WO2022122251A1

WO2022122251A1 - Laser machining of a material using a gradient filter element

Info

Publication number: WO2022122251A1
Application number: PCT/EP2021/080195
Authority: WO
Inventors: Daniel Grossmann; Daniel FLAMM
Original assignee: Trumpf Laser- Und Systemtechnik Gmbh
Priority date: 2020-12-09
Filing date: 2021-10-29
Publication date: 2022-06-16
Also published as: DE102020132797A1

Abstract

The invention relates to an apparatus (1) for machining a material (2), in particular for drilling or structuring a material (2), by means of laser pulses of a laser beam (30) of a pulsed laser (3), preferably an ultrashort pulse laser, the apparatus (1) comprising a gradient filter element (4) for impressing an intensity gradient, which extends perpendicularly to the beam propagation direction, onto the laser beam (30) so as to form a machining beam profile (32), and an imaging optical device (5) for imaging the machining beam profile (32) into the material (2).

Description

LASER PROCESSING OF A MATERIAL USING A GRADIENT FILTER ELEMENT

technical field

The present invention relates to a device and a method for processing a material, in particular for drilling or structuring a material, by means of laser pulses of a laser beam from a pulsed laser, preferably an ultra-short pulse laser.

State of the art

In principle, it is known to remove material by means of laser machining processes. For example, it is known to remove material by means of percussion drilling in order to drill a hole in a material in this way. To do this, a laser beam is used to send several laser pulses in succession to the same position on the material in order to melt and partially vaporize the material at the point of impact. When the borehole is lowered into the material, the material vaporized by the laser can drive the melted material lying in front of it out of the borehole. Such a percussion drilling process makes it possible to achieve great drilling depths that are significantly greater than the drilling depths that can be achieved with a single-pulse method.

In particular, the percussion drilling method mentioned can also be used to drill boreholes that are inclined relative to the material surface. Furthermore, the higher geometric quality and lower conicity of the bore, as well as the possibility of machining hard materials, are also advantageous properties of percussion drilling.

During the machining process of percussion drilling, special boundary conditions are often placed on the drill edge, such as a desired rise or taper angle of the drill edge. Drilling using classic Gaussian beam profiles or with ring-shaped beam profiles, as well as drilling with flat-top beam profiles only offer limited possibilities for process optimization.

It is known from US Pat. No. 8,866,043 B2 to successively introduce a corresponding drilling geometry into a material. Here, as the beam diameter becomes smaller and smaller, one Lasers drilled conical holes in a material. However, this method requires the permanent adjustment of the beam diameter and thus a high level of effort when it comes to control and adjustment.

Presentation of the invention

Proceeding from the known prior art, it is an object of the present invention to provide an improved device for processing a material and a corresponding method.

The object is achieved by a device for processing material with the features of claim 1. Advantageous developments result from the dependent claims, the description and the figures.

Accordingly, a device for processing a material, in particular for drilling or structuring a material by means of laser pulses of a laser beam of a pulsed laser, preferably an ultrashort pulse laser, is proposed, comprising a gradient filter element for impressing an intensity gradient formed perpendicularly to the beam propagation direction on the laser beam to form a processing beam profile and further comprising imaging optics for imaging the processing beam profile onto or into the material.

By means of the targeted shaping of the processing beam profile perpendicular to the beam propagation direction of the laser beam and the use of this processing beam profile for processing the material and in particular for removing material, holes can be made more reliably in the material according to the given boundary conditions, such as local removal depth and taper angle as well as slope.

In this case, the material can be essentially non-transparent material such as a metal foil or a polymer or a plastic, or consist of silicon. In this context, essentially non-transparent means that the material can partially or completely absorb the laser light of the given wavelength, so that processing energy can be introduced and the material can therefore also be processed.

The laser provides the laser pulses that form the laser beam. Instead of individual laser pulses, the laser can also provide bursts of laser pulses, each burst comprising the transmission of a number of laser pulses. In particular, the laser can be an ultra-short pulse laser, with the pulse length of the individual laser pulses preferably being shorter than 100 hp is. In particular, fundamental-mode ultrashort-pulse lasers are preferred, which provide a laser beam with a diffraction index M ² <1.5, ie have a high beam quality.

The beam profile of the laser beam can be described, for example, via a longitudinal beam cross section along the propagation direction of the laser beam and via a lateral beam cross section perpendicular to the propagation direction of the laser beam.

A processing beam profile perpendicular to the direction of beam propagation is understood to mean a spatial intensity distribution of the laser beam in the plane perpendicular to the direction of beam propagation. Typically, the beam profile perpendicular to the direction of beam propagation from the laser is a Gaussian processing beam profile. This means that each cross section in the plane perpendicular to the direction of beam propagation through the laser beam corresponds to a Gaussian bell curve. The intensity of the laser beam is greatest in the center of the laser beam, while it decreases towards the edge of the laser beam. However, the beam profile perpendicular to the beam propagation direction, starting from the laser, can also have a different shape, for example correspond to a higher laser mode. The intensity gradient is the spatial change in intensity in the beam profile.

The laser beam provided by the laser is guided through a gradient filter element, as a result of which an additional intensity gradient is introduced into the beam profile perpendicular to the direction of beam propagation and the processing beam profile is formed in this way. In particular, this means that the beam profile of the laser is transformed into a processing beam profile perpendicular to the beam propagation direction when passing through the gradient filter element. In this case, a gradient filter element is an optical element which is able to correspondingly shape the processing beam profile perpendicularly to the beam propagation direction.

In general, a gradient filter element can be, for example, a gradient filter, or an aperture, or a polarization mask, or a combination of these elements. When the laser beam passes through the gradient filter element, the processing beam profile is accordingly impressed on the incoming beam profile of the laser beam perpendicular to the direction of beam propagation.

For example, with an aperture, this can mean that the incoming Gaussian beam profile of the laser is partially clipped. If a diffraction grating is used at the same time, which bends the incoming laser beam as it passes through, corresponding Diffraction orders are cut off, so that the resulting processing beam profile is changed perpendicularly to the beam propagation direction accordingly.

The processing beam profile imposed by the gradient filter element is then imaged into the material by imaging optics.

An imaging optic can be an imaging optical component, for example. However, imaging optics can also be a collection of imaging optical components. In other words, the processing beam profile is focused into the material and an image of the processing beam profile is thereby generated in the material. In particular, the intensity gradient of the processing beam profile is also imaged, so that the spatial change in the incident laser intensity is reproduced by the gradient filter element in the image in the processing plane.

The processing beam profile is imaged accordingly in the material by the imaging optics, provided that the focal point of the imaging optics is below the surface of the material, so that the processing beam profile is imaged in the volume of the material. The processing beam profile is imaged onto the material if the focal point of the imaging optics is on the surface of the material or even above the surface.

The material absorbs the irradiated laser energy at least partially, which leads to heating of the exposed material or to a transition of the material to a temporary plasma state and evaporation of the material and thus ultimately to the desired removal of the material in the areas exposed to the image of the processing beam profile of the material leads. In particular, it is therefore also possible that, in addition to linear absorption processes, non-linear absorption processes are also used, which become accessible through the use of high laser energies and in particular through ultra-short laser pulses with high energies.

The intensity of the laser beam is maximized at the focus point by the focussing of the processing beam profile by the imaging optics, so that material removal can take place at this point, the spatial expression of which corresponds to that of the processing beam profile. In this case, the processing beam profile can have a radially decreasing intensity, for example, but the processing beam profile can also increase abruptly perpendicularly to the beam propagation direction and form a stepped profile. The shape of the processing beam profile makes it possible to prepare the laser beam for a special type of material removal or a specific process step.

For example, a specific processing beam profile can be used for planar removal, with the focus being on the homogeneity of the removal over the area. For example, a different specific processing beam profile can be used for drilling a material, with the focus being on the removal depth per laser pulse. For example, such a processing beam profile can be used in a targeted manner to locally change the removal depth of blind holes. For example, the processing beam profile can also be designed in steps, as a result of which a different removal is realized in the center of the borehole than at the edge of the borehole. In particular, the depth of removal introduced or the rate of removal can be spatially determined by the introduced intensity. For example, the surface of a material can also be structured, for example built up or polished, so that specific intensity gradients can be used for this.

It is possible to adapt the geometry of the machining process locally as a result of the lateral intensity gradient of the machining beam profile imposed by means of the gradient filter element. For example, a large, symmetrical intensity gradient can produce a borehole with a steep bore wall, i.e. a large taper angle, while a small, symmetrical intensity gradient can create a borehole with a flat bore wall, i.e. a small taper angle. When forming the bore walls arranged at an angle to the surface of the material, ie the bore walls arranged at a taper angle, the projection of the intensity distribution onto the removed flanks typically plays a role. This effect can thus be compensated for or intensified by the targeted local shaping of the intensity gradient by the gradient filter element.

It is also possible that the intensity gradient of the processing beam profile is asymmetrical to the center of the beam. As a result, for example, the laser beam with the impressed processing beam profile can produce a borehole that has a steeper edge on one side than on the other side. If only the intensity gradient is varied, but the laser energy deposited per surface element remains the same, an equally large removal depth is generated on both sides of the borehole.

The overall shape of the borehole can thus be adjusted by the intensity distribution in the processing beam profile. Successive laser pulses with the same applied processing beam profile are emitted at the same location on the material, causing the material to heat up according to the intensity distribution of the processing beam profile. By delivering the laser pulses into the material in rapid succession, it is possible to put the material into a temporary plasma state, thereby partially vaporizing the material. The vaporized material can drive further material, for example ablation products such as particles or liquid material, out of the borehole, so that the subsequent laser pulses reach and vaporize the material layers located at a greater ablation depth.

In particular, the areas of the material in which the processing beam profile has a high intensity are removed to a particularly great extent, while the areas of the material in which the processing beam profile has a low intensity are removed to a lesser extent. As a result, the intensity gradient of the processing beam profile, or the spatial intensity distribution of the processing beam profile, is reflected in the finally realized removal geometry of the borehole. In other words, the gradient filter element determines the geometry of the drilled hole drilled into the material.

The imaging optics preferably comprise two imaging components. In this case, an imaging component can in particular be an optical component with imaging properties, such as, for example, with a focusing or collimating effect. These include, among other things, imaging or curved mirrors, aspheres, beam-shaping elements, diffractive optical elements, lenses such as converging lenses or scattering lenses, Fresnel zone plates and other free-form components. Preferably, the two components have the same focal length, with the gradient filter element being at the object-side focus of the first component, the image-side focus of the first component coinciding with the object-side focus of the second component, and the material being at the image-side focus of the second component.

In the mathematical ideal case, the focal planes and the corresponding planes, in particular the processing planes, are planes which are oriented perpendicularly to the beam propagation direction and in particular are not curved and are only extended in two dimensions. In practical implementation, however, the optical components lead to slight curvatures and distortions in these planes, so that these planes are usually at least locally curved. In addition, the focal point also has a finite volume due to the components used. In particular, the focusing of light is typically limited to length scales that are of the order of the wavelength of the light used. This applies in particular both in the beam propagation direction and perpendicular to the beam propagation direction. The components used can also result in a curved focal volume instead of a flat, two-dimensional focal plane, in which an image of the laser beam is still sufficiently sharp, as specified below.

Overall, however, the orientation of this volume relative to the direction of propagation of the laser beams is given to a good approximation by the orientation of the mathematical focal plane. In the following, the focal plane is therefore always mentioned, although the accessible focal volume is always taken into account, even if it is not explicitly mentioned. Incidentally, the above explanation also refers to the processing levels used below.

In particular, this results in positioning tolerances for the positions of the components used. For example, a positioning tolerance can be up to 10% or 20%, so that a component that is supposed to be at a distance of 10 cm from a reference point, for example, still enables a sufficiently sharp image even at 9 cm and 11 cm. The images are automatically sufficiently sharp if the components are all positioned within the positioning tolerance. In addition, a "coincidence" of two planes or two points means that the associated volumes at least partially overlap.

The positioning of the components mentioned above results in so-called 4f optics, which makes it possible to image the processing beam profile generated by the gradient filter element directly in a processing plane in the material and thus to directly shape individual sub-areas of the processed material, such as the borehole walls of a Well in a drilling process, is made possible. In particular, the object-side intermediate plane of the imaging optics, namely that in which the gradient filter element is arranged, is imaged onto the workpiece. It is thus possible to access the processing plane in the material and adapt the beam shape in the processing plane by engaging in the intermediate plane of the imaging optics on the object side.

The object-side foci are the foci of the components on the in

Beam direction in the gradient filter element side facing. The image-side foci are here the focal points of the components on the side facing the material in the direction of the beam.

For example, the two components can be lenses with a focal length of 50 mm each and form the imaging optics, with the gradient filter element being 50 mm away from the first lens, ie in the object-side focal point of the first lens. The second lens in the beam direction can be 100 mm away from the first lens, so that the image-side focal point of the first lens coincides with the object-side focal point of the second lens. The material can in turn be 50 mm away from the second lens, i.e. it can be in the focal point of the second lens on the image side. Thus, the gradient filter element is 200 mm away from the material, with the 200 mm corresponding to four times the focal length of the lenses.

However, a first lens can also have a smaller focal length than the second lens or vice versa. For example, a first lens can have a focal length of 500 mm and a second lens a focal length of 10 mm. The gradient filter element is then 500 mm in the beam direction in front of the first lens. The second lens follows the first lens at a distance of 510 mm and the material is in the image-side focus of the second lens at a distance of 10 mm in the beam direction.

The imaging optics can image the processing beam profile on a reduced scale, in particular reduced by a factor of 2 to 100, into the material.

The processing beam profile can thus be generated in the object-side intermediate plane of the imaging optics with a macroscopic gradient filter element, while the material can be processed on a microscopic level in the processing plane. In this way, higher energy densities can also be achieved in the processing plane, so that not only can processing with more precise contours be achieved, but also a higher removal rate can be achieved.

For example, the gradient filter element can generate a processing beam profile with an intensity gradient in which the intensity falls to zero over a length of 1 mm from the center of the laser beam to the edge of the laser beam. If this intensity gradient is imaged on the material 100 times smaller, then the intensity in the material falls from the center of the laser beam to the edge of the laser beam to zero over a length of 10 pm. If the processing beam profile is reduced by a factor of 25, for example, then the intensity would be at a length fall from 40 pm to zero. This makes it possible to process the material on a much smaller scale

The gradient filter element can be a gradient filter.

A graduated filter can be a neutral density filter, for example, with the density of the neutral density filter being location-dependent. For example, the neutral density filter in the center of the filter can have little or no density, so that the incident laser light is transmitted, while the neutral density filter can have a high density at the edge of the filter, so that the incident laser light is not transmitted or only minimally transmitted or absorbed to the maximum becomes. In this way, a processing beam profile that differs from the beam profile of the incoming laser can be impressed on the incoming laser beam by the course of the density in the neutral density filter.

Instead of a density variation of the graduated filter, the graduated filter can also be reflective or partially reflective. In this way, the unwanted beam components can be reflected away from the laser beam instead of being absorbed. In particular, the reflected beam components can be reflected away from the incident laser beam at an angle and then guided into a beam trap in order to destroy them.

In a further preferred embodiment, the gradient filter element can include an element with a locally impressed diffraction grating, hereinafter referred to as a grating or diffraction grating, and an aperture device, with the aperture device being introduced between the first component and the second component, alternatively in front of the first component or is introduced behind the second component, is preferably introduced in the beam path after the diffraction grating and the first component and is set up to intercept selectable orders of diffraction from the beam path.

The local course of the diffraction grating on the diffraction grating is designed in such a way that either the useful beam is diffracted in a desired angular range, or the portion to be masked out is diffracted in an angular range. The undesired angular range can be specifically blocked in the further beam path, in particular also with a high laser power to be filtered.

The diffraction grating can also generate a gradient function by changing the diffraction efficiency locally, for example by adjusting the step height of the grating. Through Design of the local diffraction efficiency, for example by locally adjusting the step height of the grating, the grating can also have or assume an aperture function. Due to the locally adapted step height, locally different deflection angles are generated, which have different levels of diffraction efficiency.

The gradient filter element preferably comprises a polarization element and a polarization splitter.

In particular, provision can be made for the polarization element (460) to comprise a segmented, i.e. composite and/or progressive, birefringent optical element, in particular a nanograting or a liquid crystal, which imparts radial or azimuthal polarization to the laser beam (30).

The polarization element can preferably impose a locally variable polarization change on the laser beam, for example through segmented waveplate elements or through a continuously changing alignment of a birefringent structure, in particular a transparent element with birefringent nanostructures in the volume such as nanograting or liquid crystals. This encodes the aperture function in a local polarization. The various components can then be filtered out of the laser beam using a polarization splitter. For example, a local s-polarization then corresponds to complete transmission and a local p-polarization to vanishing transmission. The gradient functions can also be generated by means of intermediate states, for example by proportionate p and s polarization, with which a local 50 percent transmission at the polarization splitter is achieved, for example.

The polarization splitter is preferably introduced between the first and the second component, alternatively in front of the first component or behind the second component, and the polarization splitter is set up to reflect laser radiation of selectable polarization to a beam trap or to transmit it to the material to be processed.

A polarization element is an optical element that can vary the polarization of the incident laser beam depending on the location. In general, the laser beam hits the gradient filter element with a polarization defined by the laser optics. The polarization of the incident laser beam can be s-polarization, for example, ie polarized perpendicularly to the plane of incidence. When the laser light hits the gradient filter element in the form of a Polarization element hits, the polarization of the laser beam can be partially changed. For example, the polarization in the upper part of the laser beam can be an s-polarization, while in the lower part a p-polarization is specified - that is, polarized there parallel to the plane of incidence. However, the polarization can also be p-polarization in the center of the beam and have s-polarization at the edge of the beam.

The polarization element may also include a waveplate that affects the polarization and phase of the laser light. For example, a waveplate is an λ/2 plate or an λ/4 plate that rotates the polarization of the laser beam depending on the orientation of the polarization relative to an optical axis of the waveplate.

In particular, an λ/2 plate can also rotate the polarization of the incident laser beam before the laser beam falls on the actual polarization element and thus prepare the laser beam for the actual formation of the beam profile.

A polarization splitter is an optical element that deflects the incident laser beam in different directions depending on the polarization. For example, a polarization splitter can be a polarized beam splitter cube or a thin film polarizer. For example, in the example described above, the upper half of the laser beam, which is s-polarized, can be left in the beam path, while the p-polarized part of the laser beam can be reflected out of the beam path with the polarization splitter. Thus, only the desired shape of the intensity gradient remains in the beam path, which is predetermined by the polarization pattern predetermined in the polarization element. The part that is reflected out is guided into a beam trap, for example, and is absorbed there.

In an advantageous development, a further polarization element can be arranged after the polarization splitter in order to adjust the polarization during processing on the workpiece.

In an advantageous development, preforming optics are provided, according to which an imaging component, a diffractive optical element, an n-shaper or adaptive optics is preferably arranged in front of the gradient filter element, with the preforming optics preferably giving the incoming laser beam a flat-top beam profile impressed before the processing beam profile is formed in the gradient filter element. Pre-shaping the beam means that the incoming laser beam, before it hits the gradient filter element, is given a shape and, in particular, an intensity distribution that deviates from the natural beam profile of the laser. This shape can be impressed, for example, by an imaging component that collects the incident laser light from the laser, for example, in a focus point on the gradient filter element.

However, the incoming laser beam can also be given a flat-top beam profile using a diffractive optical element, a TT shaper or adaptive optics. A flat-top beam profile - deviating from the Gaussian beam profile of the incoming laser beam - has a homogeneous intensity of the laser beam over a wide range starting from the center of the laser beam and then suddenly drops to significantly lower values. The flat-top beam profile can be round or elliptical or have a polygonal contour.

This makes it possible to use the preforming optics to preform the intensity profile of the incoming laser beam before it hits the gradient filter element, so that only the intensity profile that is impressed by the gradient filter element is relevant for the processing beam profile in the material. In particular, a falling beam intensity towards the edge of the laser beam, as is the case with Gaussian beams, does not have to be compensated or balanced with the gradient filter element.

This makes it possible to increase the efficiency of the device and make better use of the laser energy made available by the laser. Additionally, using a preformed beam with a flat-top profile eliminates the need to consider the laser's natural processing beam profile when fabricating the gradient filter element.

The pulse duration of the pulsed laser beam can preferably be between 50 fs and 5000 ps, in particular between 100 fs and 10 ps, in particular 1 ps, and/or the maximum fluence can be between 0.01 J/cm ² and 100 J/cm ² , in particular between 0.1 J/cm ² and 10J/cm ² and/or the repetition rate can be between 1 kHz and 100 MHz and/or the wavelength of the laser beam can be between 50 nm and 3000 nm.

This makes it possible to process many different materials with different laser settings. The optical components used are preferably designed to be efficient enough for the wavelength used, so that optical components made of crystalline quartz or CaF2 can be used, particularly in the case of short wavelengths.

A feed device can preferably be provided, preferably a scanner optics and/or a cross table, by means of which the machining beam profile and the material can be shifted relative to one another between two machining processes and/or can be continuously shifted relative to one another.

With a feed device it is possible to position the machining beam profile at different positions in the material, for example in order to carry out a first machining process at a first location and to carry out a second machining process at a second location.

A scanner optic can, for example, be a galvanic scanner, which is located in the beam path of the laser and can deflect the beam in a targeted manner. A cross table, on the other hand, is typically located under the workpiece holder of the material, with which the material can be guided away under the laser beam.

In particular, the machining beam profile can be kept stationary during a single machining process. Kept stationary means that there is no relative movement between the material and the laser beam, or one that is negligible with regard to the structural accuracy to be produced. Since the laser beam is kept stationary on the material, successive pulses of the laser beam with the same processing beam profile are repeatedly introduced into the material at the same point, whereby the material is removed step by step. As a result, for example, percussion drilling can be carried out with the machining beam profile.

However, the processing beam profile and the material can also be moved continuously towards one another, so that the intensity distributions of the laser pulses in the material are superimposed, for example offset, in order to achieve continuous processing of the material.

The object set above is also achieved by a method for removing a material having the features of claim 10. Advantageous developments of the method result from the dependent claims and the present description and the figures. Accordingly, a method for removing a material is proposed, in particular for drilling or structuring a material, by means of the laser pulses of a laser beam of a pulsed laser, preferably an ultra-short pulse laser. According to the invention, an intensity gradient perpendicular to the beam propagation direction is impressed on the laser beam by means of a gradient filter element in order to form a processing beam profile and the processing beam profile is imaged in the material in order to remove material.

The machining beam profile preferably determines the shape of the borehole, in particular the local removal depth and the flank steepness. This applies in particular to non-continuous blind holes or bores.

In a preferred development, the processing beam profile is imaged in the material via a 4f structure, preferably reduced, particularly preferably reduced by a factor of 2 to 100.

To remove material, a plurality of successive pulses with the same processing beam profile are preferably introduced into the material, with the position of the imaging of the processing beam profile in the material being kept stationary. In this way, percussion drilling can be achieved with the machining beam profile.

The material is preferably essentially not transparent to the laser radiation and comprises materials such as a metal foil or a polymer or a plastic, or a semiconductor or a ceramic, or the material consists of silicon. In particular, the material can also be a layer system made of different materials. In particular, the layer system can also include thin intermediate layers that are transparent to the laser wavelength.

In a preferred embodiment, the processing beam profile is impressed on the laser beam with a graduated filter, and/or the processing beam profile is impressed on the laser beam with a diffraction grating, with preferably adjustable diffraction orders being intercepted with an aperture device, and/or a polarization distribution is impressed on the laser beam with a polarization element, wherein an adjustable polarization of the processing beam profile is transmitted through a polarization splitter to the material or reflected to a beam trap, so that only the desired intensity distribution remains in the processing beam profile.

The material can be a layer system and comprise at least two layers, with the uppermost layer in the direction of beam propagation being essentially transparent for the wavelength of the Laser beam is, preferably has a transparency of more than 50%, the laser beam can be focused through the top layer into a second layer, the second layer can be separated along a separation plane, and the local structures or partial layers separated from the second layer of of the top layer can be exposed by lifting or detaching the top layer.

For example, the method can be part of a so-called laser lift-off method. With the laser lift-off process, individual or multiple layers or complex components can be structured out of a layer system.

For this purpose, ultra-short laser pulses, preferably with a wavelength of less than 300 nm, particularly preferably 257 nm, are focused into the volume of the layer system through a transparent material. The laser beam is passed through a gradient filter element or a graduated filter, whereby the local structure of the processing is specified.

In this case, the transparent material can in particular be sapphire or comprise sapphire. The layer system can in particular include GaN, which is not transparent to the wavelength of the laser and thus absorbs the laser energy. This absorption can result in targeted damage or induction of a local phase transition, e.g. by melting or evaporation, or in a local chemical reaction, e.g. because the reactivity of the layered materials is increased by the higher temperature.

In a further step, the structured layer system can be separated along a separating plane, so that to a certain extent a negative image of the desired structure is detached from the actual layer system. Cuts and/or separations perpendicular to the extent of the layers of the layered structure are preferably made before the lift-off method is carried out. The detachment of the prestructured substructures can therefore be achieved by separating the substructures along a separating plane lying in a layer plane.

The detached layer system can, for example, be used on another substrate for further use. For example, the detached layer can be detached using a carrier substrate with an adhesive layer, in particular an adhesive film, and processed further on a further wafer. The carrier substrate can be in direct contact with at least one layer of the layer system, for example this can be glued on, or arranged at a small distance from the layer system, forming a gap.

In particular, this method can be used to produce pLEDs, with the individual pLEDs being structured out of the layer system.

Brief description of the figures

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

FIG. 1 A, B, C, D, E shows a schematic structure of a device according to the present disclosure and various processing beam profiles provided with the device;

FIG. 2 A, B, C, D shows a schematic structure of a device with a graduated filter as a gradient filter element;

FIG. 3A, B shows a schematic structure of a device with a diffraction grating and an aperture device as a gradient filter element;

Figure 4 A, B shows a schematic structure of a device with a

polarization element as gradient filter element;

FIG. 5 different intensity curves of the processing beam profile, which were generated by a device according to the present disclosure;

Figure 6 plan views of illustrations of various with a

Processing beam profile of an apparatus of boreholes prepared in accordance with the present disclosure; and

FIG. 7A, B a method for structuring a layer system.

Detailed description of preferred embodiments

Preferred exemplary embodiments are described below with reference to the figures. The same, similar or equivalent elements are included in the different figures Identical reference numerals are provided, and a repeated description of these elements is partially dispensed with in order to avoid redundancies.

In FIG. 1A, a structure of a device 1 for removing a material 2, in particular for drilling or structuring the material 2, is shown schematically. A laser 3 provides a laser beam 30 formed from laser pulses.

When leaving the laser, the laser beam 30 typically has a Gaussian beam profile in the plane perpendicular to the direction of propagation of the laser beam 30 . As a result, more energy is transported in the center of the laser beam 30 than in the edge regions of the laser beam 30. A lateral cross section through the Gaussian beam profile is shown schematically in FIG. 1B.

In a schematic embodiment, the laser beam 30 is therefore pre-shaped by a diffractive optical element or an n-shaper or a beam processing optics 6 . As a result, a so-called flat-top beam shape is generated from the Gaussian beam shape, for example, which is characterized in that it provides an essentially equally large intensity in the laser beam 30 over a large area. A lateral cross-section through a flat-top processing beam profile is shown schematically in Figure 1C. As shown in FIG. 1A, the beam processing optics 6 can have a focusing property, but this is not essential for the invention. Beam conditioning optics 6 without a focusing property are also possible (not shown).

The laser beam preformed in this way is then directed to a gradient filter element 4, where a processing beam profile is impressed on the laser beam 30, with which the processing process in the material 2 is to be carried out. In the example shown in FIG. 1D, the intensity distribution, which is to be used for processing the material 2, corresponds to two triangular curves along a lateral section, each of which has a maximum symmetrically to the beam propagation direction.

The processing beam profile 32 impressed on the laser beam 30 by the gradient filter element 4 is finally imaged onto the material 2 by imaging optics 5 in order to process the material 2 in this way.

In the following, lenses are always used as imaging optical components, although other imaging optical components can also be used. The imaging optics 5 are constructed as follows and positioned in the beam path: The gradient filter element 4 is in Beam direction in front of a first lens 50 at a distance which corresponds to the focal length F1 of the first lens 50. A second lens 52 with a focal length F2 is located behind the first lens 50 in the beam direction. The image-side focal point of the first lens 50 and the object-side focal point of the second lens 52 lie between the first lens 50 and the second lens 52. Both focal points coincide, so that the distance between the two lenses 50, 52 corresponds to the sum of the two focal lengths F1+F2 . The processing plane 54 is located in the material 2 behind the second lens 52. The processing plane 54 is arranged at a distance F2 from the second lens 52, which correspondingly also corresponds to the focal length of the second lens 52.

The processing beam profile 32 is imaged in the processing plane 54 by the imaging optics 5 . Here, an image can also be reduced, for example between 2 and 100 times reduced, in particular 25 times reduced. This means that the spatial extent of the beam profile after the gradient filter element is dx, for example, and is reduced to dx/25 by the imaging optics 5 . This makes it possible to process the material 2 on a significantly smaller scale, for example to drill smaller holes or produce sharper contours.

The laser pulses of the laser beam 30 strike the material 2 in the processing plane 54 and are at least partially absorbed in it. The material 2 is preferably essentially not transparent to the light of the laser beam 30.

The material 2 is kept stationary during a machining process and in particular during a drilling process, ie it is not moved away relative to the machining beam profile 32 . This makes it possible to introduce a plurality of laser pulses shaped in the form of the processing beam profile 32 onto the same point on the material 2 . This in turn makes it possible to melt and partially vaporize the material 2, with the vaporized material partially driving the melted material out of the borehole. In other words, a percussion drilling process can be performed.

After a drilling process has taken place, the material 2 and the laser beam can be repositioned relative to one another with the feed device 7 in order to start a further machining process again.

In this case, the geometry of the borehole is determined by the geometry of the processing beam profile, which was impressed by the gradient filter element 4 . For example it is possible to determine the depth of removal per drill pulse and the slope of the borehole through the geometry of the processing beam profile and the intensity gradients therein. In particular, it is also possible to rework the flanks of a borehole and in particular to adjust the steepness of the borehole.

A possible gradient filter element in the form of a graduated filter 42 is shown in FIG. 2A. Graduated filter 42 is a neutral density filter that has different optical densities depending on location. The neutral density filter is permeable for the light of the laser in the areas that are schematically colored white. In contrast, in the area that is schematically colored black, the optical density of the neutral density filter is so high that a large part of the energy - for example the entire energy - is blocked from the laser beam there. The profile of the graduated filter is thus impressed on the laser beam as a processing beam profile. If, for example, the laser beam 30 is preformed before passing through the graduated filter 42, for example has a flat-top beam profile, then the processing beam profile focused into the processing plane 54 by the imaging optics 5 corresponds exactly to the course that is specified by the graduated filter 42.

A schematic structure is shown in FIG. 2B, with the graduated filter 42 being introduced into the focus of the first lens 50 . The beam path in front of and behind the graduated filter corresponds to that of the structure from FIG.

FIG. 2C shows a schematic removal profile which is generated by the graduated filter 42. In this case, the removal profile is a cross section through a borehole shown schematically, which is generated with the gradient filter element in the form of the graduated filter 42 . It can be seen that in the areas of high transparency for the laser light, a significantly greater removal of the material 2 is achieved than at the points at which the graduated filter 42 is less transparent for the laser light. It is thus possible to determine the shape of the borehole using a gradient filter. In particular, the progression of the graduated filter 42 in the exemplary embodiment shown is step-shaped in cross section, so that there is a quasi-delta-shaped intensity gradient at the steps. This causes the borehole walls to be very steep.

FIG. 2D shows a microscopic image of a correspondingly produced drill hole. It can be clearly seen that the shape of the graduated filter is reflected in the actually drilled hole.

In FIG. 3A, an apparatus 1 using a diffraction grating 440 and an aperture 442 is shown. The diaphragm 442 eliminates unwanted beam components from the diffraction pattern deleted out, whereby due to the optical filtering in the processing plane 54 the resulting processing beam profile 32 corresponds to the diaphragm function profile.

An alternative configuration of a possible structure for carrying out the method is shown in FIG. 3B. An irradiated laser beam 30 with a Gaussian beam profile falls on the diffraction grating 440, as a result of which the laser beam is broken down into its spatial frequency components, which are focused by the first lens 50. If the aperture 442 is arranged behind the diffraction grating 440 in the beam propagation direction of the laser beam, the undesired beam components 31 can thereby be filtered out, so that the laser beam 30' can be impressed with an aperture function profile, in the example shown a trimmed Gaussian beam with soft edges.

In the embodiment shown here, the second lens 52 behind the aperture 442 ensures collimation of the laser beam 30', which is then finally free of undesired beam components 31.

FIG. 4A shows a polarization element 460 as gradient filter element 4, which imparts a location-dependent polarization to laser beam 30. The polarization element 460 can be selected to suit the desired machining process, for example. In particular, the gradient filter element can also be changed between the machining processes or drilling processes, so that drill holes with different structures can be formed with the device shown.

FIG. 4B shows a schematic structure in which the gradient filter element is formed by a polarization element 460. The polarization element 460 imposes a location-dependent polarization on the laser beam 30, which is preferably selected between the first lens 50 and the second lens 52 of the imaging optics 5 with a polarization splitter 462. However, the polarization splitter can also be arranged in front of the first lens 50 . In the example shown, the polarization splitter 462 is set in such a way that preferably s-polarized light is transmitted and imaged in the material 2 with the imaging optics 5 . The p-polarized part of the laser beam 30, on the other hand, is directed with the polarization splitter 462 in the direction of a beam trap 464 and is absorbed there.

By selecting the polarization in the polarization splitter 462, the beam can

Processing beam profile are impressed together with intensity gradients. That

Processing beam profile of the transmitted beam has an intensity distribution, which the Corresponds to the intensity profile of the graduated filter in FIG. 2A. In contrast, the laser light reflected and destroyed by means of the polarization splitter 462 has an intensity distribution that corresponds exactly to the inverse intensity distribution. There is no laser intensity in the center of the processing beam profile, while there is a very high intensity at the edge of the laser beam.

In general, both beam parts, ie s- and p-polarized beam parts, can be guided to the material 2. Typically, however, only one beam part is used for material processing. Further polarization-changing elements can be introduced between the polarization filter and the material 2, for example a λ/4 plate for generating a circular polarization.

Measurements of different intensity curves of a processing beam profile in the processing plane 54 are shown in FIG. FIG. 5A shows an intensity profile that corresponds to the intensity profile from FIG. FIG. 5B shows an intensity curve in which there is a medium-high intensity at the edge of the processing beam profile, there is no intensity in the center and there is a very high intensity in the transition region from edge to center. Such a laser beam profile can be used, for example, in the post-processing of boreholes. FIG. 5C shows an intensity profile of the processing beam profile, which corresponds to the p-polarized part from FIG. In this case, the intensity falls sharply from the edge towards the center of the laser beam 30, as a result of which more laser energy is placed at the edge of a borehole.

FIG. 6 shows various micrographs of boreholes that were produced using the device described here and the method described here. The rectangular profile of the borehole is created by the outer contour of the beam profile, which the gradient filter element 4 imposes on the laser beam 30 . The shape of the borehole, in particular the outer wall of the borehole and its steepness, is defined by the course of the intensity in the processing beam profile perpendicular to the direction of propagation and thus in particular by the intensity gradient. For example, the steepness of the outer wall of the borehole can be defined by selecting the intensity gradient. For example, in FIG. 6A, B, an outer edge of the borehole is 10 μm in each case, while the borehole tapers either to about 3 μm or only to 7 μm, depending on the selected intensity profile. In the case of the borehole in FIG. 6A, the flank steepness of the outer wall is significantly less than in FIG. 6B.

By choosing a suitable magnification, the overall size of the borehole can be controlled.

For example, boreholes can be drilled with the same through a suitable enlargement Introduce flank steepness into the material 2, however, vary the outer diameter overall. For example, in Figure 6C, a borehole was drilled with an outside edge of 15 pm and which tapers to 10 pm. The edge steepness is thus essentially the same as that of the borehole from FIG. 6B. In Figure 6D, a wellbore is shown with an outside edge of 25pm tapering to 20pm. Here the edge steepness is again greater than in FIG. 6C.

A laser lift-off method is shown schematically in FIG. 7A, in which a processing beam profile 32 structures a material 2, which in the present case is a layer system. In this case, the layer system 2 can comprise a plurality of layers 20, 21, 22, 23, 24 etc. For example, the first layer 20 in the beam propagation direction can be a first transparent layer made of sapphire, which has a material thickness of between 100 μm and 5 mm.

For example, the layers 21, 22, 23 can comprise a different material, such a layer being able to be between 1 nm and 10 μm thick, for example. For example, the layer 24 can be a carrier layer or a carrier substrate, such as a film, an adhesive or a wafer. In particular, therefore, the layer thicknesses in FIGS. 7A, B are not drawn to scale.

For example, the processing beam profile 32 may be similar to those of Figures 5A through 5C. In this case, the processing beam profile 32 is preferably adapted to the geometry of the structure to be detached in order to design the detachment process and the material damage as optimally as possible. For example, the structure to be detached can lie within the aperture image.

In other words, the detachment of each structure can preferably be achieved without further moving or traversing the processing beam profile 32 .

For example, the processing beam profile 32 can be guided through a first transparent layer 20 and introduced at a desired insertion depth. Targeted damage can be achieved here by the interaction of the processing beam profile 32 with a layer, for example the layer 21 shown as an example, so that the material 2 can be separated in the parting plane lying in the layer 21 here.

The vertical cuts are already present in the example shown, so the substructures to be detached are only connected to the rest of the layer system at layer 21 . By introducing the processing beam profile 32, a separation of the substructures can then be achieved accordingly in the separation plane. The parting plane thus coincides, for example, with a layer 21 of the layer system. A substructure can thus be detached from the layer system 2 . In particular, structures can be produced in this way which are either attached directly to a carrier substrate, for example glued, or can be transferred to a carrier substrate, for example another wafer.

In an example it is possible that only the first layer 20 is transparent. In another example, however, it is also possible for at least two or all of the layers of the layer system 2 to be transparent, or for only the last layers in the beam propagation direction to be non-transparent for the wavelength of the laser. It is also possible that the layers 20, 21, 22, 23, 24 are only partially transparent, as long as a corresponding material processing is still possible in the deepest layer, in which a material processing is still desired, by the remaining laser radiation, without the surrounding ones Layers undesirably damaging.

Pulsed laser beams with a wavelength of less than 400 nm, in particular between 250 nm -350 nm, in particular 343 nm and 257 nm, and pulse durations in the fs to ns range are preferred for this processing step.

The actual lift-off method is shown schematically in FIG. 7B. The layers processed by the structuring can be removed from one another via a carrier substrate 24 with an adhesive layer, since the material 2 was separated in the parting plane. As a result, only partial layer systems such as the substrates shown as an example in FIG. 7B, which can be pLEDs, for example, remain of the layer system.

As far as applicable, all individual features that are presented in the exemplary embodiments can be combined with one another and/or exchanged without departing from the scope of the invention.

Reference character list

1 device

2 materials

3 lasers

30 laser beam

31 unwanted beam portion

32 processing beam profile

4 gradient filter element

42 graduated filters

440 diffraction grating

442 aperture

460 polarization element

462 polarization splitter

464 beam trap

5 imaging optics

50 first lens

52 second lens

54 editing level

6 beam conditioning optics

7 feed device

Claims

Expectations

1 . Device (1) for processing a material (2), in particular for drilling or structuring a material (2), by means of laser pulses of a laser beam (30) of a pulsed laser (3), preferably an ultra-short pulse laser, comprising a gradient filter element (4) for Impressing an intensity gradient perpendicular to the beam propagation direction on the laser beam (30) to form a processing beam profile (32) and imaging optics (5) for imaging the processing beam profile (32) onto or into the material (2), characterized in that the gradient filter element (4) a polarization element (460) and a polarization splitter (462), wherein the polarization element (460) comprises a segmented, i.e. composite and/or course-like, birefringent optical element, which imparts a radial or azimuthal polarization to the laser beam (30).

2. Device according to claim 1, characterized in that the imaging optics (5) comprises two imaging components (50, 52), preferably two components of the same focal length, the gradient filter element (4) being in the object-side focal point of the first component (50). , the image-side focal point of the first component (50) coincides with the object-side focal point of the second component (52), and the material (2) is arranged in the image-side focal point of the second component (52).

3. Device according to claim 2, characterized in that the imaging optics (5) reduces the processing beam profile (32), in particular reduces it by a factor of 2 to 100, into which the material (2) is imaged.

4. Device according to one of the preceding claims, characterized in that the gradient filter element (4) comprises a graduated filter (42).

5. Device according to one of the preceding claims, characterized in that the gradient filter element (4) comprises a diffraction grating (440) and an aperture device (442), the aperture device (442) between the first component (50) and the second component (52) is introduced, is introduced alternatively in front of the first component (50) or behind the second component (52), is preferably introduced in the beam path after the diffraction grating (440) and after the first component (50) and is set up for this purpose, selectable Intercept diffraction orders from the beam path. Device according to one of the preceding claims, characterized in that the gradient filter element (4) comprises a polarization element (460) and a polarization splitter (462), the polarization element (460) preferably comprising a nanograting or a liquid crystal which the laser beam (30 ) imparts a radial or azimuthal polarization, and/or the polarization element (460) comprises a wave plate, which influences the polarization and the phase of the laser beam (30), and/or the polarization splitter (462) between the first component (50) and the second component (52) is introduced, alternatively in front of the first component (50) or behind the second component (52), and the polarization splitter (462) is set up to reflect light of selectable polarization to a beam trap (464) or in to transmit the material (2). Device according to one of the preceding claims, characterized in that a preform optics (6), preferably an imaging component, a diffractive optical element, an n-shaper or a beam processing optics (6), in front of the gradient filter element (4) is arranged, the preferably imposes a flat-top processing beam profile on the laser beam (30) before the processing beam profile (32) is formed in the gradient filter element (4). Device according to one of the preceding claims, characterized in that the pulse duration of the pulsed laser beam (30) is between 50 fs and 5000 ps, in particular between 100 fs and 10 ps, in particular 1 ps, and/or the maximum fluence is between 0.01 J/cm2 and 100J/cm2, in particular between 0.1 J/cm2 and 10J/cm2, and/or the repetition rate of the laser (3) is between 1 kHz and 100MHz, and/or the wavelength of the laser beam (30) is between 50nm and 3000nm lies. Device according to one of the preceding claims, characterized in that a feed device (7) is provided, preferably a scanner optics and / or a moving workpiece, by means of which the machining beam profile (32) and the material (2) can be shifted relative to one another between two machining processes and/or can be continuously shifted relative to one another.

10. A method for processing a material (2), in particular for drilling or structuring a material, using the laser pulses of a laser beam (30) of a pulsed laser (3), preferably an ultrashort pulse laser, characterized in that the laser beam (30) using a gradient filter element (4), an intensity gradient perpendicular to the direction of beam propagation is applied to form a processing beam profile (32) and the processing beam profile (32) is imaged in the material (2) in order to remove or process material (2).

11 . Method according to Claim 10, characterized in that the machining beam profile (32) determines the shape of the borehole, in particular the local removal depth and the flank steepness.

12. The method according to claim 10 or 11, characterized in that the processing beam profile (32) is imaged, preferably reduced, particularly preferably 2 to 100 -fold reduced, is shown.

13. The method according to any one of claims 10 to 12, characterized in that a plurality of successive pulses with the same processing beam profile (32) are introduced into the material (2) for material removal or for material processing, the position of the image of the processing beam profile (32) in the material (2) is held stationary.

14. The method according to any one of claims 10 to 13, characterized in that the material (2) comprises substantially non-transparent materials such as a metal foil, or is a polymer, or is a plastic, or is a semiconductor, or is a ceramic, or consists of silicon , or a layer system made of different materials, whereby the Layer system particularly thin and transparent for the laser wavelength

May include intermediate layers. Method according to one of Claims 10 to 14, characterized in that the processing beam profile (32) is impressed on the laser beam (30) with a graduated filter (42), and/or the processing beam profile (32) is impressed on the laser beam (30) with a diffraction grating (440 ) is impressed, with preferably adjustable orders of diffraction being intercepted with an aperture device (442), and/or a polarization distribution being impressed on the laser beam (30) with a polarization element (460), with an adjustable polarization of the processing beam profile (32) being produced by a polarization splitter (462 ) is transmitted to the material (2) or reflected to a beam trap (464), so that only the desired intensity distribution remains in the processing beam profile (32). Method according to one of Claims 10 to 15, characterized in that the material (2) is a layer system and comprises at least two layers (20, 21), the uppermost layer (20) in the direction of beam propagation being essentially transparent for the wavelength of the laser beam ( 30) and preferably has a transparency of at least 50%, the laser beam (30) is focused through the top layer (21) into a second layer (21), the second layer (21) being separated along a parting plane, and the Local structures or partial layers separated from the second layer (21) are transferred from the top layer (20) by lifting and/or detaching the top layer (20) onto a carrier substrate (24) preferably provided with an adhesive layer.