Method for manufacturing a silicon nitride ceramic substrate and silicon nitride substrate

Abstract

This invention discloses a method for preparing a silicon nitride ceramic substrate and the silicon nitride substrate itself, belonging to the field of advanced ceramic preparation. The method involves non-equilibrium three-stage gas pressure sintering of α-Si3N4, Yb2O3, MgO, LaB6, and α-Si3N4 seed crystals to prepare the silicon nitride ceramic substrate. The mass ratio of α-Si3N4:Yb2O3:MgO:LaB6:α-Si3N4 seed crystals is 85~94:3~6:1~4:1~4:1~3. This invention addresses the industry challenge of balancing high thermal conductivity with high strength and high density with low roughness in the preparation of high-performance silicon nitride substrates.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramics preparation, and in particular to a method for preparing a silicon nitride ceramic substrate and the silicon nitride substrate. Background Technology

[0002] Silicon nitride (Si3N4) ceramics are widely recognized as ideal packaging substrate materials for next-generation high-power-density electronic devices and high-end radio frequency modules due to their excellent high-temperature strength, thermal shock resistance, high resistivity and potential high thermal conductivity. However, silicon nitride is a strong covalent compound with low sintering driving force, making densification extremely difficult. It is necessary to rely on sintering aids to form a liquid phase to promote mass transport.

[0003] Existing technologies typically use rare earth or alkaline earth metal oxides such as MgO, Y2O3, and Al2O3 as sintering aids. While these aids promote densification, they also leave a large amount of low thermal conductivity glass phase at the grain boundaries, which severely scatters phonons and becomes the main bottleneck limiting the improvement of the material's thermal conductivity. To obtain high thermal conductivity, traditional processes usually require extremely high sintering temperatures (>1800℃) and long holding times. This not only leads to huge energy consumption and serious equipment wear, but also easily causes the decomposition of Si3N4 and abnormal grain growth, resulting in increased substrate surface roughness, which is not conducive to the subsequent fabrication of fine lines using processes such as laser direct writing, photolithography, and thin film deposition.

[0004] In addition, the traditional gas pressure sintering (GPS) process is usually carried out under a single, constant nitrogen pressure, which is not precise enough to control the microstructure evolution of complex multiphase systems (such as grain morphology, phase composition, and grain boundary phase regulation), making it difficult to achieve a synergistic improvement in high thermal conductivity, high strength, and low surface roughness at the same time.

[0005] Therefore, developing a sintering method that can achieve densification at relatively low temperatures and obtain silicon nitride ceramic substrates with high thermal conductivity, high strength, and low surface roughness through refined process control has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned deficiencies, the present invention provides a method for preparing a silicon nitride ceramic substrate and a silicon nitride substrate, which aims to improve at least one of the problems mentioned in the background art.

[0007] The technical solution is: a method for preparing a silicon nitride ceramic substrate, wherein the silicon nitride ceramic substrate is prepared by non-equilibrium three-stage gas pressure sintering of α-Si3N4, Yb2O3, MgO, LaB6 and α-Si3N4 seed crystals, and the mass ratio of α-Si3N4:Yb2O3:MgO:LaB6:α-Si3N4 seed crystals is 85~94:3~6:1~4:1~4:1~3.

[0008] Furthermore, the method includes the following steps: S1, α-Si3N4, Yb2O3, MgO, LaB6 and α-Si3N4 seed crystals are mixed to form a slurry, which is then cast, dried and debinded to form a silicon nitride preform; S2, the raw preform is sintered and cooled under non-equilibrium three-stage gas pressure to form a silicon nitride substrate, including the following steps: S21, under nitrogen pressure of 0.5MPa~1.0 MPa, is heated to 1400℃~1500℃ at a rate of 3℃ / min~8℃ / min and held at that temperature for 30 minutes~90 minutes; S22, heat to 1650℃~1750℃ at a rate of 5℃ / min~10℃ / min, and then increase the nitrogen pressure to 3 MPa~5 MPa within 7 minutes~15 minutes; S23, raise the nitrogen pressure to 8 MPa to 12 MPa within 3 to 6 minutes, and maintain it at 1650℃ to 1750℃ and 8 MPa to 12 MPa for 10 to 30 minutes; S24 was cooled to room temperature in the furnace.

[0009] Furthermore, S1 includes the following steps: S11, α-Si3N4 powder, Yb2O3, MgO, LaB6, and α-Si3N4 seed powder are mixed to form a mixed powder; S12, the mixed powder, solvent and dispersant are put into a ball mill jar and ball milled to obtain a uniformly distributed premixed slurry; S13, add binder and plasticizer to the premixed slurry, and continue ball milling to obtain the final slurry; S14, after vacuum degassing the final slurry, it is cast using a casting machine to obtain a green belt; S15, after the green blank is punched, it is debonded in air at 450℃~550℃ for 1 to 3 hours to obtain silicon nitride green blank.

[0010] Furthermore, the solvent is a mixture of anhydrous ethanol and toluene, with a volume ratio of ethanol to toluene of 1:1.

[0011] Furthermore, the dispersant is fish oil, and the amount used is 1.5% of the total mass of the mixed powder.

[0012] Furthermore, the binder is polyvinyl butyral, and the amount of polyvinyl butyral used is 5% of the total mass of the mixed powder.

[0013] Further, in S3, the plasticizer is dibutyl phthalate, and the amount of dibutyl phthalate used is 40% of the mass of polyvinyl butyral.

[0014] Furthermore, in S12, the ball milling time is 20 to 30 hours; in S13, the ball milling time is 10 to 15 hours; in S14, the casting is carried out with the scraper height of the casting machine set to 0.5 mm.

[0015] The present invention also provides a silicon nitride substrate.

[0016] The technical solution is: a silicon nitride substrate, which is prepared by the above method, and the silicon nitride substrate has a thermal conductivity ≥95 W / (m·K), a three-point bending strength ≥880 MPa, and a surface roughness Ra≤0.05μm.

[0017] The inventive principle of this invention: This invention employs a composite system of Yb₂O₃ and MgO. Yb 3+ Ionic radius and Si 4+ N 3- It exhibits good matching and can more effectively promote the nucleation and growth of β-Si3N4 grains; this invention introduces LaB 6（ Lanthanum boride (LB6) is a breakthrough. During sintering, LaB6 reacts with trace amounts of oxygen in the furnace and SiO2 on the surface of the raw materials to generate La2O3 and BN in situ. La2O3 forms a multi-element, low-eutectic-point liquid phase with Yb2O3, MgO, and SiO2 on the surface of the raw materials, significantly reducing the liquid phase emergence temperature and thus achieving low-temperature densification (sintering temperature can be reduced to 1650℃~1750℃). The generated BN, as a high-melting-point, high-thermal-conductivity grain boundary "pinning" phase, can effectively inhibit the excessive growth of Si3N4 grains in the later sintering stage, thereby obtaining a fine and uniform microstructure, significantly improving the mechanical strength of the substrate and reducing surface roughness. This invention adds a small amount of α-Si3N4 seeds, which act as heterogeneous nucleation points, guiding β-Si3N4 grains to grow in a "self-complementary" manner to form a highly oriented interlocking structure. This not only enhances the strength but also provides a smooth path for phonons (the main carriers of heat conduction), which helps to improve thermal conductivity.

[0018] This invention abandons traditional dry pressing and instead uses tape casting technology to prepare green bodies. This method is particularly suitable for producing large-area, thin (typically 0.1mm~1.0mm), and highly flat ceramic substrates. By optimizing the slurry formulation (including solvents, dispersants, binders, and plasticizers), a slurry with good stability and leveling properties is obtained, ensuring excellent microscopic uniformity and extremely low warpage in the green body and its subsequent sintered form.

[0019] This invention designs a dynamic gas pressure sintering curve, which achieves precise control of nitrogen pressure in stages to finely regulate densification, phase transformation, and grain boundary engineering processes. The first stage (low-temperature debinding and pre-sintering) aims to safely and slowly remove the large amount of organic binder introduced by tape casting, and to allow the composite additives to fully form a uniform liquid phase, initially achieving particle rearrangement and densification. The second stage (medium-temperature main densification) involves raising the temperature to the target sintering temperature (1650℃~1750℃) and rapidly increasing the nitrogen pressure to 3MPa~5MPa. The higher pressure effectively inhibits the high-temperature decomposition of Si3N4 and accelerates the filling of the liquid phase between particles, driving rapid densification of the green body. The third stage (high-temperature performance optimization and grain boundary engineering) involves dynamically adjusting the pressure to 8MPa~12MPa at the highest temperature. A high-pressure pulse, operating at MPa for only a short duration (10-30 minutes), strongly drives the α→β phase transformation and promotes the transformation of the glassy phase at grain boundaries into a more heat-resistant and thermally conductive crystalline phase (such as Yb₂Si₂O₇N₂, yttrium silicate). Simultaneously, the high pressure further compresses lattice defects, thereby maximizing thermal conductivity without causing grain coarsening.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs an innovative multiphase composite sintering aid system, including a Yb₂O₃-MgO main aid, a key innovative aid LaB₆, and α-Si₃N₄ seed crystals. Through the in-situ reaction of LaB₆ during sintering, La₂O₃ and BN are generated. The former, in conjunction with other oxides, forms a low-temperature liquid phase to promote densification, while the latter acts as a grain boundary pinning phase to inhibit excessive grain growth. Combined with a unique non-equilibrium three-stage gas pressure sintering process, this invention successfully prepares silicon nitride ceramic substrates with ultra-high thermal conductivity (≥95 W / (m·K)), ultra-high mechanical strength (≥900 MPa), and extremely low surface roughness (Ra≤0.05μm) at relatively low temperatures (1650℃~1750℃).

[0021] This invention employs a casting process to prepare green blanks, which is suitable for the industrial production of large-area, thin, and high-flatness substrates. It solves the industry problem of the mutual constraints between high thermal conductivity and high strength, and high density and low roughness in the preparation of high-performance silicon nitride substrates.

[0022] This invention relates to low-temperature, high-efficiency sintering: through a multi-component liquid-phase system formed by composite additives such as LaB6, the sintering temperature is reduced by 50℃~100℃, significantly saving energy, reducing production costs, and extending equipment life.

[0023] The present invention provides a superior synergistic performance improvement: the prepared silicon nitride substrate has both ultra-high thermal conductivity (≥95 W / (m·K)) and ultra-high mechanical strength (≥900 MPa), and its performance matching is better than that of existing reports.

[0024] This invention offers superior surface quality and geometric properties: the pinning effect of BN and the short-time high-voltage process effectively suppress abnormal grain growth, resulting in a nanoscale smooth surface (Ra≤0.05μm). Combined with tape casting technology, the substrate exhibits high flatness and low warpage, making it suitable for direct application in precision circuit processes such as laser direct writing and thin-film deposition.

[0025] The process of this invention is highly controllable and suitable for industrialization: the combination of "casting + unbalanced gas pressure sintering process" enables fine control over the uniformity of the blank and the microstructure of the sintering, with good repeatability, and is particularly suitable for the industrial continuous production of large-area, thin, high-performance silicon nitride substrates. Attached Figure Description

[0026] Figure 1 This is a microscopic morphology diagram of the product in Embodiment 1 of the present invention; Figure 2 This is a microscopic morphology diagram of the product in Comparative Example 2 of the present invention. Detailed Implementation

[0027] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0028] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0029] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1~5” is disclosed, the described range should be interpreted as including ranges “1~4”, “1~3”, “1~2”, “1~2 and 4~5”, “1~3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0032] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0033] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0034] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0035] Example 1 A method for preparing a silicon nitride substrate includes the following steps: S1, Preparing a silicon nitride preform, including the following steps: S11, α-Si3N4 powder, Yb2O3, MgO, LaB6, and α-Si3N4 seed powder are mixed to form a mixed powder, wherein the mass ratio of α-Si3N4 powder:Yb2O3:MgO:LaB6:α-Si3N4 seed is 92:4:2:2:2.

[0036] S12, the mixed powder, anhydrous ethanol / toluene mixed solvent (ethanol / toluene volume ratio 1:1, the amount of mixed solvent is appropriate) and dispersant (the dispersant is fish oil, the amount is 1.5% of the total mass of the mixed powder) are put into a ball mill jar, and zirconia balls are used as grinding balls. The mixture is ball milled for 24 hours to obtain a uniformly distributed premixed slurry.

[0037] S13. Add a binder (polyvinyl butyral, abbreviated as PVB, at a dosage of 5% of the total mass of the mixed powder) and a plasticizer (dibutyl phthalate, abbreviated as DBP, at a dosage of 40% of the mass of PVB) to the premixed slurry, and continue ball milling for 12 hours to ensure that the organic matter is completely dissolved and mixed evenly to obtain the final slurry.

[0038] S14. After vacuum degassing the final slurry, it is cast using a casting machine with the scraper height set to 0.5mm to obtain a green belt.

[0039] S15, after the green blank is punched, it is debonded in air at 500°C for 2 hours to obtain the raw blank.

[0040] S2, the raw preform is sintered and cooled under non-equilibrium three-stage gas pressure to form a silicon nitride substrate, including the following steps: S21 was heated to 1450℃ at a nitrogen pressure of 0.8 MPa at a rate of 5.5℃ / min and held at that temperature for 60 minutes.

[0041] S22 is heated to 1700℃ at a rate of 7.5℃ / min, and then the nitrogen pressure is increased to 4 MPa within 10 minutes.

[0042] S23, the nitrogen pressure is increased to 10 MPa within 5 minutes and maintained at 1700℃ and 10 MPa for 20 minutes.

[0043] S24 was cooled to room temperature in the furnace.

[0044] The microstructure of the silicon nitride substrate prepared in this embodiment is as follows: Figure 1 .

[0045] The silicon nitride substrate prepared in this embodiment was subjected to performance testing, and the results are shown in Table 1.

[0046] Example 2 The difference from Example 1 is as follows: In S11, the mass ratio of α-Si3N4 powder:Yb2O3:MgO:LaB6:α-Si3N4 seed crystals is 91:4:2:3:2.

[0047] S22 is: heat to 1680℃ at a rate of 7.5℃ / min, and then increase the nitrogen pressure to 4MPa within 10 minutes.

[0048] S23 is: to increase the nitrogen pressure to 10 MPa within 5 minutes and maintain it at 1680℃ and 10 MPa for 20 minutes.

[0049] The silicon nitride substrate prepared in this embodiment was subjected to performance testing, and the results are shown in Table 1.

[0050] Example 3 The difference from Example 1 is as follows: S21 is: under a nitrogen pressure of 1.0 MPa, the temperature is increased to 1450℃ at a rate of 5.5℃ / min and held for 60 minutes.

[0051] S22 is: heat to 1720℃ at a rate of 7.5℃ / min, and then increase the nitrogen pressure to 5MPa within 10 minutes.

[0052] S23 is: to increase the nitrogen pressure to 12 MPa within 5 minutes and maintain it at 1720℃ and 12 MPa for 15 minutes.

[0053] The silicon nitride substrate prepared in this embodiment was subjected to performance testing, and the results are shown in Table 1.

[0054] Example 4 The difference from Example 1 is as follows: In this embodiment, the mass ratio of α-Si3N4 powder:Yb2O3:MgO:LaB6:α-Si3N4 seed crystals in S11 is 85:3:1:1:1.

[0055] Example 5 The difference from Example 1 is as follows: In this embodiment, the mass ratio of α-Si3N4 powder:Yb2O3:MgO:LaB6:α-Si3N4 seed crystals in S11 is 94:6:4:4:3.

[0056] Comparative Example 1 The difference from Example 1 is as follows: S11 is: mixing α-Si3N4 powder, Yb2O3 and MgO powder to form a mixed powder, wherein the mass ratio of α-Si3N4 powder:Yb2O3:MgO is 94:4:2.

[0057] The silicon nitride substrate prepared in this comparative example was subjected to performance testing, and the results are shown in Table 1.

[0058] Comparative Example 2 The difference from Example 1 is as follows: S2 involves the following steps: The raw blank is sintered under constant pressure and cooled to form a silicon nitride substrate. S21 was heated to 1700℃ at a nitrogen pressure of 2 MPa at a rate of 5.5℃ / min and held at that temperature for 120 minutes.

[0059] S22 was cooled to room temperature in the furnace.

[0060] The microstructure of the silicon nitride substrate prepared in this comparative example is as follows: Figure 2 .

[0061] The silicon nitride substrate prepared in this comparative example was subjected to performance testing, and the results are shown in Table 1.

[0062] Comparative Example 3 The difference from Example 1 is as follows: S11 is: mixing α-Si3N4 powder, Yb2O3 and MgO powder to form a mixed powder, wherein the mass ratio of α-Si3N4 powder:Yb2O3:MgO is 94:4:2.

[0063] S2 involves the following steps: The raw blank is sintered under constant pressure and cooled to form a silicon nitride substrate. S21 was heated to 1850℃ at a nitrogen pressure of 2 MPa at a rate of 5.5℃ / min and held at that temperature for 120 minutes.

[0064] S22 was cooled to room temperature in the furnace.

[0065] The silicon nitride substrate prepared in this comparative example was subjected to performance testing, and the results are shown in Table 1.

[0066] Table 1 Performance Test Results Table 1 shows that Examples 1-5 all exhibit excellent comprehensive performance, verifying the effectiveness of the "LaB6 additive + seed crystal + three-stage gas pressure sintering" combination of the present invention. Comparative Example 1 (without LaB6 and seed crystal) shows a significant decrease in densification and various properties, demonstrating the key role of LaB6 in forming a low-temperature liquid phase and introducing the BN pinned phase, as well as the contribution of the seed crystal to the formation of the interlocking structure. Comparative Example 2 (using conventional constant pressure sintering) has a higher density, but its thermal conductivity and strength are not as good as the examples, demonstrating the unique advantages of the "non-equilibrium three-stage gas pressure sintering process" in promoting phase transformation, purifying grain boundaries, and improving thermal conductivity. Comparative Example 3 (conventional high-temperature process) has acceptable thermal conductivity, but its strength is not high and its surface roughness is extremely large, and its energy consumption is high, highlighting the ingenuity of the present invention in achieving a balance between high performance and high surface quality at low temperatures.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon nitride ceramic substrate, characterized in that, This method involves non-equilibrium three-stage gas pressure sintering of α-Si3N4, Yb2O3, MgO, LaB6 and α-Si3N4 seed crystals to produce silicon nitride ceramic substrates. The mass ratio of α-Si3N4:Yb2O3:MgO:LaB6:α-Si3N4 seed crystals is 85~94:3~6:1~4:1~4:1~3.

2. The method for preparing a silicon nitride ceramic substrate according to claim 1, characterized in that, The method includes the following steps: S1, α-Si3N4, Yb2O3, MgO, LaB6 and α-Si3N4 seed crystals are mixed to form a slurry, which is then cast, dried and debinded to form a silicon nitride preform; S2, the raw blank is sintered and cooled under non-equilibrium three-stage gas pressure to form a silicon nitride substrate, including the following steps: S21, under nitrogen pressure of 0.5MPa~1.0 MPa, is heated to 1400℃~1500℃ at a rate of 3℃ / min~8℃ / min and held at that temperature for 30 minutes~90 minutes; S22, heat to 1650℃~1750℃ at a rate of 5℃ / min~10℃ / min, and then increase the nitrogen pressure to 3 MPa~5 MPa within 7 minutes~15 minutes; S23, raise the nitrogen pressure to 8 MPa to 12 MPa within 3 to 6 minutes, and maintain it at 1650℃ to 1750℃ and 8 MPa to 12 MPa for 10 to 30 minutes; S24 was cooled to room temperature in the furnace.

3. The method for preparing a silicon nitride ceramic substrate according to claim 2, characterized in that, S1 includes the following steps: S11, α-Si3N4 powder, Yb2O3, MgO, LaB6, and α-Si3N4 seed powder are mixed to form a mixed powder; S12, the mixed powder, solvent and dispersant are put into a ball mill jar and ball milled to obtain a uniformly distributed premixed slurry; S13, add binder and plasticizer to the premixed slurry, and continue ball milling to obtain the final slurry; S14, after vacuum degassing the final slurry, it is cast using a casting machine to obtain a green belt; S15, after the green blank is punched, it is debonded in air at 450℃~550℃ for 1 to 3 hours to obtain silicon nitride green blank.

4. The method for preparing a silicon nitride ceramic substrate according to claim 3, characterized in that, The solvent is a mixture of anhydrous ethanol and toluene, with a volume ratio of ethanol to toluene of 1:

1.

5. The method for preparing a silicon nitride ceramic substrate according to claim 3, characterized in that, The dispersant is fish oil, and the amount used is 1.5% of the total mass of the mixed powder.

6. The method for preparing a silicon nitride ceramic substrate according to claim 3, characterized in that, The binder is polyvinyl butyral, and the amount of polyvinyl butyral used is 5% of the total mass of the mixed powder.

7. The method for preparing a silicon nitride ceramic substrate according to claim 6, characterized in that, In S3, the plasticizer is dibutyl phthalate, and the amount of dibutyl phthalate used is 40% of the mass of polyvinyl butyral.

8. The method for preparing a silicon nitride ceramic substrate according to claim 3, characterized in that, In S12, the ball milling time is 20 to 30 hours; in S13, the ball milling time is 10 to 15 hours; in S14, the casting process is carried out with the scraper height of the casting machine set to 0.5 mm.

9. A silicon nitride substrate, characterized in that, The silicon nitride substrate is prepared by the method described in any one of claims 1-8, and the silicon nitride substrate has a thermal conductivity ≥95 W / (m·K), a three-point bending strength ≥880 MPa, and a surface roughness Ra≤0.05μm.

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