Crystal growth apparatus for growing p-type silicon carbide substrate, method for growing p-type silicon carbide substrate, and p-type silicon carbide substrate

Abstract

The invention discloses a crystal growth device for growing a P-type silicon carbide substrate, a method for growing the P-type silicon carbide substrate and the P-type silicon carbide substrate. The crystal growth device used for growing the P-type silicon carbide substrate comprises a crucible, wherein the crucible comprises a main body and a cover body; the hollow cylinder base is positioned in the crucible and is used for placing a first P-type silicon carbide raw material; the shelf is located on the hollow cylinder base and used for placing a second P-type silicon carbide raw material, and the diameter of the shelf is larger than the outer diameter of the hollow cylinder base; the heating piece is located on the outer side of the crucible, and the heating piece can move in the direction, pointing to the hollow cylinder base, of the cover body. The hollow cylinder base and the shelf can be used for placing raw materials with different sizes, the heating piece can move up and down, a high-temperature line of the heating piece is aligned with a raw material area on the shelf in the early growth stage, and the raw materials in the hollow cylinder base can continuously provide an aluminum source after growing silicon carbide for a period of time in the later growth stage. And the later aluminum doping concentration is ensured.

Description

Technical Field

[0001] This application relates to the field of silicon carbide substrate preparation technology, specifically to a crystal growth apparatus for growing P-type silicon carbide substrates, a method for growing P-type silicon carbide substrates, and P-type silicon carbide substrates. Background Technology

[0002] Silicon carbide (SiC) possesses excellent physical properties, particularly its high critical electric field and high thermal conductivity, making it one of the most attractive materials for power devices. SiC exhibits a high critical breakdown electric field, which significantly increases the breakdown voltage of power semiconductor devices. At the same doping concentration, the breakdown voltages of 6H-SiC and 4H-SiC are 56 times and 46 times higher than those of silicon, respectively. This increased breakdown voltage allows for a substantial increase in the output power of SiC-based devices. SiC-based power IGBTs (Insulated Gate Bipolar Transistors) exhibit low conduction losses, moderate switching times, and good high-temperature performance, capable of withstanding voltages above 10kV. SiC-based power IGBTs will play a crucial role in future switching devices. However, currently commercially available P-type SiC single crystals suffer from poor crystal quality and high resistivity (approximately 2.5 Ω·cm), which limits the development of N-channel SiC IGBTs.

[0003] Currently, the high resistivity of p-type silicon carbide substrates is mainly due to the difficulty of Al doping. On the one hand, in the traditional PVT (physical vapor transport) growth method, Al-containing composite dopants are placed in the SiC powder region. Under the conditions required for SiC growth, the high saturated vapor pressure of the Al component leads to excessive release of the Al source in the early stages of crystal growth. This results in extremely uneven Al doping concentration in the crystal, making it difficult to achieve continuous and stable p-type doping. On the other hand, during the PVT growth of p-type SiC crystals, due to the excessive release of Al in the initial stage, a high concentration of Al appears at the growth front, severely affecting the crystal quality and leading to a high defect density. The inability to obtain a stable and continuous Al source supply during crystal growth is the fundamental reason limiting the development of p-type substrates.

[0004] Therefore, the crystal growth apparatus, methods for growing P-type silicon carbide substrates, and P-type silicon carbide substrates themselves still need improvement. Summary of the Invention

[0005] This application is based on the inventor's discoveries and understanding of the following facts and problems: Silicon carbide crystals grow at temperatures above 2000℃. At this temperature, the partial pressure of Al is significantly higher than that of silicon and carbon gases. The high initial aluminum concentration in the gas phase leads to defect formation and the nucleation of misaligned grains. Furthermore, as the growth time increases, the aluminum source is depleted, resulting in a strong exponential decrease in dopant incorporation. If the aluminum source is stored in a cooler region of the growth apparatus for P-type substrate growth, silicon and carbon gases migrate in large quantities from the hot powder region to the cooler reservoir. The sublimated silicon carbide material then deposits in the lower-temperature region, directly destroying the Al source stored in this manner.

[0006] This application improves the crystal growth apparatus by setting two feed zones in the crucible, which can hold raw materials with different particle sizes. The raw material in one feed zone is initially used to grow silicon carbide. After the silicon carbide has grown for a period of time, the raw material in the other feed zone can be used as an aluminum source to continue supplying aluminum, ensuring a continuous supply of aluminum throughout the entire growth stage. The distances between the two feed zones and the seed crystal differ. During the fabrication process, the heating element can be moved to allow raw materials from different regions to participate in the growth of silicon carbide, improving the uniformity of aluminum doping during the growth of the P-type silicon carbide substrate.

[0007] This application aims to at least partially alleviate or resolve at least one of the aforementioned problems.

[0008] In one aspect of this application, a crystal growth apparatus for growing p-type silicon carbide substrates is provided. In some embodiments of this application, the crystal growth apparatus for growing p-type silicon carbide substrates includes: a crucible comprising a body and a cover, the body having an internal cavity; a hollow cylindrical base located within the crucible for holding a first p-type silicon carbide raw material; a shelf located within the crucible and on the hollow cylindrical base for holding a second p-type silicon carbide raw material, the shelf having a diameter larger than the outer diameter of the hollow cylindrical base; and a heating element located outside the crucible, movable along the cover towards the hollow cylindrical base. The hollow cylindrical base and the shelf can hold raw materials with different dimensions. The heating element can move vertically; in the early stages of growth, the high-temperature line of the heating element is aligned with the raw material area on the shelf; in the later stages of growth, the raw material in the hollow cylindrical base can continuously provide an aluminum source after silicon carbide growth for a period of time, ensuring the aluminum doping concentration in the later stages. The space between the main body, the hollow column base, and the shelf is isolated from the internal space of the hollow column base, which can at least to some extent prevent the sublimated raw materials from entering the interior of the hollow column base, reducing or even avoiding damage to the raw materials inside the base.

[0009] In some embodiments of this application, the height of the main body is 250mm-350mm, and / or the height of the internal cavity is 230mm-340mm. This provides accommodating space for the hollow column base and shelf, and provides two material zones for placing raw materials.

[0010] In some embodiments of this application, the body satisfies at least one of the following conditions: the wall thickness of the body is 10mm-20mm; the bottom thickness of the body is 10mm-20mm; and the inner diameter of the body is 160mm-220mm. Thus, the body possesses a certain strength, making it suitable for silicon carbide preparation via the PVT method; the body also provides appropriately sized accommodating and growth spaces.

[0011] In some embodiments of this application, the hollow column base satisfies at least one of the following conditions: the height of the hollow column base is 60mm-90mm; the inner diameter of the hollow column base is 60mm-80mm; the wall thickness of the hollow column base is 3mm-5mm; and the hollow column base is a graphite component. Therefore, the hollow column base can be used to support shelves, place silicon carbide raw materials, and protect the raw materials within the hollow column base.

[0012] In some embodiments of this application, the crystal growth device satisfies at least one of the following conditions: the thickness of the shelf is 10mm-15mm; the shelf is a graphite element; the heating element includes an induction coil; a protective element is provided between the heating element and the crucible, the protective element having a receiving space for holding the cooling medium.

[0013] In some embodiments of this application, the inner diameter of the induction coil is 1.4-2 times the outer diameter of the body; and / or, the height of the induction coil is greater than the height of the body, and the difference between the height of the induction coil and the height of the body is 0.3-0.5 times the inner diameter of the induction coil.

[0014] In another aspect of this application, a method for growing a p-type silicon carbide substrate using physical vapor transport is proposed. The method utilizes the aforementioned crystal growth apparatus to grow the p-type silicon carbide substrate, comprising: placing the hollow cylindrical base within the internal cavity of the main body; placing the first p-type silicon carbide raw material within the hollow cylindrical base; placing the shelf on the hollow cylindrical base; placing the second p-type silicon carbide raw material on the shelf, wherein the particle size of the second p-type silicon carbide raw material is smaller than the particle size of the first p-type silicon carbide raw material; covering the main body with the cover; and setting a silicon carbide seed crystal. The heating element is placed on the side of the cover near the main body. A P-type silicon carbide substrate is grown on the silicon carbide seed crystal for a growth time of t1. During the early growth stage, the height center of the heating element is located on the side of the shelf away from the hollow cylindrical base, and the height difference between the height center of the heating element and the shelf is 25mm-55mm. After the first growth time, the heating element is moved 10mm-30mm along the direction from the cover towards the hollow cylindrical base. The first time is 0.3t1 to 0.6t1, and the moving speed is 0.15mm / hour-0.22mm / hour. Thus, in the early growth stage, the high-temperature line of the heating element is aligned with the raw material area on the shelf, causing the raw material on the shelf to sublimate and rise to the seed crystal for silicon carbide growth. In the later growth stage, the heating element is moved downward, and the high-temperature line of the heating element also moves downward accordingly, increasing the sublimation rate of the first P-type silicon carbide raw material and continuously supplying aluminum, thereby helping to ensure the aluminum doping concentration in the substrate.

[0015] In some embodiments of this application, the particle size of the first P-type silicon carbide raw material is 6 mm-10 mm, and / or the particle size of the second P-type silicon carbide raw material is 1 mm-4 mm. This is beneficial for improving the growth and doping of the P-type silicon carbide substrate, thereby facilitating the acquisition of a P-type silicon carbide substrate with lower resistivity and higher quality.

[0016] In some embodiments of this application, the method of growing a P-type silicon carbide substrate using physical vapor transport satisfies at least one of the following conditions: the temperature for growing the P-type silicon carbide substrate is 2100℃-2200℃; the pressure for growing the P-type silicon carbide substrate is 3 Torr-10 Torr; and the growth time is 100 hours to 140 hours.

[0017] In another aspect of this application, a p-type silicon carbide substrate is proposed. In some embodiments of this application, the p-type silicon carbide substrate is prepared using the methods described above. Therefore, the p-type silicon carbide substrate has lower resistivity and higher quality. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 A schematic diagram of a crystal growth apparatus according to an embodiment of this application is shown; Figure 2 A schematic diagram of the structure of a heating element according to an embodiment of this application is shown; Figure 3 The image shown is of the first P-type silicon carbide raw material in Embodiment 1 of this application; Figure 4 This shows the main body, the hollow cylindrical base, and the silicon carbide deposited to the bottom of the crucible in Embodiment 1 of this application; Figure 5 The resistivity of the substrate slice and the distance between the slice and the seed crystal are shown in Example 1 (sample A) and Comparative Example 1 (sample B); Figure 6 The apparatus and products for preparing P-type silicon carbide crystals using CVD in Example 1 are shown.

[0019] Explanation of reference numerals in the attached figures: 100: Crucible; 110: Main body; 111: Internal cavity; 120: Cover; 121: Lower surface of the cover; 200: Hollow cylindrical base; 300: Shelf; 400: Heating element. Detailed Implementation

[0020] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0021] In one aspect of this application, a crystal growth apparatus for growing p-type silicon carbide substrates is provided. In some embodiments of this application, reference is made to... Figure 1 The crystal growth apparatus for growing P-type silicon carbide substrates includes a crucible 100, a hollow cylindrical base 200, a shelf 300, and a heating element 400.

[0022] refer to Figure 1The crucible 100 includes a body 110 and a cover 120. The body 110 has an internal cavity 111 that can accommodate the hollow cylindrical base 200, the shelf 300, and the silicon carbide raw material, and provide growth space for the silicon carbide substrate. A silicon carbide seed crystal can be fixed on the lower surface 121 of the cover, for example, the silicon carbide seed crystal can be bonded to the lower surface of the cover. The hollow cylindrical base 200 is located inside the crucible 100 and is used to place the first P-type silicon carbide raw material. The shelf 300 is located inside the crucible 100 and on the hollow cylindrical base 200, and is used to place the second P-type silicon carbide raw material. The diameter of the shelf 300 is larger than the outer diameter of the hollow cylindrical base 200. Therefore, a receiving space can be formed between the outer periphery of the hollow cylindrical base, the shelf, and the crucible. This receiving space is isolated from the internal space of the hollow cylindrical base and is used to accommodate the silicon carbide deposited at the bottom of the crucible, which can reduce or even avoid damage to the raw materials in the hollow cylindrical base caused by this silicon carbide. The heating element 400 is located outside the crucible 100, and the heating element 400 can be positioned along the cover 120 in a direction pointing towards the hollow cylindrical base 200 (e.g., Figure 1 The heating element can be moved downwards (as shown in the X direction) after a period of growth, so that the high temperature line of the heating element moves downwards. The first P-type silicon carbide raw material in the hollow column base continuously provides aluminum elements, so that there is an aluminum source supply throughout the growth process, which is beneficial to improve the doping concentration and quality of the P-type silicon carbide substrate.

[0023] In some embodiments of this application, the crucible may be a cylindrical crucible.

[0024] In some embodiments of this application, reference is made to Figure 1 The height H of the main body 110 can be 250mm-350mm. For example, the height H of the main body 110 can be 250mm, 270mm, 300mm, 320mm, 350mm, etc. The height of the main body is within the above range, which facilitates the setting of two material areas.

[0025] In some embodiments of this application, reference is made to Figure 1 The height H1 of the internal cavity 111 can be 230mm-340mm, for example, 230mm, 250mm, 280mm, 300mm, 320mm, 340mm, etc. The height of the internal cavity within the above range can provide sufficient space for the growth of the hollow column base, shelf, raw materials and substrate.

[0026] In some embodiments of this application, reference is made to Figure 1 The wall thickness W1 of the main body 110 can be 10mm-20mm. For example, the wall thickness W1 of the main body can be 10mm, 12mm, 15mm, 17mm, 20mm, etc.

[0027] In some embodiments of this application, reference is made to Figure 1 The bottom thickness W2 of the main body 110 can be 10mm-20mm. For example, the bottom thickness W2 of the main body 110 can be 10mm, 13mm, 15mm, 18mm, 20mm, etc.

[0028] The wall thickness and bottom thickness of the main body meet the above conditions, and the main body has high strength and can play a good supporting role.

[0029] In some embodiments of this application, reference is made to Figure 1 The inner diameter D1 of the main body can be 160mm-220mm, for example, 160mm, 180mm, 200mm, 220mm, etc. An inner diameter within this range provides ample space for placing raw materials and growing the substrate, which is beneficial for substrate growth.

[0030] In some embodiments of this application, the crucible can be a graphite crucible, and both the body and the lid are made of graphite.

[0031] In some embodiments of this application, reference is made to Figure 1 The height h of the hollow column base 200 can be 60mm-90mm, for example, it can be 60mm, 65mm, 70mm, 75mm, 80mm, 85mm, 90mm, etc. This provides suitable height space for the first P-type silicon carbide raw material, which is beneficial for the supply of aluminum source in the later stages of growth.

[0032] In some embodiments of this application, the hollow cylindrical base 200 may be a hollow cylindrical base.

[0033] In some embodiments of this application, reference is made to Figure 1 The inner diameter d1 of the hollow column base 200 can be 60mm-80mm. For example, the inner diameter d1 of the hollow column base 200 can be 60mm, 65mm, 70mm, 75mm, 80mm, etc. Within the above range, a larger amount of first P-type silicon carbide raw material can be placed in the hollow column base, providing sufficient aluminum source for the later stages of growth.

[0034] In some embodiments of this application, reference is made to Figure 1 The wall thickness W3 of the hollow column base 200 can be 3mm-5mm. For example, the wall thickness W3 of the hollow column base 200 can be 3mm, 3.5mm, 4mm, 4.5mm, 5mm, etc. Bases with the above thicknesses have a certain strength and are not easily damaged during use.

[0035] In some embodiments of this application, the hollow cylindrical base 200 can be a graphite component.

[0036] In some embodiments of this application, reference is made to Figure 1 The thickness W4 of the shelf 300 can be 10mm-15mm, for example, the thickness W4 of the shelf 300 can be 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, etc. Therefore, the shelf can play a supporting role, and a larger amount of silicon carbide can be placed on the shelf.

[0037] In some embodiments of this application, the shelf 300 may be a graphite element. In some embodiments, silicon carbide raw materials with a height of 80mm-100mm may be placed on the shelf 300.

[0038] In some embodiments of this application, reference is made to Figure 1 and Figure 2 The heating element 400 may include an induction coil. The induction coil heats the crucible through an electromagnetic field, which has high energy transfer efficiency, and the temperature field can be controlled by adjusting the current frequency and power.

[0039] In some embodiments of this application, reference is made to Figure 1 and Figure 2 The inner diameter D3 of the induction coil can be 1.4-2 times the outer diameter D2 of the main body 110. Therefore, the space between the induction coil and the crucible can accommodate protective components and other parts.

[0040] In some embodiments of this application, reference is made to Figure 1 and Figure 2 The height L of the induction coil is greater than the height H of the main body 110, and the difference between the height L of the induction coil and the height H of the main body is 0.3-0.5 times the inner diameter D3 of the induction coil. Therefore, the size of the induction coil matches the size of the crucible well.

[0041] In some embodiments of this application, the number of turns of the induction coil can be 12. Of course, the number of turns of the induction coil can be adjusted according to actual needs.

[0042] In some embodiments of this application, reference is made to Figure 1 A protective element is provided between the heating element 400 and the crucible 100. Figure 1 (Not shown in the image), the protective element has a receiving space for holding the cooling medium. In some specific embodiments, the protective element can be a double-layered quartz cavity, and the cooling medium (e.g., cooling water) can be placed inside the double walls of the quartz cavity. The cooling medium can circulate, providing over-temperature protection.

[0043] The parameter design process of each component of the crystal growth device in one embodiment of this application is described in detail below: Based on the analysis of the 6-inch silicon carbide crystal growth furnace structure, considering the assembly, growth environment and ingot removal operations, the inner diameter D1 of the crucible body is ≥185mm. In this embodiment, the inner diameter D1 of the crucible body is 200mm.

[0044] Based on the frequency range F of the intermediate frequency induction power supply (commonly 8-10kHz) and the conductivity of the graphite crucible, the skin effect depth Δ of the induced current in the crucible wall is calculated. The wall thickness W1 of the crucible body is greater than or equal to Δ. The wall thickness of the crucible body is determined by the penetration depth of the skin effect current, thus allowing the determination of the outer diameter D2 of the crucible body. The outer diameter D2 of the graphite crucible body and the skin effect depth Δ satisfy the following relationship: D2 = D1 + 2 × W1 ≥ D1 + 2 × Δ.

[0045] Based on the fundamental theory of electromagnetic fields, the formula for calculating the current penetration depth Δ is:

[0046] Where ρ is the average resistivity of the graphite crucible, in Ω·m; ω is the angular frequency, equal to 2πF, in rad / s; and μ0 is the free permeability, with a value of 4π×10⁻⁶. -7 The unit is H / m; μ r is the relative permeability of the graphite crucible, in H / m; F is the current frequency, in Hz (typically used in the range of 8-12 kHz).

[0047] Considering the characteristics of using thermal insulation felt, a lower frequency is required. In this embodiment, the frequency F=8KHZ is selected, and Δ=14.65mm can be obtained from the above formula.

[0048] In this embodiment, the wall thickness of the crucible body is taken as 15mm, thus the outer diameter D2 of the crucible body is 230mm. Let D be the average diameter of the crucible body (the average of the sum of the outer and inner diameters), D = 215mm. Based on design experience, the relationship between the average diameter D of the graphite crucible body and the height H of the crucible body is:

[0049] The proportionality coefficient Y ranges from 1.2 to 1.5. Given that D = 215 mm, the height H of the crucible body can be calculated to be 258-322.5 mm. Considering the need to set up two material zones, the height H of the crucible body is set to 300 mm.

[0050] Material storage area design: In the industry, the material height in the raw material area is generally set at 70-90mm. Considering the large-particle raw materials, this application sets the material height above the shelf to 90mm. In terms of height, the shelf, the raw material area above it, and the seed crystal occupy 2 / 3 of the crucible body. The bottom thickness of the crucible body is 10mm, with the remaining 100mm space at the bottom serving as a storage area for the Al source. The height h of the base and the average diameter d (the average of the sum of the outer and inner diameters of the base) satisfy the following relationship:

[0051] With a shelf thickness of 10mm, a remaining space height of 90mm, and a base height h of 90mm, the average base diameter range is 60-75mm. Considering the larger gaps between large particles, the average diameter of the loading space is designed to be d=75mm, and the base wall thickness is designed to be 3mm. This results in an outer diameter of 78mm and an inner diameter d1 of 72mm for the base.

[0052] Design of the induction coil: Since the crucible needs to be set with upper and lower material zones, the high-temperature line needs to be moved up and down by the lifting motion of the induction coil during the growth process. Therefore, the parameters of the induction coil must also be designed to match the process.

[0053] There is a double-layered quartz cavity between the induction coil and the graphite crucible. Cooling water circulates within the double walls of the quartz cavity as over-temperature protection. The inner diameter D3 of the induction coil can be determined by the following formula:

[0054] Since D2 = 230 mm, the range of D3 is 322-460 mm. Considering the soft and hard insulation components between the outer side of the crucible and the quartz cavity, D3 is taken as 333 mm in this application.

[0055] The height L of the induction coil can be determined by the following formula: L = H + D3 × (0.3 ~ 0.5).

[0056] The height H of the crucible body is 300mm, so the value range of the height L of the induction coil is 400-466.5mm. Considering the overall height of the equipment and the height of the quartz cavity, the value of L in this embodiment is 446mm.

[0057] Based on relevant literature and market induction furnace designs, the number of turns of the induction coil is designed to be 12 turns.

[0058] In another aspect of this application, a method for growing a P-type silicon carbide substrate using physical vapor transport (PVT) is proposed, utilizing the aforementioned crystal growth apparatus. In some embodiments, the method for growing a P-type silicon carbide substrate using PVT may include the following steps: S10: Place the hollow column base 200 inside the cavity 111 of the main body 110, and place the first P-type silicon carbide raw material inside the hollow column base 200.

[0059] In some embodiments of this application, the inner wall and bottom of the main body need to be lined with graphite paper, and the thickness of the graphite paper can be 0.3mm-1mm.

[0060] In some specific embodiments, the hollow cylindrical base 200 can be placed at the center of the bottom of the main body, which helps to maintain the overall balance of the crucible.

[0061] S20: Place shelf 300 on hollow column base 200, and place the second P-type silicon carbide raw material on shelf 300.

[0062] In some embodiments of this application, graphite paper is laid on shelf 300 before placing the second P-type silicon carbide raw material.

[0063] In this application, the particle size of the second P-type silicon carbide raw material is smaller than that of the first P-type silicon carbide raw material.

[0064] In some embodiments of this application, the doping elements in the first P-type silicon carbide raw material and the second P-type silicon carbide raw material include aluminum.

[0065] In some embodiments of this application, the particle size of the first P-type silicon carbide raw material can be 6mm-10mm, for example, the particle size of the first P-type silicon carbide raw material can be 6mm, 7mm, 8mm, 9mm, 10mm, etc. The larger particle size of the above-mentioned raw material results in slower component evaporation during growth, leading to a more uniform gas phase composition. This allows for a continuous supply of aluminum in the later stages of growth, which is beneficial for uniform aluminum doping in silicon carbide, thereby contributing to the formation of a substrate with uniform doping concentration, high doping concentration, and low resistivity. In some embodiments, reference... Figure 3 The surface of the first type P silicon carbide raw material is silver-gray.

[0066] In some embodiments, the first P-type silicon carbide raw material can be synthesized by CVD and then crushed to form particles of the desired particle size. The CVD-synthesized P-type silicon carbide raw material locks the Al component into the molecular structure, resulting in more stable and uniform Al elements. Growing a P-type silicon carbide substrate using this raw material can at least partially avoid the problem of N and Al co-doping and suppress stacking fault defects.

[0067] right Figure 3The P-type silicon carbide raw material was subjected to EDS and XPS tests. The test results showed that the Al content in the P-type silicon carbide raw material was 0.23% by mass. The raw material was determined to be a high-purity material with a purity ≥ 99.99995%. Furthermore, the nitrogen content of the obtained silicon carbide raw material was tested using secondary ion mass spectrometry (SIMS), and the N content was found to be ≤ 3E15 atoms / cm³. 3 (Detection limits for the secondary ion mass spectrometer: 5E14 atoms / cm) 3 ).

[0068] In some embodiments of this application, the particle size of the second P-type silicon carbide raw material is 1mm-4mm. For example, the particle size of the second P-type silicon carbide raw material can be 1mm, 2mm, 3mm, 4mm, etc. The raw material with the above particle size can be evaporated to the seed crystal at a relatively fast rate in the early stage of growth to grow the silicon carbide substrate.

[0069] In some embodiments of this application, the second P-type silicon carbide raw material can also be synthesized by CVD and then crushed to form particles of the desired particle size.

[0070] In some embodiments, a second P-type silicon carbide material with a height of 80mm-100mm can be placed on the shelf 300 for growing a P-type silicon carbide substrate.

[0071] In some specific embodiments, the synthesis of P-type silicon carbide raw materials by CVD may include the following steps: introducing an aluminum precursor, a first carrier gas, a silicon precursor, a second carrier gas, a first gas, and argon into a reaction chamber, wherein the aluminum precursor is carried into the reaction chamber by the first carrier gas, the silicon precursor is carried into the reaction chamber by the second carrier gas, and the first gas includes hydrogen; performing a first heat treatment to generate P-type silicon carbide crystals.

[0072] In some embodiments of this application, the aluminum precursor may include trimethylaluminum (TMAl, chemical formula (CH3)3Al), which can provide aluminum to dope silicon carbide to form P-type silicon carbide crystals.

[0073] In some embodiments, the first carrier gas may include hydrogen. The first carrier gas can carry the aluminum precursor into the reaction chamber and can promote the uniform distribution of the aluminum precursor in the reaction chamber.

[0074] In some embodiments of this application, the flow rates of the aluminum precursor and the first carrier gas can be 3 L / min to 6 L / min. For example, the flow rates of the aluminum precursor and the first carrier gas can be 3 L / min, 4 L / min, 5 L / min, 6 L / min, etc. Having the flow rates of the aluminum precursor and the first carrier gas within the above range is beneficial for increasing the aluminum doping concentration.

[0075] In some embodiments of this application, the silicon precursor may include one or more of methyltrichlorosilane (MTS, chemical formula CH3Cl3Si) and silane. All of the above materials can provide silicon, providing the material basis for the formation of silicon carbide.

[0076] In some embodiments of this application, the second carrier gas may include hydrogen. The second carrier gas can carry the silicon precursor into the reaction chamber and can promote the uniform distribution of the silicon precursor in the reaction chamber.

[0077] In some embodiments of this application, the flow rates of the silicon precursor and the second carrier gas can be 12 L / min to 15 L / min, for example, 12 L / min, 13 L / min, 14 L / min, 15 L / min, etc. Flow rates of the silicon precursor and the second carrier gas within the above range are beneficial for controlling the deposition rate of silicon carbide, which not only improves the utilization rate of raw materials but also allows the deposition time to be controlled within a more reasonable range.

[0078] In some embodiments of this application, trimethylaluminum (purity 99.99995%) and methyltrichlorosilane (purity 99.99%) are both gases. Before entering the chamber for reaction, they can pass through a purifier, resulting in higher purity and more controllable aluminum and silicon precursors.

[0079] By introducing an Al atmosphere and chemically bonding Al, a 3C-SiCβ phase structure is synthesized. The Al component is less likely to volatilize prematurely, the single crystal is more stable, has a high density, and no internal cavities, which can at least to some extent avoid the introduction of impurities.

[0080] In some embodiments of this application, the first gas may include hydrogen, which may participate in the reaction to promote the formation of silicon carbide.

[0081] In some embodiments of this application, the flow rate of the first gas (e.g., hydrogen) can be 150 L / min to 180 L / min, for example, the flow rate of the first gas (e.g., hydrogen) can be 150 L / min, 160 L / min, 170 L / min, 180 L / min, etc., and the flow rate of argon can be 10 L / min to 20 L / min, for example, the flow rate of argon can be 10 L / min, 12 L / min, 15 L / min, 17 L / min, 20 L / min, etc. Adjusting the ratio of the first gas and argon can control the deposition rate of silicon carbide, thereby improving the quality of P-type silicon carbide raw materials.

[0082] In some embodiments of this application, the temperature of the first heat treatment can be 1200℃-1500℃, for example, 1300℃, 1320℃, 1350℃, 1370℃, 1400℃, 1430℃, 1450℃, etc. This allows the aluminum precursor and silicon precursor to undergo a series of reactions to generate aluminum-doped silicon carbide crystals.

[0083] In some embodiments of this application, the first heat treatment time can be 30h-70h, for example, 30h, 40h, 50h, 60h, 70h, etc. This allows for the growth of a thicker layer of silicon carbide, which is beneficial for increasing the size of the particles after crushing.

[0084] In some embodiments of this application, during the first heat treatment, the pressure in the reaction chamber is 130-150 Torr, for example, the pressure in the reaction chamber can be 130 Torr, 135 Torr, 140 Torr, 145 Torr, or 150 Torr. Lower pressure in the reaction chamber is beneficial for further reducing impurities in the product and for further improving the overall uniformity of the product.

[0085] In some embodiments of this application, the generated P-type silicon carbide crystals are crushed, and the raw materials with the required particle size can be screened using a sieve. The silicon carbide obtained by CVD deposition is a large-size product. In some embodiments, the large surface area of ​​the silicon carbide can be 50mm × 50mm, and in other embodiments, the large surface area of ​​the silicon carbide can be 1m × 1m. By crushing, particles of the required size can be obtained.

[0086] S30: Cover the main body 110 with the cover 120.

[0087] The silicon carbide seed crystal is disposed on the side of the cover 120 near the main body 110. In some embodiments, the silicon carbide seed crystal can be glued to the lower surface 121 of the cover. In other embodiments, the silicon carbide seed crystal can also be detachably fixed to the cover 120 by other means.

[0088] S40: A P-type silicon carbide substrate is grown on a silicon carbide seed crystal.

[0089] The growth time of the P-type silicon carbide substrate is t1. In the early stage of growth, the height center of the heating element 400 is located on the side of the shelf 300 away from the hollow column base 200. The height difference between the height center of the heating element 400 and the shelf 300 can be 25mm-55mm. After the first growth time, the heating element 400 is oriented along the cover 120 towards the hollow column base 200. Figure 1(In the X direction shown) move 10mm-30mm, with the first time being 0.3t1 to 0.6t1, and the moving speed being 0.15 mm / h-0.22 mm / h.

[0090] In some embodiments, during the early stages of growth, the height difference between the center of the heating element 400 and the shelf 300 can be 25mm, 30mm, 40mm, 50mm, 55mm, etc. This allows the high-temperature lines of the heating element to be aligned with the raw material area on the shelf, promoting the sublimation of the raw material on the shelf.

[0091] In some embodiments, after the first growth time, the heating element 400 is moved 10mm, 15mm, 20mm, 25mm or 30mm along the X direction, so that the high temperature line of the heating element moves toward the hollow column base to heat the first P-type silicon carbide raw material (aluminum source). Since the large particles have a slower sublimation rate, the Al source supply can be maintained for a longer time to ensure the Al doping concentration in the later stage.

[0092] The graphite crucible, base, and shelf are all made of graphite, which is a porous material. The Al source atmosphere will penetrate the graphite crucible and move with the direction of the thermal field. Moreover, there are tolerance gaps between each graphite component, and the Al source atmosphere will move through the tolerance gaps and graphite pores.

[0093] In some embodiments, the moving rate of the heating element 400 is 0.15 mm / h to 0.22 mm / h.

[0094] In some embodiments, the temperature for growing a P-type silicon carbide substrate can be 2100℃-2200℃, for example, 2100℃, 2120℃, 2150℃, 2170℃, 2200℃, etc. Growing a P-type silicon carbide substrate at the above temperatures is beneficial for the sublimation of the raw material onto the seed crystal and for the growth of the substrate.

[0095] In some embodiments, the pressure for growing a P-type silicon carbide substrate can be 3-10 Torr. Therefore, growing a P-type silicon carbide substrate under the above pressure can reduce the introduction of impurities in the gas phase, reduce the defect density of the substrate, and facilitate obtaining a P-type silicon carbide substrate with higher purity.

[0096] In some embodiments, the growth time of the P-type silicon carbide substrate can be from 100 hours to 140 hours. Under these growth times, a P-type silicon carbide substrate of suitable thickness can be formed, and after dicing, a P-type silicon carbide substrate sheet of suitable size can be obtained.

[0097] In this application, during the initial growth of silicon carbide crystals, a high-temperature wire heats and sublimates the second P-type silicon carbide raw material region. The temperature of the space below the shelf is lower than that of the second P-type silicon carbide raw material region. Using an infrared thermometer pointed at the top and bottom center of the crucible, the bottom temperature is 120°C-180°C lower than the top temperature. Due to the lower temperature in the lower region, some of the sublimated raw material is deposited downwards through the gap between the shelf and the crucible body, ultimately depositing around the hollow cylindrical base. No silicon carbide atmosphere enters the base, thus preventing damage to the Al source. While the graphite crucible wall conducts heat, heating the entire graphite crucible thermal field, the graphite paper at the bottom of the crucible provides insulation, keeping the bottom temperature low and attracting silicon carbide atmosphere deposition. Because the base is in direct contact with the shelf, the shelf receives heat from the crucible wall and conducts it to the base, resulting in a base temperature and interior temperature that is much higher than the outer periphery. Therefore, the silicon carbide atmosphere is deposited only around the outer periphery of the base, at the bottom of the crucible. The hollow cylindrical base structure for storing Al sources perfectly utilizes the thermal conductivity of graphite components and the thermal insulation effect of graphite paper to protect the Al source in the low-temperature region.

[0098] In another aspect, this application proposes a P-type silicon carbide substrate prepared using the method described above. Consequently, this P-type silicon carbide substrate exhibits uniform aluminum doping with a high doping concentration and low resistivity.

[0099] In some embodiments, the P-type silicon carbide substrate can be used in high-voltage IGBT devices, promoting the commercial application of P-type silicon carbide substrates.

[0100] The present application will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the present application in any way. Furthermore, in the following embodiments, unless otherwise specified, the materials and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0101] Example 1 Structural reference of the crystal growth device in Example 1 Figure 1 The crystal growth apparatus includes a crucible 100, a hollow cylindrical base 200, a shelf 300, and a heating element 400 (induction coil). The crucible 100 includes a main body 110 and a cover 120. The main body 110 has an internal cavity 111. The inner diameter D1 of the main body 110 is 200 mm, the wall thickness W1 is 15 mm, the outer diameter D2 is 230 mm, the height H of the main body 110 is 300 mm, and the bottom thickness W2 of the main body is 10 mm.

[0102] The hollow column base 200 has a height h of 90mm, an inner diameter d1 of 72mm, and a wall thickness W3 of 3mm. The base contains a first type P-type silicon carbide raw material (such as...). Figure 3 As shown, the surface of the raw material is silver-gray, serving as an aluminum source.

[0103] The thickness W4 of shelf 300 is 10mm. A second P-type silicon carbide raw material with a particle size of 1-4mm and a height of 90mm is placed on the shelf.

[0104] The first and second P-type silicon carbide raw materials were prepared by CVD method. The specific preparation steps are as follows: Trimethylaluminum (TMAl), a first carrier gas (H2), methyltrichlorosilane (MTS), a second carrier gas (H2), a first gas (H2), and argon (Ar) were introduced into the reaction chamber. TMAl was carried into the reaction chamber by the first carrier gas, and MTS was carried into the reaction chamber by the second carrier gas. The flow rates of MTS and the second carrier gas (H2) were 15 L / min, the flow rate of the first gas (H2) was 170 L / min, the flow rate of Ar was 18 L / min, and the flow rates of TMAl and the first carrier gas were 4 L / min. Deposition was completed for 35 hours at a temperature of 1300 °C and a pressure of 130 Torr. The weight of the product obtained after furnace tapping was approximately 40 kg.

[0105] P-type silicon carbide raw materials are produced by chemically bonding Al atoms with SiC using CVD (chemical vapor deposition) to form a new substance, Al-SiC. This chemical bonding effectively locks in the Al atoms, solving the problem of preferential Al volatilization. Traditional P-type growth experiments use mixed Al compounds (such as AlN+SiC) to grow crystals through physical particle mixing. This results in inconsistent mixing uniformity and fails to address the preferential Al volatilization issue, preventing Al from participating in the growth reaction simultaneously with SiC.

[0106] refer to Figure 6 The product is prepared using a CVD (chemical vapor deposition) furnace. Two high-purity gases, TMAl and MTS, are introduced into the equipment through a purifier, along with two high-purity gases, hydrogen and argon. The product is deposited on a stone-milled electrode rod using chemical vapor deposition. The output is a columnar solid Al-SiC with a certain height and diameter. One furnace can produce tens of kilograms or even more.

[0107] The P-type silicon carbide crystal raw materials obtained from growth are crushed, cleaned, and dried. The first and second P-type silicon carbide raw materials with the required particle size are screened using a sieve.

[0108] A silicon carbide seed crystal was bonded to the cover, and the carbon surface of the silicon carbide seed crystal was used to grow the substrate. A P-type silicon carbide substrate was grown at 2100℃ and 5 Torr pressure for 120 hours. During the initial growth phase, the height center of the induction coil was located above the shelf, and the distance between the height center of the induction coil and the upper surface of the shelf was 25 mm. After 70 hours of growth, the induction coil was moved along the cover towards the hollow cylindrical base at a speed of 0.2 mm / h, covering a distance of 10 mm.

[0109] Example 2 The difference from Example 1 is that the growth time of the P-type silicon carbide substrate is 140h. After 42h of growth, the induction coil is moved along the direction of the cover towards the hollow column base at a speed of 0.205mm / h and a distance of 20mm.

[0110] Example 3 The difference from Example 1 is that the growth time of the P-type silicon carbide substrate is 140h. After 65h of growth, the induction coil is moved along the direction of the cover towards the hollow column base, and the moving distance is 15mm.

[0111] Comparative Example 1 P-type silicon carbide crystals were grown by incorporating Al4C3 into conventional SiC powder.

[0112] A single Al compound was directly doped. Al4C3 was placed in SiC powder as a dopant for crystal growth. Nitrogen gas was introduced during the growth process. The crystal growth temperature and pressure were 2150℃ and 3 torr, respectively. The substrate (sample B) was obtained by slicing the P-type silicon carbide crystal.

[0113] Figure 4 The top view of the crucible in Example 1 shows that the base is a hollow cylinder. There is no silicon carbide crystal inside the base at the bottom of the crucible, but silicon carbide crystal is wrapped around the outside. It can be seen that the crystal growth device of this application plays the role of storing Al source and protecting Al source.

[0114] Depend on Figure 5 As can be seen, when growing P-type SiC crystal substrates using the apparatus and method of this application, sample A of Example 1 shows smaller resistivity deviations at different growth stages, while sample B of Comparative Example 1 shows larger resistivity deviations at different growth stages. The crystal resistivity of sample A is reduced by approximately 5 times compared to the prior art.

[0115] Currently, the resistivity of commercially available P-type SiC single crystals is approximately 2.5 Ω·cm, while the average resistivity of the crystal grown in Example 1 of this application is 0.32 Ω·cm. The average resistivity of the crystals grown in Examples 2 and 3 is close to that of Example 1, with small deviations in resistivity at different growth stages.

[0116] In the description of this application, the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require this application to be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this application.

[0117] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0118] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A crystal growing apparatus for growing a P-type silicon carbide substrate, characterized by comprising: The crystal growing device comprises: a crucible, the crucible comprising a main body and a cover, the main body having an internal cavity; a hollow cylinder base located in the crucible for placing a first P-type silicon carbide raw material; a shelf located in the crucible and on the hollow cylinder base for placing a second P-type silicon carbide raw material, the diameter of the shelf being greater than the outer diameter of the hollow cylinder base; a heating element located outside the crucible, the heating element being movable in a direction along the cover towards the hollow cylinder base.

2. The apparatus according to claim 1, wherein The height of the main body is 250-350 mm, and / or the height of the internal cavity is 230-340 mm.

3. The crystal growing apparatus of claim 2, wherein The main body satisfies at least one of the following conditions: the wall thickness of the main body is 10-20 mm; the bottom thickness of the main body is 10-20 mm; the inner diameter of the main body is 160-220 mm.

4. The crystal growing apparatus according to any one of claims 1 to 3, wherein The hollow cylinder base satisfies at least one of the following conditions: the height of the hollow cylinder base is 60-90 mm; the inner diameter of the hollow cylinder base is 60-80 mm; the wall thickness of the hollow cylinder base is 3-5 mm; the hollow cylinder base is a graphite element.

5. The crystal growing apparatus according to any one of claims 1 to 3, wherein The crystal growing device satisfies at least one of the following conditions: the thickness of the shelf is 10-15 mm; the shelf is a graphite element; the heating element comprises an induction coil; a protective element is provided between the heating element and the crucible, the protective element having a containing space for containing a cooling medium.

6. The crystal growing apparatus of claim 5, wherein The inner diameter of the induction coil is 1.4-2 times the outer diameter of the main body; and / or the height of the induction coil is greater than the height of the main body, the difference between the height of the induction coil and the height of the main body being 0.3-0.5 times the inner diameter of the induction coil.

7. A method for growing a P-type silicon carbide substrate by physical vapor transport, comprising: The crystal growing device of any one of claims 1-6 is used to grow a P-type silicon carbide substrate, comprising: placing the hollow cylinder base in the internal cavity of the main body and placing the first P-type silicon carbide raw material in the hollow cylinder base; placing the shelf on the hollow cylinder base and placing the second P-type silicon carbide raw material on the shelf, the particle size of the second P-type silicon carbide raw material being smaller than the particle size of the first P-type silicon carbide raw material; covering the main body with the cover, a silicon carbide seed crystal being arranged on the side of the cover close to the main body; growing a P-type silicon carbide substrate on the silicon carbide seed crystal, the growth time being t1, in the early growth stage, the height center of the heating element being located on the side of the shelf away from the hollow cylinder base, the height difference between the height center of the heating element and the shelf being 25-55 mm, after a first time of growth, moving the heating element 10-30 mm in a direction along the cover towards the hollow cylinder base, the first time being 0.3t1 to 0.6t1, and the moving rate being 0.15-0.22 mm / hour.

8. The method of claim 7, wherein, The particle size of the first P-type silicon carbide raw material is 6-10 mm, and / or the particle size of the second P-type silicon carbide raw material is 1-4 mm.

9. The method according to claim 7 or 8, characterized in that, at least one of the following conditions is satisfied: the temperature for growing the P-type silicon carbide substrate is 2100°C to 2200°C; the pressure for growing the P-type silicon carbide substrate is 3 Torr to 10 Torr; the growth time is 100 hours to 140 hours.

10. A P-type silicon carbide substrate, characterized by, the P-type silicon carbide substrate is prepared by the method of any one of claims 7 to 9.

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