A deep trench etchant for suppressing lateral etching of silicon oxide under photoresist

Abstract

This invention provides a deep trench etchant for suppressing lateral etching of silicon oxide under photoresist. The etchant, by mass percentage, comprises the following components: 3-9% hydrofluoric acid, 30-38% ammonium fluoride, 0.01-0.1% activator, and the balance being ultrapure water. The additive is a mixture of small molecules of triamine-based organic amines and macromolecules of propylene glycol block polyethers. Through the combined use of small molecules of triamine-based organic amines and long-chain macromolecular activators, the etchant exhibits low surface tension, good wettability to silicon, and is less prone to foaming. This etchant completely etches the silicon oxide in the deep trenches without residue. More importantly, it significantly suppresses lateral etching of silicon oxide under photoresist coverage, substantially reducing lateral corrosion of silicon oxide under photoresist and effectively improving device production yield.

Description

Technical Field

[0001] This invention belongs to the field of etching solution technology, specifically relating to a deep trench etching solution that inhibits lateral etching of silicon oxide under photoresist. Background Technology

[0002] In power semiconductor manufacturing processes, deep trenches of specific dimensions are typically first etched into the silicon surface using a dry etching process. Different silicon oxide dielectric layers are then deposited within these trenches, and a specific photomask is used to coat the underlying dielectric layer with a photoresist of a specific shape to protect it. Finally, wet etching is used to completely etch away the silicon oxide dielectric layer in the deep trenches that is not protected by the photoresist. However, due to the isotropic nature of the etchant, the unprotected silicon oxide dielectric layer undergoes lateral etching, which can negatively impact the yield of subsequent processes. To improve process yield, the etchant needs to significantly inhibit lateral etching of the silicon oxide dielectric layer.

[0003] Wet etching of silicon oxide dielectric layers typically utilizes buffered oxide etchants. However, these etchants suffer from high interfacial tension and poor silicon wettability, making it difficult to completely etch the silicon oxide dielectric layer in deep trenches. More importantly, buffered oxide etchants exhibit significant lateral etching effects on the silicon oxide dielectric layer protected by photoresist, reducing the yield of subsequent processes. Summary of the Invention

[0004] This invention provides a deep trench etchant that suppresses lateral etching of silicon oxide under photoresist. It has good wettability to silicon and is not prone to foaming. It can completely etch the silicon oxide medium in the deep trench and has a significant inhibitory effect on lateral etching of silicon oxide medium under photoresist protection.

[0005] The technical solution of the present invention is a deep trench etching solution for inhibiting lateral etching of silicon oxide under photoresist. The composition of the etching solution, by mass percentage, includes the following components: 3-9% hydrofluoric acid, 30-38% ammonium fluoride, 0.01-0.1% additives, and the balance being ultrapure water; wherein the additives are a mixture of triamine-based organic amine small molecules and propylene glycol block polyether macromolecular surfactants.

[0006] Furthermore, the mass ratio of triamine-based organic amine small molecules to propylene glycol block polyether macromolecules is 90-95:5-10.

[0007] Furthermore, the triamine-type organic amine small molecule is one or a combination of several of the following: tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, tri-isooctylamine, tri-n-nonylamine, etc.; preferably tri-n-octylamine.

[0008] Furthermore, the macromolecular surfactant is one or more of propylene glycol block polyethers with an average molecular weight of 1100-2900; preferably, it is a propylene glycol block polyether with a molecular weight of 2200.

[0009] Furthermore, the mass fraction of hydrofluoric acid in the etching solution is 3-9%.

[0010] Furthermore, the etching solution contains 7.1% hydrofluoric acid by mass.

[0011] Furthermore, the mass fraction of ammonium fluoride in the etching solution is 30-38%.

[0012] Furthermore, the mass fraction of ammonium fluoride in the etching solution is 34.30%.

[0013] The present invention also relates to the application of the etching solution in deep trench etching of silicon oxide media.

[0014] The present invention has the following beneficial effects: 1. In this invention, a combination of small-molecule triamine organic amine and large-molecule propylene glycol block polyether surfactant is used. The combination has high solubility in the etching solution and is not prone to foaming. The combination of the two additives results in low surface tension of the etching solution and good wettability to silicon surfaces. It performs excellently in etching deep trenches and deep holes of silicon oxide and can completely etch the silicon oxide medium deposited in deep trenches or deep holes.

[0015] 2. The synergistic use of triamine-based organic amine small molecule additives and macromolecular propylene glycol block polyether surfactants can inhibit the etching of silicon oxide media under photoresist protection, significantly reduce the lateral etching of silicon oxide media under photoresist protection by the etching solution, and improve the yield of subsequent processes. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the silicon oxide deep trench structure protected by photoresist before etching.

[0017] Figure 2 A schematic diagram of the etching of a silicon oxide deep trench structure after adding a small organic amine molecule of triamine alone (Comparative Example 4).

[0018] Figure 3 A schematic diagram of the etching of a silicon oxide deep trench structure after adding propylene glycol block polyether surfactant alone (Comparative Example 5).

[0019] Figure 4 A schematic diagram of the etching of a silicon oxide deep trench structure when the two additives are used in combination (implemented in 14). Detailed Implementation

[0020] 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.

[0021] This invention provides formulations for several etching solutions, as detailed in Table 1.

[0022] Table 1 To facilitate verification of the etching effect of the etching solution on the lateral etching of silicon oxide in the deep trench structure under photoresist protection in the above embodiments and comparative examples, a structural sheet with a similar structure was used as the experimental object. The structure before etching is as follows: Figure 1 As shown. Specific etching conditions were stirring and immersion etching, with an etching time of 8 minutes and an etching temperature of 23℃. The silicon oxide deep trench structure sample under photoresist protection was first stripped using a stripping solution, then diced using a dicing machine. After dicing, SEM was used to detect whether the dielectric layer in the trench was completely etched and the lateral etching depth of the silicon oxide under photoresist protection. The silicon oxide layer deposited in the deep trench included thermal oxide, TEOS, and doped silicon oxide. A schematic diagram illustrating the lateral etching of the silicon oxide dielectric in the deep trench structure by the etching solution when only alkanolamine molecules are added is shown below. Figure 2 As shown in the diagram. When propylene glycol block polyether is added alone, the etchant performs lateral etching of the silicon oxide dielectric in a deep trench structure. Figure 3 As shown. Figure 4 This is a schematic diagram of lateral etching of silicon oxide media in deep trenches when two additives are used in combination.

[0023] The specific experimental results are shown in Table 2.

[0024] Table 2 Table 2 shows that, as demonstrated in Examples 1 to 3, when propylene glycol block polyether is used in combination with triamine-based organic amine small molecules, the surface tension of the etching solution is low, the silicon oxide dielectric in the deep trench structure is completely etched, and the lateral etching inhibition effect on the silicon oxide dielectric under photoresist protection is significant. Furthermore, with the increase of the amount of propylene glycol block polyether added, the lateral etching inhibition effect on the silicon oxide dielectric is significant; when the addition amount is 0.003%, the lateral etching inhibition depth of the silicon oxide dielectric tends to stabilize. Examples 4 to 8 show that, when triamine-based organic amine small molecules are used in combination with propylene glycol block polyether, the length and spatial structure of the branches in the triamine-based organic amine small molecules affect the lateral etching depth of the silicon oxide dielectric. The longer the branch length, the better the lateral etching inhibition effect on the silicon oxide dielectric. When the number of carbon atoms in the branch is 8, the lateral etching inhibition effect tends to stabilize, with tri-n-octylamine being the preferred choice. Examples 8 to 13, and 11 and 14 show that when used in combination with tri-n-octylamine, the lateral etching suppression effect of propylene glycol block polyether on silicon oxide dielectric first increases and then decreases with increasing average molecular weight, reaching its optimal value at a molecular weight of 2200. These examples demonstrate that the molecular weight of the propylene glycol block polyether, along with the carbon branch length and spatial structure of the triamine-based small-molecule organic amine, affects the lateral etching suppression effect of the silicon oxide dielectric under photoresist protection in deep trenches.

[0025] Comparative Examples 1 and 2 show that the amount of triethanolamine also affects the lateral etching of silicon oxide, with an optimal triethanolamine content of 0.04%. Comparative Examples 3 and 4 show that without propylene glycol block polyether in the etching solution, the silicon oxide in the deep trench cannot be completely etched. This is because propylene glycol block polyether is a high-performance surfactant that can significantly reduce the interfacial tension in the etching solution and improve its wettability to silicon. Without propylene glycol block polyether, the interfacial tension in the etching solution is high, resulting in poor silicon wettability and preventing complete etching of the silicon oxide at the bottom of the deep trench. Comparative Examples 3 and 4 also show that using propylene glycol block polyether alone or using triamine-based organic amine molecules alone has limited inhibitory effect on the lateral etching of silicon oxide. However, when both are used synergistically, the inhibitory effect on the lateral etching of silicon oxide protected by photoresist is significant. It is speculated that this is because the macromolecules of propylene glycol block polyether and the small molecules of triamine-based organic amines have intermolecular hydrogen bonds and hydrophobic interactions. These interactions cause them to adhere tightly to the photoresist surface, protecting the silicon oxide medium from lateral etching. Comparative Example 6 shows that when the amount of propylene glycol block polyether is as low as 0.001%, the interfacial tension of the etching solution is relatively high, and the silicon oxide medium in the deep trench is not completely etched. This indicates that when the interfacial tension in the etching solution is too high, the silicon oxide medium cannot be completely etched. Comparative Example 7 shows that when tri-n-octylamine is replaced with triethanolamine in combination with propylene glycol block polyether, the inhibitory effect on lateral etching of the silicon oxide medium in the deep trench is significantly weakened. This is speculated to be because the interaction between triethanolamine and the photoresist surface is weaker. This further illustrates that only when the small molecules of triamine-based organic amines are used in combination with propylene glycol block polyether can the maximum synergistic effect be achieved.

[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 deep trench etchant for suppressing lateral etching of silicon oxide under photoresist, characterized in that: The etching solution, by mass percentage, comprises the following components: 3-9% hydrofluoric acid, 30-38% ammonium fluoride, 0.01-0.1% activator, with the balance being ultrapure water; the activator is a mixture of small molecules of triamine organic amines and macromolecules of propylene glycol block polyethers; the small molecules of triamine organic amines are one or a combination of tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, tri-isooctylamine, and tri-n-nonylamine; the propylene glycol block polyethers are one or a combination of one or a combination of those with an average molecular weight of 1100-2900; the mass ratio of the small molecules of triamine organic amines to the propylene glycol block polyethers is 90-95:5-10.

2. The etching solution according to claim 1, characterized in that: The small molecule of triamine organic amines is tri-n-octylamine.

3. The etching solution according to claim 1, characterized in that: The molecular weight of propylene glycol block polyether is 2200.

4. The etching solution according to claim 1, characterized in that: The etching solution contains 7.10% hydrofluoric acid by mass.

5. The etching solution according to claim 1, characterized in that: The mass fraction of ammonium fluoride in the etching solution is 34.30%.

6. The application of the etching solution according to any one of claims 1 to 5 in the etching of silicon oxide deep trench structures.

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