Preparation method of high-purity cobalt sputtering target, high-purity cobalt sputtering target and application thereof

Abstract

The present invention relates to the technical field of sputtering targets, and in particular to a preparation method, a high-purity cobalt sputtering target and its application. The method comprises the following steps: (1) substrate pretreatment: selecting a target substrate, processing the substrate surface, and controlling the substrate surface roughness to be below 0.1 μm; (2) high-purity cobalt deposition: using chemical vapor deposition to deposit high-purity cobalt on the substrate, and maintaining the substrate temperature at 200-400°C during deposition to obtain a high-purity cobalt sputtering target. The present invention adopts a vapor deposition method to directly deposit on the substrate surface, and directly obtains a high-purity cobalt sputtering target in a one-step method, with a uniform reaction process and good product consistency; metallic cobalt is directly deposited on a backing plate, with low internal stress in the target and high magnetic uniformity, which is beneficial to ensuring the quality of the cobalt target product and low production cost. The obtained cobalt target PTF is higher than the traditional cold and hot rolling and annealing process, and has a uniform structure and better magnetron sputtering performance.

Description

Technical Field

[0001] The present invention relates to the technical field of sputtering targets, and in particular to a preparation method of a high-purity cobalt sputtering target, the high-purity cobalt sputtering target and applications thereof. Background Art

[0002] With the continuous development of advanced semiconductor integrated circuit technology, the wiring width has entered the deep nanometer stage. When the process is as low as 7nm and below, Co can replace Cu as an internal connection material and W as a through-hole material due to its low resistivity and excellent anti-electromigration performance. In addition, high-purity Co targets are also used in integrated circuit memory chips such as 3D NAND and DRAM. Therefore, high-purity Co targets have become one of the key core materials for advanced chip processes of 7nm and below. Because high-purity Co targets are ferromagnetic, the 7nm Co targets have higher requirements for their purity, magnetic properties and uniformity, which is one of the difficulties in target preparation. In terms of welding, due to the low martensitic phase transformation temperature of high-purity Co, high-temperature welding will reduce the magnetic permeability of the target material. At low welding temperatures, it is difficult to ensure bonding performance. Therefore, the target welding rate is the second difficulty.

[0003] Cobalt is a close-packed hexagonal metal at room temperature, with a melting point of approximately 1495°C. At high temperatures, it has a face-centered cubic structure, which transforms into a close-packed hexagonal structure when cooled to approximately 421°C. While the properties of the face-centered cubic structure vary somewhat in different directions, these differences are not significant. Consequently, the magnetocrystalline anisotropy is relatively weak, and the magnetic permeability is relatively high. However, for the close-packed hexagonal structure, the atomic arrangement along the c-axis differs significantly from that in other directions, resulting in significantly different properties in this direction. Studies have shown that the c-axis is the direction of easy magnetization, allowing magnetic fields to easily pass through it, while perpendicular directions have difficulty passing through it. Therefore, when manufacturing the target material, the easy-to-magnetize c-axis should be as perpendicular to the target surface as possible, making it easier for the magnetic field to pass through, thereby improving the magnetic field's ability to penetrate, or its permeability.

[0004] Some current patents focus solely on improving the processing technology for cobalt targets, such as domestic patents 201110430577.2 and 201110431047.X. Regardless of whether the target is produced using powder metallurgy or plastic processing, these patents focus solely on achieving fine and uniform grains, without addressing the impact of the material's crystal structure on performance, let alone how to control crystallographic orientation. Consequently, they can only produce cobalt targets with low PTF. In practice, this often fails to improve PTF or involves thinning the target material itself, resulting in high costs. Domestic patent CN200310124552.5 provides a comprehensive analysis of the impact of crystallographic orientation on the PTF of cobalt targets, but its core control method relies on introducing a strong magnetic field of up to 100 A / m during processing. Such a strong magnetic field is often difficult to achieve in actual production, making it inconvenient.

[0005] Foreign patent US6652668B1 increases the magnetic permeability of a cobalt target by increasing stress through rapid cooling with liquid nitrogen after rolling. However, this target material is expensive to prepare, its purity is limited by smelting technology, and the improvement in PTF is limited. US6585866B2 increases magnetic permeability through multiple cold rolling passes. However, due to the limited plasticity of cobalt, multiple annealing passes are required, increasing the process steps, and the PTF improvement is also limited, resulting in large fluctuations in target permeability. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for preparing a high-purity cobalt sputtering target, a high-purity cobalt sputtering target and its application, which specifically include the following contents:

[0007] A method for preparing a high-purity cobalt sputtering target comprises the following steps:

[0008] (1) Substrate pretreatment: Select a target substrate and process the substrate surface to control the substrate surface roughness to below 0.1 μm. By controlling the substrate surface roughness, high-purity cobalt is more easily deposited on the substrate surface during subsequent deposition operations, and the bond is more firmly established.

[0009] (2) High-purity cobalt deposition: High-purity cobalt is deposited onto the substrate treated in step (1) by chemical vapor deposition, with the substrate temperature maintained at 200-400°C during deposition, to obtain a high-purity cobalt sputtering target. Specifically, the substrate temperature in this step can be 200°C, 220°C, 250°C, 300°C, 320°C, 350°C, or 400°C.

[0010] Preferably, in step (1), copper or aluminum alloy material is selected as the substrate of the target material.

[0011] Preferably, after the processing in step (1), the substrate surface is cleaned with an ion beam to remove impurities on the substrate surface.

[0012] Preferably, the high-purity cobalt in step (2) is obtained by reducing (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl as a raw material, and the purity of the high-purity cobalt is ≥99.9995%. The specific operation of step (2) is as follows: placing the (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl raw material in a chemical vapor deposition device, using hydrogen as a reducing gas and high-purity argon (purity not less than 99.99%) as a protective carrier gas, under a vacuum degree of 90-120 Pa, high-purity cobalt is deposited on the surface of the substrate, and a high-purity cobalt sputtering target is prepared in one step. (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl is one of several cobalt-containing CVD precursors that can be used to manufacture important functional layers of equipment. It is an important precursor for the preparation of cobalt metal, cobalt nitride, cobalt silicide, etc., and has excellent performance, especially for the application of cobalt barrier layer / liner and eutectic seed layer. By utilizing the principle of high-purity (3,3-dimethyl-1-butyne) hexacarbonyl dicobalt vapor deposition crystal directional growth purification, high-purity metal cobalt target products can be produced, with material purity reaching over 99.9995%. The density of high-purity cobalt target blanks can reach over 99.5% of the theoretical density. Through cyclic chemical deposition, large diameter, 4mm thick, purity ≥99.9995%, and density of 8.86g / cm 3 of cobalt slabs.

[0013] Preferably, the magnetic permeability of the high-purity cobalt sputtering target prepared in step (2) is ≤6.5, the magnetic permeability of the target sputtering layer is ≥75% when the thickness is 4 mm, the magnetic permeability fluctuation is ≤2%, and the thickness fluctuation is ≤0.1 mm.

[0014] Preferably, the welding rate of the high-purity cobalt sputtering target prepared in step (2) is above 99.5%.

[0015] Preferably, the vertical direction of the sputtering surface of the high-purity cobalt sputtering target prepared in step (2) is <0001> Perpendicular to the target surface, the grain size and crystal plane orientation in the direction perpendicular to the sputtering surface are consistent.

[0016] Preferably, the density of the high-purity cobalt sputtering target prepared in step (2) is above 99.5% of the theoretical density.

[0017] Preferably, the high-purity cobalt sputtering target prepared in step (2) has a length of 100-500 mm and a width of 100-500 mm, or a diameter of Φ100-500 mm and a thickness of 1-5 mm.

[0018] A high-purity cobalt sputtering target prepared by the method disclosed by the invention.

[0019] The invention discloses an application of a high-purity cobalt sputtering target in the preparation of integrated circuits.

[0020] Beneficial effects of the present invention:

[0021] (1) The existing technology usually adopts 5N high-purity cobalt ingots for forging, rolling and heat treatment to prepare target blanks, and the preparation process is long. Due to the influence of deformation and heat treatment process on the uniformity of structure and stress control, the magnetic properties of the target material usually fluctuate to a certain extent. The uniformity of magnetic permeability inside the target material and the consistency between batches are difficult to control, resulting in poor uniformity and consistency of sputtered films, which is difficult to meet the use requirements of advanced processes. The present invention adopts vapor deposition method to directly deposit on the surface of the substrate, and directly obtains high-purity cobalt sputtering target material in one step. The reaction process is uniform and the product consistency is good; the metal cobalt is directly deposited on the back plate, the internal stress of the target material is small, the magnetic permeability uniformity is high, which is conducive to ensuring the quality of the cobalt target product, and the production cost is low. The PTF of the obtained cobalt target is higher than that of the traditional cold and hot rolling and annealing process, and the structure is uniform, with better magnetron sputtering performance.

[0022] (2) Affected by smelting technology and process, Co purity of 5N is usually prepared by smelting. However, the present invention creatively applies the vapor deposition method to the preparation of sputtering targets. The vapor deposition reaction is a continuous gaseous reaction, which has a further purification effect during the deposition process and can be used to prepare metal materials with higher purity. The present invention designs and improves the technology and equipment to prepare a high-purity cobalt sputtering target in one step by vapor deposition. The cobalt purity of the prepared target is further improved compared with the existing technology, and the purity can reach 5N5. The prepared target has the characteristics of high purity, high welding rate, high magnetic permeability and high uniformity. The finished product performance of the target after processing is excellent, and the target sputtering film has good uniformity, which can meet the application requirements of advanced process integrated circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a process flow chart of the preparation method disclosed in the present invention;

[0024] Figure 2 This is the XRD pattern of the sample prepared in Example 1 of the present invention;

[0025] Figure 3 This is the XRD pattern of the sample prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments shown below do not limit the invention as described in the claims. In addition, the entire contents of the structures shown in the following embodiments are not limited to those necessary for the solution of the invention as described in the claims.

[0027] A method for preparing a high-purity cobalt sputtering target comprises the following steps (see Figure 1 shown):

[0028] S1: First, prepare the copper alloy base material;

[0029] S2: Before deposition, in order to obtain a dense and high-quality Co target blank, the deposited surface needs to be polished, then cleaned with anhydrous ethanol, and dehydrated and dried;

[0030] S3: substrate roughness ≤ 0.1 μm, and ion beam cleaning is performed;

[0031] S4: Using a vapor deposition device, continuously reducing and depositing high-purity (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl gas onto a substrate using hydrogen or other reducing gases. In the present invention, high-purity hydrogen (purity ≥ 99.999%) is used as the reaction gas, and high-purity argon is used as the protective carrier gas.

[0032] S5: Cooling the deposited target;

[0033] S6: further processing the target material according to the size requirements to obtain a finished target material.

[0034] The method disclosed in the present invention can realize the mass production of large-size, high-purity, and high-density cobalt sputtering targets. The (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl used in the present invention is one of several cobalt-containing CVD precursors that can be used to manufacture important functional layers of equipment. It is an important precursor for preparing cobalt metal, cobalt nitride, cobalt silicide, etc., especially for the application of cobalt barrier layer / liner and eutectic seed layer, it has excellent performance. The method disclosed in the present invention deposits high-purity metallic cobalt onto the cobalt target material on the backplane material through chemical vapor deposition equipment, and then produces a finished cobalt target material after precision processing. The principle of directional growth and purification of high-purity (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl vapor deposition crystals can be used to produce high-purity metallic cobalt target products, and the material purity can reach more than 99.9995%. The density of the high-purity cobalt target blank can reach more than 99.5% of the theoretical density. The large diameter, thickness of 4mm, purity ≥99.9995%, and density of 8.86g / cm3 were obtained by cyclic chemical deposition. 3 of cobalt slabs.

[0035] The vertical direction of the sputtering surface in the high-purity cobalt target blank obtained by chemical vapor deposition is the deposition direction of high-purity metal cobalt or the direction of grain production, and the vertical direction of the sputtering surface is consistent with the crystal growth orientation. By controlling the reaction temperature and gas flow rate and flow direction, the crystal orientation of the deposited cobalt target can be controlled to form a close-packed hexagonal phase, and the sputtering surface is the (0002) crystal plane of the close-packed hexagonal phase, that is, the C axis of the close-packed hexagonal phase. <0001> Vertical sputtering surface. This is beneficial to increasing the magnetic permeability of the target material and improving the film forming speed and quality of the sputtering process. After the deposition thickness reaches the dimensional requirement of 4mm, stop heating and continue to introduce H2 and Ar to cool to room temperature. After cooling is completed, the final target product is prepared by dimensional processing of the base material. By adjusting the material, shape and size of the deposition substrate, cobalt targets or cobalt target blanks of different sizes or shapes can be deposited. The size of the high-purity cobalt target blank is 100-500mm in length, 100-500mm in width, or Φ100-500mm in diameter, and the target blank thickness can be 1-5mm.

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the embodiments and the prior art are briefly introduced below. The embodiments are compared with conventional methods to highlight the characteristics of the present invention. The target materials prepared in the embodiments and comparative examples are based on a conventional target thickness of 4 mm, and the magnetic properties of the targets are tested under these conditions.

[0037] Example 1

[0038] On a flat copper alloy substrate with a diameter of Φ500mm and a thickness of 10mm. The substrate is machined and polished, then cleaned with anhydrous ethanol and dehydrated. The substrate roughness is ≤0.1μm, and after ion beam cleaning, the substrate is placed in a PECVD vacuum furnace. High-purity (3,3-dimethyl-1-butyne) hexacarbonyl dicobalt is used, high-purity hydrogen (purity ≥99.999%) is used as the reaction gas, and high-purity argon is used as the protective carrier gas, at a vacuum degree of 100Pa. The substrate is heated to 400℃ during the deposition process. Deposition is carried out on a copper alloy substrate at a deposition temperature of 400℃. Through cyclic chemical deposition, a material with a diameter of Φ440mm, a thickness of 4mm, a purity of ≥99.9995%, and a density of 8.86g / cm 3 After deposition, heating is stopped and H2 and Ar are continued to flow to cool the material to room temperature. The finished Co slab can be processed to obtain a high-purity cobalt target.

[0039] Example 2

[0040] A 2mm thick aluminum layer is welded on a flat copper alloy substrate with a diameter of Φ500mm and a thickness of 10mm by thermal diffusion welding. The substrate is polished, then cleaned with anhydrous ethanol and dehydrated. The substrate roughness is ≤0.1μm, and after ion beam cleaning, the substrate is placed in a PECVD vacuum furnace. High-purity (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl is used, high-purity hydrogen (purity ≥99.999%) is used as the reaction gas, and high-purity argon is used as the protective carrier gas. It is deposited on the aluminum alloy substrate at a vacuum degree of 100Pa and a deposition temperature of 350°C. The substrate is heated to 350°C during the deposition process. By cyclic chemical deposition, a material with a diameter of Φ440mm, a thickness of 4mm, a purity of ≥99.9995%, and a density of 8.86g / cm 3 After deposition, heating is stopped and H2 and Ar are continued to flow to cool the material to room temperature. The finished Co slab can be processed to obtain a high-purity cobalt target.

[0041] Comparative Example 1

[0042] A 99.999% cobalt ingot is forged at 1100°C for 2 hours; the forged ingot is kept at 1000°C for 1 hour, then hot rolled with a total deformation rate of 80%, and heat treated after rolling; the target blank is cold rolled with a total deformation rate of 35%; the slab obtained in (3) is heat treated with an annealing temperature of 400°C, cooled to 370°C at a cooling rate of 10°C / min, immediately taken out, and water-cooled; the Co target blank is brazed to the backing plate, and precision CNC machining is performed after welding.

[0043] Comparative Example 2

[0044] A 99.999% cobalt ingot is forged at 1100°C for 2 hours. The forged ingot is kept at 1000°C for 1 hour and then hot rolled with a total deformation rate of 80%. It is then heat treated after rolling. The target blank is cold rolled with a total deformation rate of 40%. The annealing temperature is 450°C, and the target blank is cooled to 350°C at a cooling rate of 10°C / min. It is immediately taken out and air-cooled. The Co target blank is diffusion welded to the backing plate and precision CNC machined after welding.

[0045] The targets prepared by Examples 1 and 2 and Comparative Examples 1 and 2 by rolling method were compared, and samples of the cobalt target prepared by the cold rolling method (Comparative Example 1) were taken. The following is a comparison of the microstructure differences between Example 1 and Comparative Example 1 by analyzing the XRD test method of the samples. Figure 2 and Figure 3 .from Figure 2 and Figure 3 The results of the content of each crystal plane can be obtained, see Table 1.

[0046] Table 1 Comparison of the contents of various crystal planes in the examples and comparative examples

[0047] crystal face (1000) (0002) (10-11) (10-12) (11-10) (10-13) Example 1 0.13％ 77.36％ 0.61％ 19.68％ 0.00％ 2.22％ Example 2 0.00％ 78.81％ 1.19％ 20.00％ 0.00％ 0.00％ Comparative Example 1 0.52％ 45.34％ 1.64％ 49.69％ 0.04％ 2.78％ Comparative Example 2 0.5％ 49.5％ 11.8％ 34.8％ 0.1％ 3.2％

[0048] The data in Table 1 show that, compared to targets made using conventional processes, the target material produced using the patented technology of the present invention has a microstructure in which the crystal orientation is primarily concentrated on (0002), accounting for over 90%, while the (0002) ratio in samples made using conventional processes is only 30-50%. The concentration of (0002) on the sputtering surface improves the magnetic permeability of the target material. The performance differences of the cobalt targets prepared in the embodiment and the comparative example were compared by testing magnetic properties. The results of magnetic permeability, magnetic permeability, and magnetic permeability fluctuation are shown in Table 2. The magnetic permeability (PTF) of the cobalt targets prepared in Examples 1 and 2 were measured to compare their differences in magnetic field permeability. In terms of performance, the Φ440×4mm target material obtained using the patented technology of the present invention achieved a magnetic permeability of 78%, with a magnetic permeability fluctuation of 1.1%, ensuring the strength of the target material's near-surface magnetic field and achieving better sputtering capability. In contrast, the magnetic permeability fluctuation of the cobalt targets produced using conventional methods in Comparative Examples 1 and 2 reached over 2.5%. The present invention can produce highly permeable and uniform cobalt targets.

[0049] Table 2 Comparison of magnetic permeability of examples and comparative examples

[0050] Sample number Magnetic permeability PTF (Φ440×4mm target) Permeability fluctuation Example 1 6.3 78.0％ 1.1％ Example 2 6.2 78.7％ 1.1％ Comparative Example 1 7.8 71.4％ 2.8％ Comparative Example 2 7.5 72.2％ 2.9％

[0051] It can be seen that the transmittance of the cobalt target prepared by the patent of this invention to the magnetic field is significantly better than that of the traditional forging hot rolling, cold rolling and annealing process, and meets the better performance control requirements.

[0052] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-purity cobalt sputtering target, characterized in that: The following steps are involved: (1) Substrate pretreatment: Select copper or aluminum alloy material as the substrate of the target material, process the substrate surface, control the substrate surface roughness to below 0.1μm, and use ion beam to clean the substrate surface; (2) High-purity cobalt deposition: high-purity cobalt is deposited onto the substrate treated in step (1) by chemical vapor deposition, and the temperature of the substrate is maintained at 350-400°C during deposition to obtain a high-purity cobalt sputtering target. The high-purity cobalt is obtained by reducing (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl raw material, and the purity of the high-purity cobalt is ≥99.9995%; the specific operation is: placing the (3,3-dimethyl-1-butyne) dicobalt hexacarbonyl raw material in a chemical vapor deposition device, using hydrogen as a reducing gas and high-purity argon as a protective carrier gas, and depositing high-purity cobalt on the surface of the substrate under a vacuum degree of 90-120Pa, thereby preparing a high-purity cobalt sputtering target in one step; the prepared high-purity cobalt sputtering target is a close-packed hexagonal phase, and the C axis of the close-packed hexagonal phase is 1. <0001> Vertical sputtering surface.

2. The method for preparing a high-purity cobalt sputtering target according to claim 1, wherein: The magnetic permeability of the high-purity cobalt sputtering target prepared in the step (2) is ≤6.5, the magnetic permeability of the target sputtering layer is ≥75% when the thickness is 4 mm, the magnetic permeability fluctuation is ≤2%, and the thickness fluctuation is ≤0.1 mm.

3. The method for preparing a high-purity cobalt sputtering target according to claim 1, wherein: The welding rate of the high-purity cobalt sputtering target prepared in step (2) is above 99.5%.

4. The method for preparing a high-purity cobalt sputtering target according to claim 1, wherein: The density of the high-purity cobalt sputtering target prepared in step (2) is more than 99.5% of the theoretical density.

5. The method for preparing a high-purity cobalt sputtering target according to claim 1, wherein: The high-purity cobalt sputtering target prepared in step (2) has a length of 100-500 mm and a width of 100-500 mm, or a diameter of Φ100-500 mm and a thickness of 1-5 mm.

6. A high-purity cobalt sputtering target prepared by the method according to any one of claims 1 to 5.

7. Use of the high-purity cobalt sputtering target according to claim 6 in the preparation of integrated circuits.

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