Silicon carbide seed crystal bonding composition and bonding method

Abstract

The invention discloses a silicon carbide seed crystal bonding composition and a bonding method, and the silicon carbide seed crystal bonding composition comprises the following components in percentage by mass: 25-35% of resin, 30-40% of an ionic liquid getter and the balance of a solvent, wherein the ionic liquid getter is 1-hexyl-3-methylimidazolium glycine and / or 1-butyl-3-methylimidazolium hexafluorophosphate, and the ionic liquid getter is an ionic liquid getter. The imidazolium ionic liquid getter is added into the formula of the silicon carbide seed crystal bonding composition, so that gas generated in the high-temperature curing process of the bonding composition can be captured by the imidazolium ionic liquid getter through a hydrogen bond network; and a conjugated pi electron system of the imidazole ring can generate dipole-quadrupole moment interaction with gas molecules with quadrupole moment, so that the adsorption capacity is enhanced, and the problems that an organic adhesive in the prior art generates bubbles in a high-temperature curing process, the uniformity and stability of an adhesive layer are influenced, and then the subsequent growth of silicon carbide crystals is influenced are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide seed crystal adhesives, and in particular to a silicon carbide seed crystal adhesive composition and an adhesive method. Background Art

[0002] Among semiconductor materials, third-generation semiconductors, represented by silicon carbide (SiC), have higher breakdown electric fields (10 times that of silicon), higher saturated electron drift velocities (twice that of silicon), and higher thermal conductivity (three times that of silicon) compared to first- and second-generation semiconductors. They also exhibit excellent stability in high-temperature and corrosive environments. Power electronic devices grown homoepitaxially on SiC single crystal substrates are seeing increasing application in areas such as electric vehicles and 5G communications.

[0003] The SiC substrate preparation process primarily includes the production of high-purity SiC raw materials, crystal growth, crystal processing, wafer processing, cleaning, and testing. Crystal growth typically utilizes a high-temperature sublimation method, also known as physical vapor transport (PVT). This involves bonding a SiC seed crystal to the top of a graphite plate. High-purity SiC raw material is placed beneath the plate, and then heated to a high temperature to sublime it. The sublimated material then condenses onto the SiC seed crystal to form a single crystal.

[0004] In the prior art, organic glue (914B glue) is commonly used to bond seed crystals to graphite plates. The organic solvent in the glue or the gases produced by the high-temperature reaction are volatilized by high-temperature heating, and then the glue is carbonized at an even higher temperature to achieve the purpose of bonding and fixation. However, because the active ingredients in the organic glue formula include small molecule amines, which have a low boiling point and are highly volatile, the glue has poor storage stability, seriously affecting its bonding effect and the thickness uniformity of the bonding layer. Furthermore, this bonding method generates bubbles during the high-temperature curing process, resulting in poor uniformity and stability of the bonding layer, which in turn affects the quality of subsequent silicon carbide crystal growth.

[0005] In order to improve the uniformity and stability of the adhesive during the thermal curing process, reduce the voids formed by gas aggregation, and thereby improve the stability of seed crystal bonding and the subsequent growth quality of silicon carbide crystals, it is of great significance to research and develop a stable adhesive without bubble generation during the curing process. Summary of the Invention

[0006] In response to the deficiencies in the prior art, the present invention provides a silicon carbide seed crystal bonding composition and a bonding method, wherein an imidazole ionic liquid getter is added. Gas generated during the high-temperature curing process of the bonding composition can be captured by the imidazole ionic liquid getter through a hydrogen bond network, and the conjugated π electron system of the imidazole ring can undergo dipole-quadrupole interaction with gas molecules having a quadrupole moment, thereby enhancing the adsorption capacity. This solves the problem in the prior art that organic adhesives generate bubbles during high-temperature curing, affecting the uniformity and stability of the bonding layer, and thus affecting the subsequent growth of silicon carbide crystals.

[0007] In order to solve the above technical problems, the first aspect of the present invention provides a silicon carbide seed crystal bonding composition, which comprises the following components by mass percentage: 25%-35% resin, 30%-40% ionic liquid getter, and the rest solvent;

[0008] Wherein, the ionic liquid getter is 1-hexyl-3-methylimidazolium glycine and / or 1-butyl-3-methylimidazolium hexafluorophosphate.

[0009] The present invention adds an ionic liquid getter to the adhesive composition, and the gas generated during the high-temperature curing process of the adhesive composition is captured by the ionic liquid getter through a hydrogen bond network. 1-hexyl-3-methylimidazolium glycine and 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid getters are used, and the conjugated π electron system of the imidazole ring can interact with gas molecules with quadrupole moments to generate a dipole-quadrupole moment, thereby enhancing adsorption capacity. At the same time, the viscosity of the ionic liquid decreases with increasing temperature, and the fluidity of the ionic liquid increases at high temperatures. Stress accumulation is reduced through interfacial interaction, stress release is assisted, and the thermal expansion coefficient of the bonding point is reduced, thereby ensuring good thickness uniformity of the bonding layer and improving the quality of subsequent crystal growth.

[0010] Furthermore, the resin is a cresol novolac resin. The active ingredients in the composition have a high boiling point, which makes the storage stability of the entire composition good.

[0011] Furthermore, the solvent is one or more of acetone, methanol, and isopropanol.

[0012] A second aspect of the present invention provides a method for bonding a silicon carbide seed crystal, using the silicon carbide seed crystal bonding composition described in the first aspect, comprising the following steps:

[0013] S1, coating the silicon carbide seed crystal bonding composition on the upper surface of the graphite plate, the upper and lower surfaces of the graphite paper, and the bottom surface of the seed crystal;

[0014] S2. The graphite plate coated with the silicon carbide seed crystal bonding composition, the graphite paper and the seed crystal are stacked in order from bottom to top, and then subjected to a desolvation treatment, a hot pressing treatment and a carbonization treatment.

[0015] The silicon carbide seed crystal bonding method of the present invention adopts the bonding composition described in the first aspect, avoiding problems such as bubbles generated by high-temperature curing, and improving the uniformity and stability of the bonding layer; at the same time, a layer of graphite paper is added between the seed crystal and the graphite plate as a buffer layer to further avoid gaps between the seed crystal and the graphite plate.

[0016] Furthermore, in S1, the coating method is spin coating, and the spin coating is performed in two stages, and the spin coating speed in the first stage is lower than the spin coating speed in the second stage.

[0017] Furthermore, the first stage of spin coating has a rotation speed of 300-600 r / min and a duration of 10-20 s, and the second stage of spin coating has a rotation speed of 1500-5000 r / min and a duration of 15-30 s. The two-stage spin coating improves the uniformity of the adhesive layer.

[0018] Furthermore, in S2, the desolvation treatment is performed at a temperature of 50-100°C and for a time of 20-60 seconds.

[0019] Furthermore, in S2, the heat pressing treatment is carried out in two stages, and the heat pressing temperature of the first stage is lower than the heat pressing temperature of the second stage.

[0020] Furthermore, the first stage of hot pressing is performed at a temperature of 80-150°C, with a briquette weight of 500-1000kg, and a duration of 30-60 minutes; the second stage of hot pressing is performed at a temperature of 300-400°C, with a briquette weight of 500-1000kg, and a duration of 30-60 minutes. The two-stage hot pressing further improves the uniformity and stability of the adhesive layer.

[0021] Furthermore, in S2, the temperature of the carbonization treatment is 500-900°C, and the time is 0.5-3h.

[0022] Beneficial effects of the present invention:

[0023] The present invention adds 1-hexyl-3-methylimidazolium glycine and 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid getters to the adhesive composition. Gas generated during the high-temperature curing process is captured by the ionic liquid getter through a hydrogen bond network. The conjugated π electron system of the imidazole ring can generate a dipole-quadrupole interaction with gas molecules having a quadrupole moment, thereby enhancing adsorption capacity.

[0024] The viscosity of the ionic liquid of the present invention decreases with increasing temperature. At high temperatures, the fluidity of the ionic liquid increases, which reduces stress accumulation through interfacial interaction, assists in stress release, reduces the thermal expansion coefficient of the bonding point, ensures good thickness uniformity of the bonding layer, and thus improves the quality of subsequent crystal growth.

[0025] The bonding method of the present invention adds a layer of graphite paper as a buffer layer between the seed crystal and the graphite plate to avoid a gap between the seed crystal and the graphite plate; at the same time, the bonding quality is further improved through two-stage spin coating and hot pressing treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 This is a surface picture of the adhesive layer obtained in Example 1 of the present invention;

[0028] Figure 2 This is a surface image of the adhesive layer obtained in Example 2 of the present invention;

[0029] Figure 3 This is a surface image of the adhesive layer obtained in Example 3 of the present invention;

[0030] Figure 4 This is a surface picture of the adhesive layer obtained in Comparative Example 1 of the present invention;

[0031] Figure 5 This is a surface picture of the adhesive layer obtained in Comparative Example 2 of the present invention;

[0032] Figure 6 This is a surface picture of the adhesive layer obtained in Comparative Example 3 of the present invention;

[0033] Figure 7 This is a surface picture of the adhesive layer obtained in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0034] The following will provide a clear and complete description of the technical solutions of the present invention in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] This embodiment relates to a silicon carbide seed crystal bonding composition comprising the following components, by mass percentage: 25%-35% resin, 30%-40% ionic liquid getter, and the remainder solvent; wherein the ionic liquid getter is 1-hexyl-3-methylimidazolyl glycine and / or 1-butyl-3-methylimidazolyl hexafluorophosphate. In this embodiment, 1-hexyl-3-methylimidazolyl glycine and 1-butyl-3-methylimidazolyl hexafluorophosphate ionic liquid getters are added to the bonding composition. Gases generated during the high-temperature curing process of the bonding composition are captured by the ionic liquid getter through a hydrogen bond network. Simultaneously, the conjugated π-electron system of the imidazole ring can interact with gas molecules with quadrupole moments through dipole-quadrupole interactions, enhancing adsorption capacity.

[0036] The viscosity of the ionic liquid in this embodiment decreases with increasing temperature. The fluidity of the ionic liquid increases at high temperatures, which reduces stress accumulation through interfacial interaction, assists in stress release, reduces the thermal expansion coefficient at the bonding point, ensures good thickness uniformity of the bonding layer, and thus improves the quality of subsequent crystal growth.

[0037] As a preferred embodiment, the resin is cresol novolac resin, and the active ingredients in the composition have a high boiling point, so that the storage stability of the entire composition is good. The solvent is one or more of acetone, methanol, and isopropyl alcohol.

[0038] Another embodiment relates to a method for bonding a silicon carbide seed crystal, using the silicon carbide seed crystal bonding composition described in the above embodiment, comprising the following steps:

[0039] S1, coating the silicon carbide seed crystal bonding composition on the upper surface of the graphite plate, the upper and lower surfaces of the graphite paper, and the bottom surface of the seed crystal;

[0040] S2. The graphite plate, graphite paper, and seed crystal coated with the silicon carbide seed crystal bonding composition are stacked in order from bottom to top, followed by a desolvation treatment, a heat pressing treatment, and a carbonization treatment. The silicon carbide seed crystal bonding method of this embodiment uses the bonding composition described in the above embodiment, avoiding problems such as bubbles generated by high-temperature curing and improving the uniformity and stability of the bonding layer. At the same time, a layer of graphite paper is added between the seed crystal and the graphite plate as a buffer layer to further avoid gaps between the seed crystal and the graphite plate.

[0041] As a preferred embodiment, in S1, the coating method is spin coating, which is performed in two stages, with the first stage's spin coating speed being lower than the second stage's spin coating speed. The first stage's spin coating speed is 300-600 r / min for 10-20 seconds, while the second stage's spin coating speed is 1500-5000 r / min for 15-30 seconds. This two-stage spin coating improves the uniformity of the adhesive layer.

[0042] As a preferred embodiment, in S2, the temperature of the desolventizing treatment is 50-100°C and the time is 20-60s. The hot pressing treatment is carried out in two stages, and the hot pressing temperature of the first stage is lower than the hot pressing temperature of the second stage; the hot pressing temperature of the first stage is 80-150°C, the weight of the briquette is 500-1000kg, and the time is 30-60min; the hot pressing temperature of the second stage is 300-400°C, the weight of the briquette is 500-1000kg, and the time is 30-60min. Through two stages of hot pressing, the uniformity and stability of the adhesive layer are further improved. The temperature of the carbonization treatment is 500-900°C and the time is 0.5-3h.

[0043] Example 1

[0044] This embodiment relates to a method for bonding a silicon carbide seed crystal, comprising the following steps:

[0045] (1) Spin-coating the silicon carbide seed crystal bonding composition on the upper surface of the graphite plate, the upper and lower surfaces of the graphite paper, and the bottom surface of the seed crystal;

[0046] The adhesive composition comprises, by mass percentage, 35% of 1-hexyl-3-methylimidazolyl glycine ionic liquid, 25% of cresol novolac resin, and 40% of methanol; the first stage of spin coating is performed at a rotation speed of 350 rpm for 15 seconds; the second stage is performed at a rotation speed of 1500 rpm for 15 seconds;

[0047] (2) stacking the graphite plate coated with the silicon carbide seed crystal bonding composition, the graphite paper, and the seed crystal in order from bottom to top, followed by a desolvation treatment, a hot pressing treatment, and a carbonization treatment;

[0048] Among them, the desolventizing temperature is 80℃, the time is 50s; the first hot pressing temperature is 150℃, the briquette weight is 900kg, and the holding time is 35min; the second hot pressing temperature is 300℃; the briquette weight is 1000kg, and the holding time is 60min; the carbonization temperature is 600℃, and the time is 2.5h.

[0049] Example 2

[0050] The difference between this embodiment and embodiment 1 is that the ionic liquid getter is replaced with 1-butyl-3-methylimidazolium hexafluorophosphate, and the other steps and parameters remain unchanged, specifically:

[0051] (1) Spin-coating the silicon carbide seed crystal bonding composition on the upper surface of the graphite plate, the upper and lower surfaces of the graphite paper, and the bottom surface of the seed crystal;

[0052] The adhesive composition comprises, by mass percentage, 35% 1-butyl-3-methylimidazolium hexafluorophosphate, 25% cresol novolac resin, and 40% methanol; the first stage of spin coating is performed at a rotation speed of 350 rpm for 15 seconds; the second stage is performed at a rotation speed of 1500 rpm for 15 seconds;

[0053] (2) stacking the graphite plate coated with the silicon carbide seed crystal bonding composition, the graphite paper, and the seed crystal in order from bottom to top, followed by a desolvation treatment, a hot pressing treatment, and a carbonization treatment;

[0054] Among them, the desolventizing temperature is 80℃, the time is 50s; the first hot pressing temperature is 150℃, the briquette weight is 900kg, and the holding time is 35min; the second hot pressing temperature is 300℃; the briquette weight is 1000kg, and the holding time is 60min; the carbonization temperature is 600℃, and the time is 2.5h.

[0055] Example 3

[0056] The difference between this embodiment and embodiment 1 is that the ionic liquid getter includes 15% of 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid and 20% of 1-hexyl-3-methylimidazolium glycine ionic liquid, and the other steps and parameters remain unchanged, specifically:

[0057] (1) Spin-coating the silicon carbide seed crystal bonding composition on the upper surface of the graphite plate, the upper and lower surfaces of the graphite paper, and the bottom surface of the seed crystal;

[0058] The adhesive composition comprises, by mass percentage, 15% 1-butyl-3-methylimidazolium hexafluorophosphate, 20% 1-hexyl-3-methylimidazolium glycine, 25% cresol novolac resin, and 40% methanol; the first stage of spin coating is at a rotation speed of 350 rpm for 15 seconds; the second stage is at a rotation speed of 1500 rpm for 15 seconds;

[0059] (2) stacking the graphite plate coated with the silicon carbide seed crystal bonding composition, the graphite paper, and the seed crystal in order from bottom to top, followed by a desolvation treatment, a hot pressing treatment, and a carbonization treatment;

[0060] Among them, the desolventizing temperature is 80℃, the time is 50s; the first hot pressing temperature is 150℃, the briquette weight is 900kg, and the holding time is 35min; the second hot pressing temperature is 300℃; the briquette weight is 1000kg, and the holding time is 60min; the carbonization temperature is 600℃, and the time is 2.5h.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that no ionic liquid getter is added, the mass percentage of methanol is adjusted to 75%, and other steps and parameters remain unchanged.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Example 1 is that the ionic liquid getter is replaced by inorganic powdered calcium sulfate, and the mass percentage of methanol is adjusted to 75%, while other steps and parameters remain unchanged.

[0065] Comparative Example 3

[0066] The difference between this comparative example and Example 1 is that the bonding composition includes 10% 1-hexyl-3-methylimidazolyl glycine ionic liquid, 50% cresol novolac resin and 40% methanol, and other steps and parameters remain unchanged.

[0067] Comparative Example 4

[0068] The difference between this comparative example and Example 1 is that the bonding composition includes 50% of 1-hexyl-3-methylimidazolyl glycine ionic liquid, 10% of cresol novolac resin and 40% of methanol, and other steps and parameters remain unchanged.

[0069] Comparative Example 5

[0070] 914B glue was used as the adhesive composition and its stability was compared with that of the adhesive composition of Example 1.

[0071] The adhesive compositions of Examples 1-3 and Comparative Examples 1-5 were stored for 6 months, and the viscosity before and after storage was tested to evaluate the stability of the adhesive compositions. The stability test results of the adhesive compositions of Examples 1-3 and Comparative Examples 1-5, the spin coating effects of the adhesive compositions of Examples 1-3 and Comparative Examples 1-4, and the state of the adhesive layers after carbonization are shown in Table 1. In addition, the pictures of the adhesive layers after carbonization of Examples 1-3 and Comparative Examples 1-4 are shown in Table 1. Figure 1-7 shown.

[0072] Table 1

[0073]

[0074] As shown in Table 1, the stability of the organic glue of the adhesive composition of Comparative Example 5 is poor, and the viscosity increases significantly after storage for 6 months. The formulations of Examples 1-3 and Comparative Examples 1-4 have better stability than Comparative Example 5, and the viscosity does not change much after storage for 6 months.

[0075] From Table 1 and Figure 1-7 It can be seen that the spin coating effect of Examples 1-3 is uniform, and the surface of the bonding layer is smooth after carbonization. Figure 1-3No defects; Comparative Example 2 uses a powder getter with poor dispersibility, resulting in uneven spots during spin coating, uneven coating, and obvious defects after carbonization, reference Figure 5 Comparative Example 1 does not add a getter, the adhesive composition generates bubbles during the curing process that cannot be discharged or absorbed, resulting in obvious defects in the adhesive layer, reference Figure 4 Comparative Examples 3-4 use too little or too much ionic liquid getter. When too little, the gas generated during the curing process cannot be completely absorbed. When too much, the corresponding resin ratio is relatively reduced, the bonding effect deteriorates, and obvious defects appear in the bonding layer. Figure 6-7 .

[0076] In summary, the present invention adds 1-hexyl-3-methylimidazolium glycine and 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid getters to the adhesive composition. The gas generated during the high-temperature curing process is captured by the ionic liquid getter through the hydrogen bond network, and the conjugated π electron system of the imidazole ring can undergo dipole-quadrupole interaction with gas molecules with quadrupole moment, thereby enhancing the adsorption capacity; the viscosity of the ionic liquid decreases with increasing temperature, and the fluidity of the ionic liquid increases at high temperature. The stress accumulation is reduced through interfacial interaction, which assists in releasing stress and reduces the thermal expansion coefficient at the bonding point, ensuring good thickness uniformity of the bonding layer, thereby improving the quality of subsequent crystal growth; the effective ingredients in the composition have a high boiling point, so that the storage stability of the entire composition is good; the bonding method adds a layer of graphite paper between the seed crystal and the graphite plate as a buffer layer to avoid gaps between the seed crystal and the graphite plate; at the same time, the bonding quality is further improved through two-stage spin coating and hot pressing treatment.

[0077] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A silicon carbide seed crystal bonding composition, characterized in that: Calculated by mass percentage, it includes the following components: 25%-35% resin, 30%-40% ionic liquid getter, and the rest is solvent; Wherein, the ionic liquid getter is 1-hexyl-3-methylimidazolium glycine and / or 1-butyl-3-methylimidazolium hexafluorophosphate.

2. The silicon carbide seed crystal bonding composition according to claim 1, wherein The resin is cresol novolac resin.

3. The silicon carbide seed crystal bonding composition according to claim 1, wherein The solvent is one or more of acetone, methanol and isopropanol.

4. A method for bonding silicon carbide seed crystals, characterized in that: The silicon carbide seed crystal bonding composition according to any one of claims 1 to 3 is used, comprising the following steps: S1, coating the silicon carbide seed crystal bonding composition on the upper surface of the graphite plate, the upper and lower surfaces of the graphite paper, and the bottom surface of the seed crystal; S2. The graphite plate coated with the silicon carbide seed crystal bonding composition, the graphite paper and the seed crystal are stacked in order from bottom to top, and then subjected to a desolvation treatment, a hot pressing treatment and a carbonization treatment.

5. The method for bonding silicon carbide seed crystals according to claim 4, wherein: In S1, the coating method is spin coating, and the spin coating is performed in two stages. The spin coating speed in the first stage is lower than the spin coating speed in the second stage.

6. The method for bonding silicon carbide seed crystals according to claim 5, wherein: The spin coating speed of the first stage is 300-600 r / min, and the time is 10-20 s; the spin coating speed of the second stage is 1500-5000 r / min, and the time is 15-30 s.

7. The method for bonding silicon carbide seed crystals according to claim 4, wherein: In S2, the desolvation treatment is carried out at a temperature of 50-100°C and for a time of 20-60 seconds.

8. The method for bonding silicon carbide seed crystals according to claim 4, wherein: In S2, the heat pressing treatment is carried out in two stages, and the heat pressing temperature in the first stage is lower than the heat pressing temperature in the second stage.

9. The method for bonding a silicon carbide seed crystal according to claim 8, wherein: The hot pressing temperature of the first stage is 80-150°C, the briquetting weight is 500-1000kg, and the time is 30-60min; the hot pressing temperature of the second stage is 300-400°C, the briquetting weight is 500-1000kg, and the time is 30-60min.

10. The method for bonding silicon carbide seed crystals according to claim 4, wherein: In S2, the temperature of the carbonization treatment is 500-900°C and the time is 0.5-3h.

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