Growth apparatus for semi-insulating silicon carbide crystals

Abstract

The utility model relates to a kind of semi-insulating silicon carbide crystal growth devices, involve semiconductor material preparation technical field, the semi-insulating silicon carbide crystal growth device includes growth chamber, seed crystal fixed structure being arranged in the upper portion of growth chamber and raw material containing area being arranged in the lower portion of growth chamber, further include exhaust barrier part, exhaust barrier part is arranged in raw material containing area, the surface of exhaust barrier part is equipped with micropore structure, the inside of exhaust barrier part is equipped with the gas diffusion passage being connected raw material and chamber upper portion.The utility model discloses a kind of semi-insulating silicon carbide crystal growth device, can effectively remove the impurity gas element contained in raw material, such as B, N2 etc., to further improve the resistivity of semi-insulating silicon carbide crystal.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor material preparation technology, and in particular to a semi-insulating silicon carbide crystal growth apparatus. Background Technology

[0002] Silicon carbide (SiC) crystals, as wide-bandgap semiconductor materials, have wide applications in high-temperature, high-frequency, and high-power devices. The resistivity of semi-insulating SiC crystals is a key performance indicator, but impurity gases from the raw materials can dope into the crystal during growth, leading to a decrease in resistivity. Current technologies often employ high-temperature purification or inert gas protection to reduce impurities, but these impurity gases are difficult to completely remove from the raw materials, especially when the powder packing density is uneven or the crucible structure is inappropriate, allowing them to remain in the growth chamber. For example, while conventional graphite crucibles provide a sealed environment, they lack a directional venting mechanism, allowing impurity gases to be released and mixed into the crystal during the heating stage. Furthermore, improper design of parameters such as seed crystal off-axis setting and powder particle size distribution can further exacerbate impurities. Therefore, there is an urgent need for a growth apparatus and process that can effectively remove impurity gases and improve crystal resistivity. Utility Model Content

[0003] In order to overcome the shortcomings of the prior art, this utility model proposes a semi-insulating silicon carbide crystal growth device, which aims to effectively remove impurity gaseous elements such as B and N contained in the raw materials, thereby further improving the resistivity of the semi-insulating silicon carbide crystal.

[0004] To achieve this objective, the present invention adopts the following technical solution: This utility model provides a semi-insulating silicon carbide crystal growth device, including a growth chamber, a seed crystal fixing structure disposed at the upper part of the growth chamber, and a raw material receiving area disposed at the lower part of the growth chamber. It also includes an exhaust barrier part disposed in the raw material receiving area. The surface of the exhaust barrier part is provided with a microporous structure, and the interior of the exhaust barrier part is provided with a gas diffusion channel connecting the raw material and the upper part of the chamber.

[0005] The preferred technical solution of this utility model is that the top of the exhaust barrier is provided as a microporous sealing structure.

[0006] The preferred technical solution of this utility model is that the exhaust barrier is a porous graphite column, the porous graphite column is hollow inside and has uniform micropores on its peripheral wall.

[0007] The preferred technical solution of this utility model is that a porous graphite plate is provided at the bottom of the growth chamber, and a porous graphite column is disposed on the porous graphite plate.

[0008] The preferred technical solution of this utility model is that the off-axis angle of the semi-insulating seed crystal in the seed crystal fixing structure is 0° to 4°.

[0009] The preferred technical solution of this utility model is that the diameter of the micropores in the exhaust barrier is 1-2 mm and the pore density is 10-20 pores / cm².

[0010] The preferred technical solution of this utility model is that the silicon carbide powder in the raw material containing area is a mixture of powders with three particle sizes of 8-20 mesh, 20-40 mesh and 40-80 mesh in a volume ratio of 1:1:1.

[0011] The beneficial effects of this utility model are: High impurity removal efficiency: The porous structure allows impurity gases to diffuse directionally along the pores during the heating stage, avoiding local stagnation; the secondary impurity removal activates the precipitation of impurities under high pressure, and combined with reactive gases such as HCl, effectively decomposes elements such as B and N.

[0012] Significant improvement in resistivity: Examples show that the resistivity of the crystal can reach more than 10^5 Ω·cm, which is 1-2 orders of magnitude higher than conventional methods.

[0013] Good process stability: The particle size distribution of the powder ensures uniform packing density and reduces hot spot formation; the off-axis setting of the seed crystal promotes orderly crystal growth. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of a semi-insulating silicon carbide crystal growth apparatus according to Embodiment 1 of this utility model; Figure 2 This is a top view of the exhaust barrier part of Embodiment 1 of this utility model; Figure 3 This is a bottom view of the exhaust barrier part of Embodiment 1 of this utility model.

[0016] In the picture: 1-Growth chamber; 2-Exhaust barrier; 21-Microporous structure; 3-Gas diffusion channel; 4-Porous graphite plate; 5-Semi-insulating seed crystal; 6-Silicon carbide powder. Detailed Implementation

[0017] The technical solution of this utility model will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] Example 1 This embodiment provides a semi-insulating silicon carbide crystal growth apparatus, such as... Figure 1-3As shown, it includes a growth chamber 1, a seed crystal fixing structure disposed on the upper part of the growth chamber 1, and a raw material receiving area disposed on the lower part of the growth chamber 1. It also includes an exhaust barrier 2 disposed in the raw material receiving area. The surface of the exhaust barrier 2 is provided with a microporous structure 21, and the interior of the exhaust barrier 2 is provided with a gas diffusion channel 3 connecting the raw material and the upper part of the chamber. The technical solution of this embodiment effectively removes impurity gaseous elements such as boron (B) and nitrogen (N) from the raw materials through the synergistic effect of the designed growth device structure and optimized process parameters, thereby significantly improving the resistivity of the semi-insulating silicon carbide crystal. The growth chamber, as the core sealed environment, is made of high-purity graphite material, providing a stable and inert crystal growth space, preventing external gas intrusion. Simultaneously, the internal temperature and pressure fields are controllable, laying the foundation for impurity removal. The seed crystal fixing structure located at the top of the growth chamber supports the semi-insulating seed crystal, and the optimized off-axis angle (0° to 4°) promotes orderly crystal growth and reduces defect generation, thereby indirectly reducing the risk of impurities. The raw material receiving area located at the bottom of the growth chamber is responsible for containing silicon carbide powder, which can be... Multi-level particle size distribution optimizes packing density, ensures uniform heat conduction, and avoids uneven impurity release caused by local hot spots. However, the key innovation of this technical solution lies in the introduction of the exhaust barrier. This component is set in the raw material receiving area as a functional element. Its surface has a microporous structure (the micropore diameter is preferably 1-2 mm to form a uniformly distributed gas permeation interface), and its interior has a gas diffusion channel (a continuous path connecting the raw material and the upper part of the chamber, in which no raw material powder is placed). In this technical solution, the exhaust barrier is defined as a porous medium component with a hollow structure. Its function is to guide the impurity gases (such as B, N2, etc.) released by the thermal decomposition of the raw material from the depth of the powder to the upper part of the chamber through capillary effect and pressure difference drive, and then discharge the system through the process gas flow. Specifically, during the heating stage, impurity gases are released from the silicon carbide powder and enter the gas diffusion channel inside the exhaust barrier through the microporous structure. This channel utilizes the natural convection effect generated by the temperature difference to allow the gas to diffuse upwards, preventing it from accumulating in the raw material. Simultaneously, combined with the secondary high-temperature impurity removal step in the process (such as introducing a mixed gas of HCl, H2, and Ar at a pressure of 50,000-80,000 Pa), HCl reacts with the impurity metal elements to generate volatile chlorides, which are discharged from the graphite crucible in gaseous form, further improving the impurity removal efficiency. This design achieves deep removal of impurity gases through the synergy of physical structure and chemical reaction. Its technical effect is based on the gas diffusion law, and the increase in effective diffusion area significantly improves the impurity throughput.

[0019] Preferably, the top of the exhaust barrier 2 is provided with a microporous sealing structure. The microporous sealing structure effectively prevents backflow of impurity gases or intrusion of external contaminants into the gas diffusion channel, while ensuring unidirectional gas discharge, thereby improving the directionality and efficiency of impurity removal. A microporous sealing structure is defined as a sealing interface with tiny pores (typically less than 2 mm in diameter). By constructing uniform micropores at the top of the exhaust barrier, with a porosity controlled at 30%-50%, it allows gas to pass through but blocks solid particles or large molecular impurities. This structure utilizes capillary effect and pressure difference driving principles. During crystal growth, when the raw material is heated and releases impurity gases (such as B and N2), the surface tension generated by the micropores promotes the directional diffusion of gas from the raw material area to the exhaust channel, preventing gas from partially dispersing or stagnating within the chamber. Experimental data shows that compared to a design without a sealed top, this structure can reduce the residual amount of impurity gases by approximately 15%, increase the crystal resistivity from the baseline value to above 1.5 × 10^5 Ω·cm, and achieve a batch consistency variation coefficient of less than 5%. In addition, the micropore sealing structure reduces heat loss, maintains the stability of the growth temperature, and further optimizes the crystal quality.

[0020] To achieve the above structure, preferably, the exhaust barrier 2 is a porous graphite column, wherein the interior of the porous graphite column is hollow and the peripheral wall has uniformly distributed micropores. This is preferred because the porous graphite column forms an efficient gas diffusion channel through its internal hollow structure, enhancing the transmission capacity and removal depth of impurity gases. A porous graphite column is defined as a columnar body made of high-purity graphite (purity > 99.99%), whose internal hollow section serves as a gas collection area, and the peripheral wall micropores connect the raw material to the channel. After isostatic pressing the graphite blank, micropores are machined by drilling to ensure uniform pore size and mechanical strength. This structure significantly increases the throughput of impurity gases by increasing the effective diffusion area. In the process, when the temperature rises above 1800℃, impurity elements such as B and N precipitate from the silicon carbide powder, enter the hollow section through the peripheral wall micropores (e.g., 1.5 mm in diameter), and then exit the chamber along the channel, avoiding local accumulation. Meanwhile, the chemical inertness and high-temperature stability (temperature resistance >2300℃) of graphite materials ensure the durability of the device during the crystal growth process.

[0021] Preferably, a porous graphite plate 4 is provided at the bottom of the growth chamber 1, and porous graphite columns are disposed on the porous graphite plate 4. The use of a porous graphite plate can help accelerate the gas circulation in the growth chamber, and further accelerate the discharge of impurity gases during the furnace washing stage and the growth stage.

[0022] Preferably, the off-axis angle of the semi-insulating seed crystal 5 with a fixed seed crystal structure is 0° to 4°. An off-axis angle of 0° to 4° optimizes the crystal growth orientation, promotes lattice-matched growth, thereby reducing defects and indirectly lowering impurities. The off-axis angle is defined as the angle between the seed crystal growth plane and the crystal orientation

[0001] . It is set by a precision fixture or optical alignment system, with an error controlled within ±0.1°. This angle range is based on crystallographic theory, ensuring the growth interface is parallel to the optimal crystal plane, reducing the generation of defects such as dislocations and stacking faults (defect density reduced by more than 40%). These defects are often preferred incorporation sites for impurity elements such as B and N. Experimental data show that when the off-axis angle is 2°, the crystal resistivity increases by approximately 10% compared to random angles, reaching 1.4 × 10⁵ Ω·cm, and the crystal integrity is improved by 20%. Simultaneously, this angle ensures the stability of the growth front, avoiding dendrite growth or inclusion formation, thereby improving the reliability of the semi-insulating performance.

[0023] Preferably, the micropore diameter of the exhaust barrier 2 is 1-2 mm, and the pore density is 10-20 pores / cm². This parameter balances gas flow efficiency, structural strength, and processing feasibility, maximizing the impurity diffusion rate. This range is based on gas dynamics calculations; the 1-2 mm diameter provides optimal capillary force (capillary pressure approximately 0.1-0.5 Pa), while the density of 10-20 pores / cm² ensures sufficient gas throughput (30% higher than a design with a density of 5 pores / cm²), while preventing micropore blockage or structural weakening. During the crystal growth stage, the peak impurity gas diffusion rate occurs at a pore diameter of 1.5 mm and a density of 15 pores / cm², corresponding to an impurity removal rate exceeding 95% and a resistivity stable at 1.7 × 10⁵ Ω·cm. Furthermore, this parameter reduces airflow resistance and energy consumption, demonstrating process economy.

[0024] Preferably, the silicon carbide powder 6 in the raw material containing area of ​​this embodiment is composed of powders with three particle sizes of 8-20 mesh, 20-40 mesh, and 40-80 mesh, mixed in a volume ratio of 1:1:1. This multi-stage particle size ratio optimizes the powder's bulk density, ensuring uniform heat conduction and thus promoting the uniform release of impurities. In the particle size classification, 8-20 mesh, 20-40 mesh, and 40-80 mesh correspond to coarse, medium, and fine particles, respectively. The three powders are uniformly mixed in a volume ratio of 1:1:1 using a mechanical mixer for 10-20 minutes. This ratio, based on packing theory, reduces powder porosity and avoids non-uniform impurity release caused by localized hot spots. Simultaneously, uniform packing also improves raw material utilization, reduces powder residue, and lowers production costs.

[0025] The above crystal growth process is implemented in the following steps: S0: Impurity removal step This step involves high-temperature purification of the graphite thermal field and growth chamber to remove background impurities. Specifically, the purification temperature is set to 2250℃ (optional range 2200-2300℃), and the process gas is a mixture of HCl (50 sccm), H2 (30 sccm), and Ar (200 sccm), with a treatment time of 30 hours (optional 10-50 hours). Under high-temperature conditions, HCl reacts with the graphite surface and residual B, N, and other impurities to generate volatile chlorides (such as BCl3), which are discharged with the gas flow. This step ensures the initial purity of the growth environment, laying the foundation for subsequent processes.

[0026] S1: Loading Steps High-purity silicon carbide powder is loaded into the raw material receiving area according to a predetermined particle size ratio. Specifically, the powder uses three particle sizes: 8-20 mesh, 20-40 mesh, and 40-80 mesh, and is uniformly mixed in a volume ratio of 1:1:1 to ensure a bulk density of approximately 1.6 g / cm³, reducing uneven heat conduction. Simultaneously, an exhaust barrier (in this embodiment, a porous graphite column) is vertically inserted into the powder. Its peripheral walls have a microporous structure (micropore diameter 1.5 mm, pore density 15 pores / cm²), its top is a microporous sealing structure (micropore diameter 1.5 mm, pore density 15 pores / cm²), and its bottom contacts the porous graphite plate. During loading, the crucible should be gently shaken to ensure uniform powder distribution and avoid the formation of voids. This formulation optimizes the thermal stability of the raw material and prevents uneven release of impurities due to localized hot spots.

[0027] S2: Furnace Loading Procedure The assembled growth chamber is placed into the purified graphite thermal field, with the seed crystal off-axis angle at 2°, ensuring the thermal field components are correctly aligned. Before closing the furnace lid, check the seal and purge with Ar gas (100 sccm) for 5 minutes to remove air. After loading, maintain the system pressure at atmospheric pressure and preheat the temperature to 100°C for later use. This step ensures tight integration of the growth chamber and the thermal field, providing a stable environment for subsequent high-temperature processes.

[0028] S3: Secondary high-temperature impurity removal step Immediately after loading into the furnace, a secondary high-temperature purification process is performed to deeply remove impurity gases from the raw materials. The process pressure is set to 60,000 Pa (optional 50,000-80,000 Pa), the temperature to 800℃ (optional 500-1000℃), and a mixed gas of HCl (flow rate 80 sccm), H2 (flow rate 50 sccm), and Ar (flow rate 300 sccm) is introduced for 8 hours (optional 5-10 hours). Under high pressure, impurity gases (such as B2H6, N2) precipitate from deep within the powder and enter the gas diffusion channel through the micropores (diameter 1-2 mm, pore density 15 pores / cm²) of the exhaust barrier, where they are further removed by the enhanced chemical reaction of HCl. Actual measurements show that this step can reduce the B and N content in the raw materials by more than 70%.

[0029] S4: Heating and Crystal Growth Step This process is divided into three stages: High-pressure heating stage: Ar gas is introduced into the chamber to a pressure of 70,000 Pa (optional 50,000-80,000 Pa), and the temperature is increased to 2,000℃ (optional 1,800-2,100℃) at a rate of 10℃ / min (optional 5-20℃ / min), and maintained for 4 hours (optional 3-5 hours). High pressure suppresses the volatilization of Si and stabilizes the stoichiometric ratio of the raw materials.

[0030] Pressure reduction phase: After the temperature stabilizes, reduce the pressure to 500 Pa (100-1000 Pa) within 5 hours (optional 2-10 hours) to avoid crystal defects.

[0031] Crystal growth stage: Maintain temperature at 2200℃ (optional 2100-2300℃) for 120 hours (optional 100-150 hours), with process gas flow rates of Ar 200 sccm, H2 50 sccm, and HCl 30 sccm (optional range: Ar 50-500 sccm, H2 10-100 sccm, HCl 10-100 sccm). During this period, the exhaust barrier continuously guides the impurity gases out, and the seed crystal off-axis angle is set to 2° (range 0°-4°) to optimize crystal orientation growth.

[0032] S5: Cooling and Annealing Steps After crystal growth is complete, maintain the crystal growth temperature and fill the chamber with Ar gas (flow rate 200 sccm, optional 50-500 sccm) for 10 hours (optional 5-10 hours) to stabilize the crystal structure. Then, reduce the power and cool to 1600℃ (optional 1500-1800℃) for 5 hours (optional 2-10 hours) for annealing to eliminate thermal stress. Finally, turn off the power and allow it to cool naturally to room temperature.

[0033] Example 2 The difference from Example 1 is that the micropore diameter of the exhaust barrier is 1.0 mm, the pore density is 20 pores / cm², and the seed crystal off-axis angle is 0°.

[0034] Example 3 The difference from Example 1 is that the diameter of the micropores in the exhaust barrier is 2.0 mm, the pore density is 10 pores / cm², and the seed crystal off-axis angle is 4°.

[0035] Example 4 The difference from Example 1 is that the diameter of the micropores in the exhaust barrier is 1.8 mm, the pore density is 12 pores / cm², and the seed crystal off-axis angle is 1°.

[0036] Example 5 The difference from Example 1 is that the silicon carbide powder is mixed in a volume ratio of 1:1 for 8-20 mesh and 20-40 mesh.

[0037] Comparative Example 1 The difference from Example 1 is that the growth chamber, seed crystal fixing structure, and raw material containing area are all the same, but the structure of gas diffusion channel is lacking.

[0038] Comparative Example 2 The difference from Comparative Example 1 is that the time for secondary high-temperature impurity removal is increased to 18 hours.

[0039] The resistivity and impurity content of the crystals obtained in the above cases were tested. The resistivity was detected using the non-contact eddy current method, and the impurity content was detected using glow discharge mass spectrometry (GDMS). The test results are shown in Table 1. Table 1. Comparison of the effects of semi-insulating silicon carbide crystal growth devices

[0040] The test results above show that, compared with Comparative Examples 1-2, Examples 1-5 improve the performance of semi-insulating silicon carbide crystals by constructing an exhaust barrier structure, increasing the resistivity from the order of 10³ Ω·cm to 10. 6 The resistivity is on the order of Ω·cm, with an impurity removal rate exceeding 85%. The improved resistivity of this invention is primarily attributed to the exhaust barrier structure incorporated in the embodiments. This structure, through micropores (1-2 mm in diameter) and internal gas diffusion channels, directionally exhausts impurity gases containing B, N2, etc., during the process, reducing crystal doping. In contrast, Comparative Example 1 lacks an exhaust barrier, and Comparative Example 2, even with increased secondary high-temperature impurity removal time, still cannot effectively improve impurity removal efficiency, resulting in a significant decrease in resistivity.

[0041] Comparing the differences in process parameters between different embodiments, it was found that when the powder uses three particle sizes of 8-20 mesh, 20-40 mesh and 40-80 mesh, is uniformly mixed in a volume ratio of 1:1:1, has a micropore diameter of 1.5 mm, a pore density of 15 pores / cm², and a seed crystal off-axis angle of 2°, i.e. the process of Example 1, the resistivity of the prepared semi-insulating silicon carbide crystal is significantly improved compared with other embodiments.

[0042] This utility model has been described through preferred embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this utility model. This utility model is not limited to the specific embodiments disclosed herein; other embodiments falling within the scope of the claims of this application are all within the protection scope of this utility model.

Claims

1. A semi-insulating silicon carbide crystal growth apparatus, characterized in that: It includes a growth chamber (1), a seed crystal fixing structure disposed on the upper part of the growth chamber (1), and a raw material receiving area disposed on the lower part of the growth chamber (1); It also includes an exhaust barrier (2), which is disposed in the raw material receiving area. The surface of the exhaust barrier (2) is provided with a microporous structure, and the interior of the exhaust barrier (2) is provided with a gas diffusion channel (3) connecting the raw material and the upper part of the chamber.

2. The semi-insulating silicon carbide crystal growth apparatus according to claim 1, characterized in that: The top of the exhaust barrier (2) is provided with a microporous sealing structure.

3. The semi-insulating silicon carbide crystal growth apparatus according to claim 1, characterized in that: The exhaust barrier (2) is a porous graphite column, which is hollow inside and has uniform micropores on its periphery.

4. The semi-insulating silicon carbide crystal growth apparatus according to claim 3, characterized in that: The bottom of the growth chamber (1) is provided with a porous graphite plate (4), and the porous graphite column is disposed on the porous graphite plate (4).

5. The semi-insulating silicon carbide crystal growth apparatus according to claim 1, characterized in that: The off-axis angle of the semi-insulating seed crystal (5) of the seed crystal fixed structure is 0° to 4°.

6. The semi-insulating silicon carbide crystal growth apparatus according to claim 1, characterized in that: The micropore diameter of the exhaust barrier part (2) is 1-2 mm, and the pore density is 10-20 pores / cm².

7. The semi-insulating silicon carbide crystal growth apparatus according to claim 1, characterized in that: The silicon carbide powder (6) in the raw material containing area is made by mixing powders of three particle sizes, namely 8-20 mesh, 20-40 mesh and 40-80 mesh, in a volume ratio of 1:1:1.

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