Silicon nitride target material and preparation method thereof

Abstract

The invention provides a silicon nitride target material and a preparation method thereof, and the preparation method comprises the following steps: carrying out cold isostatic pressing on silicon nitride powder, and then carrying out hot pressed sintering at segmented temperatures to obtain the silicon nitride target material. According to the preparation method provided by the invention, isostatic cool pressing and hot pressing sintering at segmented temperatures are combined, the densification of the silicon nitride target material is realized by reasonably regulating and controlling the hot pressing sintering process, a sintering aid does not need to be added, and the obtained silicon nitride target material is high in purity, high in density and excellent in processability and can meet the use requirements of the target material.

Description

Technical Field

[0001] The invention belongs to the technical field of target material preparation, and specifically relates to a silicon nitride target material and a preparation method thereof. Background Art

[0002] Silicon nitride film has a high dielectric constant, insulation strength, and the ability to block sodium ions and water molecules. It is used as a passivation film and isolation dielectric layer in microelectronic devices. At the same time, silicon nitride film also has mechanical and mechanical properties such as corrosion resistance, good thermal insulation, fatigue resistance, and friction resistance. It is used as a corrosion masking layer, thermal insulation layer, mechanical structure layer or wear-resistant layer in micro-electromechanical systems. The preparation of silicon nitride film by magnetron sputtering is inseparable from silicon nitride targets with good performance.

[0003] Silicon nitride is a compound mainly composed of covalent bonds, with a Si-N covalent bond content of up to 70%. Silicon nitride powder will decompose at 1700°C, and its own sintering self-diffusion coefficient is small. It is difficult to obtain high-density silicon nitride by general atmospheric pressure sintering. Therefore, hot pressing sintering, gas pressure sintering, hot isostatic pressing sintering and other processes are often used. Gas pressure sintering can rely on high-pressure nitrogen (1-10MPa) to inhibit the decomposition of silicon nitride. The sintering temperature can be increased to 1900°C to promote densification, but too high a temperature will cause abnormal grain growth and aggravate decomposition, resulting in an increase in micropores, defects, and density of silicon nitride after sintering. In addition, the gas pressure sintering time is long, and it is easy to have different colors inside and outside after sintering, and the structural uniformity is poor. Hot isostatic pressing (HIP) requires the use of higher gas pressure to achieve sintering without sintering aids. The process of sintering silicon nitride with sheathed HIP is complicated and the sintering cost is high. The required high-temperature glass sheath is disposable and difficult to make, and the overall cost of HIP is high. The rapid heating and cooling system during spark plasma sintering (SPS) will cause a large number of defects in the prepared silicon nitride ceramics, and the processing performance is poor, and subsequent heat treatment is required to eliminate the defects.

[0004] Hot pressing sintering generally applies axial mechanical pressure to the sintered material during the heating process to provide an additional sintering driving force for the densification of the material, which can increase the densification rate, reduce the sintering time, reduce the sintering temperature, and reduce the amount of sintering aids, thereby reducing the silicon nitride grain boundary glass phase to prevent processing cracks and reduce the impurity content. The shape of hot pressing sintering products is generally flat, which is just suitable for the shape of the target material such as the round piece / square plate.

[0005] CN111620697A discloses a silicon nitride substrate material prepared by hot pressing and sintering, which uses silicon nitride, silicon magnesium nitride and a sintering aid as raw materials, and after dry pressing and forming, hot pressing and sintering at 20-45MPa and 1700-1850°C to prepare a silicon nitride substrate. CN115677356A discloses a method for preparing a high-performance silicon nitride ceramic substrate, which mixes silicon nitride powder, additives and sintering aids for cold isostatic pressing, and then hot isostatic pressing and sintering at 160-200MPa and 1600-1700°C. In the prior art, the preparation of silicon nitride products still requires the addition of sintering aids to promote its densification, while silicon nitride targets have high requirements for purity and processing accuracy, and require that the silicon nitride sintering process be sintered without adding sintering aids. Therefore, it is necessary to provide a method for preparing a silicon nitride target material that does not require sintering aids and has excellent target performance. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a silicon nitride target material and a preparation method thereof, which can prepare a silicon nitride target material with high density and excellent performance without adding a sintering aid.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a silicon nitride target, the preparation method comprising the following steps:

[0009] The silicon nitride powder is cold isostatically pressed and then hot-pressed and sintered at different temperatures to obtain a silicon nitride target.

[0010] The preparation method provided by the present invention combines cold isostatic pressing and hot pressing sintering at staged temperatures, and realizes the densification of silicon nitride target by rationally regulating the hot pressing sintering process without adding sintering aids, thereby avoiding the influence of the aids on purity. The obtained silicon nitride target has high density and excellent processing performance, and can meet the requirements for target use.

[0011] Preferably, the purity of the silicon nitride powder is 99.9-99.99%, for example, it can be 99.9%, 99.92%, 99.94%, 99.95%, 99.96%, 99.98% or 99.99%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0012] Preferably, the D50 particle size of the silicon nitride powder is 1.0-1.2 μm, for example, 1.0 μm, 1.05 μm, 1.1 μm, 1.15 μm or 1.2 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] Preferably, the pressure of the cold isostatic pressing is 200-250 MPa, for example, 200 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa or 250 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0014] Preferably, the cold isostatic pressing time is 20-30 min, for example, 20 min, 22 min, 24 min, 25 min, 26 min, 28 min or 30 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] Preferably, the pressurization rate of the hot pressing sintering at the segmented temperature is 0.2-0.5 T / min, for example, it can be 0.2 T / min, 0.3 T / min, 0.4 T / min or 0.5 T / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] Preferably, the pressure of the hot pressing sintering at the segmented temperature is 40-60T, for example, it can be 40T, 42T, 45T, 48T, 50T, 52T, 55T, 58T or 60T, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Preferably, the temperature change rate of the hot pressing sintering of the segmented temperature is 2-15°C / min, for example, it can be 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 8°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min or 15°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] Preferably, the process of hot pressing sintering at staged temperatures includes: hot pressing sintering at a first sintering temperature, a second sintering temperature and a third sintering temperature in sequence.

[0019] Preferably, during the step-by-step hot-pressing sintering process, pressurization begins after the first sintering temperature is reached.

[0020] Preferably, the first sintering temperature is 1500-1600°C, for example, it can be 1500°C, 1520°C, 1540°C, 1550°C, 1560°C, 1580°C or 1600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the holding time of the first sintering temperature is 1-1.5h, for example, 1h, 1.1h, 1.2h, 1.3h, 1.4h or 1.5h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the second sintering temperature is 1700-1800°C, for example, it can be 1700°C, 1720°C, 1740°C, 1750°C, 1760°C, 1780°C or 1800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the holding time of the second sintering temperature is 2-4h, for example, it can be 2h, 2.2h, 2.5h, 2.8h, 3h, 3.2h, 3.5h, 3.8h or 4h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the third sintering temperature is 1200-1300°C, for example, it can be 1200°C, 1220°C, 1240°C, 1250°C, 1260°C, 1280°C or 1300°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the holding time of the third sintering temperature is 1-2h, for example, it can be 1h, 1.2h, 1.4h, 1.5h, 1.6h, 1.8h or 2h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] As a preferred technical solution of the preparation method provided by the present invention, the preparation method comprises the following steps:

[0027] (1) putting silicon nitride powder with a purity of 99.9-99.99% and a D50 particle size of 1.0-1.2 μm into a mold for cold isostatic pressing at a pressure of 200-250 MPa for a time of 20-30 min to obtain a target blank;

[0028] (2) placing the target blank obtained in step (1) into a mold, and placing it into a sintering device for sintering, maintaining a nitrogen atmosphere in the sintering device, first heating the temperature to 1500-1600°C at a heating rate of 10-15°C / min, starting to pressurize, pressurizing to 40-60T at a pressurizing rate of 0.2-0.5T / min, and then maintaining the pressure. At the same time, after maintaining the temperature at 1500-1600°C for 1-1.5h, heating the temperature to 1700-1800°C at a rate of 3-6°C / min, maintaining the temperature for 2-4h, and then cooling the temperature to 1200-1300°C at a cooling rate of 2-4°C / min, maintaining the temperature for 1-2h, and ending the heat preservation and pressure maintenance to obtain a silicon nitride target.

[0029] In a second aspect, the present invention provides a silicon nitride target material, which is prepared by the preparation method described in the first aspect.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The preparation method provided by the present invention combines cold isostatic pressing and hot pressing sintering at staged temperatures, and realizes the densification of silicon nitride target by rationally regulating the hot pressing sintering process without adding sintering aids. The obtained silicon nitride target has high purity, high density, and excellent processing performance, and can meet the requirements for target use. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0033] Example 1

[0034] This embodiment provides a method for preparing a silicon nitride target, and the preparation method comprises the following steps:

[0035] (1) Si3N4 powder with a purity of 99.95% and a D50 particle size of 1.1 μm was filled into a silica gel mold, compacted, the mold flatness was 1.0 mm, sealed, and then cold isostatically pressed at a pressure of 230 MPa for 25 min to obtain a target blank;

[0036] (2) Place the target blank in a graphite mold and fill it with BN powder around it to prevent the volatilized carbon elements from the graphite mold from penetrating into Si3N4. Place the graphite mold in the sintering furnace to ensure that it is horizontally centered. The equipment is vacuumed and the vacuum degree is reduced to 10 -2 Pa, fill with nitrogen to -0.1MPa, and evacuate to 10 -2 Pa, nitrogen was filled in to maintain the nitrogen atmosphere in the furnace chamber, and then the hot pressing sintering process was started. The temperature was raised to 1550°C at a rate of 12°C / min, and the pressurization was started when the temperature reached 1550°C. The pressure was increased to 50T at a rate of 0.4T / min and the pressure was maintained. At the same time, the temperature was maintained at 1550°C for 1.2h, and then the temperature was raised to 1750°C at a rate of 4°C / min, and the temperature was maintained for 3h. Then the temperature was lowered to 1250°C at a rate of 3°C / min, and the pressure was maintained for 1.5h. During this period, the pressure of 50T was always maintained. After the insulation was completed, the heating and pressurization were stopped, and the furnace was cooled;

[0037] (3) After sintering, the BN powder on the surface of the target blank is removed and the silicon nitride target is obtained after machining.

[0038] Example 2

[0039] This embodiment provides a method for preparing a silicon nitride target, and the preparation method comprises the following steps:

[0040] (1) Si3N4 powder with a purity of 99.95% and a D50 particle size of 1.0 μm was filled into a silica gel mold, compacted, the mold flatness was 1.0 mm, sealed, and then cold isostatically pressed at a pressure of 200 MPa for 30 min to obtain a target blank;

[0041] (2) Place the target blank in a graphite mold and fill it with BN powder around it to prevent the volatilized carbon elements from the graphite mold from penetrating into Si3N4. Place the graphite mold in the sintering furnace to ensure that it is horizontally centered. The equipment is vacuumed and the vacuum degree is reduced to 10 -2 Pa, fill with nitrogen to -0.1MPa, and evacuate to 10 -2 Pa, nitrogen was filled in to maintain the nitrogen atmosphere in the furnace chamber, and then the hot pressing sintering process was started. The temperature was raised to 1500°C at a rate of 10°C / min, and the pressurization was started when it reached 1500°C. The pressure was increased to 60T at a rate of 0.5T / min and the pressure was maintained. At the same time, the temperature was maintained at 1500°C for 1.5h, and then the temperature was raised to 1700°C at a rate of 3°C / min, and the temperature was maintained for 4h. Then the temperature was lowered to 1200°C at a rate of 2°C / min, and the temperature was maintained for 2h. During this period, the pressure of 60T was always maintained. After the insulation was completed, the heating and pressurization were stopped, and the furnace was cooled;

[0042] (3) After sintering, the BN powder on the surface of the target blank is removed and the silicon nitride target is obtained after machining.

[0043] Example 3

[0044] This embodiment provides a method for preparing a silicon nitride target, and the preparation method comprises the following steps:

[0045] (1) Si3N4 powder with a purity of 99.95% and a D50 particle size of 1.2 μm was filled into a silica gel mold, compacted, the mold flatness was 1.0 mm, sealed, and then cold isostatically pressed at a pressure of 250 MPa for 20 min to obtain a target blank;

[0046] (2) Place the target blank in a graphite mold and fill it with BN powder around it to prevent the volatilized carbon elements from the graphite mold from penetrating into Si3N4. Place the graphite mold in the sintering furnace to ensure that it is horizontally centered. The equipment is vacuumed and the vacuum degree is reduced to 10 -2 Pa, fill with nitrogen to -0.1MPa, and evacuate to 10 -2Pa, nitrogen was filled in to maintain the nitrogen atmosphere in the furnace chamber, and then the hot pressing sintering process was started. The temperature was raised to 1600°C at a rate of 15°C / min, and the pressurization was started when it reached 1600°C. The pressure was increased to 40T at a rate of 0.2T / min, and the temperature was kept at 1600°C for 1h. Then the temperature was raised to 1800°C at a rate of 6°C / min, and the temperature was kept for 2h. Then the temperature was lowered to 1300°C at a rate of 4°C / min, and the temperature was kept for 1h. During this period, the pressure of 40T was always maintained. After the insulation was completed, the heating and pressurization were stopped, and the furnace was cooled;

[0047] (3) After sintering, the BN powder on the surface of the target blank is removed and the silicon nitride target is obtained after machining.

[0048] Example 4

[0049] This embodiment provides a method for preparing a silicon nitride target. Compared with Embodiment 1, the pressure of the cold isostatic pressing in step (1) is controlled to be 180 MPa, and the rest is the same as Embodiment 1.

[0050] Example 5

[0051] This embodiment provides a method for preparing a silicon nitride target. Compared with Embodiment 1, the pressure of the cold isostatic pressing in step (1) is controlled to be 270 MPa, and the rest is the same as Embodiment 1.

[0052] Example 6

[0053] This embodiment provides a method for preparing a silicon nitride target. Compared with Embodiment 1, during the hot pressing sintering in step (2), heating and pressurizing are started simultaneously, and the rest are the same as Embodiment 1.

[0054] Example 7

[0055] This embodiment provides a method for preparing a silicon nitride target. Compared with Embodiment 1, during the hot pressing sintering process of step (2), sintering at the third sintering temperature of 1250° C. is not performed. The rest is the same as Embodiment 1.

[0056] Example 8

[0057] This embodiment provides a method for preparing a silicon nitride target. Compared with Embodiment 1, during the hot pressing sintering process of step (2), the first sintering temperature is controlled to be 1400° C., and the rest is the same as Embodiment 1.

[0058] Example 9

[0059] This embodiment provides a method for preparing a silicon nitride target. Compared with Embodiment 1, during the hot pressing sintering process of step (2), the second sintering temperature is controlled to be 1900° C., and the rest is the same as Embodiment 1.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a silicon nitride target. Compared with Example 1, the hot pressing sintering process in step (2) is as follows: heating and pressurizing at the same time, heating to 1700°C at a rate of 15°C / min, pressurizing to 50T at a rate of 0.4T / min, maintaining the temperature for 5h, and stopping heating and pressurizing after the end. The rest is the same as Example 1.

[0062] Comparative Example 2

[0063] This comparative example provides a method for preparing a silicon nitride target. Compared with Example 1, step (1) cold isostatic pressing is not performed, and the rest is the same as Example 1.

[0064] Table 1

[0065]

[0066]

[0067] It can be seen from Table 1 that:

[0068] The preparation method of the silicon nitride target provided by the present invention combines cold isostatic pressing with segmented hot pressing and sintering to improve the density of the silicon nitride target and obtain a silicon nitride target product with good purity and density. In Examples 1-3, the purity of the target is above 99.92% and the density reaches above 99.3%. Compared with Example 1, in Examples 4 and 5, the change in cold isostatic pressing pressure will cause the density of the blank before sintering to change. Under the same sintering process, the density is also different, and the purity of the material is not greatly affected; in Example 6, pressurization and heating are performed simultaneously in the temperature rise process curve, and pressurization is performed under the condition that the high temperature section is not reached and the cold pressed parts of silicon nitride are not softened. Since the sample itself has low strength and high brittleness after cold isostatic pressing (CIP), cracking occurs during the sintering process; in Example 7, since the insulation in the annealing stage is cancelled, the internal stress of the material is high during the cooling process, and the overall cooling rate is fast, which will cause cracking; in Example 8, since the sintering temperature in the first stage is not high enough, the CIP blank does not reach the softening temperature, resulting in cracking during the pressurization process; in Example 9, since the sintering temperature is too high, silicon nitride reaches the decomposition temperature, and the purity of the sample is reduced to about 99.3% after sintering.

[0069] Compared with Example 1, in Comparative Example 1, when sintering at a single temperature, the sintering temperature is reached without the pressurization process, bridges have been formed between the material particles, and it is difficult to achieve densification by continuing to pressurize. In addition, the high temperature section is maintained for a long time, and the product has a certain degree of decomposition, resulting in a purity reduction of about 99.8%; in Comparative Example 2, the purity and density of the target material are relatively low. Cold isostatic pressing can be used to achieve densification first during the sintering process, avoiding the adsorption of impurity elements during the sintering process and promoting the densification process. The purity is reduced to about 99.8% without the cold isostatic pressing process, and the density is significantly reduced to 93.2%.

[0070] In summary, the preparation method provided by the present invention combines cold isostatic pressing and hot pressing sintering at staged temperatures, and realizes the densification of silicon nitride target by rationally regulating the hot pressing sintering process without adding sintering aids. The obtained silicon nitride target has high purity, high density, and excellent processing performance, and can meet the requirements for target use.

[0071] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a silicon nitride target, characterized in that: The preparation method comprises the following steps: The silicon nitride powder is cold isostatically pressed and then hot-pressed and sintered at different temperatures to obtain a silicon nitride target.

2. The preparation method according to claim 1, characterized in that: The cold isostatic pressing pressure is 200-250 MPa; Preferably, the cold isostatic pressing time is 20-30 minutes.

3. The preparation method according to claim 1 or 2, characterized in that: The pressurization rate of the hot pressing sintering at the segmented temperature is 0.2-0.5T / min; Preferably, the pressure of the hot pressing sintering at the segmented temperature is 40-60F.

4. The preparation method according to any one of claims 1 to 3, characterized in that The process of hot pressing sintering at staged temperatures includes: hot pressing sintering at a first sintering temperature, a second sintering temperature and a third sintering temperature in sequence.

5. The preparation method according to claim 4, characterized in that: During the step-by-step hot-pressing sintering, the pressurization begins after the first sintering temperature is reached.

6. The preparation method according to claim 4 or 5, characterized in that: The first sintering temperature is 1500-1600° C.; Preferably, the holding time of the first sintering temperature is 1-1.5h; Preferably, the second sintering temperature is 1700-1800°C; Preferably, the holding time of the second sintering temperature is 2-4h; Preferably, the third sintering temperature is 1200-1300°C; Preferably, the holding time of the third sintering temperature is 1-2h.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The temperature change rate of the hot pressing sintering with segmented temperature is 2-15°C / min.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The purity of the silicon nitride powder is 99.9-99.99%; Preferably, the D50 particle size of the silicon nitride powder is 1.0-1.2 μm.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: (1) putting silicon nitride powder with a purity of 99.9-99.99% and a D50 particle size of 1.0-1.2 μm into a mold for cold isostatic pressing at a pressure of 200-250 MPa for a time of 20-30 min to obtain a target blank; (2) placing the target blank obtained in step (1) into a mold, and placing it into a sintering device for sintering, maintaining a nitrogen atmosphere in the sintering device, first heating the temperature to 1500-1600°C at a heating rate of 10-15°C / min, starting to pressurize, pressurizing to 40-60T at a pressurizing rate of 0.2-0.5T / min, and then maintaining the pressure. At the same time, after maintaining the temperature at 1500-1600°C for 1-1.5h, heating the temperature to 1700-1800°C at a rate of 3-6°C / min, maintaining the temperature for 2-4h, and then cooling the temperature to 1200-1300°C at a cooling rate of 2-4°C / min, maintaining the temperature for 1-2h, and ending the heat preservation and pressure maintenance to obtain a silicon nitride target.

10. A silicon nitride target, characterized in that: The silicon nitride target is prepared by the preparation method described in any one of claims 1 to 9.

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