Silicon nitride target and method for producing the same

Abstract

The application provides a silicon nitride target material and a preparation method thereof, and the preparation method comprises the following steps: cold isostatic pressing silicon nitride powder, and then performing hot-pressing sintering at segmented temperatures to obtain the silicon nitride target material. The preparation method combines cold isostatic pressing and hot-pressing sintering at segmented temperatures, realizes the densification of the silicon nitride target material by reasonably controlling the hot-pressing sintering process, and does not need to add a sintering aid, so that the obtained silicon nitride target material has high purity, high density and excellent processing performance, and can meet the use requirements of the target material.

Description

Technical Field

[0001] This invention belongs to the field of target material preparation technology, specifically relating to a silicon nitride target material and its preparation method. Background Technology

[0002] Silicon nitride thin films possess high dielectric constant, strong insulation, and the ability to block sodium ions and water molecules, making them suitable for use as passivation films and insulating dielectric layers in microelectronic devices. Simultaneously, silicon nitride thin films also exhibit excellent mechanical properties such as corrosion resistance, good thermal insulation, fatigue resistance, and abrasion resistance, making them ideal for use as corrosion masking layers, thermal insulation layers, mechanical structural layers, or wear-resistant layers in microelectromechanical systems. The fabrication of silicon nitride thin films via magnetron sputtering relies heavily on high-performance silicon nitride targets.

[0003] Silicon nitride is a predominantly covalent compound, with Si-N covalent bonds accounting for up to 70%. Silicon nitride powder decomposes at 1700℃ and has a low self-diffusion coefficient during sintering. Conventional atmospheric pressure sintering is insufficient to achieve high-density silicon nitride. Therefore, hot pressing (HIP), gas pressure sintering (HPS), and hot isostatic pressing (HIP) are commonly used. HPS sintering utilizes high-pressure nitrogen (1-10 MPa) to suppress silicon nitride decomposition, allowing sintering temperatures up to 1900℃ to promote densification. However, excessively high temperatures can lead to abnormal grain growth and accelerated decomposition, resulting in increased micropores, defects, and decreased density within the sintered silicon nitride. Furthermore, HPS sintering requires a long time, often resulting in inconsistent internal and external colors and poor structural uniformity. Hot isostatic pressing (HIP) requires high gas pressure to achieve sintering without sintering aids. Encased HIP silicon nitride sintering is complex and costly, requiring a high-temperature glass cladding that is disposable and difficult to manufacture, further increasing the overall cost of HIP. The rapid heating and cooling regime during spark plasma sintering (SPS) can lead to numerous defects in the prepared silicon nitride ceramics, resulting in poor processing performance. Subsequent heat treatment is required to eliminate these defects.

[0004] Hot pressing sintering generally applies axial mechanical pressure to the material to be sintered during heating, providing an external driving force for densification. This increases the densification rate, reduces sintering time, lowers sintering temperature, and allows for a reduction in the amount of sintering aids needed. This reduces the amount of silicon nitride grain boundary glass phase, preventing processing cracks and reducing impurity content. Hot-pressed sintered products are generally flat, perfectly suited to the shapes of discs / square plates and other targets.

[0005] CN111620697A discloses a silicon nitride substrate material prepared by hot pressing sintering. Using silicon nitride, magnesium silicon nitride, and sintering aids as raw materials, the substrate is prepared by dry pressing followed by hot pressing sintering at 20-45 MPa and 1700-1850 °C. CN115677356A discloses a method for preparing a high-performance silicon nitride ceramic substrate. Silicon nitride powder, additives, and sintering aids are mixed and subjected to cold isostatic pressing, followed by hot isostatic pressing sintering at 160-200 MPa and 1600-1700 °C. In the prior art, the preparation of silicon nitride products still requires the addition of sintering aids to promote densification. However, silicon nitride targets have high requirements for purity and processing precision, requiring sintering without the addition of sintering aids. Therefore, there is a need for a method for preparing silicon nitride targets that requires no sintering aids and exhibits excellent target performance. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a silicon nitride target and its preparation method, which can prepare a silicon nitride target with high density and excellent performance without adding sintering aids.

[0007] To achieve this objective, the present invention adopts the following technical solution:

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

[0009] Silicon nitride powder is subjected to cold isostatic pressing, followed by segmented hot pressing sintering to obtain silicon nitride target material.

[0010] The preparation method provided by this invention combines cold isostatic pressing and segmented temperature hot pressing sintering. By reasonably controlling the hot pressing sintering process, the densification of silicon nitride target material is achieved without adding sintering aids, thus avoiding the influence of aids on purity. The resulting silicon nitride target material has high density and excellent processing performance, which can meet the requirements for target material 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. Other unlisted values ​​within the range are also applicable.

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

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

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

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

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

[0018] Preferably, the hot pressing sintering process at the segmented temperatures includes: performing hot pressing sintering sequentially at a first sintering temperature, a second sintering temperature, and a third sintering temperature.

[0019] Preferably, during the segmented temperature hot pressing sintering process, pressure is applied after the first sintering temperature is reached.

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

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

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

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

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

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

[0026] As a preferred embodiment of the preparation method provided by the present invention, the preparation method includes the following steps:

[0027] (1) Silicon nitride powder with a purity of 99.9-99.99% and a D50 particle size of 1.0-1.2μm is loaded into a mold and subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 200-250MPa and the time of cold isostatic pressing is 20-30min to obtain the target blank.

[0028] (2) Place the target blank obtained in step (1) into a mold and place it into a sintering equipment for sintering. Maintain a nitrogen atmosphere in the sintering equipment. First, heat the blank to 1500-1600℃ at a heating rate of 10-15℃ / min, then start pressurizing. Pressurize the blank to 40-60T at a pressurization rate of 0.2-0.5T / min and then hold the pressure. At the same time, hold the blank at 1500-1600℃ for 1-1.5h, then heat the blank to 1700-1800℃ at a rate of 3-6℃ / min and hold the pressure for 2-4h. Then, cool the blank to 1200-1300℃ at a cooling rate of 2-4℃ / min and hold the pressure for 1-2h. Finally, stop the heat preservation and pressure holding to obtain the silicon nitride target material.

[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 beneficial effects of the present invention are as follows:

[0031] The preparation method provided by this invention combines cold isostatic pressing and segmented temperature hot pressing sintering. By reasonably controlling the hot pressing sintering process, the densification of silicon nitride target material is achieved without adding sintering aids. The resulting silicon nitride target material has high purity, high density, and excellent processing performance, which can meet the requirements for target material use. Detailed Implementation

[0032] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0033] Example 1

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

[0035] (1) Fill a silicone mold with Si3N4 powder with a purity of 99.95% and a D50 particle size of 1.1μm, compact it, make the mold flatness 1.0mm, seal it, and then perform cold isostatic pressing under a pressure of 230MPa for 25min to obtain the target blank.

[0036] (2) Place the target blank into the graphite mold, and fill the surrounding area with BN powder to prevent the volatilized carbon elements from the graphite mold from seeping into Si3N4. Place the graphite mold in the sintering furnace, ensuring it is horizontal and centered. Evacuate the equipment and reduce the vacuum level to 10. -2 After Pa, nitrogen gas was introduced to -0.1 MPa, and then the vacuum was re-evacuated to 10 MPa. -2 After Pa, nitrogen is introduced to maintain a nitrogen atmosphere in the furnace cavity. Then, the hot pressing sintering process begins. The temperature is initially increased to 1550℃ at a rate of 12℃ / min. When the temperature reaches 1550℃, pressure is applied at a rate of 0.4T / min to 50T and held at 1550℃ for 1.2 hours. Then, the temperature is increased to 1750℃ at a rate of 4℃ / min and held for 3 hours. Finally, the temperature is decreased to 1250℃ at a rate of 3℃ / min and held for 1.5 hours, maintaining a pressure of 50T throughout. After the holding period, heating and pressurization are stopped, and the furnace is cooled.

[0037] (3) Remove the BN powder from the surface of the sintered target blank and machine it to obtain silicon nitride target material.

[0038] Example 2

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

[0040] (1) Fill a silicone mold with Si3N4 powder with a purity of 99.95% and a D50 particle size of 1.0μm, compact it, make the mold flatness 1.0mm, seal it, and then perform cold isostatic pressing under a pressure of 200MPa for 30min to obtain the target blank.

[0041] (2) Place the target blank into the graphite mold, and fill the surrounding area with BN powder to prevent the volatilized carbon elements from the graphite mold from seeping into Si3N4. Place the graphite mold in the sintering furnace, ensuring it is horizontal and centered. Evacuate the equipment and reduce the vacuum level to 10. -2 After Pa, nitrogen gas was introduced to -0.1 MPa, and then the vacuum was re-evacuated to 10 MPa. -2 After Pa, nitrogen is introduced to maintain a nitrogen atmosphere in the furnace cavity. Then, the hot pressing sintering process begins. The temperature is initially increased to 1500℃ at a rate of 10℃ / min. When the temperature reaches 1500℃, pressure is applied at a rate of 0.5T / min to 60T and held at 1500℃ for 1.5 hours. Then, the temperature is increased to 1700℃ at a rate of 3℃ / min and held for 4 hours. Finally, the temperature is decreased to 1200℃ at a rate of 2℃ / min and held for 2 hours, maintaining a pressure of 60T throughout the process. After the holding period, heating and pressurization are stopped, and the furnace is cooled.

[0042] (3) Remove the BN powder from the surface of the sintered target blank and machine it to obtain silicon nitride target material.

[0043] Example 3

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

[0045] (1) Fill a silicone mold with Si3N4 powder with a purity of 99.95% and a D50 particle size of 1.2μm, compact it, make the mold flatness 1.0mm, seal it, and then perform cold isostatic pressing under a pressure of 250MPa for 20min to obtain the target blank.

[0046] (2) Place the target blank into the graphite mold, and fill the surrounding area with BN powder to prevent the volatilized carbon elements from the graphite mold from seeping into Si3N4. Place the graphite mold in the sintering furnace, ensuring it is horizontal and centered. Evacuate the equipment and reduce the vacuum level to 10. -2 After Pa, nitrogen gas was introduced to -0.1 MPa, and then the vacuum was re-evacuated to 10 MPa. -2After Pa, nitrogen is introduced to maintain a nitrogen atmosphere in the furnace cavity. Then, the hot pressing sintering process begins. The temperature is initially increased to 1600℃ at a rate of 15℃ / min. When the temperature reaches 1600℃, pressure is applied at a rate of 0.2T / min to 40T and held at that pressure. The temperature is then held at 1600℃ for 1 hour. The temperature is then increased to 1800℃ at a rate of 6℃ / min and held for 2 hours. The temperature is then decreased to 1300℃ at a rate of 4℃ / min and held for 1 hour. Throughout this process, the pressure is maintained at 40T. After the holding period, heating and pressurization are stopped, and the furnace is cooled.

[0047] (3) Remove the BN powder from the surface of the sintered target blank and machine it to obtain silicon nitride target material.

[0048] Example 4

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

[0050] Example 5

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

[0052] Example 6

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

[0054] Example 7

[0055] This embodiment provides a method for preparing silicon nitride target material. Compared with embodiment 1, the third sintering temperature of 1250°C is not performed during the hot pressing sintering process in step (2). All other steps are the same as in embodiment 1.

[0056] Example 8

[0057] This embodiment provides a method for preparing silicon nitride target material. Compared with Example 1, the first sintering temperature in step (2) hot pressing sintering process is 1400℃, and the rest are the same as in Example 1.

[0058] Example 9

[0059] This embodiment provides a method for preparing silicon nitride target material. Compared with Example 1, the second sintering temperature in step (2) hot pressing sintering process is controlled at 1900℃, and the rest are the same as in Example 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 are carried out simultaneously, the temperature is increased to 1700℃ at a rate of 15℃ / min, and the pressure is increased to 50T at a rate of 0.4T / min. The temperature and pressure are maintained for 5 hours. After the process is completed, the heating and pressurization are stopped. The rest is the same as in 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 omitted, and the rest is the same as in Example 1.

[0064] Table 1

[0065]

[0066]

[0067] As can be seen from Table 1:

[0068] The method for preparing silicon nitride targets provided by the present invention combines cold isostatic pressing with segmented hot pressing sintering to improve the density of silicon nitride targets, thereby obtaining silicon nitride target products with good purity and density. In Examples 1-3, the purity of the target material is above 99.92%, and the density reaches above 99.3%. Compared to Example 1, in Examples 4 and 5, changes in cold isostatic pressing pressure cause changes in the density of the blank before sintering. Under the same sintering process, the density also varies, but the purity of the material is not significantly affected. In Example 6, pressure and heating are carried out simultaneously in the heating process curve. Pressure is applied before reaching the high temperature range, and the cold-pressed silicon nitride is not softened. Due to the low strength and high brittleness of the sample after cold isostatic pressing (CIP), cracking occurs during sintering. In Example 7, because the heat preservation in the annealing stage is eliminated, the internal stress of the material is high during the cooling process, and the overall cooling rate is fast, which leads to cracking. In Example 8, because the first stage sintering temperature is not high enough, the CIP blank does not reach the softening temperature, which leads to cracking during the pressure process. In Example 9, because the sintering temperature is too high, the silicon nitride reaches the decomposition temperature, and the purity of the sample after sintering decreases to about 99.3%.

[0069] Compared to Example 1, in Comparative Example 1, during single-temperature sintering, the sintering temperature was reached before the pressurization process, and bridging had already formed between the material particles. Continuing to apply pressure made it difficult to achieve densification. Furthermore, the high-temperature period was prolonged, resulting in a certain degree of product decomposition and a decrease in purity to approximately 99.8%. In Comparative Example 2, the purity and density of the target material were both low. During the sintering process, cold isostatic pressing could achieve densification first, avoiding the adsorption of impurity elements during sintering and promoting the densification process. Without the cold isostatic pressing process, the purity decreased to approximately 99.8%, and the density decreased significantly to 93.2%.

[0070] In summary, the preparation method provided by this invention combines cold isostatic pressing and segmented temperature hot pressing sintering. By rationally controlling the hot pressing sintering process, the densification of silicon nitride targets is achieved without the need to add sintering aids. The resulting silicon nitride targets have high purity, high density, and excellent processing performance, which can meet the requirements for target use.

[0071] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 within the protection scope of the present invention.

Claims

1. A method for preparing a silicon nitride target, characterized in that, The preparation method includes the following steps: (1) Silicon nitride powder with a purity of 99.9-99.99% and a D50 particle size of 1.0-1.2μm is loaded into a mold and subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 200-250MPa and the time of cold isostatic pressing is 20-30min to obtain the target blank. (2) Place the target blank obtained in step (1) into a mold and place it into a sintering equipment for sintering. Maintain a nitrogen atmosphere in the sintering equipment. First, heat the blank to 1500-1600℃ at a heating rate of 10-15℃ / min, then start pressurizing. Pressurize the blank to 40-60T at a pressurization rate of 0.2-0.5T / min and then hold the pressure. At the same time, hold the blank at 1500-1600℃ for 1-1.5h, then heat the blank to 1700-1800℃ at a rate of 3-6℃ / min and hold the pressure for 2-4h. Then, cool the blank to 1200-1300℃ at a cooling rate of 2-4℃ / min and hold the pressure for 1-2h. Finally, stop the heat preservation and pressure holding to obtain the silicon nitride target material.

2. A silicon nitride target material, characterized in that, The silicon nitride target is prepared using the preparation method described in claim 1.

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