Method and system for stripping a semiconductor layer and workpiece - Patent Application 20070122997

Abstract

The present invention relates to a method for delaminating a semiconductor layer (4) from a layer stack (1), comprising the method steps of: A) preparing a layer stack (1) of at least three layers, the first layer being formed by a seed substrate (2), the second layer being formed by a separation layer (3) formed on the seed substrate (2), and the third layer being formed by a semiconductor layer (4) preferably epitaxially formed on the separation layer (3), and B) delaminating the semiconductor layer (4) from the layer stack (1). The invention is characterized in that before and / or during method step B), laser radiation (12) of a laser light source (11) is focused into the semiconductor layer (4), the laser radiation (12) being introduced into the semiconductor layer (4) along a lateral focusing line (6, 6') in order to create at least one modified region (7, 7') below the surface (9) of the semiconductor layer (4), in which the material of the semiconductor layer (4) is modified and which makes it possible to create separation regions (8) in the semiconductor layer (4) around the modified region (7, 7').

Description

[Technical Field]

[0001] The present application relates to a method for stripping a semiconductor layer according to the preamble of claim 1 and to a method for manufacturing a semiconductor layer according to the preamble of claim 22. Furthermore, the invention relates to a system for stripping a semiconductor layer from a layer stack according to the preamble of claim 23 and to a semi-finished product according to the preamble of claim 24. [Background technology]

[0002] For large-area electronic components, such as large-area lighting elements or solar cells, and also for mass-produced products such as semiconductor diodes, cost-effective semiconductor wafers with high electronic quality are needed, since in such components the material cost of the semiconductor wafer accounts for a substantial part of the overall product cost. To produce semiconductor wafers, a method is known in which semiconductor wafers are produced from silicon blocks ("ingots") by a sawing method. This makes it possible to produce high-quality, particularly monocrystalline, semiconductor wafers. However, the cost of production is high, also due to the material loss caused by sawing the silicon blocks.

[0003] Therefore, alternative methods have been developed in which semiconductor layers are deposited on a seed substrate and then delaminated from the carrier element, whereby the delaminated semiconductor layers become semiconductor wafers for fabricating electronic components.

[0004] It is known from the prior art to partially create a porous separation layer on the surface of a seed substrate, and then deposit a semiconductor layer on the seed substrate in an epitaxial process, whereby to separate the semiconductor layer from the seed substrate, a separation cut is performed by a laser beam, which penetrates completely through the semiconductor layer into the separation layer and / or the seed substrate, resulting in damage or reduction of the seed substrate as well.

[0005] However, this has proven to be disadvantageous in that parts of the semiconductor layer remain on the seed substrate in the peripheral region of the seed substrate, making it difficult to remove parts of the seed substrate. Furthermore, the seed substrate or the separation layer may also be damaged by the separation cutting, thereby limiting the ability of the seed substrate to be reused, as they are often unsuitable for reuse for the fabrication of further semiconductor layers or must be laboriously reprocessed.

[0006] An optimization of prior art methods for the production of semiconductor layers is known, for example, from DE 102015118042 A1, in which, prior to the deposition of the semiconductor layer, a separation layer is created on the seed substrate, at least on the treatment side of the seed substrate, over its entire surface, the semiconductor layer is deposited in an overlapping manner on the treatment side and at least on the side surfaces of the seed substrate, and the overlapping regions of the semiconductor layer are removed before separating the semiconductor layer from the seed substrate.

[0007] By depositing the semiconductor layer on top of each other, the semiconductor layer can be peeled off from the separation layer or seed substrate at the intended size. To ensure the reusability of the seed substrate, it is important that the seed substrate does not have any residue of the semiconductor layer after peeling. To ensure this, after peeling off the overlapping area, it is necessary to edge-treat the seed substrate to remove several micrometers, so that the lateral dimensions of the seed substrate decrease after each treatment. When the dimensions of the seed substrate become smaller than the minimum dimension, the seed substrate can no longer be used as a seed substrate for producing further semiconductor layers.

[0008] For industrial applications, cost reduction in the production of semiconductor layers is essential, especially through the reusability of seed substrates. At the same time, the delamination process is often very time-consuming, since it requires that the entire layer must be removed. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] German Patent Application Publication No. 102015118042 [Patent Document 2] German Patent Application Publication No. 102015121636 [Patent Document 3] German Patent Application Publication No. 102018111858 [Patent Document 4] German Patent Application Publication No. 102019130745 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention is therefore based on the object of providing a simple and fast method for detaching a semiconductor layer from a seed substrate, which ensures the reusability of the seed substrate. [Means for solving the problem]

[0011] These and further objects are achieved by a method for stripping a semiconductor layer according to claim 1, a method for producing a semiconductor layer according to claim 22, and a system for stripping a semiconductor layer according to claim 23. Furthermore, the object is also achieved by a semi-finished product according to claim 24.

[0012] Advantageous embodiments of the method are given in claims 1 to 21 and advantageous embodiments of the semi-finished product are given in claims 25 and 26.

[0013] The method according to the invention for stripping a semiconductor layer is provided in particular to be performed using the system according to the invention for stripping a semiconductor layer.The system according to the invention for stripping a semiconductor layer is provided in particular to be performed the method according to the invention for stripping a semiconductor layer.

[0014] The method according to the invention for stripping a semiconductor layer comprises: A) preparing a layer stack of at least three layers, wherein a first layer is formed by a seed substrate, a second layer is formed by a separation layer formed on the seed substrate, and a third layer is formed by a semiconductor layer formed, preferably epitaxially, on the separation layer; B) peeling the semiconductor layer from the layer stack.

[0015] The invention is characterized in that before and / or during method step B), laser radiation of a laser light source is focused into the semiconductor layer, which laser radiation is introduced into the semiconductor layer along a lateral focusing line in order to create at least one modification region below the surface of the semiconductor layer, in which modification region the material of the semiconductor layer is modified and a separation region is formed in the semiconductor layer around the modification region.

[0016] By introducing laser radiation, modified or separated regions are easily created in the semiconductor layer, thereby facilitating the release of the semiconductor layer from the layer stack or from the separation layer. In this case, the laser radiation can be intentionally focused into the semiconductor layer without adversely affecting or changing the properties of the separation layer and / or the seed substrate. Therefore, the seed substrate and / or the separation layer can be easily reused for the production of further semiconductor layers after the semiconductor layer has been released.

[0017] According to the invention, therefore, the semiconductor layer is edged in the layer stack without directly edge-treating the layer stack itself and therefore without reducing its dimensions, in particular its longitudinal extent. By not directly removing areas of the layer stack, such as during a sawing process or complete edge-treating of the layer stack with a laser, particle emissions are also reduced and contamination of the semiconductor layer is also reduced.

[0018] In the modified region, the material of the semiconductor layer is modified. By modifying, the semiconductor material, in particular, changes its crystalline structure. To achieve this, the material in the semiconductor layer is temporarily melted or evaporated, followed by recrystallization or solidification of the molten material. Therefore, by introducing laser irradiation according to the present invention into an epitaxial silicon semiconductor layer, preferably a monocrystalline silicon semiconductor layer, modified regions can be formed, for example, of polycrystalline silicon or amorphous silicon. According to the present invention, a separation region is created around the modified region. The modified region may also be identical to the separation region.

[0019] The seed substrate is preferably made of a crystalline material, in particular a monocrystalline material, preferably a semiconductor material. Alternatively, the seed substrate may also be made of a polycrystalline or amorphous material. The seed substrate may in particular be a carrier element, which in addition to the actual seed substrate comprises further regions or layers.

[0020] A preferred embodiment is characterized in that the focal line is formed by locally introducing laser radiation at multiple focal points with a certain focal depth, and at least one modified region is formed around each individual focal point. Therefore, it is sufficient to introduce laser radiation only at individual points in the semiconductor layer. The focal depth depends, in particular, on the thickness of the semiconductor layer, and when adjusting the focal depth, it should be taken into account that modified regions are created around the focal points. Preferably, the separation layer and, in particular, the seed substrate should not be modified so that they can be reused for the production of further semiconductor layers.

[0021] Preferably, the modified region at the focal point and / or the separation region created around the modified region at the focal point overlap each other laterally to form a continuous region, with the continuous overlapping region along the focal line ensuring clean release of the semiconductor layer.

[0022] In a preferred embodiment, the layer stack is moved continuously, in particular at a continuous speed, relative to the laser light source to create the focal point. Preferably, the layer stack is moved relative to a stationary laser light source. Alternatively, or preferably additionally, instead of or in addition to the laser light source, the corresponding optics for the laser irradiation can be moved in such a way that a focal point can be introduced into the semiconductor layer along the focal line.

[0023] In a further preferred embodiment, the layer stack is moved intermittently relative to the laser light source to create the focal spot, preferably the layer stack is moved relative to a stationary laser light source. Alternatively, or preferably additionally, instead of or in addition to the laser light source, the corresponding optics can also be moved in such a way that a focal spot can be introduced into the semiconductor layer along the focal line by laser irradiation.

[0024] Alternatively, the laser source or the optics for irradiating the laser can also be moved relative to the stationary layer stack.

[0025] Preferably, the laser source and / or the optical element for laser irradiation can be moved in the thickness direction relative to the surface of the semiconductor layer, towards or away from the surface of the semiconductor layer, by which irregularities and / or surface roughness can be compensated for.

[0026] An advantageous embodiment of the method according to the invention is characterized in that the laser radiation is pulsed, which makes it possible to deliberately introduce individual focal points into the semiconductor layer, and thus in a limited manner.

[0027] Preferably, the pulsed laser radiation is a short pulse in the nanosecond range.

[0028] Particularly preferably, these short pulses have a pulse length in the range of 1 ns to 150 ns, preferably 5 ns to 100 ns, particularly preferably 10 ns to 30 ns, ensuring that sufficient energy or a sufficiently high energy density is provided to achieve local melting of the semiconductor layer around the focal point, thereby creating a modified region.

[0029] Alternatively, or preferably in addition, the pulsed laser radiation is an ultrashort pulse in the picosecond or femtosecond range, which allows the modified region to be more tightly constricted and smaller in extent, thereby ensuring in particular that the entire semiconductor layer is exposed to less influence.

[0030] Preferably, pulsed laser irradiation is required in the lower mid-power range, for example 100 mW to 10 W, to create the modified region.

[0031] A further preferred embodiment is characterized in that multiple focal points are created in the semiconductor layer at different focal depths, one above the other in the thickness direction. Alternatively, or preferably in addition, multiple modified regions are created vertically, one above the other in the thickness direction. In particular, for thicker semiconductor layers, it is possible to achieve a separation region that extends correspondingly in the thickness direction, in order to ensure a clean separation of the semiconductor layer. Furthermore, the multiple focal points ensure that the perimeter and extent of the modified region are minimized relative to the separation region created. Therefore, the semiconductor layer undergoes less modification due to the multiple smaller modified regions.

[0032] Multiple focal points above and below each other in the thickness direction can be introduced in multiple successive processing steps, for example, where a focal point of a first focal line is created first and in a second step a focal point of a second focal line is created, and these focal points are spaced apart from each other in the thickness direction and located vertically above and below each other in the thickness direction.

[0033] Alternatively, vertically overlapping focal points can be generated immediately, successively, or simultaneously. This can be achieved, for example, by using corresponding optical elements in the beam path of the laser radiation. Thus, at least two focal lines are generated parallel to each other.

[0034] Additionally, alternatively, or preferably in addition, multiple focal points are created simultaneously, laterally juxtaposed. By creating multiple focal points simultaneously, the process of delaminating the semiconductor layer can be further accelerated.

[0035] In an advantageous embodiment, the laser radiation is introduced multiple times in succession at the focal point, which makes it possible to ensure, on the one hand, that a modification of the material of the semiconductor layer is also carried out in the modified region, in particular, whose extent can also be influenced by the multiple introduction of corresponding pulsed laser radiation so that the modified region has a desired extent and, in some cases, a desired shape.

[0036] A preferred embodiment is characterized in that the semiconductor layer is essentially transparent to the wavelength of the laser radiation. This ensures that when the laser radiation penetrates the semiconductor layer and / or further layers of the layer stack, the radiation is intentionally focused onto a focal point in the semiconductor layer without first being substantially absorbed. Absorption in the region of the focal point is essentially caused by exceeding a threshold energy density in this region. Multiphoton absorption processes may also occur.

[0037] In particular, the wavelength of the laser irradiation is in the range of 200 nm to 2000 nm, preferably in the range of 350 nm to 1600 nm, particularly preferably in the range of 500 nm to 1500 nm, and most preferably in the range of 1000 nm to 1350 nm.

[0038] For semiconductor layers made of silicon, the wavelength of the laser irradiation is preferably in the range of 800 nm to 2000 nm, more preferably in the range of 900 nm to 1600 nm, and particularly preferably in the range of 1000 nm to 1350 nm.

[0039] Advantageously, the isolation regions are formed in the semiconductor layer so that release of the semiconductor layer from the layer stack is easily achieved.

[0040] Preferably, the separation region extends to the surface of the separation layer and / or the semiconductor layer. A specific extension of the separation region in the thickness direction to the separation layer ensures that the semiconductor layer can be easily peeled off from the separation region. The extension of the separation region to the surface of the semiconductor layer also ensures that the separation region can be optically controlled, for example by a camera. If deviations from a specific contour or malformations occur, the laser irradiation for creating the focal point can be changed to affect or change the separation region or the optically visible part on the surface.

[0041] An advantageous embodiment is characterized in that the laser radiation is introduced into the layer stack along a focused line in such a way that a predetermined break point, in particular a crack, is created in the separation region, including the modified region, in the semiconductor layer, in particular the predetermined break point is formed through the separation region and / or the modified region.

[0042] Alternatively, or preferably additionally, the laser radiation is introduced into the layer stack along a focused line in such a way that the semiconductor layer is completely separated from the remainder of the layer stack, the remaining stack, along the separation region, so that complete separation of the semiconductor layer from the layer stack is possible solely by the laser radiation, whereby the semiconductor layer can be simply peeled off, for example by a gripping tool as a type of peeling means.

[0043] In a preferred embodiment, the semiconductor layer includes an overlapping region that is larger than the planar surface of the seed substrate and / or the separation region, and this overlapping region is formed to preferably at least partially cover one or more side surfaces of the seed substrate and / or the separation layer. Thus, the semiconductor layer has an extent larger than the planar surface of the separation layer and overlaps the side surface region. This overlapping region can also extend along the side surface of the seed substrate, or along the side surface of the separation layer if the separation layer is deposited along the seed substrate. The overlapping region may be the result of processing, and due to its formation in the peripheral region, its crystalline quality may be somewhat inferior compared to the actual semiconductor layer, for example, due to defects or offsets. The overlapping region makes it possible to create a semiconductor layer that essentially corresponds to the area of ​​the seed substrate. Furthermore, the overlapping region facilitates uniform thickness of the semiconductor layer.

[0044] The overlapping areas may be of lower quality than the material of the semiconductor layer, and may contain defects or offsets, for example, but this helps to achieve application-relevant semiconductor layers spaced from these areas and having a higher grade and better quality.

[0045] Advantageously, the overlapping region is of the same material as the semiconductor layer, and therefore is automatically formed during the manufacturing of the semiconductor layer and therefore forms part of the semiconductor layer.

[0046] Alternatively, or preferably in addition, the overlapping regions are peeled off from the semiconductor layer and / or layer stack in method step B). The overlapping regions are an obstacle to further use of the seed substrate for manufacturing semiconductor layers. Peeling off the overlapping regions therefore improves the reusability of the seed substrate. Furthermore, it is ensured that all semiconductor layers are produced based on approximately the same starting conditions, particularly in terms of the shape and configuration of the seed substrate, thus facilitating serial production.

[0047] A preferred embodiment of the method is characterized in that the focusing line and / or the modified region and / or the separation region are formed in an at least partially overlapping region, in particular when the overlapping region surrounds the sides of the seed substrate or the separation layer, so that complete separation is achieved along the focusing line.

[0048] It is further preferred that the focusing lines and / or modified and / or separated regions are formed mainly outside the overlapping regions, which ensures that the overlapping regions are cleanly and completely peeled off from the actual semiconductor layer, which is then used for further processing.

[0049] In a preferred embodiment, the focusing lines and / or the modified and / or separated regions are formed in a closed configuration, which ensures that the semiconductor layer can be separated purposefully and cleanly from the layer stack. The closed focusing lines in particular form delimited areas that can then be peeled off as semiconductor layer from the layer stack.

[0050] An advantageous embodiment is characterized in that the laser radiation is introduced into the semiconductor layer from one or more planar faces of the layer stack, so that a focused radiation can be deliberately introduced into the semiconductor layer, and only a relative movement of the layer stack and the laser radiation relative to each other is required.

[0051] Preferably, the laser radiation can also be introduced into the semiconductor layer at multiple points simultaneously, for example by splitting the laser radiation by an optical element to form respective modified regions along parallel focused lines on either side of the layer stack.

[0052] Alternatively, or preferably additionally, the laser radiation is introduced into the semiconductor layers, in particular into the overlapping region, from the side of the layer stack.

[0053] Thus, delamination of the semiconductor layer together with at least a portion of the overlapping region from the separation layer or seed substrate can be achieved intentionally.

[0054] In a further preferred embodiment, the focal depth of the laser radiation is adjustable in the thickness direction within the thickness of the semiconductor layer, so that the focal point or focal line, and therefore the modified region, can be adjusted in terms of their position within the semiconductor layer and can be adjusted and changed according to the respective prerequisites.

[0055] Preferably, the depth of focus in the thickness direction is in the range of half the thickness of the semiconductor layer and / or preferably in the range of 10 μm to 500 μm below the surface of the semiconductor layer. Preferably, therefore, the depth of focus is selected to be approximately in the middle of the thickness of the semiconductor layer.

[0056] In yet another embodiment of the method according to the invention, a focal point is created with an essentially circular or elliptical cross section. The cross section can influence, inter alia, the formation of the modified region and its configuration or extent. Preferably, the cross section of the focal point can be influenced and varied by using various optical elements in the beam path of the laser radiation.

[0057] Alternatively, or preferably in addition, modified and / or separated regions are manufactured and / or created with an essentially circular or elliptical cross-section. The cross-section of the region, and generally the creation of the modified region, is primarily determined by the cross-section and configuration of the focal point located within the modified region and by the power applied to the semiconductor layer by the laser irradiation. Absorption of the laser radiation and heating of the semiconductor material around the focal point leads to a change in the absorption properties (free charge carrier absorption) of the semiconductor layer, resulting, for example, in stronger absorption of the laser radiation by the focal point and the formation of an elongated modified region in the thickness direction. In particular, a longitudinal extension is created on the side of the modified region facing the laser irradiation. The formation of the modified region also depends on the crystalline structure of the semiconductor layer around the focal point.

[0058] An advantageous embodiment is characterized in that in method step B) the laser irradiation is introduced in such a way that the seed substrate and / or the separation layer are not affected by the laser irradiation at all. The laser irradiation can be adjusted in particular so that modifications occur only in the semiconductor layer and possibly only in the overlapping regions.

[0059] Preferably, after method step B), in particular after the reprocessing step, the seed substrate, preferably together with a separating layer, is used to produce at least one further semiconductor layer.

[0060] In a preferred embodiment, at least two focal lines are created in the semiconductor layer at different focal depths offset from each other in the transverse direction. In particular, the focal lines are formed simultaneously or successively at different focal depths. Thus, the creation of two modified regions, one above the other, is achieved in the transverse direction, thereby creating separation regions extending at an angle to the thickness direction.

[0061] A further preferred embodiment is characterized in that the laser radiation is incident on the layer stack in a direction perpendicular to the surfaces of the semiconductor layers.

[0062] Alternatively, the laser radiation can also be incident on the layer stack at an angle of incidence relative to the normal to the surface of the semiconductor layer. The angle of incidence is formed between the normal to the surface of the semiconductor layer and the laser radiation. The angle of incidence is an angle different from 0°. The position and configuration of the separation regions can be influenced by the shape of the laser radiation incident on the semiconductor layer or layer stack. In particular, the incidence of the laser radiation at an angle of incidence results in the formation of separation regions extending obliquely in the thickness direction. Preferably, the angle of incidence is in the range of ±10° to ±45°, in particular ±30°.

[0063] Advantageously, the semiconductor layer and / or the seed substrate is silicon, in particular monocrystalline silicon. However, the invention is not limited to this. The semiconductor layer may be any semiconductor, in particular a crystalline material. In particular, the semiconductor layer may also be made of germanium, or any III-V semiconductor, such as gallium nitride or gallium arsenide, or a semiconductor compound, such as silicon carbide.

[0064] Alternatively, or preferably in addition, the separation layer is porous silicon. Alternatively, the separation layer can be made of any material that, on the one hand, is a good seed layer for the semiconductor layer and / or, on the other hand, allows easy release of the semiconductor layer produced thereon.

[0065] The object of the present invention is to provide a method for manufacturing a semiconductor layer, comprising the steps of: V1) method steps for preparing a seed substrate; V2) a method step of creating a separation layer on the seed substrate; V3) a method step of depositing a semiconductor layer, preferably by epitaxy, on the separation layer of the seed substrate to produce a layer stack of the seed substrate, the separation layer and the semiconductor layer; V4) method step of peeling the semiconductor layer from the layer stack; This is further achieved by a method comprising:

[0066] The method for producing a semiconductor layer is characterized in that the delamination of the semiconductor layer is carried out by the method for delaminating a semiconductor layer as described above or by any advantageous embodiment thereof, in particular after method step V4), method steps V2) to V4) are carried out multiple times using a seed substrate.

[0067] The above object is further achieved by a system for peeling off a semiconductor layer from a layer stack, the layer stack comprising at least a seed substrate, a separation layer formed on the seed substrate, and a semiconductor layer preferably epitaxially fabricated on the separation layer, the system comprising a support for the layer stack, a peeling unit preferably for the semiconductor layer, and a laser light source for generating laser radiation.

[0068] The system is preferably configured to perform the method for stripping a semiconductor layer, as described above, or any advantageous embodiment thereof.

[0069] For this system, it is essential that the laser radiation of the laser light source is focused within the layer stack in such a way that a modified region is created below the surface of the semiconductor layer along a lateral focusing line, in which the material of the semiconductor layer is modified and preferably a separation region comprising the modified region can be created, and that the semiconductor layer is formed in such a way that it can be peeled off from the layer stack along the focusing line, in particular by a peeling unit.

[0070] The above object is further achieved by a semi-finished product, which comprises a layer stack of at least a seed substrate, in particular made of silicon, a separation layer formed on the seed substrate, and a semiconductor layer, preferably epitaxially produced on the separation layer, wherein the semiconductor layer preferably comprises an overlapping area that is larger than the planar surface of the seed substrate and / or separation layer, and which overlapping area is preferably formed so as to at least partially cover one or more side surfaces of the seed substrate and / or separation layer.

[0071] The semi-finished product according to the present invention is characterized in that a modified region and preferably a separation region including the modified region are formed along the focusing line below the surface of the semiconductor layer, and in the modified region the material of the semiconductor layer is modified.

[0072] In an advantageous embodiment, the separation region extends to the surface of the separation layer and / or the semiconductor layer, thus ensuring that the semiconductor layer can be easily peeled off from the layer stack or the separation layer.

[0073] Alternatively, or preferably in addition, a predetermined breaking point, in particular a crack, is formed through the separation region.

[0074] In a preferred embodiment, the isolation regions extend within the semiconductor layer at an angle to the thickness direction, which simplifies peeling of the semiconductor layer from the rest of the layer stack. [Brief explanation of the drawings]

[0075] Further advantageous features and embodiments are explained below with reference to exemplary embodiments and drawings, in which: [Figure 1a] 1 shows a schematic cross-sectional view of a layer stack using the method according to the invention; [Figure 1b] 1a) shows a perspective view of the layer stack of FIG. [Figure 1c] 4 shows a schematic cross-sectional view of a layer stack using the method according to the invention in a further embodiment; [Figure 2a] 1 shows schematic details of various embodiments of different shapes of focal points; [Figure 2b] 1 shows schematic details of various embodiments of different shapes of focal points; [Figure 3a] 1a) show top views of the layer stack of FIG. 1a) using the method according to the invention at different times; [Figure 3b] 1a) show top views of the layer stack of FIG. 1a) using the method according to the invention at different times; [Figure 4a] 3 shows a schematic cross-sectional view of a layer stack using an alternative embodiment of the method according to the invention; [Figure 4b] 1 shows a schematic cross-sectional view of a semiconductor layer during peeling. [Figure 5]3 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention; [Figure 6] 3 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention; [Figure 7] 3 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention; [Figure 8a] 3 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention; [Figure 8b] 3 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention; [Figure 8c] 10 shows a further schematic cross-sectional view during release of the semiconductor layer after forming the diagonally extending isolation regions; [Figure 8d] 5A-5C show schematic cross-sectional views of a layer stack using yet another embodiment of the method according to the invention at different points in time; [Figure 8e] 5A-5C show schematic cross-sectional views of a layer stack using yet another embodiment of the method according to the invention at different points in time; [Figure 9a] 3 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention; [Figure 9b] 9a) shows a further schematic cross-sectional view of the semiconductor layer during release after formation of the isolation regions;

[0076] All of the drawings are schematic and not to scale. In the drawings, like reference numerals refer to like or equivalent elements throughout. DETAILED DESCRIPTION OF THE INVENTION

[0077] 1a) and 1c) each show a schematic cross-sectional view of a layer stack 1, while FIG. 1b) shows the layer stack 1 of FIG. 1a) in a perspective view. The layer stack 1 comprises three layers arranged one above the other in a thickness direction 13. During the production of the layer stack 1, a seed substrate 2, in this case made of silicon, is first prepared. By porosification, as known, for example, from DE 102015121636 A1 or DE 102018111858 A1, a separation layer 3 is created on the seed substrate 2, which separation layer 3 covers the seed substrate 2 on at least one planar surface. In this case, the separation layer 3 surrounds the seed substrate 2 on its top planar surface 2a in the thickness direction as well as on its lateral regions. Furthermore, the region of the bottom planar surface 2b of the seed substrate 2 in the thickness direction can also be porosified in the region of the separation layer 3 adjacent to the lateral region. Therefore, the separation layer 3 is also partially formed on the bottom flat surface 2 b of the seed substrate 2 .

[0078] After the formation of the separation layer 3, a semiconductor layer 4 is formed on the separation layer 3 by epitaxy, which completely covers the separation layer 3 on the side of the separation layer 3 facing away from the top flat surface 2a of the seed substrate 2 and has an overlapping area 10 in the lateral peripheral region. This method for the formation of a semiconductor layer is known from DE 10 2019 130 745 A1.

[0079] Epitaxial deposition of the material of the semiconductor layer 4 is also carried out in the overlapping region 10, which in this case is also silicon. The seed substrate 2 is completely surrounded by the semiconductor layer 4 and the overlapping region 10, except for the bottom flat surface 2b in the thickness direction 13.

[0080] To enable the epitaxially produced semiconductor layer 4 to be detached from the layer stack 1 and thus from the seed substrate 2, the method according to the invention provides for focusing laser radiation 12 from a laser source 11 into the semiconductor layer 4. For this purpose, the laser radiation 12 is introduced at a number of positions so as to create individual focal points 5 located in the semiconductor layer 4. The focal points 5 are formed along lateral focal lines 6 in the semiconductor layer 4 with a focal depth 5a. The focal depth 5a depends in particular on the thickness of the semiconductor layer 4 and, in this case, is in the range of half the thickness of the semiconductor layer, and therefore, for example, in the range of approximately 70 μm.

[0081] A pulsed laser is used as the laser light source 11, since the use of a pulsed laser results in a corresponding formation of the focal point 5. The laser radiation 12 is composed of short pulses, the pulse length of which is in the range of 5 ns to 30 ns. The wavelength of the laser radiation 12 in this case is approximately 1064 nm or approximately 1342 nm.

[0082] The laser radiation 12 of the laser source 11 is guided and focused by an optical element 15. For clarity, in this case only one optical element 15, in the form of an optical lens, is shown in each of FIGS. 1a, 1b, and 1c. However, a mirror, a semi-transparent mirror, a diffractive optical element, or an aperture (diaphragm) can also be used as the optical element 15. As shown in FIGS. 1a and 1b, the laser source 11 and the optical element 15 are arranged above the surface 9 of the semiconductor layer 4 in the thickness direction 13 in order to focus the laser radiation 12 into the semiconductor layer 4. The laser radiation 12 is introduced into the semiconductor layer 4 in a direction essentially perpendicular to its surface 9.

[0083] 1c) shows a further embodiment of the method according to the invention, in which laser radiation 12 is introduced from the bottom side 2b of the seed substrate 2 into the semiconductor layer 4 with a focusing depth 5a for the formation of a focusing spot 5. In this case too, the laser radiation 12 is focused into the layer stack 1 in a direction essentially perpendicular to the surface of the bottom side 2b of the seed substrate 2. Depending on the materials selected for the seed substrate 2, the separation layer 3 and the semiconductor layer 4, this type of irradiation of the laser radiation 12 into the semiconductor layer 4 may also be possible. Furthermore, in FIG. 1c), the separation layer 3 and the overlapping region 10 are only partially deposited along the side of the seed substrate 2.

[0084] To create individual focal spots 5 in the semiconductor layer 4, the layer stack 1 is moved relative to the laser source 11 or laser radiation 12, which is essentially formed or arranged to be stationary in the lateral direction. The stationary arrangement of the laser radiation 12 is provided, for example, by using a stationary optical element 15 that focuses the laser radiation 12 into the semiconductor layer 4 of the layer stack 1. The laser radiation 12 is pulsed in the semiconductor layer 4 during the uniform movement of the layer stack 1, thereby creating individual focal spots 5. The lateral distance of the focal spots 5 depends on various factors, and is influenced in particular by the relative speed of the layer stack 1 with respect to the laser radiation 12 or laser source 11, and the pulse repetition rate of the laser source 11. By selecting the corresponding parameters, the distance of the focal spots 5 can be adjusted to ultimately enable the detachment of the semiconductor layer 4. A short pulse length of the laser radiation 12 can help to accelerate the creation of the focal line 6, thereby enabling the semiconductor layer 4 to be rapidly detached thereafter.

[0085] In this case, the focusing wire 6 is formed in the semiconductor layer 4 in a completely closed manner, thereby finally forming the semiconductor layer 4 to be peeled off, which is peeled off from the layer stack 1 by a peeling unit and then used for further processing, for example to produce solar cells and semiconductor components. The focusing wire 6 formed in a closed configuration defines an area inside the focusing wire 6 that essentially corresponds to the semiconductor layer 4 to be peeled off.

[0086] Around each of the focal points 5, a modified region 7 is created, in which the material of the semiconductor layer 4, in this case silicon, is modified. This modification is a change in the crystalline structure of the semiconductor layer 4, which occurs around the focal points 5 due to the introduction of laser radiation 12. The laser radiation 12 focused into the semiconductor layer 4 causes at least a brief melting and possibly evaporation of the material of the semiconductor layer 4 at the focal points 5 and in the modified regions 7. During solidification, the molten material assumes a different crystalline structure, which differs significantly, in particular significantly, from the rest of the semiconductor layer 4 around the modified regions 7. Since the semiconductor layer 4 is crystalline silicon in this case, the introduction of laser radiation 12 into the semiconductor layer 4 modifies this semiconductor layer 4 into polycrystalline and / or partially amorphous silicon in the modified regions 7.

[0087] Figure 1b) shows a perspective view of a detail of the layer stack 1 of Figure 1a). The individual focal points 5 are essentially spherical and are introduced into the semiconductor layer 4 along a focusing line 6. Around the individual focal points 5, modified regions 7 are formed which have an elongated shape in the thickness direction 13, with this elongated extent essentially lying above the focal points 5 on the side facing the laser irradiation 12.

[0088] Both the focal point 5 and the modified region 7 can have variable shapes and configurations, depending in particular on the power of the laser source 11, the wavelength of the laser radiation 12, the pulse length of the laser radiation 12, and the optical properties of the semiconductor layer 4, such as the refractive index and absorption coefficient, which generally also depend on temperature and time. For example, FIGS. 2a and 2b show two embodiments of the focal point 5 and the modified region 7 created around the focal point 5. As shown in FIG. 2a, the focal point 5 is created with an essentially circular cross section. The modified region 7 around the focal point 5 has an elliptical cross section, the major axis of which is essentially parallel to the thickness direction 13. The focal point 5 itself forms only a small part of the modified region 7. The configuration of the modified region 7, in particular its shape and size, is also influenced by the crystalline quality of the semiconductor layer 4 and by heating of the semiconductor layer 4 and the resulting changed optical properties.

[0089] FIG. 2b) shows a further embodiment in terms of the focal point 5 and the modified region 7. By changing the laser radiation 12 during its focusing into the semiconductor layer 4, for example by using further and / or further optical elements 15, in particular optical lenses, in the beam path of the laser radiation 12, the cross section of the focal point 5 can also have an elliptical configuration, the main axis of which also runs essentially parallel to or in the thickness direction 13. In this case, the modified region 7, whose shape is similar to that of the focal point 5, is also formed elliptical or oval around the focal point 5, the main axis of which is essentially parallel to the thickness direction 13. In contrast to FIG. 2a), the modified region 7 in FIG. 2b) is formed significantly larger or more elongated, the elongated extent of which is essentially on the side facing the laser radiation 12. The elongated configuration of the focal point 5 in the thickness direction 13 can be achieved, inter alia, by focusing the partial rays 12', 12'' of the laser radiation 12 at different focusing depths, and the focal points 5 for the partial rays 12', 12'' of the laser radiation 12 can be located very close together.

[0090] The focal point 5 may generally have any particular cross section, and in particular the focal point 5 may also have an elliptical cross section, the major axis of which extends essentially in the transverse direction 14 or at an angle to the thickness direction 13 and / or the transverse direction 14.

[0091] The individual focal points 5 are formed along the focal line 6 in this case such that the modified regions 7 of the focal points 5 overlap one another, as shown in Figures 1a, 1b and 1c, thus creating a continuous region in which the material of the semiconductor layer 4 has been modified.

[0092] During the formation of the modified region 7 around the focal point 5, a further region, referred to as a separation region 8, is created around the modified region 7. Although the material in the separation region 8 of the semiconductor layer 4 is not modified, the formation of the modified region 7 in the semiconductor layer 4 generates stresses in the semiconductor layer 4 around the modified region 7. These stresses create predetermined fracture points in the semiconductor layer 4 around the modified region 7 as the separation region 8. In this case, the separation region 8 has already been formed by a crack, which extends into the semiconductor layer 4, as shown in FIG. 1 . In the illustrated exemplary embodiment, the separation region 8 extends essentially along the lateral direction 14 and has only a small width in the transverse direction 17, which is perpendicular to the thickness direction 13 and the lateral direction 14 and extends into the image plane in this case. The semiconductor layer 4 is peeled off from the layer stack 1 along the separation region 8.

[0093] By moving the layer stack 1 relative to the laser source 11, a focal line 6 is introduced completely in the lateral direction 14 along the extent and dimension of the semiconductor substrate 4. Hence, a focal point 5 and a corresponding modified region 7 are also created in the overlap region 10.

[0094] As shown in FIGS. 3a and 3b, the focusing lines 6 and the separation regions 8 formed along the focusing lines 6 extend mostly inside the semiconductor layer 4, a short distance to the overlap region 10. The separation regions 8 are visible in this case by the formation of cracks extending to the surface 9 of the semiconductor layer 4, and are correspondingly shown in the top view. The focusing lines 6 or separation regions 8 also "punch through" the overlap region 10 to the end of the layer stack 1 in the lateral direction 14 only in the peripheral area of ​​the semiconductor layer 4. Most of the focusing lines 6, and therefore most of the modified regions 7 and separation regions 8, also extend inside the semiconductor layer 4. This helps ensure that the semiconductor layer 4' to be released is of high grade and quality. Offset and crystallization defects, which adversely affect the grade and quality of the semiconductor layer 4, may occur in the peripheral area of ​​the semiconductor layer 4, and therefore especially in the overlap region 10. The overlapping regions 10 can also prevent mechanical delamination of the semiconductor layer 4 if it is not removed or, as proposed in the present method, peeled or modified to be peelable from the rest of the semiconductor layer 4. To avoid the adverse effects of these defects in the semiconductor components subsequently fabricated from the semiconductor layer 4, the focusing lines 6 or separation regions 8 are formed in the semiconductor layer 4, mainly at a distance from the overlapping regions 10 and outside the peripheral area.

[0095] To finally detach the semiconductor layer 4 from the layer stack 1, the focal line 6 is introduced into the layer stack 1, and thus into the semiconductor layer 4, in a circumferential and closed configuration, as shown in FIG. 3b. This serves to ensure that a high-quality semiconductor layer 4′ to be detached is formed in the semiconductor layer 4 and can be completely detached from the layer stack 1. For this purpose, the focal line 6 with the focal point 5 and the resulting separation region 8 are first formed along the side, so that the focal line 6, or the illustrated separation region 8, is already formed in a closed configuration. Furthermore, before detaching the semiconductor layer 4′, the laser irradiation 11 is introduced at an angle to the side to create a chamfer. The beveling of the corners of the semiconductor layer 4′ particularly improves the stability of the semiconductor layer 4′. The semiconductor layer 4′ to be detached has somewhat smaller dimensions than the semiconductor layer 4, which are determined by the extent of the focal line 6 within the semiconductor layer 4.

[0096] 4a) shows a further embodiment of the method according to the invention, in which the laser radiation 12 is introduced into the semiconductor layer 4 at two points simultaneously. Thus, two focal points 5 and modified regions 7 corresponding to the focal points 5 are created simultaneously or at a short time interval in the range of the pulse repetition frequency, along two essentially parallel focal lines 6 which in this case extend into the image plane. Creating the two focal points 5 or modified regions 7 essentially simultaneously again substantially accelerates the process of peeling or detaching the semiconductor layer 4.

[0097] As shown in FIG. 4 a), in this case, the formation of focal points 5 for creating respective focal lines 6 is carried out in opposite regions of the layer stack 1. The lateral direction 14 along which the focal points 5 are created extends into the image plane of FIG. 4 a). After creating two parallel focal lines 6 with corresponding modified regions 7 and separation regions 8 along a side of the layer stack 1 in order to completely separate the semiconductor layer 4, the layer stack 1 can be rotated by approximately 90° to subsequently create focal lines 6 with corresponding modified regions 7 and separation regions 8 along the remaining two side surfaces of the layer stack 1.

[0098] 4b) shows the method step in which the semiconductor layer 4' is separated from the layer stack 1 by means of a peeling unit. As mentioned above, after the separation region 8 has been completely formed, the semiconductor layer 4' is peeled off in such a way that only the semiconductor layer 4', preferably together with only a part of the separation layer 3, is removed from the layer stack 1, as shown in FIG. 4b), while the area around the overlapping region 10 initially remains together with the remaining residual stack 16.

[0099] To ensure reusability of the seed substrate 2 for further fabrication of semiconductor layers 4, it is advantageous not only to remove the semiconductor layer 4′ to be delaminated, but also to remove the remaining portions of the semiconductor layer 4, as well as the overlapping regions 10, from the residual stack 16. These remaining portions are also preferably delaminated during delamination of the semiconductor layer 4 from the layer stack 1. The modified regions 7 or separation regions 8 are formed in such a way that delamination of the semiconductor layer 4 also allows the remaining portions, such as the overlapping regions 10 and the undelaminated portions of the semiconductor layer 4 adjacent to the overlapping regions 10, to be delaminated from the layer stack 1.

[0100] 4b), the area around the overlapping area 10 can be detached from the residual stack 16, so that the original seed substrate 2, possibly together with a part of the separation layer 3, can be used for the production of a further semiconductor layer 4. Alternatively, the detachment of the semiconductor layer 4′ from the layer stack 1 can also be performed in such a way that the peripheral area around the overlapping area 10 is also detached from the layer stack 1 at the same time as the semiconductor layer 4′. Thus, the detachment of the semiconductor layer 4′ and the peripheral area is performed in one step.

[0101] The seed substrate 2 is then left with the separation layer 3 intact, or in some cases, only partially intact as shown in FIG. 4b). This seed substrate 2 can then be used in a subsequent process for the production of a further semiconductor layer 4; in some cases, the separation layer 3 is reprocessed or newly produced on the seed substrate 2 for the production of an epitaxial semiconductor layer 4. However, the method according to the invention does not damage the seed substrate 2 at all or substantially change its dimensions. Rather, the same high-quality seed substrate 2 is always left with its dimensions essentially intact. By focusing the laser radiation 12 into the semiconductor layer 4, the seed substrate 2 is neither modified in any way nor edged in the peripheral area, for example by a laser that penetrates completely through the layer stack 1 or by sawing.

[0102] As shown in FIG. 4 a), introducing the laser radiation 12 into two focal points 5 that are formed simultaneously at a distance from one another can be achieved by various options. On the one hand, it is possible to split the laser radiation 12 of the laser source 11 by means of one or more optical elements 15 and guide the laser radiation to the desired point of use by means of further corresponding optical elements 15. This makes it possible to introduce the laser radiation 12 simultaneously into different focal points 5 in a flexible manner and in a manner that depends on the configuration of the optical elements 15. However, the beam path of the laser radiation 12 must always be checked to ensure that the laser radiation reaches the intended focal point 5.

[0103] Alternatively, multiple laser sources 11 can be used to generate the laser illumination 12, the laser illumination 12 of which is used to create the focal point 5. Therefore, multiple laser sources 11 are required, however, they can be used individually in a fast and flexible manner.

[0104] The position of the focal point 5, as well as the creation of the modified region 7, can also be determined by adjusting the laser irradiation 12. Therefore, depending on the thickness of the semiconductor layer 4 in the thickness direction 13, the focal point 5 can be created closer or farther to the surface 9 of the semiconductor layer 4. For this purpose, the focal point 5 is introduced with a focal depth 5a. However, care must be taken to create the focal point 5 in the semiconductor layer 4 and not in the separation layer 3. The focal depth 5a is therefore always smaller than the thickness of the semiconductor layer 4, since otherwise modifications or changes may occur in the separation layer 3 and especially in the seed substrate 2.

[0105] In this case, the creation of the focal point 5 is caused by a short pulse of pulsed laser radiation 12. However, it is alternatively possible to successively introduce several short pulses into the focal point 5 in order to influence in particular the configuration of the modified region 7 around the corresponding focal point 5.

[0106] In the following Figures 5 to 7 further embodiments are shown in terms of creating the focal points 5, focal lines 6, modified regions 7 and separation regions 8.

[0107] 5 shows a further embodiment of the method according to the invention, in which individual focal points 5 are created at further intervals from one another in the lateral direction 14. The modified regions 7 created around each focal point 5 do not overlap one another due to the spacing of the focal points 5. However, overlap still exists, but only of the separation regions 8 created around each modified region 7. The respective separation regions 8 therefore form a continuous region with one another, along which the semiconductor layer 4 will subsequently be peeled or separated.

[0108] The individual modified regions 7, as well as the continuous separation regions 8, are located entirely within the semiconductor layer 4, as shown in Figure 5. The separation regions 8 therefore do not reach the separation layer 3 or the surface 9 of the semiconductor layer 4 in the thickness direction 13. However, this is not necessary, since for the delamination of the semiconductor layer 4 it is sufficient that corresponding separation regions 8 are formed in the semiconductor layer 4, e.g., at predetermined break points in this case.

[0109] Figure 6 shows a further embodiment which differs substantially from Figure 5 in terms of the configuration of the separation regions 8. In contrast to the exemplary embodiment of Figure 5, the separation regions 8 in Figure 6 are created or formed in such a way that they extend down to the surface 9 of the semiconductor layer 4. In contrast to Figure 5, in Figure 6 the separation regions 8 do not extend completely down to the separation layer 3 due to the focusing points 5 of a given focusing depth 5a being closer to the surface 9 of the semiconductor layer 4. This different configuration of the separation regions 8, in particular their extent in the thickness direction 13, is essentially determined by the number and configuration of the focusing points 5 and the focusing depth 5a.

[0110] As shown in FIG. 6 , the focal points 5 along the focal line 6 are closely spaced such that the modified regions 7 created around the focal points 5 overlap one another, as do the separation regions 8. The formation of the separation regions 8 extending down to the surface 9 of the semiconductor layer 4 is evidenced by the formation of small cracks or the like at the surface 9 during processing of the layer stack 1. The formation of the separation regions 8 in the form of cracks down to the surface 9 of the semiconductor layer 4 allows a user, possibly with the aid of a camera, to visualize the formation of the separation regions 8. This provides an optical reference for a user or a monitoring system to determine whether the focal points 5, and therefore the modified regions 7 and separation regions 8, have been properly created and, possibly, whether they are in the desired and proper locations. Therefore, the creation of the focal points 5 for delaminating the semiconductor layer 4 can be monitored by the corresponding creation of the modified regions 7 and separation regions 8. 5, if modified regions 7 and separation regions 8 are formed only in semiconductor layer 4, a user or a monitoring system can determine, for example by an infrared camera, whether focal points 5 have been created with corresponding modified regions 7 and whether desired separation regions 8 have been correspondingly created or formed. However, this only becomes apparent during the subsequent peeling of semiconductor layer 4 from layer stack 1.

[0111] 7, focal points 5, 5' are created in the semiconductor layer 4 above and below each other in the thickness direction 13 at different focal depths 5a, 5a'. Creating the focal points 5, 5' at different focal depths 5a, 5a' can be performed consecutively in two operating steps in combination with creating two focal lines 6, 6' spaced apart in the thickness direction 13. Laser irradiation 12 for the different focal points 5, 5' at different focal depths 5a, 5a' is introduced consecutively into the semiconductor layer 4, where a first focal line 6 is first created at the first focal depth 5a, and then, in a similar manner, a second focal line 6' is created at the second focal depth 5a'.

[0112] Preferably, the laser radiation 12 is focused by the optical element 15 into the semiconductor layer 4 in such a way that two focal points 5, 5' are simultaneously created at two different focal depths 5a, 5a'. By these means, corresponding separation regions 8 extending from the separation layer 3 to the surface 9 of the semiconductor layer 4 are created by modified regions 7, 7' created around the two focused lines 6, 6'. However, the modified regions 7 of the individual focused lines 6 and the modified regions 7, 7' of the individual focused lines 6' do not overlap each other. For semiconductor layers 4 having a thickness greater than 200 μm, which are formed thicker in the thickness direction 13, it is particularly recommended to introduce multiple focused lines 6, 6' one above the other in the thickness direction 13. This ensures that corresponding separation regions 8 are created, which should also ensure complete detachment of the semiconductor layer 4 from the layer stack 1.

[0113] In the above figure, the laser radiation 12 was introduced into the semiconductor layer 4 in a direction essentially perpendicular to the surface 9 of the semiconductor layer 4 to create the focal spot 5 and the corresponding modified regions 7 and separation regions 8. In this case, the modified regions 7 and separation regions 8 are created mainly in the thickness direction 13, with a smaller extent or width in the transverse direction 17. The exfoliated semiconductor layer 4' therefore has side surfaces 9a created essentially perpendicular to the surface 9 of the semiconductor layer 4, as also shown schematically in FIG. 4b).

[0114] 8a) and 8b) show a further embodiment in which the semiconductor layer 4' to be released is formed with side surfaces 9a that are at an angle to the thickness direction 13. As shown in FIG. 8b), a separation region 8 extending at an angle to the thickness direction 13 is created by focus points 5, 5' that overlap and are offset relative to each other in the transverse direction 17 and are created at different focus depths 5a, 5a'. In this case, due to the offset arrangement of the two focus points 5, 5' that are created simultaneously and due to the offset arrangement of the modified regions 7, 7', a separation region 8 is created that extends obliquely to the thickness direction 13 in the semiconductor layer 4 by joining the two modified regions 7, 7' of the focus points 5, 5' that are created offset from each other.

[0115] Alternatively, the modified regions 7 and / or separation regions 8 extending obliquely relative to the thickness direction 13 may already be produced by oblique incidence of the laser radiation 12 on the surface 9 of the semiconductor layer 4, as shown in FIG. 8 a). To achieve this, it is not necessarily necessary to have two offset focal points 5, 5', as shown in FIG. 8 b). Furthermore, alternatively, the modified regions 7 and / or separation regions 8 extending obliquely relative to the thickness direction 13 can be produced by oblique and / or normal incidence of the laser radiation 12 on the surface 9 of the semiconductor layer 4, preferably if a mechanical stress is simultaneously applied to the semiconductor layer 4 or to the layer stack 1, for example by a bending force.

[0116] To create focal points 5, 5' or resulting focal lines 6, 6' offset in the transverse direction 17, the laser radiation 12 is focused into the semiconductor layer 4 at an angle of incidence α relative to the normal to the surface 9 of the semiconductor layer 4. The angle of incidence α is formed between the normal to the surface of the semiconductor layer and the central direction of the incident laser radiation 12 and does not include normal incidence of the laser radiation 12, which would represent an angle of incidence α of 0 degrees. Preferably, the angle of incidence α is in the range of ±10° to ±45°, in particular ±30°. By irradiating the laser radiation 12 at an angle, multiple focal points 5, 5' can be created simultaneously, similar to the configuration of FIG. 7. Alternatively, the focal points 5, 5' can also be created sequentially when the irradiation is at an angle.

[0117] When the semiconductor layer 4′ is peeled off from the layer stack 1, as shown in FIG. 8c), the semiconductor layer 4′ now has side surfaces 9a that are oblique to the thickness direction 13, such that the flat surface at the bottom in the thickness direction 13 has a smaller surface area than the flat surface at the top of the semiconductor layer 4′ in the thickness direction 13. As shown in FIG. 8c), a portion of the separation layer 3 remains on the to-be-peeled semiconductor layer 4′ when the semiconductor layer 4′ is peeled off. The chamfered side surfaces 9a simplify the process of removing the to-be-peeled semiconductor layer 4′ from the remainder of the layer stack, the residual stack 16. The peripheral area comprising the overlapping region 10 and the remainder of the semiconductor layer 4 remaining on the residual stack 16 is removed from the residual stack 16 in a subsequent method step, so that the seed substrate 2 can then be used for the production of a further semiconductor layer 4.

[0118] 8d) and 8e) show further embodiments for creating obliquely extending separation regions 8 in a semiconductor layer 4. The present invention is a two-step method in which, as shown in FIG. 8d), a focal point 5 is first created at a first focal depth 5a together with a corresponding modified region 7. To achieve this, laser radiation 12 is focused into the semiconductor layer 4 by an optical element 15, as described above. In a second step, as shown in FIG. 8e), a second focal point 5′ is created together with the modified region 7′ at a second focal depth 5a′ offset in the transverse direction 17, as shown in FIG. 8e). Thus, the modified regions 7, 7′ and the separation regions created around the focal points 5, 5′, which are offset in the transverse direction 17, create obliquely extending separation regions 8, similar to FIG. 8a).

[0119] 8d) and 8e), as usual, the laser radiation 12 can be introduced perpendicularly to the surface 9 of the semiconductor layer 4. Therefore, in this case, oblique incidence of the laser radiation 12 is not required to create the focal points 5, 5'. The angular extent of the separation regions 8 in the semiconductor layer 4, as well as the angle of the side surfaces 9a of the semiconductor layer 4, can be flexibly created by appropriately selecting the corresponding spacing of the focal points 5, 5' in the transverse direction 17.

[0120] 9a) and 9b) show yet another embodiment of the method according to the invention, in which laser radiation 12 is introduced laterally into the overlap region 10 of the semiconductor layer 4 via an optical element 15. A focal point 5 is created in the overlap region 10, essentially at the height of the separation layer 3. This makes it possible to create a peripheral, essentially horizontally extending separation region 8 along a focal line 6 (not shown) by incidence of the laser radiation 12 via the side of the layer stack 1, along which separation region 8 the semiconductor layer 4′ can be detached together with a part of the separation layer 3, as shown in FIG.

[0121] This embodiment provides not only the release of the semiconductor layer 4', but also the release of the overlapping region 10 surrounding the released semiconductor layer 4', as shown in Figure 9b). The released semiconductor layer 4' can then be used for further processing together with the overlapping region 10. Alternatively, the peripheral area 10 of the released semiconductor layer 4' is removed in a further processing step before being used for further processing. [Explanation of symbols]

[0122] 1-layer stack 2. Seed substrate 2a, 2b flat surface 3 separation layer 4, 4' Semiconductor layer 5, 5' focal point 5a, 5a' Focusing depth 6, 6' focusing line 7, 7' modified region 8 Separation area 9. Surface of semiconductor layer 9a Side of semiconductor layer 10 Overlapping Areas 11 Laser light source 12 Laser irradiation 12', 12'' Partial beam of laser radiation 13 Thickness direction 14 Horizontal 15 Optical Elements 16 remaining stacks 17 Transverse α angle of incidence

Claims

1. A method for stripping a semiconductor layer (4) from a layer stack (1), comprising: A) a method step of preparing a layer stack (1) of at least three layers, wherein a first layer is formed by a seed substrate (2), a second layer is formed by a separation layer (3) formed on said seed substrate (2), and a third layer is formed by said semiconductor layer (4) formed, preferably epitaxially, on said separation layer (3); B) the method step of peeling off said semiconductor layer (4) from said layer stack (1); In a method comprising:

1. A method according to claim 1, further comprising the steps of: before and / or during method step B), focusing laser radiation (12) of a laser light source (11) into the semiconductor layer (4), the laser radiation (12) being introduced into the semiconductor layer (4) along a lateral focusing line (6, 6') in order to create at least one modified region (7, 7') below the surface (9) of the semiconductor layer (4), in which the material of the semiconductor layer (4) is modified and separation regions (8) are created in the semiconductor layer (4) around the modified region (7, 7').

2. 2. The method according to claim 1, characterized in that the focal line (6, 6') is created by locally introducing the laser radiation (12) at a plurality of focal points (5, 5') at a focal depth (5a, 5a'), the at least one modified region (7, 7') is formed around each of the individual focal points (5, 5'), and the modified regions (7, 7') and / or the separate regions (8) of the focal points (5, 5') formed around the modified regions (7, 7') preferably overlap each other in a lateral direction (14) to form a continuous region.

3. 3. The method according to claim 1 or 2, characterized in that the layer stack (1) is moved uniformly, in particular at a continuous speed, relative to the laser light source (11) to create the focal point (5, 5'), or the layer stack (1) is moved intermittently relative to the laser light source (11) to create the focal point (5, 5'), preferably the layer stack (1) is moved relative to the stationary laser light source (11).

4. the laser radiation (12) is pulsed, in particular the pulsed laser radiation (12) is a short pulse in the nanosecond range, preferably having a pulse length in the range of 1 ns to 150 ns, preferably 5 ns to 100 ns, particularly preferably 10 ns to 30 ns, or Method according to any one of claims 1 to 3, characterized in that the pulsed laser radiation (12) is an ultrashort pulse in the picosecond or femtosecond range.

5. a plurality of focusing points (5, 5') are formed vertically above one another in the thickness direction (13) in the semiconductor layer (4) at different focusing depths (5a, 5a'); and / or a plurality of modified regions (7, 7') are created vertically, one above the other in the thickness direction (13); and / or Method according to any one of claims 1 to 4, characterized in that several focal points (5, 5') are created simultaneously, laterally juxtaposed to one another.

6. Method according to any one of claims 1 to 5, characterized in that the laser radiation (12) is introduced several times in succession at the focal point (5, 5').

7. 7. The method according to any one of claims 1 to 6, characterized in that the semiconductor layer (4) is essentially transparent to the wavelength of the laser radiation (12), in particular in that the wavelength is in the range of 100 nm to 2000 nm, preferably in the range of 350 nm to 1600 nm, particularly preferably in the range of 500 nm to 1500 nm, most preferably in the range of 1000 nm to 1350 nm.

8. 8. The method according to any one of claims 1 to 7, characterized in that the separation region (8) is created in the semiconductor layer (4), preferably the separation region (8) extends to the surface (9) of the separation layer (3) and / or the semiconductor layer (4).

9. 9. The method according to claim 1, wherein the laser radiation (12) is introduced into the layer stack (1) along the convergence line (6, 6') in such a way that a predetermined break point, in particular a crack, is formed in the semiconductor layer (4) in the separation region (8) including the modified region (7, 7'), in particular the predetermined break point, in particular the crack is formed through the separation region (8) and / or the modified region (7, 7') and / or the laser radiation (12) is introduced into the layer stack (1) along the convergence line (6, 6') in such a way that the semiconductor layer (4) is completely separated from the remaining stack (16) along the separation region (8).

10. 10. The method according to any one of claims 1 to 9, characterized in that the semiconductor layer (4) comprises an overlapping area (10) that is larger than the planar surface of the seed substrate (2) and / or the separation layer (3), the overlapping area (10) preferably being formed so as to at least partially cover one or more side surfaces of the seed substrate (2) and / or the separation layer (3).

11. the overlapping region (10) is made of the same material as the semiconductor layer (4), and / or 11. Method according to claim 10, characterized in that the overlapping region (10) is separated from the semiconductor layer (4) and / or from the layer stack (1) in method step B).

12. 12. A method according to claim 10 or 11, characterized in that the focusing lines (6, 6') and / or the modified regions (7, 7') and / or the separation regions (8) are at least partially formed within the overlapping region (10), preferably the focusing lines (6, 6') and / or the modified regions (7, 7') and / or the separation regions (8) are formed mainly outside the overlapping region (10).

13. Method according to any one of the preceding claims, characterized in that the focusing lines (6, 6') and / or the modified regions (7, 7') and / or the separation regions (8) are formed in a closed configuration.

14. 14. The method according to claim 1, wherein the laser radiation (12) is introduced into the semiconductor layer (4) from one or more planar faces of the layer stack (1) and / or the laser radiation (12) is introduced into the semiconductor layer (4) from a side of the layer stack (1), in particular into the overlapping region (10).

15. 15. The method according to any one of claims 1 to 14, characterized in that the focusing depth (5a, 5a') of the laser irradiation (12) is adjustable within the thickness of the semiconductor layer (4), preferably within half the thickness of the semiconductor layer and / or preferably within the range of 10 μm to 500 μm below the surface (9) of the semiconductor layer (4).

16. 16. Method according to any one of claims 1 to 15, characterized in that the focusing points (5, 5') are created with an essentially circular or elliptical cross section and / or the modified areas (7, 7') and / or the separation areas (8) are created and / or formed with an essentially circular or elliptical area cross section.

17. 17. The method according to claim 1, wherein in method step B) the laser radiation (12) is introduced in such a way that the seed substrate (2) and / or the separation layer (3) are not at all affected by the laser radiation (12), preferably the seed substrate (2), preferably together with the separation layer (3), is reused after method step B), in particular after a reprocessing step, for the production of at least one further semiconductor layer (4).

18. 18. The method according to any one of claims 1 to 17, characterized in that at least two focusing lines (6, 6') are created in the semiconductor layer (4) at different focusing depths (5a, 5a') offset from one another in the transverse direction (17), in particular the focusing lines (6, 6') are created simultaneously or successively at different focusing depths (5a, 5a').

19. 19. The method according to any one of claims 1 to 18, characterized in that the laser radiation (12) is applied into the layer stack (1) in a direction perpendicular to the surface (9) of the semiconductor layer (4).

20. 20. The method according to any one of claims 1 to 19, characterized in that the laser radiation (12) is applied into the layer stack (1) at an angle of incidence (α) relative to the normal to the surface (9) of the semiconductor layer (4), preferably creating the modified regions (7, 7') and / or the separation regions (8) extending at an angle relative to the thickness direction (13).

21. 21. The method according to any one of claims 1 to 20, characterized in that the semiconductor layer (4) and / or the seed substrate (2) are made of silicon, in particular monocrystalline silicon, and / or the separation layer (3) is made of porous silicon.

22. A method for the manufacture of a semiconductor layer (4), comprising: V1) method steps of preparing a seed substrate (2); V2) a method step of creating a separation layer (3) on said seed substrate (2); V3) a method step of depositing, preferably by epitaxy, the semiconductor layer (4) on the separation layer (3) of the seed substrate (2) to create a layer stack (1) of the seed substrate (2), the separation layer (3) and the semiconductor layer (4); V4) a method step of peeling off said semiconductor layer (4) from said layer stack (1); In a method comprising:

22. A method, characterized in that the detachment of the semiconductor layer (4) is carried out according to the method of any one of claims 1 to 21, in particular that after method step V4), method steps V2) to V4) are carried out multiple times using the seed substrate (2).

23. A system for delaminating a semiconductor layer (4) from a layer stack (1), in particular for carrying out the method according to any one of claims 1 to 21, wherein the layer stack (1) comprises at least a seed substrate (2), a separation layer (3) formed on the seed substrate (2), and the semiconductor layer (4) produced, preferably epitaxially, on the separation layer (3), the system comprising a support for the layer stack (1), a delamination unit preferably for the semiconductor layer (4), and a laser light source (11) for generating laser radiation (12), 1. A system according to claim 1, wherein the laser radiation (12) of the laser light source (11) is focused within the layer stack (1) in such a way that modified regions (7, 7') are created along lateral focusing lines (6, 6') below the surface (9) of the semiconductor layer (4), in which the material of the semiconductor layer (4) is modified and separation regions (8) containing the modified regions (7, 7') can be created, and the semiconductor layer (4) is formed in such a way that it can be peeled off from the layer stack (1) along the focusing lines (6, 6'), in particular by the peeling unit.

24. 1. A semi-finished product, in particular made of silicon, comprising a layer stack (1) of at least a seed substrate (2), a separation layer (3) formed on the seed substrate (2), and a semiconductor layer (4) preferably epitaxially produced on the separation layer (3), the semiconductor layer (4) comprising an overlapping area (10) that is larger than a planar surface of the seed substrate (2) and / or the separation layer (3), the overlapping area (10) preferably being formed so as to at least partially cover one or more side surfaces of the seed substrate (2) and / or the separation layer (3), characterized in that modified areas (7, 7') and preferably separation areas (8) comprising the modified areas (7, 7') are formed below a surface (9) of the semiconductor layer (4) along a converging line (6, 6'), in which the material of the semiconductor layer (4) is modified.

25. the separation region (8) extends to the surface (9) of the separation layer (3) and / or the semiconductor layer (4); and / or 25. Semi-finished product according to claim 24, characterized in that a predetermined breaking point, in particular a crack, is formed through the separation area (8).

26. 26. Semi-finished product according to claim 24 or 25, characterized in that the isolation regions (8) extend in the semiconductor layer (4) at an angle to the thickness direction (13).

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