Fluorine-containing etching solution

Abstract

The invention discloses a fluorine-containing silicon nitride etching solution. The etching solution 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, silicon oxide, aluminum oxide and tungsten in hot phosphoric acid and inhibit etching of silicon oxide at the same time, and the etching rate of silicon nitride is more stable than that of a phosphoric acid / hydrofluoric acid system at a high temperature due to the complexing slow-release effect of the fluorine-containing compound.

Description

Technical Field

[0001] The invention belongs to the field of electronic chemicals, and in particular relates to a fluorine-containing silicon nitride etching solution. Background Art

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

[0003] When manufacturing 3D memory cells, tungsten, aluminum oxide, titanium nitride and other film layers must be deposited in the silicon nitride / silicon oxide stack in sequence, and the integrity of the above structural layers must be ensured during the wet etching process. In particular, high-k materials such as aluminum oxide have a high etching rate in high-temperature phosphoric acid, and their etching cannot be completely suppressed by additives alone. In order to improve the etching selectivity of silicon nitride / aluminum oxide, the etching rate of silicon nitride in phosphoric acid needs to be further improved.

[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, causing the etching rate of silicon nitride to decrease continuously as the heating time of the solution increases.

[0005] To solve the above problems, it is necessary to add fluorine-containing compounds and inhibitors to phosphoric acid to prepare 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 prepare a fluorine-containing etching solution to quickly etch silicon nitride and simultaneously inhibit the etching of silicon oxide, aluminum oxide and tungsten.

[0007] The invention relates to a silicon nitride selective etching solution. The etching solution comprises 79.5-80.5% by mass of phosphoric acid, 0.03-0.06% by mass of a fluorine-containing compound, 1.5-3.0% by mass of an aluminum oxide etching inhibitor, 0.1-0.2% by mass of a tungsten etching inhibitor, 0.3-0.5% by mass of a silicon oxide etching inhibitor, and the remainder is deionized water.

[0008] In the etching solution of the present invention, the aluminum oxide 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 the present invention, the aluminum oxide etching inhibitor is chelated on the aluminum oxide surface through a trihydroxy or tricarboxylic acid structure, thereby hindering the attack of hydronium ions on the active sites on the aluminum oxide surface, thereby reducing the etching rate of the aluminum oxide.

[0010] In the etching solution of the present invention, although an aluminum oxide inhibitor is added, the reaction activity of hydronium ions in high-temperature phosphoric acid is at a high level. Even in the presence of the inhibitor, aluminum oxide will still be corroded. Therefore, in order to improve the SiN / AlO etching selectivity, a fluorine-containing compound needs to be added to increase the etching rate of silicon nitride.

[0011] In the etching solution of the present invention, the fluorine-containing compound is one of fluorophosphoric acid, hexafluorophosphoric acid, fluoroboric acid, hexafluoroarsenic acid, hexafluoroantimonic acid, hexafluorozirconic acid and hexafluorotitanic acid.

[0012] In the etching solution of the present invention, the fluorine-containing compound will firstly dissociate a small part of hydrogen fluoride in high-temperature phosphoric acid, and then ionize fluorine ions to attack silicon nitride, thereby improving the etching rate of silicon nitride.

[0013] In the etching solution of the present invention, hydrogen fluoride is continuously consumed and volatilized as the etching reaction proceeds, and the hydrogen fluoride lost in the etching solution is continuously replenished through the dissociation reaction of the fluorine-containing compound, so that compared with the single addition of hydrogen fluoride, the silicon nitride etching rate decreases more slowly, that is, the service life of the etching solution is significantly improved.

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

[0015] In the etching solution of the present invention, the tungsten etching inhibitor is one of pyrazole, 1-phenylpyrazole, 4-pyrazolecarboxylic acid, 1,3,5-trimethylpyrazole, 1-methylpyrazole-5-carboxylic acid, 3,5-pyrazoledicarboxylic 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 conjugated induction effect of the benzene ring enhances the complexing ability of pyrazole. The added amount is preferably 0.1-0.15%.

[0017] In the etching solution of the present invention, the silicon oxide etching inhibitor is choline silicate synthesized using tetramethoxysilane and choline hydroxide as raw materials, and the structural formula is as follows: .

[0018] In the etching solution of the present invention, tetramethoxysilane in the choline silicate synthesis raw material is diluted with ethanol aqueous solution to a concentration of 25-35%, the choline hydroxide concentration is 20-30%, the reaction temperature is 70-80°C, and the reaction time is 12-24h.

[0019] In some preferred cases, the synthesis temperature of choline silicate is 80° C. and the reaction time is 24 h. Too low a reaction temperature and insufficient synthesis time will lead to a decrease in the silicon oxide inhibition efficiency.

[0020] In the etching solution of the present invention, choline silicate has good compatibility with fluorine-containing compounds in phosphoric acid, and silane coupling agent can also be used as a silicon oxide inhibitor. However, the product of the reaction between silane coupling agent and hydrofluoric acid is relatively insoluble in phosphoric acid and is easy to foam, which hinders its application in phosphoric acid-hydrogen fluoride system.

[0021] In the etching solution of the present invention, if the working temperature of the etching solution is too low (less than 130° C.), the silicon nitride etching rate is too low, while if the working temperature is too high (more than 150° C.), hydrogen fluoride evaporates too quickly and the etching life is short.

[0022] Furthermore, the working temperature of the etching solution is 138-148°C, preferably 140-142°C.

[0023] The reagents and raw materials used in the present invention are commercially available.

[0024] Based on the common sense in the art, the combination of the above-mentioned preferred conditions can obtain an embodiment of the present invention with better etching effect.

[0025] The advantages of the present invention are as follows: compared with the prior art, the present invention provides a fluorine-containing silicon nitride etching solution, which simultaneously inhibits the etching of silicon oxide, aluminum oxide and tungsten.

[0026] (1) The synthesized choline silicate and fluorine-containing compounds in the etching solution of the present invention have strong compatibility, and no bubbles or insoluble substances will appear during the heating process.

[0027] (2) In the etching solution of the present invention, the SiN / SiO etching selectivity ratio is greater than 2000, the SiN / AlO etching selectivity ratio is greater than 5, and the SiN / W etching selectivity ratio is greater than 100.

[0028] (3) After continuous heating for 24 hours, the etching rate of silicon nitride in the etching solution of the present invention decreases by no more than 15%. DETAILED DESCRIPTION

[0029] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0030] 1. Preparation of silica inhibitor At room temperature, 0.3 kg of tetramethoxysilane and 0.7 kg of ethanol aqueous solution with a volume ratio of 9:1 were mixed, stirred for 30 minutes and then allowed to stand for 12 hours. Then, the tetramethoxysilane dilution and 3.5 kg of 24% choline hydroxide solution were added to the reactor, stirred and heated to 80°C for 24 hours. After the reaction was complete, the solution was subjected to rotary evaporation and vacuum drying to obtain powdered choline silicate.

[0031] 2. Preparation of etching solution At room temperature, silicon oxide inhibitor, aluminum oxide etching inhibitor, tungsten etching inhibitor and fluorine-containing compound were successively dissolved in 80.0% electronic grade phosphoric acid and stirred until clear and transparent.

[0032] 3. Etching experiment ① Etching rate detection method Etched wafers: silicon nitride, silicon oxide, aluminum oxide, and tungsten; the deposition thickness of the four film materials on the silicon semiconductor wafer is 1000Å, 300Å, 80Å, and 800Å, respectively. During the test, they were sliced ​​into 1.5cm*3cm strips.

[0033] Etching temperature: 140℃.

[0034] Etching time: silicon nitride etching 300s, silicon oxide etching 3600s, aluminum oxide etching 120s, tungsten etching 1800s.

[0035] Etching rate calculation method: Use an ellipsometer to detect the film thickness of silicon nitride, silicon oxide, and aluminum oxide before and after etching, and use a four-point probe instrument to detect the film thickness of tungsten before and after etching. The difference between the initial thickness and the thickness after the etching time is the etching rate. The SiN / SiO etching selectivity is the ratio of the silicon nitride etching rate (SiN ER) to the silicon oxide etching rate (SiOER); the SiN / AlO etching selectivity 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 is the ratio of the silicon nitride etching rate (SiN ER) to the tungsten etching rate (W ER).

[0036] ② Etching solution life detection method The time starts from when the etching solution is heated to 140°C, and the etching rate of silicon nitride is tested every 6 hours until 24 hours. The attenuation of silicon nitride etching rate = (1-initial etching rate / etching rate after 24 hours) * 100%, which represents the life of the etching solution. The smaller the attenuation, the longer the life of the etching solution.

[0037] Table 1 Components and contents of Examples and Comparative Examples

[0038] Note: In each embodiment and comparative example, the phosphoric acid concentration is 80.0%, the balance except additives is deionized water, and the etching temperature is 140°C.

[0039] Table 2 Content of different additives in the formulation of Example 4

[0040] Table 3 Etching rate and selectivity of examples and comparative examples

[0041] Table 4 Silicon nitride etching rate after continuous heating for 24 hours

[0042] Comparative Example 1 shows the etching rate and selectivity of each film layer at 140°C using 80.0% phosphoric acid. In each embodiment, the fluorine-containing compound and the silicon oxide etching inhibitor work together to more than double the etching rate of silicon nitride compared to Comparative Example 1, while the silicon oxide etching rate is maintained below 1.5Å / 30min.

[0043] Examples 1-5 and Comparative Example 5 compare the effects of different fluorine-containing compounds on the etching rate. In Example 4, the silicon nitride etching rate decays by only 12.0% after continuous heating for 24 hours, while the silicon nitride etching rate decays by 46.3% in Comparative Example 5, i.e., the phosphoric acid-hydrogen fluoride system, indicating that the thermal stability of hexafluorozirconic acid in high-temperature phosphoric acid is better than that of hydrofluoric acid. The silicon nitride etching rate decays in the remaining examples is less than 15%.

[0044] Comparative Example 3 is a formula without adding aluminum oxide inhibitors. Its aluminum oxide 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 aluminum oxide inhibitors, among which 3,4,5-trihydroxybenzoic acid has the highest inhibition efficiency and can reduce the aluminum oxide etching rate to 14.6 Å / min.

[0045] Comparative Example 4 is a formula without adding 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 and 10-13 compare the effects of tungsten inhibitors, among which 1-phenylpyrazole has the highest inhibition efficiency and can reduce the tungsten etching rate to 0.84 Å / min.

[0046] The effects of the content of each additive on the etching rate and life of the preferred formula of Examples 4 and 14-19 are shown in Table 1. Compared with Example 4, Example 14 slightly reduces the amount of hexafluorozirconic acid and choline silicate added, which is manifested as a decrease in the silicon nitride etching rate, but the attenuation after heating for 24 hours is only 10.9%. The adjustment of the additive content within the range satisfies the SiN / SiO etching selectivity ratio>2000, the SiN / AlO etching selectivity ratio>5, and the SiN / W etching selectivity ratio>100.

[0047] The above is a detailed description of an aluminum nitride etching solution for inhibiting tungsten etching of the present invention. The above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. On the basis of the present invention, some modifications or improvements can be made thereto, which is obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to 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: 79.5-80.5% by weight of phosphoric acid; 0.03-0.06% by weight of a fluorine-containing compound; 1.5-3.0% by weight of an aluminum oxide etching inhibitor; 0.1-0.2% by weight of a tungsten etching inhibitor; 0.3-0.5% by weight of a silicon oxide etching inhibitor; and the remainder is deionized water.

2. The fluorine-containing selective etching solution according to claim 1, characterized in that: The fluorine-containing compound is one of fluorophosphoric acid, hexafluorophosphoric acid, fluoroboric acid, hexafluoroarsenic acid, hexafluoroantimonic acid, hexafluorozirconic acid, and hexafluorotitanic acid.

3. The fluorine-containing selective etching solution according to claim 1, characterized in that: The aluminum oxide etching inhibitor is a combination of one or more 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.

4. The fluorine-containing selective etching solution according to claim 1, characterized in that: The tungsten etching inhibitor is a combination of one or more of pyrazole, 1-phenylpyrazole, 4-pyrazolecarboxylic acid, 1,3,5-trimethylpyrazole, 1-methylpyrazole-5-carboxylic acid, 3,5-pyrazoledicarboxylic acid, and 3,5-dimethylpyrazole-4-carboxylic acid.

5. The fluorine-containing selective etching solution according to claim 1, characterized in that: The silicon oxide etching inhibitor is choline silicate synthesized using tetramethoxysilane and choline hydroxide as raw materials, and the structural formula is as follows: 。 6. The fluorine-containing selective etching solution according to claim 1, characterized in that: The tetramethoxysilane in the choline silicate synthesis raw material is diluted with ethanol aqueous solution to a concentration of 25-35%, the choline hydroxide concentration is 20-30%, the reaction temperature is 70-80°C, and the reaction time is 12-24h.

7. The fluorine-containing selective etching solution according to claim 6, characterized in that: The tetramethoxysilane in the choline silicate synthesis raw material is diluted with ethanol aqueous solution to a concentration of 30%, the choline hydroxide concentration is 24%, the reaction temperature is 80° C., and the reaction time is 24 hours.

8. The fluorine-containing selective etching solution according to claim 1, characterized in that: The working temperature of the etching solution is 138-148°C, preferably 140-142°C.

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

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