A high-purity sputtering target production process

Abstract

The application discloses a high-purity sputtering target production process, belongs to the technical field of semiconductor materials and thin film deposition, and adopts a series of steps such as anti-oxidation purification, copper-based adaptive hot isostatic pressing, gradient grain regulation, interface matching welding and anti-oxidation post-processing, fully strengthens the characteristics of copper materials, solves defects in a targeted manner, and obtains 6N high-purity copper-based sputtering targets suitable for 12-inch or above semiconductor chip interconnection layers and liquid crystal display electrode layer deposition, so that the large-scale and stable production of high-performance copper-based sputtering targets is realized.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials and thin film deposition technology, and particularly relates to sputtering targets. Specifically, it is a production process for sputtering targets with a purity of 5N or higher required for semiconductor chips, liquid crystal displays, flat panel displays and other fields. Background Technology

[0002] Sputtering targets are core consumables in physical vapor deposition (PVD) processes, primarily used in electronic information technologies such as semiconductor chips, liquid crystal displays (LCDs), and flat panel displays (OLEDs). They consist of a target blank and a backplate. The target blank is the material bombarded by a high-speed ion beam, while the backplate serves as support and a heat carrier for the target blank. The purity, density, and grain structure of the sputtering target directly determine the uniformity, electrical properties, and defect rate of the deposited thin film.

[0003] Currently, commonly used sputtering targets include metal and alloy targets, ceramic targets, and compound targets. Among metal and alloy targets, aluminum / aluminum alloy targets are low in cost and have good oxidation resistance, but their conductivity is poor. Molybdenum / molybdenum alloy targets are high in temperature resistance and hardness, but their conductivity is extremely poor and their cost is high. Titanium / titanium alloy targets are highly corrosion resistant, but their conductivity is poor, requiring additional conductive structures, and their purity is easily affected by impurities. Copper-based targets have strong conductivity and excellent thermal conductivity. High-purity copper is free of impurities and has a relatively low cost. Among ceramic targets, ITO targets are transparent and conductive, but their conductivity is extremely poor. They contain the rare metal indium, which increases their cost. Alumina targets are insulating and wear-resistant, but completely non-conductive. Among compound targets, zinc sulfide / cadmium selenide targets have optical / photoelectric functions, but they are non-conductive, and cadmium selenide is toxic. Therefore, after comprehensive comparison, these targets either have poor conductivity, insufficient purity, or excessive cost. Only pure copper sputtering targets, due to their excellent conductivity (≥58 MS / m) and thermal conductivity (≥390 W / m·K), have become the preferred core material for the deposition of semiconductor interconnect layers and LCD motor layers. However, copper has high chemical reactivity and is easily oxidized to form copper oxide or cuprous oxide. At high temperatures, the grains are prone to coarsening, resulting in problems such as excessive oxygen impurities, abnormal grain growth, catalysis at the bonding interface at the backplane, and low raw material utilization rate in copper-based targets produced under traditional processes.

[0004] In the existing technology, there is no systematic process for copper-based targets, and there is an urgent need for a high-purity target production process that is adapted to the characteristics of pure copper. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a high-purity sputtering target production process, which enables the production of 6N-grade copper-based sputtering targets with low oxygen content, small and uniform grain size, high interfacial bonding strength, and high raw material utilization.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solution:

[0007] A high-purity sputtering target production process includes the following steps:

[0008] S1: Raw material anti-oxidation purification

[0009] S1-1: Initial Raw Material Screening

[0010] 4N grade electrolytic copper (Cu≥99.99%) was selected and detected by glow discharge mass spectrometry (GDMS) to ensure that the initial impurities were Fe≤10 ppm, Ni≤5 ppm, and O≤200 ppm, so as to avoid the introduction of high impurity raw materials into subsequent processes.

[0011] S1-2: Electrolytic refining of ionic liquids

[0012] Electrolytic copper was added to the electrolytic cell using CuCl2-EMIMCl ionic electrolyte. During the electrolysis process, metallic impurities such as Fe and Ni were removed by selective migration of ions. At the same time, the ionic liquid system isolated water and oxygen. After electrolysis, 5N5 grade copper ingots were obtained (Cu≥99.9995%), O≤90 ppm.

[0013] The ion-exchange electrolyte contains 0.5 wt% phenol antioxidant;

[0014] Electrolysis parameters: Voltage 2.7±0.2 V, cathode current density 170±10 A / m 2 Temperature 85±5 ℃;

[0015] S1-3: CO protected zone smelting

[0016] 5N5 copper ingots are placed in a vacuum zone smelting furnace, and 99.999% high-purity CO is introduced into the furnace to form a temporary dense copper oxide protective film on the copper surface, preventing further oxidation, and finally obtaining 6N grade copper raw material (Cu≥99.9999%), O≤40 ppm, C≤20 ppm;

[0017] Smelting parameters: Vacuum degree ≤ 4 × 10 -5 Pa, heating power 6±1 kW, melting zone moving speed 4±1 mm / min, repeated melting 4 times.

[0018] S2: Hot isostatic pressing of copper-based target blank

[0019] S2-1: Copper Rod Pretreatment

[0020] 6N copper raw material was machined into bars with a diameter of Φ250±5 mm, and then subjected to ultrasonic cleaning at 40 kHz to remove surface oil. The bars were then vacuum-packed to prevent oxidation during storage, with a vacuum degree ≤1×10⁻⁶. -4 Pa;

[0021] S2-2: Hot Isostatic Pressing (HIP) for Copper-Based Applications

[0022] The packaged copper rods are placed in a hot isostatic press, and a segmented temperature control method is used:

[0023] (1) From room temperature to 600℃, the heating rate is 5℃ / min, and the pressure is simultaneously increased to 100 MPa. The temperature is held for 1 h to eliminate the internal stress of the copper rod and avoid subsequent cracking.

[0024] (2) From 600℃ to 850℃, the heating rate is 3℃ / min, and the pressure is simultaneously increased to 135±5 MPa. The temperature is held for 2.5 h, and the copper is dynamically recrystallized. The high pressure promotes densification.

[0025] (3) Cooling stage: From 850℃ to 300℃, argon gas is used for forced cooling at a rate of 10℃ / min to avoid cracking of the copper target billet due to thermal expansion and contraction; from 300℃ to room temperature, natural cooling is carried out.

[0026] (4) After molding, a copper-based target blank is obtained. The density is ≥99.95% and the dimensional accuracy is ±0.5 mm by the drainage method, which reduces the allowance for subsequent processing.

[0027] S3: Gradient heat treatment

[0028] S3-1: High-temperature homogenization

[0029] The copper-based target blank is placed in an argon-protected furnace with an Ar purity of 99.999%, heated to 700±10℃, and held for 1.5 h to make the internal structure of the target blank uniform and break down the original coarse grains.

[0030] S3-2: Stepped grain growth control

[0031] The temperature was lowered to 400±10℃ at a rate of 50 ℃ / h and held for 4 h to promote uniform growth of small grains and avoid abnormal coarsening.

[0032] Then, the temperature is reduced to 150±10℃ at a rate of 20℃ / h and held for 2 hours to release the internal stress of the target billet.

[0033] Finally, the grains were air-cooled to room temperature, and the grain size was measured to be 60–70 μm, with the difference between the maximum and minimum grain size ≤8 μm. <111> Texture ratio ≥90% improves sputtering uniformity.

[0034] S4: Target-backplate interface matching diffusion welding

[0035] S4-1: Backplate Pretreatment

[0036] TU1 grade oxygen-free copper backplate is selected, with Cu≥99.99% and O≤0.003%, to avoid the diffusion of dissimilar metals and the formation of brittle phases;

[0037] The back panel surface is precision ground and Ar plasma cleaned to achieve a surface roughness Ra≤0.1 μm, removing the surface oxide layer and oil stains to ensure a clean interface.

[0038] S4-2: Copper-based diffusion welding

[0039] The copper-based target blank is assembled with the backplate, with the parallelism of the mating surfaces ≤0.02 mm, and then placed in a vacuum diffusion welding machine with a vacuum degree ≤1×10⁻⁶. -4 Pa;

[0040] Welding parameters: temperature 600±20℃, pressure 40±5 MPa, holding time 1.2 h;

[0041] After welding, a stepped cooling process is adopted: the temperature is reduced from 600℃ to 400℃ at a rate of 10℃ / min, then reduced to 200℃ at a rate of 5℃ / min, and then allowed to cool naturally to room temperature to avoid cracking due to thermal stress.

[0042] S4-3: Welding Quality Inspection

[0043] Electron probe microanalysis (EPMA) analysis showed the interface diffusion layer thickness to be 5–10 μm. Shear tests confirmed the interface bonding strength to be ≥85 MPa. Ultrasonic testing at 5 MHz showed the interface to be free of bubbles and cracks, with a defect rate ≤0.1%.

[0044] S5: Precision machining and anti-oxidation post-treatment

[0045] S5-1: Precision Grinding

[0046] The sputtering surface of the copper-based target was ground using a diamond grinding wheel to control the surface roughness Ra≤0.05 μm and flatness≤0.02 mm;

[0047] S5-2: Anti-oxidation passivation

[0048] The ground target is immediately immersed in a 3 wt% chromium trioxide (CrO3) solution, forming a dense passivation film of 5-10 nm on the surface to prevent copper oxidation;

[0049] S5-3: Sealed storage

[0050] After passivation, the target material is placed in a sealed package filled with argon gas with a purity of 99.999% and an oxygen content of ≤10 ppm to prevent oxidation during transportation and storage.

[0051] Due to the inherent characteristics of copper-based materials, such as easy oxidation, low recrystallization temperature, high plasticity, and interfacial diffusion sensitivity, this application addresses these issues by specifically suppressing defect generation and enhancing the core performance requirements through targeted reinforcement.

[0052] Firstly, the purification of raw materials is crucial. The core bottleneck in the purity of copper-based targets is the removal of oxygen and metallic impurities. This invention employs a two-step method of ionic liquid electrolysis and CO-protected zone melting, addressing the issue from two perspectives: media isolation and phase separation.

[0053] (1) Electrolytic refining of ionic liquids to isolate selective ion migration of water and oxygen

[0054] In traditional aqueous solution electrolysis, copper ions readily react with water molecules to form Cu(OH)₂, which in turn generates CuO, leading to excessive oxygen impurities. This invention employs a CuCl₂-EMIMCl ionic liquid electrolyte for electrolytic refining. The ionic liquid is composed of organic cationic EMIMCl... + and inorganic anions Cl - CuCl2 - The composition contains no free water molecules, thus preventing the hydrolysis and oxidation of copper ions at the source. It also contains 0.5 wt% phenol antioxidant, whose phenolic hydroxyl groups can capture oxygen free radicals (·OH) generated during electrolysis, further inhibiting the oxidation reaction. The reaction formula is C6H5OH + ·O → C6H4O + H2O. Based on the difference in standard electrode potential between metal ions (Cu... 2+ / Cu: +0.34 V; Fe 2+ / Fe: -0.44 V; Ni 2+ / Ni: -0.25 V), when the electrolysis voltage is controlled at 2.5~3.0 V, only Cu 2+ Cu can be preferentially reduced and deposited at the cathode. 2+ +2e - →Cu, while Fe 2+ Ni 2+ Because the electrode potential is lower, it remains in the electrolyte, thus achieving the separation of metallic impurities from copper, ultimately yielding 5N5 grade copper ingots with an oxygen content ≤90 ppm.

[0055] (2) Smelting in a CO protected zone, with deep purification based on solid-liquid partition coefficient and oxide film isolation.

[0056] The core of zone melting lies in the difference in the distribution coefficient of impurities between the solid and liquid phases of copper, k0 = solid impurity concentration / liquid impurity concentration. This difference is used to remove impurities, while CO protection is introduced to address high-temperature oxidation. The k0 of Fe in copper is approximately 0.1, and that of Ni is approximately 0.2, both less than 1, meaning that impurities have higher solubility in the liquid phase. As the melting zone (1100~1150 ℃, the melting temperature range of copper) slowly moves along the copper ingot, impurities accumulate towards the tail of the ingot. After four remelting cycles, the total impurity content in the ingot head area will decrease to ≤100 ppm. At high temperatures, CO reacts with the copper surface to form a dense cuprous oxide protective film: 2Cu + CO → Cu₂O + C. The cuprous oxide protective film is about 5-10 nm thick, which can effectively isolate the contact between air and copper, avoiding the secondary introduction of oxygen during high-temperature smelting. The generated carbon can also move to the tail of the ingot through the subsequent melting zone. At the same time, as the zone smelting continues, excess CO will reduce the temporary protective film: Cu₂O + CO → 2Cu + CO₂↑. This reaction occurs spontaneously at 1100℃. CO reduces Cu₂O to Cu, and the generated CO₂ is quickly discharged through a vacuum system. Finally, the oxygen content of the copper raw material is ≤40 ppm and the carbon content is ≤20 ppm, reaching a purity of 6N.

[0057] Secondly, the target billet is formed by hot isostatic pressing. Copper has excellent plasticity, but traditional ingots are prone to voids. This invention uses hot isostatic pressing to eliminate voids at the microscopic level and improve density by applying uniform pressure in all directions and combining it with high-temperature atomic diffusion.

[0058] The copper rod is first heated to 600℃ and held for 1 hour. During this time, the dislocations inside the copper rearrange, releasing the mechanical stress. Then, the temperature is increased to 850℃, and the pressure is simultaneously increased to 130-140 MPa. At this point, the copper enters a dynamic recrystallization state, where the grains continuously break and regenerate during plastic deformation, preventing grain coarsening. The high pressure increases the surface energy of the pores inside the copper rod, driving copper atoms to diffuse into the pores. The diffusion coefficient D = D0exp(-Q / RT). At 850℃, the self-diffusion activation energy Q of copper decreases, and the atomic diffusion rate is significantly increased. Finally, the pores are filled with copper atoms, achieving a density of 99.95%. The density of the copper rod is close to the theoretical density of copper, 8.96 g / cm³. 3 During the cooling stage, argon gas is used for forced cooling from 850℃ to 300℃ at a rate of 10℃ / min. The high thermal conductivity of argon gas is used to quickly remove heat, while avoiding warping of the copper target billet due to thermal stress caused by uneven cooling. The coefficient of thermal expansion of copper decreases as the temperature decreases, and rapid cooling can shorten the duration of the temperature difference.

[0059] Meanwhile, if there is a trace amount of unreduced Cu2O, under hot isostatic pressing, although Cu2O is not completely melted, under the self-diffusion of copper atoms, oxygen atoms in Cu2O will break through the phase interface and diffuse into the interstitial positions of the copper matrix, eventually forming a solid solution of oxygen in copper instead of Cu2O phase. Under high pressure, the pores inside the copper close, while promoting the uniform diffusion of oxygen atoms, preventing oxygen atoms from agglomerating and forming new Cu2O.

[0060] Thirdly, it involves gradient heat treatment. Copper has a low recrystallization temperature, only 200-300℃. Traditional heat treatment can easily lead to grain coarsening. This invention uses gradient temperature control, based on recrystallization kinetics and uniformity control of grain growth inhibition, to precisely control the recrystallization and grain growth process of copper.

[0061] First, high-temperature homogenization is employed, at 700℃, far exceeding the recrystallization temperature of copper. At this temperature, the dislocation density within the copper target billet decreases dramatically, breaking down the coarse grains from the initial hot isostatic pressing into fine equiaxed grains of approximately 30-40 μm. Simultaneously, compositional segregation is eliminated, laying the foundation for subsequent uniform grain growth. Then, a gradient cooling process is used, starting at 400℃, below the rapid grain growth temperature of copper. Slow cooling allows the fine grains to grow uniformly to 60-70 μm through normal grain merging, preventing some grains from rapidly engulfing surrounding smaller grains and causing size inhomogeneity. Finally, at 150℃, below the recrystallization temperature of copper, its plasticity is significantly reduced, with elongation decreasing to 15%. Slow cooling allows atoms to gradually move and adjust their lattice positions, releasing residual stress and preventing target billet cracking due to stress concentration during subsequent processing. <111> Texture forms at this time, in copper <111> Crystal planes are close-packed atomic planes with the lowest surface energy. During heat treatment, the grains will spontaneously align themselves with these planes. <111> directional growth, eventually <111> The texture accounts for ≥90%, which can make the escape rate of copper atoms uniform during sputtering and reduce the film thickness deviation.

[0062] Fourthly, the target-backplate diffusion welding is based on the interfacial reliability of atomic interdiffusion and thermal stress matching. By using composition matching and gradient cooling, the interfacial catalysis and stress cracking problems are solved, and the balance between metallurgical bonding and stress release is achieved.

[0063] (1) Metallurgical bonding of diffusion welding

[0064] The backplate uses TU1 oxygen-free copper, with Cu ≥ 99.99% and O ≤ 0.003%, which is close in cost to copper-based targets. It avoids the diffusion of dissimilar metals to form brittle intermetallic compounds such as Cu-Zn and Cu-Sn, which have low shear strength and are prone to interfacial delamination. At 600℃, the diffusion coefficient D of copper atoms is approximately 1 × 10⁻⁶. -12 m 2 / s is 10 at room temperature 6The pressure of 40 MPa ensures that the target and the backing plate are tightly bonded at the interface with a gap of ≤0.1 μm. Copper atoms at the interface break through the surface energy barrier and undergo interdiffusion. Copper atoms in the target diffuse into the backing plate, and copper atoms in the backing plate diffuse into the target, forming a Cu-Cu solid solution diffusion layer with a thickness of about 5~8 μm. This diffusion layer has no brittle phase and a shear strength ≥85 MPa.

[0065] (2) Thermal stress release by gradient cooling

[0066] The elastic modulus of copper increases with decreasing temperature. If the cooling is too rapid, interfacial thermal stress will accumulate as the elastic modulus increases, leading to cracking. Stepped cooling releases stress by adapting to the mechanical properties of copper in stages. In the 600℃ to 400℃ stage, cooling is carried out at a rate of 10℃ / min. Taking advantage of the high plasticity of copper in this range, the thermal stress is rapidly released with the slight slippage of copper atoms at the interface, while avoiding excessive growth of the diffusion layer. In the 400℃ to 200℃ stage, cooling is carried out at a rate of 5℃ / min. The elastic modulus of copper increases and the plasticity decreases. The slower cooling rate reduces the temperature gradient between the target and the backing plate, avoiding microcracks at the interface due to uneven local shrinkage. In the 200℃ to room temperature stage, natural cooling is carried out at a rate of approximately 1~2℃ / min. The coefficient of thermal expansion of copper decreases, and the amount of thermal expansion is significantly reduced. Natural cooling slowly releases the remaining stress, while the vacuum environment prevents copper from oxidizing in the low-temperature range.

[0067] Fifthly, there is the post-treatment to prevent oxidation. Copper easily reacts with air at room temperature to form Cu2O. This invention achieves long-term anti-oxidation through chemical passivation and inert atmosphere protection.

[0068] A 3 wt% chromic anhydride solution undergoes a redox reaction with a copper surface, generating a 5-10 nm thick Cr₂O₃-CuO composite passivation film. This film has a dense spinel structure, effectively isolating O₂ and H₂O from contact with the copper surface, reducing the oxidation rate to below 0.001 nm / h. Specifically, the reaction process involves CrO₃ dissolving in water to initially form chromic acid (H₂CrO₄), which further dissociates into chromate ions (CrO₄⁻) under acidic conditions. 2- and H + Cu is reacted with CrO4 2- Oxidized to Cu 2+ Cr 6+ Reduced to Cr 3+ 3Cu + 2CrO4 2- +16H + =3Cu 2+ +2Cr 3+ +8H2O, the reaction produces Cu 2+ and Cr 3+ It will react with the OH groups that weakly dissociate in the solution. - Combination: H₂O⇌H ++OH - The process generates Cu(OH)₂ and Cr(OH)₃ precipitates, which slowly dehydrate on the copper surface, forming a dense Cr₂O₃-CuO composite film: 3Cu(OH)₂ + 2Cr(OH)₃ = 3CuO + Cr₂O₃ + 6H₂O. Then, the sealed packaging of the target material is filled with high-purity argon gas, which prevents the copper from contacting air during passivation film wear, thus avoiding re-oxidation.

[0069] Compared with the prior art, the present invention has the following advantages:

[0070] (1) This application processes raw materials by ionic liquid electrolysis and CO protected area melting to improve the purity of copper, reduce the impurity content, especially the oxygen content, improve the density of copper material, and greatly reduce the defect rate of sputtered thin film particles, so as to meet the requirements of semiconductor chip for thin film purity.

[0071] (2) This application uses gradient heat treatment to precisely control the recrystallization and grain growth of copper, which significantly improves the uniformity of grains and effectively reduces the corrosion rate of the target surface during sputtering.

[0072] (3) The interface between the target material and the backing plate in this application has strong reliability. The TU1 oxygen-free copper backing plate is combined with the special diffusion welding process, and no brittle phase is generated at the interface. The bonding strength is high and the service life of the target material is extended.

[0073] (4) This application uses hot isostatic pressing to process the target material, which further improves the density and purity of the copper material. Moreover, the processing precision is high, the raw material utilization rate is greatly improved, and the production cost is effectively reduced.

[0074] (5) This application makes full use of the characteristics of pure copper target material for processing, and on this basis, makes full use of the advantages of copper-based materials, strengthens the core performance in a targeted manner, makes up for the deficiencies that may be brought about in the production process, and specifically suppresses the generation of defects, so as to achieve the synergistic optimization of the purity, density, grain uniformity and interface reliability of copper-based target material, with significant effects. Attached Figure Description

[0075] Figure 1 This is the TPt relationship diagram for hot isostatic pressing in this application;

[0076] Figure 2 This is a schematic diagram of the diffusion welding cooling process in this application;

[0077] Figure 3 This is a schematic diagram illustrating the diffusion welding effect of this application;

[0078] Figure 4 Schematic diagram for selecting the hot isostatic pressure of this application;

[0079] Figure 5This is a schematic diagram of the target-backplate shear strength under different welding processes in this application. Detailed Implementation

[0080] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0081] Example 1

[0082] This embodiment focuses on the high-purity copper-based sputtering target required for the interconnect layer of a 12-inch semiconductor chip, with dimensions of Φ300mm×15mm. Its fabrication process is achieved through the following steps.

[0083] S1: Raw material anti-oxidation purification

[0084] S1-1: Initial Raw Material Screening

[0085] 4N grade electrolytic copper is selected and tested by GDMS to ensure compliance.

[0086] Raw material specifications: 4N grade electrolytic copper ingot (Cu≥99.99%), dimensions 100 mm×50 mm×20 mm;

[0087] Detection equipment: Glow discharge mass spectrometer (Thermo Fisher ARL GDMS700, USA);

[0088] Initial impurity content: Fe=8 ppm, Ni=4 ppm, O=180 ppm, and total content of other impurities ≤8 ppm.

[0089] S1-2: Electrolytic refining of ionic liquids

[0090] Electrolytic copper is added to an electrolytic cell using an ionic electrolyte to electrolyze the copper. The ionic liquid system is kept isolated from water and oxygen to remove metallic impurities. After electrolysis, 5N5 grade copper ingots are obtained.

[0091] Equipment selected: a closed ionic liquid electrolyzer, made of PTFE (polytetrafluoroethylene), with a volume of 50 L, and equipped with a DC power supply (0~5 V / 0~500 A).

[0092] Electrolyte preparation: CuCl2-EMIMCl ionic liquid, Cu 2+ The concentration was 0.8 mol / L, with the addition of 0.5 wt% phenol antioxidant, and the magnetic stirring speed was 300 r / min.

[0093] Electrolysis parameters:

[0094] Cathode: 4N electrolytic copper (to be purified), anode: high-purity graphite (99.999% purity);

[0095] Voltage 2.7 V, cathode current density 170 A / m 2 Electrolysis temperature 85℃;

[0096] Electrolysis time: 48 h, with 1 / 3 of the electrolyte replaced every 12 h to reduce impurity density;

[0097] Product testing: The size of the electrolytic copper ingot is 120 mm × 60 mm × 25 mm. The purity of the ingot is 99.9995% as determined by GDMS, with O=85 ppm, Fe=1.2 ppm and Ni=0.8 ppm.

[0098] S1-3: CO protected zone smelting

[0099] 5N5 copper ingots are placed in a vacuum zone smelting furnace, and high-purity CO is introduced into the furnace to finally obtain 6N grade copper raw material.

[0100] Equipment selected: Vacuum zone melting furnace (Luoyang Juxing Kiln ZG-400), equipped with CO gas purification system and infrared thermometer;

[0101] Process parameters:

[0102] Loading: Fix the 5N5 copper ingot to the quartz boat and place it into the melting chamber;

[0103] Vacuum degree: 4×10 -5 Pa, vacuum is drawn by a mechanical pump in conjunction with a molecular pump;

[0104] Protective gas: High-purity CO is introduced until the pressure inside the furnace reaches 50 Pa, with a flow rate of 2 L / min;

[0105] Melting parameters: heating power 6 kW, melting zone width 50 mm, melting zone moving speed 4 mm / min, repeated melting 4 times;

[0106] Product testing: Copper raw material purity 99.99992%, O=35 ppm (tested by pulsed infrared oxygen and carbon analyzer, German Elementar ONH836), C=18 ppm, Fe=0.3 ppm, Ni=0.2 ppm.

[0107] S2: Hot isostatic pressing of copper-based target blank

[0108] S2-1: Copper Rod Pretreatment

[0109] The 6N copper raw material is processed into bars with a diameter of 250±5 mm. The surface oil is removed by ultrasonic cleaning, and then vacuum-packed to prevent oxidation during storage.

[0110] Processing equipment: Precision lathe (Shenyang Machine Tool CK6150), ultrasonic cleaner (40 kHz, 500 W);

[0111] Process steps:

[0112] Machining: 6N copper raw material is turned into a bar stock with a diameter of 250 mm and a diameter of 300 mm, and the surface roughness Ra = 1.6 μm;

[0113] Ultrasonic cleaning: Rinse with deionized water for 20 minutes to remove surface oil and dirt;

[0114] Vacuum packaging: Aluminum-plastic composite film vacuum sealing, vacuum degree 1×10 -4 Pa, Packaging machine model DZ-600.

[0115] S2-2: Hot isostatic pressing

[0116] The packaged copper rods are placed in a hot isostatic press and processed using a segmented temperature control method.

[0117] Equipment selected: Hot isostatic press (Swedish Quintus QIH-15), maximum pressure 200 MPa, temperature control accuracy ±2℃;

[0118] Hot isostatic pressing curves (e.g.) Figure 1 (as shown)

[0119] Stage 1: Room temperature → 600℃, heating rate 5℃ / min, simultaneous pressure increase to 100 MPa, hold for 1 h;

[0120] Phase 2: 600℃→850℃, heating rate 3℃ / min, simultaneous pressure increase to 135 MPa, holding for 2.5 h;

[0121] Cooling stage: 850℃→300℃, forced cooling with Ar gas, flow rate 5 m / s, cooling rate 10 ℃ / min; 300℃→room temperature, natural cooling;

[0122] Product testing: Target blank size Φ248 mm × 280 mm, density 8.957 g / cm³ 3 (Water displacement method, accuracy ±0.001 g / cm) 3 That is, 99.97% (theoretical density 8.96 g / cm³). 3 ), dimensional accuracy ±0.4 mm.

[0123] S3: Gradient heat treatment

[0124] The copper-based target blank was placed in an argon-protected furnace, heated to 700℃, held for 1.5 h, and then cooled in stages to control grain growth until it reached room temperature, at which point the grains were tested.

[0125] Equipment selected: Atmosphere-protected heat treatment furnace (Shanghai Experimental Electric Furnace SK-G12033K), Ar gas purity 99.999%, temperature control accuracy ±1℃;

[0126] Heat treatment process:

[0127] Homogenization: 700℃, heat preservation for 1.5 h, Ar gas flow rate 10 L / min;

[0128] Step-down cooling stage 1: Reduce to 400℃ at a rate of 50 ℃ / h and hold for 4 h;

[0129] Step cooling in two stages: cooling to 150℃ at a rate of 20 ℃ / h, and holding at that temperature for 2 h;

[0130] The furnace was allowed to cool naturally to room temperature, while Ar gas was used for protection at 100°C.

[0131] Detection equipment: X-ray diffractometer (XRD, Bruker D8 Discover, equipped with Cu target, two-dimensional detector, and texture attachment; Cu target λ=0.154 nm), transmission electron microscope (TEM-SAED, FEI Talos F200X, equipped with field emission gun, accelerating voltage 200 kV), electron back-radius diffractometer (EBSD, Oxford Instruments Nordlys Max3).

[0132] Test results: Grain size 65 μm, maximum-minimum grain difference 7 μm. <111> Texture accounts for 91%, and residual stress is ≤50 MPa (X-ray stress meter, PROTO LXRD).

[0133] S4: Target-backplate diffusion welding

[0134] S4-1: Backplate Pretreatment

[0135] High-purity copper backplate is selected, and the backplate surface is precision ground and Ar plasma cleaned to remove the surface oxide layer and oil stains, ensuring a clean interface.

[0136] Backplate specifications: TU1 oxygen-free copper, Cu≥99.99%, dimensions Φ300 mm×10 mm, oxygen content 0.0025%;

[0137] Pretreatment process:

[0138] Precision grinding: Grinding with an 800# diamond grinding wheel to a surface roughness Ra=0.08 μm, and the testing instrument is a surface profilometer, Taylor Hopson Form Talysurf i-Series;

[0139] Plasma cleaning: Ar plasma, power 500 W, vacuum degree 5 Pa, cleaning for 3 min.

[0140] S4-2: Diffusion Welding

[0141] The copper-based target blank is assembled and bonded to the back plate, and then placed in a vacuum diffusion welding machine. After welding, the temperature is gradually reduced to room temperature, and the welding quality is tested.

[0142] Equipment selected: Vacuum diffusion welding machine (Beijing Aeronautical Manufacturing Engineering Research Institute LD-600), vacuum degree ≤1×10 -4 Pa, pressure control accuracy ±0.5 MPa;

[0143] Welding parameters:

[0144] Assembly: The target blank (Φ248 mm) is concentrically assembled with the back plate, with a parallelism of ≤0.02 mm. The testing equipment is a laser interferometer, Zygo GOI-XP.

[0145] Welding: Temperature 600℃, pressure 40 MPa, holding time 1.2 h;

[0146] Step cooling (e.g.) Figure 2 As shown): 600℃→400℃ (10 ℃ / min)→200℃ (5 ℃ / min)→room temperature (natural cooling);

[0147] Detection results (structure at the interface as shown) Figure 3 (as shown)

[0148] Interface diffusion layer: 8 μm, electron probe microanalyzer EPMA, JEOL JXA-8230;

[0149] Shear strength: 88 MPa, universal testing machine, INSTRON 5982, shear rate 0.5 mm / min;

[0150] Ultrasonic testing: 5 MHz probe test, no bubbles or cracks at the interface, defect rate 0%.

[0151] S5: Precision machining and anti-oxidation post-treatment

[0152] S5-1: Precision Grinding

[0153] The sputtering surface of the copper-based target is ground using a diamond grinding wheel.

[0154] Equipment selected: CNC surface grinder, Taiwan Jiande KGS-84AHD, with 1500# stainless steel grinding wheels;

[0155] Process parameters: Grinding depth 0.05 mm / cycle, feed rate 100 mm / min;

[0156] Test results: Sputtering surface roughness Ra=0.03 μm, flatness 0.02 mm (laser interferometer).

[0157] 5-2: Passivation and Packaging

[0158] After grinding, the target material is immediately immersed in chromic anhydride solution, forming a dense passivation film on the surface to prevent copper oxidation. The passivated target material is then placed in an argon-filled sealed package to avoid oxidation during transportation and storage.

[0159] Passivation process: Immerse in 3 wt% chromic anhydride solution for 5 min, with CrO3 purity in the solution being 99.9%, and air dry at room temperature with humidity ≤50%;

[0160] Passivation film detection: 7 nm behind the film, detected by X-ray fluorescence thickness gauge, Oxford Instruments X-Strata920; dense and non-porous, detected by scanning electron microscope (SEM), Zeiss Sigma 300.

[0161] Sealed packaging: Ar-filled aluminum-plastic packaging, Ar purity 99.999%, oxygen content inside the packaging 8 ppm, oxygen sensor: Ametek MOCON.

[0162] S6: Final Inspection of Finished Products (Table 1)

[0163] Table 1 shows the multidimensional testing data of the product.

[0164]

[0165] Example 2

[0166] This embodiment verifies the influence of core process parameters on the oxygen content, grain size, and bonding strength of the target material through multiple sets of comparative experiments, and sets up an experimental group for the process of this invention and a control group for the prior art.

[0167] Experiment 1: Effect of electrolysis temperature on oxygen content of copper ingots

[0168] Fixed parameters: ionic liquid electrolyte (containing 0.5% phenol), current density 170 A / m 2 Electrolysis time: 48 h;

[0169] Variable: Electrolysis temperature (60℃, 70℃, 85℃, 100℃);

[0170] Control group: conventional aqueous solution electrolysis (CuSO4 solution, temperature 50℃);

[0171] The processing and testing are performed in accordance with Example 1.

[0172] Table 2 shows the detection data on the effect of electrolysis temperature on the impurity content of copper ingots.

[0173]

[0174] Conclusion: Ionic liquid electrolysis has the lowest oxygen content (85 ppm) at 85℃, which is 83.7% lower than that of traditional aqueous solution electrolysis (520 ppm), and the content of metal impurities is also lower.

[0175] Experiment 2: Effect of Zone Melting Numbers on Copper Raw Material Purity

[0176] Fixed parameters: CO protection (99.999%), temperature 1120℃, melting speed 4 mm / min;

[0177] Variable: Number of smelting attempts (1 time, 2 times, 3 times, 4 times);

[0178] Control group: Vacuum zone melting (without CO protection, 4 times);

[0179] The processing and testing are performed in accordance with Example 1.

[0180] Table 3 shows the test data on the impact of zone smelting times and environment on copper raw materials.

[0181]

[0182] Conclusion: Smelting under CO protection for four times can reduce the oxygen content to 35 ppm. Although vacuum smelting has a low carbon content, the oxygen content is as high as 180 ppm, which verifies the antioxidant effect of CO in zone smelting.

[0183] Verification 3: Effect of hot isostatic pressing pressure on the density of the target billet

[0184] Fixed parameters: temperature 850℃, holding time 2.5 h, cooling rate 10℃ / min;

[0185] Variable: Hot isostatic pressure (100 MPa, 120 MPa, 135 MPa, 150 MPa);

[0186] Control group: Traditional forging (800℃, 70% deformation);

[0187] The processing and testing are performed in accordance with Example 1.

[0188] Table 4 shows the test data on the effect of hot isostatic pressing pressure and method on the density of the target blank.

[0189]

[0190] Conclusion: At 135 MPa, the density reaches 99.97%, while traditional forging only achieves 99.55% density and poor dimensional accuracy. Although the density is higher (99.98%), porosity is lower (0.02), and dimensional accuracy is better (±0.3) at 150 MPa, a comparison of pressure change trends shows that the increase in density at 150 MPa is smaller, but the requirements for equipment are much higher, energy consumption is significantly increased, and production efficiency is reduced. Figure 4 As shown. At the same time, the processing at 150 MPa brings higher residual stress to the target blank, which is completely counterproductive. Therefore, 135 MPa is determined to be the optimal choice.

[0191] Experiment 4: Effect of welding temperature on interfacial bonding strength

[0192] Fixed parameters: pressure 40 MPa, heat preservation for 1.2 h, step cooling;

[0193] Variable: Welding temperature (550℃, 600℃, 650℃, 700℃);

[0194] Control group: Traditional brazing (Sn-Pb brazing filler metal, welding temperature 250℃);

[0195] The processing and testing are performed in accordance with Example 1.

[0196] Table 5 shows the test data on the influence of welding temperature and welding method on the bond strength between the target blank and the back plate.

[0197]

[0198] Conclusion: Combining Figure 5 It can be seen that the bonding strength is highest at 650℃ (88 MPa), but the elastic segment is slightly short, the fracture displacement is moderate, and embrittlement begins. The bonding strength (88 MPa) at 600℃ meets the requirements, the diffusion layer thickness is moderate (8 μm), the elastic segment is moderate, the strengthening is obvious, the fracture displacement is large, and the plasticity is good. The excessively high temperature (700℃) leads to an excessively thick diffusion layer (18 μm), resulting in decreased strength, a short elastic segment, a small fracture displacement, and increased brittleness. The strength of traditional brazing is only 45 MPa, the elastic segment is extremely short, there is no obvious strengthening effect, rapid fracture, significant brittleness, and a high defect rate.

[0199] Experiment 5: Overall Performance Comparison (Invention vs. Existing Technology)

[0200] Table 6 presents comparative data of the product parameters obtained in Example 1 with the industry average parameters in the prior art.

[0201]

[0202] Conclusion: The process of this invention is significantly superior to the prior art in terms of core indicators such as purity, oxygen content control, grain uniformity, and interface strength, and fully meets the stringent requirements of 12-inch semiconductors for copper-based sputtering targets.

Claims

1. A process for producing high-purity sputtering targets, characterized in that, Includes the following steps: (1) Antioxidant purification of raw materials: 4N grade electrolytic copper is selected and refined by ion electrolysis to obtain 5N5 grade copper ingots, which are then smelted in an area protected by 99.999% high-purity CO to obtain 6N grade copper raw materials. The electrolyte used in the ion electrolysis is CuCl2-EMIMCl containing 0.5wt% phenol antioxidant, the electrolysis voltage is 2.7±0.2 V, and the cathode current density is 170±10 A / m 2 The oxygen content in the 5N5 grade copper ingots obtained after treatment is ≤90 ppm at a temperature of 85±5 ℃. (2) Hot isostatic pressing of copper-based target blank: 6N copper raw material is processed into Φ250±5 mm rods, vacuum packaged and then hot isostatic pressed to obtain copper-based target blanks with a density ≥99.95%; (3) Gradient heat treatment: The copper-based target billet is homogenized at 700±10℃ for 1.5 h, and then the grain size growth is controlled by step cooling to achieve a grain size of 60~70 μm, with the difference between the maximum and minimum grain size ≤8 μm. <111> The texture accounts for ≥90%, and the step-down cooling is as follows: first, the temperature is lowered to 400±10℃ at a rate of 50 ℃ / h and held for 4 h; then, the temperature is lowered to 150±10℃ at a rate of 20 ℃ / h and held for 2 h; finally, the temperature is air-cooled to room temperature. (4) Target-backplate interface matching diffusion welding: TU1 grade oxygen-free copper backplate is selected, pretreated and assembled with copper-based target blank, and welded in a vacuum diffusion welding machine at 600±20℃ and 40±5 MPa for 1.2 h, with step cooling, and the interface bonding strength is ≥85MPa. (5) Precision machining and anti-oxidation post-treatment: The sputtering surface of the copper-based target is ground to Ra≤0.05 μm and flatness≤0.02 mm. After passivation with 3 wt% chromic anhydride solution, it is sealed and packaged with Ar gas to obtain high-purity copper-based sputtering target finished product.

2. The production process according to claim 1, characterized in that, The melting parameters used in the CO-protected zone melting are: vacuum degree ≤ 4 × 10⁻⁶. -5 The 6N grade copper raw material obtained by repeated melting 4 times with a heating power of 6±1 kW, a melting zone moving speed of 4±1 mm / min, and a heating power of 6±1 kW, has an oxygen content of ≤40 ppm and a carbon content of ≤20 ppm.

3. The production process according to claim 1, characterized in that, The copper-based target blank hot isostatic pressing process employs a segmented temperature control method: (1) From room temperature to 600℃, the heating rate is 5℃ / min, and the pressure is simultaneously increased to 100 MPa and held for 1 h; (2) From 600℃ to 850℃, the heating rate is 3℃ / min, and the pressure is simultaneously increased to 135±5 MPa, and the temperature is maintained for 2.5 h; (3) Cooling stage: from 850℃ to 300℃, argon gas is used for forced cooling at a rate of 10℃ / min to avoid cracking of the copper target billet due to thermal expansion and contraction; from 300℃ to room temperature, natural cooling is carried out.

4. The production process according to claim 3, characterized in that: The hot isostatic pressing of the copper-based target billet requires pretreatment of the 6N copper raw material, specifically by ultrasonic cleaning at 40 kHz to remove surface oil, followed by vacuum packaging with a vacuum degree ≤1×10⁻⁶. -4 Pa.

5. The production process according to claim 1, characterized in that: The gradient heat treatment is carried out in an Ar-protected furnace with Ar purity of 99.999%.

6. The production process according to claim 1, characterized in that: In the target-backplate interface matching diffusion welding process, the pretreatment of the backplate surface involves precision grinding and Ar plasma cleaning, with a surface roughness Ra≤0.1 μm, to remove the surface oxide layer and oil stains and ensure interface cleanliness.

7. The production process according to claim 1, characterized in that: In the target-backplate interface matching diffusion welding process, the gradient cooling after welding is specifically as follows: cooling from 600℃ to 400℃ at a rate of 10℃ / min, cooling to 200℃ at a rate of 5℃ / min, and then naturally cooling to room temperature.

8. The production process according to claim 1, characterized in that: The 4N grade electrolytic copper initial raw material needs to be tested to ensure that the initial impurities are Fe≤10 ppm, Ni≤5 ppm, and O≤200 ppm.

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