Process for manufacturing polycrystalline silicon carbide support substrates

Abstract

The present invention relates to a process for producing a polycrystalline silicon carbide support substrate comprising the steps of: a) growing an initial polycrystalline silicon carbide substrate on a graphite or silicon carbide seed; b) forming a stiffening carbon film on a front surface of the initial substrate, the initial substrate having, at the plane of the front surface, a first average silicon carbide grain size immediately prior to the formation of the stiffening film; c) removing the seed to free a rear surface of the initial substrate, the initial substrate having, at the plane of the rear surface, immediately following the removal of the seed, a second average silicon carbide grain size smaller than the first average size; d) thinning the rear surface of the initial substrate to a thickness where the initial substrate has, at the plane of the rear surface, a third average grain size equal to within ±30% of the first average grain size, the thinned initial substrate forming a support substrate.

Description

【Technical Field】 【0001】 The present invention relates to the field of semiconductor materials for components of microelectronics. The present invention particularly relates to a process for manufacturing a polycrystalline silicon carbide support substrate, which is particularly suitable for the production of a composite structure including a thin layer of single crystal silicon carbide disposed and configured on the support substrate. 【Background Art】 【0002】 SiC is increasingly widely used for manufacturing innovative power devices to meet the needs of emerging fields in electronics, especially in electric vehicles and the like. Specifically, power devices and integrated power supply systems based on single crystal silicon carbide can handle much higher power densities than their conventional silicon equivalents, and can do so with smaller active areas. 【0003】 However, high-quality single crystal SiC substrates (c-SiC) for the microelectronics industry are expensive and continue to be difficult to supply in large sizes. For example, in a lower-cost support substrate made from polycrystalline SiC (p-SiC), it is thus advantageous to rely on a layer transfer solution for building up a composite structure typically including a thin layer of single crystal SiC (obtained from a high-quality c-SiC substrate). One well-known thin layer transfer solution is the Smart Cut® process, which is based on implanting light ions and bonding at the bonding interface by direct bonding. 【0004】 U.S. Patent Application Publication No. 2019153616 provides a process for manufacturing a p-SiC support substrate onto which a c-SiC thin layer can be transferred. The support substrate includes particles with an average size of approximately 10 μm and has a certain degree of variation in particle size between the front and back surfaces of the support substrate with respect to the thickness of the support substrate of 0.43% or less, and the latter feature limits the residual stress in the support substrate and thus the curvature of the support substrate. 【0005】 The manufacturing process involves a first carbon-based substrate, on which a thick layer of p-SiC (typically 2 mm) is generated by chemical vapor deposition. A second p-SiC-based substrate, approximately 350 μm thick, is extracted from the p-SiC layer by removing the first carbon-based substrate and mechanically thinning both sides of the thick layer. The second base substrate has some particle size variation between the front and back surfaces of the two base substrates relative to the thickness of the second base substrate, less than 0.43%. A new p-SiC layer (typically about 400 μm) is then formed on the second base substrate by chemical vapor deposition and separated from the second base substrate, for example by laser irradiation, to form a p-SiC support substrate intended for use in composite structures. The second base substrate can then be reused. 【0006】 In practice, the step of forming the second base substrate can prove to be complex, because removing the first carbon base substrate generally induces very large curvature in the thick p-SiC layer, which can cause the thick layer to break or at least complicate or hinder the thinning step required to achieve the thickness of the second base substrate. In addition, this thinning is quite substantial (approximately 1.5 mm) and is costly in terms of p-SiC material and deposition and thinning steps. [Overview of the project] 【0007】 The present invention proposes a manufacturing process that addresses the problems mentioned above. The present invention relates to a process for manufacturing an economical and simplified polycrystalline SiC support substrate. The support substrate is more particularly suitable for manufacturing a composite structure comprising a thin c-SiC layer arranged and configured in the p-SiC support substrate. 【0008】 The present invention is a process for manufacturing a polycrystalline silicon carbide support substrate, a) A step of growing an initial polycrystalline silicon carbide substrate on a graphite or silicon carbide seed, wherein at the end of step a), the initial substrate has a free front surface and a rear surface in contact with the seed, b) A step of forming a stiffening carbon film on the front surface of the initial substrate, wherein the initial substrate has a first average silicon carbide particle size on the plane of the front surface of the initial substrate and immediately before the formation of the stiffening film. c) A step of removing the seeds and freeing the rear surface of the initial substrate, wherein the initial substrate has a second average silicon carbide particle size smaller than the first average size in the plane of the rear surface of the initial substrate and immediately after the removal of the seeds. d) A step in which the rear surface of the initial substrate is thinned to a thickness such that the plane of the thinned rear surface of the initial substrate has a third average particle size equal to a first average particle size within ±30%, wherein the thinned initial substrate forms a support substrate. It is related to the process, including 【0009】 According to other advantageous and non-limiting features of the present invention, which can be used alone or in any technically feasible combination, The stiffening film has a thickness of, for example, 10 mm, ranging from 100 nm to several millimeters. The stiffening film has a thickness between 100 nm and 10 μm. The rigid carbon film has a diamond-like or glassy carbon crystal structure. Step b) is performed by applying a polymer resin having preformed carbon-carbon bonds in three dimensions as a viscous layer on the front surface of the initial substrate, and annealing it at a temperature between 500°C and 2000°C to form a stiffening carbon film. The polymer resin is based on coal tar, phenol formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and / or polystyrene. Step b) is performed by plasma deposition, ion bombardment deposition, or vapor deposition. The manufacturing process includes, between step a) and step b), step a'), grinding the front and / or peripheral areas of the initial substrate to reduce variations in surface roughness and / or thickness of the substrate, and / or to make the peripheral areas of the initial substrate uniform. Step a') includes mechanical or mechanochemical thinning, The manufacturing process is After step d), step e) removes the stiffening film, and / or After step d), or after step e), a heat treatment step at a temperature of 1500°C or higher. Includes. 【0010】 The present invention relates to a process for manufacturing a composite structure, further comprising the above process, and also including step f) transferring a thin layer of single-crystal silicon carbide to a first or second surface of a support substrate, either directly or via an intermediate layer, to form a composite structure. 【0011】 According to other advantageous and non-limiting features of the present invention, which can be used alone or in any technically feasible combination, The intermediate layer is formed by a stiffening carbon film maintained on the first surface of the support substrate. A thin layer transfer is performed on one of the first and second surfaces of the support substrate, and an additional carbon film is positioned on the other free surface of the support substrate prior to the transfer. The additional film is preferably removed after the composite structure has undergone any heat treatment at a temperature above 1400°C required for the manufacture of the composite structure or for the manufacture of the components on and / or within the said structure. 【0012】 Other features and advantages of the present invention will become apparent from the subsequent detailed description of the invention, which is given with reference to the attached figures. [Brief explanation of the drawing] 【0013】 [Figure 1a] It is a diagram showing the steps of the manufacturing process according to the present invention. [Figure 1b] It is a diagram showing the steps of the manufacturing process according to the present invention. [Figure 1c] It is a diagram showing the steps of the manufacturing process according to the present invention. [Figure 1d] It is a diagram showing the steps of the manufacturing process according to the present invention. [Figure 1e] It is a diagram showing the steps of the manufacturing process according to the present invention. [Figure 1f] It is a diagram showing the steps of the manufacturing process according to the present invention. [Figure 2a] It is a diagram showing other steps of the manufacturing process according to the present invention. [Figure 2b] It is a diagram showing other steps of the manufacturing process according to the present invention. [Figure 2c] It is a diagram showing other steps of the manufacturing process according to the present invention. [Figure 2d] It is a diagram showing other steps of the manufacturing process according to the present invention. [Figure 3a] It is a diagram showing a modification example of the steps of the manufacturing process according to the present invention. [Figure 3b] It is a diagram showing a modification example of the steps of the manufacturing process according to the present invention. [Figure 3c] It is a diagram showing a modification example of the steps of the manufacturing process according to the present invention. [Figure 3d] It is a diagram showing a modification example of the steps of the manufacturing process according to the present invention. [Figure 3e] It is a diagram showing a modification example of the steps of the manufacturing process according to the present invention. 【Mode for Carrying Out the Invention】 【0014】 The same reference numeral in the diagram may be used for elements of the same type. The diagram is a schematic representation, not to a constant scale, for clarity. In particular, the thickness of the layers along the z-axis is not to a constant scale with respect to the lateral dimensions along the x and y axes, and the relative thickness of the layers with respect to each other is not necessarily emphasized in the diagram. 【0015】 The present invention relates to a process for manufacturing a polycrystalline silicon carbide (p-SiC) support substrate 10. 【0016】 The process first includes step a) growing an initial polycrystalline silicon carbide substrate 1 on a seed 2 of graphite or low-quality single crystal or polycrystalline silicon carbide (Figure 1a). The seed 2 is preferably in the form of a wafer, the diameter of which is substantially the target diameter with respect to the support substrate 10, e.g., 100 mm, 150 mm, 200 mm, or even 300 mm. 【0017】 The growth of the initial p-SiC substrate 1 is typically carried out by known chemical vapor deposition (CVD) techniques at temperatures between 1100°C and 1500°C. The precursor may be preferably selected from methylsilane, dimethyldichlorosilane, or dichlorosilane and i-butane, with a C / Si ratio close to or greater than 1. 【0018】 Optionally, doping species (e.g., nitrogen or phosphorus) may be introduced during CVD deposition to adjust the resistivity of the initial substrate 1 (from which the support substrate 10 will be obtained) to the specifications of the final product, particularly the target composite structure. A typical target doping level is 1E18 / cm². 3 It is greater than, or 1E20 / cm 3 It is even larger than that. 【0019】 At the end of step a), the initial substrate 1 has a free front surface 1a and a rear surface 1b in contact with the seed 2. The thickness of the initial substrate 1 is less than 1 mm, preferably less than 550 μm. It should be noted that the thickness range usually desired for the support substrate 10, which is intended for the generation of the composite structure, is 100 μm to 500 μm. 【0020】 The initial substrate 1 may contain 4H, 6H, and / or 3C type silicon carbide particles, depending on the CVD deposition conditions. 【0021】 The average size of the particles on the rear surface 1b of the initial substrate 1 is relatively small, typically less than 1 μm, or even less than 100 nm, and these particles correspond to the p-SiC material generated at the start of CVD deposition (nucleation stage) in the graphite seed 2. 【0022】 It should be noted that the size of particles bounded by grain boundaries corresponds to the largest dimension of the particles in the plane of the surface under consideration on the substrate. The average particle size is defined as the average size of the individual particles in the plane. Particle size or grain boundary distance can be measured based on images obtained by conventional scanning electron microscopy (SEM) or with electron backscatter diffraction (EBSD). The use of X-ray crystallography may also be conceivable. When the surface under consideration mainly contains particles of micrometer size (typically several microns to tens of microns), very small particles, typically less than 50 nm, are preferentially excluded from the measurement to limit the measurement uncertainty. 【0023】 As CVD deposition progresses, the p-SiC particles increase in size, eventually reaching a relatively stable average size with respect to the deposit thickness, which can vary between a few micrometers and tens of micrometers depending on the deposition conditions. 【0024】 Thus, depending on the thickness of the p-SiC deposited to grow the initial substrate 1, the average particle size on the front surface of the substrate 1 can typically vary between 1 and 10 μm. 【0025】 In this specification, the average size of p-SiC particles on the front surface 1a of the initial substrate 1 will be referred to as the first average size, and the average size of p-SiC particles on the rear surface 1b of the initial substrate 1 will be referred to as the second average size. 【0026】 The first average p-SiC particle size (front side 1a) is larger than the second average particle size (back side 1b), and the latter corresponds to the nucleation stage. 【0027】 The manufacturing process then includes step b) forming a stiffening carbon film 3 on the front surface 1a of the initial substrate 1 (Figure 1b). The stiffening film 3 has a thickness ranging from 100 nm to several millimeters, for example, 10 mm. Preferably, the thickness of the stiffening film is between 100 nm and 10 μm. 【0028】 The stiffening carbon film 3 is, in other words, sp 3 A diamond-type crystallographic structure containing carbon-carbon bonds, or sp 2 Having a glassy carbon-type structure that includes carbon-carbon bonds is advantageous. 【0029】 The stiffening film 3 may be formed by various conventional deposition techniques, particularly plasma deposition, ion bombardment deposition, or vapor deposition. 【0030】 Alternatively, step b) may be performed by coating a polymer resin containing pre-formed carbon-carbon bonds in three dimensions as a viscous layer on the front surface 1a of the initial substrate 1. This coating may be performed by centrifugation. Annealing is then performed under nitrogen at a temperature between 500°C and 2000°C, typically between 600°C and 1100°C, to form a stiffening carbon film 3 by chemical decomposition (thermal decomposition) of the resin. The selected temperature gradient is typically about 10°C / min, and the annealing time is about 1 hour. The temperature rise is controlled so that the effective temperature remains below the resin / carbon glass transition temperature. 【0031】 The polymer resin may be formed from coal tar, phenol formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and / or polystyrene, or others. 【0032】 For example, known photosensitive resins that are commonly used for photolithography steps in the field of microelectronics may be used, such as the commercially available AZ-4330, AZ-P4620 (registered trademark) (based on 1-methoxy-2-propanol acetate, diazonaphthoquinone sulfonate, 2-methoxy-1-propanol acetate, and cresol novolac resin), OCG-825 (based on ethyl 3-ethoxypropionate), and SU-8 2000 (based on cyclopentanone, triarylsulfonium / hexafluoroantimonate, propylene carbonate, and epoxy resin). 【0033】 Epoxy resins, such as Epoxy Novolac EPON® products, which are proposed for coating and protecting various surfaces in various fields (aeronautics, maritime, automotive, construction, etc.), may also be used in step b) of the process according to the present invention. 【0034】 When using resin, it is important to take into account the shrinkage that the viscous resin layer will undergo during annealing in order to determine the initial thickness of the viscous resin layer sufficient to obtain the target thickness of the stiffening film 3. The thickness shrinkage can typically be between 70% and 95%. The carbon ratio, i.e., the ratio between the mass of the polymer resin layer after thermal decomposition (corresponding to the stiffening film 3) and the initial mass of the applied polymer resin layer, must be at least 5%, and preferably greater than 50%. 【0035】 Optionally, the manufacturing process may include a') between step a) and step b) a step of grinding the front surface 1a and / or peripheral portion 1c of the initial substrate 1 to reduce the surface roughness of the surface 1a, and / or reduce variations in the thickness of the substrate 1, and / or make the peripheral portion 1c uniform. 【0036】 Step a') may include mechanical or mechanochemical thinning (polishing) of the material, which involves the removal of approximately several microns to several tens of microns. 【0037】 The manufacturing process according to the present invention then includes step c) removing the seed 2 to free the rear surface 1b of the initial substrate 1 (Figure 1c). 【0038】 When Seed 2 is made from graphite, removal can be carried out by burning the graphite by applying a heat treatment in an oxygen-rich atmosphere (e.g., air) at a temperature above 400°C, preferably above 550°C. 【0039】 It is also possible to mechanically separate seed 2, regardless of whether seed 2 is made of graphite or silicon carbide, by applying localized mechanical stress, for example, at or near the interface between seed 2 and initial substrate 1. 【0040】 If any residue remains on the rear surface 1b of the initial substrate 1 after the removal of seed 2, such residue can be burned off (if the residue is made from graphite) or removed mechanically or chemically by polishing or etching (if the residue is made from graphite or SiC). 【0041】 This removal typically results in a strong curvature of the initial substrate 1, which can be up to 500 μm for a diameter of 150 mm. This curvature is primarily attributable to stress associated with the difference in particle size between the second surface 1b (nucleated particles, small average size) and the first surface 1a. 【0042】 In the context of the present invention, the stiffening carbon film 3 significantly limits the increase in curvature during seed removal by mechanically holding the initial substrate 1 by the front surface 1a of the initial substrate 1. The curvature of the initial substrate 1 with the stiffening carbon film 3 attached does not exceed 200 μm for a substrate diameter of 150 mm, and furthermore, the curvature is even maintained below 100 μm. Within these curvature ranges, the initial substrate 1 can be processed without any problems on standard lines and equipment without any risk of damage or equipment failure, these problems are mainly encountered with curvature greater than 300 μm (diameter of 150 mm). 【0043】 Finally, the manufacturing process includes step d) thinning the rear surface 1b of the initial substrate 1. The thinned initial substrate 1 forms the support substrate 10 (Figure 1d). 【0044】 The thinning in step d) is carried out by mechanical grinding, mechanical polishing, and / or mechanochemical polishing of the rear surface 1b. The amount of material removed is typically between several tens of microns and 200 μm, depending on the initial thickness of the substrate 1 at the start of step d) and, of course, on the target thickness of the support substrate 10. 【0045】 Thinning is performed on the initial substrate 1 until the thickness of the thinned rear surface 1b' of the initial substrate 1 is such that the third average particle size is equal to the first average particle size within ±30%. In other words, if the first average size is, for example, 5 μm, then the third average size is expected to be between 4 μm and 6 μm. 【0046】 The particle sizes in the plane of the front surface 1a or the plane of the rear surface 1b may be distributed in two separate populations, with each peak essentially following a Gaussian distribution. According to the first option, the average particle size is calculated by taking the overall average including both populations, and the first and third average sizes should not differ by more than 30%. According to the second option, the first two average sizes (corresponding to the two separate populations on the front surface 1a) and the third two average sizes (corresponding to the two separate populations on the rear surface 1b) are taken into consideration, and each should not differ from the other by more than 30%. 【0047】 After thinning in step d), the thinned rear surface 1b' of the initial substrate 1 has an average p-SiC particle size that differs from the average particle size of the front surface 1a by less than 30%. The residual stress in the thinned initial substrate 1 (forming the support substrate 10) is therefore accommodating small curvatures and is at least easy to control in the manufacturing line. 【0048】 The manufacturing process may then include step e) removing the stiffening film 3, for example, by dry or wet chemical etching (Figure 1e). After this removal, the support substrate 10 has a curvature of less than 200 μm (for a diameter of 150 mm), or even less than 100 μm, due to the reduced residual stress in the volume portion of the support substrate 10. 【0049】 In this phase, the support substrate 10 has a first surface 10a, a second surface 10b, and an edge portion 10c, which correspond to the front surface 1a, the thinned rear surface 1b', and the edge portion 1c of the initial substrate 1 after step d), respectively. 【0050】 For example, to form a support substrate with a thickness of 350 μm and a diameter of 150 mm, a 500 μm initial substrate 1 may be generated at seed 2, and the initial substrate 1 has a first average p-SiC particle size of approximately 4 μm at the front surface 1a of the initial substrate 1. A step to correct the thickness uniformity of the initial substrate 1 may be performed, for example, by removing 50 μm. A 4 μm stiffening carbon film 3 is formed on this front surface 1a. After removal of graphite seed 2, the second average particle size at the rear surface 1b of the initial substrate 1 is less than 100 nm, but the curvature of the initial substrate 1 is maintained below 150 μm due to the presence of the stiffening film 3. A 100 μm removal is performed at the rear surface 1b of the initial substrate 1, and the third average particle size of p-SiC at the thinned rear surface 1b', approximately 3 μm, satisfies the equality condition of being within 30% of the first average particle size. Thus, after the removal of the stiffening film 3, the curvature of the support substrate 10 is less than 200 μm, and it is suitable for the subsequent steps to manufacture the composite structure 100. 【0051】 Optionally, after step e), a surface treatment may be applied to the first surface 10a of the support substrate 10, particularly if this surface 10a is intended to receive a thin layer 20 of the composite structure 100 in a subsequent step f) of the process. Depending on the surface roughness of the first surface 10a, this surface treatment may include mechanical grinding, machinochemical polishing, or other chemical cleaning operations. 【0052】 If the second surface 10b of the support substrate 10 is intended to receive the thin layer 20, and step d) does not achieve a sufficiently low level of roughness (typically <1 nm RMS, measured by atomic force microscopy in a 20 μm × 20 μm scan), then additional surface treatment may be further applied to the second surface 10b. 【0053】 The surface of the support substrate 10, which is intended to form the rear surface of the composite structure 100, may have a higher surface roughness, for example, approximately 10 nm RMS. 【0054】 The manufacturing process may also include a heat treatment at a temperature of 1500°C or higher, typically between 1500°C and 1900°C, after step d) or after step e), to stabilize the polycrystalline structure of the support substrate 10. Furthermore, these temperature ranges are likely to be imparted later in the process, particularly for the manufacture of composite structures. 【0055】 Thanks to the manufacturing process according to the present invention, a support substrate 10 having mechanical properties that conform to the specifications of a composite structure for a microelectronics application can be obtained in a simple manner without the need to deposit a very thick initial p-SiC substrate, which is removed by more than 80% to select a very small useful portion of p-SiC, as is done in prior art processes. In the manufacturing process according to the present invention, the thickness of the initial substrate 1 formed is 1 mm or less, and the material removal on the front surface 1a and / or rear surface 1b of the initial substrate 1 is less than 70% of the initial thickness, or even less than 50%, which results in savings in materials and technical steps. 【0056】 In the context of the manifestation of the composite structure 100, the manufacturing process according to the present invention may be continued by step f) transferring a working layer 20 made from single-crystal silicon carbide to a support substrate 10 based on molecular adhesive bonding (Figure 1f). 【0057】 There are various options known in the prior art for performing layer transfer, which will not be described in detail here. 【0058】 According to the preferred method, step f) of the process involves the injection of light chemical species according to the principles of the SmartCut® process. 【0059】 In the first step f1), a single-crystal silicon carbide donor substrate 21 is prepared, and the processed layer 20 is obtained from the donor substrate 21 (Figure 2a). The donor substrate 1 is preferably in the form of a wafer with a diameter of 100 mm, 150 mm, 200 mm, or even 300 mm (same as or very similar to the diameter of the support substrate 10), and typically with a thickness between 300 μm and 800 μm. The donor substrate has a front surface 21a and a back surface 21b. The surface roughness selected for the front surface 1a is preferably less than 1 nm RMS, or even less than 0.5 nm RMS, as measured by atomic force microscopy (AFM) in a 20 μm × 20 μm scan. The donor substrate 21 may be of polytype 4H or 6H and may have n or p type doping, depending on the requirements of the components that will be expressed on and / or within the processed layer 20 of the composite structure 100. 【0060】 The second step f2) involves introducing light chemical species into the donor substrate 21 to form a buried fragile plane 22, which defines the boundary of the processed layer 20 to be transferred, along with the front surface 21a of the donor substrate 21 (Figure 2b). 【0061】 The light species are preferably hydrogen, helium, or a co-injection of both of these species, and are injected into the donor substrate 21 to a given depth that matches the target thickness of the processed layer 20. These light species form microcavities around the given depth, distributed as thin layers parallel to the free surface 21a of the donor substrate 21, i.e., parallel to the plane (x,y) in the figure. For simplicity, these thin layers are referred to as embedded fragile planes 22. 【0062】 The energy of the light chemical species implantation is selected to reach a given depth. For example, hydrogen ions are implanted at energies between 10 keV and 250 keV to define the boundary of the processed layer 20, which has a thickness of approximately 100 nm to 1500 nm, and 5 E 16 / cm 2 ~1 E 17 / cm2 The ions will be injected at doses between these values. It should be noted that a protective layer may be deposited on the front surface 21a of the donor substrate 21 before the ion implantation step. This protective layer may be composed of a material such as silicon oxide or silicon nitride. The protective layer is removed before the next step. 【0063】 Optionally, an intermediate layer 4 may be formed on the front surface 21a of the donor substrate 21 before or after the second step f2) of introducing light chemical species (Figures 3b, 3c, 3d, 3e). This intermediate layer 4 may be made from a semiconductor material, such as silicon or silicon carbide, or from a metallic material such as tungsten, titanium, or others. The thickness of the intermediate layer 4 is advantageously limited typically between a few nanometers and tens of nanometers. 【0064】 When the intermediate layer 4 is formed before step f2), the injection energy (and potentially dose) of the light chemical species will be adjusted for crossing this additional layer. When the intermediate layer 4 is formed after step f2), care will be taken to form this layer by providing a thermal budget lower than the bubbling thermal budget, which corresponds to the appearance of blisters on the surface of the donor substrate 21 due to excessive growth and pressurization of microcavities in the embedded fragile plane 22. 【0065】 The transfer step f) then includes a third step f3) in which the donor substrate 21 is joined to the support substrate 10 at the front side 21a of the donor substrate 21 along the bonding interface 30 by molecular adhesive bonding at the first side 10a or the second side 10b of the support substrate 10 (Figure 2c). 【0066】 Optionally, the intermediate layer 4' may be deposited on the surface of the support substrate 10 that will be joined, prior to the joining step f3) (Figures 3d, 3e), and the intermediate layer 4' may be selected to have the same properties as the intermediate layer 4 mentioned for the donor substrate 21, or to have different properties from the intermediate layer 4. The intermediate layers 4 and 4' may be deposited on only one or the other of the two substrates 21 and 10 that will be joined, at the optional choice. 【0067】 The purpose of the intermediate layer(s) is essentially to increase the bond energy (particularly in the temperature range below 1100°C) due to the formation of covalent bonds at lower temperatures than in the case of the two directly bonded SiC surfaces, and another advantage of these intermediate layers(s) may be to improve the perpendicular electrical conductivity of the bond interface 30. 【0068】 In a possible modification, the intermediate layer may be formed by a stiffening carbon film 3 maintained on the first surface 10a of the support substrate 10 (Figures 3a, 3c). In this example, step e) of the manufacturing process according to the present invention is not performed, and the surface of the support substrate 10 to be bonded is the first surface 10a of the support substrate 10 to which the film 3 is attached. In the final composite structure 100, a carbon film with a diamond-type crystallographic structure is preferred to facilitate perpendicular electrical conduction through the stiffening film 3. 【0069】 Optionally, an additional carbon film 5 is placed on the opposite side of the surface to be bonded to the support substrate 10, before the bonding step f3) (Figure 3e). The properties of the additional carbon film 5 may be selected, for example, from the properties previously proposed for the stiffening film 3 in this description. 【0070】 The presence of this additional film 5 is illustrated in Figure 3e in combination with the intermediate layers 4 and 4' on the mating surfaces of the donor substrate 21 and the support substrate 10, respectively, but this additional film 5 can be realized in any of the possible configurations mentioned, in particular the configurations illustrated in Figures 3a to 3c. 【0071】 The additional film 5 may, at a later time, preferably after the composite structure 100 has undergone any heat treatment at a temperature above 1400°C required for the manufacture of the composite structure 100 or for the manufacture of components on and / or within the structure 100. 【0072】 Returning to the explanation of the bonding stage f3), and as is essentially well known, direct molecular adhesive bonding does not require adhesive material because the bond is established at the atomic level between the bonded surfaces. Several types of molecular adhesive bonding exist, and these types differ, among other things, in terms of temperature, pressure, or atmospheric conditions, or in the treatments performed before the surfaces come into contact. We can refer to bonding at room temperature, with or without prior plasma activation of the surfaces to be bonded, atomic diffusion bonding (ADB), surface activated bonding (SAB), and others. 【0073】 The mating step f3) may include a conventional sequence of chemical cleaning (e.g., RCA cleaning) and surface activation (e.g., by means of oxygen or nitrogen plasma), or other surface preparation (such as scrubbing) that is likely to improve the quality of the bonding interface 30 (low defect density, high adhesion energy), before bringing the surfaces to be mated 21a and 10a into contact. 【0074】 Finally, the fourth step f4) involves separation along the embedded fragile plane 22, which leads to the transfer of the processed layer 20 to the support substrate (Figure 2d). 【0075】 Separation along the embedded fragile plane 22 is typically performed by applying a heat treatment at a temperature between 800°C and 1200°C. Such a heat treatment causes voids and microcracks to develop in the embedded fragile plane 22, which are pressurized by light chemical species present in gaseous form, and eventually the fracture propagates along the fragile plane 22. Alternatively, or in conjunction with it, mechanical stress may be applied to the bonded joint and in particular to the embedded fragile plane 22 to propagate the fracture leading to separation, or to assist in the mechanical propagation of the fracture. The result of this separation is a semiconductor structure 100 on the one hand, comprising the support substrate 10 and the transferred processed layer 20 fabricated from single-crystal SiC, and on the other hand, the remainder 21' of the donor substrate. The level and type of doping of the processed layer 20 is determined by the selection of the properties of the donor substrate 21 or can be adjusted later by known techniques for doping semiconductor layers. 【0076】 The free surface 20a of the processed layer 20 is typically rough after separation; for example, the free surface 20a has a roughness between 5 nm and 100 nm RMS (AFM, 20 μm × 20 μm scan). A washing and / or smoothing step may be applied to restore a good surface finish (typically less than a few angstroms RMS in a 20 μm × 20 μm AFM scan). In particular, these steps may include a mechanochemical smoothing treatment of the free surface of the processed layer 20. Removal between 50 nm and 300 nm allows for effective restoration of the surface finish of the layer 20. The steps may also include a heat treatment at a temperature of at least between 1300°C and 1800°C. Such a heat treatment is applied to remove residual light chemical species from the processed layer 20 and to facilitate the rearrangement configuration of the crystal lattice of the processed layer 20. The heat treatment further allows for strengthening of the bonding interface 30. The heat treatment may include, or correspond to, the epitaxy of silicon carbide in the thin layer 20. 【0077】 Finally, it should be noted that transfer step f) may include a step of modifying the remainder 21' of the donor substrate for reuse as a donor substrate 21 for the new composite structure 100. Mechanical and / or chemical treatments similar to those applied to the composite structure 100 may be applied to the front surface 21'a of the remaining substrate 21'. 【0078】 The resulting composite structure 100 is extremely robust to very high-temperature heat treatments that may be applied to improve the quality of the processed layer 20 or to manufacture components on and / or within the layer 20. 【0079】 The composite structure 100 according to the present invention is particularly suitable for one (or more) high-voltage microelectronic components, such as Schottky diodes, MOSFET transistors, and other production elements. More generally, the composite structure 100 is suitable for power microelectronic applications, as it enables excellent vertical electrical conductivity, good thermal conductivity, and results in a high-quality c-SiC fabricated layer. 【0080】 Needless to say, the present invention is not limited to the embodiments and examples described, and realization modifications may be applied to those embodiments and examples without departing from the scope of the invention as defined by the claims.

Claims

[Claim 1] A process for manufacturing a polycrystalline silicon carbide support substrate (10), a) A step of growing an initial polycrystalline silicon carbide substrate (1) on a graphite or silicon carbide seed (2), wherein at the end of step a), the initial substrate (1) has a free front surface (1a) and a rear surface (1b) in contact with the seed (2), b) A step of forming a stiffening carbon film (3) on the front surface (1a) of the initial substrate (1), wherein the initial substrate (1) has a first average silicon carbide particle size in the plane of the front surface (1a) of the initial substrate and immediately before the formation of the stiffening film (3), c) A step of removing the seed (2) to free the rear surface (1b) of the initial substrate (1), wherein the initial substrate has a second average silicon carbide particle size smaller than the first average size in the plane of the rear surface (1b) of the initial substrate and immediately after the removal of the seed (2), d) A step of thinning the rear surface (1b) of the initial substrate (1) to a thickness such that the plane of the thinned rear surface (1b') of the initial substrate has a third average particle size equal to the first average particle size within ±30%, wherein the thinned initial substrate (1) forms the support substrate (10). The process for manufacturing, including the manufacturing process. [Claim 2] The process according to claim 1, wherein the stiffening film (3) has a thickness of, for example, 10 mm, between 100 nm and several millimeters. [Claim 3] The process according to claim 2, wherein the stiffening film (3) has a thickness between 100 nm and 10 μm. [Claim 4] The process according to claim 1, wherein the stiffening carbon film (3) has a diamond-like or glassy carbon crystal structure. [Claim 5] The process according to claim 1, wherein step b) is performed by applying a polymer resin having pre-formed carbon-carbon bonds in three dimensions as a viscous layer on the front surface of the initial substrate (1), and annealing it at a temperature between 500°C and 2000°C to form the stiffening carbon film (3). [Claim 6] The process according to claim 5, wherein the polymer resin is based on coal tar, phenol formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and / or polystyrene. [Claim 7] The process according to claim 1, wherein step b) is performed by plasma deposition, ion bombardment deposition, or vapor deposition. [Claim 8] The process according to claim 1, wherein between step a) and step b), step a') grinds the front surface (1a) and / or peripheral portion of the initial substrate (1) to reduce the surface roughness of the surface (1a), and / or to reduce variations in the thickness of the substrate (1), and / or to make the peripheral portion of the initial substrate uniform. [Claim 9] The process according to claim 8, wherein step a') includes mechanical or mechanochemical thinning. [Claim 10] After step d), step e) to remove the stiffening film, and / or After step d), or after step e), a heat treatment step at a temperature of 1500°C or higher. The process according to claim 1, including the process described in claim 1. [Claim 11] A process for manufacturing a composite structure (100), comprising the process according to any one of claims 1 to 10, and also including step f) transferring a thin layer (20) of single-crystal silicon carbide to a first surface (10a) or a second surface (10b) of the support substrate (10), either directly or via an intermediate layer, to form the composite structure (100). [Claim 12] The process according to claim 11, wherein the intermediate layer is formed by the stiffening carbon film (3) maintained on the first surface (10a) of the support substrate (10). [Claim 13] The process according to claim 11, wherein the transfer of the thin layer (20) is performed on one of the first surface and the second surface (10a, 10b) of the support substrate (10), and an additional carbon film (5) is positioned on the other free surface (10b, 10a) of the support substrate (10) prior to the transfer. [Claim 14] The process according to claim 13, wherein the additional film (5) is preferably removed after the composite structure (100) has undergone any heat treatment at a temperature above 1400°C required for the manufacture of the composite structure or for the manufacture of components on and / or within the structure (100).

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