Preparation method of ultra-fine grain copper target material

Abstract

The invention discloses a preparation method of an ultra-fine grain copper target material, which comprises the following steps: step 1, sequentially cleaning and polishing an oxygen-free copper plate to obtain a pre-rolled plate; secondly, the two pre-rolled plates are overlapped and fixed, then multi-pass rolling is conducted at the temperature below the recrystallization temperature of the oxygen-free copper plate, and rolled plates are obtained; thirdly, the rolled plate is cut from the middle, then the first step and the second step are repeated for multiple times, and a machined plate is obtained; and fourthly, the machined plate is subjected to recovery annealing and then is sequentially straightened, machined and cleaned, and the ultra-fine grain copper target material is obtained. According to the method, the copper plate is subjected to severe plastic deformation by adopting an accumulative roll-bonding technology, the refining limit of a traditional machining mode on the grain size is broken through through large dependent variable, super refining of the grain size of pure copper is achieved, the ultra-fine grain target material is obtained, used equipment is simple, the size of a prepared sample is large, continuous industrial production of ultra-fine grain plates can be achieved, and the method is suitable for industrial production. And the method is a very potential production technology for industrialization of the ultra-fine grain target material.

Description

Technical Field

[0001] The invention belongs to the technical field of high-performance sputtering target material processing, and in particular relates to a method for preparing an ultrafine-grained copper target material. Background Art

[0002] With the rapid development of information technologies such as the fifth generation of mobile communications, the Internet of Things, and artificial intelligence, the importance of integrated circuits has become more prominent, and related industries have continued to grow at a high rate. High-purity metal sputtering targets are key materials for preparing thin films using physical vapor deposition methods in the metallization process of integrated circuits. With the innovative breakthroughs in advanced devices and technologies such as 7nm and below advanced logic devices, new memory devices, and three-dimensional integration of integrated circuits, the demand for improving the performance of copper targets has become more urgent.

[0003] The grain size of the target material has a great influence on the preparation and performance of the metal film of the integrated circuit. As an important parameter index of the target material, the grain size will affect the surface morphology and IV characteristic curve of the target material after sputtering, and then affect the deposition rate and crystallization of the film. For example, the upsetting process can effectively obtain a fine and uniform microstructure and improve the sputtering performance of the target material. Generally speaking, the finer the grain of the target material, the more uniform the composition structure, the smaller the surface roughness, the better the quality of the film formed by physical vapor deposition on the silicon wafer, and the higher the utilization rate and life of the target material. At present, the preparation technology of the copper target material sold in China is mainly based on the traditional processing method, which mainly involves forging and rolling processes. The copper target material produced by the traditional processing method has a relatively coarse grain, and its size is generally 50-200µm. However, Honeywell in the United States has a monopoly in the preparation of ultrafine-grained targets with a grain size of <5µm produced by large-scale equal channel angle extrusion equipment. Moreover, relevant experimental data show that the service life of Honeywell's ultrafine-grained copper target is 300kWh longer than that of coarse-grained copper target, and the number of arcing times during the service life is greatly reduced. Based on the above excellent performance, ultrafine-grained targets are one of the future development directions of the sputtering target industry.

[0004] A large number of studies on the preparation of ultrafine-grained metal materials have been carried out at home and abroad, among which severe plastic deformation (SPD) is an effective preparation method. SPD refers to the introduction of strain far exceeding the strain required for traditional material processing (strain <2) during material processing, and processing below the recrystallization temperature so that recrystallization does not occur. During the processing process, dislocation movement, twin deformation, stacking faults and other defects will occur inside the material. The movement of these crystal defects causes dislocation cells, subgrains and large-angle grain boundaries to form inside the material, thereby refining the coarse-grained material to 100-1000nm nano / ultrafine-grained materials. The main methods of severe plastic deformation are: high-pressure torsion, reciprocating extrusion, surface mechanical grinding, equal channel angular extrusion, cumulative rolling, etc. High-pressure torsion technology can produce very large strains, and surface mechanical grinding technology has a very large strain. Both can effectively refine the grains to micrometers or even nanometers. However, both can only produce refinement on the surface of the workpiece, and are currently in the laboratory stage, and can prepare small samples, which are not suitable for industrial applications. Equal channel angular extrusion technology has very high requirements for equipment. Currently, only Honeywell has large-scale equal channel angle extrusion equipment in the world that can use this method to process large-sized ultrafine-grained targets. The cumulative rolling method was proposed by the research group of Y. Saito of Osaka University in Japan in 1998. As a newer SPD process, compared with other SPD technologies, cumulative rolling has outstanding advantages: simple equipment, which is a commonly used plate and strip rolling mill; large sample size, which can realize the continuous industrial production of ultrafine-grained plates, and is a production technology with great potential for the industrialization of ultrafine-grained materials.

[0005] In summary, ultrafine-grained targets have the advantages of good film quality, high target utilization rate and long service life. However, how to develop an ultrafine-grained preparation technology that is efficient, low-cost and can meet industrial production is an urgent problem to be solved. Therefore, a method for preparing an ultrafine-grained copper target is needed. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing an ultrafine-grained copper target material in view of the deficiencies of the above-mentioned prior art. The method uses cumulative rolling technology to perform severe plastic deformation on the copper plate, breaks through the grain size refinement limit of the traditional processing method through a large strain, realizes the super-refinement of the pure copper grain size, and obtains an ultrafine-grained copper target material. The obtained ultrafine-grained target material has fine grains, uniform structure, and small surface roughness. The film formed by physical vapor deposition on the silicon wafer is of good quality, and the target material utilization rate and life are high.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an ultrafine-grained copper target, characterized in that the method comprises the following steps: Step 1: Clean and polish the oxygen-free copper plate in sequence to obtain a pre-rolled plate; Step 2: Overlap the two pre-rolled plates obtained in step 1, then punch holes around them and fix them with iron wires, and then perform multiple rolling below the recrystallization temperature of the oxygen-free copper plate to obtain a rolled plate; Step 3, cutting the rolled plate obtained in step 2 in the middle, and then repeating steps 1 and 2 for multiple times to obtain a processed plate; Step 4: recover annealing the processed plate obtained in step 3, and then straighten, machine and clean it in sequence to obtain an ultrafine-grained copper target.

[0008] The present invention removes oil, impurities and oxide films on the surface of the oxygen-free copper plate by cleaning and polishing, so as to facilitate the stacking of the two pre-rolled plates in the process of rolling the two pre-rolled plates into one rolled plate, and also prevent the introduction of impurities. The two pre-rolled plates are fixed together by drilling holes around them and fixing them with iron wires, so as to prevent relative sliding between the two during subsequent rolling. The cumulative stacking is achieved by multiple rolling passes with intermediate cutting and repeated multiple times, and the oxygen-free copper plate is subjected to severe plastic deformation. The grain size refinement limit of the traditional processing method is broken through by a large strain, and the super-refinement of the pure copper grain size is achieved. The residual stress is removed by recovery annealing, and an ultra-fine-grained copper target is obtained.

[0009] The above-mentioned method for preparing an ultrafine-grained copper target is characterized in that the mass purity of the oxygen-free copper plate in step 1 is not less than 99%. The present invention controls the mass purity of the oxygen-free copper plate and the purity of the ultrafine-grained copper target, thereby ensuring the performance of the ultrafine-grained copper target.

[0010] The above-mentioned method for preparing an ultrafine-grained copper target is characterized in that the cleaning in step 1 is to soak the oxygen-free copper plate in acetone or ethanol for 0.5h to 2h. The present invention fully removes impurities and oil stains on the surface of the oxygen-free copper plate by soaking in acetone or ethanol.

[0011] The above-mentioned method for preparing an ultrafine-grained copper target is characterized in that the grinding in step 1 is performed by using an angle grinder with a wire brush for 2 min to 5 min, the rotation speed of the wire brush during the grinding is 5000 r / min to 11000 r / min, and the diameter of the steel wire is 0.1 mm to 0.5 mm. The present invention fully removes the oxide film on the surface of the oxygen-free copper plate by controlling the grinding parameters to ensure the effect of subsequent rolling.

[0012] The above-mentioned method for preparing an ultrafine-grained copper target is characterized in that the speed of the multi-pass rolling in step 2 is 0.1m / s~0.7m / s, the reduction amount of each pass is 5%~50%, the total reduction amount is 50%, and no lubrication is required in the multi-pass rolling. The present invention ensures the effect of multi-pass rolling by controlling the parameters of the multi-pass rolling, realizes overlapping rolling, and during the rolling process, there is no lubrication on the roller and the workpiece surface, thereby reducing impurities and oil stains on the workpiece surface.

[0013] It should be noted that in the multi-pass rolling of the present invention, when the total pressure reduction is 50%, the cumulative strain satisfy , where r is the total thickness reduction, that is, the total pressure is 50%. The cumulative strain is used to evaluate the deformation strength of various deformation modes, such as high-pressure torsion, equal channel angular extrusion, surface mechanical grinding, etc. The higher the cumulative strain, the higher the deformation strength and the more obvious the grain refinement.

[0014] The above-mentioned method for preparing an ultrafine-grained copper target is characterized in that the number of repetitions in step 3 is more than two times. The present invention controls the rolling parameters and the number of repetitions to make the cumulative strain greater than 2.4, so that the grains of the copper target can be refined to less than 5 μm.

[0015] The above-mentioned method for preparing an ultrafine-grained copper target is characterized in that the temperature of the recovery annealing in step 4 is less than 350°C, the time is 0.5h~6h, and the atmosphere is argon or nitrogen. The present invention avoids excessive growth of grains and removes the stress generated during the rolling deformation process by controlling the parameters of the recovery annealing. The present invention adopts argon or nitrogen atmosphere annealing to prevent oxidation of the copper target. By adopting argon or nitrogen atmosphere to prevent oxidation, the performance of the ultrafine-grained copper target is guaranteed.

[0016] The above-mentioned method for preparing an ultrafine-grained copper target is characterized in that the grain size of the ultrafine-grained copper target in step 4 is not greater than 5 μm.

[0017] Compared with the prior art, the present invention has the following advantages: 1. The present invention utilizes cumulative rolling technology to perform severe plastic deformation on the copper plate, breaks through the grain size refinement limit of the traditional processing method through a large strain, and realizes the super-refinement of the pure copper grain size. Moreover, this technology can realize continuous industrial production on a traditional cold-rolled plate and strip rolling mill, gets rid of the dependence on large-scale equipment, namely equal channel angular extrusion, and reduces production costs. The obtained ultrafine-grained target material has fine grains, uniform structure, and small surface roughness. The thin film deposited on the silicon wafer by the physical vapor deposition method is of good quality, and the target material utilization rate and life are high.

[0018] 2. The present invention deforms the copper plate through cumulative rolling technology to produce work hardening and improve the strength of the copper target. The technology produces preferential orientation by changing the rolling passes, that is, by adjusting the strain amount, and realizes the regulation of the crystal orientation of the target grains. The (111) close-packed plane of copper is parallel to the target plane, and the maximum percentage can reach 60%, which effectively improves the sputtering rate of the target.

[0019] 3. The present invention utilizes cumulative rolling technology to prepare ultrafine-grained copper target materials, and controls the grain size and crystal orientation by adjusting process parameters to produce ultrafine-grained copper target materials with an average grain size of less than 5µm.

[0020] 4. The present invention aims to solve the shortcomings of coarse-grained copper targets, such as low target utilization rate, short service life, coarse and uneven grain size, and large surface undulations of deposited films. By using cumulative rolling technology, an efficient and stable copper target manufacturing method is provided, aiming to obtain a high-purity copper target with uniform structure, high density, and ultrafine grains.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the process of the method for preparing ultrafine-grained copper target of the present invention.

[0023] Figure 2 This is the metallographic structure diagram of the oxygen-free copper plate used in step 1 of Example 3 of the present invention.

[0024] Figure 3 This is a scanning electron micrograph of the ultrafine-grained copper target obtained in step 4 of Example 3 of the present invention. DETAILED DESCRIPTION

[0025] Figure 1 The schematic diagram of the process of preparing the ultrafine-grained copper target of the present invention is as follows: Figure 1 It can be seen that the present invention first grinds two oxygen-free copper plates, then overlaps the two grinded pre-rolled plates, and then rolls them to obtain rolled plates, cuts the rolled plates in the middle, and repeats the grinding, overlapping, rolling and cutting processes in a cycle to finally obtain an ultrafine-grained copper target.

[0026] Example 1 This embodiment includes the following steps: Step 1: put the rolled oxygen-free copper plate with a mass purity of 99% into ethanol for cleaning for 30 minutes to remove the surface oil, and then use an angle grinder with a wire brush head to grind the surface at a speed of 11000r / min for 2 minutes to remove the oxide scale and impurities, so as to expose the fresh surface and obtain a pre-rolled plate; the diameter of the steel wire in the wire brush head is 0.25mm; Step 2: Overlap the two pre-rolled plates obtained in step 1, punch holes around them, and fix them with a wire with a diameter of 1 mm. Then, roll them at room temperature at a rolling speed of 0.1 m / s, with a reduction of 5% per pass, for 10 passes to ensure a total reduction of 50% and a cumulative strain of , and a rolled plate is obtained; in the said multiple-pass rolling, the surfaces of the rolling rollers and the workpieces are not lubricated; Step 3, cutting the rolled plate obtained in step 2 from the middle, and then repeating step 1 and step 2 twice, until the cumulative strain reaches 2.4, to obtain a processed plate; Step 4: Heat the processed plate obtained in step 3 to 300° C. in an argon atmosphere and then perform recovery annealing for 1 hour to remove residual stress, and then perform straightening, machining and cleaning in sequence, and package to obtain an ultrafine-grained copper target.

[0027] Example 2 This embodiment includes the following steps: Step 1: Place a rolled oxygen-free copper plate with a mass purity of 99.9% in acetone for 40 minutes to remove surface oil stains, and then use an angle grinder with a wire brush head to grind the surface at a speed of 5000r / min for 3 minutes to remove oxide scale and impurities, so as to expose a fresh surface and obtain a pre-rolled plate; the diameter of the steel wire in the wire brush head is 0.1mm; Step 2: Overlap the two pre-rolled plates obtained in step 1, punch holes around them, and fix them with a wire with a diameter of 1 mm. Then, roll them at room temperature at a rolling speed of 0.34 m / s, with a reduction of 10% per pass, for 5 passes to ensure a total reduction of 50% and a cumulative strain of , and a rolled plate is obtained; in the said multiple-pass rolling, the surfaces of the rolling rollers and the workpieces are not lubricated; Step 3, cutting the rolled plate obtained in step 2 from the middle, and then repeating step 1 and step 2 three times, until the cumulative strain reaches 3.2, to obtain a processed plate; Step 4: Heat the processed plate obtained in step 3 to 200° C. in an argon atmosphere and then perform recovery annealing for 0.5 h to remove residual stress, and then perform straightening, machining and cleaning in sequence, and package to obtain an ultrafine-grained copper target.

[0028] Example 3 This embodiment includes the following steps: Step 1: Place a rolled oxygen-free copper plate with a mass purity of 99.99% in ethanol for 120 minutes to remove surface oil stains, and then use an angle grinder with a wire brush head to grind the surface at a speed of 11000r / min for 5 minutes to remove oxide scale and impurities, so as to expose a fresh surface and obtain a pre-rolled plate; the diameter of the steel wire in the wire brush head is 0.25mm; Step 2: Overlap the two pre-rolled plates obtained in step 1, punch holes around them, and fix them with a wire with a diameter of 1 mm. Then, roll them at room temperature at a rolling speed of 0.7 m / s, with a reduction of 50% per pass, for one pass, ensuring that the total reduction is 50%, and the accumulated strain is , and a rolled plate is obtained; in the said multiple-pass rolling, the surfaces of the rolling rollers and the workpieces are not lubricated; Step 3, cutting the rolled plate obtained in step 2 from the middle, and then repeating step 1 and step 2 four times until the cumulative strain reaches 4.0 to obtain a processed plate; Step 4: Heat the processed plate obtained in step 3 to 250° C. in an argon atmosphere and then perform recovery annealing for 1 hour to remove residual stress, and then perform straightening, machining and cleaning in sequence, and package to obtain an ultrafine-grained copper target.

[0029] Figure 2 This is the metallographic structure diagram of the oxygen-free copper plate used in step 1 of this embodiment. Figure 3 This is a scanning electron microscopic image of the ultrafine-grained copper target obtained in step 4 of this embodiment. Figure 2 and Figure 3 It can be seen that before lamination, the average grain size of the oxygen-free copper plate is 200µm, and the average grain size of the ultrafine-grained copper target after lamination is 0.7µm, indicating that lamination greatly reduces the average grain size.

[0030] Example 4 This embodiment includes the following steps: Step 1: Place a rolled oxygen-free copper plate with a mass purity of 99.999% in ethanol for 60 minutes to remove surface oil stains, and then use an angle grinder with a wire brush head to grind the surface at a speed of 11000r / min for 2 minutes to remove oxide scale and impurities, so as to expose a fresh surface and obtain a pre-rolled plate; the diameter of the steel wire in the wire brush head is 0.5mm; Step 2: Overlap the two pre-rolled plates obtained in step 1, punch holes around them, and fix them with a wire with a diameter of 1 mm. Then, roll them at room temperature at a rolling speed of 0.1 m / s, with a reduction of 25% per pass, for 2 passes to ensure a total reduction of 50% and a cumulative strain of , and a rolled plate is obtained; in the said multiple-pass rolling, the surfaces of the rolling rollers and the workpieces are not lubricated; Step 3, cutting the rolled plate obtained in step 2 from the middle, and then repeating step 1 and step 2 five times, until the cumulative strain reaches 4.8, to obtain a processed plate; Step 4: Heat the processed plate obtained in step 3 to 300° C. in an argon atmosphere and then perform recovery annealing for 1 hour to remove residual stress, and then perform straightening, machining and cleaning in sequence, and package to obtain an ultrafine-grained copper target.

[0031] Example 5 This embodiment includes the following steps: Step 1: Place a rolled oxygen-free copper plate with a mass purity of 99.99% in ethanol for 30 minutes to remove surface oil stains, and then use an angle grinder with a wire brush head to grind the surface at a speed of 10000r / min for 2 minutes to remove oxide scale and impurities, so as to expose a fresh surface and obtain a pre-rolled plate; the diameter of the steel wire in the wire brush head is 0.25mm; Step 2: Overlap the two pre-rolled plates obtained in step 1, punch holes around them, and fix them with a wire with a diameter of 1 mm. Then, roll them at room temperature at a rolling speed of 0.34 m / s, with a reduction of 50% per pass, for one pass, ensuring that the total reduction is 50%, and the accumulated strain is , and a rolled plate is obtained; in the said multiple-pass rolling, the surfaces of the rolling rollers and the workpieces are not lubricated; Step 3, cutting the rolled plate obtained in step 2 from the middle, and then repeating step 1 and step 2 seven times, until the cumulative strain reaches 6.4, to obtain a processed plate; Step 4: Heat the processed plate obtained in step 3 to 300° C. in an argon atmosphere and then perform recovery annealing for 6 hours to remove residual stress, and then perform straightening, machining and cleaning in sequence, and package to obtain an ultrafine-grained copper target.

[0032] The ultrafine-grained copper targets prepared in Examples 1 to 5 were subjected to quality purity detection and average grain size detection and analysis, and the specific statistical results are shown in Table 1.

[0033] Table 1

[0034] Based on the above detection and analysis results, Examples 1 to 5 of the present invention use oxygen-free copper plates as raw materials and utilize cumulative rolling technology to obtain ultrafine-grained targets with uniform structure and preferential orientation.

[0035] After testing, the high entropy alloy bar prepared in this embodiment has a good appearance, no obvious casting defects, uniform composition, and no shrinkage cavities.

[0036] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an ultrafine-grained copper target, characterized in that: The method comprises the following steps: Step 1: Clean and polish the oxygen-free copper plate in sequence to obtain a pre-rolled plate; Step 2: Overlap the two pre-rolled plates obtained in step 1, then punch holes around them and fix them with iron wires, and then perform multiple rolling below the recrystallization temperature of the oxygen-free copper plate to obtain a rolled plate; Step 3, cutting the rolled plate obtained in step 2 in the middle, and then repeating steps 1 and 2 for multiple times to obtain a processed plate; Step 4: recover the processed plate obtained in step 3 and then perform straightening, machining and cleaning in sequence to obtain an ultrafine-grained copper target.

2. The method for preparing an ultrafine-grained copper target according to claim 1, characterized in that: The mass purity of the oxygen-free copper plate described in step 1 is not less than 99%.

3. The method for preparing an ultrafine-grained copper target according to claim 1, characterized in that: The cleaning in step 1 is to soak the oxygen-free copper plate in acetone or ethanol for 0.5h~2h.

4. The method for preparing an ultrafine-grained copper target according to claim 1, characterized in that: The grinding in step 1 is performed using an angle grinder with a wire brush for 2 min to 5 min. The rotation speed of the wire brush during the grinding is 5000 r / min to 11000 r / min, and the diameter of the steel wire is 0.1 mm to 0.5 mm.

5. The method for preparing an ultrafine-grained copper target according to claim 1, characterized in that: The speed of the multi-pass rolling in step 2 is 0.1m / s~0.7m / s, the reduction amount of each pass is 5%~50%, the total reduction amount is 50%, and no lubrication is required during the multi-pass rolling.

6. The method for preparing an ultrafine-grained copper target according to claim 1, characterized in that: The number of repetitions in step 3 is more than two times.

7. The method for preparing an ultrafine-grained copper target according to claim 1, characterized in that: The recovery annealing temperature in step 4 is less than 350° C., the time is 0.5 h to 6 h, and the atmosphere is argon or nitrogen.

8. The method for preparing an ultrafine-grained copper target according to claim 1, characterized in that: The grain size of the ultrafine-grained copper target material in step 4 is no greater than 5 μm.

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