High-selectivity etching solution for silicon dioxide and titanium

Abstract

The invention provides a silicon dioxide and titanium high-selectivity etching solution which comprises the following components in percentage by mass: 8 to 12 percent of hydrofluoric acid, 26 to 30 percent of nitrogen-containing alkyl amide solvent, 0.01 to 0.1 percent of surfactant and the balance of ultrapure water, wherein the surfactant is fatty acid monoglyceride. Through cooperative use of the nitrogen-containing alkyl amide solvent and the fatty acid monoglyceride, the etching liquid is low in surface tension, excellent in solubility and good in silicon surface wettability, and a silicon dioxide medium on the side wall of a deep hole is removed completely. More importantly, the etching solution can significantly inhibit etching of a metal titanium film layer, the etching selection ratio of silicon dioxide to titanium is higher than 50, and the yield of device production is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of etching solution technology, specifically relating to a highly selective etching solution for silicon dioxide and titanium. Background Technology

[0002] In MEMS devices, titanium metal layers serve several important functions, often acting as adhesion layers to enhance the bonding strength between different materials. For example, when fabricating thin films of metals such as gold and silver on silicon substrates, the direct adhesion between these metals and silicon is relatively weak. Therefore, a titanium layer is typically added between the substrate and the film to significantly improve the interfacial adhesion. Titanium's coefficient of thermal expansion is well-matched with many commonly used MEMS materials, a characteristic that helps reduce thermal stress caused by temperature changes and minimizes the risk of film warping or cracking. Furthermore, titanium has excellent electrical conductivity, making it suitable for manufacturing electrode structures in MEMS sensors or actuators, ensuring efficient transmission of electrical signals. However, in some MEMS structures, silicon dioxide is often deposited as a dielectric layer on the sidewalls of deep-hole structures to protect the titanium electrodes. Subsequent processes require complete removal of the silicon dioxide while minimizing corrosion of the titanium layer; otherwise, device performance and yield may be affected. Therefore, the etching solution must effectively remove silicon dioxide from the sidewalls of deep holes while simultaneously inhibiting corrosion of the titanium metal to ensure the overall success rate and reliability of the process.

[0003] Wet etching of silica dielectric layers typically utilizes buffered oxide etchants. However, buffered oxide etchants alone are insufficient to completely remove the silica dielectric layer from the inner walls of deep holes due to their high interfacial tension and poor wettability. Furthermore, buffered oxide etchants are generally composed of hydrofluoric acid and ammonium fluoride, which severely corrodes titanium films, thus affecting the yield of the processed devices. Summary of the Invention

[0004] This invention provides a highly selective etching solution for silicon dioxide and titanium, with low surface tension, which can cleanly etch the silicon dioxide medium on the inner wall of deep holes and effectively inhibit the corrosion of the titanium film, thereby improving the etching selectivity ratio of silicon dioxide to titanium.

[0005] The technical solution of the present invention is a highly selective etching solution of silica and titanium. The composition of the etching solution, by mass percentage, includes the following components: 8-12% hydrofluoric acid, 26-30% nitrogen-containing alkyl amide solvent, 0.01-0.1% surfactant, and the balance being ultrapure water; the surfactant is a monoglyceride.

[0006] Furthermore, the nitrogen-containing alkylamide solvent is one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-diethylacetamide, N-methylpropionamide, etc.; preferably N,N-dimethylacetamide.

[0007] Furthermore, the monofatty acid glyceride surfactant is one or more of the fatty acids having 6-14 carbon atoms; the monofatty acid glyceride is selected from any one of glyceroyl anhydride, glyceroyl heptanoate, glyceroyl caprylate, glyceroyl nonanoate, glyceroyl decanoate, glyceroyl laurate, and glyceroyl monomyristate.

[0008] Furthermore, the mass fraction of hydrofluoric acid in the etching solution is 8-12%.

[0009] Furthermore, the hydrofluoric acid in the etching solution has a mass fraction of 10%.

[0010] Furthermore, the mass fraction of the nitrogen-containing alkylamide solvent in the etching solution is 26-30%.

[0011] Furthermore, the etching solution contains 28% nitrogen-containing alkylamide solvent by mass.

[0012] The present invention also relates to the application of the etching solution in the etching of deep-hole silica dielectric structures, which can cleanly etch the silica dielectric deposited in the deep holes.

[0013] Etching effect: The etching solution can significantly inhibit the etching of the titanium film layer. The etching selectivity ratio of silicon dioxide to titanium is higher than 50, which effectively improves the yield of device production.

[0014] The present invention has the following beneficial effects: 1. In this invention, a nitrogen-containing alkylamide solvent is used in combination with hydrofluoric acid. This not only acts as a buffer to inhibit the excessively rapid etching of silicon dioxide, but also adsorbs onto the surface of metallic titanium to prevent the attack of hydrofluoric acid and achieve highly selective etching of titanium.

[0015] 2. More importantly, the nitrogen-containing alkylamide solvent and the surfactant are mono-fatty acid glycerides used synergistically, exhibiting good dispersibility and excellent solubility. This synergistic use results in a low surface tension of the etching solution and excellent wettability to silicon, effectively removing the silica dielectric layer from the inner walls of deep holes. Furthermore, the surfactant complexes and adsorbs with titanium through hydroxyl groups, inhibiting titanium corrosion. Ultimately, this etching solution can significantly improve the etching selectivity ratio between silica and titanium, increasing it to over 50, meeting the requirements of subsequent production processes. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the silicon dioxide structure of the deep hole sidewall before etching.

[0017] Figure 2 This is a schematic diagram of the complete structure of the silicon dioxide etching on the sidewall of the deep hole after etching in Example 15.

[0018] Figure 3 This is a schematic diagram of the incomplete silicon dioxide etching structure of the deep hole sidewall after etching, as shown in Comparative Example 2. Detailed Implementation

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

[0020] This invention provides formulations for several etching solutions, as detailed in Table 1.

[0021] Table 1

[0022] To facilitate verification of the etching rates of silicon dioxide and titanium in the above embodiments and comparative examples, silicon dioxide, titanium monoliths, and structural sheets with silicon dioxide deposited on the deep-hole sidewalls were used as experimental subjects, and the sheets were split for the experiment. Specific etching conditions included stirring and immersion etching, with an etching time of 2 min and an etching temperature of 23℃. After the experiment, the etching rate of silicon dioxide was detected using an ellipsometry, and the etching rate of titanium was detected using a four-point probe microanalyzer. After splitting, SEM was used to check whether the silicon dioxide medium on the deep-hole sidewalls was completely etched. The silicon dioxide medium deposited on the deep-hole sidewalls included thermal oxidative silica, CVD, PE-TEOS, and doped silicon dioxide, etc. The experimental data used thermal oxidative silica and CVD-deposited titanium as experimental subjects. Specific experimental results are shown in Table 2.

[0023] Table 2

[0024] As shown in Table 2, Examples 1 to 3 demonstrate that when a fatty acid glyceride with 6 carbon atoms is added to a mixed solution of hydrofluoric acid and N,N-dimethylformamide, the surface tension of the etching solution is low, allowing for complete etching of the silica dielectric deposited on the inner wall of the deep hole, as illustrated in the structural diagram. Figure 2As shown in the figures. Furthermore, in this system, the etching rate of titanium metal first increases and then decreases with increasing amounts of 6-carbon fatty acid glycerides, with the optimal amount being 0.02%. Examples 3 to 10 show that nitrogen-containing alkyl amide solvents significantly inhibit the etching rate of titanium with increasing carbon chain length and branching. The etching selectivity ratio of silica to titanium increases because increasing carbon chain length or nitrogen branching reduces the polarity of the system, thereby inhibiting mass transfer of the titanium etching products. Additionally, increasing carbon chain length or nitrogen branching also increases the saturation coverage of the adsorbed material on the titanium surface. A series of experiments revealed that the combined use of N,N-dimethylacetamide and hydrofluoric acid provides the best corrosion inhibition effect on titanium metal. Examples 11 to 16 show that, at the same addition amount, the corrosion inhibition effect of mono-fatty acid glycerides with different carbon numbers on titanium metal first improves and then worsens with increasing carbon number, with the optimal carbon number being 12. This is because mono-fatty acid glycerides, in the etching solution, protect themselves from the attack of hydrofluoric acid by coordinating and adsorbing with the empty d orbitals of titanium ions through the lone pair electrons on the hydroxyl and ester groups, thereby inhibiting the etching of metallic titanium. Alkyl chains with different carbon numbers have different hydrophobic interactions and different arrangement forms on the titanium surface. As the carbon number increases, the tightness of these alkyl chains adsorbed on the titanium surface first increases and then decreases.

[0025] Comparative Examples 1 and 2 show that when nitrogen-containing alkylamide solvents or mono-fatty acid glycerides are used alone in the etching solution, the corrosion inhibition effect on titanium is significantly reduced. This is because the synergistic use of the two leads to tighter adsorption on the titanium surface and weakens the mass transfer of the titanium etching products. The synergistic use of both can significantly inhibit the corrosion of metallic titanium. Example 2 also shows that when no fatty acid glycerides are added to the etching solution, the surface tension is high, making it difficult to completely remove the silica medium from the sidewalls of deep holes, as shown in the structural diagram. Figure 3 As shown in Comparative Examples 3 and 4, it can be seen that the corrosion inhibition effect on metallic titanium is greatly reduced when lauric acid or dimethyl sulfoxide is used, which further illustrates the good synergistic effect between nitrogen-containing alkyl amide solvents and mono-fatty acid glycerides in this system.

[0026] Obviously, the above embodiments and comparative examples are merely illustrative examples and are not intended to limit the scope of the invention. Those skilled in the art will recognize numerous variations and combinations of the above embodiments, and it is neither necessary nor possible to list all possible embodiments here. Therefore, any changes or modifications made based on the above embodiments are still within the scope of protection of this invention.

Claims

1. A highly selective etching solution for silicon dioxide and titanium, characterized in that: The etching solution, by mass percentage, includes the following components: 8-12% hydrofluoric acid, 26-30% nitrogen-containing alkylamide solvent, 0.01-0.1% surfactant, with the balance being ultrapure water; the surfactant is monoglyceride fatty acid glyceride.

2. The etching solution according to claim 1, characterized in that: The nitrogen-containing alkylamide solvent is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-diethylacetamide, and N-methylpropionamide.

3. The etching solution according to claim 1, characterized in that: The mono-fatty acid glyceride surfactant is one or more combinations of fatty acids with 6-14 carbon atoms.

4. The etching solution according to claim 3, characterized in that: The monofatty acid glycerides are selected from any one of the following: monoacylglycerol, monoheptanylglycerol, monocaprylic acid glycerol, monononanoic acid glycerol, monodecanoic acid glycerol, monolaurylic acid glycerol, and monomyristate glycerol.

5. The etching solution according to claim 1, characterized in that: The etching solution contains 8-12% hydrofluoric acid by mass.

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

7. The etching solution according to claim 1, characterized in that: The etching solution contains 26-30% nitrogen-containing alkylamide solvent by mass.

8. The etching solution according to claim 1, characterized in that: The etching solution contains 28% nitrogen-containing alkylamide solvent by mass.

9. The use of the etching solution according to any one of claims 1 to 8 in etching a silica medium deposited in a deep hole.

10. The application according to claim 9, characterized in that, This etching solution can significantly inhibit the etching of metallic titanium films, with an etching selectivity ratio of silicon dioxide to titanium exceeding 50.

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