Pressureless sintering high-density tantalum oxide sputtering target material and preparation method thereof

Abstract

The invention discloses a pressureless sintered high-density tantalum oxide sputtering target material and a preparation method thereof, and belongs to the technical field of resistive random access memories. The method comprises the following steps: adding a polycarboxylic acid ammonium salt dispersing agent into a tantalum oxide pre-mixed solution with the solid content of 45-60%, and performing ball milling by adopting a basket ball mill to obtain a tantalum oxide pre-mixed solution; carrying out variable-speed sanding on the tantalum oxide pre-mixed liquid by adopting a turbine disc type sand mill in a manner of first high speed and then low speed, so as to obtain tantalum oxide slurry; performing spray granulation and drying on the tantalum oxide slurry to obtain spherical tantalum oxide powder; and the spherical tantalum oxide powder is subjected to limiting pressing, degreasing and target material sintering in sequence, and the tantalum oxide sputtering target material is obtained. The tantalum oxide sputtering target material disclosed by the invention is low in impurity content, high in density, high in relative density, uniform in color and luster and free of spots, and meets the performance requirements of a resistive random access layer film layer of a resistive random access memory.

Description

Technical Field

[0001] This invention belongs to the field of resistive switching memory technology, and particularly relates to a pressureless sintering high-density tantalum oxide sputtering target and its preparation method. Background Technology

[0002] Currently, traditional memory, represented by flash memory, is facing physical limitations. Resistive random access memory (RRAM), due to its simple structure, ease of integration, and fast erase / write speeds, has become a key focus for next-generation non-volatile memory. A simple RRAM device consists of a resistive switching layer sandwiched between two metal electrodes, a top electrode and a bottom electrode, known as a metal-insulator-metal (MIM) structure. Tantalum oxide possesses excellent resistive switching characteristics and good compatibility with CMOS processes, making it suitable for fabricating the resistive switching layer of RRAM and showing great application potential.

[0003] Currently, the main methods for preparing tantalum oxide films are vacuum evaporation and magnetron sputtering. Vacuum evaporation primarily uses tantalum oxide powder as the deposition material; however, the prepared tantalum oxide film is severely affected by the particle size, morphology, and bulk density of the tantalum oxide powder, resulting in poor adhesion, uniformity, and unreliable film performance. Magnetron sputtering mainly uses reactive magnetron sputtering to prepare tantalum oxide films, employing a high-purity tantalum target as the sputtering source. The sputtered film is adjusted by controlling process parameters such as vacuum level and oxygen flow rate. However, the entire process is difficult to control and prone to adverse phenomena such as abnormal discharge and target poisoning.

[0004] If a high-purity, high-density tantalum oxide target is used for magnetron sputtering to prepare the film, all the above problems will be effectively solved. Therefore, preparing a high-purity, high-density tantalum oxide target is the key to preparing a high-performance resistive switching layer. Existing hot-pressing sintering techniques produce targets with low density, high impurity content, and uneven composition. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing a high-density tantalum oxide sputtering target by pressureless sintering. The tantalum oxide sputtering target prepared by this method has low impurity content, high density, high relative density (≥98%), uniform color, and no spots, thus meeting the performance requirements of the resistive switching layer film of resistive switching memory.

[0006] The second objective of this invention is to provide a pressureless sintering high-density tantalum oxide sputtering target.

[0007] To achieve one of the above objectives, the present invention employs the following technical solution:

[0008] A method for preparing a high-density tantalum oxide sputtering target by pressureless sintering, the method comprising the following steps:

[0009] Step S1: After adding the polycarboxylate ammonium salt dispersant 5029 to the tantalum oxide premix with a solid content of 45-60%, the mixture is ball-milled using a basket ball mill to obtain the tantalum oxide premix.

[0010] Step S2: Using a turbine disc mill, the tantalum oxide premix is ​​milled at a variable speed, first at high speed and then at low speed, to obtain tantalum oxide slurry.

[0011] Step S3: Spray granulation and drying of the tantalum oxide slurry to obtain spherical tantalum oxide powder;

[0012] Step S4: The spherical tantalum oxide powder is sequentially subjected to limiting pressing, degreasing and target sintering to obtain tantalum oxide sputtering target.

[0013] Further, in step S1, the weight ratio of tantalum oxide powder in the polycarboxylate ammonium salt dispersant and tantalum oxide premix is ​​0.1 to 0.5:1.

[0014] Furthermore, in step S1, the rotational speed of the basket mill is 950-1050 rpm;

[0015] In step S1, the ball milling time is 10 to 30 minutes.

[0016] Furthermore, in step S2, the medium of the variable speed sand mill is zirconia balls with a diameter of 0.5 to 0.8 mm;

[0017] In step S2, the high speed is 1100rpm to 1600rpm, and the number of high-speed grinding cycles is 4 to 8; the low speed is 800rpm to 1000rpm, and the number of low-speed grinding cycles is 2 to 4.

[0018] Furthermore, in step S2, the average particle size of the tantalum oxide slurry is ≤0.5 micrometers, and the viscosity is 30-55 mPa·S.

[0019] Furthermore, in step S3, the inlet air temperature of the spray granulation drying is 210℃~235℃, the outlet air temperature is 100℃~105℃, and the atomization speed is 15000~21500rpm.

[0020] Furthermore, in step S4, the degreasing temperature is 600–800°C, and the time is 8–12 hours;

[0021] In step S4, the specific process of target sintering is as follows:

[0022] Under an oxygen atmosphere, the pressed and degreased tantalum oxide powder is heated to 1350-1450°C at a heating rate of 3-5°C / min, held at that temperature for 5-10 hours, and then the power is turned off to cool it down.

[0023] To achieve the second objective mentioned above, the present invention employs the following technical solution:

[0024] A pressureless sintered high-density tantalum oxide sputtering target is prepared using the aforementioned tantalum oxide sputtering target preparation method.

[0025] Furthermore, the relative density of the tantalum oxide sputtering target is ≥98%.

[0026] In summary, the solution proposed in this invention has the following technical effects:

[0027] The spherical tantalum oxide powder of the present invention has high dispersibility and uniformity, and no cracking or corner chipping occurs during the pressing, degreasing and target sintering processes. The tantalum oxide sputtering target of the present invention has low impurity content, high density, high relative density (≥98%), uniform color, and no spots (i.e. no quality defects), which meets the performance requirements of the resistive switching layer film of resistive switching memory. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This embodiment provides a method for preparing a high-density tantalum oxide sputtering target through pressureless sintering. The method includes the following steps:

[0030] Step S1: After adding the polycarboxylate ammonium salt dispersant to the tantalum oxide premix with a solid content of 45-60%, the mixture is ball-milled using a basket ball mill to obtain the tantalum oxide premix.

[0031] To ensure the effect of subsequent variable speed grinding, the solid content of the tantalum oxide premix is ​​controlled at 45-60% in this embodiment.

[0032] To ensure dispersion and density of the sintered body in the later stage, the weight ratio of the polycarboxylate ammonium salt dispersant (such as polycarboxylate ammonium salt dispersant of model 5029) to the tantalum oxide powder in the tantalum oxide premix is ​​0.1 to 0.5:1 in this embodiment.

[0033] To ensure the smooth operation of the variable-speed sand mill in the later stage, this embodiment uses a basket ball mill for dispersion, and controls the rotation speed to be 950-1050 rpm and the ball milling time to be 10-30 min, so as to control the particle size of the ball milled powder.

[0034] Step S2: Using a turbine disc mill, the tantalum oxide premix is ​​milled at a variable speed, first at high speed and then at low speed, to obtain tantalum oxide slurry.

[0035] To avoid agglomeration caused by excessively small powder particle size and to ensure a concentrated particle size distribution in the Ta2O5 tantalum oxide slurry, this embodiment employs a turbine disc mill, performing variable-speed milling first at high speed and then at low speed. The milling media consists of zirconia balls with a diameter of 0.5–0.8 mm. After milling at a high speed of 1100 rpm–1600 rpm for 4–8 times, a low speed of 800 rpm–1000 rpm is used for 2–4 milling cycles.

[0036] The tantalum oxide slurry in this embodiment has a solid content of 45-60%, a particle size D50 ≤ 0.5 micrometers, and a viscosity of 30-55 mPa·S.

[0037] Step S3: Spray granulation and drying of the tantalum oxide slurry to obtain spherical tantalum oxide powder.

[0038] To ensure the drying effect and control the particle size of the spherical tantalum oxide powder, the inlet air temperature of the spray granulation drying in this embodiment is 210℃~235℃, the outlet air temperature is 100℃~105℃, and the atomization speed is 15000~21500rpm.

[0039] Step S4: The spherical tantalum oxide powder is sequentially subjected to limiting pressing, degreasing and target sintering to obtain tantalum oxide sputtering target.

[0040] To avoid cracking and delamination during the pressing process, and to facilitate the closure of pores between powder particles during the later sintering process and ensure the density of the sintered body, this embodiment adopts limiting pressing to obtain a tantalum oxide green body with a relative density of 42-48%.

[0041] To ensure complete removal of the dispersant, this embodiment controls the degreasing temperature at 600–800°C and the time at 8–12 hours.

[0042] To ensure uniform grain size and density, the specific sintering process of the target material in this embodiment is as follows:

[0043] Under an oxygen atmosphere, the pressed and degreased tantalum oxide powder is heated to 1350-1450°C at a heating rate of 3-5°C / min, held at that temperature for 5-10 hours, and then the power is turned off to cool it down.

[0044] The technical solution of the present invention is illustrated below using specific embodiments:

[0045] Example 1:

[0046] Step S1: Take 5 kg of tantalum oxide powder with a purity of 99.99%, weigh water, and prepare a tantalum oxide premix with a solid content of 50%. During the stirring process, add polycarboxylate ammonium salt dispersant of type 5029 to the tantalum oxide premix at a weight ratio of 0.3:1. Then, use a basket ball mill to ball mill the tantalum oxide premix at a speed of 1000 rpm for 20 minutes to obtain the tantalum oxide premix.

[0047] Step S2: Using a turbine disc mill with zirconia balls of 0.7 mm diameter as the medium, first use a high speed of 1350 rpm for 6 millings, then use a low speed of 900 rpm for 3 millings to obtain tantalum oxide slurry with an average particle size of 0.3 μm and a viscosity of 50 mPa·s.

[0048] Step S3: Spray granulation and drying of the tantalum oxide slurry to obtain spherical tantalum oxide powder, wherein the inlet air temperature of the spray granulation and drying is 225°C, the outlet air temperature is 102°C, and the atomization speed is 18000 rpm.

[0049] Step S4: The spherical tantalum oxide powder is pressed to obtain a tantalum oxide green compact with a relative density of 45%. Then, after degreasing at 600℃ for 8 hours, the pressed and degreased tantalum oxide powder is heated to 1400℃ at a heating rate of 4℃ / min under an oxygen atmosphere, held at that temperature for 7 hours, and then cooled down to obtain a tantalum oxide sputtering target with a relative density of 98.2%.

[0050] SEM observation showed that the tantalum oxide powder in this embodiment was spherical, the tantalum oxide blank was intact after pressing, and the surface of the tantalum oxide sputtering target in this embodiment was intact, with uniform color and no quality defects.

[0051] Example 2:

[0052] Step S1: Take 5 kg of tantalum oxide powder with a purity of 99.99%, weigh water, and prepare a tantalum oxide premix with a solid content of 45%. During the stirring process, add polycarboxylate ammonium salt dispersant of type 5029 to the tantalum oxide premix at a weight ratio of 0.1:1. Then, use a basket ball mill to ball mill the tantalum oxide premix for 10 minutes at a speed of 950 rpm to obtain the tantalum oxide premix.

[0053] Step S2: Using a turbine disc mill with zirconia balls of 0.5 mm diameter as the medium, first use a high speed of 1100 rpm for 4 millings, then use a low speed of 800 rpm for 2 millings to obtain tantalum oxide slurry with an average particle size of 0.4 μm and a viscosity of 55 mPa·s.

[0054] Step S3: Spray granulation and drying of the tantalum oxide slurry to obtain spherical tantalum oxide powder, wherein the inlet air temperature of the spray granulation and drying is 210°C, the outlet air temperature is 100°C, and the atomization speed is 15000 rpm.

[0055] Step S4: The spherical tantalum oxide powder is pressed to obtain a tantalum oxide green compact with a relative density of 43%. Then, after degreasing at 650°C for 10 hours, the pressed and degreased tantalum oxide powder is heated to 1350°C at a heating rate of 3°C / min under an oxygen atmosphere, held at that temperature for 5 hours, and then cooled down to obtain a tantalum oxide sputtering target with a relative density of 98%.

[0056] SEM observation showed that the tantalum oxide powder in this embodiment was spherical, the tantalum oxide blank was intact after pressing, and the surface of the tantalum oxide sputtering target in this embodiment was intact, with uniform color and no quality defects.

[0057] Example 3:

[0058] Step S1: Take 5 kg of tantalum oxide powder with a purity of 99.99%, weigh water, and prepare a tantalum oxide premix with a solid content of 60%. During the stirring process, add polycarboxylate ammonium salt dispersant of type 5029 to the tantalum oxide premix at a weight ratio of 0.5:1. Then, use a basket ball mill to ball mill the tantalum oxide premix for 30 minutes at a speed of 1050 rpm to obtain the tantalum oxide premix.

[0059] Step S2: Using a turbine disc mill with zirconia balls of 0.8 mm diameter as the medium, first use a high speed of 1600 rpm for 8 millings, then use a low speed of 1000 rpm for 4 millings to obtain tantalum oxide slurry with an average particle size of 0.3 μm and a viscosity of 45 mPa·s.

[0060] Step S3: Spray granulation and drying of the tantalum oxide slurry to obtain spherical tantalum oxide powder, wherein the inlet air temperature of the spray granulation and drying is 235°C, the outlet air temperature is 105°C, and the atomization speed is 21500 rpm.

[0061] Step S4: The spherical tantalum oxide powder is pressed to obtain a tantalum oxide green compact with a relative density of 42%. Then, after degreasing at 800℃ for 12 hours, the pressed and degreased tantalum oxide powder is heated to 1450℃ at a heating rate of 5℃ / min under an oxygen atmosphere, held at that temperature for 10 hours, and then cooled down to obtain a tantalum oxide sputtering target with a relative density of 98.1%.

[0062] SEM observation showed that the tantalum oxide powder in this embodiment was spherical, the tantalum oxide blank was intact after pressing, and the surface of the tantalum oxide sputtering target in this embodiment was intact, with uniform color and no quality defects.

[0063] Example 4:

[0064] Step S1: Take 5 kg of tantalum oxide powder with a purity of 99.99%, weigh water, and prepare a tantalum oxide premix with a solid content of 55%. During the stirring process, add polycarboxylate ammonium salt dispersant of type 5029 to the tantalum oxide premix at a weight ratio of 0.2:1. Then, use a basket ball mill to ball mill the tantalum oxide premix for 15 minutes at a speed of 980 rpm to obtain the tantalum oxide premix.

[0065] Step S2: Using a turbine disc mill with zirconia balls of 0.7 mm diameter as the medium, first use a high speed of 1200 rpm for 5 millings, then use a low speed of 850 rpm for 3 millings to obtain tantalum oxide slurry with an average particle size of 0.5 μm and a viscosity of 30 mPa·s.

[0066] Step S3: Spray granulation and drying of the tantalum oxide slurry to obtain spherical tantalum oxide powder, wherein the inlet air temperature of the spray granulation and drying is 220°C, the outlet air temperature is 103°C, and the atomization speed is 20000 rpm.

[0067] Step S4: The spherical tantalum oxide powder is pressed to obtain a tantalum oxide green compact with a relative density of 48%. Then, after degreasing at 800℃ for 8 hours, the pressed and degreased tantalum oxide powder is heated to 1380℃ at a heating rate of 3.5℃ / min under an oxygen atmosphere, held at that temperature for 6 hours, and then cooled down to obtain a tantalum oxide sputtering target with a relative density of 98.5%.

[0068] SEM observation showed that the tantalum oxide powder in this embodiment was spherical, the tantalum oxide blank was intact after pressing, and the surface of the tantalum oxide sputtering target in this embodiment was intact, with uniform color and no quality defects.

[0069] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a high-density tantalum oxide sputtering target by pressureless sintering, characterized in that, The method for preparing the tantalum oxide sputtering target includes the following steps: Step S1: After adding the polycarboxylate ammonium salt dispersant to the tantalum oxide premix with a solid content of 45-60%, the mixture is ball-milled using a basket ball mill to obtain the tantalum oxide premix. Step S2: Using a turbine disc mill, the tantalum oxide premix is ​​milled at a variable speed, first at high speed and then at low speed, to obtain tantalum oxide slurry. Step S3: Spray granulation and drying of the tantalum oxide slurry to obtain spherical tantalum oxide powder; Step S4: The spherical tantalum oxide powder is sequentially subjected to limiting pressing, degreasing and target sintering to obtain tantalum oxide sputtering target.

2. The method for preparing tantalum oxide sputtering target according to claim 1, characterized in that, In step S1, the weight ratio of tantalum oxide powder in the polycarboxylate ammonium salt dispersant and tantalum oxide premix is ​​0.1 to 0.5:

1.

3. The method for preparing tantalum oxide sputtering target according to claim 2, characterized in that, In step S1, the rotational speed of the basket ball mill is 950-1050 rpm; In step S1, the ball milling time is 10 to 30 minutes.

4. The method for preparing tantalum oxide sputtering target according to any one of claims 1 to 3, characterized in that, In step S2, the medium of the variable speed sand mill is zirconia balls with a diameter of 0.5 to 0.8 mm; In step S2, the high speed is 1100rpm to 1600rpm, and the number of high-speed grinding cycles is 4 to 8; the low speed is 800rpm to 1000rpm, and the number of low-speed grinding cycles is 2 to 4.

5. The method for preparing tantalum oxide sputtering target according to claim 4, characterized in that, In step S2, the tantalum oxide slurry has an average particle size ≤ 0.5 micrometers and a viscosity of 30–55 mPa·s.

6. The method for preparing tantalum oxide sputtering target according to claim 5, characterized in that, In step S3, the inlet air temperature of the spray granulation dryer is 210℃~235℃, the outlet air temperature is 100℃~105℃, and the atomization speed is 15000~21500rpm.

7. The method for preparing tantalum oxide sputtering target according to claim 6, characterized in that, In step S4, the degreasing temperature is 600-800°C and the time is 8-12 hours; In step S4, the specific process of target sintering is as follows: Under an oxygen atmosphere, the pressed and degreased tantalum oxide powder is heated to 1350-1450°C at a heating rate of 3-5°C / min, held at that temperature for 5-10 hours, and then the power is turned off to cool it down.

8. A pressureless sintered high-density tantalum oxide sputtering target, characterized in that, The pressureless sintered high-density tantalum oxide sputtering target is prepared using the tantalum oxide sputtering target preparation method described in any one of claims 1 to 7.

9. The tantalum oxide sputtering target according to claim 8, characterized in that, The relative density of the tantalum oxide sputtering target is ≥98%.