Method and system for producing microstructured components

Abstract

In a method for producing a microelectronic component comprising one of multiple microfunctional elements on a substrate, laser processing is performed in at least one method stage in a laser processing station under the control of a control unit. The method stage includes positioning a workpiece to be processed in a processing position of the laser processing station by means of a workpiece movement system in response to a movement signal from the control unit. The method involves observing the workpiece in a camera-based manner using a camera system, generating at least one image of a portion of the workpiece located in an object field of the camera. The image is evaluated by means of image processing for the purpose of determining positional data representing the actual position of at least one structural element of the workpiece in the object field. The actual position of the structural element is compared with a target position, and a correction signal is generated depending on the deviation between the actual position and the target position. The processing position is corrected by controlling the workpiece movement system based on the correction signals so that the actual position matches the target position. Then, for the purpose of localized laser processing of the workpiece, at least one laser beam directed at the workpiece is irradiated into at least one processing position of the workpiece.

Description

[Technical Field]

[0001] This invention relates to a method and system for producing a microstructured component comprising a plurality of microfunctional elements on a substrate, wherein laser processing is performed in at least one method stage in a laser processing station under the control of a control unit. A preferred application is the production of a micro LED display comprising a substrate on which a pixel is mounted to form a micro light-emitting diode array, the power supply structure being disposed on the substrate. [Previous Technology]

[0002] The term micro-LED (sometimes also called μLED) refers to a planar display technology based on light-emitting diodes (LEDs). A micro-LED display is a microelectronic component based on an array of tiny light-emitting diodes that form the image elements (also called pixels) of the display. In various cases, there are gaps (also called streets) between individual µLEDs. An individual pixel may consist of three sub-pixels, namely, three µLEDs for red (R), green (G), and blue (B). This means that streets can also exist between µLEDs within a pixel. Micro-LEDs are self-emissive, dimmable, and can be completely turned off, thus eliminating the need for a backlight as in liquid crystal displays (LCDs).

[0003] In the development of microLED technology as a new display technology, laser processing offers many possibilities, especially laser lift-off (LLO) for separating finished µLEDs from sapphire growth substrates, laser-induced forward transfer (LIFT) for transferring µLEDs from a donor to a substrate, and / or (for example) laser repair for µLED displays to correct yield problems and defect rates.

[0004] Laser lift-off (LLO) is a method for selectively removing one material from another. This utilizes a process in which a laser beam penetrates a transparent substrate material and undergoes a highly coupled process into a second material. LLO is commonly used in LED manufacturing for separating GaN semiconductors from a sapphire substrate wafer.

[0005] Laser-induced forward transfer (LIFT) is a type of method in which material is transferred from a starting substrate (donor) to a target substrate (acceptor) by means of laser radiation.

[0006] An overview of the use of laser-based technology in the manufacture of microLEDs can be found on the homepage of Coherent, managed by Coherent Shared Services BV, Dieselstraße 5b D-64807 Dieburg, at https: / / de.coherent.com / microled in the white paper "MicroLEDs - Laser Processes for Display Production".

[0007] Various concepts exist for production; these depend primarily on the manufacturer and their specific method variations and are implemented through different adaptations to the LLO and LIFT methods. In any case, large-scale parallel processing must be achieved to economically transfer a large number of µLEDs. This is accomplished using a mask with multiple openings or apertures that split the laser beam into corresponding partial beams once adjusted. The openings of the mask emitting laser radiation are then imaged onto the processing plane of the laser processing unit.

[0008] In this case, the arrangement of µLEDs on the epitaxial wafer can differ from that on the display. For example, the lateral spacing can be different. For instance, only every nth µLED can be transferred, thereby achieving the desired spacing on the display substrate. There is a possibility of using three different colors of µLEDs from three different epitaxial wafers. Alternatively, blue µLEDs with different color conversion layers (e.g., quantum dots) can be used.

[0009] Some manufacturers define a micro LED screen as a screen having a light-emitting diode with a light-emitting width of less than 50 µm or a light-emitting area of ​​less than 0.003 mm². The width (lateral range) of a µLED can range, for example, from more than 30 µm (<100 µm) to approximately 1 µm to 3 µm. The mesh between µLEDs is typically only approximately 6 µm to 1 µm wide. Deviations from these currently typical dimensions are possible, particularly in the direction of further miniaturization, for example, to form a screen with even higher resolution.

[0010] The cost of providing systems suitable for such processes increases almost exponentially with the demand for the possibility of producing increasingly sophisticated structures in stable processes. [Summary of the Invention]

[0011] Problems and Solutions

[0012] In view of this background, one of the problems solved by the present invention is to provide a method and system for producing microstructured components, which allow for the economical manufacture of such components even as the miniaturization of the structure to be produced increases.

[0013] To solve this problem, the present invention provides a method having the features of technical solution 1. Furthermore, a system having the features of technical solution 12 is provided. Advantageous developments are specified in the accompanying technical solutions. The wording of all technical solutions is incorporated herein by reference.

[0014] A method and system are provided for manufacturing a microstructured component comprising a plurality of microfunctional elements on a substrate. For example, such microfunctional elements may be microelectronic and / or micromechanical functional elements. One example is the production of a micro LED display comprising a substrate (display substrate) on which a pixel is carried on an electrical supply structure (also referred to as a backplane) to form a micro light-emitting diode array.

[0015] Laser processing is performed in at least one method stage of a laser processing station under the control of a control unit. This involves radiating a workpiece with laser radiation having predefined beam properties in a predefined manner to induce a change in localized boundaries on the workpiece. Laser processing may also be referred to as laser microprocessing because it may require processing accuracy in the micrometer range (e.g., several micrometers, or even less than one micrometer).

[0016] The workpiece may be a substrate that has not yet been processed, or a substrate that carries a coating and / or other functional structures.

[0017] In this method phase, a positioning operation is specifically performed. In this positioning operation, a workpiece to be processed is moved to a processing position in a laser processing station in response to a movement signal from a control unit. The positioning movement is implemented such that the workpiece is located in a sought position at a predefined time point. In this case, the workpiece can move continuously and pass through the sought position at a limited speed, such that it is located at the sought position at a target time ("dynamic positioning"). The positioning movement can also be controlled so that the movement briefly stops when the workpiece is in the target position ("static positioning").

[0018] To perform this workpiece movement, the laser processing station includes a workpiece movement system. A movement system is an electromechanical system used for movement and positioning purposes in automation, and allows an object to be moved and positioned according to a specific movement profile in two or three dimensions. They are also commonly referred to as movement and positioning systems.

[0019] A camera-based observation of one of the workpieces occurs. This observation is performed with the aid of a camera system including at least one camera, and includes image capture, i.e., capturing at least a portion of the workpiece located in the object field of the camera and also generating an image representing that portion. This may be a single image or multiple images.

[0020] In an evaluation operation, with the assistance of an evaluation unit of the system, an image is evaluated by means of image processing to determine positional data representing the actual position of at least one structural element of the workpiece in the object field at the time of image capture. The structural element is a component on the workpiece whose position is easily identifiable in the image. For example, suitable structural elements are contact pads on a backplate, alignment marks specifically applied to a particular location, one or more LEDs, or other functional elements.

[0021] In a comparison operation, the actual position of the structural element is compared with a predefined target position. Based on the comparison, a correction signal is generated depending on the deviation between the actual position and the target position.

[0022] If the actual position of a selected structural element of a workpiece, established by camera observation and image evaluation, does not correspond to the target position, or even if a potentially acceptable small deviation is allowed, it still does not correspond to the target position, a correction signal or correction value indicating the degree of deviation and indicating the need for correction is generated. If the comparison reveals that the established actual position corresponds sufficiently well to the target position, a corresponding correction signal ("no correction required") corresponding to a correction value of zero can be generated.

[0023] Based on the comparison results, and in the context of position correction by generating a correction movement, the workpiece movement system is controlled to match the actual position of the structural element with the target position as well as possible, thereby achieving a correction of the workpiece's processing position. In this case, it is not necessary to achieve the target position precisely, but it is necessary to reduce the difference between the target position and the actual position so that the actual position after position correction is within the tolerance range relative to the target position.

[0024] Finally, for the purpose of local laser treatment of the workpiece, at least one laser beam pointing towards the workpiece is irradiated onto the workpiece at at least one treatment position of the correctly positioned workpiece.

[0025] A system configured and adapted to perform the method accordingly includes a control unit, a laser processing station having a laser processing unit controllable by the control unit, and a workpiece movement system capable of moving a workpiece in response to a movement signal from the control unit. Furthermore, a camera system having a camera for observing the workpiece and for capturing one or more images is deployed, and then the one or more images are evaluated in an evaluation unit. The evaluation unit is configured to evaluate the images by means of image processing for the purpose of determining positional data representing the actual position, and also to perform a comparison between the actual position and the target position of the structural element for the purpose of generating a correction signal in case of excessive deviation. Depending on the evaluation result, the control unit corrects the processing position based on the correction signal by controlling the workpiece movement system so as to match the actual position with the target position. After evaluation and possible position correction, the actual position is located at or near the target position with high accuracy. If so, the control unit can, for the purpose of local laser processing of the workpiece, direct the laser processing unit to irradiate at least one laser beam pointing towards the workpiece into at least one processing position of the positioned workpiece.

[0026] The claimed invention is particularly based on the inventor's insights from research on commercially available workpiece movement systems (which are also commonly referred to as movement and positioning systems). It has been surprisingly found that even in the case of high-quality and correspondingly expensive workpiece movement systems, the absolute accuracy of positioning over relatively large travel distances and, if properly, over a relatively long period of time (as required in display manufacturing for the accurate positioning of very small micro-LEDs) is insufficient or almost insufficient. With travel distances on the order of 500 mm, the absolute positional error can practically reach several micrometers. In contrast, with travel distances less than 50 mm, the uncorrectable repeatability error should be less than 100 nm and therefore within the required accuracy range over a relatively short period of time after correction.

[0027] According to the inventors' suggestions, a workpiece movement system can be used for high-precision laser processing, even when it produces relatively high absolute position errors over long travel distances. This is because, for example, by using camera-based observation that includes image processing, determination of possible position errors, and orientation to correct their position, the position of the workpiece required for laser microprocessing can be set with extremely high precision in the micrometer range, even after relatively long travel distances. In this regard, implementing a camera-based position adjustment can compensate for possible structural or fundamental drawbacks of commercial workpiece movement systems using relatively cost-effective means.

[0028] According to one development, large-scale parallel processing (e.g.) can be achieved to economically transfer a large number of µLEDs. To achieve parallel processing simultaneously at multiple processing sites, a mask with multiple openings or apertures is used. This mask splits a laser beam, which needs to be adjusted, into corresponding multiple partial beams. The mask openings emitting laser radiation are then imaged onto the processing plane of the laser processing unit. In the system, the mask is configured in a mask plane optically conjugate with the processing plane. The mask openings emitting laser radiation are then imaged onto the processing plane of the laser processing unit by means of an optical imaging system. Preferably, a mask moving system is provided, which carries the mask and allows displacement of the mask in the mask plane and rotation of the mask about an axis perpendicular to the mask plane under the control of a control unit.

[0029] According to one development, a workpiece is continuously moved by means of a moving system and a laser pulse is triggered at a predefined position in each case. This results in a laser pulse frequency, a spacing between processing positions, and a specific travel speed of the substrate within the specifications of the laser system. For the purpose of image recording for correction, positioning with momentary stillness or positioning with very slow movement through a desired position is achieved, said desired position existing only for a short but sufficient time period.

[0030] A development involves working step-by-step in segments. A segment is a portion or part of an entire workpiece, which can actually be divided into multiple identical or different segments. A segment may have, for example, a rectangular shape with the same or different side lengths. In this case, the method includes generating and storing a correction value grid within a measured segment and subsequently processing this segment. In this case, the correction value is used for laser processing of the workpiece. Interpolation of intermediate values ​​at unmeasured locations is performed as needed.

[0031] According to one development, a narrow-band light system is used for camera observation and image capture. This can further help achieve extremely high positioning accuracy or minimal positioning error. In this application, the term "light" is generally used both for electromagnetic radiation from the visible spectrum and for electromagnetic radiation invisible to the naked eye (specifically, from the ultraviolet (UV) spectrum). In this application, narrow-band light is also referred to as "quasi-monochromatic" or "monochromatic" light. The terms "narrow-band," "quasi-monochromatic," or "monochromatic" are synonyms and are intended to describe electromagnetic radiation from a relatively narrow wavelength range or a narrow wavelength band. The spectral bandwidth of narrow-band light or narrow-band radiation can be significantly less than 100 nm; preferably, the spectral bandwidth of the light used for image capture can be 50 nm or less, specifically 10 nm or less. Various possibilities exist for implementing this.

[0032] According to one development, for camera observation and image capture during at least one image capture period, an illumination area of ​​the object field covering the camera on the workpiece is illuminated with narrow-band illumination light. For this purpose, the system may include an illumination system comprising an illumination source that is itself a narrow-band illumination source and / or optical devices (e.g., gratings or filters) for limiting the illumination spectrum of an illumination source to a narrower wavelength range.

[0033] By way of example, a suitable light-emitting diode (LED) or laser diode can be used as a light source for generating illumination light. In some configurations, the laser light from a laser processing unit can also be used for illumination purposes at a correspondingly lower intensity. Due to the use of quasi-monochromatic illumination light, the occurrence of chromatic aberration can be avoided or reduced to a certain extent, so that the resolution of position measurement is not significantly impaired. For beam guiding purposes, the use of monochromatic illumination light allows the use of, for example, optical systems that are typically not chromatically corrected (such as laser optical units).

[0034] Alternatively or additionally, a filter, a grating and / or some other wavelength selective device may be configured between the object plane of the camera (or the processing plane of the laser processing unit) and the camera sensor, for example, which, under the action of a bandpass filter, transmits only light from a narrow wavelength band to the camera, so that only narrow-band or quasi-monochromatic light is used to generate the image for evaluation.

[0035] In order to achieve the most uniform intensity distribution possible in the illuminated area, the lighting system can be configured to utilize the principles of Köhler lighting. As an alternative example, a ring lamp can be used as the light source.

[0036] In conjunction with camera-based position adjustment, a system is provided that enables laser processing with extremely high positioning accuracy of the processed position under economically reasonable and representative conditions.

[0037] The productive laser processing of a substrate typically occurs "instantaneously" (i.e., during substrate movement), resulting in a relatively small available time window for the exposure and formation of an image, unless a pulsed laser is used as the light source for an illumination system. In some cases, a complete "instantaneous" correction may be too late to compensate for relatively large deviations. Therefore, according to a preferred embodiment, observation and image processing are performed within a correction operation prior to laser processing, and the laser processing steps (e.g., for implementing an LLO, LIFT, or repair procedure) begin only after the corrected processing position has been set. Thus, laser processing begins as immediately as possible after a possible displacement of a workpiece used to correct a positional error. Preferably, the workpiece does not move during image acquisition, so that measurements for correction are performed with the workpiece fixed.

[0038] The correction should be performed as locally as possible (i.e., at the point where the next laser processing occurs) with the minimum possible travel distance. In other words, the area where the structural element used for position measurement is located should be as close as possible to the next processing location. For this purpose, it has proven worthwhile to progressively adopt the better processing of segments, as it only requires covering a travel distance on the order of the segment's lateral dimension (e.g., in the range of approximately 10 mm to approximately 30 mm).

[0039] Furthermore, it is considered advantageous to perform position correction immediately before starting the next processing step, specifically before an additional error may occur due to energy input during processing. This additional error can be compensated for if a new measurement is performed beforehand. The intervention time can be, for example, on the order of one second or less (e.g., as low as one millisecond). Therefore, processing should be performed immediately after position correction without any further movement unrelated to the processing (e.g., without an intervening beam analysis).

[0040] The laser processing unit includes an imaging lens for imaging a mask plane onto the processing plane of the laser processing unit, the imaging lens typically located in or near the surface of a workpiece. In a preferred embodiment, camera-based observation of a workpiece to be positioned or of a positioned workpiece is achieved by means of a camera through the imaging lens. In other words, an observation beam path extends from the workpiece or the workpiece-side object plane of the imaging lens through the imaging lens to the camera. The observation beam path that guides the illumination light to the portion to be observed preferably also passes through the imaging lens. This is particularly easy to achieve when using monochromatic illumination light, especially for beam guidance that can also be achieved using an unchromatic optical unit. Camera-based observation through a lens (TTL) achieves particularly accurate measurement results with a compact overall size of the component required for measurement. Specifically, by using TTL observation, additional errors that could occur, for example, due to the movement of a measurement camera relative to an off-axis configuration, can be avoided.

[0041] In some embodiments, the illuminated area on the workpiece is illuminated with quasi-monochromatic illumination light (UV illumination light) having an illumination wavelength in the ultraviolet range. For this purpose, the illumination system may include a light source emitting in the ultraviolet range. Compared to using visible light, using ultraviolet light for measurement offers the advantage of higher resolution due to the shorter wavelength. This means that even finer structures can be captured and evaluated more accurately by means of a camera compared to using longer wavelengths. Specifically, illumination wavelengths in the range of less than 300 nm can be used, for example, illumination wavelengths in the range of approximately 270 nm or in the range of approximately 248 nm or less.

[0042] Although observation in the UV range may be slightly more expensive due to the higher price of UV-sensitive cameras, the finer structures sought can be produced more reliably due to the higher resolution.

[0043] In many exemplary embodiments, the use of ultraviolet light for illumination offers a further advantage due to the fact that a laser wavelength in the ultraviolet range (e.g., one of 193 nm, 248 nm, 308 nm, or 355 nm) is also utilized for laser processing purposes. Specifically, an excimer laser (e.g., a KrF excimer laser with an emission wavelength of approximately 248 nm) can be used as the laser source. Such excimer lasers have proven valuable for laser processing. Using illumination light with a similar wavelength allows for good adaptation to the laser processing unit. If the illumination light has an illumination wavelength corresponding to or near the laser wavelength, it may be particularly easy to design its antireflective coating in the case of transparent optical components, such that it has an antireflective or transmission-enhancing effect for both the laser wavelength and the illumination light.

[0044] An illumination system can also be designed to utilize illumination light having one wavelength within the visible spectrum (VIS), preferably a narrow-band green light having one wavelength in the range of 490 nm to 575 nm. Therefore, a good trade-off can be achieved between deployment costs and achievable resolution, as high-quality cameras sensitive to green light can be cost-effectively obtained, and furthermore, as experiments have shown that sufficiently good spatial resolution can be achieved in many cases using illumination with narrow-band green light.

[0045] To achieve different functionalities within a compact overall system size, in a preferred embodiment, the laser processing unit includes a beam deflection device having a substrate and a beam deflection surface thereon, the beam deflection surface being obliquely oriented relative to a main axis of the laser processing unit and used to deflect the laser beam in a propagation direction substantially parallel to the extension of the main axis. Therefore, a laser radiation source and a downstream beam guiding component can be constructed such that the radiation is incident substantially in a horizontal direction, while the main axis of the laser processing unit is vertically oriented. The main axis of the laser processing unit here refers to the axis defined by the optical axis of the imaging lens.

[0046] On the other hand, in order to achieve observation through the imaging lens of the laser processing unit, it is preferable to provide an observation beam path extending between the processing plane of the laser processing unit and the camera, which is guided through a beam deflection surface. The beam deflection device is designed such that it at least partially transmits illumination light. In other words, the beam deflection surface is designed to have a specific transmittance for illumination light, i.e., it does not completely reflect and / or absorb illumination light.

[0047] The substrate of the beam deflection device may be coated with a dielectric coating that forms the beam deflection surface. The coating is preferably designed to have a very high reflectivity (e.g., greater than 99%) for the incoming laser light in the presence of an incident angle and a relatively high transmittance (e.g., in the range of 20% to 70%) for illumination light used for illumination purposes.

[0048] According to one development, the substrate of the beam deflection device is embodied as a planar plate that is transparent to illumination light and tilted (e.g., up to 45°) relative to the main axis about a first tilt axis oriented perpendicular to the main axis. For example, the substrate may be composed of synthetic fused silica or some other material that is transparent to ultraviolet and visible light and has a low coefficient of thermal expansion.

[0049] The use of this beam deflection device provides the possibility of separating the laser beam path from the observation beam path within the area of ​​the beam deflection device. However, experiments have shown that, depending on the design of the beam deflection device, this may alter the optical path in the observation beam path, potentially leading to astigmatic aberrations that impair resolution. In a preferred embodiment, an illumination transmission astigmatism compensation unit is therefore configured in the observation beam path between the beam deflection device and the camera. This astigmatism compensation unit is designed to at least partially compensate for the introduced astigmatic aberration, thereby increasing the overall resolution of the observation system.

[0050] In the case where the substrate of the beam deflection device is embodied as an illumination light transmission plane plate tilted relative to the principal axis about a first tilt axis oriented perpendicular to the principal axis, the astigmatism compensation unit preferably includes a plane plate that is transparent to the illumination light and tilted relative to the principal axis about a second tilt axis oriented perpendicular to both the principal axis and the first tilt axis. The plane plates of the beam deflection device and the astigmatism compensation unit should have the same or substantially the same thickness, such that they introduce astigmatism distortion in two mutually perpendicular directions, which are mutually compensated for due to the different orientations of the tilt axes. Therefore, the observation system can be designed such that there are no astigmatic aberrations between the object plane of the camera and the light-sensitive sensor (e.g., a CCD sensor or a CMOS sensor) that would impair the resolution of sample observation.

[0051] Precise spatial positioning of the workpiece and any functional elements that may be applied thereto is a significant contribution to achieving extremely high processing accuracy. A further contribution occurs with respect to the laser processing unit, since for positionally accurate processing, the position of the irradiating laser beam in space must be known. Furthermore, a uniform intensity distribution throughout the entire beam cross-section and a high edge steepness at the boundary of the shield aperture are important prerequisites for high processing quality.

[0052] During laser processing, ideally, each individual functional element (e.g., each micro LED) should be irradiated individually, specifically across the LED completely and uniformly, while adjacent LEDs are not irradiated by the radiation provided for one LED, but only by the laser beam assigned to them.

[0053] For the measurement acquisition of suitable variables, a preferred embodiment includes a camera-based beam analysis system integrated into a laser processing station for in-situ analysis of beam parameters of a laser beam. This enables rapid beam diagnostics, for example, in the context of setting up a laser processing station or monitoring beam quality while ensuring correct imaging of the mask onto the workpiece.

[0054] Preferably, the beam analysis system includes at least one beam analysis unit, which includes a camera configuration sensitive to the laser wavelength and having a camera having an object field located in the processing plane of the laser processing unit or in a plane optically conjugate to the processing plane. With this configuration, the camera can capture an image of a laser beam effective in the processing plane, the image being as clear as possible and allowing for good resolution, or (e.g.) an image of the illumination aperture of a mask. Thus, beam parameters and alignment parameters can then be determined and processed in an evaluation device for correcting possible errors by means of a control unit.

[0055] In some embodiments, the camera is configured with a camera sensitive to laser wavelengths, preferably a camera sensitive to ultraviolet light (UV camera), which can directly process the laser light of a UV laser. Alternatively, the camera may be configured with a camera sensitive to visible light and a planar converter disposed in an object plane of the camera and configured to convert light of the laser wavelength into light from the visible spectrum. Thus, the converter precisely emits visible light with a spatial distribution existing in the processing plane or the masking plane.

[0056] Generally, the object field of a camera is not large enough to capture all the apertures of a mask simultaneously. In reality, only subgroups of apertures are captured separately. In this case, to diagnose the complete mask structure, the camera moves over the plane to be measured in a step-and-repeat manner, and in the evaluation unit, individual images are combined by software to form an image of the complete mask, and these individual images are evaluated by means of image processing. Alternatively, individual images to be evaluated may also be used.

[0057] To ensure that the measurement of the mask position is possible at any time, the beam analysis system can be mounted at the positioning device of the receiver substrate outside the substrate stage or on a separate positioning unit. This facilitates precise positioning of the beam analysis system in the submicron range, which is a prerequisite for the accurate combination of individual images and therefore the correct analysis of laser beams in the processing plane.

[0058] Next, a high-precision lithography mask structure can be used to perform measurements of the positioning device. This high-precision lithography mask structure is imaged onto the processing position using a laser device. At the location where adjacent images are joined together, this reveals a deviation from the original structure, which represents a measure of the relative positioning error in the X and Y directions (in each case, the sum of the X and Y errors at the two positions of the recorded image). After these deviations have been calculated, the errors can then be compensated.

[0059] A camera-based beam analysis system for in-situ analysis of beam parameters of a laser beam of the type described in this application may also constitute a protectable invention independent of other features of the claimed invention. Therefore, a laser processing system having an integrated beam analysis system is also disclosed, but which does not have camera-based position correction or camera-based position adjustment.

[0060] The inventors have recognized that by observing a procedure performed directly near the processing location during laser processing, conclusions about the possibility of procedure optimization can be drawn, and procedure parameters can be optimized based on this. In some embodiments, for these purposes, a camera-based shadowgraph analysis system for in-situ observation and analysis of a rapidly performed procedure within a processing zone affected by a laser beam is integrated into the laser processing station. Thus, knowledge of the procedure performed during laser ablation can be obtained by means of "shadowgraphy" or by means of shadow generation and analysis (e.g.), and processing parameters can be corrected in the event of an unfavorable procedure. The shadowgraph analysis system is also referred to below as a "shadowing system".

[0061] A shadow analysis system or shadowing technique can be used, for example, in the context of program development and program monitoring. Another application area is in the field of repair programs, that is, program steps that enable the repair of defective components (e.g., such as µLED displays) to improve overall yield.

[0062] The shadow analysis system includes a short-pulse light source or flash light source for time-controlled incident incidence of a short illumination pulse or flash in an incident direction relative to the lateral orientation of the laser beam. Furthermore, the system includes a camera on an opposite side for capturing shadows in a processing zone irradiated by the laser beam. Additionally, an evaluation unit is deployed for evaluating camera images of the camera.

[0063] Preferably, the illumination light pulse is incident on a region of the processing zone parallel to the processing plane. Alternatively, it is possible to have a relatively shallow or acute angle of incidence, which may be, for example, less than 30° or less than 20°.

[0064] For example, a particularly critical process stage during the production of a micro-LED display involves transferring the micro-LEDs with the aid of the LIFT method, which typically employs a very small donor-acceptor gap. In-situ monitoring of the process is then desirable. Without such monitoring, parameter searching and optimization, as well as troubleshooting in the event of quality problems, proves difficult.

[0065] In some embodiments, a LIFT processing station (i.e., a laser processing station designed for a LIFT procedure) is provided, which allows for high-resolution shading over a relatively small area (measuring area). This means that in any case, within a small measuring area, for example, the flight phase of a microLED after detachment from the donor can be accurately characterized.

[0066] Furthermore, the inventors have successfully developed a configuration for a shadow analysis system that enables shadowing even when the observed processing zone is located in an area that is difficult to access laterally (e.g., near the surface of a donor substrate during the manufacture of a micro-LED display). One embodiment of such a shadow analysis system is characterized by a beam deflection system (specifically, a mirror system) having a deflection element (specifically, a deflecting mirror) disposed between a short-pulse light source and the processing zone for deflecting illumination light from a direction tilted relative to the processing plane to an incident direction parallel to the processing plane, and a deflection element (specifically, a deflecting mirror) disposed between the processing zone and a camera for deflecting radiation passing parallel to the processing plane to an incident direction of the camera tilted relative to the processing plane. Therefore, a high-performance camera can be tilted and positioned at almost any xy position on a relatively large workpiece relatively close to the processing plane, while still within the processing zone, to achieve a shading beam path extending parallel to the processing plane. This allows for monitoring of the repair process using shading. For beam deflection purposes, a prism can be used instead of a single mirror, for example.

[0067] Particularly advantageous is an embodiment in which the shadow analysis system is configured to trigger a series of illumination pulses in a manner triggered by laser pulses of laser-processed lasers, such that the portion detached from the workpiece is imaged multiple times at different times and locations by a camera sensor integrating the series of illumination pulses into an image, and the image is used for evaluation. Thus, multiple exposures are performed. This enables, for example, trajectory tracking, which involves determining and analyzing, for example, the trajectory of a portion of a µLED detached from the workpiece by means of a laser pulse. Then, program parameters can be optimized so that the trajectory at the detachment location leads to the intended mounting position at the receiver with sufficient accuracy.

[0068] A camera-based shadow analysis system for in-situ observation and analysis of a rapidly performed procedure within a processing zone affected by a laser beam of one type described in this application may also constitute a protectable invention independent of other features of the claimed invention. Therefore, a laser processing system having an integrated camera-based shadow analysis system is also disclosed, but which does not have camera-based position correction or camera-based position adjustment.

Implementation Method

[0070] The following presents some exemplary embodiments of methods and systems for producing microelectronic components using laser processing methods. Each microelectronic component includes a plurality of microfunctional elements applied on a substrate. A primary application area in the exemplary embodiments is the production of a miniature LED display. This display includes a substrate that carries a miniature light-emitting diode (µLED) array intended to form individual image elements or pixels of the display. The miniature light-emitting diode (µLED) array is applied to a power supply structure. The laser processing is performed in at least one method stage in a laser processing station; this laser processing may also be referred to as laser microprocessing because it can be used to process and / or produce fine structures having a typical structural size on the order of one or several micrometers.

[0071] Figures 1 and 2 schematically illustrate some components of a laser processing station 100 according to a prior art. The laser processing station is configured for the laser stripping (LLO) method in the case of Figure 1 and for the laser induced forward transfer (LIFT) method in the case of Figure 2.

[0072] The laser processing station 100 includes a laser processing unit 110 that works in conjunction with a laser radiation source 112 in the form of a KrF excimer laser. The laser radiation source 112 emits a laser beam 105 having a laser wavelength of approximately 248 nm, i.e., laser radiation in the deep ultraviolet (DUV) range. The laser beam is radiated in a horizontal direction parallel to the x-axis of the system coordinate system.

[0073] A laser beam, extended and / or adjusted in some other way, passes through a mask 107 disposed in a mask plane 108 and includes a grid configuration of apertures or openings 109, which in each case transmit a portion of the beam, such that a group of partial beams exit, thereby achieving parallel processing (simultaneous processing at multiple locations on the workpiece). The mask may have hundreds or thousands of mask openings 109 typically shaped in the same manner (see details). The mask openings may have various shapes, such as squares, irregular rectangles, or similar.

[0074] A portion of the beam is deflected at a beam deflection device 115 and then propagates downward toward the workpiece 150 to be processed, substantially perpendicular or parallel to one of the main axes 116 (parallel to the z-direction) of the laser processing unit 110, or at a more or less acute angle relative to the main axis 116. The beam deflection device 115 has a planar parallel substrate 117 composed of synthetic fused silica, on which a planar surface is characterized as a reflective beam deflection surface 118 by means of a dielectric coating that is highly reflective of laser radiation. The arrangement of the illumination mask opening 109 in the mask plane 108 is imaged onto the processing plane 122 of the laser processing unit with the aid of an imaging lens 120. The optical axis of the imaging lens 120 defines or corresponds to the main axis 116 of the laser processing unit. The image can be magnified, reduced, or maintained at a size (1:1 imaging). In an example, the same intensity distribution as in the mask plane exists in the processing plane, but at a reduced scale.

[0075] The laser processing station 100 includes a workpiece movement system 200 designed to position a workpiece to be processed in one of the processing positions of the laser processing station in response to a movement signal from the control unit 190.

[0076] In the configuration shown in Figure 1, the workpiece moving system 200 includes a first base station 210, which can be moved very accurately to a desired position parallel to the (horizontal) xy plane of the system coordinate system and also in the height direction (parallel to the z direction), and can also rotate about a vertical rotation axis (PHI axis). For this purpose, in this example, a precisely controllable direct electric drive is provided.

[0077] In the configuration shown in Figure 2, a second substrate stage 220 is disposed above the first substrate stage 210 and can also be moved horizontally (parallel to the xy plane) and vertically (parallel to the z direction) in any desired direction in a controlled manner, and can also be rotated about a vertical axis. The laser processing station 100 may contain two substrate stages, but in the method stage shown in Figure 1, the second substrate stage is not used and therefore is not shown.

[0078] The mask 107 is carried by a mask moving system (not shown), which, under the control of the control unit, allows the mask 107 to be displaced in the mask plane 108 (parallel to the yz plane) and rotated about an axis parallel to the x direction.

[0079] In the case shown in Figure 1, the laser processing station 100 is designed for laser lift-off (LLO). Currently, light-emitting diodes (LEDs) are typically produced from p-type and n-type doped semiconductor layers composed of gallium nitride (GaN) formed by epitaxial growth on a sapphire wafer (epitaxy wafer), which serves as a growth substrate. These layers typically have a thickness in the micrometer range and are usually structured by laser processing to form individual functional elements 155 in the form of LEDs. For example, a thin, typically metallic, interconnect layer is applied to the GaN layer stack by vapor deposition. With the help of this interconnect layer, the growth substrate carrying the GaN layer stack thereon is connected to a further planarized carrier substrate. The surface connection between the growth substrate and the GaN stack is subsequently released. Thus, the GaN stack is transferred to the carrier substrate.

[0080] The workpiece 150 in Figure 1 is shown in its configuration prior to the release of the surface connection. The upper flat substrate 152 is the growth substrate, also referred to as the donor substrate 152, because it later provides the functional element 155 for application thereon. The carrier substrate 154 supported on the first substrate stage 210 is also referred to as the acceptor substrate 154, because it accepts or receives the functional element 155. The acceptor substrate on which the GaN stack is then supported serves as the basis for further steps in the production of microelectronic components.

[0081] In the laser stripping method, the workpiece is positioned such that the processing plane 122 is located in the region between the donor substrate 152 and the GaN device 155 so as to release the surface connection between them by means of laser processing. In this case, the buffer layer located in the boundary region between the growth substrate and the GaN device is destroyed or removed by laser radiation. In this case, laser irradiation is achieved through the laser-transparent growth substrate 152.

[0082] In a subsequent LIFT operation (see FIG. 2), the individual functional elements 155 held on the (recipient) substrate 154 are then transferred to a further planar substrate 156. The planar substrate 156 is held in place by a first substrate stage 210 and has an electrical supply structure (backplane) applied by vapor deposition and structuring on its top side where the microLED is to be mounted. The bottom substrate 156 now serves as the recipient substrate. The recipient substrate 154 from FIG. 1, which carries the microelectronic functional elements 155, is flipped so that the functional elements 155 are now located on the underside of the substrate. In this orientation, the substrate now serving as the donor substrate is held by a second substrate stage 220 in FIG. 2, so that the functional elements to be transferred are located opposite the recipient substrate 156. The microLED is then detached from the donor substrate 154 and transferred to the recipient substrate 156 by means of a laser beam radiated precisely in position. In this case, the laser does not directly exert an effect through radiation force, but is used as a controlled energy input and is usually thermally triggered to induce material transfer. If the micro-LED detaches directly from the epitaxial wafer, the energy comes from the pressure generated by nitrogen released due to the decomposition of a thin GaN layer.

[0083] The donor-recipient distance 158, which is one of the measures of the flight range of the functional element to be transferred 155, is typically between 30 µm and 500 µm, and specifically between 80 µm and 200 µm.

[0084] For example, in the production of micro LED displays, the workpiece movement system 200 must be able to position the workpiece at a predefined target location with high positioning accuracy (on the order of 1 µm or less), possibly over a relatively large travel distance on the order of several hundred millimeters. In the case of the LIFT method, this is necessary for two substrate systems in order to ensure correct position transfer. The following provides an explanation of some exemplary embodiments of achieving such high positioning accuracy in an economical manner.

[0085] In the exemplary embodiment in FIG3, some components also present in the reference examples of FIG1 and FIG2 have the element symbols used therein.

[0086] The laser processing station 300 in Figure 3 is also equipped with optical, mechanical and software components to realize a camera-based position adjustment.

[0087] These include components of an illumination system 310 for illuminating an illumination area 305 on a workpiece 150 with narrow-band illumination light (i.e., green light) of approximately 528 nm from a narrow wavelength range in the visible spectrum. The illumination system is designed to provide uniform illumination of a zone to be illuminated in the illumination area 305 without imaging the light source.

[0088] The green light source 312 may include one or more LEDs. One horizontal branch of the illumination beam path passes through a light-collecting lens 316 and a downstream light-emitting field aperture 314 to a beam splitter cube 321, the planar beam splitter surface of which is inclined at 45° relative to the main axis 116 of the laser processing unit 110. The beam splitter surface reflects a first portion of the illumination light downstream onto the workpiece 150 in a direction parallel to the main axis 116. This portion passes through the planar parallel substrate 317 of the beam deflection device 315, which is transparent to green light. The dielectric coating of the planar parallel substrate 317 has a high reflectivity for UV laser light but a high transmittance for green light, so that the illumination light passes through the laser lens 120 and illuminates the illumination area 305 on the workpiece.

[0089] The light source 312 illuminates the entire illuminated area on the workpiece at each point, thereby achieving a homogenization effect. The aperture of the imaging lens 120 represents the condenser stop, and the imaging lens also functions as a condenser. This should be considered in the system design so that only the area visible in the camera is illuminated as much as possible, and the lens is fully illuminated but not overexposed, resulting in less stray light and maximum intensity of (usable) illumination.

[0090] It is particularly advantageous to image the illumination onto the aperture of the imaging lens 120 (laser lens) such that 65% to a maximum of 90% of the aperture is illuminated, and to image the light field aperture onto the processing plane 122 in a reduced manner via the laser lens such that the illuminated area is only slightly larger than the area imaged in the camera.

[0091] A portion of the illumination light that is transmitted or allowed to pass through the surface of the beam splitter is captured and absorbed by an absorber 319 and thus does not result in unwanted stray light.

[0092] The light returning from the workpiece 150 passes again parallel to the main axis 116 in the direction of a camera 340, which has high sensitivity to visible light (specifically, to green light in this example), through the imaging lens 120 (now used as a lens for camera observation), the beam deflection device 315, and the beam splitter cube 321. A tube 325 is mounted upstream of the camera and has light-absorbing properties inside it, serving as a stray light absorber.

[0093] The optical configuration is designed such that, with the aid of the imaging lens 120 (and further optical components as needed), an image of one of the processing planes 122 is incident on the photosensor of the camera 340. Therefore, the camera sensor is located in a plane optically conjugate with the processing plane 122.

[0094] Camera 340 is connected to control unit 190 for signal transmission purposes. This control unit includes an evaluation unit 195 for evaluating images from the camera by means of image processing. This evaluation is in the context of camera-based position adjustment, which will be explained later.

[0095] The beam deflection device 315 has a substrate 317 that is transparent to visible light in the form of a planar plate composed of, for example, fused silica. A dielectric coating is applied to the planar surface of the substrate 317 facing the laser beam. This dielectric coating has a high reflectivity for UV laser wavelengths (reflectance R > 99%) and a relatively high transmittance for green light illumination (transmittance T > 20%, for example, 50% to 70%). Therefore, the illumination light from the workpiece in the observation beam path passes parallel to the beam deflection device 315 in a deflected manner.

[0096] The inventors have determined that astigmatism in the image of structural elements on a workpiece can also occur in this case, limiting spatial resolution capabilities. This is primarily due to the fact that the rays in the X-ray beam do not all pass parallel to each other; that is, a portion of the beam with a varying angle of illumination is "seen" in one direction (X direction) showing a varying plate thickness, while it is not seen in the other direction (Y). This results in image distortion in one direction.

[0097] To avoid the disadvantages caused by this, an astigmatism compensation unit 330 for illumination light transmission is mounted between the beam deflection device 315 and the camera 340 in the observation beam path. This astigmatism compensation unit is shown in the y-direction in FIG3 and in the x-direction in detail 3A. The astigmatism compensation unit is formed by a plane parallel to a transparent plate inclined at 45° about an inclined axis extending parallel to the x-axis relative to the main axis 116 of the laser processing unit 110. In contrast, the beam deflection device 315 is inclined at 45° about an inclined axis inclined parallel to the y-direction (i.e., perpendicular to the inclined axis of the astigmatism compensation unit). Since this second substrate (having the same thickness and being composed of the same material, and therefore having the same optical thickness) is inserted, the radiation that generates the image on the camera chip is processed in the same way on both beam axes, so that the camera 340 can produce an image that is substantially free of astigmatism on the processing plane 122.

[0098] The configuration may also be described such that the substrate of the beam deflection device 315 is embodied as an illumination light transmission plane plate at an angle of 45° in the laser beam and thus deflecting the laser beam by 90°, and the astigmatism compensation unit includes a plane plate 330 that is transparent to the illumination light, the plane plate 330 being at an angle of 45° in the observation beam path, but being arranged on the axis of the observation beam path in such a way that it is rotated by 90° relative to the substrate 317 of the beam deflection device 315.

[0099] A narrow-bandpass filter 335 upstream of the camera 340 limits the illumination bandwidth used for image generation to approximately ±5 nm near the center wavelength of the green illumination light (which is already relatively narrow before filtering). Therefore, due to the additional filtering near the center wavelength at the bandpass filter 335, there is only a relatively small loss of intensity. Even though the imaging lens 120 is not diffracted-limited for the utilized green wavelength and the two light-transmitting thick planar plates (beam deflection device and astigmatism compensator) are located in the beam path, a high-contrast image with particularly good resolution is thus possible (in this example, approximately 2 µm). Therefore, ambient light and possibly laser plasma radiation are also shielded.

[0100] A workpiece positioning operation can be performed with the aid of camera observation as follows. First, in response to a control signal from control device 190, workpiece movement system 200 positions a base station such that a predefined actual position is achieved for one or more predefined structural elements of the workpiece. This actual position must be within the capture range of camera 340 or in the object field. Then, with the aid of the camera, at least one image of the portion of the workpiece illuminated by the lighting system and located within the capture range of the camera is generated. The image or the images are evaluated by means of image processing to determine positional data representing the actual position of the selected structural element within the capture range. For this purpose, control device 190 includes an evaluation unit 195 for evaluating the image by means of image processing.

[0101] A comparison module (using corresponding software) is also implemented in the evaluation unit. This comparison module compares the determined actual position of the structural element with a predefined target position. If there is a positioning deviation or positional deviation that cannot be tolerated, a correction signal or corresponding correction value is generated. The isotropic workpiece movement system indicates how to perform a corrective movement to bring the observed structural element to the target position or to a sufficiently good proximity to the target position. The workpiece movement system 200 then performs a corrective movement of the substrate stage.

[0102] In the case of segmented processing, within one segment to be processed in the next step, the image of the substrate is recorded and processed in a predefined grid, and the position value is calculated. In each case, the difference between the actual value and the target value is written into a correction table used for correction purposes during processing, and the values ​​between the grid points are interpolated. If there is no positional deviation, a 0 is present in the table.

[0103] The system is programmed so that laser processing by means of laser irradiation only begins when the positioning to the target position (including the required correction movement if appropriate) has been completed. In this case, the workpiece is fixed, that is, it does not move.

[0104] Referring to Figure 4, by way of example, an explanation will now be given on how the achievable spatial resolution and positioning accuracy can be further improved by means of some modifications to the setup from Figure 3. Some components of the same or substantially the same laser processing station 400 in Figures 3 and 4 have the same component symbols as in Figure 3.

[0105] An improvement can be particularly achieved if camera observation is performed using radiation from the ultraviolet range. In the exemplary embodiment of FIG4, a camera 440 (UV camera) sensitive in the ultraviolet wavelength range is used. In addition, an illumination system 410 with an illumination source 412 operating in the ultraviolet wavelength range is used. In this regard, for example, an LED with a wavelength of 270 nm can be used as the illumination source. This wavelength is indeed close enough to the laser wavelength (248 nm) that, for example, the anti-reflective coating in the imaging lens 120 is also highly effective against illumination radiation. However, at the same time, a dielectric coating with a high reflectivity to 248 nm can be provided at the beam deflection device 415, while the dielectric coating is sufficiently transparent (sufficient transmittance) for the illumination wavelength of 270 nm (see the reflectivity diagram in FIG4B).

[0106] Figure 5 illustrates the possibility of in-situ observation of a laser processing station 500 and a microLED to be transferred in a laser stripping operation using a UV camera 540. This exemplary embodiment is considered as the basis for explaining how observation of the process in the processing plane 122 can occur directly at the laser wavelength used (here, 248 nm) through the use of a camera 540 sensitive in the ultraviolet wavelength range. To achieve this, a dielectric laser deflector is used in the beam deflection device 515, which has a sufficient and defined transmittance in the ultraviolet range used (e.g., at 248 nm). For this purpose, the beam deflector can be designed as a physical beam splitter that transmits a small, defined portion of the laser radiation along the path from the workpiece 150 to the camera 540. For this purpose, the fact that each dielectric mirror has a residual transmittance for the wavelength used is taken advantage of is fundamentally unavoidable. A better mirror (i.e., a mirror with a high reflectivity) has relatively low residual transmittance. A dielectric mirror with a residual transmittance sufficient for recording an image using a UV-sensitive camera 540 can be used. Preferably, in the beam deflection device, a dedicated physical beam splitter is used, i.e., a dielectric coating having a relatively high defined reflectivity for a laser wavelength and a transmittance defined with high accuracy for the incident angle (approximately 45°) of the same laser wavelength. By way of example, a beam splitter having a transmittance in the range of approximately 0.5% to approximately 5% can be used (see the reflectivity diagram in Figure 5B).

[0107] If the work is completed step by step and it is done in sections, laser processing becomes particularly efficient and accurate. Variations of this method include generating and storing a correction value grid within a measured section and then processing this section as quickly as possible. In this case, the corrected value is used for laser processing of the workpiece. Then, the next section is measured and processed accordingly, etc.

[0108] In an illustrative case, the treatment is initially implemented in one of the entire travel ranges of various mobile systems via a defined part (section). This may mean that (for example) a 6-inch wafer is not processed in one step, but in each case step-by-step processing (for example) smaller sections of 25 x 25 mm2 or 16 x 16 mm2 or 22 x 27 mm2. Before processing in this section, the current measurement and calibration of the moving system in this section. For image processing, the coordinate table should be fixed or move so slowly that there is no interfering motion blur. However, only one grid within the section (e.g., 5 positions in the X direction multiplied by 10 positions in the Y direction) was recorded, and not the entire area of ​​the workpiece within the section, and not all processed positions. In this case, the computation of image processing and calibration values ​​is achieved during image recording in a predefined grid continuously and in parallel with it during image recording at a subsequent location. The values ​​between the melometric positions were then interpolated during the treatment. The necessary number of measurement positions is dependent on the errors appearing and dynamically adjusted for visual needs.

[0109] After the treatment in a first section, the measurement is followed by the treatment of a second section such that the measurement and processing always occur rapidly one after the other. Therefore, it can be accompanied by correction for biases that appear only within the complete treatment. In other words, when the calibration is ready, the processing is implemented and the changes should be made automatically. Depending on the need, if an abnormal, incredible deviation is measured, the operator can be informed and asked for confirmation.

[0110] In addition to one of the precise positioning of the workpiece or its structural elements in space, in terms of laser processing units, the properties of the laser beam (e.g., position in space, edge steepness, uniformity within beam cross-section, etc.) are also equally crucial in achieving extremely high precision of processing. Similarly, for example, for LIFT operation, the precise alignment of the mask aperture with the miniature LED on the donor substrate as well as the precise setting of the imaging position is crucial for the correct processing.

[0111] Some possibilities for beam analysis or beam dissection are schematically plotted in a single diagram with reference to FIG. In this case, some basic components of the laser processing unit correspond to those in FIG.

[0112] Additionally, a component of a camera-based beam analysis system 700 is provided, which is integrated into a laser processing station 600 and designed to perform in-situ analysis of the beam properties of the laser beam 105. A first beam analysis unit 720 and a second beam analysis unit 740, which may be provided as an alternative or supplement to the first beam analysis unit, are illustrated in the diagram.

[0113] The components of the first analysis group 720 are mounted below the processing plane 122 in a continuation of the laser beam illuminating this location (i.e., in a continuation of the main axis 116 of the laser processing unit 610), such that when the substrate stage 210 of the moving system 200 moves laterally to a certain extent as illustrated, so that it no longer obstructs the beam path, the laser beam can strike the beam analysis unit. With the aid of the first beam analysis unit 720, the intensity distribution in the processing plane 122 is imaged onto a planar UV-VIS converter 726 by means of a lens 724 having a suitable imaging ratio. This converter is disposed in a plane optically conjugate to the camera sensor of the camera 722. The image of the UV-VIS converter is imaged onto the visible light-sensitive camera chip of the camera 722 (VIS camera) via a further lens 728.

[0114] In an alternative variant, a camera sensitive to UV light (UV camera) is used. The inserted UV-VIS converter and its intermediate imaging can then be omitted.

[0115] To diagnose the complete mask structure of mask 107, camera 722 is gradually moved to different measurement positions above the irradiated area of ​​the processing plane 122 (i.e., parallel to the xy plane) in a step-by-step and repetitive manner. In this case, individual images are captured. The individual images are combined by software to form an image of the complete mask, and these individual images are evaluated by means of image processing.

[0116] One advantage of this variant is that the complete beam path from the laser to the processing plane 122 is included in the diagnostics and, correspondingly, any errors in one of the components from the laser to the processing plane can be identified. Furthermore, the area downstream of the processing plane (i.e., the first analysis group 720) does not contain more components than absolutely necessary for the measurement.

[0117] According to one development, a high-precision lithography mask structure can be used to measure and correct camera positioning for beam analysis. This high-precision lithography mask structure is imaged onto a processing position in a processing plane 122 with the aid of a laser device or laser processing unit 610. After recording the mask aperture at various positions of the beam analysis camera and combining individual images by software to form an image of the complete mask, positioning errors can be determined and corrected by image processing based on errors in the mask image in the boundary areas between individual images. At the position where adjacent images are joined together, this can reveal a deviation from the original structure, which represents a measure of relative positioning error in the X and Y directions (in each case, the sum of X and Y errors at the two positions of the recorded image). After these deviations have been calculated, a possible error can then be compensated.

[0118] To ensure that the measurement of the mask position is possible at any time, components of the beam analysis system 700 can be mounted on the positioning device 200, outside the substrate holder 210, or on a separate positioning unit. In this case, the precise positioning of the beam analysis system in the sub-micron range is a prerequisite for the accurate combination of individual images and thus for the correct analysis of the laser beam in the processing plane 122. Therefore, fine calibration of the positioning is very important in this range.

[0119] Alternatively or additionally, a second beam analysis unit 740 may be provided. Its components are arranged in a straight line following the laser beam 105, which acts as a beam splitter, behind the beam deflection device 515. The optical axis of the second beam analysis unit 740 extends perpendicularly to the main axis 116 of the laser processing unit. The arrangement of the camera 742, the selective imaging lens 748, the selective UV-VIS converter 746, and the lens 744 is similar to the corresponding components of the first beam analysis unit 720. Between these components and the inclined transparent plane plate of the beam deflection device 515, an astigmatism compensation unit 745, similar to the astigmatism compensation unit 530 with an inclined plane plate, is also inserted. This is because the laser beam incident on the second beam analysis unit 740 has passed through the inclined plane plate of the beam deflection device 515 and undergone astigmatism changes intended to be compensated during the process.

[0120] One advantage of the second beam analysis unit 740 is that it can also be used during laser processing (e.g.) to monitor the laser beam and / or shield 107 for quality assurance purposes. A disadvantage is that possible aberrations in the imaging lens may not be determined by means of the second beam analysis unit.

[0121] The arrangement of a UV camera 540 (which also exists in other exemplary embodiments) also allows for beam analysis or beam profiling. For this purpose, a strongly and uniformly scattering auxiliary substrate can be brought into the processing plane 122. The energy distribution on this strongly scattering plane is then imaged into the camera 540. If a plane mirror is brought into the processing plane 122, an alternative method of beam profiling is possible. In this case, as an alternative to the UV camera 540, a UV-VIS converter can also be used in conjunction with a VIS camera.

[0122] Measuring the position of the mask aperture and performing beam diagnostics, which can be corrected as needed, is an important part of measures that can be taken to ensure the highest possible accuracy of the overall processing.

[0123] Referring to Figures 7 and 9, the following provides an explanation of the further possibility of equipping a laser processing station (for example) for manufacturing micro LED displays, enabling the display to be manufactured with high precision and high yield.

[0124] Figure 7 schematically illustrates an exemplary embodiment of a laser processing station 750, which is equipped with a shadow analysis system 800 (which may also be referred to as a shadowing system 800). This allows for in-situ (i.e., during laser processing) observation of the rapidly progressing process in the processing zone 106 (i.e., the area where laser radiation irradiates and interacts with the workpiece 150).

[0125] In this regard, FIG7 schematically illustrates a possible setup for shading during a LIFT operation in one of the repair procedures. In the illustrated repair procedure, the intention is to remove a defective pixel or a defective "die" 159 from a display substrate 156 equipped with multiple pixels of the same type and simultaneously observe the process during the detachment. For this purpose, the shading system includes a short-pulse light source or flash source 810 capable of mimicking a very short light pulse of sufficient intensity (typically as low as 30 ns to 100 ns). For this purpose, LEDs are deployed to provide the necessary brightness of the illumination pulse due to the high current (possibly exceeding 100 A) during the short exposure time. The short illumination light pulse can be triggered by a laser pulse from the laser processing unit 760. For this purpose, the control unit 190 includes a delay unit that allows a light pulse to be emitted only after a predefined delay time following a laser pulse so that the process during the detachment of a die can be observed shortly after the irradiation of the laser pulse.

[0126] A light-collecting aperture 812 and a light-collecting lens element 814 of the shadow lighting are disposed downstream of the short-pulse light source 810. The path of the illumination beam starting from the light source first extends obliquely relative to the processing plane 122 (for example, at an angle of 20° to 50° relative to the processing plane 122), so that the short-pulse light source and downstream components can be positioned relatively close to the processing zone without colliding with the workpiece.

[0127] To achieve the effect that the illumination light in the processing zone 106 passes through the processing zone parallel to the processing plane 122, a first deflecting mirror 822 of a mirror system 825 is disposed between the short-pulse light source and the processing zone. The mirror element is embodied in a wedge shape, thus allowing the edge of the deflecting mirror near the processing zone to be disposed at a very small distance from the processing plane. For example, this distance can be between 50 µm and 200 µm.

[0128] On the opposite side of the first deflecting mirror 822, the mirror system 825 includes a second deflecting mirror 824, which is configured mirror-symmetrically with respect to the first deflecting mirror 822 relative to the main axis 116 of the laser processing unit and deflects light that has passed parallel to the workpiece through the processing zone 106 to a direction that extends obliquely to a camera 830 relative to the processing plane 122. If, during laser ablation, a detached particle in the zone 106 flies across the illumination beam path, the light is blocked and a shadow 826 is generated within the illumination beam path. An extraction device 840 is used to extract the detached particle by suction from the processing zone.

[0129] A camera 830 for capturing the shadow of the processing zone is positioned on the opposite side of the short-pulse light source. The optical axis of the camera is oriented at an angle (e.g., between 30° and 60°) relative to the processing plane. Due to the tilted orientation, the camera 830 can be positioned very close to the processing zone without colliding with the workpiece. A lens 832 for imaging the wafer detached from the die onto the camera is positioned between the camera and the deflecting mirror.

[0130] The shadow analysis system 800 can be configured to generate and evaluate images using multiple time-shifted illumination pulses, triggered by laser pulses from laser 112. In this example, the system is designed to observe particles with typical sizes between 3 µm and 30 µm. Multiple exposures allow for trajectory tracking, enabling particles or micro-LEDs to be identified multiple times in the captured images (especially at different times and locations). In one experimental setup, particles with velocities up to 8 m / s (80 m / s in cases of significant motion blur) can be observed, and their trajectories can be captured and analyzed.

[0131] For example, a repair procedure can be implemented as follows: Control and measure the display 150 (workpiece 150) to be evaluated and rate each pixel or each micro-LED. For example, micro-LEDs that remain dark or whose illuminance exceeds specifications are considered defective. Generate a table or matrix that identifies the locations of all defective chips.

[0132] An arithmetic unit of the control unit 190 calculates the movement or contour above the display of all defective pixel positions. This contour is progressively traversed by means of the movement system. Laser pulses are triggered at the respective positions of the defective dies. In this case, the die 159 detaches from the display substrate, is accelerated, and reaches the extraction device 840. This creates vacancies at the positions of the defective dies, which are then equipped with new dies. Therefore, new (defect-free) dies are not stacked on top of the remaining defective dies.

[0133] The shading system enables the observation and monitoring of these method steps. In particular, 100% monitoring is made possible by the mirror system 825, whose component near the workpiece is positioned at a distance of approximately 50 µm to 200 µm above the processing plane (sample plane) and can be fixedly arranged laterally relative to the imaging lens 120 of the laser processing unit configured for a LIFT program.

[0134] For quality assurance in repair applications, a solution with relatively low optical resolution can be used to make a larger area of ​​the processing zone visible and allow observation of the processing zone while the equipped display substrate is moved below the laser processing unit 760 with the aid of the moving system 200. In particular, it can be clarified whether a die has detached and accelerated; if appropriate, or if not, a new laser pulse can be triggered. Observation also allows it to be determined whether a defective die has actually reached the extraction device 840; otherwise, a note can be created in the fault log. Therefore, the use of shadow analysis in the context of repair procedures during the production of, for example, micro-LED displays can facilitate the production of virtually fault-free displays.

[0135] A repair can also be performed on a transfer substrate. This can be advantageous because there is no risk of damaging the backplane.

[0136] The significant benefits achievable as a result can be understood as follows. A modern 8K display contains approximately 100 million micro-LEDs. Experience shows that the introduction of a new technology is accompanied by a decrease in yield during manufacturing (the so-called "yield loss"), which then decreases significantly as production volume increases within a learning curve. For example, a complete display may initially contain several thousand defective pixels. However, to obtain a defect-free product, a repair procedure is performed to replace these defective components. The defective components are first removed again. This can be efficiently accomplished using a LIFT procedure. Even with a completely predetermined procedure, the repair procedure can be expected to permanently serve as a beneficial supplement to the production process.

[0137] Referring to Figure 8, another possibility for utilizing shadow analysis in the context of a LIFT procedure is explained. In this variant, for clarity, the components of the shadow analysis system 800 are labeled with the same element symbols as the corresponding components in Figure 7. Unlike the configuration in Figure 7, there is no mirror system. The short-pulse light source 810 and camera 830, mounted on opposite sides, have coaxial optical axes extending perpendicular to the main axis of the laser processing unit 760, such that the illumination beam path of the shadow analysis system extends parallel to the processing plane 122 upstream and downstream of the processing zone. This configuration can be used for parameter optimization of laser parameters in high-resolution shadowing during a LIFT operation. In this case, only a relatively small area sample 750 is analyzed, rather than an entire wafer or a complete display. Observation is performed parallel to the sample surface without a mirror. In this case, due to the fact that the illumination light is almost at no distance from the sample surface, observation can begin directly from the donor surface. High-resolution observation can be achieved by the fact that a distance of only a few centimeters can exist between the short-pulse light source 810 and the camera 830 on the acquisition side. The observable area can be relatively small; the design can advantageously make the observable area only slightly larger than the maximum donor-receptor distance. Observation at a distance of up to 500 µm, and significantly smaller as needed (e.g., as low as 100 µm or less), is usually sufficient.

[0138] Since the lower edge of the illumination beam path is positioned approximately 100 µm above the sample surface in the configuration shown in Figure 8, it is possible to observe the detached grains only from this position. One of the shadow analysis systems 900 shown in Figure 9 is configured to observe a region from the sample surface to a height of approximately 500 µm. For this purpose, the radiation from the short-pulse light source 910 is directed at a shallow angle (e.g., 10° to 30°) onto the sample surface (workpiece surface) in the processing zone 106, making the relatively highly reflective sample surface act as a deflector. The deflector 924, positioned to the side of the camera 930 behind the processing zone, is slightly tilted downwards (compared to deflector 824), making the grains in the processing zone visible in the lower region of the camera image. The radiation from the short-pulse light source 910 is then deflected from the sample surface to the camera's deflector 924 and subsequently imaged onto the wafer of the camera 930. By applying this setup, although the shading beam path no longer extends perfectly parallel to the sample surface, the entire area starting from the sample surface can be monitored with only minor imaging distortion. Therefore, the procedure for detaching the grains from the sample surface can also be visualized and evaluated.

[0139] With the aid of knowledge from shadow analysis, laser parameters can be set so that the particles to be detached (crystals, µLEDs, or the like) fly parallel to each other towards the receiver without substantially any inherent rotation or lateral offset, thus ensuring the required accuracy. Observation of the flight behavior can be achieved depending on the laser parameters, the properties of the epitaxial wafer, and other parameters. For this, observation within a narrow band is usually sufficient. Shadow analysis allows for the identification of parameters that ensure a high-quality LIFT procedure. This setup can be used to monitor the production process in a random sampling manner to identify potential quality problems.

[0140] The inventors have conducted a complex analysis and consideration of potential errors. Error considerations reveal that if the aim is to achieve the highest foreseeable processing accuracy, the sum of all errors to be considered should remain below approximately 1.5 µm. As a maximum tolerable error, the width of the channel between µLEDs can be considered a guideline value because, under one or more errors, adjacent µLEDs will be irradiated at the boundary. The edge steepness of the imaging (i.e., the area at the boundary of the mask aperture where the laser energy drops from 90% to 10%) must also be subtracted from this maximum tolerance error. This edge steepness is related to the nature of the lens used and can be, for example, 1.6 µm. If the channel width is, for example, 3 µm, this results in a maximum permissible deviation of 1.4 µm between the imaging of the mask aperture in the processing plane and the position of the associated µLED. It is thus evident that any sub-step that improves accuracy can be important, even if it only avoids errors on the order of a few tenths of a micrometer.

[0141] To further increase the processing accuracy of the method, additional measures may be useful. For example, in a camera system, there may be differences in the sensitivity of individual pixels. This can negatively affect the quality of the synthesized image, especially when it is generated from individual images. Here, correction of pixel sensitivity can be useful. For example, a correction can be achieved by repeatedly measuring the same area of ​​a laser beam of known intensity at the camera with different pixels by progressive offset and then compensating for the differences. Laser stability can also play a role when stitching together a composite image from individual images. Therefore, small differences may appear between individual pulses. Accuracy can be increased by averaging using a suitable filter. In addition, the illumination required for camera observation can cause a local energy input in the system, thereby causing image drift. For example, thermally induced image drift can be suppressed or avoided by using intermittent illumination instead of continuous illumination (e.g., by pulse width modulation during illumination). Another solution is to use an additional, possibly higher-resolution, illuminated off-axis camera system, which is spatially close to the processing lens configuration. Then, observations are performed before or after machining. [Simplified Explanation of the Diagram]

[0069] Further advantages and features of the present invention are apparent from the scope of the invention claims and from the description of the exemplary embodiments of the invention explained below with reference to the figures. Figure 1 shows a laser processing station configured for a laser stripping (LLO) method; Figure 2 shows a laser processing station configured for laser-induced forward transfer (LIFT); Figure 3 shows an exemplary embodiment of a laser processing station equipped with components for implementing camera-based position adjustment, wherein narrow-band green light is used; Figure 3A shows a detail of an astigmatism compensation unit viewed from the x-direction; Figure 4 shows an exemplary embodiment of a laser processing station equipped with components for implementing camera-based position adjustment, wherein ultraviolet light is used; Figure 4A shows a detail of an astigmatism compensation unit viewed from the x-direction; Figure 4B shows a reflectance diagram of a dielectric coating of a beam deflection device; Figure 5 shows the possibility of in-situ observation of a laser processing station and a micro-LED to be transferred for a laser stripping operation using a UV camera; Figure 5A shows a detail of an astigmatism compensation unit viewed from the x-direction; Figure 5B shows a reflectance diagram of a beam splitter having a transmittance in the range of about 0.5% to about 5%; Figure 6 illustrates an exemplary embodiment of a beam diagnostic system integrated into a laser processing station, wherein several beam analysis units that can be used alternately or cumulatively are schematically depicted in a single diagram; Figure 7 illustrates an exemplary embodiment of a shading system integrated into one of the laser processing stations; Figure 8 illustrates another exemplary embodiment of a shading system integrated into one of the laser processing stations; Figure 9 illustrates an exemplary embodiment of a shading system integrated into one of the laser processing stations, the shading system being designed for observation of a sample area close to the sample surface.

Claims

1. A method for producing a micro LED display comprising a substrate, the substrate carrying a pixel on an electrical supply structure to form a micro LED array, wherein laser processing is performed in at least one method stage in a laser processing station under the control of a control unit, the laser processing comprising parallel processing at multiple processing sites using a mask having a plurality of openings, the mask splitting a laser beam into a plurality of partial beams and the mask openings emitting laser radiation being imaged onto a processing plane of the laser processing unit; the laser processing comprising at least one of the following operations: a laser lift-off (LLO) operation selectively removing a material from another material; and a laser-induced forward transfer (LIFT) operation configured to transfer material onto the substrate by directing laser radiation onto the material with positional accuracy; the method stage comprising positioning a workpiece to be processed in a processing position of the laser processing station by means of a workpiece movement system in response to a movement signal from the control unit. The workpiece is one of an unprocessed substrate and a substrate carrying at least one of a coating and other functional structures, characterized by the following steps: observing the workpiece in a camera-based manner using a camera system, the observation including capturing at least one portion of the workpiece in an object field of the camera and also generating an image representing that portion; evaluating the image by means of image processing for the purpose of determining positional data representing the actual position of at least one structural element of the workpiece in the object field; comparing the actual position of the structural element with a target position and generating a correction signal depending on the deviation between the actual position and the target position; correcting the processing position based on the correction signals by controlling the workpiece movement system for the purpose of matching the actual position with the target position; and irradiating at least one laser beam directed at the workpiece into at least one processing position of the workpiece for the purpose of local laser processing of the workpiece.

2. The method of claim 1, wherein the workpiece is divided into multiple segments and the segments are processed sequentially, a grid of correction values ​​is generated and stored in a measured segment, and the corrected values ​​are used to subsequently process the segment for the laser processing of the workpiece.

3. The method of claim 1 or 2, wherein a narrow-band light system having a spectral bandwidth of 10 nm or less is used for camera observation and image capture, wherein at least during the capture of an image, an illumination area of ​​the object field containing the camera on the workpiece is illuminated by narrow-band illumination light having a spectral bandwidth of 10 nm or less, and / or light from a narrow wavelength band having a spectral bandwidth of 10 nm or less transmitted to the camera by means of a wavelength selective device between the object plane of the camera and the camera.

4. The method of claim 1 or 2, wherein the observation and image processing are performed in a calibration step prior to the laser processing and the laser processing step begins only after the calibrated position has been set, wherein the workpiece does not move during the image capture, such that the measurement used for the calibration is performed with the workpiece fixed.

5. The method of claim 1 or 2, wherein the laser processing unit includes an imaging lens for imaging a mask plane onto a processing plane of the laser processing unit and wherein the positioned workpiece is observed through the imaging lens by means of the camera, wherein a beam deflection device is provided having a beam deflection surface that is tilted relative to a main axis of the laser processing unit, the beam deflection device deflecting the laser beam in a propagation direction substantially parallel to the extension of the main axis, the positioned workpiece being observed through the beam deflection surface by means of the camera, and wherein an astigmatism correction is introduced in the observation beam path between the beam deflection surface and the camera.

6. The method of claim 1 or 2, wherein for the purpose of laser processing, a laser wavelength of approximately 248 nm in the ultraviolet range is used, and wherein illumination light having an illumination wavelength of less than 300 nm in the ultraviolet range is used, wherein attenuated light from a laser source for the laser processing is used specifically for the illumination of the workpiece, or wherein for the purpose of laser processing, a laser wavelength of approximately 248 nm in the ultraviolet range is used, and illumination light having an illumination wavelength in the visible spectrum (VIS) range is used, wherein the illumination light system is a narrow-band green light having a wavelength in the range of 490 nm to 575 nm for illumination.

7. The method of claim 1 or 2, wherein a beam analysis of the laser radiation in the processing plane is performed for the purpose of determining the position of the image of the mask aperture in the processing plane, the beam analysis is integrated into the laser processing station, and a control of the workpiece movement system is executed such that the position and orientation of each mask aperture in the processing plane corresponds to the position and orientation of a structural element to be processed in each laser pulse, and / or a measurement and correction for camera positioning for the beam analysis is performed using the mask structure imaged to the processing position with the aid of the laser equipment, after recording the mask aperture at different positions of the beam analysis camera, the individual images are combined by software to form an image of the complete mask, and the positioning error is determined and corrected by image processing based on the error in the image of the mask in the boundary area between the individual images.

8. The method of claim 1 or 2, wherein a beam diagnostic of the laser radiation is integrated into the laser processing station, wherein the camera system for observing the workpiece is used for the beam diagnostic by means of an auxiliary substrate mounted in the processing plane that reflects or greatly scatters the laser radiation.

9. The method of claim 1 or 2, wherein the camera system is triggered by means of a trigger signal of the laser processing, and the camera system for observing the workpiece is also used for monitoring the laser processing.

10. The method of claim 1 or 2, wherein one of the procedures for rapidly performing a process in a processing zone affected by a laser beam is observed and analyzed by means of shadow analysis, wherein the execution involves trajectory tracing involving determining and analyzing the trajectory of a portion detached from the workpiece by means of a laser pulse.

11. A system for producing a micro LED display including a substrate, the substrate carrying a pixel on an electrical supply structure to form a micro light-emitting diode array, the system comprising: A control unit (190); a laser processing station (100) having a laser processing unit (110) controllable by the control unit; wherein the laser processing station is configured to perform at least one of the following operations: a laser lift-off (LLO) operation that selectively removes a material from another material; and a laser-induced forward transfer (LIFT) operation that is configured to transfer material onto the substrate by directing laser radiation onto the material with positional accuracy; The laser processing unit includes a mask having a plurality of mask openings disposed in a mask plane and configured to split a laser beam into a plurality of partial beams, the mask openings emitting laser radiation being imaged onto a processing plane of the laser processing unit, such that the laser processing unit is configured for parallel processing at a plurality of processing positions; and a workpiece movement system (200) for positioning a workpiece (150) to be processed in a processing position of the laser processing station in response to a movement signal from the control unit (190); characterized in that a camera system having a camera (340) for observing the workpiece (150), the camera system being designed to capture at least one portion of the workpiece in the object field of the camera and also to generate an image representing the portion; An evaluation unit (195) is used to evaluate an image by means of image processing for the purpose of determining positional data representing the actual position of at least one structural element of the workpiece in the object field, and is also used to compare the actual position of the structural element with a target position and to generate a correction signal depending on a deviation between the actual position and the target position. The control unit (190) is configured to control the workpiece movement system (200) to correct the processing position based on the correction signals for the purpose of matching the actual position with the target position. The laser processing unit (110) is configured to irradiate at least one laser beam (105) directed at the workpiece (150) into at least one processing position of the workpiece (150) for the purpose of local laser processing of the workpiece.

12. The system of claim 11, wherein a mask moving system carries the mask and, under the control of the control unit, allows the mask to be displaced in the mask plane and rotated about an axis perpendicular to the mask plane.

13. The system of claim 11 or 12, wherein an illumination system (310) is used to illuminate an illumination area (305) on the workpiece (150) using narrow-band illumination light and / or wherein a wavelength selective device (335) is disposed between the object plane of the camera (340) and the camera, the wavelength selective device (335) transmitting only light from a narrow wavelength band to the camera, wherein the light used for image capture has a spectral bandwidth of 10 nm or less.

14. The system of claim 11 or 12, wherein the laser processing unit includes a beam deflection device (115) having a substrate (117) and a beam deflection surface (118) thereon, the beam deflection surface (118) being obliquely oriented relative to a main axis (116) of the laser processing unit and for deflecting the laser beam in a propagation direction substantially parallel to the main axis (116).

15. The system of claim 11 or 12, wherein an observation beam path between the processing plane (122) of the laser processing unit (110) and the camera (340) is guided through the beam deflection surface (118), the beam deflection device (115) at least partially transmits illumination light, wherein the substrate (117) of the beam deflection device is coated with a dielectric coating, the dielectric coating being designed to have a reflectance of more than 99% for incoming laser light and a transmittance in the range of 20% to 70% for illumination light in the presence of an incident angle.

16. The system of claim 14, wherein an illumination transmission astigmatism compensation unit (330) is disposed in the observation beam path between the beam deflection device (315) and the camera (340), wherein the substrate (317) of the beam deflection device is embodied as an illumination transmission plane plate tilted relative to the main axis (116) about a first tilt axis oriented perpendicular to the main axis, and wherein the astigmatism compensation unit (330) includes a plane plate that is transparent to illumination light and tilted relative to the main axis about a second tilt axis oriented perpendicular to the first tilt axis.

17. The system of claim 11 or 12, wherein a camera-based beam analysis system (700) is integrated into the laser processing station for in-situ analysis of the beam parameters of the laser beam (105).

18. The system of claim 17, wherein the beam analysis system (700) includes at least one beam analysis unit (720, 740), the at least one beam analysis unit (720, 740) including a camera configuration (722, 742) having a camera with an object field that is sensitive to laser wavelength, wherein the camera configuration includes a UV camera that is sensitive to the laser wavelength, or the camera configuration includes a camera that is sensitive to visible light and a plane converter (726, 746) disposed in an object plane of the camera and configured to convert light of the laser wavelength into light from the visible spectrum.

19. The system of claim 17, wherein the beam analysis system comprises at least one of the following units: (i) a first beam analysis unit (720) having a camera configuration sensitive to the laser wavelength and including a camera (722) having an object field located in the processing plane (122) of the laser processing unit or in a plane optically conjugate to the processing plane and disposed on the opposite side of the processing plane (122) relative to the laser processing unit (610); (ii) a second beam analysis unit (740) having a camera configuration sensitive to the laser wavelength and including a camera (742) having an object field located in a plane optically conjugate to a shielding plane (108), the camera being disposed in a continuation of an incident direction of the laser beam, the incident direction being oriented perpendicular to the main axis (116) of the laser processing unit (610).

20. The system of claim 11 or 12, wherein a camera-based shadow analysis system (800) is integrated into the laser processing station (700) for in-situ observation and analysis of a rapid procedure performed in a processing zone (106) affected by laser radiation, the shadow analysis system comprising a short-pulse light source (810) for time-controlled incident of a short illumination pulse in an incident direction laterally oriented relative to the laser beam, and a camera (830) on the opposite side for capturing shadows of the processing zone and deploying an evaluation unit for evaluating camera images of the camera.

21. The system of claim 20, wherein the shadow analysis system (800, 900) includes a beam deflection system, specifically a mirror system (825), the beam deflection system, specifically the mirror system (825) having a deflection element disposed between the short-pulse light source (810, 910) and the processing zone (106) for deflecting illumination light from a direction tilted relative to the processing plane (122) to an incident direction parallel to the processing plane (122), specifically a deflection mirror (822), and / or having a deflection element disposed between the processing zone (106) and the camera (830, 930) for deflecting radiation parallel to the processing plane or passing through the processing plane at an acute angle to an incident direction of the camera tilted relative to the processing plane, specifically a deflection mirror (824, 924).

22. The system of claim 20, wherein the shadow analysis system (800) is configured to generate an image by a plurality of illumination pulses triggered in a time-shifted manner by a laser pulse from a laser radiation source, such that the portion detached from the workpiece is imaged multiple times at different times and at different locations in the image and used to evaluate the image, wherein the execution involves trajectory tracing involving determining and analyzing the trajectory of the portion detached from the workpiece by means of a laser pulse.

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