Composite structure and associated manufacturing process

Abstract

This invention relates to a method for fabricating a composite structure comprising a thin layer made of a first single-crystal material disposed on a supporting substrate, the method comprising the following stages: a) Provide a starting substrate made of a second polycrystalline material. b) A polymer resin layer comprising pre-formed three-dimensional carbon-carbon bonds is deposited on at least one side of the starting substrate by centrifugal coating. c) Apply a first tempering to the starting substrate containing the polymer resin layer at a temperature between 120°C and 180°C to form a crosslinked polymer resin layer. d) In a neutral gas environment, a second tempering is applied at a temperature greater than 600°C to convert the cross-linked polymer resin layer into a glassy carbon film. The present invention also relates to a composite structure comprising a thin layer made of a first single-crystal material disposed on a supporting substrate, the supporting substrate comprising: a starting substrate made of a second polycrystalline material, and a glassy carbon film in frontal contact with the starting substrate.

Description

[Technical Field]

[0001] This invention relates to the fields of microelectronics and semiconductors. In particular, this invention relates to a substrate made of a polycrystalline material, comprising a surface thin film made of glassy carbon, and is particularly suitable for receiving a thin layer transferred from a donor substrate. This invention also relates to a method for fabricating the supporting substrate and a composite structure produced by transferring the thin layer onto the supporting substrate. [Previous Technology]

[0002] Silicon carbide (SiC) is increasingly used in the fabrication of high-efficiency power devices. Nevertheless, high-quality single-crystal silicon carbide (c-SiC) substrates for the microelectronics industry remain expensive and difficult to supply in large sizes. Therefore, it is advantageous to adopt layer transfer solutions to produce composite structures, which are typically made on a lower-cost support substrate, such as polycrystalline silicon carbide (p-SiC), including a thin layer made of c-SiC (generated from a high-quality c-SiC substrate and used for sensitive functional components receiving devices).

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

[0004] Due to the material's hardness and polycrystalline structure, p-SiC substrates are difficult to grind and typically have residual surface roughness, which complicates assembly via direct bonding. This is because direct bonding does not require adhesive substances but involves molecular bonds between the contacting substrate surfaces; therefore, such bonding requires excellent flatness and very low surface roughness and defect rate.

[0005] A known approach is to deposit an intermediate layer on one of the substrates to be assembled. This layer is easy to fabricate (especially with low roughness) for direct bonding assembly. It should be noted that this intermediate layer must not affect the performance characteristics of the device fabricated on the composite structure; in this case, for vertical power devices, this intermediate layer must not affect the vertical conductivity between the c-SiC thin layer and the p-SiC support substrate.

[0006] From the prior art, it is known that an intermediate metal layer can be used to ensure vertical conduction in a composite structure.

[0007] While this introduction has primarily discussed the advantages of silicon carbide-based composite structures, composite structures made of other materials, such as SiC-based composite structures, can also be considered. These structures offer high performance but are very expensive to supply in large-size substrates and are complex to fabricate for thin-layer transfer purposes. For example, composite structures made of gallium nitride (GaN) thin layers and polycrystalline support substrates made of aluminum nitride (AlN) may be mentioned. [Summary of the Invention]

[0008] This invention provides an alternative to conventional solutions that facilitates achieving low surface roughness of the support substrate and improves its electrical and thermal properties. The invention particularly relates to a polycrystalline starting substrate comprising a surface thin film made of glassy carbon, which is particularly suitable for receiving a working layer transferred from a donor substrate. The invention also relates to a method for fabricating the support substrate and a composite structure produced by transferring a thin layer onto the support substrate.

[0009] The present invention relates to a method for fabricating a composite structure comprising a thin layer of a first single-crystal material disposed on a supporting substrate, the method comprising the following stages: a) providing a starting substrate made of a second polycrystalline material; b) depositing a polymer resin layer on at least one front side of the starting substrate by centrifugal coating, the polymer resin layer comprising pre-formed three-dimensional carbon-carbon bonds; c) subjecting the starting substrate containing the polymer resin layer to a first tempering at a temperature between 120°C and 180°C to form a cross-linked polymer resin layer; d) subjecting the cross-linked polymer resin layer to a second tempering at a temperature greater than 600°C in a neutral gas environment to convert the cross-linked polymer resin layer into a glassy carbon film.

[0010] According to the advantageous features of the invention, it can be implemented alone or in any feasible combination: the method includes a stage e) of mechanically polishing and / or chemically mechanically polishing the glassy carbon film after stage d); the polymer resin is based on coal tar, phenol / formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride and / or polystyrene; the method includes a stage f) of transferring a thin layer formed of the first single crystal material directly or through an intermediate layer onto the glassy carbon film; stage f) is assembled between a donor substrate and the glassy carbon film by direct bonding to form a bonded assembly, the donor substrate including the first single crystal material from which the thin layer is generated; The donor substrate includes a weakened buried plane that defines the thin layer to be transferred on one side of the donor substrate, and stage f) separating the bonding assembly along the weakened buried plane to form a composite structure comprising the thin layer disposed on the glassy carbon film, the composite structure itself being disposed on the starting substrate, and forming the remainder of the donor substrate; the first single crystal material is selected from silicon carbide, gallium nitride, silicon, germanium silicon, germanium, III-V compounds or other semiconductor materials, or selected from piezoelectric materials; the second polycrystalline material is selected from silicon carbide, aluminum nitride, silicon, germanium silicon, germanium, III-V compounds or other semiconductor materials, or selected from piezoelectric materials; the first material and the second material are semiconductors.

[0011] The present invention also relates to a composite structure comprising a thin layer made of a first single crystal material disposed on a supporting substrate, the supporting substrate comprising: a starting substrate made of a second polycrystalline material, and a glassy carbon film in contact with the front side of the starting substrate.

[0012] According to the advantageous features of the present invention, it can be implemented alone or in any feasible combination: the starting substrate exhibits a surface roughness with peak-to-valley values ​​between 10 nm and 2 μm, which is measured by atomic force microscopy in a surface area of ​​less than or equal to 30 μm x 30 μm; the glassy carbon film exhibits a thickness between 100 nm and 4 μm; the composite structure includes an intermediate layer located between the thin layer and the glassy carbon film, the intermediate layer being selected from silicon, silicon carbide, carbon, tungsten, or titanium; 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, aluminum nitride, or other semiconductor materials.

Implementation Method

[0016] The present invention relates to a method for fabricating a composite structure 100 comprising a thin layer 10 made of a first single-crystal material disposed on a support substrate 20, the support substrate 20 being at least partially composed of a second polycrystalline material (FIG. 4d). The desired composite structure 100 allows for vertical electrical conduction between the thin layer 10 and the support substrate 20, particularly for applications involving power electronics.

[0017] Specifically, the first single-crystal 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 may be selected from 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 described above with respect to the first material but exhibiting a polycrystalline structure or containing a surface polycrystalline layer. In the composite structure 100, the first material may be combined with one or the other of the second material described above, provided that this is beneficial to the final application.

[0018] Advantageously, the composite structure 100 will be formed of a first material and a second material with approximately the same coefficient of thermal expansion.

[0019] In the following description, the case of the first material made of c-SiC and the second material made of p-SiC will be described in particular. However, this description applies to any other pair of first and second materials. When necessary, further information regarding the different properties of the first and second materials will be given.

[0020] The fabrication method first includes a stage a) of providing a starting substrate 2, which is made of polycrystalline silicon carbide (p-SiC) and presents a front side 2a and a back side 2b (Fig. 1a). The starting substrate 2 can be prepared by conventional techniques such as sintering or chemical vapor deposition.

[0021] The starting substrate 2 is preferably in the form of a wafer with a diameter of 100 mm, 150 mm, 200 mm or even 300 mm and a thickness typically between 300 and 800 micrometers.

[0022] The surface condition of the front side 2a of the starting substrate 2 is preferably selected such that the peak-to-valley roughness (hereinafter referred to as "PV roughness") is less than or equal to a few micrometers, typically less than or equal to 2 μm, 1 μm, 500 nm, 100 nm or 50 nm.

[0023] In the context of this invention, roughness is measured using atomic force microscopy (AFM) on a surface area (scanning area) of 30 μm × 30 μm or less. The measured surface area may extend, for example, beyond 5 μm x 5 μm, 10 μm x 10 μm, 20 μm x 20 μm, or 30 μm x 30 μm. PV roughness, root mean square roughness, or RMS roughness will be referred to below.

[0024] It should be remembered that, due to the hardness and polycrystalline structure of the material, it is complicated to obtain a very good surface condition on a substrate made of p-SiC: mechanical polishing or chemical mechanical polishing may result in scratches on the substrate surface, and defects (pores) may occur due to the untimely tearing of the p-SiC grains on the surface.

[0025] Figure 2 illustrates an example of the surface condition of a starting substrate 2. Although the RMS roughness remains less than 1 nm, the PV roughness may exceed 30 nm due to surface scratches. This surface condition can create physical defects (voids) at the future interface between the substrate and the thin layer of the composite structure 100: this leads to a decrease in the quality and integrity of the transferred thin layer and the conductivity of the interface.

[0026] Typically, in the context of this invention, the starting substrate 2 can exhibit a PV surface roughness of up to a few micrometers, which greatly relaxes the limitations on the manufacture or supply of the starting substrate 2.

[0027] The surface condition of the back side 2b of the starting substrate 2 is not specifically described here. Its surface condition may be similar to or worse than the front side 2a, provided that it does not affect the overall curvature or quality (defect rate) of the starting substrate 2.

[0028] To adapt to the surface state of the starting substrate 2, the manufacturing method according to the present invention provides a stage b) (Fig. 1b) including depositing a polymer resin layer 3 on at least one front side 2a of the starting substrate 2 by centrifugal coating. An important feature of this layer is that it contains pre-formed three-dimensional (3D) carbon-carbon (CC) bonds. In this layer, carbon-based polymer chains exhibiting CC bond sequences are randomly dispersed in the solvent: therefore, they more or less exhibit a random 3D structure. The more random the distribution of these chains in 3D, the less graphitization is promoted during crosslinking, and the closer it is to a glassy state.

[0029] Here, after crosslinking, the amorphous / crystalline ratio of the polymer resin layer 3 will be as high as possible so as to obtain a glassy carbon film 30 at the end of the subsequent stage d) of this method.

[0030] The polymer resin may be formed from coal tar, phenol / formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride and / or polystyrene and similar substances.

[0031] For example, known photosensitive resins commonly used in the lithography stage in the field of microelectronics can be used, such as commercial products: AZ-5214, AZ-4330, AZ-P4620 (registered trademark) (based on 1-methoxy-2-propanol acetate, diazonaphthoquinone sulfonic esters, 2-methoxy-1-propanol acetate, cresol novolac resin), OCG-825 (based on ethyl 3-ethoxypropionate), SU-8 2000 (based on cyclopentanone, triarylsulfonates / hexafluoroantimonates, propylene carbonate, epoxy resin).

[0032] Epoxy resins used for covering and protecting various surfaces (aviation, marine, automotive, construction and similar applications), such as Epoxy Novolac EPON (registered trademark), may also be used in stage b of the method according to the present invention.

[0033] The dispersion carried out by centrifugation in stage b) requires the polymer resin solution to be provided in viscous form.

[0034] This deposition method is particularly advantageous because the viscous solution will fill the depressions (pores and scratches) present on the surface of the starting substrate 2 and thus effectively flatten these micro-reliefs.

[0035] The thickness of the polymer resin layer 3 deposited in stage b) can typically vary between several hundred nanometers (e.g., 500 nm) and several micrometers (e.g., 3 to 5 μm).

[0036] The manufacturing method then includes stage c), which involves applying a tempering (the first tempering) (Fig. 1c) to the starting substrate 2 containing the polymer resin layer 3 at a temperature between 120°C and 180°C, presenting a stationary phase. The stationary phase may have a duration between a few minutes (typically 30 minutes) and a few hours (typically 2 hours). The temperature is gradually increased, preferably from ambient temperature, between 1°C / min and 5°C / min, to gradually degas the polymer resin layer 3 and remove solvents and impurities initially present in the viscous solution.

[0037] Depending on the properties of the polymer resin, intermediate stationary phases may also be provided during the first tempering thermal cycle.

[0038] After the first tempering, the polymer resin layer 3' undergoes crosslinking and thus cures on the front side 2a of the starting substrate 2. Crosslinking is characterized by the formation of bonds between carbon-based chains, which is reflected by the curing of the polymer resin layer 3'. During the subsequent stage d) of the method, the three-dimensional arrangement of polymer chains in the crosslinked polymer resin layer 3' will affect the three-dimensional orientation of chains with sp2 type bonds.

[0039] Finally, the manufacturing method includes stage d), which involves applying a second tempering, presenting a stationary phase, in a neutral gas environment at a temperature greater than 600°C, preferably greater than 700°C, to transform the crosslinked polymer resin layer 3' into a glassy carbon film 30 (Fig. 1d). The stationary phase temperature can be, for example, 650°C, 750°C, 800°C, or 850°C or higher. The temperature range of the stationary phase can reach about 1800°C, and it is important to ensure that the temperature is compatible with the properties of the second material constituting the starting substrate 2.

[0040] This second tempering leads to the carbonization of the crosslinked layer 3'. For this carbonization to occur, a glassy carbon structure is necessary, exhibiting sp² carbon-carbon (CC) atomic bonds. The glassy carbon structure can be visualized by Raman spectroscopy with a specific band (G peak) or by elliptic polarization with a specific absorption characteristic, as known in the literature.

[0041] The glassy carbon film 30 preferentially presents 100% sp2 type C-C atomic bonds; if an inclusion of another phase is present in the film 30, the percentage of sp2 atomic bonds is tolerable to be greater than 95%, or preferably greater than 99%.

[0042] The neutral gas environment for the second tempering is typically based on argon and / or under vacuum (i.e., at pressures below atmospheric pressure and as low as a few millibars). The second tempering is carried out at a rising temperature, ranging from 5°C / min to 15°C / min, and up to 50°C / min, or even 100°C / min, from the ambient temperature to the stationary phase. The duration of the stationary phase can vary from a few minutes (e.g., 30 minutes) to a few hours (e.g., 2 hours).

[0043] The glassy carbon film 30 typically exhibits a thickness between several hundred nanometers (typically 500-600 nm) and several micrometers (typically 1, 2, 3 or 4 μm). Preferably, the thickness of the glassy carbon film 30 is approximately 10 times the surface roughness of the PV of the starting substrate 2.

[0044] To obtain the target thickness of the glassy carbon film 30, it is important to consider the contraction that the viscous polymer resin layer 3 deposited in stage b) of the method will undergo during the first tempering (stage c), and particularly during the second tempering (stage d), to define its sufficient initial thickness. The thickness contraction is typically between 70% and 95%. The carbon ratio, i.e., the ratio of the weight of the glassy carbon film 30 to the initial weight of the unfolded polymer resin layer 3, must be at least 5%, preferably greater than 50%.

[0045] The starting substrate 2 containing the glassy carbon film 30 corresponds to the supporting substrate 20 according to the present invention. Figure 3 illustrates an example of the surface condition of the supporting substrate 20 on its front side 20a (i.e., the free surface side of the glassy carbon film 30). Figure 2 illustrates that, starting from the roughness of the starting substrate 2, a root mean square roughness of less than or equal to 0.8 nm RMS and a peak-to-valley roughness of less than or equal to 7 nm PV can be obtained. The roughness here is still measured by atomic force microscopy in a surface area of ​​less than or equal to 30 μm x 30 μm.

[0046] Compared to surface 2a of the starting substrate 2, the surface condition is significantly improved; maximum resorption of scratches and other pit defects can be observed, as well as RMS and PV roughness typically less than or equal to 1 nm and 10 nm, respectively. This surface condition is particularly advantageous for assembly via direct bonding, exhibiting very good interface quality.

[0047] Advantageously, the manufacturing method according to the invention includes, after stage d), a stage e) of mechanical polishing and / or chemical mechanical polishing of the glassy carbon film 30 to adjust its thickness or further improve its surface roughness.

[0048] At the end of stage e), the target is an RMS roughness of less than 1 nm, or even 0.5 nm, and a PV roughness of less than 5 nm.

[0049] In addition, the glassy carbon thin film 30 exhibits excellent electrical conductivity characteristics, with a resistivity typically less than 6.10 -3 ohm·cm.

[0050] The mechanical, electrical and thermal properties of the glassy carbon thin film 30 make the support substrate 20 an excellent candidate for fabricating the composite structure 100 by transferring a thin layer 10 of single-crystal silicon carbide (c-SiC) onto the support substrate 20.

[0051] It should be noted that these mechanical, electrical and thermal properties are also assets of the composite structure 100, whose supporting substrate 20 will include, for example, a starting substrate 2 made of p-AlN and its thin layer 10 made of, for example, c-GaN, or other combinations of the first and second materials.

[0052] Returning to the description of the SiC-based composite structure, the fabrication method according to the present invention may include a stage f of transferring a thin layer 10 of c-SiC onto a glassy carbon film 30.

[0053] Various options are known in the prior art for thin-layer transfer, which will not be elaborated here.

[0054] In a preferred mode, stage f) of the method involves implanting a light species in accordance with the principles of the Smart Cut® method.

[0055] In the first stage f1), a single-crystal silicon carbide donor substrate 1 is provided from which the thin layer 10 is formed (Fig. 4a). The donor substrate 1 is preferably provided in wafer form, having a diameter of 100 mm, 150 mm, 200 mm, or even 300 mm (the same or very similar in diameter to the support substrate 20), and a thickness typically between 300 μm and 800 μm. The donor substrate has a front side 1a and a back side 1b. The surface roughness of the front side 1a is advantageously selected to be less than 1 nm RMS, or even less than 0.5 nm RMS, which is measured by atomic force microscopy (AFM) over a surface area of, for example, 20 μm × 20 μm. The donor substrate 1 can be 4H or 6H polytype and is n-type or p-type doped, depending on the component requirements to be fabricated on and / or within the thin layer 10 of the composite structure 100.

[0056] It should be noted that the donor substrate 1 used to form the c-GaN thin layer 10 can be formed from a substrate made of GaN, SiC, Si (111) or sapphire, on which single-crystal GaN epitaxy is performed in accordance with conventional methods.

[0057] The second stage f2) corresponds to introducing a light element into the donor substrate 1 to form a weakened embedded plane 11, which, together with the front side 1a of the donor substrate 1, defines the thin layer 10 to be transferred (Fig. 4b).

[0058] The light elements are preferably hydrogen, helium, or a combination of both, and are implanted into the donor substrate 1 at a predetermined depth consistent with the target thickness of the thin layer 10. These light elements will form microcavities distributed around the predetermined depth in an extremely thin layer parallel to the free surface 1a of the donor substrate 1, i.e., parallel to the plane (x, y) in the figure. For simplicity, this extremely thin layer is referred to as the weakened embedding plane 11.

[0059] The implantation energy of the light element is selected to achieve a specific depth. For example, hydrogen ions are implanted with energies between 10 keV and 250 keV, and doses between 5E16 / cm² and 1E17 / cm², to define a thin layer 10 with a thickness on the order of 100 nm to 1500 nm. It should be noted that a protective layer may be deposited on the front side 1a of the donor substrate 1 prior to the ion implantation stage. This protective layer may be made of a material such as silicon oxide or silicon nitride. It is removed before the next stage.

[0060] As needed, the intermediate layer 4 may be formed on the front side 1a of the donor substrate 1 before or after the second stage (f2) of introducing the light element. The intermediate layer 4 may be made of a semiconductor or metallic material; for example, silicon, silicon carbide, silicon oxide (SiOC), carbon (e.g., glassy carbon or turbostratic carbon), tungsten, titanium, etc., may be selected. The thickness of the intermediate layer 4 is advantageously limited, typically between a few nanometers and tens of nanometers.

[0061] If the intermediate layer 4 is formed before stage f2), the implantation energy (and possible dose) of the light element will be adjusted to be able to penetrate the additional layer. If the intermediate layer 4 is formed after stage f2), care should be taken to form the layer by applying a thermal budget lower than the foaming thermal budget, which corresponds to the bubbles that appear on the surface of the donor substrate 1 due to the excessive growth and pressurization of the microcavities in the weakened embedding plane 11.

[0062] Transfer stage f) then includes a third stage f3), that is, along the bonding interface 5, the first surface 20a of the supporting substrate 20 is assembled with the front surface 1a of the donor substrate 1 through molecular adhesion bonding to form a bonding component 50 (Figs. 4c, 4c').

[0063] If necessary, prior to the assembly stage f3), an additional layer may be deposited on the surface of the support substrate 20 to be assembled (i.e., on the glassy carbon layer 30); this layer may be selected to have the same or different properties as the intermediate layer 4 mentioned for the donor substrate 1. The intermediate layer 4 or the additional layer may be deposited on one of the two substrates 1 and 20 to be assembled, if necessary.

[0064] The purpose of the intermediate layer is mainly to promote bonding energy (especially in the temperature range below 1100°C), because covalent bonds can be formed at a lower temperature when there is an intermediate layer compared to the case of direct assembly without these intermediate layers; another advantage of the intermediate layer is that it can further improve the vertical electrical conductivity of the bonding interface 5.

[0065] Returning to the explanation of assembly stage f3), it is well known that direct bonding via molecular adhesion does not require an adhesive substance because the bonding is established at the atomic scale between the assembled surfaces. Several types of bonding via molecular adhesion exist, differing in terms of temperature, pressure, atmospheric environment, or processing conditions before surface contact. Room temperature bonding, regardless of whether the surfaces to be assembled are pre-activated by plasma, atomic diffusion bonding (ADB), surface activated bonding (SAB), etc., are mentioned.

[0066] The assembly stage f3) may include performing a conventional sequence of chemical cleaning (e.g., RCA cleaning), surface activation (e.g., by oxygen or nitrogen plasma) or other surface preparation (e.g., by brushing, scrubbing) before bringing the surfaces 1a and 20a to be assembled into contact, to promote the quality of the bonding interface 5 (low defect rate, high adhesion energy).

[0067] Finally, the fourth stage (f4) includes separation along the weakened embedded plane 11 to transfer the thin layer 10 onto the supporting substrate 20 (Fig. 4d).

[0068] Separation along the weakened embedded plane 11 is typically achieved by applying a heat treatment to the bonding assembly 50 at a temperature between 800°C and 1200°C (if the bonding assembly 50 is based on SiC). Of course, as those skilled in the art will know, this temperature depends to a great extent on the properties of the first and second materials involved in the bonding assembly 50 and is adjusted depending on the selected materials.

[0069] This heat treatment induces the development of cavities and microcracks in the weakened embedded plane 11, as well as the pressurization of light elements present in gaseous form, until fracture propagates along the weakened embedded plane 11. Alternatively or otherwise, mechanical stress may be applied to the bonding assembly 50, particularly the weakened embedded plane 11, to propagate or mechanically assist the propagation leading to separation fracture. At the end of this separation, a composite structure 100 comprising the supporting substrate 20 and the transferred single-crystal thin layer 10 is obtained on one hand, and the remaining portion 1' of the donor substrate is obtained on the other hand. The degree and type of doping of the thin layer 10 are defined by the properties of the donor substrate 1, or may be subsequently adjusted using known techniques for doping semiconductor layers.

[0070] The free surface 10a of the thin layer 10 is typically rough after separation: for example, it exhibits a roughness between 5 nm and 100 nm RMS (AFM, 20 μm × 20 μm scan). Cleaning and / or smoothing stages can be applied to restore a good surface condition (typically, a roughness less than a few angstroms RMS when performing AFM scans exceeding 20 μm x 20 μm). In particular, these stages may include chemical mechanical smoothing of the free surface of the thin layer 10. Removal of material between 50 nm and 300 nm can effectively restore the surface condition of the thin layer 10. At least one heat treatment may also be included, for example, in the case of the SiC-based composite structure 100, treatment at temperatures between 1300 °C and 1800 °C.

[0071] This treatment is applied to remove residual light elements from the thin layer 10 and to promote lattice rearrangement. In addition, it can also strengthen the bonding interface 5.

[0072] The heat treatment may also include or correspond to the epitaxial growth of silicon carbide on the thin layer 10.

[0073] The supporting substrate 20, particularly the glassy carbon film 30, is fully compatible with the extremely high temperature heat treatment that may be applied during the preparation of the composite structure 100.

[0074] Finally, it should be noted that the transfer stage f) may include a stage of repairing the remaining portion 1' of the donor substrate for reuse as the donor substrate 1 of the new composite structure 100. Mechanical and / or chemical treatments similar to those of the composite structure 100 may be applied to the front surface 1'a of the remaining portion 1'.

[0075] The obtained composite structure 100 includes a single-crystal silicon carbide thin layer 10 disposed on a support substrate 20, the support substrate 20 including a polycrystalline silicon carbide starting substrate 2 and a glassy carbon film 30, which is in contact with the front side 2a of the starting substrate 2.

[0076] As mentioned above with reference to the manufacturing method according to the present invention, the composite structure 100 described herein refers to the case of a first material made of c-SiC and a second material made of p-SiC. The present invention also relates to composite structures 100 based on other combinations of first and second materials (not exhaustive above), particularly composite structures 100 comprising a thin layer made of c-GaN and a starting substrate 2 made of p-AlN (included in a supporting substrate 20).

[0077] The intermediate layer 4 and / or additional layers such as those mentioned in this method may be inserted between the glassy carbon film 30 and the thin layer 10 as needed. The carbon intermediate layer 4 is advantageous because it does not increase the total vertical resistance by adding a separate material interface and provides very good temperature stability.

[0078] The electrical conductivity 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·cm², or even less than 10⁻⁵ ohm·cm², or even less than 10⁻⁶ ohm·cm².

[0079] The composite structure 100 is highly resistant to the high-temperature heat treatments required when fabricating components on and / or within the layer 10. The composite structure 100 according to the invention is particularly suitable for fabricating one or more high-voltage microelectronic components, such as Schottky diodes, MOSFET transistors, etc. More broadly, the composite structure 100 is suitable for power microelectronic applications, exhibiting excellent vertical electrical conductivity, good thermal conductivity, and providing a high-quality operating layer made of single-crystal material.

[0080] Of course, the present invention is not limited to the embodiments described above, and various alternatives may be introduced without departing from the scope of the present invention as defined by the claims. [Simplified Explanation of the Diagram]

[0013] Other features and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings, in which: Figures 1a, 1b, 1c and 1d illustrate stages of a method for fabricating a support substrate according to the present invention; Figure 2 illustrates an example of the surface state of a starting substrate constituting a support substrate according to the present invention; Figure 3 illustrates an example of the surface state of a glassy carbon film constituting a support substrate according to the present invention; Figures 4a, 4b, 4c, 4c' and 4d illustrate stages of a method for fabricating a composite structure according to the present invention.

[0014] Some diagrams are schematic and are not drawn to scale for readability purposes. In particular, the layer thickness along the z-axis is not drawn to scale relative to the lateral dimensions along the x and y axes.

[0015] In diagrams or descriptive text, the same component symbols can be used to represent components of the same nature.

Claims

1. A method for fabricating a composite structure (100) comprising a thin layer (10) made of a first single-crystal material disposed on a supporting substrate (20), the method comprising the following stages: a) providing a starting substrate (2) made of a second polycrystalline material; b) depositing a polymer resin layer (3) on at least one front side (2a) of the starting substrate (2) by centrifugal coating, the polymer resin layer comprising pre-formed three-dimensional carbon-carbon bonds; c) subjecting the starting substrate (2) containing the polymer resin layer (3) to a first tempering at a temperature between 120°C and 180°C to form a crosslinked polymer resin layer (3'); d) subjecting a second tempering at a temperature greater than 600°C in a neutral atmospheric environment to convert the crosslinked polymer resin layer (3') into a glassy carbon film (30); f) The thin layer (10) formed from the first single crystal material is transferred directly or through an intermediate layer (4) to the glassy carbon film (30). The transfer involves an interface (5) bonded by molecular adhesion, which is located between one side of the glassy carbon film (30) and one side of the thin layer (10), or between one side of the glassy carbon film (30) and one side of an intermediate layer (4), and the intermediate layer is disposed between the glassy carbon film (30) and the thin layer (10).

2. The method of claim 1, which includes a stage e after stage d) of mechanical polishing and / or chemical mechanical polishing of the glassy carbon film (30).

3. The method of claim 2, wherein the polymer resin is based on coal tar, phenol / formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride and / or polystyrene.

4. The method of any one of claims 1 to 3, wherein stage f) involves the assembly between a donor substrate (1) and the glassy carbon film (30) to form a bonding assembly (50), the donor substrate comprising the first single crystal material, from which the thin layer (10) is generated.

5. As in request item 4, where: The donor substrate (1) includes a weakened embedding plane (11) that defines the thin layer (10) to be transferred on one of the front sides (1a) of the donor substrate (1), and stage f) involves separating the bonding assembly (50) along the weakened embedding plane (11) to form a composite structure (100) on one hand, which includes the thin layer (10) disposed on the glassy carbon film (30), the composite structure itself being disposed on the starting substrate (2), and on the other hand, forming the remainder of the donor substrate (1).

6. The method of claim 1, wherein the first single crystal material is selected from silicon carbide, gallium nitride, silicon, silicon germanium, germanium, III-V compound or other semiconductor materials, or selected from piezoelectric materials.

7. The method of claim 1, wherein the second polycrystalline material is selected from silicon carbide, aluminum nitride, silicon, silicon germanium, germanium, III-V group compounds or other semiconductor materials, or selected from piezoelectric materials.

8. The method 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 single-crystal material disposed on a support substrate (20), the support substrate (20) comprising: A starting substrate (2) made of a second polycrystalline material, a glassy carbon film (30) in contact with the front side (2a) of the starting substrate (2), the composite structure (100) further includes an interface (5) bonded by molecular adhesion, the interface being located between one side of the glassy carbon film (30) and one side of the thin layer (10), or between one side of the glassy carbon film (30) and one side of an intermediate layer (4), the intermediate layer being disposed between the glassy carbon film (30) and the thin layer (10).

10. The composite structure (100) of claim 9, wherein the starting substrate (2) exhibits a surface roughness with peak values ​​between 10 nm and 2 μm, which is obtained by atomic force microscopy in a surface area less than or equal to 30 μm x 30 μm.

11. The composite structure (100) of claim 9 or 10, wherein the glassy carbon film (30) has a thickness between 100 nm and 4 μm.

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

13. The composite structure (100) of claim 9, 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, aluminum nitride or other semiconductor materials.

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