An ultra-high purity copper sulfate electroplating solution, a preparation method and application thereof

Abstract

The application belongs to the technical field of electroplating technology, and particularly relates to an ultrahigh-purity copper sulfate electroplating solution and a preparation method and application thereof, wherein ultrapure copper, ultrapure sulfuric acid and ultrapure hydrochloric acid with a purity of greater than or equal to 99.9995% are used as raw materials, an electrolysis device independently designed is used, and an acidic copper sulfate solution with a purity of greater than or equal to 99.9999% can be prepared through an electrolysis method. An imidazole ionic liquid is introduced to simultaneously act as an accelerator and a leveling agent, and cooperates with an inhibitor polyethylene glycol to break through the diffusion limitation of a traditional SPS-PEG-JGB-Cl ‑ system in ultra-micropore filling, and uniform and sufficient electroplating can be achieved. The plating layer obtained through electroplating does not have pores and holes, the surface is flat, the structure has good compactness, and good wafer copper interconnection application effects are exhibited.

Description

Technical Field

[0001] This invention belongs to the field of electroplating technology, and particularly relates to an ultra-high purity copper sulfate electroplating solution, its preparation method, and its application. Background Technology

[0002] In semiconductor integrated circuit manufacturing, copper interconnect technology achieves high-density metal wiring through electrochemical deposition (ECD), the core of which lies in the precise control of the purity of the electroplating solution and the additive system. As process nodes continue to advance, the aspect ratio (AR) of interconnect structures generally exceeds 20:1, and critical dimensions shrink to below 28nm. Traditional technologies face the following key bottlenecks:

[0003] 1. Impurities in electroplating solutions induce grain boundary defects and reliability failures.

[0004] Commercially available copper sulfate (CuSO4·5H2O) generally has a purity of 4N to 5N, with a total metallic impurity content of approximately 50 to 200 ppb. The main impurities include Fe (30 to 50 ppb), Ni (20 to 30 ppb), and Na (10 to 20 ppb). These impurities cause multiple problems for the copper layer's performance after electroplating: ① Fe and Ni segregate at copper grain boundaries, forming high-resistivity intermetallic compounds (such as Cu5Fe and Cu3Ni), leading to an increase in resistivity to 2.1 to 2.3 μΩ·cm (the theoretical value for pure copper is 1.68 μΩ·cm), and a decrease in electromigration lifetime. ② Na reacts with moisture to form NaOH, corroding the Ta / TaN barrier layer and causing interfacial delamination. The delamination probability reaches 15% to 20% in thermal cycling tests (-65℃ to 150℃). ③ Unfiltered submicron particles (>0.2 μm) embed in the plating layer, resulting in a linewidth deviation exceeding ±5% after polishing and a yield loss of 3% to 5%.

[0005] 2. The high aspect ratio filling failure of traditional additive systems makes it difficult to meet the requirements for defect-free filling.

[0006] Traditional copper electroplating additive systems consist of accelerators (SPS, Bis-(3-sulfopropyl)disulfide), inhibitors (PEG 2000), and leveling agents (JGB). However, these systems struggle to achieve sufficient filling in the electroplating of submicron structures with an AR ratio greater than 8:1 (such as TSV and damascus structures), presenting the following challenges:

[0007] SPS, with its large molecular weight (246 g / mol), has a low diffusion rate in narrow pores (<50 nm), insufficient accelerator concentration at the bottom of the pore, and a deposition rate lagging behind the pore opening, resulting in a porosity as high as 5%–10% (when the pore size is <50 nm). ② PEG over-adsorbs in the strong electric field region at the pore opening, inhibiting deposition, while insufficient inhibition at the bottom of the pore results in a protrusion height of 50–100 nm, increasing the risk of short circuits after polishing. ③ JGB reduction generates aniline derivatives (such as p-phenylenediamine), whose toxicity (LD50 = 250 mg / kg) increases wastewater treatment costs, and byproduct adsorption leads to an increase in contact resistance ≥10%.

[0008] The current mainstream semiconductor integrated circuit market focuses on processes below 28nm and is gradually moving towards 3D integrated packaging, which continuously increases the requirements for copper interconnect technology. Regarding electroplating raw materials, the requirements are that individual metal impurities in the electroplating solution be <5ppb and TOC ≤1ppm. In terms of additives, there is a move towards nanoscale additives, requiring molecular size <1nm and thermal stability >200℃. Current domestic technologies are insufficient to meet these requirements, necessitating breakthroughs through the research and development of ultra-pure copper electroplating solution preparation processes and novel additives. Summary of the Invention

[0009] The purpose of this invention is to provide an ultra-high purity copper sulfate electroplating solution, its preparation method, and its application, addressing problems such as voids, high plating impurity content, poor plating uniformity, and high surface roughness that are prone to occur in process nodes below 28nm and high aspect ratio copper interconnect processes. The copper sulfate electroplating solution described herein has high purity, a simple preparation method, is environmentally friendly, and offers controllable quality.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] An ultra-high purity copper sulfate electroplating solution suitable for copper interconnects in semiconductor integrated circuits includes an ultra-high purity acidic copper sulfate solution and a composite additive. The ultra-high purity acidic copper sulfate solution includes copper sulfate, sulfuric acid, and chloride ions. The total organic carbon content in the ultra-high purity acidic copper sulfate solution is ≤1ppm, the total content of metallic impurities is <50ppb, and the number of particles >0.2μm in the product is ≤50 particles / mL. The composite additive is an imidazole ionic liquid and polyethylene glycol. The amount of imidazole ionic liquid added to the electroplating solution is 4.5-40mg / L, and the amount of polyethylene glycol added is 100-200mg / L.

[0012] Furthermore, the imidazole ionic liquid is one of 1-ethyl-3-methylimidazolium dicyandiamide, 1-propyl-3-methylimidazolium dicyandiamide, 1-butyl-3-methylimidazolium dicyandiamide, 1-propylsulfonic acid-3-methylimidazolium chloride, 1-propylsulfonic acid-3-ethylimidazolium chloride, 1-acrylpropyl-3-methylimidazolium chloride, and 1-carboxymethyl-3-methylimidazolium chloride, all with a purity of ≥99.9%; the polyethylene glycol is one of polyethylene glycol 2000, polyethylene glycol 4000, and polyethylene glycol 8000, all with a purity of ≥99.9%.

[0013] Furthermore, the concentration of imidazole ionic liquid in the ultra-high purity copper sulfate electroplating solution is 5 ppm, 10 ppm, or 20 ppm, and the concentration of polyethylene glycol is 100 ppm, 120 ppm, or 150 ppm.

[0014] Another objective of this invention is to provide a method for preparing an ultra-high purity copper sulfate electroplating solution, comprising the following steps: preparing an ultra-high purity acidic copper sulfate solution by electrolysis in an electrolytic cell, and then adding a composite additive to the prepared ultra-high purity acidic copper sulfate solution and mixing it to obtain the solution; the entire preparation process of the ultra-high purity copper sulfate electroplating solution is carried out in an environment with a cleanliness level ≥ ISO 7.

[0015] The preparation conditions for the ultra-high purity acidic copper sulfate solution are as follows: the electrolytic cell is equipped with an anode, a cathode, and an anion exchange membrane; the electrolyte for the electrolytic reaction is a mixed acid-water solution made of sulfuric acid and hydrochloric acid, wherein the sulfuric acid concentration is 0.73-1.86 mol / L and the hydrochloric acid concentration is 0.56-2.78 mol / L; hydrochloric acid and sulfuric acid of quality standard ≥ SEMI 10 are used for preparation, and the final electrolyte contains a single metal impurity content <1 ppb, a particle content >0.2 μm ≤20 particles / mL, and a total organic carbon content <0.2 ppm; the current density of the electrolytic reaction is 0.2-0.5 mA / cm². 2 The anode and the anion exchange membrane form an anode chamber, and the cathode and the anion exchange membrane form a cathode chamber. The volume ratio of the electrolyte in the anode chamber to the cathode chamber of the electrolytic cell is (1.5-2):1.

[0016] Furthermore, the anode material is ultrapure copper with a purity of ≥99.9995%; the cathode is composed of copper, platinum, gold, silver, graphite, or a composite material with copper, platinum, gold, silver, and carbon as the main materials, exhibiting overall inertness during electrolysis; the shape and size of the anode and cathode are not specifically limited and are selected according to actual conditions. The anode has an anode connection, and the cathode has a cathode connection; the specific wiring method is not required, but the wiring material must be ultrapure copper with a purity ≥99.9995%. During the electrolysis reaction, the anode is wrapped with a 10μm pore size cloth bag made of polyester filter cloth or polypropylene nonwoven fabric to prevent anode mud from falling off during electrolysis; preferably, the electrolyte volume ratio of the anode chamber to the cathode chamber is 2:1 or 1.5:1.

[0017] Furthermore, the anion exchange membrane is a quaternary ammonium anion exchange membrane, a quaternary phosphate anion exchange membrane, or a modified polybenzimidazole anion exchange membrane. Preferably, the anion exchange membrane is a quaternary ammonium anion exchange membrane of model ACE, purchased from Hangzhou Lanran Technology Co., Ltd.; or the anion exchange membrane is a quaternary ammonium anion exchange membrane of model FAA-3-50, purchased from Fumatech GmbH, Germany.

[0018] Furthermore, the shape of the electrolytic cell is not specifically limited, but is preferably cuboid; the electrolytic cell is constructed in a multi-part assembly form, and the specific volume is selected according to the actual situation; the cell body material is at least one of polytetrafluoroethylene, polypropylene, polyethylene, polyvinyl chloride or polyvinylidene fluoride.

[0019] Furthermore, the water in the mixed acid electrolyte is ultrapure water with a resistivity ≥15 MΩcm; the sulfuric acid concentration in the mixed acid electrolyte is 0.75 M, 1.3 M, or 1.85 M; the hydrochloric acid concentration in the mixed acid electrolyte is 0.55 M, 1.65 M, or 2.75 M; the electrolysis reaction is performed using direct current, and the current density of the electrolysis reaction is 0.2 mA / cm². 2 0.35mA / cm 2 or 0.5mA / cm 2 The electrolysis reaction time is based on the quality requirements of the ultra-high purity acidic copper sulfate solution. The Cu content of the resulting acidic copper sulfate solution is monitored in real time. 2+The concentration of the solution must meet the quality requirements and can be detected using conventional methods in the art, preferably inductively coupled plasma atomic emission spectrometry (ICP-AES). The typical electrolysis time is 8-15 hours, and the final solution obtained in the anode chamber is the ultra-high purity acidic copper sulfate solution. The purity of the ultra-high purity acidic copper sulfate solution is determined using conventional methods in the art, preferably using inductively coupled plasma mass spectrometry (ICP-MS). The total metal impurity content of the ultra-high purity acidic copper sulfate solution described in this invention is ≤50 ppb, with key metal impurities Fe <4.5 ppb, Ni <0.7 ppb, Na <4 ppb, and Ag <0.2 ppb. The total organic carbon content of the ultra-high purity acidic copper sulfate solution is determined using conventional methods in the art, preferably using a TOC analyzer. The total organic carbon content of the ultra-high purity acidic copper sulfate solution described in this invention is ≤1 ppm. The particle content of the ultra-high purity acidic copper sulfate solution is determined using conventional methods in the art, preferably using a laser particle size analyzer. The ultra-high purity acidic copper sulfate solution of this invention contains ≤50 particles >0.2μm / mL.

[0020] This invention also provides the application of the ultra-high purity copper sulfate electroplating solution in copper interconnect electroplating for advanced processes below 28nm and advanced packaging with aspect ratios >20:1.

[0021] The advantages of this invention are:

[0022] 1. The preparation process of ultra-high purity acidic copper sulfate solution is simple and environmentally friendly. It employs a traditional electrolysis method, using ultra-high purity (≥99.9995%) copper anodes and ultra-high purity mixed acid electrolytes. The anode and cathode chambers are separated by anion exchange membranes. During the electrolysis reaction, copper ions in the anode chamber do not diffuse to the cathode chamber and are not electrodeposited there. The copper ion concentration in the solution in the anode chamber can quickly reach the desired concentration. The entire process produces no harmful gases, wastewater, or waste residue emissions, making it environmentally friendly.

[0023] 2. The prepared acidic copper sulfate solution has high purity. The entire preparation process is carried out in a clean environment of ISO 7 or higher. The raw materials and electrolytes used are all of ultra-high purity, and the product quality can be effectively controlled by adjusting the purity and concentration of the raw materials and the electrolysis conditions. The ultra-high purity acidic copper sulfate solution described in this invention has a purity of over 99.9999%, a total organic carbon content ≤1ppm, and a particle content >0.2μm ≤50 particles / mL.

[0024] 3. This invention innovatively selects functional imidazole ionic liquids with a molecular weight of 175-255 as a single-component bifunctional additive. Its molecular weight is significantly lower than that of the traditional accelerator SPS (246 Da), resulting in a significant improvement in diffusion efficiency and overcoming the diffusion limitations of traditional SPS in micropores. Through potential-dependent adsorption behavior, it rapidly adsorbs in the low current density region (bottom of the micropore), triggering a "pore bottom accelerated filling" effect. In the high current density region (micropore opening), it competes with copper ions for adsorption, inhibiting copper protrusion and achieving surface leveling. Thus, it achieves both acceleration and leveling effects, replacing traditional multi-component additive systems. The imidazole ionic liquid selected in this invention maintains long-term physicochemical stability below 200℃ and exhibits no adverse effects during actual electroplating processes. Real-time monitoring and replenishment are required; when combined with the traditional inhibitor PEG, it can maintain a synergistic effect of acceleration, inhibition and leveling for a long time. Imidazole cations selectively adsorb onto the defect sites of copper crystal surfaces, mainly in the low current region at the bottom of the pore, playing an accelerated deposition role; PEG covers the flat crystal surface through an ether-hydrogen bond network, mainly in the high current region at the pore opening, providing continuous inhibition. The adsorption sites of the two can be staggered to avoid competitive failure; the hydrogen bonds between PEG molecules form a reversible dynamic network, and after local desorption, free molecules quickly fill the gap; the imidazole cations reduce the PEG re-adsorption energy barrier through electrostatic interaction, helping to maintain the integrity of the pore opening inhibition layer and achieving multiple synergistic effects. Attached Figure Description

[0025] Figure 1 This is a simplified schematic diagram of the electrolytic cell described in this invention;

[0026] Figure 2 This is a graph showing the acceleration effect of 1-ethyl-3-methylimidazolium dicyanamide, 1-propylsulfonic acid-3-methylimidazolium chloride, and 1-acrylonitrile-3-methylimidazolium chloride in the cathodic polarization curves (CP curves) of acidic copper sulfate solution in the embodiments of the present invention. In the figure, line a represents the addition of PEG first and then 1-acrylonitrile-3-methylimidazolium chloride (57-6), line b represents the addition of PEG first and then 1-ethyl-3-methylimidazolium dicyanamide (52-1), and line c represents the addition of PEG first and then 1-propylsulfonic acid-3-methylimidazolium chloride (89-7).

[0027] Figure 3 The scanning electron microscope (SEM) images of the copper plating layer formed on the cathode surface by fully electroplating the products prepared in Examples 1, 1-1, 1-8, 1-9 and Comparative Example 1-1 of this invention are shown.

[0028] Figure 4The XRD data of the copper plating layer formed on the cathode surface by fully electroplating the products prepared in Examples 1, 1-1, 1-8, 1-9 and Comparative Example 1-1 of the present invention are as electroplating solutions. Among them, a is Example 1, b is Example 1-1, c is Example 1-8, d is Example 1-9 and e is Comparative Example 1-1.

[0029] Figure 5 These are the CP curves of the ionic liquid additive 1-propylsulfonic acid-3-methylimidazolium chloride and the conventional accelerator SPS measured at different rotational speeds, as described in this invention; where a represents the conventional accelerator and b represents the ionic liquid additive 1-propylsulfonic acid-3-methylimidazolium chloride (89-7). Detailed Implementation

[0030] In this embodiment of the invention, the electrolytic cell has a bottom dimension of 55cm × 65cm and a height of 600mm. A baffle plate is welded inside the cell, with a hole in the center to fix the anion exchange membrane, thus dividing the cell into anode and cathode chambers. The anode copper plate has dimensions of 15cm, 13cm, and 2cm (length, width, thickness); the cathode has dimensions of 15cm, 13cm, and 1mm (length, width, thickness); the length and width of the liquid contact area between the anode and cathode are 13cm and 13cm respectively. The liquid levels in the anode and cathode chambers are the same. The entire preparation process is carried out in an ISO 7 clean environment.

[0031] In this invention, as shown in the appendix Figure 1 As shown, during the preparation of ultra-high purity acidic copper sulfate solution, under the action of a constant current DC power supply, ultra-pure copper anode ① continuously electrolyzes copper ions, which gradually diffuse into the anode chamber; under the action of cathode ②, hydrogen ions in the cathode chamber are continuously reduced to generate hydrogen gas; at the same time, under the action of anion exchange membrane, sulfate ions and chloride ions in the cathode chamber continuously enter the anode chamber.

[0032] In this embodiment of the invention,

[0033] The term "product" refers to the ultra-high purity acidic copper sulfate solution prepared in the anode chamber after the electrolytic reaction; the term "meets standards" means that the total organic carbon content of the product is <1ppm, the total content of metal impurities is <50ppb, and the number of particles >0.2μm in the product is less than 50 per mL.

[0034] Examples 1-13 refer to 13 different methods used to prepare compliant ultra-high purity acidic copper sulfate solutions. The general procedure is as follows: An acidic electrolyte is prepared using hydrochloric acid and sulfuric acid of quality standard ≥ SEMI 10, with a sulfuric acid concentration of 0.73–1.86 mol / L and a hydrochloric acid concentration of 0.56–2.78 mol / L. The acidic electrolyte is injected into the electrolytic cell, ensuring a volume ratio of (1.5-2):1 between the anode and cathode chambers. The anode and cathode chambers are separated by an anion exchange membrane (ACE or FAA-3-50). The anode uses an ultra-pure copper plate with a purity of 99.9995%–99.99995%, and the cathode uses copper, platinum, gold, silver, graphite, or a composite material with copper, platinum, gold, silver, and carbon as the main materials, exhibiting overall inertness during electrolysis. A DC power supply is connected to both the anode and cathode, and after the electrolysis reaction begins, the current density is maintained at 0.2–0.5 mA / cm². 2 After a continuous reaction for 7 hours, the copper ion concentration in the anode chamber solution was determined using ICP-AES. Electrolysis was stopped when the measured copper ion concentration reached the required level. The final solution obtained in the anode chamber is the final product. The quality of the final product was mainly determined by ICP-MS for metal impurities, TOC for total organic carbon, and laser particle size analyzer for particles >0.2 μm. The specific preparation conditions are shown in Table 1.

[0035] Table 1

[0036]

[0037] Note: The acidic copper sulfate solutions obtained in the above 10 examples all had a TOC content of <1 ppm, a total metal impurity content of <50 ppb, and <50 particles >0.2 μm per milliliter. A decrease in the electrolyte volume ratio between the anode and cathode chambers mainly leads to an increase in the TOC content of the product; excessive current density will cause an increase in the number of particles >0.2 μm per milliliter of the product; a decrease in copper anode purity mainly leads to an increase in the TOC content and metal impurity content of the product; an increase in the initial electrolyte acid concentration will lead to an increase in the metal impurity and particulate matter content of the product, while a decrease in the initial electrolyte acid concentration will lead to a decrease in the metal impurity and particulate matter content of the product.

[0038] Based on the above-mentioned qualified ultra-high purity acidic copper sulfate solution, by adding imidazole ionic liquid and polyethylene glycol, the final ultra-high purity copper sulfate electroplating solution can be obtained.

[0039] Examples 1-1 to 1-9 and Examples 2-1, 4-1, 7-1, and 9-1 refer to 13 different methods used to prepare ultra-high purity copper sulfate electroplating solutions by adding imidazole ionic liquids and polyethylene glycol;

[0040] Comparative Example 1-1 refers to the method of preparing ultra-high purity copper sulfate electroplating solution by adding the traditional SPS-PEG-JGB system.

[0041] In Examples 1-1 to 1-9 and Examples 2-1, 4-1, 7-1, and 9-1 of this invention, each ionic liquid is designated by a specific number, such as: 1-ethyl-3-methylimidazolium dicyandiamide salt (52-1), 1-propyl-3-methylimidazolium dicyandiamide salt (52-2), 1-butyl-3-methylimidazolium dicyandiamide salt (52-3), 1-propylsulfonic acid-3-methylimidazolium chloride salt (89-7), 1-propylsulfonic acid-3-ethylimidazolium chloride salt (89-8), 1-acrylonitrile-3-methylimidazolium chloride salt (57-6), and 1-carboxymethyl-3-methylimidazolium chloride salt (58-5); the specific settings are shown in Table 2.

[0042] Table 2

[0043]

[0044] Performance testing

[0045] In the electrolyte, the accelerating effect of ionic liquid additives during the electroplating process can be verified by measuring the cathodic polarization curve (CP curve). For example... Figure 2 As shown, the acidic copper sulfate solution prepared in Example 1 was used as the electrolyte (the basic components are CuSO4, H2SO4, Cl). - At a temperature of 25℃ and a scan rate of 10mV / s, after baseline stabilization, the cathode polarization curve was around -0.1V. The addition of PEG (polyethylene glycol) significantly shifted the cathode polarization curve negatively, indicating that PEG inhibits the reduction reaction of copper ions by adsorbing onto the cathode surface, thus demonstrating the inhibitory effect of PEG on cathode electroplating. Furthermore, the addition of 1-ethyl-3-methylimidazolium dicyanamide (52-1), 1-propylsulfonic acid-3-methylimidazolium chloride (89-7), and 1-acrylpropyl-3-methylimidazolium chloride (57-6) all resulted in a positive shift in the cathode potential (ΔE≈+78~117mV), proving that the addition of these three ionic liquids effectively neutralized the inhibitory effect of PEG and accelerated cathode electroplating, indicating that the three ionic liquids act as accelerators during the electroplating process. Because imidazole cations compete with PEG and preferentially adsorb onto the cathode surface, while the anions surrounding the imidazole cations participate in Cu… + Coordination acts as a "bridge" for charge transfer, promoting charge transfer and accelerating copper ion deposition. Using the products prepared in Example 1 (blank), Example 1-1, Example 1-8, Example 1-9, and Comparative Example 1-1 as electroplating solutions, the morphology of the copper cathode surface was observed using scanning electron microscopy (SEM) after thorough electroplating. Figure 3As shown in the figure, 3a, 3b, 3c, 3d, and 3e correspond to the surface morphology of the electroplated coatings of the products obtained in Example 1 (blank), Example 1-1, Example 1-8, Example 1-9, and Comparative Example 1-1, respectively. The coating obtained in the blank ultra-high purity acidic copper sulfate solution has a loose structure and high surface roughness; while the coatings corresponding to Example 1-1, Example 1-8, Example 1-9, and Comparative Example 1-1 are obviously smooth and dense. It can be seen that the blank ultra-high purity acidic copper sulfate plating solution cannot form a dense and smooth coating, mainly because the reduction barrier of copper ions is low in the blank ultra-high purity acidic copper sulfate plating solution, and the deposition process is instantaneous nucleation. In addition, there are few active sites on the cathode surface in the early stage of electroplating, and crystal nuclei are easily formed randomly at a few sites. The formed crystal nuclei grow rapidly epitaxially due to the high local copper ion concentration, forming large-sized dendrites. The uncovered areas between dendrites form micron-sized pores due to insufficient deposition, ultimately resulting in a loose, porous, and rough structure of the coating. After adding ionic liquid additives (Examples 1-1 / 1-8 / 1-9) or the traditional leveling agent JGB (Comparative Example 1-1), the smoothness and density of the coating are significantly improved. Both the imidazole cations of the ionic liquid and JGB possess planar electron-rich structures, enabling them to preferentially and selectively adsorb onto microscopic protrusions on the cathode surface, forming local diffusion barriers. This inhibits further copper ion deposition at the protrusions and drives deposition towards the recessed areas, thus achieving a leveling effect. Furthermore, the adsorbed molecules modulate the double-layer structure at the cathode / electrolyte interface, reducing the activation energy for copper ion reduction and decreasing the overpotential required for copper ion deposition. The lowering of the interfacial barrier induces the formation of high-density active sites. The increase in active sites compresses the nucleus growth space, refining the grain size to the nanometer scale (50-200 nm). Simultaneously, adjacent nucleus growth fronts rapidly meet, forming dense grain boundaries and eliminating microporosity. The ionic liquid additives, through synergistic leveling and densification functions, achieve coating control performance comparable to JGB.

[0046] In addition, the XRD data of the above five coatings were measured, such as Figure 4 As shown, all five copper plating layers are dominated by the copper (111) crystal form, indicating that the addition of ionic liquid additives does not affect the copper crystal form during the electroplating deposition process, and the copper (111) crystal form commonly used in semiconductor copper interconnects is still dominant.

[0047] Simulating the mass transfer environment in actual electroplating—mass transfer is slower inside trenches and pores, and faster at openings. Using the product prepared in Example 1 as the electrolyte, the CP curve was measured at different rotational speeds to determine the accelerating effect of the accelerator under different mass transfer environments, and to determine the difference in the accelerating effect of the accelerator inside and outside the structure. Figure 5 As shown in Figure a, the potential difference of the traditional accelerator SPS at 200 rpm and 550 rpm is 28 mV, reflecting the difference in acceleration effect between the interior and exterior of the structure, indicating that the interior of the surface structure will preferentially deposit SPS. Figure 5As shown in b, the potential difference of the ionic liquid accelerator (89-7) after action at 200 rpm and 550 rpm is 108 mV, demonstrating a more significant difference in acceleration effect between the interior and exterior of the structure compared to SPS, which is more favorable for preferential deposition inside the structure. This is related to the smaller molecular size and better molecular diffusion capability of the ionic liquid accelerator.

Claims

1. A high-purity copper sulfate electroplating solution suitable for copper interconnects in semiconductor integrated circuits, characterized in that, The product comprises an ultra-high purity acidic copper sulfate solution and a composite additive. The ultra-high purity acidic copper sulfate solution contains copper sulfate, sulfuric acid, and chloride ions. The total organic carbon content in the ultra-high purity acidic copper sulfate solution is ≤1 ppm, the total metal impurity content is <50 ppb, and the product contains ≤50 particles >0.2μm / mL. The composite additive consists of an imidazole ionic liquid and polyethylene glycol. The amount of imidazole ionic liquid added to the electroplating solution is 4.5–40 mg / L, and the amount of polyethylene glycol added is 100–200 mg / L. mg / L, wherein the imidazole ionic liquid is one of 1-ethyl-3-methylimidazolium dicyandiamide, 1-propyl-3-methylimidazolium dicyandiamide, 1-butyl-3-methylimidazolium dicyandiamide, 1-propylsulfonic acid-3-methylimidazolium chloride, 1-propylsulfonic acid-3-ethylimidazolium chloride, 1-acrylpropyl-3-methylimidazolium chloride, and 1-carboxymethyl-3-methylimidazolium chloride, all with a purity of ≥99.9%; and the polyethylene glycol is one of polyethylene glycol 2000, polyethylene glycol 4000, and polyethylene glycol 8000, all with a purity of ≥99.9%.

2. The ultra-high purity copper sulfate electroplating solution suitable for copper interconnects in semiconductor integrated circuits as described in claim 1, characterized in that: The concentration of imidazole ionic liquid in the ultra-high purity copper sulfate electroplating solution is 5 ppm, 10 ppm or 20 ppm, and the concentration of polyethylene glycol is 100 ppm, 120 ppm or 150 ppm.

3. The method for preparing the ultra-high purity copper sulfate electroplating solution according to any one of claims 1-2, characterized in that, Includes the following steps: Ultra-high purity acidic copper sulfate solution is prepared by electrolysis in an electrolytic cell, and then composite additives are added to the prepared ultra-high purity acidic copper sulfate solution and mixed to obtain the final product. The preparation conditions for the ultra-high purity acidic copper sulfate solution are as follows: the electrolytic cell is equipped with an anode, a cathode, and an anion exchange membrane; the electrolyte for the electrolytic reaction is a mixed acid-water solution made of sulfuric acid and hydrochloric acid, wherein the sulfuric acid concentration is 0.73–1.86 mol / L; the hydrochloric acid concentration is 0.56–2.78 mol / L; and the current density for the electrolytic reaction is 0.2–0.5 mA / cm². 2 The volume ratio of the electrolyte in the anode chamber to the cathode chamber of the electrolytic cell is (1.5-2):1, and the anode material is ultrapure copper with a purity of 99.9995% or higher.

4. The method for preparing the ultra-high purity copper sulfate electroplating solution as described in claim 3, characterized in that: The cathode is composed of a composite material that is inert throughout the electrolysis process; the electrolyte volume ratio between the anode chamber and the cathode chamber is 2:1 or 1.5:

1.

5. The method for preparing the ultra-high purity copper sulfate electroplating solution as described in claim 4, characterized in that: The anion exchange membrane is a quaternary ammonium anion exchange membrane, a quaternary phosphate anion exchange membrane, or a modified polybenzimidazole anion exchange membrane.

6. The method for preparing the ultra-high purity copper sulfate electroplating solution as described in claim 4, characterized in that: The electrolytic cell is made of at least one of polytetrafluoroethylene, polypropylene, polyethylene, polyvinyl chloride, or polyvinylidene fluoride.

7. The method for preparing the ultra-high purity copper sulfate electroplating solution as described in claim 4, characterized in that: The water in the mixed acid electrolyte is ultrapure water with a resistivity ≥15 MΩ cm; the sulfuric acid concentration in the mixed acid electrolyte is 0.75M, 1.3M, or 1.85M; the hydrochloric acid concentration in the mixed acid electrolyte is 0.55M, 1.65M, or 2.75M. The current density of the electrolysis reaction is 0.2 mA / cm². 2 0.35 mA / cm 2 or 0.5 mA / cm 2 .

8. The application of the ultra-high purity copper sulfate electroplating solution as described in any one of claims 1-2, characterized in that: It is used in copper interconnect plating for advanced processes below 28nm and advanced packages with an aspect ratio >20:1.

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