METHOD FOR PRODUCING A CARRIER SUBSTANCE

Description

[0001] The invention describes a method for producing a carrier substrate for transferring a transfer layer from a carrier substrate to a product substrate. The transfer layer, in particular a graphene layer, is first arranged on the carrier substrate; in particular, the transfer layer was produced or grown on a layer of the carrier substrate and is transferred to the product substrate using the transfer method.

[0002] Layer transfer processes already exist in the art. These processes are used to transfer very thin layers, especially those with thicknesses in the micrometer or even nanometer range, from one substrate to another. Many of these layers can only be produced on a specific first surface, which, however, should not simultaneously be part of the later functional component. Therefore, the layer must be transferred from the first surface to a second surface. Publication WO2018087420A1 discloses a chemical vapor deposition (CVD) system with a rotating belt system in which at least one belt serves as a substrate for the growth of a layer.

[0003] One of the best-known layer transfer processes in the semiconductor industry is the SmartCut™ process. In this process, ions, particularly hydrogen ions, are injected into a first, single-crystal substrate. The penetration depth of the hydrogen ions can be controlled by the kinetic energy and is only a few nanometers. The hydrogen ions remain in the first substrate until it is bonded to a second, oxidized substrate. A thermal process then causes the hydrogen atoms to combine into water molecules, separating the first, single-crystal substrate along the area where the hydrogen ions have accumulated. This results in a three-layer structure in which the oxide is sandwiched between two other materials, usually silicon. The transferred layer of the first substrate is very thin and, most importantly, single-crystal.The underlying oxide layer then has a positive effect on components with high switching frequencies, especially transistors.

[0004] For several years, the industry has been attempting to produce graphene on a large scale. Several methods for graphene production exist in the state of the art. Graphene flakes can already be produced on an industrial scale of tons. However, these graphene flakes are of minor importance to the semiconductor industry because they are far too small and are primarily produced through wet chemical processes, especially in solution, rather than on substrate surfaces. The goal is to produce a graphene layer either at the wafer level, i.e., across the entire surface of a wafer, or selectively on an existing wafer topology. However, producing a graphene layer at the wafer level appears to be the most promising approach.

[0005] The biggest challenge lies in producing graphene layers or other sensitive layers to be transferred cost-effectively, quickly, over large areas, and without defects. Experience has shown that large-area growth of graphene layers is preferably carried out on a metal surface, particularly a single-crystal one.

[0006] The problem, however, is that the surfaces on which graphene is to be grown on a large scale rarely correspond to the surfaces on which the graphene is to be structured and applied. The graphene must therefore be transferred from a first surface, the fabrication surface, to a second surface, the application surface. This transfer process typically involves the use of debonding agents, especially lasers, whose effects, particularly electromagnetic radiation, could destroy or damage the transfer layer or the graphene layer.

[0007] It is therefore an object of the present invention to provide a method for producing a carrier substrate which eliminates at least some, and in particular completely eliminates, the disadvantages listed in the prior art. In particular, it is an object of the invention to provide a carrier substrate manufacturing method for transferring a transfer layer from the carrier substrate to a product substrate.

[0008] The present problem is solved by the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims.

[0009] In the following text, a transfer layer, or a layer to which the transfer occurs, particularly in the form of a graphene layer, is understood to be that layer of the support substrate which is to be transferred onto the product substrate. Specifically, the transfer layer has been grown on a protective layer, or a growth layer, of the support substrate. Therefore, protective layer and growth layer are used synonymously in the following text.

[0010] The growth layer and the protective layer can, however, be two distinct layers. The growth layer is in contact with the transfer layer, so the protective layer is located between the growth layer and the substrate. For the sake of simplicity, the following text assumes that the growth layer and the protective layer are identical. This is also the more economically advantageous scenario, as only one layer needs to be deposited, thus reducing process costs.

[0011] Accordingly, a carrier substrate for transferring a transfer layer from the carrier substrate to a product substrate is disclosed, comprising at least the following layers in the following order: a base substrate, a protective layer and the transmission layer, where the transmission layer is grown on the protective layer.

[0012] The substrate has at least the aforementioned layers in the order described above. However, it is also conceivable that further intermediate layers, particularly those with specific functions, are arranged between and / or on top of the aforementioned layers. In particular, the protective layer can, for example, consist of several individual layers, each protecting the transfer layer. The protective layer acts as a barrier to protect the transfer layer, especially from influences that could facilitate transmission and damage or destroy the transfer layer. To transfer the transfer layer from the substrate to the product substrate, the adhesive properties in the area between the protective layer and the transfer layer are reduced, with the protective layer shielding the layer to be transferred.This layered structure of the substrate allows for the advantageously simple and efficient transfer of the transmission layer, without damaging the transmission layer, as it is protected by the protective layer. Furthermore, the dual function of the protective layer as both a barrier and a growth layer for the transmission layer enables more cost-effective manufacturing on an industrial scale.

[0013] The invention relates to a method for producing a carrier substrate for transferring a transfer layer from the carrier substrate to a product substrate, comprising the following steps: i) Providing a carrier substrate, ii) Applying a protective layer to the carrier substrate, iii) Cultivating a transfer layer, in particular a

[0014] Graphene layer, on the protective layer, wherein the protective layer consists of several individual layers, characterized in that, prior to the application of the protective layer in step ii), the base substrate is coated with a solvent layer, so that the protective layer is applied on the solvent layer.

[0015] The process for producing a carrier substrate involves growing a transfer layer on a protective layer. The protective layer serves both to protect the transfer layer during transfer and as the site where the transfer layer is produced or grown. The protective layer thus has a dual function, eliminating the need for an additional layer during production. Furthermore, the carrier substrate, which incorporates the protective layer, enables subsequent transfer without damaging the transfer layer. This advantageously allows for a simple separation between the location where the transfer layer is produced or grown and its use on the product substrate.

[0016] Furthermore, a method for transferring a transfer layer from the support substrate or a support substrate produced according to the method for producing a support substrate onto a product substrate is disclosed, wherein the carrier substrate is contacted with the product substrate, so that the transfer layer faces the product substrate, and wherein at least one debonding agent acts on the carrier substrate, so that the transfer layer together with the protective layer is detached from a carrier base substrate.

[0017] The method for transferring the transfer layer thus advantageously allows for a simple and efficient transfer of the transfer layer from one surface to another, in particular the transfer from a manufacturing surface to a usage surface.

[0018] The debonding process is enabled by the action of at least one debonding agent, particularly in the form of a laser, preferably an infrared laser. The protective layer protects the transfer layer from the effects of the at least one debonding agent, or shields the transfer layer from these effects, so that the transfer layer is not damaged. It is particularly intended that the transfer layer is detached from the substrate together with the protective layer, and then the protective layer is removed. The substrate is contacted with the product substrate, so that advantageously no relative movement between the contacted surfaces is possible. Before contacting, the substrate and the product substrate are aligned relative to each other, particularly by aligning their respective substrate holders.For alignment, alignment marks, which are applied to the carrier substrate and / or the product substrate, are used to ensure the most precise alignment possible. Consequently, the transfer of a transfer layer to a product substrate is advantageously simple and efficient. A particularly advantageous feature is that the transfer layer is not damaged or destroyed by the action of the debonding agents. The creation or growth of the transfer layer has already taken place on the carrier substrate. Therefore, the transfer layer can now be advantageously detached from its point of creation or growth on the carrier substrate, especially on the protective layer, and applied to the product substrate.

[0019] In a preferred embodiment of the support substrate, the transfer layer is a graphene layer. The graphene layer is arranged on top of the protective layer and is protected by the protective layer. Since the support substrate designed to transfer the graphene layer is debonded from the base substrate along with the protective layer during the transfer process, thus separating the graphene layer from the support substrate, the debonding means, particularly electromagnetic radiation, cannot damage or destroy the graphene layer. Therefore, the support substrate is ideally suited for transferring a graphene layer. The support substrate advantageously enables the simple and efficient fabrication and transfer of graphene layers in large quantities, instead of only on a laboratory scale as before. A particular advantage is that the graphene layer is grown as the transfer layer on top of the protective layer.

[0020] In another preferred embodiment of the support substrate, the roughness of the protective layer, particularly on the surface facing the transfer layer, is less than 100 µm, preferably less than 10 µm, even more preferably less than 1 µm, most preferably less than 100 nm, and most preferably less than 10 nm. Keeping the roughness of the growth layer as low as possible makes the production or growth of the transfer layer possible in the first place. Particularly thin transfer layers, especially graphene layers, must be grown on very flat, clean surfaces. The transfer layer is thus produced on the layer that also protects it from the effects of the debonding agents used during the transfer process.Preferably, the protective layer is recrystallized during its production before the growth of the transfer layer, which further simplifies or improves the growth of the transfer layer, in particular the graphene layer.

[0021] In another preferred embodiment of the carrier substrate, it is provided that the carrier substrate has at least one release layer arranged between the base substrate and the protective layer. The release layer can advantageously define the precise location for the release of the transfer layer from the base substrate. Furthermore, release along the release layer can advantageously be simple and efficient.

[0022] Furthermore, the design of the release layer allows for the advantageous specification of the necessary adhesive force between the substrate and the protective layer. In particular, the design of the release layer can define the conditions under which the transfer layer should be able to detach.

[0023] In another preferred embodiment of the carrier substrate, the transfer layer can be detached from the base substrate together with the protective layer by means of a debonding agent acting on the release layer and / or a release area. The debonding agent(s) act on the carrier substrate when a debonding process is to be carried out. The release layer or release area and the debonding agent are coordinated with each other. A release layer is a separate layer of material, whereas a release area is defined by the contact surface between the base substrate and the protective layer. Debonding in the release area can occur, for example, through the expansion of materials introduced into the contact surface areas. Therefore, a release area does not constitute a separate layer of the carrier substrate, but fulfills the same function.When the debonding agent acts on the release area or the release layer, the adhesive properties of the release layer, and in particular the adhesive properties of the protective layer and the substrate in contact, change, allowing the protective layer and the transfer layer to be detached from the substrate. This makes transferring the transfer layer from the substrate to a product substrate particularly easy and efficient.

[0024] In another preferred embodiment of the support substrate, the protective layer is made of a material with a high solubility for carbon. If the protective layer is a material with a particularly high solubility for carbon, the transfer layer, especially graphene, can be produced or grown on the protective layer by heating and cooling. During this process, the carbon is deposited on the surface of the protective layer, and the transfer layer is formed on the support substrate. Due to the special and advantageous layer structure of the support substrate, the generated transfer layer can then be easily and efficiently transferred to a product substrate.

[0025] In another preferred embodiment of the substrate, the protective layer is opaque to electromagnetic radiation. If electromagnetic radiation is used for debonding or to reduce the adhesive properties of the release layer, for example a laser, the protective layer can absorb the radiation and thus prevent damage or destruction of the transfer layer. In this embodiment, the substrate is preferably at least partially transparent to electromagnetic radiation. For example, the substrate is made of glass, preferably sapphire glass.

[0026] In another preferred embodiment of the carrier substrate, a contact layer, in particular made of a dielectric material, preferably silicon oxide, is arranged on the side of the transfer layer facing away from the protective layer. Such a contact layer enables simpler and more reliable contact during transfer to the product substrate. Furthermore, by using a dielectric material, for example silicon oxide, for the contact layer, short circuits in the product substrate can be prevented, or electrical conduction between the product substrate and the transfer layer can be permitted only at desired locations. A further contact layer can also be arranged on the product substrate. The contact layer and the further contact layer of the product substrate are preferably made of the same material and enable particularly easy contact between the carrier substrate and the product substrate.

[0027] In another preferred embodiment of the support substrate, the protective layer is a single-crystal metal layer, preferably made of nickel. The transmission layer is advantageously grown on a monocrystalline material. When using a single-crystal metal layer, the transmission layer can advantageously be grown on the protective layer. At the same time, the single-crystal metal layers are also suitable for protecting the transmission layer from the effects of an electromagnetic debonding agent, for example, a laser. A nickel-based protective layer is most preferred because a graphene layer can be particularly well produced or grown on such a nickel-based layer.

[0028] In another preferred embodiment of the carrier substrate, the transfer layer is created on the protective layer. According to this embodiment, the layer to be transferred is created directly on the protective layer. The transfer layer is thus advantageously arranged directly on the protective layer, so that the transfer layer is directly protected by the protective layer from influences acting on the other side of the protective layer. The special layer structure of the carrier substrate enables the simple and efficient transfer of the transfer layer from the carrier substrate to the product substrate.

[0029] In another preferred embodiment of the substrate, the protective layer simultaneously serves as a growth layer for the transfer layer, allowing the transfer layer to be grown on the protective layer. In this embodiment, the protective layer fulfills two functions. The first function is to protect the transfer layer from the effects of the debonding agents. The second function enables the growth of a transfer layer on the protective layer, which in this case can also be used as a growth layer. Advantageously, only one layer is needed for both protecting and growing the transfer layer, particularly the graphene layer. It is also conceivable that the protective layer consists of several layers. The layer(s) facing the release layer are designed as protective layers.The layer or layers facing away from the solvent layer enable the creation of a transfer layer. The dual function of the protective layer is thus achieved by two or more layers, with the protective layer consisting of at least two layers. Preferably, however, a single layer forms the protective layer, simultaneously providing the protective function and enabling the creation of the transfer layer.

[0030] In another preferred embodiment of the carrier substrate, the transfer layer can be detached from the carrier substrate, along with the protective layer, by at least one debonding agent acting on the release layer or a release area. The debonding agent, preferably in the form of a laser, acts on the release layer, reducing its adhesive properties and allowing the transfer layer and protective layer to be detached from the carrier substrate. The debonding agent preferably acts on the release layer. Further effects emanating from the debonding agent are reduced, or preferably prevented, by the protective layer. The protective layer thus preferably acts as a barrier to the transfer layer against these effects. In this way, the transfer layer can advantageously be debonded without damaging it.

[0031] In a preferred embodiment of the method for producing a support substrate, the protective layer is recrystallized before the transmission layer is grown in step iii). The protective layer, which preferably has a very low roughness, can thus fulfill its function as a growth layer even more effectively. The growth of the transmission layer, in particular a graphene layer, on the protective layer is therefore simplified and improved.

[0032] According to the inventive method for producing a carrier substrate, it is provided that, prior to the application of the protective layer in step ii), the base substrate is coated with a release layer, so that the protective layer is applied to the release layer. In this way, removal of the generated transfer layer can be advantageously carried out simply during subsequent transfer. In addition, the application of a release layer advantageously determines the location of removal.

[0033] In a preferred embodiment of the method for producing a carrier substrate, a contact layer is deposited on the side of the transmission layer facing away from the protective layer. The contact layer advantageously simplifies the bonding process performed during the transfer of the transmission layer. Furthermore, the contact layer can also facilitate better contact with the product substrate. Additionally, a functionalized contact layer, for example, with electrically conductive areas, can enable contact with the transmission layer in certain predetermined regions.

[0034] In a preferred embodiment of the method for producing a carrier substrate, the protective layer simultaneously serves as a growth layer for cultivating the transfer layer on the protective layer, and the transfer layer is cultivated on the protective layer. The protective layer thus advantageously fulfills the protective function and enables the formation of the transfer layer on the protective layer. Therefore, only one layer is advantageously used. However, it would also be conceivable for the protective layer to be composed of two or more layers. The layer facing the release layer, or the layer facing the release layer, is then designed to protect against the influence of the debonding agents. The additional layer or layers, acting as a growth layer, enable the formation of the transfer layer. However, it is preferred that the protective layer be formed from a single layer with a dual function.In this way, the process for producing a carrier substrate is advantageously simple and efficient.

[0035] In another preferred embodiment of the method for producing a carrier substrate, a contact layer is deposited on the transmission layer. The contact layer is preferably made of a dielectric material, particularly preferably silicon oxide. This prevents short circuits in the product substrate later on. Furthermore, contacting the carrier substrate with the product substrate can be carried out particularly easily and reliably.

[0036] In a preferred embodiment of the method for transferring a transfer layer, the support substrate is contacted with the product substrate via a contact layer applied to the transfer layer, or the support substrate is contacted with a further contact layer of the product substrate applied to the product base substrate via a contact layer applied to the transfer layer. The product substrate thus has an additional contact layer. The contact layer is preferably made of a dielectric material, particularly preferably silicon oxide. If the support substrate also has a contact layer on the transfer layer, the contact layer of the support substrate and the additional contact layer of the product substrate are particularly preferably made of the same material. Contacting during the transfer process can therefore be carried out particularly simply and efficiently.Furthermore, short circuits are prevented by contact layers.

[0037] In another preferred embodiment of the method for transferring a transfer layer, the transfer layer is bonded to the product substrate, or a contact layer arranged on the transfer layer is bonded to the product substrate. The bonding of the transfer layer to the product substrate completes the transfer.

[0038] The bonding process is preferably divided into a pre-bond and a subsequent permanent bond. In the pre-bond, a relatively weak bond is created between the two substrates, which is theoretically reversible without damage and is preferably based on surface effects. Hydrophilic surfaces are particularly advantageous in this case. The subsequent permanent bond is characterized by a strengthening of the bonds created in the pre-bond. The permanent bond is preferably achieved at an elevated temperature. However, the temperature should be as low as possible to reduce, or preferably completely prevent, potential damage to the transfer layer or any existing system components. Therefore, the temperature during permanent bonding is preferably less than 300°C, more preferably less than 200°C, even more preferably less than 100°C, most preferably less than 50°C, and most preferably room temperature.Experts in the field are familiar with such pre-bonds and permanent bonds.

[0039] The protective layer is detached from the transmission layer, particularly before, during, or after bonding the transmission layer to the product substrate. This method enables the simple and efficient transfer of a defect-free, large-area, and sensitive transmission layer. The transfer of a graphene layer onto the product substrate is especially preferred. Functional components, particularly vias, may have been previously integrated into the product substrate itself, allowing for targeted and desired electrical conductivity between the product substrate and the transmission layer only in these areas.

[0040] In the following, the term "growth layer" is used to refer to the protective layer. Since in most cases the protective layer serves to protect and to cultivate the transfer layer, the terms "growth layer" and "protective layer" will be used interchangeably. However, this does not refer to a single growth layer without a protective function; rather, a growth layer is a protective layer upon which a transfer layer can be cultivated or produced.

[0041] A particular aspect of the invention involves demonstrating a method for growing or producing, transferring, and debonding a single layer to be transferred, or a graphene layer, from a manufacturing surface of a support substrate to a user surface of a product substrate. The fundamental idea is to produce a layer system, consisting of a support substrate, a release layer, a growth layer, the graphene layer (transfer layer), and preferably a dielectric layer, in a well-defined sequence so that the layer transfer can be carried out without difficulty.

[0042] Another aspect of the invention involves creating a very specific layer structure on a support substrate, the individual layers of which fulfill different functional tasks. In particular, a release layer is used to separate the graphene layer from the support substrate. A growth layer or protective layer serves to cultivate and simultaneously protect the transfer layer or the graphene layer.

[0043] The substrate on which the transfer layer, or graphene, can be grown generally differs from the substrate on which the transfer layer, or graphene, is to be used. This separates the process of producing the transfer layer, or growing the graphene, from the location where the transfer layer, or graphene, is used. Consequently, the production of such a sensitive transfer layer, or graphene layer, is flexible and cost-effective.

[0044] The substrate and the method for transferring a transfer layer can, in principle, be used for transferring any type of layer or transfer layer. However, the transfer of a graphene layer is described as an example, since transferring such a monatomic layer requires special conditions and has not yet been implemented in this way in industry.

[0045] However, the method according to the invention is in no way limited to the transfer of a graphene layer. For example, the transfer layer can also be another carbon-based, in particular monatomic, layer.

[0046] The transmission layer preferably consists of at least one of the following material classes or materials. 2D layered materials, in particular: ∘ Graphene ∘ Graphyne ∘ Borophene ∘ Germanene ∘ Silicene ∘ Si₂BN ∘ Gallenene ∘ Stanene ∘ Plumbene ∘ Phosphorene ∘ Antimonene ∘ Bismuthene 2D supracrylic compounds: ∘ Graphane ∘ Boronitrile ∘ Borocarbonitride ∘ Germanane ∘ Germanium phosphide ∘ Transition metal dichalcogenides ∘ MXenes Layered materials with different elemental compositions, in particular: ∘ MoS₂, WS₂, MoSe₂, hBN, Ti₄N₃, Ti₄AlN₃ Van der Waals heterostructures, in particular: ∘ MoS₂-G; MoS2-hBN, MoS2-hBN-G Metal, in particular ∘ Cu, Ag, Au, Al, Fe, Ni, Co, Pt, W, Cr, Pb, Ti, Ta, Zn, Sn Semiconductors, in particular ∘ Ge, Si, Alpha-Sn, B, Se, Te, compound semiconductors, in particular ∘ GaAs, GaN, InP, InxGa1-xN, InSb, InAs, GaSb, AlN, InN, GaP, BeTe, ZnO, CuInGaSe2, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, Hg(1-x)Cd(x)Te, BeSe, HgS, AlxGa1-xAs, GaS, GaSe, GaTe, InS, InSe, InTe, CuInSe2, CuInS2, CuInGaS2, SiC, SiGe Ceramic Polymer Other materials ∘ SiO 2 ∘ Si3N4 ∘ MnO 2 ∘ TBA x H (1.07-x) Ti 1.73 O 4 *H2O ∘ CoO 2 -< ∘ TBA x H (1-x) Ca 2 Nb 3 O 10 ∘ Bi 2 SrTa 2 O 9 ∘ CS 4 W 11 O 36 2-< ∘ Ni(OH) 5 / 3 DS 1 / 3 ∘ Eu(OH) 2.5 (DS) 0.5 ∘ Co 2 / 3 Fe 1 / 3 (OH) 2 1 / 3+< ∘ [Cu 2 Br(IN 2 )] n ] .

[0047] The preferred transmission layer is a layer made of graphene.

[0048] The process for transferring the transfer layer requires, in particular, a product substrate and a support substrate. The product substrate and support substrate generally consist of a product base substrate and a support base substrate. Multiple layers can generally be deposited on the product base substrate and / or the support base substrate.

[0049] The product base substrate and the carrier base substrate can, in principle, consist of any material, but preferably belong to one of the following material classes: 1. Semiconductor material, in particular 1.1 Ge, Si, Alpha-Sn, B, Se, Te, 2. Metal, in particular 2.1 Cu, Ag, Au, Al, Fe, Ni, Co, Pt, W, Cr, Pb, Ti, Ta, Zn, Sn, 3. Compound semiconductor, in particular 3.1 GaAs, GaN, InP, InxGa1-xN, InSb, InAs, GaSb, AlN, InN, GaP, BeTe, ZnO, CuInGaSe2, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, Hg(1-x)Cd(x)Te, BeSe, HgS, AlxGa1-xAs, GaS, GaSe, GaTe, InS, InSe, InTe, CuInSe2, CuInS2, CuInGaS2, SiC, SiGe, 4. Glass, in particular 4.1. Metallic glasses 4.2. Non-metallic glasses, in particular 4.2.1 Organic non-metallic glasses 4.2.2 Inorganic non-metallic glasses, in particular 4.2.2.1 Non-oxide glasses, in particular 4.2.2.1.1 Halide glasses 4.2.2.1.2 Chalcogenide glasses 4.2.2.2 Oxide glasses, in particular 4.2.2.2.1 Phosphatic glasses 4.2.2.2.2 Silicate glasses, in particular 4.2.2.2.2.1 Aluminosilicate glasses 4.2.2.2.2.2 Lead silicate glasses 4.2.2.2.2.3 Alkali silicate glasses, in particular 4.2.2.2.2.3.1 Alkaline earth silicate glasses 4.2.2.2.2.4 Borosilicate glasses 4.2.2.2.2.5 Quartz glass 4.2.2.2.3 Borate glasses, in particular 4.2.2.2.3.1 Alkali borate glasses 4.3. Materials called glasses but not glasses 4.3.1 Sapphire glass. The substrates are described in more detail below. Product substrate

[0050] In one first embodiment The product substrate consists solely of the base substrate. It therefore has no coating whatsoever. A layerless base substrate can serve, in particular, as a starting point for a transferred graphene layer, which is then structured as a conduction layer. Another substrate can subsequently be bonded to this conduction layer. Alternatively, it could be assembled with individual chips. The preferred base substrate is a wafer, especially a silicon wafer.

[0051] In one second embodimentA layer, hereinafter referred to as the contact layer, is located on the product substrate. The contact layer is preferably a dielectric layer, most preferably a silicon oxide layer. It is called a contact layer because it is contacted in a subsequent process step with the transfer layer to be transferred, in particular a graphene layer, or with a layer deposited on it. The contact layer is preferably a dielectric layer, most preferably an oxide, and most preferably a silicon oxide. The oxide can be produced thermally or grow naturally in an oxygen atmosphere. Such a dielectric layer can facilitate the transfer process of the transfer layer or the graphene layer, or may even be necessary for the desired end result.

[0052] In one third embodimentFunctional units, in particular microchips, memory devices, MEMs, LEDs, etc., were previously fabricated in the base product substrate. In a particularly preferred extended embodiment, the base product substrate is coated with a contact layer after the fabrication of the functional units. In further process steps, the dielectric contact layer is then opened above the contacts of the functional units, in particular lithographically. The openings thus created can then be filled with an electrical material, in particular a metal, in further process steps. These through-holes are referred to as TSVs (through silicon vias) in the semiconductor industry. This transforms the contact layer into a hybrid layer. The through-holes represent the electrical domains, and the surrounding dielectric layer represents the dielectric domains.In later process steps, the transfer layer, or graphene layer, is then transferred to the contact layer, thus establishing contact between the graphene and the functional units via the TSVs. It is also conceivable to omit the contact layer and use only the base substrate containing the functional units, onto which the transfer layer is transferred.

[0053] A contact layer makes it possible to select a material with certain properties that the product substrate itself does not possess. For example, silicon is an intrinsic semiconductor and therefore exhibits conductivity even at room temperature, albeit very low conductivity. In many cases, the surface onto which the transfer layer or graphene layer is applied should be dielectric to prevent a short circuit after the graphene transfer layer material has been structured. Since silicon can be oxidized using known methods, silicon oxide is a preferred material for a dielectric layer.

[0054] Using this method, a transmission layer, for example a graphene layer, can then be transferred onto one of the aforementioned product substrates, which can subsequently be structured. In particular, the transmission layer is structured in such a way that it appropriately connects the conductive contacts of the functional units, especially via the TSVs.

[0055] Preferably, the product substrate is a wafer, particularly preferably a silicon wafer. carrier substrate

[0056] The substrate consists of at least a base substrate, a growth layer, and the transfer layer placed on top, in particular the previously produced graphene layer. The layers are deposited on the substrate in a specific sequence. These layers must necessarily be applied in this order. However, it is conceivable that further layers may be located between the aforementioned layers, serving different purposes. In particular, a release layer could be placed between the base substrate and the protective layer.

[0057] In one first embodiment The support substrate consists of at least one base support substrate, a solvent layer deposited on it, a growth layer produced on the solvent layer and the transfer layer arranged on it, in particular in the form of a graphene layer produced on it.

[0058] The first layer is a debonding layer, whose purpose is to separate the base substrate from the other layers in a debonding process.

[0059] The second layer is a growth layer on which the transfer layer is arranged, or on which the graphene layer is to be produced or grown. The growth layer can, in principle, have any desired morphology and grain structure, but is preferably single-crystal. The growth layer is preferably a metal layer, and in a particularly preferred embodiment, a metal layer with a solubility for carbon. The solubility for carbon should preferably decrease with decreasing temperature, so that precipitation, especially on the surface of the growth layer, is possible.

[0060] A particularly advantageous characteristic of the growth layer or protective layer is that it acts as a barrier to the debonding method used. It prevents or at least reduces the passage of influences that are necessary for the debonding process at the release layer but should not affect the transfer layer or the graphene layer. These include temperature input, but especially the effects of electromagnetic radiation, particularly laser radiation. The growth layer therefore acts not only as the site of graphene growth but also as a barrier between the graphene layer and the site of the debonding process, which takes place at the release layer.The characteristic feature of the protective layer is, in particular, that it is designed in relation to the debonding process used in such a way that, on the one hand, the creation of the transfer layer can take place, but at the same time, this transfer layer is protected by the protective layer from an excessive influence of the debonding process.

[0061] The protective layer or growth layer should also have the lowest possible roughness. Roughness is specified either as mean roughness, quadratic roughness, or mean roughness depth. The determined values ​​for mean roughness, quadratic roughness, and mean roughness depth generally differ for the same measuring length or area, but are within the same order of magnitude. Therefore, the following numerical ranges for roughness should be understood as values ​​for mean roughness, quadratic roughness, or mean roughness depth. The roughness of the growth layer is less than 100 µm, preferably less than 10 µm, even more preferably less than 1 µm, most preferably less than 100 nm, and most preferably less than 10 nm.

[0062] The roughness of the solvent layer is also as low as possible, particularly to minimize the roughness of the growth layer formed on the solvent layer. The roughness of the solvent layer is less than 100 µm, preferably less than 10 µm, even more preferably less than 1 µm, most preferably less than 100 nm, and most preferably less than 10 nm. The solvent layer can, in principle, consist of any material that leads to separation from the growth layer using the aforementioned debonding methods. Preferably, however, the solvent layer is not a polymer, since a polymer would cause unnecessary and undesirable contamination of the equipment used in the process according to the invention. The solvent layer therefore preferably consists of a metal, an alloy, or a semiconductor material. For the sake of completeness, the most important material classes that can be used as a solvent layer are listed below. 1. Semiconductor material, in particular 1.1 Ge, Si, Alpha-Sn, B, Se, Te, 2. Metal, in particular 2.1 Cu, Ag, Au, Al, Fe, Ni, Co, Pt, W, Cr, Pb, Ti, Ta, Zn, Sn, 3. Compound semiconductor, in particular 3.1 GaAs, GaN, InP, InxGa1-xN, InSb, InAs, GaSb, AlN, InN, GaP, BeTe, ZnO, CuInGaSe2, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, Hg(1-x)Cd(x)Te, BeSe, HgS, AlxGa1-xAs, GaS, GaSe, GaTe, InS, InSe, InTe, CuInSe2, CuInS2, CuInGaS2, SiC, SiGe, 4. Polymers 4.1. Carbon-based polymers 4.2. Silicon-based polymers

[0063] The solvent layer preferably consists of an epitaxially produced GaN layer. This GaN layer is epitaxially formed on the support substrate, particularly a sapphire substrate. By using a very thin GaN layer, a contaminating polymer layer can be avoided.

[0064] In a further embodiment, the dissolution layer is designed as a dissolution zone, thus eliminating the need for a dissolution layer if ions, preferably hydrogen ions, are implanted in the growth layer and / or the support substrate, which, under thermal stress, would otherwise damage the growth layer and / or the support substrate. This process is known in the semiconductor industry as the SmartCut™ process. Thus, the dissolution zone with the introduced ions takes over the function of the dissolution layer.

[0065] If the debonding process uses electromagnetic radiation, particularly a laser, the thickness of the protective layer can prevent or at least reduce the transmission of electromagnetic radiation to the transfer layer. In this case, the protective layer is thicker than 1 nm, preferably thicker than 100 nm, more preferably thicker than 1 µm, most preferably thicker than 100 µm, and most preferably thicker than 1 mm.

[0066] If the debonding process involves heat, the protective layer can be made of a material with the lowest possible thermal conductivity to at least delay heat transfer until the debonding process is complete. The thermal conductivity is between 0.1 W / (m*K) and 5000 W / (m*K), preferably between 1 W / (m*K) and 2500 W / (m*K), more preferably between 10 W / (m*K) and 1000 W / (m*K), and most preferably between 100 W / (m*K) and 450 W / (m*K).

[0067] The third layer is the transmission layer, or the graph layer to be transmitted, which is created, deposited, or separated by any process.

[0068] In one secondIn one embodiment, at least one further layer, in particular a contact layer, is deposited on the graphene layer. The contact layer is preferably made of the same material or a very similar material to a contact layer of the product substrate, provided the product substrate also has a contact layer. Preferably, the contact layer is also an oxide, most preferably a silicon oxide. In particular, the application of an oxide as the final layer on the graphene layer has the advantage that the support substrate can now be bonded to the product substrate using a fusion bond. In this case, the product substrate preferably also has an oxide layer. This makes it particularly easy to establish the connection between the two substrates.

[0069] The contact layer is preferably hydrophilic. A measure of hydrophobicity or hydrophilicity is the contact angle formed between a test liquid droplet, particularly water, and the surface to be measured. Hydrophilic surfaces flatten the liquid droplet because the adhesive forces between the liquid and the surface dominate over the cohesive forces of the liquid, resulting in low contact angles. Hydrophobic surfaces lead to a more spherical shape of the liquid droplet because the cohesive forces of the liquid dominate over the adhesive forces between the liquid and the surface. The contact angle is less than 90°, preferably less than 45°, even more preferably less than 30°, most preferably less than 10°, and most preferably less than 5°. A hydrophilic contact layer is particularly advantageous for improved and simpler data transfer.

[0070] The substrate preferably consists of a material that possesses optimal properties for the debonding method used. If the debonding process is to be carried out using heat, materials with high thermal conductivity are suitable for the fastest possible heat transfer to the solvent layer. The thermal conductivity is between 0.1 W / (m*K) and 5000 W / (m*K), preferably between 1 W / (m*K) and 2500 W / (m*K), even more preferably between 10 W / (m*K) and 1000 W / (m*K), and most preferably between 100 W / (m*K) and 450 W / (m*K).

[0071] The following describes a process for transferring the graph layer. Processes Carrier substrate manufacturing process

[0072] In the first process step of a manufacturing process for a carrier substrate, the base substrate is coated with a solution layer (release layer).

[0073] In a secondIn a manufacturing step for a support substrate, a growth layer is applied, particularly deposited, onto the solution layer. The growth layer is preferably single-crystal. Producing a single-crystal growth layer on a solution layer, especially a polymeric one, is virtually impossible. Therefore, in a particular embodiment, the growth layer is not produced on the solution layer by a deposition process, but rather transferred to the solution layer by another layer transfer process. The SmartCut™ process would be conceivable here. Any other layer transfer process would also be suitable.

[0074] In a thirdIn a manufacturing step for a carrier substrate, a transfer layer is applied to or created on the growth layer. This transfer layer is preferably a graphene layer, which is produced or grown. The growth of the graphene layer can be carried out using any known method from the prior art.

[0075] It is conceivable, for example, that carbon atoms were dissolved at higher temperatures in the resulting growth layer, and that the system is then cooled in a further intermediate step to such an extent that the solubility of carbon in the material is reduced. This causes carbon to precipitate, particularly at the surface, and allow a graphene layer to form.

[0076] In another embodiment, the carbon is not located within the growth layer, but is supplied to the growth layer from the outside through appropriate deposition processes. For example, molecular beam epitaxy, PVD, or CVD processes could be used.

[0077] In an extension of the third process step, a further layer is deposited on the transmission layer or graphene layer, which serves in particular to optimize the contacting in later process steps. Therefore, this layer is referred to as the contacting layer. The contacting layer is in particular an oxide layer and preferably made of the same material as a contact layer of the product substrate. Layer transfer process

[0078] The layer transfer process is described in detail below.

[0079] In a firstIn this process step, the carrier substrate is aligned relative to the product substrate. This alignment is achieved mechanically and / or optically. Preferably, dedicated alignment systems are used, which align the carrier and product substrates relative to each other using alignment marks.

[0080] In a second In this process step, the carrier substrate is contacted relative to the product substrate. This contact can be made either immediately over the entire surface or via point contact. A fusion bonding system is preferably used.

[0081] In a thirdIn the next process step, the substrate is separated from the growth layer along the release layer using a debonding process, particularly with a laser. The growth layer acts as a barrier to the graphene layer. The growth layer is preferably designed such that the debonding process used, especially the laser, does not impair, and in particular does not destroy, the transfer layer or the graphene layer. This makes the layer structure a novel feature compared to the prior art. The individual possible debonding processes are described in more detail below. Debond process

[0082] In a first,In preferred debonding processes, electromagnetic radiation, in particular a laser, is used. The substrate is at least partially transparent to the electromagnetic radiation, while the solvent layer is preferably maximally absorbent. The growth layer is also absorbent with respect to the electromagnetic radiation, so that photons, in particular those not absorbed by the solvent layer, are prevented from penetrating to the downstream transfer layer or graphene layer.

[0083] The solvent layer preferably has a high solubility in water. Accordingly, the use of a microwave source for the local introduction of heat through capacitive heating of the water would be another conceivable possibility for debonding.

[0084] In a second,In less preferred debonding methods, the solvent layer is subjected to an electric and / or magnetic field. The solvent layer is then designed such that exceeding a certain electric and / or magnetic field strength results in a physical effect leading to the solvent layer dissolving or at least to a reduction in the adhesion of the solvent layer to the growth layer and / or the first substrate.

[0085] In a third,In the least preferred debonding process, heat is used. The heat source is preferably located on the side of the support substrate. Preferably, a heat sink, in particular active cooling, is located on the side of the product substrate. The heat is preferably transported to the release layer to create a separation between the support substrate or release layer and the growth layer. Preferably, the thermal stress on the transfer layer or graphene layer is minimal. Accordingly, in this case, the growth layer should be designed to be a poor thermal conductor and ideally also a poor heat storage medium. This embodiment is less preferred because the generation of an increased temperature causes thermal expansion of the different layers of the layer system.In general, each layer exhibits a different coefficient of thermal expansion. While a polymer-based solution layer can relieve thermal stress through flow, other layers in the system are much more susceptible to thermal stress.

[0086] In a fourth The process step can be handled differently with the growth layer.

[0087] In one first variant of the fourth In the next process step, the growth layer is simply removed, exposing the transfer layer or graphene layer. This removal can be achieved through chemical and / or physical processes. Removing the growth layer is particularly essential if the transfer layer or graphene layer needs to be structured after the layer transfer.

[0088] In one second variant of the fourthIn the process, the growth layer is structured through several process steps to serve as an etching mask for the underlying transmission layer or graphene layer. After etching the transmission layer or graphene layer, the now structured etching layer can be completely removed, as it is no longer needed as an etching mask.

[0089] In one third variant of the fourth In this process step, the growth layer itself is left as a functional layer above the transmission layer or graphene layer and, if necessary, structured. However, since the growth layer is in most cases an electrical material, i.e., a conductive, especially metallic, layer, which would short-circuit any structured transmission layer or graphene layer, especially across its entire surface, it is removed in most cases.

[0090] In another embodiment, the debonding method involves a simple mechanical separation. The two substrates are fixed in such a way that when at least one of them is subjected to pressure, a stress, preferably a tensile stress, is created between the release layer and the growth layer, thus separating the release layer from the growth layer. It would, of course, be more advantageous if the separation occurred between the transfer layer and the growth layer. In this case, a release layer could be dispensed with entirely. Furthermore, the growth layer would not need to be removed from the transfer layer in subsequent process steps. However, the adhesion between the transfer layer and the growth layer is usually very strong, so this preferred case will almost never occur.The force required to separate the two substrates is preferably applied over a small area, particularly at a point, especially at at least one point on the periphery of the substrates. The force is greater than 0.01 N, preferably greater than 0.1 N, more preferably greater than 1 N, most preferably greater than 10 N, and most preferably greater than 100 N. Mechanical separation can be achieved particularly easily if a predetermined breaking point is created in the slurry layer. This predetermined breaking point can be created with a blade, particularly a razor blade, a wire, or a nozzle that forces a fluid onto the slurry layer.

[0091] However, the use of electromagnetic radiation for debonding is particularly preferred. In particular, the use of a laser as the debonding medium is the preferred method. In this case, the substrate should have the highest possible transparency, or more precisely, transmissivity, for the electromagnetic radiation used. Preferably, the substrate is a glass substrate, and most preferably a sapphire substrate. The transparency is described by the transmittance, which indicates the ratio of transmitted to incident radiation. However, the transmittance depends on the thickness of the body being irradiated and is therefore not a material-specific property. The transmittance values ​​are therefore given per unit length of 1 cm.With respect to the selected thickness of 1 cm and for the respective selected wavelength, the material has in particular a transmittance greater than 10%, preferably greater than 20%, more preferably greater than 50%, most preferably greater than 75%, and most preferably greater than 99%.

[0092] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. These show schematic representations of: Figure 1 shows a first embodiment of a carrier substrate not covered by the scope of protection of the claims, Figure 2 shows a second embodiment of a carrier substrate, Figure 3 shows a first embodiment of a product substrate, Figure 4 shows a second embodiment of a product substrate, Figure 5 shows a third embodiment of a product substrate, Figure 6 shows a first process step of a first method according to the invention, Figure 6 shows a second process step of a first method according to the invention, Figure 6 shows a third process step of a first method according to the invention and Figure 6 shows a fourth process step of a first method according to the invention.

[0093] In the figures, identical components or components with the same function are marked with the same reference symbols.

[0094] The figures omit the depiction of unnecessary components, particularly the substrate holder, as they are not required to describe the process. The figures and their individual parts are not drawn to scale. This non-scale representation enhances the clarity of the figures. In particular, the transfer layer 6, which is described below as an example of a graphene layer 6, is shown very thick, even though it is only a monatomic layer. Furthermore, the protective layer 5 and the growth layer 5 are depicted as a single layer in the figures. This is the preferred embodiment, in which the protective layer 5 serves both as a protective and a growth layer 5. In any case, a protective layer 5 is provided. However, it is also conceivable that an additional growth layer is arranged on top of the protective layer 5 to create the transfer layer 6.However, a layer with the protective function is preferred, which is also suitable for generating or growing a transmission layer 6.

[0095] The Figure 1Figure 1 shows a carrier substrate 1 with a fabricated layer system in a first embodiment. The layer system consists of a solvent layer 4 applied to the carrier substrate 3. A growth layer 5, or protective layer 5, is located on the solvent layer 4. The growth layer 5 is preferably transferred to the solvent layer 4 itself by a layer transfer process or deposited directly onto the solvent layer 4 by a physical or chemical deposition process. A transfer layer 6, or graphene layer 6, is produced on the growth layer 5. The thicknesses of the carrier substrate 3, the solvent layer 4, the growth layer 5, and especially the graphene layer 6 are not shown to scale. In particular, the graphene layer 6, as a monatomic layer, would have to be shown much thinner, especially as a single line.To improve the presentation, a scale representation is omitted.

[0096] The Figure 2 Figure 1 shows a support substrate 1' with a fabricated layer system in a second embodiment. The support substrate 1' has a deposited or transferred contact layer 8 on the transfer layer 6 or the graphene layer 6.

[0097] The Figure 3 Figure 1 shows a product substrate 2 in a first embodiment. The product substrate 2 consists, in particular, only of the base product substrate 7.

[0098] The Figure 4 Figure 2 shows a product substrate 2' in a second embodiment. The product substrate 2' consists of a base product substrate 7 and a contact layer 8 deposited or transferred thereon. The contact layer 8 is preferably a dielectric layer, most preferably a silicon oxide layer.

[0099] The Figure 5Figure 2 shows a product substrate 2'' in a third embodiment. The product substrate 2'' consists of a base substrate 7'. Components 9, particularly functional ones, have already been manufactured in the base substrate 7'. Preferably, a contact layer 8' has been deposited over the base substrate 7'. The contact layer 8' preferably has electrically conductive vias 10, which are intended to connect the components 9, particularly functional ones, to the transmission layer or graphene layer (not shown). This embodiment would also be conceivable without the contact layer 8'. In this case, the vias 10 would also be omitted, and a transmission layer or graphene layer (not shown) would directly contact the contact points of the components 9, particularly functional ones (not shown).The contact layer 8' is preferably a dielectric layer, most preferably a silicon oxide layer.

[0100] The following Figures 6a to 6d We demonstrate a first method or process for transferring a transfer layer using a support substrate 2' and a product substrate 2' as examples. However, the process can be carried out using any support substrate-product substrate combination, in particular also using support substrates and / or product substrates that are not explicitly shown, provided that the layer system, consisting of the solution layer 4, the growth layer 5 and the transfer layer 6 or the graphene layer 6 to be transferred, especially in this order, is present.

[0101] Furthermore, in the following figures, the product substrate 2' is shown on the top side and the support substrate 1' on the bottom side. It is also conceivable that the support substrate 1' is located on the top side and the product substrate 1' on the bottom side. For the sake of clarity, substrate holders, bonding devices, and alignment devices are omitted from the illustrations.

[0102] The Figure 6aFigure 1 shows a first process step of a first method or process for transferring a transfer layer, in which a product substrate 2', consisting of a product base substrate 7 and a contact layer 8, is aligned relative to a support substrate 1. The contact layer 8 is preferably an oxide, most preferably a silicon oxide. The support substrate 1 consists of a support base substrate 3, a release layer 4, a growth layer 5, and the transfer layer 6, or graphene layer 6, to be transferred. How the graphene layer 6 was created or transferred onto the growth layer 5 is not relevant for understanding the process and is therefore not described in detail. The alignment can be mechanical and / or optical. In the case of optical alignment, alignment marks (not shown) are located on the product substrate 2' and the support substrate 1.

[0103] The Figure 6b The figure shows a second process step of the first process, in which contact is made between the support substrate 1 and the product substrate 2'. The figure does not illustrate exactly how the contact is made, as this is not relevant to the process. Preferably, however, the contact is made by a device in which at least one of the two substrates 1, 2' is curved. The contacting process is therefore preferably carried out using a fusion bonding system. In a particularly preferred embodiment of the process, the product substrate 2', in particular the upper one, is curved, while the support substrate 1, in particular the lower one, is fixed across its entire surface.

[0104] The Figure 6cFigure 1 shows a third process step of the first process. The release layer 4 is exposed to a debonding agent 11. Preferably, the debonding agent 11 is a laser. The debonding agent preferably acts on the release layer 4 via the substrate 3. The growth layer 5 acts as a protective shield for the underlying graphene layer 6. Since the graphene layer 6 is a monoatomic layer, it could be destroyed by high-intensity debonding agent 11. The growth layer 5, which is preferably also used to create the graphene layer 6, thus serves as a protective shield. The growth layer 5 must therefore be designed such that the debonding agent 11 used is blocked as effectively as possible during the debonding process, or at least that any influence of the debonding agent 11 on the transfer layer 6 is significantly reduced.If the debonding agent 11 is a laser, the growth layer 5 should have the lowest possible transmissivity for the photons of the laser 11. If the debonding agent 11 is, for example, heat introduced by a heat source, the growth layer 5 should have the lowest possible thermal conductivity to impede heat transfer to the graphene layer 6.

[0105] Those skilled in the art are aware that any number of other layers can be located between the release layer 4 and the growth layer 5, each fulfilling the specific task of protecting the transfer layer 6. For example, it would be conceivable to insert another layer between the release layer 4 and the growth layer 5 that absorbs the laser radiation or heat of a debonding agent 11 extremely well. For the sake of simplicity, however, this property is combined in a single growth layer 5 to avoid complicating the description or the illustration. In particular, it is advantageous if the growth layer 5, which is preferably used to grow the graphene layer 6, also serves simultaneously as its protective layer for the applied debonding agent 11. This allows for a very cost-efficient process because it is not necessary to deposit further expensive layers.A further advantage is that the growth layer 5 is particularly preferably a metal layer, most preferably a nickel layer. Metals are known to be very good infrared absorbers. The preferred debonding medium 11 is a laser, preferably an infrared laser. In this particular case, the metallic growth layer 11 can therefore serve simultaneously as the growth layer 5 and as a protective layer due to its solid-state properties. If the debonding medium 11 were a heat source, a metallic growth layer 5 would naturally be less than ideal due to its relatively high thermal conductivity. In this case, further layers are preferably inserted between the growth layer 5 and the release layer 4, especially those with low thermal conductivity.

[0106] The Figure 6dFigure 1 shows a first variant of a fourth process step of the first process, in which the also transferred growth layer 5 (no longer shown) has already been removed. This results in a transfer layer 6, or graphene layer 6, on a product substrate 2e, which represents the end product of the process. The product substrate 2e, in particular the transferred graphene layer 6, can then be further processed in subsequent process steps. The two other variants for the use of growth layer 5, which have already been mentioned, are not shown here, as no further conclusions about the actual process can be drawn from them. Reference symbol list

[0107] 1 Support substrate 2, 2', 2", 2e Product substrate 3 Support base substrate 4 Solution layer 5 Growth layer, protective layer 6 Transmission layer, graphene layer 7, 7' Product base substrate 8, 8' Contact layer 9 Functional units 10 Via 11 Debonding compound

Claims

1. A method for the preparation of a carrier substrate (1) for transferring a transfer layer (6) from the carrier substrate (1) onto a product substrate (2, 2', 2", 2e) with the following steps. i) provision of a carrier base substrate (3), (ii) application of a protective layer (5) on the carrier base substrate (3), (iii) breeding of a transfer layer (6), in particular a graphene layer, on the protective layer (5), wherein the protective layer (5) consists of a plurality of individual layers, characterised in that the carrier base substrate (3) is coated with a release layer (4) before the application of the protective layer (5) in step ii), so that the protective layer (5) is applied to the release layer (4).

2. The method according to claim 1, wherein the protective layer (5) is recrystallised prior to the breeding of the transfer layer (6) in step iii) .

3. The method according to at least one of the preceding claims, wherein a contact layer (8, 8') is deposited on the transfer layer (6) on the side facing away from the transfer layer (5).