A BOE etching solution and its preparation method

Abstract

This application relates to the field of etching solution technology, specifically disclosing a BOE etching solution and its preparation method. The BOE etching solution comprises the following raw materials: hydrofluoric acid, ammonium fluoride, a metal corrosion inhibitor, a composite buffer regulator, perfluorobutyl polyoxyethylene ether, and ultrapure water; the metal corrosion inhibitor is a complex of benzotriazole-imidazolium-grafted polyethyleneimine and aminotrimethylenephosphonic acid; the composite buffer regulator includes ammonium hydrogen fluoride, boric acid, and amino acids. The BOE etching solution of this application can be used in back-end metal wiring processes such as integrated circuits, MEMS devices, and 3D NAND, and is particularly suitable for etching silicon dioxide containing tungsten, aluminum, and titanium metals. It features high etching rate, low metal corrosion, and excellent metal surface protection, effectively solving the technical pain points of existing BOE etching solutions, such as severe metal corrosion and difficulty in simultaneously achieving etching and protection.

Description

Technical Field

[0001] This application relates to the field of etching solution technology, and more specifically, to a BOE etching solution and its preparation method. Background Technology

[0002] BOE (Buffered Oxide Etch) is one of the most crucial wet etchants in the semiconductor and micromachining fields, specifically designed for the precise etching of thin films such as silicon dioxide and silicon nitride. Through a buffer system formed by hydrofluoric acid (HF) and ammonium fluoride (NH4F), it achieves controllable, uniform, and highly selective removal of the oxide layer, and is widely used in integrated circuit manufacturing, MEMS device fabrication, and display panel manufacturing processes. Its core reaction involves the reaction of SiO2 and HF to generate soluble fluorosilicic acid. The addition of ammonium fluoride stabilizes the solution pH, regulates the etching rate, and protects the photoresist, making it a key material for achieving high-precision microstructure fabrication.

[0003] In related technologies, patent application CN111892931A discloses a BOE etching solution, which comprises the following components by mass percentage: hydrofluoric acid 2%–15%, ammonium fluoride 5%–45%, nitric acid 2%–9%, ​​acetic acid 0.5%–2%, ultrapure water 26%–90%, and a penetrant 0.5%–3%; hydrogen gas is injected into the etching solution. This technical solution, by introducing a trace amount of hydrogen gas into the etchant, catalyzes the etching solution, improving its wettability on the silicon oxide layer surface and reducing the surface tension of the BOE etching solution; the pore size etched can reach 1.0 μm, demonstrating strong penetration into complex microscopic surfaces.

[0004] However, while the etchants in the aforementioned prior art can effectively improve the wettability and penetration of silicon oxide layers and meet the etching requirements of silicon oxide films, they lack effective corrosion inhibition capabilities for metal wiring and metal barrier layers, such as back-end metal wiring (BEOL), 3D NAND, and logic devices. In particular, the etchants in the aforementioned technologies also contain nitric acid components, and the strong oxidizing properties of nitric acid will further aggravate the corrosion of tungsten, aluminum, and titanium metals. Even conventional BOE etchants without nitric acid cannot prevent non-selective erosion of these metals due to their buffering system. This problem is even more prominent in actual working conditions such as open contact holes and slight over-etching. During the etching process, the corrosion rate of tungsten, aluminum, and titanium metals can reach the nm / min level, which can lead to thinning, denting, or even open circuits in the metal lines, increased leakage current, decreased electrical stability, and long-term reliability degradation of the devices. This cannot meet the high precision and high reliability process requirements of advanced semiconductor devices. Therefore, developing a high-selectivity BOE etchant with a high etching rate for silicon dioxide and extremely low corrosion for metals such as tungsten, aluminum, and titanium has become an urgent technical challenge to be solved. Summary of the Invention

[0005] In order to develop a high-selectivity BOE etching solution with high etching rate for silicon dioxide and extremely low corrosion for metals such as tungsten, aluminum, and titanium, this application provides a BOE etching solution and its preparation method.

[0006] The BOE etching solution provided in this application adopts the following technical solution: A BOE etching solution comprises the following raw materials in parts by weight: 8-20 parts of hydrofluoric acid; 20-30 parts of ammonium fluoride; Metal corrosion inhibitor 1.5-2.5 parts; 2-4 parts of compound buffer regulator; 0.05-0.3 parts of perfluorobutyl polyoxyethylene ether; 60-80 parts ultrapure water; The metal corrosion inhibitor is a complex of benzotriazole-imidazolium grafted polyethyleneimine and aminotrimethylenephosphonic acid; The composite buffer regulator includes ammonium bifluoride, boric acid, and amino acids.

[0007] By adopting the above technical solution, a complex of benzotriazole-imidazolium grafted with polyethyleneimine and aminotrimethylenephosphonic acid is introduced as a metal corrosion inhibitor. Compared with traditional single benzotriazole inhibitors, this modified inhibitor can form a stable and dense protective structure on the metal surface through optimized molecular structure design, effectively isolating hydrofluoric acid from contact with the metal surface, inhibiting the occurrence of metal corrosion reaction from the root, solving the hidden dangers of metal line thinning, denting or even open circuit, and ensuring the structural integrity of the device.

[0008] To address the issues of instability in conventional BOE etching solution buffer systems, which can lead to non-selective metal corrosion and fail to balance etching rate and metal protection, this application's technical solution designs a composite buffer regulator containing ammonium bifluoride, boric acid, and amino acids to replace the traditional single buffer system. This precisely stabilizes the pH environment of the etching solution, ensuring the high etching activity of hydrofluoric acid on silicon dioxide while weakening its corrosive ability on metals. This avoids aggravated metal corrosion caused by buffer system instability and, in turn, synergizes with metal corrosion inhibitors to further enhance metal protection.

[0009] Furthermore, the introduction of perfluorobutyl polyoxyethylene ether in the solution effectively improves the wettability of the etching solution, avoiding over-etching problems caused by the etching solution's inability to fully wet high aspect ratio structures, and further reducing the additional corrosion of metals caused by over-etching. The weight proportions of each raw material component are scientifically formulated to ensure that the etching solution achieves a high etching rate for silicon dioxide while minimizing corrosion of tungsten, aluminum, and titanium metals. This makes it suitable for the high-precision and high-reliability process requirements of advanced semiconductor devices such as back-end metal wiring, 3D NAND, and logic devices, solving a technical problem that the industry urgently needs to address.

[0010] Optionally, the metal corrosion inhibitor is prepared using the following method: (1) Dissolve polyethyleneimine in N,N-dimethylformamide, add benzotriazole-5-carboxylic acid and imidazole-4-carboxylic acid, add carbodiimide as a catalyst, and react at 40-50℃ for 12-20h to obtain benzotriazole-imidazole grafted polyethyleneimine. (2) Add aminotrimethylene phosphonic acid dropwise to benzotriazole-imidazolium-grafted polyethyleneimine. After the addition is complete, heat to 60-80℃ and stir for 5-6 hours. After the reaction is complete, obtain the metal corrosion inhibitor by vacuum distillation and recrystallization.

[0011] By adopting the above technical solution and through a two-step precise and controllable reaction design, the directional optimization of the inhibitor molecular structure is achieved, thereby forming a stable and efficient metal surface protection structure. While effectively inhibiting the corrosion of tungsten, aluminum, and titanium metals, it ensures a high etching rate of hydrofluoric acid on silicon dioxide.

[0012] The structural limitations of traditional inhibitors are overcome by a two-step grafting reaction: First, using carbodiimide as a catalyst, benzotriazole-5-carboxylic acid and imidazole-4-carboxylic acid undergo an amidation condensation reaction with polyethyleneimine, directionally grafting the benzotriazole ring and imidazole ring onto the polyethyleneimine backbone to form an intermediate; Second, through the nucleophilic addition reaction of aminotrimethylenephosphonic acid with the intermediate, phosphonic acid groups are introduced, ultimately forming a multi-component synergistic molecular structure, giving the inhibitor multiple metal adsorption sites, good water solubility and stability, and avoiding molecular aggregation. Regarding the formation of protective structures on metal surfaces, the optimized inhibitor molecules form a dense and stable monomolecular protective film on the surfaces of tungsten, aluminum, and titanium metals through multiple anchoring adsorption processes. The benzotriazole and imidazole rings achieve rapid adsorption by forming coordination bonds between nitrogen atoms and metal ions. Phosphonic acid groups form hydrogen bonds and coordination bonds with hydroxyl groups on the metal surface, enhancing the binding strength. The polyethyleneimine backbone ensures uniform molecular spreading. Simultaneously, vacuum distillation and recrystallization purification during the preparation process ensure the purity and molecular uniformity of the inhibitor, further improving the stability and density of the protective film and effectively isolating hydrofluoric acid from the metal surface. The dense protective film physically isolates hydrofluoric acid corrosion, while the functional groups of the inhibitor form stable complexes with metal ions, reducing metal ion activity, inhibiting electrochemical corrosion, and significantly reducing the metal corrosion rate. It functions stably even under extreme conditions, effectively solving the problem of severe metal corrosion in conventional BOE etching solutions. Meanwhile, the inhibitor molecules exhibit high adsorption selectivity for metal surfaces, preferentially adsorbing onto the metal surface without interfering with the contact between hydrofluoric acid and silicon dioxide. Furthermore, by controlling the reaction conditions and regulating the grafting density of functional groups, excessive aggregation or adsorption of the inhibitor onto the silicon dioxide surface is avoided, ensuring the normal progress of the etching reaction and achieving the dual goals of low metal corrosion and high silicon dioxide etching.

[0013] Optionally, in step (1), the mass ratio of polyethyleneimine to N,N-dimethylformamide is 1:(5-10), and the mass ratio of polyethyleneimine, benzotriazole-5-carboxylic acid and imidazole-4-carboxylic acid is 5:(1-2):(0.5-1).

[0014] Optionally, in step (1), the amount of carbodiimide added is 10%-15% of the mass of polyethyleneimine.

[0015] Optionally, in step (2), the mass ratio of benzotriazole-imidazolium-grafted polyethyleneimine and aminotrimethylenephosphonic acid is 1:(0.1-0.5).

[0016] Optionally, the composite buffer regulator comprises ammonium bifluoride, boric acid, and amino acids in a mass ratio of (1-3):(1-1.5):1.

[0017] By adopting the above technical solution, the synergistic buffer system formed by ammonium bifluoride, boric acid, and amino acids can be precisely stabilized within the optimal pH range of the etching solution. This ensures both the efficient etching performance of hydrofluoric acid on silicon dioxide and reduces its corrosiveness. At the same time, the synergistic effect of amino acids with boric acid and ammonium bifluoride further enhances the stability of the buffer system, preventing the aggravation of metal corrosion caused by pH fluctuations. Together with the metal corrosion inhibitor, it forms a double protection, significantly improving the metal protection effect.

[0018] Optionally, the amino acid is one of glycine, alanine, and proline.

[0019] By adopting the above technical solution, one of glycine, alanine, and proline is selected. The amino and carboxyl groups in its molecular structure can form a stable buffer system with other components in the composite buffer regulator. At the same time, it can form hydrogen bonds with metal corrosion inhibitor molecules, promoting the adsorption and arrangement of the inhibitor on the metal surface, further enhancing the density of the metal protective film and improving the corrosion inhibition effect. Meanwhile, these amino acids are chemically stable and do not decompose in the acidic environment of the etching solution, and can maintain buffering and synergistic effects for a long time, ensuring the stability of the etching solution performance.

[0020] Optionally, the hydrofluoric acid is an aqueous solution of hydrofluoric acid with a mass concentration of 45%-50%.

[0021] Optionally, the raw materials may also include 0.1-1.0 parts of hydroxyethylidene diphosphonic acid.

[0022] By adopting the above technical solution and adding hydroxyethylidene diphosphonic acid to the raw materials, the problem of trace metal impurities in the etching solution easily adsorbing onto the metal surface, damaging the metal protective film, and thus aggravating metal corrosion is specifically solved. Hydroxyethylidene diphosphonic acid has excellent chelating properties, effectively chelating trace metal impurities in the etching solution and preventing them from depositing on the metal surface to form corrosion pits. Simultaneously, it can form a weak coordination with the metal surface, helping to enhance the stability of the metal protective film, further reducing the metal corrosion rate, decreasing device leakage current and abnormal contact resistance, and improving the long-term reliability of the device.

[0023] This application also provides a method for preparing BOE etching solution, which adopts the following technical solution: A method for preparing a BOE etching solution includes the following steps: S1. Add the composite buffer conditioner and ammonium fluoride to ultrapure water and stir for 15-20 minutes until completely dissolved to obtain a mixed buffer solution. Add the metal corrosion inhibitor, perfluorobutyl polyoxyethylene ether and optional hydroxyethylidene diphosphonic acid to the mixed buffer solution in sequence, and continue stirring for 25-30 minutes to obtain the base solution. S2. Control the ambient temperature to 20-25℃, add hydrofluoric acid dropwise to the base solution at a rate of 0.5-1ml / min, and continue stirring for 30-40min after the addition is complete. Let it stand for 10-15min to remove air bubbles and obtain BOE etching solution.

[0024] By adopting the above technical solution, the preparation method employs a two-step approach. First, a mixed buffer solution is prepared and various auxiliary components are added to form a base solution. Then, hydrofluoric acid is added dropwise under controlled conditions. The steps are simple and reasonable, ensuring uniform dispersion of each component and avoiding localized metal corrosion or uneven etching rates caused by excessively high local component concentrations. At the same time, the reaction environment temperature and hydrofluoric acid drop rate are strictly controlled to prevent hydrofluoric acid volatilization from causing component imbalance, ensuring stable etching solution performance, strong repeatability, and the ability to achieve large-scale industrial production, ensuring that the etching solution can stably exert its technical effects.

[0025] In summary, this application has the following beneficial effects: 1. This application employs a benzotriazole-imidazolium grafted polyethyleneimine and aminotrimethylenephosphonic acid complex as a metal corrosion inhibitor. This inhibitor is prepared through a two-step, precisely controllable grafting reaction, effectively overcoming the structural limitations of traditional single benzotriazole inhibitors. This inhibitor possesses multiple metal adsorption sites, good water solubility, and stability. Through multiple anchoring adsorption, it forms a dense and stable monomolecular protective film on the surface of tungsten, aluminum, and titanium metals, physically isolating them from hydrofluoric acid corrosion. Simultaneously, it forms stable complexes with metal ions, inhibiting electrochemical corrosion and significantly reducing the metal corrosion rate. Even under extreme conditions such as open contact holes and slight over-etching, it can function stably, fundamentally solving the hidden dangers of metal line thinning and depression, and ensuring the structural integrity of the device.

[0026] 2. This application employs a composite buffer regulator composed of ammonium bifluoride, boric acid, and amino acids to replace the traditional single buffer system, effectively solving the problems of unstable buffering and non-selective metal corrosion caused by conventional BOE etching solutions. This composite buffer regulator, through scientific formulation, forms a synergistic buffer system that precisely stabilizes the pH of the etching solution within the optimal range. This ensures both the high etching activity of hydrofluoric acid on silica and reduces its corrosiveness, preventing aggravated metal corrosion due to pH fluctuations. The amino acids selected are glycine, alanine, or proline. The amino and carboxyl groups in their molecules can form stable buffer pairs with ammonium bifluoride and boric acid, and simultaneously form hydrogen bonds with metal corrosion inhibitors, promoting the adsorption and arrangement of inhibitors on the metal surface, further enhancing the metal protection effect. This buffer system is chemically stable and does not decompose in the acidic environment of the etching solution, maintaining its buffering performance for a long time, providing a stable environment for the inhibitors to function, and improving the overall stability of the etching solution.

[0027] 3. This application achieves the dual goals of "high silica etching rate + low metal corrosion" through the synergistic effect of its components, thus improving the overall performance of the etching solution and the reliability of the device. The metal corrosion inhibitor and the composite buffer regulator form a core synergy. The stable pH environment of the buffer regulator ensures the stability of the inhibitor's molecular structure and good adsorption effect, while the inhibitor strengthens the metal protection effect of the buffer system by forming a protective film. This synergistic effect effectively solves the industry pain point that conventional BOE etching solutions struggle to balance etching rate and metal protection. Simultaneously, perfluorobutyl polyoxyethylene ether improves the wettability of the etching solution, reducing the additional corrosion of the metal caused by over-etching. Optional addition of hydroxyethylidene diphosphonic acid chelates trace metal impurities, further optimizing the metal protection effect. The synergistic combination of components and preparation method results in a stable and highly repeatable etching solution, adapting to the high-precision process requirements of advanced semiconductor devices, balancing practicality and industrial production feasibility, and significantly improving the electrical stability and long-term reliability of the device. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments.

[0029] Preparation example of metal corrosion inhibitor Preparation Example 1 Metal corrosion inhibitors are prepared using the following method: (1) Take 10g of polyethyleneimine and dissolve it in 50g of N,N-dimethylformamide. Stir until completely dissolved (stirring rate 300r / min, stirring time 15min); then add 2g of benzotriazole-5-carboxylic acid and 1g of imidazole-4-carboxylic acid. After mixing evenly, add 1g of carbodiimide (10% of the mass of polyethyleneimine) as a catalyst. Control the reaction temperature at 40℃ and stir the reaction at a constant temperature for 20h to obtain the benzotriazole-imidazole grafted polyethyleneimine intermediate.

[0030] (2) Take 20g of the benzotriazole-imidazolium-grafted polyethyleneimine intermediate prepared above, and slowly add 2g of aminotrimethylenephosphonic acid (the mass ratio of benzotriazole-imidazolium-grafted polyethyleneimine to aminotrimethylenephosphonic acid is 1:0.1) at a dropping rate of 0.3ml / min. After the dropping is completed, raise the reaction temperature to 60℃ and stir at a constant temperature for 5h. After the reaction is completed, perform vacuum distillation under a vacuum of 0.08MPa and a temperature of 70℃ to remove the solvent and a small amount of unreacted raw materials. Then use ethanol as the recrystallization solvent, cool to 0℃ and let it stand to crystallize. After filtration and drying, the metal corrosion inhibitor is obtained.

[0031] Preparation Example 2 Metal corrosion inhibitors are prepared using the following method: (1) Take 10g of polyethyleneimine and dissolve it in 75g of N,N-dimethylformamide. Stir until completely dissolved (stirring rate 350r / min, stirring time 12min); then add 3g of benzotriazole-5-carboxylic acid and 1.5g of imidazole-4-carboxylic acid. After mixing evenly, add 1.25g of carbodiimide (12.5% ​​of the mass of polyethyleneimine) as a catalyst. Control the reaction temperature at 45℃ and stir the reaction at a constant temperature for 16h to obtain the benzotriazole-imidazole grafted polyethyleneimine intermediate.

[0032] (2) Take 20g of the benzotriazole-imidazolium-grafted polyethyleneimine intermediate prepared above, and slowly add 6g of aminotrimethylenephosphonic acid (the mass ratio of benzotriazole-imidazolium-grafted polyethyleneimine to aminotrimethylenephosphonic acid is 1:0.3) at a dropping rate of 0.4ml / min. After the dropping is completed, raise the reaction temperature to 70℃ and stir at a constant temperature for 5.5h. After the reaction is completed, perform vacuum distillation under a vacuum of 0.09MPa and a temperature of 75℃ to remove the solvent and a small amount of unreacted raw materials. Then use ethanol as the recrystallization solvent, cool to 2℃ and let it stand to crystallize. After filtration and drying, the metal corrosion inhibitor is obtained.

[0033] Preparation Example 3 Metal corrosion inhibitors are prepared using the following method: (1) Take 10g of polyethyleneimine and dissolve it in 100g of N,N-dimethylformamide. Stir until completely dissolved (stirring rate 400r / min, stirring time 10min); then add 4g of benzotriazole-5-carboxylic acid and 2g of imidazole-4-carboxylic acid. After mixing evenly, add 1.5g of carbodiimide (15% of the mass of polyethyleneimine) as a catalyst. Control the reaction temperature at 50℃ and stir the reaction at a constant temperature for 12h to obtain the benzotriazole-imidazole grafted polyethyleneimine intermediate.

[0034] (2) Take 20g of the intermediate prepared above and slowly add 10g of aminotrimethylenephosphonic acid (the mass ratio of benzotriazole-imidazolium-grafted polyethyleneimine to aminotrimethylenephosphonic acid is 1:0.5) at a dropping rate of 0.5ml / min. After the addition is complete, raise the reaction temperature to 80℃ and stir at a constant temperature for 6h. After the reaction is completed, perform vacuum distillation under a vacuum of 0.1MPa and a temperature of 80℃ to remove the solvent and a small amount of unreacted raw materials. Then use ethanol as the recrystallization solvent, cool to 4℃ and let it stand to crystallize. After filtration and drying, the metal corrosion inhibitor is obtained.

[0035] Preparation Example 4 Metal corrosion inhibitors are prepared using the following method: (1) Take 10g of polyethyleneimine and dissolve it in 100g of N,N-dimethylformamide. Stir until completely dissolved (stirring rate 400r / min, stirring time 10min); then add 4g of benzotriazole-5-carboxylic acid and 2g of imidazole-4-carboxylic acid. After mixing evenly, add 1.5g of carbodiimide (15% of the mass of polyethyleneimine) as a catalyst. Control the reaction temperature at 50℃ and stir the reaction at a constant temperature for 12h to obtain the benzotriazole-imidazole grafted polyethyleneimine intermediate, which is the metal corrosion inhibitor of this preparation example.

[0036] Preparation Example 5 Metal corrosion inhibitors are prepared using the following method: Benzotriazole, imidazole, and aminotrimethylenephosphonic acid were directly mixed in a mass ratio of 2:1:1. Anhydrous ethanol was added as a dispersant, and the mixture was stirred at 300 r / min for 30 min at room temperature until homogeneous. Then, the mixture was dried in a vacuum drying oven at 50 °C for 12 h to remove the ethanol and obtain a compound metal corrosion inhibitor.

[0037] Example Example 1 A BOE etching solution, the raw material components and dosages of which are shown in Table 1. The hydrofluoric acid is a 45% (w / w) aqueous solution; the metal corrosion inhibitor is the metal corrosion inhibitor prepared in Preparation Example 1; the composite buffer is prepared by combining ammonium bifluoride, boric acid, and glycine in a (w / w) mass ratio of 1:1:1.

[0038] A BOE etching solution, the preparation method of which is as follows: S1. Add composite buffer conditioner and ammonium fluoride to ultrapure water and stir for 15 min until completely dissolved to obtain mixed buffer solution. Add metal corrosion inhibitor, perfluorobutyl polyoxyethylene ether and optional hydroxyethylidene diphosphonic acid to the mixed buffer solution in sequence, and continue stirring for 25 min to obtain base solution. S2. Control the ambient temperature at 20℃, add hydrofluoric acid dropwise to the base solution at a rate of 0.5ml / min, continue stirring for 30min after the addition is complete, let stand for 10min to remove air bubbles, and obtain BOE etching solution.

[0039] Example 2 A BOE etching solution, the raw material components and dosages of which are shown in Table 1. The hydrofluoric acid is a 48% (w / w) aqueous solution; the metal corrosion inhibitor is the metal corrosion inhibitor prepared in Preparation Example 2; the composite buffer is prepared by combining ammonium bifluoride, boric acid, and glycine in a (w / w) ratio of 2:1.2:1.

[0040] A BOE etching solution, the preparation method of which is as follows: S1. Add composite buffer conditioner and ammonium fluoride to ultrapure water and stir for 18 min until completely dissolved to obtain mixed buffer solution. Add metal corrosion inhibitor, perfluorobutyl polyoxyethylene ether and optional hydroxyethylidene diphosphonic acid to the mixed buffer solution in sequence, and continue stirring for 28 min to obtain base solution. S2. Control the ambient temperature at 22℃, add hydrofluoric acid dropwise to the base solution at a rate of 0.8 ml / min, continue stirring for 35 min after the addition is complete, let stand for 12 min to remove air bubbles, and obtain BOE etching solution.

[0041] Example 3 A BOE etching solution, the raw material components and dosages of which are shown in Table 1. The hydrofluoric acid is a 50% (w / w) aqueous solution; the metal corrosion inhibitor is the metal corrosion inhibitor prepared in Preparation Example 3; the composite buffer is prepared by combining ammonium bifluoride, boric acid, and glycine in a (w / w) ratio of 3:1.5:1.

[0042] A BOE etching solution, the preparation method of which is as follows: S1. Add composite buffer conditioner and ammonium fluoride to ultrapure water and stir for 20 min until completely dissolved to obtain mixed buffer solution. Add metal corrosion inhibitor, perfluorobutyl polyoxyethylene ether and optional hydroxyethylidene diphosphonic acid to the mixed buffer solution in sequence, and continue stirring for 30 min to obtain base solution. S2. Control the ambient temperature at 25℃, add hydrofluoric acid dropwise to the base solution at a rate of 1ml / min, continue stirring for 40min after the addition is complete, let stand for 15min to remove air bubbles, and obtain BOE etching solution.

[0043] Table 1. Raw material components and dosage (g) of etching solutions in Examples 1-3

[0044] Example 4 A BOE etching solution, which differs from Example 3 in that 0.1g of hydroxyethylidene diphosphonic acid is added to the raw materials in this example.

[0045] Example 5 A BOE etching solution, which differs from Example 3 in that 0.5g of hydroxyethylidene diphosphonic acid is added to the raw materials in this example.

[0046] Example 6 A BOE etching solution, which differs from Example 3 in that 1.0g of hydroxyethylidene diphosphonic acid is added to the raw materials in this example.

[0047] Example 7 A BOE etching solution, which differs from Example 3 in that the metal corrosion inhibitor in this example is the metal corrosion inhibitor prepared in Preparation Example 2.

[0048] Example 8 A BOE etching solution differs from Example 3 in that the composite buffer regulator in this example is prepared by compounding ammonium bifluoride, boric acid and glycine in a mass ratio of 2:2:1.

[0049] Comparative Example Comparative Example 1 A BOE etching solution was prepared according to Example 1 in the patent application document with publication number CN111892931A entitled "A BOE Etching Solution".

[0050] Comparative Example 2 A BOE etching solution, which differs from Example 6 in that no metal corrosion inhibitor is added in this comparative example.

[0051] Comparative Example 3 A BOE etching solution, which differs from Example 6 in that the metal corrosion inhibitor used in this comparative example is the metal corrosion inhibitor prepared in Preparation Example 5.

[0052] Comparative Example 4 A BOE etching solution, which differs from Example 6 in that the metal corrosion inhibitor in this comparative example is the metal corrosion inhibitor prepared in Preparation Example 4.

[0053] Comparative Example 5 A BOE etching solution, which differs from Example 6 in that an equal amount of boric acid is used instead of the composite buffer regulator in this comparative example.

[0054] Performance testing 1. Silicon dioxide etching rate test Methods: A dense silica film with a thickness of 500 nm was grown on the surface of an 8-inch single-crystal silicon wafer using a thermal oxidation method. The silicon wafer was cut into standard test pieces of 2 cm × 2 cm. The initial silica thickness at nine uniformly distributed points on each test piece was measured using a spectroscopic ellipsometry, and the average value was taken as the initial thickness. The test pieces were completely immersed in the etching solution at a constant temperature of 25℃ ± 0.2℃ and etched for 5 min. Immediately after etching, the pieces were removed, rinsed with ultrapure water for 30 s, and dried with high-purity nitrogen. The remaining silica thickness at the same points was measured again using an ellipsometry, and the average etching rate was calculated. The results are shown in Table 2.

[0055] 2. Corrosion rate testing of tungsten, aluminum, and titanium metals Operating method: High-purity tungsten, aluminum, and titanium films with a thickness of 300 nm were deposited on the surface of an 8-inch single-crystal silicon wafer using magnetron sputtering. These films were then cut into 2cm × 2cm standard test pieces. The initial sheet resistance of five evenly distributed points on each test piece was measured using a four-probe sheet resistance meter, and the average value was used to calculate the initial metal thickness. The test pieces were then completely immersed in a constant-temperature etching solution at 25℃ ± 0.2℃ for 30 minutes, immediately removed, rinsed with ultrapure water for 30 seconds, and dried with high-purity nitrogen. The sheet resistance at the same points was measured again, and the remaining metal thickness was calculated. The average etching rate was then calculated. The results are shown in Table 2.

[0056] 3. Metal surface roughness test Methods: Metal test pieces after the above metal corrosion rate test were used to measure the surface roughness Ra of the metal using atomic force microscopy (AFM). The average value of the test results from three different regions of each test piece was taken as the final data to characterize the degree of corrosion damage to the metal surface. The results are shown in Table 3.

[0057] Table 2. Test results of silicon dioxide etching performance and metal corrosion rate.

[0058] Table 3 Metal Surface Roughness

[0059] Analyzing the test data in Tables 2 and 3, from the perspective of metal corrosion inhibition effect, the etching solution of Comparative Example 1 exhibited corrosion rates of 3.27 nm / min for tungsten, 4.52 nm / min for aluminum, and 2.81 nm / min for titanium, with surface roughness Ra exceeding 7 nm for all three. This is because it contains nitric acid components and lacks an effective metal corrosion inhibitor; the strong oxidizing properties of nitric acid exacerbate metal corrosion, preventing the formation of a stable metal protective structure. In contrast, the metal corrosion rates of Examples 1-8 of this application are all ≤0.05 nm / min, and the surface roughness Ra is ≤0.59 nm, significantly better than Comparative Example 1. The core reason is that this application uses a complex of benzotriazole-imidazolium grafted polyethyleneimine and aminotrimethylenephosphonic acid as a metal corrosion inhibitor, which can form a dense monomolecular protective film on the metal surface, physically isolating hydrofluoric acid corrosion while inhibiting electrochemical corrosion, thus fundamentally solving the problem of severe metal corrosion.

[0060] Analyzing the detection data in Tables 2 and 3, Comparative Example 2, without the addition of a metal corrosion inhibitor, showed a surge in metal corrosion rate to 1.52-2.64 nm / min and a significant increase in surface roughness, indicating that the metal corrosion inhibitor is key to achieving low metal corrosion. Comparative Example 3, using a simple compounded inhibitor, and Comparative Example 4, using an intermediate without grafted aminotrimethylenephosphonic acid, both exhibited corrosion rates and surface roughness far exceeding those of the examples, verifying that the metal corrosion inhibitor of this application is more stable and has stronger metal adsorption capacity. Comparative Example 5, using boric acid alone instead of the composite buffer regulator, showed a significant increase in corrosion rate, demonstrating that the composite buffer regulator composed of ammonium bifluoride, boric acid, and amino acids can stabilize the pH of the etching solution, forming a synergistic protection with the metal corrosion inhibitor and preventing pH fluctuations from exacerbating metal corrosion.

[0061] Analyzing the test data in Table 2, regarding the etching performance of silicon dioxide, the etching rates of Examples 1-8 of this application are consistently between 8.2-17.6 nm / min, all of which meet the high-precision etching requirements of advanced semiconductor devices. Furthermore, the etching rate increases with the amount of hydrofluoric acid used, indicating that the metal corrosion inhibitor and composite buffer regulator in this application do not interfere with the etching activity of hydrofluoric acid on silicon dioxide, achieving the dual goals of "high silicon dioxide etching rate + low metal corrosion," thus solving the industry's pain point of difficulty in achieving both simultaneously. In contrast, Comparative Example 1 has an etching rate of only 10.3 nm / min and poor etching uniformity, demonstrating that existing technologies sacrifice etching performance while improving metal protection, further highlighting the superiority of the technical solution in this application.

[0062] Furthermore, in Examples 4-6, the addition of hydroxyethylidene diphosphonic acid further reduced the metal corrosion rate and surface roughness, indicating that this component can chelate trace metal impurities in the etching solution, preventing them from damaging the metal protective film and helping to improve the metal protection effect. In Example 8, the composite buffer regulator was poorly proportioned, resulting in a deterioration in the corrosion rate and surface roughness, which verified the scientific nature of the component proportions in this technical solution.

[0063] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A BOE etching solution, characterized in that, The raw materials include the following parts by weight: 8-20 parts of hydrofluoric acid; 20-30 parts of ammonium fluoride; Metal corrosion inhibitor 1.5-2.5 parts; 2-4 parts of compound buffer regulator; 0.05-0.3 parts of perfluorobutyl polyoxyethylene ether; 60-80 parts ultrapure water; The metal corrosion inhibitor is a complex of benzotriazole-imidazolium grafted polyethyleneimine and aminotrimethylenephosphonic acid; The composite buffer regulator includes ammonium bifluoride, boric acid, and amino acids.

2. The BOE etching solution according to claim 1, characterized in that, The metal corrosion inhibitor was prepared using the following method: (1) Dissolve polyethyleneimine in N,N-dimethylformamide, add benzotriazole-5-carboxylic acid and imidazole-4-carboxylic acid, add carbodiimide as a catalyst, and react at 40-50℃ for 12-20h to obtain benzotriazole-imidazole grafted polyethyleneimine. (2) Add aminotrimethylene phosphonic acid dropwise to benzotriazole-imidazolium-grafted polyethyleneimine. After the addition is complete, heat to 60-80℃ and stir for 5-6 hours. After the reaction is complete, obtain the metal corrosion inhibitor by vacuum distillation and recrystallization.

3. The BOE etching solution according to claim 2, characterized in that: In step (1), the mass ratio of polyethyleneimine to N,N-dimethylformamide is 1:(5-10), and the mass ratio of polyethyleneimine, benzotriazole-5-carboxylic acid and imidazole-4-carboxylic acid is 5:(1-2):(0.5-1).

4. The BOE etching solution according to claim 2, characterized in that: In step (1), the amount of carbodiimide added is 10%-15% of the mass of polyethyleneimine.

5. The BOE etching solution according to claim 2, characterized in that: In step (2), the mass ratio of benzotriazole-imidazolium-grafted polyethyleneimine and aminotrimethylenephosphonic acid is 1:(0.1-0.5).

6. The BOE etching solution according to claim 1, characterized in that: The composite buffer regulator comprises ammonium bifluoride, boric acid, and amino acids in a mass ratio of (1-3):(1-1.5):

1.

7. The BOE etching solution according to claim 1, characterized in that: The amino acid is one of glycine, alanine, and proline.

8. The BOE etching solution according to claim 1, characterized in that: The hydrofluoric acid is an aqueous solution of hydrofluoric acid with a mass concentration of 45%-50%.

9. The BOE etching solution according to claim 1, characterized in that: The raw materials also include 0.1-1.0 parts of hydroxyethylidene diphosphonic acid.

10. A method for preparing a BOE etching solution according to any one of claims 1-9, characterized in that, The steps include the following: S1. Add the composite buffer conditioner and ammonium fluoride to ultrapure water and stir for 15-20 minutes until completely dissolved to obtain a mixed buffer solution. Add the metal corrosion inhibitor, perfluorobutyl polyoxyethylene ether and optional hydroxyethylidene diphosphonic acid to the mixed buffer solution in sequence, and continue stirring for 25-30 minutes to obtain the base solution. S2. Control the ambient temperature to 20-25℃, add hydrofluoric acid dropwise to the base solution at a rate of 0.5-1ml / min, and continue stirring for 30-40min after the addition is complete. Let it stand for 10-15min to remove air bubbles and obtain BOE etching solution.

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