Fluorine-containing etching solution

Abstract

The application discloses a fluorine-containing silicon nitride etching solution, which comprises phosphoric acid, a fluorine-containing compound, an aluminum oxide etching inhibitor, a tungsten etching inhibitor, a silicon oxide etching inhibitor and deionized water. The etching solution can realize selective etching of silicon nitride to silicon oxide, aluminum oxide and tungsten in hot phosphoric acid, while inhibiting etching of the silicon oxide, and the etching rate of the silicon nitride is more stable at high temperature than that of a phosphoric acid / hydrofluoric acid system due to the complexing and slow-release effect of the fluorine-containing compound.

Description

Technical Field

[0001] This invention belongs to the field of electronic chemicals, and specifically relates to a fluorine-containing silicon nitride etching solution. Background Technology

[0002] 3D NAND technology overcomes the limitations of 2D or planar NAND flash memory by vertically stacking multiple layers of data storage cells. It boasts superior precision, supports higher storage capacity in a smaller space, and can create storage devices with storage capacity several times higher than similar NAND technologies. This effectively reduces costs and energy consumption, and can fully meet the needs of many consumer mobile devices and the most demanding enterprise deployments.

[0003] During the manufacturing of 3D memory cells, tungsten, aluminum oxide, and titanium nitride films must be deposited sequentially within a silicon nitride / silicon oxide stack. The integrity of these structural layers must be maintained during wet etching. In particular, high-k materials such as aluminum oxide exhibit high etching rates in high-temperature phosphoric acid, and additives alone cannot completely suppress this etching. To improve the etch selectivity of the silicon nitride / alumina ratio, the etching rate of silicon nitride in phosphoric acid needs to be further increased.

[0004] Fluoride ions have a significant promoting effect on the etching of silicon nitride. Adding hydrofluoric acid to high-temperature phosphoric acid can increase the etching rate of silicon nitride. However, hydrogen fluoride is relatively volatile, which causes the etching rate of silicon nitride to decrease continuously as the heating time of the chemical solution increases.

[0005] To address the above issues, fluorine-containing compounds and inhibitors need to be added to phosphoric acid to formulate a silicon nitride selective etching solution with a stable etching rate. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to formulate a fluorine-containing etching solution that can rapidly etch silicon nitride while inhibiting the etching of silicon oxide, aluminum oxide and tungsten.

[0007] This invention relates to a selective etching solution for silicon nitride, wherein the etching solution comprises 79.5-80.5% by mass phosphoric acid, 0.03-0.06% by mass fluorine-containing compound, 1.5-3.0% by mass alumina etching inhibitor, 0.1-0.2% by mass tungsten etching inhibitor, 0.3-0.5% by mass silicon oxide etching inhibitor, and the balance being deionized water.

[0008] In the etching solution of this invention, the alumina etching inhibitor is one of 3,4,5-trihydroxybenzoic acid, 2,3,4-trihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, 3,4,5-trihydroxybenzamide, 2-phosphonobutane-1,2,4-tricarboxylic acid, and pyrrole-2,3,5-tricarboxylic acid.

[0009] In the etching solution of this invention, the alumina etching inhibitor is chelated on the alumina surface through a trihydroxy or tricarboxylic acid structure, which hinders the attack of hydrated hydrogen ions on the active sites of the alumina surface, thereby reducing the etching rate of alumina.

[0010] Although an alumina inhibitor is added to the etching solution of this invention, the reactivity of hydrated hydrogen ions in high-temperature phosphoric acid is at a high level. Even with the presence of the inhibitor, alumina will still be corroded. Therefore, in order to improve the SiN / AlO etching selectivity, fluorine-containing compounds need to be added to increase the etching rate of silicon nitride.

[0011] In the etching solution of this invention, the fluorinated compound is one of fluorophosphoric acid, hexafluorophosphoric acid, fluoroboric acid, hexafluoroarsic acid, hexafluoroantimonic acid, hexafluorozirconic acid, and hexafluorotitanic acid.

[0012] In the etching solution of this invention, the fluorine-containing compound first partially dissociates into hydrogen fluoride in high-temperature phosphoric acid, and then ionizes into fluoride ions to attack silicon nitride, thereby increasing the etching rate of silicon nitride.

[0013] In the etching solution of this invention, as the etching reaction proceeds, hydrogen fluoride is continuously consumed and volatilized. The hydrogen fluoride lost in the etching solution is continuously replenished through the dissociation reaction of fluorine-containing compounds. Therefore, compared with simply adding hydrogen fluoride, the silicon nitride etching rate decreases more slowly, that is, the etching solution life is significantly improved.

[0014] Furthermore, the fluorinated compound in the etching solution of the present invention is preferably hexafluorozirconic acid, and the addition amount is preferably 0.04-0.05%.

[0015] In the etching solution of this invention, the tungsten etching inhibitor is one of pyrazole, 1-phenylpyrazole, 4-pyrazole carboxylic acid, 1,3,5-trimethylpyrazole, 1-methylpyrazole-5-carboxylic acid, 3,5-pyrazole dicarboxylic acid, and 3,5-dimethylpyrazole-4-carboxylic acid.

[0016] In the etching solution of the present invention, the tungsten etching inhibitor is preferably 1-phenylpyrazole. The conjugation-induced effect of the benzene ring enhances the complexing ability of pyrazole, and the addition amount is preferably 0.1-0.15%.

[0017] In the etching solution of this invention, the silicon oxide etching inhibitor is choline silicate synthesized from tetramethoxysilane and choline hydroxide, with the following structural formula:

[0018] .

[0019] In the etching solution of this invention, the tetramethoxysilane in the choline silicate synthesis raw material is diluted with an aqueous ethanol solution to a concentration of 25-35%, the concentration of choline hydroxide is 20-30%, the reaction temperature is 70-80℃, and the reaction time is 12-24h.

[0020] In some preferred cases, the synthesis temperature of silicic choline is 80°C and the reaction time is 24 hours. Too low a reaction temperature and insufficient synthesis time will lead to a decrease in the inhibition efficiency of silicon dioxide.

[0021] In the etching solution of this invention, silicic acid choline has good compatibility with phosphoric acid and fluorine-containing compounds. Silane coupling agents can also be used as silicon oxide inhibitors. However, the products of the reaction between silane coupling agents and hydrofluoric acid are difficult to dissolve in phosphoric acid and are prone to foaming, which hinders their application in the phosphoric acid-hydrofluoric acid system.

[0022] In the etching solution of this invention, if the working temperature of the etching solution is too low (<130℃), the silicon nitride etching rate is too low, while if the working temperature is too high (>150℃), the hydrogen fluoride evaporates too quickly, resulting in a short etching life.

[0023] Furthermore, the working temperature of the etching solution is 138-148℃, preferably 140-142℃.

[0024] The reagents and raw materials used in this invention are all commercially available.

[0025] Based on common knowledge in the field, the combination of the above-mentioned preferred conditions can yield examples of better etching effects of the present invention.

[0026] The advantages of this invention are: compared with the prior art, this invention provides a fluorine-containing silicon nitride etching solution that simultaneously inhibits the etching of silicon oxide, aluminum oxide and tungsten.

[0027] (1) The silicate choline synthesized in the etching solution of the present invention has strong compatibility with fluorine-containing compounds, and no bubbles or insoluble substances will appear during the heating process.

[0028] (2) The etching solution of the present invention has a SiN / SiO etching selectivity ratio >2000, a SiN / AlO etching selectivity ratio >5, and a SiN / W etching selectivity ratio >100.

[0029] (3) The etching rate of silicon nitride is reduced by no more than 15% after continuous heating in the etching solution of the present invention for 24 hours. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. These embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0031] 1. Preparation of silica inhibitors

[0032] At room temperature, 0.3 kg of tetramethoxysilane and 0.7 kg of an ethanol-water solution with a volume ratio of 9:1 were mixed and stirred for 30 min, then allowed to stand for 12 h. Then, a diluted tetramethoxysilane solution and 3.5 kg of a 24% choline hydroxide solution were added to a reaction vessel, stirred, and heated to 80 °C for 24 h. The resulting solution was then rotary evaporated and vacuum dried to obtain powdered choline silicate.

[0033] 2. Preparation of etching solution

[0034] At room temperature, silicon oxide inhibitor, aluminum oxide etching inhibitor, tungsten etching inhibitor, and fluorine-containing compound were dissolved sequentially in 80.0% electronic grade phosphoric acid and stirred until clear and transparent.

[0035] 3. Etching Experiment

[0036] ① Methods for detecting etching rate

[0037] Etching wafers: silicon nitride, silicon oxide, aluminum oxide, and tungsten; the deposition thicknesses of the four film materials on the silicon semiconductor wafers were 1000 Å, 300 Å, 80 Å, and 800 Å, respectively, and all were sliced ​​into strips of 1.5 cm * 3 cm during testing.

[0038] Etching temperature: 140℃.

[0039] Etching time: Silicon nitride etching 300s, silicon oxide etching 3600s, aluminum oxide etching 120s, tungsten etching 1800s.

[0040] Etching rate calculation method: The film thicknesses of silicon nitride, silicon oxide, and aluminum oxide before and after etching are measured using an ellipsometry. The film thickness of tungsten before and after etching is measured using a four-point probe instrument. The difference between the initial thickness and the thickness after a certain time is divided by the etching time to obtain the etching rate. The SiN / SiO etching selectivity ratio is the ratio of the silicon nitride etching rate (SiN ER) to the silicon oxide etching rate (SiO ER); the SiN / AlO etching selectivity ratio is the ratio of the silicon nitride etching rate (SiN ER) to the aluminum oxide etching rate (AlO E / R); the SiN / W etching selectivity ratio is the ratio of the silicon nitride etching rate (SiN ER) to the tungsten etching rate (W ER).

[0041] ②Etching solution life test method

[0042] Timing begins when the etching solution is heated to 140°C. The etching rate of silicon nitride is tested every 6 hours until 24 hours. The decay of the silicon nitride etching rate is calculated as (1 - initial etching rate / etching rate after 24 hours) * 100%. This value characterizes the lifespan of the etching solution. The smaller the decay, the longer the lifespan of the etching solution.

[0043] Table 1. Components and contents of the examples and comparative examples

[0044]

[0045] Note: In all examples and comparative examples, the phosphoric acid concentration was 80.0%, the remainder was deionized water except for additives, and the etching temperature was 140°C.

[0046] Table 2. Different additive contents in the formulation of Example 4

[0047]

[0048] Table 3. Etching rates and selectivity ratios of the examples and comparative examples

[0049]

[0050] Table 4. Silicon nitride etching rate after 24 hours of continuous heating

[0051]

[0052] Comparative Example 1 shows the etching rate and selectivity of each film layer at 140°C using 80.0% phosphoric acid. In each example, the combined effect of fluorine-containing compounds and silicon oxide etching inhibitors resulted in the etching rate of silicon nitride being more than doubled compared to Comparative Example 1, while the etching rate of silicon oxide remained below 1.5 Å / 30 min.

[0053] Examples 1-5 and Comparative Example 5 compared the effects of different fluorinated compounds on the etching rate. In Example 4, the silicon nitride etching rate decreased by only 12.0% after continuous heating for 24 hours, while in Comparative Example 5, the silicon nitride etching rate decreased by 46.3% in the phosphoric acid-hydrofluoric acid system. This indicates that hexafluorozirconic acid has better thermal stability in high-temperature phosphoric acid than hydrofluoric acid. The silicon nitride etching rate decrease in the other examples was less than 15%.

[0054] Comparative Example 3 is a formulation without added alumina inhibitors. Its alumina etching rate is increased to 38.5 Å / min under the action of fluorine-containing compounds compared with Comparative Example 1. Examples 4 and 6-9 compare the effects of alumina inhibitors. Among them, 3,4,5-trihydroxybenzoic acid has the highest inhibition efficiency, which can reduce the alumina etching rate to 14.6 Å / min.

[0055] Comparative Example 4 is a formulation without tungsten inhibitors. Its tungsten etching rate is increased to 13.3 Å / min under the action of fluorine-containing compounds compared with Comparative Example 1. Examples 4, 10-13 compared the effects of tungsten inhibitors. Among them, 1-phenylpyrazole has the highest inhibition efficiency, which can reduce the tungsten etching rate to 0.84 Å / min.

[0056] Examples 4 and 14-19 illustrate the effects of the additive content in the optimized formulations on etching rate and lifetime. Example 14, compared to Example 4, slightly reduced the amounts of hexafluorozirconic acid and choline silicate, resulting in a decrease in the silicon nitride etching rate, but the decay after 24 hours of heating was only 10.9%. Adjustments to the additive content within the specified ranges satisfied the following conditions: SiN / SiO etching selectivity > 2000, SiN / AlO etching selectivity > 5, and SiN / W etching selectivity > 100.

[0057] The foregoing has provided a detailed description of an aluminum nitride etching solution for inhibiting tungsten etching according to the present invention. The above description is merely a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Modifications or improvements can be made to the present invention, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A fluorine-containing silicon nitride etching solution, characterized in that the etching solution comprises the following raw materials: Phosphoric acid with a mass content of 79.5-80.5%; fluorine-containing compounds with a mass content of 0.03-0.06%. 1.5-3.0% by mass of alumina etching inhibitor; 0.1-0.2% by mass of tungsten etching inhibitor; 0.3-0.5% by mass of silicon dioxide etching inhibitor; the balance is deionized water; The fluorinated compound is one of the following: fluorophosphoric acid, hexafluorophosphoric acid, fluoroboric acid, hexafluoroarsic acid, hexafluoroantimonic acid, hexafluorozirconic acid, and hexafluorotitanic acid; The alumina etching inhibitor is one or a combination of 3,4,5-trihydroxybenzoic acid, 2,3,4-trihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, 3,4,5-trihydroxybenzamide, 2-phosphonobutane-1,2,4-tricarboxylic acid, and pyrrole-2,3,5-tricarboxylic acid. The tungsten etching inhibitor is one or more of the following: pyrazole, 1-phenylpyrazole, 4-pyrazole carboxylic acid, 1,3,5-trimethylpyrazole, 1-methylpyrazole-5-carboxylic acid, 3,5-pyrazole dicarboxylic acid, and 3,5-dimethylpyrazole-4-carboxylic acid. The silicon oxide etching inhibitor is choline silicate synthesized from tetramethoxysilane and choline hydroxide, with the following structural formula: 。 2. The fluorine-containing silicon nitride etching solution according to claim 1, characterized in that: In the raw materials for the synthesis of choline silicate, tetramethoxysilane is diluted with an aqueous ethanol solution to a concentration of 25-35%, choline hydroxide concentration is 20-30%, reaction temperature is 70-80℃, and reaction time is 12-24h.

3. The fluorine-containing silicon nitride etching solution according to claim 2, characterized in that: In the raw materials for the synthesis of choline silicate, tetramethoxysilane is diluted with an aqueous ethanol solution to a concentration of 30%, choline hydroxide concentration is 24%, reaction temperature is 80℃, and reaction time is 24h.

4. The fluorine-containing silicon nitride etching solution according to claim 1, characterized in that: The etching solution operates at a temperature of 138-148℃.

5. The fluorine-containing silicon nitride etching solution according to claim 1, characterized in that: The etching solution operates at a temperature of 140-142℃.

6. The fluorine-containing silicon nitride etching solution according to claim 1, characterized in that: The etching solution has a SiN / SiO etching selectivity ratio >2000, a SiN / AlO etching selectivity ratio >5, and a SiN / W etching selectivity ratio >100.

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