Preparation method and application of high-orientation, low-dielectric coating on silicon carbide surface

Abstract

The present invention provides a method for preparing a highly oriented, low-dielectric coating on a silicon carbide surface and its application. The coating forms a highly oriented MFI-type molecular sieve structure on the silicon carbide surface. The coating is prepared using a secondary growth method. Because the coating and substrate are connected via intermolecular hydrogen bonds, unlike traditional coatings that rely on van der Waals forces, the coating exhibits superior adhesion and resists detachment even in high-temperature environments. Furthermore, dodecylguanidine monohydrochloride is used as a twinning inhibitor, making the coated seed layer less susceptible to twinning during subsequent growth. This improves the orientation and compactness of the MFI-type molecular sieve coating and increases its service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor materials, and in particular relates to a preparation method and application of a high-orientation, low-dielectric coating on the surface of silicon carbide. Background Art

[0002] As a wide bandgap semiconductor material, SiC is widely used in power electronics and high-temperature devices due to its excellent properties such as high thermal conductivity, high temperature resistance and corrosion resistance. However, in high-frequency or high-voltage scenarios, it is particularly necessary to prepare a low-dielectric, high-orientation coating on the SiC surface.

[0003] Low dielectric properties can effectively reduce parasitic capacitance, minimize signal delays in high-frequency applications, and improve device efficiency and speed. They also enhance insulation performance, reduce surface leakage current and breakdown risks, and ensure stability in high-voltage environments. For example, MFI zeolite molecular sieves offer advantages such as high-temperature resistance, acid and alkali resistance, a low dielectric index, and stable physical and chemical properties, making them suitable for coating SiC surfaces.

[0004] Highly oriented coatings further optimize these advantages. Their ordered crystal structure improves coating uniformity, density, and adhesion, reduces interfacial defects and stress concentration, and thus enhances compatibility with the SiC substrate. Furthermore, highly oriented coatings offer enhanced resistance to oxidation and external contamination, protecting the surface and extending device life. Regarding thermal management, the highly oriented structure helps optimize heat conduction paths while maintaining low dielectric properties, preventing localized overheating.

[0005] Therefore, the preparation of low-dielectric, highly oriented coatings is of great significance for promoting the application of SiC in high-performance electronic devices (such as power devices and high-frequency circuits), and can significantly improve their electrical, thermal and mechanical properties.

[0006] Techniques for depositing breakdown-resistant protective coatings on SiC surfaces typically include chemical vapor deposition (CVD), physical vapor deposition (PVD), or spin-on polymer coating. For example, CVD is commonly used to deposit low-dielectric materials such as SiO2 or Si3N4, a mature process with good uniformity. PVD is suitable for preparing thin, dense coatings, while spin-on polymer coating is gaining attention due to its simplicity and low cost.

[0007] For example, patent application CN118894727A discloses a composite material and a method for preparing the same. The composite material comprises sintered silicon carbide and a silicon carbide coating attached to the surface of the sintered silicon carbide; the silicon carbide coating comprises a second coating and a first coating between the second coating and the sintered silicon carbide. The method for preparing the composite material comprises: (1) performing a first deposition on the surface of the sintered silicon carbide by a CVD method to obtain a preform comprising the first coating; (2) performing a second deposition on the surface of the first coating by a CVD method to obtain a precursor comprising the second coating; and (3) heat-treating the precursor to obtain a composite material. The composite material has high electrical resistance and low carrier mobility, and can effectively prevent the generation of high electric fields and avoid sparking of components.

[0008] However, CVD and PVD processes often require high temperatures, potentially affecting the performance of the SiC substrate. Furthermore, the equipment is expensive and the deposition rate is slow. While spin-coating polymers is easy to implement, they suffer from poor thermal stability and adhesion, and are prone to failure at high temperatures. Furthermore, stress mismatch at the interface between the coating and the SiC can lead to delamination, and uneven thickness control can also weaken the insulation effect. Summary of the Invention

[0009] In order to solve the above-mentioned technical problems existing in the prior art, the present invention provides a preparation method and application of a highly oriented, low dielectric coating on the surface of silicon carbide, which generates a layer of coating with a highly oriented MFI type molecular sieve structure on the surface of silicon carbide, and can solve the problems of poor thermal stability and adhesion of the coating.

[0010] The present invention provides a method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface, comprising the following steps:

[0011] (1) The MFI type molecular sieve seed crystals are prepared by hydrothermal synthesis, and the raw materials include silicon source, alkali source and water;

[0012] (2) depositing the MFI type molecular sieve seed crystals on the surface of the silicon carbide wafer to form a seed layer;

[0013] (3) The raw materials are silicon source, alkali source and water, and dodecylguanidine monohydrochloride (CAS: 13590-97-1) is added and mixed evenly to obtain a coating synthesis liquid, wherein the molar ratio of dodecylguanidine monohydrochloride to silicon source is 0.1-0.5:1;

[0014] (4) The silicon carbide wafer containing the seed layer obtained in step (2) is placed in the coating synthesis liquid obtained in step (3) to perform a hydrothermal synthesis reaction to obtain a high-orientation, low-dielectric coating on the silicon carbide surface.

[0015] Preferably, in step (1), the silicon source is tetraethyl orthosilicate (TEOS), and the alkali source is tetrapropylammonium hydroxide (TPAOH).

[0016] Preferably, in step (1), the molar ratio of the silicon source, the alkali source and the water is 1:0.25-0.35:165; in step (3), the molar ratio of the silicon source, the alkali source and the water is 1:0.15-0.35:180-300; the proportion of the alkali source in the silicon source, the alkali source and the water in step (3) is lower than the proportion of the alkali source in the silicon source, the alkali source and the water in step (1), and it is only necessary to allow the gaps in the middle of the seed crystals to grow full so that the crystals are connected to avoid the formation of a large number of twins on the coating surface.

[0017] More preferably, in step (1), the molar ratio of the silicon source, the alkali source and water is 1:0.32:165.

[0018] Preferably, in step (1), the temperature of hydrothermal crystallization in the hydrothermal synthesis method is 175°C.

[0019] Preferably, in step (3), the silicon source, the alkali source, and water are first mixed uniformly, and then dodecylguanidine monohydrochloride is added and mixed uniformly to obtain a coating synthesis solution. The silicon source, the alkali source, and water are mixed to perform a hydrolysis reaction of the silicon source, and then the dodecylguanidine monohydrochloride is added to effectively prevent the hydrolysis of the silicon source from being affected.

[0020] Preferably, in step (3), the molar ratio of dodecylguanidine monohydrochloride to the silicon source is 0.3:1.

[0021] Preferably, in step (2), MFI type molecular sieve seed crystals are coated on the surface of the silicon carbide wafer coated with a binder, and then the binder is removed to deposit the MFI type molecular sieve seed crystals on the surface of the silicon carbide wafer.

[0022] Further preferably, in step (2), a polymer tape is first bonded to the surface of the silicon carbide wafer, the MFI type molecular sieve seed crystals prepared in step (1) are ground and dispersed, the MFI type molecular sieve seed crystals are covered on the surface of the polymer tape, and then rubbed in a counterclockwise direction. Due to the hydrogen bonding between the polymer material and the MFI type molecular sieve seed crystals, the crystals self-assemble to form an MFI type molecular sieve seed crystal layer. The rubbed silicon carbide wafer is calcined, the polymer tape is removed, and the MFI type molecular sieve seed crystals are deposited on the surface of the silicon carbide wafer.

[0023] More preferably, the polymer tape is made of any one of PET (polyethylene terephthalate), BOPP (biaxially oriented polypropylene) and PVC (polyvinyl chloride).

[0024] The present invention also provides a composite material comprising silicon carbide and a high-orientation, low-dielectric coating on the surface of silicon carbide prepared by the above-mentioned method for preparing a high-orientation, low-dielectric coating on the surface of silicon carbide.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention adopts a secondary growth method to prepare the coating. Since the coating and the substrate are connected by intermolecular hydrogen bonds, which is different from the van der Waals forces between traditional coatings and substrates, the coating has good bonding strength and will not fall off in a high-temperature environment. In addition, dodecylguanidine monohydrochloride is used as a twinning inhibitor, so that the surface of the coated seed layer is not prone to twinning during the subsequent intergrowth process, thereby improving the orientation and density of the MFI molecular sieve coating and increasing its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is an atomic force microscope scan of the surface of the silicon carbide wafer in Example 1;

[0028] Figure 2 This is a scanning electron micrograph of the hydrothermal synthesis of the MFI type molecular sieve seed crystals prepared in Example 1;

[0029] Figure 3 This is a scanning electron microscope image of the oriented seed layer coated with the adhesive tape on the silicon carbide surface in Example 1;

[0030] Figure 4 This is a scanning electron microscope image of the oriented seed layer directly applied manually on the silicon carbide surface in Example 1;

[0031] Figure 5 is a scanning electron microscope image of the high-orientation, low dielectric index coating prepared on the silicon carbide surface in Example 1;

[0032] Figure 6 is a graph showing the change in dielectric index over time of the high-orientation, low-dielectric-index coating prepared on the silicon carbide surface in Example 1;

[0033] Figure 7 This is the highly oriented XRD pattern of the highly oriented, low dielectric index coating prepared on the silicon carbide surface in Example 1. Figure 7 * indicates the characteristic peak of silicon carbide substrate;

[0034] Figure 8 is a scanning electron microscope image of the coating finally obtained in Example 2;

[0035] Figure 9 This is a graph showing the change in dielectric index over time of the high-orientation, low-dielectric-index coating prepared on the silicon carbide surface in Example 2;

[0036] Figure 10 is a scanning electron microscope image of the coating finally obtained in Example 3;

[0037] Figure 11This is a graph showing the change in dielectric index over time of the high-orientation, low-dielectric-index coating prepared on the silicon carbide surface in Example 3;

[0038] Figure 12 This is a scanning electron microscope image of the anti-oxidation coating containing twins on the surface of silicon carbide prepared in Comparative Example 1;

[0039] Figure 13 is a scanning electron microscope image of the coating finally prepared in Comparative Example 2;

[0040] Figure 14 This is a scanning electron microscope image of the seed layer obtained after clockwise rubbing in Comparative Example 3;

[0041] Figure 15 is a scanning electron microscope image of the coating finally prepared in Comparative Example 4;

[0042] Figure 16 This is a scanning electron microscope image of the coating finally prepared in Comparative Example 5. DETAILED DESCRIPTION

[0043] Example 1

[0044] (1) Preparation of MFI type molecular sieve seed crystals

[0045] The size of the MFI molecular sieve seed coated on the silicon carbide surface can be 500 nm-1 μm. The surface of the silicon carbide wafer used is flat and smooth, and the roughness (Ra) is controlled within 5 nm. Figure 1 As shown. The preparation of MFI type molecular sieve seeds is mainly prepared by hydrothermal synthesis, and the experimental formula used is TPAOH: TEOS: H2O = 0.32: 1: 165 (molar ratio). The specific experimental method is as follows: First, add 6.1 g of 25wt% TPAOH aqueous solution to 65.1 g of deionized water, stir evenly, and then add 5.0 g of TEOS reagent dropwise (TEOS purity is 98%, the impurity is water, the same below). The mixed solution is continuously stirred at room temperature for 4 hours to complete the aging process. The solution obtained at this time is clear and transparent. The above solution is loaded into a high-pressure reactor, and the high-pressure reactor is placed in a rotary oven. The rotary oven speed is set to 30 rpm and the reaction is carried out at 175 ° C for 80 min. After the reaction is completed, the reactor is quenched, the powder at the bottom of the reactor is taken out, and centrifuged and washed until it is close to neutral. Finally, it is placed in a 60 ° C oven for drying. The prepared seeds are as shown Figure 2 shown.

[0046] (2) Coating of MFI-type oriented seed layer

[0047] First, adhere a PET (polyethylene terephthalate) transparent tape to the surface of the silicon carbide wafer, then take the MFI type molecular sieve seed crystals in step (1) and place them in a mortar for grinding. After they are completely dispersed, use a key to take the seed crystals and cover the surface of the tape. Then use a finger wearing a nitrile glove to manually rub in a counterclockwise direction. Due to the hydrogen bonding between the polymer material and the MFI type molecular sieve seed crystals, the crystals will self-assemble to form an MFI type molecular sieve seed crystal layer. The effect obtained after rubbing is shown in the figure. Figure 3 The samples were calcined in a tubular reactor, the polymer tape removed, and the oriented seeds deposited on the surface of the silicon carbide wafer. The calcination conditions were: oxygen flow rate 5-15 mL / min, furnace temperature 300°C, heating rate 0.5°C / min, and calcination time 5 h.

[0048] The seed layer obtained by directly rubbing the seed on the silicon carbide wafer is Figure 4 , it can be seen that there are obvious defects in the seed layer, which will cause the coating prepared later to be not dense enough and have holes, and will not play the role of low dielectric index.

[0049] (3) Preparation of coating synthetic liquid

[0050] An MFI zeolite coating was prepared by secondary growth using a formulation containing dodecylguanidine monohydrochloride (DGH) as a twinning inhibitor. The method was as follows: 1.3 g of a 25 wt% TPAOH aqueous solution was added to 32.9 g of ultrapure water and stirred continuously to form a homogeneous solution. 2.0 g of TEOS was then added dropwise to the solution. After stirring at room temperature for 3.5 hours, the resulting solution became clear and transparent. 0.76 g of DGH was then added, and stirring continued for 30 minutes to obtain the desired coating solution. The molar ratio of TPAOH, TEOS, DGH, and water was 0.17:1:0.3:200.

[0051] (4) Preparation of high-orientation, low-dielectric-index coatings

[0052] The silicon carbide wafer containing the seed layer obtained in step (2) is fixed vertically in a high-pressure reactor, and then the coating synthesis liquid obtained in step (3) is slowly added into the reactor along the inner wall. After sealing, it is placed in an oven at 150°C for 4 hours. After the synthesis is completed, the obtained silicon carbide wafer containing the coating is taken out, then washed with ultrapure water and dried in a clean room. The scanning electron microscope image of the prepared coating is shown as follows: Figure 5As shown in the figure, the coating has good compactness and a second layer. The second layer enhances the continuous flakes and makes the coating more oriented. An appropriate amount of the second layer helps to improve the dielectric strength of the coating, enabling it to withstand higher electric field strengths, thereby improving the reliability of electronic components. The local second layer can also promote the adhesion between the coating and the substrate, reducing the risk of coating shedding. Figure 6 The prepared coating showed a low dielectric index after testing, which was about 2.9 after stabilization. Figure 7 The orientation of the prepared coating is demonstrated, and the characteristic orientation peaks of the single crystal at (020), (040), (060), (080), and (0100) planes can be clearly seen, which fully confirms the high orientation of the coating prepared on the SiC surface.

[0053] Example 2

[0054] The difference from Example 1 is that in step (3), 1.15 g of a 25 wt% TPAOH aqueous solution is added to 30.5 g of ultrapure water and stirred continuously to form a uniform solution. Then, 2.0 g of TEOS is added dropwise to the above solution. After stirring at room temperature for 3.5 h, the resulting solution becomes clear and transparent. Then, 0.25 g of DGH reagent is added thereto and stirring is continued for 30 min to prepare the desired coating synthesis solution. Here, the molar ratio of TPAOH, TEOS, DGH and water is 0.15:1:0.1:180. The morphology of the obtained coating is as follows: Figure 8 As shown in the figure, when the molar ratio of DGH to TEOS is 0.1:1, the obtained coating is still dense and highly oriented, and also has the characteristics of low dielectric index, such as Figure 9 As shown, the dielectric index is around 3.1. Unlike Example 1, the coating not only has a second layer but also a small amount of a third layer. The interfaces between the layers may have defects, such as pores and cracks, which may affect the overall performance of the coating. In addition, the difference in thermal expansion coefficient between different layers may lead to the generation of interfacial stress, which in turn affects the stability and life of the coating.

[0055] Example 3

[0056] The difference from Example 1 is that in step (3), 2.7 g of a 25 wt% TPAOH aqueous solution is added to 50.8 g of ultrapure water and stirred continuously to form a uniform solution. Then, 2.0 g of TEOS is added dropwise to the above solution. After stirring at room temperature for 3.5 h, the resulting solution becomes clear and transparent. Then, 1.26 g of DGH reagent is added thereto and stirring is continued for 30 min to prepare the desired coating synthesis solution. Here, the molar ratio of TPAOH, TEOS, DGH and water is 0.35:1:0.5:300. From Figure 10 It can be seen that when the molar ratio of DGH to TEOS is 0.5:1, the coating has good orientation and exhibits the characteristics of low dielectric index, such as Figure 11 As shown in the figure, the dielectric index is about 3.0 after stabilization. However, the obtained coating is only a dense single layer, and there is basically no second layer or third layer.

[0057] Comparative Example 1

[0058] Different from Example 1, in step (3), DGH is not added.

[0059] Figure 12 The coating prepared on the surface of a silicon carbide wafer using a formula that does not contain DGH reagent is shown. It can be seen that there are many twins on the surface of the coating. Twins will cause irregularities in the morphology and lattice arrangement of the crystals, which will have a certain impact on the density of the coating. This also fully demonstrates the twinning inhibition effect of the DGH reagent.

[0060] Comparative Example 2

[0061] The difference from Example 1 is that in step (3), polyhexamethylene biguanide hydrochloride (PHMB) is added as a twinning inhibitor instead. The specific method is as follows: 1.3 g of a 25 wt% TPAOH aqueous solution is added to 32.9 g of ultrapure water and stirred continuously to form a uniform solution, and then 2.0 g of TEOS is added dropwise to the above solution. After stirring at room temperature for 3.5 h, the synthetic solution becomes clear and transparent. Then 0.64 g of PHMB reagent (average molecular weight of 1700) is added thereto, and stirring is continued for 30 min to prepare the required coating synthetic solution. Here, the molar ratio of TPAOH, TEOS, PHMB and water is 0.17:1:0.008:200. As Figure 13 As shown, the effect of using other guanidine polymers on the surface of silicon carbide wafers is not good, and there are obvious holes on the coating surface.

[0062] Comparative Example 3

[0063] The difference from Example 1 is that in step (2), the seed layer is manually rubbed in a clockwise direction with fingers wearing nitrile gloves. The SEM image of the seed layer obtained after rubbing is as follows: Figure 14 As shown, the seed layer cannot form a single layer distribution, and excess seeds will appear on the surface of the wafer, resulting in poor coating orientation.

[0064] Comparative Example 4

[0065] The difference from Example 1 is that 0.13 g of DGH reagent was added. The morphology of the coating obtained is as follows Figure 15As shown in the figure, further reducing the DGH content to a DGH:TEOS (molar ratio) of 0.05:1 results in the coating remaining dense, but twins appear on the surface. The presence of twins in the coating leads to surface unevenness and poor crystal orientation. Poor coating orientation means irregular arrangement of the coating molecules or crystals, which can reduce the coating's functionality and reliability.

[0066] Comparative Example 5

[0067] The difference from Example 1 is that 2.01 g of DGH reagent was added to make the DGH:TEOS (molar ratio) = 0.8:1. The morphology of the coating obtained is as follows Figure 16 As shown, it can be seen that the density of the coating is relatively poor. When the DGH content is too high, the inhibitory effect of DGH is too strong, resulting in a significant decrease in the growth rate of the coating. This situation makes it impossible for the coating to form a dense structure in a short period of time, affecting the density of the coating. The poor density of the coating not only leads to an uneven surface, but may also cause defects such as pores and cracks, which will directly affect the effect of the coating. More importantly, the low dielectric index characteristics of the coating are difficult to be effectively exerted. Low dielectric index materials are commonly used in electronic devices to reduce signal transmission losses or improve insulation. If the coating is not dense enough, the presence of pores or cracks will cause the dielectric constant to increase, resulting in a decrease in its performance in practical applications. Therefore, in the process of preparing the coating, the amount of DGH added must be precisely controlled to avoid excessive addition to ensure that the coating can maintain its ideal structure and function and exert its expected low dielectric index effect.

Claims

1. A method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface, characterized in that: The following steps are involved: (1) The MFI type molecular sieve seed crystals are prepared by hydrothermal synthesis, and the raw materials include silicon source, alkali source and water; (2) depositing the MFI type molecular sieve seed crystals on the surface of the silicon carbide wafer to form a seed layer; (3) The raw materials are silicon source, alkali source and water, and dodecylguanidine monohydrochloride is added and mixed evenly to obtain a coating synthesis liquid, wherein the molar ratio of dodecylguanidine monohydrochloride to silicon source is 0.1-0.5:1; (4) placing the silicon carbide wafer containing the seed layer obtained in step (2) into the coating synthesis solution obtained in step (3) to perform a hydrothermal synthesis reaction to obtain a high-orientation, low-dielectric coating on the surface of the silicon carbide; In step (2), a polymer tape is first bonded to the surface of the silicon carbide wafer, the MFI type molecular sieve seed crystals prepared in step (1) are ground and dispersed, the MFI type molecular sieve seed crystals are covered on the surface of the polymer tape, and then rubbed in a counterclockwise direction, the rubbed silicon carbide wafer is calcined, and the polymer tape is removed, so that the MFI type molecular sieve seed crystals are deposited on the surface of the silicon carbide wafer.

2. The method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface according to claim 1, characterized in that: In step (1) and step (3), the silicon source is ethyl orthosilicate, and the alkali source is tetrapropylammonium hydroxide.

3. The method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface according to claim 1, characterized in that: In step (1), the molar ratio of the silicon source, the alkali source and the water is 1:0.25-0.35:165; in step (3), the molar ratio of the silicon source, the alkali source and the water is 1:0.15-0.35:180-300; the proportion of the alkali source in the silicon source, the alkali source and the water in step (3) is lower than the proportion of the alkali source in the silicon source, the alkali source and the water in step (1).

4. The method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface according to claim 3, characterized in that: In step (1), the molar ratio of the silicon source, the alkali source and water is 1:0.32:

165.

5. The method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface according to claim 1, characterized in that: In step (1), the temperature of hydrothermal crystallization in the hydrothermal synthesis method is 175°C.

6. The method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface according to claim 1, characterized in that: In step (3), the silicon source, the alkali source and water are first mixed evenly, and then dodecylguanidine monohydrochloride is added and mixed evenly to obtain a coating synthesis solution.

7. The method for preparing a high-orientation, low-dielectric coating on a silicon carbide surface according to claim 1, wherein: In step (3), the molar ratio of dodecylguanidine monohydrochloride to the silicon source is 0.3:

1.

8. A composite material, characterized in that The invention comprises silicon carbide, and a high-orientation, low-dielectric coating on the surface of silicon carbide is prepared on the surface of silicon carbide by using the method for preparing a high-orientation, low-dielectric coating on the surface of silicon carbide according to any one of claims 1 to 7.

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