A cofeb alloy target and a method for manufacturing the same

Abstract

The application belongs to the field of target material preparation and discloses a preparation method of a CoFeB alloy target material, which comprises the following steps: boron particles are put into a smelting crucible according to the proportion of iron, cobalt and boron in the CoFeB alloy target material, then cobalt sheets and iron sheets are put into the smelting crucible and covered on the surface of the boron particles, a device furnace cover is covered, vacuumizing, heating and atomization operations are performed, the collected alloy powder is sieved after the device is cooled, and the CoFeB alloy raw material with a particle size of less than 150 um is obtained; the prepared CoFeB alloy raw material is put into a cladding for hot isostatic pressing sintering, the sintered CoFeB alloy material is machined, and the CoFeB alloy target material is obtained; through the above operations, the loss of boron in the smelting process is inhibited, and then the content of each component in the generated CoFeB alloy target material is accurately controlled.

Description

Technical Field

[0001] This invention relates to the field of target preparation, and more particularly to a CoFeB alloy target and its preparation method. Background Technology

[0002] We live in an era of information explosion, especially with the advancement of technologies such as artificial intelligence and cloud computing, which are causing an explosive expansion and increase in global data volume. Modern memory technology is primarily centered around electronic computers. Based on current computer information technology, it can be categorized into semiconductor storage, magnetic storage, and optical storage according to the information storage medium and method. Among these, magnetic storage is widely used due to its high storage density and resistance to data loss. CoFeB, as a crucial alloy material in spintronics, is widely used in magnetic tunnel junctions and magnetic random access memory (MRAM).

[0003] Chinese patent application 202211462233.4 discloses a CoFeB alloy target. The CoFeB alloy target of this invention comprises the following elemental composition by mass percentage: 15-35% cobalt, 50-60% iron, and 15-30% boron.

[0004] Furthermore, the preparation method of CoFeB alloy target material is disclosed, including the following steps:

[0005] (1) Batching: Weigh cobalt metal, iron metal and crystalline boron according to the elemental composition and content in the CoFeB alloy target material. When weighing the crystalline boron, 0.4-0.8% of crystalline boron should be added to the boron mass percentage content in the CoFeB alloy target material to obtain a mixture.

[0006] (2) Melting: The mixture is melted in an inert gas atmosphere, and the melt is cooled to 1350-1450℃ to obtain an alloy melt;

[0007] (3) Atomization: The alloy melt is atomized, and the powder obtained after atomization is sieved to obtain the alloy powder;

[0008] (4) Hot pressing sintering: Boron nitride is sprayed into the mold in sequence, molybdenum paper is covered, and then the alloy powder is placed on the molybdenum paper of the mold for pre-pressing; under vacuum conditions, the pre-pressed alloy powder is hot pressed and sintered to obtain the CoFeB alloy target.

[0009] However, during the preparation process, the boron raw material will be lost to some extent. As can be seen from the examples and comparative examples of this scheme, the boron content in the final CoFeB alloy target is significantly lower than the boron content in the raw material. In the examples and comparative examples of this scheme, the boron content in the CoFeB alloy target decreased by 0.4%-0.8% during the reaction process.

[0010] The problem this solution aims to solve is: how to provide a method for preparing CoFeB alloy targets to reduce boron loss during the preparation process. Summary of the Invention

[0011] The purpose of this application is to provide a method for preparing CoFeB alloy targets. This method reduces the generation of boron oxide during the reaction process by using a special placement order of boron particles, cobalt sheets and iron sheets in the crucible during melting. At the same time, it reduces the volatilization of boron oxide, thereby suppressing the loss of boron during melting and allowing precise control of the content of each component in the generated CoFeB alloy targets.

[0012] In addition, this application also provides a CoFeB alloy target.

[0013] To achieve the above objectives, this application discloses a method for preparing a CoFeB alloy target, comprising the following steps:

[0014] Step 1: According to the ratio of iron, cobalt and boron in the CoFeB alloy target, put boron particles into the melting crucible, then put cobalt sheets and iron sheets into the melting crucible and cover the surface of the boron particles. Cover the furnace lid and perform vacuuming, heating and atomization operations. After the equipment cools down, sieve the collected alloy powder to obtain CoFeB alloy raw material with a particle size <150um.

[0015] Step 2: Place the CoFeB alloy raw material obtained in Step 1 into a sleeve for hot isostatic pressing sintering, and machine the sintered CoFeB alloy material to obtain the CoFeB alloy target.

[0016] The boron particles have a diameter of 6-12 mm.

[0017] Preferably, the CoFeB alloy target material contains 20%-30% cobalt by mass, 60%-75% iron by mass, and 3%-8% boron by mass.

[0018] Preferably, the CoFeB alloy target material contains 22%-26% cobalt by mass, 68%-72% iron by mass, and 5%-8% boron by mass.

[0019] Preferably, step 1 specifically includes:

[0020] According to the iron-cobalt-boron ratio in the CoFeB alloy target, boron particles are added into a melting crucible. Then, cobalt and iron sheets are added into the melting crucible and covered on the surface of the boron particles. The boron, iron, and cobalt sources are heated and melted in a nitrogen atmosphere with a pressure of 2-5 kPa at a melting temperature of 1450-1550℃. Then, it is transferred to a holding crucible at a temperature of 1350-1400℃ for atomization at a pressure of 20-30 Bar. After the CoFeB alloy melt is completely atomized and the melting crucible and holding crucible are cooled to below 200℃, the obtained CoFeB alloy powder is collected and passed through a 100-mesh sieve to obtain CoFeB alloy raw material with a particle size of <150 μm.

[0021] Preferably, step 2 specifically includes:

[0022] The inner wall of the casing is lined with ceramic fiber paper. The CoFeB alloy raw material obtained in step 1 is then placed into the casing in layers, with ceramic fiber paper, a backing plate, and another layer of ceramic fiber paper arranged sequentially between each layer of CoFeB alloy raw material. The casing is then heated to degas at a temperature of 450-550℃ until the vacuum degree inside the casing is <4*10. -3 After Pa, the enclosure is closed;

[0023] The sealed cladding is hot isostatically pressed at 850-950℃ and 130-160MPa for 3-5 hours, and the cladding is removed to obtain the alloy ingot.

[0024] Alloy ingots are machined to obtain alloy targets.

[0025] Preferably, the boron particles have a particle size of 6-12 mm.

[0026] Preferably, the purity of the boron particles is 3N-3N5, the purity of the cobalt sheet is 3N-3N5, and the purity of the iron sheet is 3N-4N.

[0027] In addition, a CoFeB alloy target material is disclosed, which is prepared using the above-mentioned method for preparing CoFeB alloy targets.

[0028] Preferably, the difference between the cobalt, iron, and boron content in the alloy target and the cobalt, iron, and boron content in the alloy raw material is less than 0.2%.

[0029] The beneficial effects of this application are as follows: By using a special placement order of boron particles, cobalt sheets and iron sheets in sequence during melting, this application reduces the generation of boron oxide during the reaction process and reduces the volatilization of boron oxide, thereby suppressing the loss of boron during melting and enabling precise control of the content of each component in the generated CoFeB alloy target. Attached Figure Description

[0030] Figure 1This is a schematic diagram of the alloy ingot in Example 1;

[0031] Figure 2 This is a schematic diagram of the alloy target material in Example 1. Detailed Implementation

[0032] The present invention will now be clearly and completely described in conjunction with embodiments thereof. It should be noted that, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0033] Example 1

[0034] Step 1: Weigh out Co flakes with a purity of 3N, Fe flakes with a purity of 3N5, and B particles with a purity of 3N and a particle size of 8mm according to the ratio of Co: 24.5wt%, Fe: 69.3wt%, and B: 6.2wt%. Add them to the melting crucible of the atomization equipment in the order of B, Fe, and Co. Evacuate the equipment to below 20Pa, then fill it with nitrogen to a pressure of 3KPa. Then heat the melting crucible to 1500℃. After the oxide scale on the surface of the CoFeB melt in the melting crucible is broken, transfer the CoFeB melt from the melting crucible to a heat-preserving crucible at a temperature of 1380℃ for atomization at a pressure of 25Bar. After the CoFeB alloy melt is completely atomized and cooled to room temperature, collect the CoFeB alloy powder and pass it through a 100-mesh sieve to obtain CoFeB alloy raw material with a particle size of <150um.

[0035] Step 2: Design the sheath according to the finished product dimensions. The sheath material is low-carbon steel. Ceramic fiber paper is laid on the inner wall of the sheath. CoFeB alloy raw materials are layered and compacted inside the sheath, with ceramic fiber paper, a pad, and another layer of ceramic fiber paper arranged sequentially between each layer of CoFeB alloy raw materials. The sheath cover plate with a degassing port is then welded to the top of the sheath, and the degassing pipe is welded to the degassing port. A helium mass spectrometer leak detector is used to check for leaks in the sheath. After leak detection, degassing is performed by heating to 450℃ until the vacuum degree inside the sheath reaches 3*10⁻⁶. -3 After Pa, the degassing tube near the sheath is flattened and the excess part is cut off to create a sealed vacuum environment inside the sheath.

[0036] The sealed cladding is placed in a hot isostatic pressing furnace, and the vacuum is drawn to below 1000Pa. Then the pressure is increased and the temperature is raised to 850℃ and the pressure is 130MPa. It is maintained for 4 hours. After sintering, the cladding is removed from the furnace and the CoFeB alloy ingot is obtained by cutting it with an angle grinder.

[0037] The obtained CoFeB alloy ingot is cut into CoFeB alloy target blanks by wire cutting, and then the finished CoFeB alloy target material is obtained by surface grinding and external cylindrical machining.

[0038] Example 2

[0039] The process is basically the same as in Example 1, except that in step 1: Co flakes with a purity of 3N, Fe flakes with a purity of 3N5, and B particles with a purity of 3N and a particle size of 8mm are weighed according to the ratio of Co: 24.5wt%, Fe: 69.3wt%, and B: 6.2wt%. The particles are then added to the melting crucible of the atomization equipment in the order of B, Fe, and Co. The vacuum is evacuated to below 20Pa, and then nitrogen is added to a pressure of 3KPa. The melting crucible is then heated to 1550℃. After the oxide scale on the surface of the CoFeB melt in the melting crucible is broken, the CoFeB melt is transferred from the melting crucible to a heat-preserving crucible at a temperature of 1400℃ for atomization at a pressure of 20Bar. After the CoFeB alloy melt is completely atomized and cooled to room temperature, the CoFeB alloy powder is collected and passed through a 100-mesh sieve to obtain CoFeB alloy raw material with a particle size of <150um.

[0040] Example 3

[0041] The process is basically the same as in Example 1, except that in step 2: A casing is designed according to the finished product dimensions. The casing material is low-carbon steel. Ceramic fiber paper is placed on the inner wall of the casing. CoFeB alloy raw materials are layered and compacted inside the casing. Then, graphite paper, a pad, and another layer of graphite paper are sequentially placed between each layer of CoFeB alloy raw materials. A casing cover plate with a degassing port is welded to the top of the casing, and a degassing pipe is welded to the degassing port. A helium mass spectrometer is used to check for leaks in the casing. After leak detection, degassing is performed by heating to 450°C until the vacuum degree inside the casing reaches 3*10... -3 After Pa, the degassing tube near the sheath is flattened and the excess part is cut off to create a sealed vacuum environment inside the sheath.

[0042] Comparative Example 1

[0043] The process is basically the same as in Example 1, except that in step 1: Co flakes with a purity of 3N, Fe flakes with a purity of 3N5, and B particles with a purity of 3N and a particle size of 8mm are weighed according to the ratio of Co: 24.5wt%, Fe: 69.3wt%, and B: 6.2wt%. The Co, Fe, and B particles are added to the melting crucible of the atomization equipment in the order of Co, Fe, and B. The vacuum is evacuated to below 20Pa, and then nitrogen is added to a pressure of 3KPa. The melting crucible is then heated to 1500℃. After the oxide scale on the surface of the CoFeB melt in the melting crucible is broken, the CoFeB melt is transferred from the melting crucible to a heat-preserving crucible at a temperature of 1380℃ for atomization at a pressure of 25Bar. After the CoFeB alloy melt is completely atomized and cooled to room temperature, the CoFeB alloy powder is collected and passed through a 100-mesh sieve to obtain CoFeB alloy raw material with a particle size of <150um.

[0044] Comparative Example 2

[0045] The process is basically the same as in Example 1, except that in step 1: Co flakes with a purity of 3N, Fe flakes with a purity of 3N5, and B particles with a purity of 3N and a particle size of 8mm are weighed according to the ratio of Co: 24.5wt%, Fe: 69.3wt%, and B: 6.2wt%. The Co, B, and Fe particles are added to the melting crucible of the atomization equipment in the order of Co, B, and Fe. The vacuum is evacuated to below 20Pa, and then nitrogen is added to a pressure of 3KPa. The melting crucible is then heated to 1500℃. After the oxide scale on the surface of the CoFeB melt in the melting crucible is broken, the CoFeB melt is transferred from the melting crucible to a heat-preserving crucible at a temperature of 1380℃ for atomization at a pressure of 25Bar. After the CoFeB alloy melt is completely atomized and cooled to room temperature, the CoFeB alloy powder is collected and passed through a 100-mesh sieve to obtain CoFeB alloy raw material with a particle size of <150um.

[0046] Performance testing:

[0047] The components were detected using ICP.

[0048] Carbon content was detected using a carbon-sulfur analyzer;

[0049] Oxygen content is measured using an oxygen and nitrogen meter.

[0050] Table 1: Performance Test Results

[0051]

[0052]

[0053] Results analysis:

[0054] As can be seen from Examples 1 and 2, changing the melting temperature, atomization temperature, and atomization pressure has no significant impact on the final performance of the target material.

[0055] As can be seen from Examples 1 and 3, when graphite paper is used instead of ceramic paper, the iron content after the reaction is slightly reduced. We speculate that this is because the iron reacts with the graphite paper, which causes a certain degree of iron loss. At the same time, the reaction between the iron and the graphite paper introduces more carbon, leading to an increase in the carbon content of the target material.

[0056] As can be seen from Example 1 and Comparative Examples 1-2, when the order of Co, B and Fe is changed in the atomization device, the boron content fluctuates significantly before and after the reaction. We speculate that the reason may be that the contact area between boron and oxygen increases during the reaction, the formation rate of boron oxide increases, and boron oxide is easily volatilized during the reaction, which leads to a decrease in boron content.

[0057] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a CoFeB alloy target, characterized in that, Includes the following steps: Step 1: According to the ratio of iron, cobalt and boron in the CoFeB alloy target, put boron particles into the melting crucible, then put iron sheets and cobalt sheets into the melting crucible in sequence and cover the surface of boron particles. Heat the melting crucible containing boron particles, iron sheets and cobalt sheets, atomize and sieve to obtain CoFeB alloy raw material with a particle size <150μm. Step 2: Place the CoFeB alloy raw material obtained in Step 1 into a sleeve for hot isostatic pressing sintering, and machine the sintered CoFeB alloy material to obtain the CoFeB alloy target. The boron particles have a particle size of 6-12 mm; The CoFeB alloy target contains 20%-30% cobalt, 60%-75% iron, and 3%-8% boron by mass.

2. The method for preparing the CoFeB alloy target according to claim 1, characterized in that, The CoFeB alloy target contains 22%-26% cobalt, 68%-72% iron, and 5%-8% boron by mass.

3. The method for preparing the CoFeB alloy target according to claim 1, characterized in that, Step 1 specifically involves: The ratio of iron, cobalt, and boron in the CoFeB alloy target material was determined. Boron particles were added to a melting crucible, followed by iron and cobalt sheets which were then added to the crucible and covered the surface of the boron particles. The boron particles, iron sheets, and cobalt sheets were heated and melted in a nitrogen atmosphere at a pressure of 2-5 kPa at a melting temperature of 1450-1550℃. The mixture was then transferred to a holding crucible at a temperature of 1350-1400℃ for atomization at a pressure of 20-30 bar. After the CoFeB alloy melt was completely atomized and the melting and holding crucibles were cooled to below 200℃, the resulting CoFeB alloy powder was collected and passed through a 100-mesh sieve to obtain CoFeB alloy raw material with a particle size of <150 μm.

4. The method for preparing the CoFeB alloy target according to claim 1, characterized in that, Step 2 specifically involves: The inner wall of the casing is lined with ceramic fiber paper. The CoFeB alloy raw material obtained in step 1 is then placed into the casing in layers, with ceramic fiber paper, a backing plate, and another layer of ceramic fiber paper arranged sequentially between each layer of CoFeB alloy raw material. The casing is then heated to degas at a temperature of 450-550℃ until the vacuum degree inside the casing is <4×10⁻⁶. -3 After Pa, the enclosure is closed; The sealed cladding is hot isostatically pressed at 850-950℃ and 130-160MPa for 3-5 hours, and the cladding is removed to obtain the alloy ingot. Alloy ingots are machined to obtain alloy targets.

5. The method for preparing the CoFeB alloy target according to claim 1, characterized in that, The boron particles have a purity of 3N-3N5, the cobalt sheet has a purity of 3N-3N5, and the iron sheet has a purity of 3N-4N.

6. A CoFeB alloy target material, characterized in that, The CoFeB alloy target was prepared using the preparation method described in any one of claims 1-5.

7. The alloy target material according to claim 6, characterized in that, The difference between the boron content in the alloy target and the boron content in the alloy raw materials used to prepare the alloy target is less than 0.2 wt%.

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