High-performance silicon oxide etching solution

Abstract

The invention 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 aniline micromolecules and alkyl glycoside macromolecules. Through compounding use of aniline micromolecules and high-surface-activity alkyl glycoside macromolecules, the etching solution is low in surface tension, silicon oxide in a groove is etched completely without residues, wettability to silicon carbide is good, damage to silicon carbide is low, and the roughness of etched silicon carbide is lower than 0.1 nm. More importantly, the etching solution has an angle of less than 45 degrees after lateral etching of the silicon oxide covered by the photoresist, and meanwhile, the photoresist is not stripped, so that the yield of device production can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of etching liquids, and in particular relates to a high-performance silicon oxide etching liquid. Background Art

[0002] Since the third-generation silicon carbide semiconductor has the advantages of wide bandgap, high critical breakdown electric field strength, high thermal conductivity, strong chemical stability, etc., the power devices made of it have the advantages of high withstand voltage, high frequency operation capability, high temperature working capability, etc., and are widely used in new energy vehicles, photovoltaic power generation, rail transportation, smart grid, etc. In the power semiconductor manufacturing process of silicon carbide substrate, generally a layer of silicon oxide is deposited on the surface of silicon carbide first, and then a layer of photoresist is coated, and a photomask of a specific shape is 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. Due to the isotropy of the etching solution, the etching solution will have a lateral etching effect on the silicon oxide dielectric layer protected by the photoresist. Unlike silicon substrate power devices, the lateral etching angle of the silicon oxide dielectric under the photoresist is required to be less than 45 degrees, otherwise it will affect the yield of the subsequent process. In order to improve the yield of the process, the etching solution is required to completely corrode the silicon oxide dielectric not covered by the photoresist and the lateral etching of the silicon oxide dielectric covered by the photoresist is less than 45 degrees.

[0003] The wet etching of the silicon oxide dielectric layer is generally completed using a buffered oxide etchant. However, it is difficult to completely etch the silicon oxide dielectric layer in the groove using only the buffered oxide etchant due to its large surface tension and poor wettability to silicon carbide. More importantly, the buffered oxide etchant generally etches the silicon oxide protected by the photoresist at an angle greater than 50 degrees, which makes it difficult to meet the requirements of subsequent processes. Summary of the invention

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

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

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

[0007] Furthermore, the aromatic amine small molecule of the aniline class is one or a combination of aniline, o-toluidine, m-toluidine, p-toluidine, p-ethylaniline, 2,4,5-trimethylaniline, 3-isopropylaniline, p-methoxyaniline, 4-methoxy-m-phenylenediamine, etc.; p-ethylaniline is preferred.

[0008] Furthermore, the alkyl glycoside is one or a combination of straight-chain alcohols with an alkyl carbon number of 8-12; preferably, the alkyl glycoside has an alkyl carbon number of 9.

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

[0010] Furthermore, the mass fraction of hydrofluoric acid in the etching solution is 7.80%.

[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 invention also relates to the application of the etching solution in silicon oxide medium deep trench etching.

[0014] The present invention has the following beneficial effects: 1. In the present invention, a small molecule aniline and a large molecule alkyl glycoside surfactant are used in combination, which have high solubility in the etching solution and good compatibility. The two additives are used in combination, the etching solution has low surface tension and good wettability for the silicon carbide surface, and 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 residue.

[0015] 2. Due to the π-π conjugation effect between aniline and photoresist, the hydrogen bond interaction between alkyl glycoside and photoresist and the high surface activity, the synergistic use of small molecule aniline additives and large molecule alkyl glycoside surfactants can significantly reduce the lateral etching angle of silicon oxide under the photoresist and the photoresist, meeting the needs of subsequent process production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 . Schematic diagram of the silicon oxide groove structure under photoresist protection before etching.

[0017] Figure 2 . Schematic diagram of etching of silicon oxide groove structure after adding aniline small molecules alone in Comparative Example 4.

[0018] Figure 3 . Schematic diagram of etching of silicon oxide groove structure after adding alkyl glycoside macromolecules alone in Comparative Example 3.

[0019] Figure 4 . Schematic diagram of the silicon oxide groove structure after etching when the two additives in Example 14 are used in combination. DETAILED DESCRIPTION

[0020] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0021] The present invention provides multiple etching solution formulas for illustration, as shown in Table 1.

[0022] Table 1

[0023] In order to verify the lateral etching of silicon oxide and the damage of silicon carbide in the groove structure under the protection of photoresist by the etching solution in the above embodiments and comparative examples, a structural sheet and a silicon carbide flat sheet with similar structure were used as experimental objects. Figure 1 As shown. The specific etching conditions are stirred immersion etching, the etching time is 5 min, and the etching temperature is 23°C. After the experiment, the structure was split using a splitting machine. After splitting, SEM was used to detect whether the dielectric layer in the groove was completely etched and the lateral etching angle of silicon oxide under the protection of the photoresist. The damage of silicon carbide after etching is measured by AFM to measure the roughness of silicon carbide after etching. The silicon oxide layer deposited in the groove includes thermal oxygen, CVD, PE-TEOS, doped silicon oxide, etc. When aniline small molecules are added alone, the schematic diagram of the lateral etching angle of the silicon oxide medium in the groove structure caused by the etching solution is shown in Figure 2 When alkyl glycoside is added alone, the schematic diagram of the lateral etching angle of the etching solution on the silicon oxide medium in the groove structure is shown in Figure 3 shown. Figure 4 . is a schematic diagram of the lateral etching angle of silicon oxide medium in the groove structure when the two additives are used in combination.

[0024] The specific experimental results are shown in Table 2.

[0025] Table 2

[0026] As shown in Table 2, when the alkyl glycoside macromolecule and the aniline small molecule are compounded and used, 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 the protection of the photoresist is less than 45 degrees, and the roughness of the etching solution for silicon carbide is also less than 0.1nm. In addition, with the increase of the amount of alkyl glycoside added, the lateral etching angle of the silicon oxide medium first decreases and then increases, and when its addition amount is 0.005%, the lateral etching angle of silicon oxide is the smallest. As can be seen from Examples 4 to 13, when the aniline small molecule is compounded and used with the alkyl glycoside of 8 carbon numbers, the spatial structure and chain length of the side chain in the aniline small molecule will affect the lateral etching angle of the silicon oxide medium, and the aniline in the para-substituted alkyl is more excellent to the lateral etching angle of silicon oxide, and the angle is smaller. This shows that steric hindrance will affect its interaction with the photoresist, and then affect the lateral etching angle, and the effect is best when selecting p-ethylaniline and the alkyl glycoside to be compounded and used. It can be seen from Examples 14 to 16 that when used in combination with p-ethylaniline, as the number of carbon atoms in the alkyl polyglycoside increases, the lateral etching angle for the silicon oxide medium first decreases and then increases, and when the number of carbon atoms in the alkyl polyglycoside is 9, the silicon oxide lateral etching angle is optimal, which is 30 degrees. It can be seen from the above examples that the length of the alkyl carbon chain in the alkyl polyglycoside and the length, substitution position and spatial structure of the substituent branch of the aniline small molecule will affect the lateral etching angle of the silicon oxide medium under the photoresist in the groove.

[0027] As can be seen from Comparative Examples 1 and 2, the amount of p-ethylaniline also affects the lateral etching angle of the silicon oxide medium, and the optimum amount of p-ethylaniline is 0.04%. As can be seen from Comparative Examples 3 to 5, when there is no alkyl polyglycoside in the etching solution, the silicon oxide medium in the groove cannot be completely etched and has residues. This is because alkyl polyglycoside is a high-performance green surfactant that can significantly reduce the interfacial tension in the etching solution and improve the wettability of the etching solution to silicon carbide. When there is no alkyl polyglycoside, the interfacial tension in the etching solution is large, and the wettability to silicon carbide is poor, and it is impossible to infiltrate the bottom of the groove groove to completely etch the silicon oxide medium. It can also be seen from Comparative Examples 3 to 5 that when alkyl polyglycoside is used alone or benzene small molecules are used alone, the etching solution has limited effect on reducing the lateral etching angle of the silicon oxide medium, but when the two are used in coordination, the lateral etching angle of the silicon oxide medium can be significantly reduced. It is speculated that the reason is that the alkyl glycoside macromolecule has a large number of hydroxyl groups and benzene small molecules have intermolecular hydrogen bond interactions, and the photoresist contains more polar groups and benzene rings. The compounded additives and the photoresist have strong hydrogen bonds and π-π bond interactions, which makes it easier for the etching solution to penetrate deep into the photoresist and reduce the lateral etching angle. It can be seen from Comparative Example 6 that when the alkyl glycoside is compounded with aliphatic amines, the lateral etching angle of the silicon oxide medium is larger, which is speculated to be because the benzene ring plays a greater role.

[0028] Obviously, the above embodiments and comparative examples are only examples for clear demonstration, and are not limited to the above embodiments. For those skilled in the art, the above embodiments have many variations or combinations, and it is not necessary and impossible to cite all the embodiments here. Therefore, the changes or modifications based on the above embodiments are still within the protection scope of the present invention.

Claims

1. A high performance silicon oxide etching solution, Features: The etching solution comprises the following components by mass percentage: 5-9% hydrofluoric acid, 30-38% ammonium fluoride, 0.02-0.2% activator, and the balance is ultrapure water; the activator is a mixture of aniline organic amine small molecules and alkyl glycoside macromolecules.

2. The etching solution according to claim 1, Features: The mass ratio of the aniline small molecule to the alkyl glycoside is 90-95:5-10.

3. The etching solution according to claim 1 or 2, Features: The aniline small molecule is one or a combination of aniline, o-toluidine, m-toluidine, p-toluidine, p-ethylaniline, 2,4,5-trimethylaniline, 3-isopropylaniline, p-methoxyaniline, and 4-methoxy-m-phenylenediamine; p-ethylaniline is preferred.

4. The etching solution according to claim 1, Features: The alkyl glycoside may be one or a combination of straight-chain alcohols having an alkyl carbon number of 8-12; preferably, the alkyl glycoside has an alkyl carbon number of 9.

5. The etching solution according to claim 1, Features: The mass fraction of hydrofluoric acid in the etching solution is 5-9%.

6. The etching solution according to claim 1, Features: The mass fraction of hydrofluoric acid in the etching solution is 7.80%.

7. The etching solution according to claim 1, Features: The mass fraction of ammonium fluoride in the etching solution is 30-38%.

8. The etching solution according to claim 1, Features: The mass fraction of ammonium fluoride in the etching solution is 36.40%.

9. Use of the etching solution according to any one of claims 1 to 8 in etching of silicon oxide recessed structures.

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