Buffered etching solution for inhibiting aluminum oxide and application thereof

Abstract

The application discloses a kind of buffer oxide etching liquid for inhibiting aluminum and application, and the main component of the etching liquid is hydrofluoric acid, ammonium fluoride, organic acid, surfactant and ultrapure water.The etching liquid of the application is used for the etching of silicon oxide film, and can inhibit aluminum layer etching;Organic acid can accelerate the etching rate of silicon oxide, and form organic acid-aluminum film to protect the aluminum surface from being further etched;Surfactant can react with the aluminum surface aluminum oxide to produce chemical adsorption, thereby inhibiting the corrosion of aluminum surface;The etching liquid described in the application has high selectivity to silicon oxide layer and aluminum layer, and the etching rate selection ratio is greater than or equal to 37.The etching liquid described in the application can adjust the content of each component to meet the etching selection ratio requirement of silicon oxide layer to aluminum layer in different processes.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor etching solution technology, specifically relating to a buffer oxide etching solution for inhibiting aluminum etching and its application. Background Technology

[0002] In MOS field-effect transistors, silicon oxide is often used as an insulating layer between the gate and the semiconductor material, and also as a capacitive layer between the gate and the source / drain, controlling the electric field of the gate on the channel. In semiconductor processing, aluminum is commonly used to fabricate electrodes and wires in n-type silicon materials. Due to its excellent conductivity and machinability, it can form stable connections with other components. Furthermore, aluminum forms a reliable interface between silicon wafers and silicon oxide, and is also used to manufacture electrodes and wires for oxide field-effect transistors (MOSFETs). However, in these applications, excess silicon oxide needs to be removed later, and currently, dry etching and wet etching are commonly used. Dry etching is time-consuming, and the surface residue is significant, often requiring further cleaning, significantly increasing the overall process time. Wet etching typically uses buffered oxide etchant (BOE) for etching and cleaning. For etching silicon dioxide, a BOE is typically used, whose main components are hydrofluoric acid, ammonium fluoride, and water. However, conventional BOE etching solutions corrode aluminum or other materials rapidly, resulting in a low selectivity ratio that fails to meet the high selectivity requirements of advanced processes. Therefore, in order to improve the selectivity ratio, additives are generally introduced to reduce the corrosion of aluminum or other materials by BOE etching solutions.

[0003] Chinese patent CN108384548A discloses a buffered etching solution for non-metallic oxides, which introduces a slow-release agent and a penetrant into a hydrofluoric acid-ammonium fluoride system, making the etching solution non-etchable on the contact layer ILD film and GI film layer, while reducing the etching rate on polycrystalline silicon substrates and glass substrates. CN113429974A discloses a BOE etching solution for composite film layers, which adds n-octanoic acid as an additive to a hydrofluoric acid-ammonium fluoride system, making etching applicable to both single substrates and composite substrates, while also considering CD loss and the required angle. CN115595154A discloses a selective etching solution for SiGe and Si, which is prepared by using a composite oxidant, a fluorine source (including hydrofluoric acid and ammonium fluoride), a buffer composition, and a chelating agent with water to obtain an etching solution with good selectivity for SiGe and weak corrosivity to Si.

[0004] However, conventional BOE etching solutions currently have relatively low selectivity for aluminum and are prone to etching aluminum during silicon oxide etching. Therefore, it is necessary to develop an etching solution that can inhibit the erosion of aluminum during the etching process. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a buffer oxide etching solution for inhibiting aluminum etching and its application. This solution can reduce the etching rate of aluminum while rapidly etching silicon oxide, thereby meeting the etching selectivity requirements of the silicon oxide layer to the aluminum layer in different processes.

[0006] To achieve the above objectives, the present invention provides a buffer oxide etching solution for inhibiting aluminum oxidation, which is composed of the following raw materials in parts by weight: 3%-12% hydrofluoric acid, 15%-25% ammonium fluoride, 15%-35% organic acid, 0.005%-0.05% surfactant, and the balance being ultrapure water.

[0007] Preferably, the hydrofluoric acid is electronic grade and has a mass concentration of 48-50%.

[0008] Preferably, the ammonium fluoride is electronic grade and has a mass concentration of 38-41%.

[0009] Preferably, the organic acid is citric acid (purity ≥ 90%) or glacial acetic acid (purity ≥ 99%).

[0010] Preferably, the surfactant is an amide surfactant.

[0011] More preferably, the amide surfactant is selected from any one of tetrahydro-3-furan carboxamide (purity ≥97%), succinamide (purity ≥98%), cyclopropionamide (purity ≥98%), crotonamide (purity ≥98%), and mandelic acid amide (purity ≥98%).

[0012] Preferably, the resistivity of the ultrapure water at 25°C is ≥18 megohms.

[0013] The present invention also provides the application of a buffer oxide etching solution for inhibiting aluminum in the etching and / or cleaning of silicon oxide thin films.

[0014] Preferably, the silicon oxide thin film contains FSG, Thermal Oxide, and TEOS.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. Hydrofluoric acid in the buffer oxide etching solution is used to rapidly etch silicon oxide films, while ammonium fluoride is used to provide fluoride ions, thereby stabilizing the etching rate of the etching solution.

[0017] 2. Amide surfactants are a class of organic compounds containing carbonyl and amino groups. When applied to buffer oxide etching solutions, the amino groups in the amide molecules can chemically adsorb onto the aluminum oxide on the aluminum surface, forming an inorganic / organic composite protective film, thereby inhibiting further corrosion of the aluminum surface. In addition, the C=O groups in the amide molecules can form coordinate bonds with metal ions, thereby improving the inhibition effect on metal ions, such as aluminum.

[0018] 3. The introduction of organic acids into the buffer oxide etching solution is based on the chemical reaction between acids and aluminum. When the aluminum surface comes into contact with oxygen, an oxidation reaction occurs, forming aluminum oxide. Aluminum oxide can further react with organic acids. For example, when it encounters acetic acid, it can form a stable aluminum acetate film (Al(OAc)3) and effectively adsorb onto the aluminum surface, forming a dense protective layer that prevents oxygen and other corrosive substances from contacting the aluminum, thereby reducing corrosion. When aluminum oxide encounters citric acid, the multiple carboxyl groups (-COOH) in the citric acid molecule can react with the aluminum oxide on the aluminum surface to form aluminum citrate complex, thus forming an aluminum citrate film (Al(C6H7O7)), which can also protect the aluminum surface from further etching. In addition, organic acids can increase the hydrogen ion content in the etching solution, thereby accelerating the etching rate of silicon oxide.

[0019] 4. The preparation method of this invention is simple, and while maintaining stable and efficient etching of silicon oxide, it can reduce the etching of aluminum, has a high selectivity, and does not produce particulate contamination, which can meet the requirements of high-end processes. Furthermore, when using the buffer oxide etching solution prepared by this invention for wet etching, etching and cleaning can be performed in one step, shortening the time and reducing costs. Attached Figure Description

[0020] Figure 1 The clarified buffer oxide etching solution prepared in Example 1.

[0021] Figure 2 The turbid buffer oxide etching solution prepared for Comparative Example 5.

[0022] Figure 3 This is a schematic diagram of the etching of the aluminum trench structure sheet in Example 8. Detailed Implementation

[0023] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0024] In the following examples and comparative examples, the hydrofluoric acid used was electronic grade hydrofluoric acid with a concentration of 49%, the ammonium fluoride used was electronic grade ammonium fluoride with a mass concentration of 40%, the citric acid had a purity of 90%, the glacial acetic acid had a purity of 99%, the tetrahydro-3-furan carboxamide had a purity of 97%, the succinamide had a purity of 98%, the cyclopropionamide had a purity of 98%, the crotonamide had a purity of 98%, and the mandelic acid had a purity of 98%.

[0025] Example 1

[0026] A buffered oxide etching solution was obtained by mixing 4.0% hydrofluoric acid, 18% ammonium fluoride, 20% glacial acetic acid, and 0.01% tetrahydro-3-furan carboxamide, and then adding ultrapure water to bring the solution to 100%. The mixture was stirred thoroughly for 60 minutes to ensure homogeneity. Figure 1 ).

[0027] Example 2

[0028] The buffer oxide etching solution is obtained by mixing 5% hydrofluoric acid, 18% ammonium fluoride, 25% glacial acetic acid, and 0.01% crotonamide, and then replenishing it with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0029] Example 3

[0030] The buffer oxide etching solution is obtained by mixing 7.0% hydrofluoric acid, 18% ammonium fluoride, 25% glacial acetic acid, and 0.05% succinamide, and then replenishing with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0031] Example 4

[0032] The buffer oxide etching solution is obtained by mixing 6.0% hydrofluoric acid, 18% ammonium fluoride, 30% glacial acetic acid and 0.03% cyclopropionamide, and then replenishing with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0033] Example 5

[0034] The buffer oxide etching solution is obtained by mixing 5% hydrofluoric acid, 18% ammonium fluoride, 25% citric acid, and 0.04% mandelic acid, and then replenishing with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0035] Example 6

[0036] The buffer oxide etching solution is obtained by mixing 4.0% hydrofluoric acid, 18% ammonium fluoride, 30% citric acid, and 0.03% tetrahydro-3-furan carboxamide, and then replenishing it with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0037] Example 7

[0038] The buffer oxide etching solution is obtained by mixing 6.0% hydrofluoric acid, 18% ammonium fluoride, 20% citric acid, and 0.008% cyclopropamide, and then replenishing with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0039] Comparative Example 1

[0040] The buffer oxide etching solution is obtained by mixing 5.0% hydrofluoric acid and 18% ammonium fluoride, and then replenishing with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0041] Comparative Example 2

[0042] The buffer oxide etching solution is obtained by mixing 6.0% hydrofluoric acid, 18% ammonium fluoride, and 25% glacial acetic acid, and then replenishing the solution with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0043] Comparative Example 3

[0044] The buffer oxide etching solution is obtained by mixing 4.0% hydrofluoric acid, 18% ammonium fluoride, and 0.02% succinamide, and then replenishing with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0045] Comparative Example 4

[0046] The buffer oxide etching solution is obtained by mixing 5.0% hydrofluoric acid, 18% ammonium fluoride, 40% glacial acetic acid, and 0.03% mandelic acid, and then replenishing with ultrapure water to 100%. The mixture is stirred thoroughly for 60 minutes to ensure uniform mixing.

[0047] Comparative Example 5

[0048] A buffered oxide etching solution is obtained by mixing 5.0% hydrofluoric acid, 18% ammonium fluoride, 20% citric acid, and 0.1% tetrahydro-3-furan carboxamide, and then adding ultrapure water to bring the solution to 100%. The mixture is stirred thoroughly for 60 minutes to ensure homogeneity. Figure 2 ).

[0049] Example 8

[0050] The buffer oxide etching solutions prepared in the above examples and comparative examples were placed in PFA bottles and then placed in a low-temperature constant temperature bath. The temperature was set to 25°C. After the temperature of the buffer oxide etching solution was lowered by the temperature of the low-temperature constant temperature bath, silicon oxide wafers, aluminum sheets, and aluminum trench structure sheets were placed in the bath and slowly etched by stirring. The thickness of the silicon oxide wafers was measured at the same position using an elliptic polarization spectrometer before and after etching. The thickness of the aluminum sheets was measured at the same position using a four-probe method. The etching rates of the silicon oxide wafers and aluminum sheets were calculated based on the thickness difference before and after etching and the etching time. The results are shown in Table 1. The morphology and crystallization of the trenches before and after etching were observed using a super depth-of-field microscope. The etching schematic diagram is shown in [Table 1]. Figure 3 The results are shown in Table 1:

[0051] Table 1 Properties, etching rate, and etch selectivity of buffered oxide etching solution

[0052]

[0053] Note: FSG stands for silicon dioxide wafer, and Al stands for aluminum sheet.

[0054] As shown in Table 1, the buffer oxide etching solutions prepared in Examples 1-7 are clear and do not introduce other impurities during the etching process, thus avoiding contamination of the etching material. Furthermore, their etching rate on silicon oxide wafers is [missing information]. The etching rate of the aluminum sheet is Between these values, the selectivity is above 37, reaching a maximum of 53. Therefore, the buffer oxide etching solutions prepared in Examples 1-7 have a significant inhibitory effect on the aluminum layer and can effectively protect the aluminum during the etching process. Comparative Example 1 prepared an etching solution using only hydrofluoric acid and ammonium fluoride, which significantly reduced the etching rate of silicon oxide wafers while accelerating the etching rate of aluminum wafers, resulting in a selectivity of only 22.8. Comparative Example 2 did not add a surfactant to the buffer oxide etching solution; although the etching rate of aluminum was reduced, the selectivity was not high. Comparative Example 3 did not add an organic acid to the buffer oxide etching solution; although the etching rate of aluminum wafers decreased, the etching rate of silicon oxide wafers also decreased significantly, reaching only 22.8. The selectivity of the solution was relatively low, so the etching inhibition effect on aluminum was not obvious. In Comparative Example 4, the addition of excessive organic acid could achieve a higher selectivity, but crystallization was found around the aluminum trench during the etching process, which was not conducive to the next step of the process. In Comparative Example 5, the buffer oxide etching solution prepared by adding excessive surfactant was turbid, which would cause particulate contamination of the wafer during etching, which was not conducive to the next step of the process.

Claims

1. A buffer oxide etching solution for inhibiting aluminum etching, characterized in that: It is composed of the following raw materials in parts by weight: 3%-12% hydrofluoric acid, 15%-25% ammonium fluoride, 15%-35% organic acid, 0.005%-0.05% surfactant, and the balance being ultrapure water; the organic acid is citric acid or glacial acetic acid; the surfactant is an amide surfactant; the amide surfactant is any one of tetrahydro-3-furan carboxamide, succinamide, cyclopropionamide, crotonamide, and mandelic acid.

2. The buffer oxide etching solution for inhibiting aluminum etching according to claim 1, characterized in that: The hydrofluoric acid is electronic grade and has a mass concentration of 48-50%.

3. The buffer oxide etching solution for inhibiting aluminum etching according to claim 1, characterized in that: The ammonium fluoride is electronic grade and has a mass concentration of 38-41%.

4. The buffer oxide etching solution for inhibiting aluminum etching according to claim 1, characterized in that: The resistivity of the ultrapure water at 25°C is ≥18 megohms.

5. The application of a buffer oxide etchant for inhibiting aluminum as described in any one of claims 1-4 in the etching of silicon oxide thin films.

6. The application according to claim 5, characterized in that: The silicon oxide film is made of FSG, Thermal Oxide, or TEOS.

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