Method for preparing high-density molybdenum target material through gradient sintering

Abstract

The invention belongs to the technical field of molybdenum target material preparation, and particularly relates to a method for preparing a high-density molybdenum target material through gradient sintering. The preparation method comprises the following steps: step 1, precursor activation and molding: preparing nano composite powder coated with an organic film on the surface from micron-sized molybdenum powder and stearic acid through a ball milling process, carrying out cold isostatic pressing molding to obtain an initial blank, and degreasing; step 2, multi-stage gradient sintering densification: putting the initial green body into a sintering furnace, and regulating and controlling the pressure (50 MPa to 100 MPa to normal pressure) and the temperature (1200 DEG C to 1500 DEG C to 1800 DEG C) in stages in sequence; and 3, in-situ deoxidation and surface finishing are conducted, specifically, H-CH mixed gas is introduced in the whole sintering process, the sintered target material is subjected to argon ion bombardment, and the high-density molybdenum target material is obtained. Under the condition that hot isostatic pressing equipment is not needed, the compactness of the target material is larger than or equal to 99.8%, the average grain size is smaller than or equal to 10 micrometers, the oxygen content is smaller than or equal to 200 ppm, and the requirements of the tip field are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of molybdenum target preparation, and particularly relates to a method for preparing a high-density molybdenum target by gradient sintering. Background Art

[0002] As a key material for the copper interconnect barrier layer of semiconductor chips and the coating of high-resolution display panels, the density of molybdenum targets directly affects the uniformity of sputtering film formation and the reliability of devices. With the progress of technology and the continuous improvement of display performance, the density requirement for targets has been increased from 98% to ≥99.5%. Existing processes are difficult to meet the industrialization requirements of high density, fine crystallization, and low cost.

[0003] Traditional molybdenum target preparation processes mainly include: Powder metallurgy method: Cold pressing molybdenum powder into a shape and then sintering at a high temperature of 1800 - 2000°C. However, the grain coarsening (average grain size > 50μm) and residual porosity > 5% result in a density that can only reach 92% - 95% of the theoretical value. Hot isostatic pressing method (HIP): Pressing molybdenum powder in a high-temperature and high-pressure argon environment. Although the density can be increased to ≥98%, the equipment investment is high, and a hard oxide layer is easily formed on the surface of the target, with an oxygen content > 800ppm. Melting and casting method: Preparing a molybdenum ingot by vacuum arc melting and then rolling. However, the grain size distribution is uneven, and there is a high risk of introducing impurity elements such as Fe and Ni.

[0004] Above, traditional sintering relies on high-temperature diffusion densification, with insufficient grain boundary migration rate, incomplete pore closure, and low densification efficiency; high-temperature and long-time sintering leads to abnormal grain growth, with a grain size > 50μm, reducing the sputtering crack resistance of the target; metal impurities such as Fe and NI are easily introduced during the arc melting process, reducing the density and uniformity of the target. Summary of the Invention

[0005] The present invention aims to solve the problems of insufficient density and poor sputtering performance caused by low densification efficiency, grain coarsening, and impurity pollution in traditional molybdenum target preparation processes, and provides a method for preparing a high-density molybdenum target by gradient sintering.

[0006] The present invention is achieved through the following technical solutions: A method for preparing a high-density molybdenum target by gradient sintering, comprising the following steps: Step 1, precursor activation and forming: Preparing a nano-composite powder with an organic film-coated surface by ball milling micron-sized molybdenum powder and stearic acid, then cold isostatically pressing at 300 MPa into an initial green body, and degreasing in a hydrogen atmosphere at 600°C for 2 hours. Step 2, multi-stage gradient sintering densification: Put the initial green body into a sintering furnace and perform the following steps in sequence: keep it at 1200°C under a pressure of 50 MPa for 1 hour; raise the temperature to 1500°C and increase the pressure to 100 MPa, and keep it for 2 hours; keep it at 1800°C under normal pressure for a short time of 10 minutes. Step 3: In-situ deoxidation and surface finishing: During the whole sintering process, a H2-CH4 mixed gas is introduced. After sintering, the target is bombarded with argon ions to obtain a high-density molybdenum target.

[0007] Preferably, in Step 1, the particle size D50 of the micron-sized molybdenum powder is 4.2 - 6 μm.

[0008] Preferably, in Step 1, the mixing ratio of molybdenum powder to stearic acid is 200:1 by mass.

[0009] Preferably, in Step 1, the mixing ratio of molybdenum powder to stearic acid is 500:1 by mass.

[0010] Preferably, in Step 3, the volume ratio of the H2-CH4 mixed gas is 95:5.

[0011] Preferably, in Step 3, the argon ion bombardment energy is 500 eV.

[0012] The beneficial effects of the present invention are as follows: 1. Through the synergistic technology of surface activation of nano-molybdenum powder - multi-stage gradient densification sintering - carbon-assisted in-situ deoxidation, the present invention realizes a target density ≥ 99.8%, an average grain size ≤ 10 μm, and an oxygen content ≤ 200 ppm without the need for hot isostatic pressing equipment. At the same time, the single-sintering production capacity is increased to more than 500 kg, and it is suitable for the continuous production of large-sized targets with a diameter of more than 800 mm, meeting the requirements of the cutting-edge fields.

[0013] 2. The present invention adopts the method of surface organic coating activation of nano-molybdenum powder, and prepares nano-composite powder by ball milling modification with stearic acid, which inhibits agglomeration and improves sintering activity, providing highly reactive raw materials for gradient densification.

[0014] 3. The present invention adopts the method of multi-stage pressure-temperature gradient coupling sintering, and regulates the pressure (50 MPa → 100 MPa → normal pressure) and temperature (1200°C → 1500°C → 1800°C) in stages, coordinating grain boundary diffusion and pore closure, and realizing the balance between densification and grain refinement.

[0015] 4. The present invention adopts the carbon-assisted in-situ deoxidation technology, uses the carbon atoms cracked from methane in the H2-CH4 mixed gas to occupy the grain boundary oxygen vacancies, and synchronously reduces the residual oxides, reducing the oxygen content to below 200 ppm. Specific embodiments

[0016] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0018] The reagents and raw materials used in the embodiments and comparative examples of the present invention can be obtained through commercial channels without special instructions.

[0019] Example 1 A method for preparing a high-density molybdenum target by gradient sintering specifically includes the following steps: Step 1, precursor activation and forming: Mix 500 kg of micron-sized molybdenum powder with D50 = 5 μm and 2.5 kg of stearic acid at a mixing ratio of 200:1, and prepare a nanocomposite powder with an organic film-coated surface through a ball milling process. The particle size D50 of the nanocomposite powder is 80 nm.

[0020] Subsequently, at 300 MPa, cold isostatically press it into an initial green body with a diameter of 800 mm, with a density of 7.5 g / cm³, and then degrease it in a hydrogen atmosphere at 600 °C for 2 hours to synchronously pre-reduce the surface oxide.

[0021] Step 2, multi-stage gradient sintering densification: Put the initial green body into a sintering furnace, adjust the temperature and pressure of the sintering furnace, and sequentially perform: Medium-temperature activation sintering: Keep it at 1200 °C and 50 MPa for 1 hour to trigger grain boundary diffusion to achieve preliminary densification; High-pressure pore closure: Heat up to 1500 °C and pressurize to 100 MPa, and keep it for 2 hours to accelerate pore shrinkage and grain refinement; High-temperature grain boundary optimization: Keep it at 1800 °C under normal pressure for a short time of 10 minutes to eliminate residual stress and regulate the grain boundary structure.

[0022] Step 3, in-situ deoxidation and surface finishing: Introduce a H2-CH4 mixed gas into the sintering furnace throughout the sintering process, with a volume ratio of H2 to CH4 of 95:5. Use methane cracking carbon atoms to fill the grain boundary oxygen vacancies, and simultaneously generate CO gas and discharge it; After sintering, the surface of the target is bombarded with argon ions at an energy of 500 eV to remove the oxide layer and improve the surface finish, resulting in a high-performance molybdenum target.

[0023] The surface finish was measured by a surface roughness meter, and Ra = 0.1 μm was measured. The density was measured by a true density meter and found to be 99.8%. The oxygen content was measured by an oxygen, nitrogen, and hydrogen analyzer and found to be 150 ppm.

[0024] Example 2 A method for preparing a high-density molybdenum target by gradient sintering, specifically including the following steps: Step 1, precursor activation and forming: Mix micron-sized molybdenum powder with D50 = 6 μm and stearic acid in a mass ratio of 200:1, and prepare a nano-composite powder with an organic film on the surface through a ball milling process. The particle size D50 of the nano-composite powder is 90 nm, and the mass fraction of stearic acid is 0.5%.

[0025] Subsequently, at 300 MPa, it is cold isostatically formed into an initial green body with a diameter of 800 mm and a density of 7.6 g / cm³. Then, it is degreased in a hydrogen atmosphere at 600 °C for 2 hours to synchronously pre-reduce the surface oxides.

[0026] Step 2, multi-stage gradient sintering densification: Put the initial green body into a sintering furnace, adjust the temperature and pressure of the sintering furnace, and perform the following steps in sequence: Medium-temperature activation sintering: Keep it at 1200 °C and 50 MPa for 1 hour to trigger grain boundary diffusion and achieve preliminary densification; High-pressure pore closure: Heat up to 1500 °C and pressurize to 100 MPa, keep it for 2 hours to accelerate pore shrinkage and grain refinement; High-temperature grain boundary optimization: Keep it at 1800 °C under normal pressure for a short time of 10 minutes to eliminate residual stress and regulate the grain boundary structure.

[0027] Step 3, in-situ deoxidation and surface finishing: During the whole sintering process, a H2-CH4 mixed gas is introduced into the sintering furnace, and the volume ratio of H2 to CH4 is 95:5. The carbon atoms cracked from methane are used to fill the oxygen vacancies at the grain boundaries, and CO gas is simultaneously generated and discharged; After sintering, the surface of the target is bombarded with argon ions at an energy of 500 eV to remove the oxide layer, resulting in a high-performance molybdenum target.

[0028] After detection, the surface finish Ra is 0.1 μm, the density is 99.8%, and the oxygen content is 150 ppm.

[0029] Example 3 A method for preparing a high-density molybdenum target by gradient sintering, specifically including the following steps: Step 1, Precursor Activation and Molding: Mix micron-sized molybdenum powder with D50 = 4.2 μm and stearic acid at a mass ratio of 500:1, and prepare a nano-composite powder with an organic film-coated surface through a ball-milling process. The particle size D50 of the nano-composite powder is 120 nm, and the mass fraction of stearic acid contained therein is 0.2%.

[0030] Subsequently, at 300 MPa, cold isostatic pressing is performed to form an initial green body with a diameter of 800 mm, whose density ≥ 6.8 g / cm³. Then, it is degreased in a hydrogen atmosphere at 600 °C for 2 hours to synchronously pre-reduce the surface oxide.

[0031] Step 2, Multi-stage Gradient Sintering Densification: Place the initial green body into a sintering furnace, adjust the temperature and pressure of the sintering furnace, and sequentially perform: Medium-temperature activation sintering: Keep it at 1200 °C and 50 MPa for 1 hour to trigger grain boundary diffusion to achieve preliminary densification; High-pressure pore closure: Heat up to 1500 °C and pressurize to 100 MPa, keep it for 2 hours to accelerate pore shrinkage and grain refinement; High-temperature grain boundary optimization: Keep it at 1800 °C under normal pressure for a short time of 10 minutes to eliminate residual stress and regulate the grain boundary structure.

[0032] Step 3, In-situ Deoxidation and Surface Finishing: During the whole sintering process, introduce a H2-CH4 mixed gas into the sintering furnace, with the volume ratio of H2 to CH4 being 95:5. Use the pyrolysis of methane to fill the grain boundary oxygen vacancies with carbon atoms, and simultaneously generate CO gas for discharge; After sintering, the surface of the target is treated by argon ion bombardment with an energy of 500 eV to remove the oxide layer, and a high-performance molybdenum target is obtained.

[0033] After testing, the surface roughness Ra is 0.1 μm, the density is 99.3%, and the oxygen content is 180 ppm.

[0034] Comparative Example 1 This comparative example provides a method for preparing a molybdenum target, which is different from Example 1 in that the raw material molybdenum powder is not modified by stearic acid, and specifically includes the following steps: Step 1, Cold isostatically press micron-sized molybdenum powder with D50 = 5 μm into an initial green body at 300 MPa.

[0035] Step 2: Place the initial green body into a sintering furnace, adjust the temperature and pressure of the sintering furnace, and sequentially perform the following: Insulate for 1 hour at 1200 °C and 50 MPa to trigger grain boundary diffusion and achieve preliminary densification; raise the temperature to 1500 °C and increase the pressure to 100 MPa, and insulate for 2 hours to accelerate pore shrinkage and grain refinement; insulate for 10 minutes at 1800 °C under normal pressure to eliminate residual stress and regulate the grain boundary structure.

[0036] Step 3: Introduce a H2-CH4 mixed gas into the sintering furnace throughout the sintering process. The volume ratio of H2 to CH4 is 95:5. Use the pyrolysis of methane to fill the grain boundary oxygen vacancies with carbon atoms, and simultaneously generate CO gas and discharge it; after sintering, the surface of the target is bombarded with argon ions, and the bombardment energy is 500 eV to remove the oxide layer.

[0037] The obtained molybdenum target is detected to have a surface finish Ra of 0.25 μm, a relative density of 95.2%, and an oxygen content of 650 ppm.

[0038] Comparative Example 2 A method for preparing a molybdenum target, which is different from Example 1 in that the initial green body does not undergo gradient sintering, and specifically includes the following steps: Step 1: Mix micron-sized molybdenum powder with D50 = 5 μm and stearic acid in a mass ratio of 200:1, and prepare a nano-composite powder with an organic film coated on the surface through a ball milling process. The particle size D50 of the nano-composite powder is 80 nm, and the mass fraction of stearic acid it contains is 0.5%.

[0039] Subsequently, cold isostatically press it into an initial green body at 300 MPa, with a density ≥ 7.5 g / cm³, and then degrease it in a hydrogen atmosphere at 600 °C for 2 hours.

[0040] Step 2: Place the initial green body into a sintering furnace, and insulate for 2 hours at a temperature of 1800 °C and a pressure of 100 MPa.

[0041] Step 3: Introduce a H2-CH4 mixed gas into the sintering furnace throughout the sintering process. The volume ratio of H2 to CH4 is 95:5. Use the pyrolysis of methane to fill the grain boundary oxygen vacancies with carbon atoms, and simultaneously generate CO gas and discharge it; after sintering, the surface of the target is bombarded with argon ions, and the bombardment energy is 500 eV to remove the oxide layer.

[0042] The obtained molybdenum target is detected to have a surface finish Ra of 0.3 μm, a relative density of 94.6%, and an oxygen content of 480 ppm.

[0043] Comparative Example 3 A method for preparing a molybdenum target, which is different from Example 1 in that pure hydrogen is used instead of CH4, and specifically includes the following steps: Step 1: Mix micron-sized molybdenum powder with D50 = 5 μm and stearic acid at a mass ratio of 200:1, and prepare a nano-composite powder with an organic film-coated surface through a ball milling process. The particle size D50 of the nano-composite powder is 80 nm, and the mass fraction of stearic acid it contains is 0.5%.

[0044] Subsequently, cold isostatically press it into an initial green body at 300 MPa, with its density ≥ 7.5 g / cm³, and then degrease it in a hydrogen atmosphere at 600 °C for 2 hours.

[0045] Step 2: Place the initial green body into a sintering furnace, adjust the temperature and pressure of the sintering furnace, and introduce H2 into the sintering furnace throughout the sintering process. Perform the following steps in sequence: hold at 1200 °C and 50 MPa for 1 hour to trigger grain boundary diffusion to achieve preliminary densification; raise the temperature to 1500 °C and increase the pressure to 100 MPa, hold for 2 hours to accelerate pore shrinkage and grain refinement; hold at 1800 °C under normal pressure for 10 minutes.

[0046] Step 3: After sintering, the surface of the target is treated by argon ion bombardment with an energy of 500 eV to remove the oxide layer. The obtained molybdenum target is detected to have a surface roughness Ra of 0.25 μm, a relative density of 98.2%, and an oxygen content of 380 ppm.

[0047] Above, according to the final data comparison between Example 1 and Comparative Examples 1 - 3, through the preparation method of Example 1, a target with a relative density ≥ 99.8%, an average grain size ≤ 10 μm, and an oxygen content ≤ 200 ppm is achieved. At the same time, the single-sintering production capacity is increased to more than 500 kg, and it is adapted to the continuous production of large-sized targets with a diameter of more than 800 mm, meeting the requirements of the cutting-edge field.

[0048] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-density molybdenum target by gradient sintering, characterized in that, It includes the following steps: Step 1, precursor activation and shaping: Prepare a nano-composite powder with an organic film-coated surface by ball-milling micron-sized molybdenum powder and stearic acid. Subsequently, cold isostatically press it into an initial green body at 300 MPa and degrease it in a hydrogen atmosphere at 600 °C for 2 hours; Step 2, multi-stage gradient sintering densification: Put the initial green body into a sintering furnace and perform the following operations in sequence: keep it at 1200 °C under a pressure of 50 MPa for 1 hour; heat it to 1500 °C and increase the pressure to 100 MPa, and keep it for 2 hours; keep it at 1800 °C under normal pressure for a short time of 10 minutes; Step 3, in-situ deoxidation and surface finishing: Introduce a H2-CH4 mixed gas throughout the sintering process. After sintering, bombard the target with argon ions to obtain a high-density molybdenum target.

2. The method for preparing a high-density molybdenum target by gradient sintering according to claim 1, wherein, In Step 1, the particle size D50 of the micron-sized molybdenum powder is in the range of 4.2 - 6 μm.

3. A method for preparing a high-density molybdenum target by gradient sintering according to claim 1, characterized in that, In Step 1, the mixing ratio of molybdenum powder to stearic acid is 200:1 by mass.

4. A method for preparing a high-density molybdenum target by gradient sintering according to claim 1, characterized in that, In Step 1, the mixing ratio of molybdenum powder to stearic acid is 500:1 by mass.

5. A method for preparing a high-density molybdenum target by gradient sintering according to claim 1, characterized in that, In Step 3, the volume ratio of the H2-CH4 mixed gas is 95:

5.

6. A method for preparing a high-density molybdenum target by gradient sintering according to claim 1, characterized in that, In Step 3, the argon ion bombardment energy is 500 eV.