Novel aluminum etching liquid

Abstract

The invention discloses a novel aluminum etching solution, and belongs to the technical field of semiconductor packaging. The etching liquid comprises the following components in percentage by mass: 10%-50% of phosphoric acid, 1%-10% of an oxidizing agent, 1%-10% of a buffering agent, 0.01%-1% of a catalyst, 0.01%-1% of a complexing agent and the balance of water. Through the synergistic effect of the catalyst and the oxidizing agent, the etching rate and stability are ensured while the content of phosphoric acid is reduced, and the problems that an existing high-concentration phosphoric acid system is serious in pollution and rapid in rate attenuation are solved. The etching liquid is uniform in etching effect, free of precipitation, high in process adaptability and suitable for high-precision etching of aluminum / aluminum alloy layers in the field of semiconductor packaging, and has remarkable environmental protection benefits and industrial application value.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging technology, specifically to a novel aluminum etching solution. Background Technology

[0002] In semiconductor packaging processes, the aluminum / aluminum alloy layer on the substrate surface needs to be etched to expose the substrate (such as silicon or silicon dioxide) to meet the requirements of subsequent processes. For example... Figure 1 As shown, the aluminum etching solution targets an aluminum / aluminum alloy layer 1 deposited on the surface of a substrate and a substrate 2 underneath. The substrate may be made of materials such as silicon or silicon dioxide. The function of the aluminum etching solution is to etch away the aluminum / aluminum alloy layer 1 at a predetermined rate, exposing the substrate 2. Figure 2 As shown, the surface aluminum layer gradually becomes thinner as it is etched, exposing the silicon / silicon dioxide material of the substrate layer, and the device changes from partially darkening to completely darkening. Figure 2 From left to right: the start of etching, when more than 50% of the surface silicon layer is exposed (the time point used to calculate the etching rate below), and the end of etching. The degree and time of etching can also be determined by the color of the device. The substrate is cleaned with water (immersion or rinsing) to ensure a clean surface before subsequent processes. An ideal aluminum etching solution should have stable etching rate, uniform etching effect, and be environmentally friendly.

[0003] In existing technologies, aluminum etching solutions mostly employ a high-concentration phosphoric acid-nitric acid system, which relies on a high concentration of phosphoric acid (typically up to 80%) to achieve the etching function. The high concentration of phosphoric acid dissolves the passivation layer formed on the aluminum surface and, through complexation, inhibits the regeneration of the passivation layer, thereby ensuring the etching rate.

[0004] For example, Chinese patent application CN119592954A, published on March 11, 2025, discloses an aluminum etching solution composed of the following raw materials by mass percentage: 55-75% phosphoric acid, 1.5-8.5% nitric acid, 2-10% glacial acetic acid, 1-6% additives, and the balance being deionized water. The additives consist of surfactants accounting for 0.005-1% of the total mass percentage of the aluminum etching solution and buffers accounting for 1-5%. After mixing all the raw materials, it can be used to etch aluminum, silicon, and copper.

[0005] However, this system has significant drawbacks: Serious environmental pollution: High-concentration phosphoric acid is highly corrosive, easily volatilizes and produces harmful gases during use, and the waste liquid has a high phosphoric acid content, making it difficult and costly to treat, which does not meet environmental protection requirements. Poor etching rate stability: As the etching reaction proceeds, the phosphoric acid concentration gradually decreases, and its ability to dissolve the passivation layer and inhibit complexation is greatly weakened, resulting in a rapid slowdown in the etching rate. This makes it impossible to guarantee the consistency of batch etching and affects product yield. Limited process adaptability: The high-concentration phosphoric acid system is sensitive to process parameters such as etching temperature and stirring rate. Fluctuations in these parameters can easily lead to uneven etching, making it difficult to meet the requirements of high-precision semiconductor packaging.

[0006] To address the aforementioned issues, this invention optimizes the formulation by introducing a catalyst and buffer to work synergistically, thereby reducing the phosphoric acid content while maintaining etching rate and stability, thus providing a more environmentally friendly and efficient novel aluminum etching solution. Summary of the Invention

[0007] The purpose of this invention is to provide a novel aluminum etching solution with low phosphoric acid content, fast and stable etching rate, and environmental friendliness, thereby overcoming the defects of existing high-concentration phosphoric acid system aluminum etching solutions, such as serious pollution and poor etching rate stability, and meeting the high-precision etching requirements of the semiconductor packaging field.

[0008] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a novel aluminum etching solution, which comprises the following components by mass fraction: 10%-50% phosphoric acid, 1%-10% oxidant, 1%-10% buffer, 0.01%-1% catalyst, 0.01-1% complexing agent, and the balance being water.

[0009] Preferably, the oxidant is selected from at least one of hydrogen peroxide, nitric acid and its salts, and persulfate and its salts.

[0010] Preferably, the buffer is selected from at least one of acetic acid, citric acid, malic acid and its anions.

[0011] Furthermore, the anion salt is a sodium salt or an ammonium salt of the anion.

[0012] Preferably, the catalyst is selected from at least one of copper or iron oxides, hydroxides, or copper or iron anions.

[0013] Furthermore, the copper or iron anion salt is a copper ion salt or an iron ion salt that is easily soluble in water.

[0014] Furthermore, the copper or iron ion salt is a copper or iron sulfate.

[0015] Preferably, the complexing agent is pyrophosphate or a salt thereof, or an amino acid or a salt thereof.

[0016] Furthermore, the pyrophosphate is sodium pyrophosphate, and the amino acid is glycine.

[0017] Preferably, the content of the components, by mass fraction, ranges as follows: phosphoric acid 22%-40%, oxidant 3-8%, buffer 3-8%, catalyst 0.1%-1%, complexing agent 0.1%-1%, and the balance is water.

[0018] In a second aspect, the present invention provides a method for preparing the novel aluminum etching solution as described above, comprising the following steps: taking phosphoric acid, oxidant, buffer, catalyst, complexing agent and water in proportion, stirring and mixing until all components are completely dissolved to obtain the aluminum etching solution.

[0019] In a third aspect, the present invention further discloses the application of the novel aluminum etching solution described above in the etching of aluminum / aluminum alloy layers in semiconductor devices.

[0020] Preferably, in etching applications, the etching process is as follows: the temperature of the etching solution is maintained at 55-60°C, and the device with an aluminum / aluminum alloy layer on its surface is introduced into the etching solution until the aluminum / aluminum alloy layer on the substrate surface is etched to the desired degree.

[0021] Compared with the prior art, the beneficial effects of the present invention are: Significantly improved environmental performance: The phosphoric acid mass fraction is only 10%-50%, far lower than the 55-75% of existing technologies, which reduces the difficulty and cost of waste liquid treatment, reduces the emission of harmful gases, and is more environmentally friendly and operator-friendly. Fast and stable etching rate: Through the synergistic effect of catalyst and oxidant, the etching rate can reach 95-157 Å / sec, which is comparable to existing high-efficiency etching solutions; and after long-term etching (24h), the rate decrease is only 10%-11% (the decrease in existing technology can reach more than 39%), which can ensure the consistency of mass production. Uniform etching effect: The buffer stabilizes the pH value of the system, avoiding uneven etching caused by violent local reactions. The substrate surface is clean after etching, with no residue or excessive corrosion. High process adaptability: It has low sensitivity to process parameters such as temperature and stirring rate, has a wide operating window, and does not require complex process control equipment, thus lowering the production threshold. No risk of precipitation: The amount of catalyst is controlled at 0.01%-1%, and combined with 1%-10% oxidant, which can avoid the problem of metal precipitation caused by excessive catalyst and extend the service life of etching solution. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the device affected by the aluminum etching solution.

[0023] Figure 2 It refers to the changes in the appearance of a device during the etching process under the action of aluminum etching solution.

[0024] Figure 3 This is an image showing the etching solution of the present invention placed in a transparent cup for observation. The etching solution in the image has a formula with added copper salt as a catalyst and is a light blue transparent solution.

[0025] Figure 4 The image shows a clear, transparent etching solution with precipitate placed in a transparent cup for observation; black particles are visible.

[0026] In the diagram: 1. Aluminum / aluminum alloy layer; 2. Substrate. Detailed Implementation

[0027] In view of the shortcomings of the prior art, the present invention provides a novel aluminum etching solution. The novel aluminum etching solution formulation of the present invention comprises the following five components: Component ① is phosphoric acid, with a mass fraction of 10%-50%; Component ② is an oxidant (optional: hydrogen peroxide, nitric acid, sodium nitrate, persulfate, sodium persulfate), with a mass fraction of 1%-10%; Component ③ is a buffer (optional: acetic acid, citric acid, malic acid, etc., and their anions salts, such as sodium acetate, ammonium citrate, etc.), with a mass fraction of 1%-10%; Component ④ is a catalyst (optional: copper or iron oxides, hydroxides, or copper or iron anions salts, such as water-soluble copper ion salts like copper sulfate, iron ion salts like ferric sulfate), with a mass fraction of 0.01%-1%; Component ⑤ is a complexing agent (optional: pyrophosphate or its salts such as sodium pyrophosphate, or amino acids or their salts such as glycine), with a mass fraction of 0.01%-1%; Component ⑥ is water, with a mass fraction of 30%-80%.

[0028] Existing technologies typically employ high-concentration phosphoric acid, which both dissolves the passivation layer and exhibits complexing properties during the reaction, inhibiting passivation layer formation and accelerating the reaction rate. However, as the etching process progresses, the phosphoric acid concentration decreases significantly, losing this property and drastically slowing down the etching rate. The novel etching solution of this invention improves upon common aluminum etching solution formulations by incorporating a small amount of catalyst, allowing for a reduced acid content while maintaining a relatively fast etching rate and a stable etching rate even after prolonged etching. The addition of the catalyst opens the pathway for the displacement reaction. After the low-concentration phosphoric acid consumes the surface passivation layer, it reacts rapidly with aluminum metal, causing the aluminum to diffuse into the solution as soluble ions, thereby inhibiting the formation of the passivation layer. Furthermore, the inert metal ions (relative to aluminum) in the catalyst work in conjunction with the oxidant, with the oxidant oxidizing the relatively inert metal ions in the catalyst back to their ionic form and returning them to the solution. Insufficient catalyst results in an insufficient etching rate, while excessive catalyst leads to insufficient recovery by the oxidant, causing inert metal to precipitate on the surface, forming various forms of precipitation. Excessive oxidant leads to passivation dominating the reaction, preventing further etching of the aluminum metal by the acid and catalyst due to the passivation layer, thus halting the etching process. Buffers stabilize the pH of the etching solution and promote more uniform surface etching. Complexing agents, in practical applications, form readily soluble complexes with metal ions in the solution, facilitating their dissolution and diffusion and reducing the negative impact of their deposition on the etching rate.

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicating orientation or positional relationships, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] I. Experimental Materials Phosphoric acid, nitric acid, sodium nitrate, hydrogen peroxide, acetic acid, ammonium citrate, copper sulfate, ferric sulfate, deionized water; substrate to be etched (silicon substrate with a 4μm thick aluminum layer). Unless otherwise specified, all reagents are commercially available. Commercially available reagents can be prepared by calculating appropriate amounts according to the specifications of the purchased reagents.

[0032] II. Examples and Comparative Formulations Prepare aluminum etching solution according to the formula shown in the table below: Table 1. Composition of Aluminum Etching Solution Formulations in Each Example

[0033] III. Preparation and Etching Process Preparation: Take each component according to the above formula, stir at 25°C for 15 minutes until each component is completely dissolved to obtain the etching solution; Etching: Pour an appropriate amount of the formulated etching solution into the etching solution tank, heat it to keep the temperature of the etching solution at 55-60℃, immerse the substrate to be etched (aluminum surface layer thickness 4 micrometers) into the etching solution, the aluminum surface begins to react, record the time from the start of immersion until more than 50% of the aluminum layer is etched to expose the silicon substrate (the surface aluminum layer is more than 50% of the darkened silicon), and calculate the etching rate. Stability test: Each etching solution was used to etch aluminum at a mass of 0.5% of the etching solution mass. The system was allowed to continue etching for 24 hours to consume the effective material in the system. The etching rate was then tested using the same process as described above, and the rate stability was evaluated based on the changes in the etching rate.

[0034] Figure 3The image shows an observation of the etching solution prepared according to the present invention placed in a transparent cup. The etching solution has a formulation with added copper salt as a catalyst, so the solution is light blue and transparent.

[0035] IV. Experimental Results Table 2 below shows the results of tests conducted according to the above process for the embodiments and comparative examples: Table 2 Test Experiment Results

[0036] V. Results Analysis The initial etching rate of Example 2 was 108 Å / sec, which was much higher than that of Comparative Example 1 (42 Å / sec) without catalyst, demonstrating that the catalyst can effectively improve the etching rate at low phosphoric acid concentrations.

[0037] After 24 hours of etching, the rate decrease in the examples was only 11.0% to 19.6%, with the average decrease concentrated between 11% and 13%, excluding the extreme value of the lower limit of the buffer. In contrast, the decrease in Comparative Example 5 (insufficient buffer) reached 38.7%, demonstrating the stability advantage of the formulation of this invention.

[0038] Comparative Example 2 (excess catalyst and no complexing agent) and Comparative Example 3 (insufficient oxidant) showed metal precipitation, and Comparative Example 4 (excess oxidant) caused etching to stop due to passivation. However, the Examples did not have such problems, which shows the rationality of the proportions of each component.

[0039] Figure 4 The image shows the etching solution after etching using the formula of Comparative Example 2, placed in a transparent cup. After etching, the etching solution remains clear and transparent, but a dark precipitate appears in the solution, and black particles can be seen at the bottom of the cup.

[0040] Any aspects of this invention not described in detail are well-known to those skilled in the art.

[0041] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications and equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A novel aluminum etching solution, characterized in that, The novel aluminum etching solution contains the following components by mass fraction: 10%-50% phosphoric acid, 1%-10% oxidant, 1%-10% buffer, 0.01%-1% catalyst, 0.01%-1% complexing agent, and the balance being water.

2. The novel aluminum etching solution according to claim 1, characterized in that, The oxidant is selected from at least one of hydrogen peroxide, nitric acid and its salts, and persulfate and its salts.

3. The novel aluminum etching solution according to claim 1, characterized in that, The buffer is selected from at least one of acetic acid, citric acid, malic acid and its anions.

4. The novel aluminum etching solution according to claim 3, characterized in that, The anion salt is a sodium or ammonium salt of the anion.

5. The novel aluminum etching solution according to claim 1, characterized in that, The catalyst is selected from at least one of copper or iron oxides, hydroxides, or copper or iron anions.

6. The novel aluminum etching solution according to claim 5, characterized in that, The copper or iron anions are copper or iron ions that are readily soluble in water.

7. The novel aluminum etching solution according to claim 6, characterized in that, The copper or iron ion salt is a copper or iron sulfate.

8. The novel aluminum etching solution according to claim 1, characterized in that, The complexing agent is pyrophosphate or its salt, or an amino acid or its salt.

9. The novel aluminum etching solution according to claim 1, characterized in that, The components, by mass fraction, range as follows: phosphoric acid 22%-40%, oxidant 3-8%, buffer 3-8%, catalyst 0.1%-1%, complexing agent 0.01-1%, and the balance is water.

10. The method for preparing the novel aluminum etching solution according to any one of claims 1-9, characterized in that, Includes the following steps: Take phosphoric acid, oxidant, buffer, catalyst, complexing agent and water in proportion, stir and mix until all components are completely dissolved to obtain the aluminum etching solution.

11. The application of the novel aluminum etching solution according to any one of claims 1-9 in the etching of aluminum / aluminum alloy layers in semiconductor devices.

12. The application according to claim 11, characterized in that, The etching process is as follows: the temperature of the etching solution is maintained at 55-60℃, and the device with an aluminum / aluminum alloy layer on the surface is put into the etching solution until the aluminum / aluminum alloy layer on the substrate surface is etched to the required degree.

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