Composite Structures and Related Manufacturing Processes

Abstract

The invention relates to a manufacturing process for a composite structure comprising a thin layer made of a first monocrystalline material arranged on a support substrate, the manufacturing process comprising the steps of: a) providing a starting substrate made from a second polycrystalline material; b) depositing, by centrifugal coating, a polymeric resin layer comprising three-dimensional preformed carbon-carbon bonds on at least the front surface of the starting substrate; c) subjecting the starting substrate provided with the polymer resin layer to a first annealing at a temperature between 120° C. and 180° C. to form a crosslinked polymer resin layer; d) applying a second annealing at a temperature above 600° C. under a neutral atmosphere to convert the crosslinked polymer resin layer into a glassy carbon film; Includes. The invention also relates to a composite structure comprising a thin layer made of a first monocrystalline material arranged on a support substrate, said support substrate comprising: a starting substrate made from a second polycrystalline material; a glassy carbon film in contact with the front surface of the starting substrate; Includes.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to the fields of microelectronics and semiconductors. In particular, the present invention relates to a substrate made of a polycrystalline material with a surface film made of glassy carbon and which is particularly suitable for receiving a thin layer transferred from a donor substrate. The present invention also relates to said support substrate and to a process for the manufacture of a composite structure resulting from the transfer of a thin layer onto the support substrate.

[0002] [Background technology] Silicon carbide (SiC) is being used more and more widely for the manufacture of high-performance power devices. Nevertheless, high-quality monocrystalline SiC (c-SiC) substrates for the microelectronics industry are still expensive and difficult to supply in large sizes. It is therefore preferred to use layer transfer solutions to manufacture composite structures comprising a thin layer typically made of c-SiC (obtained from a substrate made of high-quality c-SiC and intended to receive the sensitive functional components of the device) on a low-cost support substrate made, for example, from polycrystalline SiC (p-SiC).

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

[0004] Substrates made from p-SiC are difficult to polish as a result of the hardness of the material and the polycrystalline structure, and generally exhibit a residual roughness that complicates assembly by direct bonding, since direct bonding does not require an adhesive substance but involves a molecular bond between the surfaces of the contacting substrates, and therefore such bonding requires excellent flatness and also very low surface roughness and defects.

[0005] For the purpose of assembly by direct bonding, 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 (in particular low roughness). It should be noted that this intermediate layer must not affect the performance qualities of the device provided on the composite structure, in this case in vertical power devices, such an intermediate layer must not affect the vertical electrical conductivity between the thin layer made of c-SiC and the supporting substrate made of p-SiC.

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

[0007] This introduction essentially refers to the advantages of composite structures based on silicon carbide, but composite structures based on other materials, which are high-performance but expensive for large substrates and complex to prepare for the purpose of thin layer transfer, as is the case with SiC, may also be of interest. For example, mention may be made of composite structures comprising a thin layer made of gallium nitride (GaN) and a polycrystalline support substrate, for example made of aluminum nitride (AlN).

[0008] Subject of the Invention The present invention provides an alternative solution to state of the art solutions, facilitating the achievement of a low surface roughness of the support substrate and facilitating the electrical and thermal properties of the support substrate. The present invention relates in particular to a polycrystalline starting substrate with a surface film made of glassy carbon, which is particularly suitable for receiving a working layer transferred from a donor substrate. The present invention also relates to a process for the manufacture of said support substrate and of a composite structure resulting from the transfer of a thin layer onto the support substrate.

[0009] [Summary of the Invention] The invention relates to a manufacturing process for a composite structure comprising a thin layer made of a first monocrystalline material arranged on a support substrate, the manufacturing process comprising the steps of: a) providing a starting substrate made from a second polycrystalline material; b) depositing, by centrifugal coating, a polymeric resin layer comprising three-dimensional preformed carbon-carbon bonds on at least the front surface of the starting substrate; c) subjecting the starting substrate provided with the polymer resin layer to a first annealing at a temperature between 120° C. and 180° C. to form a crosslinked polymer resin layer; d) applying a second annealing at a temperature above 600° C. under a neutral atmosphere to convert the crosslinked polymer resin layer into a glassy carbon film; Includes.

[0010] According to preferred features of the present invention, taken alone or in any feasible combination, The process comprises, after step d), a step e) of mechanical and / or chemical-mechanical polishing of the glassy carbon film, the polymer resin is based on coal tar, phenol / formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride and / or polystyrene; The process comprises a step f) of transferring a thin layer formed from a first monocrystalline material onto the glassy carbon film, either directly or via an intermediate layer, Step f) comprises assembling, by direct bonding, a donor substrate comprising the first monocrystalline material from which the thin layer is obtained and the glassy carbon film to form a bonded assembly; the donor substrate comprises, at the front side of said substrate, a weak embedding plane defining the thin layer to be transferred, step f) consisting in separating the bonded assembly along the weak embedding plane to give, on the one hand, a composite structure comprising the thin layer arranged on the glassy carbon film, itself arranged on the starting substrate, and, on the other hand, the remaining part of the donor substrate, the first monocrystalline material is selected 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 selected 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 made of a first monocrystalline material arranged on a support substrate, said support substrate comprising: a starting substrate made from a second polycrystalline material; a glassy carbon film in contact with the front surface of the starting substrate; Includes.

[0012] According to preferred features of the present invention, taken alone or in any feasible combination, The starting substrate exhibits a surface roughness between 10 nm and 2 μm as measured by atomic force microscopy over a surface area of ​​30 μm×30 μm or less; The glassy carbon films exhibit thicknesses between 100 nm and 4 μm, the composite structure comprises an intermediate layer between the thin layer and the glassy carbon film, the intermediate layer being selected from silicon, silicon carbide, carbon, tungsten or titanium; The first monocrystalline material is selected from silicon carbide, gallium nitride or other semiconductor materials, and the second polycrystalline material is selected from silicon carbide, aluminum nitride or other semiconductor materials.

[0013] Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0014] [Figure 1a] 3A-3D are diagrams illustrating steps in the manufacturing process of a support substrate according to the present invention. [Figure 1b] 3A-3D are diagrams illustrating steps in the manufacturing process of a support substrate according to the present invention. [Figure 1c] 3A-3D are diagrams illustrating steps in the manufacturing process of a support substrate according to the present invention. [Figure 1d] 3A-3D are diagrams illustrating steps in the manufacturing process of a support substrate according to the present invention. [Diagram 2] 1 is a diagram showing an example of a surface state of a starting substrate constituting a support substrate according to the present invention; [Diagram 3] FIG. 2 is a diagram showing an example of the surface state of a glassy carbon film constituting a support substrate according to the present invention. [Figure 4a] 1A-1D are diagrams illustrating steps in a manufacturing process for a composite structure according to the present invention. [Figure 4b] 1A-1D are diagrams illustrating steps in a manufacturing process for a composite structure according to the present invention. [Figure 4c] 1A-1D are diagrams illustrating steps in a manufacturing process for a composite structure according to the present invention. [Figure 4c-2] (FIG. 4c') A diagram showing stages in the manufacturing process of a composite structure according to the invention. [Figure 4d] 1A-1D are diagrams illustrating steps in a manufacturing process for a composite structure according to the present invention.

[0015] Some of the drawings are diagrammatic representations that are not to scale for ease of reading, in particular the layer thicknesses along the z-axis are not to scale relative to the lateral dimensions along the x- and y-axes. The same reference numbers may be used in the drawings or description for elements of the same nature.

[0016] [Mode for carrying out the invention] The invention relates to a manufacturing process for a composite structure 100 comprising a thin layer 10 made of a first monocrystalline material arranged on a support substrate 20 at least partially composed of a second polycrystalline material (FIG. 4d). The target composite structure 100 allows vertical electrical conduction between the thin layer 10 and the support substrate 20, in particular for power electronics applications.

[0017] In particular, the first monocrystalline material may be selected 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 selected from silicon carbide (p-SiC), aluminum nitride (p-AlN), silicon (p-Si), or any other material as described above for the first material, but which exhibits a polycrystalline structure or is provided with a surface polycrystalline layer. In the composite structure 100, the first material mentioned may of course be combined with one or the other of the above-mentioned second materials, provided that this is suitable for the final application. Preferably, the composite structure 100 is formed from first and second materials exhibiting similar thermal expansion coefficients.

[0018] In the remainder of the description, the case of a first material made of c-SiC and a second material made of p-SiC is specifically described. Nevertheless, this description applies to any other first and second material pairs. When a particular situation requires any other first and second material pair, further information is provided about the different properties of the first and second materials.

[0019] The manufacturing process first comprises a step a) of providing a starting substrate 2 made of polycrystalline silicon carbide (p-SiC) exhibiting a front surface 2a and a rear surface 2b (FIG. 1a). The starting substrate 2 may be prepared by conventional techniques such as sintering or chemical vapor deposition.

[0020] The starting substrate 2 is preferentially in the form of a wafer having a diameter of 100 mm, 150 mm, 200 mm, indeed even 300 mm, and typically having a thickness between 300 and 800 microns.

[0021] The surface condition of the front surface 2a of the starting substrate 2 is preferentially selected such that the peak-to-valley roughness (hereinafter referred to as "PV roughness") is less than a few micrometers, typically less than 2 μm, 1 μm, 500 nm, 100 nm or 50 nm.

[0022] In the context of the present invention, roughness is measured by atomic force microscopy (AFM) on a surface area (scan area) of 30 μm×30 μm or less. The measured surface area can extend, for example, over 5 μm×5 μm, 10 μm×10 μm, 20 μm×20 μm or 30 μm×30 μm. Reference is subsequently made to PV roughness, or root mean square or RMS roughness.

[0023] It should be noted that as a result of the hardness of the material and the polycrystalline structure, obtaining very good surface conditions on substrates made from p-SiC is complicated, and mechanical or chemical-mechanical polishing can lead to the formation of scratches and the appearance of defects (holes) on the surface of the substrate as a result of untimely detachment of p-SiC particles at the surface.

[0024] An example of the surface condition of the starting substrate 2 is given in Fig. 2. While the RMS roughness remains below 1 nm, a PV roughness is observed that can exceed 30 nm as a result of the presence of scratches at the surface. Such a surface condition can generate physical defects (holes) at the future interface between the substrate and the thin layer of the composite structure 100, which reduces the quality and integrity of the transferred thin layer, as well as reducing the electrical conductivity of the interface.

[0025] Typically, in the context of the present invention, the starting substrate 2 is capable of exhibiting a PV surface roughness of up to a few micrometers, which significantly eases the constraints of manufacturing or supplying the starting substrate 2.

[0026] The surface condition of the back surface 2b of the starting substrate 2 is not specified here: the surface condition may be similar to or even worse than that of the front surface 2a, provided that this does not affect the curvature or quality (defectiveness) of the starting substrate 2 overall.

[0027] In order to adapt to the surface condition of the starting substrate 2, the manufacturing process according to the invention provides a step b) which comprises depositing, by centrifugal coating, at least on the front surface 2a of the starting substrate 2, a polymer resin layer 3 (FIG. 1b). An important feature of this layer is that it contains preformed carbon-carbon (C-C) bonds in three dimensions (3D). In this layer, carbon-based polymer chains exhibiting a sequence of C-C bonds are randomly dispersed in the solvent and therefore exhibit a more or less random 3D structure. The more randomly dispersed these chains are in 3D, the less graphitization is promoted during crosslinking and the closer they approach the glassy state.

[0028] Here, a polymer resin layer 3 resulting in an amorphous / crystalline ratio as high as possible is promoted in order to obtain, after crosslinking, a glassy carbon film 30 at the end of the subsequent stage d) of the process.

[0029] The polymeric resins may be formed from coal tar, phenol / formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and / or polystyrene, and the like.

[0030] For example, commercially available products, AZ-5214, AZ-4330, AZ-P4620 (based on 1-methoxy-2-propanol acetate, diazonaphthoquinone sulfonate, 2-methoxy-1-propanol acetate, cresol novolac resin), OCG-825 (based on ethyl 3-ethoxypropionate), SU-8 2000 (based on cyclopentanone, triarylsulfonium / hexafluoroantimonate salts, propylene carbonate, and epoxy resin) Known photosensitive resins, such as those commonly used in photolithography steps in the field of microelectronics, may be used.

[0031] Epoxy resins, such as, for example, the product Epoxy Novolac EPON®, which are provided for coating and protecting various surfaces in various sectors (aviation, marine, automotive, architectural, etc.), may also be used in step b) of the process according to the invention.

[0032] The centrifugal diffusion carried out in step b) requires that the polymer resin solution is provided in a viscous form.

[0033] This deposition method is particularly suitable since the viscous solution fills the depressions (holes and scratches) present in the surface of the starting substrate 2, thus effectively planarizing these micro-reliefs.

[0034] The thickness of the polymer resin layer 3 deposited in step b) may typically vary between a few hundred nanometers (eg 500 nm) and a few microns (eg 3-5 μm).

[0035] The manufacturing process then comprises a step c) consisting of applying an annealing (said first annealing) at a temperature between 120° C. and 180° C., which exhibits a stationary phase, to the starting substrate 2 provided with the polymer resin layer 3 (FIG. 1c). The stationary phase can have a duration between a few minutes (typically 30 minutes) and a few hours (typically 2 hours). The temperature is preferably increased gradually, i.e. between 1° C. / min and 5° C. / min, from ambient temperature to the stationary phase, so as to gradually degas the polymer resin layer 3 and to expel the solvents and impurities initially present in the viscous solution.

[0036] Depending on the nature of the polymer resin, an intermediate stationary phase may also be provided in the first annealing thermal cycle.

[0037] Following the first annealing, the polymer resin layer 3' is crosslinked and thus solidifies with respect to the front surface 2a of the starting substrate 2. The crosslinking is characterized by the formation of bonds between the carbon-based chains, which is reflected by the solidification of the layer 3'. The arrangement of the three-dimensional polymer chains in the crosslinked polymer resin layer 3' is then reversed during the next step d) of the process by the formation of bonds between the carbon-based chains.2 This type of bond affects the three-dimensional orientation of the chains.

[0038] Finally, the manufacturing process comprises a step d) consisting of applying a second annealing, exhibiting a stationary phase, at a temperature above 600° C., preferentially above 700° C., in a neutral atmosphere, to transform the crosslinked polymer resin layer 3′ into a glassy carbon film 30 (FIG. 1d). The stationary phase temperature may be, for example, 650° C., 750° C., 800° C. or also 850° C. or higher. This stationary phase temperature may range up to about 1800° C., care being taken to maintain compatibility with the properties of the second material constituting the starting substrate 2.

[0039] This second annealing results in the carbonization of the cross-linked layer 3'. 2 It is essential to produce a glassy carbon structure that exhibits carbon-carbon (C-C) atomic bonds of the type that can be characterized by Raman spectroscopy with a specific band (G-band) signature or by ellipsometry with a specific absorption signature, as known in the literature.

[0040] The glassy carbon film 30 is preferably 100% sp 2 If inclusions of another phase are present in the film 30, the sp 2 The proportion of atomic bonds may be allowed to be greater than 95%, or preferentially greater than 99%.

[0041] The neutral atmosphere of the second annealing is typically argon-based and / or under vacuum (i.e., below atmospheric pressure and up to a few mbar). The second annealing is carried out with a temperature ramp from ambient temperature to the stationary phase, which may range from 5° C. / min to 15° C. / min, and up to 50° C. / min, in fact even up to 100° C. / min. The duration of the stationary phase may vary between a few minutes (e.g., 30 minutes) and a few hours (e.g., 2 hours).

[0042] The glassy carbon film 30 typically exhibits a thickness between a few hundred nanometers (typically 500-600 nm) and a few micrometers (typically 1, 2, 3 or 4 μm). Preferentially, the glassy carbon film 30 exhibits a thickness of the order of 10 times the PV surface roughness of the starting substrate 2.

[0043] In order to define a sufficient starting thickness of the polymer resin layer 3 in order to obtain the target thickness of the glassy carbon film 30, it is important to take into account the shrinkage that the viscous polymer resin layer 3 (deposited in stage b) of the process) undergoes during the first annealing (stage c)), and especially during the second annealing (stage d)). The thickness shrinkage can typically be between 70% and 95%. The carbon ratio, i.e. the ratio between the weight of the glassy carbon film 30 and the starting weight of the spread polymer resin layer 3, must be at least 5% and preferentially more than 50%.

[0044] The starting substrate 2 provided with the glassy carbon film 30 corresponds to the support substrate 20 according to the invention. Figure 3 shows an example of the surface state of the support substrate 20 on the side of its front surface 20a, i.e. on the side of the free surface of the glassy carbon film 30. Starting from the roughness of the starting substrate 2 shown in Figure 2, a root-mean-square roughness of 0.8 nm RMS or less and a peak-to-valley roughness of 7 nm PV or less can be obtained, where the roughness is still measured by atomic force microscopy over a surface area of ​​30 μm x 30 μm or less.

[0045] The surface condition is significantly improved with respect to the surface 2a of the starting substrate 2, with a strong resorption of scratches and other hollow defects, as well as a roughness typically below 1 nm RMS and 10 nm PV, which is particularly beneficial for assembly by direct bonding with very good interface quality.

[0046] Preferably, the manufacturing process according to the present invention comprises, after step d), a step e) of mechanically and / or chemically mechanically polishing the glassy carbon film 30 in order to adjust the thickness of the glassy carbon film 30 or to further improve the surface roughness of the glassy carbon film 30.

[0047] At the end of step e), for example, an RMS roughness of less than 1 nm, in practice even 0.5 nm, and a PV roughness of less than 5 nm is targeted.

[0048] Furthermore, the glassy carbon film 30 exhibits excellent electrical conductivity properties, typically 6.10 -3 It has a resistivity of less than Ω·cm.

[0049] 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 made of single crystal silicon carbide (c-SiC) onto said support substrate 20.

[0050] It should be noted that these mechanical, electrical and thermal properties are also an advantage in the composite structure 100, the support substrate 20 of which comprises a starting substrate 2 made, for example, from p-AlN, and the thin layer 10 of which is made, for example, from c-GaN or other combination of a first material and a second material.

[0051] Returning to the description of the SiC-based composite structure, the manufacturing process according to the invention can therefore include a step f) of transferring a thin layer 10 made of c-SiC onto the glassy carbon film 30 .

[0052] Various options exist for carrying out thin layer transfer that are known from the state of the art but will not be described exhaustively here.

[0053] According to a preferred mode, step f) of the process comprises the injection of light seeds according to the principle of the Smart Cut® process.

[0054] In a first phase f1), a donor substrate 1 made of monocrystalline silicon carbide from which the thin layer 10 is obtained is provided (FIG. 4a). The donor substrate 1 is preferentially provided in the form of a wafer, with a diameter of 100 mm, 150 mm, 200 mm, indeed even 300 mm (identical to or very similar to the diameter of the support substrate 20) and a thickness typically between 300 μm and 800 μm. It shows a front side 1a and a rear side 1b. The surface roughness of the front side 1a is preferably chosen to be less than 1 nm RMS, indeed even less than 0.5 nm RMS, for example measured by atomic force microscope (AFM) over a surface area of ​​20 μm×20 μm. The donor substrate 1 is of polytype 4H or 6H and can exhibit n-type or p-type doping, depending on the requirements of the components to be prepared on and / or in the thin layer 10 of the composite structure 100.

[0055] It is noted that the donor substrate 1 intended for forming the thin layer 10 made of c-GaN may be formed from a base substrate made of GaN, SiC, Si(111) or sapphire on which single-crystal GaN epitaxy may be performed according to conventional processes.

[0056] A second phase f2) corresponds to the introduction of light species into the donor substrate 1 to form, at its front surface 1a, a weak buried surface 11 that defines the thin layer 10 to be transferred (FIG. 4b).

[0057] Light species, preferentially hydrogen, helium or a co-implantation of these two species, are implanted at a determined depth in the donor substrate 1, which corresponds to the target thickness of the thin layer 10. These light species form microcavities around the determined depth, distributed in a fine layer parallel to the free surface 1a of the donor substrate 1, i.e. parallel to the plane (x,y) in the figure. This fine layer is called, for simplicity, the weakly buried plane 11.

[0058] The implant energy of the light species is selected to reach a determined depth. For example, hydrogen ions are implanted at energies between 10 keV and 250 keV and at a density of 5E16 / cm 2 From 1E17 / cm 2 to define a thin layer 10 presenting a thickness of the order of 100 nm to 1500 nm. It is noted that, prior to the ion implantation stage, it is possible to deposit a protective layer on the front side 1a of the donor substrate 1. This protective layer may for example consist of a material such as silicon oxide or silicon nitride. The protective layer is removed before the next phase.

[0059] Optionally, an intermediate layer 4 may be formed on the front side 1a of the donor substrate 1 before or after the second phase f2) of introduction of light species. This intermediate layer 4 may be made of a semiconducting or metallic material, for example it is possible to choose silicon, silicon carbide, silicon oxycarbide (SiOC), carbon, for example glassy or turbostratic carbon, tungsten, titanium, etc. The thickness of the intermediate layer 4 is preferably limited to typically a few nanometers to a few tens of nanometers.

[0060] If the intermediate layer 4 is formed before phase f2), the implantation energy (and potentially the dose) of the light species is adjusted to the traverse of this additional layer. If the intermediate layer 4 is formed after phase f2), care is taken to form this layer by applying a thermal budget lower than the bubbling thermal budget, which corresponds to the appearance of bubbles at the surface of the donor substrate 1 due to an excessively large growth and pressurization of microcavities in the weak embedding plane 11.

[0061] Subsequently, the transfer stage f) comprises a third phase f3) of assembling the donor substrate 1 on its front side 1a, on the support substrate 20 on its first side 20a, by molecular adhesion bonding along the bonding interface 5 to form a bonded assembly 50 (Figures 4c, 4c').

[0062] Optionally, an additional layer can also be deposited on the face to be assembled of the support substrate 20 (i.e. on the glassy carbon layer 30) before the assembly phase f3), which can be chosen to be of the same nature as the intermediate layer 4 described for the donor substrate 1 or of a different nature. The intermediate layer 4 or the additional layer can optionally be deposited only on one or the other of the two substrates 1, 20 to be assembled.

[0063] The purpose of the intermediate layers is essentially to facilitate the bonding energy (especially in the temperature range below 1100° C.) as a result of the formation of covalent bonds at lower temperatures than would be the case for direct assembly without these intermediate layers, another advantage of this (these) intermediate layers may be to further improve the vertical electrical conduction of the bonding interface 5.

[0064] Returning to the description of the assembly phase f3), direct bonding by molecular adhesion, as is well known per se, does not require an adhesive substance since a bond is established on an atomic scale between the surfaces to be assembled. In particular, there are several types of bonding by molecular adhesion, which differ in the conditions of temperature, pressure, atmosphere or treatment before bringing the surfaces into contact: room temperature bonding with or without prior plasma activation of the surfaces to be assembled, atomic diffusion bonding (ADB), surface activated bonding (SAB), etc.

[0065] The assembly phase f3) may include a conventional sequence of chemical cleaning (e.g. RCA cleaning), surface activation (e.g. with oxygen or nitrogen plasma) or other surface preparation (cleaning (scrubbing) by brushing, etc.) prior to bringing the surfaces 1a, 20a to be assembled into contact, which tends to promote the quality of the bonding interface 5 (low defectivity, high adhesion energy).

[0066] Finally, the fourth phase f4) involves separation along the weakly embedded planes 11, so that the thin layer 10 is supported on the support substrate 20 (FIG. 4d).

[0067] The separation along the weak embedding plane 11 is typically achieved by subjecting the bonded assembly 50 to a heat treatment at a temperature of 800° C. to 1200° C. (when describing a SiC-based bonded assembly 50). Naturally, this temperature strongly depends on the nature of the first and second materials contained in the bonded assembly 50, as known to those skilled in the art, and naturally adjusts according to the materials selected.

[0068] Such a heat treatment induces the development of cavities and microcracks in the weak buried surface 11 and their pressurization by light species present in gaseous state until a crack propagates along said weak surface 11. Alternatively or jointly, a mechanical stress can be applied to the bonded assembly 50, in particular to the weak buried surface 11, so as to mechanically propagate or help propagate the crack leading to the separation. As a result of this separation, a composite structure 100 is obtained, on the one hand, comprising the support substrate 20 and the transferred thin monocrystalline layer 10, and, on the other hand, the remainder 1' of the donor substrate. The level and type of doping of the thin layer 10 is defined by the choice of the characteristics of the donor substrate 1 or can be adjusted subsequently by known techniques for the doping of semiconductor layers.

[0069] The free surface 10a of the thin layer 10 is usually rough after separation, for example exhibiting a roughness RMS between 5 nm and 100 nm (AFM, 20 μm×20 μm scan). In order to recover a good surface state (typically a roughness of less than a few Angstroms RMS over a 20 μm×20 μm scan by AFM), cleaning and / or smoothing phases can be applied. In particular, these phases can include chemical-mechanical smoothing treatments of the free surface of the thin layer 10. A removal of between 50 nm and 300 nm allows to effectively recover the surface state of said layer 10. The phases can also include at least one heat treatment, for example at a temperature between 1300 ° C and 1800 ° C for a composite structure 100 based on SiC.

[0070] Such a treatment is applied in order to expel residual light species from the thin layer 10 and to promote a rearrangement of the crystal lattice of the thin layer 10. Furthermore, such a treatment makes it possible to strengthen the bonding interface 5.

[0071] The heat treatment may also include or correspond to the epitaxy of silicon carbide on the thin layer 10 .

[0072] The support substrate 20 , and in particular the glassy carbon film 30 , are potentially perfectly compatible with the very high temperature heat treatments applied during the preparation of the composite structure 100 .

[0073] Finally, it is noted that the transfer step f) may include a step of reconditioning the remainder 1' of the donor substrate with a view to reuse as a donor substrate 1 in a new composite structure 100. Mechanical and / or chemical treatments similar to those applied to the composite structure 100 may be applied to the front side 1'a of the remainder substrate 1'.

[0074] The resulting composite structure 100 comprises a thin layer 10 made of monocrystalline silicon carbide disposed on a support substrate 20, said support substrate 20 including a starting substrate 2 made of polycrystalline silicon carbide and a glassy carbon film 30 in contact with the front surface 2a of the starting substrate 2.

[0075] As described above with reference to the manufacturing process according to the invention, the composite structure 100 is described here in the case of a first material made of c-SiC and a second material made of p-SiC. The invention also relates to composite structures 100 based on other pairs of first and second materials (mentioned above in a non-exhaustive manner), in particular a composite structure 100 comprising a thin layer made of c-GaN and a starting substrate 2 (contained in a support substrate 20) made of p-AlN.

[0076] An intermediate layer 4 and / or additional layers as described in the process may optionally be inserted between the glassy carbon film 30 and the thin layer 10. In the case of an intermediate layer 4 made from carbon, it is advantageous in that it does not add a separate material interface that would tend to increase the total normal resistance, and it offers very good temperature stability.

[0077] The electrical conduction at the interface between the thin layer 10 and the intermediate layer 4 or the glassy carbon film 30 is preferably -4 Ω cm 2 In fact, even 10 -5 Ω cm 2 Less than, in fact, even 10 -6 Ω cm 2 is less than.

[0078] Such a composite structure 100 is extremely robust against high temperature heat treatments that tend to be applied to manufacture components on and / or in said layer 10. The composite structure 100 according to the invention is particularly suitable for the preparation of one or more high voltage microelectronic components, such as, for example, Schottky diodes, MOSFET transistors, etc. More generally, the composite structure 100 is suitable for power microelectronic applications, allowing excellent vertical electrical conduction, good thermal conductivity and providing high quality processed layers made from single crystal material.

[0079] Of course, the invention is not limited to the described embodiments and alternative embodiments can be introduced without departing from the scope of the invention as defined by the claims.

Claims

1. A process for manufacturing a composite structure (100) comprising a thin layer (10) made of a first monocrystalline material disposed on a support substrate (20), said manufacturing process comprising: a) providing a starting substrate (2) made from a second polycrystalline material; b) depositing, by centrifugal coating, on at least the front surface (2a) of said starting substrate (2), a polymer resin layer (3) comprising three-dimensional preformed carbon-carbon bonds; c) subjecting the starting substrate (2) provided with the polymer resin layer (3) to a first annealing at a temperature between 120°C and 180°C to form a cross-linked polymer resin layer (3'); d) applying a second annealing at a temperature above 600°C under a neutral atmosphere to convert the crosslinked polymer resin layer (3') into a glassy carbon film (30); f) transferring the thin layer (10) formed from the first monocrystalline material directly onto the glassy carbon film (30) or via an intermediate layer (4), the transferring step including a molecular adhesion bonding interface (5) between the surface of the glassy carbon film (30) and the surface of the thin layer (10), or between the surface of the glassy carbon film (30) and a surface of an intermediate layer (4) disposed between the glassy carbon film (30) and the thin layer (10); manufacturing process, including

2. 2. The manufacturing process of claim 1, further comprising, after step d), a step e) of mechanically and / or chemically mechanically polishing the glassy carbon film (30).

3. 3. The manufacturing process according to claim 1 or 2, wherein the polymer resin is based on coal tar, phenol / formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride and / or polystyrene.

4. 3. The manufacturing process according to claim 1 or 2, wherein step f) comprises assembling a donor substrate (1) comprising the first monocrystalline material from which the thin layer (10) is obtained and the glassy carbon film (30) to form a bonded assembly (50).

5. the donor substrate (1) comprises a weakly buried surface (11) on its front side (1a) that defines the thin layer (10) to be transferred, Step f) separates the bonded assembly (50) along the weak embedding plane (11) to give, on the one hand, a composite structure (100) comprising the thin layer (10) disposed on the glassy carbon film (30), itself disposed on the starting substrate (2), and, on the other hand, the remaining part of the donor substrate (1), 5. The manufacturing process of claim 4.

6. 3. The manufacturing process according to claim 1 or 2, wherein the first monocrystalline material is selected from silicon carbide, gallium nitride, silicon, silicon germanium, germanium, III-V compounds or other semiconductor materials, or from piezoelectric materials.

7. 3. The manufacturing process of claim 1 or 2, 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.

8. 3. The manufacturing process of claim 1, wherein the first material and the second material are semiconductors.

9. A composite structure (100) comprising a thin layer (10) made of a first monocrystalline material disposed on a support substrate (20), said support substrate (20) comprising: a starting substrate (2) made from a second polycrystalline material; a glassy carbon film (30) in contact with the front surface (2a) of the starting substrate (2); wherein the composite structure (100) further comprises an interface (5) bonded by molecular adhesion between a surface of the glassy carbon film (30) and a surface of the thin layer (10), or between a surface of the glassy carbon film (30) and a surface of an intermediate layer (4) disposed between the glassy carbon film (30) and the thin layer (10).

10. 10. The composite structure (100) of claim 9, wherein the starting substrate (2) exhibits a surface roughness of between 10 nm and 2 μm in elevations measured by atomic force microscopy over a surface area of ​​30 μm x 30 μm or less.

11. 11. A composite structure (100) according to claim 9 or 10, wherein said glassy carbon film (30) exhibits a thickness between 100 nm and 4 μm.

12. 12. The composite structure (100) of claim 11, comprising an intermediate layer (4) between said thin layer (10) and said glassy carbon film (30) selected from silicon, silicon carbide, carbon, tungsten or titanium.

13. 11. The composite structure (100) of claim 9 or 10, wherein the first monocrystalline material is selected from silicon carbide, gallium nitride, or other semiconductor material, and the second polycrystalline material is selected from silicon carbide, aluminum nitride, or other semiconductor material.

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