Method and system for stripping semiconductor layer, and semi-finished product

Abstract

The invention relates to a method for stripping a semiconductor layer (4) from a layer stack (1), comprising the following steps: A) providing a layer stack (1) of at least three layers, a first layer being formed from a seed substrate (2), a second layer being formed from a separation layer (3) formed on the seed substrate (2), and a third layer being formed from a semiconductor layer (4) preferably epitaxially formed on the separation layer (3), and B) stripping 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 source (11) is focused into the semiconductor layer (4), the laser radiation (12) being introduced into the semiconductor layer (4) along a transverse focus line (6, 6 ') in order to form at least one modified region (7, 7') below the surface (9) of the semiconductor layer (4), the material of the semiconductor layer (4) is modified and a separation region (8) may be formed within the semiconductor layer (4) around the modified region (7, 7 ').

Description

[0001] describe

[0002] The present application relates to a method for removing a semiconductor layer according to the preamble of claim 1 and a method for producing a semiconductor layer according to the preamble of claim 22. Furthermore, the present invention relates to a system for removing a semiconductor layer from a layer stack according to the preamble of claim 23 and a semi-finished product according to the preamble of claim 24.

[0003] Economical semiconductor wafers of high electronic quality are required for large-surface electronic components (such as large-surface lighting elements or solar cells) and for mass-produced products such as semiconductor diodes. In these components, the material costs of the semiconductor wafers account for a significant portion of the overall product cost. Several methods are known for producing semiconductor wafers, in which they are processed from a silicon block ("ingot") by slicing. This enables the production of high-quality semiconductor wafers, particularly single-crystalline silicon wafers. However, the production costs are high, also due to material losses during slicing of the silicon block.

[0004] Therefore, alternative methods have been developed in which the semiconductor layer is deposited onto a seed substrate and subsequently detached from the carrier element. The detached semiconductor layer thus becomes the semiconductor wafer used to produce the electronic components.

[0005] A known method involves forming a porous separation layer on a portion of the surface of a seed crystal substrate, followed by epitaxial deposition of a semiconductor layer on the seed crystal substrate. To remove the semiconductor layer from the seed crystal substrate, a laser beam is used for lift-off cutting. This laser beam completely penetrates the semiconductor layer and extends to the separation layer and / or seed crystal substrate, which can damage the seed crystal substrate and degrade its performance.

[0006] However, a drawback has proven to be that portions of the semiconductor layer remain on the seed crystal substrate in the surrounding area, and these residues are difficult to remove. Furthermore, the seed crystal substrate or the separation layer can be damaged by the peeling process, making the seed crystal substrate often unsuitable for reuse in producing another semiconductor layer or requiring laborious reprocessing, thus limiting its reusability.

[0007] For example, DE 10 2015 118 042 A1 discloses an optimization solution for a conventional method for producing a semiconductor layer. Prior to depositing the semiconductor layer, a separation layer is formed over the entire surface of at least one processed surface of a seed crystal substrate. The semiconductor layer is then deposited in an overlapping manner on the processed surface and at least one side surface of the seed crystal substrate. Prior to peeling the semiconductor layer from the seed crystal substrate, the overlapping region of the semiconductor layer is removed.

[0008] Through overlapping deposition, the semiconductor layer can be peeled off from the separation layer or seed substrate in the desired dimensions. To ensure the reusability of the seed substrate, it is important that no residue of the semiconductor layer remains on the peeled seed substrate. To ensure this, the seed substrate is edge-treated after peeling off the overlapping area and a few microns of thickness are removed, so that the lateral dimensions of the seed substrate decrease after each use. Once the seed substrate's dimensions fall below a minimum dimension, it can no longer be used as a seed substrate for producing additional semiconductor layers.

[0009] For industrial applications, it is essential to reduce the production costs of semiconductor layers, especially through the reusability of seed substrates. At the same time, the stripping process is often very slow because the entire layer must be removed.

[0010] It is therefore an object of the present invention to provide a simple and rapid method for detaching a semiconductor layer from a seed substrate, wherein the reusability of the seed substrate is ensured.

[0011] These and other 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 semifinished product according to claim 24.

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

[0013] The method for stripping a semiconductor layer according to the invention is provided in particular by the implementation of the system for stripping a semiconductor layer according to the invention. The system for stripping a semiconductor layer according to the invention is provided in particular for implementing the method for stripping a semiconductor layer according to the invention.

[0014] The method for stripping a semiconductor layer according to the present invention comprises the following steps:

[0015] A) providing 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 preferably epitaxially formed on the separation layer, and

[0016] B) Peeling the semiconductor layer off the layer stack.

[0017] The invention is characterized in that, before and / or during method step B), laser radiation from a laser source is focused into the semiconductor layer, wherein the laser radiation is introduced into the semiconductor layer along a transverse focus line to form at least one modification region below the surface of the semiconductor layer, wherein in the modification region the material of the semiconductor layer is modified and a separation region can be formed around the modification region in the semiconductor layer.

[0018] By introducing laser radiation, modified or separation regions are easily formed within the semiconductor layer, which facilitates the separation of the semiconductor layer from the layer stack or separation layer. The laser radiation can be focused specifically into the semiconductor layer without negatively affecting or altering the properties of the separation layer and / or the seed substrate. Consequently, after the semiconductor layer has been separated, the seed substrate and / or the separation layer can be easily reused to produce further semiconductor layers.

[0019] According to the invention, the semiconductor layers are edge-processed within the layer stack without requiring direct edge processing of the layer stack itself, thereby avoiding a reduction in the dimensions of the layer stack (in particular its longitudinal extension). Since no areas of the layer stack are directly removed (such as during sawing or laser edge processing of the entire layer stack), the release of particles is reduced and the semiconductor layers are less contaminated.

[0020] In the modification region, the material of the semiconductor layer is modified. The modification alters the semiconductor material, particularly its crystal structure. To achieve this, the material in the semiconductor layer is briefly melted or evaporated, and the melted material recrystallizes or solidifies. Thus, according to the present invention, laser radiation can be introduced into an epitaxial, preferably monocrystalline, silicon semiconductor layer to form a modification region, for example, made of polycrystalline silicon or amorphous silicon. According to the present invention, a separation region is formed around the modification region. The modification region can also be identical to the separation region.

[0021] The seed substrate is preferably a crystalline material, in particular a single-crystalline material, more preferably a semiconductor material. Alternatively, the seed substrate can also be a polycrystalline material or an amorphous material. The seed substrate can in particular be a carrier element which, in addition to the actual seed substrate, further comprises other regions or layers.

[0022] A preferred embodiment is characterized in that the focal line is formed by locally introducing the laser radiation at a plurality of focus points at the focal depth, and at least one modified region is formed around each individual focus point. Thus, the laser radiation only needs to be introduced at individual points within the semiconductor layer. The focal depth depends, in particular, on the thickness of the semiconductor layer, wherein the formation of the modified regions around the focus points must be taken into account when adjusting the focal depth. Preferably, the separation layers, in particular the seed substrate, should not be modified so that they can be reused for producing further semiconductor layers.

[0023] Preferably, the modified regions and / or the separated regions formed by the modified regions around the focal point overlap each other in a lateral direction and form a continuous region. The overlapping and continuous regions along the focal line ensure clean peeling of the semiconductor layer.

[0024] In a preferred embodiment, the layer stack is continuously moved relative to the laser source, in particular at a constant speed, to form the focal point. Preferably, the layer stack is moved relative to a stationary laser source. Alternatively or preferably in addition, corresponding optical elements for the laser irradiation can be moved instead of or in addition to the movement of the laser source, so that the focal point can be introduced into the semiconductor layer along the focal line.

[0025] In a further preferred embodiment, the layer stack is intermittently moved relative to the laser source to form the focal point, preferably the layer stack is moved relative to a stationary laser source. Alternatively or preferably additionally, instead of or in addition to moving the laser source, corresponding optical elements can also be moved, so that a focal point can be introduced into the semiconductor layer along the focal line by the laser radiation.

[0026] Alternatively, the laser source or the optical element for the laser radiation can also be moved relative to the stationary layer stack.

[0027] 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. In this way, irregularities and / or surface roughness can be compensated.

[0028] An embodiment of the method according to the invention is characterized in that the laser radiation is pulsed. Pulsed laser radiation allows the intentional and thus limited introduction of individual focal points into the semiconductor layer.

[0029] Preferably, the pulsed laser radiation is short pulses in the nanosecond range. Particularly preferably, the pulse length of these short pulses is in the range of 1 nanosecond to 150 nanoseconds, preferably in the range of 5 nanoseconds to 100 nanoseconds, and particularly preferably in the range of 10 nanoseconds to 30 nanoseconds. The short pulses ensure that sufficient energy or a sufficiently high energy density is provided to achieve localized melting of the semiconductor layer around the focal point, thereby forming the modified region.

[0030] Alternatively or additionally, the pulsed laser radiation is preferably an ultrashort pulse in the picosecond or femtosecond range. Ultrashort pulses ensure that the modified region can be more strictly limited in its extension and in particular can be smaller, so that the semiconductor layer as a whole is less affected.

[0031] Preferably, pulsed laser radiation only needs to be in the lower medium power range of laser radiation, for example 100 mW to 10 W, in order to form the modified area.

[0032] A further preferred embodiment is characterized in that a plurality of focal points are formed within the semiconductor layer at different focal depths, arranged one above the other in the thickness direction. Alternatively or preferably in addition, a plurality of modified regions are formed vertically one above the other in the thickness direction. With thicker semiconductor layers, in particular, it is possible to form a corresponding separation region extending in the thickness direction, thereby ensuring a clean separation of the semiconductor layer. Furthermore, the plurality of focal points ensures that the perimeter and extension of the modified region are minimized relative to the separation region formed. Consequently, due to the presence of a plurality of smaller modified regions, the semiconductor layer is modified to a lower degree.

[0033] Multiple focal points arranged one above the other in the thickness direction can be introduced by a plurality of sequential processing steps. For example, a focal point on a first focal line is first formed, and in a second step, a focal point on a second focal line is formed. These focal points are spaced apart from one another in the thickness direction and arranged vertically one above the other in the thickness direction. Alternatively, vertically superimposed focal points can also be formed sequentially or simultaneously. This can be achieved, for example, by using appropriate optical elements in the optical path of the laser radiation. Thus, at least two mutually parallel focal lines are formed.

[0034] Alternatively or preferably in addition, a plurality of focal spots are formed simultaneously side by side in the lateral direction. By forming a plurality of focal spots simultaneously, the lift-off process of 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. This ensures, on the one hand, that the material of the semiconductor layer is also modified in the modification region. In particular, by correspondingly introducing multiple pulsed laser radiation, the extent of the modification region can also be influenced so that it has the desired extent and, if appropriate, shape.

[0036] A preferred embodiment is characterized in that the semiconductor layer is substantially transparent to the wavelength of the laser radiation. This ensures that the laser radiation is purposefully focused to a focal point within the semiconductor layer without initially being significantly absorbed upon penetrating the semiconductor layer and / or other layers in the layer stack. 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 radiation 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, most preferably in the range of 1000 nm to 1350 nm.

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

[0039] Advantageously, the separation region is formed within the semiconductor layer, so that detachment of the semiconductor layer from the layer stack can be facilitated.

[0040] Preferably, the separation region extends to the surface of the separation layer and / or the semiconductor layer. The 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 layer. The extension of the separation region to the surface of the semiconductor layer also ensures that it can be optically controlled, for example, by a camera. In the event of deviations from a specific contour or deformity, the laser radiation used to form the focus can be modified to influence or change the optically visible portion of the separation region or surface.

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

[0042] Alternatively or preferably in addition, laser radiation is introduced into the layer stack along a focal line, in such a way that the semiconductor layer is completely detached from the rest of the layer stack (i.e., the remaining stack) along the separation region. Complete detachment of the semiconductor layer from the layer stack is thus achieved solely by laser radiation, which allows the semiconductor layer to be easily detached using a detachment tool such as a gripper.

[0043] In a preferred embodiment, the semiconductor layer includes an overlapping region that is larger than the planar side of the seed substrate and / or the separation layer, and the overlapping region preferably at least partially covers one or more sides of the seed substrate and / or the separation layer. Therefore, the extension range of the semiconductor layer is larger than the planar side of the separation layer and overlaps on the side region. The overlapping region can also extend along the side of the seed substrate, or when the separation layer is deposited along the seed substrate, the overlapping region can extend along the side of the separation layer. The overlapping region may be a product of the process, and since it is formed in the peripheral area, its crystalline quality is slightly worse than that of the actual semiconductor layer, for example, due to defects or dislocations. Through the overlapping region, a semiconductor layer that is substantially equivalent to the area of ​​the seed substrate can be formed. In addition, the overlapping region helps to achieve uniformity in the thickness of the semiconductor layer.

[0044] The quality of these overlapping areas may be lower than that of the semiconductor layer material and may include, for example, defects or dislocations. However, this helps to achieve an application-relevant semiconductor layer that is separated from these areas and has a higher grade and better quality.

[0045] Advantageously, the overlapping region is made of the same material as the semiconductor layer. Thus, the overlapping region is automatically formed during the production of the semiconductor layer and thus forms part of the semiconductor layer.

[0046] Alternatively or preferably in addition, in method step B), the overlapping region is stripped from the semiconductor layer and / or layer stack. This overlapping region would hinder further use of the seed substrate in semiconductor layer production. Therefore, stripping the overlapping region improves the reusability of the seed substrate. Furthermore, this ensures that all semiconductor layers are produced under virtually identical starting conditions, in particular with respect to the shape and configuration of the seed substrate, thereby facilitating mass production.

[0047] A preferred embodiment of the method is characterized in that the focus line and / or the modified region and / or the separation region are at least partially formed in the overlapping region. In particular, when the overlapping region surrounds the side of the seed crystal substrate or the separation layer, a complete peeling can be achieved along the focus line.

[0048] It is further preferred that the focus line and / or the modified region and / or the separation region are mainly formed outside the overlapping region. This ensures that the overlapping region can be cleanly and completely peeled off from the actual semiconductor layer for subsequent processing.

[0049] In a preferred embodiment, the focus line and / or the modification region and / or the separation region are formed in a closed configuration. This ensures that the semiconductor layer can be purposefully and cleanly separated from the layer stack. In particular, the closed focus line forms a defined region that can subsequently be separated from the layer stack as a semiconductor layer.

[0050] An advantageous embodiment is characterized in that the laser radiation is introduced into the semiconductor layer from one or more planar sides of the layer stack. Thus, the focus can be introduced into the semiconductor layer in a targeted manner, wherein only a relative movement between the layer stack and the laser radiation is required.

[0051] Preferably, the laser radiation can also be introduced into the semiconductor layer at multiple points simultaneously. For example, the laser radiation can be split by means of optical elements so that corresponding modification regions are formed along parallel focus lines on opposite sides of the layer stack.

[0052] Alternatively or preferably in addition, the laser radiation is introduced into the semiconductor layer from the side of the layer stack, in particular into the overlapping region. Thus, the semiconductor layer (including at least part of the overlapping region) can be selectively separated from the separation layer or seed substrate.

[0053] In a further preferred embodiment, the focal depth of the laser radiation is adjustable within the thickness of the semiconductor layer in the thickness direction. Thus, the position of the focal point or focal line and the modification area within the semiconductor layer is adjustable and can be adapted and varied according to the respective requirements.

[0054] 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 microns to 500 microns below the surface of the semiconductor layer. Preferably, the depth of focus is selected so that it is approximately in the middle of the thickness of the semiconductor layer.

[0055] In yet another embodiment of the method according to the invention, the focal point is formed with a circular or elliptical cross-section. The cross-section can particularly influence the formation of the modified region and its configuration or extent. The cross-section of the focal point can be influenced and varied, preferably by using various optical elements in the beam path of the laser radiation.

[0056] Alternatively or preferably in addition, the modification region and / or separation region is formed and / or created to have a substantially circular or elliptical region cross section. The region cross section, and thus the overall formation of the modification region, depends primarily on the cross section and configuration of the focal point located within the modification region and the power of the laser radiation applied to the semiconductor layer. Absorption of the laser radiation and heating of the semiconductor material around the focal point leads to changes in the absorption properties of the semiconductor layer (free carrier absorption), which, for example, results in increased absorption of the laser radiation at the focal point and the formation of an elongated modification region in the thickness direction. In particular, a longitudinal extension is formed on the side of the modification region facing the laser radiation. The formation of the modification region also depends on the crystal structure of the semiconductor layer around the focal point region.

[0057] An advantageous embodiment is characterized in that, in method step B), the laser radiation is introduced in such a way that the seed substrate and / or the separation layer are not affected in any way by the laser radiation. The laser radiation can be adjusted, in particular, in such a way that modifications occur only in the semiconductor layer (and optionally also in the overlapping region).

[0058] Preferably, after method step B), in particular after a post-treatment step, the seed substrate (preferably together with the separation layer) can be used for the production of at least one further semiconductor layer.

[0059] In a preferred embodiment, at least two focal lines are formed in the semiconductor layer at different focal depths that are offset from one another in the lateral direction. In particular, the focal lines are formed simultaneously or sequentially at different focal depths. This results in the formation of two modified regions arranged one above the other in the lateral direction, which result in the formation of a separation region extending at an angle to the thickness direction.

[0060] A further preferred embodiment is characterized in that the laser radiation is incident on the layer stack in a direction perpendicular to the surface of the semiconductor layer. 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 region can be influenced by the radiation shape of the laser radiation when it is incident on the semiconductor layer or the layer stack. In particular, the incident angle of the laser radiation leads to the formation of a separation region which extends obliquely in the thickness direction. Preferably, the angle of incidence is in the range of ±10° to ±45°, in particular ±30°.

[0061] Advantageously, the semiconductor layer and / or the seed crystal substrate is silicon, in particular single-crystal silicon. However, the present invention is not limited thereto. The semiconductor layer can be any semiconductor, in particular a crystalline material. In particular, the semiconductor layer can also be germanium, or any III-V semiconductor (such as gallium nitride or gallium arsenide), or a semiconductor compound such as silicon carbide.

[0062] Alternatively or preferably in addition, the separation layer is porous silicon. Alternatively, the separation layer can be formed from any material which, on the one hand, can serve as a good seed layer for the semiconductor layer and / or, on the other hand, can facilitate the peeling off of the semiconductor layer produced thereon.

[0063] The above object can be further achieved by a method for manufacturing a semiconductor layer, the method comprising the following steps:

[0064] V1) providing a seed crystal substrate;

[0065] V2) forming a separation layer on the seed crystal substrate;

[0066] V3) depositing a semiconductor layer on the separation layer of the seed substrate, preferably by epitaxy, to form a layer stack of seed substrate, separation layer and semiconductor layer; and

[0067] V4) Peeling the semiconductor layer off the layer stack.

[0068] The method for producing a semiconductor layer is characterized in that the stripping of the semiconductor layer is performed by the above-mentioned method for stripping a semiconductor layer or any advantageous embodiment thereof. In particular, after step V4), steps V2) to V4) are performed multiple times on the seed crystal substrate.

[0069] The above-mentioned object is further achieved by a system for peeling a semiconductor layer from a layer stack, wherein the layer stack comprises at least a seed substrate, a separation layer formed on the seed substrate and a semiconductor layer preferably formed epitaxially on the separation layer, wherein the system comprises a support for the layer stack, preferably a peeling unit for the semiconductor layer and a laser source for generating laser radiation.

[0070] The system is preferably configured for performing the above-described method for stripping a semiconductor layer or any advantageous embodiment thereof.

[0071] The key to the system is that the laser radiation of the laser source is focused into the layer stack in such a way that a modification region is formed below the surface of the semiconductor layer along a lateral focus line, in which modification region the material of the semiconductor layer is modified, and preferably a separation region including the modification region can be formed and the semiconductor layer is formed so that it can be peeled off from the layer stack along the focus line, in particular by a peeling unit.

[0072] The above-mentioned purpose is further achieved by a semi-finished product, which includes at least a seed substrate, a separation layer formed on the seed substrate, and a layer stack of a semiconductor layer preferably formed epitaxially on the separation layer, specifically a semi-finished product formed of silicon, wherein the semiconductor layer preferably includes an overlapping area, which is larger than the flat surface of the seed substrate and / or the separation layer, and the overlapping area is preferably formed to at least partially cover one or more sides of the seed substrate and / or the separation layer.

[0073] The semi-finished product according to the invention is characterized in that a modification region is formed below the surface of the semiconductor layer along the focus line, and preferably a separation region is formed including the modification region, wherein the material of the semiconductor layer is modified within the modification region.

[0074] In an advantageous embodiment, the separation region extends to the surface of the separation layer and / or the semiconductor layer. This therefore ensures that the semiconductor layer can be easily peeled off from the layer stack or the separation layer.

[0075] Alternatively or preferably additionally, a predetermined breaking point, in particular a crack, is formed by the separation region.

[0076] In a preferred embodiment, the separation region extends within the semiconductor layer at an angle to the thickness direction. By extending the separation region at an angle to the thickness direction, peeling the semiconductor layer from the remaining layer stack can be simplified.

[0077] Other advantageous features and embodiments will be described below in conjunction with exemplary embodiments and accompanying drawings. In the accompanying drawings:

[0078] Figure 1a ) shows a schematic cross-sectional view of a layer stack using the method according to the invention;

[0079] Figure 1b ) shows Figure 1a ) Middle stacked perspective view;

[0080] Figure 1c ) shows a schematic cross-sectional view of a layer stack using the method according to the invention in another embodiment;

[0081] Figure 2a )and Figure 2b ) are schematic detail diagrams showing various embodiments of focusing points of different shapes;

[0082] Figure 3a ) and 3b) show the use of the method according to the present invention at different time points Figure 1a ) a top view of the layer stack in;

[0083] Figure 4a ) shows a schematic cross-sectional view of a layer stack using an alternative embodiment of the method according to the invention;

[0084] Figure 4b ) shows a schematic cross-sectional view during the semiconductor layer lift-off;

[0085] Figure 5 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention;

[0086] Figure 6 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention;

[0087] Figure 7 shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention;

[0088] Figure 8a ) and 8b) each show a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the present invention;

[0089] Figure 8c ) shows another schematic cross-sectional view during lift-off of the semiconductor layer after forming the obliquely extending separation region;

[0090] Figure 8d ) and 8e) 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;

[0091] Figure 9a ) shows a schematic cross-sectional view of a layer stack using yet another embodiment of the method according to the invention; and

[0092] Figure 9b ) shows that in the formation Figure 9a ) during the peeling of the semiconductor layer after the separation region in FIG.

[0093] All drawings are schematic diagrams and are not drawn to scale. In the various drawings, the same reference numerals refer to the same or equivalent elements.

[0094] Figure 1a )and Figure 1c ) each show a schematic cross-sectional view of the layer stack 1, and Figure 1b ) shows Figure 1a ) is a perspective view of a layer stack 1 in FIG. The layer stack 1 comprises three layers, which are arranged one above the other in the thickness direction 13. During the production of the layer stack 1, a seed substrate 2 is first provided, which in the present case is made of silicon. By means of a porosification process (for example, methods known from DE 10 2015 121 636 A1 or DE 10 2018 111 858 A1), a separation layer 3 is formed on the seed substrate 2, which covers at least one planar side of the seed substrate 2. In the present case, the separation layer 3 covers the planar side 2a at the top of the seed substrate 2 in the thickness direction, and also covers the side areas of the seed substrate 2. In addition, the region of the bottom planar side 2b of the seed substrate 2 in the thickness direction can also be made porous in the region where the separation layer 3 is adjacent to the side areas. Therefore, the separation layer 3 is also partially formed on the bottom planar side 2b of the seed substrate 2.

[0095] After forming the separation layer 3, a semiconductor layer 4 is formed on the separation layer 3 by epitaxy. The semiconductor layer 4 completely covers the side of the separation layer 3 facing away from the top plane 2a of the seed crystal substrate 2 and has an overlapping region 10 in the lateral peripheral region. This method for forming a semiconductor layer is described in DE 10 2019 130 745 A1.

[0096] Epitaxial deposition of the material of the semiconductor layer 4 also takes place in the overlapping region 10 . In the present case, this is also silicon. Apart from the bottom plane 2 b in the thickness direction 13 , the seed substrate 2 is completely surrounded by the semiconductor layer 4 and the overlapping region 10 .

[0097] In order to be able to peel the epitaxially produced semiconductor layer 4 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 plurality of locations for forming individual focal points 5, which are located within the semiconductor layer 4. The focal points 5 are formed at a focal depth 5a along a transverse focal line 6 within the semiconductor layer 4. The focal depth 5a depends in particular on the thickness of the semiconductor layer 4 and in the present case lies in the range of half the thickness of the semiconductor layer, for example approximately 70 micrometers.

[0098] A pulsed laser is used as the laser source 11, since this results in a corresponding formation of the focus 5. The laser radiation 12 consists of short pulses, the pulse length of which is in the range of 5 nanoseconds to 30 nanoseconds. In the present case, the wavelength of the laser radiation 12 is approximately 1064 nanometers or approximately 1342 nanometers.

[0099] The laser radiation 12 of the laser source 11 is guided and focused by an optical element 15. Figure 1a ), 1b) and 1c) each show only one optical element 15, which in the present case is in the form of an optical lens. However, a reflector, a partially transmitting mirror, a diffractive optical element or a stop (aperture) can also be used as the optical element 15. Figure 1a ) and 1b), in order to focus the laser radiation 12 into the semiconductor layer 4, a laser source 11 and an optical element 15 are arranged above the surface 9 of the semiconductor layer 4 in the thickness direction 13. The laser radiation 12 is introduced into the semiconductor layer 4 essentially in a direction perpendicular to the surface 9 of the semiconductor layer 4.

[0100] Figure 1c ) shows another embodiment of the method according to the invention, in which the laser radiation 12 is introduced into the semiconductor layer 4 from the bottom side 2b of the seed substrate 2 to form the focus 5 at the focus depth 5a. Again, the laser radiation 12 is focused into the layer stack 1 essentially perpendicularly to 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 way of injecting the laser radiation 12 into the semiconductor layer 4 is also possible. In addition, Figure 1c ), the separation layer 3 and the overlapping region 10 are only partially deposited along the side surfaces of the seed substrate 2 .

[0101] To form the individual focal spots 5 in the semiconductor layer 4, in the present case, the layer stack 1 is moved relative to the laser source 11, or in the present case, the laser radiation 12 is essentially arranged or positioned stationary in the lateral direction. The stationary arrangement of the laser radiation 12 can be provided, for example, by using stationary optical elements 15, which focus the laser radiation 12 into the semiconductor layer 4 of the layer stack 1. During the uniform movement of the layer stack 1, the laser radiation 12 is radiated into the semiconductor layer 4 in the form of pulses and thus forms the individual focal spots 5. The lateral spacing of the focal spots 5 depends on various factors, in particular the speed of the movement of the layer stack 1 relative to the laser radiation 12 or the laser source 11, and the pulse repetition frequency of the laser source 11. By selecting the corresponding parameters, the spacing of the focal spots 5 can be adjusted to ultimately achieve the removal of the semiconductor layer 4. The short pulse length of the laser radiation 12 helps to accelerate the formation of the focal line 6, so that the semiconductor layer 4 can then be removed quickly.

[0102] In the present case, the focus line 6 is formed in the semiconductor layer 4 so as to be completely closed, so that the semiconductor layer 4 to be removed is finally formed, which is removed from the layer stack 1 by the removal unit and is subsequently used for further processing, for example, for the production of solar cells and semiconductor components. The focus line 6 formed in a closed configuration defines a region within the focus line 6 that substantially corresponds to the semiconductor layer 4 to be removed.

[0103] A modification region 7 is formed around each of the focal points 5, in which the material of the semiconductor layer 4 (in the present case, silicon) is modified. The modification is a change in the crystal structure of the semiconductor layer 4, which is caused by the introduction of laser radiation 12 around the focal points 5. The laser radiation 12 focused into the semiconductor layer 4 causes at least temporary melting, and in some cases, possible evaporation, of the material of the semiconductor layer 4 at the focal points 5 and in the modification region 7. During solidification of the molten material, it assumes a different crystal structure, which differs significantly, and in particular, noticeably, from the crystal structure of the remainder of the semiconductor layer 4 around the modification region 7. In the present case, since the semiconductor layer 4 is crystalline silicon, the introduction of laser radiation 12 into the semiconductor layer 4 causes it to be converted into polycrystalline silicon and / or partially amorphous silicon within the modification region 7.

[0104] Figure 1b ) shows Figure 1a ). The individual focal points 5 are essentially spherical in shape and are introduced into the semiconductor layer 4 along a focal line 6. A modified region 7 is formed around the individual focal points 5, which is elongated in the thickness direction 13, with this elongated extension being primarily located on the side of the focal point 5 facing the laser radiation 12.

[0105] The shape and configuration of both the focus 5 and the modified region 7 are variable and depend 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 the absorption coefficient), which are generally also temperature- and time-dependent. Figure 2a )and Figure 2b ) shows two embodiments of the focal point 5 and the modified area 7 formed around the focal point 5. Figure 2a ), the focal point 5 is formed to have a substantially circular cross-section. The modified region 7 surrounding the focal point 5 has an elliptical cross-section, with its major axis substantially parallel to the thickness direction 13. The focal point 5 itself forms only a small portion of the modified region 7. The configuration of the modified region 7, in particular its shape and size, is also affected by the crystal quality of the semiconductor layer 4, the heating of the semiconductor layer 4, and the resulting changes in the optical properties.

[0106] Figure 2b) shows another embodiment with respect to the focal point 5 and the modified region 7. By modifying the laser radiation 12 during focusing of the laser radiation 12 onto the semiconductor layer 4 (for example, by using other and / or different optical elements 15, in particular optical lenses, in the beam path of the laser radiation 12), the focal point 5 can also have an elliptical cross section, wherein its main axis is also substantially parallel to the thickness direction 13 or extends along the thickness direction 13. In this case, the modified region 7 is similar in shape to the focal point 5 and also forms an ellipse around the focal point 5, with its main axis being substantially parallel to the thickness direction 13. Figure 2a )compared to, Figure 2b ) is formed significantly larger or longer, wherein the elongated extension is mainly located on the side facing the laser radiation 12. The elongated configuration of the focus point 5 in the thickness direction 13 can be achieved in various ways, including focusing the partial beams 12', 12" of the laser radiation 12 at different focus depths, wherein the focus points 5 for the partial beams 12', 12" of the laser radiation 12 can be located in close proximity.

[0107] The focal point 5 may generally have any particular cross section, in particular the focal point 5 may also have an elliptical cross section, the main axis of which extends substantially in the transverse direction 14 or at an angle to the thickness direction 13 and / or the transverse direction 14 .

[0108] In the present case, the individual focus points 5 are formed along the focus line 6, so that Figure 1a ), 1b) and 1c), the modified regions 7 of the focal point 5 overlap with each other. Therefore, a continuous region is formed by the overlap of the individual modified regions 7, in which the material of the semiconductor layer 4 is modified.

[0109] During the formation of modified region 7 around focal point 5, another region, referred to as separation region 8, is formed around modified region 7. Although the material of semiconductor layer 4 within separation region 8 is not modified, the formation of modified region 7 within semiconductor layer 4 induces stress in semiconductor layer 4 around modified region 7. This stress results in the formation of a predetermined breaking point, serving as separation region 8, within semiconductor layer 4 around modified region 7. In the present case, separation region 8 is formed by a crack, which, as shown in FIG1 , extends within semiconductor layer 4. In the exemplary embodiment shown, separation region 8 extends substantially along lateral direction 14 and has a smaller width in lateral direction 17, which is perpendicular to thickness direction 13 and lateral direction 14 and, in the present case, extends into the image plane. Semiconductor layer 4 is delaminated from layer stack 1 along separation region 8.

[0110] By shifting the layer stack 1 relative to the laser source 11 , the focal line 6 is introduced completely in the lateral direction 14 along the extension and dimensions of the semiconductor substrate 4 . Consequently, a focal point 5 and a corresponding modification region 7 are also formed in the overlap region 10 .

[0111] like Figure 3a ) and 3 b), the focus line 6 and the separation region 8 formed along the focus line 6 extend primarily within the semiconductor layer 4 and are relatively close to the overlap region 10. In the present case, the separation region 8, which is formed by a crack extending to the surface 9 of the semiconductor layer 4, can be seen from the top view (and is shown accordingly in the figure). The focus line 6 or the separation region 8 "penetrates" the overlap region 10 in the peripheral region of the semiconductor layer 4 only in the lateral direction 14, to the end of the layer stack 1. A large part of the focus line 6, and thus a large part of the modification region 7 and the separation region 8, extend within the semiconductor layer 4. This is to ensure that the semiconductor layer 4 ′ to be peeled off has a high grade and quality. In the peripheral region of the semiconductor layer 4, and in particular in the overlap region 10, offsets and crystallization defects can occur, which have a negative impact on the grade and quality of the semiconductor layer 4. In the case where the overlapping region 10 of the semiconductor layer 4 is not removed, or is not peeled off or modified in a peelable manner from the rest of the semiconductor layer 4 as suggested in the method of the present application, the overlapping region 10 may also hinder the mechanical peeling of the semiconductor layer 4. In order to avoid these defects from negatively affecting the semiconductor components subsequently manufactured from the semiconductor layer 4, the focus line 6 (or the separation region 8) is mainly formed outside the peripheral area of ​​the semiconductor layer 4 and at a certain distance from the overlapping region 10.

[0112] In order to finally peel the semiconductor layer 4 from the layer stack 1 , the focusing line 6 is introduced completely into the layer stack 1 and thus into the semiconductor layer 4 in a closed configuration, as shown in FIG. Figure 3b ). This is to ensure that a semiconductor layer 4' to be peeled off is formed in the semiconductor layer 4 of good quality, which semiconductor layer 4' can also be completely peeled off from the layer stack 1. For this purpose, a focus line 6 with a focus point 5 and a resulting separation region 8 are first formed along the side surface, so that the focus line 6 or the separation region 8 shown is formed in a closed configuration. In addition, before peeling off the semiconductor layer 4', laser radiation 11 is introduced into the side surface at a certain angle to form a chamfer. In particular, by chamfering the corners of the semiconductor layer 4', the stability of the semiconductor layer 4' can be increased. The size of the semiconductor layer 4' to be peeled off is slightly smaller than the semiconductor layer 4, and this size is determined by the extension of the focus line 6 in the semiconductor layer 4.

[0113] Figure 4a) shows another embodiment of the method according to the invention, in which laser radiation 12 is introduced into the semiconductor layer 4 at two points simultaneously. Consequently, two focal points 5 and corresponding modified regions 7 are formed simultaneously or at short intervals within the pulse repetition frequency range, along two essentially parallel focal lines 6, which in the present case extend into the image plane. The essentially simultaneous formation of the two focal points 5 or modified regions 7 again significantly accelerates the exfoliation or release process of the semiconductor layer 4.

[0114] In the current situation, if Figure 4a ) shows that the formation of the focus points 5 for forming the respective focus lines 6 is performed in opposite regions of the layer stack 1. The lateral direction 14 along which the focus points 5 are formed extends to Figure 4a ). In order to completely peel off the semiconductor layer 4, after forming two parallel focus lines 6 and corresponding modification regions 7 and separation regions 8 along the side surfaces of the layer stack 1, it is only necessary to rotate the layer stack 1 by approximately 90° so that the focus lines 6 and corresponding modification regions 7 and separation regions 8 can then be formed along the remaining two sides of the layer stack 1.

[0115] Figure 4b ) now shows a method step in which the semiconductor layer 4' is peeled off from the layer stack 1 by means of a peeling unit. As described above, after the separation region 8 has been completely formed, the semiconductor layer 4' is Figure 4b ), in which case only the semiconductor layer 4 ′, preferably only part of the separating layer 3 , is removed from the layer stack 1 , while the region surrounding the overlapping region 10 initially remains with the rest of the remaining stack 16 .

[0116] In order to ensure that the seed substrate 2 can be reused for further production of semiconductor layers 4, it is advantageous to remove not only the semiconductor layer 4 ′ to be stripped off, but also the remaining parts of the semiconductor layer 4 and the overlapping region 10 from the remaining stack 16. These remaining parts are preferably also stripped off during the stripping of the semiconductor layer 4 from the layer stack 1. The modified region 7 or separation region 8 is formed in such a way that, when the semiconductor layer 4 is stripped off, the remaining parts, such as the overlapping region 10 and the unstripped parts of the semiconductor layer 4 adjacent to the overlapping region 10, can also be stripped off from the layer stack 1.

[0117] exist Figure 4b), in a method step following the state shown in FIG. , the region surrounding the overlap region 10 can be removed from the remaining stack 16, so that the original seed substrate 2 and, in this case, a portion of the separation layer 3 can be used to produce another semiconductor layer 4. Alternatively, the semiconductor layer 4' can be peeled off from the layer stack 1 in such a way that, while peeling off the semiconductor layer 4', the peripheral region surrounding the overlap region 10 is also removed from the layer stack 1. Thus, the peeling off of the semiconductor layer 4' and the peripheral region is performed in one step.

[0118] Subsequently, the complete separation layer 3 is retained on the seed crystal substrate 2, or only a portion of the separation layer 3 is retained as appropriate, such as Figure 4b ). The seed substrate 2 can then be used in a subsequent process for producing further semiconductor layers 4, wherein, as the case may be, the separation layer 3 on the seed substrate 2 can be reprocessed or a new separation layer 3 can be produced on the seed substrate 2 to produce the epitaxial semiconductor layer 4. However, the method according to the invention does not cause any damage to the seed substrate 2 and does not significantly change its dimensions. On the contrary, the same high-quality seed substrate 2 remains, its dimensions essentially intact. By focusing the laser radiation 12 into the semiconductor layer 4, the seed substrate 2 does not undergo any modification, and its peripheral areas are not trimmed due to complete penetration of the laser through the layer stack 1 or by sawing, etc.

[0119] like Figure 4a ), simultaneous introduction of laser radiation 12 at two focal points 5 at a distance from one another can be achieved in a variety of ways. On the one hand, the laser radiation 12 from the laser source 11 can be split by one or more optical elements 15 and then directed to the desired location of use by further corresponding optical elements 15. This flexible approach, dependent on the configuration of the optical elements 15, allows simultaneous introduction of laser radiation 12 at different focal points 5. However, the optical path of the laser radiation 12 must always be checked to ensure that it reaches the predetermined focal point 5.

[0120] Alternatively, a plurality of laser sources 11 can be used to generate the laser radiation 12, wherein the laser radiation 12 of one laser source 11 is used to form one focus 5. Thus, a plurality of laser sources 11 are required, which can however be used individually in a fast and flexible manner.

[0121] The position of the focal point 5 and the formation of the modified region 7 can also be determined by adjusting the laser radiation 12. Depending on the thickness of the semiconductor layer 4 in the thickness direction 13, the focal point 5 can thus be formed closer to or further away from the surface 9 of the semiconductor layer 4. For this purpose, the focal point 5 is introduced at a focal depth 5a. However, care must be taken to form the focal point 5 within the semiconductor layer 4 and not within the separation layer 3. Therefore, the focal depth 5a is always smaller than the thickness of the semiconductor layer 4, otherwise modifications or changes could occur in the separation layer 3 and, in particular, in the crystalline substrate 2.

[0122] In the present case, the formation of the focus 5 is caused by short pulses of the pulsed laser radiation 12. Alternatively, however, a plurality of short pulses can also be introduced successively at the focus 5 and thereby influence in particular the configuration of the modification region 7 around the respective focus 5.

[0123] In the following Figures 5 to 7 In FIG. 4 , further embodiments regarding the formation of the focus point 5 , the focus line 6 , the modification area 7 and the separation area 8 are shown.

[0124] Figure 5 Another embodiment of the method according to the invention is shown, in which the individual focal points 5 are formed at a greater distance from one another in the lateral direction 14. Due to the spacing between the focal points 5, the modified regions 7 formed around each focal point 5 do not overlap with one another. However, there is still overlap, but only with the separation regions 8 formed around each modified region 7. Consequently, the respective separation regions 8 form a continuous region along which the semiconductor layer 4 will subsequently be stripped or released.

[0125] like Figure 5 As shown, the individual modified regions 7 as well as the continuous separation regions 8 are located completely within the semiconductor layer 4. Consequently, in the thickness direction 13, the separation regions 8 extend neither to the separation layer 3 nor to the surface 9 of the semiconductor layer 4. However, this is not absolutely necessary, since for the detachment of the semiconductor layer 4 it is sufficient if the corresponding separation regions 8 are formed within the semiconductor layer 4, for example at the predetermined breaking point in the present case.

[0126] Figure 6 Shown with Figure 5 Another embodiment of the invention mainly differs from the configuration of the separation area 8. Figure 5 Compared to the exemplary embodiment, Figure 6 The separation region 8 is formed in a manner extending to the surface 9 of the semiconductor layer 4. Since the focus point 5 is at a specific focus depth 5a and is Figure 5 The difference is that in Figure 6The intermediate focus 5 is closer to the surface 9 of the semiconductor layer 4, so that the separation region 8 does not extend to the separation layer 3. This different configuration of the separation regions 8, and in particular their extension in the thickness direction 13, is mainly determined by the number and configuration of the focus points 5 and the focus depth 5a.

[0127] like Figure 6 As shown in , the focal points 5 along the focal line 6 are closely spaced, so that, similar to the separation regions 8, the modification regions 7 formed around the individual focal points 5 overlap one another. The formation of the separation regions 8 extending to the surface 9 of the semiconductor layer 4 can be manifested by the formation of small cracks or similar traces on the surface 9, which are generated during the processing of the layer stack 1. Since the formation of the separation regions 8 extends to the surface 9 of the semiconductor layer 4 in the form of cracks, this can be seen by the user with the help of a camera or the like. Therefore, this provides the user or the monitoring system with an optical criterion that can be used to determine whether the focal points 5 and thus the modification regions 7 and the separation regions 8 have been properly formed, and if necessary, whether they are in the expected proper positions. Therefore, the formation of the focal points 5 for stripping the semiconductor layer 4 by correspondingly forming the modification regions 7 and the separation regions 8 can be monitored. For example, as Figure 5 As shown in the exemplary embodiment of FIG, when the modification region 7 and the separation region 8 are formed only within the semiconductor layer 4, a user or a monitoring system can determine, for example, by means of an infrared camera, whether the focus point 5 has been formed together with the corresponding modification region 7 and whether the intended separation region 8 has been formed or created accordingly. However, this will only become apparent during the subsequent peeling of the semiconductor layer 4 from the layer stack 1.

[0128] In yet another exemplary embodiment of the method according to the present invention, the focusing points 5, 5' are formed in the semiconductor layer 4 with different focusing depths 5a, 5a' distributed vertically in the thickness direction 13, as shown in FIG. Figure 7 . The formation of the focal points 5, 5' at different focal depths 5a, 5a' in combination with the formation of two focal lines 6, 6' spaced apart in the thickness direction 13 can be performed sequentially in two operating steps. The laser radiation 12 for forming the different focal points 5, 5' at different focal depths 5a, 5a' is introduced sequentially into the semiconductor layer 4, wherein first a first focal line 6 is formed at a first focal depth 5a and subsequently a second focal line 6' is formed in a similar manner at a second focal depth 5a'.

[0129] Preferably, the laser radiation 12 is focused into the semiconductor layer 4 by means of an optical element 15 in such a way that two focal points 5, 5' are simultaneously formed at two different focal depths 5a, 5a'. By these means, the modified regions 7, 7' formed around the two focal lines 6, 6' form corresponding separation regions 8, which extend from the separation layer 3 to the surface 9 of the semiconductor layer 4. However, the modified regions 7, 7' of the individual focal lines 6, 6' do not overlap with one another. For semiconductor layers 4 formed in the thickness direction 13 with a thickness exceeding 200 micrometers, it is particularly advisable to arrange a plurality of focal lines 6, 6' above and below in the thickness direction 13. This ensures the formation of corresponding separation regions 8, which also ensure complete detachment of the semiconductor layer 4 from the layer stack 1.

[0130] In the above figures, the laser radiation 12 is introduced into the semiconductor layer 4 substantially perpendicularly to the surface 9 of the semiconductor layer 4 for forming the focal point 5 and the corresponding modification region 7 and separation region 8. In this case, the formation of the modification region 7 and separation region 8 occurs mainly in the thickness direction 13, with a smaller extension or width in the lateral direction 17. As a result, the exfoliated semiconductor layer 4' has side faces 9a formed substantially perpendicularly to the surface 9 of the semiconductor layer 4, as shown in FIG. Figure 4b ) is also schematically shown in FIG.

[0131] Figure 8a )and Figure 8b ) shows another embodiment in which the semiconductor layer 4' to be peeled off is formed to have a side surface 9a that is at an angle to the thickness direction 13. Figure 8b ), a separation region 8 extending at an angle to the thickness direction 13 is formed by focusing points 5, 5' superimposed and offset from each other in the lateral direction 17 and formed at different focusing depths 5a, 5a'. In the present case, due to the offset arrangement of the two focusing points 5, 5' formed simultaneously and by the offset arrangement of the modification regions 7, 7', a separation region 8 is formed, which connects the modification regions 7, 7' of the two focusing points 5, 5' formed offset from each other, thereby extending in the semiconductor layer 4 in a direction oblique to the thickness direction 13.

[0132] Alternatively, the modification regions 7 and / or separation regions 8 extending obliquely with respect to the thickness direction 13 may have been formed by oblique incidence of the laser radiation 12 with respect to the surface 9 of the semiconductor layer 4, as in Figure 8a ). To achieve this, it is not absolutely necessary to Figure 8b) are two offset focus points 5, 5' shown in FIG. As a further alternative, if, at the same time, a preferably mechanical stress is applied to the semiconductor layer 4 or the layer stack 1 (e.g., by a bending force), then, by oblique incidence and / or perpendicular incidence of the laser radiation 12 relative to the surface 9 of the semiconductor layer 4, modified regions 7 and / or separation regions 8 extending obliquely with respect to the thickness direction 13 can be formed.

[0133] In order to form the focal points 5, 5' or the focal lines 6, 6' formed from these focal points 5, 5' in an offset arrangement in the lateral direction 17, the laser radiation 12 is focused into the interior of the semiconductor layer 4 at an angle of incidence α 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 midway direction of the incident laser radiation 12 and completely excludes vertical incidence of the laser radiation 12, which corresponds to 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 causing the laser radiation 12 to be incident at a certain angle, a plurality of focal points 5, 5' can be formed simultaneously, which is consistent with the embodiment of the present invention. Figure 7 Alternatively, when the laser radiation is incident at a certain angle, the focusing points 5, 5' can also be formed in sequence.

[0134] When the semiconductor layer 4' is peeled off from the layer stack 1 (eg Figure 8c ), the semiconductor layer 4' now has a side surface 9a that is inclined relative to the thickness direction 13, so the area of ​​the plane located below in the thickness direction 13 is smaller than the area of ​​the plane located above in the thickness direction 13 of the semiconductor layer 4'. When the semiconductor layer 4' to be peeled off is peeled off, a portion of the separation layer 3 remains on the semiconductor layer 4', as shown in FIG. Figure 8c ). The chamfered side surface 9a simplifies the removal of the semiconductor layer 4' to be peeled off from the remainder of the layer stack (remaining stack 16). The peripheral region with the overlapping region 10 remaining on the remaining stack 16 and the remaining portion of the semiconductor layer 4 are removed from the remaining stack 16 in a subsequent method step, so that the seed crystal substrate 2 can be used subsequently to produce further semiconductor layers 4.

[0135] Figure 8d )and Figure 8e ) shows another embodiment for forming an obliquely extending separation region 8 inside a semiconductor layer 4. This method is a two-step method, wherein first a focus point 5 and a corresponding modified region 7 are formed at a first focus depth 5a, as shown in FIG. Figure 8d). To achieve this, as previously described, the laser radiation 12 is focused into the interior of the semiconductor layer 4 by means of an optical element 15. In a second step, a second focus 5' with a modified region 7' ​​is formed at a second focus depth 5a' offset in the lateral direction 17. The separation region formed around the modified regions 7, 7' and the focus 5, 5' and its modified regions 7, 7' offset in the lateral direction 17 result in the formation of an obliquely extending separation region 8, which is in accordance with Figure 8a ) is similar.

[0136] In accordance with Figure 8d )and Figure 8e ), as is conventional, the laser radiation 12 can be introduced in a direction perpendicular to the surface 9 of the semiconductor layer 4. In this case, therefore, it is not necessary to form the focal points 5, 5' by oblique incidence of the laser radiation 12. By appropriately selecting the respective spacing of the focal points 5, 5' in the lateral direction 17, the angled, oblique extension of the separation region 8 in the semiconductor layer 4, as well as the inclination angle of the side surface 9a of the semiconductor layer 4, can be flexibly formed.

[0137] Figure 9a )and Figure 9b ) shows a further embodiment of the method according to the invention, in which the laser radiation 12 is introduced laterally into the overlapping region 10 of the semiconductor layer 4 via an optical element 15. A focal point 5 is formed in the overlapping region 10 and is approximately at the level of the separation layer 3. This results in the formation of a peripheral, approximately horizontally extending separation region 8 along a focus line 6 (not shown) by the lateral injection of the laser radiation 12 into the layer stack 1, as shown in FIG. Figure 9b ), the semiconductor layer 4' can be peeled off together with a portion of the separation layer 3.

[0138] This embodiment provides not only the exfoliation of the semiconductor layer 4', but also the exfoliation of the overlapping region 10 including the exfoliated semiconductor layer 4', such as Figure 9b ). The semiconductor layer 4' thus stripped off can subsequently be further processed together with the overlapping region 10. Alternatively, the peripheral region 10 of the stripped off semiconductor layer 4' is removed in a further processing step before being used for further processing.

[0139] Reference Mark List

[0140] 1-layer stacking

[0141] 2 Seed crystal substrate

[0142] 2a, 2b plane side

[0143] 3 separation layer

[0144] 4,4' semiconductor layer

[0145] 5,5' focus point

[0146] 5a,5a' Focus depth

[0147] 6,6' focusing line

[0148] 7,7' modified area

[0149] 8 Separation Area

[0150] 9 Surface of semiconductor layer

[0151] 9a Side surface of semiconductor layer

[0152] 10 Overlapping Area

[0153] 11 Laser Source

[0154] 12 Laser radiation

[0155] 12', 12" split beam of laser radiation

[0156] 13 Thickness direction

[0157] 14 Horizontal direction

[0158] 15 Optical Elements

[0159] 16 remaining stacks

[0160] 17 lateral direction

[0161] α angle of incidence

Claims

1. A method for peeling off a semiconductor layer (4) from a layer stack (1), the method comprising the following steps: A) providing said 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) preferably epitaxially formed on said separation layer (3), B) peeling the semiconductor layer (4) from the layer stack (1), It is characterized in that Before and / or during method step B), laser radiation (12) from a laser source (11) is focused into the semiconductor layer (4), wherein the laser radiation (12) is introduced into the semiconductor layer (4) along a transverse focus line (6, 6') to form at least one modification region (7, 7') below the surface (9) of the semiconductor layer (4), wherein in the modification region (7, 7') the material of the semiconductor layer (4) is modified and a separation region (8) is formed around the modification region (7, 7') in the semiconductor layer (4).

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

3. The method according to any one of the preceding claims, characterized in that In order to form the focal point (5, 5'), the layer stack (1) is moved at a uniform speed relative to the laser source (11), in particular at a constant speed; or in order to form the focal point (5, 5'), the layer stack (1) is moved intermittently relative to the laser source (11), preferably the layer stack (1) is moved relative to a stationary laser source (11).

4. The method according to any one of the preceding claims, characterized in that The laser radiation (12) is pulsed, in particular the pulsed laser radiation (12) is short pulses in the nanosecond range, preferably with a pulse length in the range of 1 nanosecond to 150 nanoseconds, preferably from 5 nanoseconds to 100 nanoseconds, particularly preferably from 10 nanoseconds to 30 nanoseconds, or The pulsed laser radiation (12) is an ultrashort pulse of picosecond or femtosecond order.

5. The method according to any one of the preceding claims, characterized in that In the thickness direction (13), a plurality of focus points (5, 5') are formed vertically above and below each other at different focus depths (5a, 5a') in the semiconductor layer (4), and / or wherein a plurality of modified regions (7, 7') are formed vertically above and below each other in the thickness direction (13), and / or In the transverse direction, a plurality of focusing points (5, 5') are formed simultaneously and side by side with each other.

6. The method according to any one of the preceding claims, characterized in that The laser radiation (12) is introduced multiple times in succession at the focus point (5, 5').

7. The method according to any one of the preceding claims, characterized in that The semiconductor layer (4) is substantially transparent to the wavelength of the laser radiation (12), in particular 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. The method according to any one of the preceding claims, characterized in that The separation region (8) is formed in the semiconductor layer (4), and preferably the separation region (8) extends to the surface (9) of the separation layer (3) and / or the semiconductor layer (4).

9. The method according to any one of the preceding claims, characterized in that The laser radiation (12) is introduced into the layer stack (1) along the focus line (6, 6') so that a predetermined breaking point, in particular a crack, is formed in the separation region (8) including the modified region (7, 7') within the semiconductor layer (4), in particular wherein the breaking point is formed by the separation region (8) and / or the modified region (7, 7'), and / or wherein the laser radiation (12) is introduced into the layer stack (1) along the focus line (6, 6') so that the semiconductor layer (4) is completely peeled off from the remaining stack (16) along the separation region (8).

10. The method according to any one of the preceding claims, characterized in that The semiconductor layer (4) includes an overlapping region (10), which is larger than the planar side of the seed substrate (2) and / or the separation layer (3), and the overlapping region (10) is preferably formed to at least partially cover one or more side surfaces of the seed substrate (2) and / or the separation layer (3).

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

12. The method according to claim 10 or 11, wherein: The focus line (6, 6') and / or the modification area (7, 7') and / or the separation area (8) are at least partially formed within the overlap area (10), preferably wherein the focus line (6, 6') and / or the modification area (7, 7') and / or the separation area (8) are mainly formed outside the overlap area (10).

13. The method according to any one of the preceding claims, characterized in that The focal line (6, 6') and / or the modification area (7, 7') and / or the separation area (8) are formed in a closed configuration.

14. The method according to any one of the preceding claims, characterized in that The laser radiation (12) is introduced into the semiconductor layer (4) from one or more planar sides of the layer stack (1), and / or the laser radiation (12) is introduced into the semiconductor layer (4) from a side surface of the layer stack (1), in particular into the overlapping region (10).

15. The method according to any one of the preceding claims, characterized in that The focus depth (5a, 5a') of the laser radiation (12) can be adjusted within the thickness range of the semiconductor layer (4), and preferably within the range of half the thickness of the semiconductor layer and / or preferably within the range of 10 micrometers to 500 micrometers below the surface (9) of the semiconductor layer (4).

16. The method according to any one of the preceding claims, characterized in that The focusing point (5, 5') is formed with a substantially circular or elliptical cross section and / or the modification area (7, 7') and / or the separation area (8) is formed and / or created with a substantially circular or elliptical area cross section.

17. The method according to any one of the preceding claims, characterized in that 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 in any way affected by the laser radiation (12), preferably wherein the seed substrate (2), preferably together with the separation layer (3), is reused for the production of at least one further semiconductor layer (4) after method step B), in particular after a further processing step.

18. The method according to any one of the preceding claims, characterized in that At least two focus lines (6, 6') are formed in the semiconductor layer (4) with different focus depths (5a, 5a') offset from each other in a lateral direction (17), in particular wherein the focus lines (6, 6') are formed simultaneously or sequentially at the different focus depths (5a, 5a').

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

20. The method according to any one of the preceding claims, characterized in that The laser radiation (12) is incident on the layer stack (1) at an angle of incidence (α) to the normal to the surface (9) of the semiconductor layer (4), wherein the modification region (7, 7') and / or the separation region (8) are preferably formed to extend at an angle to the thickness direction (13).

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

22. A method for producing a semiconductor layer (4), comprising the following method steps: V1) providing a seed crystal substrate (2); V2) forming a separation layer (3) on the seed crystal substrate (2); V3) depositing a semiconductor layer (4) on the separation layer (3) of the seed substrate (2), preferably by epitaxy, to form a layer stack (1) of the seed substrate (2), the separation layer (3) and the semiconductor layer (4); and V4) peeling the semiconductor layer (4) from the layer stack (1), It is characterized in that The semiconductor layer (4) is lifted off by a method according to any one of claims 1 to 21, in particular wherein, after method step V4), method steps V2) to V4) are performed multiple times on the seed substrate (2).

23. A system for stripping a semiconductor layer (4) from a layer stack (1), the system being particularly suitable 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) preferably formed epitaxially on the separation layer (3), wherein the system comprises a support for the layer stack (1), preferably a stripping unit for the semiconductor layer (4) and a laser source (11) for generating laser radiation (12), It is characterized in that The laser radiation (12) of the laser source (11) is focused into the layer stack (1) so that a modification region (7, 7') is formed below the surface (9) of the semiconductor layer (4) along a transverse focus line (6, 6'), in which the material of the semiconductor layer (4) is modified, and a separation region (8) comprising the modification region (7, 7') can be formed and in which the semiconductor layer (4) is formed so as to be stripped from the layer stack (1) along the focus line (6, 6'), in particular by the stripping unit.

24. A semi-finished product comprising a layer stack (1) of at least a seed substrate (2), a separation layer (3) formed on the seed substrate (2) and the semiconductor layer (4) preferably formed epitaxially on the separation layer (3), the semi-finished product being in particular made of silicon, wherein the semiconductor layer (4) comprises an overlapping region (10), the overlapping region (10) being larger than a planar side of the seed substrate (2) and / or the separation layer (3), the overlapping region (10) preferably being formed to at least partially cover one or more side faces of the seed substrate (2) and / or the separation layer (3), characterised in that Below the surface (9) of the semiconductor layer (4), a modification region (7, 7') and preferably a separation region (8) comprising the modification region (7, 7') are formed along a focus line (6, 6'), wherein the material of the semiconductor layer (4) is modified in the modification region (7, 7').

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

26. The semi-finished product according to claim 24 or 25, characterized in that The separation region (8) extends within the semiconductor layer (4) at an angle to the thickness direction (13).

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