Structure and process for seed bonding

Abstract

The application discloses a structure and a process method for seed crystal bonding, relates to the technical field of silicon carbide processing, and comprises a crucible upper cover, a graphite layer and a seed crystal. An adhesive layer is arranged between the crucible upper cover and the graphite layer and between the seed crystal and the graphite layer. The structure further comprises a limiting piece and a pressing block. The limiting piece is provided with a through upper-and-lower accommodating portion. The size and shape of the bottom of the accommodating portion are matched with those of the crucible upper cover. The size and shape of the top of the accommodating portion are matched with those of the pressing block. A buffer layer is further arranged between the pressing block and the seed crystal. The application can solve the production problems of seed crystal deviation and uneven solidification during hot-press bonding of the seed crystal and graphite paper.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide processing technology, and more specifically to a structure and process method for seed crystal bonding. Background Technology

[0002] The seed crystal bonding to graphite paper followed by adhesive film sintering and curing is a crucial process in semiconductor material fabrication. The main steps include: fixing the seed crystal onto graphite paper using adhesive, and then using a hot-pressing tray to heat-press the seed crystal and graphite paper, causing the adhesive film to cure and achieving a tight bond between the seed crystal and the graphite paper. This process is essential for ensuring the stability and quality of the seed crystal during subsequent crystal growth.

[0003] However, the current process directly uses a hot press tray to press the seed crystal onto the graphite paper, which easily leads to the following problems: 1) Seed crystal misalignment: When applying pressure to the seed crystal using a hot press tray, the friction is small before the adhesive film is cured, which can easily cause the seed crystal to slide, resulting in uneven hot pressing force and affecting the bonding quality; 2) Uneven curing: During the hot pressing process, there is no fixture to keep the perimeter warm, resulting in a large temperature difference between the central and edge areas, leading to uneven curing and the appearance of bubbles. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to propose a structure and process method for seed crystal bonding, which can solve the production problems of seed crystal displacement and uneven curing that occur when hot-pressing graphite paper with seed crystals.

[0005] To address the aforementioned technical problems, one objective of this invention is to provide a structure for seed crystal bonding, comprising a crucible cover, a graphite layer, and a seed crystal. An adhesive layer is provided between the crucible cover and the graphite layer, and between the seed crystal and the graphite layer. The structure also includes a limiting member and a pressing block. The limiting member has a through-hole receiving portion. The bottom of the receiving portion matches the size and shape of the crucible cover, and the top of the receiving portion matches the size and shape of the pressing block. A buffer layer is also provided between the pressing block and the seed crystal.

[0006] Preferably, the adhesive layer is applied by spraying. Spraying ensures a uniform distribution of the adhesive layer. Compared to manual application or mechanical pressing, spraying technology utilizes high-pressure airflow or electrostatic adsorption to uniformly spray the adhesive material as microparticles or a mist onto the surface where the seed crystal and graphite paper meet. This not only improves the uniformity of the adhesive layer but also ensures that every minute part of the bonding interface is fully covered, thereby enhancing the strength and stability of the bond. Furthermore, spraying allows for better control of the adhesive layer thickness. The thickness of the adhesive layer has a crucial impact on the bonding effect; too thick a layer may lead to incomplete curing, affecting bond strength, while too thin a layer may not provide sufficient bonding area, reducing bond stability. Spraying technology allows for precise control of the adhesive layer thickness by adjusting parameters of the spraying equipment, such as spraying pressure, spraying speed, and nozzle size, thus meeting different bonding requirements.

[0007] Preferably, a first heat insulation layer is provided between the compact and the seed crystal.

[0008] Preferably, the buffer layer is a graphite felt.

[0009] Preferably, the adhesive layer comprises the following components in parts by weight: 40-70 parts of waterborne epoxy resin, 30-60 parts of anhydrous ethanol, 0.2-0.5 parts of wetting agent, 0.1-0.3 parts of leveling agent, and 0.2-0.6 parts of silane coupling agent. By optimizing the component ratio, introducing organic solvents to dilute the resin in the adhesive to reduce viscosity, and adding additives such as wetting agents, leveling agents, and silane coupling agents, the wettability, leveling, and adhesion of the adhesive and the bonding substrate are improved, thereby enhancing the bonding quality and effectively addressing issues such as seed crystal misalignment and uneven curing.

[0010] Preferably, the waterborne epoxy resin is one or more of phenolic epoxy resin, waterborne epoxy resin emulsion, and nonionic amine adduct. Phenolic epoxy resin is known for its high heat resistance, high strength, and chemical stability, and can significantly improve the high-temperature resistance and mechanical strength of the adhesive. Waterborne epoxy resin emulsion, due to its good dispersibility and environmental friendliness, facilitates uniform coating of the adhesive between the seed crystal and graphite paper, while reducing environmental pollution. Nonionic amine adduct has good flexibility and adhesion, which helps to improve the adhesive's adaptability to different material surfaces. Combining one or more of these three types of epoxy resin can fully leverage their respective advantages, forming a complementary effect, thereby further improving the overall performance of the seed crystal adhesive and ensuring the strength and stability of the bond.

[0011] Preferably, the waterborne epoxy resin is a phenolic epoxy resin and a non-ionic amine adduct, with a weight ratio of 1:(0.5-0.8). Combining the phenolic epoxy resin and the non-ionic amine adduct at a weight ratio of 1:0.6 is based on a thorough understanding and optimization of their properties. The high heat resistance and high strength of the phenolic epoxy resin provide a solid foundation for the adhesive, while the flexibility and adhesion of the non-ionic amine adduct compensate for some of the shortcomings of the phenolic epoxy resin. By precisely controlling the ratio of the two, a balance and optimization of performance can be achieved, resulting in an adhesive that possesses high strength and heat resistance while also exhibiting good flexibility and adhesion.

[0012] Preferably, the wetting agent is one or more of an EO / EP block copolymer and a siloxane-based twin-structure surfactant. The EO / EP block copolymer has a good balance of hydrophilicity and lipophilicity, enabling it to form a uniform wetting layer on the seed crystal and graphite paper surfaces, which facilitates the uniform coating of the adhesive between them. The siloxane-based twin-structure surfactant, due to its unique molecular structure, can form a stable adsorption layer at the interface, reducing surface tension and further promoting the wetting and penetration of the adhesive, thus facilitating the removal of air bubbles that were previously located between the adhesive and the bonding surface.

[0013] To address the aforementioned technical problems, a second objective of this invention is to provide a process method for seed crystal bonding, comprising the following steps:

[0014] S0, the seed crystal is attached to the graphite paper with the adhesive layer, and the seed crystal is placed in the middle of the crucible lid with the seed crystal facing upwards;

[0015] S1, The position of the seed crystal is calibrated by the assembly limit component to prevent slippage during the hot pressing process of the seed crystal;

[0016] S2, a buffer layer is placed on top of the seed crystal;

[0017] S3, the pressure block is placed on the buffer layer to press down the seed crystal, so that the force is evenly distributed;

[0018] S4, proceed with subsequent hot pressing.

[0019] Preferably, in S0 and S1, a spraying process is used for bonding.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) By setting a limiting component that restricts the horizontal movement of the crucible cover and the pressure block, and setting a buffer layer between the pressure block and the seed crystal, it is ensured that the seed crystal is firmly attached to the crucible cover during bonding, and the movement of the fixture in the vertical direction is effectively restricted. Through the synergistic effect of the three, the problems of offset and uneven curing during the hot pressing bonding process of the seed crystal are fundamentally solved, and the production efficiency and product quality are significantly improved.

[0022] (2) The adhesive layer technology used in the structure for seed crystal bonding of the present invention improves the wettability, leveling and adhesion of the adhesive and the bonding substrate by optimizing the component ratio, introducing organic solvents to dilute the resin in the adhesive to reduce the viscosity, and adding wetting agents, leveling agents and silane coupling agents, etc., thereby improving the bonding quality.

[0023] (3) The structure and process method for seed crystal bonding provided by the present invention are simple and easy to implement, with significant effects. The produced crystals have good quality and high yield, and are suitable for large-scale promotion and application. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a perspective view of the seed crystal bonding method in Example 1;

[0026] Figure 2 This is a top view of the structure used for seed crystal bonding in Example 1;

[0027] Figure 3 for Figure 2 A cross-sectional view along the AA direction;

[0028] Figure 4 This is an exploded view of the seed crystal bonding method in Example 1;

[0029] Figure 5 This is a perspective view of the limiting component in Example 1.

[0030] In the picture:

[0031] 1-Limiting component; 2-Pressure block; 3-Containing part; 4-Cruise lid; 5-Seed crystal; 6-Buffer layer; 7-Graphite layer. Detailed Implementation

[0032] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0033] Examples 1-9

[0034] A structure for seed crystal bonding, such as Figure 1-5 As shown in the attached diagram, due to the very small thickness of the adhesive layer, it is omitted from the actual drawing. The structure includes a crucible cover 4, a graphite layer 7, and a seed crystal 5. Adhesive layers are provided between the crucible cover 4 and the graphite layer 7, and between the seed crystal 5 and the graphite layer. It also includes a limiting member 1 and a pressing block 2. The limiting member 1 has a through-hole receiving portion 3. The bottom of the receiving portion matches the size and shape of the crucible cover, and the top of the receiving portion matches the size and shape of the pressing block. A buffer layer 6 is also provided between the pressing block and the seed crystal. In this embodiment, the graphite layer 7 is made of conventional graphite paper. The adhesive layer 8 is applied by spraying. The core of the limiting component lies in its internal, precisely shaped and sized receiving section: its bottom is designed to conform to the contour of the crucible lid, ensuring a stable fit during installation and providing a stable reference surface for seed crystal positioning; while the top of the receiving section closely matches the shape and size of the pressure block. This design not only allows the pressure block to precisely align with the seed crystal and apply pressure, but also reduces pressure loss during transmission through the tight contact surface, ensuring uniform pressure distribution. Furthermore, the buffer layer added between the pressure block and the seed crystal acts as a medium for pressure transmission. It absorbs and disperses some of the impact force applied by the pressure block, preventing the seed crystal from shifting due to direct pressure, and its elastic properties ensure that the pressure on the seed crystal surface is gentler and more uniform. This helps the adhesive between the graphite paper and the seed crystal to cure evenly, avoiding seed crystal shifting due to excessive local pressure. In summary, this solution, through the precise matching of the limiting components, the accurate application of pressure by the pressing block, and the gentle transfer of the buffer layer, works synergistically to fundamentally solve the problems of misalignment and uneven curing during the hot pressing bonding process of seed crystals, significantly improving production efficiency and product quality.

[0035] During the hot pressing process, if the fixture does not provide insulation around the perimeter, the temperature difference between the central and edge areas will be significant, leading to uneven curing and air bubbles. Preferably, a first insulation layer is also provided between the pressing block 2 and the seed crystal 5. During the hot pressing bonding process, the seed crystal needs to maintain a certain temperature to ensure effective curing of the adhesive. The presence of the first insulation layer can effectively reduce heat loss during the transfer of heat from the pressing block to the seed crystal, maintaining the temperature stability around the seed crystal. This not only helps the adhesive to cure evenly and quickly, but also avoids changes in internal stress of the seed crystal due to temperature fluctuations, thereby reducing the risk of the seed crystal sliding due to temperature changes. Furthermore, the buffer layer 6 is graphite soft felt. Graphite soft felt, as a buffer layer, also has the effect of the first insulation layer. Graphite soft felt has excellent flexibility and elasticity, which can play a good buffering role when the pressing block applies pressure, protecting the seed crystal from direct impact and damage. At the same time, the good thermal insulation performance and thermal stability of graphite soft felt can maintain stable physical and chemical properties in high-temperature environments, and will not deform or fail due to temperature changes. These characteristics not only effectively prevent the seed crystal from shifting due to uneven stress during hot pressing, but also improve the overall heat preservation efficiency and stability of the fixture.

[0036] Preferably, the limiting member 1 is cylindrical. The cylindrical limiting member not only has the advantages of simple structure, ease of processing and installation, but also provides stable support and positioning for the seed crystal during hot pressing. The cylindrical design gives the limiting member stronger rigidity and stability in the vertical direction.

[0037] Preferably, the limiting component 1 is further provided with a second heat insulation layer. As a key component of the fixture, the temperature stability of the limiting component directly affects the positioning accuracy and bonding effect of the seed crystal. The second heat insulation layer can effectively isolate the influence of the external environment on the temperature of the limiting component, maintain a constant internal temperature of the limiting component, and thus ensure that the seed crystal is always in an ideal temperature environment during hot pressing. This not only helps to reduce the thermal stress generated by the temperature change of the seed crystal, but also avoids the seed crystal displacement problem caused by temperature gradient. Furthermore, the material of the limiting component 1 is graphite. Graphite has excellent heat insulation performance and thermal stability, and can maintain stable physical and chemical properties in high-temperature environments. It will not deform or be damaged due to temperature changes. At this time, the limiting component itself acts as a second heat insulation layer. These characteristics make graphite an ideal choice for the limiting component material, which can not only effectively prevent the seed crystal from shifting due to temperature changes during hot pressing, but also improve the overall thermal efficiency and stability of the fixture.

[0038] Preferably, the flatness of the pressure block 2 is less than or equal to 5 μm. As the component that directly acts on the seed crystal, the flatness of the pressure block's surface directly affects the uniformity of stress on the seed crystal and the bonding effect. A pressure block with high flatness ensures a more uniform pressure distribution on the seed crystal surface when pressure is applied, avoiding seed crystal damage or displacement caused by excessive local pressure. In addition, a pressure block with high flatness can also increase the contact area between the adhesive and the seed crystal, enhance the bonding strength, and ensure the stability and reliability of the bonding effect. Furthermore, the material of the pressure block 2 is 316 stainless steel. 316 stainless steel has excellent corrosion resistance and high temperature resistance, and will not deform or be damaged due to corrosion or high temperature.

[0039] The above-mentioned process for seed crystal bonding includes the following steps:

[0040] Step 1: Adhere the seed crystal to the graphite layer using an adhesive layer. Specifically, a spraying process is used. Wipe the silicon surface of the seed crystal clean with alcohol, place it in a 60-degree oven and bake for 10 minutes. Then, place the seed crystal under the nozzle of a YMUS ultrasonic spraying machine for spraying. The spraying power and ultrasonic frequency are both the middle values ​​of the equipment's range. The equipment automatically sprays the adhesive film. After spraying, place the seed crystal in a 60-degree oven to dry the alcohol for 10 minutes. Then, attach the graphite layer and the sprayed surface of the seed crystal together, and remove air bubbles during the pressing process.

[0041] Step 2: Using the same spraying process, attach the other side of the graphite layer to the crucible cover with an adhesive layer, placing the seed crystal facing upwards in the middle of the crucible cover;

[0042] Step 3: Assemble the limiting components to calibrate the position of the seed crystal to prevent slippage during the hot pressing process.

[0043] Step 4: Cover the seed crystal with a buffer layer and a pressure block in sequence to ensure that the force is evenly distributed.

[0044] Step 5: Perform subsequent hot pressing. Specifically, assemble the above-installed structure into the hot pressing fixture and place it in the hot press. The parameters of the hot pressing process are: pressure: 100 kg; heating rate: 30 min to 150 degrees, hold for 30 min, 30 min from 150 to 350 degrees, hold for 40 min, and then cool to 150 degrees to remove the seed crystal.

[0045] The adhesive layer is a self-made special seed crystal bonding adhesive, the composition and content of which are shown in Table 2, including water-based epoxy resin, anhydrous ethanol, wetting agent, leveling agent, and silane coupling agent.

[0046] Table 1 below shows the source and type of raw materials used in the embodiments and comparative examples of this application. Unless otherwise specified, all reagents were obtained commercially available.

[0047] Table 1 - Sources and types of raw materials used in the embodiments of this application

[0048]

[0049]

[0050] The preparation method of the above-mentioned seed crystal bonding adhesive includes the following steps:

[0051] (1) The preparation temperature is 23±2℃ and the humidity is 15%-25%. According to the ratio, first add anhydrous ethanol, turn on the stirring speed and adjust it to 600rpm / min, then add water-based epoxy resin, dissolve and stir at room temperature for 10min until completely dissolved to obtain the premix.

[0052] (2) Adjust the speed to 1200-1500 rpm / min, add the wetting agent, leveling agent and silane coupling agent slowly dropwise, stir for 10 min until completely dissolved, and obtain the mixture;

[0053] (3) Filter the mixture from step (2) with qualitative filter paper to remove undissolved impurities in the glue and obtain seed crystal bonding glue.

[0054] Comparative Example 1

[0055] Commercially available seed crystal adhesive was used as a comparison.

[0056] Table 2 - Content of each component in Examples 1-7

[0057]

[0058]

[0059] Test methods;

[0060] Viscosity testing method: According to the rotational viscometer method in GB / T 10247-2008, the viscosity of the adhesive was determined using an NDJ-5S instrument. The prepared adhesive was placed in a glass bottle and kept at a constant temperature of 25℃ for 30 minutes. The instrument parameters were set as follows: rotor #1, rotation speed 12 revolutions, measurement time 15 seconds, unit mPa·s. After the sample results stabilized, the average value of three tests was taken and recorded. The test results are shown in Table 3.

[0061] Hot-press curing of the adhesive film: The bonding surfaces of the graphite paper and the seed crystal need to be sprayed with isopropyl alcohol solution, wiped clean with a lint-free cloth, and placed in a 60℃ oven for 10 minutes. The glued graphite paper and seed crystal are then placed in a drying oven for 10 minutes to remove the solvent. The bonding surfaces are then joined together, and hot-press curing is performed according to the set process. After the adhesive film has been hot-pressed and cured, the surface is observed for bubbles, uneven adhesive spots, and the thickness of the adhesive film. It should be noted that because the seed crystal adhesive in Comparative Example 1 has a high viscosity, a spraying process cannot be used; only a conventional hand-coating process can be used. The test results are shown in Table 3.

[0062] Surface condition after seed crystal growth: The hot-pressed seed crystal, graphite paper, and crucible cover are used for subsequent crystal growth. After the silicon carbide crystal growth is completed, observe whether there is ablation on the surface where the silicon carbide crystal and the glue are in contact. The test results are shown in Table 3.

[0063] The results of the above test methods are shown in Table 3.

[0064] Table 3 - Performance test results of examples and comparative examples

[0065]

[0066]

[0067] As shown in the table above, the viscosity (25℃) of the seed crystal bonding adhesive prepared in this embodiment of the invention is 300-850 mPa·s. According to the inventors' experiments, it exhibits good spraying performance within a viscosity (25℃) range of 100-1000 mPa·s, which can greatly reduce the amount of adhesive used and significantly improve the production efficiency of adhesive application. The hot-pressed cured adhesive film is bubble-free, and there is no visible ablation on the surface where the silicon carbide crystal and adhesive come into contact after seed crystal growth, nor is there any unevenness; the adhesive layer is uniformly coated. Moreover, compared to the hand coating process of Comparative Example 1, the thickness of the cured adhesive film in the sprayed embodiment is smaller, reaching 0.05-0.1 mm, while the thickness of the cured adhesive film in the hand coating process is generally 0.2-0.3 mm. Since the coating thickness can be further reduced, the overall hot-pressing process time can be reduced from the original 4.5 h to less than 2 h.

[0068] As can be seen from the comparison between Examples 1-3 and Example 4, reducing the proportion of anhydrous ethanol solvent will lead to a slight decrease in the uniformity of the hot-pressed curing adhesive, but will not have a significant impact on the crystal growth of the seed crystal.

[0069] Interfacial undulations in the crystal can lead to inconsistent nitrogen doping concentrations, resulting in uneven coloring of the removed wafers and impacting the yield of subsequent chip production. A comparison of Examples 5 and 4 shows that increasing the proportion of wetting agent and decreasing the proportion of leveling agent further improves crystal surface smoothness. The inventors believe that this adjustment not only enhances the wettability and uniform distribution of the adhesive but also provides more favorable conditions for crystal growth by limiting excessive adhesive flow. The combined effect of these factors significantly improves the surface smoothness of the crystal.

[0070] The presence of textures in the adhesive film indicates slight unevenness, but the degree is relatively minor. During crystal growth, bulges are likely to occur in this area. A comparison of Examples 7 and 8 shows that, under the same compounding ratio, the thermosetting adhesive film obtained by the combination of phenolic epoxy resin and nonionic amine adduct has no textures, the grown crystals are of better quality, and the crystal surface is smoother.

[0071] A comparison of Example 9 and Example 1 shows that selecting a siloxane-based twin-structure surfactant as a wetting agent not only promotes substrate wetting and adhesive penetration by reducing surface tension and improving wetting performance, but also significantly improves bonding quality and strength by reducing bubble generation and enhancing film adhesion. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the present invention.

Claims

1. A structure for seed crystal bonding, comprising a crucible cover, a graphite layer, and a seed crystal, wherein adhesive layers are provided between the crucible cover and the graphite layer, and between the seed crystal and the graphite layer, characterized in that: It also includes a limiting component and a pressing block. The limiting component has a through-hole receiving part. The bottom of the receiving part matches the size and shape of the crucible cover. The top of the receiving part matches the size and shape of the pressing block. A buffer layer is also provided between the pressing block and the seed crystal. The buffer layer is graphite soft felt. The adhesive layer comprises the following components in parts by weight: 40-70 parts of waterborne epoxy resin, 30-60 parts of anhydrous ethanol, 0.2-0.5 parts of wetting agent, 0.1-0.3 parts of leveling agent, and 0.2-0.6 parts of silane coupling agent.

2. The structure for seed crystal bonding according to claim 1, characterized in that: The adhesive layer is applied by spraying.

3. A process method for seed crystal bonding using the structure for seed crystal bonding according to any one of claims 1-2, comprising the following steps: S0, the seed crystal is bonded to the graphite layer through an adhesive layer; S1, attach the other side of the graphite layer to the crucible cover with an adhesive layer, and place the seed crystal in the middle of the crucible cover with the seed crystal facing upwards; S2, The position of the seed crystal is calibrated by the assembly limit component to prevent slippage during the hot pressing process of the seed crystal; S3, a buffer layer and a pressure block are placed on top of the seed crystal to ensure that the force is evenly distributed; S4, proceed with subsequent hot pressing.

4. The process method for seed crystal bonding according to claim 3, characterized in that: In S0 and S1, a spray coating process is used for bonding.

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