DE102020123785A1 - Method of processing a material - Google Patents

Abstract

The present invention relates to a method for processing a material (300) to be processed using a laser beam (200), in particular for cutting silicon wafers, the laser beam (200) being directed onto a light modulator (110) for phase and/or amplitude modulation in order to impress an intensity distribution on the laser beam (200) which corresponds to a continuous processing contour (400), and the laser beam (200) for processing the material (300) with the imprinted processing contour (400) is imaged onto the material (300) and the laser beam (200) for processing is kept stationary relative to the material (300) to be processed.

Description

technical field

The present invention relates to a method for processing a material to be processed using a laser beam, in particular for cutting contours such as microchips from silicon wafers.

State of the art

It is known to use multi-spot optics for processing a material, in particular for cutting out microchips from silicon wafers, in which case an incident laser beam is split into a plurality of partial laser beams that are offset relative to one another and the various partial laser beams are then guided parallel to one another along a predetermined dividing line across the wafer. to then separate it along the dividing line.

In order to guide the partial laser beams over the wafer, axis and scanner systems are used that either move the partial laser beams or the material or both. The use of such systems requires complex measuring and positioning processes, since the partial laser beams have to sweep over the specified dividing line over the entire width of the processing region and must not deviate from it. In particular, damage to the holder foil and the workpiece holder can occur at the edge of the wafer if individual partial laser beams have to move beyond the edge of the material.

the end EP2186596A1 systems are known that use a light modulator to compensate for aberrations and wavefronts of a laser beam. However, the focus here is on point-by-point imaging of the laser beam onto a material to be cut.

the end EN112013002095T5 beam-shaping devices are known which approximately enable a desired intensity and phase distribution of a laser beam, but these beam-shaping units are not used for processing a material.

Presentation of the invention

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

The object is achieved by a method for processing a material to be processed, in particular for cutting out a chip from a silicon wafer, using a laser beam with the features of claim 1. Advantageous developments of the method result from the dependent claims and the present description and the figures.

Accordingly, a method for processing a material to be processed using a laser beam, in particular for cutting silicon wafers, is proposed, the laser beam being directed onto a light modulator for phase and/or amplitude modulation in order to impress the laser beam with an intensity distribution which has a continuous Machining contour corresponds, and the laser beam for machining the material with the embossed machining contour is imaged on the material and the laser beam for machining is kept stationary relative to the material to be machined.

The material can be, for example, a metallic workpiece or an Invar film, but also other workpieces that can be processed using a laser beam, such as glass, ultra-thin glass, polymers, polymer films, ceramics or silicon. A silicon wafer can in particular be any wafer based on silicon, such as Si, SiO2 and SOI (“silicon on insulator”) as well as doped variants thereof.

The laser beam is preferably generated by a laser beam source in such a way that it has a Gaussian basic mode with well-defined linear polarization. A Gaussian intensity distribution or a Gaussian basic mode is, in particular, an intensity distribution whose lateral cross-sectional profile through the center of the beam always corresponds to a Gaussian bell-shaped curve, that is, in particular, is radially symmetrical. In particular, the laser beam can also be pulsed.

A light modulator is understood to mean a device which is set up to influence light, in particular an incident laser beam, in one or more properties in two spatial dimensions. In this case, the light modulator can be set up in particular to influence a lateral phase distribution, a polarization distribution, an intensity or amplitude distribution and/or a propagation direction of the light, in particular of the laser beam. The propagation direction can also be influenced, preferably indirectly, by influencing the phase distribution in particular.

A light modulator can be, for example, a nanolattice or a hybrid element or a diffractive optical element which imparts a defined phase distribution to the laser beam due to their inherent structure or design be able. For example, a light modulator can also be a spatial light modulator whose cells or pixels influence the laser beam through adjustable birefringent properties. However, a light modulator can also just be an effective diaphragm, for example a perforated diaphragm, which influences the amplitude distribution of the laser beam.

A lateral distribution means a distribution of a property of the laser beam in a plane perpendicular to the direction of propagation of the laser beam, preferably in the processing plane of the material. For example, a lateral intensity distribution is a distribution of intensity in a plane perpendicular to the laser beam, so that the intensity of the laser beam across the beam cross-section depends on the location relative to the center of the beam. For example, the lateral distribution can be a Gaussian distribution, so that the intensity of the laser beam depends on the distance from the center of the beam. The intensity distribution can also be provided as a flat-top intensity distribution, in which the intensity is essentially constant within a determinable distance from the beam center and the intensity preferably falls to zero outside the determinable distance. A lateral intensity distribution also means that the intensity distribution of a laser beam only has an intensity that is sufficient for processing at a certain distance. For example, circular intensity distributions are possible. More generally, rectangular or square beam shapes can also be possible, in which case the intensity then only has a value that is sufficient for processing at the locations on the respective sides.

Similarly, lateral phase distributions can also be possible, with the phase of the laser beam depending on the location relative to the center of the beam. For example, this can also be understood as a so-called wavefront. For example, the optical or electromagnetic field on one side of the laser beam can oscillate asynchronously or out of phase with respect to the other side of the laser beam. However, any other conceivable phase distributions are also possible.

Analogously, lateral polarization distributions can also be possible, with the polarization of the laser beam depending on the location relative to the center of the beam. For example, a first half of the beam can be s-polarized and a second half of the beam can be p-polarized.

Light modulators can have the property that they influence the phase and/or amplitude and/or polarization distribution of the laser beam. In a first step of the method, however, the amplitude and/or phase distribution of the laser beam is only influenced in isolation. This can be achieved in particular by an initial polarization direction, so that the light modulator does not impress any further polarization distribution on the laser beam.

In particular, the laser beam can be directed onto the light modulator in such a way that, after a first modulation, it then undergoes a second modulation in order to impress the laser beam with an overall intensity distribution that corresponds to the continuous processing contour with which the actual material processing is then carried out. Likewise, the laser beam can be directed onto the light modulator in such a way that after the second modulation it experiences a third modulation, a fourth modulation, etc.

The processing contour is the shape of the laser beam that corresponds to the geometry of the area to be processed of the material to be processed in the processing plane of the material to be processed. In other words, the machining contour has the shape of the geometry to be machined, but can also have a different dimension, for example, so that the machining contour only acquires the dimensions to be machined in the material to be machined by mapping it onto the machining plane, for example by means of a machining optic.

The processing contour can be of flat design in order to process a correspondingly flat area in the material to be processed—for example, to remove the corresponding flat area of the material. However, the processing contour can also simply follow the border of any surface, or be a line of any shape. The closed border of a surface in the processing plane can be used, for example, to cut out the bordered area from the material—for example, to cut out individual microchips from a silicon wafer.

The processing contour is formed in particular by that part of the laser beam whose intensity is high enough to process the material.

In the case of an application for cutting or separating the material to be processed, the processing contour also corresponds to the desired (continuous) separating line or a region of this.

The processing contour is continuous. That can mean that the machining contour is not composed of individual spots of a laser.

For example, the processing contour can be given by a coherent light field that is significantly larger in at least one dimension, for example 10 times larger, than an individual spot. For example, the minimum diameter of an individual spot of a laser with a wavelength of 1 μm can also be 1 μm due to focusing. Accordingly, a processing contour is continuous if a coherent light field is generated over a distance of 10 µm.

It is thus possible to produce a continuous processing edge, for example a separating edge. Furthermore, it is possible in this way to achieve simultaneous processing of the entire processing contour without a relative movement having to be applied between the material to be processed and the laser beam. In other words, a microchip, for example, can be completely cut out at the same time as the machining contour is positioned.

A processing contour can in particular be composed of different continuous processing contours. In particular, the composite machining contour is also continuous if the composite machining contour only includes continuous machining contours. For example, a first processing contour can be a round, two-dimensional and coherent light field and a second processing contour can be the outer contour, ie the border, of a rectangle or a line made up of straight lines. Both contours are continuous in the sense that they are not formed from individual spots, but are each a coherent field of light. If both continuous processing contours are impressed on the laser beam, the processing contour is compound and continuous.

The laser beam with the embossed processing contour or outline is imaged onto the material, whereby the laser energy is introduced into the material according to the laser intensity. By introducing the laser energy, material is detached from the original material compound. This can take place, for example, through processes known as laser ablation, laser drilling, laser roughing, laser polishing, or laser drilling.

Since the laser beam is imaged onto the material with the defined phase, polarization and amplitude distribution and the laser energy is introduced into the material, material is only removed where the intensity of the laser beam is high enough to carry out one of the above processes. In particular, the geometric shape of the ablation in the material is thus determined by the shape of the machining contour of the laser beam.

In particular, the laser beam is imaged and also focused in the processing plane of the material, preferably by means of processing optics. For example, the processing plane can lie exactly on the surface of the material, but it can also lie above the surface, but in particular below the surface, ie in the volume of the material. In particular, the processing plane can be focused into different depths of the material by the processing optics, and the depth can also change during the processing process.

If the laser beam is kept stationary when the machining contour is introduced, this means in particular that there is no relative lateral movement between the laser beam and the material. This applies in particular in the x and y direction, in which there is then no movement while the machining contour is being machined at the same time. A lateral relative movement between the material and the laser beam can mean that the laser beam moves on the material, with either the material being moved via an axis system, for example with a feed, or the laser being moved with a scanner system, for example a laser scanner.

Such a lateral relative movement between the laser beam and the material does not occur in the process. This eliminates any feed process or linear axis movement with an axis system to cut along the machining contour. In particular, no multiple passes with parallel feed trajectories are necessary in the case of flat machining contours, as a result of which a particularly large amount of process time can be saved. Since there is no feed and the partial laser beams of a multi-beam optics do not have to be moved over the edge of the material as in the prior art, the holder film of the material and the workpiece holder are protected or not damaged by laser radiation.

A light modulator can therefore image a laser beam in the final processing contour, the so-called final geometry or final contour, on the material and introduce laser energy accordingly into the material. This simplifies the method according to the prior art, since only a single positioning of the laser beam and material has to be carried out. An alignment of the workpiece along the axes of a This eliminates the need for an axis or scanner system, which means that more cost-effective positioning systems can be used. Only the machining contour has to be positioned in relation to the workpiece, however - at least when using a closed contour - individual contour sections do not have to be positioned in relation to one another.

The material can be removed simultaneously along the entire machining contour, preferably removed in layers.

Simultaneous removal occurs when the proportional laser energy of the shaped laser beam is applied to all points of the processing contour at the same time or within certain time limits, for example within the pulse duration or within the pulse cycle duration. For example, in a square processing contour, the same amount of laser energy is applied to each side of the square. In addition, the laser energy is applied to all sides at the same time.

In this context, removing layer by layer can mean that material is removed uniformly from the original material composite at the location of the introduced machining contour. The depth of the material removal is essentially the same at every point of the irradiated processing contour. In particular, the laser beam can be used to remove material, for example by laser drilling, laser milling, laser polishing, laser cutting, or the like.

In particular, a layered removal can also mean that the shape of the removal is closed. In contrast to material removal using multi-spot optics, where each partial laser beam causes material removal at a spatial distance from another partial laser beam, no partial laser beams are introduced into the material, but rather a processing contour with a continuous surface and/or contour. Thus, in particular, different partial laser beams cannot be inferred from the ablation pattern in the material, since only a single laser beam is introduced.

The light modulator can be a spatial light modulator.

A spatial light modulator is a device that is set up to influence light, in particular an incident laser beam, in two dimensions, it being set up in particular to change a phase distribution, a polarization distribution, an intensity or amplitude distribution and/or a propagation direction of the light, in particular the laser beam.

The spatial light modulator can be controllable and/or programmable, so that the influencing of the light by the spatial light modulator can be adjusted, in particular can be predetermined, and it can in particular be changed in a targeted manner and on request. The light modulator can be embodied as a liquid crystal display, and is preferably embodied as an LCOS-SLM (Liquid Crystal on Silicon Spatial Light Modulator).

The incident laser beam falls on the display area of the spatial light modulator, where, for example by controlling its cells or pixels, the laser beam can be given a phase distribution, polarization distribution, and/or intensity or amplitude distribution in two dimensions, and preferably at the same time influence the direction of propagation of the light can. In particular, the influencing of the propagation direction preferably results indirectly from the influencing of the phase distribution in particular.

The influence of the laser beam results, for example, from the birefringent property of each pixel. In this context, birefringence is understood to mean the property that the laser light experiences an influence on the polarization and the phase, depending on the polarization direction of the laser beam relative to an optical axis of the liquid crystal pixel.

Each pixel of the light modulator can be controlled individually, so that each pixel can individually modify the phase and the polarization of the incident light bundle of the laser beam. The size of the effect can be controlled via the “brightness” or modulation of the pixel. The totality of pixels of the spatial light modulator thus results in a beam influencing structure with which, for example, the phase, amplitude and/or polarization of the laser beam can be influenced individually via the lateral and longitudinal beam cross section.

In particular, it is possible with a spatial light modulator to specifically influence one of the above distributions and leave the other distributions essentially unaffected. For example, a special lateral intensity distribution can be impressed on the laser beam in reflection, and in a further step the phase distribution can be adapted to the lateral intensity distribution.

The display area in the display plane of the light modulator can be divided into a plurality of display areas, in particular at least two display areas. In this case, the first display area can be that display area be with which the laser beam first interacts along its direction of propagation, the laser beam subsequently interacting with the second display area. Thus, the laser beam can interact twice or more with the same spatial light modulator.

Interaction of the laser light with the display area of the spatial light modulator means that the laser beam hits the display area, with its phase, polarization, and/or intensity or amplitude distribution changing according to the beam influencing structure and the laser beam then or during this time being reflected in particular by the display area will. Alternatively, it is also possible for the laser beam to pass through the display area or be guided through the display area. In this case, the display area transmits the laser beam.

If the laser beam has interacted with the spatial light modulator, for example first with the first and then with the second display area has interacted, and has thereby been impressed with a lateral intensity and polarization or phase distribution, then beam shaping can be carried out, for example by preferably filtering out beam components of the laser beam with a specific polarization behind the second display area, in particular beam components with a specific polarization being at least partially or completely removed from the beam path, or only beam components with a specific polarization being left in the beam path. In particular, beam components of the laser beam with a specific polarization can be selected as the useful beam. The amplitude distribution of the laser beam in the target plane can thus be shaped directly by means of polarization filtering/polarization separation. In this way, polarization effects in particular can be used to optimize the process in terms of efficiency and quality.

The second display area can also be used to correct aberrations. The first display area can also be used additionally or alternatively to correct aberrations.

When interacting with the first display area, the laser beam can have a first lateral amplitude distribution applied, which is very homogeneous, for example. Thereafter, the homogeneous amplitude distribution can be masked by the second display area, so that only part of the amplitude distribution is directed to the material to be processed. It may also be the case that the phase distribution is homogenized during the interaction with the second display area, ie that a homogeneous wavefront of the laser beam is generated.

By interacting with one of the display areas, the laser beam can also be given a phase distribution that corresponds to a converging, that is to say a focused, laser beam.

Overall, the sequence of the interactions with the display areas is not necessarily important, since mathematically speaking, each interaction corresponds to a multiplication of the incident laser light by the corresponding Jones matrix of the respective pixel. In this case, in the case of adjustable or controllable spatial light modulators, the entries, ie modulations of the Jones matrices multiplied on one another, can in principle be chosen arbitrarily, as long as the end result corresponds to the overall desired beam influencing structure. In principle, it is therefore also possible to provide the overall system with more degrees of freedom for optimizing the individual beam influencing structures by interacting with a plurality of display areas. Nevertheless, it can be advantageous for the method and the optical structure to let the laser beam interact with the individual beam influencing structures in a certain order.

By imprinting intensity and phase distributions on the beam through the various interactions with the display areas, it is possible to create any processing contours. Tailored spatial intensity distributions for different machining processes have proven to be particularly advantageous.

In particular, it is also possible to switch quickly between different processing contours, since only a corresponding control command to the spatial light modulator(s) is required.

The processing contour is preferably caused by a first beam influencing structure caused by a first display area of the light modulator and a second beam influencing structure caused by a second display area of the light modulator, the first display area and the second display area preferably emitting the laser beam in the form of a lateral intensity and/or Affect phase and / or polarization distribution.

The display areas can display, for example, a beam influencing structure that the is shaped in such a way that the laser beam interacting with the display area is given the desired beam properties. This can also be realized, for example, with computer-aided, feedback display areas that adapt the beam influencing structure continuously or once so that the image of the laser beam in the processing plane corresponds to the desired beam shape.

In particular, the beam influencing structures can be different. For example, in a first display area, a beam influencing structure can impress the laser beam with an amplitude distribution, for example a round shape. The interaction with the first display area changes the phase distribution, for example, so that the phase in the beam cross section can be homogenized via a second beam influencing structure in a second display area.

This has the advantage that a specific property of the laser beam can be optimized for each interaction, so that mutual dependencies of the laser properties are reduced or possibly isolated.

Before imaging the material, the laser beam can be directed onto another light modulator in order to locally influence the polarization of the processing contour.

After the laser beam has been given a defined amplitude and phase distribution, the laser beam can also be given a local polarization distribution. This polarization distribution is advantageously carried out by interaction with a further light modulator.

This has the particular advantage that the quality of the processing can thus be varied via the polarization.

The machining contour can be open or closed, with a closed machining contour preferably being circular, rectangular or square.

A machining contour is open if it has a start and end point. For example, a straight line, a curved line, such as a U-shaped line, or an angular line, i.e. a line composed of straight lines at different angles, are an open machining contour.

The processing contour is closed if it has no start and end point at least in sections. For example, O-shaped lines, eight-shaped lines, triangular or n-sided line arrangements are closed machining contours. 4-shaped or 6-lines are also at least partially closed machining contours, in which case the machining contours are composed of closed and open machining contours.

A round processing contour can mean that the contour of the geometry is completely round, i.e. it has a curvature at every point of the contour. In particular, this can mean that the contour of the machining contour is a circle. But it can also mean that the geometry is an ellipse. In particular, this can mean that the geometry is straight in sections, that is to say has no curvature over part of the contour length of finite distance, such as a semicircle or crescent.

A rectangular machining contour means that adjacent sides of the contour always meet at right angles, with two opposite sides being equal in length. A square machining contour is a rectangular machining contour where all sides are the same size.

However, the rectangular contour can also mean that the corners of the rectangle are rounded. In particular, for the rectangle, the radii of curvature of the rounded corners are smaller than the smallest side of the rectangle.

Round processing contours can only be introduced into the material with difficulty using scanners and axis systems, so that one advantage of the proposed method is that round geometries can be separated from the material particularly easily. Rectangular contours can be introduced into the material much more easily using scanners and axis systems, but repositioning and alignment steps are always necessary at the corners in order to bring the sides of the rectangle together at right angles. The advantage of the proposed method also lies in the fact that it is particularly easy to separate rectangular machining contours from the material.

A shape to be cut out can be completely imaged in the material by the machining contour, and the cutting out of the shape to be cut out in the material can be performed with the laser beam kept stationary.

In particular, it is possible that the processing contour is introduced into the material as a whole and thus no movement of the laser or the material is necessary. This avoids the laser beam having to be moved beyond the edge of the material, as is usual when cutting with multi-spot optics, which can prevent damage to the workpiece holder.

In particular, the method allows the actual machining contour to be mapped onto the material, so that the workpiece no longer has to be rotated during the method if the desired machining contour is not linear.

In addition, the material is not removed point by point along the contour, as is the case with pulsed multi-beam optics. This achieves a higher quality of the cutting edge.

The laser beam can be provided by an ultra-short pulse laser, with the pulse duration being between 300 fs and 10 ps, in particular 1 ps, and/or the maximum fluence being between 0.3 J/cm ² and 30 J/cm ² , in particular between 1 J /cm ² and 5 J/cm ² , and/or the focus diameter, and thus the smallest detail that can be introduced, of the processing contour is between 5 μm and 50 μm, in particular 9 μm.

An ultrashort pulsed laser enables the introduction of laser energy into the material on very short time scales. The time scale in which the laser energy is introduced into the material is the so-called pulse duration of the ultra-short laser pulse. The pulse duration can be between 300 fs and 10 ps. In particular, the pulse duration can be 1 ps. Pulse trains, in particular so-called bursts, including gigahertz bursts, can also be generated.

The fluence of a laser pulse results from the intensity distribution of the beam, i.e. the spatial beam profile, for example, as well as from the pulse duration and describes the laser energy introduced into the material per square centimeter. The maximum fluence here can be between 0.3 J/cm ² and 30 J/cm ² , preferably between 1 J/cm ² and 5 J/cm ² .

The laser beam is usually bundled with an optic, for example a lens, so that the intensity or the fluence of the laser beam in the focus, ie the area with the smallest diameter of the laser beam, is particularly large. The diameter of the beam in the focus is the so-called focus diameter, which defines the smallest detail that can be introduced into the processing contour. The focus diameter thus limits the spatial resolution of the processing contour.

For example, a laser beam with a focus diameter of 40 µm cannot introduce a round processing contour with a diameter of 3 µm into the material.

The wavelength of the laser beam can be in particular between 300 nm and 1600 nm, preferably between 450 nm and 1600 nm, in particular 515 nm or 1030 nm are possible. However, the wavelength can also be below or above the range mentioned here.

The processing contour can be between 0.5×0.5 mm ² and 20×20 mm ² in size.

A size of 0.5×0.5 mm ² to 20×20 mm ² can mean that the smallest edge length of a rectangle is 0.5 mm, or the largest edge length of a rectangle is 20 mm. In particular, this can mean that the smallest processing contour is a square with an edge length of 0.5 mm or the largest processing contour is a square with an edge length of 20 mm.

However, it can also mean that the diameter of a circle is between 0.5 mm and 20 mm, or that in the case of an elliptical machining contour the long and short axes of the ellipse are between 0.5 and 20 mm.

For example, a rectangle can be 5×15 mm ² . For example, an ellipse may have a major axis of 17mm and a minor axis of 1mm.

The laser beam can interact multiple times, in particular twice, with the same spatial light modulator, the spatial light modulator then displaying the first and second display areas simultaneously.

This may mean that the laser beam, after interacting with a display area of the spatial light modulator, is again directed to the same spatial light modulator, thereby interacting with a display area of the spatial light modulator.

In this case, the display area can in particular be another display area of the same spatial light modulator.

This has the advantage that a single spatial light modulator can affect the laser beam twice in different ways. For example, an intensity distribution can be imposed on the laser beam during the first interaction. For example, a phase distribution and/or polarization distribution can be impressed on the laser beam during the second interaction will. A multiple interaction thus increases the degrees of freedom with regard to the adjustable distribution parameters. In addition, it is significantly more cost-effective to install only one spatial light modulator in the device.

The phase, polarization and the processing contour of the laser beam can be adjusted by a combination of at least two wave plates, in particular a λ/4 plate and a λ/2 plate.

A wave plate is a so-called retardation plate which, depending on the material used, thickness and alignment of the optical axis, imparts a certain phase delay to the light passing through, depending on its polarization direction.

With a λ/2 plate, a special form of wave plate, it is possible to uniformly rotate the entire polarization of the beam, ie at every point of the processing contour. For example, the polarization of an s-polarized processing contour in sections can be converted into a processing contour that is p-polarized in sections, while the p-polarization in sections of the same processing contour converts a processing contour that is s-polarized in sections. It is thus possible, in particular, to rotate the polarization in such a way that a subsequent polarizer filters out the unwanted beam parts.

With a λ/4 plate, also a special form of waveplate, it is possible to convert a linear polarization into a circular polarization depending on its orientation to the optical axis of the λ/4 plate. At the same time, a circularly polarized beam part can be converted into a linear polarization. It is thus possible, in particular, to set the polarization of the desired beam parts in such a way that they pass through a subsequent polarizer and the unwanted beam parts are filtered out.

The phase and polarization along the processing contour can be adjusted by the targeted positioning and adjustment of the λ/2 plate and λ/4 plate. Thus, for example, specific contours can be set for processing in the processing plane. For example, rectangular contours for chips can be cut directly from silicon wafers in this way, with the magnitude of the beam shape on the workpiece corresponding to the desired chip geometry.

The processing contour impressed on the laser beam can be sharpened when it passes through a polarizer, in particular a thin-film polarizer.

When the laser beam interacts with the display area of the spatial light modulator, it can be difficult to determine the precise polarization state of the light in the processing area if the exact intensity and phase distribution are already specified. A simultaneous adjustment of the polarization can therefore under certain circumstances only be approximately achieved.

It is therefore possible with a polarizer to only transmit polarization components of a specific polarization direction, so that the undesired beam components can be filtered out of the laser beam.

The filtering of a specific polarization results in a sharp processing contour in the processing plane, since the unwanted parts of the beam have been filtered out. To a certain extent, the subsequent filtering of the polarization in the beam path increases the number of adjustment degrees of freedom in the display areas, since less consideration needs to be given to the precise polarization distribution when generating the phase and intensity distribution.

Since the filtering of undesired polarization parts also influences the intensity distribution in the beam path, it can make sense to check the beam properties with a feedback device and adjust the settings of the display areas accordingly.

Before the laser beam is imaged with the impressed processing contour, the polarization of the laser beam can be adjusted locally by interaction with a further light modulator.

The laser beam can be made to interact behind the second display area with a third display area of an addressable spatial light modulator, for example the same or another spatial light modulator. In this case, a third beam influencing structure is produced by driving the light modulator in the third display area. This third beam influencing structure is preferably different from the first beam influencing structure and from the second beam influencing structure.

A phase influencing structure is produced both in the first display area and in the second display area as the beam influencing structure. Preferably, the first phase influencing structure in the ers th display area influences a first amplitude distribution of the laser beam after a first propagation path and homogenizes a phase distribution in a cross-sectional plane of the laser beam through the second phase influencing structure in the second display area and/or influences a second amplitude distribution after a second propagation path.

In the third display area, a polarization influencing structure is produced as the third beam influencing structure, by means of which the polarization of the laser beam is locally influenced.

The addition of a further beam influencing structure makes it possible to influence the polarization distribution of the laser beam along the processing contour in a targeted manner and essentially separately from the intensity and phase distribution. To a certain extent, a further spatial light modulator adds a further degree of freedom to the method, so that overall the intensity, phase and polarization distribution can be set optimally.

Furthermore, beam components of the laser beam with specific polarization can be filtered behind the third display area, which can again contribute to a sharpening of the contour. For this purpose, the polarization is preferably rotated locally, in particular pixel by pixel, by means of the polarization influencing structure such that there is maximum transmission and maximum reflection of the corresponding beam components at the thin-film polarizer.

In particular, the first two display areas can be used to generate a desired intensity distribution that is as sharp as possible, for example a flat-top laser beam. The third display area can be used in particular in connection with the polarization separation in order to define the final shape of the laser beam.

Overall, the method can be used to generate laser beams with very high quality in terms of intensity distribution, particularly with regard to the outer contour and homogeneity, due to the highly flexible beam shaping process.

For example, it is possible that part of the machining contour is p-polarized while another part is s-polarized. It is also possible for an s-polarized part to transition into a p-polarized part, with the size of the transition region being given by the polarization influencing structure.

The polarization of the laser beam with the imprinted machining contour can always be locally perpendicular to the machining contour.

The use of a further spatial light modulator also allows local adjustment of the polarization of the laser radiation via a further polarization influencing structure. The polarization can thus be adapted locally to the contour and the process efficiency or the quality of the process can be increased.

In this context, locally perpendicular means that the direction of polarization is always perpendicular to the machining contour at every location of the machining contour. In the case of a rectangle, for example, the polarization on opposite sides can be parallel to one another, while the polarization on adjacent sides is perpendicular to one another. In particular, in the case of a circular processing contour, the polarization can always run radially, so that the direction of polarization always points to the center of the circle.

The locally perpendicular polarization can in particular ensure that the edges of the separated material have always been processed with the same direction of polarization, which increases the quality of the cut edges, for example.

The light modulator or light modulators can be selected from a group of light modulators consisting of spatial light modulators, nanogrids, hybrid elements, efficient apertures and diffractive optical elements.

This has the advantage that the spatial light modulators can be replaced by more cost-effective alternatives for fixed processing contours and fixed processes.

character list

• 1 eine schematische Darstellung eines optischen Aufbaus zur Durchführung des Verfahrens;
• 2 eine weitere schematische Darstellung eines optischen Aufbaus zur Durchführung des Verfahrens mit einem räumlichen Lichtmodulator;
• 3 eine weitere schematische Darstellung eines optischen Aufbaus zur Durchführung des Verfahrens mit zwei räumlichen Lichtmodulatoren;
• 4 verschiedene Bearbeitungskonturen;
• 5 A, B ein Vergleich des vorgeschlagenen Verfahrens mit einem Verfahren nach dem Stand der Technik;
• 6 eine schematische Darstellung einer Bearbeitungskontur auf der lateralen Ausdehnung der Bearbeitungskontur lokal senkrechter Polarisation des Bearbeitungsstrahls; und
• 7 eine schematische Darstellung einer weiteren Bearbeitungskontur und Bearbeitungsprozesses.

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

• 1 a schematic representation of an optical structure for carrying out the method;
• 2 a further schematic representation of an optical structure for carrying out the method with a spatial light modulator;
• 3 a further schematic representation of an optical structure for carrying out the method with two spatial light modulators;
• 4 various machining contours;
• 5A,B a comparison of the proposed method with a prior art method;
• 6 a schematic representation of a processing contour on the lateral extent of the processing contour of locally perpendicular polarization of the processing beam; and
• 7 a schematic representation of a further machining contour and machining process.

Detailed description of preferred embodiments

Preferred exemplary embodiments are described below with reference to the figures. Elements that are the same, similar or have the same effect are provided with identical reference symbols in the different figures, and a repeated description of these elements is sometimes dispensed with in order to avoid redundancies.

Because of the diverse possible applications of a spatial light modulator, in particular with regard to the adjustable amplitude, phase and polarization distributions, the method is discussed below only on the basis of the spatial light modulator. Alternatively, however, other light modulators can also be used instead of the spatial light modulator, provided they influence the laser beam in the same way.

1 FIG. 12 shows a schematic representation of an arrangement 100 for shaping an incident laser beam 200, which has a controllable spatial light modulator 110. FIG. The spatial light modulator 110 can be embodied as a liquid crystal display, which can specify freely selectable, in particular programmable or electronically adjustable, beam influencing structures in the display areas 1111, 1112.

The display plane 111 of the light modulator 110 can be divided into a plurality of display areas and display a first beam influencing structure in at least a first display area 1111 and a second beam influencing structure in a second display area 1112 .

The beam guidance optics 130 shown very schematically are set up to cause the laser beam 200 to interact along its propagation direction first with the first display area 1111 and then with the second display area 1112 . In the exemplary embodiment illustrated here, the beam guidance optics 130 have a first mirror 131 which is arranged in order to direct the laser beam 200 coming from the first display area 1111 to the second display area 1112 . It is possible that an imaging optical arrangement with at least one imaging optical element is additionally provided between the first display area 1111 and the second display area 1112 in the beam path of the laser beam 200, for example a lens. It is also possible for the mirror 131 to be designed as an imaging optical element. The first display area 1111 and the second display area 1112 are preferably each arranged in a focal plane of the imaging optical element or the imaging optical arrangement such that a 2f arrangement is implemented.

The beam guidance optics 130 also have a second mirror 133 here, which deflects the laser beam 200 behind the second display area 1112 in the direction of the material 300 to be processed.

The laser beam 200 is first interacted with the mirror 131 on the first display area 1111 and is then interacted with the second display area 1112 . By driving the light modulator 110, a first beam influencing structure is generated in the first display area 1111 and a second beam influencing structure, in particular different from the first, is generated in the second display area 1112.

In particular, a phase influencing structure is preferably generated both in the first display area 1111 and in the second display area 1112 as a beam influencing structure, with the first phase influencing structure in the first display area 1111 preferably producing a first amplitude distribution of the laser beam after a first propagation path, in particular in the plane of the second display area 1112, is provided. A phase distribution in a cross-sectional plane of the laser beam 200 is homogenized by the second phase influencing structure in the second display region 1112 . Alternatively or additionally, a second amplitude distribution after a second propagation path, in particular on a target level or processing level 310, is influenced by the phase influencing structure in the second display area 1112.

In particular, it is possible for a flat-top intensity distribution of the laser beam 200 to be generated on the second display region 1112 by means of the first phase-influencing structure, with a phase curvature of the flat-top being smoothed out by the second phase-influencing structure and thus the wavefront of the laser beam 200 being flattened, and/or a specific propagation behavior or a specific depth of field of laser beam 200 is set, and/or influences a spatial angular distribution of laser beam 200, and/or influences a homogeneity or inhomogeneity of laser beam 200 in a targeted manner, and/or influences an outer contour of laser beam 200, in particular preferably sharpened.

In particular, continuous processing contours can be imaged on the material 300 by the beam influencing structures, so that a continuous processing of the material 300 is possible.

Arrangement 100 preferably has processing optics 170, which are arranged and set up to image laser beam 200 coming from light modulator 110 onto a workpiece 300, in particular onto processing plane 310 of workpiece 300, which is also referred to as the target plane.

The processing optics 170 can be embodied as a telescope 171, particularly preferably as a 4f telescope, through which the second display area 1112 is imaged onto the processing plane 310 in such a way that the electric field of the laser beam 200 is both in phase and in the plane of the second display area 1112 Amplitude exactly corresponds to the electric field in the processing plane 310, possibly up to an increase, reduction and / or polarization change.

Thus, as part of the method, the workpiece 300 is irradiated with the laser beam 200 behind the light modulator 110 .

In 2 a laser beam source 220 is shown, from which the laser beam 200 emanates and through which the laser beam 200 is preferably generated. The laser beam source 220 can in particular be embodied as an ultra-short pulse laser which is set up to generate laser pulses with a temporal pulse width in the order of magnitude of picoseconds to femtoseconds.

Furthermore, in 2 a decoupling optics 140 is provided, which can also easily be used in the in 1 shown first embodiment can be provided, is only not shown there explicitly. The decoupling optics 140 are set up and arranged in order to direct a partial laser beam coming from a display area 1111, 1112 of the plurality of display areas 1111, 1112 onto a diagnostic device 150, with which the beam quality can be assessed.

The diagnostic device 150 is fed back to the spatial light modulator 110 to ensure a desired intensity distribution or amplitude distribution, a phase distribution, and/or a polarization distribution of the laser beam. In this way, in particular, a closed control circuit for controlling the at least one property of the laser beam 200 can be implemented.

Diagnostic device 150 is preferably set up to determine a correction of a phase shift if a linear polarization, in particular of laser beam 200, is aligned on light modulator 110 in such a way that light modulator 110 changes the polarization state of laser beam 200 depending on its activation and a phase shift between the two display areas occurs.

Diagnostic device 150 is preferably set up to determine the correction of the activation for a plurality of display areas as a function of a beam parameter and/or a beam effect of laser beam 200 on light modulator 110 - preferably globally or locally - with the beam parameter preferably being selected from a group consisting of: a fluence, an intensity, and an average power. The jet effect is preferably a temperature.

In 2 the arrangement 100 has beam shaping optics 160 which are arranged and set up to change, in particular to rotate, a polarization, in particular a linear polarization, of the laser beam 200 between the first display area 1111 and the second display area 1112 . In this case, the beam shaping optics 160 have a first λ/2 plate 162 here, which gives the laser beam 200 in front of the first display area 1111 a first linear polarization that is aligned in a defined manner. The beam shaping optics 160 also has a first λ/4 plate 163 which is arranged in front of the first mirror 131 in such a way that the laser beam 200 passes it twice on its path from the first display area 1111 to the second display area 1112 . The first λ/4 plate can be used to rotate the first linear polarization into a second linear polarization, with which the laser beam then hits the second display area 1112 .

The first linear polarization is preferably aligned parallel to a specific crystal axis of the two crystal axes of the preferably birefringent crystals of the light modulator 110, so that the polarization of the laser beam 100 in the first display area 1111 is not changed, but only the phase and/or amplitude distribution of the laser beam is changed .

The polarization of the laser beam 200 is rotated by the first λ/4 plate 163 in such a way that the second linear polarization is no longer aligned parallel to the specific crystal axis of the crystals of the light modulator, so that the polarization of the laser beam 200 is now changed in the second display area 1112 , in particular locally, in particular pixel by pixel, can be rotated.

For example, the laser light can have a p-polarization after passing through the first λ/2 plate 162, so that the polarization of the beam is not changed by interaction with the first display area 1111. After passing through the λ/4 plate 163 twice, the laser beam 200 has an s-polarization, so that the polarization can be rotated by an interaction with the second display area 1112 .

In the exemplary embodiment illustrated here, the beam shaping optics 160 have a polarization separating device 161 behind the second display area 1112, which is arranged and set up to filter and/or separate from one another the differently polarized beam components of the laser beam 200 coming from the second display area 1112. Thus, in particular, the laser beam 200 can be shaped as desired with high sharpness, but intensity curves can also be displayed.

The polarization separating device 161 has a thin-film polarizer 1612, through which beam components with a specific polarization are transmitted and beam components with a specific other polarization are reflected. The polarization separating device 161 also has a beam trap 1613, into which undesired beam components, which were coupled out by means of the thin-film polarizer 1612, are directed and destroyed there. The beam shaping optics 161 also have a second λ/2 plate 1611, through which the polarization changed by the spatial light modulator 110 can be aligned with the thin-film polarizer. Additionally or alternatively, the preferably adjustable λ/2 plate can be used to set the extent to which undesired beam components are deflected by the thin-layer polarizer 1612 .

In the embodiment shown here, the laser beam 200 is deflected between the first λ/2 plate 162 and the first display area 1111 by means of a third mirror 135 .

In addition to the telescope 171, the processing optics 170 also have a fourth mirror 174 for deflecting the laser beam 200, the processing lens 172, and also a second λ/4 plate 173, with the second λ/4 plate 173 preferably circularly polarized light is generated, which can have advantages with regard to the processing of the workpiece 300 .

As part of the proposed method, at least one property of the laser beam is preferably determined using diagnostic device 150, with the first beam influencing structure and/or the second beam influencing structure being changed as a function of the at least one property determined. For this purpose, the partial laser beam is preferably decoupled from the beam path.

In 3 the arrangement 100 has a further spatial light modulator 110'. The additional spatial light modulator 110' is preferably part of the beam path of the processing optics 170, with the laser beam 200 falling through a lens 175 and interacting via a deflection mirror 177 with the third display area 1113 in the display plane 112 of the further spatial light modulator 110'.

The polarization of the laser beam 200 can be adjusted with the λ/2 plate 173 in such a way that the interaction with the third display area 1113 allows a rotation of the polarization. In particular, the polarization can be rotated locally along the processing contour. This means that the polarization is always orthogonal to the processing contour, as a result of which the material can be processed in an advantageous manner and, in particular, a homogeneous edge quality is achieved independently of the spatial orientation of the respective contour.

After the interaction with the third display area 1113, the laser beam 200 is directed via a further deflection mirror 178 and a further lens 176 through the decoupling optics 140 onto the material 300 to be processed and imaged thereon.

At least one property of the laser beam 200 can be analyzed with the diagnostic device 150 via the decoupling optics 140, so that the activation of the two spatial light modulators 110 and 110′ can be selected via electronic feedback so that in the processing plane 310 the laser beam 200 has the desired intensity distribution, Has phase distribution and polarization distribution.

In 4 a possible progression of the beam shape along the beam path is shown. For example, in 4A shows what the intensity distribution of the beam looks like after a Gaussian beam has interacted with the first display area 1111 . It can be clearly seen that the intensity distribution is approximately quadratic has a shape that deviates significantly from a Gaussian intensity distribution. However, it is also evident that the intensity is not yet completely homogeneous, so further steps to optimize the beam shape are necessary.

For this reason, the beam can be directed to the second display area 1112 for further interaction, as in FIG 4B is shown. During the deflection process, the laser beam can pass through a λ/4 plate twice, which rotates the polarization of the laser beam in such a way that the polarization no longer corresponds to a specific crystal axis of the liquid crystal display, so that the interaction with the second display area 1112 influences the polarization there can. In addition, the second interaction with the second display area 1112 is capable of further homogenizing the intensity distribution and smoothing the edges of the intensity distribution and thus modifying the laser beam 200 for subsequent sharpening.

In 4C 1 shows the intensity distribution after the laser beam 200 has come into alternating registration with the second display area 1112 and has been sharpened by a thin-film polarizer 1612 by rejecting the undesired beam components. During the passage of the laser beam 200 through the thin-film polarizer 1612, all undesired directions of polarization were removed from the beam, so that a defined polarization distribution remains in the beam.

After passing through the thin film polarizer 1612, which completes the contour sharpening, a further transition can be made via a spatial light modulator, allowing the polarization to be locally tuned depending on the desired process outcome.

In 4D Various beam shapes are shown that may result when, for example, the sharpened laser beam 200 interacts with the display area 1113 of another spatial light modulator 110'. However, the interaction of the laser beam with the second display area 1112 can already partially rotate the polarization of the laser beam 200 such that during the sharpening process the filtering of the undesired directions of polarization results in a corresponding processing contour.

In 4E a composite machining contour is shown comprising two squares with different side lengths, with both squares centered on top of each other. Both squares are continuous machining contours on their own, so the composite machining contour is also continuous.

In a further variant, however, the processing contours shown with their desired amplitude distribution can also be achieved after the interaction with the first display area 1111, with the subsequent interactions merely sharpening or optimizing the corresponding processing contours.

The laser beam can be made available by an ultra-short pulse laser to introduce such machining contours. For example, the pulse duration can be between 300 fs and 10 ps, for example 1 ps. The maximum fluence is between 0.3 J/cm ² and 30 J/cm ² , in particular between 1 J/cm ² and 5 J/cm ² . The focus diameter and thus the smallest detail of the machining contour that can be introduced can be between 5 μm and 50 μm, in particular 9 μm. For example, it is therefore not possible to switch off the checkerboard pattern 4D with a uniform grid smaller than 9 µm.

In 5A a prior art method of separating a material is shown. Shown is the introduction of a plurality of focal points along a dividing line, which results in the desired processing contour 400. In order to cut the material 300 along the dividing line with the multiplicity of focal points arranged in a row, the multiplicity of focal points must be shifted along the dividing line via a relative feed. Since each focal point can remove part of the material thickness, it is necessary for each focal point to cover every point on the dividing line. In particular, this means that some of the focus points extend beyond the edge of the material, which can damage the workpiece holder (shown schematically by the decreasing black value of the dividing lines).

In 5B the method proposed here is shown analogously, in which the processing contour 400 is simultaneously introduced into the material 300 with a stationary laser beam. By introducing laser energy into each point of the processing contour 400, it is possible to cut the material 300 without a relative advance between the laser beam 200 and the material 300 being necessary. Rather, it is possible for the laser beam 200 to remain stationary during the actual cutting process, that is to say there is no relative movement between the laser beam carrying the processing contour and the material to be processed, in particular in the x and y directions.

When the laser pulses are emitted onto the material 300 by the proposed arrangement, the laser energy is distributed evenly over the corresponding processing contour, as a result of which uniform material removal is possible is. In particular, it is possible to process all points or areas of the processing contour 400 simultaneously with this method. It is also possible for the material to be removed in layers at the same time according to the processing contour, ie the depth of removal along the processing contour 400 is always the same.

The processing contours shown can have dimensions of 0.5x0.5 mm ² up to 20x20 mm ² . For example, the square machining contours can have a size of 5×5 mm ² . In this way, for example, microchips can each be cut out of a silicon wafer with one exposure.

In 6 a processing contour 400 applied to a material 300 is shown, which partially has a curved shape and in which the local polarization 500 is always perpendicular to the course of the processing contour 400 . After the laser beam 200 has interacted with the first two display areas of the spatial light modulator and has been given an optimal polarization, for example by the λ/2 plate 173, the third display area 1113 of the further spatial light modulator 110' can have the polarization 500 of the laser beam 200 rotate locally. In particular, this is possible because due to the λ/2 plate 173 the entire beam has a well-defined polarization which can be rotated in such a way that the polarization of the entire beam becomes rotatable according to the polarization influencing structure of the display area 1113 .

In particular, the locally rotated polarization is perpendicular everywhere on the processing contour 400. For example, the polarization 500 on the upper and lower sides of the processing contour 400 is oriented vertically, whereas the polarization 500 on the left side is oriented horizontally. The polarization on the right side of the processing contour 400, on the other hand, does not have a fixed orientation, but varies with the curvature of the processing contour 400.

7 shows a machining process in which a part with the shape of the letter "F" is to be cut out of a material 300. In 7A For this purpose, a first continuous processing contour 400 is impressed on the laser beam 200, with which the material 300 can be separated along the upper part of the overall contour. In 7B a continuous processing contour 400 is impressed on the laser beam 200, with which the material 300 can be separated along the lower part of the overall contour, so that the material 300 is then separated along the overall contour. Both the processing contour 400 of 7A as well as the 7B are continuous. In 7C is shown that the continuous machining contours 400 of the figures 7A, B can also be assembled into a continuous processing contour 400, so that the material 300 can be separated in one step along the final contour.

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 List

100

arrangement

110

spatial light modulator

110'

another spatial light modulator

1111

first display area

1112

second display area

1113

third display area

130

beam delivery optics

131

first mirror

133

second mirror

140

decoupling optics

150

diagnostic facility

160

beam shaping optics

161

polarization separator

1611

λ/2 plate

1612

thin film polarizer

162

λ/2 plate

163

λ/4 plate

170

processing optics

171

telescope

172

processing lens

173

λ/4 plate

174

fourth mirror

175

lens

176

lens

177

deflection mirror

178

deflection mirror

200

laser beam

220

laser beam source

300

material

310

editing level

400

processing contour

500

local polarization

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited 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.

Patent Literature Cited

• EP 2186596 A1 [0004]
• DE 112013002095 T5 [0005]

Claims (15)

Method for processing a material (300) to be processed by means of a laser beam (200), in particular for cutting silicon wafers, wherein the laser beam (200) is directed onto a light modulator (110) for phase and/or amplitude modulation in order to impress an intensity distribution on the laser beam (200) which corresponds to a continuous processing contour (400), and the laser beam (200) for processing the material (300) with the embossed processing contour (400) is imaged onto the material (300) and the laser beam (200) for processing is kept stationary relative to the material (300) to be processed. procedure after claim 1 , characterized in that material (300) along the processing contour (400) is removed simultaneously, preferably is removed in layers. procedure after claim 1 or 2 , characterized in that the light modulator (110) is a spatial light modulator. procedure after claim 3 , characterized in that the processing contour (400) is caused by a first display area (1111) of the light modulator (110) formed first beam influencing structure and a second beam influencing structure then passed through by a second display area (1112) of the light modulator (110), wherein the first display area (1111) and the second display area (1112) influence the laser beam (200) preferably in the form of a lateral intensity and/or phase and/or polarization distribution. Method according to one of the preceding claims, characterized in that the laser beam (200) is directed onto a further light modulator (110') before imaging onto the material (300) in order to locally influence the polarization of the processing contour (400). Method according to one of the preceding claims, characterized in that the processing contour (400) is of open or closed design, a closed processing contour (400) preferably being of circular, rectangular or square design. Method according to one of the preceding claims, characterized in that a contour to be cut out in the material (300) is completely imaged by the processing contour (400) and the cutting out of the contour to be cut out in the material (300) is carried out with the laser beam (200) held stationary . Method according to one of the preceding claims, characterized in that the laser beam (200) is provided by an ultra-short pulse laser, the pulse duration being between 300 fs and 10 ps, in particular 1 ps, and/or the maximum fluence being between 0.3 J/cm ² and 30 J/cm ² , in particular between 1 J/cm ² and 5 J/cm ² , and/or the focus diameter and thus the smallest detail that can be introduced of the processing contour is between 5 μm and 50 μm, in particular 9 μm is. Method according to one of the preceding claims, characterized in that the machining contour (400) is between 0.5×0.5 mm ² to 10×20 mm ² or 0.25 mm ² to 200 mm ² in size. Method according to one of the preceding claims, characterized in that the laser beam (200) interacts multiple times, in particular twice, with the same spatial light modulator (110), the spatial light modulator (110) simultaneously having a first display area (1111) and a second display area (1112) indicates. Method according to one of the preceding claims, characterized in that phase, polarization and the processing contour (400) of the laser beam (200) by a combination of at least two wave plates (162, 163, 173), in particular of a λ / 4 plate and a λ/2 platelets. Method according to one of the preceding claims, characterized in that the processing contour (400) is sharpened as it passes through a polarizer (1612), in particular a thin-film polarizer. Method according to one of the preceding claims, characterized in that before imaging the laser beam (200) with the impressed processing contour (400), the polarization of the laser beam (200) is adjusted locally by interaction with a further light modulator (110'). procedure after Claim 13 , characterized in that the polarization of the laser beam (200) with the impressed machining contour (400) is always locally perpendicular to the machining contour (400). Method according to one of the preceding claims, characterized in that the light modulator or light modulators (110, 110') is or are selected from a group of light modulators consisting of spatial light modulators, nanogrids, hybrid elements, efficient diaphragms and diffractive optical elements.

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