CN114907129A - Preparation method of low-dielectric-constant and high-strength silicon nitride - Google Patents

Preparation method of low-dielectric-constant and high-strength silicon nitride Download PDF

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CN114907129A
CN114907129A CN202210565829.0A CN202210565829A CN114907129A CN 114907129 A CN114907129 A CN 114907129A CN 202210565829 A CN202210565829 A CN 202210565829A CN 114907129 A CN114907129 A CN 114907129A
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silicon nitride
powder
purity
graphite
ball milling
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朱伟
张扬
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Gemch Material Technology Suzhou Co ltd
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Abstract

The invention relates to the field of preparation of silicon nitride, and discloses a preparation method of silicon nitride with low dielectric constant and high strength. The method comprises the following steps: selecting raw materials, adding the raw materials into a liquid medium for ultrasonic dispersion, and then adding the suspension into a ball milling tank body; after ball milling, carrying out vacuum drying on the mixed powder, and after the powder is completely dried, screening the powder; calculating the weight of the mixed powder according to the product requirement, and then filling the mixed powder into a graphite die; placing the graphite mould below a pressure head of a vacuum hot-pressing furnace, and carrying out hot-pressing sintering on the graphite mould; and after the mold is cooled, taking out the silicon nitride blank, and machining the silicon nitride blank. Reasonable raw material selection and vacuum hot pressing are adopted to prepare the alloy material which can meet the requirements of the wear-resistant bearing, the thermocouple protection tube and the corrosion resistance field, in particular to the field of semiconductor devices with higher requirements on electrical property and corrosion resistance.

Description

Preparation method of low-dielectric-constant and high-strength silicon nitride
Technical Field
The invention relates to the field of preparation of silicon nitride, in particular to a preparation method of silicon nitride with low dielectric constant and high strength.
Background
The silicon nitride ceramic material has the advantages of low specific gravity, high hardness, good wear resistance, high strength, high fracture toughness, excellent thermal conductivity and thermal shock resistance and the like, and can be said to be a 'universal player' in a ceramic material. The semiconductor is widely and successfully applied in various fields such as electronic power, semiconductor devices, aerospace, mechanical and chemical engineering, ceramic bearings and the like, and is more praised as the most promising third-generation semiconductor.
Silicon nitride belongs to a compound with high covalent bond, has low diffusion coefficient, is difficult to be densified through surface molecular or atomic diffusion in the sintering process, and has a decomposition phenomenon at high temperature, so pure silicon nitride is difficult to obtain a densified product.
Therefore, liquid phase sintering is adopted for preparing the silicon nitride ceramics, namely, some auxiliary agents with lower melting points or capable of forming eutectic with silicon nitride to form low melting points are added. Common sintering aids include MgO and Al 2 O 3 、ZrO 2 、Re 2 O 3 And (Re ═ La, Nd, Gd, Y, Yb, Sc), MexFy (Me ═ Mg, Y, Yb), and the like. The addition of the sintering aid reduces the preparation cost to a certain extent, enhances the toughness and the bending resistance of the silicon nitride ceramic, but has adverse effects on the thermal conductivity, the hardness and the electrical property of the silicon nitride ceramic.
The focus ring is a commodity used in an etching process in wafer fabrication, which fixes a wafer in a proper position to maintain a plasma density and prevent contamination of a side surface of the wafer, and the conventional focus ring is fabricated using quartz and silicon, but with the advanced wafer fabrication, a dry etching method is used, and a material demand for higher strength, higher corrosion resistance, higher hardness, lower dielectric constant and lower dielectric loss is increased.
Therefore, the present invention is needed to prepare a low dielectric constant, high strength silicon nitride ceramic material for use as a focus ring in a semiconductor device.
Disclosure of Invention
In order to solve the technical problems, the invention provides a preparation method of a silicon nitride ceramic material with low dielectric constant and high strength.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a preparation method of low dielectric constant and high strength silicon nitride comprises the following steps:
s1: selecting raw materials, namely, 90 to 95 mass percent of alpha-phase silicon nitride powder, 0.5 to 3 mass percent of MgO and 0.2 to 1.5 mass percent of Al 2 O 3 1% -6% of SiO 2 0.2% -1% of Y 2 O 3 1-5% of beta-phase silicon nitride powder is added into a liquid medium, and ultrasonic dispersion is carried out for 20-60 min to obtain first mixed powder;
adding the first mixed powder and the suspension into a ball milling tank body adapted to a planetary ball mill, and processing to obtain second mixed powder;
s2: pre-treating, namely drying the second mixed powder in vacuum, and screening the powder after the powder is completely dried to obtain third mixed powder;
s3: filling a mold, selecting a graphite mold, filling graphite paper on the bottom and the side wall of a cavity of the graphite mold, calculating the weight of the third mixed powder according to the product requirement, adding the powder to the graphite paper in the cavity in a grading manner, and covering the graphite paper on the powder;
s4: hot-pressing sintering, namely placing the graphite mould at a corresponding position below a pressure head of a vacuum hot-pressing furnace, pre-pressing, vacuum hot-pressing and sintering the graphite mould, and finally cooling the graphite mould to normal temperature along with the furnace;
s5: and (4) forming, after the mould is cooled, taking out the silicon nitride blank, and machining the silicon nitride blank to meet the requirement of the required product.
In a preferred embodiment of the present invention, the α -phase silicon nitride powder has a purity of 4N or more, an α -phase content of 92% to 95%, a D50 of 0.5 μm to 5 μm, a MgO purity of 3N, D50 of 0.5 μm to 2 μm, and Al 2 O 3 Purity of not less than 4N, D50 ≥ 0.5 μm-2 μm, SiO 2 Has a purity of not less than 3N, D50 ≥ 0.2 μm-2 μm, Y 2 O 3 The purity of the beta-phase silicon nitride powder is not less than 4N, D50 but 0.2-2 mu m, and the purity of the beta-phase silicon nitride powder is not less than 4N, D50 but 0.5-5 mu m.
As a preferable scheme of the invention, the ball milling rotating speed of the planetary ball mill is 200r/min-400r/min, the ball milling time is 4h-16h, and the loading capacity is 1/3-2/3 of the volume of the ball milling tank body.
As a preferred scheme of the invention, the grinding balls selected by the planetary ball mill are high-purity silicon nitride balls, the sizes of the high-purity silicon nitride balls comprise phi 3mm, phi 6mm and phi 10mm, and the proportion of the grinding balls added into the ball milling tank body is 3-5: 2-4.
As a preferred scheme of the invention, the ball milling tank body is a polyurethane tank or a nylon tank.
As a preferable scheme of the invention, in S2, the required drying temperature is 40-120 ℃ and the drying time is 8-24 h.
As a preferable scheme of the invention, the screening treatment adopts a screen mesh of 80-150 meshes.
As a preferable scheme of the invention, the graphite paper needs to be adjusted and leveled every time the powder is added to the graphite paper in a plurality of times.
As a preferable scheme of the present invention, the bottom and the side wall of the cavity of the graphite mold, and both surfaces of the graphite paper are sprayed with a high temperature resistant release agent.
As a preferred scheme of the invention, in S4, the graphite mold is pre-pressed for 0.5Mpa-2MPa, the furnace body is vacuumized to be below 800Pa, the temperature is raised to 450 ℃ -650 ℃ at 5 ℃/min-10 ℃/min, and the temperature is kept for 1h-4 h;
then heating to 1000-1200 ℃ at the speed of 3-8 ℃/min, and preserving heat for 0.5-4 h; then closing the vacuum system, introducing high-purity N2 to pressure balance, and heating to 1650-1750 ℃ at a speed of 2-5 ℃/min;
boosting the pressure to 15-35 MPa, and keeping the temperature for 1-6 h; after the heat preservation is finished, the pressure is removed, and the temperature is reduced to 1400-1600 ℃ at the speed of 2-5 ℃/min.
In conclusion, the invention has the following beneficial effects:
1. a reasonable sintering auxiliary agent system is selected, so that the hardness, the bending strength and the fracture toughness of the silicon nitride ceramic are ensured, the oxidation resistance and the corrosion resistance of the silicon nitride ceramic are improved, and the dielectric constant and the dielectric loss value of the silicon nitride ceramic are reduced.
2. The powder is crushed and dispersed by adopting ultrasonic dispersion and a high-speed planetary ball mill as well as optimizing ball milling parameters and medium selection, so that the powder with finer particle size and more uniform dispersion is obtained.
3. Vacuum hot pressing is adopted for sintering, and high-quality silicon nitride ceramics with high density, uniform microstructure and controllable phase composition are successfully prepared through reasonable process parameter setting.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic view of the process for preparing the silicon nitride ceramic material of the present invention.
Fig. 2 is a schematic view showing a structure in which the mixed powder of the present invention is charged into a graphite mold.
FIG. 3 is a schematic view of the SEM microstructure according to the first embodiment of the invention.
FIG. 4 is a SEM microstructure morphology of a second embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
As shown in fig. 1, an embodiment of the present invention is a method for preparing low-k, high-strength silicon nitride, comprising the steps of:
s1: selection of the raw materials, in one example, by natureThe weight percentage of the alpha-phase silicon nitride powder is 90 to 95 percent, MgO is 0.5 to 3 percent, and Al is 0.2 to 1.5 percent 2 O 3 1% -6% of SiO 2 0.2% -1% of Y 2 O 3 And 1-5% of beta-phase silicon nitride powder is added into a liquid medium, and ultrasonic dispersion is carried out for 20-60 min to obtain first mixed powder.
Wherein the purity of alpha-phase silicon nitride powder is not less than 4N, the alpha-phase content is 92-95%, D50 is 0.5-5 μm, the purity of MgO is not less than 3N, D50 is 0.5-2 μm, Al 2 O 3 Purity of not less than 4N, D50 ≥ 0.5 μm-2 μm, SiO 2 Purity of not less than 3N, D50 ≥ 0.2 μm-2 μm, Y 2 O 3 The purity of the beta-phase silicon nitride powder is not less than 4N, D50 but 0.2-2 mu m, and the purity of the beta-phase silicon nitride powder is not less than 4N, D50 but 0.5-5 mu m.
D50 shows that, among all the particles having the particle diameters in the sample, the ratio of the data particle size described above in D50 was 50%, and the ratio of the data particle size described below in D50 was also 50%.
And then adding the first mixed powder and the suspension into a ball milling tank body adapted to a planetary ball mill, and processing to obtain second mixed powder.
And the ball milling tank body is a polyurethane tank or a nylon tank.
In one example, the ball milling speed of the planetary ball mill is 200r/min-400r/min, the ball milling time is 4h-16h, and the loading capacity is 1/3-2/3 of the volume of the ball milling tank body.
The selected grinding balls are high-purity silicon nitride balls, the sizes of the grinding balls comprise phi 3mm, phi 6mm and phi 10mm, when the grinding ball mill is used, three grinding balls with different sizes are added into the ball milling tank body together with powder, and the ratio of the three added grinding balls is 3-5: 2-4, so that the grinding effect of the powder is facilitated.
S2: and (4) pretreating the powder in the step S1, performing vacuum drying on the ball-milled second mixed powder, wherein in one example, the required drying temperature is 40-120 ℃, the drying time is 8-24 h, screening the powder after the powder is completely dried, and selecting one of 80-150 meshes as a screen mesh for reducing powder agglomeration and enabling the powder to be more uniform. Thereby obtaining a dried third mixed powder.
S3: filling the powder in the step S2, as shown in fig. 2, selecting a graphite mold 1, spraying a high temperature resistant release agent on both the bottom and the side wall of the cavity 2 of the graphite mold 1, then padding graphite paper 3 on the bottom and the side wall of the cavity 2 of the graphite mold 1, and spraying a high temperature resistant release agent on both surfaces of the graphite paper 3, at this time, calculating the weight of the third mixed powder according to the product requirement, adding the powder to the graphite paper 3 in the cavity 2 in a fractional manner, adjusting the powder to be flat when the powder is added to the graphite paper 3 in a fractional manner each time, and then covering the graphite paper 3 on the powder.
S4: and S3, performing hot-pressing sintering on the graphite mold 1 containing the powder, placing the graphite mold 1 at a corresponding position below a pressure head of a vacuum hot-pressing furnace, performing pre-pressing, vacuum hot-pressing and sintering on the graphite mold 1, and finally cooling to the normal temperature along with the furnace, specifically, in one example, pre-pressing the graphite mold 1 by 0.5Mpa-2MPa, vacuumizing a furnace body to below 800Pa, heating to 450 ℃ -650 ℃ at 5 ℃/min-10 ℃/min, and preserving heat for 1h-4 h.
Then heating to 1000-1200 ℃ at the speed of 3-8 ℃/min, and preserving heat for 0.5-4 h; then the vacuum system is closed, high-purity N2 is introduced until the pressure is balanced, and the temperature is raised to 1650-1750 ℃ at the speed of 2-5 ℃/min.
Boosting the pressure to 15-35 MPa, and keeping the temperature for 1-6 h; after the heat preservation is finished, the pressure is removed, and the temperature is reduced to 1400-1600 ℃ at the speed of 2-5 ℃/min.
S5: and (3) forming the product, taking out the silicon nitride blank after the mold is cooled, and machining the silicon nitride blank to meet the requirement of the required product.
The technical scheme of the invention provides a preparation method of silicon nitride with low dielectric constant and high strength. Selecting SiO 2 、Al 2 O 3 、Y 2 O 3 And at least three of MgO are used as sintering auxiliary agents, alpha-phase silicon nitride is used as a main material, and beta-phase silicon nitride with a certain mass fraction is introduced as a seed crystal. The main system has the advantages of MgO and Al 2 O 3 The composite phase is obviously reduced to the sintering temperature and promotedThe material densification and SiO treatment are advanced 2 Si with similar physicochemical properties to silicon nitride in-situ generation 2 N 2 O、Y 2 O 3 And the addition of beta-phase silicon nitride is beneficial to adjusting the phase composition of the material. Because of higher oxidation resistance and corrosion resistance, the dielectric constant and the dielectric loss value are lower, and the CET is almost the same as the Si 2 N 2 The generation of the O phase and the adjustable composition of the silicon nitride phase ensure that the silicon nitride ceramic has better and excellent comprehensive properties compared with other sintering aid systems, and can be used as a focusing ring of a semiconductor device due to the characteristics of low dielectric constant, low dielectric loss and high strength.
According to the invention, a reasonable sintering auxiliary agent system is selected, so that the hardness, the bending strength and the fracture toughness of the silicon nitride ceramic are ensured, the oxidation resistance and the corrosion resistance of the silicon nitride ceramic are improved, and the dielectric constant and the dielectric loss value of the silicon nitride ceramic are reduced.
The powder is crushed and dispersed by adopting ultrasonic dispersion and a high-speed planetary ball mill together with optimized ball milling parameters and medium selection, so that the powder with finer particle size and more uniform dispersion is obtained.
Vacuum hot pressing is adopted for sintering, and high-quality silicon nitride ceramics with high compactness, uniform microstructure and controllable phase composition are successfully prepared through reasonable process parameter setting.
With reference to the above implementation contents, the technical solutions of the present application are exemplified for the sake of clarity and easy understanding, but it should be noted that the contents to be protected by the present application are not limited to the following examples 1 to 5.
Example 1
As shown in FIGS. 1 to 4, 90 mass% of alpha-phase silicon nitride powder (purity. gtoreq.4N, alpha-phase content 95%, D50 ═ 0.8 μm), 1.5 mass% of MgO (purity. gtoreq.3 3N, D50 ≥ 0.2 μm), and 1 mass% of Al 2 O 3 (purity. gtoreq.4 4N, D50 ═ 0.5 μm), 5% SiO 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1% Y 2 O 3 Adding beta-phase silicon nitride powder (purity is not less than 4N, D50 ═ 0.5μm) with purity not less than 4N, D50 ≥ 0.2 μm and 1.5% into liquid medium, and ultrasonic dispersing for 30min, then adding the suspension into a planetary ball mill tank. Wherein the ball-material ratio is 2: 1, the ball milling rotating speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2 of the volume of the ball milling tank. The proportion of large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: 3, and the ball milling tank body is a nylon tank.
And (3) carrying out vacuum drying on the powder subjected to ball milling at the drying temperature of 60 ℃ for 14h, and sieving the completely dried powder by using a 100-mesh sieve.
The screened powder is loaded into a hot-pressing graphite die 1 after calculating the required weight according to the size of a product, graphite paper 3 is firstly padded at the bottom and around the inside of the die when the die is loaded, the powder is added into a graphite cavity in multiple times, each layer is added to enable the powder to be smooth, then the graphite paper 3 is placed, and the graphite die 1 and the graphite paper 3 are uniformly sprayed with a high-temperature-resistant release agent.
The graphite mold 1 is arranged under a pressure head of a vacuum hot-pressing furnace, and the mold is pre-pressed for 1MPa, and sintering parameters are set. Firstly, vacuumizing a furnace body to below 400Pa, heating to 650 ℃ at the speed of 10 ℃/min, and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and preserving heat for 0.5 h; then closing the vacuum system, introducing high-purity N2 to pressure balance, and heating to 1700 ℃ at the speed of 5 ℃/min; boosting the pressure to 20MPa, and keeping the temperature for 1.5 h; after the heat preservation is finished, removing the pressure, and cooling to 1400 ℃ at the speed of 5 ℃/min; and then, after the temperature is reduced to room temperature along with the furnace, taking out the die for demoulding operation, and carrying out various machining on the silicon nitride blank to meet the requirements of the required product.
Example 2
Alpha-phase silicon nitride powder (purity is more than or equal to 4N, alpha-phase content is 95%, D50 is 0.8 mu m), 2% MgO (purity is more than or equal to 3N, D50 is 0.2 mu m), and 1% Al with the mass fraction of 90% 2 O 3 (purity. gtoreq.4 4N, D50 ═ 0.5 μm), 5% SiO 2 Adding beta-phase silicon nitride powder (purity is not less than 3N, D50 ═ 0.2 μm) and 2% (purity is not less than 4N, D50 ═ 0.5 μm) into liquid medium, carrying out ultrasonic dispersion for 30min, and then adding the suspension into a planetary ball mill. Wherein the ball-material ratio is 2: 1, the ball milling rotation speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2 of the volume of the ball milling tank. Selecting three sizes of phi 3mm, phi 6mm and phi 10mmThe proportion of the ball milling tank is 3: 4: 3, and the ball milling tank body is a nylon tank.
And (3) carrying out vacuum drying on the powder subjected to ball milling at the drying temperature of 60 ℃ for 14h, and sieving the completely dried powder by using a 100-mesh sieve.
The screened powder is loaded into a hot-pressing graphite die 1 after calculating the required weight according to the size of a product, graphite paper 3 is firstly padded at the bottom and around the inside of the die when the die is loaded, the powder is added into a graphite cavity in multiple times, each layer is added to enable the powder to be smooth, then the graphite paper 3 is placed, and the graphite die 1 and the graphite paper 3 are uniformly sprayed with a high-temperature-resistant release agent.
And placing the graphite mold 1 under a pressure head of a vacuum hot-pressing furnace, pre-pressing the mold for 1MPa, and setting sintering parameters. Firstly, vacuumizing a furnace body to be below 100Pa, heating to 650 ℃ at the speed of 10 ℃/min, and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and preserving heat for 0.5 h; then closing the vacuum system, introducing high-purity N2 to pressure balance, and heating to 1700 ℃ at the speed of 5 ℃/min; boosting the pressure to 20MPa, and keeping the temperature for 1.5 h; after the heat preservation is finished, removing the pressure, and cooling to 1400 ℃ at the speed of 5 ℃/min; and then, after the temperature is reduced to room temperature along with the furnace, taking out the die for demoulding operation, and carrying out various machining on the silicon nitride blank to meet the requirements of the required product.
Example 3
Alpha-phase silicon nitride powder (purity is more than or equal to 4N, alpha-phase content is 95 percent, D50 is 0.8 mu m), MgO (purity is more than or equal to 3N, D50 is 0.2 mu m) with the mass fraction of 90 percent, and SiO with the mass fraction of 5 percent 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1.5% Y 2 O 3 Adding beta-phase silicon nitride powder (purity is more than or equal to 4, 4N, D50 and less than or equal to 0.2 mu m) with the purity of 1.5 percent (purity is more than or equal to 4, 4N, D50 and less than or equal to 0.5 mu m) into a liquid medium for ultrasonic dispersion for 30min, and then adding the suspension into a planetary ball mill. Wherein the ball-material ratio is 2: 1, the ball milling rotating speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2 of the volume of the ball milling tank. The proportion of large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: 3, and the ball milling tank body is a nylon tank.
And (3) carrying out vacuum drying on the powder subjected to ball milling at the drying temperature of 60 ℃ for 14h, and sieving the completely dried powder by using a 100-mesh sieve.
Calculating the required weight of the screened powder according to the product size, then loading the powder into a hot-pressing graphite mould 1, filling graphite paper 3 at the bottom and around the inside of the mould during mould loading, adding the powder into a graphite cavity in multiple times, leveling the powder when adding each layer, then placing the graphite paper 3, and uniformly spraying a high-temperature-resistant release agent on the graphite mould 1 and the graphite paper 3.
The graphite mold 1 is arranged under a pressure head of a vacuum hot-pressing furnace, and the mold is pre-pressed for 1MPa, and sintering parameters are set. Firstly, vacuumizing a furnace body to be below 100Pa, heating to 650 ℃ at the speed of 10 ℃/min, and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and preserving heat for 0.5 h; then closing the vacuum system, introducing high-purity N2 to pressure balance, and heating to 1700 ℃ at the speed of 5 ℃/min; boosting the pressure to 20MPa, and keeping the temperature for 1.5 h; after the heat preservation is finished, removing the pressure, and cooling to 1400 ℃ at the speed of 5 ℃/min; and then, after the temperature is reduced to room temperature along with the furnace, taking out the die for demoulding, and carrying out various machining on the silicon nitride blank to meet the requirements of the required product.
Example 4
Alpha-phase silicon nitride powder (purity is more than or equal to 4N, alpha-phase content is 95%, D50 is 0.8 mu m), 1.5% MgO (purity is more than or equal to 3N, D50 is 0.2 mu m), and 1% Al with the mass fraction of 90% 2 O 3 (purity. gtoreq.4 4N, D50 ═ 0.5 μm), 5% SiO 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1% Y 2 O 3 Adding beta-phase silicon nitride powder (purity is not less than 4N, D50-0.5 mu m) with the purity being not less than 4N, D50-0.2 mu m and 1.5% into a liquid medium for ultrasonic dispersion for 30min, and then adding the suspension into a planetary ball mill tank. Wherein the ball-material ratio is 2: 1, the ball milling rotating speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2 of the volume of the ball milling tank. The proportion of large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: 3, and the ball milling tank body is a nylon tank.
And (3) carrying out vacuum drying on the powder subjected to ball milling at the drying temperature of 60 ℃ for 14h, and sieving the completely dried powder by using a 100-mesh sieve.
The screened powder is loaded into a hot-pressing graphite die 1 after calculating the required weight according to the size of a product, graphite paper 3 is firstly padded at the bottom and around the inside of the die when the die is loaded, the powder is added into a graphite cavity in multiple times, each layer is added to enable the powder to be smooth, then the graphite paper 3 is placed, and the graphite die 1 and the graphite paper 3 are uniformly sprayed with a high-temperature-resistant release agent.
The graphite mold 1 is arranged under a pressure head of a vacuum hot-pressing furnace, and the mold is pre-pressed for 1MPa, and sintering parameters are set. Firstly, vacuumizing a furnace body to be below 100Pa, heating to 650 ℃ at the speed of 10 ℃/min, and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and preserving heat for 0.5 h; then closing the vacuum system, introducing high-purity N2 to pressure balance, and heating to 1700 ℃ at the speed of 5 ℃/min; boosting the pressure to 20MPa, and keeping the temperature for 1 h; after the heat preservation is finished, removing the pressure, and cooling to 1400 ℃ at the speed of 5 ℃/min; and then, after the temperature is reduced to room temperature along with the furnace, taking out the die for demoulding operation, and carrying out various machining on the silicon nitride blank to meet the requirements of the required product.
Example 5
Alpha-phase silicon nitride powder (purity is more than or equal to 4N, alpha-phase content is 95%, D50 is 0.8 mu m), 1% MgO (purity is more than or equal to 3N, D50 is 0.2 mu m), and 5% SiO with mass fraction of 92% 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1% Y 2 O 3 Adding beta-phase silicon nitride powder (purity is not less than 4N, D50 and not more than 0.5 mu m) with the purity being not less than 4N, D50 and the purity being not less than 0.2 mu m into a liquid medium for ultrasonic dispersion for 30min, and then adding the suspension into a planetary ball mill pot. Wherein the ball-material ratio is 2: 1, the ball milling rotating speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2 of the volume of the ball milling tank. The proportion of large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: 3, and the ball milling tank body is a nylon tank.
And (3) carrying out vacuum drying on the powder subjected to ball milling at the drying temperature of 60 ℃ for 14h, and sieving the completely dried powder by using a 100-mesh sieve.
Calculating the required weight of the screened powder according to the product size, then loading the powder into a hot-pressing graphite mould 1, filling graphite paper 3 at the bottom and around the inside of the mould during mould loading, adding the powder into a graphite cavity in multiple times, leveling the powder when adding each layer, then placing the graphite paper 3, and uniformly spraying a high-temperature-resistant release agent on the graphite mould 1 and the graphite paper 3.
The graphite mold 1 is arranged under a pressure head of a vacuum hot-pressing furnace, and the mold is pre-pressed for 1MPa, and sintering parameters are set. Firstly, vacuumizing a furnace body to be below 100Pa, heating to 650 ℃ at the speed of 10 ℃/min, and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and preserving heat for 0.5 h; then closing the vacuum system, introducing high-purity N2 to pressure balance, and heating to 1700 ℃ at the speed of 5 ℃/min; boosting the pressure to 20MPa, and keeping the temperature for 1.5 h; after the heat preservation is finished, removing the pressure, and cooling to 1400 ℃ at the speed of 5 ℃/min; and then, after the temperature is reduced to room temperature along with the furnace, taking out the die for demoulding operation, and carrying out various machining on the silicon nitride blank to meet the requirements of the required product.
Comparative example 1
Alpha-phase silicon nitride powder (purity is more than or equal to 4N, alpha-phase content is 95%, D50 is 0.8 mu m), 1.5% MgO (purity is more than or equal to 3N, D50 is 0.2 mu m), and 1% Al with the mass fraction of 90% 2 O 3 (purity. gtoreq.4 4N, D50 ═ 0.5 μm), 5% SiO 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1% Y 2 O 3 Adding beta-phase silicon nitride powder (the purity is not less than 4N, D50 and not less than 0.2 mu m) with the purity being not less than 4, N, D50 and 1.5 percent (the purity is not less than 4, N, D50 and not more than 0.5 mu m) into a liquid medium for ultrasonic dispersion for 30min, and then adding the suspension into a planetary ball milling tank, wherein the ball-material ratio is 2: 1, the ball milling rotating speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2. The proportion of large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: and 3, selecting a ball milling tank body as a nylon tank.
And carrying out spray granulation treatment on the uniformly mixed composite powder. Selecting PVA as a binder, adding PVA with the weight of 1.2% of the powder into deionized water, adding the powder into the solution after the PVA is fully dissolved, and continuously stirring the mixture in the adding process to form uniform suspension with the solid content of 65%; and then polyethylene glycol in an amount of 0.5% by weight of the powder and polyether-modified silicon in an amount of 0.2% by weight of the powder are added. And (4) fully mixing the suspension, and then carrying out spray granulation, wherein the feeding mode is a peristaltic pump feeding mode. The granulation parameters are as follows: the temperature of the air inlet is set to 280 ℃, the temperature of the air outlet is set to 100 ℃, and the rotating speed of the centrifugal disc is 8500 r/min; the obtained granulated powder had a particle size of 200 mesh, a water content of 1.2%, a bulk density of 4.54g/cm3, and a flowability of 35 s.
And (3) carrying out cold press molding on the granulated powder, wherein the molding pressure is 180MPa, and the pressure maintaining time is 5min, so that a biscuit with certain strength is obtained.
Carrying out pressureless N2 protective sintering on the biscuit, firstly, vacuumizing a furnace body to be below 100Pa, heating to 650 ℃ at the speed of 10 ℃/min, and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and keeping the temperature for 0.5 h; and then closing the vacuum system, introducing high-purity N2, heating to 1700 ℃ at the speed of 5 ℃/min, preserving heat for 1.5h to obtain a silicon nitride blank, and machining to obtain the product.
Comparative example 2
Alpha-phase silicon nitride powder (purity is more than or equal to 4N, alpha-phase content is 95%, D50 is 0.8 mu m), 1.5% MgO (purity is more than or equal to 3N, D50 is 0.2 mu m), and 1% Al with the mass fraction of 90% 2 O 3 (purity. gtoreq.4 4N, D50 ═ 0.5 μm), 5% SiO 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1% Y 2 O 3 Adding beta-phase silicon nitride powder (the purity is not less than 4N, D50 and not less than 0.2 mu m) with the purity being not less than 4N, D50 and the purity is not less than 4N, D50 and not more than 0.5 mu m) into a liquid medium for ultrasonic dispersion for 30min, and then adding the suspension into a planetary ball milling tank, wherein the ball-material ratio is 2: 1, the ball milling speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2. The proportion of large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: 3, and the ball milling tank body is a nylon tank.
And carrying out spray granulation treatment on the uniformly mixed composite powder. Selecting PVA as a binder, adding PVA with the weight of 1.2% of the powder into deionized water, adding the powder into the solution after the PVA is fully dissolved, and continuously stirring the mixture in the adding process to form uniform suspension with the solid content of 65%; and then polyethylene glycol in an amount of 0.5% by weight of the powder and polyether-modified silicon in an amount of 0.2% by weight of the powder are added. And (4) fully mixing the suspension, and then carrying out spray granulation, wherein the feeding mode is peristaltic pump feeding. The granulation parameters are as follows: the temperature of the air inlet is set to 280 ℃, the temperature of the air outlet is set to 100 ℃, and the rotating speed of the centrifugal disc is 8500 r/min; the obtained granulated powder had a particle size of 200 mesh, a water content of 1.2%, a bulk density of 4.54g/cm3, and a flowability of 35 s.
And (3) performing cold press molding on the granulation powder, wherein the molding pressure is 180MPa, and the pressure maintaining time is 5min, so that a biscuit with certain strength is obtained.
Sintering the biscuit in air pressure, firstly introducing high-purity N2 into a furnace body until the pressure in the furnace reaches 0.5MPa, firstly heating to 650 ℃ at a speed of 10 ℃/min and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and preserving heat for 0.5 h; and continuously introducing N2 to ensure that the pressure in the furnace reaches 1MPa, heating to 1700 ℃ at the speed of 5 ℃/min, preserving the heat for 1.5h to obtain a silicon nitride blank, and machining to obtain the product.
Comparative example 3
Alpha-phase silicon nitride powder (purity is more than or equal to 4N, alpha-phase content is 95%, D50 is 0.8 mu m), 1.5% MgO (purity is more than or equal to 3N, D50 is 0.2 mu m), and 1% Al with the mass fraction of 90% 2 O 3 (purity. gtoreq.4 4N, D50 ═ 0.5 μm), 5% SiO 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1% Y 2 O 3 Adding beta-phase silicon nitride powder (the purity is not less than 4N, D50 and not less than 0.2 mu m) with the purity being not less than 4, N, D50 and 1.5 percent (the purity is not less than 4, N, D50 and not more than 0.5 mu m) into a liquid medium for ultrasonic dispersion for 30min, and then adding the suspension into a planetary ball milling tank, wherein the ball-material ratio is 2: 1, the ball milling rotating speed is 250r/min, the ball milling time is 8h, and the loading capacity is 1/2. The proportion of large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: 3, and the ball milling tank body is a nylon tank.
And carrying out spray granulation treatment on the uniformly mixed composite powder. Selecting PVA as a binder, adding PVA with the weight of 1.2% of the powder into deionized water, adding the powder into the solution after the PVA is fully dissolved, and continuously stirring the mixture in the adding process to form uniform suspension with the solid content of 65%; and then polyethylene glycol in an amount of 0.5% by weight of the powder and polyether-modified silicon in an amount of 0.2% by weight of the powder are added. And (4) fully mixing the suspension, and then carrying out spray granulation, wherein the feeding mode is peristaltic pump feeding. The granulation parameters are as follows: the temperature of the air inlet is set to 280 ℃, the temperature of the air outlet is set to 100 ℃, and the rotating speed of the centrifugal disc is 8500 r/min; the obtained granulated powder had a particle size of 200 mesh, a water content of 1.2%, a bulk density of 4.54g/cm3, and a flowability of 35 s.
And (3) performing cold press molding on the granulation powder, wherein the molding pressure is 180MPa, and the pressure maintaining time is 5min, so that a biscuit with certain strength is obtained.
And (3) sintering the biscuit in an SPS mode, pre-vacuumizing the sintering equipment to be below 100Pa, closing a vacuum system and introducing N2. Firstly, heating to 1000 ℃ at a heating rate of 150 ℃/min, and preserving heat for 5 min; and then heating to 1700 ℃ at the heating rate of 200 ℃/min, preserving the heat for 10min to obtain a silicon nitride blank, and machining to obtain the product.
Comparative example 4
The mass fraction of 90 percent of a-phase silicon nitride powder (the purity is more than or equal to 4N, a phase content is less than or equal to 90 percent, D50 is 0.8 mu m), 1.5 percent of MgO (the purity is more than or equal to 3N, D50 is 0.2 mu m), and 1 percent of Al 2 O 3 (purity. gtoreq.4 4N, D50 ═ 0.5 μm), 5% SiO 2 (purity. gtoreq.3 3N, D50 ═ 0.2 μm), 1% Y 2 O 3 (purity is not less than 4N, D50 and not more than 0.2 mu m), 1.5 percent of beta-phase silicon nitride powder (purity is not less than 4N, D50 and not more than 0.5 mu m) is added into a liquid medium for ultrasonic dispersion for 30min, and then the suspension is added into a planetary ball milling tank, wherein the ball-material ratio is 2: 1, the ball milling rotating speed is 250r/min, the ball milling time is 8h, and the loading capacity is the volume of the ball milling tank 1/2. The proportion of the large, medium and small sizes of phi 3mm, phi 6mm and phi 10mm is 3: 4: 3, and the selected ball mill tank body is a nylon tank.
And carrying out spray granulation treatment on the uniformly mixed composite powder. Selecting PVA as a binder, adding PVA with the weight of 1.2% of the powder into deionized water, adding the powder into the solution after the PVA is fully dissolved, and continuously stirring the mixture in the adding process to form uniform suspension with the solid content of 65%; and then polyethylene glycol in an amount of 0.5% by weight of the powder and polyether-modified silicon in an amount of 0.2% by weight of the powder are added. And (4) fully mixing the suspension, and then carrying out spray granulation, wherein the feeding mode is peristaltic pump feeding. The granulation parameters are as follows: the temperature of the air inlet is set to 280 ℃, the temperature of the air outlet is set to 100 ℃, and the rotating speed of the centrifugal disc is 8500 r/min; the obtained granulated powder had a particle size of 200 mesh, a water content of 1.2%, a bulk density of 4.54g/cm3, and a flowability of 35 s.
And (3) carrying out cold press molding on the granulated powder, wherein the molding pressure is 180MPa, and the pressure maintaining time is 5min, so that a biscuit with certain strength is obtained.
Carrying out pressureless N2 protection sintering on the biscuit, firstly, vacuumizing a furnace body to be below 100Pa, heating to 650 ℃ at the speed of 10 ℃/min, and preserving heat for 2 h; then heating to 1000 ℃ at the speed of 7 ℃/min, and keeping the temperature for 0.5 h; and then closing the vacuum system, introducing high-purity N2, heating to 1700 ℃ at the speed of 5 ℃/min, preserving heat for 1.5h to obtain a silicon nitride blank, and machining to obtain the product.
Performance test
The silicon nitrides of examples 1-5 and comparative examples 1-4 were tested for compactness, flexural strength, dielectric constant, and α → β phase transformation ratio, with specific data shown in table 1.
TABLE 1 data of performance tests on silicon nitride of examples 1-5 and comparative examples 1-4
Density/% Flexural strength/MPa Dielectric constant α → β transformation ratio/%)
Example 1 99.7 1201 4.5 100
Example 2 99.5 1185 5.2 100
Example 3 99.6 1194 4.8 100
Example 4 99.5 1123 6.2 90.1
Example 5 99.6 1159 5.9 95.4
Comparative example 1 90.8 574 2.3 100
Comparative example 2 98.7 728 3.9 100
Comparative example 3 99.5 964 7.1 48.6
Comparative example 4 98.1 1059 3.7 93.7
It can be seen from the performance test data in table 1 that in examples 1 to 3, silicon nitride products with high density, high flexural strength and low dielectric constant can be obtained according to the sintering system specified in the present invention and different system proportions and selections.
From example 4, it can be seen that the phase transformation ratio of a-phase silicon nitride → β -phase silicon nitride can be controlled by controlling the sintering parameters, and silicon nitride products with different overall properties can be obtained.
From example 5, it can be seen that the phase transformation ratio of the a-phase silicon nitride → the β -phase silicon nitride can be controlled by the selection and proportion of the sintering system, so as to obtain silicon nitride products with different overall properties.
As can be seen from comparative example 1, pressureless sintered silicon nitride has a low density, and the bending strength is low due to a large amount of internal porosity although the phase transition is completed by 100%; the main reason for the low dielectric constant is also the presence of more pores in the product.
As can be seen from example 1 and comparative example 2, the density and bending strength of the gas pressure sintered silicon nitride were poor, and the low dielectric constant was caused by the large number of internal pores.
As can be seen from comparative example 3, although the silicon nitride has a high degree of compactness, the sintering time is short, the phase transformation ratio of the alpha-phase silicon nitride to the beta-phase silicon nitride is low, and Si 2 N 2 The less amount of O produced results in lower bending strength and higher dielectric constant of the product.
Comparative example 4 shows that the selected raw materials have important influence on the sintering process, because the silicon nitride sintering process is liquid phase sintering, the sintering driving force is mainly liquid phase and phase change, and the sintering phase change driving force is weakened when the alpha phase of the selected raw material is lower, so that the densification process is not facilitated, and the bending strength of the product is lower.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A preparation method of silicon nitride with low dielectric constant and high strength is characterized by comprising the following steps:
s1: selecting raw materials, namely, 90 to 95 mass percent of alpha-phase silicon nitride powder, 0.5 to 3 mass percent of MgO and 0.2 to 1.5 mass percent of Al 2 O 3 1% -6% of SiO 2 0.2% -1% of Y 2 O 3 1% -5% of beta-phase silicon nitride powder is added into a liquid medium, and ultrasonic dispersion is carried out for 20min-60min to obtain first mixed powder;
adding the first mixed powder and the suspension into a ball milling tank body adapted to a planetary ball mill, and processing to obtain second mixed powder;
s2: pre-treating, namely drying the second mixed powder in vacuum, and screening the powder after the powder is completely dried to obtain third mixed powder;
s3: filling a mold, namely selecting a graphite mold, filling graphite paper on the bottom and the side wall of a cavity of the graphite mold, calculating the weight of the third mixed powder according to the product requirement, adding the powder to the graphite paper in the cavity in a grading manner, and covering the graphite paper on the powder;
s4: hot-pressing sintering, namely placing the graphite mold at a corresponding position below a pressure head of a vacuum hot-pressing furnace, prepressing, vacuum hot-pressing and sintering the graphite mold, and finally cooling the graphite mold to normal temperature along with the furnace;
s5: and (4) forming, after the mould is cooled, taking out the silicon nitride blank, and machining the silicon nitride blank to meet the requirement of the required product.
2. The method as claimed in claim 1, wherein the α -phase silicon nitride powder has a purity of 4N or more, an α -phase content of 92 to 95%, a D50 of 0.5 to 5 μm, a MgO purity of 3N, D50 of 0.5 to 2 μm, and Al 2 O 3 Purity of not less than 4N, D50 ≥ 0.5 μm-2 μm, SiO 2 The purity of (A) is not less than 3N, D50 ≥ 0.2 μm-2 μm, Y 2 O 3 The purity of the beta-phase silicon nitride powder is not less than 4N, D50 but 0.2-2 mu m, and the purity of the beta-phase silicon nitride powder is not less than 4N, D50 but 0.5-5 mu m.
3. The method for preparing silicon nitride with low dielectric constant and high strength as claimed in claim 1, wherein the ball milling rotation speed of the planetary ball mill is 200r/min-400r/min, the ball milling time is 4h-16h, and the loading capacity is 1/3-2/3 of the volume of the ball milling tank.
4. The method for preparing silicon nitride with low dielectric constant and high strength according to claim 3, wherein the planetary ball mill selects the high-purity silicon nitride balls as the grinding balls, the sizes of the high-purity silicon nitride balls comprise phi 3mm, phi 6mm and phi 10mm, and the ratio of the grinding balls added into the ball mill tank body is 3-5: 2-4.
5. The method of claim 1, wherein the ball mill pot is a polyurethane pot or a nylon pot.
6. The method of claim 1, wherein the drying temperature is 40-120 ℃ and the drying time is 8-24 h in S2.
7. The method of claim 1, wherein the screen mesh used in the screening process is 80-150 mesh.
8. The method of claim 1, wherein the graphite paper is leveled after each powder is added to the graphite paper.
9. The method of claim 1, wherein a high temperature release agent is sprayed on the bottom and side walls of the cavity of the graphite mold and on both surfaces of the graphite paper.
10. The method for preparing silicon nitride with low dielectric constant and high strength according to claim 1, wherein in S4, the graphite mold is pre-pressed to 0.5Mpa-2Mpa, the furnace body is vacuumized to below 800Pa, the temperature is raised to 450 ℃ -650 ℃ at 5 ℃/min-10 ℃/min, and the temperature is maintained for 1h-4 h;
then heating to 1000-1200 ℃ at the speed of 3-8 ℃/min, and preserving heat for 0.5-4 h; then closing the vacuum system, introducing high-purity N2 to pressure balance, and heating to 1650-1750 ℃ at a speed of 2-5 ℃/min;
boosting the pressure to 15-35 MPa, and keeping the temperature for 1-6 h; after the heat preservation is finished, the pressure is removed, and the temperature is reduced to 1400-1600 ℃ at the speed of 2-5 ℃/min.
CN202210565829.0A 2022-05-23 2022-05-23 Preparation method of low-dielectric-constant and high-strength silicon nitride Pending CN114907129A (en)

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