Aluminum etching solution, preparation method and application thereof

Abstract

The application belongs to the technical field of etching liquid, and particularly relates to an aluminum etching liquid, a preparation method and application thereof. The aluminum etching liquid, with the total mass of the formula being 100%, comprises 50-70% of phosphoric acid, 6-11% of nitrate salt slow-release acid source, 3-8% of organic carboxylic acid buffer stabilizer, 1-4% of aluminum ion high-efficiency complexing agent, 0.5-3% of etching accelerator, 0.1-1.5% of anionic surfactant, and the balance of water. The aluminum etching liquid provided by the application has good etching life and etching stability, can greatly reduce the treatment amount of waste liquid and the replacement frequency of fresh tank liquid, does not need to monitor and supplement nitric acid or acetic acid in the whole life cycle, significantly reduces the operation difficulty and maintenance cost, realizes convenient production, and ensures stable etching performance and greatly improves product yield due to stable tank liquid components.

Description

Technical Field

[0001] This invention belongs to the field of etching solution technology, specifically relating to an aluminum etching solution, its preparation method, and its application. Background Technology

[0002] Aluminum and aluminum alloys are widely used in electronics, aerospace, and decorative building materials due to their excellent electrical and thermal conductivity and lightweight properties. Chemical etching is one of the key processes in aluminum surface treatment, used to create specific textures, patterns, or clean surfaces. Among these, wet etching is widely used in specific steps such as cleaning, resist removal, and bulk processing due to its high selectivity and low cost.

[0003] Wet etching is mainly carried out using etching solutions. Currently, commonly used aluminum etching solutions suffer from short lifespan and unstable etching effects. On the one hand, aluminum etching solutions often use nitric acid as the main oxidant, but as nitric acid is consumed, its etching ability decreases, requiring frequent replenishment. Fluctuations in etching ability lead to uneven etching results. On the other hand, etching byproducts increase the viscosity of the etching solution, reduce its fluidity, and cause local differences in etching effects. In addition, high concentrations of aluminum ions can also form a protective film on the aluminum surface with some components in the solution, hindering the etching process.

[0004] For example, patent CN117779038A discloses a low-phosphoric acid molybdenum-aluminum etching solution and its preparation method. The etching solution is composed of phosphoric acid, acetic acid, nitric acid, additives, and water. Although the fluidity of the solution is enhanced by reducing the phosphoric acid content and increasing the acetic acid content, acetic acid has a low boiling point and is easily volatilized at the working temperature of the etching solution (usually 40-80℃). Simultaneously, acetic acid is continuously lost as the workpiece is carried out of the solution; moreover, nitric acid is reduced to nitrogen oxides during the reaction, causing a rapid decrease in the nitric acid concentration in the etching solution and weakening the etching ability. To maintain a stable etching effect, operators must regularly check the concentrations of nitric acid and acetic acid in the solution and frequently replenish them. This not only increases the complexity of operation and production costs but also leads to unstable etching quality due to fluctuations in chemical composition, making it difficult to guarantee the product qualification rate. Furthermore, during the etching process, aluminum is continuously dissolved and enters the solution as aluminum ions. As the etching volume increases, the aluminum ion concentration in the solution continues to rise. When the aluminum ion concentration exceeds a certain limit (usually above 1500-2000 ppm in traditional solutions), it increases the viscosity of the etching solution, leading to poorer fluidity of the solution, increased loss of workpiece carry-out, and obstruction of fresh solution exchange to the workpiece surface. High concentrations of aluminum ions inhibit the attack of hydrogen ions on the aluminum surface and may form a dense passivation film or viscous diffusion layer on the aluminum surface when interacting with phosphate ions, hindering the etching reaction from continuing, significantly reducing the etching rate, and causing defects such as unevenness, flow marks, and white spots on the etched surface.

[0005] Therefore, it is essential to provide a new aluminum etching solution that can solve the problems of short service life and unstable etching effect of existing etching solutions. Summary of the Invention

[0006] In order to solve the above-mentioned technical problems, one of the objectives of the present invention is to provide an aluminum etching solution.

[0007] The technical solution adopted in this invention is as follows:

[0008] An aluminum etching solution, based on 100% of the total formula mass, comprises: 50-70% phosphoric acid, 6-11% nitrate-based slow-release acid source, 3-8% organic carboxylic acid buffer stabilizer, 1-4% aluminum ion high-efficiency complexing agent, 0.5-3% etching accelerator, 0.1-1.5% anionic surfactant, and the balance being water; wherein the aluminum ion high-efficiency complexing agent is an imidazole phosphate compound.

[0009] Preferably, the amount of phosphoric acid used is not limited to 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, or 70%.

[0010] Preferably, the nitrate-based slow-release acid source is any one or a combination of sodium nitrate, ammonium nitrate, and potassium nitrate. The amount of the nitrate-based slow-release acid source is not limited to 6%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or 11%.

[0011] Preferably, the organic carboxylic acid buffer stabilizer is a hydroxycarboxylic acid and / or a thiophene carboxylic acid. The amount of the organic carboxylic acid buffer stabilizer is not limited to 3%, 3.5%, 4%, 4.5%, 5%, 6%, 6.5%, 7%, 7.5%, or 8%.

[0012] Preferably, the hydroxycarboxylic acid is any one or a combination of citric acid, tartaric acid, malic acid, lactic acid, salicylic acid, chlorogenic acid, caffeic acid, and gluconic acid.

[0013] Preferably, the thiophene carboxylic acid is any one or a combination of 2,5-thiophene dicarboxylic acid, 3,4-thiophene dicarboxylic acid, thiophene-2-carboxylic acid, and thiophene-3-carboxylic acid.

[0014] Preferably, the organic carboxylic acid buffer stabilizer is composed of citric acid and 2,5-thiophene dicarboxylic acid in a mass ratio of (1~4):3. The mass ratio is not limited to 1:3, 1:2, 2:3, 2.5:3, 1:1, 3.5:3, or 4:3.

[0015] Preferably, the imidazole phosphate compound is any one or a combination of 1,3-dimethylimidazolium phosphate, 1-butyl-3-methylimidazolium phosphate, and 1-ethyl-3-methylimidazolium phosphate. The amount of the imidazole phosphate compound used is not limited to 1%, 1.4%, 1.9%, 2.2%, 2.6%, 3%, 3.5%, or 4%.

[0016] Preferably, the etching accelerator is any one or a combination of ammonium sulfate, ammonium bifluoride, and sodium fluoride. The amount of the etching accelerator is not limited to 0.5%, 1%, 1.5%, 1.8%, 2%, 2.3%, 2.6%, 2.9%, or 3%.

[0017] Preferably, the anionic surfactant is any one or a combination of sodium α-olefin sulfonate, fatty acid methyl ester sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium lauryl ether sulfate, sodium cocoyl glutamate, and alkyl polyoxyethylene ether phosphate salt. The amount of the anionic surfactant used is not limited to 0.1%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.2%, or 1.5%.

[0018] In the above aluminum etching solution formulation:

[0019] Replacing traditional nitric acid with a slow-release nitrate acid source enables long-term stability of the etching oxidation potential, solving the problem of needing to replenish nitric acid in traditional systems. During the etching process, as hydrogen ions are continuously consumed at the reaction interface, nitrate substances can release active oxidizing components through ion exchange and equilibrium shift. This avoids the drawbacks of generating harmful gases during the reaction of traditional nitric acid systems and eliminates the need to replenish acid due to oxidant depletion.

[0020] Organic carboxylic acid buffer stabilizers can stabilize the pH of the system by utilizing the dissociation equilibrium of carboxyl groups, avoiding the problems of sudden drop in etching capacity or over-etching caused by hydrogen ion consumption. In this invention, hydroxycarboxylic acids and / or thiophene carboxylic acids are selected as organic carboxylic acid buffer stabilizers. Their unique functional groups (hydroxyl and thiophene rings) can further form soluble and stable complexes with aluminum ions generated during etching, inhibiting the formation of aluminum phosphate precipitates and the increase in system viscosity. When hydroxycarboxylic acids and thiophene carboxylic acids are combined, they have a synergistic effect, which can improve the complexation capacity and etching stability of aluminum ions, and help extend the service life of the aluminum etching solution.

[0021] The P=O group of imidazole phosphate is a strong base ligand stronger than that of phosphate, exhibiting a higher affinity for aluminum ions. Furthermore, the imidazole cation can further enhance the coordination ability of P=O through electron-withdrawing effects, thereby forming a stable aluminum-imidazole phosphate coordination bond. After aluminum ions are coordinated by imidazole phosphate, the imidazole ring constructs a hydrophobic shell, forming a core-shell structure, transforming the aluminum ions from hydrophilic particles to hydrophobic particles. The complexes repel each other due to surface hydrophobicity and are separated by a solvation layer. Therefore, even if the aluminum ion concentration in the etching system accumulates to 3000-5000 ppm, it can still maintain low viscosity and excellent fluidity, and the etching performance will not degrade.

[0022] The second objective of this invention is to provide a method for preparing an aluminum etching solution as described above. According to the required proportions of the aluminum etching solution, phosphoric acid, nitrate-based slow-release acid source, organic carboxylic acid buffer stabilizer, aluminum ion high-efficiency complexing agent, etching accelerator, and anionic surfactant are added to water, mixed and dissolved to obtain the solution.

[0023] Preferably, after dissolution, a filtration step is performed to remove any undissolved solids that may be present.

[0024] The third objective of this invention is to provide an application of the aluminum etching solution described above in etching Mo / Al / Mo substrates.

[0025] The beneficial effects of this invention are as follows:

[0026] A brand-new aluminum etching solution formula is provided. By using nitrate-based slow-release acid sources, organic carboxylic acid buffer stabilizers, and highly efficient aluminum ion complexing agents, the effective lifespan of the etching solution is significantly extended, greatly reducing the amount of waste liquid to be treated and the frequency of replacing fresh solution. Throughout the entire lifespan, there is no need to monitor or replenish nitric acid or acetic acid, which significantly reduces the difficulty of operation and maintenance costs, enabling convenient production. Moreover, the stable composition of the solution ensures stable etching performance and greatly improves product yield. Attached Figure Description

[0027] Figure 1 The image shows a planar SEM image of a molybdenum-aluminum-molybdenum substrate etched with an aluminum etching solution containing 5000 ppm aluminum ions, prepared in Example 1.

[0028] Figure 2 The image shows a planar SEM image of a molybdenum-aluminum-molybdenum substrate etched with an aluminum etch solution containing 5000 ppm aluminum ions, prepared for Comparative Example 1.

[0029] Figure 3 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Example 1. In the image, a and a correspond to the etching results of the aluminum ion concentrations of 0 ppm, 1000 ppm, 3000 ppm, and 5000 ppm, respectively.

[0030] Figure 4 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Example 7. In the image, a and a correspond to the etching results of the aluminum ion concentrations of 0 ppm, 1000 ppm, 3000 ppm, and 5000 ppm, respectively.

[0031] Figure 5 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Comparative Example 1. In the image, a and b correspond to the etching solution with aluminum ion concentrations of 0 ppm and 1000 ppm, respectively.

[0032] Figure 6 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Comparative Example 2. In the image, a and b correspond to the etching solution with aluminum ion concentrations of 0 ppm and 1000 ppm, respectively.

[0033] Figure 7 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Comparative Example 3. In the image, a and b correspond to the etching solution with aluminum ion concentrations of 0 ppm and 1000 ppm, respectively.

[0034] Figure 8 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Comparative Example 4. In the image, a and b correspond to the etching solution with aluminum ion concentrations of 0 ppm and 1000 ppm, respectively. Detailed Implementation

[0035] To facilitate understanding, the technical solution of the present invention will be described in more detail below with reference to embodiments. Unless otherwise stated, the terms used herein have the meanings conventionally understood by those skilled in the art.

[0036] An aluminum etching solution, based on 100% of the total formula mass, comprises: 50-70% phosphoric acid, 6-11% nitrate-based slow-release acid source, 3-8% organic carboxylic acid buffer stabilizer, 1-4% aluminum ion high-efficiency complexing agent, 0.5-3% etching accelerator, 0.1-1.5% anionic surfactant, and the balance being water; wherein the aluminum ion high-efficiency complexing agent is an imidazole phosphate compound.

[0037] According to the above formulation, Examples 1-7 were prepared, and the formulations of each group are shown in Table 1. Meanwhile, the traditional phosphoric acid + nitric acid + acetic acid etching solution system was used as Comparative Example 1, the etching solution system lacking organic carboxylic acid buffer stabilizer was used as Comparative Example 2, the etching solution system lacking aluminum ion high-efficiency complexing agent was used as Comparative Example 3, and the etching solution system using diethyltriaminepentaacetic acid as aluminum ion high-efficiency complexing agent was used as Comparative Example 4. The formulations of Comparative Examples 1-4 are shown in Table 1.

[0038] Table 1. Etching solution formulations for Examples 1-7 and Comparative Examples 1-4

[0039]

[0040] 1. Etching efficiency test

[0041] Following the formulations of Examples 1-7 and Comparative Examples 1-4, four sets of 100 mL aluminum etching solutions were prepared for each. After complete dissolution, 0 g, 0.1 g, 0.3 g, and 0.5 g of aluminum sheets were added to each solution and allowed to dissolve completely, resulting in aluminum etching solutions with aluminum ion concentrations of 0 ppm, 1000 ppm, 3000 ppm, and 5000 ppm, respectively. These solutions were then placed in a 40°C water bath to etch molybdenum-aluminum molybdenum substrates with film thicknesses of 1000 Å / 4000 Å / 150 Å. The etching endpoint time (EPD) for each set of aluminum etching solutions was recorded, representing the time required for the substrate to just become transparent during the etching process. The results are shown in Table 2.

[0042] Table 2. Etching results of etchant solutions in Examples 1-7 and Comparative Examples 1-4

[0043]

[0044] Figure 1 This is a planar SEM image of a molybdenum-aluminum-molybdenum substrate etched using an aluminum etching solution with an aluminum ion concentration of 5000 ppm prepared in Example 1. Figure 2 The image shows a planar SEM image of a molybdenum-aluminum-molybdenum substrate etched with an aluminum etch solution containing 5000 ppm aluminum ions, prepared for Comparative Example 1.

[0045] Combine Table 2 and Figure 1 , Figure 2 As can be seen, in Examples 1-6, because nitrate-based slow-release acid sources, organic carboxylic acid buffer stabilizers, and highly efficient aluminum ion complexing agents were used simultaneously, even when the aluminum ion concentration increased to 5000 ppm, the etching rate remained minimally changed, and the etching performance was essentially the same. In the etching solution of Example 7, the organic carboxylic acid buffer stabilizer was a mixture of citric acid and 2,5-thiophene dicarboxylic acid. Compared to the single citric acid in Example 1 and the single 2,5-thiophene dicarboxylic acid in Example 6, the etching life and etching effect were better, indicating that there is a synergistic effect between hydroxycarboxylic acid and thiophene carboxylic acid. The synergistic effect is far greater than that of a single hydroxycarboxylic acid or thiophene carboxylic acid. Their dissociation constants are complementary, resulting in a better buffering effect, significantly improving the complexing capacity and etching stability of aluminum ions, and helping to extend the service life of the aluminum etching solution.

[0046] Comparative Example 1 uses a traditional phosphoric acid, nitric acid, and acetic acid system. It can be observed that as the aluminum ion concentration increases, the EPD gradually increases, meaning the etching rate gradually slows down. This is because as the aluminum ion concentration increases, the solution viscosity increases, and aluminum ions accumulate on the substrate surface. Slower mass transfer leads to a higher aluminum ion concentration at the interface, promoting the formation of a dense aluminum phosphate passivation film. The passivation film significantly reduces the etching rate, further slowing down hydrogen ion activity and the shift in chemical equilibrium, resulting in a sharp decrease in the etching rate. Ultimately, this leads to an uneven etched surface with noticeable residue, such as... Figure 2 As shown, the etching performance of the etching solution has basically failed.

[0047] In Comparative Example 2, no organic carboxylic acid buffer stabilizers were added to the etching solution. As the aluminum ion concentration in the solution increased, the system's fluidity gradually decreased, the viscosity gradually increased, and the etching performance rapidly declined, resulting in a gradually increasing EPD and severe surface residue. In Comparative Example 3, no efficient aluminum ion complexing agent was added. As the aluminum ion concentration in the solution increased, a large number of aluminum ions continuously consumed phosphate ions, and hydrogen ions in the solution were continuously consumed, leading to a sharp decrease in etching lifetime and a significant slowdown in etching rate. In Comparative Example 4, diethyltriaminepentaacetic acid was used as an efficient aluminum ion complexing agent. It binds aluminum ions through the coordination of carboxyl and amine groups. However, in the phosphoric acid and potassium nitrate system of aluminum etching solutions, its complexing ability is far inferior to imidazole phosphate compounds. When the aluminum ion concentration increased to 3000 ppm, the complexing ability decreased significantly, the EPD increased significantly, and the etching rate and etching uniformity were reduced.

[0048] 2. Etching stability test

[0049] Following the etching efficiency test method, aluminum etching solutions with aluminum ion concentrations of 0 ppm, 1000 ppm, 3000 ppm, and 5000 ppm were prepared according to the formulations of Examples 1-7 and Comparative Examples 1-4, respectively. These solutions were placed in a 40°C water bath and used to etch molybdenum-aluminum molybdenum substrates at 1000 Å, 4000 Å, and 150 Å. The etching time for each group was over-etch (OE), i.e., the time for 1 + 30% EPD (0 ppm). Ideally, this OE time should be sufficient to etch the required side etching amount (CD bias, defined as the single-sided distance between the end of the photoresist and the end of the metal layer, preferably 0.35~0.45 μm in this test) and etching cone angle (Taper, defined as the cross-sectional angle from the bottom edge of the metal to the lower edge protected by the photoresist, preferably 45°~55° in this test).

[0050] The etched molybdenum-aluminum molybdenum substrate was observed cross-section by SEM, and the etching cone angle and CD bias were measured. The corresponding experimental data were recorded as shown in Table 3.

[0051] Table 3. Etching effects of etching solutions in Examples 1-7 and Comparative Examples 1-4

[0052]

[0053] Figure 3 The images shown are cross-sectional SEM images of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Example 1. The ad images correspond to the etching solution results with aluminum ion concentrations of 0 ppm, 1000 ppm, 3000 ppm, and 5000 ppm, respectively. Figure 4 The images shown are cross-sectional SEM images of the molybdenum-aluminum-molybdenum substrate etched by the aluminum etching solution prepared in Example 7. The ad images correspond to the etching solution results with aluminum ion concentrations of 0 ppm, 1000 ppm, 3000 ppm, and 5000 ppm, respectively. Figure 5 This is a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched using the aluminum etching solution prepared in Comparative Example 1. Figure 6 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Comparative Example 2. Figure 7 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched using the aluminum etching solution prepared in Comparative Example 3. Figure 8 The image shows a cross-sectional SEM image of a molybdenum-aluminum-molybdenum substrate etched with the aluminum etching solution prepared in Comparative Example 4. Figures 5-8 In the figure, a and b correspond to the etching solutions with aluminum ion concentrations of 0 ppm and 1000 ppm, respectively.

[0054] Combined with Table 3 Figure 3-8 It can be seen that in Comparative Example 1, because the system used a traditional phosphoric acid, nitric acid, and acetic acid system, the main etching component HNO3 was consumed as the aluminum ion concentration increased. Therefore, the etching performance gradually and rapidly decreased, and the CD bias decreased rapidly, making it impossible to completely etch all the aluminum metal on the surface within the specified etching time. In Comparative Examples 2 and 3, due to the lack of important components (organic carboxylic acid buffer stabilizers or highly efficient aluminum ion complexing agents), when the etching solution contained aluminum ions at concentrations of 3000 ppm and 5000 ppm, the etching performance of the solution was affected by the excessively high aluminum ion concentration, resulting in a slower etching rate. Consequently, the aluminum layer could not be completely etched away within the OE time, leaving a large amount of metal residue on the surface. Even when using existing aluminum ion complexing agents, Comparative Example 4 showed a decreasing trend in etching stability as the aluminum ion concentration continued to increase, no longer meeting the etching requirements. In Examples 1-6, the etching rate and effect of the etching solution with aluminum ion concentration ranging from 0 ppm to 5000 ppm showed little change. This is because the formula contains nitrate-based slow-release acid source, organic carboxylic acid buffer stabilizer, and aluminum ion high-efficiency complexing agent. The interaction of these components achieves an ultra-long service life of the etching solution, and no acid replenishment is required, resulting in stable etching performance.

[0055] The above test results show that the aluminum etching solution provided by the present invention has good etching life and etching stability, and is easy to use. It has a large tolerance window for aluminum ion concentration and can be widely used in the etching of aluminum substrates.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aluminum etching solution, characterized in that, The formulation comprises, by weight (100%): 50-70% phosphoric acid, 6-11% nitrate-based slow-release acid source, 3-8% organic carboxylic acid buffer stabilizer, 1-4% aluminum ion high-efficiency complexing agent, 0.5-3% etching accelerator, 0.1-1.5% anionic surfactant, with the balance being water; the aluminum ion high-efficiency complexing agent is an imidazole phosphate compound selected from any one or more combinations of 1,3-dimethylimidazolium phosphate, 1-butyl-3-methylimidazolium phosphate, and 1-ethyl-3-methylimidazolium phosphate; the organic carboxylic acid buffer stabilizer is composed of citric acid and 2,5-thiophene dicarboxylic acid in a mass ratio of (1-4):3; the etching accelerator is any one or more combinations of ammonium sulfate, ammonium bifluoride, and sodium fluoride.

2. The aluminum etching solution as described in claim 1, characterized in that, The nitrate-based slow-release acid source is any one or a combination of sodium nitrate, ammonium nitrate, and potassium nitrate.

3. The aluminum etching solution as described in claim 1, characterized in that, The anionic surfactant is any one or a combination of sodium α-olefin sulfonate, fatty acid methyl ester sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium lauryl ether sulfate, sodium cocoyl glutamate, and alkyl polyoxyethylene ether phosphate salt.

4. A method for preparing an aluminum etching solution as described in any one of claims 1-3, characterized in that, According to the required ratio of the aluminum etching solution, add phosphoric acid, nitrate-based slow-release acid source, organic carboxylic acid buffer stabilizer, aluminum ion high-efficiency complexing agent, etching accelerator, and anionic surfactant to water, mix and dissolve to obtain the solution.

5. The application of an aluminum etching solution as described in any one of claims 1-3 in etching a Mo / Al / Mo substrate.

Images