DE102022114645A1 - Method and device for processing at least a portion of a layer system - Google Patents

Abstract

The present invention relates to a method and a device for processing at least one partial region (1) of a layer system, in particular a micro-LED, using ultra-short laser pulses of a laser beam (20) of an ultra-short pulse laser (2), wherein the at least one partial region (1) on a Boundary layer (130) is arranged 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) are applied, whereby the at least one partial area (1) is processed, the ultra-short laser pulses being introduced into the boundary layer in the form of a laser burst.

Description

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.

EP2872751 shows a method for forward deposition of a material onto a carrier substrate using ultrashort laser pulses, but the wavelength of the ultrashort laser pulses is 350nm to 2µm.

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 area of a layer system, in particular a micro-LED, is proposed using ultrashort laser pulses of a laser beam of an ultrashort pulse laser, wherein at least one partial area 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 ultrashort laser pulses are introduced into the boundary layer in the form of a laser burst.

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 are 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. The method is described below 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 produce light of a specific wavelength when a voltage or current is applied , preferably output a visible wavelength. 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 10µm. For example, a micro LED can be square and 20×20µm2 or 30×30µm2.

The micro-LEDs are typically manufactured on a substrate. For this purpose, the p- and n-doped semiconductors are deposited one after the other on 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, the substrate can deteriorate the optical properties if the light from the microLEDs 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 essentially transparent substrate can consist of sapphire or a polymer or a plastic or silicon or comprise one of the aforementioned materials. For example, the substrate can be made of silicon carbide SiC. For example, the substrate can be made of sapphire, which is particularly robust in relation to the wavelength used. 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 can separate the GaN into liquid gallium and gaseous nitrogen in the boundary layer. 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 sub-area, in particular the micro-LED, can therefore in particular be the laser-induced forward transmission of the sub-area and/or the laser lift-off of a sub-area of a substrate.

According to the invention, the ultrashort laser pulses are introduced into the boundary layer in the form of a laser burst.

By successively applying a large number of laser pulses to the boundary layer in a laser burst, the laser energy is accumulated to a certain extent until the processing threshold is reached of the sub-area is exceeded. This is possible, for example, if the repetition rate of the laser pulses is greater than the reciprocal of the heat diffusion time. The laser pulses then work together like a single laser pulse. In particular, it is possible that none of the laser pulses exceeds the processing threshold of the partial area, so that a single laser pulse cannot process the partial area. However, a laser burst of such laser pulses can introduce the laser pulses into the boundary layer in such rapid succession that the partial area can be processed accordingly.

In particular, the processing of the sub-areas can be optimized through the tailored temporal energy input. For example, the energy input of a laser pulse from an excimer laser can be recreated or complex pulse patterns can be used to process the partial areas with minimal damage. Accordingly, the LLO and LIFT procedures can be optimized using laser bursts.

The length of the laser bursts can be between 20ps and 100ns, preferably between 100ps and 10ns.

In particular, the length of the laser bursts is of the order of magnitude of the laser pulses of an excimer laser, but with the difference that the individual laser pulses and the energy transfer through the laser pulses can be adapted for the partial areas. In addition, the significantly shorter pulse duration compared to an excimer laser reduces the heat input and thus avoids material tension in the partial areas.

With the pulse lengths specified above, numerous laser pulses can be arranged in one laser burst. For example, with a laser burst length of 10ns, five hundred laser pulses with a laser pulse duration of 20ps can be introduced into the boundary layer. But it is also possible for a laser burst to comprise, for example, 2 or 5 or 10 or 50 or 100 or 200 or 400 pulses.

The repetition rate of the laser bursts can be greater than 1 kHz, preferably greater than 100 kHz, particularly preferably between 100 kHz and 10 MHz.

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

The repetition rate of the laser pulses in the laser burst can be greater than 200MHz, preferably greater than 500MHz, particularly preferably greater than 1000MHz.

The laser pulses can accordingly have a fixed time interval within the laser burst.

The time between two laser pulses of a laser burst should be less than 5ns, preferably less than 2ns, particularly preferably less than 1ns.

This makes it possible for the distances between two successive laser pulses in a laser burst to be different. For example, the energy input into the boundary layer can be adjusted in such a way that the development of undesirable material stress in the boundary layer is reduced.

For example, a second laser pulse can have a distance of 500ps from the first laser pulse. For example, a third laser pulse can have a distance of 400ps from the second laser pulse. For example, a fourth laser pulse can have a distance of 300ps from the third laser pulse. The laser pulses can therefore in particular be a negative or a positive chirp.

The distances between the laser pulses can be greater than the length of the laser pulses.

This ensures that the laser pulses are successively introduced into the boundary layer and that the laser pulses do not overlap. In particular, this avoids interference between the laser pulses. In particular, a particularly high pulse density in the laser burst can be achieved by a small distance between the laser pulses.

The length of the laser bursts can be smaller, preferably significantly smaller, than the time intervals that result from the repetition rate of the laser bursts.

The length of the laser bursts is significantly smaller if it is less than a tenth, preferably less than a fiftieth, than the time intervals that result from the repetition rate of the laser bursts.

For example, the time interval between the laser bursts is only 1µs at a repetition rate of 1 MHz. The laser burst can consist of ten laser pulses, each with a length of 100fs. The distance between the laser pulses can, for example, be 1ns each, i.e. correspond to a repetition rate of the laser pulses of 1GHz. The ten Laser pulses are therefore emitted in approximately 10ns. This time corresponds to only one hundredth of the time interval between the laser bursts.

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 index M ² being less than 1.5.

Accordingly, the basic transversal electrical mode TEM00 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, the beam cross section in the TE00 mode is smaller than in the higher modes, allowing more targeted processing of the sub-areas. The diffraction index indicates the deviation of the laser beam from the ideal TE00 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 resulting vapor pressure, which detaches the partial area from the substrate.

The laser pulses of a laser burst can at least partially have different pulse lengths and/or have different polarizations.

At least partially different can mean that only one laser pulse has a different pulse length than the other laser pulses of the laser burst.

For example, a first laser pulse can be very short and have a length of 300 fs, while the pulse length drops to 100ps for the last laser pulse of the laser burst with approximately the same pulse energy over the duration of the laser burst. For example, the laser pulses can be alternately long and short. For example, the laser pulses can first have a first length and then have a second length. By controlling the pulse length, the time of energy input into the boundary layer can be adjusted, so that the processing of the partial areas can be optimized.

For example, a first laser pulse of the laser burst can have an s-polarization and a second laser pulse can have a p-polarization. However, it is also possible for the electric field vectors of the different polarizations to assume any angle between and 90°, for example 30° or 45°.

The laser pulses of a laser burst can at least partially have different pulse energies.

For example, two consecutive laser pulses can have different laser pulse energy. For example, a first laser pulse can have a first laser pulse energy and a second laser pulse can have a second laser pulse energy and a third laser pulse can again have the first laser pulse energy. By controlling the laser pulse energy, the size of the energy input into the boundary layer can be adjusted, so that the processing of the partial areas can be optimized.

In particular, the chemical reactions to be generated or the mechanical effect of the impact on the boundary layer are thereby optimized. For example, this creates pulse defects or intermediate states, which can be amplified by the following pulses with different pulse parameters.

The laser pulses of the laser burst can have different focus positions in the boundary layer.

Due to the quasi-simultaneous effect of the laser pulses on a time scale of the order of nanoseconds, the boundary layer of the sub-area can be exposed to the laser energy in a spatially very homogeneous manner. In particular, the focus positions of the laser pulses can lie within the geometry of the partial areas. It is also possible for the envelope of the laser pulses to have a shape that corresponds to the geometric extent of the partial area.

For example, a partial area can have a dimension of 10×20µm2. Six different laser pulses can be used per laser burst of twelve laser pulses which focus positions are acted upon, with four focus positions being arranged in the corners of the partial area and two in the middle of the long sides. For example, the laser burst can have a length of 0.1 ns. For example, all focus positions can be affected by two laser pulses. For example, all focus positions can be subjected to successive laser pulses or each focus position can be subjected to every six laser pulses.

The focus positions of the laser pulses can be adapted to different partial geometries. For example, the distribution of the focus positions in the boundary layer can be adjusted by a beam shaping device. This means that different sub-areas can be processed, so that particularly efficient processing of different micro-LEDs is achieved and production costs can be reduced.

The laser pulses of the laser burst can at least partially have a different beam shape.

The beam shape can in particular be provided by a beam shaping device, as described further below.

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. 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 take place within the duration of the laser burst, which, for example, enable a targeted formation of a pressure wave, which is advantageous for the LLO and/or LIFT process.

The above task is further solved by a device with the features of claim 8. 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 region 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 region being arranged at a boundary layer on a substrate , 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 is set up to introduce the ultra-short laser pulses into the boundary layer in the form of a laser burst.

For example, such processing optics can be a lens or a mirror or a telescope, with which in particular the position of the focal plane in the beam propagation direction can be determined. 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 at least one frequency doubling crystal, which is designed to double the frequency of the incident laser beam or to halve the wavelength.

The basic laser beam can, for example, 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. As a result, the ultrashort pulse laser can provide a total laser beam with a wavelength between 250nm and 270nm.

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.

The device can comprise a beam shaping device which is designed to impart a beam shape to the laser beam, wherein the beam shaping device can be an acousto-optical deflector and/or a microlens array and/or a diffractive optical element.

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.

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. For example, deflections in the x and y directions can be created using a combination of two acousto-optical deflectors in a deflector unit.

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.

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.

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 ultrashort pulse laser may be configured to form the laser bursts internally or the device may include a pulse generator configured to form the laser bursts externally.

For example, the ultra-short pulse laser can receive a signal from a pulse generator through a control input, so that a corresponding laser burst is triggered. However, it can also be the case that the ultra-short pulse laser has an internal circuit that is set up to trigger a corresponding laser burst. It may also be the case that the ultrashort pulse laser has such an internal circuit, but the signal from this circuit can be overwritten by an external pulse generator.

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

Short description of the characters

• 1A, B, C eine schematische Darstellung des erfindungsgemäßen Verfahrens;
• 2A, B eine schematische Darstellung eines Laserbursts;
• 3 eine weitere schematische Darstellung eines Laserbursts;
• 4A, B eine weitere schematische Darstellung eines Laserbursts;
• 5 eine weitere schematische Darstellung eines Laserbursts;
• 6 eine weitere schematische Darstellung des erfindungsgemäßen Verfahrens;
• 7 eine weitere schematische Darstellung des erfindungsgemäßen Verfahrens;
• 8 eine weitere schematische Darstellung des erfindungsgemäßen Verfahrens; und
• 9 eine schematische Darstellung der erfindungsgemäßen Vorrichtung.

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

• 1A, B , C a schematic representation of the method according to the invention;
• 2A, B a schematic representation of a laser burst;
• 3 another schematic representation of a laser burst;
• 4A, B another schematic representation of a laser burst;
• 5 another schematic representation of a laser burst;
• 6 a further schematic representation of the method according to the invention;
• 7 a further schematic representation of the method according to the invention;
• 8th a further schematic representation of the method according to the invention; and
• 9 a schematic representation of the device according to the invention.

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.

In 1A A simplified processing method, in particular an LLO or LIFT method, is shown schematically, in which a partial area 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 202 of a laser burst 200 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 μm 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 an active matrix 32 in a further step. In particular, the layer thicknesses in the 1A, B 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 1nm and 10µm 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 with the laser pulses 202 of the laser burst 200 running therein. Since the substrate 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 laser energy introduced by the ultra-short laser pulses 202 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 32, 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 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.

In 1C a possible, general composition of laser bursts 200 is shown, which are successively introduced into the boundary layer 130. Several laser pulses 202 with different pulse energy or time intervals are combined.

The ultra-short laser pulses of the laser bursts 200 have a pulse duration of between 50fs and 1000ps, preferably between 100fs and 100ps, particularly preferably between 50fs and 20ps. The length of the laser bursts can be between 20ns and 100ns, preferably between 100ps and 10ns. The repetition rate of the laser bursts can be greater than 1kHz, preferably greater than 10kHz, particularly preferably greater than 100kHz. The repetition rate of the laser pulses in the laser burst can be greater than 200MHz, preferably greater than 500MHz. However, it is also possible for the time of two consecutive laser pulses 202 of a laser burst 200 to be less than 20 ns, preferably less than 1 ns. The wavelength of the laser beam 20 can be between 50nm and 300nm, preferably between 250nm and 270nm. 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 first laser burst 200 in 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 laser burst 202 is a specific sequence of laser pulses 202 which all have the same pulse length but increasing pulse intervals and decreasing pulse intensities. The third laser burst 200 shows a GHz laser burst 200 in which the laser pulses 202 have a distance of a few nanoseconds or where the distance is less than 1 ns. The fourth laser burst 200 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 bursts 200 have a time interval that corresponds to the repetition frequency of the laser burst. The repetition frequency of the laser bursts can, for example, be synchronous with a clock frequency of the ultra-short pulse laser 2. The laser bursts 200 have different lengths, which are shorter, preferably significantly shorter, than the time interval that results from the repetition frequency of the laser bursts. The pulse lengths and pulse intervals are therefore not shown to scale.

In addition to the temporal variation of the laser bursts 202, a beam shape can also be impressed on each laser pulse 202 of the laser bursts 200, for example in such a way that the beam shapes of the various laser pulses 202 are all different. It is also possible that each laser pulse 202 has a different position in the interface 130.

In 2 Laser bursts 200 with five laser pulses 202 are shown as an example. In 2A A laser burst 200 with five laser pulses 202 is shown schematically, the length of the laser burst 200 being shorter than 10 ns. The laser pulses 200 all have the same length, for example 20ps. In addition, the time interval between the laser pulses 202 is the same. Accordingly, the laser pulses 202 can be assigned a repetition frequency of, for example, 100MHz.

In 2 B is a schematic of the Laserburst 200 2A shown, but the distance between the laser pulses 202 increases as time progresses. The distances between the laser pulses 202 increase, for example. For example, the time interval between the first and second laser pulses is 20ns, while the time interval between the fourth and fifth laser pulses 202 is 50ns. The increase in the time distance can be traced, for example, using the dashed lines, which are always arranged at fixed time intervals.

In 3 A laser burst 200 with six laser pulses 202 is shown schematically and has a length of 200ps. The laser pulses 202 of the laser burst 200 have at least partially different pulse lengths. For example, the first laser pulse 202 may have a length of 100ps, the second laser pulse 202 may have a length of 50fs, the third laser pulse 202 may have a length of 20ps, the fourth laser pulse 202 may have a length of 100ps, the fifth laser pulse 202 may have a length of 100fs and the sixth laser pulse 202 can have a length of 100fs. Both the first and fourth laser pulses 202 have the same pulse length. The fifth and sixth laser pulses 202 also have the same pulse length. The pulse lengths are in particular at least partially different.

In 4 Two laser bursts 200, each with four laser pulses 202, are shown schematically, the laser pulses 202 having at least partially different pulse energies. The first and fourth laser pulses each have the same pulse energy, while the second and third laser pulses have different pulse energies. The laser bursts 200 are each 500ps long. In 4A The laser pulses also have different pulse lengths, while in 4B the laser pulses 202 have the same length.

In 5 A laser burst 200 with five laser pulses 202 is shown schematically, the laser pulses 202 having at least partially different pulse lengths, at least partially different pulse durations and different pulse spacings. In particular, the pulse intervals become shorter as the laser burst time increases.

In 6 A method is shown with which partial areas 1 can be processed using several laser pulses 202 of a laser burst 200. For this purpose, the focus positions between each laser pulse 202 of the laser burst 200 are reoriented in the boundary layer 130. Each laser burst 200 includes, for example, ten laser pulses 200, which are numbered from #1 to #10, with each laser pulse 202 having a different focus position in the boundary layer 130. For example, the first focus position can be acted upon by the laser pulses #1, #2, the second focus position can be acted upon by the laser pulses #3, #4, the third focus position can be acted upon by the laser pulses #5, #6, and the fourth focus position can be acted upon by the laser pulses #7, #8 are applied and the fifth focus position is acted upon by the laser pulses #9, #10. The exposure of the boundary layer 130 in all focus positions, for example, does not last longer than 10 ns in total, so that the exposure occurs instantaneously or simultaneously on the time scale of heat transport. In particular, individual subareas 1 can be processed with the repetition frequency of the laser bursts 200. If the repetition frequency is around 10MHz, ten million Miko-LEDs 1 can be processed per second, for example. An active matrix 32 of a display with 3840 by 2160 micro-LEDs 1 could theoretically be populated in less than a second.

In 7 Another method is shown 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 a different beam shape. 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) can be a multi-focus distribution, which has, for example, six individual focus zones.

In 8th Another method is shown with which partial areas 1 can be processed using several laser pulses 202 of a laser burst 200. Neither the focus position nor the beam shape of the laser pulses 202 is changed. Instead, the entire boundary layer 130 of the subregion 1 is successively exposed to the laser pulses 202 of the laser burst 200.

In 9 a device according to the invention is shown. 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: Laser beam 20 impresses a beam shape, 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 it, 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 of 257nm or 258nm 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, can be transferred into the respective focus zones via processing optics 5.

In particular, the acute-optical deflectors can be used for rapid beam deflection, so that the laser pulses 202 of a laser burst 200 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 delivery of 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 controller 7 can also be connected to a feed device 6, so that the feed device 6 can be moved, for example, between the laser bursts 200 or the laser pulses 202 in order to achieve a rough positioning of the substrate 30 under the processing optics 5.

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

Sub-area

11

first layer

12

pn junction

13

second layer

2

Ultrashort pulse laser

20

laser beam

200

Laser burst

202

Laser pulse

22

Multifocus distribution

220

Single focus

30

Substrate

32

additional substrate

4

Beam shaping optics

5

Processing optics

6

feed device

7

steering

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2872751 [0006]

Claims (15)

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 (1) 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 ultrashort laser pulses being introduced into the boundary layer in the form of a laser burst. Procedure according to Claim 1 , characterized in that the processing of the sub-area (1) is a laser-induced forward transmission of the micro-LED (1) and/or a laser lift-off of the sub-area (1). Procedure according to one of the Claims 1 or 2 , characterized in that the substrate consists of sapphire or a polymer or a plastic or silicon or comprises one of the aforementioned materials. Method according to one of the preceding claims, characterized in that - the pulse duration of the ultra-short laser pulses (202) is between 50fs and 1000ps, preferably between 100fs and 100ps, particularly preferably between 50fs and 20ps, and / or - the length of the laser bursts ( 200) is between 20ps and 100ns, preferably between 100ps and 10ns, and/or - the repetition rate of the laser bursts (200) is greater than 1 kHz, preferably greater than 10kHz, particularly preferably greater than 100kHz st, and/or - the Repetition rate of the laser pulses (202) in the laser burst (200) is greater than 200MHz, preferably greater than 500MHz, particularly preferably greater than 1000MHz or the time between two laser pulses (202) of a laser burst (200) is less than 5ns, preferably less than 2ns , particularly preferably less than 1 ns, 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, whereby the Diffraction index M ² is less than 1.5, and/or - the fluence is between 0.05J/cm2 and 10J/cm2, preferably between 0.1 J/cm2 and 1J/cm2. Method according to one of the preceding claims, characterized in that the laser pulses (202) of a laser burst (200) at least partially have different pulse lengths and/or have different polarizations. Method according to one of the preceding claims, characterized in that the laser pulses (202) of a laser burst (200) have at least partially different pulse energies. Method according to one of the preceding claims, characterized in that the laser pulses (202) of the laser burst (200) have different focus positions in the boundary layer (130). Method according to one of the preceding claims, characterized in that the laser pulses (202) of the laser burst (200) at least partially have a different beam shape. 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), wherein the ultra-short pulse laser (2) is set up to provide a laser beam (20) made up of ultra-short laser pulses (202), wherein 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), 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, the device for this purpose is set up to introduce the ultra-short laser pulses (202) into the boundary layer (130) in the form of a laser burst (200). Device according to Claim 9 , characterized in that the ultra-short pulse laser (2) provides a basic laser beam with a wavelength of 1030nm and comprises a frequency doubling crystal which is set up to double the frequency of the incident laser beam or halve the wavelength, the basic laser beam being passed twice through the 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, thus providing a laser beam (20) with a wavelength of 257nm or 258nm. Device according to one of the Claims 9 or 10 , characterized by a beam shape mung device (4) which is set up to impose a beam shape on the laser beam (20), the beam shaping device (4) being an acousto-optical deflector and/or a microlens array and/or a diffractive optical element. Device according to one of the Claims 9 until 11 , 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 the Claims 9 until 12 , characterized in that the ultra-short pulse laser (2) is set up to shape the laser bursts (200) internally or that the device comprises a pulse generator which is set up to shape the laser bursts (200) externally. Device according to one of the Claims 9 until 13 , characterized by a controller (7) which is communicatively connected to the ultra-short pulse laser (2) and/or the pulse generator and the beam shaping device (4) and is set up to control the ultra-short pulse laser and/or the pulse generator and the beam shaping device (4). . Device according to Claim 14 , 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 communicatively connected to the control (7).

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