High performance silicon oxide etching solution

Abstract

The application provides a high-performance silicon oxide etching solution, which comprises the following components in percentage by mass: 5-9% of hydrofluoric acid, 30-38% of ammonium fluoride, 0.02-0.2% of an active agent, and the balance of ultrapure water; wherein the additive is a mixture of an aniline small molecule and an alkyl polyglycoside macromolecule. By using the aniline small molecule and the high-surface-tension alkyl polyglycoside macromolecule in combination, the surface tension of the etching solution is low, the silicon oxide in the groove is etched completely and without residue, the etching solution has good wettability and low damage to silicon carbide, and the roughness of the silicon carbide after etching is lower than 0.1 nm. More importantly, the etching solution has a low angle (lower than 45 degrees) after lateral etching of the silicon oxide under the photoresist coverage, and the photoresist does not appear to be peeled off, so that the yield of device production can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of etching solution technology, and specifically relates to a high-performance silicon oxide etching solution. Background Technology

[0002] Due to its wide bandgap, high critical breakdown electric field strength, high thermal conductivity, and strong chemical stability, silicon carbide (SiC) third-generation semiconductors are widely used in power devices with high voltage withstand capability, high frequency operation capability, and high temperature operating capability, making them ideal for applications such as new energy vehicles, photovoltaic power generation, rail transportation, and smart grids. In the manufacturing process of power semiconductors on SiC substrates, a layer of silicon oxide is typically deposited on the SiC surface first, followed by a layer of photoresist. A photomask of a specific shape is then used for exposure and development to form a pattern. Finally, wet etching is used to completely etch the silicon oxide dielectric layer not covered by the photoresist to form a groove. Because of the isotropic nature of the etching solution, it has a lateral etching effect on the silicon oxide dielectric layer protected by the photoresist. Unlike power devices on silicon substrates, the lateral etching angle of the silicon oxide dielectric under the photoresist must be less than 45 degrees; otherwise, it will affect the yield of subsequent processes. To improve the yield, the etching solution needs to completely corrode the silicon oxide dielectric not covered by the photoresist, and the lateral etching angle of the silicon oxide dielectric under the photoresist must be less than 45 degrees.

[0003] Wet etching of silicon oxide dielectric layers is generally performed using buffered oxide etchants. However, buffered oxide etchants alone are insufficient to completely etch the silicon oxide dielectric layer within the grooves due to their high surface tension and poor wettability to silicon carbide. More importantly, the lateral etching angle of buffered oxide etchants on silicon oxide protected by photoresist is generally greater than 50 degrees, which is difficult to meet the requirements of subsequent processes. Summary of the Invention

[0004] This invention provides a high-performance silicon oxide etching solution with good wettability to silicon carbide, which can completely etch the silicon oxide medium in the groove, and the lateral etching angle of the silicon oxide medium under photoresist protection is less than 45 degrees.

[0005] The technical solution of the present invention is a high-performance silicon oxide etching solution, wherein the composition of the etching solution by mass percentage includes the following components: 5-9% hydrofluoric acid, 30-38% ammonium fluoride, 0.02-0.2% additives, and the balance being ultrapure water; wherein the additives are a mixture of aniline small molecules and alkyl glycoside macromolecules.

[0006] Furthermore, the mass ratio of aniline small molecules to alkyl glycoside macromolecules is 90-95:5-10.

[0007] Furthermore, the aromatic amine small molecules of the aniline class are one or a combination of several of the following: aniline, o-toluidine, m-toluidine, p-toluidine, p-ethylaniline, 2,4,5-trimethylaniline, 3-isopropylaniline, p-methoxyaniline, 4-methoxym-phenylenediamine, etc.; preferably p-ethylaniline.

[0008] Furthermore, the alkyl glycoside contains one or more straight-chain alcohols with 8-12 alkyl carbons; preferably, it contains alkyl glycosides with 9 alkyl carbons.

[0009] Furthermore, the mass fraction of hydrofluoric acid in the etching solution is 5-9%.

[0010] Furthermore, the etching solution contains 7.80% 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 36.40%.

[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:

[0015] 1. In this invention, a combination of small-molecule aniline surfactants and large-molecule alkyl glycoside surfactants is used. The surfactants have high solubility in the etching solution and good compatibility. The combination of the two additives results in low surface tension of the etching solution and good wettability on silicon carbide surfaces. It performs excellently in etching silicon oxide grooves and deep holes, and can completely etch the silicon oxide medium deposited in the grooves or deep holes without any residue.

[0016] 2. Due to the π-π conjugation effect between aniline and photoresist, and the hydrogen bond interaction between alkyl glycosides and photoresist with high surface activity, the synergistic use of small molecule aniline additives and large molecule alkyl glycoside surfactants can significantly reduce the lateral etching angle between silicon oxide and photoresist under the photoresist, meeting the needs of subsequent production processes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the silicon oxide trench structure protected by photoresist before etching.

[0018] Figure 2 A schematic diagram of the etching of the silicon oxide groove structure after adding aniline small molecules alone in Comparative Example 4.

[0019] Figure 3 A schematic diagram of the etching of the silicon oxide groove structure after adding alkyl glycoside macromolecules alone in Comparative Example 3.

[0020] Figure 4 A schematic diagram of the etching of the silicon oxide groove structure when the two additives are used in combination in Example 14. Detailed Implementation

[0021] 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.

[0022] This invention provides formulations for several etching solutions, as detailed in Table 1.

[0023] Table 1

[0024]

[0025] To facilitate verification of the effects of etching solution on the lateral etching of silicon oxide and damage to silicon carbide in the photoresist-protected groove structure in the above embodiments and comparative examples, structural wafers and silicon carbide flat wafers with similar structures were used as experimental subjects. The structures before etching are as follows: Figure 1 As shown. Specific etching conditions were stirring and immersion etching, with an etching time of 5 minutes and an etching temperature of 23℃. After the experiment, the structural wafer was diced using a dicing machine. After dicing, SEM was used to inspect whether the dielectric layer in the groove was completely etched and the lateral etching angle of the silicon oxide under photoresist protection. The damage after silicon carbide etching was measured using AFM to assess the roughness of the etched silicon carbide. The silicon oxide layer deposited in the groove included thermal oxidation, CVD, PE-TEOS, and doped silicon oxide. A schematic diagram showing the lateral etching angle of the silicon oxide dielectric in the groove structure when aniline-based small molecules were added alone is shown below. Figure 2 As shown in the diagram. When alkyl glycosides are added alone, the schematic diagram shows the lateral etching angle of the etching solution for the silicon oxide dielectric in the groove structure. Figure 3 As shown. Figure 4 This is a schematic diagram showing the lateral etching angle of the silicon oxide dielectric in the groove structure when two additives are used in combination.

[0026] The specific experimental results are shown in Table 2.

[0027] Table 2

[0028]

[0029] Table 2 shows that, as demonstrated in Examples 1 to 3, when alkyl glycoside macromolecules are used in combination with aniline small molecules, the surface tension of the etching solution is low, the silicon oxide medium in the groove is completely etched, and the lateral etching angle of the silicon oxide medium under photoresist protection is less than 45 degrees. The roughness of the silicon carbide after etching is also less than 0.1 nm. Furthermore, with the increase of alkyl glycoside addition, the lateral etching angle of the silicon oxide medium first decreases and then increases, reaching its minimum when the addition amount is 0.005%. Examples 4 to 13 show that when aniline small molecules are used in combination with 8-carbon alkyl glycosides, the spatial structure and chain length of the branches in the aniline small molecules affect the lateral etching angle of the silicon oxide medium. Aniline with para-substituted alkyl groups exhibits a better lateral etching angle and a smaller angle. This indicates that steric hindrance affects its interaction with the photoresist, thus affecting the lateral etching angle. The optimal effect is achieved when p-ethylaniline is used in combination with alkyl glycosides. As can be seen from Examples 14 to 16, when used in combination with p-ethylaniline, the lateral etching angle of the silicon oxide medium first decreases and then increases with the increase of the number of alkyl carbons in the alkyl glycoside. When the number of alkyl carbons is 9, the lateral etching angle of the silicon oxide is optimal, which is 30 degrees. From the above examples, it can be seen that the alkyl carbon chain length in the alkyl glycoside, as well as the substituent branch length, substitution position, and spatial structure of the aniline-like small molecules, all affect the lateral etching angle of the silicon oxide medium under the photoresist in the groove.

[0030] Comparative Examples 1 and 2 show that the amount of p-ethylaniline also affects the lateral etching angle of the silicon oxide medium, with an optimal dosage of 0.04%. Comparative Examples 3 to 5 show that when the etching solution lacks alkyl glycosides, the silicon oxide medium in the groove cannot be completely etched, leaving residue. This is because alkyl glycosides are high-performance, green surfactants that can significantly reduce the interfacial tension in the etching solution and improve its wettability to silicon carbide. Without alkyl glycosides, the interfacial tension in the etching solution is high, resulting in poor wettability to silicon carbide and preventing complete etching of the silicon oxide medium to the bottom of the groove. Comparative Examples 3 to 5 also show that using alkyl glycosides alone or using benzene-based small molecules alone has a limited effect on reducing the lateral etching angle of the silicon oxide medium. However, when both are used synergistically, the lateral etching angle of the silicon oxide medium can be significantly reduced. It is speculated that this is because the large alkyl glycoside molecules have a large number of hydroxyl groups that interact with the small benzene molecules through intermolecular hydrogen bonds. Meanwhile, photoresists contain many polar groups and benzene rings. The resulting additives exhibit strong hydrogen and π-π bond interactions with the photoresist, making it easier for the etchant to penetrate deep into the photoresist and reducing the lateral etching angle. Comparative Example 6 shows that when alkyl glycosides are combined with aliphatic amines, the lateral etching angle of the silicon oxide dielectric is larger, presumably because the benzene rings play a more significant role.

[0031] 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 high-performance silicon oxide etching solution, characterized in that: The etching solution, by mass percentage, comprises the following components: 5-9% hydrofluoric acid, 30-38% ammonium fluoride, 0.02-0.2% surfactant, with the balance being ultrapure water; the surfactant is a mixture of small molecules of aniline organic amines and large molecules of alkyl glycosides. The small molecules of the aniline class are one or more combinations of aniline, o-toluidine, m-toluidine, p-toluidine, p-ethylaniline, 2,4,5-trimethylaniline, 3-isopropylaniline, p-methoxyaniline, and 4-methoxym-phenylenediamine; the alkyl glycosides are one or more combinations of straight-chain alcohols with 8-12 alkyl carbons. The mass ratio of the aniline small molecules to the alkyl glycosides is 90-95:5-10.

2. The etching solution according to claim 1, characterized in that: The small molecule of the aniline class is p-ethylaniline.

3. The etching solution according to claim 1, characterized in that: The alkyl glycoside is an alkyl glycoside with 9 alkyl carbons.

4. The etching solution according to claim 1, characterized in that: The etching solution contains 7.80% 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 36.40%.

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