Method for preparing a support substrate made of polycrystalline material and method for manufacturing a composite structure including said support substrate

Abstract

The invention relates to a method for preparing a support substrate made of polycrystalline material, the preparation method comprising the following steps: a) providing a raw disc made of polycrystalline material, having two faces; b) rough grinding of at least one of the faces of the raw disc, with a grinding wheel, the abrasive grit of which has an average size greater than or equal to 10 μm, to obtain a surface-ground disc having at least one surface-ground face; c) applying a heat treatment to the surface-ground disc, at a temperature above a growth temperature of the raw disc employed in step a), and below a melting temperature of the polycrystalline material, so as to obtain an annealed disc, d) thinning the annealed disc, from the at least one surface-ground face, said thinning including fine grinding with a grinding wheel, the abrasive grit of which has an average size of less than 10 μm, so as to obtain the support substrate.

Description

Method for preparing a support substrate made of polycrystalline material and method for manufacturing a composite structure including said support substrate FIELD OF THE INVENTION

[0001] The present invention relates to the field of semiconductor materials for microelectronic components. It relates in particular to a method for preparing a support substrate made of polycrystalline material, in particular SiC, capable of being used for the manufacture of a composite structure including a thin monocrystalline layer transferred onto said support substrate. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] SiC is increasingly used for the manufacturing of innovative devices (power components, radio frequencies, etc.), to meet the needs of emerging electronics fields, such as electric vehicles. Indeed, power devices and integrated power systems based on monocrystalline silicon carbide can handle a much higher power density compared to their traditional silicon counterparts, and this with smaller active area dimensions.

[0003] High-quality monocrystalline SiC (c-SiC) substrates for the microelectronics industry remain expensive and difficult to source in large quantities. It is therefore advantageous to use layer transfer solutions to develop composite structures typically comprising a thin monocrystalline SiC layer (derived from the high-quality c-SiC substrate) on a lower-cost support substrate, for example polycrystalline SiC (p-SiC). Electronic components can then be produced on and / or in the thin layer. It should also be noted that a composite structure can provide additional functionalities and performances, in particular by providing a support substrate with advantageous mechanical, electrical and / or thermal properties.

[0004] A well-known thin film transfer solution is the Smart Cut process TM, based on an implantation of light ions and on an assembly, by direct bonding, between a monocrystalline donor substrate and a support substrate, at the level of a bonding interface.

[0005] To be compatible with a thin-film transfer process, the support substrate must have as little curvature or deformation as possible. Low curvature is also desired to ensure the performance of the manufacturing steps (e.g., photolithography) of the components on / in the thin layer of the composite structure.

[0006] Document FR3132381 proposes a method for manufacturing a non-deformable p-SiC wafer.

[0007] Starting from a p-SiC wafer separated from its growth substrate, this process comprises a heat treatment step at a temperature between 1650°C and 2000°C, followed by a thinning step including in particular very rough grinding, rough grinding and fine grinding. The heat treatment is likely to cause deformation of the wafer. The thinning is then adapted to include a correction of said deformation, by locally adjusted material removal.

[0008] SUBJECT OF THE INVENTION

[0009] The present invention provides a method for preparing a support substrate made of polycrystalline material, in particular p-SiC, as an alternative to the methods of the prior art, which promotes low curvature of the support substrate and which minimizes manufacturing costs. The invention also relates to a method for manufacturing a composite structure including said support substrate.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] The invention relates to a method for preparing a support substrate made of polycrystalline material, the preparation method comprising the following steps:

[0012] (a) the supply of a raw disc made of polycrystalline material, having two faces;

[0013] (b) the rough grinding of at least one of the faces of the raw disc, with a grinding wheel whose abrasive grains have an average size greater than or equal to 10 μm, to obtain a ground disc having at least one ground face,

[0014] (c) applying a heat treatment to the ground disc, at a temperature higher than a growth temperature of the raw disc implemented in step (a), and lower than a melting temperature of the polycrystalline material, to obtain an annealed disc,

[0015] d) thinning the annealed disc, at the level of the -at least one- ground face, said thinning including fine grinding with a grinding wheel whose abrasive grains have an average size of less than 10μm, to obtain the support substrate.

[0016] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combination: step a) comprises the following sub-steps: a1) chemical vapor deposition of a layer formed from the polycrystalline material, on a growth substrate, a2) removal of the growth substrate to obtain the raw disc; the polycrystalline material is silicon carbide or aluminum nitride; the heat treatment of step c) is carried out at a temperature greater than or equal to 1600°C for a duration greater than or equal to 10 min; step b) is applied to both faces of the raw disc, and / or step d) is applied to both faces of the raw disc; the rough grinding, applied to one and / or the other of the faces of the raw disc, removes a first thickness greater than or equal to 150 μm;the heat treatment of step c) is carried out at a temperature greater than or equal to 1700°C, preferably greater than or equal to 1800°C, still more preferably greater than or equal to 1850°C, or even more preferably greater than or equal to 2000°C; the fine grinding of step d), applied to one and / or the other of the faces of the annealed disc, removes a second thickness less than or equal to 50μm; the second thickness is less than or equal to 20μm, preferably between 5μm and 20μm; the fine grinding of step d) is carried out with a grinding wheel whose abrasive grains have an average size less than or equal to 5μm, less than or equal to 4μm, or even less than or equal to 3μm;step d) comprises, after fine grinding, a surface preparation comprising polishing, cleaning, annealing, etching and / or deposition of a film, so as to obtain a surface condition of the support substrate compatible with direct assembly on another substrate; step d) comprises, after fine grinding, a surface preparation comprising only cleaning and / or annealing and / or plasma activation and / or deposition of a film, so as to obtain a surface condition of the support substrate compatible with direct assembly on another substrate.;

[0017] The invention also relates to a method of manufacturing a composite structure comprising the following steps:

[0018] - the preparation of a support substrate made of a polycrystalline material as above, and

[0019] - the transfer of a thin layer of monocrystalline material, from a donor substrate, onto said support substrate.

[0020] Advantageously, the polycrystalline material is chosen from silicon carbide and aluminum nitride.

[0021] Advantageously, the monocrystalline material is chosen from silicon carbide, gallium nitride, gallium oxide, diamond, silicon, germanium, indium phosphide.

[0022] The manufacturing method may further comprise a step of forming electronic components in or on the thin layer. BRIEF DESCRIPTION OF THE FIGURES

[0023] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0024]

[0025]

[0026]

[0027]

[0028] La, la', la, laet lapresent a method for preparing a support substrate according to the present invention;

[0029]

[0030] Laet present composite structures resulting from a manufacturing process in accordance with the invention;

[0031]

[0032] Laet lapresent sectional images, obtained by scanning electron microscopy, of discs ground after step b) of a method according to the present invention; in particular, the surface work-hardened layer can be observed.

[0033] The same references in the figures may be used for elements of the same type. Some figures are schematic representations which, for the sake of readability, are not to scale. In particular, the thicknesses of the layers along the z axis are not to scale with respect to the lateral dimensions along the x and y axes; and the relative thicknesses of the layers are not necessarily respected in the figures. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention relates to a method for preparing a support substrate 200 made of polycrystalline material. Preferably, said material is silicon carbide (SiC) or aluminum nitride (AlN).

[0035] There are several techniques for producing or growing polycrystalline materials in the form of discs, intended to form substrates or wafers, particularly for the semiconductor industry. These techniques include manufacturing by sintering, PVT (Physical Vapor Transport), CVD (Chemical Vapor Deposition) or HTCVD (High Temperature Chemical Vapor Deposition), etc.

[0036] The first step a) of the preparation method according to the invention corresponds to the provision of a raw disc 2 made of polycrystalline material, produced by one of the aforementioned known techniques. The raw disc 2 has two faces which extend substantially parallel to a main plane (x,y).

[0037] CVD manufacturing has the advantage of a dense disc, without porosity, unlike sintering; another advantage is that the internal stresses in the disc after CVD growth are lower compared to those present in a disc produced by sintering.

[0038] Preferably, step a) involves a first sub-step a1) of chemical vapor deposition (CVD) of a layer 2' of polycrystalline material, on a so-called growth substrate 2'' ().

[0039] In the case where the polycrystalline material is SiC, this technique involves a gas mixture comprising at least one silicon precursor gas (such as a silane or a chlorosilane) and / or at least one carbon precursor gas (such as an alkane or an alkene), and / or at least one silicon and carbon precursor gas (such as methyltrichlorosilane, abbreviated MTCS), and, if necessary, at least one doping gas. These gases can be diluted in a carrier gas, which can be a reducing gas such as hydrogen and / or an inert gas such as argon. From this gas mixture, the polycrystalline SiC layer 2' is formed on the growth substrate 2''. The latter is preferably made of purified fine-grained isostatic graphite, to form a 3C-SiC polytype. The reactor temperature during CVD deposition of SiC should be between about 1000°C and about 1600°C.For example, the deposition can be carried out on a graphite disc, with a diameter approaching a nominal 150 mm and a thickness greater than 2 mm to ensure sufficient flatness of the growth substrate / p-SiC layers assembly. The diameter and thickness of the 2'' graphite disc can of course vary, if one wishes to prepare a support substrate with a diameter of 100 mm, 200 mm or other.

[0040] The following sub-step a2) corresponds to the removal of the growth substrate 2'' to obtain a raw disc 2 made of polycrystalline material having two faces 2a,2b (').

[0041] Continuing with the previous example relating to SiC, the 2'' graphite growth substrate, coated with the 2' p-SiC deposition layer, is machined, then oxidized in air typically at 900°C to remove any graphite residue. Note that the removal of the 2' graphite could also be carried out by purely mechanical machining techniques or even essentially by burning / oxidation. In practice, a raw 2 p-SiC disc is often recovered at each face of the 2'' growth substrate.

[0042] For a diameter of 150mm or 200mm, the thickness of the raw disc 2 of polycrystalline material provided in step a) is typically between 700μm and 3000μm.

[0043] The method then comprises a step b) consisting of a rough grinding of at least one of the faces 2a, 2b of the raw disc 2, with a grinding wheel adapted to a high removal of material.

[0044] As is known per se, a grinding wheel is a rotationally symmetrical tool composed of abrasive grains embedded in a binding matrix. The abrasive grains are, for example, diamond grains. To grind one face of the raw disc 2, the grinding wheel is rotated and gradually lowered to abrade the polycrystalline material and thus remove material to a certain thickness.

[0045] The grinding in step b) is called “coarse” because it uses a grinding wheel with a large grain size.

[0046] In particular, the abrasive grains have an average size (or average diameter) greater than or equal to 10μm, typically between 10μm and 160μm. Average size means the average of the sizes (diameters or equivalent diameters) of the abrasive grains forming the grinding wheel.

[0047] In other words, the mesh (or grit in English) of the grinding wheel, the value of which varies inversely with the size of the abrasive grains, is less than or equal to 2000, typically between 100 and 2000.

[0048] Preferably, the abrasive grains have an average size greater than or equal to 18μm, typically between 18μm and 50μm (i.e. a wheel mesh between 350 and 1000), or even between 50μm and 160μm (i.e. a wheel mesh between 100 and 350).

[0049] This rough grinding causes the formation of a superficial damaged region, which can extend over several micrometers, several tens of micrometers, or even a few hundred micrometers (for example, between 15μm and 600μm).

[0050] The damaged region comprises two layers: a surface hardened layer 21 and an underlying stressed layer 22. The hardened layer 21 is characterised by the presence of significant surface scratches (in particular causing high surface roughness) and the presence of cracks and stresses in the material. It has a typical thickness of between 0.5μm and 50μm, or even between 5μm and 50μm for the largest average abrasive grain sizes.

[0051] The stressed layer 22, as its name suggests, is characterized by stresses in the material, but without cracks. It is located below the work-hardened layer 21 and has a typical thickness between 10μm and 500μm.

[0052] The thicknesses of the work-hardened layer 21 and of the constrained layer 22 depend in particular on the size of the abrasive grains of the grinding wheel.

[0053] The damaged region with its two layers 21, 22 can be characterized in particular by transmission electron microscopy (TEM or TEM). The hardened layer 21 can also be identified by scanning electron microscopy (SEM or SEM): two examples are illustrated in Figures 3a and 3b, with a hardened layer 21, in which cracks can be seen extending, and which has a thickness of the order of 4 μm and 10 μm respectively.

[0054] Advantageously, the rough grinding is carried out on the two faces 2a, 2b of the raw disc 2. Indeed, the raw disc 2 usually has a large variation in thickness (TTV) and requires grinding on the side of the face where the growth (CVD) took place. In addition, the face initially in contact with the growth substrate 2'' has a nucleation zone with very small grains, a zone likely to create a stress differential with the other face (at which the grains have grown), and which it is therefore preferable to grind as well.

[0055] Preferably, the rough grinding removes a thickness (called first thickness) on one or each face 2a, 2b of the raw disc 2, greater than or equal to 10 μm, greater than or equal to 50 μm, greater than or equal to 150 μm, greater than or equal to 250 μm, greater than or equal to 500 μm, greater than or equal to 1 mm. The first thickness is advantageously between 100 μm and 300 μm, in particular when the raw disc 2, provided in step a), has been produced by a chemical vapor deposition (CVD) technique.

[0056] At the end of this step, we obtain a so-called rectified disc 20 which has two faces 20a, 20b ().

[0057] After step c), a ground disc 20 with a diameter of 150mm has a typical thickness of between 400μm and 800μm. For a ground disc 20 with a diameter of 200mm, the typical thickness is between 550μm and 900μm.

[0058] The following step c) provides for the application of a heat treatment to the ground disc 20. The temperature and duration of the heat treatment are defined so as to relax all or part of the stresses present in the constrained layer 22 (said layer having been generated by the rough grinding step b). Here, only one constrained layer 22 is referred to, but as can be seen in the, the ground disc 20 may have two superficial damaged regions (therefore two constrained layers 22) at one and the other of its faces 20a, 20b, if they have both been ground in step b).

[0059] The heat treatment is carried out at a temperature higher than the growth / formation temperature of the raw disc 2 and lower than the melting temperature of the polycrystalline material.

[0060] In particular, the temperature applied in step c) is greater than or equal to 1500°C (for example in the case of p-AlN), or even greater than or equal to 1600°C (for example in the case of p-SiC) for a duration greater than or equal to 10 min.

[0061] Preferably, the heat treatment of step c) is even carried out at a temperature greater than or equal to 1700°C, 1800°C, 1850°C, or even 2000°C. Also preferably, the duration of the heat treatment is greater than or equal to 30 min, greater than or equal to 1 h, or even greater than or equal to 2 h. The annealing atmosphere is advantageously neutral, for example based on argon. The heat treatment can advantageously be carried out under a pressure greater than atmospheric pressure.

[0062] At the end of this step, we obtain a disc called annealed 20' ().

[0063] This heat treatment, carried out after the rough grinding and prior to thinning by fine grinding (next step d)) allows healing of all or part of the stressed layer 22 and possibly partial healing of the work-hardened layer 21 of the damaged region (of one or both faces 20a, 20b) of the ground disc 20. This healing results in a rearrangement of the polycrystalline structure and a relaxation (therefore a reduction) of the stresses present in the damaged region.

[0064] The annealed disc 20' then comprises a first annealed layer 21', formerly the work-hardened layer 21 of the ground disc 20. The first annealed layer 21' extends over the same thickness as the work-hardened layer 21, but can benefit from a lower level of defectivity and stress due to the heat treatment.

[0065] The annealed disc 20' also comprises a second annealed layer 22', located under the first annealed layer 21', and formerly the stressed layer 22 of the ground disc 20. The second annealed layer 22' is wholly or partly relaxed, that is to say that it is no longer likely (or less likely) to generate deformation of the disc during subsequent thinning or heat treatment steps. The second annealed layer 22' extends over the same thickness as the stressed layer 22.

[0066] The method then comprises a step d) of thinning the annealed disc 20', at the level of the -at least one- face ground during step b). This step aims to remove the first annealed layer 21', while the second annealed layer 22' is retained at least in part, preferably, it is retained in full or in major part (more than 80%, or even more than 90%).

[0067] Step d) includes fine grinding with a grinding wheel whose abrasive grains have an average size (or average diameter) less than or equal to 10 μm (i.e. a wheel mesh greater than or equal to 2000). Preferably, the average size of the abrasive grains is less than or equal to 8 μm, 7 μm, 6 μm, 5 μm, 4 μm, or even 3 μm (corresponding respectively to a wheel mesh greater than or equal to approximately 2400, 2800, 3300, 4000, 5000, 7000).

[0068] At the end of step e), the support substrate 200 () is obtained.

[0069] Due to the application of the heat treatment in step c), it is possible to remove less material by fine grinding in this step d). According to the invention, the fine grinding aims to remove all of the first annealed layer 21' or in any case a major part of it (typically more than 90%, or even more than 95%); on the other hand, it does not remove the underlying second annealed layer 22' or only a minor part of it (typically less than 20%, less than 10%, or even less than 5%), because the potential damage that the second annealed layer 22' could cause on the curvature is deactivated by step c).

[0070] Advantageously, the fine grinding removes a thickness (called second thickness) on one or each face 20a, 20b of the annealed disc 20', less than or equal to 50μm, less than or equal to 20μm, preferably between 5μm and 20μm.

[0071] For a diameter of 150mm, the support substrate 200, after fine grinding, typically has a thickness of between 110μm and 400μm; for a diameter of 200mm, its typical thickness is between 110μm and 600μm.

[0072] Very fine grain grinding wheels experience significant and rapid wear with the thickness removed, so it is not economically advantageous to remove too much material with these wheels. Their advantage, however, is that they provide very favorable preliminary surface finishes (low roughness and low thickness of induced damaged region).

[0073] Because the thickness to be removed is small in step d), due to the application of the heat treatment directly after the rough grinding, it is economically viable to carry out the fine grinding with a grinding wheel whose abrasive grains are fine, or even very fine, such as having an average size less than or equal to 5μm, less than or equal to 4μm, or even less than or equal to 3μm.

[0074] For example, step d) may be carried out on a 20' annealed p-SiC disc with a 4000 mesh or even 8000 mesh grinding wheel, by applying a rotation of the head supporting the wheel ("spindle") between 1000 and 2000 revolutions per minute (rpm) and a rotation of the plate supporting the 20' annealed disc of the order of 200 to 400 rpm, with a removal speed of between 0.1 μm / s and 0.5 μm / s, for example 0.15 μm / s.

[0075] After the fine grinding, step d) advantageously comprises a surface treatment comprising chemical-mechanical polishing, cleaning, annealing, chemical etching (wet or dry) and / or film deposition, so as to obtain a surface condition of the support substrate 200 compatible with direct assembly on another substrate. Such a surface condition typically corresponds to a roughness less than or equal to 1 nm RMS (measured by atomic force microscopy on 20 μm x 20 μm scans).It should be noted that, when fine grinding, with a grinding wheel whose abrasive grains have an average size less than or equal to 3 µm, is applied in step d), there is no need to add any mechanical or chemical-mechanical polishing step; only cleaning (or cleaning sequence), film deposition, annealing and / or plasma activation are preferably carried out before assembly of the support substrate 200 for the manufacture of the composite structure 100. This is an important advantage because the polishing steps are expensive and likely to differentially etch the grains of the polished face, which tends to degrade the surface quality, which is critical for assembly.

[0076] Taking into account the successive application of steps b), c) and d), without any other intervening step, the curvature of the p-SiC support substrate 200 remains within a reasonable range, being derived from a raw disc 2 of economically viable thickness and after implementation of a simple process, minimizing manufacturing costs.

[0077] Curvature can be measured using a white light confocal sensor that scans a surface of the substrate, the latter being placed on a support plane of the measuring tool. For a 200 support substrate with a diameter of 150mm or 200mm, the curvature is typically less than or equal to 150μm, 100μm, or even 50μm.

[0078] The sequence of steps b), c) and d) also presents an economic interest because the rough grinding is rapid and the associated grinding wheel supports thick removals without prohibitive wear. In addition, step d) requiring low removal, a high grinding wheel mesh can be used, which facilitates the subsequent surface treatment aimed at obtaining a surface condition of the support substrate 200 compatible with direct assembly on another substrate.

[0079] The support substrate 200 thus prepared is intended to be used for the manufacture of a composite structure 100. The method of manufacturing this structure 100 comprises the transfer of a thin layer 10 made of a monocrystalline material onto said support substrate 200. Although any known method of thin layer transfer can be used, reference can in particular be made to the Smart Cut method. TM, based on the formation of a fragile plane buried in a donor substrate made of monocrystalline material, by ion implantation of light species (for example, H, He or a combination of these two species), and on a direct assembly (by molecular adhesion) between said donor substrate and the support substrate. A separation in the buried fragile plane then makes it possible to transfer a thin monocrystalline layer 10, originating from the donor substrate, onto the support substrate 200 (), while retaining the rest of the donor substrate for future reuse.

[0080] The thin monocrystalline layer 10 may in particular be made of silicon carbide, diamond, silicon, II-VI or III-V semiconductor compounds (for example AlN, GaN, etc.), gallium oxide (Ga2O3), or any wide bandgap semiconductor material.

[0081] For example, the thin layer 10 of the composite structure 100 has a thickness of between a few tens of nm and a few hundreds of nm, for example, between 50 nm and 800 nm. We will see later that epitaxy steps can be implemented on said thin layer 10, so as to thicken it (homoepitaxy) or to grow other materials (heteroepitaxy), for the needs of the electronic components to be manufactured. The thin layer 10 has an electrical resistivity adapted to the application and the components targeted.

[0082] In the composite structure 100, the support substrate 200 has a thickness and a curvature as previously stated. The range of radius of curvature of the support substrate 200 makes the latter perfectly compatible with the specifications of a composite structure 100 provided with a thin monocrystalline layer 10, with the method of manufacturing such a structure 100 and with the subsequent development of microelectronic components on and / or in the thin layer 10. Note that the curvature of the composite structure 100 remains close to the curvature of the support substrate 200.

[0083] The composite structure 100 may comprise a continuous or discontinuous intermediate layer 30, arranged between the thin layer 10 and the support substrate 200 and composed of at least one metallic or semiconductor material (). As is known per se, with reference to a method for manufacturing the composite structure 100, the intermediate layer 30 may be formed on the side of the thin layer 10, on the side of the support substrate 200 or on both sides, prior to assembly along a bonding interface of the donor substrate and the support substrate 200. The intermediate layer 30 may for example be composed of silicon, silicon carbide, tungsten and / or titanium. Its thickness is typically between a few nm and a few hundred nm, preferably between 2 nm and 50 nm.

[0084] The composite structure 100 obtained is extremely robust to very high temperature heat treatments that may be applied to improve the quality of the thin layer 10 or to manufacture components on and / or in said layer 10. The support substrate 200 in the composite structure 100 is stable and does not see its curvature increase prohibitively during the high temperature heat treatments applied to the composite structure 100 for its manufacture and subsequently.

[0085] The composite structure 100 according to the invention is particularly suitable for the production of one (or more) electronic component(s), in particular high voltage, such as for example Schottky diodes, MOSFET or HEMT transistors, and / or high frequencies (RF), in and / or on the thin layer.

[0086] Of course, the invention is not limited to the embodiments and examples described, and variant embodiments can be made without departing from the scope of the invention.

Claims

Method for preparing a support substrate (200) made of polycrystalline material, the preparation method comprising the following steps: a) providing a raw disc (2) made of polycrystalline material, having two faces (2a, 2b);b) the rough grinding of at least one of the faces (2a, 2b) of the raw disc (2), with a grinding wheel whose abrasive grains have an average size greater than or equal to 10 μm, to obtain a ground disc (20) having at least one ground face (20a, 20b), c) the application of a heat treatment to the ground disc (20), at a temperature higher than a growth temperature of the raw disc (2) implemented in step a), and lower than a melting temperature of the polycrystalline material, to obtain an annealed disc (20'), d) the thinning of the annealed disc (20'), at the level of the -at least one- ground face (20a, 20b), said thinning including a fine grinding with a grinding wheel whose abrasive grains have an average size less than 10 μm, to obtain the support substrate (200).; Preparation method according to claim 1, wherein step a) comprises the following sub-steps:a1) chemical vapor deposition of a layer formed from the polycrystalline material (2'), on a growth substrate (2''),a2) removal of the growth substrate (2'') to obtain the raw disc (2). Preparation method according to one of the preceding claims, in which the polycrystalline material is silicon carbide (SiC) or aluminum nitride (AlN). Preparation process according to one of the preceding claims, in which the heat treatment of step c) is carried out at a temperature greater than or equal to 1600°C for a duration greater than or equal to 10 min. Preparation method according to one of the preceding claims, in which step b) is applied to both faces of the raw disc (2), and / or step d) is applied to both faces of the raw disc (2). Preparation method according to one of the preceding claims in which the rough grinding, applied to one and / or the other of the faces of the raw disc (2), removes a first thickness greater than or equal to 150μm. Preparation process according to one of the preceding claims, in which the heat treatment of step c) is carried out at a temperature greater than or equal to 1700°C, preferably greater than or equal to 1800°C, even more preferably greater than or equal to 1850°C, or even more preferably greater than or equal to 2000°C. Preparation method according to one of the preceding claims, in which the fine grinding of step d), applied to one and / or the other of the faces of the annealed disc (20'), removes a second thickness less than or equal to 50μm. Preparation method according to claim 8, in which the second thickness is less than or equal to 20μm, preferably between 5μm and 20μm. Preparation method according to one of the preceding claims, in which the fine grinding of step d) is carried out with a grinding wheel whose abrasive grains have an average size less than or equal to 5μm, less than or equal to 4μm, or even less than or equal to 3μm. Preparation method according to one of the preceding claims, in which step d) comprises, after fine grinding, a surface preparation comprising only cleaning, annealing, plasma activation and / or deposition of a film, so as to obtain a surface condition of the support substrate (200) compatible with direct assembly on another substrate. Method for manufacturing a composite structure (100) comprising:- the preparation of a support substrate (200) made of a polycrystalline material in accordance with the method according to one of claims 1 to 11, and- the transfer of a thin layer (10) made of a monocrystalline material, from a donor substrate (1), onto said support substrate (200). A method of manufacturing a composite structure (100) according to claim 12, wherein the polycrystalline material is silicon carbide (SiC) or aluminum nitride (AlN), and wherein the monocrystalline material is selected from silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond, silicon, germanium, indium phosphide (InP). A manufacturing method according to one of claims 12 and 13, further comprising forming electronic components in or on the thin layer (10).

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