Graphite device with tantalum-tantalum carbide composite coating and flow fluctuation preparation method thereof

Abstract

The invention belongs to the technical field of chemical vapor deposition (CVD), and particularly relates to a graphite device of a tantalum-tantalum carbide composite coating and a flow fluctuation preparation method of the graphite device. The method comprises the following steps: firstly, depositing a tantalum metal buffer layer on the surface of a graphite matrix through a periodic flow fluctuation CVD (Chemical Vapor Deposition) technology, and then controlling and depositing a tantalum carbide coating on the buffer layer by adopting the flow fluctuation technology. The thermal mismatch stress of a film base is effectively relieved through the tantalum buffer layer, the bonding strength, compactness, toughness and thermal shock resistance of the coating are synergistically improved through the process of circularly switching high flow and low flow in combination with flow fluctuation, and the technical problem that a traditional tantalum carbide coating is prone to cracking and stripping is solved. The invention also provides the graphite device which is prepared by the method and has long service life and high reliability.

Description

Technical Field

[0001] This invention belongs to the field of chemical vapor deposition (CVD) technology, specifically relating to a graphite device with a tantalum-tantalum carbide composite coating and its flow fluctuation preparation method. Background Technology

[0002] Tantalum carbide (TaC) coatings are widely used for protecting graphite components in semiconductor crystal growth equipment due to their high melting point, excellent high-temperature stability, and ablation resistance. In high-temperature processes such as silicon carbide (SiC) crystal growth, where ambient temperatures often exceed 2000℃, traditional SiC coatings cannot meet the requirements due to phase transformation instability, making tantalum carbide coatings an ideal alternative. Chemical vapor deposition (CVD) is currently the mainstream method for preparing this type of coating, but it still has the following key problems: First, there is a significant difference in the coefficient of thermal expansion between the tantalum carbide coating and the graphite substrate. During high-temperature thermal cycling, the coating is prone to cracking or peeling due to thermal stress, which seriously affects the service life and process stability of the device.

[0003] Secondly, traditional CVD processes often employ constant flow gas supply, resulting in uneven distribution of reactant gases on the substrate surface. This can easily lead to problems such as large fluctuations in coating thickness, stress concentration in the structure, and grain coarsening, affecting the uniformity, density, and thermal shock resistance of the coating.

[0004] Patent document CN113549895A proposes a method for in-situ generation of tantalum carbide coating on the surface of graphite substrate. However, this method relies on the carbon source of graphite itself, has poor applicability to high-density graphite, and does not set an intermediate buffer layer, which cannot effectively alleviate the thermal mismatch stress of the film substrate. The bonding strength and thermal shock resistance of the coating are still insufficient.

[0005] Therefore, there is an urgent need to develop a novel tantalum carbide composite coating preparation method that can systematically solve problems such as weak film-substrate adhesion, high coating stress, and poor structural uniformity, in order to meet the long-term protection requirements of graphite devices under high temperature and strong thermal shock environments. Summary of the Invention

[0006] The objective of this invention is to provide a method for preparing a tantalum carbide composite coating on a graphite substrate. This method introduces a tantalum metal buffer layer between the graphite substrate and the tantalum carbide coating, and employs a periodically flow-controlled chemical vapor deposition process to systematically solve problems such as poor coating adhesion, easy cracking, insufficient thermal shock resistance, and poor uniformity. Specific objectives include: First, a method for preparing a tantalum carbide composite coating on the surface of a graphite substrate is provided. This method involves introducing a tantalum metal buffer layer between the graphite substrate and the tantalum carbide coating, and preparing the coating using a periodically flow-controlled chemical vapor deposition process.

[0007] Second, a graphite device prepared by the above method is provided, wherein a tantalum metal buffer layer is provided between the graphite substrate and the tantalum carbide coating.

[0008] The technical solution of the present invention is as follows: On one hand, a method for preparing a tantalum carbide composite coating on the surface of a graphite substrate is provided, comprising the following steps: S1: Provides a graphite matrix; S2: A tantalum metal buffer layer is deposited on the surface of the graphite substrate using chemical vapor deposition technology; S3: A tantalum carbide coating is deposited on the surface of the tantalum metal buffer layer by chemical vapor deposition. In the deposition process of S2 and S3, periodic flow fluctuation control is adopted. The periodic flow fluctuation control includes at least one cycle, and each cycle contains a first stage and a second stage with different flow rates.

[0009] Preferably, in the periodic flow fluctuation control, the total gas flow rate in the second stage is K times that in the first stage, where the value of K ranges from 1.5 to 3.0.

[0010] Preferably, the first and second phases are of equal duration, forming a fixed cycle, wherein the duration of a single segment of the fixed cycle is 3 to 10 minutes.

[0011] Preferably, in step S2, a mixed gas consisting of tantalum pentachloride, hydrogen and inert carrier gas is introduced, wherein the molar ratio of tantalum pentachloride, hydrogen and inert carrier gas is 1:(10~20):(10~30).

[0012] Preferably, in step S3, a mixed gas consisting of tantalum pentachloride, methane, hydrogen and an inert carrier gas is introduced, wherein the molar ratio of tantalum pentachloride, methane, hydrogen and inert carrier gas is 1:(1~2):(10~20):(10~30).

[0013] Preferably, the molar ratio of tantalum pentachloride, methane, hydrogen and inert carrier gas is 1:(1~1.5):(15~20):(10~20).

[0014] Preferably, in step S2, the deposition thickness of the tantalum metal buffer layer is 1~10μm; in step S3, the deposition thickness of the tantalum carbide coating is 10~50μm.

[0015] Preferably, in steps S2 and S3, the reaction temperature of the chemical vapor deposition is 1200~1600℃.

[0016] Preferably, after step S3, step S4 is further included: performing a progressive cooling treatment on the deposited workpiece, the progressive cooling treatment including: (1) After deposition, keep in situ at the reaction temperature for 2 to 4 hours; (2) Then, within 6 to 10 hours, the temperature of the reaction chamber is reduced to 700 to 800°C and kept at that temperature for 2 to 4 hours; (3) Finally, the temperature of the reaction chamber is reduced to room temperature within 20 to 40 hours.

[0017] On the other hand, the present invention provides a graphite device, including a graphite substrate and a tantalum carbide coating on the surface of the graphite substrate, wherein a tantalum metal buffer layer is provided between the graphite substrate and the tantalum carbide coating; the tantalum carbide coating and the tantalum metal buffer layer are prepared by the method for preparing a tantalum carbide composite coating on the surface of a graphite substrate.

[0018] Compared with the prior art, the advantages of the present invention are: (1) Synergistically Enhanced Film-Substrate Bonding: This invention innovatively introduces a tantalum metal buffer layer. Tantalum metal has good plasticity, effectively absorbing and relaxing the thermal stress generated between the tantalum carbide coating and the graphite substrate due to the mismatch in their coefficients of thermal expansion. Simultaneously, through the CVD process, the tantalum layer can form a strong chemical bond and physical wetting with the graphite substrate, and achieve good lattice matching and bonding with the upper tantalum carbide coating, thus fundamentally solving the problem of easy coating detachment. Experimental data in the examples show that the coating bonding strength prepared by the method of this invention reaches as high as 13.62 MPa, far superior to the comparative example without a buffer layer (9.48 MPa).

[0019] (2) Synergistically Optimized Overall Coating Performance: The core of this invention lies in the adoption of a periodic flow fluctuation control strategy. This strategy breaks the equilibrium growth mode of constant flow CVD by actively and periodically changing the supply rate of the reactive gas. Experimental data shows that this unique process, combined with the tantalum metal buffer layer, produces a synergistic effect, resulting in breakthrough improvements in three inherently restrictive indicators: bonding strength, thickness uniformity, and thermal shock resistance (see Example 1). Compared to the constant flow process with only a buffer layer (Comparative Example 2), the coating bonding strength of this invention is improved by approximately 16%, the thickness uniformity is improved by approximately 76%, and no cracks are observed after 10 severe thermal shock cycles.

[0020] Excellent coating uniformity and consistency: Flow fluctuations keep the reaction atmosphere in dynamic equilibrium in the reaction chamber, avoiding the axial and radial concentration gradients in the reaction chamber caused by gas depletion under constant flow conditions, thereby significantly improving the uniformity of coating thickness. For example, the coating thickness non-uniformity of Example 1 of the present invention is only ±2.1%, which is much lower than that of Comparative Example 2 with constant flow feeding (±8.7%).

[0021] High process controllability and reliability: This invention clearly defines the key parameters of flow fluctuation (such as the multiple K and period T), resulting in good process repeatability and easy industrial application. The unique progressive cooling process further avoids the risk of coating cracking caused by rapid cooling. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a process flow diagram of a method for preparing a tantalum carbide composite coating on a graphite substrate according to the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments.

[0024] Example 1

[0025] like Figure 1 As shown, a method for preparing a tantalum carbide composite coating on a graphite substrate specifically includes the following steps: (1) Substrate preparation: Circular isostatic graphite with dimensions D150 / 140×40mm was selected as the matrix, with a coefficient of thermal expansion of 5.0×10⁻⁶. -6 K -1 Its density is 1.77 g / cm³. 3 The graphite substrate was placed in a high-temperature furnace and calcined at 1050°C for 1.5 hours to remove low-melting-point impurities and oil stains from the surface. After being removed from the furnace, the surface of the graphite substrate was mechanically processed to achieve a surface roughness Ra of 1.6. Then, it was ultrasonically cleaned with anhydrous ethanol and dried.

[0026] (2) Deposition of tantalum metal buffer layer: The pretreated graphite substrate was fixed with a molded graphite support coated with tantalum carbide and placed in the CVD reaction chamber. After evacuating to 4 mmHg, the temperature of the reaction chamber was raised to 1400℃ at a heating rate of 9.2℃ / min and held for 1 hour. After the holding period, the deposition of tantalum metal buffer layer began. A mixed gas composed of TaCl5, H2 and Ar was introduced, with a molar ratio of 1:15:10. The deposition process was controlled by periodic flow fluctuations, with each cycle lasting 10 minutes. First stage (5 minutes): Control the total flow rate of the mixed gas to Q1 (e.g., 1~4 L / min) to stabilize the pressure in the reaction chamber at 1500 Pa.

[0027] Second stage (5 minutes): Instantly increase the total flow rate of the mixed gas to twice Q1 (i.e., K=2), at which point the pressure in the reaction chamber rises to 3000 Pa.

[0028] The above cycle was repeated three times, with a total deposition time of 30 minutes. Finally, a dense tantalum metal buffer layer with a uniform thickness of approximately 5 μm was obtained on the graphite substrate surface.

[0029] (3) Deposition of tantalum carbide coating: After the buffer layer deposition is completed, the reaction chamber is kept in situ at 1400℃ for 1 hour. Then, the deposition of tantalum carbide coating begins. A mixed gas composed of TaCl5, CH4, H2 and Ar is introduced into the reaction chamber in a molar ratio of 1:1:15:10. The deposition process is also controlled by the above-mentioned periodic flow fluctuation, with each cycle lasting 10 minutes. First stage (5 minutes): Control the total flow rate of the mixed gas to Q1, so that the pressure in the reaction chamber is stabilized at 1500 Pa.

[0030] Second stage (5 minutes): Instantly increase the total flow rate of the mixed gas to twice Q1 (i.e., K=2), at which point the pressure in the reaction chamber rises to 3000 Pa.

[0031] This cycle was repeated 18 times, with a total deposition time of 180 minutes. A uniform tantalum carbide coating of approximately 30 μm thickness was ultimately obtained on the tantalum metal buffer layer.

[0032] (4) Cooling treatment: After deposition, the flow of reaction gas was stopped, and the reaction chamber was kept in situ at 1400℃ for 3 hours. Then, the temperature was reduced to 750℃ over approximately 8 hours at a cooling rate of approximately 1.7℃ / min, and held at this temperature for 3 hours. Finally, the temperature was slowly cooled to room temperature over 30 hours. Before opening the furnace lid, the reaction chamber was purged three times with high-purity argon gas.

[0033] Comparative Example 1 The only difference between this comparative example and Example 1 is that the step of depositing the tantalum metal buffer layer is omitted. That is, after the graphite substrate pretreatment, the tantalum carbide coating is deposited directly at the same temperature (1400℃) using the same flow fluctuation control process and gas ratio (TaCl5:CH4:H2:Ar=1:1:15:10) as in Example 1. The total deposition time is adjusted to be the same as the tantalum carbide layer deposition time in Example 1.

[0034] Comparative Example 2 The only difference between this comparative example and Example 1 is that, instead of flow fluctuation control, a constant flow feeding method is used when depositing the tantalum metal buffer layer and the tantalum carbide coating.

[0035] (1) Substrate preparation: This step is exactly the same as in Example 1. Substrate from the same batch with a coefficient of thermal expansion of 5.0 × 10⁻⁶ is selected. - 6 K -1 The isostatically pressed graphite was used as the matrix and underwent the same cleaning and pretreatment process.

[0036] (2) Deposition of tantalum metal buffer layer (constant flow mode): The deposition process adopts a constant flow feeding mode without flow fluctuation control. The pretreated graphite substrate is placed in the same CVD reaction chamber, and after being evacuated to 4 mmHg, the temperature of the reaction chamber is raised to 1400℃ at a heating rate of 9.2℃ / min and held for 1 hour. After the holding period, the deposition of tantalum metal buffer layer begins. A mixed gas composed of TaCl5, H2 and Ar is introduced, with the same molar ratio as in Example 1, which is 1:15:10. The mixed gas is continuously introduced at the flow rate of the second stage in Example 1 (i.e., 2 times Q1), and the pressure of the reaction chamber is controlled to be stable at 3000 Pa. The deposition continues for 30 minutes, and finally a tantalum metal buffer layer with a thickness of about 5 μm is obtained on the surface of the graphite substrate.

[0037] (3) Deposition of tantalum carbide coating (constant flow mode): The deposition process also adopted a constant flow feeding mode. After the buffer layer deposition was completed, the reaction chamber was kept in situ at 1400°C for 1 hour, which was the same as in Example 1. Subsequently, the deposition of tantalum carbide coating began. A mixed gas composed of TaCl5, CH4, H2 and Ar was introduced into the reaction chamber, with the same molar ratio as in Example 1, which was 1:1:15:10. The above mixed gas was continuously introduced at the flow rate and pressure of the second stage in Example 1, i.e., the pressure was stabilized at 3000 Pa, and the deposition was continued for 180 minutes. Finally, a tantalum carbide coating with a thickness of about 30 μm was obtained on the tantalum metal buffer layer.

[0038] (4) Cooling treatment: This step is exactly the same as in Example 1. After deposition, the reaction gas supply is stopped, and the reaction chamber is kept in situ at 1400°C for 3 hours. Subsequently, the temperature is reduced to 750°C over approximately 8 hours at a cooling rate of approximately 1.7°C / min, and held at this temperature for 3 hours. Finally, it is slowly cooled to room temperature over 30 hours. Before opening the furnace lid, the reaction chamber is purged three times with high-purity argon gas.

[0039] The superior effects achieved by this invention stem from the active intervention of "periodic flow fluctuation control" in the kinetics of chemical vapor deposition. Its mechanism of action is as follows: This strategy actively disrupts the steady-state growth environment of constant-flow deposition by periodically switching between high flow rates (high supersaturation) and low flow rates (low supersaturation).

[0040] During the high flow rate stage, the concentration of gaseous reactants increases sharply, and the supersaturation increases significantly, which tends to promote a large number of nucleations on the substrate surface. This is conducive to the formation of fine grains, laying a dense foundation for the coating.

[0041] During the low flow rate stage, the supersaturation of the gas phase decreases, and the reaction driving force shifts to promote the continuous growth of existing crystal nuclei, making it easier to form coarse grains. This process helps to release the growth stress accumulated in the coating and improve toughness.

[0042] This dynamic growth pattern, characterized by alternating nucleation and growth, effectively suppresses columnar crystal structures, grain boundary defects, and stress concentrations that occur under constant current conditions due to a single growth mechanism. Macroscopically, this manifests as effective relaxation of internal stress within the coating, significantly enhanced toughness, and consequently, superior thermal shock resistance, ultimately achieving a synergistic breakthrough in bonding strength, uniformity, and thermal shock resistance. This mechanism, combined with the role of the tantalum buffer layer in alleviating thermal mismatch stress in the film-substrate relationship, constitutes the theoretical basis for the technical effects achieved in this invention.

[0043] Performance Testing and Results Analysis The coating samples obtained in Example 1, Comparative Example 1 and Comparative Example 2 were subjected to performance tests, and the results are shown in Table 1.

[0044] Table 1: Performance test results of coating samples obtained in Example 1, Comparative Example 1 and Comparative Example 2

[0045] Based on the analysis of the table above, the examples, and the comparative examples, the following conclusions can be drawn: Bond strength: Example 1 showed the highest bond strength (13.62 MPa), while Comparative Example 1 (without buffer layer) showed the lowest (9.48 MPa). This indicates that the tantalum metal buffer layer plays a decisive role in improving the film-substrate adhesion. Although the bond strength of Comparative Example 2 (constant current, with buffer layer) (11.74 MPa) was higher than that of Comparative Example 1, it was significantly lower than that of Example 1. This suggests that the combination of flow fluctuation control and the buffer layer can produce a synergistic effect, further improving the adhesion.

[0046] Coating uniformity: The extremely low thickness non-uniformity (±2.1%) in Example 1 is directly due to flow fluctuations, which is much lower than that in Comparative Example 2 (±8.7%). The periodic airflow scouring disrupts the stable boundary layer formed on the substrate surface under constant flow conditions, making the distribution of reactive gases more uniform, thereby fundamentally improving the uniformity of the coating.

[0047] Thermal shock resistance: The coating of Example 1 remained intact after 10 severe thermal shock cycles, while Comparative Example 1 showed severe cracks, and Comparative Example 2 also showed slight cracks. The excellent thermal shock resistance of Example 1 indicates that its coating has few internal defects, low internal stress levels, and good toughness. This is consistent with the mechanism analysis described above, in which flow fluctuations suppress crack initiation and promote stress relaxation through a dynamic growth mode.

[0048] In summary, periodic flow fluctuation control is a powerful process technique that can fundamentally optimize the growth kinetics and stress state of CVD coatings. Its combination with a tantalum buffer layer produces a synergistic effect, systematically solving several technical challenges in the preparation of high-performance tantalum carbide coatings.

[0049] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

Claims

1. A method for preparing a tantalum carbide composite coating on a graphite substrate, characterized in that, Includes the following steps: S1: Provides a graphite matrix; S2: A tantalum metal buffer layer is deposited on the surface of the graphite substrate using chemical vapor deposition technology; S3: A tantalum carbide coating is deposited on the surface of the tantalum metal buffer layer by chemical vapor deposition. In the deposition process of S2 and S3, periodic flow fluctuation control is adopted. The periodic flow fluctuation control includes at least one cycle, and each cycle contains a first stage and a second stage with different flow rates.

2. The method according to claim 1, characterized in that, In periodic flow fluctuation control, the total gas flow rate in the second stage is K times that in the first stage, where K ranges from 1.5 to 3.

0.

3. The method according to claim 1, characterized in that, The first and second phases last for the same amount of time, forming a fixed cycle. The duration of a single segment of the fixed cycle is 3 to 10 minutes.

4. The method according to claim 1, characterized in that, In step S2, a mixed gas consisting of tantalum pentachloride, hydrogen and inert carrier gas is introduced, wherein the molar ratio of tantalum pentachloride, hydrogen and inert carrier gas is 1:(10~20):(10~30).

5. The method according to claim 1, characterized in that, In step S3, a mixed gas consisting of tantalum pentachloride, methane, hydrogen and inert carrier gas is introduced, wherein the molar ratio of tantalum pentachloride, methane, hydrogen and inert carrier gas is 1:(1~2):(10~20):(10~30).

6. The method according to claim 5, characterized in that, The molar ratio of tantalum pentachloride, methane, hydrogen and inert carrier gas is 1:(1~1.5):(15~20):(10~20).

7. The method according to claim 1, characterized in that, In step S2, the deposition thickness of the tantalum metal buffer layer is 1~10μm; in step S3, the deposition thickness of the tantalum carbide coating is 10~50μm.

8. The method according to claim 1, characterized in that, In steps S2 and S3, the reaction temperature for chemical vapor deposition is 1200~1600℃.

9. The method according to claim 1, characterized in that, Following step S3, step S4 is further included: performing a progressive cooling process on the deposited workpiece, the progressive cooling process comprising: (1) After deposition, keep in situ at the reaction temperature for 2 to 4 hours; (2) Then, within 6 to 10 hours, the temperature of the reaction chamber is reduced to 700 to 800°C and kept at that temperature for 2 to 4 hours; (3) Finally, the temperature of the reaction chamber is reduced to room temperature within 20 to 40 hours.

10. A graphite device, comprising a graphite substrate and a tantalum carbide coating on the surface of the graphite substrate, characterized in that, A tantalum metal buffer layer is provided between the graphite substrate and the tantalum carbide coating; the tantalum carbide coating and the tantalum metal buffer layer are prepared by the method described in any one of claims 1 to 9.

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