Silicon oxide etching solution for inhibiting titanium corrosion

Abstract

The invention provides a silicon oxide etching solution for inhibiting titanium corrosion, which comprises the following components in percentage by mass: 6 to 10 percent of hydrofluoric acid, 16 to 24 percent of ammonium fluoride, 0.01 to 0.16 percent of active agent and the balance of ultrapure water, wherein the additive is a bio-based fatty acid methyl ester ammonium sulfonate surfactant and quinoline sulfonic acid aromatic heterocyclic sulfonic acid. The bio-based fatty acid methyl ester ammonium sulfonate surfactant and the quinoline sulfonic acid aromatic heterocyclic sulfonic acid additive are compounded for use, so that the etching solution is low in surface tension and good in wettability, and can completely etch a pore region silicon oxide medium. More importantly, the etching solution can efficiently inhibit etching of a metal titanium film layer, the etching selection ratio of silicon oxide to titanium is greatly improved, and the yield of device production is effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of etching solution, and particularly relates to a silicon oxide etching solution for inhibiting titanium corrosion. BACKGROUND

[0002] Titanium metal layer has a wide application in MEMS devices. The titanium metal layer can be used as an adhesion layer to improve the bonding force between different materials. For example, when depositing a metal thin film such as gold or silver on a silicon substrate, a titanium metal layer can be deposited between the silicon substrate and the metal thin film to enhance the bonding of the thin film and the substrate because the adhesion of these metals to silicon is poor. Titanium has a relatively matched thermal expansion coefficient: the thermal expansion coefficient of titanium is relatively matched with many metals and substrate materials, which can effectively reduce the problems such as film warping or cracking caused by a large difference in thermal expansion coefficient. In addition, titanium metal has good electrical conductivity and can be used to make electrodes in MEMS devices. For example, in some sensors or actuators that require high conductivity, a titanium metal layer can be used as an electrode material to ensure stable transmission of electrical signals. However, in MEMS deep hole structures, titanium metal electrodes are often protected by a silicon oxide medium for subsequent processes, and finally the silicon oxide medium needs to be etched clean, and the corrosion of the titanium metal layer should be minimized, otherwise it will affect the yield of subsequent process devices. In order to improve the yield of process devices, the etching solution needs to etch the deep hole silicon oxide medium layer clean and inhibit the corrosion of the titanium metal layer.

[0003] The wet etching of the silicon oxide medium layer is generally completed by using a buffered oxide etching solution. However, it is difficult to completely remove the silicon oxide medium layer in the deep hole using only the buffered oxide etching solution due to its high surface tension and poor wettability. More importantly, the buffered oxide etching solution is generally composed of hydrofluoric acid and ammonium fluoride, which severely corrodes the titanium metal and affects the yield of process devices. SUMMARY

[0004] The application provides a silicon oxide etching solution for inhibiting titanium corrosion, which has low interfacial tension, can completely etch the silicon oxide medium in the deep hole, and can inhibit the corrosion of the titanium metal film layer.

[0005] The technical solution of the application is a silicon oxide etching solution for inhibiting titanium corrosion. The composition of the etching solution, by mass percentage, includes the following components: 6-10% of hydrofluoric acid, 16-24% of ammonium fluoride, 0.01-0.16% of an active agent, and the balance of ultrapure water; the additive is a mixture of a bio-based fatty acid methyl ester ammonium sulfonate surfactant and a quinoline sulfonic acid aromatic heterocyclic sulfonic acid.

[0006] Further, the mass ratio of the bio-based fatty acid methyl ester ammonium sulfonate surfactant to the quinoline sulfonic acid aromatic heterocyclic sulfonic acid is 10-20:80-90.

[0007] Further, the bio-based fatty acid methyl ester ammonium sulfonate surfactant is one or a combination of fatty acid carbon number 8-16; preferably ammonium laurate methyl sulfonate with carbon number 10-16, and further preferably ammonium laurate methyl sulfonate with carbon number 12.

[0008] Further, the quinoline sulfonic acid aromatic heterocyclic sulfonic acid is one or a combination of 8-hydroxyquinoline-5-sulfonic acid, 8-ethoxyquinoline-5-sulfonic acid, quinoline-8-sulfonic acid, etc.; preferably 8-hydroxyquinoline-5-sulfonic acid.

[0009] Further, the mass fraction of hydrofluoric acid in the etching solution is 6-10%, and at the same time, any value in 6-10% is within the protection scope of the present application.

[0010] Further, the mass fraction of hydrofluoric acid in the etching solution is 8-9%, and further preferably 8.3%.

[0011] Further, the mass fraction of ammonium fluoride in the etching solution is 16-24%, and at the same time, any value in 16-24% is within the protection scope of the present application.

[0012] Further, the mass fraction of ammonium fluoride in the etching solution is 20-22%, and further preferably 20.50%.

[0013] The present application also relates to the application of the etching solution in the etching of deep hole structure of silicon oxide medium.

[0014] The present application has the following beneficial effects: 1. In the present application, bio-based fatty acid methyl ester ammonium sulfonate surfactant and quinoline sulfonic acid aromatic heterocyclic sulfonic acid are used in combination, which has good solubility in the etching solution and is converted from biomass, in line with the concept of green chemistry. The synergistic use of the two additives can lower the surface tension of the etching solution and improve the wettability, so that the silicon oxide medium in the deep hole can be etched clean.

[0015] 2. More importantly, the fatty acid methyl ester ammonium sulfonate surfactant is adsorbed and arranged on the surface of titanium through d-orbital coordination and electrostatic attraction between anions and cations, and the quinoline sulfonic acid additive is adsorbed on the surface of titanium through d-Π conjugation and electrostatic attraction of sulfonic acid groups. The synergistic effect of the two additives can make the adsorption and arrangement on the surface of titanium more compact, thereby inhibiting the attack of hydrofluoric acid on titanium, greatly reducing the corrosion of titanium, greatly improving the etching selectivity ratio of silicon oxide to titanium, and increasing the selectivity ratio from 2.33 to 38.35, meeting the needs of subsequent process production. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 . Schematic diagram of deep hole silicon oxide structure before etching.

[0017] Figure 2 Figure 1 is a schematic diagram of a deep hole silicon oxide etching complete structure after etching in Example 1.

[0018] Figure 3 Figure 2 is a schematic diagram of a deep hole silicon oxide etching incomplete structure after etching in Comparative Example 2. DETAILED DESCRIPTION

[0019] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application.

[0020] The present application provides the formula of multiple etching solutions, which are shown in Table 1.

[0021] Table 1

[0022] In order to verify the etching rate of the etching solution for silicon oxide and titanium metal in the above examples and comparative examples, the silicon oxide, titanium metal monolithic and deep hole structure silicon oxide structure sheet are used as experimental objects, and the sheets are broken for experiment. The specific etching conditions are stirring immersion etching, and the etching time is 2 min, and the etching temperature is 23°C. After the experiment, the etching rate of silicon oxide is detected by using an ellipsometer, the etching rate of titanium metal is detected by using a four-point probe instrument, and whether the silicon oxide medium in the deep hole is etched completely is detected by using SEM after the sheet is broken. The silicon oxide medium deposited in the deep hole includes thermal oxygen, CVD, PE-TEOS, doped silicon oxide, etc., and the experimental data are all for thermal oxygen silicon oxide and PVD deposited titanium as experimental objects. The specific experimental results are shown in Table 2.

[0023] Table 2

[0024] As can be seen from Table 2, from Examples 1 to 3, when the quinoline sulfonic acid type additive is used in combination with the fatty acid methyl ester ammonium sulfonate type surfactant, the surface tension of the etching solution is low, and the silicon oxide medium in the deep hole can be etched completely, such as the structure schematic diagram Figure 2. The etching rate of titanium first increased and then decreased with the increase of the amount of ammonium fatty acid methyl ester sulfonate with a carbon number of 8, and the optimal amount was 0.018%. As can be seen from Examples 3 to 7, the branched structure of quinoline sulfonic acid type additives also affects the corrosion inhibition of titanium, in which the inhibition effect of 8-hydroxyquinoline-5-sulfonic acid is the best, and the optimal amount screened is 0.12%. The 8-hydroxyquinoline-5-sulfonic acid has the best inhibition effect because the molecular structure contains both hydroxyl and sulfonic acid groups, which can coordinate with the d orbitals of titanium and then adsorb on the surface to prevent the attack of hydrofluoric acid on titanium. As can be seen from Examples 8-15, the carbon chain length of ammonium fatty acid methyl ester sulfonate also affects its corrosion inhibition effect on titanium, and the best effect is obtained for fatty acid methyl ester sulfonate with a carbon number of 12. It is speculated that the active agent coordinates with titanium through the sulfonic acid group and the adsorption force between anions and cations on one end, and the arrangement of the other end in the etching solution is affected by the length of the carbon chain. When the carbon chain length is 12, the additive is most closely adsorbed on the surface of titanium, so the inhibition effect is the best.

[0025] As can be seen from Comparative Examples 1 to 3, the corrosion inhibition effect of titanium is significantly reduced when only one of the additives is used. The synergistic interaction of the two makes the adsorption on the surface of titanium more closely, so the corrosion of titanium can be efficiently inhibited. When 8-hydroxyquinoline-5-sulfonic acid is used alone, the silicon oxide medium in the deep hole cannot be etched completely, which is due to the large surface tension of the etching solution, which is difficult to completely infiltrate into the deep hole to etch it completely, as shown in the structural diagram Figure 3 . As can be seen from Comparative Examples 4 and 5, when 8-hydroxyquinoline or fatty acid methyl ester is used, the corrosion inhibition effect on titanium is greatly reduced because of the lack of strong interaction of sulfonic acid groups with titanium.

[0026] Obviously, the above examples and comparative examples are only examples made for clarity, and are not limited to the above examples. For those skilled in the art, there are many changes or combinations of the above examples, and it is not necessary and impossible to enumerate all the examples here. Therefore, the changes or variations made based on the above examples are still within the protection scope of the present application.

Claims

1. A silicon oxide etching solution for inhibiting titanium corrosion, characterized in that: The etching solution, by mass percentage, comprises the following components: 6-10% hydrofluoric acid, 16-24% ammonium fluoride, 0.01-0.16% surfactant, with the balance being ultrapure water; the surfactant is a mixture of bio-based fatty acid methyl ester sulfonate ammonium surfactants and quinoline sulfonic acid aromatic heterocyclic sulfonic acids.

2. The etching solution according to claim 1, characterized in that: The mass ratio of the bio-based fatty acid methyl ester sulfonate ammonium surfactant to the quinoline sulfonic acid aromatic heterocyclic sulfonic acid is 10-20:80-90.

3. The etching solution according to claim 1 or 2, characterized in that: The bio-based fatty acid methyl ester sulfonate ammonium surfactant is one or a combination of several fatty acids with 8-16 carbon atoms.

4. The etching solution according to claim 3, characterized in that: The bio-based fatty acid methyl ester sulfonate ammonium surfactant is one or a combination of several fatty acids with 10-16 carbon atoms.

5. The etching solution according to claim 1, characterized in that: The quinoline sulfonic acid is one or a combination of several of the following: 8-hydroxyquinoline-5-sulfonic acid, 8-ethoxyquinoline-5-sulfonic acid, and quinoline-8-sulfonic acid; preferably 8-hydroxyquinoline-5-sulfonic acid.

6. The etching solution according to claim 1, characterized in that: The etching solution contains 6-10% hydrofluoric acid by mass.

7. The etching solution according to claim 1, characterized in that: The etching solution contains 8-9% hydrofluoric acid by mass.

8. The etching solution according to claim 1, characterized in that: The mass fraction of ammonium fluoride in the etching solution is 16-24%.

9. The etching solution according to claim 1, characterized in that: The mass fraction of ammonium fluoride in the etching solution is 20-22%.

10. The application of the etching solution according to any one of claims 1 to 9 in the etching of deep-hole silicon oxide dielectric containing metal electrodes.

Images