Tooling structure for chemical vapor deposition and in-situ self-cleaning method thereof

Abstract

The application relates to a tool structure applied to chemical vapor deposition and an in-situ self-cleaning method thereof, and belongs to the technical field of high-temperature deposition equipment. The method solves the problems of low efficiency, easy damage to the tool, introduction of pollutants and high cost of the existing method for removing harmful coating on the surface of the tool. The method comprises the following steps: fixing a substrate by using a tool with a microstructure on the surface, performing chemical vapor deposition, and obtaining a coating; the thermal expansion coefficient alpha a of the coating is less than the thermal expansion coefficient alpha b of the tool structure; and cooling, so that the coating deposited on the surface of the tool falls off. In the cooling stage after deposition, the difference between the thermal expansion behaviors of the tool and the coating and the protruding microstructure on the surface of the tool can convert the shearing thermal stress between the tool and the coating into tensile peeling stress, and the coating deposited on the tool can be spontaneously and in-situ peeled off by using the thermal stress concentration effect, so that the damage of the coating accumulation to the tool is avoided from the root, and the additional cost and side effects of the traditional cleaning process are eliminated.​​​​

Description

Technical Field

[0001] This invention relates to the field of high-temperature deposition equipment technology, and in particular to a tooling structure for chemical vapor deposition and its in-situ self-cleaning method. Background Technology

[0002] Chemical vapor deposition (CVD) is a process that uses heat to drive a chemical reaction to generate a coating material by introducing a gaseous precursor feedstock into a high-temperature reaction apparatus. In practical applications, it is often necessary to use in-furnace fixtures to fix the substrate workpiece. However, the fixture and the workpiece undergo chemical deposition simultaneously. Long-term exposure to the high-temperature deposition environment can cause the coating accumulated on the fixture surface to affect the fixture's assembly compatibility and service life.

[0003] Current technologies for treating tooling surface coatings generally remain at the "passive removal" stage, which involves physically or chemically stripping away the coating from the tooling surface after deposition. While physical removal methods (such as mechanical grinding, sandblasting, and ultrasonic vibration) can remove the coating, they carry the risk of incomplete cleaning and damage to the integrity of the tooling surface. Chemical cleaning methods (such as acid / alkali immersion) can dissolve some of the coating, but they may introduce contaminant residues that interfere with subsequent deposition processes. It is evident that existing physical or chemical stripping methods are not only inefficient in removing coatings, but also struggle to balance the conflict between removal effectiveness and tooling protection, and they also incur additional costs associated with CVD coating preparation.

[0004] Therefore, there is an urgent need for a method that can efficiently and with low loss remove coatings from tooling surfaces in order to improve the assembly accuracy and lifespan of CVD tooling and reduce coating preparation costs. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a tooling structure for chemical vapor deposition and its in-situ self-cleaning method, in order to solve at least one of the problems of existing methods for removing harmful coatings from the surface of CVD tooling: low efficiency, easy damage to tooling, interference with subsequent deposition processes, and high cost.

[0006] On one hand, embodiments of the present invention provide an in-situ self-cleaning method for chemical vapor deposition tooling structures, the method comprising:

[0007] (1) A raised microstructure design is performed on the surface of the tooling structure;

[0008] (2) The workpiece to be deposited is fixed using the tooling structure described above, and chemical vapor deposition is performed to obtain a coating, wherein the coefficient of thermal expansion of the coating is α. a The coefficient of thermal expansion α of the tooling structure is less than that of the tooling structure. b ;

[0009] (3) Cooling causes the coating deposited on the tooling surface to peel off;

[0010] During the cooling process, the microstructure transforms the shear thermal stress generated between the tooling structure and the coating into tensile peel stress, and the shear thermal stress generated between the tooling structure and the coating is greater than the interfacial adhesion strength between the tooling structure and the coating.

[0011] Furthermore, in step (1), the microstructure includes a series of triangular prisms, wherein the side edges of the triangular prisms are parallel to the plane of the tooling structure, the two side edges are located on the surface of the tooling structure, and one side edge is away from the surface of the tooling structure, forming a ridge.

[0012] Furthermore, the base of the triangular prism is a right-angled triangle.

[0013] Furthermore, the included angle α between the two lateral faces of the triangular prism constituting the ridge is 45° < α < 75°.

[0014] Furthermore, the radius of the rounded corner of the ridge is r1 < 0.5 mm.

[0015] Furthermore, the included angle β between two adjacent sides of the adjacent triangular prism is 45° < β < 75°, forming a valley, wherein the processing radius r2 of the valley is < 0.5 mm.

[0016] Furthermore, the included angle β is equal to the included angle α.

[0017] Furthermore, the length L of the side perpendicular to the surface of the tooling structure that forms the ridge b For 1mm≤L b ≤5mm.

[0018] Furthermore, the length L forming the other side of the ridge c For 3mm≤L c ≤12mm.

[0019] Furthermore, in step (2), the thickness h of the coating is 10 μm < h < 1500 μm;

[0020] Furthermore, α a Less than α b More than 30%.

[0021] Furthermore, in step (3), the cooling rate is 1-50°C / min.

[0022] Furthermore, the material constituting the tooling structure is one of graphite, silicon carbide, or high-temperature resistant alloy materials.

[0023] Furthermore, the material constituting the coating is one of boron nitride, boron nitride, silicon carbide, silicon dioxide, and metal carbides.

[0024] On the other hand, embodiments of the present invention also provide a tooling structure for chemical vapor deposition, wherein the tooling structure is the tooling structure used in the method, wherein the surface of the tooling structure has raised microstructures, the microstructures including continuously arranged triangular prisms, wherein the side edges of the triangular prisms are parallel to the plane of the tooling structure, the two side edges are located on the surface of the tooling structure, and one side edge is away from the surface of the tooling structure, forming a ridge.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] 1. Compared with existing technologies that use physical or chemical removal methods to "passively clean" the coating on the tooling surface after the deposition process, this invention utilizes the difference in thermal expansion coefficients between the tooling material and the coating material. The surface of the tooling used to fix the substrate workpiece to be deposited during the CVD process is designed with raised microstructures, unlike the flat surface of traditional tooling. The raised microstructures enable the thermal stress generated between the tooling and the coating to be concentrated and released in a directional manner during the cooling stage after deposition, and the thermal stress is transformed from shear thermal stress to tensile peeling stress. When the shear thermal stress is greater than the interfacial adhesion strength between the tooling structure and the coating, the harmful coating on the tooling surface can be self-peeled and detached along the microstructure surface, thereby giving the tooling of this invention the ability of "active in-situ self-cleaning".

[0027] The in-situ self-cleaning method for tooling structures described in this invention breaks through the technical limitations of traditional physical / chemical post-treatment processes, realizing active in-situ, non-contact removal of the coating on the tooling surface. This not only improves the coating removal efficiency but also avoids the mechanical damage and chemical pollution caused by traditional cleaning methods. It eliminates the need for an additional independent cleaning process, thereby improving the assembly accuracy and service life of the tooling while enhancing the efficiency and economic benefits of the CVD process.

[0028] 2. This invention designs the microstructure of the tooling surface as continuously arranged triangular prisms, which transforms the shear thermal stress between the two sides of the ridge and the coating into tensile peel stresses. The shear thermal stresses are then concentrated sequentially at the ridges and valleys, allowing the coating to begin peeling from the tooling at the ridges and break at the valleys, thus achieving the peeling and detachment of the coating from the tooling surface. Figure 4-8 As shown.

[0029] 3. This invention adjusts the geometry of the triangular prism, including the shape of the base triangle, the included angle between the two sides forming the ridge and valley, the machining radius of the ridge and valley, and the length of the two sides forming the ridge. Combined with the coating thickness and the difference in thermal expansion coefficients between the coating and the tooling, on the one hand, the tensile peel stress at which the coating peels from the tooling is greater than the interfacial adhesion strength between the coating and the tooling. This causes the coating to begin peeling from the tooling at coating defects (i.e., the α-angle region), and under the stress concentration effect and lever principle, it can rapidly expand on both sides of the ridge, quickly peeling off the coating on both sides. On the other hand, the maximum bending stress on the coating is less than the coating's bending strength, thus ensuring that the coating on both sides can be completely peeled off, and ultimately breaks at the valley (i.e., the β-angle region).

[0030] 4. The tooling structure provided by this invention for chemical vapor deposition can achieve in-situ self-cleaning during the chemical vapor deposition process, breaking through the technical limitations of traditional physical / chemical post-processing. It can not only improve the coating removal efficiency, but also avoid mechanical damage and chemical pollution caused by traditional cleaning methods. There is no need to add an independent cleaning process. While improving the tooling assembly accuracy and service life, it also improves the efficiency and economic benefits of CVD process.

[0031] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0032] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0033] Figure 1 A front view of a tooling structure used in chemical vapor deposition (CVD) processes: (1) conventional tooling; (2) the tooling of this invention;

[0034] Figure 2 Top view of the tooling structure used in chemical vapor deposition (CVD) process: (1) conventional tooling; (2) tooling of the present invention;

[0035] Figure 3 This is a schematic diagram of the microstructure of the CVD tooling surface with a coating deposited according to the present invention;

[0036] Figure 4A schematic diagram of the interfacial thermal stress direction generated between the tooling and the surface coating during the cooling process after CVD deposition: (1) conventional tooling; (2) tooling of the present invention;

[0037] Figure 5 This is a schematic diagram showing the structure at the ridges of the microstructure on the surface of the tooling of the present invention (i.e., the points of concentration of interfacial thermal stress), where the coating begins to peel off from the tooling.

[0038] Figure 6 This is a schematic diagram showing the complete peeling of the coating on the inclined surface c of the microstructure of the tooling surface of the present invention;

[0039] Figure 7 This is a schematic diagram showing the concentration of interfacial stress at the ridges and valleys of the microstructure on the surface of the tooling of the present invention during self-peeling of the coating on the inclined surface c and vertical surface b of the microstructure.

[0040] Figure 8 This is a schematic diagram showing the coating on the surface microstructure of the tooling of the present invention breaking at the ridge.

[0041] Figure 9 The peeling of the coating on the tooling surface during the cooling stage after CVD deposition: (1) Example 1; (2) Comparative Example 1;

[0042] Figure label:

[0043] 1- Inclined plane c; 2- Vertical plane b; 3- Angle α; 4- Angle β. Detailed Implementation

[0044] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0045] During the process of preparing a coating on the surface of a substrate workpiece using chemical vapor deposition (CVD), the coating is also deposited simultaneously on the surface of the furnace tooling used to fix the workpiece. Because the tooling is exposed to a high-temperature reaction environment for a long time, the coating deposits accumulated on the surface will cause dual harm to the performance of the tooling: First, the thickening of the coating directly changes the size of the tooling, reducing its accuracy and assembly adaptability; Second, due to the difference in the coefficient of thermal expansion between the tooling substrate and the coating material, the interfacial thermal stress continues to accumulate when the temperature fluctuates, which may cause tooling deformation or even cracking and failure of precision structures, seriously restricting the service life of the tooling.

[0046] To address the serious damage that coatings pose to CVD tooling, traditional solutions focus on tooling replacement or post-treatment stripping techniques. Specifically, post-treatment stripping involves physically or chemically removing the coating from the surface of the tooling after deposition. While physical removal methods (such as mechanical grinding, sandblasting, and ultrasonic vibration) can remove the coating, they carry the risk of incomplete cleaning and damage to the integrity of the tooling surface. Chemical cleaning methods (such as acid / alkali immersion) can dissolve some of the coating, but may introduce contaminating residues that interfere with subsequent deposition processes. Therefore, existing post-treatment stripping techniques are not only inefficient but also struggle to balance the trade-off between effective removal and tooling protection, and they also incur additional costs associated with CVD coating preparation.

[0047] Therefore, the present invention provides an in-situ self-cleaning method for chemical vapor deposition tooling structures, the method comprising:

[0048] (1) A raised microstructure design is performed on the surface of the tooling structure;

[0049] (2) The workpiece to be deposited is fixed using the tooling structure described above, and chemical vapor deposition is performed to obtain a coating, wherein the coefficient of thermal expansion of the coating is α. a The coefficient of thermal expansion α of the tooling structure is less than that of the tooling structure. b ;

[0050] (3) Cooling causes the coating deposited on the tooling surface to peel off;

[0051] During the cooling process, the microstructure transforms the shear thermal stress generated between the tooling structure and the coating into tensile peel stress, and the shear thermal stress generated between the tooling structure and the coating is greater than the interfacial adhesion strength between the tooling structure and the coating.

[0052] It should be noted that when a composite structure undergoes temperature changes, thermal stress will be generated at the interface of heterogeneous materials due to the difference in thermal expansion coefficients, which may cause the composite structure to deform or break. Such thermal stress is usually regarded as a design defect that needs to be avoided.

[0053] Breaking away from the traditional "passive removal" approach, the inventors discovered during their research on how to efficiently remove coatings from tooling surfaces that the difference in the coefficients of thermal expansion of the materials that induce tooling damage can be transformed into a starting point for coating removal. They proposed a tooling optimization design strategy based on a thermodynamic self-peeling mechanism. This strategy transforms the interfacial thermal stress between heterogeneous materials into a driving force for efficient coating peeling through tooling structural innovation. Specifically, utilizing the difference in the coefficients of thermal expansion between the tooling material and the coating material, the surface of the tooling used to fix the workpiece to be deposited during CVD is designed with raised microstructures, unlike the flat surfaces of current tooling, thus breaking through the physical boundary limitations of traditional tooling designs. These raised microstructures allow for the concentration and directional release of thermal stress generated between the tooling and the coating during the cooling stage after deposition, transforming the shear thermal stress between the tooling and coating into tensile peeling stress of the coating. When the shear thermal stress exceeds the interfacial adhesion strength between the tooling structure and the coating, the coating on the tooling surface can self-peel and detach, thereby endowing the tooling of this invention with the ability of "active in-situ self-cleaning."

[0054] It should be noted that, in order to ensure the tooling's role in fixing the substrate workpiece and regulating the deposition flow field while utilizing the tooling surface microstructure to achieve the transformation and directional concentration of thermal stress at the coating interface, this invention needs to define the shape of the tooling surface microstructure.

[0055] Specifically, in step (1), the microstructure is a continuous arrangement of triangular prisms, such as... Figure 3 As shown, the lateral edges of the triangular prism are parallel to the plane of the tooling structure, with two side edges located on the surface of the tooling structure and one side edge away from the surface of the tooling structure, forming a ridge. The tooling surface of this invention employs a continuously arranged array of micro-triangular prisms, which has the advantages of: minimal change in the macroscopic shape of the tooling, avoiding significant alterations to the main structure and mechanical design; and simultaneously, this microscopic configuration effectively maintains the stability of the deposition flow field, minimizing its disturbance.

[0056] It should be noted that the microstructure of the tooling surface in this invention is designed as a continuous arrangement of triangular prisms. This design allows the shear thermal stress between the two sides of the ridge and the coating to be transformed into tensile peel stresses. Specifically, when cooling, because the coefficient of thermal expansion of the coating is less than that of the substrate, the coating shrinks less than the substrate. The coating is pushed at the ridge of the tooling, and the coating on one side is subjected to tensile peel stress derived from the shear stress between the coating on the other side and the tooling. Figure 4As shown, the coating on the inclined plane c is subjected to an upward tensile peeling force F1, which comes from the shear thermal stress between the vertical plane b and the deposited coating. The coating on the inclined plane b is subjected to a tensile peeling force F2 along the inclined plane, which comes from the shear thermal stress between the inclined plane b and the deposited coating.

[0057] Compared with existing furnace tooling, the triangular prism microstructure on the surface of the tooling of this invention has ridges. On the one hand, it transforms the originally uniformly distributed shear stress, i.e., the thermal stress direction parallel to the interface between the tooling and the coating (interface adhesion is best at resisting this type of stress), into tensile peel stress, i.e., the thermal stress direction perpendicular to the interface between the tooling and the coating. This stress distribution is extremely uneven (different directions and different magnitudes). On the other hand, the ridge design is equivalent to artificially creating defects on the coating growing along the tooling. Under the action of tensile peel stress, the coating is very easy to peel off from the tooling at the defect.

[0058] It should be noted that after the coating peels off at the ridge, under the action of stress concentration and leverage principle, the tensile peel stress is almost entirely concentrated at the leading edge of the crack, causing great damage to the bonding interface. This stress rapidly propagates on inclined surfaces c and b, quickly and completely peeling off the coating from the inclined surfaces. Figure 5 , 6 As shown.

[0059] It should be noted that, depending on the interfacial adhesion strength between the coating and the slope and the magnitude of the tensile peel stress on the coating, the coatings on the slopes b and c may peel off simultaneously, or the coating on one slope may peel off first, followed by the coating on the other slope. In the latter case, when the coating on one slope is completely peeled off, the force generated by the expansion of the coating on that slope is completely concentrated on the coating on the other slope, making it easier for the coating on the other slope to be peeled off from the tooling.

[0060] It should be noted that after the coating on both the inclined and vertical surfaces is peeled off, the tensile peel stress from the two inclined surfaces is further concentrated at the coating bending points (i.e., the ridges), such as... Figure 7 As shown, and causing the coating to break at the ridge, as Figure 8 As shown; thus, the present invention has achieved the purpose of actively and completely peeling off the coating on the tooling in situ.

[0061] This invention innovatively transforms the destructive factor of thermal expansion interface thermal effect in traditional processes into an enabling tool for actively controlling coating peeling. This allows the new tooling structure of this invention to achieve active online in-situ self-cleaning during the CVD deposition process, breaking through the technical limitations of traditional physical / chemical post-treatment processes. It realizes active in-situ, non-contact removal of the coating on the tooling surface, which not only improves the coating removal efficiency but also avoids the mechanical damage and chemical pollution caused by traditional cleaning methods. It eliminates the need for an additional independent cleaning process, thereby improving the tooling assembly accuracy and service life while enhancing the efficiency and economic benefits of the CVD process.

[0062] It should be noted that, in order to improve the machining accuracy and service life of the microstructure on the surface of the tooling of the present invention, the present invention needs to define the shape of the triangle at the base of the triangular prism.

[0063] Specifically, in step (1), the base of the triangular prism is a right-angled triangle. This invention uses a right-angled triangle as the base of the triangular prism primarily based on three considerations: First, by utilizing the characteristic that the hypotenuse and short side of a right-angled triangle are unequal, the coating experiences different stresses on adjacent surfaces. The torque formed by this stress difference helps induce initial peeling of the coating. Second, this configuration has good mechanical stability, which is beneficial for resisting operational impacts and internal stresses, extending the tooling life. Finally, the right-angled geometric features make it easier to achieve machining positioning and forming in machining processes (such as milling and grinding), which is beneficial for improving manufacturing accuracy and efficiency.

[0064] It should be noted that, in order to ensure that the coating can be peeled off from the tooling surface during the cooling stage after deposition, and to prevent the coating from breaking in an undefined area during the peeling process, resulting in insufficient peeling, the present invention needs to define the included angle between the two sides forming the ridge of the triangular prism.

[0065] Specifically, in step (1), the included angle α between the two sides of the triangular prism constituting the ridge is 45° < α < 75°. If the included angle α is too large, it is easy for part of the coating to peel off and break, leaving another part on the tooling; if the included angle α is too small, it is easy for the coating to not peel off or to peel off insufficiently.

[0066] It should be noted that, in order to ensure the concentration effect of thermal stress generated between the coating and the tooling at the corner of the microstructure, the present invention needs to limit the machining fillet radius of the corner α.

[0067] Specifically, in step (1), the radius of the processed rounded corner of the ridge is r1 < 0.5 mm. If the radius of the processed rounded corner is too large, the stress concentration effect will not be obvious when the initial peeling is started, and the initial peeling at the α corner will not occur.

[0068] It should be noted that, in order to ensure that the coating can be peeled off from the tooling surface during the cooling stage after deposition, and to prevent the coating from breaking in an undefined area during the peeling process, resulting in insufficient peeling, the present invention needs to limit the included angle between the two adjacent sides of the adjacent triangular prisms.

[0069] Specifically, in step (1), the included angle β between the two adjacent sides of the adjacent triangular prism is 45° < β < 75°, forming a valley; if the included angle β is too large, it is easy for the coating to peel off a part and break, leaving a part on the tooling; if the included angle β is too small, it is easy for the coating to not peel off or to peel off insufficiently.

[0070] It should be noted that, in order to ensure the concentration effect of thermal stress generated between the coating and the tooling at the corner of the microstructure, the present invention needs to limit the machining fillet radius of the corner β.

[0071] Specifically, in step (1), the radius of the processed corner of the ridge is r2 < 0.5 mm. If the radius of the processed corner is too large, the concentration effect of thermal stress at the β corner will not be obvious, the coating will not easily break at the β corner area, and some coating residue will easily remain and not peel off.

[0072] It should be noted that, in order to ensure that the coating can be peeled off from the tooling surface during the cooling stage after deposition, and to prevent the coating from breaking in undefined areas during the peeling process, resulting in insufficient peeling, the present invention needs to limit the length of the two sides forming the ridge.

[0073] Specifically, in step (1), the length L of the side perpendicular to the surface of the tooling structure forming the ridge is... b For 1mm≤L b ≤5mm, if L b If the length is too long, the coating on the bevel will peel off partially and break off, leaving some residue on the tooling and preventing complete peeling; if L b If it's too short, the coating may not peel off or peel off insufficiently.

[0074] Specifically, in step (1), the length L of the other side of the ridge is formed. c For 3mm≤L c ≤12mm, if L c If the length is too long, the coating on the bevel will peel off partially and break off, leaving some residue on the tooling and preventing complete peeling; if L c If it's too short, the coating may not peel off or peel off insufficiently.

[0075] It should be noted that, in order to ensure that the coating can be completely peeled off from the tooling surface during the cooling stage after deposition and can break off at the included angle β region, the present invention needs to limit the thickness of the coating prepared by CVD.

[0076] Specifically, in step (2), the thickness h of the coating is 10μm < h < 1500μm; if the coating thickness is too large, the peeled coating will not easily break at the included angle β region; if the coating thickness is too small, the coating may break outside the β region, resulting in the remaining part of the coating not being peeled off, leading to insufficient coating peeling.

[0077] It should be noted that, in order to ensure the peeling effect, the present invention needs to limit the difference in the coefficient of thermal expansion between the coating and the tooling material.

[0078] Specifically, the coefficient of thermal expansion α of the coating a The coefficient of thermal expansion α of the tooling material is less than that of the tooling material. b More than 30%.

[0079] It should be noted that, in order to ensure the self-peeling effect of the coating, the present invention needs to limit the cooling rate during the post-deposition cooling stage.

[0080] Specifically, in step (3), the cooling rate is 1-50℃ / min. If the cooling rate is too low, the coating will not peel off on its own; if the cooling rate is too high, it will damage the tooling or equipment itself.

[0081] It should be noted that, in order for the coating to be able to peel off and detach from the tooling surface during the cooling stage after deposition, the present invention needs to limit the materials used to prepare the tooling and the coating.

[0082] Specifically, in step (1), the material constituting the tooling structure is one of graphite, silicon carbide, or high-temperature resistant alloy materials.

[0083] Specifically, in step (2), the material constituting the coating is one of boron nitride, boron nitride, silicon carbide, silicon dioxide, and metal carbide.

[0084] It should be noted that the peeling process of the coating on the surface of the tooling microstructure of the present invention is not only related to the materials of the tooling and the coating (such as the difference in thermal expansion coefficients between the tooling and the coating, the modulus of the coating, the coating strength, the interfacial bonding strength between the coating and the tooling) and the coating thickness, but also to the shape and size of the microstructure on the surface of the tooling. Among them, the various factors affecting the coating peeling effect coordinate with each other and work together, ultimately enabling the coating on the surface of the tooling to actively peel off in situ during the cooling stage after CVD deposition.

[0085] This invention takes into account that the tooling thickness (millimeter-level) is much larger than the coating thickness (micrometer-level). It can be simplified to assume that during the cooling stage after CVD deposition, the deformation of the tooling is dominant; that is, the coating is forced to completely follow the deformation of the substrate. The effect of the coating's stiffness on the overall deformation of the substrate can be ignored. Therefore, it can be concluded that the coating experiences thermal strain under temperature changes. The calculation formula is Equation (1):

[0086] Equation (1);

[0087] The formula for calculating the total thermal stress F on the coating is Equation (2):

[0088] Equation (2);

[0089] In equations (1) and (2), E is the Young's modulus of the coating, which is determined by the type of material in the coating and is a constant when the coating material remains unchanged; α a and α b Here, represents the coefficient of thermal expansion of the coating and the tooling, respectively; A is the cross-sectional area of ​​the coating that undergoes thermal deformation, A = h × s (where h is the coating thickness and s is the coating width); L is the side length of the coating that undergoes thermal deformation; ΔT is the temperature change.

[0090] It should be noted that when the temperature drops, because the coefficient of thermal expansion of the coating is less than that of the substrate, i.e., the shrinkage of the coating is less than that of the substrate, the coating is pushed at the sharp corners of the tooling (such as the ridge of a triangular prism). This causes the thermal stress generated between the coating and the tooling on one side of the sharp corner to be transformed into tensile peel stress of the coating on that side. When the shear thermal stress is greater than the interfacial bonding strength between the tooling structure and the coating, the coating on the surface of the tooling can self-peel and fall off.

[0091] Specifically, the tensile peel stress borne at one side boundary (stress concentration point) of the ridge originates from the shear stress between the other side and the coating.

[0092] According to some preferred embodiments of the present invention, the tensile peel stress σ experienced by the inclined surface c at the ridge is... c It can be calculated from equation (3):

[0093] Equation (3);

[0094] Among them, F b The thermal stress between the inclined plane b and the coating; L b α is the length of the inclined plane b; α is the included angle between the two lateral faces of the triangular prism that forms the ridge.

[0095] When the inclined plane c is subjected to tensile peel stress σ cThe interfacial adhesion strength between the coating and the mold on the inclined surface c is greater than (σ). 界面C Only when σ occurs will the coating peel off from the slope c, i.e., σ c >σ 界面 Combining with equation (3), the length L of the inclined plane b is obtained. b Equation (4) must be satisfied:

[0096] Equation (4);

[0097] Similarly, the length L of the inclined plane c can be obtained. c Equation (5) must be satisfied:

[0098] Equation (5);

[0099] It should be noted that, in order to ensure that the coating can be completely peeled off on the slope and break at the valley, the maximum stress on the coating on the slope during the peeling process is less than the bending strength of the coating. Due to the lever effect, the maximum bending stress on the coating is given by equation (6):

[0100] Equation (6)

[0101] In equation (6), L is the lever arm length. Combining equations (1) and (2), the maximum bending moment that the coating on the inclined plane c bears during peeling is given by equation (7):

[0102] Equation (7);

[0103] The maximum bending moment that the coating on the inclined plane b experiences during peeling is given by equation (8):

[0104] Equation (8);

[0105] During the coating peeling process of this invention, the maximum bending stress on the inclined coating is required to be less than the bending strength (σ) of the coating. 涂层 ), that is, σ c '<σ 涂层 And σ b '<σ 涂层 :

[0106] <σ 涂层 Equation (9);

[0107] <σ 涂层 Equation (10);

[0108] It should be noted that when the materials of the tooling and coating, and the CVD process conditions are fixed, the interfacial bonding strength between the coating and the inclined surface of the tooling microstructure, as well as the difference in their coefficients of thermal expansion, the coating thickness, the coating flexural strength, the coating modulus, and ΔT, can be determined. According to equations (4) and (5), the length L of the inclined surface can be determined. c L b The angle of the ridge can be determined according to equations (9) and (10).

[0109] It should be noted that in order to ensure the integrity of the tooling and the complete peeling of the coating from the tooling surface during the coating self-peeling process, the strength of the coating and the tooling itself needs to be limited.

[0110] Specifically, the bonding strength between the coating and the tooling (σ) 界面b σ 界面c The tensile strength (σ) must be less than that of the coating and tooling material itself. 涂层 σ 工装 Otherwise, peeling may occur inside the tooling or coating (in layman's terms, the tooling or coating itself cracks).

[0111] According to some preferred embodiments of the present invention, the material parameters of some common coatings and tooling materials are shown in Table 1, and the shape and size of the triangular prism microstructure on the tooling surface, as well as the cooling rate during the deposition cooling stage, are shown in Table 2.

[0112] Table 1 Material parameters of common coatings and tooling materials

[0113]

[0114] Table 2. Shape and size of the triangular prism microstructure on the tooling surface, and the cooling rate after deposition.

[0115]

[0116] On the other hand, embodiments of the present invention also provide a tooling structure for chemical vapor deposition, wherein the tooling structure is the tooling structure used in the method, wherein the surface of the tooling structure has raised microstructures, the microstructures including continuously arranged triangular prisms, wherein the side edges of the triangular prisms are parallel to the plane of the tooling structure, the two side edges are located on the surface of the tooling structure, and one side edge is away from the surface of the tooling structure, forming a ridge.

[0117] This invention designs the microstructure of the tooling surface as continuously arranged triangular prisms, enabling the shear thermal stress formed between the two sides of the ridge and the coating to be transformed into tensile peel stresses. That is, when cooling, because the coefficient of thermal expansion of the coating is less than that of the substrate, the coating shrinks less than the substrate, and the coating is pushed at the ridge of the tooling. One side of the coating is subjected to tensile peel stress transformed from the shear stress between the coating on the other side and the tooling. Figure 4 As shown, the coating on the inclined plane c is subjected to an upward tensile peeling force F1, which comes from the shear thermal stress between the vertical plane b and the deposited coating. The coating on the inclined plane b is subjected to a tensile peeling force F2 along the inclined plane, which comes from the shear thermal stress between the inclined plane b and the deposited coating.

[0118] Compared with existing furnace tooling, the triangular prism microstructure on the surface of the tooling of this invention has ridges. On the one hand, it transforms the originally uniformly distributed shear stress, i.e., the thermal stress direction parallel to the interface between the tooling and the coating (interface adhesion is best at resisting this type of stress), into tensile peel stress, i.e., the thermal stress direction perpendicular to the interface between the tooling and the coating. This stress distribution is extremely uneven (different directions and different magnitudes). On the other hand, the ridge design is equivalent to artificially creating defects on the coating growing along the tooling. Under the action of tensile peel stress, the coating is very easy to peel off from the tooling at the defect.

[0119] It should be noted that after the coating peels off at the ridge, under the action of stress concentration and leverage principle, the tensile peel stress is almost entirely concentrated at the leading edge of the crack, causing great damage to the bonding interface. This stress rapidly propagates on inclined surfaces c and b, quickly and completely peeling off the coating from the inclined surfaces. Figure 5 , 6 As shown.

[0120] It should be noted that, depending on the interfacial adhesion strength between the coating and the slope and the magnitude of the tensile peel stress on the coating, the coatings on the slopes b and c may peel off simultaneously, or the coating on one slope may peel off first, followed by the coating on the other slope. In the latter case, when the coating on one slope is completely peeled off, the force generated by the expansion of the coating on that slope is completely concentrated on the coating on the other slope, making it easier for the coating on the other slope to be peeled off from the tooling.

[0121] The present invention will be further explained and illustrated below through examples and comparative examples.

[0122] Example 1

[0123] An in-situ self-cleaning method for CVD tooling structures includes:

[0124] (1) The material of the CVD furnace tooling is graphite (the coefficient of thermal expansion at 0~500℃ is 5.2×10). -6 / K), a long strip plate tooling with dimensions of 210mm × 1200mm; the microstructure of the tooling surface is designed as a continuous arrangement of triangular prisms, the lateral edges of the triangular prisms are parallel to the plane of the tooling, the two lateral edges are located on the surface of the tooling, and one lateral edge is away from the surface of the tooling structure, forming a ridge. The adjacent faces of adjacent triangular prisms are imagined as ridge valleys. The structural schematic diagram is shown below. Figure 3 As shown;

[0125] The base of the triangular prism is a right triangle, the hypotenuse b is perpendicular to the horizontal surface of the tooling, the included angle α between the two sides forming the ridge is equal to the included angle β between the two adjacent sides of the adjacent triangular prism, which is 70.5°, and the machining radius of the rounded corner is 0.1mm; the length of the vertical side b is 1mm, and the length of the hypotenuse c is 3mm.

[0126] (2) The workpiece to be deposited is fixed using the tooling structure described in step (1), and chemical vapor deposition is performed at a temperature of 1000℃ to obtain a boron nitride coating (the coefficient of thermal expansion in the range of 0~500℃ is 2.4×10). -6 The thickness of / K) is 20-40μm;

[0127] (3) The workpiece and tooling were cooled at a rate of 3℃ / min. When cooled to room temperature, it was found that a large area of ​​the coating deposited on the surface of the tooling was peeled off, with a peeling area >90%. Figure 9 As shown in (1).

[0128] Example 2

[0129] (1) The material of the CVD furnace tooling is graphite (the coefficient of thermal expansion at 0~500℃ is 4.8×10). -6 / K), a square prism-shaped tooling with dimensions of 50mm × 50mm × 1000mm; the surface microstructure of the tooling is designed as a continuous arrangement of triangular prisms, the lateral edges of the triangular prisms are parallel to the plane of the tooling, the two lateral edges are located on the surface of the tooling, and one lateral edge is away from the surface of the tooling structure, forming a ridge. The adjacent faces of adjacent triangular prisms are imagined as ridge valleys. The structural schematic diagram is shown below. Figure 3 As shown;

[0130] The base of the triangular prism is a right triangle, the hypotenuse b is perpendicular to the horizontal surface of the tooling, the included angle α between the two sides forming the ridge is equal to the included angle β between the two adjacent sides of the adjacent triangular prism, which is 66.4°, and the machining radius of the rounded corner is 0.2mm; the length of the vertical side b is 2mm, and the length of the hypotenuse c is 5mm.

[0131] (2) The workpiece to be deposited is fixed using the tooling structure described in step (1), and chemical vapor deposition is performed at 1200℃ to obtain a silicon nitride coating (the coefficient of thermal expansion at room temperature is 2.81×10). -6 The thickness of / K) is 40-50μm;

[0132] (3) The workpiece and tooling were cooled at a cooling rate of 5℃ / min. When cooled to room temperature, it was found that the coating deposited on the surface of the tooling was peeled off in large areas, with a peeling area of ​​>90%.

[0133] Comparative Example 1

[0134] The same method as in Example 1 was used, except that in step (1), the CVD furnace tooling was a traditional long strip flat plate tooling with a flat surface and no microstructure design. After cooling, it was found that although the coating on the tooling surface would peel off, the peeling was incomplete. Figure 9 As shown in (2).

[0135] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An in-situ self-cleaning method applied to a chemical vapor deposition tool structure, characterized by, The method comprises: (1) designing a convex microstructure on the surface of the tool structure; (2) The tool structure is used to fix the deposition substrate workpiece, chemical vapor deposition is carried out, and a coating is obtained, wherein the thermal expansion coefficient α a of the coating is less than the thermal expansion coefficient α b of the tool structure; (3) cooling, the coating deposited on the surface of the tool structure is peeled off; wherein, during the cooling process, the convex microstructure converts the shear thermal stress generated between the tool structure and the coating into tensile peeling stress, and the shear thermal stress generated between the tool structure and the coating is greater than the interfacial bonding strength between the tool structure and the coating; the convex microstructure comprises a continuous arrangement of triangular prisms, wherein the side edges of the triangular prisms are parallel to the plane of the tool structure, two side edges are located on the surface of the tool structure, and one side edge is away from the surface of the tool structure to form a ridge; wherein the coating on one side of the triangular prism is subjected to tensile peeling stress converted from the shear stress between the coating on the other side and the tool.

2. The method of claim 1, wherein, The bottom surface of the triangular prism is a right-angled triangular bottom surface.

3. The method according to claim 1 or 2, characterized in that, The included angle α between the two side surfaces of the triangular prism constituting the ridge is 45°<α<75°; And / or, the machining fillet radius r1 of the ridge is less than 0.5mm.

4. The method of claim 3, wherein, The included angle β between the two adjacent side surfaces of the adjacent triangular prisms is 45°<β<75°, forming a valley, wherein the machining fillet radius r2 of the valley is less than 0.5mm; And / or, the included angle β is equal to the included angle α.

5. The method of claim 2, wherein, a length L of a side of the ridge perpendicular to the surface of the tool structure b 1 mm ≤ L b ≤ 5 mm; and / or the length L of the other side of the ridge c is 3 mm ≤ L c ≤ 12 mm.

6. The method of claim 1, wherein, In step (2), the thickness h of the coating is 10μm<h<1500μm; and / or, a a less than a b more than 30% of a 7. The method of claim 1, wherein, In step (3), the cooling rate is 1-50℃ / min.

8. The method of claim 1, wherein, The material constituting the tool structure is one of graphite, silicon carbide, and high-temperature alloy material; And / or, the material constituting the coating is one of boron nitride, silicon carbide, silicon dioxide, and metal carbide.

9. A tooling structure for use in chemical vapor deposition, comprising: The tool structure is cleaned in situ by the method of any one of claims 1-8, the surface of the tool structure has a convex microstructure, and the convex microstructure comprises a continuous arrangement of triangular prisms, wherein the side edges of the triangular prisms are parallel to the plane of the tool structure, two side edges are located on the surface of the tool structure, and one side edge is away from the surface of the tool structure to form a ridge.

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