Buffer oxide etching solution with vertical side etch angle

Abstract

The application discloses a buffer oxide etching solution with a vertical side etching angle. The etching solution is mainly composed of hydrofluoric acid, ammonium fluoride, a surfactant and ultrapure water. The surfactant used in the application is concentrated at the solid-liquid interface due to its strong hydrophobicity, and the hydroxyl functional groups in the surfactant interact with each other, so that the reaction rate of the interface is smoother, and the side wall morphology at the vertical angle is obtained in the side etching process. Meanwhile, the low surface tension ensures the cleaning effect and uniformity of the side wall surface of the gate oxide layer. The etching solution disclosed by the application can effectively improve the angle in the lateral etching process, and meanwhile, the integrity and smoothness of the side wall are ensured.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit etching solution technology, specifically relating to a buffer oxide etching solution with a vertical side etching angle. Background Technology

[0002] Functional electronic chemicals refer to specialized chemicals used in the electronics industry. They are commonly used in the cleaning and etching processes during the manufacturing of integrated circuit structures. Chemicals used in wet cleaning and etching processes have high requirements for quality, strong functionality, and high product precision.

[0003] With the rapid development of integrated circuits, the dimensions of processes such as IGBTs and MEMS are constantly decreasing. Gate oxide layers are commonly used in transistors to ensure good threshold voltage and current. Reducing the thickness of the gate oxide layer enhances the current drive capability of the transistor, improving speed and power characteristics. While reducing the gate oxide layer thickness in process shrinkage can effectively improve transistor performance, insufficient density in subsequent thin-film filling processes can reduce oxide layer reliability. Furthermore, defective oxide layers can lead to circuit leakage and electronic component failure. Therefore, improving the lateral etching angle can significantly enhance the reliability of microelectronic integrated circuit manufacturing.

[0004] CN114351143B discloses a germanium etching solution with controllable lateral etching amount, which is prepared by using an oxidant, a fluoride ion source, a viscosity modifier, a pH modifier and high-purity water to obtain a germanium etching solution that can improve the lateral etching ability; CN114016031A discloses a rapid etching solution and its preparation method, which is prepared by using sulfuric acid, hydrogen peroxide, an anti-lateral etching agent, a wetting agent and a stabilizer to obtain an etching solution that can slow down the etching rate of the etching solution on the side when etching copper, thereby significantly reducing the phenomenon of lateral etching of the circuit.

[0005] However, in the current etching process for gate oxide layers, the commonly used etchant often produces a slanted side etching angle during the etching process. The slanted side etching angle will affect the density of the subsequent thin film filling process. Therefore, it is necessary to develop an etchant that can have a vertical side etching angle during the etching process to reduce the impact on subsequent processes. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a buffered oxide etchant with a vertical lateral etching angle, which is used to improve the angle of lateral etching of the oxide layer and increase the yield of the process.

[0007] To achieve the above objectives, the present invention provides a buffer oxide etching solution with a vertical side etching angle, wherein the buffer oxide etching solution comprises 0.01-1% hydrofluoric acid, 30-40% ammonium fluoride, 0.0001-0.01% surfactant, and the balance being ultrapure water.

[0008] Preferably, the hydrofluoric acid is electronic grade and has a mass concentration of 48-50%.

[0009] Preferably, the ammonium fluoride is electronic grade and has a mass concentration of 38-40%.

[0010] Preferably, the resistivity of the ultrapure water at 25°C is not less than 18 megohms.

[0011] Preferably, the surfactant is a fluoroalkyl alcohol surfactant.

[0012] More preferably, the isomeric fluoroalkyl alcohol surfactant is any one of isomeric hexafluorobutanol, isomeric perfluorobutanol, isomeric pentafluoropentanol, and isomeric undecylfluorohexanol.

[0013] The beneficial effects of this invention are as follows: the use of a low hydrofluoric acid and high ammonium fluoride system reduces the corrosion rate, making the buffer oxide etching solution more uniform and stable during localized corrosion; at the same time, the introduction of isomeric fluoroalkyl alcohol surfactants into the buffer oxide etching solution reduces the surface tension, and the strong hydrophobicity and group interaction of the surfactants make the corrosion of the solid-liquid interface smoother, which can ensure that the angle is completely perpendicular when laterally corroding the oxide layer, reducing the difficulty of the subsequent filling process. Attached Figure Description

[0014] Figure 1 The diagram shows the etching results of different etching solutions; A in the diagram is before etching, B is the etching result using the buffered oxide etching solution prepared in Comparative Example 3, and C is the etching result using the buffered oxide etching solution prepared in Example 1; 1 in the diagram is photoresist, 2 is oxide film, and 3 is silicon substrate. Detailed Implementation

[0015] 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.

[0016] Example 1

[0017] The buffer oxide etching solution formula is as follows: 0.1% hydrofluoric acid, 35% ammonium fluoride, 0.001% isohexafluorobutanol, and the balance is ultrapure water.

[0018] Example 2

[0019] The buffer oxide etching solution formula is: 0.2% hydrofluoric acid, 35% ammonium fluoride, 0.001% isomeric perfluorobutanol, and the balance is ultrapure water.

[0020] Example 3

[0021] The buffer oxide etching solution formula is: 0.1% hydrofluoric acid, 39% ammonium fluoride, 0.001% isohexafluorobutanol, and the balance is ultrapure water.

[0022] Example 4

[0023] The buffer oxide etching solution formula is: 0.1% hydrofluoric acid, 35% ammonium fluoride, 0.002% isopentafluoropentanol, and the balance is ultrapure water.

[0024] Example 5

[0025] The buffer oxide etching solution formula is as follows: 0.2% hydrofluoric acid, 35% ammonium fluoride, 0.0005% isomeric undecylfluorohexanol, and the balance is ultrapure water.

[0026] Example 6

[0027] The buffer oxide etching solution formula is as follows: 0.01% hydrofluoric acid, 30% ammonium fluoride, 0.0008% isomeric undecylfluorohexanol, and the balance is ultrapure water.

[0028] Example 7

[0029] The buffer oxide etching solution formula is as follows: 0.5% hydrofluoric acid, 32% ammonium fluoride, 0.003% isohexafluorobutanol, and the balance is ultrapure water.

[0030] Example 8

[0031] Buffer oxide etching solution formulation: 1% hydrofluoric acid, 40% ammonium fluoride, 0.0007% isomeric perfluorobutanol, with the balance being ultrapure water.

[0032] Comparative Example 1

[0033] A buffer oxide etching solution was prepared using an excess of surfactant. The specific formula was: 0.1% hydrofluoric acid, 35% ammonium fluoride, 0.1% isomeric perfluorobutanol, and the balance being ultrapure water.

[0034] Comparative Example 2

[0035] No surfactants are added to the buffer oxide etching solution. The specific formula is: 0.1% hydrofluoric acid, 35% ammonium fluoride, and the balance is ultrapure water.

[0036] Comparative Example 3

[0037] A buffer oxide etching solution was prepared using excess hydrofluoric acid. The specific formula was: 2% hydrofluoric acid, 35% ammonium fluoride, and 0.001% isohexafluorobutanol.

[0038] Comparative Example 4

[0039] A buffer oxide etching solution was prepared using a small amount of ammonium fluoride. The specific formula was: 0.1% hydrofluoric acid, 15% ammonium fluoride, 0.001% isomeric perfluorobutanol, and the balance was ultrapure water.

[0040] Comparative Example 5

[0041] Buffer oxide etching solution formulation: 0.1% hydrofluoric acid, 35% ammonium fluoride, 0.001% isohexylamine, with the balance being ultrapure water.

[0042] Results detection: After the buffer oxide etching solution was prepared and mixed evenly, the surface tension of the buffer oxide etching solution in the above examples and comparative examples was detected by a surface tension meter. The results are shown in Table 1.

[0043] Place the PFA bottle containing the cleaning solution into a low-temperature thermostat and heat it to 23°C. After the temperature stabilizes for a period of time, place the bottle with the cleaning solution into the thermostat. Figure 1 The wafer with structure A was placed in the etching solution and etched for 10 minutes. After etching, the lateral etching angle at position 5 in Figure (3) was measured by SEM. The results are shown in Table 1.

[0044] Table 1. Surface tension and etching performance of buffer oxide etching solutions with different formulations.

[0045] Example 1 24.51 vertical line ≈90 Example 2 23.91 vertical line ≈90 Example 3 22.06 vertical line ≈90 Example 4 21.27 vertical line ≈90 Example 5 21.98 vertical line ≈90 Example 6 22.47 vertical line ≈90 Example 7 21.69 diagonal line ≈87 Example 8 23.01 diagonal line ≈83 Comparative Example 1 20.57 Irregular vertical lines, with residue ≈90 Comparative Example 2 72.18 Irregular oblique straight lines, with residue ≈72 Comparative Example 3 24.84 diagonal line ≈77 Comparative Example 4 25.68 Irregular oblique lines ≈79 Comparative Example 5 61.23 Irregular diagonal lines, with residue ≈80

[0046] As shown in Table 1, the surface tension of Examples 1-6 is less than 25 mN / m. The low surface tension makes the etching solution easier to perform lateral etching. At the same time, the corrosion rate of low hydrofluoric acid and high ammonium fluoride is slower, and the local corrosion uniformity is more stable. The strong hydrophobicity and group interaction of the surfactant make the corrosion of the solid-liquid interface smoother, forming a vertical lateral corrosion angle ( Figure 1 C) This is beneficial for the density of subsequent dielectric layer filling; In Examples 7 and 8, the hydrofluoric acid content is higher, the etching rate is faster, which affects the effect of the additive on the smoothness of the sidewall layout, resulting in a slight shift in the angle.

[0047] In Comparative Example 1, the excessive surfactant caused the solution to be turbid, resulting in uneven etching in certain areas and incomplete filling of the dielectric layer in subsequent processes. In Comparative Example 2, the absence of surfactant increased surface tension and weakened lateral etching ability, leading to residue formation on the sidewall surface and the formation of angled corrosion. In Comparative Example 3, the excessive hydrofluoric acid content resulted in a too-fast localized corrosion rate, and the additives could not completely smooth the corrosion rate at the solid-liquid interface, leading to angled corrosion. Figure 1B); In Comparative Example 4, the ammonium fluoride content is low, the local corrosion rate is unstable, and oblique corrosion will also form, increasing the difficulty of subsequent medium filling process; In Comparative Example 5, hexylamine is selected as a surfactant, the surface tension of the buffer oxide etching solution is significantly increased, and the local corrosion rate is unstable, forming irregular oblique corrosion.

Claims

1. A buffered oxide etching solution with a vertical lateral etching angle, characterized in that: The buffer oxide etching solution consists of 0.01-1% hydrofluoric acid, 30-40% ammonium fluoride, 0.0001-0.01% surfactant, with the balance being ultrapure water; the surfactant is an isomeric fluoroalkyl alcohol surfactant, which is any one of isomeric hexafluorobutanol, isomeric perfluorobutanol, isomeric pentafluoropentanol, and isomeric undecylfluorohexanol.

2. The buffer oxide etching solution with a vertical lateral etching angle according to claim 1, characterized in that: The hydrofluoric acid is electronic grade with a mass concentration of 48-50%.

3. The buffer oxide etching solution with a vertical lateral etching angle according to claim 1, characterized in that: The ammonium fluoride is electronic grade and has a mass concentration of 38-40%.

4. The buffer oxide etching solution with a vertical lateral etching angle according to claim 1, characterized in that: The resistivity of the ultrapure water at 25°C is not less than 18 megohms.

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