Green and efficient recovery method for diffusion welding target material

Abstract

The invention relates to the field of magnetron sputtering target materials, and discloses a green and efficient recovery method of a diffusion welding target material. The method comprises the steps that firstly, a heat treatment means is adopted, heat treatment is conducted above the heterogeneous metal alloying temperature, element diffusion occurs on a welding interface, a continuous and thick intermetallic compound phase is generated within a certain thickness range, the brittleness of the interface is increased, and then the welding interface is separated through quenching treatment and mechanical treatment; and then the atomic diffusion layer and the middle layer on the target blank or the back plate are removed through a machining means, and finally the complete high-purity metal target blank and the complete high-purity metal back plate are obtained after cleaning and drying. According to the recycling method, impurities are prevented from being introduced into the high-purity metal target blank in the recycling process, the integrity of the target blank and the backboard is good, and meanwhile the recycling method has the advantages of being short in process, low in cost, capable of saving resources, environmentally friendly, efficient and the like.

Description

Technical Field

[0001] The invention relates to the field of magnetron sputtering target materials, and in particular to a green and efficient recovery method for diffusion welding target materials. Background Art

[0002] Magnetron sputtering targets are a key raw material in the semiconductor industry. During the sputtering coating process, the target is exposed to high-voltage electric and magnetic fields, bombarded by various high-energy particles. This causes the target atoms to sputter and deposit onto the substrate, forming a thin film. For high-power, high-efficiency sputtering targets, diffusion welding is typically used to connect the target blank to the backing plate, which is typically made of high-strength and high-thermal-conductivity metals such as copper alloy and aluminum alloy. Certain target types may also incorporate an intermediate layer to improve weldability and weld strength while reducing weld stress.

[0003] Since semiconductors belong to the high-precision manufacturing industry, the requirements for the quality stability and precision control of key materials are extremely stringent. Target materials are prone to problems such as dimensional deviations or poor surface quality during the processing process. Even if they are repaired, they cannot meet the use requirements and can only be scrapped. On the other hand, due to the principles of magnetron sputtering and the semiconductor industry's strict requirements for film consistency and uniformity, the actual utilization rate of sputtering targets is usually less than 30% of the net weight of the target blank. Even with long-life design, it is difficult to exceed 40%. There are still a large amount of high-quality, high-value-added high-purity metals in residual or scrapped targets at the end of their service life. Therefore, the recycling of targets is of great significance for target manufacturers to reduce production costs and provide new profit growth points.

[0004] Several patents have explored methods for separating the target blank from the backing plate. Patent Document 1 (CN 104342618) uses pressure from a hydraulic press to separate the target blank and backing plate, while Patent Document 2 (CN 105798733) uses friction from a grinder to separate the target blank and backing plate. Neither method is completely effective, resulting in low target recovery efficiency. Patent Document 3 (CN 109266854A) utilizes a combined acid-base dissolution method to remove the backing plate, effectively recovering the target material. However, the acid-base solution may affect the purity of the target blank, and the backing plate cannot be recycled. Patent Document 4 (CN 109207729A) uses a combination of turning and chemical methods to remove the backing plate. While the integrity and purity of the separated target blank can be maintained, the recycling value of the backing plate turnings is low, preventing optimal economic efficiency. Patent document 5 (CN 111748693A) utilizes the different melting points of the target blank (such as titanium, tantalum) and the backing plate (such as aluminum, copper) materials to heat the backing plate material to a liquid state and recover it, thereby achieving the effect of separating the target blank and the backing plate. However, heterogeneous metal structural parts will inevitably undergo intermetallic diffusion under long-term high temperature conditions, thereby affecting the purity of the target blank. Summary of the Invention

[0005] Technical problem to be solved by the invention In view of the above problems, the present invention proposes a green and efficient recycling method suitable for diffusion welding target materials to address the problems in the existing technology such as incomplete separation of target material and backing plate, high recycling cost, low recycling efficiency, non-recyclable backing plate material and environmental unfriendliness.

[0006] Means for solving technical problems The present invention is achieved through the following technical solutions: A green and efficient method for recycling diffusion welding targets comprises the following steps: (1) Place the residual target or scrapped recyclable target at the end of its service life in an annealing furnace for heat treatment; (2) The target material after heat treatment is taken out from the annealing furnace and placed in a water tank for rapid cooling; (3) Mechanical treatment is used to separate the target welding interface after rapid cooling; (4) using machining means to remove the atomic diffusion layer and / or intermediate layer on the target blank or backing plate after being processed in step (3); (5) After cleaning and drying the target blank or backing plate obtained in step (4), a complete high-purity metal target blank and backing plate are obtained for recycling and reuse.

[0007] Furthermore, the temperature of the heat treatment in step (1) is higher than the temperature at which the heterogeneous metal elements form intermetallic compounds, and the holding time is 1 to 3 hours, thereby causing element diffusion of the different metals at the welding interface and generating a continuous and coarse intermetallic compound phase within a thickness range of 100 to 500 μm, while the grains grow rapidly, increasing the interface brittleness.

[0008] Furthermore, the heat treatment atmosphere in step (1) is a vacuum or an inert gas. When it is a vacuum, the vacuum degree in the furnace is ≤100 Pa; when it is a non-vacuum, the inert gas in the furnace is nitrogen, helium, neon, argon, or krypton, and the inert gas pressure is 0.05~0.11 MPa.

[0009] Furthermore, in step (2), the time for transferring the heat-treated target from the high-temperature furnace to the water tank is ≤30s, and the water tank temperature is ≤20°C. This is because the high-temperature target after heat treatment will produce a higher residual stress level after rapid cooling, and a high density of dislocations will be formed inside, thereby initiating microcracks. In addition, the non-uniform shrinkage effect caused by the difference in linear expansion coefficients between heterogeneous metals in the target material can also be superimposed, thereby increasing the cracking tendency of the welding interface.

[0010] Furthermore, the mechanical treatment in step (3) is hydraulic vibration hammering, with a hydraulic tonnage of 50-100t, an excitation frequency of 5-50Hz, and a maximum amplitude of ≤15mm.

[0011] Furthermore, the machining in step (4) includes but is not limited to turning, milling, drilling, boring, sawing, grinding, etc., and the thickness of the atomic diffusion layer removed by machining is ≥500 μm.

[0012] Furthermore, the recyclable target materials described in the present invention include but are not limited to titanium targets, tantalum targets, tungsten targets, cobalt targets, nickel platinum targets and aluminum scandium targets, the back plate materials include but are not limited to aluminum alloys, copper alloys, titanium alloys and molybdenum alloys, and the intermediate layer materials include but are not limited to aluminum alloys, magnesium alloys and zinc alloys.

[0013] Furthermore, the diameter of the recyclable target material of the present invention is 300~550mm, preferably 400~550mm; the target material thickness is 20~30mm, preferably 22~28mm; wherein, the target blank thickness is 5~10mm, preferably 5.5~7mm; the intermediate layer thickness is 0~10mm, preferably 5~8mm; the backing plate thickness is 10~20mm, preferably 15~20mm.

[0014] Finally, ICP-MS is used to analyze the impurities of the recovered high-purity target blank. The impurity content of the main alloy elements in the back plate or middle layer of the target blank must be ≤1ppm, and other key impurity elements have no obvious changes compared to the original target material.

[0015] Beneficial technical effects of the present invention: The present invention adopts heat treatment means to generate continuous coarse brittle phase and large-sized grains at the heterogeneous metal welding interface, and then separates the two by rapid cooling treatment and hydraulic vibration hammering treatment, and then removes the intermediate layer and atomic diffusion layer by machining means, and finally obtains a high-integrity high-purity metal target blank and backing plate. It can be seen that, first of all, the present invention greatly improves the recovery efficiency, and avoids the problem of low efficiency of mechanical processing methods, while avoiding the problem of environmental pollution by chemical corrosive agents such as acid and alkali solutions, meeting the current requirements of energy conservation and environmental protection. Secondly, heat treatment and hydraulic vibration treatment can effectively avoid the introduction of impurities during the separation process, and ensure the purity and integrity of the target blank as much as possible. At the same time, the backing plate also has a high recovery value. The recovered target blank and backing plate can be put back into use after a little processing. Finally, the recovery method of the present invention is simple in process, significantly reduces the recovery complexity and recovery cost, and is applicable to most diffusion welding targets. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the implementation process of the present invention.

[0017] Figure 2 This is an SEM photo of the welding interface of the recovered target material in Example 1. DETAILED DESCRIPTION

[0018] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific embodiments.

[0019] The present invention provides a green and efficient method for recycling a diffusion welding target, which comprises the following steps: (1) Place the residual target or scrapped recyclable target at the end of its service life in an annealing furnace for heat treatment; (2) The target material after heat treatment is taken out from the annealing furnace and placed in a water tank for rapid cooling; (3) Mechanical treatment is used to separate the target welding interface after rapid cooling; (4) using machining means to remove the atomic diffusion layer and / or intermediate layer on the target blank or backing plate after being processed in step (3); (5) After cleaning and drying the target blank or backing plate obtained in step (4), a complete high-purity metal target blank and backing plate are obtained for recycling and reuse.

[0020] Refer to the attached Figure 1 , specifically describe the recovery method of the present invention in detail, the detailed steps are as follows: (1) Placing the residual target or scrapped recyclable target at the end of its service life in an annealing furnace for heat treatment, which generates intermetallic compounds and increases the tendency of cracking at the welding interface; (2) The target material after heat treatment is taken out of the annealing furnace and then placed in a water tank for rapid cooling, which further increases the cracking tendency of the welding interface; (3) Mechanical treatment is used to separate the target welding interface after rapid cooling; (3-1) When the backplane does not contain an intermediate layer, proceed according to the above steps (4) and (5); (3-2) If the backing plate contains an intermediate layer, confirm whether the target blank and the intermediate layer are separated. (4-1) If separation has occurred, remove the intermediate layer on the backing plate and the atomic diffusion layer on the target blank by machining; (4-2) If separation has not occurred, remove the intermediate layer on the target blank and the atomic diffusion layer on the backing plate by machining. Then, follow the above step (5).

[0021] Finally, ICP-MS is used to analyze the impurities of the recovered high-purity target blank. Usually, the impurity content of the main alloy elements in the back plate or middle layer of the target blank needs to be ≤1ppm. When other key impurity elements have no obvious changes compared to the original target material, it is in a usable state.

[0022] In Example 1, the recycled target used is a 12-inch diffusion-welded tantalum target, wherein the target blank is made of 5N high-purity tantalum with a thickness of 6.5 mm, the intermediate layer is made of aluminum alloy with a thickness of 5 mm, and the backing plate is made of copper alloy with a thickness of 15 mm. The target to be recycled is placed in an annealing furnace for heat treatment at a temperature of 540°C for 3 hours and a vacuum degree in the furnace of ≤100 Pa. During the heat treatment process, a continuous and coarse brittle phase distribution area is generated within 100 μm of the welding interface between the target backing plate and the intermediate layer, as shown in FIG. Figure 2 As shown. After the insulation is completed, it is transferred to a cold water tank for rapid cooling within 30 seconds. Next, a hydraulic vibrating pile hammer with a tonnage of 80t is used to separate the target material. The excitation frequency is 20Hz. During the vibration process, cracks gradually initiate and crack in the brittle phase distribution area, obtaining a complete copper alloy backing plate. The aluminum alloy intermediate layer and atomic diffusion layer attached to the target blank are then removed by general turning, and a high-purity tantalum target blank is obtained after cleaning and drying. Finally, the recovered high-purity tantalum target blank is analyzed for impurities using ICP-MS. The content of the impurity element aluminum is still less than 0.5ppm, and other key elements such as niobium, tungsten, and molybdenum have no significant changes compared to the original target material.

[0023] In Example 2, the recycled target used was a 12-inch diffusion-welded tungsten target, with a target blank made of 5N high-purity tungsten and a thickness of 6.5 mm, an intermediate layer made of aluminum alloy and a thickness of 10 mm, and a backing plate made of copper alloy and a thickness of 10 mm. The target to be recycled was placed in an annealing furnace for heat treatment at a temperature of 540°C for 1 hour in an inert atmosphere of argon at a pressure of 0.08 MPa. After the insulation period, the target was transferred to a water tank within 30 seconds. Due to the significant difference in thermal expansion coefficients between high-purity tungsten and aluminum alloy, microcracks were observed at the weld interface between the target blank and the intermediate layer after rapid cooling. The target was then separated using a 50-ton hydraulic vibrating hammer with an excitation frequency of 10 Hz. During the vibration process, cracks at the weld interface between the target blank and the intermediate layer gradually expanded until both were completely cracked. The atomic diffusion layer on the target blank and the aluminum alloy intermediate layer attached to the backing plate were then removed by CNC vertical lathe machining. After cleaning and drying, a complete high-purity tungsten target blank and copper alloy backing plate were obtained. The impurity analysis of the recovered high-purity tungsten target blank was performed using ICP-MS, where the content of the impurity element aluminum was still less than 0.5ppm, and the content of other key elements such as iron, nickel, and chromium were all less than 1ppm.

[0024] In Example 3, the recycled target used is a 12-inch diffusion-welded cobalt target, wherein the target blank is made of 5N high-purity cobalt with a thickness of 6.5 mm, the intermediate layer is made of aluminum alloy with a thickness of 10 mm, and the back plate is made of copper alloy with a thickness of 10 mm. Due to processing errors, the surface quality of the target material does not meet the standards. Further repair will cause the thickness to exceed the lower tolerance limit and can only be scrapped. The target material to be recycled is placed in an annealing furnace for heat treatment. The heat treatment temperature is 540 ° C, the heat treatment time is 3 h, and the vacuum degree in the furnace is ≤ 100 Pa. During the heat treatment process, a continuous and coarse brittle phase distribution area is generated within 100 μm of the target back plate and the intermediate layer welding interface. After the insulation is completed, it is transferred to a cold water tank for rapid cooling within 30 seconds. Next, a hydraulic vibrating pile hammer with a tonnage of 80 t is used to separate the target material. The excitation frequency is 20 Hz. During the vibration process, cracks gradually initiate and crack in the brittle phase distribution area to obtain a complete copper alloy back plate. The aluminum alloy intermediate layer and atomic diffusion layer adhering to the target blank are then removed by CNC horizontal lathe machining. After cleaning and drying, a high-purity tantalum target blank is obtained. ICP-MS analysis of the recovered high-purity cobalt target blank reveals that the impurity element aluminum remains below 0.5 ppm, while other key elements such as iron, nickel, and chromium are all below 1 ppm.

[0025] In Example 4, the recycled target used was a 12-inch diffusion-welded titanium target, wherein the target blank was made of 5N high-purity titanium with a thickness of 6.5 mm, and the backing plate was made of aluminum alloy with a thickness of 20 mm. Due to a processing error, the target diameter exceeded the lower tolerance limit and had to be scrapped. The target to be recycled was placed in an annealing furnace for heat treatment at a temperature of 620°C and a heat treatment time of 2 h. The inert atmosphere in the furnace was argon and the pressure was 0.08 MPa. During the heat treatment process, a continuous and coarse brittle phase distribution area was generated within 100 μm of the welding interface between the high-purity titanium target blank and the aluminum alloy backing plate. After the insulation was completed, it was transferred to a water tank within 30 seconds. Due to the large difference in thermal expansion coefficients between high-purity titanium and aluminum alloy, microcracks were observed at the welding interface between the target blank and the backing plate after rapid cooling. Next, a 50-ton hydraulic vibrating pile hammer was used to separate the target material with an excitation frequency of 20 Hz. During the vibration process, the cracks at the interface between the target blank and the backing plate gradually expanded until they were completely cracked. The atomic diffusion layer on the target blank is then removed by grinding. After cleaning and drying, a complete high-purity titanium target blank and aluminum alloy backing plate are obtained. ICP-MS analysis of the recovered high-purity titanium target blank reveals that the impurity element aluminum remains below 0.5 ppm, while other key elements such as iron and copper are below 1 ppm.

[0026] In comparative example 1, the recycled target used is a 12-inch diffusion-welded tungsten target, wherein the target blank is made of 5N high-purity tungsten with a thickness of 6.5 mm, the middle layer is made of aluminum alloy with a thickness of 8 mm, and the back plate is made of copper alloy with a thickness of 12.5 mm. The recovered target is placed in an annealing furnace for heat treatment at a temperature of 460°C and a heat treatment time of 1 h. The inert atmosphere in the furnace is argon and the air pressure is 0.08 MPa. During the heat treatment process, no obvious brittle phase distribution area was found at the welding interface between the target back plate and the middle layer, and no microcracks were found in the target blank and the middle layer. After the insulation was completed, it was transferred to a cold water tank within 30 seconds, and then a hydraulic vibrating pile hammer with a tonnage of 50 t was used to separate the back plate and the middle layer, with an excitation frequency of 10 Hz. After 10 minutes of vibration hammering, the back plate and the middle layer were still not completely separated.

[0027] In comparative example 2, the recycled target used is a 12-inch diffusion-welded tungsten target, in which the target blank is made of 5N high-purity tungsten with a thickness of 6.5 mm, the middle layer is made of aluminum alloy with a thickness of 8 mm, and the back plate is made of copper alloy with a thickness of 12.5 mm. The recovered target is placed in an annealing furnace for heat treatment at a temperature of 500 ° C and a heat treatment time of 3 h. The inert atmosphere in the furnace is argon and the air pressure is 0.08 MPa. During the heat treatment process, a continuous and coarse brittle phase distribution area is generated within 30 μm of the welding interface between the target back plate and the middle layer. After the insulation is completed, it is transferred to a cold water tank within 30 seconds. Then, a hydraulic vibrating pile hammer with a tonnage of 120 t is used to separate the back plate and the middle layer, and the excitation frequency is 60 Hz. During the vibration hammering process, the tungsten target blank is broken. At this time, the middle layer and the back plate are not completely separated, and the recovery value of the target is greatly reduced.

[0028] As can be seen from the above-mentioned examples and comparative examples, the heat treatment temperature in Comparative Example 1 was 460°C. Compared with the example, which was higher than the temperature for forming intermetallic compounds, no obvious brittle phase distribution area was found at the welding interface between the backing plate and the intermediate layer, and no microcracks were found between the target blank and the intermediate layer, resulting in the subsequent mechanical separation being unsuccessful. For Comparative Example 2, although the heat treatment temperature was 500°C, the hydraulic vibratory hammer was too large during separation, resulting in the tungsten target blank being fragmented, and the intermediate layer and the backing plate not being completely separated. In contrast, each step in Examples 1 to 4 was within the scope of the present invention, and a complete, recyclable, high-purity metal target blank and backing plate were obtained.

[0029] 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 green and efficient method for recycling a diffusion welding target, comprising the following steps: (1) Placing the residual targets or scrapped recyclable targets at the end of their service life in an annealing furnace for heat treatment; (2) Taking the heat-treated target out of the annealing furnace and placing it in a water tank for rapid cooling; (3) Mechanical treatment is used to separate the target welding interface after rapid cooling; (4) using machining means to remove the atomic diffusion layer and / or intermediate layer on the target blank or backing plate processed in step (3); (5) After cleaning and drying the target blank or backing plate obtained in step (4), a complete high-purity metal target blank and backing plate are obtained for recycling and reuse.

2. A green and efficient method for recycling diffusion welding targets according to claim 1, characterized in that: The heat treatment temperature in step (1) is higher than the temperature at which the heterogeneous metal elements generate intermetallic compounds, and the holding time is 1 to 3 hours.

3. The green and efficient recovery method of a diffusion welding target according to claim 1, characterized in that: The heat treatment atmosphere in step (1) is vacuum or inert gas. When it is a vacuum, the vacuum degree in the furnace is ≤100Pa; when it is a non-vacuum, the inert gas in the furnace is nitrogen, helium, neon, argon, or krypton, and the gas pressure is 0.05~0.11MPa.

4. The green and efficient recovery method of a diffusion welding target according to claim 1, characterized in that: The time for transferring the heat-treated target from the annealing furnace to the water tank in step (2) is ≤30s, and the water tank temperature is ≤20°C.

5. The green and efficient recovery method of a diffusion welding target according to claim 1, characterized in that: In step (3), the mechanical treatment is hydraulic vibration hammering, the hydraulic tonnage is 50-100t, the excitation frequency is 5-50Hz, and the maximum amplitude is ≤15mm.

6. The green and efficient recovery method of a diffusion welding target according to claim 1, characterized in that: In step (4), the machining is turning, milling, drilling, boring, sawing, or grinding.

7. A green and efficient method for recycling a diffusion welding target according to any one of claims 1 to 6, characterized in that: The recyclable target material includes a titanium target, a tantalum target, a tungsten target, a cobalt target, a nickel-platinum target or an aluminum-scandium target; the back plate material is an aluminum alloy, a copper alloy, a titanium alloy or a molybdenum alloy; the middle layer material is an aluminum alloy, a magnesium alloy or a zinc alloy.

8. A green and efficient method for recycling a diffusion welding target according to any one of claims 1 to 7, characterized in that: The diameter of the recyclable target material is 300~550mm; the thickness of the target material is 20~30mm; among which, the thickness of the target blank is 5~10mm; the thickness of the intermediate layer is 0~10mm; and the thickness of the back plate is 10~20mm.

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