs and 1000ps, preferably between 100fs and 100ps, particularly preferably between 50fs and 20ps.

The laser pulses can also be part of a so-called laser burst, with each laser burst comprising several laser pulses. During the length of the laser burst, the laser pulses can follow one another very closely, for example at intervals of a few picoseconds to nanoseconds. The laser bursts can in particular be GHz bursts, in which the sequence of successive laser pulses of the respective burst takes place in the GHz range.

The sub-area of the layer system can in particular be a sub-area of a multi-layer system. For example, such a subarea is a micro-LED, a mini-LED or another LED. However, a layer system can also only include one layer of a material. In the following, the process is described primarily using a micro-LED.

Micro-LEDs are generally localized pn junctions of semiconductors, in particular III/V semiconductors, such as gallium nitride GaN, which emit light of a specific wavelength, preferably a visible wavelength, when a voltage or current is applied. However, it is also possible for a micro-LED to also emit light in the UV range or in the IR range.

A micro LED has external dimensions of a few micrometers. For example, micro-LEDs can be round or rectangular and have a diameter or edge length of a few 10pm. For example, a micro LED can be square and 20x20pm2 or 30x30pm2.

The micro-LEDs are typically manufactured on a substrate. For this purpose, the p- and n-doped semiconductors are deposited one after the other onto the substrate. The first layer of the micro-LED is accordingly arranged at a boundary layer on the substrate. In addition, the first layer on the substrate has, for example, a p-doping and the second layer on the first layer has an n-doping. A pn junction is created at the interface between the p- and n-doped layers, which generates light when a voltage or current is applied. The layers are then separated along the layer normal, so that a large number of micro-LEDs are created on the substrate.

What is particularly problematic here is that the substrate can influence the functionality of the micro-LEDs, since, for example, the substrate only allows insufficient removal of the heat generated when the micro-LEDs are operated. In addition, it can Substrate the optical properties deteriorate if the light from the micro-LEDs first has to penetrate through the substrate before it reaches the observer. For this reason, it is advantageous to remove the substrate from the micro LED.

For this purpose, the substrate can be or comprise a substantially transparent material such as sapphire or a polymer or a plastic, or consist of silicon or comprise silicon, such as silicon carbide SiC. Substantially transparent means that the material can partially or completely transmit the laser light of the given wavelength, for example more than 80% or more than 85% or more than 90% or more than 95% or more than 99% of the light , so that the laser beam can penetrate through the substrate and the micro-LED underlying the beam propagation direction can also be processed. The laser beam can therefore be guided through the at least partially transparent substrate.

Finally, the laser energy can be at least partially absorbed in the boundary layer, since the micro-LED is typically not transparent to the laser wavelength. The boundary layer here comprises in particular a substrate-side section of the micro-LED, which is determined by the penetration depth of the laser beam into the micro-LED. However, the boundary layer can also or additionally comprise a buffer layer that has been applied to the substrate in order to reduce the lattice mismatch between the substrate and the micro-LED.

For example, in the case of a gallium nitride GaN micro-LED, the introduced laser energy in the boundary layer can separate the GaN into liquid gallium and gaseous nitrogen. This creates a vapor pressure in the boundary layer that separates the microLED from the substrate. However, it can also be the case that the micro-LED is detached from the substrate and, for example, transferred to a carrier substrate, for example to an underlying active matrix or a transfer layer. The processing of the partial area can therefore in particular be the laser-induced forward transmission of the partial area and/or the laser lift-off of a partial area of a substrate.

According to the invention, the focus position of the ultra-short laser pulses of the laser beam in the boundary layer is adjusted with pulse precision. In particular, the position of the ultra-short laser pulses of the laser beam in the boundary layer can be adapted to the geometry of the partial region with pulse precision.

The term “focus” in general is understood as a targeted increase in intensity, whereby the laser energy converges into a “focus area” or a “focus zone”. In particular, the term “focus” will be used below regardless of the beam shape actually used and the methods used to bring about an increase in intensity. By a By “focusing” the laser pulses, the location of the intensity increase along the beam propagation direction can be influenced. For example, the intensity increase can be quasi-point-shaped and the focus area can have a Gaussian-shaped intensity cross section, as provided by a Gaussian laser beam. The intensity increase can also be designed in a line shape, resulting in a Bessel-shaped focus area around the focus position, as can be provided by a non-diffracting beam. Furthermore, other more complex beam shapes are also possible, the focus position of which extends in three dimensions, such as a multi-focus distribution of Gaussian laser beams and/or non-Gaussian intensity distributions, as described further below.

The focus position here is the location or coordinate of the focus zone in the plane, in particular the focal plane, perpendicular to the direction of propagation of the laser pulses. The focus position can be, for example, the center of gravity coordinate or the center coordinate.

The focus position can be adjusted with pulse precision so that each laser pulse is directed into a different focus zone and accordingly each laser pulse can act on a different location in the boundary layer. However, it is also possible for different laser pulses to affect the same location.

Through such pulse-precise adjustment of the focus position, a partial area to be processed can be scanned in a thermally optimized manner using laser pulses. Accordingly, the method has the advantage that the process quality can be optimized and that the processing throughput can be increased with full flexibility.

In addition, a specific area on the substrate can also be addressed and processed in this way. In particular, this makes it possible to jump from one partial area to another partial area on the substrate from laser pulse to laser pulse, for example to skip partial areas in the processing process and at the same time maintain a high process speed.

The fact that the focus position can be adjusted with pulse precision also enables highly dynamic processing of the partial areas on the substrate. In particular, the processing speed is then only limited by the repetition rate of the laser pulses.

The wavelength of the laser beam can be between 50nm and 300nm, preferably between 250nm and 270nm. The wavelength can in particular be designed such that the subregion at the wavelength has a particularly high absorption and the substrate has a low absorption. This allows the partial area to be processed through the substrate. In addition, smaller focus zones can also be formed with small wavelengths, so that particularly small structures on the substrate can be targeted.

The ultrashort pulse laser can be operated in its basic mode, with the diffraction coefficient M ² being less than 1.5.

Accordingly, the basic transversal electrical mode TEMOO can be used as the laser mode, which has a pure Gaussian beam shape in the beam cross section and therefore in principle has the highest beam quality. In particular, in the TEOO mode the beam cross section is smaller than in the higher modes, so that a more targeted processing of the sub-areas is possible. The diffraction coefficient indicates the deviation of the laser beam from the ideal TEOO mode.

The fluence can be between 0.05J/cm2 and 10J/cm2, preferably between 0.1J/cm2 and 1J/cm2.

The processing quality can be adjusted using the fluence, as the energy deposited in the boundary layer directly influences the LLO or LIFT process. For example, the deposited energy has an influence on the magnitude of the vapor pressure that is created, which detaches the microLED from the substrate.

The repetition rate of the laser pulses can be greater than 10 kHz, preferably greater than 1 MHz.

The processing speed in particular can be adjusted by the repetition rate of the laser pulses. For example, a partial area can be processed with a laser pulse. Accordingly, more partial areas can be processed if a high repetition rate of the laser pulses is selected.

The repetition rate of the laser pulses can be, for example, 10MHz, so that over ten million partial areas can be processed per second. This enables a particularly high throughput of partial areas.

The laser beam of the ultrashort pulse laser can have a defined polarization, preferably linearly polarized. Polarization describes the alignment, in particular the spatially or temporally variable alignment of the electric field vector of the laser beam relative to the direction of propagation of the laser beam.

For example, a laser beam can be s-polarized, or p-polarized, or circularly polarized, or elliptically polarized. In that the laser beam has a defined polarization, high-performance components can be used in particular that require a defined input polarization. In this sense, the method can also be used with particularly high laser powers due to the defined polarization.

The position of the laser pulses can be adjusted using a beam shaping device, the beam shaping device being a diffractive optical element and/or a microlens array and/or preferably an acousto-optical deflector.

A diffractive optical element is designed to influence the incident laser beam in one or more properties in two spatial dimensions. Typically, a diffractive optical element is a specially shaped diffraction grating, whereby the incident laser beam is brought into the desired beam shape through diffraction.

Microlens arrays include arrangements of multiple microlenses. Microlenses are small lenses, in particular lenses with a typical distance from lens center to lens center (“pitch”) of 0.1 to 10 mm, preferably 1 mm, whereby each individual lens in the arrangement can have the effect of a normal, macroscopic lens. With the multiple microlens arrays, an angular spectrum is generated from the (at least essentially) collimated input laser beam, with a large number of partial laser beams being created depending on the distance between the microlens arrays due to interference and diffraction effects. The variable change in the interference pattern results in a variation in the number of partial laser beams.

In an acousto-optical deflector unit, an acoustic wave is generated using an alternating voltage on a piezo crystal in an optically adjacent material, which periodically modulates the refractive index of the material. The wave can propagate through the optical material, for example as a propagating wave or as a wave packet, or as a standing wave. The periodic modulation of the refractive index creates a diffraction grating for an incident laser beam. An incident laser beam is diffracted at the diffraction grating and thereby at least partially deflected at an angle to its original beam propagation direction. The grating constant of the diffraction grating and thus the deflection angle depends, among other things, on the wavelength of the acoustic wave and therefore on the frequency of the applied alternating voltage. Over a Combining two acousto-optical deflectors in one deflector unit, for example, deflections in the x and y directions can be generated.

The acousto-optical deflector unit can in particular be a polarization-dependent acousto-optic deflector unit and can therefore be particularly suitable for performance. For example, the actus-optical deflector unit can be a quartz-based deflector unit.

The above-mentioned beam shaping devices enable particularly rapid repositioning of the laser pulses in the boundary layer.

Successive laser pulses can have different focus positions in the boundary layer, preferably the greatest possible distance from one another within the geometry of the partial region that has not yet been acted upon.

By distributing the successive laser pulses in the boundary layer, the heat input can be controlled particularly well. In particular, this reduces the risk of a partial area being damaged by excessive energy input. In particular, the optimized heat distribution can reduce unwanted cracking.

Successive laser pulses preferably have the greatest possible distance from one another. For example, if a first laser pulse is guided into the upper left corner of a rectangular boundary layer of a partial area, then the second laser pulse can be guided into the lower right corner, for example. A third laser pulse can then be directed to the bottom left corner, and so on.

In particular, each individual partial area can be scanned with a large number of laser pulses.

The laser pulses can at least partially have a different beam shape, preferably have a multi-focus distribution.

The beam shape of a laser beam can be characterized, for example, by the intensity distribution in the plane in which the focus zone of the laser beam lies, perpendicular to the beam propagation direction. This level is the so-called focal level. The beam shape can also be characterized by the intensity distributions in the planes in which the beam propagates. For example, the laser beam can be linear in the focal plane. However, it can also be the case that the laser beam is elongated in the beam propagation direction, resulting in, for example, a Bessel-shaped focus area around the focus position, as can be provided by a non-diffracting beam. A beam shape can also be given by the fundamental mode or a higher TE mode.

Furthermore, the beam shape also includes more complex beam shapes, such as a so-called multi-focus distribution, in which the laser beam forms a large number of focus zones.

The multifocus distribution is a spatial distribution of individual focus zones, so-called individual foci. The multifocus distribution includes at least two individual foci, with the individual foci being spatially separated from one another. However, the individual foci can all lie in the same focal plane, so that the individual foci can all be found in one plane along the beam propagation direction of the laser beam, but have different coordinates in the focal plane perpendicular to the beam propagation direction.

A multi-focus distribution is provided by a so-called beam shaping device, whereby the incident laser beam can be divided into a plurality of partial laser beams that are guided to different individual foci. Beam shaping includes the design of the multi-focus distribution. The beam shaping can also include the design of the individual foci, such as the formation of Gaussian or non-diffractive laser beams.

By distributing the laser energy to different individual foci, the laser energy is also distributed in the boundary layer. In this way, in particular, a flat processing of the micro-LED can be achieved, whereby lateral material stresses are reduced. In a sense, the multifocus distribution can be used to imitate a homogeneous flattop beam shape with the individual foci, although each individual focus is, for example, Gaussian. Accordingly, the requirements for the phase front of the laser beam are significantly lower than for a flattop beam. For example, the ultrashort pulse laser can be operated in its basic mode and does not require multimode operation.

In particular, a multifocus distribution can be a grid-shaped arrangement of Gaussian focus zones. For example, a first laser pulse can propagate in a TE00 mode, while a second laser pulse has a distribution of 4x4 TE00 modes and a third laser pulse has a focus zone elongated in the beam propagation direction. Accordingly, multi-stage energy deposition processes can be used, which, for example, enable a targeted shaping of a pressure wave, which is advantageous for the LLO and/or LIFT process.

For example, the focus position of the multi-focus distribution can be adjusted with pulse precision for processing partial areas. For example, a substrate can be scanned with a multifocus distribution of 3 times 3 individual foci. This means that the boundary layer of the sub-areas can be acted upon in a spatially homogeneous manner, but the process speed still corresponds to the repetition frequency of the laser pulses.

The partial areas to be affected can be selected using a diagnostic device.

A diagnostic device may contain a database containing the coordinates of the functioning portions together with an identification number of the substrate. The coordinates of the functioning subareas can be determined, for example, during functionality tests. The diagnostic device communicates indirectly with the beam shaping device, so that only functioning partial areas are processed.

The above task is further solved by a device with the features of claim 10. Advantageous developments of the method result from the subclaims as well as the present description and the figures.

Accordingly, a device for processing a partial area of a layer system, in particular a micro-LED, is proposed, comprising an ultra-short pulse laser and processing optics, the ultra-short pulse laser being set up to provide a laser beam made up of ultra-short laser pulses, the partial area being arranged at a boundary layer on a substrate is, wherein the substrate is essentially transparent to the wavelength of the ultra-short laser pulses of the laser beam, the processing optics being set up to transfer the laser beam into the boundary layer and to apply the ultra-short laser pulses to it, whereby the partial area is processed. According to the invention, the device comprises a beam shaping device which is designed to adjust the focus position of the ultra-short laser pulses of the laser beam in the boundary layer with pulse precision.

For example, such processing optics can be a lens or a mirror or a telescope, which in particular determines the position of the focal plane in the direction of beam propagation can be. This allows the focal plane to overlap with the boundary layer between the substrate and the partial area.

The ultrashort pulse laser can provide a basic laser beam with a wavelength of 1030 nm and include a frequency doubling crystal that is designed to double the frequency of the incident laser beam or halve the wavelength.

The basic laser beam can be guided twice through the frequency doubling crystal, preferably sequentially through a first frequency doubling crystal and then through a second frequency doubling crystal, whereby the frequency of the basic laser beam is quadrupled overall, or the wavelength of the basic laser beam is quartered overall and thus a laser beam with one wavelength between 250nm and 270nm is provided.

The ultra-short laser pulses are particularly suitable for such frequency doubling due to their high pulse peak intensities, as these non-linear effects typically scale with the intensity used. This makes it particularly easy to provide wavelengths in the UV range or DUV (Deep UV) range with ultra-short laser pulses.

At least one optical component of the device can comprise CaF or crystalline quartz, or can be made of CaF or crystalline quartz and/or can be designed as a reflective element.

For example, the processing optics can be such an optical component. However, it is also possible for a mirror and/or a lens system, which guides the laser beam from the ultrashort pulse laser to the beam shaping device, to be such an optical component.

Optical components made of CaF or crystalline quartz are particularly suitable for UV and/or DUV applications because they have very low absorption for the short wavelengths. Reflective elements have the advantage that the UV rays do not penetrate and interact with the material of the optical components. In particular, undesirable non-linear effects can be avoided.

The device can have a controller that is communicatively connected to the ultrashort pulse laser and the beam shaping device and is set up to control the ultrashort pulse laser and the beam shaping device.

For example, the controller can be an FPGA and/or a computer and/or a microchip. By communicatively connecting the controller to the beam shaping device and the ultrashort pulse laser, the controller can send and receive corresponding control signals. In particular, it is possible for the pulse output to be controlled by the ultrashort pulse laser. In particular, this makes it possible for the adjustment of the focus position to be controlled by the beam shaping device. In particular, it is possible for the adjustment of the focus position and the delivery of the laser pulses to be coordinated with one another.

The control commands or their execution can be synchronized with the seed frequency of the laser in all connected devices, so that a common time base exists for all components.

The device can have a feed device, preferably a scanner, particularly preferably a galvano scanner, which is set up to direct the laser beam in the focal plane, the feed device being communicatively connected to the controller.

Both the feed device and scanner optics can be synchronized via the seed frequency, so that a common time base exists for the feed, beam deflection, beam shaping and control of the pulsed laser.

The device can also have a diagnostic device which contains a database with the coordinates of functioning micro-LEDs on the substrate and which is communicatively connected to the controller or is formed as part of the controller.

Short description of the characters

Preferred further embodiments of the invention are explained in more detail by the following description of the figures. Show:

Figure 1A, B, C shows a schematic representation of the method according to the invention;

Figure 2A, B, C, D, E, F shows a further schematic representation of the method according to the invention;

Figures 3A, B show a further schematic representation of the invention

procedure;

Figures 4A, B show a further schematic representation of the invention

procedure;

Figure 5 is a schematic representation of the device according to the invention; and Figures 6A, B show a further schematic representation of the invention

Contraption.

Detailed description of preferred embodiments

Preferred exemplary embodiments are described below with reference to the figures. The same, similar or identical elements in the different figures are given identical reference numbers, and a repeated description of these elements is partly omitted in order to avoid redundancies.

1 A schematically shows a simplified processing method, in particular an LLO or LIFT method, in which a partial area 1 in the form of a micro-LED 1 is transferred from a substrate 30 directly to an active matrix 32. The simplified processing procedure applies analogously to general subareas 1 of the shift system.

For this purpose, a laser beam 20 is provided by an ultra-short pulse laser 2 (not shown) in which the ultra-short laser pulses run. In the initial state, the micro-LED 1 is arranged on a boundary layer 130 on the substrate 30.

For example, the substrate 30 can be made of sapphire, which can have a material thickness between 100 pm and 5 mm. However, it is also possible for the substrate 30 to be a carrier layer or a carrier substrate, such as a film, an adhesive or a wafer, from which the micro-LEDs 1 are transferred to a display panel in a further step. In particular, the layer thicknesses in Figures 1A, B are not drawn to scale.

The micro-LEDs 1 can have several layers 11, 12, 13, for example a layer 11 made of n-doped gallium nitride (GaN) and a layer 13 made of p-doped GaN. A pn junction 12 is formed between the two layers 11, 13, in which light of a characteristic wavelength is produced when a current or voltage is applied. The layers 11, 13 can be between 1 nm and 1 opm thick, for example. For example, the vertical cuts may already be present in the layer system, or may have been introduced into the layer system in a previous process step, so that the micro-LEDs 1 to be removed are only connected to the substrate via the boundary layer 130.

The boundary layer 130 between the micro-LED 1 and the substrate 30 is exposed to the laser beam 20 or the laser pulses 202 running therein. Since the substrate is 30 is transparent to the wavelength of the laser beam 20, the laser beam 20 can be guided through the substrate 30 to the boundary layer 130.

For example, the GaN of the first layer 11 of the micro-LED 1 may not be transparent to the wavelength of the laser beam 20, so that the introduced laser energy of the ultra-short laser pulses is absorbed there. The energy introduced can separate the GaN into liquid gallium and gaseous nitrogen at the interface, whereby a vapor pressure is formed at the interface 130, which detaches the micro-LED 1 from the substrate 30. At the same time, the micro-LED 1 can be separated from the substrate, for example by laser ablation at the interface 130. To a certain extent, targeted damage along the boundary layer 130 can be achieved through the interaction of the laser beam 20 with the first layer, so that the micro-LED 1 can be separated along the boundary layer 130. The detachment of the micro-LED 1 from the substrate 30 is called laser lift-off (LLO).

At the same time, the micro-LEDs 1 can be transferred to a carrier substrate 32 by the resulting forces. In particular, micro-LEDs 1 can be attached directly to a carrier substrate, for example glued, or transferred to a carrier substrate, for example another wafer. In particular, the micro-LED 1 can be applied to an active matrix as a carrier substrate 32, which is designed to provide a voltage and/or power supply to the micro-LED 1.

In Figure 1B, the carrier substrate 32 is approximately an adhesive layer. Since the micro-LEDs 1 were separated from the substrate 30 at the boundary layer 130 and transferred to the adhesive layer 32, the desired micro-LEDs 1 remain on the carrier substrate 32 when the substrate 30 is removed.

1C shows a possible processing strategy or pulse sequence, which are introduced one after the other into the boundary layer 130. Several laser pulses 202 with different pulse energy or time intervals are combined.

The ultra-short laser pulses have a pulse duration of between 50fs and 1000ps, preferably between 100fs and 100ps, particularly preferably between 50fs and 20ps. The repetition rate of the laser pulses can be greater than 10 kHz, preferably greater than 1 MHz. However, in a Laserburst 200 the repetition rate can be significantly higher. The wavelength of the laser beam 20 can be between 50nm and 300nm, preferably 257 or 258nm. In addition, the laser 2 can be operated in its basic mode. The fluence can be between 0.05J/cm2 and 10J/cm2, preferably between 0.1J/cm2 and 1J/cm2. The section of the pulse sequence in Figure 1C initially consists of two laser pulses 202, with the first laser pulse 202 being longer than the second laser pulse 202. However, the second laser pulse 202 has a higher intensity. The second section of the pulse sequence is a specific sequence of laser pulses 202, all of which have the same pulse length but increasing pulse intervals and decreasing pulse intensities. The third section of the pulse sequence shows a GHz laser burst 200 in which the laser pulses 202 are a few nanoseconds apart or where the distance is less than 1 ns. The fourth section of the pulse sequence again shows two laser pulses 202 with the same pulse length, but the second laser pulse 202 has a lower intensity than the first laser pulse 202.

All laser pulses 200 have a time interval that corresponds, for example, to the seed frequency of the ultrashort pulse laser 2. Accordingly, the laser pulses 200 can be synchronous to a clock frequency of the ultra-short pulse laser 2.

2A shows a method according to the invention with which partial areas 1 can be processed using several laser pulses 202. For this purpose, the focus positions between each laser pulse 202 in the boundary layer 130 are adjusted. The laser pulses 202 are, for example, part of a pulse sequence which, for example, comprises ten laser pulses 200 which are numbered from #1 to #10. Each laser pulse 202 can have a different focus position in the boundary layer 130, so that the focus position of the ultra-short laser pulses 202 of the laser beam in the boundary layer 130 is adjusted with pulse precision. For example, the repetition rate of the laser pulses 202 can be between 10 kHz and 50 MHz, approximately 25 MHz. For example, the first focus position can be acted upon by the laser pulses #1, #6, the second focus position can be acted upon by the laser pulses #2, #7, the third focus position can be acted upon by the laser pulses #3, #8, and the fourth focus position can be acted upon by the laser pulses #4, #9 are applied and the fifth focus position is acted upon by the laser pulses #5, #10. The exposure of the boundary layer 130 in all focus positions takes only 1 ps at a repetition rate of, for example, 10MHz.

Such a rapid repositioning of the focus positions can be made possible, for example, with an acousto-optical deflector, as described further below.

A further method according to the invention is shown in FIG. 2B. For this purpose, the boundary layer 130 of the partial area 1 is exposed to 16 laser pulses 202, with the focus position between the laser pulses 202 being adjusted. This creates a pattern of 4 by 4 focus zones in the boundary layer 130, where the laser pulses 202 are introduced. Through this sequential scanning of the partial area 1, the thermal energy input can be optimized. In Figure 2C A micro-LED 1 processed using this process can be seen, which bears the signature of the 16 laser pulses.

A further method according to the invention is shown in FIG. 2D. Here, six laser pulses are introduced one after the other into the boundary layer 130 of a partial area 1. The six laser pulses 202, numbered from #1 to #6, are introduced one after the other in different focus positions. The successively acted upon positions are not directly adjacent, so that the thermal effect is distributed over the entire boundary layer 130 and thus the thermal introduction is optimized.

Analogously, a process strategy is shown in FIG. 2E, whereby the focus positions of the laser pulses 202 are always as far apart as possible. For example, position #2 is the furthest away from #1. Likewise, position #3 is the furthest apart, and so on.

A further method according to the invention is shown in FIG. 2F. Here, only one laser pulse 202 is emitted per partial area 1, with successive laser pulses 202 acting on the boundary layers 130 of different partial areas 1. For example, in a first pass, the first focus position of the ultra-short laser pulses 202 is initially placed in the lower left corner of the partial area 1. Only when the partial area 1, or even just a part of the partial area 1 of a substrate 30, has been processed, is the boundary layer of the first partial area 1 acted upon again. It is accordingly possible for the laser beam 20 to jump back and forth between the laser pulses 202 between the different partial areas and to act on the partial areas 1 sequentially, so to speak, at different focus positions. This makes it possible to control the build-up and release of material tensions in particular, thereby optimizing the process quality. For the focus positions on the individual subareas, a process strategy as shown in Figures 2D, E can be used.

3 shows a further method with which partial areas 1 can be processed using several laser pulses 202 of a laser burst 200. Not only is the focus position between the laser pulses 202 changed. The laser pulses 202 also have different beam shapes, which can be impressed by beam shaping optics 4 (not shown). The different beam shapes are represented by the different symbols (circle, square, triangle, hexagon). For example, a first beam shape (circle) can be a Gaussian TE00 mode. For example, a second beam shape (square) can be a higher TE mode. For example, a third beam shape (triangle) may be a complex beam shape that extends in three spatial dimensions. For example, a fourth beam shape (hexagon) be a multi-focus distribution that has, for example, six individual focus zones.

For example, each laser pulse 200 can have its own beam shape impressed on it.

In Figure 3A, a partial area 1 is exposed to four different beam shapes and eight laser pulses 202. The different beam shapes are introduced into the boundary layer 130 in different focus positions. However, it is also possible for different partial areas 1 to be exposed to different beam shapes, as shown in FIG. 3B.

4A shows a further method according to the invention, with which several partial areas 1 can be processed successively. For this purpose, the multifocus distribution 22 is reoriented on the substrate 30 between each laser pulse 202 of the ultrashort pulse laser 2. Each laser pulse 202 of the ultrashort pulse laser 2 is divided into six individual foci 220 and introduced into the boundary layer 130. Each laser pulse has a pulse energy of more than 1 pJ, so that around a sixth of it reaches each individual focus. With a diameter of the individual foci of 20pm, the fluence is approximately 0.05J/cm2. In particular, the partial areas 1 can be processed with the repetition frequency of the ultra-short pulse laser 2. If the repetition frequency is around 10MHz, ten million Miko-LEDs 1 can be processed per second. In particular, a diagnostic device 8 (not shown) can know the positions of the functioning partial areas 1 on the substrate 30, so that the laser pulses 202 are only introduced into the interfaces 130 of the partial areas 1, which can later be used in a display. This allows the quality of such a display to be increased and, in particular, pixel errors to be avoided during production. Such skipping of the faulty partial areas 1 is not accompanied by a loss of process speed, since the laser beam 20 can skip the distance between two pulses.

4B, analogous to FIG. 4A, shows a method in which a multifocus distribution 22 of 3 times 3 individual foci is repositioned on the substrate 30 between each laser pulse 202 of the ultrashort pulse laser 2 in order to process microLEDs. The empty grid locations correspond, for example, to the faulty micro-LEDs. To process the six micro-LEDs 1, only six laser pulses 202 are required.

A device according to the invention is shown very schematically in FIG. Here, the ultra-short pulse laser 2 is set up to provide a laser beam 20 made up of ultra-short laser pulses 202. The beam shaping device 4 is set up to impose a beam shape on the laser beam 20, while the processing optics 5 is set up to transfer the laser beam 20 into the boundary layer 130 between partial area 1 and substrate 30 and to apply the ultra-short laser pulses 202 to this, whereby the partial area 1 is processed. The ultra-short pulse laser 2 can in particular provide a basic laser beam with a wavelength of 1030 nm and include a frequency doubling crystal (not shown) which is designed to double the frequency of the incident laser beam or halve the wavelength, the basic laser beam being guided successively through two frequency doubling crystals, for example becomes. As a result, the frequency of the basic laser beam is quadrupled overall, or the wavelength of the basic laser beam is quartered overall. A laser beam 20 with a wavelength between 250nm and 270nm is therefore provided.

The beam shaping device 4 can in particular be an acousto-optical deflector and/or a microlens array and/or a diffractive optical element which imprints a beam shape on the laser beam 20. The partial laser beams, which are formed from the laser beam 20 by the beam shaping device 4, can be transferred into the respective focus zones via processing optics 5.

In particular, the acousto-optic deflectors can be used for rapid beam deflection so that the laser pulses 202 can be quickly repositioned. However, it is also possible for the laser pulses 202 to be repositioned, for example, by a polarization-dependent deflection, such as a birefringent crystal, so that only the polarization of the laser pulse 202 needs to be adjusted for rapid repositioning. Such repositioning elements can be designed as part of the beam shaping device.

The optical components of the device can comprise CaF or crystalline quartz, or are made of CaF or crystalline quartz and/or can be designed as reflective elements, making the optical components particularly suitable for UV and DUV applications.

In addition, the device can have a feed device 6 in order to move the laser beam 20 and/or the substrate 30 with the partial region 1 relative to one another. For example, such a feed device can be an xyz table.

The device can have a controller 7 which coordinates the various components of the device with one another. For example, the ultra-short pulse laser 2 can be connected to the controller 7, so that the controller 7 can trigger the emission of a laser pulse 202 or a laser burst 200. The controller 7 can further be connected to the beam shaping device 4, so that the laser pulses 202 can be quickly repositioned. In this way, the focus positions can also be adapted to the geometric shape of the sub-area 1. The control 7 can also be connected to a feed device 6, see above that the feed device 6 can be moved, for example, between the laser pulses 202 in order to achieve a rough positioning of the substrate 30 under the processing optics 5.

A part of the device according to the invention is shown schematically in FIG. 6A. The ultra-short pulse laser 2 provides a laser beam 20 in which the laser pulses 202 of the laser 2 run.

In the embodiments shown, the laser beam 20 is typically guided through a beam shaping device 4, which is, for example, an acousto-optical deflector unit. The laser beam 20 can be focused using an adjacent lens and is then optionally guided through a filter element 54 where the beam profile of the laser beam 12 can be manipulated and optimized for the processing process. In particular, this allows spatial frequencies to be filtered out so that the laser pulses 10 imaged on the material 2 have a high contrast.

The image of the filter element 54 is finally imaged by the processing optics 5 into the boundary layer 130 of the partial area 1. This can be done, for example, by the processing optics 5 being a telescope.

In the case shown, the optional filter element 54 is in front of the first lens 50 in the beam direction at a distance which corresponds to the focal length F1 of the first lens. In the beam direction behind the first lens 50 there is a second lens 52. Between the first lens 50 and the second lens 52 lie the image-side focal point of the first lens 50 and the object-side focal point of the second lens 52. Both focal points coincide, so that the distance between the both lenses 50, 52 correspond to the sum of the focal lengths F1 + F2. Accordingly, the telescope used is Fourier optics. The focal plane is located behind the second lens 52 in the boundary layer 130 of the partial area 1. The focal plane is arranged from the lens 52 at a distance F2, which corresponds to the focal length of the second lens 52.

The laser pulses 202 of the laser beam 20 hit the boundary layer 130 in the focal plane and are at least partially absorbed there, whereby the partial area 1 is processed. During the processing process, the laser beam 20 can be moved relative to the material 2 with the feed device 6. However, rapid deflection of the individual laser pulses is achieved via the actus-optical deflector 4.

Instead of a substrate moved by means of the feed device 6 or in addition to the feed device 6, a scanner, for example a galvano scanner 62, can be used between the lenses 50, 52 of the processing optics 5, as shown in Figure 6B. In particular Position and/or angle information from the galvano scanner 62 and/or the feed device 6 can be recorded at a high measuring rate via corresponding encoders, so that synchronization with the laser pulses 202 is possible.

To the extent applicable, all individual features shown in the exemplary embodiments can be combined and/or exchanged with one another without departing from the scope of the invention.

Reference symbol list

1 section

11 first layer

12 pn junction

13 second layer

2 ultra-short pulse lasers

20 laser beam

200 laser burst

202 laser pulse

22 multi-focus distribution

220 single focus

30 substrate

32 additional substrate

4 beam shaping optics

5 processing optics

50 first lens

52 second lens

54 filter element

6 feed device

62 scanners

7 Control

8 diagnostic device

Claims

Expectations

1 . Method for processing at least one partial region (1) of a layer system, in particular a micro-LED, by means of ultra-short laser pulses of a laser beam (20) of an ultra-short pulse laser (2), the at least one partial region (l) being at a boundary layer (130) on a substrate ( 30), wherein the substrate (30) is essentially transparent to the wavelength of the ultra-short laser pulses of the laser beam (20), the boundary layer (130) passing through the substrate (30) with the ultra-short laser pulses (200) of the laser beam ( 20) is applied, whereby the at least one partial area (1) is processed, the position of the ultra-short laser pulses (202) of the laser beam (20) in the boundary layer (130) being adjusted with pulse precision.

2. The method according to claim 1, characterized in that the processing of the sub-area (1) is a laser-induced forward transmission of the sub-area (1) and / or a laser lift-off of the sub-area (1).

3. Method according to one of claims 1 or 2, characterized in that the position of the ultra-short laser pulses (202) of the laser beam (20) in the boundary layer (130) is adapted to the geometry of the partial region (1) with pulse precision.

4. Method according to one of the preceding claims, characterized in that

- the pulse duration of the ultra-short laser pulses is between 50fs and 1000ps, preferably between 100fs and 100ps, particularly preferably between 50fs and 20ps, and/or

- The wavelength of the laser beam (20) is between 50nm and 300nm, preferably between 250nm and 270nm, and/or

- the laser (2) is operated in its basic mode, with the diffraction coefficient M ² being less than 1.5, and/or

- the fluence is between 0.05J/cm2 and 10J/cm2, preferably between 0.1 J/cm2 and 1 J/cm2.

5. Method according to one of the preceding claims, characterized in that the repetition rate of the laser pulses is greater than 10 kHz, preferably greater than 1 MHz.

6. Method according to one of the preceding claims, characterized in that the laser beam (20) of the ultra-short pulse laser (2) has a defined polarization, preferably linearly polarized.

7. Method according to one of the preceding claims, characterized in that the position of the laser pulses (202) is adjusted using an acousto-optical deflector.

8. Method according to one of the preceding claims, characterized in that successive laser pulses (202) have different focus positions in the boundary layer (130), preferably the greatest possible distance from one another within the geometry of the partial region (1) that has not yet been acted upon.

9. Method according to one of the preceding claims, characterized in that the laser pulses at least partially have a different beam shape, preferably have a multi-focus distribution.

10. Method according to one of the preceding claims, characterized in that the partial areas (1) to be acted upon are selected by a diagnostic device.

11. Device for processing at least a partial area (1) of a layer system, in particular a micro-LED, comprising an ultra-short pulse laser (2) and processing optics (5), the ultra-short pulse laser (2) being set up to produce a laser beam (20) made up of ultra-short laser pulses ( 202), wherein the at least one partial region (1) is arranged at a boundary layer (130) on a substrate (30), the substrate (30) being at least partially transparent to the wavelength of the ultra-short laser pulses (202) of the laser beam (20). is, wherein the processing optics (5) is set up to transfer the laser beam (20) into the boundary layer (130) and to apply the ultra-short laser pulses (202) to it, whereby the at least one partial area (1) is processed, one Beam shaping device (4) is provided, which is designed to adjust the position of the ultra-short laser pulses (202) of the laser beam (20) in the boundary layer (130) with pulse precision.

12. The device according to claim 11, characterized in that the ultra-short pulse laser (2) provides a basic laser beam with a wavelength of 1030 nm and comprises at least one frequency doubling crystal, which is set up to double the frequency of the incident laser beam or to halve the wavelength, wherein the basic laser beam is guided twice through the frequency doubling crystal, preferably sequentially through a first frequency doubling crystal and then through a second frequency doubling crystal, whereby the frequency of the basic laser beam is quadrupled overall, or the wavelength of the basic laser beam is quartered overall and thus a laser beam (20). a wavelength between 250nm and 270nm is provided. Device according to one of claims 11 or 12, characterized in that the beam shaping device (4) is an acousto-optical deflector and/or a microlens array and/or a diffractive optical element. Device according to one of claims 11 to 13, characterized in that at least one optical component of the device comprises CaF or crystalline quartz, or is made of CaF or crystalline quartz and / or is designed as a reflective element. Device according to one of claims 11 to 14, characterized by a control (7) which is communicatively connected to the ultra-short pulse laser (2) and/or the beam shaping device (4) and is set up to control the ultra-short pulse laser and/or the beam shaping device (4). to control. Device according to claim 15, characterized by a feed device (6), preferably a scanner, particularly preferably a galvano scanner (62), for moving the laser beam (20) in the focal plane, the feed device (6) being communicative with the control (7 ) connected is. Device according to one of claims 15 or 16, characterized by a diagnostic device (8) which contains a database with the coordinates of functioning partial areas (1) on the substrate (30) and which is communicatively connected to the controller (7), or as Part of the control (7) is formed.