COMPOSITE STRUCTURE COMPRISING A SILICON CARBIDE SUPPORT LAYER AND MANUFACTURING PROCESS
By forming trenches and reacting the substrate with carbon to create a discontinuous silicon carbide layer, the method addresses thermal expansion issues in silicon carbide deposition, ensuring crack-free and deformed-free support layers for electronic components.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- SOITEC SA
- Filing Date
- 2024-12-10
- Publication Date
- 2026-06-12
AI Technical Summary
The deposition of polycrystalline silicon carbide (poly-SiC) on silicon or graphite substrates is hindered by thermal expansion differences, leading to excessive deformation and cracking, which complicates the production of electronic components.
A method involving the formation of trenches in a substrate, filling them with a second material, reacting it with carbon to form a discontinuous silicon carbide layer, and depositing a silicon carbide support layer on this layer to mitigate thermal expansion issues.
The method reduces cracking and deformation of the silicon carbide support layer, enabling efficient and crack-free deposition, suitable for use in electronic components.
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Abstract
Description
Title of the invention: COMPOSITE STRUCTURE COMPRISING A SILICON CARBIDE SUPPORT LAYER AND MANUFACTURING METHOD TECHNICAL FIELD OF THE INVENTION
[0001] The technical field of the invention is that of substrates used in the manufacture of electronic components. The invention relates more particularly to a composite structure comprising a silicon carbide (SiC) support layer and a method for manufacturing this composite structure. TECHNOLOGICAL BACKGROUND OF THE INVENTION
[0002] Interest in silicon carbide (SiC) has increased considerably in recent years because this semiconductor material can increase power handling capacity. In particular, power electronics components and integrated power systems based on monocrystalline SiC can handle a much higher power density than their silicon counterparts, and with smaller active area dimensions.
[0003] Bulk substrates of single-crystal SiC for the microelectronics industry remain expensive and difficult to source in large sizes. Furthermore, when electronic components are fabricated on a bulk substrate, it is often necessary to thin the substrate on the back side to meet size and / or electrical conductivity specifications.
[0004] It is therefore advantageous to use thin film transfer solutions to develop multilayer structures comprising a single-crystal silicon carbide (SiC) useful layer on a lower crystalline quality semiconductor support substrate, typically polycrystalline SiC (poly-SiC), the useful layer then being used to form electronic components.
[0005] The poly-SiC support substrate must be of sufficient thickness to be compatible with the manufacture of electronic components. Even if it is of lower quality than the mono-SiC active layer, the support substrate remains a significant cost contributor.
[0006] The poly-SiC support substrate can be obtained by depositing a thick layer of poly-SiC onto a temporary silicon or graphite substrate, and then removing the temporary substrate. However, depositing poly-SiC onto silicon or graphite presents numerous difficulties. In particular, the difference in coefficients of thermal expansion between SiC on the one hand and silicon or graphite on the other leads to excessive deformation of the poly-SiC layer in the case of a thick deposit and cracks in the poly-SiC layer in the case of a thin deposit. Summary of the invention
[0007] The invention aims to limit the deformation of a SiC support layer or the appearance of cracks in a SiC support layer when this support layer is deposited on a silicon or graphite substrate.
[0008] According to a first aspect of the invention, this objective is approached by providing a method for manufacturing a composite structure, comprising the following steps: • provide a substrate in a first material, the substrate comprising a first face and a second face opposite to the first face; • form a plurality of first trenches in the substrate, the first trenches extending from the first face; • fill at least partially the first trenches with a second material, one of the first and second materials being silicon and the other of the first and second materials being graphite; • reacting silicon with carbon to form a first discontinuous layer of silicon carbide; and • deposit a first layer of silicon carbide support on the first discontinuous layer of silicon carbide and on the first face of the substrate when the second material is silicon or on the first discontinuous layer of silicon carbide and the second material when the second material is graphite.
[0009] In a first embodiment, the first material is graphite and the second material is silicon.
[0010] In a second embodiment, the first material is silicon and the second material is graphite.
[0011] In addition to the characteristics mentioned in the preceding paragraphs, the manufacturing process according to the first aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: • the second material in the first trenches forms a flat surface with the first face of the substrate; • the second material completely fills the first trenches; • the first support layer is made of polycrystalline silicon carbide; • The first support layer is deposited using a deposition technique chemical vapor phase; • the reaction step of silicon with carbon and the deposition step of the first support layer are carried out successively in the same deposition chamber; • the first discontinuous layer of silicon carbide is located in the vicinity of the first face of the substrate; • the first trenches have a depth of between 1% and 30% of the thickness of the substrate; • the first trenches have a width between 10 pm and 1 mm; • the step of depositing the first layer of support is completed at a temperature higher than the melting point of silicon and lower than the melting point of silicon carbide; • The manufacturing process also includes the following steps: • form a plurality of second trenches in the substrate, the second trenches extending from the second face; • fill at least partially the second trenches with the second material; • form a second discontinuous layer of silicon carbide by reaction of silicon with carbon; and • deposit a second layer of silicon carbide support on the second discontinuous layer of silicon carbide and on the second face of the substrate when the second material is silicon or on the second discontinuous layer of silicon carbide and on the second material when the second material is graphite. • the second material in the second trenches forms a flat surface with the second face of the substrate; • the second material completely fills the second trenches; • the second support layer is made of polycrystalline silicon carbide; • the second support layer is deposited using a technique of chemical vapor deposition; • the second discontinuous layer of silicon carbide is located in the vicinity of the second face of the substrate; and • the second trenches have a depth of between 1% and 30% of the thickness of the substrate; • The second trenches have a width between 10 µm and 1 mm.
[0012] A second aspect of the invention relates to a composite structure comprising: • a substrate made of a first material, the substrate comprising a first face and a second face opposite to the first face; • a plurality of first trenches extending into the substrate from the first face and filled at least partially with a second material, one of the first and second materials being silicon and the other of the first and second materials being graphite; • a first discontinuous layer of silicon carbide located in contact with the second material when the second material is silicon, or in contact with the first face when the second material is graphite; and • a first silicon carbide support layer disposed on the first discontinuous silicon carbide layer and on the first face of the substrate when the second material is silicon or disposed on the first discontinuous silicon carbide layer and the second material when the second material is graphite.
[0013] Preferably, the composite structure according to the second aspect of the invention further comprises: • a plurality of second trenches extending into the substrate from the second face and filled at least partially with the second material; • a second discontinuous layer of silicon carbide located in contact with the second material when the second material is silicon, or in contact with the second face when the second material is graphite; and • a second silicon carbide support layer disposed on the second discontinuous silicon carbide layer and on the second face of the substrate when the second material is silicon or disposed on the second discontinuous silicon carbide layer and the second material when the second material is graphite.
[0014] In a first embodiment, the first material is graphite and the second material is silicon.
[0015] In a second embodiment, the first material is silicon and the second material is graphite.
[0016] A third aspect of the invention relates to a composite structure comprising: • a graphite substrate, the substrate comprising a first face and a second face opposite the first face; • a plurality of first trenches extending into the substrate from the first face; • a first discontinuous layer of silicon carbide occupying the first trenches; and • a first layer of silicon carbide support placed on the first discontinuous layer of silicon carbide and on the first face of the substrate.
[0017] Preferably, the composite structure according to the third aspect of the invention further comprises: • a plurality of second trenches extending into the substrate from the second face; • a second discontinuous layer of silicon carbide occupying the second trenches; and • a second layer of silicon carbide support disposed on the second discontinuous layer of silicon carbide and on the second face of the substrate. BRIEF DESCRIPTION OF THE FIGURES
[0018] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the accompanying figures, among which: • Figures IA to 1E represent a first implementation of the composite structure manufacturing process according to the invention; and • Figures 2A to 2E represent a second implementation method of the composite structure manufacturing process according to the invention.
[0019] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION
[0020] Figures IA to 1E represent, in schematic cross-section view, steps SI to S5 of a manufacturing process for a composite structure 1 according to a first implementation method.
[0021] The first step SI, represented by [Fig.1A], consists of providing a substrate 10. The substrate 10 is formed of a first material, graphite in this first embodiment.
[0022] The substrate 10 comprises a first face 10a and a second face 10b opposite the first face 10a. The substrate 10 may be in the form of a circular plate. The first and second faces 10a-10b (also called principal faces or front and back faces, respectively) of the substrate 10 are preferably planar and parallel to each other.
[0023] The substrate 10 can have a thickness of between 500 pm and 20 mm.
[0024] At step S2 of [Fig.2B], first trenches lia are formed in the substrate 10. The first trenches 1 la extend (in the substrate 10) from the first face 10a, and preferably perpendicular to this first face 10a.
[0025] The first trenches can be formed by engraving, for example by means of a plasma or a laser, or by machining, typically by means of a diamond saw.
[0026] The first trenches 1a preferably have a depth between 1% and 30% of the thickness of the substrate 10. The depth of the first trenches 1a and the thickness of the substrate 10 are measured perpendicular to the first face 10a. The width of the first trenches 1a (measured parallel to the first face 10a, in the plane of cut of [Fig.1B]) can be between 10 µm and 1 mm.
[0027] The first trenches 1a are preferably straight. At least part of the first trenches 1a may extend parallel to each other. The distance between two consecutive first trenches 1a may be between 10 µm and 10 mm. The first trenches 1a are preferably regularly spaced from each other.
[0028] Viewed from above, the first trenches 1 can form different patterns. For example, part of the first trenches 1la extend in one direction and another part of the first trenches lia extend in a second direction intersecting the first direction. When the second direction is perpendicular to the first direction, the first trenches lia form a rectangular grid in the first face 10a of the substrate 10.
[0029] At step S3 of [Fig. IC], the first trenches 1 are filled, at least partially, with a second material 12, here silicon.
[0030] As illustrated in [Fig.IC], the second material 12 in the first trenches preferably forms a flat surface with the first face 10a of the substrate 10. Such a configuration can be obtained by depositing the second material 12 so that it overflows onto the first face 10a of the substrate 10, and then removing the excess second material 12 (on the first face 10a), for example by chemical polishing.
[0031] Depending on the technique used to deposit the second material 12 and the dimensions of the first trenches 1la, the second material 12 may completely fill the first trenches 1la, or conversely, only partially fill them. The first trenches 1la may in particular contain voids.
[0032] The filling of the first trenches lia can in particular be carried out by a chemical vapor deposition (CVD) technique, by the deposition of silicon in the form of a powder followed by the melting of the powder, or by any other known filling technique.
[0033] Step S4 of [Fig. 1D] is a so-called carbonization step consisting of reacting (chemically) the silicon in the first trenches 1a with carbon, so as to form a first discontinuous layer of silicon carbide (SiC) 13a. The first discontinuous layer of SiC 13a is located in the vicinity of the first face 10a of the substrate 10. By "discontinuous layer," we mean a layer that has through holes or openings, in other words, a layer that is not solid. In this first embodiment, the first discontinuous layer 13a has (in top view) the same pattern as that formed by all the first trenches 1a. It is located in the first trenches 1a or vertically above the first trenches 1a.
[0034] Thus, on the side of the first face 10a of the substrate 10, a hybrid surface composed of graphite and SiC is obtained. The SiC of the first discontinuous layer 13a can be single-crystal or polycrystalline.
[0035] The carbonization step S4 is advantageously carried out in a chemical vapor deposition (CVD) reactor by injecting one or more carbon precursors into the reactor's deposition chamber. No silicon precursor is introduced into the chamber at this step S4.
[0036] No chemical reaction occurs between the graphite of the substrate 10 and the carbon precursor(s).
[0037] The silicon in the first trenches 1a may not be completely transformed into SiC. In other words, after the carbonization step S4, some silicon may remain embedded in the substrate 10, beneath the first discontinuous layer 13a of SiC. The first discontinuous layer 13a preferably has a thickness between 0.05 pm and 0.3 pm.
[0038] The free face, or upper face, of the first discontinuous layer 13a may be located above the first face 10a of the substrate 10, at the level of the first face 10a (i.e., in the plane), or below the first face 10a, depending on the degree to which the first trenches 1a are filled by the second material 12. In particular, when the second material 12 fills the first trenches 1a up to the first face 10a, at least part of the first discontinuous layer 13a of SiC is disposed on the first face 10a (see [Fig. 1D]). Conversely, when the second material 12 does not completely fill the first trenches 1a, the first discontinuous layer 13a may be set back from the first face 10a.
[0039] In other words, the first discontinuous layer 13a can form a step with the first face 10a of the substrate 10.
[0040] With reference to [Fig. 1E], the manufacturing process then comprises a step S5 of depositing a first layer of SiC support 14a onto the first face 10a of the substrate 10 and on the first discontinuous layer 13a of SiC. The first support layer 14a is preferably deposited using a CVD technique, by simultaneously injecting one or more carbon precursors and one or more silicon precursors into the deposition chamber.
[0041] The SiC of the first support layer 14a is preferably polycrystalline. The first support layer 14a may have a thickness between 200 µm and 1500 µm.
[0042] The first discontinuous SiC layer 13a promotes the growth of the first SiC support layer 14a and reduces the impact of the difference between the coefficient of thermal expansion of graphite and that of SiC. The first SiC support layer 14a is thus free of cracks and does not show excessive deformation.
[0043] The first discontinuous layer 13a further enables the deposition of the first support layer 14a at a temperature above the melting point of silicon (i.e., above 1414 °C) but below the melting point of SiC (2730 °C). Any remaining silicon (if present) in the first trenches 1a is then in a molten state, but it does not affect the deposition, as it is buried beneath the first discontinuous layer 13a of SiC. A high deposition temperature increases the deposition rate, thus enabling the desired SiC thickness to be obtained quickly.
[0044] Alternatively, the deposition of the first support layer 14a can be accomplished at a temperature strictly lower than the melting temperature of silicon.
[0045] The carbonization step S4 and the deposition step S5 of the first support layer 14a are advantageously carried out (successively) in the same deposition chamber (first by injecting the carbon precursor(s), then by also injecting the silicon precursor(s)). The manufacturing process is thus simplified and exposure of the structure shown in [Fig. 1D] to air is avoided.
[0046] The composite structure 1 obtained at the end of step S5 of [Fig. 1E] therefore comprises: • the graphite substrate 10; • the first trenches lia, filled at least partially with silicon (here the second material 12) when it has not been totally transformed into SiC; • the first discontinuous layer 13a of SiC arranged in contact with the silicon remaining in the first trenches 1 la; and • the first support layer 14a in SiC.
[0047] When the silicon has been completely transformed into SiC in the S4 carbonization step, the first discontinuous layer 13a of SiC occupies (all or part) of the first Lia trenches. As described previously, it can also extend beyond the first Lia trenches.
[0048] Figures 2A to 2E represent, again in schematic cross-sectional view, a second method of implementing the manufacturing process.
[0049] This second embodiment differs from the first embodiment (Figs. 1A-1E) essentially in that the substrate 10 (supplied in step S1 of [Fig. 2A]) is silicon (and not graphite) and in that the second material 12 filling (at least partially) the first trenches 1a (in step S3 of [Fig. 2C]) is graphite (rather than silicon). Thus, the configuration of the first and second materials is reversed compared to the first embodiment.
[0050] Step S2 of formation of the first trenches 1 ([Fig.2B]) and step S4 of carbonization ([Fig.2D]) are preferably carried out in the manner described above in relation to figures IB and 1D.
[0051] Since the substrate 10 is made of silicon, the first discontinuous layer 13a of SiC covers the first face 10a of the substrate 10 outside the first trenches 1 la and therefore presents a pattern which corresponds to the "negative" of the first trenches lia.
[0052] In step S5 of [Fig. 2E], the first SiC support layer 14a is deposited on the first discontinuous SiC layer 13a and on the second material 12 (arranged in the first trenches 1a), here graphite. The deposition is carried out at a temperature strictly below the melting point of silicon.
[0053] The composite structure 1' obtained at the end of step S5 of [Fig.2E] comprises: • the silicon substrate 10; • the first trenches were filled at least partially with graphite; • the first discontinuous layer 13a of SiC disposed on the first face 10a of the substrate 10; and • the first support layer 14a in SiC.
[0054] The composite structure 1 ([Fig.1E]) or 1' ([Fig.2E]) can be used as a starting substrate for the manufacture of electronic components, starting for example by transferring a useful semiconductor layer onto the first support layer 14a, the useful layer being for example made of single-crystal silicon carbide, gallium(III) oxide (Ga2O3), an IILV semiconductor material (such as GaN) or an ILVI semiconductor material.
[0055] Alternatively, the substrate 10 can be removed (after step S5) to obtain a self-supporting SiC substrate, this substrate comprising the first support layer 14a and optionally the first discontinuous layer 13a.
[0056] The material located inside the first trenches 1 la (graphite, silicon and / or SiC) is advantageously removed at the same time as the substrate 10.
[0057] The removal of the substrate 10 can be accomplished in various ways. Examples include: • a chemical etching of the substrate 10; • a shrinkage by thermal damage of the material composing the substrate 10; for example, in the case of graphite, shrinkage by thermal damage can occur at a temperature between 600°C and 1000°C in the presence of oxygen: the graphite of the substrate 10 is then burned; • a removal by grinding (“grinding”) of the substrate 10.
[0058] As shown in the figures, the manufacturing process according to the first or second embodiment may include treating the second face 10b of the substrate 10 in a similar or identical manner to the first face 10a, so that the composite structure 1,1' comprises two discontinuous layers 13a, 13b of SiC and two support layers 14a, 14b of SiC arranged on either side of the substrate 10.
[0059] It is thus possible to obtain a composite structure 1,1' which is balanced, in terms of mechanical stresses, or even which is symmetrical with respect to the substrate 10.
[0060] The manufacturing process then comprises the following additional steps: • S2': the formation of second trenches 11b in substrate 10 (in graphite or silicon, respectively), the second trenches 11b extending from the second face 10b, preferably perpendicular to this second face 10b; • S3': the (partial or total) filling of the second trenches 11b by the second material (silicon or graphite, respectively); • S4': the formation of the second discontinuous 13b layer of SiC, at proximity of the second face 10b of the substrate 10, by reaction between silicon and carbon; • S5': the deposition of a second 14b SiC support layer on the second discontinuous layer 13b and on the second face 10b of the substrate 10 when the second material 12 is silicon or on the second discontinuous layer 13b and on the second material 12 when the second material is graphite.
[0061] Preferably, step S2' of forming the second trenches 11b, step S3' of filling the second trenches 11b, and step S5' of depositing the second support layer 14b relating to the second face 10b of the substrate 10 are carried out respectively in the same way as steps S2, S3, and S5 relating to the first face 10a. In particular, the second trenches 11b may have the same shape, arrangement, and dimensions as the first trenches 1a (the dimension values given previously for the first trenches 1a are applicable to the second trenches 11b).
[0062] The second discontinuous layer 13b of SiC is preferably formed at the same time as the first discontinuous layer 13a, during the carbonization step S4.
[0063] The second support layer 14b, preferably in polycrystalline SiC, may have a thickness equal to or substantially equal (± 10%) to the thickness of the first support layer 14a, so that the composite structure 1,1' is globally balanced in terms of mechanical stresses.
[0064] Similar to the first discontinuous layer 13a, the second discontinuous layer 13b of SiC promotes the growth of the second SiC support layer 14b and reduces the impact of the difference between the coefficient of thermal expansion of graphite and that of SiC. The second SiC support layer 14b is thus free of cracks and does not exhibit excessive deformation.
[0065] Thus, after the removal of the substrate 10 (and the material contained in the first and second trenches), two self-supporting SiC substrates are obtained, instead of just one.
[0066] When the two faces 10a-10b of the substrate 10 have been treated, the removal of the substrate 10 can in particular be carried out by laterally slicing the composite structure 1, 1' through the substrate 10 (preferably along a plane parallel to the first and second faces 10a-10b), and then removing each part of the substrate 10, typically by engraving or grinding.
Claims
Demands
1. A method for manufacturing a composite structure (1, 1'), comprising the following steps: - providing (S1) a substrate (10) of a first material, the substrate (10) comprising a first face (10a) and a second face (10b) opposite the first face (10a); - forming (S2) a plurality of first trenches (1a) in the substrate (10), the first trenches (1a) extending from the first face (10a); - filling (S3) at least partially the first trenches (1a) with a second material (12), one of the first and second materials being silicon and the other of the first and second materials being graphite; - reacting (S4) the silicon with carbon so as to form a first discontinuous layer of silicon carbide (13a);and - deposit (S5) a first support layer (14a) of silicon carbide on the first discontinuous layer (13a) of silicon carbide and on the first face (10a) of the substrate (10) when the second material (12) is silicon or on the first discontinuous layer (13a) of silicon carbide and the second material (12) when the second material is graphite.;
2. Method according to claim 1, wherein the second material (12) completely fills the first trenches (1a).
3. A method according to any one of claims 1 and 2, wherein the first support layer (14a) is made of polycrystalline silicon carbide.
4. A method according to any one of claims 1 to 3, wherein the step (S4) of reacting silicon with carbon and the step (S5) of depositing the first support layer (14a) are carried out successively in the same deposition chamber.
5. A method according to any one of claims 1 to 4, wherein the first material is graphite and the second material (12) is silicon.
6. A method according to any one of claims 1 to 4, wherein the first material is silicon and the second material (12) is graphite.
7. A method according to any one of claims 1 to 6, wherein the first trenches (lia) have a depth of between 1% and 30% of the thickness of the substrate (10).
8. A method according to any one of claims 1 to 7, wherein the first trenches (lia) have a width between 10 pm and 1 mm.
9. A method according to any one of claims 1 to 8, wherein the step (S5) of depositing the first support layer (14a) is carried out at a temperature above the melting temperature of silicon and below the melting temperature of silicon carbide.
10. A method according to any one of claims 1 to 9, further comprising the following steps: - forming (S2') a plurality of second trenches (11b) in the substrate (10), the second trenches (11b) extending from the second face (10b); - filling (S3') at least partially the second trenches (11b) with the second material (12); - forming (S4') a second discontinuous layer of silicon carbide (13b) by reaction of silicon with carbon; and - depositing (S5') a second support layer of silicon carbide (14b) on the second discontinuous layer of silicon carbide (13b) and on the second face (10b) of the substrate (10) when the second material (12) is silicon or on the second discontinuous layer of silicon carbide (13b) and on the second material (12) when the second material is graphite.
11. Composite structure (1, 1') comprising: - a substrate (10) of a first material, the substrate (10) comprising a first face (10a) and a second face (10b) opposite the first face (10a); - a plurality of first trenches (1la) extending in the substrate (10) from the first face (10a) and filled at least partially with a second material (12), one of the first and second materials being silicon and the other of the first and second materials being graphite; - a first discontinuous layer of silicon carbide (13a) located in contact with the second material (12) when the second material (12) is silicon or in contact with the first face (10a) when the second material is graphite; and - a first support layer (14a) of silicon carbide disposed on the first discontinuous layer of silicon carbide (13a) and on the first face (10a) of the substrate (10) when the second material (12) is silicon or disposed on the first discontinuous layer of silicon carbide (13a) and the second material (12) when the second material is graphite.
12. Composite structure (1, 1') according to claim 11, further comprising: - a plurality of second trenches (11b) extending into the substrate (10) from the second face (10b) and filled at least partially with the second material (12); - a second discontinuous layer of silicon carbide (13b) located in contact with the second material (12) when the second material is silicon or in contact with the second face (10b) when the second material is graphite; and - a second support layer (14b) of silicon carbide disposed on the second discontinuous layer of silicon carbide (13b) and on the second face (10b) of the substrate (10) when the second material is silicon or disposed on the second discontinuous layer of silicon carbide (13b) and the second material (12) when the second material is graphite.
13. Composite structure (1, 1') according to any one of claims 11 and 12, wherein the first material is graphite and the second material (12) is silicon.
14. Composite structure (1, 1') according to any one of claims 11 and 12, wherein the first material is silicon and the second material (12) is graphite.
15. Composite structure (1) comprising:
16. - a graphite substrate (10), the substrate (10) comprising a first face (10a) and a second face (10b) opposite the first face (10a); - a plurality of first trenches (1 la) extending into the substrate (10) from the first face (10a); - a first discontinuous layer of silicon carbide (13a) occupying the first trenches (lia); and - a first support layer (14a) of silicon carbide disposed on the first discontinuous layer of silicon carbide (13a) and on the first face (10a) of the substrate (10). Composite structure (1, 1') according to claim 15, further comprising: - a plurality of second trenches (11b) extending into the substrate (10) from the second face (10b); - a second discontinuous layer of silicon carbide (13b) occupying the second trenches (11b); and - a second support layer (14b) of silicon carbide disposed on the second discontinuous layer of silicon carbide (13b) and on the second face (10b) of the substrate (10).