Structure and process method for bonding seed crystals

Abstract

The invention discloses a structure and a process method for seed crystal bonding, and relates to the technical field of silicon carbide processing, the structure comprises a crucible upper cover, a graphite layer and a seed crystal, adhesive layers are 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, a containing part penetrating through the upper part and the lower part is arranged in the limiting piece, and the pressing block is arranged in the containing part. The bottom of the accommodating part is matched with the crucible upper cover in size and shape, the top of the accommodating part is matched with the pressing block in size and shape, and a buffer layer is further arranged between the pressing block and the seed crystal. According to the invention, the production problems of deviation and non-uniform solidification of the seed crystal when the seed crystal is bonded with the graphite paper in a hot pressing manner can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide processing, and in particular to a structure and a process method for seed crystal bonding. Background Art

[0002] The process of sintering and curing the adhesive film after the seed crystal is bonded to the graphite paper is a key process in the preparation of semiconductor materials. The main steps of this process include: fixing the seed crystal on the graphite paper by gluing, and then hot pressing the seed crystal and graphite paper using a hot pressing tray to cure the adhesive film, thereby achieving a close bond between the seed crystal and the graphite paper. This process is crucial to ensure the stability and quality of the seed crystal in the subsequent crystal growth process.

[0003] However, the current process is to directly use a hot pressing tray to hot press the seed crystal onto graphite paper, so the following problems are prone to occur: 1) The seed crystal is offset: when the hot pressing tray is used to apply pressure to the seed crystal, the friction force 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 jig to insulate the surrounding area, resulting in a large temperature difference between the middle area and the edge area, resulting in uneven curing and the appearance of bubbles. Summary of the invention

[0004] In order to overcome the defects 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 offset and uneven curing when the seed crystal is hot-pressed and bonded to graphite paper.

[0005] In order to solve the above technical problems, one of the purposes of the present invention is to provide a structure for seed crystal bonding, including a crucible cover, a graphite layer and a seed crystal, an adhesive layer is arranged between the crucible cover and the graphite layer, and between the seed crystal and the graphite layer, and also includes a limiter and a pressing block, the limiter is provided with a receiving portion running through the upper and lower parts, the bottom of the receiving portion matches the size and shape of the crucible cover, the top of the receiving portion matches the size and shape of the pressing block, and a buffer layer is also arranged between the pressing block and the seed crystal.

[0006] Preferably, the adhesive layer is provided by spraying. The spraying method can ensure the uniform distribution of the adhesive layer. Compared with manual application or mechanical pressing, the spraying technology uses high-pressure airflow or electrostatic adsorption principle to evenly spray the adhesive material in the form of tiny particles or mist on the surface where the seed crystal contacts the graphite paper, which not only improves the uniformity of the adhesive layer, but also ensures that every tiny part of the bonding interface can be fully covered, thereby enhancing the strength and stability of the bonding. Furthermore, the spraying method is conducive to controlling the thickness of the adhesive layer. The thickness of the adhesive layer has a crucial influence on the bonding effect. Too thick may lead to incomplete curing and affect the bonding strength, while too thin may not provide enough bonding area and reduce the bonding stability. Spraying technology can accurately control the thickness of the adhesive layer by adjusting the parameters of the spraying equipment, such as spraying pressure, spraying speed, nozzle size, etc., so as to meet different bonding requirements.

[0007] Preferably, a first heat-insulating layer is further provided between the pressing block and the seed crystal.

[0008] Preferably, the buffer layer is graphite soft 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 into the glue to dilute the resin, reducing the viscosity, and adding additives such as wetting agents, leveling agents, and silane coupling agents, the wettability, leveling properties, and adhesion of the glue and the bonding substrate are improved, the bonding quality is improved, and the problems of seed crystal offset and uneven curing are further improved.

[0010] Preferably, the water-based epoxy resin is one or more of phenolic epoxy resin, water-based epoxy resin emulsion, and non-ionic 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 bonding glue. Water-based epoxy resin emulsion is conducive to the uniform coating of glue between seed crystals and graphite paper due to its good dispersibility and environmental protection, while reducing pollution to the environment. Non-ionic amine adducts have good flexibility and adhesion, which helps to improve the adaptability of glue to surfaces of different materials. Combining one or more of these three types of epoxy resins can give full play to their respective advantages and form a complementary effect, thereby further improving the comprehensive performance of seed crystal bonding glue and ensuring the firmness and stability of bonding.

[0011] Preferably, waterborne epoxy resin is phenolic epoxy resin and nonionic amine adduct, and the weight ratio of the two is 1: (0.5-0.8). Phenolic epoxy resin and nonionic amine adduct are combined with the weight ratio of 1: 0.6, which is based on the in-depth understanding and optimization consideration of both performances. The high heat resistance and high strength of phenolic epoxy resin provide a solid foundation for glue, while the flexibility and adhesion of nonionic amine adduct can make up for the shortcomings of phenolic epoxy resin in some aspects. By accurately controlling the ratio of the two, it is possible to achieve balance and optimization in performance, so that glue, while having high strength and heat resistance, also possesses good flexibility and adhesion.

[0012] Preferably, the wetting agent is one or more of EO / EP block copolymer and siloxane twin structure surfactant. EO / EP block copolymer has a good balance of hydrophilicity and lipophilicity, and can form a uniform wetting layer on the surface of the seed crystal and graphite paper, which helps to evenly coat the glue between the two. The siloxane twin structure surfactant can form a stable adsorption layer at the interface due to its unique molecular structure, reduce surface tension, further promote the wetting and penetration of the glue, and help to discharge the bubbles originally between the glue and the bonding surface.

[0013] In order to solve the above technical problems, the second object of the present invention is to provide a process method for seed crystal bonding, comprising the following steps:

[0014] S0, bonding the seed crystal to the graphite paper through the adhesive layer, and placing the seed crystal upward in the middle of the crucible cover;

[0015] S1, assembling the limiter to calibrate the position of the seed crystal to prevent the seed crystal from sliding during hot pressing;

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

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

[0018] S4, performing 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 providing a limiter to limit the horizontal movement of the crucible cover and the pressing block, and providing a buffer layer between the pressing block and the seed crystal, it is ensured that the seed crystal is firmly attached to the crucible cover during bonding, and the vertical movement of the fixture is effectively limited. Through the synergistic effect of the three, the offset and uneven curing problems 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 technical solution of the adhesive layer used in the structure for seed crystal bonding of the present invention improves the wettability, leveling and adhesion of the glue and the bonding substrate by optimizing the component ratio, introducing an organic solvent into the glue to dilute the resin, reducing the viscosity, and adding auxiliary agents such as a wetting agent, a leveling agent and a silane coupling agent, 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 crystals produced are of good quality and high yield, and are suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 It is a three-dimensional diagram for bonding seed crystals according to the first embodiment;

[0026] Figure 2 is a top view of a structure for seed crystal bonding according to Embodiment 1;

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

[0028] Figure 4 An exploded view of the seed crystal bonding method according to the first embodiment;

[0029] Figure 5 It is a three-dimensional diagram of the limiting member of the first embodiment.

[0030] In the figure:

[0031] 1-limiting member; 2-pressing block; 3-accommodating portion; 4-crucible upper cover; 5-seed crystal; 6-buffer layer; 7-graphite paper. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually carried out according to conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to 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, since the thickness of the adhesive layer is very small, the accompanying drawings omit the display. The structure includes a crucible cover 4, a graphite layer 7 and a seed crystal 5. An adhesive layer is 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 stopper 1 and a pressing block 2. The stopper 1 is provided with a receiving portion 3 that runs through the upper and lower parts. 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 provided by spraying. The built-in accommodating part of the limiter, which runs through the top and bottom and has a precisely matched shape and size, plays a core role: its bottom is designed according to the contour of the crucible cover, ensuring that the limiter can fit firmly on the crucible cover during installation, providing a stable reference surface for the positioning of the seed crystal; and the top of the accommodating part is closely matched with the shape and size of the pressing block. Such a design not only enables the pressing block to accurately apply pressure to the position of the seed crystal, but also reduces the loss during the pressure transmission process through the close contact surface, ensuring the uniformity of pressure distribution. Furthermore, the buffer layer added between the pressing block and the seed crystal, as a medium for pressure transmission, can absorb and disperse part of the impact force applied by the pressing block to prevent the seed crystal from shifting due to direct pressure, and through its elastic properties, ensure that the pressure on the surface of the seed crystal is softer and more uniform, which helps the adhesive between the graphite paper and the seed crystal to solidify evenly and avoids the problem of seed crystal shifting due to excessive local pressure. In summary, this solution fundamentally solves the problems of offset and uneven curing during the hot pressing bonding of the seed crystal through the synergistic effect of the precise matching of the limit parts, the accurate pressure of the pressure block, and the gentle transfer of the buffer layer, and significantly improves production efficiency and product quality.

[0035] Among them, during the hot pressing process, if the fixture does not insulate the surrounding area, the temperature difference between the middle area and the edge area is large, resulting in uneven curing and 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 the effective curing of the adhesive. The presence of the first insulation layer can effectively reduce the loss of heat during the transfer from the pressing block to the seed crystal, and maintain the stability of the temperature around the seed crystal. This not only helps the adhesive to cure evenly and quickly, but also avoids changes in the internal stress of the seed crystal caused by temperature fluctuations, thereby reducing the risk of the seed crystal sliding due to temperature changes. Further, the buffer layer 6 is graphite soft felt. Graphite soft felt serves as a buffer layer and has the effect of the first insulation layer. Graphite soft felt has excellent flexibility and elasticity, and 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 a high temperature environment, and will not deform or fail due to temperature changes. These characteristics can not only effectively prevent the seed crystal from shifting due to uneven force during the hot pressing process, but also improve the overall thermal insulation efficiency and stability of the fixture.

[0036] Preferably, the shape of the stopper 1 is cylindrical. The cylindrical stopper not only has the advantages of simple structure, easy processing and installation, but also can provide stable support and positioning for the seed crystal during the hot pressing process. The cylindrical design makes the stopper have stronger rigidity and stability in the vertical direction.

[0037] Preferably, the limiter 1 is also provided with a second thermal insulation layer. As a key component of the jig, the temperature stability of the limiter directly affects the positioning accuracy and bonding effect of the seed crystal. The second thermal insulation layer can effectively isolate the influence of the external environment on the temperature of the limiter, maintain the constant temperature inside the limiter, and ensure that the seed crystal is always in an ideal temperature environment during the hot pressing process. This not only helps to reduce the thermal stress caused by temperature changes in the seed crystal, but also avoids the problem of seed crystal offset caused by temperature gradient. Furthermore, the material of the limiter 1 is graphite. Graphite has excellent thermal insulation performance and thermal stability, can maintain stable physical and chemical properties in a high temperature environment, and will not be deformed or damaged due to temperature changes. At this time, the limiter itself plays the role of a second thermal insulation layer. These characteristics make graphite an ideal choice for the limiter material, which can not only effectively prevent the offset problem of the seed crystal caused by temperature changes during the hot pressing process, but also improve the overall thermal efficiency and stability of the jig.

[0038] Preferably, the flatness of the pressing block 2 is less than or equal to 5um. As a component that directly acts on the seed crystal, the flatness of the surface of the pressing block directly affects the force uniformity and bonding effect of the seed crystal. A pressing block with high flatness can ensure that when pressure is applied, the pressure distribution on the surface of the seed crystal is more uniform, avoiding the problem of seed crystal damage or deviation caused by excessive local pressure. In addition, a pressing 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 pressing block 2 is 316 stainless steel. 316 stainless steel has excellent corrosion resistance and high temperature resistance, and will not be deformed or damaged due to corrosion or high temperature.

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

[0040] Step 1, the seed crystal is bonded to the graphite layer through the adhesive layer. Specifically, the spraying process is adopted, the silicon surface of the seed crystal is wiped clean with alcohol, placed in a 60-degree oven, and baked for 10 minutes, and then the seed crystal is placed under the nozzle of the YMUS ultrasonic glue sprayer for spraying. The glue spraying power and ultrasonic frequency are both in the middle of the equipment range. The equipment automatically sprays the glue film. After spraying, the seed crystal is placed in a 60-degree oven to dry the alcohol and processed for 10 minutes. Then, the graphite layer and the glue spraying surface of the seed crystal are bonded, and bubbles are discharged during the pressing process;

[0041] Step 2: Using the same spraying process, the other side of the graphite layer is bonded to the upper cover of the crucible through the adhesive layer, and the seed crystal is placed in the middle of the upper cover of the crucible with the seed crystal facing upwards;

[0042] Step 3, assembling a stopper to calibrate the position of the seed crystal to prevent the seed crystal from sliding during hot pressing;

[0043] Step 4, a buffer layer and a pressing block are sequentially placed on the top of the seed crystal to make the force uniform;

[0044] Step 5, perform subsequent hot pressing. Specifically, assemble the above-mentioned installed structure in a hot pressing tooling and place it in a hot pressing machine. The parameters of the hot pressing process are: pressure: 100kg; heating rate: 30min to 150 degrees, hold for 30min, 30min from 150 to 350 degrees, hold for 40min, then cool to 150 degrees to take out the seed crystal.

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

[0046] The following Table 1 lists the sources and types of raw materials used in the examples and comparative examples of the present application. Unless otherwise specified, the reagents were all commercially available.

[0047] Table 1 - Sources and models of raw materials in the examples of this application

[0048]

[0049]

[0050] The preparation method of the seed crystal bonding glue comprises the following steps:

[0051] (1) The preparation temperature is 23±2°C and the humidity is 15%-25%. Anhydrous ethanol is first added according to the ratio, the stirring speed is adjusted to 600 rpm / min, and then the water-based epoxy resin is added. The mixture is dissolved and stirred at room temperature for 10 minutes until it is completely dissolved to obtain a premix;

[0052] (2) adjusting the speed to 1200-1500 rpm / min, slowly adding the wetting agent, leveling agent, and silane coupling agent in a dropwise manner, stirring for 10 min until they are completely dissolved, and obtaining a mixture;

[0053] (3) filtering the mixture of step (2) through qualitative filter paper to remove undissolved impurities in the glue to obtain seed crystal bonding glue.

[0054] Comparative Example 1

[0055] Commercially available seed crystal glue was used as a comparative example.

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

[0057]

[0058]

[0059] Testing methods;

[0060] Viscosity test method: According to the rotational viscometer method in GB / T 10247-2008, NDJ-5S was used to measure the viscosity of the glue. The prepared glue was placed in a glass bottle at a constant temperature of 25°C for 30 minutes. The instrument parameters were set as follows: rotor 1#, speed 12 rpm, sample time 15s, unit mpa.s. When the sample result was stable, the average value of the test results was taken after three tests and the value was recorded. The test results are shown in Table 3.

[0061] Hot-pressing and curing 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 dust-free cloth, and placed in a 60°C oven for 10 minutes. Place the graphite paper and seed crystal sprayed with glue in a drying oven for 10 minutes to remove the solvent, then fit the bonding surfaces together and perform hot-pressing and curing according to the set process. After the hot-pressing and curing of the adhesive film is completed, observe the surface for bubbles, uneven glue spots, and the thickness of the film. It should be noted that due to the high viscosity of the seed crystal glue in Comparative Example 1, the spraying process cannot be used, and only the 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. When the growth of the silicon carbide crystal is completed, observe whether the surface of the silicon carbide crystal in contact with the glue is ablated. The test results are shown in Table 3.

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

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

[0065]

[0066]

[0067] It can be seen from the above table that the viscosity (25°C) of the seed crystal bonding glue prepared in the embodiment of the present invention is 300-850mpa.s. According to the inventor's experiments, the viscosity (25°C) has good spraying performance in the range of 100-1000mpa.s, which can greatly reduce the amount of glue used and greatly improve the production efficiency of glue coating. The hot pressing cured adhesive film is free of bubbles, and after the seed crystal grows, there is no visible ablation on the surface where the silicon carbide crystal and the glue are in contact, and there is no unevenness, and the coating of the adhesive layer is uniform. Moreover, compared with the hand-coating process of comparative example 1, the thickness of the cured adhesive film of the embodiment using spraying is smaller, reaching 0.05-0.1mm, while the thickness of the cured adhesive film of the hand-coating process is generally 0.2-0.3mm. Since the coating thickness can be further reduced, the time consumption of the hot pressing process can be reduced as a whole, from the original 4.5h to less than 2h.

[0068] From the comparison between Examples 1-3 and Example 4, it can be seen that reducing the proportion of anhydrous ethanol solvent will lead to a moderate decrease in the uniformity of the hot pressing curing adhesive, but has little effect on the crystals grown from the seed crystals.

[0069] The crystal interface fluctuations will lead to inconsistent nitrogen doping concentrations, and the cut wafers will have uneven colors, affecting the yield of subsequent chip production. By comparing Example 5 with Example 4, it can be seen that increasing the proportion of wetting agent and reducing the leveling agent is conducive to further improving the surface flatness of the crystal. The inventor believes that this adjustment not only enhances the wettability and uniform distribution ability of the glue, but also provides more favorable conditions for the growth of the crystal by limiting the excessive flow of the glue. The combined effect of these factors significantly improves the surface flatness of the crystal.

[0070] The film has lines, which means that the film is slightly uneven here, but the degree is relatively minor. Bumps are likely to appear here during crystal growth. From the comparison between Example 7 and Example 8, it can be seen that at the same compounding ratio, the hot press-cured film obtained by the combination of phenolic epoxy resin and non-ionic amine adduct has no lines, the quality of the grown crystals is better, and the surface of the crystals is smoother.

[0071] By comparing Example 9 with Example 1, it can be seen that the selection of the twin structure surfactant of siloxane as the wetting agent not only promotes the wetting of the substrate and the penetration of the glue by reducing the surface tension and improving the wetting performance, but also significantly improves the bonding quality and strength by reducing the generation of bubbles and improving the adhesion of the film. Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A structure for bonding seed crystals, comprising a crucible cover, a graphite layer and a seed crystal, wherein an adhesive layer is provided between the crucible cover and the graphite layer, and between the seed crystal and the graphite layer, wherein: It also includes a limiter and a pressing block. The limiter is provided with a receiving portion that passes through the top and the bottom. The bottom of the receiving portion matches the size and shape of the crucible cover. 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.

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

3. The structure for seed crystal bonding according to claim 1, characterized in that: A first heat-insulating layer is also arranged between the pressing block and the seed crystal.

4. The structure for seed crystal bonding according to claim 1, characterized in that: The buffer layer is graphite soft felt.

5. The structure for seed crystal bonding according to claim 1, characterized in that: 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.

6. The structure for seed crystal bonding according to claim 5, characterized in that: The waterborne epoxy resin is one or more of phenolic epoxy resin, waterborne epoxy resin emulsion, and non-ionic amine adduct.

7. The structure for seed crystal bonding according to claim 6, characterized in that: The waterborne epoxy resin is a phenolic epoxy resin and a non-ionic amine adduct, and the weight ratio of the two is 1: (0.5-0.8).

8. The structure for seed crystal bonding according to claim 5, characterized in that: The wetting agent is one or more of EO / EP block copolymer and silicone twin structure surfactant.

9. A process for seed crystal bonding, comprising the following steps: S0, bonding the seed crystal to the graphite layer through the adhesive layer; S1, bonding the other side of the graphite layer to the upper cover of the crucible through the adhesive layer, and placing the seed crystal facing upward in the middle of the upper cover of the crucible; S2, assembling the limiter to calibrate the position of the seed crystal to prevent the seed crystal from sliding during hot pressing; S3, a buffer layer and a pressing block are sequentially placed on the top of the seed crystal to make the force uniform; S4, performing subsequent hot pressing.

10. The process for seed crystal bonding according to claim 5, characterized in that: In S0 and S1, the bonding is done by spraying.

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