Silicon nitride ceramic substrate and preparation and application thereof

Abstract

The invention discloses a silicon nitride ceramic substrate and preparation and application thereof, and the method comprises the following steps: mixing alpha-Si3N4 and an auxiliary agent mixture, sealing, carrying out ball milling, drying, grinding into powder, sieving, granulating by using a polysilazane-cyclohexane solution, loading into a mold, sealing, carrying out cold isostatic pressing molding, presintering at 600 DEG C in an inert atmosphere, cutting, and sintering to obtain the silicon nitride ceramic substrate. And carrying out high-temperature sintering in an inert atmosphere of 1800-1900 DEG C. The problems that in the prior art, a tape casting method is large in organic solvent amount and low in rough adhesive discharge shrinkage yield; in order to solve the problems of hard ceramic, extremely difficult cutting and low efficiency of a hot-pressing method in the prior art, a polysilazane-cyclohexane solution is adopted for granulation, polysilazane is subjected to crosslinking-dehydrogenation to form a Si-C-N pre-ceramic network through pre-sintering treatment, and meanwhile, cutting is performed after pre-sintering, so that the preparation period is remarkably shortened, the environmental pollution is reduced, and the product yield is improved; and low-cost and large-scale production of the silicon nitride ceramic substrate can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a ceramic substrate, in particular to a silicon nitride ceramic substrate and its preparation and application. BACKGROUND

[0002] With the development of semiconductor electronic devices towards high voltage, large current, high power and miniaturization, electronic packaging technology is facing more severe challenges. As a complex system, device packaging requires materials not only to have high thermal conductivity to effectively dissipate heat, but also to withstand thermal stress caused by temperature gradient and repeated thermal cycling. The packaging substrate, as a key component of power semiconductor devices, bears multiple functions such as supporting chips, electrical insulation and heat conduction channels. Ceramic materials are considered as ideal substrate materials due to their high thermal conductivity, excellent thermal shock resistance, good insulation and mechanical properties. Among them, Si3N4 ceramic not only has outstanding mechanical properties and excellent thermal shock resistance (can withstand rapid cooling and heating above 1000℃ without breaking), but also has a theoretical thermal conductivity of single crystal of 450 W / (m·K) at room temperature, so it is recognized as one of the ideal materials for preparing high-performance ceramic substrates.

[0003] At present, through sintering aids optimization, process improvement and material modification, the research of Si3N4 ceramic substrate has made significant progress, with a bending strength of >800 MPa and a thermal conductivity of >90 W / (m·K). However, from laboratory samples to large-scale production, it needs to overcome complex engineering challenges. Process stability, cost control and performance balance are the key factors restricting industrialization. Therefore, to realize the industrialization of high-performance Si3N4 ceramic substrate, further exploration is still needed in the aspects of process integration and engineering application.

[0004] The preparation of silicon nitride ceramic substrates currently follows two main technical routes: Route 1 is "tape casting-gas pressure sintering," which involves casting thin green sheets, followed by debinding and sintering to directly obtain substrates of predetermined dimensions; Route 2 is "hot pressing sintering-cutting," which involves first obtaining bulk material through hot pressing sintering, followed by precision cutting. Although Route 1 is adopted by most manufacturers, its reliance on tape casting processes is complex, requiring the use of large amounts of organic reagents, resulting in a heavy environmental processing burden. In addition, the large shrinkage rate of the green sheets during debinding easily introduces defects during the sintering stage, leading to a low product yield. Existing document 1 (Chinese invention patent application with publication number CN119350042A) discloses a silicon nitride ceramic substrate and its preparation method, which is prepared from the following raw materials in parts by weight: 80-100 parts silicon nitride, 5-10 parts carbon nanotubes, 5-10 parts sintering aid, 5-10 parts binder, 1-3 parts dibutyl phthalate, 1-3 parts ammonium polyacrylate, and 50-70 parts deionized water. The binder is sulfonic acid-modified polyvinyl alcohol, and rare earth fluorides and nano-iron particles are deposited on the surface of the carbon nanotubes. The silicon nitride ceramic substrate prepared by this invention has high mechanical strength and excellent thermal conductivity. Moreover, it adopts a water-based tape casting process, avoiding the use of large amounts of organic solvents, resulting in fewer safety and environmental problems during large-scale production, and can meet the application requirements of highly integrated circuit packaging substrate materials. However, the process in document 1 is essentially still a tape casting-gas pressure sintering route. Because organic matter such as binders and plasticizers in the slurry accounts for 45 wt% to 50 wt% of the total powder, there is still a 15% to 20% volume shrinkage during the debinding stage, leading to easy cracking and warping of the thin blanks, resulting in a yield rate of only 65% ​​to 70%. Debinding takes as long as 6 to 10 hours, resulting in a lengthy production cycle. Furthermore, the strength of the raw blank is only 3 MPa to 5 MPa, and the breakage rate during transport reaches 5% to 8%. These bottlenecks severely restrict the industrialization process. Although Route 2 avoids the tape casting process, the silicon nitride ceramic after hot pressing and sintering has extremely high hardness, making subsequent cutting and processing extremely difficult, resulting in low processing efficiency and high tool / wire wear. Taking diamond wire cutting as an example, the feed rate for a 114 mm × 114 mm substrate is only about 0.1 mm / min, and a single cut can take up to 19 hours, significantly increasing production costs. Summary of the Invention

[0005] The purpose of this invention is to provide a silicon nitride ceramic substrate and its preparation and application, which solves the problems of low yield caused by excessive organic solvents and shrinkage during casting and the low efficiency of ceramics in hot pressing. It significantly shortens the preparation cycle, reduces environmental pollution, and improves product yield, which helps to realize the low-cost large-scale production of silicon nitride ceramic substrates.

[0006] To achieve the above objectives, the present invention provides a method for preparing a silicon nitride ceramic substrate, the method comprising: (1) Mix α-Si3N4 with additives, add grinding balls and solvent, seal, ball mill, dry, grind into powder, sieve, and granulate using polysilazane-cyclohexane solution to obtain granulated powder; (2) The granulated powder is loaded into the mold, sealed, and cold isostatically pressed to obtain the green body; the green body is pre-sintered at 600℃ in an inert atmosphere. (3) Cut the pre-sintered blank and sinter it at high temperature in an inert atmosphere of 1800℃~1900℃ to obtain silicon nitride ceramic substrate. The polysilazane-cyclohexane solution contains 5% to 25% polysilazane by mass. The additive mixture is composed of non-oxide sintering aids and rare earth compound sintering aids; The non-oxide sintering aid is MgSiN2; The rare earth compound sintering aid is any one or more of Y2O3, Yb2O3, Er2O3, Y3Si2C2 and Er3Si2C2.

[0007] Preferably, the mass fraction of polysilazane in the polysilazane-cyclohexane solution is 5% to 20%.

[0008] More preferably, the mass fraction of polysilazane in the polysilazane-cyclohexane solution is 10%~20%, and the volume ratio of the polysilazane-cyclohexane solution to the mass ratio of the mixed powder is 50mL:100g.

[0009] Preferably, the mass ratio of the α-Si3N4 to the additive mixture is (87 ~ 93): (7 ~ 13); the mass ratio of the non-oxide sintering aid to the rare earth compound sintering aid is (3 ~ 6): (4 ~ 7).

[0010] More preferably, the mass ratio of α-Si3N4 to the additive mixture is 92:8; and the mass ratio of the non-oxide sintering aid to the rare earth compound sintering aid is 3:5.

[0011] Preferably, the grinding ball is a silicon nitride grinding ball; the solvent is anhydrous ethanol; and the weight ratio of the grinding ball, solvent, and mixture of α-Si3N4 and additives is 4:3:1.

[0012] Preferably, the pressure of the cold isostatic pressing is 150MPa ~ 200MPa, the constant pressure time is 2 min ~ 5 min, and the pre-sintering treatment time is 1h ~ 2h.

[0013] Preferably, the cutting is performed using diamond wire, with a wire feed rate of 10 mm / min to 20 mm / min and a thickness of 0.3 mm to 0.7 mm.

[0014] Preferably, the high-temperature sintering time is 4h to 8h and the pressure is 1 MPa to 3 MPa.

[0015] Preferably, the inert atmosphere is a nitrogen atmosphere.

[0016] The present invention provides a silicon nitride ceramic substrate prepared by the method described above.

[0017] This invention provides an application of the silicon nitride ceramic substrate as described above in the packaging of semiconductor electronic devices.

[0018] The silicon nitride ceramic substrate of the present invention, its preparation and application, solves the problems of low yield due to excessive organic solvents and adhesive shrinkage in the casting method, and low efficiency due to the hardness and difficulty in cutting ceramics in the hot pressing method, and has the following advantages: 1. This invention uses a solution of polysilazane dissolved in cyclohexane as the granulation solution. By utilizing the excellent binding properties of polysilazane itself, the green body formed by cold isostatic pressing of the granulated powder maintains structural integrity during subsequent handling and sintering, thus avoiding the risk of breakage.

[0019] 2. The present invention can crosslink and dehydrogenate polysilazane to form a Si-CN pre-ceramic network through low-temperature pre-firing treatment, which further densifies the green body and gives it cuttable strength. It directly skips the traditional casting-degreasing process, completely eliminates the approximately 20% shrinkage and cracking defects caused by the removal of organic matter, and greatly improves the product yield. 3. This invention does not require the extensive use of harmful solvents such as toluene, PVB, and DBP in the casting process, making the process green. The blank can be cut into thin sheets after low-temperature pre-sintering. Compared with the existing hot pressing sintering-ceramic slicing process, which cuts the ceramic after it is fully fired, this invention significantly shortens the processing time, effectively reduces production costs, and helps to achieve low-cost large-scale production of silicon nitride ceramic substrates. Attached Figure Description

[0020] Figure 1 This is a process flow diagram for preparing a silicon nitride ceramic substrate according to Example 1 of the present invention. Detailed Implementation

[0021] 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.

[0022] Example 1 A silicon nitride ceramic substrate and its preparation method are described. Example 1 of this invention includes a process flow diagram for preparing the silicon nitride ceramic substrate, comprising: (1) Weigh an appropriate amount of α-Si3N4 powder as the reference raw material, add 3wt.%MgSiN2, 2wt.%Y2O3 and 3wt.%Y3Si2C2 into a polytetrafluoroethylene ball mill jar, then add silicon nitride grinding balls and anhydrous ethanol, seal and perform planetary ball milling. The mass ratio of α-Si3N4 powder, MgSiN2, Y2O3 and Y3Si2C2 in the raw material is 92∶3∶2∶3; the weight ratio of silicon nitride balls, anhydrous ethanol and raw material is 4∶3∶1, the ball milling time is 4h, and the ball mill speed is 350 r / min. After the above ball milling slurry is dried in an oven at 80℃, it is taken out and ground into powder, and then passed through a 300-mesh sieve to obtain a uniformly mixed powder; the above mixed powder is granulated using a prepared polysilazane-cyclohexane solution to obtain granulated powder. The polysilazane content in the polysilazane-cyclohexane solution is 5 wt.%, and the volume ratio of the polysilazane-cyclohexane solution to the mass ratio of the mixed powder is 50 mL: 100 g.

[0023] (2) The granulated powder is loaded into a rubber mold of a customized size, then sealed and placed in a cold isostatic press for cold isostatic pressing. The target pressure for cold isostatic pressing is 150 MPa, and the constant pressure time is 3 min. The block blank formed by cold isostatic pressing is taken out and placed in a sintering furnace for low-temperature pre-sintering treatment. The density of the pre-sintered blank is 58.3%, and the flexural strength is 14.2 MPa. The low-temperature pre-sintering treatment is carried out under a nitrogen protective atmosphere, with a target temperature of 600℃. The heating rate from room temperature to 300℃ is 1℃ / min, the heating rate from 300℃ to 600℃ is 3℃ / min, and the constant temperature time at 600℃ is 1 h.

[0024] Because the pre-sintered green body has a strength of only 14 MPa, its mechanical integrity is insufficient to withstand the stress of diamond multi-wire cutting, leading to green body breakage. Therefore, qualified thin sheets cannot be produced, and the preparation process is terminated at this step, without further gas pressure sintering.

[0025] Example 2 A silicon nitride ceramic substrate and its preparation method, such as Figure 1The diagram shows the process flow chart for preparing a silicon nitride ceramic substrate in Example 1 of the present invention. The method includes: (1) Weigh an appropriate amount of α-Si3N4 powder as the reference raw material, add 3wt.%MgSiN2, 2wt.%Y2O3 and 3wt.%Y3Si2C2 into a polytetrafluoroethylene ball mill jar, then add silicon nitride grinding balls and anhydrous ethanol, seal and perform planetary ball milling. The mass ratio of α-Si3N4 powder, MgSiN2, Y2O3 and Y3Si2C2 in the raw material is 92∶3∶2∶3; the weight ratio of silicon nitride balls, anhydrous ethanol and raw material is 4∶3∶1, the ball milling time is 4h, and the ball mill speed is 350 r / min. After the above ball milling slurry is dried in an oven at 80℃, it is taken out and ground into powder, and then passed through a 300-mesh sieve to obtain a uniformly mixed powder; the above mixed powder is granulated using a prepared polysilazane-cyclohexane solution to obtain granulated powder. The polysilazane-cyclohexane solution contains 10 wt.% polysilazane, and the volume ratio of the polysilazane-cyclohexane solution to the mass ratio of the mixed powder is 50 mL: 100 g.

[0026] (2) The granulated powder is loaded into a rubber mold of a customized size, then sealed and placed in a cold isostatic press for cold isostatic pressing. The target pressure for cold isostatic pressing is 150 MPa, and the constant pressure time is 3 min. The block blank formed by cold isostatic pressing is taken out and placed in a sintering furnace for low-temperature pre-sintering treatment. The density of the pre-sintered blank is 68.9%, and the flexural strength is 101.2 MPa. The low-temperature pre-sintering treatment is carried out under a nitrogen protective atmosphere, with a target temperature of 600℃. The heating rate from room temperature to 300℃ is 1℃ / min, the heating rate from 300℃ to 600℃ is 3℃ / min, and the constant temperature time at 600℃ is 1 h.

[0027] (3) The pre-sintered blank was cut using diamond multi-wire cutting to obtain blank sheets. The diamond wire feed rate was 10 mm / min, and the thickness of the blank sheets was 0.35 mm. The cut blank sheets were placed in a pressure sintering furnace for further high-temperature sintering to obtain silicon nitride ceramic substrates with a density of 98.5%, a flexural strength of 751.3 MPa, and a thermal conductivity of 96.8 W / (m·K). The blank sheets were all filled with boron nitride powder and stacked sequentially in boron nitride crucibles. The target temperature for high-temperature sintering was 1850℃, the holding time was 6 h, the heating rate was 15℃ / min, and the pressure was 3 MPa. During cooling, the cooling rate from 1850℃ to 1100℃ was 10℃ / min, and the cooling from 1100℃ to room temperature was carried out with the furnace.

[0028] Example 3 A silicon nitride ceramic substrate and its preparation method are basically the same as in Example 2, except that: In step (1), the polysilazane content in the polysilazane-cyclohexane solution is 15 wt.%. In step (2), the pre-sintered green body has a density of 73.3% and a bending strength of 135.5 MPa.

[0029] In step (3), the substrate has a density of 98.6%, a bending strength of 789.2 MPa, and a thermal conductivity of 91.6 W / (m·K).

[0030] Example 4 A silicon nitride ceramic substrate and its preparation method are basically the same as in Example 2, except that: In step (1), the polysilazane content in the polysilazane-cyclohexane solution is 20 wt.%. In step (2), the pre-sintered green body has a density of 77.5% and a bending strength of 166.4 MPa.

[0031] In step (3), the substrate has a density of 98.3%, a bending strength of 825.6 MPa, and a thermal conductivity of 80.5 W / (m·K).

[0032] Table 1. Properties of silicon nitride preforms and substrates prepared in Examples 1-4 A comparative analysis of the data in Table 1 regarding the specific operations in Examples 1-4 of this invention reveals that the density and flexural strength of the pre-sintered green body both increase with the increase of polysilazane content, with the strength increase being particularly significant. This is attributed to the Si-CN precursor ceramic network formed by the cross-linking and dehydrogenation of polysilazane, which effectively enhances the strength of the green body. After pressure sintering, the density of the substrate does not change significantly, but the flexural strength continues to increase with the increase of polysilazane content, while the thermal conductivity shows a decreasing trend. This is because polysilazane induces the formation of SiC and Si3N4 nanocrystalline phases at high temperatures (>1500°C). These uniformly distributed nanoparticles, acting as a second phase, have a significant nano-toughening effect, thereby improving the flexural strength of the substrate. However, these nanophases also introduce a large number of crystal interfaces, increasing phonon scattering and hindering heat conduction, leading to a decrease in thermal conductivity.

[0033] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a silicon nitride ceramic substrate, characterized in that, The method includes: (1) Mix α-Si3N4 with additives, add grinding balls and solvent, seal, ball mill, dry, grind into powder, sieve, and granulate using polysilazane-cyclohexane solution to obtain granulated powder; (2) The granulated powder is loaded into the mold, sealed, and cold isostatically pressed to obtain the green body; the green body is pre-sintered at 600℃ in an inert atmosphere. (3) Cut the pre-sintered blank and sinter it at high temperature in an inert atmosphere of 1800℃~1900℃ to obtain silicon nitride ceramic substrate. The polysilazane-cyclohexane solution contains 5% to 25% polysilazane by mass. The additive mixture is composed of non-oxide sintering aids and rare earth compound sintering aids; The non-oxide sintering aid is MgSiN2; The rare earth compound sintering aid is any one or more of Y2O3, Yb2O3, Er2O3, Y3Si2C2 and Er3Si2C2.

2. The method according to claim 1, characterized in that, The mass fraction of polysilazane in the polysilazane-cyclohexane solution is 5% to 20%.

3. The method according to claim 1, characterized in that, The mass ratio of α-Si3N4 to the additive mixture is (87~93):(7~13); the mass ratio of the non-oxide sintering aid to the rare earth compound sintering aid is (3~6):(4~7).

4. The method according to claim 1, characterized in that, The grinding ball is a silicon nitride grinding ball; the solvent is anhydrous ethanol; the weight ratio of the grinding ball, solvent and α-Si3N4 and additive mixture is 4:3:

1.

5. The method according to claim 1, characterized in that, The pressure of the cold isostatic pressing is 150MPa ~ 200MPa, and the constant pressure time is 2 min ~ 5 min; the time of the pre-sintering treatment is 1h ~ 2h.

6. The method according to claim 1, characterized in that, The cutting is performed using diamond wire with a wire feed rate of 10 mm / min to 20 mm / min and a thickness of 0.3 mm to 0.7 mm.

7. The method according to claim 1, characterized in that, The high-temperature sintering time is 4h~8h and the pressure is 1MPa~3MPa.

8. The method according to claim 1, characterized in that, All inert atmospheres are nitrogen atmospheres.

9. A silicon nitride ceramic substrate prepared by the method according to any one of claims 1 to 8.

10. The application of the silicon nitride ceramic substrate as described in claim 9 in the packaging of semiconductor electronic devices.

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