Silicon carbide component for the production of silicon carbide single crystals

Abstract

The invention relates to a piece of polycrystalline silicon carbide exhibiting improved porosity and homogeneity properties, its use as a source of silicon carbide for the growth of silicon carbide single crystals, its manufacturing process, and a PVT growth process employing such a piece of silicon carbide.

Description

Title of the invention: Silicon carbide component for the production of silicon carbide single crystals

[0001] The invention relates to a piece of polycrystalline silicon carbide having improved porosity and homogeneity properties, its use as a source of silicon carbide for the growth of silicon carbide single crystals, its manufacturing process, and a PVT growth process employing such a piece of silicon carbide.

[0002] Silicon carbide (SiC) is a material with potential for a wide variety of advanced applications. Originally used as an abrasive due to its hardness, SiC is now used in diverse applications such as sealing rings, diesel engines, electronic circuits, industrial heat exchangers, gas turbines and high-temperature conversion systems.

[0003] Silicon carbide is particularly interesting for the production of semiconductor materials. Indeed, its wide band gap (three times greater than that of silicon), its high critical breakdown field, its high thermal conductivity (three times greater than that of silicon), and its high electron saturation velocity make silicon carbide an essential material for power electronics. SiC power semiconductors, for example, can increase energy conversion efficiency, withstand higher voltages and currents, and resist higher operating temperatures than conventional silicon-based devices. All these factors offer essential advantages for devices such as data center power supplies, wind or solar power modules, and electric vehicle drive converters.

[0004] Silicon carbide materials used in power electronics are generally very pure wafers made from single-crystal balls. These single-crystal balls are generally prepared by physical vapor transport (PVT) (also called the PVT process or PVT growth process). The PVT process is a method for producing and growing silicon carbide single crystals that involves heating a SiC source, sublimating this SiC source, and recrystallizing the SiC gas and other products of SiC sublimation onto a seed material itself made of SiC. Other methods can be used, such as solution growth or chemical vapor deposition (CVD).

[0005] Generally, a SiC powder as a source material is sublimated at temperatures above 2000°C and crystallizes on a slightly cooler seed (seedling material). Appropriate selection of the SiC powder source during PVT growth is a prerequisite for obtaining high crystalline quality in the final SiC sphere.

[0006] SiC powder can be produced by a process known as the "Acheson" process, which is described in particular in Ellefsen et al., 2019, Materials, 12, 3272, 1-10. In a custom-made furnace, high-purity quartz sand and carbon black are subjected to a high-temperature reaction to produce a raw material, which is then crushed, ground, and sieved to remove fine and coarse fractions and adjust the size distribution in the resulting powder. Finally, the resulting powder undergoes chemical treatment to remove impurities. The bulk density of this powder is on the order of 1.8 g / cm³, which is strictly less than 57%. Furthermore, the silicon carbide single crystal produced from this SiC source has a low height after 144 hours of growth, indicating a low growth rate and low process efficiency.

[0007] US patent 11,421,339 B2 describes a SiC powder (particle diameter of 300 pm) coated with porous sintered silicon carbide (hole diameter of 150 pm) as a SiC source. However, this SiC source does not exhibit a high growth rate with a low dislocation concentration.

[0008] Thus, the object of the present invention is to provide a source of SiC allowing a high furnace filling rate, and in particular a source of SiC allowing a high growth rate while ensuring a low concentration of dislocations and / or a higher furnace utilization efficiency, to meet the growing demand for SiC power semiconductor devices.

[0009] The invention has as its first object a part comprising silicon carbide, characterized in that it has a relative density ranging from about 60 to 95%, in that the silicon carbide is polycrystalline, and in that said part has: - a Vickers hardness polydispersity index PHV such that 0% < PHv < 70%, and / or - a thermal conductivity polydispersity index at 1173°C Po such that 0% < Po < 30%.

[0010] This density range makes it possible to obtain a part suitable for use in physical transport processes in the vapor phase.

[0011] In the present invention, the term "polycrystalline" means that the silicon carbide is in the form of several small crystals called crystallites, of varying size, shape, and orientation, separated by grain boundaries. In contrast, a single crystal or monocrystalline material is in the form of a single crystal.

[0012] In the present invention, the polycrystalline character can be determined using a transmission electron microscope (TEM), by X-ray diffraction (XRD) or by identification of at least two grains within the material.

[0013] X-ray diffraction makes it possible, in particular, to identify several crystalline phases or to measure the size of the crystals of a crystalline phase using the Debye-Scherrer method. Since one crystalline phase is largely predominant, this method uses the peak profile to determine the broadening due to the size of the crystallites. The standard used to determine the broadening due to the apparatus is a single-crystal silicon sample. Considering an aspect ratio K of 0.89 and using the following formula, the average size of the crystallites is found, and if this size is less than half the size of the sample, the polycrystalline nature of the part is confirmed:

[0014] [Math.l] O D = . ---- VB2 — with D being the average size of the crystallites (nm), X being the wavelength (nm), B being the bandwidth at half the peak (rad), b being the bandwidth at half the height of the standard peak and 0 being the position of the peak (rad).

[0015] The identification of two grains within the material can be carried out by following the procedure described in ASTM E2627-13, entitled "Standard Practice for Determining Average Grain Size Using Electron Backscatter Diffraction (EBSD) in Fully Recrystallized Polycrystalline Materials." The procedure must be followed up to and including point 12.2. This procedure must be repeated on at least 60 distinct 1 mm² patches, or on as many 1 mm² patches as possible for parts with a surface area of ​​less than 60 mm². If, across all the scans performed, at least two grains are identified, the polycrystalline nature of the part is confirmed.

[0016] The silicon carbide of the part of the invention can be in the form of one or more phases such as the alpha 4H phase, the alpha 6H phase, the alpha 2H phase, the beta (3C) phase or the 15R phase.

[0017] The part of the invention has a relative density ranging from about 60% to about 95%, preferably from about 65% to about 90%, and particularly preferably from about 68% to about 85%.

[0018] In the present invention, the density of the part (in g / cm³) is determined according to ASTM B962-17 (Standard test methods for the density of compacted or sintered powder metallurgy products using Archimedes' principle). It is then possible to deduce the relative density of the part, which corresponds to a ratio of the measured density of the piece obtained according to Archimedes' principle (in g / cm3) and the theoretical density of the piece which is 3.21 g / cm3.

[0019] A relative density below 60% can lead to an excessive decrease in thermal conductivity and / or a deterioration in hardness. A density above 95% is difficult to achieve without sintering additives, and / or is difficult to achieve inexpensively.

[0020] According to a preferred embodiment of the invention, the part essentially comprises silicon carbide. In other words, silicon carbide preferably represents at least about 95% by mass, and particularly preferably at least about 96% by mass, relative to the total mass of the part.

[0021] According to a preferred embodiment of the invention, the carbon and silicon elements represent at least 99% by mass approximately, and particularly preferably at least 99.8% by mass approximately, relative to the total mass of the part.

[0022] The part may further comprise one or more unavoidable impurities, in particular chosen from the following elements: B, Al, S, Fe, Cu, Mg, Ni, and Y.

[0023] According to a particularly preferred embodiment, the part is made of silicon carbide and one or more unavoidable impurities, in particular chosen from the following elements: B, Al, S, Fe, Cu, Mg, Ni, and Y.

[0024] In the present invention, each of the unavoidable impurities represents preferably at most about 50 ppm, and particularly preferably at most about 25 ppm (relative to the total mass of the part).

[0025] When the part includes several unavoidable impurities, they preferably represent a total content of at most about 1000 ppm, particularly preferably of at most about 500 ppm, and even more particularly preferably of at most about 100 ppm (relative to the total mass of the part).

[0026] In the present invention, the abbreviation "ppm" means "parts per million by mass". In other words, the ppm content of an element or unavoidable impurity is expressed relative to the total mass of the part.

[0027] Preferably, the part is made of silicon carbide and one or more of the following unavoidable impurities with the corresponding contents: - at most approximately 1 ppm, and particularly preferably at most approximately 0.5 ppm of boron (B), - at most approximately 50 ppm, and particularly preferably at most approximately 25 ppm of aluminium (Al), - at most approximately 7 ppm, and particularly preferably at most approximately 5 ppm of sulfur (S), - at most approximately 15 ppm, and particularly preferably at most approximately 10 ppm of iron (Fe), - at most approximately 1 ppm, and particularly preferably at most approximately 0.5 ppm of copper (Cu), - at most approximately 5 ppm, and particularly preferably at most approximately 2 ppm of magnesium (Mg), - at most approximately 0.5 ppm, and particularly preferably at most approximately 0.2 ppm of nickel (Ni), - at most about 0.5 ppm, and particularly preferably at most about 0.2 ppm of yttrium (Y).

[0028] The part of the invention has the advantage of being a homogeneous part in terms of mechanical and / or physico-chemical properties.

[0029] According to a preferred embodiment of the invention, the part has both a Vickers hardness polydispersity index PHV such that 0% < PHv < 70%, and a thermal conductivity polydispersity index at 1173°C Po such that 0% < Po < 30%.

[0030] The part particularly preferentially exhibits a Vickers hardness polydispersity index PHv such that 1% < PHv < 60%.

[0031] The part according to the invention can have a Vickers hardness ranging from approximately 510 to 3050 kgf / mm2, and preferably from approximately 550 to 2500 kgf / mm2.

[0032] In the present invention, the Vickers hardness can be determined according to ASTM E384-11, with a load of 1 kg.

[0033] According to a preferred embodiment of the invention, the part has a polydispersity index of thermal conductivity at 1173°C Po such that 1% < Po < 20%.

[0034] In the present invention, the thermal conductivity at 1173°C can be determined from the thermal diffusivity measurements obtained according to the Flash method as defined in ISO 18755:2022. In particular, the flash method makes it possible to determine the thermal diffusivity and then the use of a mathematical relationship and a reference makes it possible to access the thermal conductivity.

[0035] The part according to the invention can have a thermal conductivity at 1173°C ranging from 10 to 50 W.cm-hK-1 approximately, and preferably from 25 to 45 W.cm-hK-1 approximately.

[0036] The part preferably comprises carbon and silicon so that the carbon / silicon atomic ratio ranges from approximately 0.85 to 1.05, and particularly preferably from approximately 0.9 to 1.

[0037] The part of the invention is preferably a sintered part. In other words, it preferably results from a sintering process, and particularly preferably from a flash sintering process.

[0038] The term "sintering" refers to a thermal process consisting of heating a solid mass of material for a given time to a temperature below the melting point of the material (solidification by the action of heat). The high temperature causes the particles to fuse together to form a solid part.

[0039] Flash sintering differs from conventional sintering in that the heat source is an electric current (direct, pulsed direct, or alternating), applied via electrodes. This current passes through the conductive pressing chamber and, in appropriate cases, also through the sample. It is this electric current that heats the sample directly within it. Generally speaking, flash sintering allows materials to be consolidated in much shorter times.

[0040] The present invention has as its second object the use of a part as defined in the first object of the invention as a source of silicon carbide for the growth of silicon carbide single crystals.

[0041] Thanks to the suitable porosity and homogeneity of the part conforming to the first object, it is possible to use it as a source of silicon carbide to grow silicon carbide single crystals, in particular in a physical vapor phase transport process.

[0042] This makes it possible in particular to improve the growth rate of silicon carbide single crystals while ensuring a low concentration of dislocations.

[0043] The present invention has as its third object a method for manufacturing a part as defined in the first object, characterized in that it comprises at least the following steps: i) pre-compact a silicon carbide powder at a pressure of at least approximately 3 MPa, and ii) perform a flash sintering of the pre-compacted powder at a temperature of no more than approximately 2200 °C.

[0044] The process of the invention makes it possible to produce a part exhibiting sufficiently precise and controlled homogeneity.

[0045] Step i)

[0046] The silicon carbide powder used in step i) may comprise carbon and silicon such that the carbon / silicon atomic ratio ranges from approximately 0.85 to 1.15, and particularly preferably from approximately 0.95 to 0.99.

[0047] The silicon carbide powder is preferably a nanometric powder, in particular in the form of particles having an average size of approximately 10 to 80 nm, and particularly preferably of approximately 25 to 40 nm.

[0048] In the present invention, the average size of the silicon carbide particles can be determined by measuring the specific surface area (specific surface area referred to as SS) solids by gas adsorption or BET measurement as defined in ISO 9277:2022 according to the formula size = 6000 / (SS * density).

[0049] Silicon carbide powder preferably has a specific surface area of ​​approximately 20 to 200 m2 / g, and particularly preferably of approximately 30 to 70 m2 / g.

[0050] In the present invention, the specific surface area can be determined by gas adsorption or BET measurement as defined in ISO 9277:2022.

[0051] The silicon carbide in the powder is preferably in the form of at least one beta (3C) crystalline phase. This phase preferably represents at least 98% of the phase(s) present in said powder.

[0052] Step i) of pre-compaction can be carried out on the silicon carbide powder placed in a mold. The mold can be used to give a desired shape to the part comprising silicon carbide.

[0053] The process may then include, before step i), a step il) in which the silicon carbide powder is placed or introduced into a mold.

[0054] The mold is preferably made of a material resistant to temperatures above approximately 2300°C and pressures above approximately 80 MPa. Suitable materials may be graphite or alpha-phase silicon carbide.

[0055] The mold can be wrapped or lined with a flexible sheet to ensure electrical contact between the mold and the silicon carbide powder to be pre-compacted and sintered. Graphite powders can also be sprayed onto the flexible sheet.

[0056] Step i) is preferably carried out by uniaxial pressing at a pressure of at least about 3 MPa, and particularly preferably at a pressure ranging from about 5 to 20 MPa.

[0057] Uniaxial pressing is preferably manual.

[0058] Step i) is preferably carried out at room temperature (i.e. about 18-25°C).

[0059] The pre-compaction time can range from approximately 1 to 30 minutes.

[0060] The pre-compaction step i) is preferably carried out under ambient environment (i.e. atmospheric pressure and / or ambient temperature).

[0061] Step ii)

[0062] In a particular embodiment, step ii) is carried out at a pressure ranging from approximately 35 to 80 MPa.

[0063] In a particular embodiment, step ii) is carried out at a temperature ranging from approximately 1700 to 2200°C.

[0064] The flash sintering time ii) can range from a few seconds to a few hours approximately, and in particular from 2 to 130 minutes approximately.

[0065] Step ii) can be carried out with a heating rate of approximately 50 to 300°C.min-1, and preferably approximately 80 to 200°C.min-1.

[0066] At the end of step ü) a solid mass is obtained which corresponds to a part conforming to the first object of the invention.

[0067] The process may further include a step iii) of cooling.

[0068] Step iii) may include cooling the part from step ii) to a temperature of approximately 1000°C while maintaining a pressure identical to that applied in step ii), followed by cooling to ambient temperature (i.e. approximately 18-25°C) at atmospheric pressure.

[0069] The part can then be removed from the mold.

[0070] Step ii) is preferably carried out under vacuum.

[0071] Step iO)

[0072] According to a preferred embodiment of the invention, the process further comprises, before step i) or before step il) if it exists, a step iO) during which the silicon carbide powder is granulated.

[0073] Granulation can be carried out for 24h to 100h, and preferably for 72h.

[0074] Such a step iO) of granulation can increase the typed density of the silicon carbide powder, in particular without adding binders or additives.

[0075] The typed density obtained at the end of step iO) is preferably greater than about 0.15 g / cm3, and particularly preferably greater than about 0.2 g / cm3.

[0076] Such a granulation step iO) is advantageously carried out according to the protocol as described in patent EP2648834B1.

[0077] In particular, step i0) includes introducing nanometric silicon carbide particles into a container having an inner wall of circular or substantially circular cross-section and setting in motion all the particles along said inner wall by rotating the container around an axis of rotation passing through said container, the setting in motion of the particles being carried out dry and the rotation of the container being carried out continuously at a constant speed for several consecutive hours.

[0078] The packed density, also known as the packed specific gravity, is used to evaluate the amount of material present in a given volume, which includes both the volume occupied by the material and the empty spaces between the grains or particles. Thus, the packed density of a granular or powdered material can vary depending on how it is handled, whether it is compressed or compacted.

[0079] The measurement of the tapped density can follow the following protocol: in a 100 ml graduated cylinder (internal diameter: 28 mm), 5 g of powder is poured and, after tapping 20 times to a height of 2 cm, the graduation is read and the density is calculated from the volume.

[0080] The present invention relates as a fourth object to a physical vapor-phase transport growth process (i.e., PVT growth process) characterized in that it comprises at least the following steps: a) heating a part as defined in the first object of the invention as a silicon carbide (SiC) source, to form a gas comprising carbon and / or silicon, such as a gas comprising gaseous silicon carbide (SiC), gaseous silicon dicarbide (SiC2), gaseous carbon, gaseous silicon, and / or gaseous disilicon carbide (Si2C), and b) the recrystallization of a gas comprising carbide and / or silicon on a seeding material made of silicon carbide (SiC).

[0081] The heating a) allows the sublimation of the piece as defined in the first object of the invention to be initiated and creates vapors which rise and are deposited on an exposed surface of the seeding material and cause the growth of the ball.

[0082] In particular, the process is implemented in a physical vapor transport growth chamber containing a part as defined in the first object of the invention as a silicon carbide (SiC) source and a seeding material consisting of silicon carbide (SiC) (silicon carbide seed) on a seed holder.

[0083] The growth chamber is preferably filled with an ambient gas such as argon and then evacuated to a pressure of a maximum of 1 mbar.

[0084] The growth chamber can be filled with nitrogen if doping is implemented.

[0085] Step a) is carried out by heating the growth chamber to a temperature ranging from approximately 1700 to 2300°C.

[0086] At the end of step a), the silicon carbide (SiC) source is sublimated.

[0087] During step b), the silicon carbide seed is exposed to the source of silicon carbide (SiC) sublimated to grow a silicon carbide crystal in a direction extending away from the seed holder.

[0088] The pressure of the growth chamber preferably goes from 0 to about 1 mbar.

[0089] The part as defined in the first object of the invention can also be used as a spray target.

[0090] Examples

[0091] Measurement techniques

[0092] Technique for measuring the polycrystalline nature of the part of the invention

[0093] Transmission electron microscopy (TEM) analyses were carried out on the sintered samples with a JEOL JEM-2000EX model microscope, operating at 200 kV.

[0094] Density measurement technique

[0095] The density was determined according to ASTM B962-17 (Standard test methods for the density of compacted or sintered powder metallurgy products using Archimedes' principle).

[0096] Purity measurement technique

[0097] The chemical composition was analyzed by high-resolution glow discharge mass spectrometry (HR-GDMS) using an instrument sold under the trade name "Nu Astrum - HR-GDMS" by AMETEK. The GDMS analyses were performed in the core of the samples with a very high-purity indium binder. The experimental conditions included the use of argon (6N+) as the discharge gas, the application of an excitation voltage of 1 kV, and the maintenance of a discharge current of 2.0 mA. The insulator is composed of 100% alumina. A set of Relative Sensitivity Factors (RSFs) specific to SiC was used for normalization. This is a multiplication factor applied to the ratio of the measured ionic currents to calculate the concentration ratio.The analysis of a large number of Certified Reference Materials, combined with inter-laboratory tests, has made it possible to establish a solid basis of RSFs relating to the matrices analyzed.

[0098] The detection mode is set to Faraday, with an ion counting integration time of 160 ms per cycle. The resolution is 3500. The silicon current is set to approximately 6 x 10¹¹ A. The experimental procedure includes plasma preparation, parameter adjustment, calibration with the reference material, Faraday data acquisition, and subsequent data analysis to identify the characteristic peaks of the elements present in the alumina. The samples to be analyzed are decomposed, and the materials are collected in the core and pressed with a 7N purity indium tool. To eliminate any potential surface contamination, the samples are sprayed into the plasma for a few minutes before any acquisition.

[0099] Hardness measurement technique

[0100] To facilitate Vickers hardness measurements, the samples were first encapsulated by hot embedding, then polished to remove surface roughness and obtain a mirror-like finish.

[0101] Vickers hardness measurements were performed using a 1 kg load with a Vickers indenter as described in ASTM E384-11. A total of 20 Vickers hardness measurements were taken on the surface of a sample. The surface was divided into 20 equal plots, and a measurement was taken on each plot. This approach allowed for a comprehensive evaluation of the hardness distribution over the entire surface of the sample.

[0102] Homogeneity of hardness

[0103] A hardness polydispersity index, denoted PDV, was established using the following relationship: PHv = (H9o-Dio) / H5o, where: - H50 represents the Vickers hardness at 10% cumulative distribution, i.e., the point where 10% of the total measurements consist of lower hardness values; - H50 represents the median Vickers hardness (50% cumulative distribution), i.e., the point where 50% of the total measurements consist of lower hardness values. - H90 represents the Vickers hardness at 90% cumulative distribution, i.e. corresponds to the point where 90% of the total measurements consist of lower hardness values.

[0104] Technique for measuring thermal conductivity

[0105] Thermal conductivity is directly calculated from thermal diffusivity measurements obtained using the Flash method by heating the sample to 1173°C.

[0106] By using density and specific heat (specific heat capacity as defined below) as functions of temperature for a reference sample such as thermographite, and taking into account the density of the sample to be measured, it becomes possible to calculate the thermal conductivity by comparative measurements of the thermal diffusivity between the reference and the sample. These two properties are related by the following equation: o(T) = D(T) p(T) Cp(T), in which: o(T) represents the thermal conductivity in W.cm-hK-1, D(T) represents the thermal diffusivity in cm2.s-*, p(T) is the density in g.cm-3, and Cp(T) represents the specific heat capacity in Jg-hK-1.

[0107] All measurements were carried out in accordance with ISO 18755:2022. A total of 20 measurements were taken on the sample surface. The surface was divided into 20 equal plots, and one measurement was taken on each plot. This approach allowed for a comprehensive evaluation of the thermal conductivity distribution over the entire sample surface.

[0108] Homogeneity of thermal conductivity

[0109] A polydispersity index of thermal conductivity, denoted Po, was established using the following relation: Po = (090-010) / 050, in which: - Oio represents the thermal conductivity at 1173°C for a cumulative distribution of 10%, i.e., corresponds to the point where 10% of the total measurements consist of lower thermal conductivity values. - 050 represents the median thermal conductivity at 1173°C (50% cumulative distribution), i.e., corresponds to the point where 50% of the total measurements consist of lower thermal conductivity values. - o90 represents the thermal conductivity at 1173°C with a cumulative distribution of 90%, i.e. corresponds to the point where 90% of the total measurements consist of lower thermal conductivity values.

[0110] Example 1

[0111] A part according to the invention was prepared in the manner detailed below.

[0112] A nanometric silicon carbide powder (average particle size of approximately 37 nm), commercially available from Nanomakers under the reference "NMSiC6N@35", was used in this Example 1. The specific surface area of ​​the silicon carbide nanopowder was determined to be 63 m² / g. The carbon / silicon atomic ratio was measured to be 0.96.

[0113] 50 g of said silicon carbide powder was granulated (step i0) and then introduced in a graphite mold lined with very high-purity graphite paper such as "Papyex®" supplied by Mersen (step 11)). The packed density of the granulated powder is 0.28 g / cm³. Pre-compaction of the powder (step 1)) was carried out by manual uniaxial pressing at 3 MPa. Subsequently, the graphite mold containing the pre-compacted powder was placed in a flash sintering system (step 2)) (also known as "Spark Plasma Sintering," or SPS sintering) sold under the trade name "Fuji-SPS model 8.40" by Fuji Electronic Industrial Co., LTD. By applying a pressure of 35 MPa, the pre-compacted powder was heated to 1830°C at a rate of approximately 200°C / min. The temperature and pressure were maintained for 8 minutes. Next, the heating system was switched off and the temperature decreased naturally, maintaining pressure until the temperature fell below 1000°C.A sintered body with a density of 61% and a diameter of 55 mm was obtained.

[0114] Other sintered bodies with a density of 65% having a diameter of 110 mm, 150 mm and 210 mm were also obtained according to the same protocol and by introducing 215, 400 and 775 g of powder respectively.

[0115] The SiC part obtained according to the invention has a density of 61%, a Vickers hardness polydispersity index of 53%, and a thermal conductivity polydispersity index at 1173°C of 23%.

[0116] TEM micrographs show the polycrystalline nature of the samples with a multitude of crystallites ranging in size from 10 nm to 100 pm.

[0117] Example 2

[0118] A part according to the invention was prepared in the manner detailed below.

[0119] A nanometric silicon carbide powder (average particle size of approximately 37 nm), commercially available from Nanomakers under the reference "NMSiC6N@35", was used in this Example 2. The specific surface area of ​​the silicon carbide nanopowder was determined to be 63 m² / g. The carbon / silicon atomic ratio was measured to be 0.96.

[0120] 50 g of said silicon carbide powder was granulated (step i0) and then introduced in a graphite mold lined with very high-purity graphite paper such as "Papyex®" supplied by Mersen (step 11)). The packed density of the granulated powder is 0.27 g / cm³. Pre-compaction of the powder was carried out by manual uniaxial pressing at 3 MPa (step 1)). Subsequently, the graphite mold containing the pre-compacted powder was placed in a flash sintering system (step 2) (also known as "Spark Plasma Sintering," or SPS sintering) sold under the trade name "Fuji-SPS model 8.40" by Fuji Electronic Industrial Co., LTD. Applying a pressure of 43 MPa, the pre-compacted powder was heated to 1930°C at a rate of approximately 200°C / min. The temperature and pressure were maintained for 5 minutes. Next, the heating system was switched off and the temperature decreased naturally, maintaining pressure until the temperature fell below 1000°C.A sintered body with a density of 67% and a diameter of 55 mm was obtained.

[0121] Other sintered bodies with a density of 67% having a diameter of 110 mm, 150 mm and 210 mm were also obtained according to the same protocol and by introducing 215, 400 and 775 g of powder respectively.

[0122] The SiC part as obtained according to the invention has a density of 67%, a Vickers hardness polydispersity index of 41% and a thermal conductivity polydispersity index at 1173°C of 18%.

[0123] TEM micrographs show the polycrystalline nature of the samples with a multitude of crystallites ranging in size from 10 nm to 100 pm.

[0124] Example 3

[0125] A part according to the invention was prepared in the manner detailed below.

[0126] A nanometric silicon carbide powder (average particle size of approximately 37 nm), commercially available from Nanomakers under the reference "NMSiC6N@35", was used in this Example 3. The specific surface area of ​​the silicon carbide nanopowder was determined to be 63 m² / g. The carbon / silicon atomic ratio was measured to be 0.96.

[0127] 50 g of said silicon carbide powder was granulated (step i0) and then introduced in a graphite mold lined with very high purity graphite paper such as " Papyex®, supplied by Mersen (step 11), had a type density of 0.25 g / cm³. The powder was pre-compacted by manual uniaxial pressing at 3 MPa (step 1). The graphite mold containing the pre-compacted powder was then placed in a flash sintering system (step 2) (also known as Spark Plasma Sintering, or SPS sintering), sold under the trade name "Fuji-SPS model 8.40" by Fuji Electronic Industrial Co., LTD. Applying a pressure of 43 MPa, the pre-compacted powder was heated to 1930°C at a rate of approximately 200°C / min. The temperature and pressure were maintained for 10 minutes. Next, the heating system was switched off and the temperature decreased naturally, maintaining pressure until the temperature fell below 1000°C. A sintered body with a density of 70% and a diameter of 55 mm was obtained.

[0128] Other sintered bodies with a density of 70% having a diameter of 110 mm, 150 mm and 210 mm were also obtained according to the same protocol and by introducing 215, 400 and 775 g of powder respectively.

[0129] The SiC part obtained according to the invention has a density of 70%, a Vickers hardness polydispersity index of 32% and a thermal conductivity polydispersity index at 1173°C of 11%.

[0130] TEM micrographs show the polycrystalline nature of the samples with a multitude of crystallites ranging in size from 10 nm to 100 pm.

[0131] Comparative example 4

[0132] A part not conforming to the invention was prepared in the manner detailed below.

[0133] A nanometric silicon carbide powder (average particle size of approximately 37 nm), commercially available from Nanomakers under the reference "NMSiC6N@35", was used in this comparative example 4. The specific surface area of ​​the silicon carbide nanopowder was determined to be 63 m² / g. The carbon / silicon atomic ratio was measured to be 0.96.

[0134] 50 g of said silicon carbide powder was introduced into a mold in Graphite lined with very high-purity graphite paper such as "Papyex®" supplied by Mersen. The typed density of the powder is 0.05 g / cm³. The powder was pre-compacted by manual uniaxial pressing at 3 MPa. The graphite mold containing the pre-compacted powder was then placed in a flash sintering system (also known as Spark Plasma Sintering, or SPS sintering) sold under the trade name "Fuji-SPS model 8.40" by Fuji Electronic Industrial Co., LTD. Applying a pressure of 35 MPa, the pre-compacted powder was heated to 1830°C at a rate of approximately 200°C / min. The temperature and the pressure was maintained for 8 minutes. Then the heating system was switched off and the temperature decreased naturally, maintaining the pressure until the temperature fell below 1000°C.

[0135] The SiC piece as obtained has a density of 52%, a Vickers hardness polydispersity index of 73% and a thermal conductivity polydispersity index at 1173°C of 54%.

[0136] TEM micrographs show the polycrystalline nature of the samples with a multitude of crystallites ranging in size from 10 nm to 100 pm.

[0137] Comparative example 5

[0138] A part not conforming to the invention was prepared in the manner detailed below.

[0139] A nanometric silicon carbide powder (average particle size of approximately 37 nm), marketed by Nanomakers under the reference "NMSiC6N@35", was used in this comparative example 5. The specific surface area of ​​the silicon carbide nanopowder was determined to be 63 m² / g. The carbon / silicon atomic ratio was measured to be 0.96.

[0140] 50 g of said silicon carbide powder was introduced into a mold in Graphite was lined with very high-grade graphite paper, such as "Papyex®" supplied by Mersen. The typed density of the powder was 0.04 g / cm³. The powder was pre-compacted by manual uniaxial pressing at 3 MPa. The graphite mold containing the pre-compacted powder was then placed in a flash sintering system (also known as Spark Plasma Sintering, or SPS sintering) sold under the trade name "Fuji-SPS model 8.40" by Fuji Electronic Industrial Co., LTD. Applying a pressure of 43 MPa, the pre-compacted powder was heated to 1930°C at a rate of approximately 200°C / min. The temperature and pressure were maintained for 5 minutes. The heating system was then deactivated, and the temperature was allowed to decrease naturally, maintaining the pressure until the temperature fell below 1000°C. A sintered body with a density of 62% and a diameter of 55 mm was obtained.

[0141] The SiC piece as obtained has a density of 62%, a Vickers hardness polydispersity index of 82% and a thermal conductivity polydispersity index at 1173°C of 45%.

[0142] TEM micrographs show the polycrystalline nature of the samples with a multitude of crystallites ranging in size from 10 nm to 100 pm.

[0143] Comparative example 6

[0144] A part not conforming to the invention was prepared in the manner detailed below.

[0145] A nanometric silicon carbide powder (average particle size of approximately 37 nm), marketed by Nanomakers under the reference "NMSiC6N@35", was used in this comparative example 6. The specific surface area of ​​the silicon carbide nanopowder was determined to be 63 m² / g. The carbon / silicon atomic ratio was measured to be 0.96.

[0146] 50 g of said silicon carbide powder was introduced into a mold in Graphite was lined with very high-purity graphite paper, such as "Papyex®" supplied by Mersen. The typed density of the powder was 0.04 g / cm³. The powder was pre-compacted by manual uniaxial pressing at 3 MPa. The graphite mold containing the pre-compacted powder was then placed in a flash sintering system (also known as Spark Plasma Sintering, or SPS sintering) sold under the trade name "Fuji-SPS model 8.40" by Fuji Electronic Industrial Co., LTD. Applying a pressure of 43 MPa, the pre-compacted powder was heated to 1930°C at a rate of approximately 200°C / min. The temperature and pressure were maintained for 10 minutes. The heating system was then switched off, and the temperature was allowed to decrease naturally, maintaining the pressure until the temperature fell below 1000°C. A sintered body with a density of 78% and a diameter of 55 mm was obtained.

[0147] The SiC piece as obtained has a density of 78%, a Vickers hardness polydispersity index of 79% and a thermal conductivity polydispersity index at 1173°C of 34%.

[0148] TEM micrographs show the polycrystalline nature of the samples with a multitude of crystallites ranging in size from 10 nm to 100 pm.

[0149] Example 7 of a physical vapor phase transport process

[0150] A SiC seed crystal was placed in the upper part of a growth chamber in a physical vapor transport (PVT) furnace. This furnace comprises a graphite crucible, a temperature control system, a high-vacuum pumping system, and pressure and temperature sensors. The graphite crucible was loaded with SiC source material as prepared in any one of Examples 1 to 3 and Comparative Examples 4 to 6. The furnace temperature was gradually increased to initiate the sublimation of the SiC source material. The temperature was controlled at different locations within the furnace to create a thermal gradient between the SiC source and the SiC seed, allowing sublimation at the source and single-crystal condensation at the seed. This condensation initiates the growth of a single crystal. Growth continues until the crystal reaches the desired size.Then, the temperature was gradually decreased to stop the growth and allow the crystal and the furnace to... cool. This process takes place under a temperature of 2180°C measured at the SiC source and 2130°C measured at the seed, under vacuum (0.65 mbar).

[0151] The growth rate was determined as the crystal thickness divided by the growth time.

[0152] The dislocation density (after KOH etching) was determined after cutting and polishing a disk called a "wafer" according to the method described in the article "Measurement of Dislocation Density in SiC Wafers Using Production XRT" (Soukhojak, A. et al., 2022, 1062, 304-308). The device used is commercially available under the name "XRTmicron" sold by RIGAKU.

[0153] Table 1 below illustrates the results of the growth rate of SiC single crystals (in pm / h) and of dislocation concentration (number of dislocations / cm2).

[0154] [Tables 1] SiC source material Growth rate (in pm / h) Dislocation concentration (number of dislocations / cm²) Example 1 302 pm / h < 3000 / cm² Comparative example 4 10S pm / h < 3000 / cm² Example 2 411 pm / h < 3000 / cm² Comparative example 5 212 pm / h < 3000 / cm² Example 3 503 pm / h < 3000 / cm² Comparative example 6 24S pm / h < 3000 / cm²

Claims

1. Demands A part comprising silicon carbide, characterized in that it has a density ranging from 60% to 95%, in that the silicon carbide is polycrystalline, and in that said part has: - a Vickers hardness polydispersity index PHV such that 0% < PHV < 70%, and / or - a polydispersity index of thermal conductivity at 1173°C Po such that 0% < Po < 30%.

2. Part according to claim 1, characterized in that it has a Vickers hardness polydispersity index PHv such that 1% < PHv < 60%.

3. Part according to claim 1 or 2, characterized in that it has a polydispersity index of thermal conductivity at 1173°C Po such that 1% < Po < 20%.

4. Part according to any one of the preceding claims, characterized in that it is a sintered part 5. Part according to any one of the preceding claims, characterized in that it further comprises one or more unavoidable impurities selected from the following: B, Al, S, Fe, Cu, Mg, Ni, and Y.

6. Part according to claim 5, characterized in that each of the unavoidable impurities represents at most 50 ppm.

7. Use of a part as defined in any of the preceding claims as a source of silicon carbide for the growth of silicon carbide single crystals.

8. A method for manufacturing a part as defined in any one of claims 1 to 6, characterized in that it comprises at least the following steps: i) pre-compact a silicon carbide powder at a pressure of at least 3 MPa, and ii) perform a flash sintering of the pre-compacted powder at a temperature of no more than 2200°C.

9. A process according to claim 8, characterized in that the silicon carbide powder is a nanometric powder in the form of particles having an average size ranging from 10 to 80 nm.

10. A growth process by physical transport in the vapor phase, characterized in that it comprises at least the following steps: a) heating a part as defined in any one of claims 1 to 6 as a silicon carbide source, to form a gas comprising carbon and / or silicon, such as a gas comprising gaseous silicon carbide, gaseous silicon dicarbide, gaseous carbon, gaseous silicon, and / or gaseous disilicon carbide, and b) the recrystallization of a gas comprising carbide and / or silicon on a seeding material made of silicon carbide.