Method for manufacturing a composite structure including a monocrystalline thin layer transferred onto a carrier substrate

Abstract

The invention relates to a method for manufacturing a composite structure comprising a thin layer of monocrystalline material arranged on a carrier substrate made of polycrystalline material, the manufacturing method comprising the following steps: a) providing a raw disk made of polycrystalline material having two faces; b) measuring at least one curvature parameter of the raw disk so as to define a first face with a convex profile and a second face with a concave profile, and selecting the first face to correspond to a front face of the carrier substrate at the end of step c); c) preparing the carrier substrate from the raw disk, involving mechanical and / or chemical treatment of the faces of the raw disk, the carrier substrate having a front face and a rear face corresponding to the first face and the second face of the raw disk, respectively; d) transferring the thin layer onto the front face of the carrier substrate in order to obtain the composite structure.

Description

Method for manufacturing a composite structure including a single-crystal thin film transferred onto a supporting substrate FIELD OF INVENTION

[0001] The present invention relates to the field of semiconductor materials for microelectronic components. It relates in particular to a method for manufacturing a composite structure comprising a single-crystal thin film transferred onto a support substrate, the curvature characteristics of which, in the early stages of its fabrication, allow the face on which the thin film will be placed to be defined, so that the curvature of the composite structure, after thinning of the support substrate, remains low. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Silicon carbide (SiC) composite structures, which consist of a thin layer of monocrystalline SiC (m-SiC) deposited on a polycrystalline SiC (p-SiC) substrate, are particularly well-suited for the development of power components. The high-quality m-SiC thin layer enables the fabrication of high-performance components. The p-SiC substrate reduces material costs compared to a bulk monocrystalline substrate and can provide additional functionalities and performance benefits, particularly related to its mechanical, electrical, and / or thermal properties.

[0003] Of course, many composite structures, other than the aforementioned m-SiC / p-SiC, can also be considered, with different single-crystal materials for the thin layer and different single- or polycrystalline materials for the supporting substrate.

[0004] A well-known thin-film transfer solution is the Smart Cut process. TM This process involves the implantation of light ions to form a fragile plane embedded in a single-crystal donor substrate, and the direct bonding of said single-crystal donor substrate to a support substrate at a bonding interface. Separation is then achieved, through thermal and / or mechanical activation, along the embedded fragile plane, leading to the transfer of a thin layer of single-crystal material from the donor substrate onto the support substrate.

[0005] It is common practice, after microelectronic devices have been fabricated on and / or within the thin film, to thin the substrate from its back side, particularly to minimize the electrical resistance of vertical devices and to improve heat dissipation performance. The substrate, with a diameter of, for example, 150 mm, 200 mm, or even more, can typically be reduced from an initial thickness greater than 450 micrometers to a final thickness of less than 250 micrometers, or even less than 100 micrometers.

[0006] It is important to control and minimize the deformation (curvature) of thinned composite structures, to avoid their breakage or degradation, and to allow the continuation of the chip individualization and packaging steps.

[0007] SUBJECT OF THE INVENTION

[0008] The present invention proposes a method for manufacturing a composite structure including a single-crystal thin film transferred onto a support substrate made of polycrystalline material: the curvature characteristics of the support substrate, in the early stages of its development, make it possible to define the face on which the thin film will be placed, in order to minimize the curvature of the composite structure, after the final thinning of the support substrate.

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] The invention relates to a method for manufacturing a composite structure comprising a thin layer of monocrystalline material deposited on a support substrate of polycrystalline material, the manufacturing method comprising the following steps:

[0011] a) the supply of a raw disc made of polycrystalline material, having two faces;

[0012] b) the measurement of at least one curvature parameter of the raw disk, so as to define a first face with a convex profile and a second face with a concave profile, and the selection of the first face to correspond to a front face of the support substrate at the end of the following step c);

[0013] c) the preparation of the support substrate from the raw disc, involving mechanical and / or chemical treatment of the faces of said raw disc, the support substrate having a front face and a back face, corresponding respectively to the first and second face of the raw disc;

[0014] d) the transfer of the thin layer onto the front face of the support substrate, to obtain the composite structure.

[0015] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: step a) comprises the following substeps: a1) chemical vapor deposition of a layer formed of the polycrystalline material on a growth substrate, a2) removal of the growth substrate to obtain the raw disc; step a) comprises a substep a3) of mechanical grinding of both faces of the raw disc, involving material removal to a thickness greater than or equal to three times an average grain size measured at each face; the mechanical grinding is carried out by coarse grinding only, using a wheel having a mesh size of less than 2000; the polycrystalline material is silicon carbide (SiC), aluminum nitride (AlN) or silicon;The single-crystal material is selected from silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond, silicon, germanium, indium phosphide (InP); at least one curvature parameter measured in step b) is the arc of the rough disk; the arc of the rough disk, measured on the side of the first convex profile face, is between 30 micrometers and 600 micrometers for a rough disk diameter of 150mm or 200mm; step c) includes heat treatment at a temperature greater than or equal to 1500°C; the manufacturing process further includes the following step: e) the formation of microelectronic components on and / or in the thin layer of the composite structure;the manufacturing process further includes the following step: f) thinning the back face of the substrate supporting the composite structure, before or after step e), to obtain a thinned composite structure in which the substrate supporting has a final thickness less than or equal to 350 micrometers, 180 micrometers, or even 110 micrometers. BRIEF DESCRIPTION OF THE FIGURES

[0016] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0017]

[0018] Laet and present composite structures that can be produced by the manufacturing process according to the invention;

[0019]

[0020] Laet and present an embodiment of step a) of a manufacturing process according to the invention;

[0021] This presents step b) of a manufacturing process according to the invention;

[0022] This presents step c) of a manufacturing process according to the invention;

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] Figures 5a, 5b, 5c, 5c', 5c'', 5d present sub-steps of step d) of a manufacturing process according to the invention;

[0029] This presents step f) of a manufacturing process according to the invention.

[0030] The same references in the figures can be used for elements of the same type. Some figures are schematic representations which, for the sake of clarity, are not drawn to scale. In particular, the layer thicknesses along the z-axis are not to scale with respect to the lateral dimensions along the x and y axes; and the relative thicknesses of the layers are not necessarily to scale in the figures. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention relates to a method for manufacturing a composite structure 100 comprising a thin layer 10 of monocrystalline material deposited on a support substrate 20 of polycrystalline material. The thin layer 10 may be in direct contact with the support substrate 20, or indirectly, via an intermediate layer 30. As is usually the case in the semiconductor industry, the composite structure 100 is in the form of a circular wafer with a diameter, for example, 150 mm, 200 mm, or even larger.

[0032] Preferably, the polycrystalline material is silicon carbide (SiC), aluminum nitride (AlN), silicon (Si), or another material. The monocrystalline material can be chosen from silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond, silicon, germanium, and indium phosphide (InP).

[0033] For power electronics applications, the intermediate layer 30 of the composite structure 100, if present, is advantageously formed of one or more metallic or semiconductor material(s).

[0034] The manufacturing process includes a first step a) of supplying a raw disc 2 made of polycrystalline material. The raw disc 2 has two faces 2a, 2b which extend substantially parallel to a principal plane (x,y). For a diameter of 150 mm or 200 mm, the thickness of the raw disc 2 of polycrystalline material supplied in step a) is typically between 500 μm and 3000 μm.

[0035] Several techniques exist for the fabrication or growth of polycrystalline materials in the form of discs, intended to form substrates or wafers (known as "wafers" in English), particularly for the semiconductor industry. These techniques include, among others, sintering, PVT (Physical Vapor Transport), CVD (Chemical Vapor Deposition), and HTCVD (High Temperature Chemical Vapor Deposition).

[0036] According to a preferred embodiment, the raw disk 2 is formed by a chemical vapor deposition (CVD) technique. Step a) may then include a substep a1) including the chemical vapor deposition of a layer 2' formed of the polycrystalline material on a growth substrate 2'' (); a substep a2) of removal of the growth substrate 2'' then takes place to lead to obtaining the raw disk 2 ().

[0037] In another preferred embodiment, step a) includes a substep a3) of mechanically grinding the two faces 2a,2b of the raw disk 2, typically carried out after substep a2) or after the processing of the raw disk 2 by another technique.

[0038] This grinding, advantageously performed with a coarse grinding wheel (i.e., one with a mesh size of less than 2000), involves removing material to a thickness greater than or equal to three times the average grain size measured at each face (2a, 2b). Thus, the thickness ground on one face may differ from that removed on the other. Note that the average grain size at a given face corresponds to the arithmetic mean of the grain sizes of 100 nm or larger in the plane of that face. These grain sizes can be measured, for example, by scanning electron microscopy (SEM) or electron backscattering diffraction (EBSD).

[0039] After deposition or sintering, the raw disk 2 often exhibits different grain sizes and / or irregularities from one face to the other, which notably cause problems with flatness (high thickness variation "TTV") and inhomogeneity of mechanical properties: this is why a substep a3) is advantageous. It can involve material removal on the order of a few micrometers to a few hundred micrometers (for example, between 10 μm and 300 μm) at faces 2a, 2b. When the raw disk 2 is fabricated by CVD, it is common to remove a greater thickness on the face opposite the one that was in contact with the growth substrate 2'', because it has more irregularities and is less flat.

[0040] It is preferable not to introduce a stress differential between the two faces 2a,2b during this grinding. A differential of less than 10-20% is expected.

[0041] In the case where the polycrystalline material is SiC, the CVD technique involves a gas mixture comprising at least one silicon precursor gas (such as a silane or a chlorosilane) and / or at least one carbon precursor gas (such as an alkane or an alkene), and / or at least one silicon and carbon precursor gas (such as methyltrichlorosilane, abbreviated MTCS), and, if necessary, at least one dopant gas. These gases may be diluted in a carrier gas, which can be a reducing gas such as hydrogen and / or an inert gas such as argon. From this gas mixture, the polycrystalline SiC 2' layer forms on the growth substrate 2''. The latter is preferably graphite, to form a 3C-SiC polytype. The reactor temperature during CVD deposition of SiC is typically between 1000°C and 1600°C.As an example, the deposition can be carried out on a graphite disk, 150 mm in diameter and approximately 2 mm thick, to ensure sufficient flatness of the growth substrate / p-SiC layer(s) assembly. The diameter and thickness of the 2" graphite disk can, of course, vary if a support substrate with a diameter of 100 mm, 200 mm, or other dimensions is desired.

[0042] The 2" graphite growth substrate, coated with the 2" p-SiC deposition layer, is machined and then oxidized in air, typically at 900°C, to remove any remaining graphite. Note that the 2" graphite could also be removed using purely mechanical machining techniques or primarily by burning / oxidation. In practice, a raw 2" p-SiC disk is often recovered from each face of the 2" growth substrate.

[0043] As mentioned previously, mechanical rectification (sub-step a3) can be applied to the faces of the raw disk 2.

[0044] After its release from the growth substrate 2" or after its rough grinding, the raw disk 2 exhibits residual stresses related to the difference in coefficients of thermal expansion between the growth substrate material 2" (e.g., graphite) and the polycrystalline material (e.g., SiC), as well as to the grain sizes varying from one face of the disk 2 to the other. These stresses are partially relieved by the deformation of the raw disk 2: thus, it usually exhibits a non-zero curvature. This is true regardless of the manufacturing technique used for the raw disk 2.

[0045] The manufacturing process according to the invention then includes a second step b) comprising the measurement of at least one curvature parameter of the raw disk 2 ().

[0046] Advantageously, the measured curvature parameter is the arc A, also called "bow" in Anglo-Saxon terminology. The arc corresponds to the deviation of the central point of the median surface S of the measured wafer (which is free, not held or fixed on a support plate) from a reference plane P established by three uniformly spaced points on a circle whose diameter is smaller by a specified value than the diameter of the measured wafer. The median surface S is defined by the points on the wafer equidistant from the two faces.

[0047] Other curvature parameters can also be measured during step b) of the process, such as the deformation or "warp", which reflects the difference between the maximum and minimum distances of the median surface S of the insert (free) from the reference plane P. The value of the deformation is usually greater than the value of the arc because the curvature of the insert rarely follows a uniform profile.

[0048] The curvature parameters of the raw disk 2 can, for example, be measured using a confocal white light sensor that scans a surface of the disk, the latter being placed on a support plane for the measuring tool, equipped with three support pins. Alternatively, they can be determined by capacitive measurement techniques.

[0049] From the -at least one- parameter measured in step b), the process plans to identify the two faces 2a,2b of the raw disk 2 as follows:

[0050] - the face with a convex profile is defined as the first face 2a, and

[0051] - the face with a concave profile is the second face 2b.

[0052] Step b) further includes the selection of the first face 2a to correspond to the future front face 20a of the support substrate 20 which will be obtained at the end of the following step c).

[0053] As an example, the arc A of the rough disc 2, measured from the side of the first convex face 2a, is between 30 micrometers and 600 micrometers, for a diameter of the rough disc 2 of 150 mm or 200 mm. When substep a3) of grinding is applied, the arc A range of the rough disc 2 can be reduced, typically to less than 500 micrometers.

[0054] The next step (c) of the manufacturing process consists of preparing the support substrate 20 from the blank disk 2. This preparation includes mechanical and / or chemical treatment of faces 2a, 2b of the blank disk 2. This treatment may include, in particular, mechanical grinding and / or chemical polishing and / or chemical etching, well-known techniques in the field of semiconductor substrates. The purpose of such treatment is to bring the blank disk 2 to a target thickness (the initial thickness of the support substrate 20) and to achieve a surface finish compatible with subsequent assembly by molecular bonding. The diameter of the blank disk 2 can also be adjusted using contouring techniques.

[0055] Optimizing the preparation parameters means that it is not uncommon to significantly improve the curvature of the support substrate 20, compared to the initial curvature of the raw disk 2.

[0056] According to the method of the invention, the front face 20a of the support substrate 20 is chosen to correspond to the first face 2a (face having a convex profile), and the rear face 20b is chosen to correspond to the second face 2b ().

[0057] The treatment applied to the two faces 2a,2b of the raw disc 2, during the preparation of the support substrate 20 in step c), may include: coarse grinding with a grinding wheel adapted to a high material removal rate, typically between a few tens of micrometers and a few hundred micrometers; for example, the mesh (or grit) of the grinding wheel, the value of which varies inversely with the size of the abrasive grains, is less than 2000, typically between 100 and 1000; fine grinding with a grinding wheel whose mesh is greater than or equal to 2000, for example between 2000 and 8000, or even up to 30000 or more; the removal rate is typically between a few micrometers and a few tens of micrometers;one or more mechano-chemical polishing processes, each inducing a material removal of between a few tens of nanometers and a few micrometers.

[0058] One or more cleaning steps may be applied between the aforementioned thinning stages, particularly following polishing. Heat treatment at temperatures of 1500°C or higher may also be applied to disc 2, before, after, or between thinning stages.

[0059] If the treatment applied to each of the faces 2a,2b of the raw disk 2 is similar, it is unlikely to introduce an asymmetry of stress between the front 20a and rear 20b faces of the support substrate 20. That being said, it is possible that the material removals, the processing times or even the thinning sequences applied are different for the front face 20a and for the rear face 20b, in order to minimize the arc and / or deformation for the next assembly step, or because the surface properties targeted for the two faces differ.

[0060] At the end of step c), the support substrate 20 has a typical thickness between 250 micrometers and 500 micrometers, for example, between 325 μm and 375 μm for a substrate with a diameter of 150 mm and between 350 μm and 500 μm for a substrate with a diameter of 200 mm. The curvature of the support substrate 20 is low; for example, the arc measured on the side of its front face 20a is between 0 and 75 micrometers, or even between 0 and 50 micrometers, in the case of a diameter of 150 mm or 200 mm. Furthermore, it has a surface finish compatible with direct bonding (by molecular adhesion) to another substrate. Such a surface condition typically corresponds to a roughness less than or equal to 1nm RMS (measured by atomic force microscopy on scans of 5μm x 5μm or more).

[0061] The manufacturing process finally includes a fourth step d) transferring a thin film 10 into a single-crystal material onto said support substrate 20 (Figures 5a to 5d). Although any known thin-film transfer process can be used, the Smart Cut process is particularly noteworthy. TMThis involves the formation of a buried brittle plane 11 in a donor substrate 1 made of single-crystal material, by ionic implantation of light species (e.g., H, He, or a combination of these two species) (,). Direct assembly (by molecular adhesion) occurs between the implanted face of the donor substrate 1 and the front face 20a of the support substrate 20, defining a bonding interface 40, and forming a bonded assembly 50 (). Separation within the buried brittle plane 11 then allows the transfer of a thin single-crystal layer 10, originating from the donor substrate 1, onto the support substrate 20, resulting in the composite structure 100, while preserving the remaining 1' of the donor substrate for future reuse ().

[0062] An intermediate layer 30 may optionally be formed on the donor substrate 1, on the support substrate 20 or on each of these two substrates, before assembly (',''): said intermediate layer 30 will be intercalated between the thin layer 10 and the support substrate 20 in the composite structure 100.

[0063] Thermal, mechanical, and / or chemical finishing treatments are usually applied to the free surface 10a of the transferred thin film 10 to restore its high crystallographic quality and surface condition. Similar treatments can be applied to the free face 1'a of the remaining 1' of the donor substrate for reuse.

[0064] As an example, the thin film 10 of the composite structure 100 has a thickness ranging from a few tens of nm to a few hundred nm, for example, between 50 nm and 800 nm. Epitaxial steps can be performed on this thin film 10 to thicken it (homoepitaxy) or to grow other materials (heteroepitaxy), depending on the requirements of the electronic components to be manufactured. The thin film 10 has an electrical resistivity suitable for the application and the intended components.

[0065] In the composite structure 100, the support substrate 20 has a thickness and curvature as previously stated. The range of curvature radii (inversely proportional to the arc) of the support substrate 20 makes it perfectly compatible with the specifications of a composite structure 100 equipped with a single-crystal thin film 10, with the manufacturing process of such a structure 100, and with the subsequent fabrication of microelectronic components on and / or in the thin film 10. The warp of a composite structure 100 (e.g., m-SiC / p-SiC) with a diameter of 200 mm remains less than 150 μm, typically between 20 μm and 100 μm.

[0066] The composite structure 100 may include a continuous or discontinuous intermediate layer 30, disposed between the thin layer 10 and the support substrate 200 and composed of at least one metallic or semiconductor material. The intermediate layer 30 may, for example, be composed of silicon, silicon carbide, tungsten, and / or titanium. Its thickness is typically between a few nm and a few hundred nm, preferably between 2 nm and 50 nm.

[0067] The manufacturing process may further include a step e) of forming microelectronic components on and / or within the thin film 10 of the composite structure 100. The components targeted, particularly high-voltage components, are, for example, Schottky diodes, MOSFET or HEMT transistors, and / or high-frequency (RF) components, etc. As mentioned previously, it may be necessary to increase the thickness of the thin film 10 to construct high-voltage components. Epitaxial growth can then be performed on the free face 10a of the thin film 10.

[0068] The manufacturing process according to the invention can finally include a step f) of thinning the back face 20b of the support substrate 20 of the composite structure 100, before or after step e), to obtain a thinned composite structure 120 in which the support substrate 20 has a final thickness less than or equal to 350 micrometers, 180 micrometers, or even 110 micrometers ().

[0069] This thinning step is usually performed after the components have been manufactured, and before they are individualized into chips or packaged. Such thinning can also be performed before the components are manufactured.

[0070] The applicant observed that the final thinning of the composite structure 100 significantly increases the curvature of the thinned composite structure 120, even though the composite structure 100 already exhibits a reasonable curvature. This thinning, which is usually achieved by mechanical grinding, causes the arc of the structure, measured on the side of the thin layer 10 (i.e., on the side of the front face 20a of the support substrate 20), to shift in the direction of concavity. This is primarily due to the stress associated with the damaged layer on the back face 20b of the thinned support substrate 20. This damaged layer is characterized by a very rough thinned surface and by a work-hardened and stressed area within the material.

[0071] Furthermore, the applicant observed that, although masked by the slight deformation of the support substrate 20 and the composite structure 100 after step d) or step e), a residual stress state remains in the support substrate 20, the characteristics of which are predefined from the raw disk stage 2. The thinning of the rear face 20b (which corresponds to the second face 2b, with a concave profile, of the raw disk 2) causes the return and accentuation of the concavity of said face 20b. The deformation in the direction of the concavity of the rear face 20b is accompanied by a deformation in the direction of the convexity of the front face 20a.

[0072] This behavior is particularly interesting because it allows us to compensate for the effect of mechanical rectification, which tends, as previously stated, to make the front face 20a of the support substrate 20 evolve in the direction of concavity, and consequently to make the rear face 20b of the support substrate 20 evolve in the direction of convexity.

[0073] We understand here the importance of step b) of measuring the curvature parameter of the raw disk 2, during which the first face 2a and the second face 2b are defined according to their curvature profile, and selected to become respectively the front face 20a and the back face 20b of the support substrate 20 prepared in the following step c).

[0074] The manufacturing process advantageously provides for not introducing stress asymmetry between the faces of the raw disk 2 when a step a3) of mechanical rectification of the two faces 2a,2b is applied, so as not to (or only weakly) modify the initial stress state, predefined from the raw disk 2 stage, and thus to make the compensation effect more predictable.

[0075] The thinned composite structure 120 (e.g. m-SiC / p-SiC 200mm) according to the invention can exhibit a final arc, measured from the front face 20a side of the support substrate 20 (i.e., from the thin film side 10), of between 100 micrometers and 1000 micrometers.

[0076] Of course, the invention is not limited to the embodiments and examples described, and alternative embodiments can be made without departing from the scope of the invention.

Claims

Method of manufacturing a composite structure (100) comprising a thin layer (10) of monocrystalline material disposed on a support substrate (20) of polycrystalline material, the manufacturing process comprising the following steps: a) supplying a raw disk (2) of polycrystalline material, having two faces (2a, 2b); b) measuring at least one curvature parameter of the raw disk (2), so as to define a first face (2a) having a convex profile and a second face (2b) having a concave profile, and selecting the first face (2a) to correspond to a front face (20a) of the support substrate (20) at the end of the following step c);c) the preparation of the support substrate (20) from the raw disk (2), involving a mechanical and / or chemical treatment of the faces (2a,2b) of said raw disk (2), the support substrate (20) having a front face (20a) and a back face (20b), corresponding respectively to the first (2a) and the second (2b) face of the raw disk (2); d) the transfer of the thin film (10) onto the front face (20a) of the support substrate (20), to obtain the composite structure (100). Manufacturing process according to claim 1, wherein step a) comprises the following substeps: a1) chemical vapor deposition of a layer (2') formed of the polycrystalline material, on a growth substrate (2''), a2) removal of the growth substrate (2'') to obtain the raw disc (2). Manufacturing method according to any one of the preceding claims, wherein step a) comprises a substep a3) of mechanical grinding of both faces (2a,2b) of the raw disc (2), involving material removal over a thickness greater than or equal to three times an average grain size measured at each face (2a,2b). Manufacturing method according to the preceding claim, wherein the mechanical grinding is carried out by coarse grinding only, using a wheel having a mesh size of less than 2000. A manufacturing process according to any one of the preceding claims, wherein the polycrystalline material is silicon carbide (SiC), aluminum nitride (AlN), or silicon. A manufacturing process according to any one of the preceding claims, wherein the single-crystal material is selected from silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond, silicon, germanium, indium phosphide (InP). Manufacturing method according to any one of the preceding claims wherein the -at least one- curvature parameter measured in step b) is the arc (A) of the raw disk (2). Manufacturing method according to the preceding claim, wherein the arc (A) of the raw disc (2), measured from the side of the first face (2a) with convex profile, is between 30 micrometers and 600 micrometers for a diameter of raw disc (2) of 150mm or 200mm. A manufacturing process according to any one of the preceding claims, wherein step c) comprises a heat treatment at a temperature greater than or equal to 1500°C. Manufacturing method according to any one of the preceding claims, further comprising the following step: e) the formation of microelectronic components on and / or in the thin layer (10) of the composite structure (100). A manufacturing process according to the preceding claim, further comprising the following step: f) thinning the back face (20b) of the support substrate (20) of the composite structure (100), before or after step e), to obtain a thinned composite structure (120) in which the support substrate (20) has a final thickness less than or equal to 350 micrometers, 180 micrometers, or even 110 micrometers.

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