A raw material loading method for growing a SiC single crystal by a PVT method and application thereof

Abstract

This invention provides a raw material loading method for growing SiC single crystals using the PVT method and its application. This method cleverly utilizes the axial temperature gradient from the bottom to the top of the PVT furnace. The bottom layer (C powder) is located in a relatively low-temperature zone, its main function being to adsorb the permeated silicon liquid and initiate an in-situ synthesis reaction, while also acting as a "buffer" for the gaseous Si / C ratio. The middle layer (Si powder) is located in a medium-temperature zone (above ~1414℃), where the silicon powder can be controlled to melt, and the liquid silicon permeates downwards to the bottom C powder layer via capillary action. The top layer (SiC powder) is located in the highest temperature zone, serving as the main sublimation source, providing a stable Si-C gaseous composition, and its textured surface enhances sublimation uniformity.

Description

Technical Field

[0001] This invention belongs to the field of advanced semiconductor material preparation technology, specifically relating to a raw material loading method for growing silicon carbide (SiC) single crystals by physical vapor transport (PVT) and its application. Specifically, it relates to a method for actively controlling the crystal growth environment by adjusting the gas phase stoichiometry (Si / C ratio) in situ during the growth process through a precisely designed multilayer heterogeneous raw material structure. Background Technology

[0002] Currently, the PVT method for growing SiC crystals typically uses high-purity SiC powder as raw material, which sublimates and decomposes at high temperatures into gaseous components containing Si and C (such as Si, Si₂C, or SiC₂), which are then transported to the seed crystal for crystallization. However, this method has an inherent limitation: the gaseous environment within the growth chamber is determined by its thermodynamic equilibrium, making it difficult to actively and dynamically adjust over a wide range according to process requirements. This limitation poses a significant challenge for growing specific crystal forms (such as high-purity 4H-SiC), suppressing specific defects, or achieving specific doping concentrations and uniformity.

[0003] To address the aforementioned issues, although some researchers have proposed the idea of ​​mixing different raw materials, simple physical mixing (such as mixing C powder, Si powder and SiC powder) can lead to silicon melting during heating, triggering violent and uncontrollable exothermic reactions, causing thermal instability, material crusting, and even safety accidents, making it unsuitable for practical production. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a raw material loading method for growing SiC single crystals by PVT and its application. This method involves physically separating and loading carbon powder, silicon powder, and silicon carbide powder in a specific order, and utilizing the inherent axial temperature gradient within the PVT furnace to allow each raw material to undergo controllable physicochemical changes within its optimal temperature range, thereby achieving a leap from "passively accepting" the gas phase environment to "actively creating" an ideal gas phase environment.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a raw material loading method for growing SiC single crystals by PVT method, comprising the following steps:

[0007] S1: Place graphite powder at the bottom of the growth device, place crystalline silicon powder on the upper surface of the graphite powder and cover it with graphite powder, place silicon carbide powder on the upper surface of the crystalline silicon powder and cover it with crystalline silicon powder, and then compact it; the mass ratio of graphite powder, crystalline silicon powder and silicon carbide powder is (0.1~2):(0.1~2):(6~10);

[0008] S2: Texture the upper surface of the compacted silicon carbide powder to form a concave structure.

[0009] Preferably, the mass ratio of graphite powder, crystalline silicon powder, and silicon carbide powder is (0.5~1.5):(0.5~1.5):(8~10).

[0010] Preferably, the graphite powder has an average particle size range of 80-200 mesh, the crystalline silicon powder has an average particle size range of 100-325 mesh, and the silicon carbide powder has an average particle size range of 200-400 mesh.

[0011] Preferably, the average particle size of the graphite powder is greater than the average particle size of the crystalline silicon powder, and the average particle size of the crystalline silicon powder is greater than or equal to the average particle size of the silicon carbide powder.

[0012] Preferably, the compaction process is performed at a pressure of 5 to 15 MPa.

[0013] Preferably, the recessed structure is a groove.

[0014] Preferably, the groove includes, but is not limited to, concentric annular grooves, spiral grooves, or radial grooves.

[0015] Preferably, the depth of the trench is 3-10 mm and the width is 3-8 mm.

[0016] Preferably, the number of concentric annular grooves is 3 to 5.

[0017] Secondly, the present invention provides a method for growing silicon carbide crystals, wherein the raw material loading adopts the method described above.

[0018] This invention provides a raw material loading method for growing SiC single crystals using the PVT method. This method cleverly utilizes the axial temperature gradient from the bottom to the top of the PVT furnace. The bottom layer (C powder) is located in a relatively low-temperature region, primarily functioning to adsorb the permeated silicon liquid and initiate in-situ synthesis reactions, while also acting as a "buffer" for the gaseous Si / C ratio. The middle layer (Si powder) is located in a medium-temperature region (above ~1414℃), where the silicon powder melts controllably, and the liquid silicon permeates downwards to the bottom C powder layer via capillary action. The top layer (SiC powder) is located in the highest temperature region, serving as the main sublimation source, providing a stable Si-C gaseous composition, and its textured surface enhances sublimation uniformity.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) Safety and controllability: Physical separation filling fundamentally avoids direct mixing of C powder and Si powder, preventing violent and uncontrollable exothermic reactions. The melting, penetration and reaction process of silicon is mild and controllable, ensuring process safety and thermal stability.

[0021] (2) Active control of gas phase components: by precisely setting M C M Si M SiC The mass ratio of these three components can "program" the gas phase environment of the growth chamber. For example, if a silicon-rich atmosphere is needed to promote 4H-SiC crystal stability or compensate for silicon volatilization, M can be appropriately increased. Si The ratio of M can be increased appropriately when a carbon-rich atmosphere is needed to suppress specific defects or for carbon space-assisted doping. C The proportion of M. SiC As the main component, it ensures a stable supply of the basic sublimation source. This design enables a wide range of active and predictable adjustment of the gas-phase Si / C ratio, which is impossible with traditional single SiC feedstock.

[0022] (3) In-situ synthesis and self-purification: The in-situ synthesis reaction occurring in the lower layer produces highly reactive SiC, which can be used as a supplementary sublimation source. This reaction can also effectively fix excess silicon, playing a certain "self-purification" role and reducing the contamination of hot-field components by silicon vapor. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the loading process of the present invention.

[0024] Among them, 1-growth crucible, 2-buffer reaction layer (graphite powder), 3-silicon source supply layer (crystalline silicon powder), 4-main sublimation source layer (silicon carbide powder), 5-formed trench, 6-scraper, 7-compacted block.

[0025] Figure 2 Image of silicon carbide crystals grown in Example 1;

[0026] Figure 3 Image of silicon carbide crystals grown in Example 2;

[0027] Figure 4 Image of silicon carbide crystals grown in Example 3;

[0028] Figure 5 Image of silicon carbide crystal grown in Comparative Example 1. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] To address the problems existing in the PVT method for growing SiC crystals in the prior art, this invention provides a safe, controllable, and programmable raw material loading method. This method involves physically separating and loading carbon powder, silicon powder, and silicon carbide powder in a specific order, and utilizing the inherent axial temperature gradient within the PVT furnace to allow each raw material to undergo controllable physicochemical changes within its optimal temperature range.

[0031] Specifically, the present invention provides a raw material loading method for growing SiC single crystals using the PVT method, comprising the following steps:

[0032] S1: Place graphite powder at the bottom of the growth device, place crystalline silicon powder on the upper surface of the graphite powder and cover it with graphite powder, place silicon carbide powder on the upper surface of the crystalline silicon powder and cover it with crystalline silicon powder, and then compact it; the mass ratio of graphite powder, crystalline silicon powder and silicon carbide powder is (0.1~2):(0.1~2):(6~10);

[0033] S2: Texture the upper surface of the compacted silicon carbide powder to form a concave structure.

[0034] In some embodiments of the present invention, it is preferable to pretreat the raw materials. Specifically, the present invention performs sieving and vacuum drying on high-purity graphite powder (C), high-purity crystalline silicon powder (Si), and high-purity silicon carbide powder (SiC) to remove dust, impurities, and adsorbed water.

[0035] After pretreatment, according to the present invention, a predetermined mass M is weighed. C Graphite powder is used as a buffer reaction layer and is evenly filled into the bottom of the growth apparatus, preferably the bottom of the raw material chamber of the growth crucible. After filling, it is preferable to use a flat-bottomed compactor to lightly compact it to make its upper surface flat.

[0036] Then, according to the present invention, a predetermined mass M is weighed. Si Crystalline silicon powder is carefully spread on the graphite powder layer as a silicon source supply layer to ensure complete coverage and uniform thickness.

[0037] Subsequently, the predetermined mass M was weighed. SiC Silicon carbide powder is used as the main sublimation source layer and filled on the silicon powder layer, completely covering the silicon powder layer.

[0038] In this invention, after the silicon carbide powder is filled, compaction is preferably performed. The compaction is preferably performed using a compaction block with a slightly convex bottom surface, and the compaction pressure is 5~15 MPa, such as 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, or 15 MPa.

[0039] It is important to note that if the compaction pressure is too low, the compaction effect will be insignificant, leaving numerous voids between powder particles, leading to poor thermal conductivity and a loose structure. Conversely, if the pressure is too high, the powder will be over-compacted, compressing the porosity to an excessively low level, resulting in poor air permeability and the risk of agglomeration or pre-sintering at high temperatures. Therefore, this invention controls the compaction pressure at the range of 5-15 MPa to achieve a sufficiently high density to improve thermal conductivity and prevent splashing, while simultaneously retaining sufficient porosity to ensure good air permeability.

[0040] In this invention, the mass ratio of graphite powder, crystalline silicon powder, and silicon carbide powder in the above-mentioned raw material loading method is a key parameter. This is because this invention aims to control the degree of in-situ reaction and the adjustment range of the gas-phase Si / C ratio. As a preferred embodiment, the mass ratio of graphite powder, crystalline silicon powder, and silicon carbide powder is (0.1~2):(0.1~2):(6~10), more preferably (0.5~1.5):(0.5~1.5):(8~10), and even more preferably 1:1:9.

[0041] In some embodiments of the present invention, the average particle size of the graphite powder ranges from 80 to 200 mesh, the average particle size of the crystalline silicon powder ranges from 100 to 325 mesh, and the average particle size of the silicon carbide powder ranges from 200 to 400 mesh.

[0042] As a preferred technical solution, in this invention, the average particle size of the graphite powder is greater than the average particle size of the crystalline silicon powder, and the average particle size of the crystalline silicon powder is greater than or equal to the average particle size of the silicon carbide powder. This arrangement is made to meet the following requirements:

[0043] (1) Ensure that molten silicon can effectively penetrate downwards and prevent upward backflow.

[0044] When the silicon powder (middle layer) melts, it is simultaneously subjected to capillary forces from both the upper (fine SiC layer) and lower (coarse C layer). Since the lower capillary force is weaker (larger pore size) and the upper capillary force is stronger (smaller pore size), the liquid preferentially moves towards the direction with the weaker capillary force. Therefore, the structure of "coarse C > medium Si > fine SiC" creates a "capillary force ramp" for the molten silicon, guiding it smoothly downwards into the carbon powder layer, which is a prerequisite for achieving a controllable reaction.

[0045] (2) Optimize the functions of each layer to achieve a balance between reaction and transport.

[0046] Lower layer (coarse C powder) - buffer and reaction layer: The coarse particle size creates large pores, which provide a rapid channel for molten silicon infiltration. In addition, the gas phase diffusion provides space, allowing reaction byproducts (such as CO) to be discharged smoothly and reactants (Si vapor) to enter smoothly. It also provides a huge specific surface area, allowing the C powder to fully contact the infiltrated Si liquid, promoting the in-situ reaction of Si+C to form SiC.

[0047] Middle layer (medium-sized Si powder) - silicon source supply layer: The particle size is between the two, playing a transition and isolation role. It cannot be too coarse (otherwise the amount of silicon per unit volume is too small and may collapse prematurely), nor too fine (otherwise it will be like mud, hindering its own melting and downward penetration).

[0048] Upper layer (fine SiC powder) - main sublimation source and sealing layer:

[0049] The fine particle size results in a huge specific surface area, enabling it to serve as a highly efficient and uniform primary sublimation source. At the same time, the dense structure effectively "covers" the underlying silicon powder layer, acting like a sealing cap to physically prevent premature and excessive volatilization of silicon vapor, while guiding the sublimation gas flow smoothly upward.

[0050] (3) Maintain structural stability and prevent interlayer mixing

[0051] During the initial loading and heating stages, the powder system is subject to vibration and thermal convection disturbances. The "fine top, coarse bottom" structure provided by this invention is stable and can effectively prevent fine particles from falling into the gaps between coarse particles. If the structure is reversed to "coarse top, fine bottom," the coarse particles in the upper layer will sink into the particles in the lower layer, causing interlayer mixing.

[0052] After compaction, according to the present invention, it is preferable to perform a texturing treatment on the upper surface of the compacted silicon carbide powder to form a concave structure. This is to increase the effective sublimation surface area and achieve uniform and controllable release of the gas phase source.

[0053] In some embodiments of the present invention, the recessed structure is a groove, which includes, but is not limited to, concentric annular grooves, spiral grooves, or radial grooves. For concentric annular grooves, the number of concentric annular grooves is 3 to 5, such as 3, 4, or 5.

[0054] The depth of the groove is 3 to 10 mm, such as 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm; the width is 3 to 8 mm, such as 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm.

[0055] In addition, the present invention also provides a method for growing silicon carbide crystals, wherein the raw material loading adopts the method described above.

[0056] The above growth method can employ standard PVT growth technology, and this invention does not impose any particular limitations. The standard PVT process can be described as follows: evacuating the system to a vacuum level below 5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced to a pressure of 5~20 kPa, preferably 10~15 kPa; the temperature of the raw material zone is controlled within the range of 2150~2250℃, preferably 2180~2200℃, and the temperature of the seed crystal zone is kept 80~120℃ lower than that of the raw material zone, preferably 90~100℃; under these conditions, growth is carried out for 100~120 hours, preferably 110~115 hours.

[0057] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention are all commercially available products.

[0058] Example 1

[0059] (1) 120 mesh high-purity graphite powder, 180 mesh high-purity crystalline silicon powder and 250 mesh high-purity SiC powder were sieved and dried under vacuum at 200°C for 4 hours.

[0060] (2) Weigh M C =100 g of graphite powder, put it into the bottom of crucible (1), and scrape it slightly. Weigh M Si =100 g of crystalline silicon powder was evenly spread on the graphite powder layer (2). M was weighed. SiC =1200 g silicon carbide powder was loaded into a crucible and covered with a silicon powder layer (3). A pressure of 10 MPa was applied using an arc-shaped pressure block (7) to compact the powder. Four concentric circular grooves were scraped on the surface of the compacted powder using a scraper with a tooth depth of 5 mm and a tooth width of 5 mm, which was concentric with the loading crucible.

[0061] (3) Seal the crucible in the growth furnace, evacuate it, and then fill it with an appropriate amount of high-purity argon as the growth atmosphere.

[0062] The silicon carbide single crystal ingot is obtained by growing it using the standard PVT process and slowly cooling it to room temperature.

[0063] The standard PVT process involves evacuating the system to a vacuum level below 5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced to a pressure of 10 kPa; the temperature of the raw material zone is controlled at 2200℃, and the temperature of the seed crystal zone is kept 100℃ lower than that of the raw material zone; growth is carried out under these conditions for 100 hours.

[0064] Figure 2The silicon carbide crystal grown in Example 1 has a basically flat surface with a few visible pits.

[0065] Example 2

[0066] (1) 100-mesh high-purity graphite powder, 200-mesh high-purity crystalline silicon powder and 350-mesh high-purity SiC powder were sieved and dried under vacuum at 200°C for 4 hours.

[0067] (2) Weigh M C =150 g of graphite powder, put it into the bottom of crucible (1), and scrape it slightly. Weigh M Si =150 g of crystalline silicon powder was evenly spread on the graphite powder layer (2). M was weighed. SiC =1800 g of silicon carbide powder was loaded into a crucible and covered with a layer of silicon powder (3). A pressure of 15 MPa was applied using an arc-shaped pressure block (7) to compact the powder. Five concentric circular grooves were scraped on the surface of the compacted powder using a scraper with a tooth depth of 3 mm and a tooth width of 3 mm, which was concentric with the loading crucible.

[0068] (3) Seal the crucible in the growth furnace, evacuate it, and then fill it with an appropriate amount of high-purity argon as the growth atmosphere. Use the standard PVT process of Example 1 for growth, and slowly cool it to room temperature according to the program to obtain silicon carbide single crystal ingot.

[0069] Figure 3 The silicon carbide crystal grown in Example 2 has a smooth and flat surface and excellent quality.

[0070] Example 3

[0071] (1) 120 mesh high-purity graphite powder, 200 mesh high-purity crystalline silicon powder and 300 mesh high-purity SiC powder were sieved and dried under vacuum at 200°C for 4 hours.

[0072] (2) Weigh M C =200 g of graphite powder, put it into the bottom of crucible (1), and scrape it slightly. Weigh M Si =200 g of crystalline silicon powder was evenly spread on the graphite powder layer (2). M was weighed. SiC =1800 g of silicon carbide powder was loaded into a crucible and covered with a layer of silicon powder (3). A pressure of 5 MPa was applied using an arc-shaped pressure block (7) to compact the powder. Five concentric circular grooves were scraped on the surface of the compacted powder using a scraper with a tooth depth of 10 mm and a tooth width of 8 mm, which was concentric with the loading crucible.

[0073] (3) Seal the crucible in the growth furnace, evacuate it, and then fill it with an appropriate amount of high-purity argon as the growth atmosphere. Use the standard PVT process of Example 1 for growth, and slowly cool it to room temperature according to the program to obtain silicon carbide single crystal ingot.

[0074] Figure 4The silicon carbide crystal grown in Example 3 has a smooth and flat surface and excellent quality.

[0075] Comparative Example 1 - Simple Filling Method with Single Raw Material (Traditional Method)

[0076] Raw material preparation:

[0077] High-purity silicon carbide powder (SiC): 1400 g of SiC powder of the same batch and particle size (250 mesh) as in Example 1 of this invention was used. It was also vacuum-dried at 200°C for 4 hours.

[0078] Filling process:

[0079] 1400 g of SiC powder was poured directly into a growth crucible of identical specifications to that in Example 1 of this invention. Using a standard graphite scraper, the powder surface was simply smoothed until it was roughly parallel to the top edge of the crucible. No step-by-step filling, no mechanical compaction, and no surface texturing treatment were performed. The filled crucible was then directly placed into the crystal growth furnace.

[0080] Crystal growth:

[0081] Crystal growth was performed using the same growth equipment, temperature field program, pressure control, and growth time as in Embodiment 1 of the present invention to ensure consistency of growth conditions.

[0082] Figure 5 The silicon carbide crystal grown in Comparative Example 1 has poor growth quality, with obvious wrinkles on the crystal surface and poor smoothness.

[0083] Comparative Example 2

[0084] The same high-purity graphite powder (C, 120 mesh), crystalline silicon powder (Si, 180 mesh), and silicon carbide powder (SiC, 250 mesh) were used as in Example 1 of this invention. The total mass was consistent with that of Example 1 (C: 100 g, Si: 100 g, SiC: 1200 g). The dehydration and drying treatment was also exactly the same.

[0085] Loading process (reverse order):

[0086] Bottom Layer: 1200 g of silicon carbide powder (SiC) is placed at the bottom of the growth crucible and compacted using a pressure block at 10 MPa. Middle Layer: 100 g of crystalline silicon powder (Si) is carefully spread over the compacted SiC layer as the middle layer. Top Layer: 100 g of graphite powder (C) is placed in the crucible and covers the silicon powder layer. Since graphite powder is coarse-grained, it is not heavily compacted here; only lightly leveled.

[0087] The surface texture of the top layer of C powder is not applied (because it is granular and cannot effectively form grooves).

[0088] Crystal growth:

[0089] Crystal growth was performed using the same growth equipment, temperature field program, pressure control, and growth time as in Embodiment 1 of the present invention.

[0090] Initial growth phenomena: The pressure inside the growth chamber fluctuated continuously and violently when it reached the melting point of silicon, accompanied by a strong pressure spike, triggering a safety alarm. After growth, the furnace was severely contaminated.

[0091] Raw material condition: The raw materials in the crucible are severely bonded and caking, with the SiC layer, solidified Si blocks and C powder mixed into a hard, difficult-to-separate whole.

[0092] Crystal growth status: Growth failed. Only sporadic and irregular polycrystalline deposits were observed at the seed crystal site, making it impossible to form a continuous single crystal.

[0093] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for loading raw materials for growing SiC single crystals using the PVT method, characterized in that, Includes the following steps: S1: Place graphite powder at the bottom of the growth device, place crystalline silicon powder on the upper surface of the graphite powder and cover it with graphite powder, place silicon carbide powder on the upper surface of the crystalline silicon powder and cover it with crystalline silicon powder, and then compact it; the mass ratio of graphite powder, crystalline silicon powder and silicon carbide powder is (0.1~2):(0.1~2):(6~10); S2: Texture the upper surface of the compacted silicon carbide powder to form a concave structure.

2. The raw material filling method according to claim 1, characterized in that, The mass ratio of graphite powder, crystalline silicon powder, and silicon carbide powder is (0.5~1.5):(0.5~1.5):(8~10).

3. The raw material filling method according to claim 1 or 2, characterized in that, The graphite powder has an average particle size range of 80-200 mesh, the crystalline silicon powder has an average particle size range of 100-325 mesh, and the silicon carbide powder has an average particle size range of 200-400 mesh.

4. The raw material filling method according to any one of claims 1 to 3, characterized in that, The average particle size of the graphite powder is greater than the average particle size of the crystalline silicon powder, and the average particle size of the crystalline silicon powder is greater than or equal to the average particle size of the silicon carbide powder.

5. The raw material filling method according to any one of claims 1 to 4, characterized in that, The compaction process uses a pressure of 5~15 MPa.

6. The raw material filling method according to any one of claims 1 to 5, characterized in that, The recessed structure is a groove.

7. The raw material filling method according to claim 6, characterized in that, The grooves include, but are not limited to, concentric annular grooves, spiral grooves, or radial grooves.

8. The raw material filling method according to claim 6 or 7, characterized in that, The depth of the groove is 3~10 mm and the width is 3~8 mm.

9. The raw material filling method according to any one of claims 6 to 8, characterized in that, The number of concentric circular grooves is 3 to 5.

10. A method for growing silicon carbide crystals, characterized in that, The raw materials are filled using the method described in any one of claims 1 to 9.

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