Composite structure and manufacturing method thereof

Abstract

The invention relates to a method for manufacturing a composite structure comprising a thin layer of a first monocrystalline layer arranged on a carrier substrate, the manufacturing method comprising: a) a step of providing an initial substrate of a second polycrystalline material, b) a step of depositing, by spin coating, at least on one front surface of the initial substrate, a layer of polymer resin comprising preformed 3D carbon-carbon bonds, c) performing a first annealing step at a temperature between 120°C and 180°C on the initial substrate provided with the polymer resin layer, in order to form a layer of cross-linked polymer resin, d) performing a second annealing step at a temperature greater than 600°C, in a neutral atmosphere, in order to convert the layer of cross-linked polymer resin into a glassy carbon film. The invention also relates to a composite structure comprising a thin layer of a first monocrystalline material arranged on a carrier substrate, the carrier substrate including: - an initial substrate made of a second polycrystalline material, - a glassy carbon film in contact with the front surface of the initial substrate.

Description

COMPOSITE STRUCTURE AND ASSOCIATED MANUFACTURING METHOD FIELD OF THE INVENTION

[0001] The present invention relates to the field of microelectronics and semiconductors. In particular, the invention relates to a substrate made of polycrystalline material comprising a surface film of vitreous carbon, and particularly suitable for receiving a thin layer transferred from a donor substrate. The invention also relates to a method for manufacturing said support substrate and the composite structure resulting from the transfer of the thin layer onto the support substrate. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Silicon carbide (SiC) is increasingly used for the fabrication of high-performance power devices. However, 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 c-SiC layer (derived from a high-quality c-SiC substrate and intended to accommodate the sensitive functional parts of the devices) on a lower-cost support substrate, for example polycrystalline SiC (p-SiC).

[0003] A well-known thin-film transfer solution is the Smart Cut® process, based on the implantation of light ions into a donor substrate (c-SiC) and on assembly, by direct bonding, at a bonding interface between the donor substrate and a support substrate (e.g. p-SiC).

[0004] Due to the hardness of the material and the polycrystalline structure, p-SiC substrates are difficult to polish and generally have residual surface roughness which complicates assembly by direct bonding. Indeed, direct bonding does not use adhesive substances but involves molecular bonds between the surfaces of the substrates in contact: such bonding therefore requires excellent flatness as well as very low surface roughness and defects.

[0005] It is known to deposit an intermediate layer on one and / or the other of the substrates to be assembled, said layer being easy to prepare (low roughness, in particular) for assembly by direct bonding. It should be noted that this intermediate layer must not affect the performance of the devices developed on the composite structure; in this case, for vertical power devices, such an intermediate layer must not affect the vertical electrical conductivity between the thin c-SiC layer and the p-SiC support substrate.

[0006] In particular, the use of metallic intermediate layers to ensure vertical conduction in the composite structure is known from the state of the art.

[0007] Although this introduction mainly discusses the interest of composite structures based on silicon carbide, composite structures based on other materials, which are efficient but expensive in large substrates and complex to prepare for thin-layer transfer, such as SiC, may also be concerned. For example, a composite structure comprising a thin layer of gallium nitride (GaN) and a polycrystalline support substrate, for example aluminum nitride (AlN) can be mentioned. SUBJECT OF THE INVENTION

[0008] The present invention proposes a solution, alternative to the solutions of the state of the art, which promotes the obtaining of a low surface roughness of the support substrate and promotes its electrical and thermal properties. The invention relates in particular to an initial polycrystalline substrate comprising a surface film of vitreous carbon, particularly suitable for receiving a useful layer transferred from a donor substrate. The invention also relates to a method for manufacturing said support substrate and the composite structure resulting from the transfer of the thin layer onto the support substrate. BRIEF DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a method for manufacturing a composite structure comprising a thin layer of a first monocrystalline material arranged on a support substrate, the manufacturing method comprising the following steps: a) providing an initial substrate of a second polycrystalline material, b) depositing by spin coating, at least on a front face of the initial substrate, a layer of polymer resin comprising carbon-carbon bonds preformed in three dimensions, c) applying a first annealing at a temperature between 120°C and 180°C to the initial substrate provided with the layer of polymer resin, to form a layer of crosslinked polymer resin, d) applying a second annealing at a temperature above 600°C, under a neutral atmosphere, to transform the layer of crosslinked polymer resin into a glassy carbon film.

[0010] According to advantageous characteristics of the invention, taken alone or in any feasible combination: the method comprises, after step d), a step e) of mechanical and / or chemical-mechanical polishing of the vitreous carbon film; the polymer resin is based on coal tar, phenol formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and / or polystyrene; the method comprises a step f) of transferring a thin layer formed from the first monocrystalline material directly onto the vitreous carbon film or via an intermediate layer; step f) implements an assembly between a donor substrate comprising the first monocrystalline material, from which the thin layer will be obtained, and the vitreous carbon film, by direct bonding, to form a bonded assembly;the donor substrate comprises a buried fragile plane which delimits, with a front face of said substrate, the thin layer to be transferred, and step f) implements a separation of the bonded assembly along the buried fragile plane, to give rise on the one hand, to a composite structure including the thin layer arranged on the vitreous carbon film, itself arranged on the initial substrate, and on the other hand, the remainder of the donor substrate; the first monocrystalline material is chosen from silicon carbide, gallium nitride, silicon, silicon-germanium, germanium, III-V compounds, or other semiconductor materials, or from piezoelectric materials; the second polycrystalline material is chosen from silicon carbide, aluminum nitride, silicon, silicon-germanium, germanium, III-V compounds or other semiconductor materials, or from piezoelectric materials;the first material and the second material are semiconductors.;

[0011] The invention also relates to a composite structure comprising a thin layer of a first monocrystalline material arranged on a support substrate, said support substrate including:- an initial substrate of a second polycrystalline material,- a glassy carbon film, in contact with the front surface of the initial substrate.

[0012] According to advantageous characteristics of the invention, taken alone or in any feasible combination: the initial substrate has a surface roughness of between 10nm and 2μm peak-to-trough, measured by atomic force microscopy over a surface area less than or equal to 30μm x 30μm; the glassy carbon film has a thickness of between 100nm and 4μm; the composite structure comprises an intermediate layer, between the thin layer and the glassy carbon film, chosen from silicon, silicon carbide, carbon, tungsten or titanium; the first monocrystalline material is chosen from silicon carbide, gallium nitride, or other semiconductor materials, and the second polycrystalline material is chosen from silicon carbide, aluminum nitride, or other semiconductor materials.

[0013] Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figures in which:

[0014]

[0015]

[0016]

[0017] Figures 1a, 1b, 1c and 1d show steps of a method of manufacturing a support substrate, in accordance with the invention;

[0018] This presents an example of the surface state of an initial substrate making up a support substrate in accordance with the invention;

[0019] This presents an example of the surface state of a glassy carbon film forming a support substrate in accordance with the invention;

[0020]

[0021]

[0022]

[0023]

[0024] Figures 4a, 4b, 4c, 4c', 4d show steps in the method of manufacturing a composite structure, in accordance with the invention.

[0025] Some figures are schematic representations which, for readability purposes, are not to scale. In particular, the layer thicknesses along the z axis are not to scale with the lateral dimensions along the x and y axes.

[0026] The same references in the figures or in the description may be used for elements of the same nature. DETAILED DESCRIPTION OF THE INVENTION

[0027] The invention relates to a method for manufacturing a composite structure 100 comprising a thin layer 10 made of a first monocrystalline material arranged on a support substrate 20, which is at least partly composed of a second polycrystalline material (). The composite structure 100 in question allows vertical electrical conduction between the thin layer 10 and the support substrate 20, in particular for power electronics applications.

[0028] In particular, the first monocrystalline material may be chosen from silicon carbide (c-SiC), gallium nitride (c-GaN), silicon, silicon-germanium, germanium, III-V compounds, or other semiconductor materials, or piezoelectric materials such as lithium tantalate, lithium niobate, etc. The second polycrystalline material may be chosen from silicon carbide (p-SiC), aluminum nitride (p-AlN), silicon (p-Si), or any material stated above with reference to the first material but having a polycrystalline structure or comprising a surface polycrystalline layer. In the composite structure 100, the first materials stated may be associated with one or other of the second materials above, provided of course that this is of interest for the final application.Advantageously, the composite structure 100 will be formed from a first and a second material having similar thermal expansion coefficients.

[0029] In the remainder of the description, we will describe in particular the case of a first material in c-SiC and a second material in p-SiC. This description nevertheless applies to any other pair of first and second materials. When certain situations require it, details will be provided for the different natures of first and second materials.

[0030] The manufacturing method firstly comprises a step a) of providing an initial substrate 2 made of polycrystalline silicon carbide (p-SiC), having a front face 2a and a rear face 2b (). The initial substrate 2 can be produced by a conventional technique such as sintering or chemical vapor deposition.

[0031] The initial substrate 2 is preferably in the form of a wafer with a diameter of 100mm, 150mm, 200mm or even 300mm and a thickness typically between 300 and 800 microns.

[0032] The surface condition of the front face 2a of the initial substrate 2 is preferably chosen so that the peak-to-valley roughness (hereinafter called “PV roughness” with reference to “peak-to-valley” according to English terminology) is less than or equal to a few micrometers, typically less than or equal to 2 μm, 1 μm, 500 nm, 100 nm, or even 50 nm.

[0033] In the context of the present invention, roughness is measured by atomic force microscopy (AFM) over a surface area (scan area or "scan") less than or equal to 30μm x 30μm. The measured surface area may, for example, extend over 5μm x 5μm, 10μm x 10μm, 20μm x 20μm or 30μm x 30μm. We will subsequently refer to PV roughness and root mean square roughness or RMS.

[0034] Remember that it is complex to obtain a very good surface finish on a p-SiC substrate, due to the hardness of the material and the polycrystalline structure: mechanical or chemical-mechanical polishing can generate the formation of scratches on the surface of the substrate and the appearance of defects (holes) due to the untimely tearing of p-SiC grains on the surface.

[0035] An example of the surface condition of an initial substrate 2 is given in. Although the RMS roughness remains less than 1 nm, a PV roughness that can exceed 30 nm is observed due to the presence of scratches on the surface. Such a surface condition is likely to generate physical defects (holes) at the future interface between the substrate and the thin layer of the composite structure 100: this leads to degradation of the quality and integrity of the transferred thin layer as well as the electrical conductivity of the interface.

[0036] Typically, in the context of the present invention, the initial substrate 2 may have a PV surface roughness of up to a few micrometers, which greatly relaxes the manufacturing or supply constraints of the initial substrate 2.

[0037] The surface condition of the rear face 2b of the initial substrate 2 is not specified here. It may be similar to that of the front face 2a or more degraded, provided that it does not globally affect the curvature or the quality (defectivity) of the initial substrate 2.

[0038] To accommodate the surface state of the initial substrate 2, the manufacturing method according to the invention provides a step b) comprising a deposition by spin coating, at least on the front face 2a of the initial substrate 2, of a layer of polymer resin 3 (). An important characteristic of this layer is that it comprises carbon-carbon (CC) bonds preformed in three dimensions (3D). In this layer, the carbon polymer chains, which have sequences of CC bonds, are randomly dispersed in a solvent: they thus have a more or less random 3D structure. The more these chains are randomly dispersed in 3D, the less graphitization will be favored and the closer we will get to a glassy state, during crosslinking.

[0039] Here, a layer of polymer resin 3 is favored, leading to the highest possible amorphous / crystalline ratio, after crosslinking, to obtain a glassy carbon film 30, at the end of a subsequent step d) of the process.

[0040] The polymer resin may be formed from coal tar, phenol formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and / or polystyrene, etc.

[0041] For example, known photosensitive resins, usually used for photolithography steps in the field of microelectronics, can be used, such as commercial products:

[0042] - AZ-5214, AZ-4330, AZ-P4620 (registered trademarks) (based on 1-methoxy-2-propanol acetate, diazonaphthoquinonesulfonic esters, 2-methoxy-1-propanol acetate, Cresol novolak resin),

[0043] - OCG-825 (based on ethyl-3-ethoxypropionate),

[0044] - SU-8 2000 (based on cyclopentanone, triarylsulfonium / hexafluoroantimonate salts, propylene carbonate, epoxy resin).

[0045] Epoxy resins, such as for example the product Epoxy Novolac EPON (registered trademark) proposed for covering and protecting different surfaces in various fields (aeronautics, marine, automotive, construction, etc.), can also be used in step b) of the process according to the invention.

[0046] The centrifugal spreading carried out in step b) requires that the polymer resin solution be in a viscous form.

[0047] This deposition method is particularly advantageous because the viscous solution fills the hollows (holes and scratches) present on the surface of the initial substrate 2 and therefore effectively planarizes these microreliefs.

[0048] The thickness of the polymer resin layer 3 deposited in step b) can typically vary between a few hundred nanometers (for example 500nm) and several microns (for example 3 to 5 μm).

[0049] The manufacturing method then comprises a step c) consisting of applying an annealing (called first annealing), having a temperature plateau at a temperature between 120°C and 180°C, to the initial substrate 2 provided with the polymer resin layer 3 (). The plateau can have a duration between a few minutes (typically 30 min) and a few hours (typically 2 h). A gradual temperature rise, namely between 1°C / min and 5°C / min, from room temperature to the plateau is preferred, so as to gradually degas the polymer resin layer 3 and to evacuate the solvent and impurities initially present in the viscous solution.

[0050] Intermediate stages may also be planned in the thermal cycle of the first annealing, depending on the nature of the polymer resin.

[0051] Following the first annealing, the polymer resin layer 3' is crosslinked, therefore solidified against the front surface 2a of the initial substrate 2. The crosslinking is characterized by the formation of bonds between the carbon chains, which will result in the solidification of the layer 3'. The arrangement, in the crosslinked polymer resin layer 3', of the polymer chains in 3 dimensions will influence the 3-dimensional orientation of the sp2-type bond chains, during the following step d) of the process.

[0052] Finally, the manufacturing method comprises a step d) consisting of the application of a second annealing having a plateau at a temperature greater than 600°C, preferably greater than 700°C, under a neutral atmosphere, to transform the crosslinked polymer resin layer 3' into a vitreous carbon film 30 (). The plateau temperature may for example be 650°C, 750°C, 800°C or even 850°C, or more. The temperature of this plateau may go up to approximately 1800°C, taking care to remain compatible with the nature of the second material making up the initial substrate 2.

[0053] This second annealing causes carbonization of the 3' crosslinked layer. It is essential that this carbonization gives rise to a glassy carbon structure, which has sp2 carbon-carbon (CC) atomic bonds. The glassy carbon structure can be characterized by Raman spectroscopy, with a particular band signature (G-band), or by ellipsometry, with a specific absorption signature as known in the literature.

[0054] The glassy carbon film 30 advantageously has 100% of CC atomic bonds of sp2 type; if inclusions of another phase are present in the film 30, it may be tolerated that the percentage of sp2 atomic bonds is greater than 95%, or preferably greater than 99%.

[0055] The neutral atmosphere of the second annealing is typically argon-based and / or vacuum (i.e. at a pressure below atmospheric and up to a few mBar). The second annealing is carried out with a temperature rise that can range from 5°C / min, to 15°C / min, and up to 50°C / min, or even 100°C / min, from room temperature to the plateau. The duration of the plateau can vary between a few minutes (for example 30 min) and a few hours (for example 2 h).

[0056] The glassy carbon film 30 typically has a thickness of between a few hundred nanometers (typically 500-600nm) and a few micrometers (typically 1, 2, 3 or 4μm). Preferably, the glassy carbon film 30 has a thickness of the order of ten times the surface roughness PV of the initial substrate 2.

[0057] It is important to take into account the contraction that the viscous layer of polymer resin 3 (deposited in step b) of the method) will undergo during the first annealing (step c) and especially during the second annealing (step d), to define its initial thickness sufficient to obtain the targeted thickness of glassy carbon film 30. The contraction in thickness can typically be between 70% and 95%. The carbon ratio, that is to say the ratio between the mass of the glassy carbon film 30 and the initial mass of the layer of polymer resin 3 spread, must be at least 5%, preferably greater than 50%.

[0058] The initial substrate 2 provided with the glassy carbon film 30 corresponds to the support substrate 20 according to the present invention. 1 shows an example of the surface condition of the support substrate 20 on the side of its front face 20a, that is to say on the side of the free face of the glassy carbon film 30. A quadratic mean roughness less than or equal to 0.8nm RMS and a peak-to-trough roughness less than or equal to 7nm PV can be obtained, starting from the roughnesses of the initial substrate 2 indicated in. The roughnesses are here again measured by atomic force microscopy on a surface area less than or equal to 30μm x 30μm.

[0059] The surface condition is significantly improved compared to the surface 2a of the initial substrate 2; we observe a strong resorption of scratches and other hollow defects and a roughness typically less than or equal to 1nm RMS and 10nm PV. This surface condition is particularly favorable for assembly by direct bonding with very good interface quality.

[0060] Advantageously, the manufacturing method according to the invention comprises, after step d), a step e) of mechanical and / or chemical-mechanical polishing of the vitreous carbon film 30, to adjust its thickness or to further improve its surface roughness.

[0061] At the end of step e), we aim for example for an RMS roughness of less than 1nm, or even 0.5nm, and a PV roughness of less than 5nm.

[0062] In addition, the glassy carbon film 30 exhibits excellent electrical conduction characteristics, with a resistivity typically less than 6.10 -3ohm.cm.

[0063] The mechanical, electrical and thermal properties of the glassy carbon film 30 make the support substrate 20 an excellent candidate for the manufacture of a composite structure 100 by transferring a thin layer 10 of monocrystalline silicon carbide (c-SiC) onto said support substrate 20.

[0064] Note that these mechanical, electrical and thermal properties are also an advantage in a composite structure 100 whose support substrate 20 would comprise, for example, an initial substrate 2 made of p-AlN and whose thin layer 10 would be, for example, made of c-GaN, or other combinations of first and second materials.

[0065] Returning to the description of a composite structure based on SiC, the manufacturing method according to the invention can thus comprise a step f) of transferring a thin layer 10 of c-SiC onto the glassy carbon film 30.

[0066] There are various options known from the state of the art for performing thin layer transfer, which will not be described exhaustively here.

[0067] According to a preferred embodiment, step f) of the method involves implantation of light species according to the principle of the Smart Cut® method.

[0068] In a first phase f1), a donor substrate 1 made of monocrystalline silicon carbide, from which the thin layer 10 will be derived, is provided (). The donor substrate 1 is preferably in the form of a wafer with a diameter of 100mm, 150mm, 200mm or even 300mm (identical to or very close to that of the support substrate 20) and a thickness typically between 300μm and 800μm. It has a front face 1a and a rear face 1b. The surface roughness of the front face 1a is advantageously chosen to be less than 1nm RMS, or even less than 0.5nm RMS, measured by atomic force microscopy (AFM) over a surface area of, for example, 20μm x 20μm. The donor substrate 1 may be of polytype 4H or 6H, and have n or p type doping, depending on the needs of the components which will be produced on and / or in the thin layer 10 of the composite structure 100.

[0069] Note that the donor substrate 1 intended to form a thin layer 10 in c-GaN can be formed from a base substrate in GaN, SiC, Si(111) or sapphire on which an epitaxy of monocrystalline GaN will be carried out, according to conventional processes.

[0070] A second phase f2) corresponds to the introduction of light species into the donor substrate 1 to form a buried fragile plane 11 delimiting, with a front face 1a of the donor substrate 1, the thin layer 10 to be transferred ().

[0071] The light species are preferably hydrogen, helium or a co-implantation of these two species, and are implanted at a determined depth in the donor substrate 1, consistent with the thickness of the targeted thin layer 10. These light species will form, around the determined depth, microcavities distributed in a thin layer parallel to the free surface 1a of the donor substrate 1, i.e. parallel to the (x,y) plane in the figures. This thin layer is called the buried fragile plane 11, for the sake of simplification.

[0072] The implantation energy of the light species is chosen to achieve the determined depth. For example, hydrogen ions will be implanted at an energy between 10 keV and 250 keV, and at a dose between 5E16 / cm 2 and 1E17 / cm 2, to delimit a thin layer 10 having a thickness of the order of 100nm to 1500nm. Note that a protective layer may be deposited on the front face 1a of the donor substrate 1, prior to the ion implantation step. This protective layer may be composed of a material such as silicon oxide or silicon nitride for example. It is removed prior to the next phase.

[0073] Optionally, an intermediate layer 4 may be formed on the front face 1a of the donor substrate 1, before or after the second phase f2) of introducing the light species. This intermediate layer 4 may be made of a semiconductor material or a metallic material; for example, silicon, silicon carbide, silicon oxycarbide (SiOC), carbon, for example a vitreous or turbostratic carbon, tungsten, titanium, etc. may be chosen. The thickness of the intermediate layer 4 is advantageously limited, typically between a few nanometers and a few tens of nanometers.

[0074] In the case where the intermediate layer 4 is formed before phase f2), the implantation energy (and potentially the dose) of the light species will be adjusted to the crossing of this additional layer. In the case where the intermediate layer 4 is formed after phase f2), care will be taken to form this layer by applying a thermal budget lower than the bubbling thermal budget, said bubbling thermal budget corresponding to the appearance of blisters on the surface of the donor substrate 1 due to growth and excessive pressurization of the microcavities in the buried fragile plane 11.

[0075] The transfer step f) then comprises a third phase f3) of assembling the donor substrate 1, on its front face 1a side, on the support substrate 20, on its first face 20a side, by molecular adhesion bonding, along a bonding interface 5 to form a bonded assembly 50 (figures 4c, 4c').

[0076] Optionally, an additional layer may also be deposited on the face to be assembled of the support substrate 20 (namely on the glassy carbon layer 30), prior to the assembly phase f3); it may be chosen to be of the same nature or of a different nature from the intermediate layer 4 mentioned for the donor substrate 1. An intermediate or additional layer 4 may optionally be deposited only on one or other of the two substrates 1, 20 to be assembled.

[0077] The purpose of the intermediate layer(s) is essentially to promote the bonding energy (particularly in the temperature range below 1100°C), due to the formation of covalent bonds at lower temperatures than in the case of direct assembly without this(these) intermediate layer(s); another advantage of this(these) intermediate layer(s) may be to further improve the vertical electrical conduction of the bonding interface 5.

[0078] Returning to the description of the assembly phase f3), and as is well known in itself, direct bonding by molecular adhesion does not require an adhesive material, because bonds are established at the atomic scale between the assembled surfaces. Several types of bonding by molecular adhesion exist, which differ in particular by their conditions of temperature, pressure, atmosphere or treatments prior to bringing the surfaces into contact. Examples include bonding at room temperature with or without prior plasma activation of the surfaces to be assembled, bonding by atomic diffusion ("Atomic diffusion bonding" or ADB according to English terminology), bonding with surface activation ("Surface-activated bonding" or SAB), etc.

[0079] The assembly phase f3) may comprise, prior to bringing the faces 1a, 20a to be assembled into contact, conventional sequences of chemical cleaning (for example, RCA cleaning), surface activation (for example, by oxygen or nitrogen plasma) or other surface preparations (such as cleaning by brushing), capable of promoting the quality of the bonding interface 5 (low defectivity, high adhesion energy).

[0080] Finally, a fourth phase f4) comprises the separation along the buried fragile plane 11, which leads to the transfer of the thin layer 10 onto the support substrate 20 ().

[0081] The separation along the buried fragile plane 11 is usually carried out by applying a heat treatment to the bonded assembly 50, at a temperature between 800°C and 1200°C (in the described case of a SiC-based bonded assembly 50). Of course, this temperature strongly depends on the nature of the first and second materials involved in the bonded assembly 50, as is known to those skilled in the art, and will naturally be adjusted according to the materials chosen.

[0082] Such a heat treatment induces the development of cavities and microcracks in the buried fragile plane 11, and their pressurization by the light species present in gaseous form, until the propagation of a fracture along said fragile plane 11. Alternatively or jointly, a mechanical stress can be applied to the bonded assembly 50 and in particular at the buried fragile plane 11, so as to propagate or help to mechanically propagate the fracture leading to separation. At the end of this separation, on the one hand the composite structure 100 comprising the support substrate 20 and the transferred monocrystalline thin layer 10 is obtained, and on the other hand, the remainder 1' of the donor substrate. The level and type of doping of the thin layer 10 are defined by the choice of the properties of the donor substrate 1 or can be adjusted subsequently via known techniques for doping semiconductor layers.

[0083] The free surface 10a of the thin layer 10 is usually rough after separation: for example, it has a roughness of between 5nm and 100nm RMS (AFM, 20μm x 20μm scan). Cleaning and / or smoothing phases may be applied to restore a good surface condition (typically, a roughness of less than a few angstroms RMS, on a 20μm x 20μm scan by AFM). In particular, these phases may comprise a mechanical-chemical smoothing treatment of the free surface of the thin layer 10. A removal of between 50nm and 300nm makes it possible to effectively restore the surface condition of said layer 10. They may also comprise at least one heat treatment, for example at a temperature of between 1300°C and 1800°C in the case of the composite structure 100 based on SiC.

[0084] Such a heat treatment is applied to remove residual light species from the thin layer 10 and to promote the rearrangement of its crystal lattice. It also makes it possible to strengthen the bonding interface 5.

[0085] The heat treatment may also include or correspond to an epitaxy of silicon carbide on the thin layer 10.

[0086] The support substrate 20, and in particular the glassy carbon film 30, is perfectly compatible with the potentially very high temperature heat treatments applied during the development of the composite structure 100.

[0087] Finally, note that the transfer step f) may comprise a step of reconditioning the remainder 1' of the donor substrate with a view to reuse as donor substrate 1 for a new composite structure 100. Mechanical and / or chemical treatments, similar to those applied to the composite structure 100, may be implemented at the level of the front face 1'a of the remaining substrate 1'.

[0088] The composite structure 100 obtained comprises a thin layer 10 of monocrystalline silicon carbide arranged on the support substrate 20, said support substrate 20 including an initial substrate 2 of polycrystalline silicon carbide and a glassy carbon film 30, in contact with the front surface 2a of the initial substrate 2.

[0089] As mentioned previously with reference to the manufacturing method according to the invention, the composite structure 100 is described here in the case of a first material in c-SiC and a second material in p-SiC. The invention also relates to a composite structure 100 based on other pairs of first and second materials (stated in a non-exhaustive manner previously), in particular a composite structure 100 comprising a thin layer in c-GaN and an initial substrate 2 (included in the support substrate 20) in p-AlN.

[0090] An intermediate layer 4 and / or an additional layer as mentioned in the method may possibly be interposed between the glassy carbon film 30 and the thin layer 10. The case of an intermediate carbon layer 4 is advantageous in that it does not add a separate material interface likely to increase the total vertical resistance and provides very good temperature resistance.

[0091] The electrical conduction at the interface between the thin layer 10 and the intermediate layer 4 or the glassy carbon film 30 is advantageously less than or equal to 10 -4 ohm.cm 2 , or even less than 10 -5 ohm.cm 2 , or even less than 10 -6 ohm.cm 2 .

[0092] Such a composite structure 100 is extremely robust to high-temperature heat treatments that may be applied to manufacture components on and / or in said layer 20. The composite structure 100 according to the invention is particularly suitable for the production of one (or more) high-voltage microelectronic component(s), such as for example Schottky diodes, MOSFET transistors, etc. It more generally meets power microelectronic applications, by allowing excellent vertical electrical conduction, good thermal conductivity and by providing a useful layer of high-quality monocrystalline material.

[0093] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

A method for manufacturing a composite structure (100) comprising a thin layer (10) of a first monocrystalline material disposed on a support substrate (20), the manufacturing process comprising the following steps: a) supplying an initial substrate (2) of a second polycrystalline material, b) deposition by centrifugal coating, at least on a front face (2a) of the initial substrate (2), of a layer of polymer resin (3) having preformed carbon-carbon bonds in three dimensions, c) applying a first anneal at a temperature between 120°C and 180°C to the initial substrate (2) with the layer of polymer resin (3), to form a crosslinked polymer resin layer (3'), d) applying a second anneal at a temperature above 600°C, under a neutral atmosphere, to transform the crosslinked polymer resin layer (3') into a glassy carbon film (30), f) transferring the thin layer (10) formed from the first single-crystal material,directly onto the vitreous carbon film (30) or via an intermediate layer (4), said transfer involving a molecular adhesion interface (5) between a face of the vitreous carbon film (30) and a face of the thin layer (10), or between a face of the vitreous carbon film (30) and a face of an intermediate layer (4) disposed between said vitreous carbon film (30) and the thin layer (10). Manufacturing process according to the preceding claim, comprising, after step d), a step e) of mechanical and / or mechano-chemical polishing of the vitreous carbon film (30). A manufacturing process according to the preceding claim, wherein the polymer resin (3) is based on coal tar, phenol formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and / or polystyrene. A manufacturing process according to any one of the preceding claims, wherein step f) implements an assembly between a donor substrate (1) comprising the first single-crystal material, from which the thin layer (10) will be derived, and the glassy carbon film (30), to form a bonded assembly (50). A manufacturing process according to the preceding claim, wherein: - the donor substrate (1) comprises a buried fragile plane (11) which delimits, with a front face (1a) of said substrate (1), the thin layer (10) to be transferred, and - step f) implements a separation of the bonded assembly (50) along the buried fragile plane (11), to give rise, on the one hand, to a composite structure (100) including the thin layer (10) disposed on the glassy carbon film (30), itself disposed on the initial substrate (2), and on the other hand, the remainder of the donor substrate (1). A manufacturing process according to any one of the preceding claims, wherein the first single-crystal material is selected from silicon carbide, gallium nitride, silicon, silicon-germanium, germanium, III-V compounds, or other semiconductor materials, or from piezoelectric materials. A manufacturing method according to any one of the preceding claims, wherein the second polycrystalline material is selected from silicon carbide, aluminum nitride, silicon, silicon-germanium, germanium, III-V compounds or other semiconductor materials, or from piezoelectric materials. A manufacturing process according to any one of the preceding claims, wherein the first material and the second material are semiconductors. Composite structure (100) comprising a thin layer (10) of a first single-crystal material disposed on a support substrate (20), said support substrate (20) comprising: - an initial substrate (2) of a second polycrystalline material, - a glassy carbon film (30), in contact with the front surface (2a) of the initial substrate (2), the composite structure (100) further comprising a molecular adhesion bonding interface (5) between a face of the glassy carbon film (30) and a face of the thin layer (10) or between a face of the glassy carbon film (30) and a face of an intermediate layer (4) disposed between said glassy carbon film (30) and the thin layer (10). Composite structure (100) according to the preceding claim in which the initial substrate (2) has a surface roughness of between 10nm and 2μm peak-to-pit, measured by atomic force microscopy on a surface area less than or equal to 30μm x 30μm. Composite structure (100) according to one of the two preceding claims, wherein the vitreous carbon film (30) has a thickness between 100nm and 4μm. Composite structure (100) according to the preceding claim comprising an intermediate layer (4), between the thin layer (10) and the glassy carbon film (30), selected from silicon, silicon carbide, carbon, tungsten or titanium. Composite structure (100) according to any one of claims 9 to 12, wherein the first single-crystal material is selected from silicon carbide, gallium nitride, or other semiconductor materials, and the second polycrystalline material is selected from silicon carbide, aluminium nitride, or other semiconductor materials.

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