A rapid preparation method of reaction sintered silicon nitride substrate

Abstract

The application discloses a kind of reaction sintering silicon nitride substrate fast preparation methods, it is related to substrate preparation technical field.Processes include: S1: pulping;S2: flow casting;S3: powder laying;S4: glue removal;S5: oscillation nitriding;S6: sintering;The oscillation nitriding of the application adopts first stage, second stage, third stage, the temperature, pressure, airflow of three stages are synergized oscillation cycle, and the cycle number is 1 time.The application is synergized oscillation by temperature, pressure, airflow, and in the first stage high pressure low airflow promotes nitriding start, in the third stage low pressure high airflow inhibits dissolved silicon, simultaneously using one-time temperature cycle Shorten total nitriding time to 2.5-5h, effectively avoid dissolved silicon defects.

Description

Technical Field

[0001] This invention relates to the field of substrate preparation technology, specifically a rapid preparation method for reaction-sintered silicon nitride substrates. Background Technology

[0002] Insulated gate bipolar transistors (IGBTs) are core semiconductor power devices for energy conversion and transmission. They are key products in emerging industries and are widely used in rail transit, smart grids, ultra-high voltage power transmission, and new energy electric vehicles.

[0003] Silicon nitride (Si3N4) ceramic substrates possess superior overall performance and are supporting materials for IGBTs in the third-generation semiconductor industry. Their preparation technology has long been monopolized by companies such as Toshiba, Denka, Maruwa, JFC, and Hitachi Metals.

[0004] There are three main categories of methods for preparing silicon nitride ceramic wafers: gas pressure sintering, hot pressing sintering, and reaction sintering. Among these, reaction sintering uses silicon powder as the main material. After casting and binding, the silicon powder is reacted with nitrogen at 1200-1400℃ in a sintering furnace, followed by sintering at 1700-1900℃ to form silicon nitride ceramic wafers. This is currently the most advanced technology in silicon nitride ceramic wafer processing. However, during the nitriding process of the silicon powder green body at 1200-1400℃, the high temperature often results in intense exothermic reactions causing silicon melting, while the lower temperature and shorter time lead to incomplete nitriding, affecting sintering. The excessively long nitriding time significantly increases the production cost of reaction-sintered silicon nitride ceramic wafers.

[0005] In summary, to address the aforementioned problems, this invention proposes a rapid preparation method for reaction-sintered silicon nitride substrates. Summary of the Invention

[0006] The purpose of this invention is to provide a rapid preparation method for reaction-sintered silicon nitride substrates to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A rapid preparation method for reaction-sintered silicon nitride substrates includes the following steps: S1: The sintering aid, silicon powder, PVB binder, dispersant, plasticizer and solvent are mixed and ball-milled, and then vacuum degassed to obtain a slurry; S2: The slurry is coated onto the film strip, dried, and then cut to form a cast film green body; S3: Apply BN slurry to the surface of the cast green body by spraying powder to obtain a powder-coated green body; S4: Stack the powdered green blanks and place them in a debinding furnace to remove the glue, thus obtaining the debinded blanks; S5: Place the debonded blank in a gas pressure sintering furnace for oscillating nitriding to obtain a pre-nitrided blank; S6: The pre-nitrided blank is placed into a gas pressure sintering furnace for sintering. After sintering, the temperature and pressure are naturally reduced, and then the surface is treated and cleaned to obtain a silicon nitride substrate.

[0008] Furthermore, in S5, the process conditions for the oscillating nitriding are as follows: First stage: Temperature 1150-1170℃, pressure 1-2MPa, gas flow rate 10-15L / min; Second stage: Temperature 1250-1300℃, pressure 0.5-1MPa, gas flow rate 20-30L / min; Third stage: Temperature 1350-1420℃, pressure 0.1-0.5MPa, gas flow rate 30-40L / min; First, heat to the first stage at a rate of 2.5-5℃ / min, hold for 0.5-1h, and then depressurize for 10-20min. Then, heat from the first stage to the second stage at a rate of 2.5-5℃ / min, hold for 0.5-1h, and then depressurize for 10-20min. Next, heat from the second stage to the third stage at a rate of 2.5-5℃ / min, hold for 0.5-1h, and then pressurize for 10-20min. Then, cool from the third stage to the second stage at a rate of 5-10℃ / min, hold for 0.2-0.5h, and then pressurize for 10-20min. Next, cool from the second stage to the first stage at a rate of 5-10℃ / min, hold for 0.5-1h, and then pressurize for 10-20min. After completing the cycle, heat to 1420℃ at a rate of 2-5℃ / min.

[0009] Furthermore, the atmosphere for the oscillating nitriding is nitrogen.

[0010] In the above technical solution, the oscillating nitriding of temperature, pressure and airflow specifically involves the temperature first rising from the first stage temperature to the second stage temperature to the third stage temperature, and then cooling down, repeating once. Repeating more than once would make the process too complicated and not conducive to industrial production. Without repetition, the nitriding time would be too long, or silicon dissolution might easily occur. During the repetition process, the pressure and airflow also oscillate and cycle accordingly.

[0011] Furthermore, in S1, the process conditions for ball milling are: ball milling speed 50-220 r / min, ball milling time 6-12 h; The vacuum degassing process conditions are: vacuum degree of -20 to -50 kPa and degassing time of 100-120 min.

[0012] Further, in S1, the mass ratio of the sintering aid, silicon powder, PVB (polyvinyl butyral) binder, dispersant, and plasticizer is (4-6):100:(10-20):(0.5-3.5):(5-10).

[0013] Furthermore, the amount of PVB adhesive added is 5-10% of the total mass of the slurry.

[0014] Furthermore, the dispersant is a polyacrylic acid dispersant; The solvent is one or a mixture of several of ethanol, isopropanol, and ethyl acetate; The plasticizer is one or a mixture of several of PEG (polyethylene glycol), dimethyl phthalate, and dibutyl phthalate; The sintering aid is a mixture of two or more of the following: yttrium oxide, magnesium oxide, magnesium silicide, magnesium nitride, yttrium nitrate, and magnesium acetate.

[0015] Furthermore, in S2, the coating process is performed using a casting machine with a belt speed of 0.05-1.0 m / min; The drying temperature is 20-80℃; The dimensions of the cast green blank are: length 50-300mm, width 50-200mm, and thickness 0.15-0.8mm.

[0016] Furthermore, in S3, the BN (boron nitride) slurry includes BN powder, deionized water, and organic additives; The solid content of the BN slurry is 3-8%; The mass ratio of BN powder to organic additives is 1:(0.05-0.15).

[0017] Furthermore, the median particle size of the BN powder is 3-10 μm; The organic additives are BN slurry dispersant and binder. The BN slurry dispersant is one or a mixture of several of polycarboxylate salts, amine salts, and polyethylene glycol-type polyols. The binder is one or a mixture of several of polyvinyl alcohol, carboxymethyl cellulose, and water-soluble phenolic resin.

[0018] Furthermore, the amount of powder applied is 0.05-0.3g / piece.

[0019] Furthermore, in S4, the process conditions for the stacking are: 10-20 pieces / stack; The process conditions for glue removal are as follows: pure nitrogen atmosphere, air volume 300-800L / min, pressure 20-50Pa, heating rate 0.2-1℃ / min, glue removal temperature 500-600℃, and glue removal time 12-24h.

[0020] Furthermore, in S6, the sintering process conditions are: increasing the temperature to 1800-1900℃ at a rate of 2-5℃ / min, and holding at a pressure of 0.5-2MPa for 5-10 hours.

[0021] Furthermore, the silicon powder undergoes pretreatment before use, and the pretreatment process conditions are as follows: (1) Soak silicon powder in hydrofluoric acid aqueous solution for 5-15 min, wash with deionized water until neutral, oxidize in water bath at 80-90℃ for 0.5-3 h, and dry to obtain oxidized silicon powder; (2) Disperse the oxidized silicon powder and sodium dodecylbenzenesulfonate in deionized water, add nickel chloride hexahydrate (NiCl2·6H2O) and polyvinylpyrrolidone, stir for 30-40 min, add sodium borohydride aqueous solution under nitrogen atmosphere and ice bath conditions, continue stirring and react for 30-60 min, then filter and vacuum dry to obtain pretreated silicon powder.

[0022] Further, in step (1), the concentration of the hydrofluoric acid aqueous solution is 3-5%; The oxygen content on the surface of the oxidized silicon powder is 4-4.5%.

[0023] In the above technical solution, thermogravimetric analysis is used to determine the oxygen content of the oxidized silicon powder to ensure that it falls within the range of 4-4.5%. If the measured result is lower than 4%, the water bath oxidation time is appropriately extended; if it is higher than 4.5%, the water bath oxidation time is shortened. By adjusting the water bath oxidation time, the surface oxygen content of the oxidized silicon powder is kept within the range of 4-4.5%. When the oxygen content of silicon powder is less than 4%, the SiO gas phase is insufficient, and nitriding is mainly solid-phase diffusion, which is slow, has high residual silicon, and is prone to local overheating and silicon dissolution. When it is higher than 4.5%, the SiO partial pressure in the system is too high, which easily generates Si2N2O impurities with low thermal conductivity, which damages thermal conductivity and density.

[0024] Further, in step (2), the mass ratio of the oxidized silicon powder, sodium dodecylbenzenesulfonate, deionized water, nickel chloride hexahydrate, polyvinylpyrrolidone, and sodium borohydride aqueous solution is 10:(0.1-0.2):(50-100):(0.2-0.8):(0.2-1):(0.5-1). The concentration of the sodium borohydride aqueous solution is 3-5%.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. This invention uses an oscillating nitriding method to prepare silicon nitride ceramic wafers by reactive sintering of silicon powder. High and low temperature oscillating nitriding is adopted, and the effects of temperature, gas pressure and airflow on the degree / rate of nitriding are fully combined. The nitriding process is carefully designed to effectively avoid the occurrence of silicon dissolution and reduce the normal nitriding holding time of 8-10h to 2.5-5h, which significantly improves production efficiency.

[0026] 2. This invention achieves high pressure, low temperature, and low airflow in the first stage of oscillatory nitriding to increase the degree of nitriding. In the third stage, it achieves high temperature, low pressure, and high airflow to control the nitriding speed, thereby avoiding silicon dissolution. In addition, the high and low temperature cycling can shorten the total nitriding time and achieve rapid heating and cooling rates, which helps to improve production efficiency and safety.

[0027] 3. This invention pre-treats silicon powder to control the oxygen content on the silicon powder surface to 4-4.5%. Utilizing the characteristic of silicon powder generating SiO (silicon oxide) gas at this oxygen content and rapidly forming α-Si3N4 (α-phase silicon nitride) via chemical vapor deposition, the α-phase content in the product is increased without generating harmful impurity phases, resulting in extremely low residual silicon content. Then, Ni nanoparticles are loaded onto the silicon powder surface. The Ni nanoparticles can directly catalyze the dissociation of nitrogen molecules into active nitrogen atoms, enabling silicon and nitrogen to react rapidly via a gas-solid direct nitriding pathway. This effectively reduces the nitriding temperature and time. Furthermore, the Ni nanoparticles promote N2 dissociation and in-situ catalyze the generation of a large number of α-Si3N4 whiskers, significantly improving the bending strength of the substrate.

[0028] 4. This invention pre-treats silicon powder, enabling rapid initiation of nitriding in the first stage of oscillatory nitriding without prolonged induction; the second stage of oscillatory heating and cooling can regulate whisker growth behavior, resulting in a more uniform whisker aspect ratio distribution and improved consistency of substrate mechanical properties; the third stage, due to the low residual silicon content, allows for higher heating rates to complete the final sintering, further improving production efficiency; the combination of silicon powder pre-treatment and oscillatory nitriding further reduces nitriding time. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the rapid preparation method for silicon nitride substrates of the present invention; Figure 2 These are electron microscope images of silicon nitride substrates prepared in Example 1 and Comparative Example 1 of the present invention; Figure 2 In the text, a: Example 1; b: Comparative Example 1. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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] In the following embodiments, the parts are by weight. It should be noted that there are no special restrictions on the purchasers of any of the raw materials involved in this invention. Exemplary examples include: the average particle size of silicon powder is 2 μm; the average particle size of yttrium oxide is 0.5 μm; the average particle size of magnesium oxide is 0.5 μm; the median particle size of BN powder is 5 μm; the polyacrylic acid dispersant is Dispex AA4040; the polycarboxylate dispersant for BN slurry is T / 36-DF; the binder is polyvinyl alcohol (HPS); the PVB binder is JST; the plasticizer PEG is PEG200; the polyvinylpyrrolidone is K30; and other raw materials are commercially available.

[0032] BN slurry comprises BN powder, deionized water, and organic additives; the solid content of BN slurry is 5%; the mass ratio of BN powder to organic additives is 1:0.1; the organic additives are compounded from BN slurry dispersant polycarboxylate and binder polyvinyl alcohol in a mass ratio of 1:1.

[0033] Example 1: A rapid preparation method for reaction-sintered silicon nitride substrates, comprising the following steps: S1: Mix 5 parts of sintering aid, 100 parts of silica powder, 15 parts of PVB binder, 2 parts of polyacrylic acid dispersant, 8 parts of plasticizer PEG, and 57 parts of ethanol. Ball mill at 150 r / min for 8 h, and then degas under vacuum of -30 kPa for 110 min to obtain a slurry. The sintering aid is a mixture of yttrium oxide and magnesium oxide in a mass ratio of 1:1. S2: Using a casting machine, the slurry is coated onto the film at a belt speed of 0.5m / min. After drying at 50℃, it is cut to produce a casting green body with a length of 200mm, a width of 150mm, and a thickness of 0.5mm. S3: Using a powder coating machine, BN slurry is applied to the surface of the cast green body by spraying powder to obtain a powder-coated green body; the powder coating amount is 0.2g / piece; S4: Stack the powdered green blanks in a debinding furnace at 15 pieces / stack for debinding. Under pure nitrogen, air volume of 500L / min and pressure of 30Pa, heat the blanks to 550℃ at a heating rate of 0.5℃ / min and debind for 18 hours to obtain the debinded green blanks. S5: Place the debinding blank in a pressure sintering furnace for oscillating nitriding. First, heat to the first stage at a rate of 3℃ / min, hold for 0.8 hours, and then depressurize for 15 minutes. Then, heat from the first stage to the second stage at a rate of 3℃ / min, hold for 0.8 hours, and then depressurize for 15 minutes. Next, heat from the second stage to the third stage at a rate of 3℃ / min, hold for 0.8 hours, and then depressurize for 15 minutes. Finally, cool from the third stage back to the second stage at a rate of 8℃ / min, and hold for 0.3 hours. After the heat preservation period, the pressure is increased for 15 minutes; then the temperature is decreased from the second stage to the first stage at a rate of 8℃ / min, and the heat preservation period is 0.8 hours. After the heat preservation period, the pressure is increased for 15 minutes; after the cycle ends, the temperature is increased to 1420℃ at a rate of 3℃ / min to obtain the pre-nitrided billet; First stage: temperature 1160℃, pressure 1.5MPa, gas flow rate 12L / min; Second stage: temperature 1280℃, pressure 0.8MPa, gas flow rate 25L / min; Third stage: temperature 1380℃, pressure 0.3MPa, gas flow rate 35L / min; S6: The pre-nitrided blank is placed in a gas pressure sintering furnace and heated to 1850°C at a rate of 3°C / min. It is then sintered at a pressure of 1MPa for 8 hours. After sintering, the temperature and pressure are naturally reduced, and then surface treatment and cleaning are performed to obtain a silicon nitride substrate.

[0034] Example 2: A rapid preparation method for reaction-sintered silicon nitride substrates, comprising the following steps: S1: Mix 4 parts of sintering aid, 100 parts of silica powder, 10 parts of PVB binder, 0.5 parts of polyacrylic acid dispersant, 5 parts of plasticizer PEG, and 80.5 parts of ethanol. Ball mill at 50 r / min for 12 h, and then degas under vacuum of -20 kPa for 120 min to obtain a slurry. The sintering aid is a mixture of yttrium oxide and magnesium oxide in a mass ratio of 1:1. S2: Using a casting machine, the slurry is coated onto the film at a belt speed of 0.05m / min. After drying at 20℃, it is cut to produce a casting green body with a length of 50mm, a width of 50mm, and a thickness of 0.15mm. S3: Using a powder coating machine, BN slurry is applied to the surface of the cast green body by spraying powder to obtain a powder-coated green body; the powder coating amount is 0.05g / piece; S4: Stack the powdered green blanks in a debinding furnace at 10 pieces / stack for debinding. Under pure nitrogen, air volume of 300L / min and pressure of 20Pa, heat the blanks to 500℃ at a heating rate of 0.2℃ / min and debind for 24 hours to obtain the debinded green blanks. S5: Place the debinding blank in a pressure sintering furnace for oscillating nitriding. First, heat to the first stage at a rate of 2.5℃ / min, hold for 1 hour, and then depressurize for 10 minutes. Then, heat from the first stage to the second stage at a rate of 2.5℃ / min, hold for 1 hour, and then depressurize for 10 minutes. Next, heat from the second stage to the third stage at a rate of 2.5℃ / min, hold for 1 hour, and then depressurize for 10 minutes. Finally, cool from the third stage back to the second stage at a rate of 5℃ / min, and hold for 0 minutes. After 5 hours of heat preservation, pressurize for 10 minutes; then cool down from the second stage to the first stage at a rate of 5℃ / min, hold for 1 hour, and pressurize for 10 minutes after the heat preservation. After the cycle ends, heat up to 1420℃ at a rate of 2℃ / min to obtain the pre-nitrided billet. First stage: temperature 1150℃, pressure 1MPa, gas flow rate 10L / min; Second stage: temperature 1250℃, pressure 0.5MPa, gas flow rate 20L / min; Third stage: temperature 1350℃, pressure 0.1MPa, gas flow rate 30L / min. S6: The pre-nitrided blank is placed in a gas pressure sintering furnace and heated to 1800℃ at a rate of 2℃ / min. It is then sintered at a pressure of 0.5MPa for 10 hours. After sintering, the temperature and pressure are naturally reduced, and then the surface is treated and cleaned to obtain a silicon nitride substrate.

[0035] Example 3: A rapid preparation method for reaction-sintered silicon nitride substrates, comprising the following steps: S1: Mix 6 parts of sintering aid, 100 parts of silica powder, 20 parts of PVB binder, 3.5 parts of polyacrylic acid dispersant, 10 parts of plasticizer PEG, and 60.5 parts of ethanol. Ball mill at 150 r / min for 8 h, and then degas under vacuum of -50 kPa for 120 min to obtain a slurry. The sintering aid is a mixture of yttrium oxide and magnesium oxide in a mass ratio of 1:1. S2: Using a casting machine, the slurry is coated onto the film at a belt speed of 1.0 m / min. After drying at 80℃, it is cut to produce a casting green body with a length of 300 mm, a width of 200 mm, and a thickness of 0.8 mm. S3: Using a powder coating machine, BN slurry is applied to the surface of the cast green body by spraying powder to obtain a powder-coated green body; the powder coating amount is 0.3g / piece; S4: Stack the powdered green blanks in a debinding furnace at a rate of 20 pieces / stack for debinding. Under pure nitrogen, air volume of 800L / min and pressure of 50Pa, heat the blanks to 600℃ at a heating rate of 1℃ / min and debind for 12 hours to obtain the debinded green blanks. S5: Place the debinding blank in a pressure sintering furnace for oscillating nitriding. First, heat to the first stage at a rate of 5℃ / min, hold for 0.5h, and then depressurize for 20min. Then, heat from the first stage to the second stage at a rate of 5℃ / min, hold for 0.5h, and then depressurize for 20min. Next, heat from the second stage to the third stage at a rate of 5℃ / min, hold for 0.5h, and then depressurize for 20min. Finally, cool from the third stage back to the second stage at a rate of 10℃ / min, and hold for 0.5h. After 2 hours of heat preservation, pressurize for 20 minutes; then cool down from the second stage to the first stage at a rate of 10℃ / min, hold for 0.5 hours, and pressurize for 20 minutes after the heat preservation. After the cycle ends, heat up to 1420℃ at a rate of 5℃ / min to obtain the pre-nitrided billet. First stage: temperature 1170℃, pressure 2MPa, gas flow rate 15L / min; Second stage: temperature 1300℃, pressure 1MPa, gas flow rate 30L / min; Third stage: temperature 1420℃, pressure 0.5MPa, gas flow rate 40L / min. S6: The pre-nitrided blank is placed in a gas pressure sintering furnace and heated to 1900℃ at 5℃ / min. It is then sintered at a pressure of 2MPa for 5 hours. After sintering, the temperature and pressure are naturally reduced, and then surface treatment and cleaning are performed to obtain a silicon nitride substrate.

[0036] Example 4: Based on Example 1, the only difference from Example 1 is that the silicon powder is pretreated before use. The pretreatment process conditions are as follows: (1) The silicon powder was soaked in a 4% hydrofluoric acid aqueous solution for 10 min, washed with deionized water until neutral, oxidized in an 85℃ water bath for 2 h, and dried to obtain oxidized silicon powder; the oxygen content on the surface of the oxidized silicon powder was 4.2%; (2) Disperse 10 parts of oxidized silicon powder and 0.15 parts of sodium dodecylbenzenesulfonate in 80 parts of deionized water, add 0.5 parts of nickel chloride hexahydrate and 0.4 parts of polyvinylpyrrolidone, stir for 35 min, add 0.8 parts of sodium borohydride aqueous solution with a concentration of 4% under nitrogen atmosphere and ice bath conditions, continue stirring and react for 40 min, then filter and vacuum dry to obtain pretreated silicon powder.

[0037] Example 5: Based on Example 1, the only difference from Example 1 is that the silicon powder is pretreated before use. The pretreatment process conditions are as follows: (1) The silicon powder was soaked in a 3% hydrofluoric acid aqueous solution for 5 minutes, washed with deionized water until neutral, oxidized in an 80℃ water bath for 3 hours, and dried to obtain oxidized silicon powder; the oxygen content on the surface of the oxidized silicon powder was 4.5%; (2) Disperse 10 parts of oxidized silicon powder and 0.1 parts of sodium dodecylbenzenesulfonate in 50 parts of deionized water, add 0.2 parts of nickel chloride hexahydrate and 0.2 parts of polyvinylpyrrolidone, stir for 30 min, add 0.5 parts of 3% sodium borohydride aqueous solution under nitrogen atmosphere and ice bath conditions, continue stirring and react for 60 min, then filter and vacuum dry to obtain pretreated silicon powder.

[0038] Example 6: Based on Example 1, the only difference from Example 1 is that the silicon powder is pretreated before use. The pretreatment process conditions are as follows: (1) The silicon powder was soaked in a 5% hydrofluoric acid aqueous solution for 15 min, washed with deionized water until neutral, oxidized in a 90℃ water bath for 0.5 h, and dried to obtain oxidized silicon powder; the oxygen content on the surface of the oxidized silicon powder was 4%; (2) Disperse 10 parts of oxidized silicon powder and 0.2 parts of sodium dodecylbenzenesulfonate in 100 parts of deionized water, add 0.8 parts of nickel chloride hexahydrate and 1 part of polyvinylpyrrolidone, stir for 40 min, add 1 part of 5% sodium borohydride aqueous solution under nitrogen atmosphere and ice bath conditions, continue stirring and react for 30 min, then filter and vacuum dry to obtain pretreated silicon powder.

[0039] Comparative Example 1: Based on Example 1, S5 was replaced with conventional nitriding, specifically including the following: S5: Place the debinding blank in a pressure sintering furnace and perform conventional nitriding. Heat the blank to 1160℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 6 hours. Then heat the blank to 1260℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 3 hours. Finally, heat the blank to 1380℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 1 hour to obtain a pre-nitrided blank.

[0040] Comparative Example 2: Based on Comparative Example 1, the nitriding time was adjusted, specifically including the following: S5: Place the debinding blank in a pressure sintering furnace and perform conventional nitriding. Heat the blank to 1160℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 4 hours. Then heat the blank to 1260℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 3 hours. Finally, heat the blank to 1380℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 1 hour to obtain a pre-nitrided blank.

[0041] Comparative Example 3: Based on Comparative Example 1, the nitriding time was adjusted, specifically including the following: S5: Place the debinding blank in a pressure sintering furnace and perform conventional nitriding. Heat the blank to 1160℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 6 hours. Then heat the blank to 1260℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 2 hours. Finally, heat the blank to 1380℃ at a heating rate of 1℃ / min and nitrid at a nitriding pressure of 0.5MPa for 1 hour to obtain a pre-nitrided blank.

[0042] Comparative Example 4: Based on Example 4, the only difference from Example 4 is that the silicon powder was pretreated before use. The pretreatment process conditions were as follows: the silicon powder was soaked in hydrofluoric acid aqueous solution for 10 minutes, washed with deionized water until neutral, oxidized in a water bath at 85°C for 2 hours, and dried to obtain pretreated silicon powder; the oxygen content on the surface of the pretreated silicon powder was 4.2%.

[0043] Comparative Example 5: Based on Example 4, the only difference from Example 4 is that the silicon powder was pretreated before use. The pretreatment process conditions were as follows: silicon powder and sodium dodecylbenzenesulfonate were dispersed in deionized water, nickel chloride hexahydrate and polyvinylpyrrolidone were added, and after stirring for 35 min, a 4% sodium borohydride aqueous solution was added under nitrogen atmosphere and ice bath conditions. The reaction was continued to be stirred for 40 min, and then filtered and vacuum dried to obtain pretreated silicon powder. The mass ratio of silicon powder, sodium dodecylbenzenesulfonate, deionized water, nickel chloride hexahydrate, polyvinylpyrrolidone, and sodium borohydride aqueous solution was 10:0.15:80:0.5:0.4:0.8.

[0044] Testing methods: The silicon nitride substrates prepared in Examples 1-6 and Comparative Examples 1-5 were used as samples. The presence of black spherical silicon particles was visually inspected to determine whether silicon was dissolved. The density of the samples was tested using the water displacement method. The bending strength of the samples was tested using the three-point bending test method. The thermal conductivity of the samples was tested using the laser flash method.

[0045]

[0046] Conclusion: The data in the table above shows that: Examples 1-3 employ oscillatory nitriding, resulting in silicon nitride substrates that do not undergo silicon melting. Example 1 promotes rapid nitriding initiation through a first-stage high-pressure, low-gas flow; a second-stage medium-pressure, medium-gas flow balances heat release; and a third-stage low-pressure, high-gas flow suppresses violent reactions and removes heat. Combined with a single heating and cooling cycle, uniform nitriding and densification are achieved in a very short time, while effectively reducing lattice oxygen content and porosity, resulting in thermal conductivity superior to traditional long-time processes.

[0047] Examples 4-6, based on Example 1, added silicon powder pretreatment to further improve the substrate performance; precise control of oxygen content puts the silicon powder surface in a chemically activated state, generating high-purity α-Si3N4 through SiO vapor deposition, laying the foundation for high thermal conductivity; at the same time, chemically reduced Ni nanoparticles are uniformly anchored on the silicon powder surface, directly catalyzing N2 dissociation and inducing a large number of α-Si3N4 whiskers to grow in situ, and the bridging and pull-out effects of the whiskers significantly improve bending strength.

[0048] Comparative Example 1, based on Example 1, did not employ oscillatory nitriding but instead used conventional nitriding. Although no silicon dissolution occurred, the total nitriding time was 10 hours, significantly longer than that of Example 1. Comparative Example 2, based on Comparative Example 1, adjusted the nitriding time at 1160°C to 4 hours, resulting in silicon dissolution. Comparative Example 3, based on Comparative Example 1, adjusted the nitriding time at 1260°C to 2 hours, also resulting in silicon dissolution. This demonstrates that the parameter combination of the oscillatory nitriding process of the present invention has criticality and synergy, and is not a simple conventional selection.

[0049] Comparative Example 4, based on Example 4, did not involve Ni nanoparticle loading during silicon powder pretreatment, but only retained surface oxygen content control. Its performance was significantly worse than that of Example 4, indicating that Ni nanoparticle catalysis plays an important role in whisker formation and strength improvement. Comparative Example 5, based on Example 4, did not involve surface oxygen content control during silicon powder pretreatment, but only involved Ni nanoparticle loading. Its performance was significantly worse than that of Example 4, indicating that surface oxygen content control and Ni catalysis have a synergistic effect, and the combined effect of the two is better than single modification.

[0050] Test results show that neither Example 1 nor Comparative Example 1 will experience silicon dissolution, while Comparative Example 2 and Comparative Example 3 will experience silicon dissolution, further demonstrating that the oscillating nitriding in Example 1 can achieve stable nitriding in a short time.

[0051] like Figure 2 As shown, compared with Example 1 and Comparative Example 1, Example 1 has fewer pores. Comparative Example 1 is generally dense but has obvious pores in a few places. The obvious pores may be due to the influence of impurities during the sintering process, and there may also be a small amount of incomplete nitriding, which may cause a small amount of dissolved silicon material to be lost during substrate sintering and result in pores.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for rapidly producing a reaction-sintered silicon nitride substrate, characterized by: Includes the following steps: S1: The sintering aid, silicon powder, PVB binder, dispersant, plasticizer and solvent are mixed and ball-milled, and then vacuum degassed to obtain a slurry; S2: The slurry is coated onto the film strip, dried, and then cut to form a cast film green body; S3: Apply BN slurry to the surface of the cast green body by spraying powder to obtain a powder-coated green body; S4: Stack the powdered green blanks and place them in a debinding furnace to remove the glue, thus obtaining the debinded blanks; S5: Place the debonded blank in a gas pressure sintering furnace for oscillating nitriding to obtain a pre-nitrided blank; S6: The pre-nitrided blank is placed into a gas pressure sintering furnace for sintering. After sintering, the temperature and pressure are naturally reduced, and then the surface is treated and cleaned to obtain a silicon nitride substrate.

2. The method according to claim 1, wherein the method is characterized by: In S5, the process conditions for the oscillating nitriding are as follows: First stage: Temperature 1150-1170℃, pressure 1-2MPa, gas flow rate 10-15L / min; Second stage: Temperature 1250-1300℃, pressure 0.5-1MPa, gas flow rate 20-30L / min; Third stage: Temperature 1350-1420℃, pressure 0.1-0.5MPa, gas flow rate 30-40L / min; First, heat to the first stage at a rate of 2.5-5℃ / min, hold for 0.5-1h, and then depressurize for 10-20min. Then, heat from the first stage to the second stage at a rate of 2.5-5℃ / min, hold for 0.5-1h, and then depressurize for 10-20min. Next, heat from the second stage to the third stage at a rate of 2.5-5℃ / min, hold for 0.5-1h, and then pressurize for 10-20min. Then, cool from the third stage to the second stage at a rate of 5-10℃ / min, hold for 0.2-0.5h, and then pressurize for 10-20min. Next, cool from the second stage to the first stage at a rate of 5-10℃ / min, hold for 0.5-1h, and then pressurize for 10-20min. After completing the cycle, heat to 1420℃ at a rate of 2-5℃ / min.

3. The method of claim 1, wherein the method further comprises: In S1, the amount of PVB adhesive added is 5-10% of the total mass of the slurry.

4. The method of claim 1, wherein the method further comprises: The dispersant is a polyacrylic acid dispersant; The solvent is one or a mixture of several of ethanol, isopropanol, and ethyl acetate; The plasticizer is one or a mixture of several of PEG, dimethyl phthalate, and dibutyl phthalate; The sintering aid is a mixture of two or more of the following: yttrium oxide, magnesium oxide, magnesium silicide, magnesium nitride, yttrium nitrate, and magnesium acetate.

5. The method of claim 1, wherein the method further comprises: In S2, the coating is applied using a casting machine with a belt speed of 0.05-1.0 m / min; The drying temperature is 20-80℃; The dimensions of the cast green blank are: length 50-300mm, width 50-200mm, and thickness 0.15-0.8mm.

6. The method of claim 1, wherein the method is characterized by: In S3, the BN slurry includes BN powder, deionized water, and organic additives; The amount of powder applied is 0.05-0.3g per tablet; The median particle size of the BN powder is 3-10 μm; The organic additives are BN slurry dispersant and binder. The BN slurry dispersant is one or a mixture of several of polycarboxylate salts, amine salts, and polyethylene glycol-type polyols. The binder is one or a mixture of several of polyvinyl alcohol, carboxymethyl cellulose, and water-soluble phenolic resin.

7. The rapid preparation method for reaction-sintered silicon nitride substrate according to claim 1, characterized in that: In S4, the process conditions for glue removal are: pure nitrogen atmosphere, air volume 300-800L / min, pressure 20-50Pa, heating rate 0.2-1℃ / min, glue removal temperature 500-600℃, and glue removal time 12-24h.

8. The rapid preparation method for reaction-sintered silicon nitride substrate according to claim 1, characterized in that: In S6, the sintering process conditions are: increasing the temperature to 1800-1900℃ at a rate of 2-5℃ / min, and holding at a pressure of 0.5-2MPa for 5-10 hours.

9. The rapid preparation method for reaction-sintered silicon nitride substrate according to claim 1, characterized in that: The silicon powder undergoes pretreatment before use. The pretreatment process conditions are as follows: (1) Soak silicon powder in hydrofluoric acid aqueous solution for 5-15 min, wash with deionized water until neutral, oxidize in water bath at 80-90℃ for 0.5-3 h, and dry to obtain oxidized silicon powder; (2) Disperse the oxidized silicon powder and sodium dodecylbenzenesulfonate in deionized water, add nickel chloride hexahydrate and polyvinylpyrrolidone, stir for 30-40 min, add sodium borohydride aqueous solution under nitrogen atmosphere and ice bath conditions, continue stirring and react for 30-60 min, then filter and vacuum dry to obtain pretreated silicon powder.

10. The rapid preparation method of reaction-sintered silicon nitride substrate according to claim 1, characterized in that: In step (1), the oxygen content on the surface of the oxidized silicon powder is 4-4.5%; In step (2), the mass ratio of the oxidized silicon powder, sodium dodecylbenzenesulfonate, deionized water, nickel chloride hexahydrate, polyvinylpyrrolidone, and sodium borohydride aqueous solution is 10:(0.1-0.2):(50-100):(0.2-0.8):(0.2-1):(0.5-1).

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