Rare earth element-doped silicon carbide porous material block as well as preparation method and application thereof

Abstract

The invention discloses a rare earth element-doped silicon carbide porous material block and a preparation method and application thereof, the rare earth element-doped silicon carbide porous material block comprises an intermediate and a silicon carbide film coated on the surface of the intermediate, and the intermediate comprises a porous silicon carbide block and a rare earth compound located in the pores. The rare earth compound powder is doped into the pores of the silicon carbide block, so that the rare earth elements are uniformly distributed in the whole crystal growth process in time and space, the polymorphic proportion in the silicon carbide crystal is remarkably reduced, and the quality of the silicon carbide crystal is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and in particular to a porous silicon carbide block doped with rare earth elements, a preparation method thereof, and applications thereof. Background Art

[0002] SiC, with its unique properties such as large bandgap, high critical breakdown field strength, high electron mobility, and high thermal conductivity, has become an ideal material for the production of high-temperature, high-frequency, high-power, radiation-resistant, short-wavelength luminescent and optoelectronic integrated devices. The unique physical properties of SiC determine its application in important fields such as artificial satellites, rockets, radar, communications, fighter jets, non-interference electronic ignition devices, and jet engine sensors. However, the production process of SiC materials faces many problems and challenges, especially in growth techniques such as physical vapor transport (PVT), which easily form a variety of different crystal structures, namely polytypes. This is mainly because the silicon carbide crystal structure is composed of alternating silicon and carbon atoms. The main difference between different types of silicon carbide polytypes lies in the stacking order of these atomic layers. Changes in factors such as temperature, pressure, gas flow rate, and raw material purity directly affect the deposition method of atoms, thereby leading to the emergence of different polytypes. Different types of polytypes will result in different electrical, optical and mechanical properties of silicon carbide products. In order to suppress the formation of unwanted polytypes and improve the quality of silicon carbide single crystals, methods that can be taken include precise control of growth parameters, optimization of seed crystal selection and processing, and improvement of growth technology.

[0003] Currently, adding some rare earth elements during the growth process of SiC materials can reduce polymorphism and promote the stable growth of specific crystal forms (such as 4H-SiC). For example, patent US20090053125A1 discloses that adding Ce silicide, carbide or oxide during the growth of 4H-SiC single crystals can suppress the generation of polymorphic defects. In this invention, CeSi2 or CeC2 is placed in a small graphite crucible, dispersed and embedded in the SiC powder source. During the crystal growth process, it sublimates into the gas phase and is eventually doped into the silicon carbide lattice, thereby promoting the growth of 4H-SiC and suppressing the generation of other polymorphs. From a process perspective: placing the cerium silicide or carbide in a small graphite crucible and then embedding it in the SiC powder source, the cerium compound cannot be evenly distributed in the powder, which inevitably leads to the uneven distribution of cerium in the gas phase component in time and space during the entire crystal growth process, which is also not conducive to the suppression of crystal forms. Similarly, simply mixing the dopant with silicon carbide powder without incorporating it into the powder will result in uneven distribution over time throughout the crystal growth process, even if spatially uniform distribution is achieved. This is because the melting point and sublimation rate of cerium silicide or carbide differ from those of silicon carbide, leading to uneven distribution over time. Chinese patent CN111892055B discloses synthesizing silicon carbide powder containing rare earth elements using rare earth element silicide and high-purity silicon-carbon powder, and growing crystals using this rare earth element-doped silicon carbide powder. During the growth process, the rare earth elements in the silicon carbide powder are gradually released as the powder sublimates, thereby suppressing the occurrence of polymorphism. In reality, the rare earth elements in the rare earth element-containing silicon carbide powder prepared by this method are not evenly distributed throughout the silicon carbide. Taking Ce compounds as an example, the chemical reaction mechanism for SiC growth is as follows: under carbon-rich conditions in SiC single crystal rods, PVT growth, silicides, and (lower-order) carbides undergo chemical transformations, leading to the formation of stable higher-order carbides. Ce reactions include: SiCe2+4C → 2SiC+CeC2, and Ce2C3+C → 2CeC2. Most rare earth silicides and carbides have high melting points, typically above 1500-1800°C. The atomic radius of rare earth elements is generally larger than the covalent radius of Si and C in the SiC lattice, leading to the low solubility of rare earth elements in SiC. Based on the reaction mechanism, Ce has difficulty incorporating into the SiC crystal form, let alone achieving uniform distribution within the SiC synthetic powder. Furthermore, after high-temperature mixing of Ce-containing compounds with SiC powder and subsequent cooling, the Ce-containing SiC powder produced has the Ce compound suspended on the outside of the SiC powder, resulting in a similar effect to direct Ce doping during actual growth.

[0004] Therefore, there is an urgent need for a method that can uniformly distribute rare earth elements in SiC powder in both space and time, so as to obtain SiC materials with a smaller polymorphic ratio and improve the quality of silicon carbide crystals. Summary of the Invention

[0005] The purpose of the present invention is to provide a porous silicon carbide block doped with rare earth elements, a preparation method and application thereof, so as to solve the problem that the above-mentioned method of reducing the polymorphism of silicon carbide materials by adding rare earth elements to silicon carbide cannot ensure the uniform distribution of rare earth elements in space and time, and thus cannot significantly reduce the polymorphic content in silicon carbide.

[0006] To achieve the above objectives, the first aspect of the present invention provides a porous silicon carbide block doped with rare earth elements, including an intermediate and a silicon carbide film coated on the surface of the intermediate, wherein the intermediate includes a porous silicon carbide block and a rare earth compound located in the pores.

[0007] Preferably, the shape of the silicon carbide block is at least one of spherical, cylindrical, square, and blocky, the size of the silicon carbide block is 0.1 to 1 cm, and the pore size distribution of the silicon carbide block is 10 to 200 μm.

[0008] The divided silicon carbide blocks of the present invention are filtered through a sieve to obtain irregular particles. The maximum diameter of the irregular particles is 0.1 to 1 cm. The irregular particles include the above-mentioned spherical, cylindrical and square particles.

[0009] Preferably, the average particle size of the rare earth compound is less than or equal to the minimum value of the pore size of the silicon carbide block, that is, the average particle size of the rare earth compound is less than or equal to 10 μm, so as to ensure that the rare earth compound powder can enter the pores of the silicon carbide block.

[0010] Preferably, the rare earth compound is at least one of rare earth silicide, rare earth carbide, and rare earth oxide.

[0011] Preferably, the rare earth element in the rare earth compound is selected from at least one of lanthanide elements, scandium and yttrium; and the lanthanide element is selected from at least one of cerium, lanthanum, praseodymium and neodymium.

[0012] A second aspect of the present invention provides a method for preparing a porous block of silicon carbide doped with rare earth elements, comprising the following steps:

[0013] S1: dividing the silicon carbide raw material to obtain silicon carbide blocks;

[0014] S2: adding rare earth compound powder to the silicon carbide block, mixing and shaking, so that the rare earth compound enters the pores of the silicon carbide block to obtain an intermediate;

[0015] S3: depositing a silicon carbide film on the surface of the intermediate by CVD to obtain a porous silicon carbide block doped with rare earth elements.

[0016] SiC material has polymorphism, and different polytypes have different atomic stacking sequences, such as 6H is ABCACB and 4H is ABAC. In conventional PVT growth, the 6H polytype is stable, and the stable growth of 4H-SiC crystals is difficult. Foreign polytypes such as 6H or 15R are prone to appear, which will cause crystal defects and reduce the yield of high-quality 4H-SiC. During the growth of silicon carbide crystals, uncontrollable disturbances in growth conditions such as temperature and pressure fluctuations, growth interface contamination (such as carbon particles released by graphite crucibles or carburized SiC sources) are common causes of instability of the 4H polytype. Although the existing technology has put forward some suggestions for stabilizing 4H growth (such as growing on the carbon surface of the seed crystal, selecting suitable growth conditions, avoiding growth interference, etc.), it is still impossible to completely eliminate foreign polytypes. Although existing technologies can partially address the polymorphic problem of silicon carbide crystals by adding rare earth elements to silicon carbide raw materials, Ce may affect the formation and dissociation of metastable nuclei of foreign polytypes by changing the chemical equilibrium of molecules in the gas phase. However, due to the inability of rare earth elements to be evenly distributed in space and time, the polymorph content in silicon carbide crystals remains at a high level. Based on this, the present invention dopes rare earth compound powder into the porous silicon carbide block and encapsulates the rare earth compound powder in the porous silicon carbide block by coating the surface of the intermediate with a silicon carbide film through CVD deposition. This step achieves a spatially uniform distribution of rare earth elements in the silicon carbide block.

[0017] Preferably, in step S2, the amount of rare earth compound added is 0.01 to 0.5 g / g; the oscillation frequency is 10 to 100 Hz, and the oscillation time is 10 min to 1 h.

[0018] Preferably, in step S3, the temperature during the CVD deposition process is 1000-1400° C., and the time is 5-50 hours.

[0019] A third aspect of the present invention provides an application of a porous silicon carbide block doped with a rare earth element, and an application of the porous silicon carbide block doped with a rare earth element in the preparation of silicon carbide materials.

[0020] Preferably, a silicon carbide porous block doped with rare earth elements and silicon carbide powder are mixed to obtain a mixed material, and the mixed material is subjected to crystal growth to obtain a silicon carbide crystal material.

[0021] Preferably, the crystal growth parameters are: conditions for growing silicon carbide crystals using the PVT method: growth temperature 2100-2300°C; axial temperature gradient 10-50°C / m, growth pressure 10-100Torr, growth rate 0.05-0.8mm / h, and growth time 50-200h.

[0022] During the growth process of silicon carbide crystals, the rare earth elements in the porous silicon carbide block doped with rare earth elements obtained by the present invention will be gradually released as the silicon carbide powder sublimates, thereby achieving a uniform distribution of rare earth elements over time. This can effectively inhibit the generation of polymorphs in the silicon carbide crystals, especially significantly reducing the probability of occurrence of polymorphs in the later stage.

[0023] Preferably, the thickness of the silicon carbide material is greater than 25 mm.

[0024] Therefore, the present invention adopts the above-mentioned porous silicon carbide block doped with rare earth elements and its preparation method and application, which has the following beneficial effects:

[0025] (1) The present invention achieves uniform distribution of rare earth elements in time and space during the entire growth process by incorporating rare earth compound powder into the pores of the silicon carbide block, significantly reduces the proportion of polymorphs in the silicon carbide crystal, and improves the quality of the silicon carbide crystal.

[0026] (2) The present invention mixes a rare earth-doped silicon carbide porous material block and a conventional silicon carbide powder in proportion, and then uses the mixture for crystal growth. As the initial mixture decomposes, the silicon carbide layer on the outside of the rare earth-doped silicon carbide block begins to decompose preferentially. In the middle and late stages of growth, the rare earth inside the porous material also begins to be released as the silicon carbide decomposes, thereby maintaining the carbon-silicon ratio in the atmosphere in the middle and late stages stable and improving the quality of silicon carbide crystals with thicker thickness.

[0027] (3) The present invention can significantly reduce the polymorphic ratio in the later stage of silicon carbide growth, and helps to stably grow 4H crystalline silicon carbide when the crystal thickness is greater than 35 mm. Even when the thickness of the silicon carbide crystal reaches more than 50 mm, the low polymorphic ratio can still be maintained.

[0028] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a preparation flow chart of the present invention;

[0030] Figure 2 is the SEM image of silicon carbide block;

[0031] Figure 3 This is a powder appearance diagram of a rare earth compound;

[0032] Figure 4 This is the appearance of the silicon carbide crystal prepared in Comparative Example 1;

[0033] Figure 5 This is the appearance of the silicon carbide crystal prepared in Example 5. DETAILED DESCRIPTION

[0034] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the present invention is not limited to this embodiment.

[0035] In the embodiment, the crystal form of the porous silicon carbide raw material and the silicon carbide powder used for crystal growth are both α-phase silicon carbide, while the silicon carbide layer is prepared by CVD method, which is β-phase silicon carbide, which will decompose and transform into α-phase silicon carbide under high temperature growth.

[0036] Example 1

[0037] like Figure 1 As shown, a method for preparing a porous block of silicon carbide doped with rare earth elements specifically comprises the following steps:

[0038] S1: The silicon carbide raw material is divided into silicon carbide blocks. The silicon carbide blocks are irregular particles in the shape of blocks, spheres, columns, squares or flakes. The maximum diameter of the particles is 0.1 cm, and the pore size distribution of the silicon carbide blocks is 10 to 200 μm. Figure 2 This is the SEM image of the silicon carbide block.

[0039] S2: Add a powder of a rare earth compound to the silicon carbide block, mixing and shaking. The rare earth compound is cerium oxide, and the particle size distribution of the cerium oxide is 0.01 to 0.5 μm. The shaking frequency is 80 Hz, and the mixing time is 40 minutes. This allows the rare earth compound to penetrate the pores of the silicon carbide block, thereby obtaining an intermediate. The weight gain of the silicon carbide block is 0.015 g cerium oxide / g. Figure 3 This is the appearance of cerium oxide powder.

[0040] S3: A silicon carbide film is deposited on the surface of the intermediate using the CVD method. Initially, a 10 μm silicon carbide thin layer is formed at 1400°C. At this point, the encapsulation effect has been achieved. The reaction temperature is then increased to 1500°C and heated for 2 hours to accelerate the reaction rate and deposition rate, shorten the process time, and ultimately obtain a porous silicon carbide block doped with rare earth elements.

[0041] Examples 2 to 4

[0042] The difference between this embodiment and embodiment 1 is that the size of the silicon carbide block and the weight gain of the silicon carbide block are different, as shown in Table 1 for details.

[0043] Table 1 Statistics of the weight of rare earth compound dopants that can be mixed into porous silicon carbide blocks of different sizes

[0044]

[0045]

[0046] Unit weight gain of the rare earth compound = (mass of the intermediate - mass of the original silicon carbide block) / mass of the original silicon carbide block.

[0047] It should be noted that when SiC blocks of varying sizes are mixed, the internal space for rare earth powder varies. After mixing, the weight gain of each porous SiC block will exhibit a range of distributions. The reason for using porous SiC blocks of varying sizes to mix with rare earth powder is that different sizes of rare earth-doped porous SiC blocks decompose at different rates at high temperatures. The rare earth-doped porous SiC blocks are mixed with conventional SiC powder in a suitable proportion and then used for crystal growth. During the initial decomposition of the mixture, the SiC layer on the outer surface of the rare earth-doped SiC blocks begins to decompose preferentially. In the middle and late stages of growth, the rare earths within the porous SiC blocks begin to be released as the SiC decomposes, maintaining a stable carbon-silicon ratio in the atmosphere and improving the quality of thicker SiC crystals. As the size of the porous SiC blocks increases, the rare earth compounds within the SiC are released later during growth, optimizing crystal growth in the later stages.

[0048] Examples 5 to 8

[0049] The specific process of preparing silicon carbide crystals from porous silicon carbide blocks doped with rare earth elements is as follows:

[0050] A porous silicon carbide block doped with rare earth elements and silicon carbide powder are mixed to form a mixture. The silicon carbide powder has a solid structure and is not porous. The particle size of the silicon carbide powder is 5 mm and the purity is less than 5 ppm. The mixture is then crystallized to obtain a silicon carbide crystal material. The crystal growth parameters are: PVT method for growing silicon carbide crystals: growth temperature of 2200°C, axial temperature gradient of 25°C / m, growth pressure of 50 Torr, growth rate of 0.5 mm / h, and growth time of 70 hours. The thickness of the silicon carbide crystal material is 35 mm.

[0051] The doping amount of the porous silicon carbide blocks doped with rare earth elements in Examples 5 to 8 is shown in Table 2. The doping amount of the porous silicon carbide blocks doped with rare earth elements = the percentage of the porous silicon carbide blocks doped with rare earth elements in the total mass of the porous silicon carbide blocks doped with rare earth elements and the silicon carbide powder. The appearance of the silicon carbide crystal prepared in Example 5 is shown in Table 2. Figure 4 .

[0052] Comparative Example 1

[0053] A conventional method for growing silicon carbide crystals comprises the following steps:

[0054] 1. Loading stage:

[0055] (1) Assemble a graphite crucible, a seed crystal, and SiC powder (wherein the silicon carbide powder is silicon carbide particles of different particle sizes). The seed crystal is a 4H crystal type silicon carbide seed crystal with a small deflection angle between 0 and 4.

[0056] 2. Crystal growth stage

[0057] 1) Pump the pressure in the growth chamber to 10 -6 mbar below, and raise the temperature to a first temperature of 1200°C for 5 hours;

[0058] 2) introducing an inert gas into the growth chamber and raising the pressure to a growth pressure of 100 mbar for 2 hours. The purity of the inert gas is greater than 99.9999%.

[0059] 3) Heating stage: while maintaining the growth pressure in the chamber constant, the first temperature was raised to a second temperature of 2200° C. to grow silicon carbide crystals. The crystal growth parameters were the same as in Examples 5 to 7, and the growth time was 70 h.

[0060] 3. After the growth is completed, the silicon carbide crystal is taken out from the growth device after cooling. Figure 4 As shown, this is the appearance of the silicon carbide crystal prepared in Comparative Example 1.

[0061] Comparative Example 2

[0062] The difference from Example 5 is that during the silicon carbide crystal preparation process, the silicon carbide powder is directly mixed with the rare earth compound, and the silicon carbide crystal is prepared under the same crystal growth conditions.

[0063] Table 2 Statistics of polymorphic ratios under different doping methods (single crucible loading amount is 3 kg)

[0064]

[0065]

[0066] Note: The initial stage of crystal growth refers to the time from the initial temperature to the growth temperature during the entire crystal growth cycle, and the middle and late stages of crystal growth refer to the last 20% of the entire crystal growth cycle.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A porous block of silicon carbide doped with rare earth elements, characterized in that: The invention comprises an intermediate and a silicon carbide film coated on the surface of the intermediate. The intermediate comprises a silicon carbide block with multiple pores and a rare earth compound located in the multiple pores.

2. The porous block of silicon carbide doped with rare earth elements according to claim 1, characterized in that: The shape of the silicon carbide block is at least one of spherical, cylindrical, and square, the size of the silicon carbide block is 0.1-1 cm, and the pore size distribution of the silicon carbide block is 10-200 μm.

3. The porous block of silicon carbide doped with rare earth elements according to claim 2, characterized in that: The average value of the particles of the rare earth compound is less than or equal to the minimum value of the pore size of the silicon carbide block.

4. The porous silicon carbide block doped with rare earth elements according to claim 1, characterized in that: The rare earth compound is at least one of rare earth silicide, rare earth carbide, and rare earth oxide.

5. The porous block of silicon carbide doped with rare earth elements according to claim 1, characterized in that: The rare earth element in the rare earth compound is selected from at least one of lanthanide elements, scandium and yttrium; and the lanthanide element is selected from at least one of cerium, lanthanum, praseodymium and neodymium.

6. The method for preparing a porous block of silicon carbide doped with rare earth elements according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: dividing the silicon carbide raw material to obtain silicon carbide blocks; S2: adding rare earth compound powder to the silicon carbide block, mixing and shaking, so that the rare earth compound enters the pores of the silicon carbide block to obtain an intermediate; S3: depositing a silicon carbide film on the surface of the intermediate by CVD to obtain a porous silicon carbide block doped with rare earth elements.

7. The method for preparing a porous block of silicon carbide doped with rare earth elements according to claim 6, characterized in that: In step S2, the amount of rare earth compound added is 0.01-0.5 g / g; the oscillation frequency is 10-100 Hz, and the oscillation time is 10 min-1 h.

8. The method for preparing a porous block of silicon carbide doped with rare earth elements according to claim 6, wherein: In step S3, the temperature during the CVD deposition process is 1000-1400° C., and the time is 5-50 hours.

9. Use of a porous silicon carbide block doped with a rare earth element according to any one of claims 1 to 5, characterized in that: Application of porous silicon carbide blocks doped with rare earth elements in the preparation of silicon carbide crystal materials.

10. The use of a porous silicon carbide block doped with rare earth elements according to claim 9, characterized in that: The silicon carbide porous material block doped with rare earth elements and silicon carbide powder are mixed to obtain a mixed material, and the mixed material is subjected to crystal growth to obtain a silicon carbide crystal material.

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