A graphite crucible structure

Abstract

The application relates to the field of crucibles for crystal growth, in particular to a graphite crucible structure. The graphite crucible structure comprises a base, an adjusting ring, a porous homogeneous plate, a seed crystal holder and a top cover; the base, the adjusting ring and the porous homogeneous plate are sequentially connected from bottom to top, the seed crystal holder is arranged at the bottom of the top cover, the porous homogeneous plate is provided with homogeneous holes, the porous homogeneous plate is horizontally arranged on the adjusting ring, a raw material sublimation zone is arranged below the porous homogeneous plate, a crystal growth zone is arranged between the porous homogeneous plate and the seed crystal holder, gaseous substances generated by raw material sublimation are reformed through the porous homogeneous plate, and laminar flow with uniform flow velocity and concentration distribution in a radial plane is formed in the crystal growth zone. The turbulent airflow is converted into uniform and parallel laminar flow through the porous homogeneous plate, the whole seed crystal growth surface is uniformly supplied, the crystal is effectively promoted to grow in a stable and equal-diameter mode, the defect density of dislocations, microtubules and the like in the crystal is greatly reduced, the radial uniformity and overall yield of the wafer are improved, and high-quality crystals with uniform radial properties are obtained.

Description

Technical Field

[0001] This invention relates to the field of crucibles for crystal growth, and in particular to a graphite crucible structure. Background Technology

[0002] Silicon carbide single crystals, as a key substrate material for third-generation semiconductors, are mainly grown in a high-temperature vacuum or inert gas environment via the PVT (physical vapor transport) method. In this method, silicon carbide raw material powder sublimates in the high-temperature zone at the bottom of a graphite crucible, and the resulting gaseous substances (mainly Si, Si2C, SiC2, etc.) are transported to the lower-temperature zone at the top, where they crystallize and grow on the seed crystal.

[0003] Existing graphite crucibles are typically simple cylindrical structures, internally divided into a raw material zone and a growth zone. This structure has significant drawbacks: due to the inherent radial inhomogeneity of the thermal field and the limited internal space of the crucible, the gaseous substances generated during the sublimation of the raw material are prone to centrally convergent or turbulent natural convection during transport to the seed crystal. This results in uneven radial distribution of the gas phase composition and flow rate at the crystal growth interface, causing localized oversaturation or undersaturation at the growth interface. Ultimately, this leads to severe radial resistivity inhomogeneity, high-density dislocations, and microtube defects in the grown crystal, severely impacting crystal quality, usable area, and production yield. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the background technology by proposing a graphite crucible structure that transforms turbulent airflow into uniform and parallel laminar flow through a porous homogeneous plate, uniformly supplying the entire seed crystal growth surface. This effectively promotes uniform and stable crystal growth, significantly reduces the density of defects such as dislocations and microtubes in the crystal, improves the radial uniformity and overall yield of the wafer, and obtains a high-quality crystal with uniform radial properties.

[0005] The technical solution of this invention provides a graphite crucible structure, comprising a base, an adjusting ring, a porous homogenizing plate, a seed crystal holder, and a top cover. The base, adjusting ring, and porous homogenizing plate are connected sequentially from bottom to top. The seed crystal holder is disposed at the bottom of the top cover. The porous homogenizing plate is provided with homogenizing holes and is horizontally disposed on the adjusting ring, located below the seed crystal holder. The area below the porous homogenizing plate is the raw material sublimation zone, and the area between the porous homogenizing plate and the seed crystal holder is the crystal growth zone. The gaseous substances generated by the sublimation of the raw material are reformed by the porous homogenizing plate and form a laminar flow in the crystal growth zone with uniformly distributed flow rate and concentration in the radial plane.

[0006] Preferably, the ratio of the base wall thickness t to the inner diameter D of the graphite crucible structure satisfies: 0.08≤t / D≤0.15.

[0007] Preferably, the porous homogeneous plate is made of high-purity graphite or silicon carbide coated graphite, and the thickness L of the porous homogeneous plate is 8mm-12mm.

[0008] Preferably, the total height H of the graphite crucible structure total The ratio of the inner diameter to the inner diameter D satisfies: 0.8 ≤ H total / D≤1.5.

[0009] Preferably, the height H of the raw material sublimation zone source H, the total height of the graphite crucible structure total 35%-45%, crystal growth region height H growth The inner diameter D of the graphite crucible structure satisfies: H growth ≥0.5D.

[0010] Preferably, the pore diameter d of the homogeneous pores ranges from 50 μm to 500 μm.

[0011] Preferably, the overall porosity φ of the porous homogeneous plate is in the range of 20%-40%.

[0012] Preferably, the radial plane of the porous homogeneous plate is divided into at least two concentric annular regions, and within the annular regions, the distribution of homogeneous pores satisfies the following condition: the original airflow velocity and the local porosity are inversely proportional.

[0013] Preferably, the radial plane of the porous homogeneous plate is divided into three concentric annular regions: a central region, a transition region, and an edge region. The inner diameter of the crucible body is D, the radius of the central region ranges from 0 to D / 6, the radius of the transition region ranges from D / 6 to D / 3, and the radius of the edge region ranges from D / 3 to D / 2; the local porosity φ of the edge region... edge The local porosity φ in the transition zone mid With respect to the local porosity φ in the central region center Satisfy: φ edge <φ mid <φ center .

[0014] Preferably, the multiple homogeneous holes on the porous homogenizing plate are arranged in an equilateral triangular or square grid, and the number of homogeneous holes per unit area is n=4φ. local / (πd²), where φ local φ represents the local porosity, d represents the homogeneous pore diameter, and φ represents the local porosity. local Based on its location, it corresponds to φ. edge or φ mid or φ center .

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention sets a porous homogenizing plate inside the crucible structure, and actively rectifyes and homogenizes the sublimation gas flow through the principle of fluid dynamics. When the turbulent gas flow passes through the porous homogenizing plate, it is forced to be diverted, damped and reorganized, and transformed into a uniform and parallel laminar flow, which is uniformly supplied to the entire seed crystal growth surface. This can effectively promote the uniform and stable growth of the crystal, significantly reduce the density of defects such as dislocations and microtubes in the crystal, improve the radial uniformity and overall yield of the wafer, and obtain a high-quality crystal with uniform radial properties. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention; Figure 2 This is a structural cross-sectional view of an embodiment of the present invention; Figure 3 A top view of the radial partitioning differential design for a porous homogeneous plate.

[0017] Attached reference numerals: 1. Base; 2. Adjustment ring; 3. Perforated homogenizing plate; 4. Seed crystal holder; 5. Top cover; 51. Threaded interface. Detailed Implementation

[0018] like Figures 1-3 As shown in the figure, the graphite crucible structure proposed in this embodiment is an overall annular cylindrical structure, including a base 1, an adjusting ring 2, a porous homogenizing plate 3, a seed crystal holder 4, and a top cover 5. The base 1, adjusting ring 2, and porous homogenizing plate 3 are connected sequentially from bottom to top. Silicon carbide raw material powder is contained inside the base 1. The seed crystal holder 4 is located at the bottom of the top cover 5 and is used to attach and fix the seed crystal. The top of the top cover 5 is provided with a threaded interface 51 for threaded connection with other mechanisms that can drive the crucible to move.

[0019] The porous homogenizing plate 3 is made of high-purity graphite or silicon carbide-coated graphite. The porous homogenizing plate 3 has homogenizing holes and is horizontally positioned on the adjusting ring 2, below the seed crystal holder 4. The area below the porous homogenizing plate 3 is the raw material sublimation zone, and the area between the porous homogenizing plate 3 and the seed crystal holder 4 is the crystal growth zone. The structural parameters of the graphite crucible and the internal porous homogenizing plate 3 are designed in synergy based on fluid dynamics and thermodynamics principles, so that the gaseous substances generated by the sublimation of the raw materials, after being reformed by the porous homogenizing plate 3, form a laminar flow with uniform velocity and concentration in the radial plane within the crystal growth zone.

[0020] The adjusting ring 2 is equipped with a mounting base. By adjusting the position of the mounting base, the distance between the porous homogeneous plate 3 and the seed crystal holder 4 can be adjusted, thereby changing the volume ratio between the upper and lower cavities to adapt to the needs of different process formulas or raw material quantities, thus enhancing the process adaptability of the crucible.

[0021] (1) Design requirements for base 1 in the crucible structure: The sidewall of base 1 has a uniform axial wall thickness. The wall thickness t is determined based on mechanical strength and thermal stress optimization criteria. The combined effects of the total gravity load of the crucible and its internal raw materials, as well as the pressure difference between the inside and outside of the process, are equivalent to the equivalent design pressure Peq acting on the cylinder wall. Based on the principle that circumferential stress is the control stress, the minimum wall thickness is taken as the larger of the following two values: ; ; The wall thickness t shall not be less than the minimum wall thickness t calculated based on the stress formula for thin-walled containers, the bending strength of graphite material at the highest operating temperature, and a preset safety factor. min Furthermore, the final value of the wall thickness t was optimized through thermo-structural coupling simulation (using dedicated thermo-structural coupling simulation modules in finite element software such as ANSYS or ABQUS) to ensure that, at the highest operating temperature, the maximum thermal stress generated by the radial temperature difference in the crucible body does not exceed 30% of the high-temperature tensile strength of the graphite material. The final determined ratio of the base wall thickness t to the inner diameter D of the graphite crucible structure satisfies: 0.08 ≤ t / D ≤ 0.15. The equal wall thickness design helps to form a uniform radial thermal field.

[0022] (2) Design requirements for the total height of the crucible structure: Based on the optimization criteria of reaction space and flow field morphology, the total height H of the graphite crucible structure was determined. total The ratio of the height to the inner diameter D (i.e., the height-to-diameter ratio) satisfies: 0.8 ≤ H total / D≤1.5, preferably 1.0≤H total / D≤1.2.

[0023] (3) Design requirements for the installation position of the porous homogeneous plate 3: Installation follows the principle of functional zone height ratio, with the material sublimation zone height H... source H, the total height of the graphite crucible structure total 35%-45%, crystal growth region height H growth The inner diameter D of the graphite crucible structure satisfies: H growth ≥0.5D, thus providing ample space for the homogenized airflow.

[0024] (4) Design requirements for porous homogeneous plate 3: Aperture Design: The aperture d of the multiple homogeneous holes on the porous homogeneous plate 3 is determined based on the anti-clogging criterion and the flow control criterion. The lower limit d of the aperture d is... min ≥kD 95 D 95 The cumulative particle size distribution of silicon carbide raw material powder is 95%, where k is a coefficient of 3-5; the upper limit of pore size d is... maxSatisfy the following condition: Within the target process pressure range for silicon carbide crystal growth, the Knudsen number K of gas molecules within the homogeneous pores. n <0.01; Based on the above criteria, the pore diameter d of the homogeneous pores is determined to be in the range of 50μm-500μm, preferably 100μm-300μm.

[0025] Overall porosity design: The overall porosity φ of the porous homogeneous plate 3 is determined based on the target pressure drop criterion and the mass transfer requirement criterion. First, based on the target silicon carbide crystal growth rate and the stoichiometric relationship of the chemical reaction, the total volumetric flow rate Q of the gaseous substances generated by the sublimation of the raw materials is estimated. Then, the target pressure drop ΔP required by the porous homogeneous plate 3 is set, which accounts for 20% to 60% of the total gas pressure loss inside the graphite crucible structure. Finally, based on the flow model of viscous fluid through the porous medium, combined with the determined pore size d, the thickness L of the porous homogeneous plate 3, the gas dynamic viscosity μ at the process temperature, the cross-sectional area A of the porous homogeneous plate 3, the volumetric flow rate Q, and the target pressure drop ΔP, the overall porosity φ is calculated by inversion. ; The overall porosity φ of the porous homogeneous plate 3 is found to be in the range of 20%-40%, and the thickness L of the porous homogeneous plate 3 is 8mm-12mm.

[0026] Design of Homogeneous Pore Distribution: The distribution of multiple homogeneous pores on the porous homogeneous plate 3 is designed based on the airflow compensation criterion. The radial plane of the porous homogeneous plate 3 is divided into at least two concentric annular regions. Within the annular regions, the distribution of homogeneous pores satisfies the following condition: the original airflow velocity and the local porosity are inversely proportional. That is, a lower local porosity is set in regions with higher original airflow velocity (or material flux), and a higher local porosity is set in regions with lower original airflow velocity (or material flux). The local porosity of each annular region, after area-weighted averaging, equals the overall porosity φ.

[0027] The radially partitioned differential distribution design of the porous homogeneous plate 3 is as follows: the radial plane of the porous homogeneous plate 3 is divided into three concentric annular regions: a central region, a transition region, and an edge region, as shown in the figure. Figure 3 The crucible body has an inner diameter of D, a central region radius of 0-D / 6, a transition region radius of D / 6-D / 3, and an edge region radius of D / 3-D / 2; the local porosity φ in the edge region is... edge The local porosity φ in the transition zone mid With respect to the local porosity φ in the central region center Satisfy: φ edge <φ mid <φ center .

[0028] Homogeneous hole arrangement: Multiple homogeneous holes on the porous homogeneous plate 3 are arranged in an equilateral triangular or square grid, with the number of homogeneous holes per unit area n=4φ. local / (πd²), where φ local φ represents the local porosity, d represents the homogeneous pore diameter, and φ represents the local porosity. local Based on its location, it corresponds to φ. edge or φ mid or φ center That is, when determining the number of homogeneous pores in the central region, transition region, and edge region, φ local Take the φ corresponding to each region center φ mid and φ edge .

[0029] The parameters are determined based on a specific case as follows: 1. Crucible structure design parameters: Inner diameter D: 200mm (8 inches); Wall thickness t: Based on material property calculations and thermal stress simulation, t=24mm is taken, satisfying t / D=0.12, which is within the range of 0.08-0.15; Total height H total Take 240mm, height-to-diameter ratio H total / D=1.2, which is within the range of 1.0-1.2.

[0030] Set the initial height H of the raw material sublimation zone source It is 100mm (approximately H) total (42%), the initial height H of the crystal growth region growth It is 140mm, which meets the H requirement. growth ≥0.5D.

[0031] 2. Design parameters of porous homogeneous plate 3: 2.1 Plate thickness L: 10mm.

[0032] 2.2, Pore diameter d: Raw material powder D 95 =50μm, take k=4, then d min ≥200μm. The mean free path of the gas at process pressure is approximately 0.2mm. To maintain viscous flow K... n If the value is less than 0.01, the aperture needs to be much larger than this value. Taking all factors into consideration, the designed aperture d = 200 μm is selected.

[0033] 2.3 Overall porosity φ: The estimated flow rate of vaporized silicon at a target growth rate of 0.3 mm / h is converted to a standard state volumetric flow rate of Q ≈ 4.14 × 10⁻⁶. −5 m 3 / s. The target pressure drop ΔP of the porous homogeneous plate 3 is set to 35% of the total system pressure drop. According to the formula... Substituting parameters such as μ, A, d, L, Q, and ΔP, the overall porosity is calculated to be approximately 30%.

[0034] Within the temperature and pressure range of the PVT method for silicon carbide crystal growth, the mixed gaseous material generated by sublimation is considered equivalent to a gas with Si2C as the main component. At the preferred process temperature of 2300℃, the dynamic viscosity μ of the gas can be taken as approximately 7.0 × 10⁻⁶. -5 Pa·s, this value is derived from publicly available literature data and estimates of the dynamic properties of high-temperature gases. For different design target temperatures, adjustments can be made based on the principle that gas viscosity increases with increasing temperature.

[0035] Homogeneous pore distribution pattern: The plate surface with radius R=100mm is divided into the following three regions: Central region: radius 0-33mm (≈R / 3), local porosity φ is set. center =38%.

[0036] Transition zone: radius 33-67mm, local porosity φ set. mid =30%.

[0037] Edge region: radius 67-100mm, set local porosity φ edge =25%.

[0038] When this crucible structure is applied to crystal growth, the temperature of the raw material sublimation zone is raised to 2100℃-2300℃ via an external heating system, while the temperature at the seed crystal is slightly lower, creating a temperature gradient. During growth, the external drive structure slowly rotates the entire crucible via a threaded interface 51. After the raw material sublimates, the gaseous material passes through the porous homogeneous plate 3, reaching the seed crystal in a uniform flow pattern and crystallizing. After tens to hundreds of hours, a high-quality silicon carbide single crystal is grown.

[0039] In this embodiment, a porous homogenizing plate 3 is set inside the crucible structure. Through the principle of fluid dynamics, the sublimation gas flow is actively rectified and homogenized. When the turbulent gas flow passes through the porous homogenizing plate 3, it is forcibly split, damped and reorganized, and transformed into a uniform and parallel laminar flow. This uniformly supplies the entire seed crystal growth surface. Growth takes place in a uniform and stable material supply environment created at the crystal growth interface, which effectively suppresses the phenomenon of local oversaturation or undersaturation at the growth interface. It systematically solves the gas flow uniformity problem in the PVT method from the source and the path, which can effectively promote the uniform diameter and stable growth of crystals, significantly reduce the density of defects such as dislocations and microtubes in the crystal, improve the radial uniformity and overall yield of the wafer, and obtain a high-quality crystal with uniform radial properties.

[0040] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A graphite crucible structure, characterized in that, It includes a base (1), an adjusting ring (2), a porous homogenizing plate (3), a seed crystal holder (4), and a top cover (5); the base (1), the adjusting ring (2), and the porous homogenizing plate (3) are connected sequentially from bottom to top, the seed crystal holder (4) is set at the bottom of the top cover (5), the porous homogenizing plate (3) is provided with homogenizing holes, the porous homogenizing plate (3) is horizontally set on the adjusting ring (2), located below the seed crystal holder (4), the area below the porous homogenizing plate (3) is the raw material sublimation zone, and the area between the porous homogenizing plate (3) and the seed crystal holder (4) is the crystal growth zone. The gaseous substances generated by the sublimation of the raw materials are reformed by the porous homogenizing plate (3) and form a laminar flow with uniform flow rate and concentration in the radial plane in the crystal growth zone.

2. The graphite crucible structure according to claim 1, characterized in that, The ratio of the wall thickness t of the base (1) to the inner diameter D of the graphite crucible structure satisfies: 0.08≤t / D≤0.

15.

3. The graphite crucible structure according to claim 1, characterized in that, The porous homogeneous plate (3) is made of high-purity graphite or silicon carbide coated graphite.

4. The graphite crucible structure according to claim 1, characterized in that, The total height H of the graphite crucible structure total The ratio of the inner diameter to the inner diameter D satisfies: 0.8 ≤ H total / D≤1.

5.

5. The graphite crucible structure according to claim 1, characterized in that, Raw material sublimation zone height H source H, the total height of the graphite crucible structure total 35%-45%, crystal growth region height H growth The inner diameter D of the graphite crucible structure satisfies: H growth ≥0.5D.

6. The graphite crucible structure according to claim 1, characterized in that, The pore diameter d of the homogeneous pores ranges from 50μm to 500μm.

7. The graphite crucible structure according to claim 1, characterized in that, The overall porosity φ of the porous homogeneous plate (3) ranges from 20% to 40%.

8. The graphite crucible structure according to claim 1, characterized in that, The radial plane of the porous homogeneous plate (3) is divided into at least two concentric annular regions. Within the annular regions, the distribution of homogeneous pores satisfies the following condition: the original airflow velocity and the local porosity are inversely proportional.

9. A graphite crucible structure according to claim 8, characterized in that, The radial plane of the porous homogeneous plate (3) is divided into three concentric annular regions: a central region, a transition region, and an edge region. The inner diameter of the crucible body structure is D. The radius of the central region is 0-D / 6, the radius of the transition region is D / 6-D / 3, and the radius of the edge region is D / 3-D / 2. The local porosity φ of the edge region is... edge The local porosity φ in the transition zone mid With respect to the local porosity φ in the central region center Satisfy: φ edge <φ mid <φ center .

10. A graphite crucible structure according to claim 9, characterized in that, The porous homogeneous plate (3) has multiple homogeneous holes arranged in an equilateral triangular or square grid, with the number of homogeneous holes per unit area n=4φ. local / (πd²), where φ local φ represents the local porosity, d represents the homogeneous pore diameter, and φ represents the local porosity. local Based on its location, it corresponds to φ. edge or φ mid or φ center .

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