Method and system for producing microelectronic components with a layer structure

Abstract

In a method for producing microelectronic components, which have a carrier and at least one microelectronic functional layer system applied to the carrier, a functional layer system is formed on a front side of a growth substrate and a layered carrier is arranged on a side of the functional layer system opposite the growth substrate so that an arrangement is formed having the carrier, the functional layer system and the growth substrate. Laser radiation is radiated from the rear of the growth substrate through the growth substrate such that, in a boundary region between the growth substrate and the functional layer system, the laser radiation weakens or destroys a connection between the growth substrate and the functional layer system in the boundary region in locally limited regions or over a large area. The functional layer system or parts thereof are transferred to the substrate in order to form the microelectronic component. The boundary region is irradiated by means of direct laser interference patterning (DLIP), wherein a laser beam emitted from a primary laser radiation source is split into at least two partial beams and the partial beams are guided such that at least two partial beams which are coherent with one another extend through the growth substrate and a spatial intensity pattern is produced in a superimposition region of the coherent laser beams, which spatial intensity pattern has radiation microzones with constructive interference and relatively high power density of the laser radiation next to regions of destructive interference and low power density of the laser radiation in relation to the radiation microzones, wherein in the boundary region damaged microzones, which are arranged laterally spaced from one another, are produced by the laser radiation of the radiation microzones.

Description

[0001] Method and system for manufacturing microelectronic components with layered structure

[0002] FIELD OF APPLICATION AND STATE OF THE ART

[0003] The invention relates to a method for producing microelectronic components according to the preamble of claim 1 and to a system suitable for carrying out the method according to the preamble of claim 11. Furthermore, the invention relates to the use of a device for direct laser beam interference structuring for irradiating a boundary region between a growth substrate and a functional layer system in order to weaken or destroy a connection between the growth substrate and the functional layer system in a laser lift-off process or a LIFT process.

[0004] When manufacturing microelectronic components, such as optoelectronic devices, the task often arises of separating a layer stack consisting of a large number of layers between two defined layers in order to obtain two individual layer stacks. For example, light-emitting diodes (LEDs) are now often manufactured by epitaxially growing p- and n-doped semiconductor layers of gallium nitride (GaN) on a sapphire wafer serving as the growth substrate. These layers each have a thickness of a few pm; the total thickness of the various GaN layers can, for example, be less than 10 pm. Before further processing, the GaN layers can be structured, for example by laser processing, in order to produce individual components or prepare for their production.A thin, usually metallic, bonding layer is applied to the GaN layer stack, for example, by vapor deposition. This bonding layer is used to connect the growth substrate with the GaN layer stack on top to a flat, layered carrier. Later, the planar bond between the growth substrate and the GaN stack is removed. This allows the GaN stack to be transferred to the carrier. The carrier, with the GaN stack supported on it, serves as the basis for manufacturing the microelectronic component.

[0005] The separation of the functional layer stack containing the carrier and the GaN layer stack from the growth substrate is now usually performed using the so-called laser lift-off process. In this process, a buffer layer located at the interface between the growth substrate and the GaN layers is destroyed or removed by laser irradiation. The irradiation is carried out from the back of the growth substrate and through it, with the laser beam focused on the buffer layer or the interface. The growth substrate can then be separated from the other layers by applying external force.

[0006] Such a process is described, for example, in the article "Laser Lift-Off: Lower Construction Heights in Microelectronics through Substrate Transfer" by R. Delmdahl in: Photonik 2 (2013, pages 54 to 56). For fast and reliable layer separation, two excimer laser processing strategies are generally used, which differ in the geometry of the homogeneous laser field. The laser lift-off is either carried out by sweeping a line beam of suitable length as a line scan or by gradually assembling rectangular laser processing fields.

[0007] Document DE 10 2017 205 635 A1 describes further laser lift-off processes and devices. In order to irradiate relatively large cutting surfaces with a laser within a short processing time, some embodiments provide for a laser beam with a line profile to be irradiated, and a relative movement between the laser beam and the workpiece occurs transversely to the long axis of the line profile. Step-and-repeat processes are also mentioned.

[0008] US 10297503 B2 describes laser lift-off processes in which a laser beam, after passing through a beam former, passes through a diffractive optical element (DOE) or a beam splitter mask with a plurality of apertures and is thus split into a plurality of laterally offset partial beams of smaller beam cross-section, which fall onto the layer to be irradiated in a predeterminable arrangement with mutual spacing.

[0009] Also well known are the so-called LIFT processes, where the abbreviation LIFT stands for Laser-Induced Forward Transfer. At the beginning of the process, there is a defined small distance between the growth substrate with the GaN layer stack on it and the layer-like, flat carrier. Local laser irradiation then damages the connection between the growth substrate and layer stack in irradiated segments of the GaN layer stack. This splits the GaN into Ga and nitrogen, with the resulting gas pressure detaching the flat segments from the growth substrate and accelerating them towards the layer-like, flat carrier. After the processing step, the locally laser-irradiated segments are located on the layer-like, flat carrier and are no longer connected to the growth substrate.

[0010] Today, these processes are carried out using comparatively expensive UV lasers with high pulse energy and complex optics, resulting in relatively high wear on the aforementioned components. According to the inventors' observations, the consistently very high laser fluence throughout the entire processing area can also occasionally lead to damage in the GaN layer stack. This could impair the function of the microelectronic component in question and thus reduce the yield of the LLO or LI FT process accordingly.

[0011] TASK AND SOLUTION

[0012] Against this background, the invention is based on the object of designing a method and a system of the generic type in such a way that it can be implemented relatively inexpensively and in which the separation step with which the growth substrate serving as a temporary substrate is separated from the other layers can be carried out more reliably than before.

[0013] To achieve this object, the invention provides a method having the features of claim 1. Furthermore, a system having the features of claim 11 is provided. Furthermore, according to claim 14, the use of a device for direct laser beam interference structuring (DLIP) for irradiating a boundary region between a growth substrate and a functional layer system to weaken or destroy a connection between the growth substrate and the functional layer system or parts thereof in a laser lift-off process or a LIFT process is provided. Advantageous further developments are specified in the dependent claims. The wording of all claims is incorporated into the content of the description by reference.

[0014] The method is used to produce microelectronic components comprising a carrier and at least one microelectronic functional layer system applied to the carrier. In the method, a functional layer system is formed on the front side of a growth substrate. A layered carrier is then arranged on the side of the functional layer system facing away from the growth substrate. This forms an assembly comprising the carrier, the functional layer system, and the growth substrate.

[0015] The carrier can be arranged in surface contact with the functional layer system and connected to it, so that a workpiece in the form of a layer composite is formed which comprises the carrier, the functional layer system and the growth substrate in the form of a layer stack. This is the case, for example, with LLO processes. The arrangement can also be such that a small distance remains between the free surface of the functional layer system and the carrier. This is the case, for example, with LIFT processes. The workpiece (layer composite with carrier, functional layer system and growth substrate) or the arrangement (functional layer system on growth substrate and the carrier separated from it) can then be fastened to a workpiece carrier in such a way that the back of the growth substrate opposite the front side is accessible for subsequent laser processing.During laser processing, laser radiation is irradiated from the back of the growth substrate through the growth substrate in such a way that the laser radiation locally limits or weakens or destroys an initially still existing connection between the growth substrate and the functional layer system in the boundary area or over a large area.

[0016] This enables the transfer of the functional layer system or parts thereof to the carrier to form the microelectronic component. In the LLO process, a functional layer stack comprising the carrier and the functional layer system applied thereto is separated from the growth substrate. Thus, a substrate transfer of the entire functional layer system takes place from the growth substrate to the carrier. In the LIFT process, the transfer can be performed selectively, so that only selected parts or segments of the functional layer system are transferred to the carrier over a short flight path.

[0017] These processes enable economical production, especially of semiconductor structures, on increasingly larger and more sensitive substrates.

[0018] According to one formulation of the invention, the boundary region is irradiated by means of direct laser beam interference structuring (DLIP). A laser beam emitted by a primary laser radiation source is split into at least two partial beams, and the partial beams are guided such that at least two coherent partial beams pass through the growth substrate. A spatial intensity pattern is created in an overlap region of the coherent laser beams. This spatial intensity pattern comprises radiation microzones with constructive interference and a relatively high laser radiation power density, alongside regions of destructive interference and a low laser radiation power density relative to the radiation microzones. This creates microzones damaged by the laser radiation of the radiation microzones in the boundary region, arranged in a manner spaced laterally apart from one another.

[0019] The boundary area is irradiated using a process variant of direct laser beam interference patterning (DLIP). Direct laser interference patterning (DLIP) is a laser-based technology that uses the physical principle of interference between high-intensity, coherent laser beams to create functional periodic microstructures. A corresponding laser processing system has a laser-optical arrangement for laser structuring, in which a laser beam emitted by a primary laser radiation source is split into at least two partial beams, which are guided in such a way that at least two interfering partial beams impinge on an area to be processed. A spatial intensity pattern is generated in the area of ​​the overlapping, coherent laser beams.The areas of constructive interference form the radiation microzones, which cause the formation of microzones in the boundary material, while the areas of destructive interference (or extinction) lead to the unirradiated or only weakly irradiated intermediate regions between neighboring microzones. Unlike other processing methods, such as laser writing, the beam diameter of the partial beams does not need to be focused, or at least not to a minimum beam diameter. This allows a significantly larger area to be processed per laser pulse.

[0020] When two coherent laser beams are superimposed, a line pattern is created. Preferably, three or four laser beams are caused to interfere, creating essentially point-like microzones in the irradiated area. The microzones are then spaced apart in three or more different lateral directions.

[0021] According to the inventors' experience, commercially available laser processing systems for direct laser beam interference structuring can be used in the inventive method. For example, a laser-optical arrangement according to EP 3466 598 A1 can be used. The disclosure of this document is incorporated by reference into the present description.

[0022] A solution to the problem formulated in the task can also be described as follows: the laser radiation from a primary laser radiation source is processed or irradiated without the use of a beam splitter mask in such a way that radiation microzones with a high power density of the laser radiation are generated in the boundary region. In the boundary region, damaged microzones are generated by the laser radiation of the radiation microzones, which are arranged with relatively small average lateral distances from one another. These distances can be in the single-digit or low double-digit micrometer range. In the material of the boundary region, a fine pattern of relatively small, locally limited zones is generated in which the power density of the laser radiation is sufficient to damage or weaken the boundary region or the material in the boundary region to such an extent that a separation along the boundary region ordetachment from the growth substrate becomes possible. The term "microzone" expresses that the lateral dimensions of the zones of the boundary area, which were damaged and / or destroyed due to the locally increased power density, are in the single-digit micrometer range or smaller in at least one lateral direction. The average lateral distances between immediately adjacent microzones are also very small, lying in the single-digit or low double-digit micrometer range. The term "distance" refers to the minimum center-to-center distance between immediately adjacent microzones, i.e., the center-to-center distance in the direction in which the center-to-center distance assumes its smallest value.

[0023] In a radiation microzone, the intensity or power density of the laser radiation is increased by beam conditioning compared to the area surrounding the radiation microzone to such an extent that the power density is sufficient to initiate the processes required to weaken the material in the boundary region and to create the weakened microzones there. Compared to the radiation microzones, the power density in the areas between immediately adjacent radiation microzones is orders of magnitude lower, so that the laser radiation does not directly lead to weakening or destruction within the boundary region. However, neighboring microzones are located so closely together that, starting from the areas of the microzones directly damaged by laser radiation, attenuation is generated throughout the entire part of the boundary region covered by microzones, and the components to be separated can be reliably separated.

[0024] When the functional layer system or parts thereof are transferred to the carrier to form the microelectronic component, a separation of the components to be separated from one another takes place along the boundary area that is locally weakened or destroyed in the area of ​​the microzones, whereby the separation, starting from the microzones, also runs through the intermediate areas adjacent to the microzones that are not directly weakened.

[0025] It has been shown that with such a fine distribution of very small microzones, sufficient weakening of the functional layer system in the boundary region can be achieved without affecting the adjacent layer materials to the extent that is sometimes the case with significantly larger weakened zones. This type of laser processing is therefore particularly gentle on the areas adjacent to the boundary region. Preferably, many microzones, e.g. more than 100 or more than 500 or more than 1000 or more than 2000, are created simultaneously in one processing step. This means that despite the small dimensions of the microzones and the distances between them, even larger areas of the boundary region can be weakened in a relatively short time and thus prepared for separation.

[0026] Using DLIP technology, it is possible to process the laser radiation provided by the primary laser radiation source without the use of a beam splitter mask with multiple apertures, creating a fine distribution of microzones. This contributes to the power provided by the primary laser radiation source being used with particularly high efficiency for attenuation in the boundary region. By omitting the use of a beam splitter mask, losses that occur in conventional systems with beam splitter masks due to this type of geometric beam splitting can be avoided. In other words, practically no laser power is wasted; instead, a high proportion of the laser energy provided by the primary laser radiation source can be used to attenuate the layer system in the boundary region.The energy of the laser radiation is largely retained; it is only locally redistributed. Thus, there is no process-related additional attenuation of the laser radiation beyond losses of real components, such as reflection or scattering at interfaces.

[0027] Due to the high efficiency in utilizing the laser power provided by the primary laser radiation source, the method does not require the use of high-pulse lasers as the primary laser radiation source. In preferred embodiments, a suitable solid-state laser is used as the primary laser radiation source, which generates laser radiation from the ultraviolet region of the electromagnetic spectrum (UV solid-state laser), particularly at wavelengths below 400 nm. Particularly useful is the wavelength range in which sapphire (as a typical material for the growth substrate) is largely transparent and the GaN layer material sufficiently absorbs the radiation, for example, in the range between 160 nm and 400 nm.

[0028] Commercially available short or ultrashort pulse lasers can be used, e.g. with pulse durations in the range of a few 10 fs to a few 100 ns. Diode-pumped IR lasers with Nd:YAG, Yb:YAG, Nd:YVO4 or Nd:YLF as the laser medium can be used as the primary laser radiation source. Their radiation is converted to wavelengths in the UV range using frequency conversion, e.g. frequency tripling, so that wavelengths in the range around 350 nm are available. Laser wavelengths in the deeper UV wavelength range around 266 nm can be generated using frequency quadrupling. These are also suitable for the process but are not preferred due to the comparatively shorter lifetime of the crystals used for frequency quadrupling and due to the higher wear. Wavelengths around 350 nm are therefore currently preferred, among other reasons because the photon energy is large enough for the LLO and LIFT applications considered here.

[0029] The optimal dimensions of the microzones and the spacing can vary from application to application. Based on the inventors' experience, very good results can be achieved in most cases by sizing the microzones in at least one lateral direction in the range of approximately 0.5 pm to 3 pm. Alternatively or additionally, the average lateral spacing between immediately adjacent microzones can be in the range of approximately 1 pm to approximately 15 pm.

[0030] As a rule, it is advantageous to create point-shaped microzones. The term "point-shaped" here means that the individual microzones are essentially round. This means, in particular, that diameter variations in different diametrical directions are limited to a maximum of 20%, and especially to a maximum of 10%, of the largest diameter.

[0031] Alternatively, the microzones can also have other shapes, such as oval, approximately square, approximately rectangular, or linear. This makes it possible to better adapt the shape of the microzones to the application, for example, by using a microzone shape (and size) that matches the shape (and size) of the micro-LEDs to be transferred.

[0032] Occasionally, only two superimposed partial beams are used, resulting in an interference pattern with linear radiation microzones through two-beam interference. The use of linear microzones allows for largely uniform irradiation of the entire wafer if a suitable pulse spacing is set. The lateral width can be in the above-mentioned range (approximately 0.5 pm to approximately 3 pm), while the length can be significantly larger, e.g., several hundred pm or approximately 1 mm or more.

[0033] In the DLIP process, under certain boundary conditions (e.g., low-interference coupling into the growth substrate), the microzones can, due to the system's inherent nature, exhibit a periodic micro-grid arrangement, which is beneficial for creating conditions that are as uniformly distributed as possible across the entire irradiated boundary region. With regard to the spatial distribution of the microzones in the boundary region, the process offers numerous possibilities. It may be sufficient to create all microzones in an irradiated area essentially according to a uniform grid. If necessary, combinations of two or more different grid arrangements can also be created sequentially.In one embodiment, microzones are generated in a surface region of the boundary layer in at least two processing steps carried out one after the other, wherein in a first processing step a first micro-grid arrangement of first microzones is generated and in a subsequent second processing step second microzones are generated in intermediate regions between the first microzones, which second microzones are distributed according to a second micro-grid arrangement.

[0034] In some cases, it is also possible that a more or less statistical distribution of microzones is generated in the boundary area, whose lateral distances and lateral sizes vary statistically within certain size ranges, in particular within the size ranges already mentioned here.

[0035] The present application also relates to the use of a system for direct laser beam interference structuring (DLIP) for irradiating a boundary region between a growth substrate and a functional layer system to weaken or destroy a connection between the growth substrate and the functional layer system in a laser lift-off process or a LIFT process.

[0036] According to the inventors' findings, the use of suitable variants of direct laser beam interference structuring (DLIP) in the context of laser lift-off processes or LIFT processes offers advantages not only with regard to targeted attenuation in the boundary region, but can also contribute elsewhere to reducing the overall costs of manufacturing processes that work with laser lift-off operations and / or LIFT operations.

[0037] Many process variants possible within the scope of the invention can use growth substrates that are separated from a larger block of substrate material by a mechanical separation process. For example, sapphire wafers that can be used as growth substrates can nowadays usually be sawed from a larger block of sapphire. The surfaces obtained in this way can be relatively rough. This, in turn, can lead to problems when coupling the laser radiation into the growth substrate in conventional laser processing methods. To avoid such problems, it was proposed, for example, in DE 102017205635 A1 to bring a liquid layer made of a liquid transparent to the laser radiation into contact with the (rough) back of the growth substrate before irradiating the laser beam and to irradiate the laser beam through the liquid layer.This significantly improved the efficiency of laser beam coupling, even on rough back surfaces. Alternatively, the back surface can be prepared for laser processing by lapping and / or polishing to create a sufficiently smooth coupling surface.

[0038] Investigations by the inventors have now shown that such complex and costly additional measures in preparation for laser processing can be dispensed with if suitable variants of direct laser beam interference structuring are used to irradiate the boundary region. If the roughness of the coupling surface is not too great, essentially only the character of the distribution of the microzones changes. If the back of the growth substrate used as the coupling surface is polished or smoothed in some other way (e.g., lapping and polishing) or provided with an immersion layer, regular lateral distributions of microzones with well-defined sizes can be created. If, on the other hand, coupling is carried out via an unpolished coupling surface, more statistically distributed microzones with a broader size and spacing distribution are created.

[0039] In this respect, this process variant for generating microzones appears to be relatively insensitive to problems induced by surface roughness. According to a further development, a growth substrate can be used which has a surface roughness on the back with a mean roughness Ra of more than 0.1 pm, with the mean roughness preferably being in the range of 0.5 pm to 1 pm. This allows a wafer separated from a block of material by sawing to be used as the growth substrate, and the laser radiation can be irradiated onto the back side created by sawing without an intermediate polishing step and, in some applications, even without the otherwise usual lapping process. This eliminates a costly polishing step, making the manufacturing process significantly more cost-effective.

[0040] The invention also relates to a system for producing microelectronic components comprising a carrier and at least one microelectronic functional layer system applied to the carrier. The system can be used, among other things, to perform LLO processes and LIFT processes. A direct laser beam interference structuring (DLIP) device is used to irradiate a boundary region between a growth substrate and a functional layer system in order to weaken or destroy a bond between the growth substrate and the functional layer system during a laser lift-off process or a LIFT process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Further advantages and aspects of the invention emerge from the claims and from the description of embodiments of the invention, which are explained below with reference to the figures.

[0042] Fig. 1 shows a schematic section through a workpiece in the form of a layered composite with an exemplary layer structure during laser processing by means of direct laser beam interference structuring;

[0043] Fig. 2 shows an example of a laser processing station configured to use direct laser beam interference structuring to weaken a layer within a layer structure and prepare it for separation as part of a laser lift-off process;

[0044] Fig. 3A, 3B show micrographs of an overview (3A) and a detail (3B) of a regular pattern of microzones in the boundary area of ​​an irradiated workpiece produced by the use of DLIP when irradiated through a polished backside of a growth substrate;

[0045] Fig. 4 shows an example of a regular micro-grid arrangement of microzones produced in two consecutive processing steps with different settings of a DLIP device;

[0046] Fig. 5 shows an example of the distribution of microzones after DLIP structuring through an unpolished backside of a growth substrate.

[0047] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] Various aspects of inventive methods and systems for producing microelectronic components using a laser lift-off method and / or a LIFT method are described below using exemplary embodiments. The microelectronic components resulting from the method comprise a generally relatively thin, flat carrier and at least one microelectronic functional layer system applied to the carrier. Fig. 1 shows a schematic section through a workpiece 100 in the form of a layered composite with an exemplary layer structure. The workpiece 100 is an intermediate product produced during the method, which is subjected, among other things, to laser beam processing. Fig. 2 shows an example of a laser processing station 200 provided for this purpose.

[0049] The workpiece 100 here is a wafer composite for the production of LEDs, but other layer materials and sequences, as well as wafer materials, are also conceivable. The process is illustrated below using the production of power LEDs for the automotive sector; however, the applicability of the invention is not limited to this embodiment.

[0050] The workpiece 100 shown in Fig. 1 and Fig. 2 has a growth substrate 110 in the form of a flat sapphire wafer. P-doped and n-doped semiconductor layers 132, 134 made of gallium nitride (GaN) are formed by epitaxial growth on the front side 112 of the growth substrate, which has been machined flat with high precision. A thin buffer layer 120 is formed in the boundary region to the growth substrate. The buffer layer can be a separate layer, e.g., made of undoped GaN, or a thin sublayer of the first GaN layer. The GaN layers are generally each a few pm thick; the total thickness of the layer system with the various GaN layers can, for example, be less than 10 pm.

[0051] Before further processing, the GaN layers can be structured, for example by laser processing, to produce individual components or prepare for their production. These components are formed from parts or segments of the initially large-area grown layer system and, in turn, represent layer systems with the same layer structure but with smaller lateral dimensions.

[0052] A connecting layer 136, usually a few micrometers thick, is applied to the GaN layer stack, for example by vapor deposition. This connecting layer can consist of gold, platinum, chromium, or other metals, for example. With the help of this connecting layer, the growth substrate with the GaN layer stack located thereon is connected to a layer-like, flat carrier 140. In the example case, the carrier is formed by a thin pane of glass, but can also consist of another material, e.g., a semiconductor material such as silicon. The connecting layer 136 and the adjacent GaN layers, optionally with further layers, form a functional layer system 130, which is essentially responsible for the functionality of the component to be manufactured and, in the finished component, is carried by the carrier or an associated section of the carrier 140.The layer composite with the carrier 140 and the functional layer system 130 is referred to here as functional layer stack 150.

[0053] The sapphire wafers used as growth substrates are usually cut from a larger sapphire block (sapphire ingot) with a saw. Sawing produces surfaces with high roughness. The back side 114 of a sapphire growth substrate, for example, can have a medium surface roughness (R a ) in the range of 1 pm or slightly below.

[0054] In the example case, the back is polished to R a approx. 0.3 nm smoothed to avoid greater scattering losses when coupling the laser radiation.

[0055] Fig. 2 schematically shows a laser processing station 200 configured for laser lift-off (LLO) as part of a system for manufacturing microelectronic components. The system includes a workpiece carrier 210 for holding the workpiece 100. The workpiece is mounted on the workpiece carrier with the back side 114 of the growth substrate 110 facing upwards.

[0056] The laser processing station 200 comprises a workpiece movement system 280, which is configured to position a workpiece to be processed in a desired processing position of the laser processing station in response to movement signals from the control unit 290. In the configuration of Fig. 2, the workpiece movement system 280 comprises the workpiece carrier 210, which can be moved very precisely to a desired position parallel to the (horizontal) xy plane of the system coordinate system and in the vertical direction (parallel to the z direction), as well as rotated about a vertical rotation axis (PHI axis). In the example, precisely controllable electric direct drives are provided for this purpose.

[0057] Furthermore, the movement system 280 includes a second workpiece carrier 220 above the first workpiece carrier 210, which can also be moved in any direction horizontally (parallel to the xy plane) and vertically (parallel to the z direction) and rotated about a vertical axis. The two workpiece carriers can be positioned independently of each other. In LLO processes, the upper second workpiece carrier is not used. It is used in LIFT processes to hold the growth substrate at a distance above the lower workpiece carrier.

[0058] The laser processing station is used to irradiate laser radiation from the rear side 114 of the growth substrate 110 through the growth substrate in such a way that the laser radiation is directed into a flat boundary region between the growth substrate 110 and the functional layer system 130 (see Fig. 1), and a connection between the growth substrate 110 and the functional layer system 130 is weakened or destroyed in the boundary region. The boundary region can, for example, be located in the buffer layer 120 or contain it.

[0059] A special feature is that the boundary region is irradiated using a process variant of direct laser interference patterning (DLIP). Direct laser interference patterning (DLIP) is a laser-based technology that utilizes the physical principle of interference between high-intensity, coherent laser beams to create functional periodic microstructures on surfaces. In contrast to conventional applications, DLIP is used here to weaken a thin layer (boundary region) located inside the workpiece at a distance from its free surfaces.

[0060] The laser processing station has a laser-optical arrangement 300 for laser structuring. A raw laser beam LSR emitted by a primary laser radiation source 310 is split into three coherent partial beams TS1, TS2, and TS3 by means of three physical beam splitters 312-1, 312-2, and 312-3. The primary laser radiation source 310 is an ultrashort pulse laser with a solid-state laser medium, which emits in the ultraviolet range at a wavelength of approximately 355 nm.

[0061] The three partial beams are guided via a 45° deflection mirror 314 and focusing optics 315 such that they interfere with each other in a three-dimensionally extended overlap region (interference volume IVOL, see Fig. 1). The focusing optics 315 can be formed by a single lens or a lens system with multiple lenses. The three partial beams are arranged at the vertices of an equilateral triangle symmetrically to the center of the focusing optics or its optical axis 314.

[0062] Fig. 1 schematically illustrates the situation with two coherent partial beams TS1, TS2. The partial beams each propagate in directions of propagation aligned at an acute angle W to the optical axis AX of the focusing optics 315. They are offset azimuthally by 120° from each other. The angle W is continuously adjustable.

[0063] The structure of the laser-optical arrangement 300 is intended only as an example. Commercially available DLIP systems exist that can be used for the purpose discussed here. Documents EP 3 466 598 B1 and EP 3 735 332 B1 show some examples of systems that could be used in principle.

[0064] The interfering partial beams penetrate the transparent growth substrate 110 largely without absorption; the laser radiation is only strongly absorbed upon impact with the buffer layer 120, where it changes the material. A spatial intensity pattern is generated in an overlap region of the coherent laser beams (partial beams TS1, TS2, TS3). Relatively high laser power densities are generated locally in the regions of constructive interference. The small volume regions where the laser power density is sufficient to weaken the material of the boundary region are referred to herein as radiation microzones. Where these extend into the boundary region material, microzones MZ are formed in the boundary region material, in which the boundary region material is evaporated and / or otherwise destroyed or weakened. The microscopically small microzones MZ are spaced apart from one another in a regular micro-grid arrangement.In areas of destructive interference, intermediate areas remain which are not irradiated or only weakly irradiated, e.g. between neighboring microzones.

[0065] Although the power density only has a direct weakening effect on the boundary material (here GaN) in the area of ​​the radiation microzones and causes the microzones there, a surface weakening is nevertheless achieved, because the material in the intermediate areas ZB between the processing points (microzones) is also removed by the nitrogen pressure as a result of the decomposition of the nitride.

[0066] To illustrate the changes in the irradiated boundary region, Figs. 3A and 3B show microscopic images of the structures in the boundary region of an irradiated workpiece during a series of tests. Fig. 3A essentially shows the entire, approximately circular area (enclosed by the dashed line LP) that was irradiated by a single laser pulse, i.e., essentially the interface between the areal boundary region and the interference volume. A transition region to a neighboring pulse can be seen at the right edge. Fig. 3B shows an enlarged section of the central region of the circular processing area irradiated by a pulse.

[0067] It is clearly visible that a regular structure of more or less circular microzones (MZ) was created in the interference volume according to a rectangular grid. A single pulse simultaneously generated several hundred microzones (MZ) evenly distributed across the area in the approximately circularly irradiated region. According to the intensity distribution within the interfering partial beams, the microzones (MZ) are more pronounced in the central region than at the radial edge of the illuminated region (LP). The mean diameter (DMZ) of the individual circular microzones was approximately 1.9 pm, corresponding to a microzone area of ​​approximately 2.8 to 2.9 pm. 2The smallest distance AB of a microzone to an immediately adjacent microzone, measured between the centers of the respective microzones, was approximately 5.1 pm. The microzones are evenly distributed within a region irradiated by a pulse; in the overlapping regions with the neighboring pulse, overlaps of offset grid arrangements can occur.

[0068] The distance AB of the microzones (i.e. the interference period) can be adjusted in the selected arrangement by varying the angle of incidence W between the interfering partial beams and the optical axis in the processing zone, e.g. in the range between approx. 1 pm and approx. 15 pm.

[0069] The overall pulse size, i.e., the size of the area LP that can be irradiated with a single pulse, can also be adjusted by varying the size of the interfering partial beams in the processing zone. This can be achieved, for example, by adjusting the raw beam diameter or varying the focus or image scale of the optics used. This variation of the overall pulse size also causes a change in the intensity within the areas of constructive interference, i.e., the individual spot energy, which can also be adjusted by selecting the laser pulse energy.

[0070] The size of the individual microzones (MZ), also referred to as single-spot size, is continuously adjustable in the selected arrangement within a range of approximately 0.5 pm to approximately 3 pm. The diameter / size of the individual spots varies depending on the laser energy used and the angle of incidence W between the interfering partial beams and the optical axis in the processing zone.

[0071] If the edge drop in laser intensity towards the edge of a partial beam is perceived as disturbing due to a Gaussian-like profile, edge regions with lower intensity can be masked out by a suitable mask in some embodiments.

[0072] As a rule, it is advantageous to avoid multiple irradiations during the transition to the next pulse to prevent an uneven distribution of attenuation at the boundary area, which is difficult to control. However, the lateral offset from pulse to pulse can also be adjusted with a defined overlap so that individual points are hit multiple times (by multiple pulses), thus continuing the interference processing pattern over large areas. This overlap allows the positions at the edge of the processing zone that were initially treated with insufficient fluence to be treated with sufficient fluence overall.

[0073] In the example, a raw LSR laser beam was used. If necessary, homogenization of the primary laser beam can be provided.

[0074] The process allows for the creation of different surface patterns of microzones. For example, individual pulses can be generated at a distance without overlap, and then other grids with different laser power and / or spot sizes and / or spot spacing can be generated in the interstices, for example, to avoid excessive energy input in the transition area between adjacent irradiation zones.

[0075] It is also possible to change the structure during processing, for example, spiraling it from the outside to the inside. For example, a tighter grid can be created in the outer region than in the inner region. Dot grids with different single-spot dimensions and spacings are also possible, or grids with alternating large and small effects. Fig. 4 shows an example in which microzones were created in a surface area of ​​the boundary layer in at least two sequential processing steps. In a first processing step, a first micro-grid arrangement of first microzones MZ1 with first diameters D1 and first spacings AB1 was created. Then, in a subsequent second processing step, with a changed average laser power, second microzones MZ2 of smaller diameter D2 were created in intermediate regions between the first microzones MZ1, distributed according to a second micro-grid arrangement with second spacings AB2.

[0076] Another embodiment was designed to realize a gentle successive processing, but at the same time to implement a complete processing of the entire surface.

[0077] The DLIP process is designed as a two-beam interference method to generate microzones in the form of lines, for example with a line spacing of 5 pm and a line width of 1 pm. The optics were aligned so that the lines run parallel to the Y direction. The size of the irradiated area was limited by a mask for each of the two partial beams so that, after imaging these masks onto the interface, the size was 200 pm x 200 pm. This allowed edge regions of the partial beams with low fluence to be masked out and prevented from reaching the interface. The image was deflected line by line in the X direction using a polygon scanner at a speed of 200 m / s. An ultrashort pulse laser with a laser pulse repetition frequency of 1 MHz was used for processing. This resulted in a pulse spacing of 200 pm, and the area was completely processed by merging the 200 pm images.In the Y-direction, the sample was moved so uniformly by means of a positioning axis that the offset at the moment of line change was 200 pm, so that here too, neighboring processing zones directly abut one another.

[0078] The use of a method or device for direct laser beam interference structuring (DLIP) to irradiate a boundary area between a growth substrate and a functional layer system for the purpose of weakening or destroying a bond between a growth substrate and a functional layer system in a laser lift-off process, or LIFT process, offers, in addition to the aforementioned advantages, further benefits with regard to the quality of the finished product and the associated costs. These advantages also demonstrate the suitability of this process for structuring flat areas inside a workpiece, i.e., areas that are not located on the free surfaces of the workpiece.

[0079] The advantages arise, among other things, from the fact that the quality of coupling the laser radiation into the workpiece material is not as demanding as with conventional laser processing. As mentioned in the introduction, in some conventional processes, the back of the wax substrate, which serves as the entrance surface for the laser radiation, must be polished before laser processing to prevent disruptive scattering. Alternatively, the coupling surface can be smoothed using an immersion technique.

[0080] In contrast, when applying the DLIP approach, sapphire wafers can be used as growth substrates immediately after sawing from a sapphire block, without prior polishing of the coupling surface. This will be demonstrated below using experimental data.

[0081] When using DLIP, there is an additional advantage in terms of a large tolerance for the permissible deviation of the Z position during processing: the three or four individual beams are focused by the focusing optics and superimposed in a larger area above the focal plane. In this area (also known as the interference volume), in which the beams overlap, the interference pattern is created that does not change in the Z direction, i.e. the XY position of the individual interference points is independent of Z. The processing position is above the focus position and, in the example shown, has a diameter of approximately 250 pm. The tolerance of the Z position is around a factor of 4 of this diameter. In this example, a possible wafer bow (i.e. a possible deformation of the wafer) of up to approximately 1 mm can be tolerated without Z tracking. The intensity of the laser radiation changes only comparatively little in this area.The high depth of field of the DLIP process can thus be used to implement the process more cost-effectively without compromising the quality of the final product.

[0082] In conventional laser lift-off processes, care had to be taken to ensure that the coupling of the laser radiation into the growth substrate was not severely impaired by scattering effects, which is why the coupling surface was smoothed by polishing or the use of an immersion layer. Laser lift-off using direct laser beam interference structuring (DLIP), on the other hand, is significantly less sensitive to scattering effects due to the roughness of the coupling surface. This will be explained using Fig. 5. Fig. 5 shows a microscopic image of DLIP structuring through an unpolished backside of a growth substrate with an average surface roughness of approximately R a=1 pm. In this case, the processing zone in the boundary area no longer has the defined, uniform pattern as when coupling through a polished back, but essentially shows a stochastic structuring in which the microzones MZ, which have arisen in the area with particularly high radiation intensity, have a certain size distribution within the single-digit micrometer range and below, and the lateral distances to immediately adjacent microzones are no longer uniform, but vary statistically over a certain distance range. This stochastic structuring is attributed to the formation of speckles due to scattering of the radiation at the rough coupling surface and a largely stochastic superposition in the processing plane. Here, too, there is a weakening of the boundary layer orof the boundary area in such a way that the components can subsequently be separated from each other along the boundary area. This variant is particularly suitable when a large-area laser lift-off is required, for example, to detach an entire layer system from a wafer.

[0083] The process and device can be used for a variety of applications. In some applications, such as the production of high-performance LEDs, such as light-emitting diodes for car or truck headlights, the layer system is typically removed from the sapphire substrate in one continuous layer and then separated into individual LEDs. Unpolished growth substrates are particularly suitable in such cases.

[0084] There are also applications in which the individual functional components are already present in individual layers on the growth substrate and must be removed individually. One such application is the laser lift-off of micro-LEDs for display applications. Here, the LEDs are already individualized and must be removed individually. This has traditionally been achieved using laser processing systems that operate with excimer laser sources and use mask projection techniques. These techniques can be replaced by suitably designed DLIP techniques and devices. This allows very small LEDs with, for example, square or rectangular shapes and edge lengths in the range of 3 pm to 10 pm to be removed individually by removing the LED regions using one or a few of the DLIP micro-zones. The micro-zones should then be arranged as uniformly as possible in the center of each of the micro-LEDs.This can be achieved by appropriately adjusting the spot sizes and distances between the spots of the micro-grid arrangement.

[0085] For technical implementation, the following options are available, either as an alternative or in addition to those described above. The combination and superposition of the partial beams can be achieved using a focusing element, e.g., a lens, an objective, a focusing mirror, or an axicon. Other options for generating the interference pattern can also be used, for example, using a grating, such as a reflection grating. Lasers with pulse durations in the ps or ns range can be used, for example.

[0086] The use of DLIP devices and processes in laser lift-off (LLO) or LIFT offers several advantages. Among other things, the alternating processing in this process at the microscale requires less laser power per irradiated area than with homogeneous irradiation. Therefore, cost-effective solid-state lasers with comparatively low pulse energy but high pulse repetition frequencies in the MHz range can be used. High laser pulse repetition frequencies enable high throughput when applying this process. Furthermore, the alternating processing in this process places less mechanical stress on parts of the layer system adjacent to the boundary area, thus increasing production yield.

[0087] A further advantage of the process is that the generated pattern of microzones is stored as an interference pattern across the entire laser beam diameter, allowing hundreds to thousands of microzones (weakening zones in micro- or nano-dimensions) to be created in the boundary region with just a single laser pulse within a few nanoseconds to femtoseconds. The beam diameter does not need to be focused; rather, depending on the required pulse energy, it can even be widened to create microscopically small structures while covering a significantly larger processing area per laser pulse. The focusing optics do not serve to individually focus the individual partial beams in the boundary region, but rather to redirect the partial beams entering parallel to one another toward the targeted processing area.

[0088] Compared to laser marking, a very high depth of field can be achieved because DLIP does not rely on precise focusing of the laser beam. Instead, it creates a spatial "interference volume" with three-dimensionally extended radiation microzones, within which the boundary area is uniformly structured with the corresponding interference pattern. This makes the process less sensitive to variations in the workpiece's position in the z-direction, allowing for more cost-effective systems to be used for z-direction positioning.

Claims

Patent claims 1. A method for producing microelectronic components comprising a carrier and at least one microelectronic functional layer system applied to the carrier, comprising the following steps: Forming a functional layer system on a front side of a growth substrate; Arranging a layered carrier on a side of the functional layer system opposite the growth substrate to form an arrangement comprising the carrier, the functional layer system and the growth substrate; Irradiating laser radiation from the back of the growth substrate through the growth substrate in such a way that the laser radiation weakens or destroys a connection between the growth substrate and the functional layer system in the boundary region in locally limited areas or over a large area; Transferring the functional layer system or parts thereof to the carrier to form the microelectronic component, characterized in that the boundary region is irradiated by means of direct laser beam interference structuring (DLIP), wherein a laser beam emitted by a primary laser radiation source is split into at least two partial beams and the partial beams are guided such that at least two coherent partial beams pass through the growth substrate and a spatial intensity pattern is created in an overlap region of the coherent laser beams, which has radiation microzones with constructive interference and a relatively high power density of the laser radiation next to regions of destructive interference and low power density of the laser radiation relative to the radiation microzones, wherein microzones damaged by the laser radiation of the radiation microzones are created in the boundary region,which are arranged in an arrangement with lateral distances from each other., 2. Method according to claim 1, characterized in that a lateral extent of the microzones in at least one lateral direction is in the range from 0.5 pm to 3 pm and / or that average lateral distances of the microzones are in the range from 1 pm to 15 pm and / or that more than 100, in particular more than 1000 microzones are produced simultaneously in one processing step.

3. Method according to claim 1 or 2, characterized in that the laser beam emitted by the primary laser radiation source is divided into three or four partial beams.

4. Method according to one of the preceding claims, characterized in that essentially point-shaped or oval or approximately square or approximately rectangular microzones are produced or that line-shaped microzones are produced.

5. Method according to one of the preceding claims, characterized in that the microzones in the boundary region form a periodic micro-grid arrangement or are distributed according to a stochastic distribution of sizes of the microzones and the lateral distances.

6. Method according to one of the preceding claims, characterized in that microzones are produced in a surface region of the boundary layer in at least two processing steps carried out one after the other, wherein in a first processing step a first grid of first microzones is produced and in a subsequent second processing step second microzones are produced in intermediate regions between first microzones.

7. Method according to one of the preceding claims, characterized in that a wax substrate is used which has a surface roughness on the back with a mean roughness value R aof more than 0.1 pm, wherein the mean roughness value is preferably in the range from 0.5 pm to 1 pm.

8. Method according to one of the preceding claims, characterized in that a wafer separated from a block of material by sawing is used as the growth substrate and that the laser radiation is irradiated onto the back side of the growth substrate produced by sawing without an intermediate lapping step and / or polishing step.

9. Method according to one of the preceding claims, characterized in that pulsed laser radiation from a UV solid-state laser is used to irradiate the boundary region.

10. Method according to the preamble of claim 1, in particular according to one of the preceding claims, characterized in that the laser radiation is irradiated without the use of a beam splitter mask in such a way that radiation microzones of high power density of the laser radiation are generated in the boundary region in such a way that microzones damaged by the laser radiation of the radiation microzones are generated in the boundary region, which microzones are arranged with average lateral distances in the micrometer range from one another.

11. A system for producing microelectronic components comprising a carrier (140) and at least one microelectronic functional layer system (130) applied to the carrier, comprising: a workpiece carrier (210) for receiving an arrangement comprising a growth substrate (110), a functional layer system formed on a front side of the growth substrate, and a carrier arranged on a side of the functional layer system opposite the growth substrate; a laser processing station (200) for irradiating laser radiation from a rear side (114) of the growth substrate (110) through the growth substrate such that the laser radiation is guided into a boundary region between the growth substrate and the functional layer system, and a connection between the growth substrate (110) and the functional layer system (130) is weakened or destroyed in the boundary region, characterized in thatthat the laser processing station (200) has a laser-optical arrangement for laser structuring, in which a laser beam (LSR) emitted by a primary laser radiation source (210) can be divided into at least two partial beams (TS1, TS2), and the partial beams can be guided such that at least two coherent partial beams (TS1, TS2) pass through the growth substrate (110), and in an overlap region of the coherent partial beams, a spatial intensity pattern is generated, which has radiation microzones with constructive interference and a relatively high power density of the laser radiation next to regions of destructive interference and a low power density of the laser radiation relative to the radiation microzones, wherein in the boundary region, microzones damaged by the laser radiation of the radiation microzones can be generated, which microzones are arranged at lateral distances (AB) from one another.

12. System according to claim 11, characterized in that the laser processing station (200) is configured to radiate the laser radiation without the use of a beam splitter mask in such a way that radiation microzones of high power density of the laser radiation are created in the boundary region in such a way that microzones (MZ) damaged by the laser radiation of the radiation microzones can be created in the boundary region, which microzones are arranged with average lateral distances (AB) in the micrometer range from one another.

13. System according to claim 11 or 12, characterized in that the laser processing station (200) has a workpiece movement system (280) which is designed to move a workpiece to be processed in a desired processing position of the laser processing station in response to movement signals from the control unit (290). position, wherein the workpiece movement system (280) has a first workpiece carrier (210) which can be moved parallel to a horizontal plane of a system coordinate system and in the vertical direction to a desired position and can be rotated about a vertical axis of rotation, wherein preferably the movement system (280) additionally has a second workpiece carrier (220) above the first workpiece carrier (210) which can be moved horizontally and vertically in any desired direction in a controlled manner independently of the first workpiece carrier (210) and can be rotated about a vertical axis.

14. System according to one of claims 11 to 13, characterized in that the system is configured to carry out the method according to one of claims 1 to 10.

15. Use of a device for direct laser beam interference structuring (DLIP) for irradiating a boundary region between a growth substrate and a functional layer system to weaken or destroy a connection between the growth substrate and the functional layer system in a laser lift-off process or a LIFT process.

16. Use according to claim 15, characterized in that a laser beam emitted by a primary laser radiation source is split into at least two partial beams, preferably into three or four partial beams, and the partial beams are guided in such a way that at least two partial beams which are coherent with one another pass through the growth substrate and in an overlap region of the coherent laser beams a spatial intensity pattern is created which has radiation microzones with constructive interference and a relatively high power density of the laser radiation next to regions of destructive interference and a low power density of the laser radiation relative to the radiation microzones, wherein in the boundary region microzones damaged by the laser radiation of the radiation microzones are produced which lie in an arrangement with lateral distances from one another.

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