Preparation method of high-homogeneity and high-stability copper target material

Abstract

The invention discloses a preparation method of a high-homogeneity and high-stability copper target material, which comprises the following steps of: 1, cutting off a riser of a high-purity copper cast ingot, and turning to obtain a pretreated high-purity copper cast ingot; secondly, the pretreated high-purity copper ingot is heated and subjected to heat preservation in a furnace and then forged to obtain a forged copper blank; thirdly, the forged copper blank is subjected to room-temperature circumferential rolling treatment, and a rolled copper blank is obtained; fourthly, the rolled copper blank is subjected to two-stage annealing heat treatment, and a copper target blank is obtained; and 5, machining, cleaning and packaging to obtain the high-homogeneity and high-stability copper target material. According to the method, the high-purity copper cast ingot is sequentially subjected to pretreatment, forging, room-temperature circumferential rolling, two-stage annealing, machining, cleaning and packaging, preparation of the high-quality copper target material which is uniform in structure, controllable in crystal orientation and excellent in heat stability is achieved, the sputter coating quality is improved, and the method is easy to operate, high in controllability, high in production efficiency and suitable for industrial production. Meanwhile, raw materials and production cost are saved, and the method is suitable for large-scale popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of sputtering target material preparation, and in particular relates to a method for preparing a high-homogeneity and high-stability copper target material. Background Art

[0002] Sputtering coating technology uses high-speed particles to bombard the target surface under vacuum conditions, ultimately depositing the bombarded particles onto a substrate. It effectively utilizes the sputtering phenomenon to produce various thin films. Compared to traditional vacuum evaporation, sputtering coating offers significant advantages, including: strong adhesion between the film and the substrate; high film uniformity; high controllability of the film's composition; and ease of industrial production. Therefore, sputtering coating technology plays a vital role in the discovery of new materials, the development of new functions, and the application of new devices. Among these, magnetron sputtering coating technology can achieve high-rate deposition under low-temperature, low-loss conditions, and is widely used in high-tech industries such as semiconductors, photovoltaics, flat-panel displays, and information storage.

[0003] Compared to aluminum, copper targets have lower resistivity, higher thermal conductivity, and better resistance to electromigration. They account for 15%-25% of all sputtering targets and represent a significant market demand. In the semiconductor field, copper targets are primarily used as interconnect materials for integrated circuits at 90-7nm technology nodes, reducing latency, improving computational efficiency, and enhancing the reliability of integrated circuits. As targets continue to develop toward larger sizes, higher purity, and higher sputtering rates, and as chips continue to move toward smaller technology nodes and greater centralization, the requirements for controlling copper targets' purity, structural uniformity, crystal orientation, and thermal stability are becoming increasingly stringent.

[0004] Patent CN11113857402B discloses a method for preparing an alloy high-purity copper target material. The method sequentially subjects the copper billet to one forging and stretching + one heat treatment, two forging and stretching + two heat treatments, three forging and stretching + four forging and stretching + static pressing + rolling + four heat treatments. Multiple forging and heat treatments are used to achieve microstructure refinement to a certain extent. However, since uneven force is easily caused by rolling in this process, the uniformity of the target blank microstructure is difficult to ensure, and the preparation cycle is long and cumbersome.

[0005] Patent CN114892135B discloses a high-purity copper target material, its preparation method and application. By subjecting a high-purity copper ingot to a first hot forging + a first heat treatment, a second hot forging + a second heat treatment, and a static pressing + a cold rolling treatment in sequence, an unannealed copper target blank is obtained. The operation is simple, easy to industrialize, and the structure is highly uniform. However, the biggest problem with the unannealed state is that the structure is poorly stable during sputtering, and recovery and recrystallization are very likely to occur, and even target deformation may occur, seriously affecting the quality of the sputtering coating and the target life.

[0006] Patent CN103173729B discloses a method for manufacturing a copper target for sputtering. This invention achieves a close-packed {111} plane ratio of 13% or more and 30% or less by casting, hot-rolling, and cold-rolling oxygen-free copper with a purity of 3N or higher. This method controls the crystal orientation, thereby improving the sputtering coating rate and coating quality to a certain extent. However, the target prepared by this method exhibits poor unannealed microstructure stability during the sputtering process, which is detrimental to the quality of the sputtering coating. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned existing technologies and provide a method for preparing a highly homogeneous and highly stable copper target. This method uses a process of room temperature circumferential rolling combined with a two-stage annealing heat treatment to avoid the surface and internal gradient distribution of the copper target and the phenomenon of abnormal grain growth, effectively control the grain nucleation rate and growth rate, improve the overall structural uniformity and thermal stability of the copper target, and achieve precise control of crystal orientation, thereby improving the stability and quality of the coating. This solves the problem that the existing preparation process is difficult to ensure the uniformity of the copper target structure and has poor stability, which affects the quality of the sputtering coating.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a high-homogeneity and high-stability copper target material, characterized in that the method includes pretreatment, forging, room temperature circumferential rolling, two-stage annealing heat treatment, machining, and cleaning and packaging. The specific steps are as follows: Step 1: Pretreatment: Remove the riser from the high-purity copper ingot with a mass purity of 99.9999% or more, remove the surface oxide layer by turning, and then clean it. The turning depth is more than 2mm to obtain a pretreated high-purity copper ingot; Step 2, forging: the pretreated high-purity copper ingot obtained in step 1 is placed in a furnace for heating and insulation, and then forged, first drawn to 200% to 320% of the original length, then upset to 30% to 50% of the drawn length, and the upsetting and drawing process is repeated at least three times, and finally formed to obtain a forged copper billet; Step 3, room temperature circumferential rolling: the forged copper billet obtained in step 2 is subjected to room temperature circumferential rolling treatment, and the total rolling deformation is 30% to 60%, to obtain a rolled copper billet; Step 4: Double-stage annealing heat treatment: The rolled copper billet obtained in step 3 is subjected to double-stage annealing heat treatment by heating it to a temperature in a furnace and then air-cooling it to room temperature to obtain a copper target billet; Step 5: Machining, cleaning and packaging: The copper target material blank obtained in step 4 is subjected to machining, straightening, vacuum annealing, cleaning and packaging to obtain a copper target material with high homogeneity and high stability.

[0009] The above-mentioned method for preparing a high-homogeneity and high-stability copper target is characterized in that, before the heating and heat preservation in step 2, a glass protective lubricant for copper alloy deformation is evenly coated on the surface of the pretreated high-purity copper ingot and air-dried, and the heating and heat preservation temperature is 580°C~850°C, and the heat preservation time is 1h~2h. By uniformly coating the surface of the pretreated high-purity copper ingot with a glass protective lubricant for copper alloy deformation in advance, not only the temperature drop during the forging process is significantly slowed down, but the glass protective lubricant can also disperse the experience during the deformation process, avoid cracking of the billet, improve the deformation ability of the high-purity copper ingot, and thus improve production efficiency; by controlling the temperature and heat preservation time of the heating and heat preservation, it can not only ensure that the high-purity copper ingot has good deformation ability, but also avoid the coarsening and abnormal growth of grains caused by excessive temperature, which is beneficial to ensure the uniformity of the structure of the product copper target.

[0010] The above-mentioned method for preparing a highly homogeneous and stable copper target is characterized in that the pressing amount per pass of the room temperature circumferential rolling treatment in step 3 is 1 mm to 2 mm, and the angle between the rolling directions of adjacent passes is 60° to 120°. By controlling the process parameters of the room temperature circumferential rolling treatment, the uneven deformation of the surface and core of the copper billet caused by conventional unidirectional rolling is effectively avoided, and the formation of strong texture and gradient structure during annealing is weakened, thereby improving the structural uniformity of the copper target.

[0011] The above-mentioned method for preparing a high-homogeneity and high-stability copper target is characterized in that the process of the double-stage annealing heat treatment described in step 4 is: first, heat it to a high temperature of 500°C to 600°C and then put it into a furnace for 10min to 40min, then heat it to a low temperature of 350°C to 450°C and then put it into a furnace for 1h to 3h, and then air cool it to room temperature. The present invention adopts a double-stage annealing heat treatment, that is, first heat it to a high temperature for a short time to effectively increase the nucleation rate of recrystallization, and then heat it for a long time at a low temperature to avoid excessive growth of recrystallized grains, thereby achieving the purpose of effectively refining the structure and improving the uniformity of the structure by controlling the nucleation rate and growth rate of the grains.

[0012] The above-mentioned method for preparing a highly homogeneous and highly stable copper target is characterized in that the highly homogeneous and highly stable copper target prepared in step 5 has an average grain size of no more than 30 μm, a maximum grain size of no more than 50 μm, an orientation ratio of the closest-packed {111} planes of 55% or greater, and excellent uniformity in both the grain size and crystal orientation in both the transverse and longitudinal structures. The copper target prepared by the present invention exhibits highly uniform grain size and crystal orientation distribution, making it suitable as a high-quality sputtering target for semiconductor thin films.

[0013] Typically, the microstructure of the copper target is observed using an optical microscope to analyze the uniformity and grain size range of the structure. An X-ray diffractometer is used to detect and analyze the crystal orientation at different locations. The {111} orientation ratio is calculated by taking the sum of the intensities of the {111}, {200}, {220}, {311}, and {222} orientations in the measured X-ray diffraction data as 100% and the percentage of the {111} intensity relative to the total intensity as the orientation ratio.

[0014] Furthermore, even with circulating cooling water on the backing plate, sputtering targets experience significant temperature rise during high-power sputtering, especially as sputtering approaches higher power. In practice, the temperature of the target's outermost surface reaches approximately 700°C, while temperatures near the surface can reach 500°C. The copper target prepared in this study was heated and maintained at 500°C to verify its thermal stability.

[0015] Compared with the prior art, the present invention has the following advantages: 1. The present invention significantly weakens the uneven stress distribution caused by unidirectional rolling deformation through the process of combining room temperature circumferential rolling with double-stage annealing heat treatment, avoids the surface and internal gradient distribution and abnormal grain growth in the longitudinal structure of the copper target, and improves the uniformity of the copper target from the surface to the core. At the same time, the high uniformity reduces the loss of target blank machining, which is beneficial to improving the target blank utilization rate, saving raw materials and reducing costs.

[0016] 2. The present invention effectively controls the grain nucleation rate and growth rate of the rolled copper billet through the process design of double-stage annealing heat treatment, thereby refining the structure and avoiding excessive growth of the structure, improving the overall structural uniformity of the annealed copper target billet, and is conducive to ensuring the stability and uniformity of the copper target sputtering coating.

[0017] 3. The present invention achieves good control of the crystal orientation of the copper target through the process design of room temperature circumferential rolling combined with double-stage annealing heat treatment. The orientation rate of the most densely packed {111} plane is above 55%, thereby improving the sputtering coating rate and film uniformity of the copper target.

[0018] 4. The present invention adopts a process design of room temperature circumferential rolling combined with double-stage annealing heat treatment, which improves the thermal stability of the entire copper target material structure by changing the stress distribution state and recrystallization behavior of the copper target material, thereby improving the stability and quality of the sputtering coating.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the metallographic structure diagram of the copper target prepared in Example 1 of the present invention.

[0021] Figure 2 This is a diagram showing the average grain size distribution of the longitudinal structures of the copper targets prepared in Example 1 of the present invention and Comparative Example 1.

[0022] Figure 3 This is a distribution diagram of the closest-packed plane orientation rate of the longitudinal structure of the copper target prepared in Example 1 of the present invention and Comparative Example 1.

[0023] Figure 4 The metallographic structures of the copper targets prepared in Example 1 and Comparative Example 1 of the present invention and kept at 500° C. for 2 h are shown. DETAILED DESCRIPTION

[0024] Example 1 This embodiment includes the following steps: Step 1: Pretreatment: Remove the riser from the high-purity copper ingot with a mass purity of 99.9999% or more, remove the surface oxide layer by turning, and then clean it. The turning depth is 2mm to obtain a pretreated high-purity copper ingot; Step 2, forging: The surface of the pretreated high-purity copper ingot obtained in step 1 is evenly coated with a copper alloy deformation protective lubricant and air-dried, then heated to 850°C in a furnace and kept warm for 1 hour before forging. The ingot is first drawn to 200% of its original length, then upset to 30% of its drawn length, and the upsetting and drawing process is repeated three times. Finally, the ingot is formed to obtain a forged copper rod blank with a diameter of 120 mm. Step 3, room temperature circumferential rolling: Cut a 20 mm high billet from the forged copper rod billet obtained in step 2, and perform room temperature circumferential rolling treatment, with a downward pressure of 1 mm per pass, an angle of 60° between adjacent rolling directions, and a total rolling deformation of 50%, to obtain a rolled copper billet; Step 4, double-stage annealing heat treatment: the rolled copper billet obtained in step 3 is first placed in a furnace at a high temperature of 500°C and kept warm for 30 minutes, air-cooled to room temperature, then placed in a furnace at a low temperature of 400°C and kept warm for 3 hours, and air-cooled to room temperature to obtain a copper target billet; Step 5: Machining, cleaning and packaging: The copper target blank obtained in step 4 is machined, straightened, vacuum annealed, cleaned and packaged to obtain a high-homogeneity and high-stability copper target with a diameter × thickness of 180 mm × 9 mm.

[0025] Figure 1 The metallographic structure diagram of the copper target prepared in this embodiment is as follows: Figure 1 It can be seen that the structure of the copper target is completely recrystallized, with fine grains, uniform grain size distribution, and no abnormal growth.

[0026] Comparative Example 1 This comparative example comprises the following steps: Step 1: Pretreatment: Remove the riser from the high-purity copper ingot with a mass purity of 99.9999% or more, remove the surface oxide layer by turning, and then clean it. The turning depth is 2mm to obtain a pretreated high-purity copper ingot; Step 2, forging: The surface of the pretreated high-purity copper ingot obtained in step 1 is evenly coated with a copper alloy deformation protective lubricant and air-dried, then heated to 850°C in a furnace and kept warm for 1 hour before forging. The ingot is first drawn to 200% of its original length, then upset to 30% of its drawn length, and the upsetting and drawing process is repeated three times. Finally, the ingot is formed to obtain a forged copper rod blank with a diameter of 120 mm. Step 3, room temperature circumferential rolling: Cut a 20 mm high billet from the forged copper rod billet obtained in step 2, and perform unidirectional rolling at room temperature, with a downward pressure of 1 mm per pass, and the rolling direction of adjacent passes being consistent, and a total rolling deformation of 50%, to obtain a rolled copper billet; Step 4: Single-stage annealing heat treatment: the rolled copper billet obtained in step 3 is placed in a furnace at 500° C. and kept warm for 1 hour, and then air-cooled to room temperature to obtain a copper target billet; Step 5: Machining, cleaning and packaging: The copper target blank obtained in step 4 is machined, straightened, vacuum annealed, cleaned and packaged to obtain a copper target with a diameter×thickness of 180 mm×9 mm.

[0027] Figure 2 The average grain size distribution diagram of the longitudinal structure of the copper target prepared in Example 1 of the present invention and Comparative Example 1 is shown in FIG. Figure 3 The closest packed plane orientation rate distribution diagram of the longitudinal structure of the copper target prepared in Example 1 of the present invention and Comparative Example 1 is shown in FIG. Figure 4 The metallographic organization diagrams of the copper targets prepared in Example 1 and Comparative Example 1 of the present invention and kept at 500°C for 2h are shown in Figure (a) for Example 1 and Figure (b) for Comparative Example 1. Figures 2 to 4 It can be seen that the average grain size of the copper target prepared in Example 1 is about 28.5 μm, the maximum grain size is about 46 μm, the orientation rate of the most densely packed {111} plane is about 58%, and both the transverse and longitudinal structures show excellent uniformity, including not only the grain size, but also its crystal orientation distribution shows high uniformity. The copper target grains do not grow significantly after being kept at 500°C for 2 hours, and have excellent thermal stability. Therefore, the copper target prepared by the method of the present invention is suitable as a high-quality sputtering target for semiconductor thin films; while the copper target prepared in Comparative Example 1 has an average grain size of about 36 μm, a maximum grain size of 116 μm, and an orientation rate of the most densely packed {111} plane is about 28%. Therefore, the copper target prepared by the method of the present invention has poor organizational uniformity, the surface and internal grain sizes are gradiently distributed, the proportion of the most densely packed plane is low and uneven, and its organizational stability is poor. The copper target grains grow significantly after being kept at 500°C for 2 hours.

[0028] In summary, the present invention greatly improves the structure of the copper target material, including the uniformity and stability of grain size and crystal orientation, through the process of room temperature circumferential rolling combined with double-stage annealing heat treatment.

[0029] Example 2 This embodiment includes the following steps: Step 1, pretreatment: remove the riser of a high-purity copper ingot with a mass purity of 99.99999% or more, then remove the surface oxide layer by turning, and clean it, with a turning depth of 3mm, to obtain a pretreated high-purity copper ingot; Step 2, forging: The surface of the pretreated high-purity copper ingot obtained in step 1 is evenly coated with a copper alloy deformation protective lubricant for glass and air-dried, then heated to 580°C in a furnace and kept warm for 2 hours before forging. The ingot is first drawn to 320% of the original length, then upset to 50% of the drawn length, and the upset-drawing process is repeated four times. Finally, the ingot is formed to obtain a forged copper plate blank with a length × width × thickness of 450 mm × 330 mm × 50 mm. Step 3, room temperature circumferential rolling: The forged copper sheet obtained in step 2 is subjected to room temperature circumferential rolling, with a pressing amount of 2 mm per pass, an angle between adjacent rolling directions of 90°, and a total rolling deformation of 60%, to obtain a rolled copper billet; Step 4, double-stage annealing heat treatment: the rolled copper billet obtained in step 3 is first heated to a high temperature of 600°C and placed in a furnace for 10 minutes, air-cooled to room temperature, then heated to a low temperature of 450°C and placed in a furnace for 1 hour, air-cooled to room temperature, to obtain a copper target billet; Step 5: Machining, cleaning and packaging: The copper target blank obtained in step 4 is machined, straightened, vacuum annealed, cleaned and packaged to obtain a high-homogeneity and high-stability copper target with a length × width × thickness of 500 mm × 100 mm × 10 mm.

[0030] After testing, the average grain size of the copper target prepared in this embodiment is about 20.5μm, the maximum grain size is about 36μm, the orientation rate of the most densely packed {111} plane is about 56%, and both the transverse and longitudinal structures show excellent uniformity, including not only the grain size but also the crystal orientation distribution. The copper target grains do not grow significantly after being kept at 500℃ for 2h, and have excellent thermal stability. Therefore, the copper target prepared by the method of the present invention is suitable as a high-quality semiconductor thin film sputtering target. Example 3 This embodiment includes the following steps: Step 1, pretreatment: a high-purity copper ingot with a mass purity of 99.99996% is cut off from the riser, and then the surface oxide layer is removed by turning, and the surface is cleaned, and the turning depth is 2.4 mm to obtain a pretreated high-purity copper ingot; Step 2, forging: The surface of the pretreated high-purity copper ingot obtained in step 1 is evenly coated with a copper alloy deformation protective lubricant and air-dried, then heated to 650°C in a furnace and kept warm for 2 hours before forging. The ingot is first drawn to 320% of its original length, then upset to 30% of the drawn length, and the upsetting and drawing process is repeated four times. Finally, the ingot is formed to obtain a forged copper rod blank with a diameter of 140 mm. Step 3, room temperature circumferential rolling: Cut a 50 mm high billet from the forged copper rod blank obtained in step 2, and perform room temperature circumferential rolling treatment, with a downward pressure of 1 mm per pass, an angle of 120° between adjacent rolling directions, and a total rolling deformation of 30%, to obtain a rolled copper billet; Step 4, double-stage annealing heat treatment: the rolled copper billet obtained in step 3 is first heated to a high temperature of 500°C and placed in a furnace for 40 minutes, air-cooled to room temperature, then heated to a low temperature of 350°C and placed in a furnace for 3 hours, air-cooled to room temperature, to obtain a copper target billet; Step 5: Machining, cleaning and packaging: The copper target blank obtained in step 4 is machined, straightened, vacuum annealed, cleaned and packaged to obtain a high-homogeneity and high-stability copper target with a diameter × thickness of 200 mm × 9 mm.

[0031] After testing, the average grain size of the copper target prepared in this embodiment is about 24 μm, the maximum grain size is about 46.5 μm, the orientation rate of the most densely packed {111} plane is about 57%, and both the transverse and longitudinal structures show excellent uniformity, including not only the grain size but also the crystal orientation distribution. The copper target grains do not grow significantly after being kept at 500°C for 2 hours, and have excellent thermal stability. Therefore, the copper target prepared by the method of the present invention is suitable as a high-quality sputtering target for semiconductor thin films. The above description 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 variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a high-homogeneity and high-stability copper target, characterized in that: The method includes pretreatment, forging, room temperature circumferential rolling, two-stage annealing heat treatment, machining, cleaning and packaging. The specific steps are as follows: Step 1: Pretreatment: Remove the riser from the high-purity copper ingot with a mass purity of 99.9999% or more, remove the surface oxide layer by turning, and then clean it. The turning depth is more than 2mm to obtain a pretreated high-purity copper ingot; Step 2, forging: the pretreated high-purity copper ingot obtained in step 1 is placed in a furnace for heating and insulation, and then forged, first drawn to 200% to 320% of the original length, then upset to 30% to 50% of the drawn length, and the upsetting and drawing process is repeated at least three times, and finally formed to obtain a forged copper billet; Step 3, room temperature circumferential rolling: the forged copper billet obtained in step 2 is subjected to room temperature circumferential rolling treatment, and the total rolling deformation is 30% to 60%, to obtain a rolled copper billet; Step 4: Double-stage annealing heat treatment: The rolled copper billet obtained in step 3 is subjected to double-stage annealing heat treatment by heating it to a temperature in a furnace and then air-cooling it to room temperature to obtain a copper target billet; Step 5: Machining, cleaning and packaging: The copper target material blank obtained in step 4 is subjected to machining, straightening, vacuum annealing, cleaning and packaging to obtain a copper target material with high homogeneity and high stability.

2. The method for preparing a high-homogeneity and high-stability copper target according to claim 1, wherein: Before the heating and insulation in step 2, a glass protective lubricant for copper alloy deformation is evenly coated on the surface of the pretreated high-purity copper ingot and air-dried. The heating and insulation temperature is 580° C. to 850° C., and the insulation time is 1 h to 2 h.

3. The method for preparing a high-homogeneity and high-stability copper target according to claim 1, wherein: The pressing amount of each pass of the room temperature circumferential rolling treatment in step 3 is 1 mm to 2 mm, and the angle between the rolling directions of adjacent passes is 60° to 120°.

4. The method for preparing a high-homogeneity and high-stability copper target according to claim 1, wherein: The process of the double-stage annealing heat treatment in step 4 is: first, heat it to a high temperature of 500℃~600℃ and put it into the furnace for 10min~40min, then heat it to a low temperature of 350℃~450℃ and put it into the furnace for 1h~3h, and then air-cool it to room temperature.

5. The method for preparing a high-homogeneity and high-stability copper target according to claim 1, wherein: The average grain size of the high-homogeneity and high-stability copper target described in step 5 does not exceed 30 μm, the maximum grain size does not exceed 50 μm, the orientation rate of the closest-packed {111} plane is above 55%, and the grain size and crystal orientation of the transverse and longitudinal structures show excellent uniformity.

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