Graphite disc and ring for epitaxial growth of silicon carbide

Abstract

The graphite disc and the graphite ring are used as a bearing base for epitaxial growth of silicon carbide, the graphite disc and the graphite ring are integrally formed, the graphite ring is located on the outer side of the graphite disc in the radial direction of the graphite disc, and the height of the graphite disc is smaller than that of the graphite ring in the axial direction of the graphite disc. The graphite plate and the graphite ring are provided with an open slot in a surrounding manner and coated with a tantalum carbide coating, the graphite plate and the graphite ring are integrally arranged, the technical defect that mechanical weak points exist at the joint of the graphite plate and the graphite ring of an existing device is overcome, the mechanical strength and the mechanical rigidity of the device are effectively enhanced, and the service life of the device is prolonged. And the possibility of deformation in the subsequent high-temperature baking process is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor epitaxial growth equipment and materials technology, and in particular to a graphite disk and ring for silicon carbide epitaxial growth. Background Technology

[0002] Silicon carbide, a third-generation semiconductor, has great potential for application in fields such as electric vehicles and 5G communications due to its excellent properties such as high breakdown field strength and high thermal conductivity. Its epitaxial process is a key step in the fabrication of high-performance power devices. This process is usually carried out at a high temperature of about 1600°C, with the wafer substrate placed on a graphite disk and ring inside the cavity.

[0003] The core bottleneck of current technology lies in the fact that the existing structural designs of graphite disks and rings used for silicon carbide epitaxial growth have mechanical weaknesses at the joints and insufficient overall thickness. This makes them prone to inherent defects such as initial deformation under thermal stress, resulting in a significant decrease in structural stability after repeated high-temperature epitaxy and subsequent high-temperature baking and cleaning cycles. Furthermore, existing graphite disks and rings used for silicon carbide epitaxial growth are based on graphite substrates. The graphite substrate itself deteriorates in high-temperature corrosive gases through continuous corrosion and volatilization, leading to a decrease in density and a loose microstructure, which in turn causes a reduction in mechanical strength and stiffness.

[0004] The aforementioned structural weaknesses, combined with material degradation, lead to cumulative deformation of the graphite disk and ring. This deformation directly causes deformation of the wafer substrate placed on top, resulting in the unintended deposition of reactive gases on the back side of the wafer, causing anomalies such as fogging, black spots, and markings. Simultaneously, the volatilization of the graphite substrate inevitably introduces carbon atom impurities into the epitaxial layer, increasing epitaxial defects and leading to increased chip leakage and reduced lifespan. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects in the prior art where graphite disks and rings are prone to deformation under high temperature epitaxy and high temperature baking and cleaning conditions, thereby providing a graphite disk and ring for silicon carbide epitaxial growth.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A graphite disk and ring for silicon carbide epitaxial growth, comprising: Graphite disk; A graphite ring is integrally formed with the graphite disk. Along the radial direction of the graphite disk, the graphite ring is located on the radial outer side of the graphite disk. Along the axial direction of the graphite disk, the height of the graphite disk is less than the height of the graphite ring. The graphite disk and the graphite ring are surrounded by an opening groove. Both the graphite disk and the graphite ring are coated with tantalum carbide.

[0007] Preferably, the tantalum carbide coating thickness is 30~40µm.

[0008] Preferably, the projections of the graphite disk and the graphite ring are spaced apart along the axial direction; A graphite connecting part is also provided between the graphite disk and the graphite ring. The graphite connecting part is set at an angle to the axial direction. The outer edge of the graphite connecting part is fixed to the graphite ring, and the inner edge of the graphite connecting part is fixed to the graphite disk.

[0009] Preferably, along the radial inner side of the graphite disk, the graphite ring has a planar portion protruding towards the graphite disk.

[0010] Preferably, the height of the graphite disk is the same everywhere along the axial direction.

[0011] Preferably, the graphite disk and the graphite ring are arranged in parallel along the radial direction, and the projected portions of the graphite disk and the graphite ring overlap.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: The graphite disk and ring provided in the above technical solution for silicon carbide epitaxial growth, by designing the graphite disk and ring as an integral structure, fundamentally eliminates the mechanical weaknesses at the connection points of traditional split structures, significantly enhancing the overall structural strength and rigidity. This integrated and robust design, combined with the specific layout of the graphite ring being higher than the graphite disk in the axial direction, can effectively resist thermal stress during high-temperature epitaxy and subsequent cleaning cycles, significantly reducing the possibility of device deformation. The reduction in deformation directly avoids defects such as back-side fogging, black spots, and markings caused by unevenness of the support substrate, thereby improving the yield and electrical performance consistency of the epitaxial wafer. A tantalum carbide coating is applied to the surface of both the graphite disk and the graphite ring, forming a dense and chemically stable protective layer. This tantalum carbide coating can effectively prevent carbon atoms in the graphite matrix from volatilizing into the epitaxial growth gas at high temperatures, eliminating carbon impurities from contaminating the silicon carbide epitaxial layer at the source, ensuring the crystal purity of the epitaxial layer, which is crucial for reducing device leakage current and extending chip lifespan. On the one hand, the integrated design of the graphite disk and graphite ring simplifies the processing steps and reduces the manufacturing cost of the product. On the other hand, the robust structure and high-temperature resistant tantalum carbide coating enable the device to withstand repeated high-temperature baking and cleaning. This cleaning process can efficiently remove byproducts generated at the edges of the device, including the opening slot area, during the growth process, allowing the graphite disk and graphite ring to be reused, significantly extending their service life, and significantly reducing the consumable cost per wafer, resulting in outstanding economic benefits. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0014] Figure 1 A top view of the graphite disk and ring for silicon carbide epitaxial growth provided by the present invention; Figure 2 A bottom view of the graphite disk and ring for silicon carbide epitaxial growth provided by the present invention. Figure 3 A cross-sectional view of the graphite disk and ring for silicon carbide epitaxial growth provided by the present invention.

[0015] Explanation of reference numerals in the attached figures: 1. Graphite disk; 2. Graphite ring; 21. Opening groove; 22. Flat part; 3. Graphite connecting part. Detailed Implementation

[0016] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., 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 the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0018] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0019] Please see Figures 1 to 3 This invention provides a graphite disk and ring for silicon carbide epitaxial growth. The core of this device lies in the combination of integrated structural design and surface coating technology. It mainly includes three core parts: a graphite disk 1, a graphite ring 2, and a graphite connecting part 3 that connects the two.

[0020] Existing split designs, whether bolted or nested, all possess a physical interface. During high-temperature cycling at 1600℃, the thermal expansion of graphite and the minute gaps between different components lead to stress concentration, becoming the starting point for deformation. This invention, through integral molding, makes the graphite disk 1 and graphite ring 2 a continuous, homogeneous single component, fundamentally eliminating this interface and completely solving the problem of mechanical weak points at the connection. The resulting technical effect of this integral molding design is a significant improvement in the overall structural integrity of the device, providing a structural foundation for preventing deformation during subsequent high-temperature baking processes.

[0021] An integrated structure means that forces can be transmitted continuously throughout the entire component, rather than being interrupted or reflected at the interface. This integrated structure results in an order-of-magnitude increase in the bending and torsional stiffness of the device. The technological benefit of an integrated structure is that the device exhibits greater stability when subjected to its own weight, wafer weight, and the impact of high-temperature airflow, and is less prone to minute vibrations or tremors, providing a more stable growth environment for silicon carbide epitaxial layers.

[0022] The taller graphite ring 2 forms a robust "fence" or "moat," providing strong lateral support and constraint for the internal graphite disk 1. When the device is heated, the high-rigidity structure of the graphite ring 2 effectively suppresses the upward warping of the edges of the graphite disk 1, keeping the deformation of the entire device within a very small range. This structure not only resists vertical deformation but, more importantly, suppresses edge warping, one of the main deformation modes leading to defects on the back side of the wafer. This design effectively ensures the wafer yield.

[0023] The opening slot 21, enclosed by the graphite disk 1 and the graphite ring 2, offers technical benefits beyond merely creating a structural void. Firstly, it provides an optimized flow channel for the process gas carried on the graphite disk 1, facilitating more uniform laminar flow and preventing eddies at the wafer edges. Secondly, it provides space for other components within the cavity, such as temperature probes and lifting pins. A further benefit is that the slot design helps reduce byproduct deposition caused by gas stagnation at the device's edge areas, allowing subsequent high-temperature baking and cleaning to more efficiently clean these areas, extending the device's cleaning cycle and lifespan.

[0024] Tantalum carbide has a melting point of 3880℃ and excellent chemical inertness. In an epitaxial environment of 1600℃, it forms a dense, non-porous physical barrier. The direct technical effect of coating the device surface with tantalum carbide is to completely isolate the graphite matrix from corrosive high-temperature gases, reducing the volatility of graphite to near zero, thereby preventing carbon impurities from contaminating the epitaxial layer. The technical benefits derived from coating the device surface with tantalum carbide are multifaceted: First, the coating itself has high hardness and wear resistance, enhancing the mechanical strength of the device surface and reducing the possibility of scratches during wafer loading and unloading; second, because the coating protects the graphite matrix from corrosion, the device's microstructure remains stable over a long period, meaning its mechanical strength and stiffness will not decrease due to material degradation, further extending the device's deformation resistance life.

[0025] If the tantalum carbide coating is too thin, for example, less than 20 μm, there may be risks of pinholes or incomplete coverage, failing to completely block the diffusion path of carbon atoms, resulting in incomplete protection. If the coating is too thick, for example, greater than 60 μm, due to the difference in thermal expansion coefficients between tantalum carbide and the graphite substrate, the excessively thick coating will generate huge internal stress under drastic temperature changes, easily leading to coating cracking and peeling. Once peeled off, the protective effect is completely lost. A thickness of 30~40 μm ensures the formation of a continuous, non-porous, dense protective layer while controlling the thermal mismatch stress between the coating and the substrate within a safe range, guaranteeing the long-term reliability of the coating. The technical advantage derived from controlling the thickness of the tantalum carbide coating is that this optimized thickness range ensures performance while also taking into account process cost and deposition efficiency, achieving the best balance between performance and economy.

[0026] like Figure 3 As shown, the inclined graphite connector 3 forms a structure similar to a "truss" or "cable-stayed bridge." When the device is heated, the radial and axial expansion of the graphite ring 2 is transmitted to the graphite disk 1 through the graphite connector 3. Because the graphite connector 3 is inclined, this force can be decomposed into vertical and horizontal components, thereby effectively dispersing the concentrated stress over a larger area. In contrast, a simple vertical connecting wall would directly transmit stress, easily leading to fracture at the connection point. The technical effect of the graphite connector 3 is that it greatly enhances the device's resistance to thermal shock and thermal cycling. This structural design allows energy to be absorbed and released more evenly during repeated heating and cooling, reducing the generation and propagation of microcracks caused by localized stress concentration, fundamentally improving the device's fatigue life, and laying the structural foundation for the device to be used repeatedly in high-temperature environments.

[0027] The "axial projection interval setting" is the geometric prerequisite for realizing the inclined graphite connector 3. It causes the graphite disk 1 and graphite ring 2 to be offset in the vertical direction, providing space for the inclined installation of the graphite connector 3. This non-coplanar three-dimensional structure has higher structural stability and resistance to deformation compared to traditional planar structures. The resulting technical effect is that the complex spatial structure makes the entire device a highly rigid three-dimensional frame, which can effectively transfer and balance thermal or mechanical stresses from any direction.

[0028] The connection point between the graphite connector 3 and the graphite ring 2 is a critical area of ​​stress concentration. The planar portion 22 acts as a "reinforcing rib" or "base" at this connection point, increasing the connection area and dispersing the pressure exerted by the graphite connector 3 on the graphite ring 2. This significantly enhances the structural strength of the connection point, preventing cracks or fractures in this area during long-term thermal cycling. A further benefit of the planar portion 22 is that it provides additional support to the bottom of the graphite ring 2, enhancing the overall stability of the device and making it more stable when placed on the graphite disk 1.

[0029] The upper surface of graphite disk 1 is the bearing surface that directly contacts the wafer substrate. Any slight tilt or unevenness on this surface, even with varying heights, can cause the wafer to bend under gravity or experience uneven stress distribution at high temperatures. This ensures the wafer remains in an ideal, level state throughout the entire epitaxial growth process. The resulting technical benefits include uniform heating and a uniform supply of reactive gases, which is crucial for growing high-quality silicon carbide epitaxial layers with uniform thickness, uniform doping, and low defect density, directly improving the consistency of device electrical performance and yield.

[0030] The "radial parallel arrangement" ensures that the main bearing surfaces of the graphite disk 1 and graphite ring 2 are parallel, which is the foundation for ensuring the overall stability of the device. The "projection overlap," together with the "projection interval," defines the precise three-dimensional installation position of the graphite connector 3. This precise geometric relationship ensures that the inclined graphite connector 3 can connect the disk and ring at the optimal angle, thereby maximizing structural strength and stiffness. This meticulously designed geometric layout allows the entire device to achieve a mechanically optimized state, achieving the highest structural efficiency with minimal material, embodying the unity of lightweight and high strength.

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The graphite surface is surface-treated for 20-30 minutes by heating the reaction chamber to 1800°C and introducing H2 at a rate of 5 L / min. Then, a mixture of H2, tantalum pentachloride (TaCl5), and methane (CH4) is introduced in a gas ratio of 10:1:2. The reaction temperature is 1600-1800°C, the reaction pressure is 5000-8000 Pa, and the reaction time is 3 hours. After deposition, the temperature is gradually lowered to room temperature.

[0032] The integrated processing technology for graphite disk 1 and graphite ring 2 is as follows: Graphite disk 1 and graphite ring 2 are processed as a single piece, using a single high-purity isostatic graphite blank, and are formed in one go using a five-axis CNC machine tool. This avoids the interface stress concentration caused by traditional split connections, ensuring that graphite disk 1 and graphite ring 2 are continuous and homogeneous single components.

[0033] The processing includes roughing, finishing and polishing stages: roughing removes excess material, finishing ensures dimensional accuracy, and polishing optimizes surface roughness to reduce the risk of scratches during wafer placement.

[0034] After processing, ultrasonic testing is used to ensure that there are no defects inside the graphite disk 1 and graphite ring 2, so as to provide a uniform substrate for subsequent coating processes.

[0035] High-purity isostatic graphite is selected, with a purity of not less than 99.99% and a density of not less than 1.80 g / cm³. This ensures the material's mechanical strength and low volatility at high temperatures of 1600~1800°C.

[0036] Dimensional accuracy and positional tolerance are controlled within ±0.05mm. This ensures that the geometric parameters such as the height difference and parallelism between the graphite disk 1 and the graphite ring 2 are consistent, thereby uniformly distributing thermal stress during high-temperature cycling.

[0037] The spindle speed of a five-axis CNC machine tool should not be less than 10,000 rpm, and the feed rate should be controlled at 0.1~0.5 mm / min to avoid micro-cracks during machining.

[0038] Processing is carried out in a constant temperature and humidity workshop with a temperature of 20±2°C and a humidity of ≤50% to prevent graphite from absorbing moisture and affecting dimensional stability.

[0039] This process, through integrated design, uniformly distributes thermal stress, controlling deformation to below 0.1mm (reference). <c278>This significantly extends the lifespan of the device.

[0040] Process and parameters of tantalum carbide coating: The tantalum carbide coating is formed on the surface of graphite disks and rings using chemical vapor deposition (CVD). The process consists of three stages: pretreatment, deposition, and post-treatment.

[0041] Pretreatment: The device is placed in the reaction chamber and heated to 1800°C. Hydrogen gas (H2) is introduced for surface treatment at a flow rate of 5 L / min for 20-30 min. This removes surface impurities and enhances coating adhesion.

[0042] Deposition: After pretreatment, reactive gases (tantalum pentachloride TaCl5 and methane CH4) are introduced, causing a chemical reaction on the graphite surface to form a TaC coating. The deposition process is strictly controlled in terms of temperature and pressure to ensure a uniform and pore-free coating.

[0043] Post-processing: After deposition, the temperature is gradually reduced to room temperature at a rate of 5°C / min to avoid thermal shock. Surface polishing is then performed to achieve a coating surface roughness Ra ≤ 0.2 μm, reducing wafer contact defects.

[0044] Deposition temperature: 950~1050°C. This temperature range is below the 1600°C degradation point of graphite, but above the activation energy of the TaC reaction, ensuring a dense coating. Temperatures above 1050°C can cause stress cracking in the coating; temperatures below 950°C result in a slow deposition rate and a higher risk of pinholes.

[0045] Reaction gases: tantalum pentachloride (TaCl5) and methane (CH4), in a flow ratio of 1:3. TaCl5 provides the tantalum source, and CH4 provides the carbon source. The flow ratio is optimized to 1:3 to avoid carbon excess or tantalum deficiency, ensuring the coating stoichiometry of TaC.

[0046] Deposition pressure: 8 kPa. This low-pressure environment promotes gas diffusion and forms a uniform coating; gas pressure above 10 kPa will cause particle deposition, while gas pressure below 5 kPa will reduce deposition efficiency.

[0047] Deposition time: 3 hours. Combined with temperature and pressure, this time ensures a coating thickness of 30-40 μm, consistent with the polishing requirements indicated in red.

[0048] Post-processing parameters: Polishing was performed using diamond polishing paste with a particle size of 0.5 μm, resulting in a final surface roughness Ra ≤ 0.2 μm. This improves the coating's abrasion resistance and reduces wafer handling scratches.

[0049] The process is implemented in a standard CVD equipment, the gas source is readily available, and the cost is controllable: TaCl5 consumption is about 0.5 kg / batch, and the total process time is about 4 hours.

[0050] Parameter settings ensure coating performance: a dense layer is formed at 950-1050°C with a thickness of 30-40 μm, and the carbon impurity concentration is less than 10¹. 5 atoms / cm³, significantly reducing epitaxial layer defects.

[0051] During silicon carbide epitaxial growth, this apparatus is placed at the bottom of the reaction chamber. The wafer substrate is placed on a graphite disk 1 with uniform height. When the temperature is raised to 1600℃, the integrated structure and the inclined graphite connectors 3 work together to uniformly distribute the enormous thermal stress, and the overall deformation of the apparatus can be controlled to below 0.1 mm. The tantalum carbide coating on the surface completely blocks graphite volatilization, ensuring that the carbon impurity concentration in the epitaxial layer is below 10¹. 5 atoms / cm³. In subsequent hydrogen baking and cleaning at 1750℃, its robust structure and stable coating allow it to withstand over 500 cycles, significantly extending its service life beyond that of traditional devices.

[0052] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A graphite disk and ring for silicon carbide epitaxial growth, used as a support base for silicon carbide epitaxial growth, characterized in that, include: Graphite disk (1); A graphite ring (2) is integrally formed with the graphite disk (1). Along the radial direction of the graphite disk (1), the graphite ring (2) is located on the radial outer side of the graphite disk (1). Along the axial direction of the graphite disk (1), the height of the graphite disk (1) is less than the height of the graphite ring (2). The graphite disk (1) and the graphite ring (2) are surrounded by an opening groove (21). The graphite disk (1) and the graphite ring (2) are both coated with tantalum carbide coating.

2. The graphite disk and ring for silicon carbide epitaxial growth according to claim 1, characterized in that, The thickness of the tantalum carbide coating is 30~40um.

3. The graphite disk and ring for silicon carbide epitaxial growth according to claim 1, characterized in that, Along the axial direction, the projections of the graphite disk (1) and the graphite ring (2) are spaced apart; A graphite connecting part (3) is provided between the graphite disk (1) and the graphite ring (2). The graphite connecting part (3) is set at an angle to the axial direction. The outer edge of the graphite connecting part (3) is fixed to the graphite ring (2), and the inner edge of the graphite connecting part (3) is fixed to the graphite disk (1).

4. The graphite disk and ring for silicon carbide epitaxial growth according to claim 1, characterized in that, Along the radial inner side of the graphite disk (1), the graphite ring (2) has a planar portion (22) protruding toward the graphite disk (1).

5. The graphite disk and ring for silicon carbide epitaxial growth according to claim 1, characterized in that, Along the axial direction, the height of the graphite disk (1) is the same everywhere.

6. The graphite disk and ring for silicon carbide epitaxial growth according to claim 1, characterized in that, Along the radial direction, the graphite disk (1) and the graphite ring (2) are arranged in parallel, and the projected portions of the graphite disk (1) and the graphite ring (2) overlap.

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