Seed wafer bonding process, seed wafer carbonization bracket and application of seed wafer carbonization bracket
By forming a dense carbon film and a graphite paper buffer layer on the surface of the seed chip, the problem of inconsistent warping between the silicon carbide seed chip and the crucible cover was solved, efficient seed chip bonding was achieved, the crystal quality and carbonization efficiency were improved, and the cost was reduced.
Patent Information
- Application Number
- CN202510769262.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-10
- Publication Date
- 2025-09-09
AI Technical Summary
In the existing technology, when the silicon carbide seed chip is directly bonded to the crucible cover, inconsistent warping is likely to occur, resulting in loose bonding and bubble generation, affecting the bonding quality of the seed chip. Uneven glue coating also leads to pores and poor density, which in turn causes reverse sublimation and hexagonal void defects on the back of the crystal.
A dense carbon film is formed on the surface of the seed wafer as a protective layer, and graphite paper is bonded to the surface of the carbon film away from the seed wafer as a buffer layer, which is then bonded to the crucible cover. A graphite seed wafer carbonization bracket is used to simultaneously carbonize multiple seed wafers, simplifying operations and improving efficiency.
Effectively inhibit reverse sublimation on the back side of silicon carbide crystals, improve crystal quality, reduce costs, and ensure bonding quality and carbonization efficiency.
Smart Images
Figure CN120608331A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of crystal growth technology, and in particular to a seed wafer bonding process, a seed wafer carbonization bracket and applications thereof. Background Art
[0002] Physical vapor transport (PVT) has become the mainstream method and technology for growing silicon carbide crystals. Seed wafer bonding is a key step in the crystal growth process. Usually, the silicon carbide seed wafer and the crucible lid are coated with organic glue for bonding. However, the crucible lid and the silicon carbide seed wafer have different degrees of warping. If the two are directly bonded with organic glue, problems such as weak bonding and bubble generation are likely to occur, thereby affecting the seed crystal bonding quality.
[0003] Related technologies use graphite paper as a buffer layer or insert it between the seed wafer and the crucible lid. This paper can level the warping of the seed wafer and the crucible lid, while also mitigating the thermal expansion coefficient of the two, thereby improving bonding quality. However, uneven adhesive coating on the seed wafer surface can also cause pores at the bonding point, leading to poor adhesive density and, in turn, reverse sublimation on the back of the crystal and hexagonal void defects on the wafer. Therefore, developing an efficient seed wafer bonding process that can effectively suppress reverse sublimation on the back of the silicon carbide seed wafer remains a current challenge.
[0004] Application Contents
[0005] The present application aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, one purpose of the present application is to propose a seed wafer bonding process, a seed wafer carbonization bracket, and their application. Using the seed wafer bonding process of the present application for crystal growth can effectively solve the problem of reverse sublimation on the back side of silicon carbide crystals. In addition, using the seed wafer carbonization bracket of the present application during the seed wafer bonding process can improve the seed wafer carbonization efficiency and reduce costs.
[0006] In a first aspect of the present application, a seed wafer bonding process is proposed, comprising:
[0007] forming an organic glue layer on the silicon surface of the seed wafer, and carbonizing the organic glue layer to form a carbon film, thereby obtaining a seed wafer containing the carbon film;
[0008] bonding graphite paper to the surface of the carbon film away from the seed wafer to obtain a mixed seed wafer;
[0009] The surface of the graphite paper away from the seed wafer is bonded to the crucible cover.
[0010] In the seed chip bonding process, a dense carbon film is formed on one surface of the seed chip. The carbon film can serve as a protective layer for the seed chip. Therefore, during the subsequent bonding steps, even if pores appear in other adhesive layers on the surface of the seed chip, the carbon film can still play a protective role, thereby preventing reverse sublimation on the back of the seed crystal and improving the crystal quality.
[0011] In addition, the seed wafer bonding process according to the above embodiment of the present application may also have the following additional technical features:
[0012] In some embodiments of the present application, the seed wafer bonding process needs to meet at least one of the following conditions:
[0013] The vacuum degree of the carbonization is ≤0.01mbar;
[0014] The carbonization temperature is 700°C to 900°C;
[0015] The organic adhesive layer is at least one of a photoresist layer, an epoxy resin adhesive layer, and a phenolic resin adhesive layer, thereby facilitating the organic adhesive to form a carbon film with good density.
[0016] In some embodiments of the present application, bonding graphite paper to the surface of the carbon film remote from the seed wafer includes forming a photoresist layer on the surface of the carbon film remote from the seed wafer and on one surface of the graphite paper, and heat treating the carbon film at 180° C. to 230° C. for 30 to 90 minutes. The graphite paper can serve as a buffer layer, helping to improve bonding quality.
[0017] In some embodiments of the present application, bonding the surface of the graphite paper away from the seed wafer to the crucible lid includes forming a resin adhesive layer on the surface of the graphite paper away from the seed wafer and the surface of the crucible lid, and heat treating the resin adhesive layer at 400°C to 600°C for 30 minutes to 90 minutes. This allows the seed wafer to be tightly bonded to the crucible lid, facilitating smooth crystal growth.
[0018] In a second aspect of the present application, a seed crystal carbonization bracket is provided, comprising:
[0019] at least two support studs;
[0020] At least two spacers are provided on the support stud and spaced apart axially along the support stud. The seed chip carbonization bracket can simultaneously hold multiple seed chips. During the carbonization step in the bonding process, multiple seed chips can be placed on the spacers for carbonization, which greatly saves time and improves carbonization efficiency.
[0021] In some embodiments of the present application, two studs are included and are symmetrically arranged about the center of the spacer, thereby helping to make the spacer bear uniform force in the horizontal direction.
[0022] In some embodiments of the present application, screw holes are provided on the outer periphery of the spacers, and the studs are passed through the screw holes, which helps to adjust the number of spacers according to different process requirements.
[0023] In some embodiments of the present application, the spacer has a recessed portion for placing the seed wafer, thereby helping to prevent the seed wafer from sliding off.
[0024] In some embodiments of the present application, the seed crystal carbonization bracket satisfies at least one of the following conditions:
[0025] The material of the spacer is graphite;
[0026] The support studs are made of graphite, which can ensure that the structure of the seed crystal carbonization bracket is maintained under high temperature conditions.
[0027] In the third aspect of the present application, the above-mentioned seed chip carbonization bracket can be used in the seed chip bonding process of the present application, thereby having all the features and advantages of the above-mentioned seed chip carbonization bracket, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 This is a flow chart of the seed wafer bonding process according to one embodiment of the present application.
[0029] Figure 2 This is a schematic diagram of the structure of a seed chip carbonization bracket according to an embodiment of the present application.
[0030] Figure 3 This is a schematic cross-sectional view of a seed chip carbonization bracket according to an embodiment of the present application.
[0031] Figure 4 This is a schematic diagram of the spacer structure of an embodiment of the present application.
[0032] Figure 5 This is a back view of the crystal after growth according to an embodiment of the present application.
[0033] Figure 6 This is a back view of the crystal after growth in a comparative example of the present application.
[0034] Reference numerals: 1, support stud 2, spacer 3, screw hole 4, seed chip DETAILED DESCRIPTION
[0035] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present application, but should not be understood as limiting the present application.
[0036] This application is based on the following findings and knowledge of the applicant:
[0037] As mentioned above, when the surface of the seed crystal is unevenly coated with glue, pores will be generated at the bonding point. The thermal conductivity of the pores is different from that of the colloid. The temperature of the pore area is higher than that of the surrounding adhesive area, which causes heat evaporation on the back of the seed crystal and escapes along the pores, resulting in reverse sublimation of the back of the crystal and hexagonal void defects in the chip. Usually, a dense carbon film is formed on the surface of the seed crystal as a protective layer to solve this problem to a certain extent. In related technologies, methane gas is introduced into the graphite cavity to form a dense carbon film on the surface of the seed crystal by deposition. However, this method is complicated to operate and requires more equipment.
[0038] The applicant has conducted in-depth exploration of the above issues, taking into account that the organic glue used in the bonding process of the seed chip can be cured under certain conditions to form a carbon film, and the operation is simple. It only needs to be evenly coated on the surface of the seed chip. The carbon film obtained by carbonizing the organic glue has excellent density. At the same time, there is no need to use additional raw materials, and the organic glue in the subsequent bonding process can be directly used, which can reduce costs to a certain extent.
[0039] In the first aspect of the present application, a seed wafer bonding process is proposed, referring to Figure 1 , including the following steps:
[0040] S10: forming an organic adhesive layer on the silicon surface of the seed wafer, and carbonizing the organic adhesive layer to form a carbon film, thereby obtaining a seed wafer containing the carbon film.
[0041] In this step, an organic glue is formed on the silicon surface of the seed wafer. The organic glue can be evenly coated on the surface of the seed wafer using a glue spinner, vacuum glue coating equipment, or manual scraping with a scraper. The thickness of the organic glue is not required here, and it is carbonized at high temperature under vacuum conditions to form a dense carbon film. The organic glue is composed of a high molecular polymer. Under vacuum and high temperature conditions, the high molecular polymer begins to decompose and the chemical bonds break. The carbon-containing groups gradually undergo a condensation reaction, and the carbon atoms connect and cross-link with each other, eventually forming a relatively stable carbon film. After a period of high temperature, the hardness of the carbon film increases and adheres to the surface of the seed wafer to form a carbon film with a certain hardness, wear resistance, and stable chemical properties.
[0042] In some embodiments of the present application, the vacuum degree of carbonization is ≤0.01mbar, specifically, it can be 0.01mbar, 0.008mbar, 0.006mbar, 0.004mbar, 0.002mbar, 0.001mbar, etc. The above vacuum range helps to carry out carbonization under stable conditions, and at the same time helps to avoid side reactions of organic glue during the carbonization process.
[0043] In some embodiments of the present application, the carbonization temperature is 700°C to 900°C, specifically, 700°C, 750°C, 800°C, 850°C, 900°C, etc. The carbonization temperature within the above range is conducive to the efficient and sufficient carbonization reaction, and can basically avoid the problems such as the slow carbonization reaction or even the failure to reach the temperature for the carbonization reaction due to too low a carbonization temperature, and the changes in the carbon film structure due to too high a carbonization temperature, thereby affecting the performance of the carbon film.
[0044] In some embodiments of the present application, the organic adhesive layer is at least one of a photoresist layer, an epoxy resin adhesive layer, and a phenolic resin adhesive layer. The photoresist contains ingredients such as photosensitive resin, which can effectively increase the degree of cross-linking of organic matter. Under certain conditions, the carbon film layer formed by carbonization has good density. At the same time, the photoresist, epoxy resin adhesive, and phenolic resin adhesive have a certain ability to buffer thermal stress, so the carbon film formed by carbonization can serve as a buffer layer to alleviate the thermal stress generated by temperature changes. As a result, the above-mentioned organic adhesive layer helps to form a carbon film with good density and buffering effect on the surface of the seed chip.
[0045] S20: Graphite paper is bonded to the surface of the carbon film away from the seed wafer to obtain a mixed seed wafer.
[0046] In this step, a photoresist layer is coated on the surface of the carbon film away from the seed chip and the surface of one side of the graphite paper, the two surfaces coated with the photoresist are bonded, and heat treated at 180°C to 230°C for 30min to 90min to obtain a mixed seed chip. Specifically, the heat treatment temperature is 180°C to 230°C, and specifically, it can be 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, etc. The above temperature range helps the photoresist to fully spread and penetrate on the surface of the seed chip and the surface of the graphite paper, further improving the bonding effect, and basically avoiding the problems of excessive thermal decomposition of the photoresist due to too high temperature to produce volatile substances, resulting in local uneven bonding, and poor bonding effect due to too low temperature; the heat treatment time can be 30min to 90min, and specifically, it can be 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc. The above bonding time helps the seed chip and the graphite paper to be firmly bonded, thereby improving the quality of crystal growth, and basically avoiding the waste of time cost caused by too long heat treatment time, and the problem of weak bonding due to too short heat treatment time, affecting crystal growth.
[0047] Specifically, both the seed chip and the crucible cover have different degrees of warping. If the seed chip is directly brought into contact with the crucible cover, problems such as loose bonding, uneven glue, and bubbles may easily occur. Therefore, a flexible buffer layer, namely graphite paper, is added between the seed chip and the crucible cover. This can not only level the warping of the seed chip and the crucible cover, but also buffer the difference in thermal expansion between the seed chip and the crucible cover, thereby further improving the bonding quality.
[0048] In some embodiments of the present application, the photoresist in this step and the photoresist in the organic glue in step S10 are the same photoresist. Using the same glue can, on the one hand, ensure good compatibility between different interfaces. Using the same glue layer in different steps of seed chip bonding can, to a certain extent, avoid the problems of delamination and cracking caused by using glue layers of different properties between different interfaces; on the other hand, it can reduce the risk of impurities being introduced. Using a single glue layer can avoid cross-contamination between different glue layers, which is helpful to the growth of crystals to a certain extent.
[0049] S30: bonding the surface of the graphite paper away from the seed wafer to the crucible cover.
[0050] In this step, a resin glue layer is respectively coated on the surface of the graphite paper away from the seed chip and the surface of the crucible cover, the two surfaces coated with the resin glue are bonded, and heat treated at 400°C to 600°C for 30min to 90min. Specifically, the heat treatment temperature can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, etc. The above heat treatment temperature helps to make the graphite paper and the crucible cover tightly bonded, and can basically avoid the influence of volatile substances produced by excessive pyrolysis of the resin glue due to too high a heat treatment temperature on the bonding effect, and the problem of weak bonding due to too low a heat treatment temperature, which affects the subsequent crystal growth quality. The heat treatment time can be 30min to 90min. The above bonding time helps to make the graphite paper and the crucible cover firmly bonded, thereby improving the crystal growth quality, and can basically avoid the waste of time cost due to too long a heat treatment time, and the problem of weak bonding due to too short a heat treatment time, which affects crystal growth.
[0051] In the second aspect of the present application, a seed chip carbonization bracket is proposed, referring to Figure 2 The carbonization bracket comprises at least two support studs 1 and at least two spacers 2, each of which is disposed on the support studs and spaced axially along the support studs. The carbonization bracket for seed chips has a multi-layer structure and can accommodate multiple seed chips simultaneously. During the carbonization step in the bonding process, multiple seed chips can be placed on the spacers for carbonization, significantly saving time and improving carbonization efficiency.
[0052] Specifically, refer to Figure 3The spacer 2 carries the seed chip 4, and each spacer carries a seed chip, which can prevent the surface of the seed chip coated with organic glue from being affected by the small molecular compounds produced by the volatilization of the organic glue when heated, which affects the upper target seed chip.
[0053] In some embodiments of the present application, the seed chip carbonization bracket includes two studs, which are symmetrically arranged about the center of the spacer. From a mechanical perspective, the symmetrical arrangement of the two support studs can provide support for the spacer from two symmetrical directions, so that the spacer is evenly stressed in the horizontal direction, avoiding uneven stress that may cause the seed chip carbonization bracket to tilt. From a practical perspective, the provision of two studs facilitates the direct placement of the seed chip into the spacer, avoiding the problem of having to remove the studs before placing the seed chip when multiple studs are used to place the seed chip.
[0054] In some embodiments of the present application, reference is made to Figure 4 The outer periphery of the spacer is provided with a screw hole 3, and the stud is passed through the screw hole. According to different process requirements, such as the number of seed chips, carbonization reaction space requirements, etc., the number of spacers can be increased or decreased at will, which helps to improve the flexibility of the seed chip carbonization bracket.
[0055] In some embodiments of the present application, the spacer has a recessed portion for placing the seed wafer. The recessed portion is designed on the spacer to prevent the seed wafer on the spacer from sliding off when the seed wafer carbonization bracket is tilted.
[0056] In some embodiments of the present application, the spacers and support studs in the seed chip carbonization bracket are made of graphite. Graphite has an extremely high melting point, which ensures that the material does not melt or soften during the carbonization process, maintaining the stability of the seed chip carbonization bracket structure and ensuring normal carbonization of the seed chip.
[0057] In the third aspect of the present application, the above-mentioned seed chip carbonization bracket can be used in the seed chip bonding process of the present application, thereby having all the features and advantages of the above-mentioned seed chip carbonization bracket, which will not be repeated here.
[0058] The present application is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present application in any way. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or in the product instructions shall be followed.
[0059] Example 1
[0060] The seed wafer bonding method of the present application is used to coat, bond, and grow 4H-silicon carbide seed wafers, specifically as follows:
[0061] 1. Use a scraper to apply photoresist on one side of the 4H-SiC seed wafer. Visually check that it is evenly coated. Place the 4H-SiC seed wafer coated with photoresist on a seed wafer carbonization bracket and place it in a tube furnace. Carbonize it at a vacuum degree of 0.0017 mbar and a temperature of 800°C to obtain a 4H-SiC seed wafer containing a carbon film.
[0062] 2. Use a scraper to apply photoresist on the surface of the carbon film and one side of the graphite paper. Lay the two surfaces coated with photoresist together, place them in a hot pressing heat treatment furnace, and heat treat them at 220°C for 60 minutes to obtain a mixed seed wafer.
[0063] 3. Use a scraper to apply epoxy resin glue on one surface of the graphite paper on the mixed seed wafer and the crucible cover, and then put the two surfaces coated with epoxy resin glue into a hot press heat treatment furnace and heat treat at 500°C for 60 minutes.
[0064] 4. Grow the bonded seed crystals using the physical vapor transport method for 160 hours. After growth, take a photo of the back of the crystals with a camera. Figure 5 .
[0065] Comparative Example 1
[0066] The 4H-SiC seed wafers were glued, bonded and grown using the seed wafer bonding method in the related art, as follows:
[0067] 1. Use a scraper to apply photoresist on one surface of the seed wafer and one surface of the graphite paper, fit the two surfaces coated with photoresist together, place them in a hot pressing heat treatment furnace, and heat treat them at 220°C for 60 minutes to obtain a mixed seed wafer.
[0068] 2. Use a scraper to apply epoxy resin glue on one surface of the graphite paper on the mixed seed wafer and the crucible cover, and then put the two surfaces coated with epoxy resin glue into a heat treatment furnace and heat treat at 500°C for 60 minutes.
[0069] 3. Grow the bonded seed crystals using the physical vapor transport method for 160 hours. After growth, take a photo of the back of the crystals with a camera. Figure 6 .
[0070] from Figure 5 and Figure 6 It can be seen that compared with Comparative Example 1, the back of the crystal obtained in Example 1 is smooth and has no back penetration phenomenon, indicating that the silicon carbide crystal prepared according to this study is of good quality and has a good bonding layer density. Therefore, the use of the seed wafer bonding process of this application is conducive to improving crystal quality.
[0071] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.
[0072] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.
[0073] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.
Claims
1. A seed wafer bonding process, characterized in that: include: forming an organic glue layer on the silicon surface of the seed wafer, and carbonizing the organic glue layer to form a carbon film, thereby obtaining a seed wafer containing the carbon film; bonding graphite paper to the surface of the carbon film away from the seed wafer to obtain a mixed seed wafer; The surface of the graphite paper away from the seed wafer is bonded to the crucible cover.
2. The seed wafer bonding process according to claim 1, wherein: Meet at least one of the following conditions: The vacuum degree of the carbonization is ≤0.01mbar; The carbonization temperature is 700°C to 900°C; The organic adhesive layer includes at least one of a photoresist layer, an epoxy resin adhesive layer, and a phenolic resin adhesive layer.
3. The seed wafer bonding process according to claim 1, wherein: Bonding graphite paper on the surface of the carbon film away from the seed wafer comprises: A photoresist layer is formed on the surface of the carbon film away from the seed wafer and the surface of one side of the graphite paper, and heat-treated at 180° C. to 230° C. for 30 min to 90 min.
4. The seed wafer bonding process according to claim 1, wherein: Bonding the surface of the graphite paper away from the seed wafer to the crucible cover comprises: A resin adhesive layer is formed on the surface of the graphite paper away from the seed wafer and the surface of the crucible cover, and heat treatment is performed at 400° C. to 600° C. for 30 minutes to 90 minutes.
5. A seed crystal carbonization bracket, characterized in that: include: at least two support studs; At least two spacers are provided on the support stud and spaced apart along the axial direction of the support stud.
6. The seed crystal carbonization bracket according to claim 5, characterized in that: The two studs are symmetrically arranged about the center of the spacer.
7. The seed crystal carbonization bracket according to claim 5, characterized in that: A screw hole is provided on the outer periphery of the spacer, and the stud is passed through the screw hole.
8. The seed crystal carbonization bracket according to claim 5, characterized in that: The spacer has a recessed portion for placing the seed wafer.
9. The seed crystal carbonization bracket according to claim 5, characterized in that: Meet at least one of the following conditions: The material of the spacer is graphite; The support stud is made of graphite.
10. Use of the seed chip carbonization bracket according to any one of claims 5 to 9 in a seed chip bonding process.